Sensorless Commutation Method for Low-Voltage BLDC Motors Based on Unfiltered Line Voltage

This study presents a filterless and sensorless commutation method for low-voltage brushless DC motors. The proposed method utilizes controlled DC-link inverter instead of the Pulse-Width Modulation (PWM) scheme. Therefore, motor voltages and currents become free from the high-frequency noise of PWM switching, thereby decreasing motor losses. Consequently, the method does not require any Low-Pass Filter (LPF) and it does not involve speed-dependent phase delay caused by the LPF. However, current commutation deteriorates waveform of line voltages. Thus, specific functions are defined to compensate for the current commutation spikes and remove false zero-crossing points of line voltages. Furthermore, the use of unfiltered line voltages eliminates the requirement of any phase shifter. Hence, the main superiority of the proposed method over preceding sensorless commutation methods is the simultaneous elimination of the phase shifter and LPF, which makes the method simple and cost-effective. The simulation and experimental results show the effectiveness and validity of the method

Numerical simulation of nanofluids flow and heat transfer through isosceles triangular channels

Nanofluids are stable suspensions of nanoparticles in conventional heat transfer fluids (base fluids) that exhibit better thermal characteristics compared to those of the base fluids. It is important to clarify various aspects of nanofluids behavior. In order to identify the thermal and hydrodynamic behavior of nanofluids flowing through non-circular ducts, in the present study the laminar flow forced convective heat transfer of Al2O3/water nanofluid thorough channels with isosceles triangle cross section with constant wall heat flux was studied numerically. The effects of nanoparticle concentration, nanofluid flow rate and geometry of channels on the thermal and hydrodynamic behavior of nanofluids were studied. The single-phase model was used in simulations under steady state conditions. Results reveal that the local and average heat transfer coefficients of nanofluids are greater than those of the base fluid. Heat transfer coefficient enhancement of nanofluids increases with increase in nanoparticle concentration and Reynolds number. The local heat transfer coefficient of the base fluid and that of the nanofluids decrease with the axial distance from the channel inlet. Results also indicate that an increase in the apex angle of the channel, decreases the Nusselt number and heat transfer coefficient. The wall friction coefficient decreases with increasing axial distance from the channel inlet and approaches a constant value in the developed region. Friction coefficient and pressure drop decrease by increasing the apex angle of the channels

The Use of Cumulative Disciplinary Score in an Integrated Curriculum to Prevent Deliberate Omission of Course Content

Background & Objective: Student assessment is one of the most challenging issues of an integrated curriculum. While calculating an overall score is in line with the goals of integrated curriculum, it poses the risk that some students will deliberately leave out the content of some disciplines, based on the fact that they have lower credits in each block exam. In the present study, we describe the experience of Tehran University of Medical Sciences, Iran, where an integrated medical curriculum has been launched since September 2011 as part of curriculum reform initiative. Methods: In the first academic year, students passed 4 blocks: Molecule and Cell; Tissue; Development and Function; Cardiovascular Function; Blood circulation; and Blood-Respiratory Function. Each block included anatomy, histology, physiology, and embryology. The overall block score was reported at the end of each block. In addition, a cumulative disciplinary score was calculated at the end of the academic year through the summation of the weighted subscores of each discipline in each block. Results: At the end of the year, the number of students who had failed in histology, anatomy, embryology, and physiology were 15, 17, 44, and 3, respectively. They were required to take a disciplinary examination before the beginning of the next academic year. Conclusion: A comparison of the number of students who failed disciplines with low credits (e.g. histology) with those who failed disciplines with high credits (e.g. physiology) suggests that the former had systematically been ignored by some students. The calculation of a cumulative disciplinary score may reduce the deliberate omission of course content in integrated blocks. Key Words: Integration, Student assessment, Cumulative disciplinary scor

A Case Based-Shared Teaching Approach in Undergraduate Medical Curriculum: A Way for Integration in Basic and Clinical Sciences

To present a multiple-instructor, active-learning strategy in the undergraduate medical curriculum. This educational research is a descriptive one. Shared teaching sessions, were designed for undergraduate medical students in six organ-system based courses. Sessions that involved in-class discussions of integrated clinical cases were designed implemented and moderated by at least 3 faculties (clinicians and basic scientists). The participants in this study include the basic sciences medical students of The Tehran University of Medical Sciences. Students’ reactions were assessed using an immediate post-session evaluation form on a 5-point Likert scale. Six two-hour sessions for 2 cohorts of students, 2013 and 2014 medical students during their two first years of study were implemented from April 2014 to March 2015. 17 faculty members participated in the program, 21 cases were designed, and participation average was 60 % at 6 sessions. Students were highly appreciative of this strategy. The majority of students in each course strongly agreed that this learning practice positively contributed to their learning (78%) and provided better understanding and application of the material learned in an integrated classroom course (74%). They believed that the sessions affected their view about medicine (73%), and should be continued in future courses (80%). The percentage demonstrates the average of all courses. The program helped the students learn how to apply basic sciences concepts to clinical medicine. Evaluation of the program indicated that students found the sessions beneficial to their learning

Analyzing the Quality of Objective Structured Clinical Examination in Tehran University of Medical Sciences

Introduction: With the  increasing popularity of performance-based assessments, it is necessary to employ proper indicators to ensure their quality. The present study examines the metrics of Objective Structured Clinical Examination (OSCE). Methods: In this descriptive, cross-sectional research in 10 pre-internship OSCE stations of Tehran University of Medical Sciences in 2012, the cut-off score was determined by borderline regression method and the failure rate was calculated. Root Mean Square Error (RMSE) was used to estimate error rate threshold.  Internal consistency was calculated using Cronbach’s alpha and then, the Standard Error of Measurement (SEM) was determined. Alpha if item deleted, R2 coefficient, intergrade discrimination, difficulty and discrimination indices were calculated for each station. A total of 266 students participated in this exam. Results: A total of 266 students participated in this exam. The OSCE total cut-off score was 52.55 (out of 100). Four students (1.5%) failed the exam and the RMSE equaled 0.45. SEM was 4.84 and Cronbach’s alpha was calculated at 0.70 where the alpha if item deleted scores varied from 0.64 to 0.70. The R2 coefficient ranged from 0.16 to 0.85 and the intergrade discrimination ranged between 0.66 and 1.93. The ranges of difficulty and discrimination indices were 0.71-0.89 and 0.12-0.44 respectively. Conclusion: The internal consistency, SEM and threshold error rate were all acceptable. The alpha if item deleted was in the acceptable range in all stations. In two stations, the R2 value was lower than the desired range. The intergrade discrimination value was appropriate in all stations except one. The stations were not too difficult or highly discriminative which is considered favorable in criterion-referenced exams

Sequential Objective Structured Clinical Examination based on item response theory in Iran

Purpose In a sequential objective structured clinical examination (OSCE), all students initially take a short screening OSCE. Examinees who pass are excused from further testing, but an additional OSCE is administered to the remaining examinees. Previous investigations of sequential OSCE were based on classical test theory. We aimed to design and evaluate screening OSCEs based on item response theory (IRT). Methods We carried out a retrospective observational study. At each station of a 10-station OSCE, the students’ performance was graded on a Likert-type scale. Since the data were polytomous, the difficulty parameters, discrimination parameters, and students’ ability were calculated using a graded response model. To design several screening OSCEs, we identified the 5 most difficult stations and the 5 most discriminative ones. For each test, 5, 4, or 3 stations were selected. Normal and stringent cut-scores were defined for each test. We compared the results of each of the 12 screening OSCEs to the main OSCE and calculated the positive and negative predictive values (PPV and NPV), as well as the exam cost. Results A total of 253 students (95.1%) passed the main OSCE, while 72.6% to 94.4% of examinees passed the screening tests. The PPV values ranged from 0.98 to 1.00, and the NPV values ranged from 0.18 to 0.59. Two tests effectively predicted the results of the main exam, resulting in financial savings of 34% to 40%. Conclusion If stations with the highest IRT-based discrimination values and stringent cut-scores are utilized in the screening test, sequential OSCE can be an efficient and convenient way to conduct an OSCE

Sequential OSCE based on item response theory

Data for this study was gathered from 10 stations of a pre-internship OSCE in Tehran University of Medical Sciences. In each station, a trained, professional rater observed the students’ performance and graded them, according to a scoring rubric, on a Likert-type scale (1: fail to 5: competent). Data from 266 examinees were included in the study

Misconceptions and Integration

Introduction: Pervasive beliefs regarding curricular reform and integration have flourished among medical students, faculty members and medical school administrators. These concepts have extensively impacted the reform process, sometimes by resisting the reforms and sometimes by diverting the curriculum from its planned objectives. In the current paper, we have tried to address the challenges of integration in MD program by looking at the existing literature and the experience of the international universities. Methods: We collected the questions frequently asked during the curricular reform process. We, then, evaluated them, and selected 5 main ideas. In order to find their answers, we searched the literature using these keywords: integration, reform, and undergraduate medical curriculum. Results: The findings are discussed in five sections: 1) Reform is not equivalent to integration, 2) Integration can be implemented in both high school and graduate programs, 3) Organ-system based integration is not the only method available for integration, 4) Integration of two phases (basic sciences and physiopathology) can be considered but it is not mandatory, 5) Integration does not fade basic sciences in favor of clinical courses. Conclusions: It seems that medical education literature and prior experience of the leading universities do not support most of the usual concepts about integration. Therefore, it is important to consider informed decision making based on best evidence rather than personal opinions during the curricular reform process