Upravljanje proizvodnom jedinicom spojenom na mrežu tijekom nesimetričnih napona na mreži temeljeno na kliznom režimu

The increasing presence of inverter-based distributed generation (DG) units in distribution networks (DNs) requires control methods that achieve high performance not only during normal operating conditions, but also under unbalanced conditions. With a high probability, a type of voltage unbalance in DNs is unequal three-phase voltage magnitudes at the fundamental system frequency. This can occur temporarily due to faults or permanently due to uneven distribution of unbalanced loads, on the three-phases of the DN. This paper proposes a sliding mode (SM) based controller for grid-connected DG units, under unbalanced grid voltage condition. The proposed control strategy employs a nonlinear control scheme to directly cancel out the negative-sequence (NS) components of DG output current under unbalanced voltage condition; and directly regulate the positive-sequence (PS) active and reactive power injected by DG units to main-grid. The control method proposed in this paper is shown to be robust and stable system parameter uncertainties. The validity and effectiveness of the proposed controller is verified by using time-domain simulation studies, under the MATLAB/Simulink software environment.Povećanje udjela distribuiranih proizvodnih jedinica povezanih na mrežu frekvencijskim pretvaračima zahtjeva metode upravljanja koje dobro djeluju tijekom normalnih uvjeta na mreži kao i u nesimetričnim uvjetima. Najčešći tip nesimetričnog napona na distribuiranoj jedinici je nesimetrična amplituda trofaznog napona na fundamentalnoj frekvenciji. To se događa privremeno zbog kvarova ili trajno zbog nejednake distribucije nesimetričnih tereta na tri faze distribuirane proizvodne jedinice. U ovom radu predlaže se regulator temeljen na kliznom režimu za upravljanje proizvodnom jedinicom spojenom na mrežu tijekom nesimetričnih napona na mreži. Predložena strategija upravljanja koristi nelinearnu shemu upravljanja kako bi se izravno poništile inverzne komponente izlazne struje tijekom nesimetričnih uvjeta; i izravno upravlja direktnom komponentom radne i jalove snage isporučene u mrežu. Metoda upravljanja predložena u ovom radu pokazala se kao robusna i stabilna uz nesigurne parametre sustava. Opravdanost i učinkovitost predloženog regulatora provjerena je korištenjem simulacija u MATLAB/Simulinku

Unveiling and unraveling aggregation and dispersion fallacies in group MCDM

Priorities in multi-criteria decision-making (MCDM) convey the relevance preference of one criterion over another, which is usually reflected by imposing the non-negativity and unit-sum constraints. The processing of such priorities is different than other unconstrained data, but this point is often neglected by researchers, which results in fallacious statistical analysis. This article studies three prevalent fallacies in group MCDM along with solutions based on compositional data analysis to avoid misusing statistical operations. First, we use a compositional approach to aggregate the priorities of a group of DMs and show that the outcome of the compositional analysis is identical to the normalized geometric mean, meaning that the arithmetic mean should be avoided. Furthermore, a new aggregation method is developed, which is a robust surrogate for the geometric mean. We also discuss the errors in computing measures of dispersion, including standard deviation and distance functions. Discussing the fallacies in computing the standard deviation, we provide a probabilistic criteria ranking by developing proper Bayesian tests, where we calculate the extent to which a criterion is more important than another. Finally, we explain the errors in computing the distance between priorities, and a clustering algorithm is specially tailored based on proper distance metrics

Supply Chain Management and Management Science: A Successful Marriage

The last century has witnessed extant studies on the applications of Management Science (MS) to a diverse set of Supply Chain Management (SCM) issues. This paper provides an overview of the contribution of MS within SCM. A framework is developed in this paper with a sampling of MS contributions to major SCM dimensions. Future research directions are presented

Logistics Decisions in Descriptive Freight Transportation Models: A Review

The objective of this paper is to provide an inventory of approaches to descriptively (as opposed to normatively) model logistics decisions within the context of freight transport modelling. Rather than taking transport modelling frameworks as a starting point, as has been the case in the literature so far, we depart from a framework of logistics decisions. The framework is developed by combining elements of over a dozen existing frameworks from the supply chain management literature. Based on this comprehensive framework, we review freight modelling approaches from the literature. We find that freight modelling can be extended by taking into account previously uncovered areas of logistics decisions, such as those related to marketing or logistics systems forecasting and planning, as well as in areas that are well known from an optimization perspective but not from a descriptive perspective, such as routing and scheduling decisions. We conclude with a systematic listing of such areas, which can be used by researchers and transport modelling practitioners to develop further those transport models that take agent decision making as a starting point

Identification of the Components of Open and Distance Education and Human Resource Development in Iranian Universities

The purpose of the present research was to examine the role of open and distance education on human resource development in Payame Noor University (PNU). The population consisted of consisted of 1082 PhD students of PNU in the period 2011-2012, of whom 321 students were selected as the sample using stratified random sampling. The instrument was a questionnaire developed by the researcher with high validity and reliability (Cronbach’s alpha of 0.898 for open and distance education and 0.972 for human resource development). The data were analyzed using descriptive and inferential statistics (path analysis). Technology, interaction, and facilities were identified as the components of open and distance education (with 22 indices), knowledge, attitude, skill, and behavior were identified as the components of human resource development (with 29 indices). By prioritizing the components and indices of open and distance education and human resource development using LISREL 8.53 (path analysis), a conceptual model is developed which shows that proper design, implementation, and evaluation of distance education in universities can develop the knowledge, attitude, skill, and behavior of its human resources. Since PNU is one of the administrators of Iran’s distance education system, it must train its human resources accordingly.Hence it will be of great help in promoting and developing distance education and heuman resource development. Keywords: Open and distance education, human resources development, components, conceptual mode

On the drivers of demand for innovative freight transportation services

Contemporary innovations in freight transportation and logistics are instrumental in achieving more integrated, efficient, and sustainable services in the global market. While much attention is going to how contemporary innovations, including technology-enabled and management innovations, change the supply of services, little work is done on depicting their changing relationship with freight transportation demand. We present findings from a comprehensive study among Global Fortune 500 companies aimed at understanding what drives the demand for modern transportation services. We investigate the importance of three key service attributes that are growing in importance, i.e., operational control of transport mode, service flexibility and ancillary value-added services. We measure the influence of contextual factors on the choice of service, including supply chain strategy, demand volatility, internal flexibility and industry type. This leads to recommendations for shippers on how they can adjust their supply chains in the future to benefit from new freight services. Our findings also stress the need for the logistics industry to adopt modern service choice approaches

The Prevalence of Mental Health Problems and the Associated Familial Factors in Adolescents in the South of Iran

Background Mental health problems are common among adolescents. Proper screening and rehabilitation could improve adolescents’ function at the present time and in the future. This study aimed to assess the prevalence of psychiatric disorders and the associated familial factors among high school students. Materials and Methods The present cross-sectional study was conducted on 630 high school students (315 boys and 315 girls) aged 13-17 years in Jahrom, Iran. The participants were selected using random cluster sampling. The data were collected using the self-report version of strength and difficulties questionnaire (SDQ), and were analyzed using the SPSS statistical software, version 16.0. Results: The results showed that 22.38% of the students had total difficulty (14.9% of boys, and 29.8% of girls). The highest prevalence was related to peer relationship problems (23%) followed by conduct problems (18.1%), hyperactivity (11.1%), pro-social behaviors (6.3%), and emotional problems (5.7%). The results of multivariate logistic regression analysis revealed that female gender (odds ratio [OR]: 2.52, 95% confidence interval [CI]: 1.68-3.66) increased the odds; while grade 9 (OR=0.52, 95% CI: 0.32-0.83), and number of siblings (OR: 0.88, 95% CI: 0.78-0.99) decreased the odds of mental health problems (

Toxicological Effects of Silver Nanoparticles on Nile Tilapia (Oreochromis niloticus)

The wide use of nano-sized metallic materials could result in the release of these particles into the environment. In addition, due to the dissolution of these nano-materials, some of the adverse effects could result from the dissolved metals. On the other hand, dietary supplements play a key role in improving the immunity of consumers; hence, the use of immune stimulants such as mushroom seems to be very necessary. In this study, the dietary effect of Pleurotus ostreatus mushroom was investigated on serum immunity and liver histopathological indices of Oreochromis niloticus exposed to silver nanoparticles (AgNPs). Serum total protein level enhanced with increasing prebiotic concentration. Serum immunoglobulin and albumin levels increased in the group treated with Pleurotus ostreatus. The amount of these indices significantly increased at the concentration of 0.2 mg/kg; however, glucose value decreased in both of the experimental groups. Serum ALT and ALP levels significantly reduced in the combined treatment group (AgNPs and mushroom) at the concentration of 0.2 mg/kg, in contrast with the control group. In the combination treatment group (AgNPs and mushroom), the serum AST level significantly reduced at concentrations of 0.1 mg/kg and 0.2 mg/kg; however, it increased at the concentration of 0.05 mg/kg compared with the control group, indicating that immunological indices could improve due to the combined use of AgNPs and mushroom. The overall conclusion of this study shows that the use of mushroom at 0.2 mg/kg in combination with AgNPs could partially improve the effect of AgNPs on tilapia