Uncertainty in the Fluctuations of the Price of Stocks

We report on a study of the Tehran Price Index (TEPIX) from 2001 to 2006 as an emerging market that has been affected by several political crises during the recent years, and analyze the non-Gaussian probability density function (PDF) of the log returns of the stocks' prices. We show that while the average of the index did not fall very much over the time period of the study, its day-to-day fluctuations strongly increased due to the crises. Using an approach based on multiplicative processes with a detrending procedure, we study the scale-dependence of the non-Gaussian PDFs, and show that the temporal dependence of their tails indicates a gradual and systematic increase in the probability of the appearance of large increments in the returns on approaching distinct critical time scales over which the TEPIX has exhibited maximum uncertainty.Comment: 5 pages, 5 figures. Accepted to appear in IJMP

Design, analysis and control of a magnetically-coupled multi-port multi-operation-mode residential micro-grid

© 2017 IEEE. This paper proposes topology of a magnetically coupled residential micro-grid consisting of a multi-port DC-DC converter and a single phase grid-connected bi-directional inverter. It integrates photovoltaic (PV) and fuel cell energies to supply the residential load via a common high-voltage dc bus linked to a single phase bidirectional inverter. A battery is used to store the surplus energy of the system and stabilize the bus voltage of the fuel cell port. The multi-port converter includes a three port phase shift converter for integrating renewable sources, a bidirectional buck-boost converter for charging and discharging the battery and an interleaved boost converter for boosting the PV voltage and maximum power point tracking. Using interleaved topology has reduced the effects of both high frequency current ripple and low frequency voltage ripple propagated from inverter on the maximum power point tracking (MPPT) performance. The steady state operation and control strategy of the proposed micro-grid are discussed and simulation results are presented

Copper loss analysis of a multiwinding high-frequency transformer for a magnetically-coupled residential microgrid

© 2018 IEEE. Improvements in characteristics of magnetic materials and switching devices have provided the feasibility of replacing the electrical buses with high-frequency magnetic links in small-scale microgrids. This can effectively reduce the number of voltage conversion stages, size, and cost of the microgrid, and isolate the sources and loads. To optimally design the magnetic link, an accurate evaluation of copper loss of the windings considering both the current waveforms and parasitic effects are required. This paper studies the copper loss analysis of a three-winding high-frequency magnetic link for residential microgrid applications. Due to the nonsinusoidal nature of the voltages and currents, the loss analysis is carried out on a harmonic basis taking into account the variations of phase shift, duty ratio, and amplitude of the waveforms. The high-frequency parasitic phenomena including the skin and proximity effects are taken into account. The maximum and minimum copper loss operating conditions of the magnetic link and their dependency on the phase shift angle and the duty ratio of the connected waveforms are studied. A prototype of the microgrid including the magnetic link is developed to validate the theoretical analysis, evaluate the microgrid efficiency, and perform the loss breakdown

Accurate copper loss analysis of a multi-winding high-frequency transformer for a magnetically-coupled residential micro-grid

© 2017 IEEE. Improvements in characteristics of magnetic materials and switching devices have provided the feasibility of replacing the electrical buses with high frequency magnetic links in micro-grids. This effectively reduces the number of voltage conversion stages, and the size and cost of the renewable energy system. It also isolates the converter ports, which increases the system safety and facilitates bidirectional power flow and energy management. To design the magnetic link optimally, an accurate evaluation of copper loss of the windings considering both current waveforms and parasitic effects is required. This paper studies the accurate copper loss analysis of a three-winding high-frequency magnetic link for residential micro-grid applications. Due to the non-sinusoidal nature of the voltage and currents, the loss analysis is carried out on a harmonic basis taking into account variations of phase shift, duty ratio and amplitude of waveforms. The high frequency skin and proximity effects have are taken into account. The maximum and minimum copper loss operating points of the converter and their dependency on the phase shift and duty ratio of the waveforms are studied and simulation results are presented

A magnetically coupled multi-port, multi-operation-mode micro-grid with a predictive dynamic programming-based energy management for residential applications

© 2018 Elsevier Ltd This paper presents the development of a residential micro-grid topology based on a combination of common magnetic and electrical buses. The magnetic bus interfaces two low voltage dc buses linking a PV and a fuel cell to a high voltage dc bus connected to a grid-tied single-phase bidirectional inverter. A battery is used to store the surplus energy of the system and stabilise the dc voltage of the fuel cell bus. A synchronised bus voltage balance (SBVB) technique is used to reduce the conduction losses and increase the soft switching operation range of the converters. To improve the maximum power point tracking (MPPT) performance and system efficiency, appropriate control techniques and compensation blocks are designed. The proposed micro-grid is able to operate in multiple grid-connected and off-grid operation modes according to a predictive 2D dynamic programming-based energy management. A mode selection and transition strategy is developed to select the appropriate operation mode and smooth the mode transition. A detailed study of the micro-grid including steady-state operation, small signal modelling, controller design, and energy management is presented. A prototype of the system is developed, and experimental tests are conducted for an energy management scenario

Comparison of working memory, divided and selective attention in children with different types of attention deficit hyperactivity disorder- ADHD

Introduction: Attention Deficit and Hyperactivity are among the most common behavioral disorders in children which include three subgroups including inattention, hyperactivity - impulsivity (disinhibition) and mixed form. Attention Deficit and Hyperactivity Disorder might be along with basic symptoms in memory and attention and Working memory and various forms of selective and divided attention are compared in this study in hyperactive children and children with attention deficit.Method: in this study, 40 hyperactive children and children with attention deficit who have referred to children's psychiatric and occupational therapy centers in Tehran in 2016 have been selected as sample using stratified random sampling. This was a descriptive-analytic study. Data were collected using Kim Karad’s working memory test and Stroop’s selective and divided attention test. Obtained data were analyzed using SPSS software.Findings: findings showed significant difference between average working memory of three groups of children with attention deficit, hyperactivity and mixed form.  In this way that working memory in mixed form group had the weakest average, attention deficit had moderate average and hyperactive had the highest average. Comparison of selective and divided attention also indicated a significant difference between groups. In this way that, selective attention of children with mixed form with the least of all and it was the highest of all in hyperactive children. Divided attention or attention management was also the weakest in mixed form group and it had a higher average than the rest in hyperactive type.Discussion and conclusion: based on objectives and method of the research which was comparative, findings showed that active visual memory was more damaged in children with mixed form compare to two types of hyperactive children or children attention deficit. Also, findings related to comparison of selective and divided attention showed that selective and divided attention was lower in hyperactive children with mixed attention deficit compared to hyperactive children and was lower than attention deficit type in the next level.Keywords: selective attention, divided attention, hyperactive, attention deficit, mixe

Design and analysis of protection circuits for safe operation of direct matrix converters

© 2017 IEEE. This paper is concerned with the process of current commutation and overvoltage protection in matrix converters. The mechanisms involved in the commutation process and clamp circuit are described and simulation waveforms are presented. A four-step semi-soft commutation strategy is described that this technique relies on knowledge of the output current direction and the ability to control the direction of current within the switches. Also a clamp circuit is demonstrated by simulation as an overvoltage protection for matrix converter. Simulation results are presented using a simulation model of the three-phase direct matrix converter in MATLAB/Simulink

Short communication: Monogenean species from freshwater fishes of Zanjan province, Iran

This parasitological research was conducted from September 2002 to August 2003 on the freshwater fishes in Zanjan province. Totally 155 fishes including Capoeta capoeta idellaI (91), Carassius auratus (8), Leuciscus cephalus (18), Ctenopharyngodon idella (10), Barbus lacerta (8), Allburnoides bipunctatus (10) and Alburnus filippi (10), were seined from five different stations. The fishes were transferred to Laboratory of Aquatic Organisms Research in Science Faculty of Shahid Beheshti University. The skin and gills of fishes were studied under light and stereomicroscope. The identified monogenean parasites included seven Dactylogyrus species as: D. chramuli, D. gracilis, D. Lenkorani and D. pulcher from Capoeta capoeta gracilis; D. lamellatus from Ctenopharyngodon idella; D. goktschaicus from Barbus lacerta and D. vistulae from Albunoides bipunctatus and Alburnus filippi. Various Gyrodactylus spp. from skin and gills of different fish specimens and one Paradiplozoon sp. from gill of Alburnoides bipunctatus were observed. This is the first parasitological investigation that has been done on the freshwater fishes of Zanjan province