Light effect in photoionization of traps in GaN MESFETs

Trapping of hot electron behavior by trap centers located in buffer layer of a wurtzite phase GaN MESFET has been simulated using an ensemble Monte Carlo simulation. The results of the simulation show that the trap centers are responsible for current collapse in GaN MESFET at low temperatures. These electrical traps degrade the performance of the device at low temperature. On the opposite, a light-induced increase in the trap-limited drain current, results from the photoionization of trapped carriers and their return to the channel under the influence of the built in electric field associated with the trapped charge distribution. The simulated device geometries and doping are matched to the nominal parameters described for the experimental structures as closely as possible, and the predicted drain current and other electrical characteristics for the simulated device including trapping center effects show close agreement with the available experimental data.Comment: 5 pages, 2 figure

Clinical reasoning assessment through medical expertise theories: Past, present and future directions

Exploration into the concept of "medical expert" dates back to more than 50 years ago, yet yielding three leading theories in the area of clinical reasoning, namely, knowledge structure, hypotheticdeductive, and dual process. Each theory defines "medical expert" in a dissimilar way. Therefore, the methods of assessment through which the experts are identified have been changed during the time. In this paper, we tried to categorize and introduce some widely used tests for identification of experts within the framework of existing main theories. Implementation of the proposed categorization for providing future assessment tools is discussed

A model for evaluation of faculty members� activities based on meta-evaluation of a 5-year experience in medical school

Background: There is a global interest for deploying faculty members� activities evaluation systems, however implementing a fair and reliable system is a challenging issue. In this study, the authors devised a model for evaluation of faculty members� activities with regard to their viewpoints and meta-evaluation standards. Materials and Methods: The reliability of the current faculty members� activities metrics system was investigated in Medical School of Tehran University of Medical Sciences in 2014. Then authors conducted semi-structured interviews regarding meta-evaluation standards and designed a questionnaire based on interviews� results which were delivered to faculty members. Finally, they extracted the components of the model regarding interviews� content analysis and questionnaire�s factor analysis and finalized them in a focus group session with experts. Results: Reliability of the current system was 0.99 (P < 0.05). The final model had six dimensions (mission alignment, accuracy, explicit, satisfaction, appropriateness, and constructiveness) derived from factor analysis of the questionnaire and nine factors (consensus, self-reporting, web-based system, evaluation period, minimum expectancies, analysis intervals, verifiers, flexibility, and decision making) obtained via qualitative content analysis of the interviews. Conclusion: In this study, the authors presented a model for faculty members� activities evaluation based on meta-evaluation of the existing system. The model covered conceptual and executive aspects. Faculty members� viewpoints were the core component of this model, so it would be acceptable in a medical school to use the model for evaluating their activities. © 2015 Journal of Research in Medical Sciences

Skin tag as a cutaneous marker for impaired carbohydrate metabolism: A case-control study

Background: Skin tags are common benign skin tumors usually occurring on the neck and major flexors of older people. A possible association with impaired carbohydrate metabolism has been suggested in previous studies, but the results are not conclusive. Objective: To investigate and compare the prevalence of diabetes and impaired glucose tolerance (IGT) in patients with skin tag and a control group. Patients and methods: A case-control study was conducted in individuals over 15 years old, comparing cases (n=104) with at least three skin tags and age-, sex-, and body mass index (BMI)-matched controls (n=94) without skin tag. Cases and controls were recruited from patients consecutively seen at an academic outpatient dermatology clinic. All patients underwent a standard 2-h oral glucose tolerance test with 75 g glucose. Results: Patients with skin tag had higher frequency of diabetes than the control group (23.07 vs. 8.51, �2 -test, P=0.005). The difference in the frequency of IGT was not significant (13.46 vs. 10.63, �2 -test, P=0.543). There was a positive correlation between the total number of skin tags and the mean fasting plasma glucose (Pearson correlation, r=0.260, P=0.031); patients with more than 30 skin tags were particularly at an increased risk of diabetes (52.0). No correlation was found between the number of skin tags and BMI. We did not find any correlation between the anatomical localization of skin tags and impaired carbohydrate metabolism, except for skin tags under the breast in women. Conclusion: These results showan increased risk of diabetes mellitus in patients with multiple skin tags. With regard to the importance of early diagnosis of diabetes, we recommend a high level of suspicion for impaired carbohydrate metabolism in patients with skin tag. © 2007 The International Society of Dermatology

Evaluation of iterative methods for solving nonlinear scalar equations

This study is aimed at performing a comprehensive numerical evalua-tion of the iterative solution techniques without memory for solving non-linear scalar equations with simple real roots, in order to specify the most efficient and applicable methods for practical purposes. In this regard, the capabilities of the methods for applicable purposes are be evaluated, in which the ability of the methods to solve different types of nonlinear equations is be studied. First, 26 different iterative methods with the best performance are reviewed. These methods are selected based on performing more than 46000 analyses on 166 different available nonlinear solvers. For the easier application of the techniques, consistent mathematical notation is employed to present reviewed approaches. After presenting the diverse methodologies suggested for solving nonlinear equations, the performances of the reviewed methods are evaluated by solving 28 different nonlinear equations. The utilized test functions, which are selected from the re-viewed research works, are solved by all schemes and by assuming different initial guesses. To select the initial guesses, endpoints of five neighboring intervals with different sizes around the root of test functions are used. Therefore, each problem is solved by ten different starting points. In order to calculate novel computational efficiency indices and rank them accu-rately, the results of the obtained solutions are used. These data include the number of iterations, number of function evaluations, and convergence times. In addition, the successful runs for each process are used to rank the evaluated schemes. Although, in general, the choice of the method de-pends on the problem in practice, but in practical applications, especially in engineering, changing the solution method for different problems is not feasible all the time, and accordingly, the findings of the present study can be used as a guide to specify the fastest and most appropriate solution technique for solving nonlinear problems

An early Little Ice Age brackish water invasion along the south coast of the Caspian Sea (sediment of Langarud wetland) and its wider impacts on environment and people

Caspian Sea level has undergone significant changes through time with major impacts not only on the surrounding coasts, but also offshore. This study reports a brackish water invasion on the southern coast of the Caspian Sea constructed from a multi-proxy analysis of sediment retrieved from the Langarud wetland. The ground surface level of wetland is >6 m higher than the current Caspian Sea level (at -27.41 m in 2014) and located >11 km far from the coast. A sequence covering the last millennium was dated by three radiocarbon dates. The results from this new study suggest that Caspian Sea level rose up to at least -21.44 m (i.e. >6 m above the present water level) during the early Little Ice Age. Although previous studies in the southern coast of the Caspian Sea have detected a high-stand during the Little Ice Age period, this study presents the first evidence that this high-stand reached so far inland and at such a high altitude. Moreover, it confirms one of the very few earlier estimates of a high-stand at -21 m for the second half of the 14th century. The effects of this large-scale brackish water invasion on soil properties would have caused severe disruption to regional agriculture, thereby destabilizing local dynasties and facilitating a rapid Turko-Mongol expansion of Tamerlane’s armies from the east.N Ghasemi (INIOAS), V Jahani (Gilan Province Cultural Heritage and Tourism Organisation) and A Naqinezhad (University of Mazandaran), INQUA QuickLakeH project (no. 1227) and to the European project Marie Curie, CLIMSEAS-PIRSES-GA-2009-24751

Tcle challenges of the ward round teaching based on the experiences of medical clinical teachers

Background: Holding educational sessions in a clinical environment is a major concern for faculty members because of its special difficulties and restrictions. This study attempts to recognize the challenges of the ward round teaching through investigating the experiences of clinical teachers in 2011. Materials and Methods:This qualitative research is carried out through purposive sampling with maximum variation from among the clinical teachers of major departments in Isfahan University of Medical Sciences (9 persons). The sampling continued until data saturation. Data were collected through semi-structured interview and analyzed through Collaizzi method. Data reliability and validity was confirmed through the four aspects of Lincoln and Guba method (credibility, conformability, transferability, and dependability). Results: Three major themes and their related sub-themes (minor themes) were found out including the factors related to the triad of clinical teaching (patient, learner, and clinical teacher) (concern about patient�s welfare, poor preparation, lack of motivation, ethical problems), factors related to the educational environment (stressful environment, humiliating environment and poor communication) and the factors related to the educational system of the clinical environment (poor organizing and arrangement of resources, poor system�s monitoring, bad planning and inadequate resource). Conclusion: Ward round teaching has many concerns for teachers, and this should be recognized and resolved by authorities and teachers. If these problems are not resolved, it would affect the quality of clinical teaching. © 2015, Isfahan University of Medical Sciences(IUMS). All rights reserved