Three-Dimensional Simulation of Plasma Deformation During Contact Opening in a Circuit Breaker,Including the Analysis of Kink Instability and Sausage Instability

A three-dimensional （3-D） transient model has been developed to investigate plasma deformation driven by a magnetic field and its influence on arc stability in a circuit breaker. The 3-D distribution of electric current density is obtained from a current continuity equation along with the generalized Ohm＇s law; while the magnetic field induced by the current flowing through the arc column is calculated by the magnetic vector potential equation. When gas interacts with an arc column, fundamental factors, such as Ampere＇s law, Ohm＇s law, the turbulence model, transport equations of mass, momentum and energy of plasma flow, have to be coupled for aria- lyzing the phenomenon. The coupled interactions between arc and plasma flow are described in the fl＇amework of time-dependent magnetohydrodynamic （MHD） equations in conjunction with a K-~ turbulence model. Simulations have been focused on sausage and kink instabilities in plasma （these phenomena are related tO pinch effects and electromagnetic fields）. The 3-D sjm- ulation reveals the relation between plasma deformation and instability phenomena, which affect arc stability during circuit breaker operation. Plasma deformation is the consequence of coupled interactions between the electromagnetic force and plasma flow described in simulations.

The Effects of SF_6-Cu Mixture on the Arc Characteristics in a Medium Voltage Puffer Gas Circuit Breaker due to Variation of Thermodynamic Properties and Transport Coefficients

In a gas circuit breaker,metal vapor resulting from electrode erosion is injected into the arc plasma.The arc then burns in a mixture of SF;and electrode vapor,which has properties significantly different from those of pure SF;.Thermodynamic properties and transport coefficients of thermal plasmas formed in SF;-copper vapor mixtures change as a function of temperature and pressure.The property that is mostly affected by the presence of copper is electrical conductivity,which is important in magnetohydrodynamic（MHD） analysis.In this study,the transport coefficients of SF;in the presence of 10 percent copper are considered as the basis of MHD simulation.Comparisons are made between the results during arc formation for pure SF;and SF;-Cu mixture in a medium voltage（MV） circuit breaker.According to the transport coefficients influenced by the SF;-Cu mixture,the distribution of the electric potential, temperature,electromagnetic force density and current density of the arc column are presented and discussed.Also,the arc stability and pinch effect near current zero with 3-D simulation are investigated,which is advantageous to improving the efficiency of arc plasma simulation.

Assessment of drought hazard,vulnerability and risk in Iran using GIS techniques

The drought has enormous adverse effects on agriculture,water resources and environment,and causes damages around the world.Drought risk assessment and prioritization of drought management can help decision makers and planners to manage the adverse effects of drought.This paper aims to determine the risk of drought in Iran.At the first stage,standardized precipitation index(SPI)was calculated for the period 1981–2016.Then the probability map of different drought classes or drought hazard probability map were prepared.After that the indicator-based vulnerability assessment method was used to determine the drought vulnerability index.Five indices including climate,topography,waterway density,land use and groundwater resources were chosen as the most critical factors of drought in Iran and followed by the analytical hierarchy process questionnaire,the weights of each index were obtained based on expert opinions.Fuzzy membership maps of each index and sub-index were prepared using ArcGIS software.The drought vulnerability map of Iran was plotted using these weights and maps of each indicator.Finally,the drought risk map of Iran was provided by multiplying drought hazard and vulnerability maps.According to the 43-completed questionnaires by experts,climate index has the highest vulnerability to drought.Climate does not have an important role in drought hazard index,but it is the most crucial factor to classified drought vulnerability index.The results showed that central,northeast,southeast and west parts of Iran are at high risks of drought.There are regions with different risks in Iran due to unusual weather and climatic conditions.We realized that the climate and the groundwater situation is almost the same in the central,east and south parts of Iran,because the land use plays a crucial role in the drought vulnerability and risk in these areas.The drought risk decreases from the center of Iran to the southwest and northwest.

Analysis of Chaotic Ferroresonance Phenomena in Unloaded Transformers Including MOV

We study the effect of a parallel metal oxide surge arrester on the ferroresonance oscillations of transformers. It is expected that the arresters generally cause ferroresonance drop out. Simulation has been done on a three phase power transformer with one open phase. Effect of varying input voltage is studied. The simulation results reveal that connecting the arrester to transformers poles, exhibits a great mitigating effect on ferroresonant over voltages. Phase plane along with bifurcation diagrams are also presented. Significant effect on the onset of chaos, the range of parameter values that may lead to chaos and magnitude of ferroresonant voltages is obtained, shown and tabulated.

Exploring the potential and safety of quantum dots in allergy diagnostics

Biomedical investigations in nanotherapeutics and nanomedicine have recently intensified in pursuit of new therapies with improved efficacy.Quantum dots(QDs)are promising nanomaterials that possess a wide array of advantageous properties,including electronic properties,optical properties,and engineered biocompatibility under physiological conditions.Due to these characteristics,QDs are mainly used for biomedical labeling and theranostic(therapeutic-diagnostic)agents.QDs can be functionalized with ligands to facilitate their interaction with the immune system,specific IgE,and effector cell receptors.However,undesirable side effects such as hypersensitivity and toxicity may occur,requiring further assessment.This review systematically summarizes the potential uses of QDs in the allergy field.An overview of the definition and development of QDs is provided,along with the applications of QDs in allergy studies,including the detection of allergen-specific IgE(sIgE),food allergens,and sIgE in cellular tests.The potential treatment of allergies with QDs is also described,highlighting the toxicity and biocompatibility of these nanodevices.Finally,we discuss the current findings on the immunotoxicity of QDs.Several favorable points regarding the use of QDs for allergy diagnosis and treatment are noted.

Comparative Study on Characteristics and Cytotoxicity of Bifunctional Magnetic-Silver Nanostructures: Synthesized Using Three Different Reducing Agents

Magnetic-silver nanostructures were synthesized via optimized chemical conditions, and their characteristics and cytotoxicity were compared as candidates for the magnetic delivery of silver nanoparticles toward cancer cells. Magnetic-silver nanostructures were prepared through the reduction of silver ions in the presence of iron oxide nanoparticles using three different reducing agents （glucose, maltose and sodium citrate）. Their physicochemical characteristics were determined using ultraviolet-visible spectroscopy, X-ray diffraction analysis, transmission electron microscopy, selected area electron diffraction analysis, Fourier transformed infrared spectroscopy, atomic absorption spectroscopy, vibrating sample magnetometry and differential scanning calorimetry. Cytotoxic activities were evaluated against a human liver hepatocellular carcinoma cell line. Fabricated nanostructures, which exhibit differences in size, silver content, magnetic saturation value and cytotoxicity, represent sufficient superparamagnetic properties and considerable cytotoxicity to be suggested as effective tools in magnetic targeting of silver nanoparticles as an approach to cancer therapy.