Devices Selection and Topology Comparison for Medium Voltage DC Solid State Circuit Breakers

DC grid has been treated as a viable solution to solve green-house effect and reduce the cost of fossil fuels. Compared with AC grid, DC grid shows many inherent advantages, such as high efficiency power delivery, less expensive to deploy and no need for phase and frequency synchronization. However, over current protection for DC grid require fast response. To solve this problem, solid state DC circuit breakers need to be promoted. In this thesis, thermal property was taken into consideration to find the most suitable semiconductor devices. Per unitized thermal resistance of the heat sink to the ambient was used to find the reasonable conducting current. Module MOV topology and one MOV topology were compared to see the voltage and current stress ANSYS Simplorer is used to assist in the process. Simulation is used to see the waveform of the current stress and the voltage stress under ideal and non-ideal condition. According to the results, during the ideal condition the current stress and the voltage stress are almost the same. However, under the non-ideal condition, the current stress and voltage stress are different, and the module MOV mode topology is much more reliable and has less current and voltage stress

A Comparative Analysis of the Causes of the Heroine's Tragedy in Tess of the D'Urbervilles and A Rose for Emily

From the perspective of feminist theory, this paper absorbs and inherits the existing research results, makes a deep interpretation of the two works, and makes a richer comparison and exploration of the tragic causes of Tess and Emily, which is conducive to a better understanding of the value of the works, revealing the significance of the works, and hoping to provide a new perspective to think for the study of their works and calling on the society to recognize the female subject status and self-identity, then to get rid of the shackles of traditional thoughts and to master the fate of themselves

External uniform electric field removing flexoelectric effect in epitaxial ferroelectric thin films

Using the modified Landau-Ginsburg-Devonshire thermodynamic theory, it is found that the coupling between stress gradient and polarization, or flexoelectricity, has significant effect on ferroelectric properties of epitaxial thin films, such as polarization, free energy profile and hysteresis loop. However, this effect can be completely eliminated by applying an optimized external, uniform electric field. The role of such uniform electric field is shown to be the same as that of an ideal gradient electric field which can suppress the flexoelectricty effect completely based on the present theory. Since the uniform electric field is more convenient to apply and control than gradient electric field, it can be potentially used to remove the flexoelectric effect induced by stress gradient in epitaxial thin films and enhance the ferroelectric properties.Comment: 5 pages, 3 figure

A Conceptual Model of Trust Influencing Factors in Robo-Advisor Products: A Qualitative Study

As an integration of e-commerce and traditional financial service, robo-advisor is a promising product that recommends portfolios to individual investors based on modern technologies. However, this industry faces many challenges such as slow adoption and distrust from customers. This paper extends prior literatures in robo-advisor by exploring trust influencing factors and their detailed sub-factors from the perspective of five dimensions of trust. In this study, we not only validated previous factors of trust in the context of robo-advisor, but also found several new factors influencing customers’ feelings. A conceptual model is further proposed. The data analysis is based on semi-structured interviews with 27 investors. Understanding trust factors of robo-advisor helps the service vendors provide a better product for individual investors and facilitates faster adoption behavior from customers, which promotes further development of the industry

Mitigation of nutrient leaching from bioretention systems using amendments

Bioretention systems have been showcased to be effective in reducing stormwater quantity and improving stormwater quality. However, the systems can also leach nutrients, especially during their initial operation, which needs to be mitigated to optimize their benefits. To examine the efficiency of six amendments selected primarily for reducing phosphorus (P) leaching, six amended and two control cells were constructed and monitored soon after their construction in the field of the 2020 growing season. The effects of the amendments on both the hydrological performance (in terms of water retention rate (WRR)) and water quality performance (in terms of the event mean concentration and pollutant removal rate) were investigated. The results showed that all amendments had the capability of preventing or mitigating P leaching from bioretention systems to varying degrees, with the water treatment residual (WTR) outperforming all other amendments, followed by the activated aluminum (AA) and sorptiveMEDIA (SM) amendments. In addition, some of the amendments (i.e., drywall (DRY), WTR, and SM) were also found to be beneficial in reducing the nitrogen (N) leaching to a slight degree, whereas eggshell (EGG) introduced an extra source of N leached. Furthermore, the temporal evolution of the P leaching of the amendment cells was found to be different from that of the control cells. The same result was not observed for the temporal evolution of the N leaching, implying that the amendments (except EGG) did not largely affect the N leaching. Among the amendments’ effect on WRR, there was no obvious difference. Whereas the observed differences between the control cells and some amendment cells in vegetation growth and antecedent media moisture condition might imply their potential impacts on the hydrologic performance. Overall, other than P leaching, the use of amendments affected other functions of bioretention systems, which should be taken into consideration when selecting an amendment for practice

Spectral tracing of deuterium for imaging glucose metabolism.

Cells and tissues often display pronounced spatial and dynamical metabolic heterogeneity. Common glucose-imaging techniques report glucose uptake or catabolism activity, yet do not trace the functional utilization of glucose-derived anabolic products. Here we report a microscopy technique for the optical imaging, via the spectral tracing of deuterium (STRIDE), of diverse macromolecules derived from glucose. Based on stimulated Raman-scattering imaging, STRIDE visualizes the metabolic dynamics of newly synthesized macromolecules, such as DNA, protein, lipids and glycogen, via the enrichment and distinct spectra of carbon-deuterium bonds transferred from the deuterated glucose precursor. STRIDE can also use spectral differences derived from different glucose isotopologues to visualize temporally separated glucose populations using a pulse-chase protocol. We also show that STRIDE can be used to image glucose metabolism in many mouse tissues, including tumours, brain, intestine and liver, at a detection limit of 10 mM of carbon-deuterium bonds. STRIDE provides a high-resolution and chemically informative assessment of glucose anabolic utilization