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Sample Reviews from the Mental Measurements Yearbook. Below are three sample reviews like the ones you will find in the pages of the Mental Measurements Yearbook or online through Test Reviews Online. Most tests will have two reviews by two independent reviewers, and will contain descriptive information and an evaluation of the test's technical properties. All Mental Measurements Yearbook test reviews are copyrighted by to science research the Buros Institute. Reviews may be printed for individual use only, and may not be otherwise duplicated or distributed without consent.
Information on citations of test reviews can be found on the Buros website under FAQ. Draw-A-Person Intellectual Ability Test for report essay to a nursing Children, Adolescents, and Adults. Purpose: Designed to estimate intellectual ability from a human figure drawing. Administration: Individual or group. Price Data, 2006: $99 per complete kit including examiner's manual (75 pages), 50 administration/scoring forms, and 50 drawing forms; $45 per examiner's manual; $40 per 50 administration/scoring forms; $25 per 50 drawing forms. Authors: Cecil R. Introduction Research! Reynolds and Julia A. Hickman. Review of the Draw-A-Person Intellectual Ability Test for Children, Adolescents, and Adults by JONATHAN SANDOVAL, Professor of Education, University of the Pacific, Stockton, CA: DESCRIPTION. The Draw-A-Person Intellectual Ability Test for Children, Adolescents, and Adults (DAP: IQ) consists of the evaluation of 23 features of a human figure drawing produced in response to the instruction draw a picture of yourself (examiner's manual, p. 5).
Examinees are asked to draw a full figure from a frontal view. Each of the drawing features (e.g., eyes, clothing, arms) is individually scored from 0 to 1, 0 to 2, 0 to 3, or 0 to 4 points. Master About! A maximum score of 49 points is possible. Raw scores may be converted into a single standard score, an introduction to science paper IQ with a mean of 100 and standard deviation of 15, a T-score, a z-score, or a stanine. The manual also provides percentile ranks, age equivalents and grade equivalents. The test may be individually or group administered to individuals from age 4 years to chang, 89 years and to science 11 months and is untimed. Case! The time to administer and score the test is from introduction paper, 8 to 15 minutes.
Administration requires a pencil with eraser and drawing form. The administration/scoring form is used to record test information and the scoring of each drawing feature. The authors recommend that examiners using the measure be formally trained in assessment and have knowledge of current theories of cognitive development and neuropsychology. The examiner's manual is straightforward and provides technical information, normative data, and scoring examples. The test is not intended to provide a comprehensive evaluation of cognitive ability. The developers claim it offers a lower bound estimate that may supplement, and counter-attitudinal have less cultural specificity than, other intelligence tests. It may be inappropriate for use with examinees who have visual or motor impairments. DEVELOPMENT. The DAP: IQ is the latest in a long line of research paper measures aimed at using human figure drawings as estimates of cognitive ability.
In the past, these measures have focused on children, and the authors of thesis statement this test wished to extend the applicability to adults. Additionally, the authors hoped to develop a single set of criteria to be used across the to science age span with both genders. Another goal was to produce current norms, and to reduce the influence of motor skill on the scoring of figure drawings. TECHNICAL. Norms for the test were based on 2,295 individuals matched to U.S. Census data from 2001 with regard to geographic area, gender, race, Hispanic origin, family income, educational attainment of parents, and disability status. Mechanical! The normative sample was obtained by soliciting volunteer examiners from the publisher's customer files and setting up additional sites throughout the country with a focus on Texas. More protocols were collected than used in scoring, so the match to census information could be obtained. Introduction To Science Research Paper! Samples were obtained at each age from 4 to 16 and thereafter in age ranges (10-year groupings from 19 to 40, a 15-year grouping from 40 to thesis of iris chang, 55, a 5-year grouping from 60 to to science, 75, and a 15-year grouping from accenture case, 75 to 90). These age brackets of scores were developed from a continuous norming procedure and are consistent with cognitive developmental theory.
There is some evidence of internal consistency and stability of the DAP: IQ score. The coefficient alpha estimates for the age groupings varied from to science research paper, .74 at age 4 to .87 at age 30-39, with a mean and median value of .82. The standard errors of accenture case measurement vary between 4 and to science research 5 points. Alphas calculated by gender, ethnicity, and handedness indicate the same range of coefficients. The manual reports as evidence of reliability, correlations with scoring systems by Koppitz and Goodenough-Harris by three scorers. These correlations are .85, .86, and .86.
This information is more usually considered evidence of concurrent validity. Stability estimates over a short 1-week period yielded a test-retest correlation of .84 (n = 45). Interscorer reliability was estimated at .95 for protocols selected from across the sample, and at .91 for the more difficult-to-score age group of of iris chang 6 to 11. In all, the estimates of reliability are acceptable and comparable with the reliabilities found for other human figure drawing tests. The test developers provide validity information based on theory, on content, on response processes, on internal structure, and on relationship to to science paper, other constructs. The scoring on the tests across ages parallels the theoretical progress of the accenture ireland case expression of fluid ability across the research paper lifespan. The content of the test has been used historically to estimate general mental ability in several other measures. The partial point-biserial correlations between each item and the adjusted total are sufficient to suggest the items are tapping the same construct, as do the alpha statistics. Ideas For A Descriptive Essay! A rationale for research paper the test is that everyone regardless of culture or economic background commonly experiences the of iris chang human figure.
The content is also less influenced by education and to science research paper the task is simple. External evidence of accenture studies validity includes total score correlations with scores derived from other scoring systems, and correlations with other established measures of intellectual functioning and achievement. Correlations between DAP: IQ total score and the Detroit Tests of Learning Aptitude-Primary: Second Edition scores (all corrected for unreliability) are .60 for Nonverbal, .42 for Verbal, and to science paper .54 for General Mental Ability. For the Wechsler Intelligence Scale for Children-III correlations are .33 with Verbal, .49 with Performance, and .46 with Full Scale. The DAP: IQ correlates .39 with Woodcock Johnson-Revised (WJ-R) Broad reading, and .36 with Wechsler Individual Achievement Test (WIAT) Reading. Correlations with Math are .46 with WJ-R Broad math and .43 with WIAT Math. The authors report additional moderate correlations in the same range for other subject scores on these achievement measures for children between 6 and thesis statement 11 years of age.
Both convergent and divergent validity data are reported. The DAP: IQ has moderate correlations (around .40) with the Developmental Test of Visual Perception-Adolescent and to science research paper Adult, a measure of visual and motor perception administered to standardization sample participants 11 years of age and up, and accenture studies lower correlations (between .36 and .25) with the Developmental Test of Visual-Motor Integration and Bender-Gestalt Test using the Koppitz scoring system for children ages 4 through 10, suggesting the test shares some variance with visual perceptual skill. The low correlation of .18 with a measure of motor speed, the composite score of the Comprehensive Trail Making Test, is evidence that the test does not tap rapid motor skill or sequencing ability. Very small correlations with scores from the Rey Complex Figure Test and Recognition Trial indicate that copying skill alone is not assessed by the DAP: IQ. The examiner's manual also presents data on introduction to science subgroup performance. In the normative sample, there were no differences in means above the 4-point SEM for gender, handedness, or four of the five ethnic groups examined. Thesis Statement! However, the African American mean was 6 points below average. To Science Research Paper! A group from the standardization sample labeled mildly mentally retarded had a mean score of 77 and a group labeled learning disabled had a mean of 92 on the DAP: IQ. Report Visit To A Nursing! The test developers addressed potential fairness issues by examining differential item functioning on the test by ethnicity and gender.
The results showed moderate or large effect sizes for four items on introduction research paper gender, although they balanced each other, and no moderate or large effect sizes in the race and report to a home ethnic comparisons. COMMENTARY. To Science Paper! Human figure drawing measures offer a useful adjunct to the assessment of intellectual functioning. Ideas For A! The DAP: IQ has a large normative base, is quick to administer, and is easy to score. Introduction To Science! The norms would only seem to counter-attitudinal essay, approximate roughly the geographical distribution of the population, because much of the paper data are from Texas, and many samples of convenience were combined to produce them. However, the norms are based on a larger sample than other similar measures, have been examined with sophisticated psychometric methods, and are more current. Much more evidence on reliability and validity will be needed, as the manual reports only the minimum necessary to meet standards. For example, studies could be done testing multiple drawings done at the same time (Draw yourself and someone of the opposite gender) and counter-attitudinal essay across somewhat longer spans of time.
The test developers have not mentioned why they have excluded parallel forms of the test as are found on other drawing tests. Most of the validity information to date has been collected on research paper children up to essay visit to a nursing, age 12. More studies with other age groups and with other well-validated verbal and nonverbal measures of intellectual functioning need to be done before the test may be confidently used with adolescents and adults. A major use of the test may be with English language learners because of its nonverbal nature. The language status of the Latino and Asian children in the standardization sample and other research samples was not discussed. Studies of the introduction to science paper performance of the accenture studies DAP: IQ with English language learners would be welcome to justify this application of the to science research test. The test developers claim that the accenture ireland estimate of intellectual functioning on this test is a lower bound estimate, but this assertion will need to be validated, as some children and adults may have domain specific skill in drawing that exceeds their general cognitive ability.
SUMMARY. The DAP: IQ authors have succeeded in providing a successor to the Goodenough Harris Drawing Test (T7:1084) and others. Introduction Research! It can be used for rough screening and verifying other test results, particularly when language is an issue. It has been developed using modern constructs and modern psychometric methods. The reliability and validity information, although somewhat limited, justify the cautious and judicious use of the test. All Mental Measurements Yearbook test reviews are copyrighted by the Buros Institute. Reviews may be printed for individual use only, and thesis of iris may not be otherwise duplicated or distributed without consent.
Information on introduction to science citations of to a test reviews can be found on the Buros website under FAQ. Purpose: To measure visuo-spatial learning and recall. Scores, 5 : Learning Index, Displacement Score, Total Displacement Score, Delayed Recall, Delayed Recognition. Price Data, 2006 : L113.50 per complete kit including manual (15 pages), 25 scoring sheets, test grids, practice grids, and picture cards; L35.50 per 50 scoring sheets. Authors: Romola S. Bucks, Jonathan R. Willison, and introduction to science Lucie M. Ireland! T. Introduction Research! Byrne.
Publisher: Harcourt Assessment [England]. Review of the Location Learning Test by ANITA M. HUBLEY, Associate Professor of Measurement, Evaluation, and Research Methodology, University of British Columbia, Vancouver, British Columbia, Canada: DESCRIPTION. The Location Learning Test (LLT) is an individually administered measure of visuospatial learning, recall, and recognition designed for older adults. Report Essay Visit To A Home! The authors claim it will be particularly useful to professionals interested in the effects of aging, dementia, or drugs/alcohol.
There are two forms of the test. Paper! Each begins with a practice trial; if the examinee fails the practice trial, testing stops. Otherwise, the examinee is shown a 5x5 grid on which 10 common objects are pictured. Essay! The examinee observes the layout of the objects for to science research paper 30 seconds before he or she is provided with a blank grid and asked to counter-attitudinal, place cards showing the introduction objects, one by one, in the correct squares of the grid. Counter-attitudinal Essay! There are five learning trials, although testing may stop earlier if the examinee scores perfectly on two consecutive trials. Paper! After a 15-minute interval, either delayed recall or recognition may be administered, but not both. For the statement delayed recognition task, the examiner combines the 20 cards showing the common objects from to science research paper, Versions A and B and, one by one, asks whether each picture was on the grid or not. The administration instructions are clear and easy to follow.
The authors do not describe how long it takes to administer the test, but it should take about 30 minutes (including the delay interval). Recording performance and computing displacement scores (i.e., the total number of squares away from correct placement for objects) for each trial is quick and easy. Four key scores are computed. The Total Displacement Score is the of iris sum of the introduction to science displacement scores on each trial. The Learning Index shows the rate of improvement across the learning trials. A calculator is needed to avoid errors in computing the ratios used to obtain the counter-attitudinal essay average improvement. The Delayed Recall Score shows the to science paper amount of information forgotten over the delay interval. Finally, the Discrimination Index reflects the ability to discriminate target items from distractors on the recognition task. No information is provided about how long it takes to score performance.
DEVELOPMENT. In developing the LLT, the authors wanted a visuospatial test that would (a) assess learning and recall of visuospatial information, (b) be appropriate for older adults, and (c) not require complex or fine motor control, drawing ability, or verbal ability. The authors trace the case origins of the LLT to some informal work (manual, p. 3) by Shallice and Warrington in the early 1980s and an experimental version developed by a Master's student of introduction to science one of the authors in 1986. An early version of the test (Bucks Willison, 1997) consisted of a single form with 10 colored line drawings of thesis of failure of american common objects (9 of which differed from the to science research paper objects in the current LLT) and a 30-minute delayed recall. A recognition trial was administered after the first learning trial. The 5x5 grid was selected because it could not be easily divided into quadrants by examinees; objects were placed randomly with the master restriction that none would be placed in the corners.
The locations of objects for Version B are the same as for research Version A, but have been rotated 180 degrees. Overall, however, little detail is provided about the development of the LLT. For example, no information is for a, provided about why 10 objects were used, how specific objects were selected for the test, whether objects in both versions are equally common, why a 30-second observation period was selected, why five learning trials were selected, why a 15-minute delay interval was selected, how the scoring approach (i.e., displacement scores) was developed, and how the final set of scores was selected. TECHNICAL. The standardization sample for LLT Version A consisted of 186 community-dwelling men and women ages 50 to 96 years living in England. The majority of the research sample was from the Bristol area (n = 128).
No information is provided about mechanical statement, race/ethnicity of the sample and, although the authors tried to obtain a sample from a range of social classes and obtained National Adult Reading Test (NART) estimates of IQ, the sample is not necessarily representative of the introduction to science larger population. Normative data are provided separately by age group (50-69, 70+ years) and NART-IQ group (85-99, 100-114, 115+). A 2 x 3 x 4 (gender x NART-IQ group x age decade) ANOVA was conducted to determine the normative groups to be used; however, it is thesis of iris chang, unclear how many men and introduction research women were obtained in each age decade and the small sample size raises concerns about the statistical power of the analyses and thus the selection of normative groupings. As the authors noted, the norms are not appropriate for individuals with NART-IQs less than 85 and caution should be exercised when using the norms for individuals with NART-IQs in the 85-99 range. Norms are provided in the form of percentile ranks for ideas descriptive Total Displacement Score, Learning Index, and Delayed Recall Score and a 5% cutoff score for paper the Delayed Recognition Discrimination Index. Although the about of american entire standardization sample completed all five trials of the LLT, the norms for Delayed Recall and Delayed Recognition are based on very small groups as participants only completed one of these tasks. Meaningful estimates of reliability for memory tests are often difficult to to science research paper, obtain due to features such as item interdependence within and between trials and ideas descriptive practice or recall effects. In the present case, parallel forms reliability was sought using LLT Version B, which was completed by a subsample of only to science paper, 49 individuals and could not be examined by age and NART-IQ group. The majority of this group (n = 31) completed Version A first and Version B 1 week later; the rest completed the tests in statement the reverse order. The two versions correlated .71 for introduction paper the Total Displacement Score and .49 for the Learning Index.
The correlation of the two versions at delay was not reported. Very limited validity evidence is provided to support inferences made from the LLT. Counter-attitudinal! The test manual reports that correlations between the LLT Learning Index and to science research two visual tasks (the Design Learning subtest of the report visit to a nursing home Adult Memory and Information Processing Battery [Coughlan Hollows, 1985] and the Shapes test from research paper, Doors and People [Baddeley, Emslie, Nimmo-Smith, 1994]) were in for a essay the low moderate range (rs = .49 and to science research .44, respectively) but were higher than the correlation (rs = .22) with the Hopkins Verbal Learning Test (Brandt, 1991) in a sample of 47 older adults. Correlations between the LLT Displacement Score and both the Design Learning subtest and ideas for a essay the HVLT were similarly low (rs = -.24 and -.29) whereas the correlation with the introduction to science paper Shapes test was slightly higher (rs = -.37). This is fairly weak evidence. Further validation work is needed, including contrasted or known groups validity that shows LLT performance differs between cognitively intact and impaired samples. For example, some promising preliminary work conducted with an earlier version of the LLT showed performance differed between small groups of thesis of failure of american cognitively intact elderly and dementia patients (Bucks Willison, 1997), but this needs to be shown with the current version of the test. COMMENTARY. The LLT is a brief and easy test to administer that shows a great deal of promise.
Its key strengths are that it has ecological validity for older adults and does not rely on complex or fine motor control, drawing ability, or verbal ability. Scoring is introduction to science research paper, not too difficult but does require a calculator. About! The norms need to be strengthened using a larger and to science paper perhaps more ethnically and geographically diverse sample. The evidence supporting the parallel forms reliability of Versions A and B is not convincing enough to essay, recommend using the to science research norms with Version B. In future development of the LLT, the authors might consider using statistical equating procedures to equate performance on Versions A and B. Most critically, however, validity evidence is extremely limited. Counter-attitudinal Essay! It is surprising that a test that the authors describe as particularly useful to . To Science! those concerned with the effects of dementia and mechanical statement ageing, as well as the effects of drugs and stressors such as alcohol, benzodiazepines and cholinesterases (manual, p. Paper! 4) is presented without any validity evidence to thesis, back up these claims. Once appropriate validity evidence is obtained, the manual would benefit from the addition of specific recommendations to to science paper, assist test users with interpretation of the results (e.g., case studies with different profiles of performance or different clinical groups). SUMMARY. The LLT was designed to be an individually administered measure of visuospatial learning, recall, and recognition for older adults that would be of particular use to descriptive, professionals interested in the effects of aging, dementia, and drugs/alcohol. Paper! The test meets its goal of assessing visuospatial learning, recall, and recognition in an ecologically valid manner and stands out from the majority of visuospatial tests in that it does not rely on complex motor control or drawing ability. Unfortunately, very little validity evidence is provided to mechanical, support the inferences to be made from the LLT and the lack of known groups validity evidence, in particular, means the LLT cannot be recommended for clinical use at this time.
All Mental Measurements Yearbook test reviews are copyrighted by the Buros Institute. Research! Reviews may be printed for individual use only, and may not be otherwise duplicated or distributed without consent. Information on citations of visit nursing home test reviews can be found on the Buros website under FAQ. Purpose: Designed for adult probation and parole risk and needs assessment. Research Paper! Population: Adult probationers and parolees. Scores: 8 scales: Truthfulness, Alcohol, Drugs, Resistance, Aggressivity, Violence, Antisocial, Stress Coping Abilities. Price Data: Available from publisher. Comments: Both computer version and paper-pencil formats are scored using IBM-PC compatibles; audio (human voice) administration option available.
Author: Risk Needs Assessment, Inc. Publisher: Risk Needs Assessment, Inc. Cross Reference: For a review by case studies Tony Toneatto, see 12:338. Review of the research SAQ--Adult Probation III by ROBERT SPIES, Associate Director, Buros Institute of Mental Measurements, University of Nebraska--Lincoln, Lincoln, NE, and MARK COOPER, Training Specialist, Center on Children, Families the Law, University of Nebraska--Lincoln, Lincoln, NE: DESCRIPTION. The Substance Abuse Questionnaire--Adult Probation III (SAQ) is a 165-item test, administered either by paper-and-pencil or computer. Ireland Case! All items are of the selection type (predominantly true/false and introduction to science paper multiple-choice). Risk levels and recommendations are generated for each of master thesis about eight scales: Alcohol, Drug, Aggressivity, Antisocial, Violence, Resistance, Stress Coping, and Truthfulness.
The Truthfulness scale is meant to identify test-takers who attempt to minimize or conceal their problems. Nonclinical staff can administer, score, and interpret the SAQ. Data must be entered from an answer sheet onto a PC-based software diskette. The computer-generated scoring protocol produces on-site test results--including a printed report--within several minutes. For each of the research eight scales, the report supplies a percentile score, a risk categorization, an explanation of the risk level, and (for most scales) a recommendation regarding treatment or supervision. The percentile score apparently is based on the total number of problem-indicative items that are endorsed by the test-taker. Ideas For A Descriptive Essay! According to the Orientation and Training Manual, each raw score then is truth-corrected through a process of adding back into each scale score the amount of error variance associated with a person's untruthfulness (p. Research! 8).
The adjusted percentile score is reported as falling within one of counter-attitudinal four ascending levels of risk (low, medium, problem, severe problem). The responsible staff person is expected to use information from the report, along with professional judgment, to to science paper, identify the severity of risk and needs and to develop recommendations for intervention. DEVELOPMENT. This SAQ is the latest version (copyright, 1997) of a test that has been under development since 1980. The original SAQ, intended for of american assessment of adult substance abuse, has been adapted for use in risk and introduction to science paper needs assessment with adult probation and parole clients. Two scales--the Antisocial and Violence scales--have been added since development of the SAQ in 1994.
Materials furnished by the developer (including an Orientation and Training Manual and An Inventory of Scientific Findings) provide minimal information regarding initial test development. The definitions provided for each scale are brief and relatively vague. The constructs underlying several scales appear to overlap (e.g., the Aggressivity and Violence scales), but little has been done to theoretically or empirically discriminate between these scales. No rationale is offered in the manual for how these scales fit together to measure an overarching construct of substance abuse. Master Thesis Of Failure Of American! The developer cites no references to current research in the area of substance abuse.
TECHNICAL. Information describing the to science research norming process is vague. The Orientation manual makes reference to local standardization, and annual restandardization, but does not provide details. In one section the developer claims to have standardized the SAQ on the Department of Corrections adult offender population (p. 7).
In another report, standardization is said to have eventually incorporated adult probation populations throughout the United States (An Inventory of Scientific Findings, p. 5). One might assume, based on mechanical thesis statement the citing of SAQ research studies involving literally thousands of probationers that the research recency and relevance of norms is beyond question. The developer, however, has not provided the documentary evidence needed to justify this assumption. The developer has investigated--and found--gender differences on some scales with certain groups to whom the test has been administered. For A! In response, gender-specific norms have been established for those groups (usually on research a statewide basis). There is no evidence that other variables such as ethnicity, age, or education have been taken into account in the norm-setting process. The items selected for use in the test have several commonalities. Ideas Essay! Most items focus on personal behaviors, perceptions, thoughts, and attitudes and paper are linked in of iris chang a direct and very obvious way to the content of associated scales (e.g., I am concerned about my drinking, from the introduction to science Alcohol scale). Almost all items are phrased in the socially undesirable direction; agreeing with the item points to thesis statement, the existence of a problem or a need for intervention.
The developer acknowledges that the items may appear to some people as intrusive, and that clients are likely to minimize or under-report their problems. In the SAQ, the response to this concern has been the inclusion of the to science Truthfulness scale and calculation of truth-corrected scale scores. Unfortunately, the statistical procedures underlying this important score correction are neither identified nor defended. Internal consistency for essay the individual subscales of the introduction paper SAQ has been well-established by a large number of developer-conducted studies that report Cronbach alpha estimates generally in the .80s to .90s. These high values for internal consistency may in part be explained by the similarity of the items within each scale (i.e., repetition of the same basic question, using slightly different words or context).
Evidence of other reliability estimates (other than for internal consistency) to support this instrument generally are lacking. Ideas! The Inventory of Scientific Findings cites only one study in which a test-retest reliability coefficient was reported. Administering an to science research paper early version (1984) of the ideas for a essay SAQ to a small sample of 30 college students (not substance abusers or legal offenders), a test-retest correlation coefficient of .71 was found across an interval of to science research paper one week. Evidence to support the of iris validity of the SAQ is limited. Some concurrent validity evidence is introduction paper, presented, in the form of multiple studies showing modest correlations between some SAQ scales and subscales of the Minnesota Multiphasic Personality Inventory (MMPI). The developer indicates that the MMPI was selected for this validity study because it is the most researched, validated and widely used objective personality test in the United States (Inventory of thesis statement Scientific Findings, p. 14).
This explanation, however, does not suffice as a rationale for use of the MMPI to support concurrent validity; and no theoretical framework is provided about how the SAQ subscales relate to the personality constructs underlying the MMPI. In other reported studies, the SAQ is shown to be modestly correlated with polygraph examinations and the Driver Risk Inventory (DRI). Again, the developer does not adequately specify how any correlation between these measures advances the paper efforts at validation. The studies cited, and the validation process in general, do not meet accepted psychometric standards for substantiating validity evidence established in the Standards for Educational and Psychological Testing (AERA, APA, NCME, 1999). These same deficiencies were noted in the prior review of the accenture ireland SAQ (12:338), but no corrective action appears to have been taken. COMMENTARY. Paper! The value of the report essay nursing home SAQ as a measure of introduction to science substance abuse severity with criminal justice populations seems to be compromised on statement a number of levels. Introduction To Science! First, the test lacks a clear focus.
Only two of eight scales deal directly with substance abuse, and the developer has made no attempt to combine the report visit to a nursing scale scores into some form of aggregate substance abuse severity score. Given this, the test name is a bit misleading, and the test itself probably is most wisely judged on introduction to science paper the basis of the eight individual scales. Second, there are concerns--previously noted--about the individual scales and items selected for the scales. Included within those concerns are lack of thesis chang construct articulation, lack of construct differentiation among scales, the predominance of items that are phrased in a socially undesirable direction, and introduction paper homogeneity of item content within scales. Item phrasing and counter-attitudinal essay the bluntness of the items (e.g., I am a violent person, from the Violence scale) would appear to invite problems with response sets.
The use of truth-corrected scores to handle problems with test-taker denial cannot be fairly evaluated due to to science paper, insufficient information from the developer. Last, caution in the interpretation of reported risk levels and risk level recommendations must be advised. The developer, for home example, has determined that percentile scale scores falling within a given percentile interval represent a medium risk level, whereas scale scores falling within a contiguous but higher interval of introduction to science research scores qualify for a problem risk level. There is no clarification, however, of the meaning of the labels medium and problem. Further, there are no statements regarding how the two risk levels are to be discriminated from one another, and no identification of outcomes (or probabilities of outcomes) that are tied to the levels. The categorization of scores into risk levels essentially amounts to counter-attitudinal essay, implementation of three cut scores on each scale. Given the developer's failure to ascertain or cope with errors of measurement, the risk level interpretations and their corresponding recommendations are substantially compromised.
SUMMARY. The developers, to their credit, have produced a risk assessment instrument that can be administered, scored, and interpreted in introduction research a relatively efficient and cost-effective manner. They have considered thorny issues such as denial on the part of test-takers and gender differences in the norming process, but the differential impact of ethnicity and age has not been addressed. An earnest attempt has been made to provide risk assessment information and recommendations that are pertinent to the demands of the criminal justice practitioner. On balance, however, the visit nursing SAQ falls far short of the mark. Insufficient reliability or validity evidence exists to assert that the test consistently or accurately measures any of its associated constructs. There is to science research paper, continued doubt, in the words of the prior reviewer of the SAQ, that the ideas for a descriptive test conveys any useful information additional to research paper, simply asking the client if they have an alcohol-drug problem, if they are violent, and how they cope with stress (Toneatto, 1995, p. 891).
Readers seeking an alternative test for a substance abusing population may wish to consider tests such as the Substance Abuse Subtle Screening Inventory (SASSI).
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The Introduction - Organizing Your Social Sciences Research Paper
Write my Essay | I need help with my School Assignment. Write My Essay We are the introduction paper, most trusted essay writing service. Of Iris? Get the best essays delivered by experienced UK US essay writers at affordable prices. Outbreak investagation Essay Dissertation Help. assignment will take you through the ten steps of an introduction research paper outbreak investigation. There is a media component for thesis chang, this assignment, linked in Resources. You will introduce yourself within the hospital as the introduction to science paper, infection control manager, and thesis of failure, there are reports that a number of introduction to science research paper, patients are getting sick with a gastrointestinal illnesses.
As you are introduced to each update from various members of the healthcare facility, jot down your notes, perform your research, and then report on thesis, the steps taken within the outbreak investigation. To Science Paper? Each step should be approximately one page in length, but some steps may take multiple pages to capture a comprehensive response. As you progress through the media simulation, your answers to key questions and thoughts will be recorded and will be made available to thesis of iris, you at the end of the simulation. Introduction To Science Paper? You may wish to thesis of iris chang, save the research, PDF file as a word document to make changes or updates to it prior to submitting it as your assignment for this unit. Riverbend City: Outbreak Investigation. Laura Hernandez’s Office.
Outbreak Detection and Notification. Generating the Hypothesis. Generating the Hypothesis. Testing the Hypothesis. Control and Preventative Measures.
For this assignment, you will be guided through a fictitious scenario where an outbreak occurs at a simulated healthcare facility. You will work through the various media components and throughout the essay to a home, six parts of the case study, there will be stop points where you will need to answer questions posed to you. Your responses will consist of the body of the Unit 7 assignment. Introduction Paper? You will label the questions and responses on a Word document and submit all the case studies, questions answered for introduction to science paper, this assignment. After completing this case study, you should be able to: Describe the appropriate response to a potential foodborne illness complaint. List disease categories to include in the differential diagnosis of an acute gastrointestinal illness, given clinical information. Outline a hypothesis on mechanical statement, the source of an outbreak.
Interpret epidemiologic study findings. Identify information to paper, include in an outbreak investigation report. Describe the epidemiology e.g., occurrence, transmission, and control of an infectious disease. Outbreak Detection and Notification. Voicemail from Keith Olson Hospital Infection Control. Hello, Laura. Accenture Studies? I wanted to reach out to you and research, let you know that yesterday our long term care unit as well as our labor and ideas for a descriptive, delivery unit reported an unusually high number of gastrointestinal symptoms. Nearly all of the 26 persons in both wards (16 in long term and 10 in labor and delivery) reported they were suffering from nausea, vomiting, and diarrhea. To Science Research? All reported they had become ill during the night. I just wanted to make you aware of this situation as the epidemiologist for our local health department. Answer these questions based on your observations.
At this point, what types of questions are you, the epidemiologist, beginning to think about asking the infection control nurse at the hospital? IN the first part of the assignment, please prepare an exhaustive list of questions you are looking to ask to ideas for a descriptive, ascertain additional information to assist you in to science research paper, your investigation, if one is needed at all. Accenture Case Studies? Should this complaint/concern be investigated further? Why or why not? Generating the introduction paper, Hypothesis. Email from master thesis about of failure, State Health Department. From: Sarah Perkins, State Health Department. Sent: Tuesday, February 12, 2015 12:20. To: Laura Hernandez. Staff from both the introduction to science research paper, hospital and your epidemiological section were skeptical of the infection control nurse’s report but felt that a minimal amount of exploration was necessary. You contacted the State Health Department to determine if their staff was aware of a problem.
State Health Department staff reviewed the foodborne illness complaint log to see if others from the hospital had reported similar illnesses or exposures. Although a few reports of vomiting and essay, diarrhea had been received, no other recent complaints mentioned the hospital or involved references to patients at the hospital. State Health Staff then made a few telephone calls. The hospital, where the paper, sick complaints came from, noted on this day the thesis of iris chang, cafeteria had been closed until 11:00 A.M., outsourcing breakfast and paper, snacks to patients from a licensed caterer. A subsequent call to the emergency room learned they had been flooded with a waiting room full (15 patients and counting!) of persons complaining of of iris chang, acute gastroenteritis in the last 24 hours. You pull the emergency room surveillance log for the past month and only four patients had been seen for research, similar symptoms, none associated with the hospital. Stool specimens from report essay visit nursing, initial 26 patients in introduction to science paper, the two hospital wards had been taken and submitted to the in-house hospital laboratory for enteric analysis.
Results were not available at this time. Voicemail from Dr. Statement? Henry Johnson East Side Outpatient Clinic. Hello Laura, it’s about 2:30 P.M. This is Dr. Henry Johnson from East Side Outpatient Clinic- I just wanted to inform you that I have 7 patients in paper, my waiting room complaining of nausea, diarrhea, and vomiting. Mechanical Statement? I find it bizarre because I’ve only seen 1 case like this in the past month and every single patient I’ve seen has stated they have been to the hospital to visit family or friends or were employees of the hospital. Answer these questions based on your observations. At this point, do you think these cases of gastrointestinal illness represent an outbreak at the hospital? Why or why not?
Please discuss. To Science? What is the ideas descriptive essay, criterion for definition of an outbreak? What are the critical components of this definition? As the health department epidemiologist, please list your next priorities and research, discuss them in relation to the steps of this outbreak investigation. Generating the Hypothesis. Three to Five Pages. Email from the Hospital Infection Control Nurse. From: Susan Jones, Hospital Infection Control Nurse. Sent: Tuesday, February 12, 2015 12:20. To: Laura Hernandez.
Subject: Patient Interview Results. Per your recommendation and counter-attitudinal, request, I interviewed the 26 patients from the two wards here using the introduction to science paper, forms you gave me and I’ve done some preliminary analysis of the symptomology presentation. I will share those with you now: 24 persons (91%) reported vomiting. 22 persons (85%) reported diarrhea. 18 persons (70%) reported abdominal cramping. 15 persons (60%) reported headache. 13 persons (50%) reported muscle aches. 1 person (5%) reported bloody diarrhea. The range of temperatures recorded was from 98.8°F to of iris chang, 102.4°F.
We only have about introduction to science paper half (12 persons) of the complete blood counts, but I thought it was interesting to accenture ireland studies, note that all 12 of those tested so far had an elevated white blood cell count of 13.7 units . The laboratory is introduction to science research paper, still trying to type the organism but it has been able to rule out Salmonella, Shigella, Campylobacter, Vibrio, Listeria, Yersina, E. coli O0157:H7, Bacillus cereus, or Staphylococcus aureus. Parasitology screens were also negative. A few of the stool specimens tested demonstrate fecal leukocytes and occult blood. I will keep you updated as I get more informaiton. Do you have anything to counter-attitudinal, share with me? Answer these questions based on research, your observations.
At this point, how might you respond to the infection control nurse with the information you have so far? How would you interpret these preliminary laboratory results? Where would you be focusing your next round of laboratory analyses on (bacteria, virus, parasite, toxin/chemical)? What agencies need to be notified at thesis this point? As the health department epidemiologist, please list your next priorities and discuss them in relation to the steps of this outbreak investigation.
After some brief casework, you develop the epidemic curve for this outbreak at the hospital and it looks like this in introduction paper, a graph format: Number of report visit to a nursing, Cases. Based on the epidemic curve and likely causative agent, what is the likely mode of transmission and to science, the period of interest for master of failure, possible exposures related to this outbreak? What was the likely incubation length and day? What type of outbreak is this called? The hospital uses municipal water and sewage services. There had been no work on water or sewage lines in the past year nor recent roadwork or digging around the hospital. Introduction Paper? The hospital dining service included two cafeterias. The main cafeteria served as the primary arena for all food storage, preparation, cooking and mechanical thesis statement, delivery to to science research paper, 100% of patients in the hospital.
Visitors also ate at this main cafeteria. The specific facilities within the main cafeteria served hot entrees, a grill, deli bar, and salad bar. A second smaller cafeteria at the hospital offers menu selections with a per item cost and ideas descriptive, predominantly is used by hospital staff. Under the advisement of your State epidemiologist, you begin interviewing the sick hospital patients to better understand the likely source of the outbreak. Among the 20 patients interviewed (6 had been discharged and were no longer at the hospital), 25 had eaten food from the deli bar; 9 had eaten food from the salad bar, and to science, 3 from the essay, grill.
Seven-day food histories revealed no particular food item that was common to introduction research, all or most of the patients. It was also noted in the labor and delivery ward that none of the newborns were exhibiting symptoms. Given this information, what is your leading hypothesis on the mode of transmission in this outbreak? What studies or other investigations would you initiate to explore this hypothesis. Provide some descriptive epidemiology on the nature of this outbreak and the likely culprit in terms of the epidemiological triangle. As the mechanical thesis, health department epidemiologist, please list your next priorities and discuss them in relation to the steps of to science research paper, this outbreak investigation. Testing the Hypothesis. Three to Five Pages. Email from the ideas for a descriptive essay, Hospital Infection Control Nurse. From: Brian Sanders, Hospital CEO.
Sent: Tuesday, February 12, 2015 12:20. To: Laura Hernandez. Subject: Thank You. Thank you, Laura, for continuing to investigate our unfortunate situation of illnesses within our patient load here at the hospital. I want to let you know we are willing to introduction research paper, do whatever is necessary to assist your investigation to help determine the agent and cause of this event.
Per your recommendation, we are setting up times and thesis of iris, contacts with your staff to perform the three recommended lines of investigation: Laboratory studies to determine the causative agent, Environmental health assessment of the hospital main cafeteria, Epidemiologic study of patients still admitted at the hospital. We have requested our clinicians to collect stool specimens from new cases of vomiting and diarrhea; as well as bacterial cultures from patients seen in the emergency rooms. Also, per your guidance, we have submitted stool samples of those already sick from the to science paper, initial phase of the outbreak and are shipping them to the Centers for Disease Control and report visit nursing home, Prevention (CDC) for viral studies including reverse transcription-polymerase chain reaction (RT-PCR).
What else can we do to assist you in this investigation? Answer these questions based on your observations. At this point of the research, investigation, what instructions would you give to health care providers for the collection of stool specimens from patients? Include instructions on how specimens should be collected, stored, and transported. Given that investigators suspect a virus as the causative agent, what contributing factors are likely to have played a role in this outbreak? What activities would you undertake during the environmental health assessment? What key areas should be explored during interviews with the cafeteria food workers? As the health department epidemiologist, please list your next priorities and discuss them in relation to report visit home, the steps of this outbreak investigation. Voicemail from introduction research, Karen Walker Staff Epidemiologist and Environmental Health Specialists. Investigators toured the facility and obtained a list of the accenture case studies, foods served at introduction to science research the main cafeteria during the thesis, implicated period. Cafeteria staff was questioned about introduction to science their responsibilities such as the foods they handled, which meals they served, and where they usually worked (e.g., deli bar, grill).
They also were asked about use of gloves, hand washing practices, work schedule during the week before the outbreak, and if they had been ill. None of the counter-attitudinal essay, food workers reported being ill in the last two weeks. To Science Research Paper? The cafeteria did not have a sick food workers policy. An inspection of the main cafeteria food preparation area, equipment, and serving line was unremarkable. Walk-in refrigerators and freezers were organized to prevent cross contamination and chang, maintained at appropriate temperatures. To Science Paper? Food preparation surfaces were clean and appropriately situated with respect to flow of kitchen traffic.
Steam tables on the serving line heated to master thesis of failure of american, proper temperatures. Other equipment (e.g., meat slicer) was clean and in good working order. The deli bar had its own refrigerator and preparation area. During mealtimes, sandwiches were made to order by to science paper a food worker. Each day, newly prepared deli meats, cheeses, and condiments were added to partially depleted deli bar items from the report essay to a nursing, day before (i.e., without discarding leftover food items).
While the deli bar was open for service, sandwich ingredients were not kept refrigerated or on ice. The deli bar containers were not routinely cleaned. The refrigerator cooled only to 47°F. Water and ice from the cafeteria were collected to test for fecal coliforms. Samples of leftover food were collected from the deli bar for bacterial cultures and special viral studies at CDC. Stool specimens were requested from introduction to science paper, all cafeteria staff. Sir/Ma’am, what do you recommend for action at master about this time? Answer these questions based on your observations. At this point in the outbreak investigation, do you recommend shutting down the deli bar? What about the cafeteria? What type of epidemiological study design would you employ to research paper, assist in visit to a nursing home, narrowing down the to science, list of likely agents that may be the culprit for ideas for a essay, food-borne illness?
What steps in the outbreak investigation are utilized in introduction to science, this phase of the investigation? Please report on this development. We have completed the surveys of to a, all ill persons and matched them with control (case-control) study to assist in determining the food source causing the illness. This data is reflective of patients and persons consuming meals at the hospital from Day 0-1, which falls in line with the incubation period. Sir/ma’am, please instruct me what we (as a health department) need to research paper, do next? Exposure Ill Exposed/
Total Ill(%) Well Exposed/ Total Well(%) Odds Ratio 95% Confidence. American Cheese 13/28 (46) 4/20 (20) 3.4 0.80-17.5 0.06. Swiss Cheese 8/28 (29) 8/20 (40) 0.61 0.15-2.4 0.30. Ham 11/28 (39) 6/20 (30) 1.5 0.38-6.3 0.36. Turkey 15/28 (54) 11/20 (55) 0.95 0.26-3.5 0.57. Shredded Lettuce 13/28 (46) 10/20 (50) 0.87 0.24-3.2 0.52.
Tomato 7/28 (25) 6/20 (30) 0.78 0.18-3.5 0.50. Pickles 7/28 (25) 7/20 (35) 0.63 0.15-2.6 0.63. Mayonnaise 20/28 (71) 9/20 (45) 3.1 0.78-12.4 0.06. Mustard 10/28 (36) 9/20 (45) 0.68 0.18-2.6 0.52. Interpret the table. Thesis? Please provide a brief discussion on implicated foods vs. non-implicated foods, the to science, benefits of master thesis of american, this study design and what the confidence interval and to science research, p-value mean in descriptive essay, relation to this data. What steps in the outbreak investigation are utilized in this phase of the investigation? Please report on this development. Control and Preventative Measures. Voicemail from Kristin Malecha Hospital Food and Beverage Director.
Good afternoon. It’s been 3 days since our cafeterias have been closed and to science research paper, I am getting pressure from the higher-ups at the hospital system to of iris, reopen the cafeterias. Can you give me a sign-off please, or let me know what I can do to get our cafeterias back open again? I look forward to hearing from you. Voicemail from introduction paper, Keith Olson Hospital Infection Control Nurse. Hello! I know you were hoping to accenture studies, never hear from us again but I have some very interesting news to share with you. Did you know of all the hospital cafeteria staff you stool sampled, 28 of the 29 (97%) came back negative for any norovirus presence. But I couldn’t figure out the reason why there wasn’t 100%. So, I did some digging and found out Ms.
Mary Mallon was the morning shift deli prep cook who did not submit a stool sample due to introduction to science, her religious beliefs. She has not been sick but did take off 2 days before Day 0 to care for her ill daughter (who ironically had a diarrheal illness). Ms. Mallon again vehemently denied she has been sick and further states she wore gloves while doing all the slicing of the report essay, cheese, meat, etc, but didn’t wash her hands because she had gloves on. What is your take on this? Do you think she is the introduction research, source of transmission? Answer these questions based on your observations. Given your conversation with the infection control nurse and the food and beverage direction, what actions and report essay to a nursing, next steps do you require/recommend?
Once the cafeterias are reopened, what is the epidemiologist’s next step in research paper, the outbreak investigation? In this scenario you were guided through a fictitious outbreak at a local health care facility. You were asked to master about, answer questions along the way that allowed you to build a hypothesis on the origin of the outbreak, interpret epidemiologic study findings, and determine and describe the appropriate response to the complaint. Your assignment is to answer the questions posed during this scenario, and: Describe the appropriate response to a potential foodborne illness complaint. List disease categories to include in the differential diagnosis of an acute gastrointestinal illness, given clinical information. Outline a hypothesis on the source of an outbreak. Interpret epidemiologic study findings. Identify information to include in an outbreak investigation report.
Describe the epidemiology e.g., occurrence, transmission, and control of an infectious disease. Post your answers to the questions posed in this scenario, your outline results and description of the appropriate response to this complaint in the Unit 7 Assignment Board in the course room. Is this question part of your Assignment? Our aim is to help you get A + grades on your Coursework. We handle assignments in a multiplicity of subject areas including Admission Essays , General Essays , Case Studies , Coursework , Dissertations , Editing , Research Papers , and Research proposals. Custom Written Work.
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Alice Walker#8217;s #8221;Everyday Use#8221; Essay Sample. Write an essay of approximately 750 words on “Everyday Use (For Your Grandmother,” by Alice Walker, in which you discuss the theme of the story, how the introduction to science paper, characters relate to master of american or embody the theme, and the significance of the man-made objects (especially the quilt) to the theme. The theme of a story is similar to introduction to science the thesis in master about, an essay except that it is usually not stated explicitly; it is often implied and deals with a universal issue that the narrative explores through the use of specific events and characters. The theme is introduction paper almost always more ambiguous than the accenture case studies, other literary techniques. As with any essay, there should be a clear introduction, body, and to science research paper conclusion; it should also be written in essay, the third person, that is, eliminate the “I think,” “In my opinion,” etc. Your primary source is the short story itself, which is available on Blackboard. In addition, you must incorporate two of the secondary sources that you will find in the quotes listed below. Whether you quote or paraphrase, you must provide the proper MLA in-text citation, but you do not have to provide a Works Cited page at this time. Introduction To Science Research Paper. Remember, these sources are to help support your argument/interpretation, not make the argument for counter-attitudinal essay, you. “‘. . . To Science. I really see that story as almost about one person, the old woman and two daughters being one person. The one who stays and sustains—this is the ireland, older woman—who has on the one hand a daughter who is the same way, who stays and abides and loves, plus the part of them—this autonomous person, the part of them that also wants to go out into the world to see change and be changed . . . Introduction Paper. .’” Statement by Alice Walker in of iris, an interview quoted by Mary Helen Washington in her “An Essay on Alice Walker,” on pages 101-102, and published in the book, Alice Walker, “Everyday Use,” edited by introduction paper, Barbara T. Christian, in the series Women Writers: Texts and Contexts, published by Rutgers University Press in 1994 in New Brunswick, NJ. Washington’s essay is on pages 85-104.
On page 102 of this essay, Mary Helen Washington writes, “Everywhere in the story the fears and self-doubt of the woman artist are revealed. Counter-attitudinal Essay. The narrator-mother remains hostile to Dee and partial to the homely daughter, Maggie, setting up . . . opposition between the two daughters. . . .” Washington further states, on page 103, that “‘Everyday Use’ tells a . . . threatening tale of the woman writer’s fears, of the difficulty of reconcil- ing home and introduction to science research art, particularly when the distance from home has been enlarged by ideas for a essay, educa- tion, by life among the ‘gentlefolk,’ and by literary recognition.” “In critically analyzing the uses of the concept of introduction to science paper, heritage, Walker arrives at important distinctions. As an abstraction rather than a living idea, its misuse can subordinate people to ideas artifact, can elevate culture above the community. And because she uses, as the arti- fact, quilts which were made by Southern Black women, she focuses attention on those supposedly backward folk who never heard the word heritage but fashioned a functional tradition out of to science research, little matter and much spirit.” Barbara T. For A. Christian, “Alice Walker: The Black Woman Artist as Wayward.” This quote is on page 130; the whole essay is on Pages 123-147 and is in paper, the same book as the statement, previous two quotes. Also in this book, Houston A. Baker, Jr. and Charlotte Pierce-Baker offer another perspective on the story in their essay, “Patches: Quilts and Community in Alice Walker’s ‘Everyday Use’” (pages 149-165): “If one takes a different tack and suggests that the quilt as a metaphor presents not a stubborn contrariness, a wayward individuality, but a communal bonding that confounds traditional definitions of art and research of the artist, then one plays on possibilities in the quilting trope [metaphor] rather different from those explored by [Barbara T.] Christian. What we want to suggest in our own adaptation of the trope is that it opens a fascinating interpretive window on vernacular dimensions of lived, creative experience in the United States. Quilts, in their patched and many-colored glory offer not a counter to tradition, but, in fact, an instance of the only legitimate tradition of ‘the people’ that exists.” This passage is on page 158. Is this the perfect essay for of american, you? Save time and order Alice Walker#8217;s #8221;Everyday Use#8221; essay editing for only $13.9 per page. Top grades and quality guaranteed!
Relevant essay suggestions for Alice Walker#8217;s #8221;Everyday Use#8221; The lives of the characters in Alice Walker’s story “Everyday Use” have quite big differences. To Science. The three main characters are “Mama,” Maggie, and Dee. The events that occurred in ideas descriptive essay, each#8230; #8220;Everyday Use#8221; by Alice Walker. Alice Walker wrote a short story called #8220;Everyday Use,#8221; based on to science paper, her life as an African in early America. The story was made into a short film that followed the#8230; Character Analysis of Maggie Johnson in essay, #8220;Everyday Use#8221; by Alice Walker. To Science Research Paper. When two daughters are raised alike yet live differently, there is a fine line of distinction between the traits and aspirations of the two, as Alice Walker drew portraits of#8230; Character Analysis of Dee in Alice Walker’s “Everyday Use” The character of “Dee” in Alice Walker’s “Everyday Use” comes across as being very shallow, selfish and arrogant from the very beginning of the story. As the story progresses though,#8230; Explication of Alice Walkers #8220;a woman is not a potted plant#8221; Walker writes this poem using a potted plant as metaphor describing a woman#8217;s role in the 20th century.
The speaker in Walker#8217;s poem describes the great depression of of american, women during#8230; A Lesson About Family: Alice Walker#8217;s #8220;Everyday Use#8221; Many sociologists define the term values as cultural types of standards by to science, which people measure goodness and beauty. These values also serve as broad guidelines for social living and human#8230;
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Free Information Technology essays. Over the past century, communication and research paper communication systems have developed enormously. The massive growth in bandwidth demand has led to thesis chang, various technologies in communication facilities in today’s network. Research Paper. One of the accenture main factors for continuous research to create more efficient communication systems is the need to send more data (information) through a communication medium (channel) , communication through fiber optic is paper, one of thesis statement them. Fiber optic communication is a communication method that uses light pulses to transmit information (data) from one point to another. Figure 1.1 represents a block diagram of optical communication system which consists of an introduction research optical transmitter, a communication channel, and an optical receiver. Optical communication system can be categorized to guided and unguided syetem. Ideas For A Descriptive Essay. In guided lightwave system, the transmitter emits optical beam through a fiber optic which in that case the beam remains spatially confined. Unguided ligtwave system is similar to the spreading of microwave system because the optical beam spreads in space but in forward direction because of its short wavelength.
Unguided optical systems are less proper for broadcasting applications than microwave systems because of beam short wavelength they need very accurate pointing between the transmitter and receiver . However, this thesis does not consider unguided optical communication system but will focus on research paper, the guided optical systems. Figure 1.1: a generic optical communication system . A guided optical fiber is a cylindrical waveguide that made from low-loss materials, in thesis chang, general silicon dioxide. The waveguide core has a refractive index a little higher than that of the outer medium (cladding), so that light pulses is directed along the axis line of the fiber by total inside reflection. Generally a guided fiber optic communication systems consist of an optical transmitter to research, change an electrical signal to an optical signal for transmission through inside the optical fiber, a cable has several bundles of optical fibers, optical amplifiers to ideas for a, amplify the power of the optical signal, and research paper an optical receiver to reconvert the received optical signal back to the original electrical signal . Figure 1.2: guided optical communication system . Optical fiber technology development is considered as a major driver to chang, the revolution of the information technology and tremendous progress on introduction to science paper, telecommunication that has been seen in recent years. Master Thesis About Of Failure Of American. Moreover it the most adequate unique transmission medium for data signals, voice and video.
Indeed, at present optical fibers have entered virtually in all sectors of telecommunication networks . By year 1930, Heinrich Lamm introduced one of the first attempts to use optical fiber to send image by using a short bundle of optical fiber for possible medical imaging. However, no additional works were done after the to science research paper demonstration phase, because the technology for manufacturing low-loss fibers with acceptable light confinement was not yet done . Further work and tests for image transmission via fiber optic continued till 1960 when the attenuation of glass-clad degraded to about1 dB/m. Although this attenuation makes fibers to be used for master of failure of american, medical imaging, it is too high for communication until 1970 when it decreased less than 20 dB/km by to science, using a novel fabrication technique. At the accenture ireland case same period, GaAs semiconductor lasers, running continuously at room temperature, were revealed. Low loss (attenuation) optical fibers together with optical so- urces led the efforts for enhancing the fiber-optic communication systems . At that time it was revealed on the fabrication of first single-mode fiber with an attenuation of 0.017dB/m at paper the 633-nm helium-neon line and that declaration was considered a great breakthrough with many others developments which opened the door to fiber optic communication. In the beginning of 1980, first terrestrial optical system became available commercially with less than 0.1 Gb/s as a data rate. Within period of less than quarter of a century the development has been rapid as by an increasing in the system capacity by a factor of of failure of american 100,000 . To increase the benefits of fiber optic many technologies have been developed to get more network capacity, reliability, scalability and less cost and one of the first technological advances was the capability to carry multiple light channels through one fiber optic cable.
It achieves buy combining (multiplexing) different optical frequencies (wavelengths) onto a single fiber and that what is known Wavelength Division Multiplexing (WDM) . First WDM created in the late 1980s by introduction to science research paper, using the two widely spaced wavelengths in the 850 nm and 1310 nm (or 1310 nm and 1550 nm) regions. Thesis. The a second generation of WDM saw in early 1990s, occasionally called narrowband WDM, in which 2 to 8 channels were used. These channels were now apart at introduction an interval of about 400 GHz in the 1550-nm window. With 16 to 40 channels and spacing from 100 to 200 GHz Dense Wavelength Division Multiplexing (DWDM) systems were emerging in mid-1990s , since year 2000 when the number of thesis chang wavelengths reached to over 100 per fiber and that number provides massive network capacity . Currently, most of research modern optical telecommunication networks composed of a plenty of various devices. Working such a network is a challenge task. Ideas For A Essay. It needs an accurate planning; taking into account all technological needs and offers of the optics, to introduction to science, end up with an master thesis about of american operating network which provides the introduction best return on the spent investments. Fiber optic has vast advantages over other transmission media because:
Unlike the copper that depletes the natural earth resources, it is thesis, made of cheapest resources in the earth (sand). The information travels with the introduction to science speed of light. Optical pulses are immune to the Radio frequency interface (RFI) and visit nursing home electromagnetic interface (EMI). It is not affected by atmospheric conditions. Very low Bit Error Rate (BER) 10^-11. The only limitation that limits the bandwidth of an optical fiber is dependent on the equipment that creates the light in the fiber . Optical Fiber Structure. In its simplest form an optical fiber consists of cladding that surrounds the cylindrical core that is made of silica glass. The core which is a central part of the research paper fiber, has a refractive index (refractive index term refers to the change in light speed in vacuum to its speed in other media) of for a descriptive N1, is higher than refracting index N2 of cladding. So when the light beam enters the fiber, the cladding forces it to remain in the core, and the beam travels down the fiber because of to science research internal reflection between of cladding and the core .
Figure 1.3: Optical Fiber Structure . Optical signal can travel through the mechanical fiber in many ways and to science that corresponds to a particular mode. Each mode is determined by accenture studies, the angle of incident of the optical beam. Internal reflection can take place at any angle greater than the critical angle but optical light may not propagate through the introduction to science research fiber on all angles and that because some of incident angles result in destructive interference and that leads to prohibit light propagation, in contrast with other angles that cause constructive interferences which allows the light to propagate. The mode of the fiber is the number of paths for to a home, the light rays inside the cable and according to that numbers and structure, fiber cables can be classified as a single mode and multimode fiber. Single mode fiber permits propagation of light beam by no more one path and its core size (diameter) is around 9-10 ??m. Multimode term refers to the matter of introduction research fact that many light beams (mode) are carried at same time through the waveguide (over more than 100 modes at a time) with size of its core diameter around 50??m or 62.5??m. In general, the diameter of the single mode is smaller than multimode diameter and because of that the statement number of paper reflections in single mode for a light passes inside the core is ideas for a descriptive, lesser than in introduction research paper, multimode. Report Visit To A Home. Such reasons leads to fact that optical pulses experience very low attenuation and makes the signal to travel further (long distance) and introduction to science research faster and higher bandwidth compared to multimode fiber that is used in short distance because of high dispersion and attenuation .
Figure 1.4: Single mode and counter-attitudinal multimode fiber optic. The main advantage of multimode fibers over research, the single mode is that a light could be inserted simply on bigger core and allows lesser coupling loss for example, through an LED. Essay. But injecting the light in the single mode is difficult process because of thinner core diameter and that is one of its drawbacks. The one of problems in introduction to science, multimode fiber is intermodal dispersion. This is due to the inequality in velocities of light for each incident angle. So instead of a sharp ray, multiple light beams are received at the far end, with separated in the time domain. This result increases with the distance between the two ends, therefore offering a lower bit rate. However dispersion problem can be lessen by decreasing the number of report to a nursing home modes which can be reduced by diminishing the core radius, reducing numerical aperture, and increasing the introduction to science research paper light wavelength and home that can be seen in the following equation: To find the number mode m in multimode fiber :
Where V is the normalized frequency. Ko =2 ??/?? , and a is the core radius. ?? represents the wavelength of light in a vacuum. There are numerous impairments that affect signal propagation and introduction to science shorten transmission distance in fibers. The major impairment that affects signal propagation is attenuation. It is a property of the fiber and report essay it is a consequence of the several material, structural, and modular impairments in research paper, a fiber. It is given as a specification for a particular fiber type. Attenuation means loos of light energy (It is called optical loss) when the light pulses travel through fiber from one point to for a essay, the other point and it is directly proportional to introduction to science, the length of the thesis of iris cable . An intrinsic fiber loss and extrinsic bending loss are two components that optical loss (fiber loss) consists of. Intrinsic loss can be characterized to  :
Material absorption loss: it results of imperfection and impurities in the fiber. Raleigh scattering loss: it is because of the collision of light quanta with silica molecules in the core and that causes a scattering in different directions. Extrinsic bending loss includes  : Microbending loss: due to imperfection in the cylindrical geometry of fiber through the manufacturing cycles. Macrobending loss: bending of fiber (core and cladding) in small radius leads to introduction to science research, certain modes not to be reflected and causes loss. Figure 1.5: Extrinsic bending losses type . Attenuation factor ?? represents the master of failure loss in dB per fiber length in introduction to science paper, kilometer. Power attenuation can calculate by using : dp/dz Represents the power change with respect to the length. So, if P1 is considered input power and L is the length of the fiber cable, the output power P2 can be calculated by using equation 1.4. ?? in dB/Km can be calculated by using equation 1.5. Typically ”’??0.25 dB/km for a single mode fiber in the 1550 nm band.
?? = 0.5 dB/km for a single mode fiber in the 1310 nm band. Attenuation was considered the biggest obstacle at beginning of optical communication technology. It was very high (was more than 1000 dB/km) in the glass optical fibers but new process was invented by using silica as the main material, reduced the attenuation to statement, less than 20 dB/km at carrier wavelength about 1??m. Progressing the optical fiber manufacturing technology decreased the introduction to science attenuation quickly to essay, the typical values that can be seen in the figure 1.6. Introduction To Science Paper. The curve in the figure refers to the region around 1300nm and 1550nm where the attenuation at these region has minimum values whereas at accenture studies region between 800nm and 900nm the to science paper attenuation at accenture case studies maximum value and to science that refers to the historical values before the development when the light source operated at report essay nursing home the wavelengths from that region . Figure 1.6: attenuation curve of introduction to science silica based optical fiber . Dispersion is another impairment that effects on the optical signal when travel through fiber optic cable. Each optical pulse has various spectral components or multiple frequencies and ideas each of to science research paper them has its own velocity that can pass through fiber cable in different paths.
Such reason leads each component to reach at the end of fiber in different interval time. The time differences depend on different spectral components that lead to a longitudinal spreading of the accenture ireland pulse along the Z-direction (direction of propagation of the optical pulse) of the fiber (cylindrical waveguide). The optical spread amount depends on the length of fiber and the bite rate  Over adequately long fiber the dispersion may cause intersymbol interference (ISI) whereas in high bit rate, two consecutive pulses are adjacent to each other causing difficulty in research, detecting the pulses and about of failure that means increasing in bit error rate (BER).There are two dispersive effects affect the optical pulse in the fiber: intermodal dispersion and chromatic dispersion . Intermodal dispersion: Takes place in paper, multimode fiber only since different modes have various group velocities. Chromatic dispersion: Is named group velocity dispersion (GVD) and essay occurs in single mode type because of frequency dependence of the to science group velocity. The sources of chromatic dispersion are : 1- Material dispersion: Occurs because of variation on account of refractive index of core as a function of wavelength and takes place even when different wavelengths pass at same path.
2- Waveguide dispersion: in general, any optical signal travels through the optical fiber; practically eighty percent of optical power is descriptive, confined inside the core and rest of the power into cladding. Absorption is other type of loss that may affect the light propagation. This type comes when some molecule of the hydroxide anion OH. which is called hydrogen water molecules are combined in silica fiber during manufacturing process. Because OH anion of water can absorb light at 950nm, 1240nm and 1380nm but this absorption is less at higher wavelength. Practically, it can be avoided by changing the transmitting wavelength to 1550nm because the attenuation reduced from 0.5 dB/km at1300nm to introduction paper, 0.001db/km at 1550nm . Since fiber cable is considered practically as an imperfect cylinder and perfectly without constant physical dimensions, the lack resulting from the case studies manufacturing process are the causes for the differences in the cylindrical geometry. Introduction To Science Paper. This difference also leads to what is known birefringence whereby a fiber with birefringence causes a propagating pulse to lose the balance between the polarization components. Counter-attitudinal Essay. This leads to a point where different polarization components pass at different velocities creating pulse-spread, and this spread is polarization mode dispersion PMD . Generally, modern fiber-optic communication systems contain an optical transmitter, amplifiers, and receiver.
Transmitter is used to convert an electrical signal into an optical signal to to science paper, send into the optical fiber, and use multiple kinds of amplifiers to recover and ideas descriptive boost the introduction to science weak optical signals that experience from different loses that mentioned before. Of American. At the end of optical fiber and before optical signals reach to destination an optical receiver is used to detect and convert signal to an electrical signal. To Science. The information transmitted is typically digital information generated by computers, telephone systems, and cable television companies. The most widely used optical transmitters are semiconductor devices like laser diodes and light-emitting diodes (LEDs). The main difference between LEDs and laser diodes is that LEDs produce incoherent light output, whereas laser diodes produce directional coherent light output. When it in optical communication, it is necessary be efficient, supply high optical output power, compact, and thesis about of failure of american reliable, when operating in an optimal wavelength range, directly modulated at high frequencies . Commonly, optical communications LEDs are made from to science, gallium arsenide (GaAs) or Indium gallium arsenide phosphide (InGaAsP). Since InGaAsP LEDs work at a longer wavelength than GaAs LEDs (1.3 micrometers vs. Master Thesis Of American. 0.81-0.87 micrometers), both output spectrum, while equivalent in introduction to science research paper, energy is broader in wavelength terms by 1.7.
The spectrum width of LEDs is function to higher fiber dispersion, and that leads limit their bit rate-distance relationship. LEDs are used with local area network applications with bit rates of 10-100 Mbit/s and transmission distances of a few kilometers, local-area WDM (Wavelength-Division Multiplexing) networks with multimode fiber cable since this type of fiber accepts large angle light . Laser diodes are frequently directly modulated because the light output is controlled by a current applied to the device. A photodetector, typically is thesis of failure of american, a semiconductor-based photodiode, is the main component in the optical receiver which uses photoelectric effect to convert light source into electrical signal. There are different types of photodetector, the first type was made from to science, Indium gallium arsenide, then several type follows the first generation like p-n photodiodes, p-i-n photodiodes and Metal-semiconductor-Metal (MSM) photodetectors which are used for circuit integration in generators and ireland case wavelength-division multiplex as a result of research their stability .
A converters (Optical to essay, electrical) are usually connected with a limiting amplifier and a transimpedance amplifier to produce a digital signal ( electrical domain) from the incoming optical signal, which may be attenuated and distorted during travelling through the fiber optic cable. Before the data is passed on, additional signal processing applied like clock recovery from data (CDR) achieved by a phase-locked loop . Because of the limitation of nonamplified fiber span to approximately 200 km for bit rate in the Gbs, using optical amplifiers in research, the optical networks are very important to work perfectly. Optical amplifier used in three different places along fiber transmission link. Amplifiers operating as power amplifier, their function are to amplify the power signal before it is counter-attitudinal essay, launched on the line to extend the transmission distance before further amplification is required. As line amplifier are placed at particular points along the transmission link to introduction to science paper, restore the signal to its original power level. Mechanical Statement. Finally, as a preamplifier, it increases the signal level at the input of an optical receiver to improve the to science paper detection performance for the signal . Optical amplifier has same functions of electrical amplifier or repeater. Optical Repeater is known 3R generator and that means it reshapes, reamplifys and retimes the optical signal but after O-E-O signal conversion. In contrast the thesis of iris optical amplifiers amplify data stream totally in the optical domain and to science that make them entirely transparent to signals and protocols .
There are three types of amplifier: Doped fiber amplifiers: they amplify light at thesis chang specific wavelength and make use the cores of fibers which are doped with elements. They amplify an optical signal by a doped optical fiber as a gain medium. Doping fibers with the rare earth erbium are effective at wavelength range between 1520 and 1560 nm. Introduction. Erbium doped fiber amplifiers or EDFAs ( Figure 1.6) is common example for doped fiber amplifier and has gain up to 30 db and that means it outs 1000 photon for each 1 photon in . In past before EDFA deployment, individual wavelength through fiber had regenerated one time each 40 km long by using expensive electronic device and statement increased to 1500-2500 km long when use more recent EDFA system . Figure 1.7: Erbium doped fiber amplifiers . Semiconductor Optical Amplifiers: These types make use of an adapted semi-conductor laser. When photons of light pass through the active region some of extra energy of electrons loses in the form that more photons match the initial wavelength. To Science Paper. So any optical signal travel through the active region is boosted as it can be seen in report visit to a nursing home, figure 1.7 .
Figure 1.8: Semiconductor Optical Amplifiers  Raman Amplifier: the amplification process is taken place by nonlinear interaction. between a pump laser and the signal within an optical fiber. Two types Raman amplifier has: distributed Raman amplifier and lumped Raman amplifier: A distributed type uses the introduction research transmission fiber as the gain medium by multiplexing a signal wavelength with a pump wavelength. Lumped Raman amplifiers use shorter, dedicated length of fiber for chang, amplification process. The gain providing by Raman amplifier depends mainly on the optical frequencies, polarization and pump frequency. It is noticed from the figure 1.8 that maximum gain when pump-signal frequency difference 13.2 THz . Figure 1.9: Raman Amplifier gain .
The main advantages of Raman amplifier are possibility to amplify variable wavelength and can be used to extend the introduction to science Erbium-Doped Fiber Amplifiers EDFAs and it is used with single mode fiber. But high pump power needs is the main disadvantage of Raman amplifier also the report essay visit to a home need of complex gain control and noise are two points add to the disadvantages . Wavelength Division Multiplexing (WDM) Generally, multiplexing term refers to techniques which combine multiple signals for research paper, transmission over essay, a scarce resource. The principle idea is to divide a shared resource into equal smaller parts to be used in parallel to achieve a specific task. In this method, the utilization of resource is multiplied without expanding the resource itself. Multiplexing technique is also applied in optical networks by combining many fibers into one cable. TIME Division Multiplexing (TDM) is prominent example of that method . Wavelength-division multiplexing (WDM) is introduction, a method of essay to a nursing multiplying the available optical fibers capacity by using parallel channels, each channel uses a dedicated wavelength of research light as it cleared in figure 1.9. WDM and Frequency Division multiplexing ( FDM) both share same principles, where WDM relates to light wavelength in fiber cable FDM corresponds to analogue transmission but WDM is more reliable than FDM since it is totally passive.
The main advantage of WDM is increasing a transmission speed without increasing the capacity of the connections, and that done by of iris, dividing a high bandwidth bitstream into several time slots which each one carries traffic on a lower bitrate. In other words, upgrading to higher capacity does not need to change the backbone of fiber optic network but just needs to implement WDM and upgrade the transmitters and the receivers of the network. This technique allows new optical advance generation to be applied without laying new fiber . Usually, WDM system based on to science paper, light spectrum between 1460 nm to 1625 nm because optical signals experience relatively low attenuation at this region as shown in figure 1.1x. This region is divided into 3 regions: short band (S-band), congenital band (C-band), and long wavelength band (L-band). Most of WDM systems use C-band and report essay visit nursing extended to use L and S bands to increase capacity of system .
Figure 1.1x WDM regin. Figure 1.10: Wavelength division multiplexing (WDM) Before proceeding to examine different type of WDM, it will be necessary to summarize the usage of introduction paper WDM technology advantages: Upgrade the capacity of current fiber networks without adding new fibers. Add transparency feature to optical channels since they can transport any transmission format: analog, digital at different a synchronize bit rate.
Add scalability feature since any additional demand, it is required to buy and master thesis about of american install equipment at the fiber’s end. Use wavelengths for routing and switching and that adds another dimension to time and space. Depends on wavelength pattern, WDM is divided into two types: Dense WDM (DWDM): It is chosen for transporting very large amounts of to science data traffic over long distances in the telecommunication system. From the size of data that can carry it is considered an optimal way of combining advanced technology functionality with cost efficient transport. Thesis About Of Failure Of American. DWDM able to transport 76-96 lambdas (channels) in introduction to science, conventional band (C-band) in the 1550nm region with 50 GHz spacing and supports 120-160 wavelengths (called ultra-dense WDM) in the L-band with 12.5 GHz spacing. In general, DWDM channels can carry data with 10-100 Gb/s as a bit rates and can reach to 3000km as maximum distance and in transoceanic system, transparent link can reach up to 20,000km.
Recently, commercial systems have ability to transport accumulated traffic capacity in the range of 100 Tb/s . The long distances that DWDM can reach comes from the advantage of the thesis of iris operating window of the EDFA Amplifier to boost the introduction to science paper optical channels . Coarse WDM (CWDM): it is ireland, similar to DWDM by using light wavelength to introduction to science, send signals over a single fiber. It uses 20nm wavelength spacing and it is wider than DWDM and counter-attitudinal that is why CDWM is less costly than DWDM. In addition CDWM supplies only introduction to science paper eight or 16 out of 18 lambdas (in c- band) between any two CDWM multiplexers, which are usually passive, over a pair of single fiber. Wavelengths of CDWDM can carry payload 1.2, 25, 4, 5, or 10 Gb/s which . The maximum distance link that CWDM supports is 100km and that because of CWDM uses a specific wavelength range that cannot be amplified by EDFA amplifier . CWDM is suitable for essay, low-latency and high bandwidth but it is low scalable, complex installation, cost, and to science research paper operation than DWDM . WDM enabling equipment. DWDM systems consist of several main components as show in figure : Figure 1.11 DWDM system structure.
Optical Transmitters and Transponders. To increase the master thesis about of failure of american number of wavelengths in 1550nm band and minimize the signal impairments effects like dispersion, the optical transmitter should be very high resolution, accuracy narrow-band lasers. Such lasers allow close channel spacing. To Science. The optical transmitter lessens loss of essay power and attenuation which to allow optical signal to pass long distances through fiber optic and a high level of introduction to science research signal integrity. Optical amplifiers can be used by these lasers to amplify the signal strength to of iris chang, extend the transmission distance  .
The design of the laser systems should be: Follow the introduction to science ITU-T wavelength frequencies for counter-attitudinal essay, interoperability and component selection issues . Laser system should be tunable to introduction research, control the emission wavelength on demand . Some of DWDM systems use a component called a transponder, which uses optical-to electrical-to optical(O-E-O) conversion to convert a broadband optical signal to essay, specific wavelengths (1330nm or 15550nm to a precision narrow-band wavelength). This conversion is necessary for introduction to science, devices which are not equipped with precision narrowband lasers to multiplex onto chang a single fiber, like ATM switches, routers . They used to amplify optical signals to decrease the effects of power loss and attenuation that coming from passing light pulses through optical fiber. To Science Research Paper. Use the optical amplifier or not in the DWDM depends on the optical transmitter technology and fiber optic long because not all DWDM network types need to boost the optical signals before sending since the signal reaches to fiber end’s terminal at case studies level which photodetector at receiving side can detect and recover. Additionally, optical amplifier technology is the key to achieving the research high-volume transmission, DWDM high speed to occur . Optical Multiplexers and Demultiplexers.
Optical multiplexers and demultiplexers are very important devices and they are considered a core of thesis DWDM technology. Optical multiplexers are used to paper, combine transmit optical signals that have different wavelengths into master thesis about of failure a composite signal which have boosts by optical amplifier if need to amplify before sending onto single optical amplifier. Optical demultiplexrs have opposite function to introduction to science research paper, multiplexer by splitting the composite optical signals into their component wavelengths at the receiving terminal .  Typically, optical multiplexers are passive devices, and work like high precision prisms to split up the individual colors of the DWDM signal . Optical receivers are used to detect arriving optical signals and convert them to a suitable signal for processing by thesis of iris, the receiving device . Typically, optical receivers are passive wideband devices that have ability to detect light over wide range of wavelength between 1300 to 1550 nm region . Remote Optical add/remove Dense multiplexer (ROADM) Remote Optical Add/Drop Multiplexers (ROADMs) are essential devices in DWDM for adding or dropping specific wavelengths (channels) from a fiber that is dense wave division multiplexed and bypass other remaining wavelengths. Usually, they are installed in a multi wavelength fiber span . ( Figure 1.12: Remote Optical add/remove Dense multiplexer (ROADM) . Hierarchy of to science research optical network. Geographically, optical networks are segmented into four tiers, each one depends on the number of users served, demand capacity, geographic area which the tier covers.
Figure 1.13 presents 4 tiers that optical network serves: metro access, metro-core, regional, and backbone tier . Essay. Metro access partition is at the network edge where the end-users can exchange traffic (collects/distributes) with the network; it serves 10-100 users with few kilometers distance long. The main reason to to science paper, build this network is to mechanical thesis, serve the end-user in introduction to science research paper, direct way . Moving up the hierarchy, metro-core tier aggregates the traffic from thousands of customers that relate to access networks and interconnects number of central offices of telecommunication or cable distribution head-end office by home, passing 10s to100s of kilometers. Jump to regional networks which interconnect multiple of paper metro-core networks, each network in this tier is responsible for carrying portion of traffic that passes several metro-core areas. The entire regional networks serve about100s to 1000s of users who cover hundred to a thousand kilometers . Last tier in the four-layer is Backbone (long-haul) networks which span 1000s of kilometers and ideas for a descriptive share millions of users because of carrying the inter-regional networks traffic .
Figure 1.13: Hierarchy of optical network . There is other network architecture based on three-layer as in figure 1.14. Application layer is the top of this model which contains voice, video, and data services. The next layer is to science research, called intermediate layer which based on electronic technology such as Asynchronous Transfer Mode (ATM) switches, SONET/SDH switches, and IP routers. Thesis. These electronic devices pass their payloads to Optical layer (configurable WDM layer) to be carried into introduction to science research paper wavelengths and routed dynamically through optical nodes by using WDM technology and optical switches . Figure 1.14: three layer model . According to , multiwave optical network can be divided into two layers: logical layer and physical layer and thesis about of american each layer is expanded to sub- layers as introduced in figure 1.15. Logical layers can be acted as a packet/cell-switched client logical network (LN) and all electronic components are contained in this layer, while physical layers contain optical components and acts as a server for only one logical network or more. The interface between two layers in to science paper, term of hardware can be noticed in figure 1.16 which is located at external port of Network Access Station (NAS). NAS is considered as a cut line between optical and for a essay electronic domain and each NAS connects to Optical Network Node (ONN) via one or more pairs of fiber which is called access link. Physical layer is spitted to: Optical layer and introduction to science Fiber layer.
Optical layer focuses on generation and transmission of optical connection, routing, and survivability and has four sub-layers: Optical/waveband path, ?? channel , Optical connection, and Transmission channel. Logical connection (LC) is established between external ports (electronic domain) of two NASs through optical nodes and carries logical signal in studies, electronic format like IP packets, ATM cells, or analog video. Every LC is research, carried by what is called a Transmission channel that is used to ideas for a descriptive essay, convert logical signal in electronic domain (logical layer) to transmission signal (Optical domain) which is part of optical layer (figure 1.15). The conversion process usually happens in the transmission processor (TP) that exists in NAS with taking into account the requirements of the optical device that transports it for example the introduction research bandwidth of the optical transmitter (OT), optical receiver (OR), and spectrum channel. Optical connection (OC) is a connection established according to the organized actions between nodes (ONN) and stations (NAS).
It is used to tune the transceiver of NASs to the assigned wavelength of the ??-channel. Fiber layer encompassing the descriptive essay features of the supporting the research paper infrastructure of fiber. Ireland. The fiber layer is introduction to science research paper, subdivided further into the fiber link sublayer and fiber section sublayer. Essay. Virtual connection (VC) is created between two end systems and based on logical path LC which is sublayer from logical layer. In this case Logical path has two logical connections (LC) terminated by introduction, Logical Switching Nod (LSN). Figure 1.15: Optical network layer . Figure 1.16: Layered view of ideas optical network connections . Figure 1.17:Typical connection with multiple hope . Optical network concepts. A network using fiber optic as a transmission medium provides a connections for users to enable communication between them by transporting data from a source to a destination. To perform this process, it requires an intermediate stage which data can be processed for control operation and follows the essentials of optical networking functions.
For successful transportation of optical signals, it essentially follows the methodology of paper interconnection different optical devices altogether and operational procedures. The structure of simple optical network can be seen in the figure 1.18 which depicts number of interconnected nodes with link of optical fibers. Each optical node may act as a transceiver unit with multifunction. It can receive, transmit and processing/switching (if necessary) the thesis of iris chang traffic. Generally, the physical connections of to science research paper optical fiber is point-to-point when connects nodes together. Such links are populated by one or more pairs of fiber and each fiber in pair carries traffic in one direction (unidirectional) or in both directions (bidirectional) and ireland last one is not common . Logical link can be established by introduction research, using fiber links when optical signal traverses through one or many nodes (uninterrupted optical signal) to reach the for a descriptive destination. Ideally, a single wavelength ?? is assigned to each channel (link) to travel from source to introduction to science research paper, destination across multiple optical nodes (uninterrupted link). Ideas Essay. Lightpath is a term used to refer to the signal carried on to science, a specific wavelength, data can be transmitted over these lightpaths in thesis, time of the connections set up and apply controlling mechanism to validate the whole data transmission between each transmitting and receiving node .
As a result, optical transport networks are considered circuit-switched which preconfigure optical circuit path to the bitstreams directly from source to destination between nodes. Bitrate of to science any bitstream is determined by the transmitter and receiver devices. Although there are different devices operate on different bitrate available in the market such 2.5Gb/s or 10Gb/s, different bitrate circuits can be used with each other on the same WDM network because of report essay visit its transparently for different bitrates. This important property of DWM is called grooming which means combining different lower bitrate bitstreams into one with higher bitrate as a shared connection part . Figure 1.18: Optical network structure . Optical network node and switching elements. An optical node plays main role in WDM network since it achieves several tasks depending upon network requirements and its type.
Sending, receiving, resending or redirecting optical signals to node’s neighboring connected nodes are the main functions of introduction to science optical node. It can also function as a router or a switch when resend or redirect optical signals to mechanical thesis statement, desired networking nodes, and to science as a router when directs an of failure input signal wavelength to introduction to science research, a specified output port . When the desired signal can be isolated from an incoming multiplexed signal and ideas routed by the router to a specific port then it is called wavelength router. But if the wavelength of the isolated signal is changed before routing to the output port, then router is known wavelength converting router and in other case is wavelength routing switch( optical switch) in case of paper switching the wavelength to the complaint signal wavelength . MEMS methods connecting arrays of micromirrors that can deflect an optical signal to the appropriate receiver. Search our thousands of essays:
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