Distribution by Scientific Domains
Distribution within Medical Sciences

Kinds of Requests

  • bandwidth request
  • first request
  • maternal request
  • patient request
  • repeat request

  • Terms modified by Requests

  • request form

  • Selected Abstracts

    Validation of a brief symptom questionnaire (ReQuest in Practice) for patients with gastro-oesophageal reflux disease

    G. RUBIN
    Summary Background, A clinical need exists for a means of assessing symptom control in patients with gastro-oesophageal reflux disease. The ReQuest questionnaire has been extensively validated for symptom assessment in both erosive and non-erosive gastro-oesophageal reflux disease but was designed for research purposes. We derived a shorter version (ReQuest in Practice) that would be more convenient for clinical practice. Aim, To validate ReQuest in Practice in patients suffering from gastro-oesophageal reflux disease. Methods, Multicentre, non-interventional, crossover comparison. Patients completed ReQuest in Practice followed by ReQuest or vice versa. Before and after a planned endoscopy, patients completed the health-related quality of life questionnaire GERDyzer. Internal consistency and the Intraclass Correlation Coefficient were calculated. Construct validity was evaluated by correlation with ReQuest and GERDyzer. Results, There was high internal consistency of ReQuest in Practice (Cronbach's alpha: 0.9) and a high Intraclass Correlation Coefficient of 0.99. The measurement error of ReQuest in Practice was 4.1. High correlation between ReQuest in Practice and ReQuest (Spearman correlation coefficient: 0.9) and GERDyzer (Spearman correlation coefficient: 0.8) demonstrated construct validity. Conclusions, ReQuest in Practice was proven to be valid and reliable. Its close correlation with ReQuest makes it a promising tool to guide the clinical management of patients across the full spectrum of both erosive and non-erosive gastro-oesophageal reflux disease. [source]

    International validation of ReQuest in patients with endoscopy-negative gastro-oesophageal reflux disease

    K. D. Bardhan
    Summary Background :,Reflux Questionnaire (ReQuest), a newly developed gastro-oesophageal reflux disease-sensitive scale, can be used to reliably evaluate the effect of treatment on gastro-oesophageal reflux disease symptoms. Aim :,International validation of this scale, in patients suffering from endoscopy-negative gastro-oesophageal reflux disease. Methods :,In this open, multicentre and multinational clinical trial 840 endoscopy-negative gastro-oesophageal reflux disease patients received pantoprazole 20 mg daily for 28 days. The long and short versions of ReQuest were completed both in the pre-treatment and treatment phases. For scale development an item reduction analysis was performed. Internal consistency, test,retest reliability and responsiveness were calculated for psychometric analysis. Construct validity was evaluated by comparison with the Gastrointestinal Symptom Rating Scale and the Psychological General Well-being questionnaire by means of correlation coefficients. Results :,Factor analyses confirmed the content validity of both long and short version of ReQuest. Psychometric calculations proved high internal consistency (Cronbach's alpha: 0.9), test,retest reliability [Intraclass Correlation Coefficient: 0.9 (long vs. long) and 0.8 (short vs. short)], and responsiveness (Responsiveness Index 320.3) of the scale, for which also good construct validity was achieved (correlation coefficient: Gastrointestinal Symptom Rating Scale ,0.6; Psychological General Well-being ,0.4). Conclusion :,ReQuest proved valid, reliable, and responsive in this multinational clinical trial to evaluate treatment response in endoscopy-negative gastro-oesophageal reflux disease patients. [source]

    AODV-RIP: improved security in mobile ad hoc networks through route investigation procedure

    Byung-Seok Kang
    Abstract Most routing protocols in mobile ad hoc networks (MANETs) place an emphasis on finding paths in dynamic networks without considering security. As a result, there are a number of attacks that can be used to manipulate the routing in MANET. A malicious node that sends a modified control message to an intermediate node can disturb the network using a control message. To solve this problem, we introduce AODV protocol with route investigation procedure (AODV-RIP). It uses two additional control messages to defeat security attacks that can occur in AODV routing protocol. When an intermediate node that is on the path between the source node and the destination node receives a control message, it sends a Rroute Investigation Request (IREQ) message to the destination node in order to check the reliability of the control message. According to the existence of Route Investigation Reply (IREP), the intermediate node decides whether it transmits the control message to the source node or not. Consequently, the intermediate node that receives the control message confirms that it is using two additive control messages: IREQ and IREP. Through this investigation procedure, the source node can obtain a reliable path for transmitting data packets to an intentional destination node. The simulation results show an improvement in the packet delivery ratio and end-to-end delay at the expense of a moderate increase of the control message overhead compared with the current routing protocols. Copyright © 2009 John Wiley & Sons, Ltd. [source]

    CCLRC Portal infrastructure to support research facilities

    Asif Akram
    Abstract The emergence of portal technology is providing benefits in developing portlet interfaces to applications to meet the current and future requirements of CCLRC facilities support. Portlets can be reused by different projects, e.g. the high-profile Integrative Biology project (with the University of Oxford), and in different Java Specification Request 168 Portlet Specification (JSR 168) compliant portal frameworks. Deployment and maintenance of applications developed as portlets becomes easier and manageable. A community process is already beginning and many portal frameworks come with free-to-use useful portlets. As rendering is carried out in the framework, applications can be easily accessible and internationalized. Portlets are compatible with J2EE, thus providing additional capabilities required in the service-oriented architecture (SOA). We also describe how Web service gateways can be used to provide many of the functionalities encapsulated in a portal server in a way to support Grid applications. Portals used as a rich client can allow users to customize or personalize their user interfaces and even their workflow and application access. CCLRC facilities will be able to leverage the work so far carried out on the National Grid Service (NGS) and e-HTPX portals, as they are fully functional and have received detailed user feedback. This demonstrates the usefulness of providing advanced capabilities for e-Research and having the associated business logic in a SOA loosely coupled from the presentation layer for an Integrated e-Science Environment. Copyright © 2006 John Wiley & Sons, Ltd. [source]

    Making a Request for a Service in Spanish: Pragmatic Development in the Study Abroad Setting

    Rebeca Bataller
    Abstract: This study addresses the development of the request strategies used in two service encounter scenarios by 31 nonnative speakers of Spanish spending 4 months living and studying in Valencia, Spain. The main method of data collection was an open role-play in which participants interacted with a Spanish native speaker. Results show that while there were some aspects of the learners' request production that changed after the study abroad experience, there were other aspects that remained unaffected. Knowing which aspects from the nonnative speakers' request production are acquired and which ones are not after a student has been immersed in the target culture for 4 months is relevant to informing second language acquisition, specifically the field of interlanguage pragmatics in the study abroad setting. [source]

    AHRQ's FY 2005 Budget Request: New Mission, New Vision

    Agency for Healthcare Research, Carolyn M. Clancy Director, Quality
    First page of article [source]

    Request to BACCN researchers

    Julie Scholes

    A Coroner's Request for Closure: The Value of the Stored Electrogram

    Pacemaker diagnostics can be useful to troubleshoot both during life and after death. A 58-year old man with a single chamber ventricular pacemaker and a previous His bundle ablation died suddenly. Interrogation of his pacemaker revealed the cause of death not as pacemaker malfunction, but a fatal ventricular arrhythmia. [source]

    Disobeying an Illegitimate Request in a Democratic or Authoritarian System

    Stefano Passini
    Crimes of obedience in the form of illegal or immoral acts committed in response to orders from authority occur in many contexts. In particular, under some circumstances of threats, people can easily accept restrictions upon democratic procedures. Recent studies have underlined the role of legitimacy in understanding the authority relationship and the importance of evaluating the legitimacy of the request rather than the legitimacy of the authority in preventing the rise of authoritarianism. The purpose of this study was to verify if people respond differently when an illegitimate request is put forward by a democratic or an authoritarian authority. The results on 224 subjects confirmed that people tend to be more obedient when they perceive authorities as democratic, notwithstanding the legitimacy of their requests. [source]

    Request for Notice of Motions for the Australian Veterinary Association Annual General Meeting 24 May 2006 (First Request)

    Article first published online: 1 JUN 200
    No abstract is available for this article. [source]

    2002 Vincent duVigneaud Award: American Peptide Society Request for Nominations

    Article first published online: 9 OCT 200
    No abstract is available for this article. [source]

    Request for Clarifications on paper published

    ACTA PAEDIATRICA, Issue 12 2009
    Rita Clementi
    No abstract is available for this article. [source]

    Request for existing experimental datasets on color differences

    Manuel Melgosa
    Abstract The Technical Committee 1-55 of the International Commission on Illumination on "Uniform color space for industrial color difference evaluation" is requesting the submission of datasets for use in developing a new approximately uniform color space for industrial use. The data should be submitted to the TC Chair, Dr. Manuel Melgosa at the University of Granada. © 2007 Wiley Periodicals, Inc. Col Res Appl, 32, 159, 2007 [source]

    Differentiation and integration: guiding principles for analyzing cognitive change

    Robert S. Siegler
    Differentiation and integration played large roles within classic developmental theories but have been relegated to obscurity within contemporary theories. However, they may have a useful role to play in modern theories as well, if conceptualized as guiding principles for analyzing change rather than as real-time mechanisms. In the present study, we used this perspective to examine which rules children use, the order in which the rules emerge, and the effectiveness of instruction on water displacement problems. We found that children used systematic rules to solve such problems, and that the rules progress from undifferentiated to differentiated forms and toward increasingly accurate integration of the differentiated variables. Asking children to explain both why correct answers were correct and why incorrect answers were incorrect proved more effective than only requesting explanations of correct answers, which was more effective than just receiving feedback on the correctness of answers. Requests for explanations appeared to operate through helping children notice potential explanatory variables, formulate more advanced rules, and generalize the rules to novel problems. [source]

    Understanding and Responding to Patients' Requests for Assistance in Dying

    Judith Kennedy Schwarz
    Purpose: To explore how nurses experience and respond to patients' requests for assistance in dying (AID). Design and Methods: A phenomenological study of 10 self-selected nurses. Findings: Four major themes: Being Open to Hear and Hearing; Interpreting and Responding to the Meaning; Responding to Persistent Requests for AID, and Reflections. When faced with persistent requests for AID, participants provided a continuum of interventions: refusal, providing palliative care that might secondarily hasten dying, respecting and not interfering with patients' or families' plans to hasten dying, and providing varying types and degrees of direct AID. Their responses were context-driven rather than rule-mandated, and they drew a distinction between secondarily hastening and directly causing death. Conclusions: Few nurses in this study unequivocally agreed or refused to directly help a patient die. Most struggled alone and in silence to find a morally and legally acceptable way to help patients who persisted in requesting AID. Regardless of how they responded, many described feelings of conflict, guilt, and moral distress. [source]

    Requests for information by family and friends of cancer patients calling the National Cancer Institute's Cancer Information Service

    PSYCHO-ONCOLOGY, Issue 8 2006
    Lila J. Finney Rutten
    Abstract Purpose: To characterize their information needs, we examined the main topics of inquiry and discussion (subjects of interaction, SOI) of calls made by family and friends of cancer patients to the National Cancer Institute's Cancer Information Service's (CIS) 1-800-4-CANCER telephone information service and summarized differences by sociodemographic characteristics. Design and analysis: Data from 26 789 family or friends of cancer patients calling the CIS between September 2002 and August 2003 were analyzed. Frequencies, ,2's, and logistic regressions were conducted to ascertain sample characteristics and sociodemographic correlates of each SOI. Results and conclusions: The greatest proportion of calls concerned specific treatment information (54.9%) and general cancer site information (36.9%). Calls about specific treatment information were more likely among Asians, Hawaiian Natives, and Pacific Islanders (OR=1.23, 1.04,1.45), and those with higher education (OR=1.21, 1.18,1.25). As age increased, the odds of calls about specific treatment information also increased (OR=1.05, 1.03,1.07). Females (OR=0.78, 0.72,0.84), Hispanics (OR=0.77, 0.67,0.89), African-Americans (OR=0.68, 0.61,0.76), and American-Indians and Alaskan Natives (OR=0.74, 0.58,0.93) were less likely to inquire about specific treatment information. Inquiries about general cancer site information were more likely among females (OR=1.14, 1.06,1.23) and less likely among younger callers (OR=0.95, 0.93,0.97) and African-Americans (OR=0.87, 0.78,0.98). Differences in inquiries made by sociodemographic subgroups can inform the CIS' and other cancer-related organizations' efforts to develop and disseminate cancer information for family and friends of cancer patients. Copyright © 2005 John Wiley & Sons, Ltd. [source]

    Effects of Administrators' Aspirations, Political Principals' Priorities, and Interest Groups' Influence on State Agency Budget Requests

    This article addresses a long-standing question in public budgeting: What factors influence bureau/agency budget request decisions? Empirical results confirm the complexity of variables that explain different levels of budget requests by over 1,000 state administrative agencies. The expected significant influence of administrator (agency head) aspirations was clearly present. But other important sources enter into the decision of agencies to satisfy rather than maximize. These include the strategic roles, activities, and priorities of governors, legislatures, and interest groups. These political principals' influence operates to constrain, discipline, or even augment agency budget requests. [source]

    ORIGINAL RESEARCH,ERECTILE DYSFUNCTION: Journey into the Realm of Requests for Help Presented to Sexual Medicine Specialists: Introducing Male Sexual Distress

    Edoardo S. Pescatori MD
    ABSTRACT Introduction., The recent availability of noninvasive pharmacological remedies for male sexual function triggered an exponential increase in the number of men requesting help in the sexuality area. Aim., The Italian Society of Andrology explored requests for help, not included in formerly established clinical categories of sexual medicine. Methods., A central board of 67 andrologists identified new areas of requests for help, instrumental for a web-based questionnaire, forwarded to 912 members of the Italian Society of Andrology. Results were submitted to an independent consensus development panel. Main Outcome Measures., A questionnaire response rate of 30.8% was considered acceptable according to standard response rates of medical specialist samples. Results., The Central Board interaction identified two new domains of requests for help: sexual distress and unconventional requests for pro-erectile medications. Web-based questionnaire results suggested that such domains account for 29% and 9% respectively of all requests for help already presented by male patients at sexual medicine clinics. The Independent Consensus Development Panel issued a final consensus document; herewith, the statement defining male sexual distress: A non-transitory condition and/or feeling of inadequacy such as to impair "sexual health" (WHO working definition). Inadequacy can originate both from physiological modifications of male sexual functions, and from diseases, dysfunctions, dysfunctional symptoms and dysmorphisms, both of andrological and non-andrological origin, which do not relate to "erectile dysfunction" (NIH Consensus Development Panel definition), but that might also induce erectile dysfunction. Sexual Distress can lead to a request for help which needs to be acknowledged. Conclusion., The Italian Society of Andrology identified two new areas of requests for help concerning male sexual issues: sexual distress and unconventional requests for pro-erectile medications. These domains, which do not represent new diseases, nonetheless induce the sufferers to seek help and, accordingly, need to be acknowledged. Pescatori ES, Giammusso B, Piubello G, Gentile V, and Pirozzi Farina F. Journey into the realm of requests for help presented to sexual medicine specialists: Introducing male sexual distress. J Sex Med 2007;4:762,770. [source]

    Administrative discretion and the Access to Information Act: An "internal law" on open government?

    Alasdair Roberts
    However, critics complain that some politically sensitive requests - often filed by journalists or political parties - are given differential treatment, with longer delays and tougher decisions on disclosure. An econometric analysis of 2,120 requests handled by Human Resources Development Canada in 1999,2001 suggests that the complaints have some merit. Requests that were identified as sensitive, or that came from the media or political parties, were found to have longer processing time, even after other considerations were accounted for. The probability that such requests would exceed statutory response times was also significantly higher. The analysis illustrates a broader point: that internal bureaucratic procedures play an important role in defining what the right to information means in practice. The analysis also highlights the need to give the federal information commissioner better tools to deal with problems of delay. Sommaire: La Loi sur l'accès à l'information du Canada assure le droit à l'information gouvernementale pour tous les Canadiens. Cependant, les critiques se plaignent du fait que certaines demandes épineuses sur le plan politique - requêtes souvent déposées par des journalistes ou des partis politiques - font l'objet d'un traitement différentiel, avec des délais plus longs et des décisions plus strictes au moment de la divulgation. Une analyse économétrique de 2 120 requêtes traitées par Développement des Ressources humaines Canada de 1999 à 2001 laisse entendre que les plaintes sont en partie justifiées. On a constaté que les requêtes dites «sensibles», ou qui viennent des média ou des partis politiques, prenaient plus de temps à traiter, même compte tenu d'autres considérations. En outre, ces requêtes risquaient souvent de dé passer le temps de réponse légal. L'analyse illustre un point plus général, à savoir que les procédures bureaucratiques internes jouent un rôle important en définissant ce que le droit à l'information signifie dam la pratique. L'analyse souligne également qu'il est néessaire de dormer au Commissaire fédéral à l'information de meilleurs outils pour faire face aux problèmes de délai. [source]

    Continuing Progressive Deterioration of the Environment in the Aral Sea Region: Disastrous Effects on Mother and Child Health

    ACTA PAEDIATRICA, Issue 5 2001
    O Ataniyazova
    Scientists, non-governmental experts (NGOs) and governmental officials from the Central Asian Republics and an international group of invited scientists and NGO representatives participated in a workshop on the disastrous health problems in the Aral Sea Region. Various serious problems were reported in more than 20 presentations. Particular emphasis was put on the way in which adverse environmental factors such as contaminated water and food have contributed to the deterioration of human health, particularly that of mothers and children. Conclusion: There is an urgent request that the international community assists local scientists to develop programmes to improve the health of the population in the Aral Sea Region. [source]

    Ethics Seminars: Withdrawal of Treatment in the Emergency Department,When and How?

    Kelly Bookman MD
    Abstract Although increasing discussion has occurred within emergency medicine about indications for withholding cardiac life support and other resuscitative interventions, emergency physicians (EPs) may be less familiar with the ethical, legal, and practical issues surrounding withdrawal of life support that has already been initiated. Both physicians and out-of-hospital personnel must act rapidly in critical situations and must assume that the patient has the desire to be resuscitated, unless clear evidence exists to the contrary. Often, only after initial life-saving actions have stabilized the patient is there time to reflect and determine a patient's desires regarding such interventions. When the EP can clearly discern a patient's previously stated wishes during the emergency department (ED) stay, these wishes should be honored in the ED. Respecting a patient's request to avoid unwanted, invasive treatments near death may involve withdrawing interventions that could not be withheld during the first few minutes of care. In this article, the authors use a case of out-of-hospital stabilization of a patient as a springboard to review the ethical and legal framework for withdrawal of life-sustaining care, as well as the practical issues involved with withdrawal of such care in the ED. [source]

    Lower-extremity selective voluntary motor control in patients with spastic cerebral palsy: increased distal motor impairment

    Aim, Multiple impairments contribute to motor deficits in spastic cerebral palsy (CP). Selective voluntary motor control (SVMC), namely isolation of joint movement upon request, is important, but frequently overlooked. This study evaluated the proximal to distal distribution of SVMC impairment among lower extremity joints. Method, Using a recently developed tool, the Selective Control Assessment of the Lower Extremity (SCALE), we evaluated the SVMC of the hip, knee, ankle, subtalar joint, and toes in a cross-sectional, observational study of 47 participants with spastic, diplegic, hemiplegic, and quadriplegic CP (22 males, 25 females; mean age 11y 9mo, SD 4y 8mo; Gross Motor Function Classification System levels I,IV). Results, Statistically significant decreases in SCALE scores from hip to toes were found using the Page statistical test for trend (p<0.001). Statistically significant differences (p<0.05) were found between all joint pairs, except toes versus subtalar, toes versus ankle, and right ankle versus subtalar joints. Cross-tabulation of score frequencies for all pairs revealed that proximal joint scores were higher or equal to distal ones 81 to 100% of the time. Excluding toes versus subtalar joints, proximal scores exceeded distal ones 94 to 100% of the time. Interpretation, We confirmed increasing proximal to distal SVMC impairment, which may have implications for treatment and research. [source]

    On Optimal Rules of Persuasion

    ECONOMETRICA, Issue 6 2004
    Jacob Glazer
    A speaker wishes to persuade a listener to accept a certain request. The conditions under which the request is justified, from the listener's point of view, depend on the values of two aspects. The values of the aspects are known only to the speaker and the listener can check the value of at most one. A mechanism specifies a set of messages that the speaker can send and a rule that determines the listener's response, namely, which aspect he checks and whether he accepts or rejects the speaker's request. We study mechanisms that maximize the probability that the listener accepts the request when it is justified and rejects the request when it is unjustified, given that the speaker maximizes the probability that his request is accepted. We show that a simple optimal mechanism exists and can be found by solving a linear programming problem in which the set of constraints is derived from what we call the L -principle. [source]

    Monetary Policy, Credit and Aggregate Supply: The Evidence from Italy

    ECONOMIC NOTES, Issue 3 2002
    Riccardo Fiorentini
    This paper concerns theory and evidence of the monetary transmission mechanisms. Current research has deeply investigated factors, such as dependence of firms on bank credit, that amplify the impact of monetary policy impulses on aggregate demand exerting strong but temporary effects on output and employment. We present an intertemporal macroeconomic equilibrium model of a competitive economy where current production is financed by bank credit, and then we use it to identify supply,side effects of the credit transmission mechanism in data drawn from the Italian economy. We find evidence that the ,credit variables' identified by the model , the overnight rate as a proxy of monetary policy and a measure of credit risk , have permanent effects on employment and output by altering credit supply conditions to firms. To save on space, mathematical proofs, statistical tests and data sources have been gathered in two separate appendices that can be examined on request. (J.E.L.: E2, E5). [source]

    Power flow congestion relief by using customer-side energy storage systems

    Ken Furusawa
    Abstract In recent years, energy storage systems have increasingly been expected as a means of load leveling of the annual load factor. Of course there is an effect of installing the energy storage systems at the substation. But some customers operate their storage system in an integrated way and it also has an effect of increasing the load factor. In this paper the authors proposed that the energy storage systems on the customer side be used for congestion relief on transmission networks. However, it is not clear which kind of customer has the effect of relieving transmission line congestion. First, this paper assumes the authors determine the optimal configuration of energy equipment including energy storage systems. We propose a new contract whereby electric utility subsidizes a part of the entrance cost of the energy storage systems and customers change the output pattern of energy storage according to the request of the electric utility. This paper evaluates the possibility that the contract gives merit to both the electric utility and the customer. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 158(1): 36,45, 2007; Published online in Wiley InterScience ( DOI 10.1002/eej.20299 [source]

    A more practical strategy for interfacing microscale solution phase IEF with commercially available very narrow range IPG strips for optimal protein separation

    ELECTROPHORESIS, Issue 12 2007
    Article first published online: 18 JUN 200
    This article has been removed from Wiley InterScience prior to final publication at the request of the authors. [source]

    Texas Nameplate Company: A Profile of Environmental Success

    Kirsten Koepsel
    An initially ignored customer request started a small Texas company on the road to environmental excellence. Ten years later, it offers an example of solid accomplishment,with more achievements sure to come. © 2001 John Wiley & Sons, Inc. [source]

    Long-term outcomes of children treated with the ketogenic diet in the past

    EPILEPSIA, Issue 7 2010
    Amisha Patel
    Summary Purpose:, The ketogenic diet has well-established short- and long-term outcomes for children with intractable epilepsy, but only for those actively receiving it. However, no information exists about its long-term effects years after it has been discontinued. Methods:, Living subjects were identified who were treated at the Johns Hopkins Hospital with the ketogenic diet from November 1993 to December 2008 for ,1 month, and had discontinued it ,6 months prior to this study. Of 530 patients who were eligible, 254 were successfully contacted by phone or e-mail with a survey and request for laboratory studies. Results:, Questionnaires were completed by 101 patients, with a median current age of 13 years (range 2,26 years). Median time since discontinuing the ketogenic diet was 6 years (range 0.8,14 years). Few (8%) still preferred to eat high fat foods. In comparison to the 52% responder rate (>50% seizure reduction) at ketogenic diet discontinuation, 79% were now similarly improved (p = 0.0001). Ninety-six percent would recommend the ketogenic diet to others, yet only 54% would have started it before trying anticonvulsants. Lipids were normal (mean total cholesterol 158 mg/dl), despite most being abnormal while on the ketogenic diet. The mean Z scores for those younger than age 18 years were ,1.28 for height and ,0.79 for weight. In those 18 years of age or older, the mean body mass index (BMI) was 22.2. Discussion:, This is the first study to report on the long-term effects of the ketogenic diet after discontinuation. The majority of subjects are currently doing well with regard to health and seizure control. [source]

    Survivable wavelength-routed optical network design using genetic algorithms

    Y. S. Kavian
    The provision of acceptable service in the presence of failures and attacks is a major issue in the design of next generation dense wavelength division multiplexing (DWDM) networks. Survivability is provided by the establishment of spare lightpaths for each connection request to protect the working lightpaths. This paper presents a genetic algorithm (GA) solver for the routing and wavelength assignment problem with working and spare lightpaths to design survivable optical networks in the presence of a single link failure. Lightpaths are encoded into chromosomes made up of a fixed number of genes equal to the number of entries in the traffic demand matrix. Each gene represents one valid path and is thus coded as a variable length binary string. After crossover and mutation, each member of the population represents a set of valid but possibly incompatible paths and those that do not satisfy the problem constraints are discarded. The best paths are then found by use of a fitness function and these are assigned the minimum number of wavelengths according to the problem constraints. The proposed approach has been evaluated on dedicated path protection and shared path protection. Simulation results show that the GA method is efficient and able to design DWDM survivable real-world optical mesh networks. Copyright © 2007 John Wiley & Sons, Ltd. [source]

    E-model based comparison of multiple description coding and layered coding in packet networks

    Yugang Zhou
    We examine the performance of multiple description coding (MDC) with and without the use of automatic repeat request (ARQ) protocols for packet network communication, in comparison with layered coding (LC). The rate-distortion lower bound of MDC and LC are incorporated into an E-model based performance measure, which accounts for the additional costs of excess rates and delay incurred from using ARQ. The results show that the relative merits of the schemes depend on the values of the packet loss rates and round-trip-time (RTT). LC is superior for small RTT and unaided MDC is superior for large RTT. For moderate RTT, LC is preferred for small packet loss rates and MDC aided by ARQ is preferred for large packet loss rates. Copyright © 2007 John Wiley & Sons, Ltd. [source]