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Context: Post-traumatic stress disorder (PTSD) is a chronic psychiatric disorder that occurs as a result of an accident or lifethreatening event. The purpose of our study was to examine the prevalence of PTSD in the Iranian population from 2000 to 2015 through a meta-analysis of the published studies to review the epidemiologic evidence of PTSD after disasters and wars and to examine PTSD determinants. Evidence Acquisition: The electronic databases including PubMed, Embase, Web of Science, Magiran, etc. were explored to find related papers. Two authors independently reviewed and extracted data via an extraction sheet, and disagreements were resolved by holding a meeting with a third author. Meta-analysis was performed using "metaprop" command in STATA 11 software. Studies with < 25 participants were excluded from our analysis. Results: Ultimately, 47 studies were included in this meta-analysis. Primary PTSD was investigated in 44 studies and secondary PTSD in six studies. Forty studies investigated natural PTSD and five studies technical PTSD. PTSD related to childbirth, job, earthquake, war, burn, accident, and rape events were investigated in seven, six, nine, nine, two, two, and two studies, respectively, and their pooled prevalence were 25%, 30%, 58%, 47%, 40%, 11%, and 74%, respectively. Conclusion: The results revealed that the burden of PTSD among the Iranian population exposed to wars and disasters is high. PTSD was correlated with a range of factors including demographic and background factors and characteristics of the event exposure. [ABSTRACT FROM AUTHOR]

Background: Many studies have shown that stress adversely effects cognitive function. However, the effect of acute mental stress is not well understood. Objectives: In this study, the effect of match-related stress on cognitive performance factors before and after matches has been studied among female futsal players of Pol-e Dokhtar, Lorestan province, in the west of Iran. Methods: Futsal players' perceptive and cognitive functions were studied using paced auditory serial test (PASAT) before and after each match. Ten female futsal players from Pol-e Dokhtar, Lorestan, with an average age of 20± were tested using PASAT, 60 minutes before and after each match. Their cognitive function was measured using criteria, such as general mental health (GMH), sustained attention (SA), average response speed (ARS), and mental fatigue (MF). Moreover, the changes in salivary cortisol concentration were also measured. Results: The results indicated that in female futsal players, cortisol concentration in plasma was much higher before the match, compared with its concentration after the match. It should also be noted that general health, sustained attention, and response speed were higher after the match. On the other hand, their mental fatigue after the match was significantly lower than before the match. Conclusions: It could be concluded that, before the match, stress level could highly effect individuals' cognitive function. This impaired cognitive function seems to be due to severe mental stress, which in turn increases blood cortisol level. [ABSTRACT FROM AUTHOR]

Cascaded H-bridge multilevel power electronic converters generally require several dc sources. An alternative option is to replace all the separate dc sources feeding the H-bridge cells with capacitors, leaving only one H-bridge cell with a real dc voltage source. This will yield a cost-effective converter. However, the required capacitor voltage balancing is challenging. In this paper, using the phase-shift modulation approach, a new control method for cascaded H-bridge multilevel converters fed with only one independent dc source is presented. The proposed method has a wide voltage regulation range for the replacement capacitors in the H-bridge cells. Experimental and simulation results support the proposed control method. [ABSTRACT FROM PUBLISHER]

This paper describes a research conducted on a single-phase flying capacitor active rectifier. An online process that reduces the total number of switching events, which leads to a reduction of switching losses in the converter, is introduced. This method is based on redundant state selection, which is used to regulate the voltage of flying capacitors. The proposed approach is general and can be applied to flying capacitor converters with any number of levels. Furthermore, in order to control the inrush current at the start of operation and avoid extra voltage and current stress for active switches and capacitors, a start-up procedure that precharges the flying capacitors is proposed. With this precharge procedure, no additional hardware is needed. Simulation and laboratory results demonstrate these new concepts. [ABSTRACT FROM PUBLISHER]

This paper considers achieving the minimum total harmonic distortion (THD) or frequency-weighted THD (WTHD) of the staircase-modulated output voltage of single-phase multilevel inverters, with or without elimination of the lowest order harmonics. The minimal THD values, together with the corresponding step angles and dc voltage source ratios, have been obtained for the 5-, 7-, 9-, 11-, and 13-level cases; accounting for the device voltage drops when the load is resistive or is moderately inductive is described. Similarly, the minimal WTHD values, together with the corresponding step angles and dc source voltage ratios, have been obtained for the five-, seven-, and nine-level waveform cases. The results show that requiring harmonic elimination leads to larger W/THD than the minimum W/THD that can be achieved without this requirement. Furthermore, a 13-level waveform is needed to attain a voltage THD less than 5%, and a nine-level waveform is needed to attain a WTHD less than 0.5%. Experimental measurements are presented as verification of the analytical results. [ABSTRACT FROM PUBLISHER]

Two active capacitor voltage balancing schemes are proposed for single-phase (H-bridge) flying-capacitor multilevel converters. They are based on the circuit equations of flying-capacitor converters. Consequently, they can be implemented using straightforward control rules. In particular, the first technique is based on an algorithm which follows the standard multilevel modulation. Then, it utilizes a redundant state selection table for capacitor voltage balancing. In the second method, multiple duty cycles are defined and modulated in direct response to the capacitor voltages. The most important advantage of these two proposed methods is that they can be utilized to converters with any desired number of levels in their output voltage. Moreover, the analysis and implementation of both methods are straightforward. Through simulation and experimental implementation, these methods are shown to be effective on capacitor voltage regulation in flying-capacitor multilevel converters. [ABSTRACT FROM PUBLISHER]

Multilevel power electronic converters have gained popularity in high-power applications due to their lower switch voltage stress and modularity. Cascaded H-bridge converters are a promising breed of multilevel converters which generally require several separate dc voltage sources. By utilizing the redundant switching states, it is possible to replace the separate dc voltage sources with capacitors and keep only the one with the highest voltage level. Redundancy in the charge and discharge modes of the capacitors is assumed to be adequate for their voltage regulation. However, the effects of the output current of the converter as well as the time duration of the redundant switching states have been neglected. In this paper, the impacts of the connected load to the cascaded H-bridge converter as well as the switching angles on the voltage regulation of the capacitors are studied. This paper proves that voltage regulation is only attainable in a much limited operating conditions that it was originally reported. In addition, based on the analysis of the converter, a simplified formula is found which can be used to find those modulation indices that regulate the voltage of the capacitor. This formula can be used in harmonic minimization problems while capacitor voltage regulation is ensured. Simulation and laboratory results are provided to confirm the analysis. [ABSTRACT FROM PUBLISHER]

Many static synchronous compensators (STATCOMs) utilize multilevel converters due to the following: 1) lower harmonic injection into the power system; 2) decreased stress on the electronic components due to decreased voltages; and 3) lower switching losses. One disadvantage, however, is the increased likelihood of a switch failure due to the increased number of switches in a multilevel converter. A single switch failure, however, does not necessarily force an (2n + 1)-level STATCOM offline. Even with a reduced number of switches, a STATCOM can still provide a significant range of control by removing the module of the faulted switch and continuing with (2n - 1) levels. This paper introduces an approach to detect the existence of the faulted switch, identify which switch is faulty, and reconfigure the STATCOM. This approach is illustrated on an eleven-level STATCOM and the effect on the dynamic performance and the total harmonic distortion (THD) is analyzed. [ABSTRACT FROM AUTHOR]