Comparative Analysis of Medium Voltage AC and DC Network Infrastructure Models

An increasing amount of consumer devices and end-use applications of electricity at the low voltage level that require a direct current (DC) power source have continued to advance in modern day society. At the same time the existing alternating current (AC) infrastructure that has served so well over the past century is beginning to show its age and vulnerability, leading to increased outages and reduced reliability. Also, the amount of high voltage direct current (HVDC) transmission system installations continue to increase around the world because of their proven superiority to high voltage alternating current (HVAC) in certain scenarios. However, with the widespread development and maturation in recent years of low voltage DC devices and systems, as well as large scale HVDC systems, no DC-based infrastructure or delivery system exists to efficiently connect the two together. Such an infrastructure would be developed through a medium voltage DC (MVDC) architecture. In order to properly analyze the benefits of a MVDC infrastructure for power distribution networks, a comparison between MVDC and MVAC architectures is necessary to identify advantages and disadvantages of both approaches. Investigating an architecture that would supply DC power to loads that is not much different in function to the existing AC grid system used today may bring with it increased efficiencies, therefore leading to economic operational and reliability benefits. To the author's knowledge, this thesis provides the first system scale comparative analysis of this nature comparing MVAC and MVDC. The preliminary design for such a system to supply DC power was created in this thesis using the PSCAD software package. The system analyzed utilizes a medium voltage DC bus rated at 20kV with a set of interconnected loads and generation. The DC system, while complicated with its wide array of power electronic converters, grants the ability to control power flow into the system from the different generation sources and to the loads. While the infrastructure design created is an initial step for a larger system, it lays the foundation for the future development of a DC distribution system for real world applications

Postan 3 - Extended Postoptimal Analysis Package for Minos

This paper is one of the series of 11 Working Papers presenting the software for interactive decision support and software tools for developing decision support systems. These products constitute the outcome of the contracted study agreement between the System and Decision Sciences Program at IIASA and several Polish scientific institutions. The theoretical part of these results is presented in the IIASA Working Paper WP-88-071 entitled "Theory, Software and Testing Examples in Decision Support Systems" which contains the theoretical and methodological backgrounds of the software systems developed within the project. This paper presents the POSTAN 3 package. This package constitutes the tool for postoptimal analysis for linear and linear-fractional programming problems. POSTAN consists of a number of FORTRAN routines which are incorporated into MINOS, the well known linear and nonlinear programming code developed at the Stanford University. The postoptimal analysis is performed after MINOS has found an optimal solution and is initiated by extending the original MINOS specification file. The main function of POSTAN is ranging with respect to parameters specified by the user and computing the sensitivity coefficients

Postan - A Package for Postoptimal Analysis (An Extension of Minos)

This paper presents a new software package which has been developed in collaboration with IIASA The new package, POSTAN, is designed for postoptimal analysis of linear programming problems, and is embedded in the well-known linear and nonlinear programming code MINOS. POSTAN is composed of a number of FORTRAN subroutines which may be called by adding some new keywords to the original list of MINOS specifications. The main function of POSTAN is to determine the ranges in which certain parameters may be changed without affecting the optimal solution and/or the optimal basis. In this paper the authors outline the general form of the linear programming problems studied, describe the six new subroutines in some detail, and illustrate this description with a printout obtained in the solution of a sample problem. The mathematical theory behind the software package is given in an Appendix

Banks’ profitability determinants in post-crisis European Union

The purpose of this article is to examine the impact of selected internal and external factors on a bank’s profitability. The research investigates the impact of operational size, liquidity, risk appetite, management efficiency, product diversification, concentration, GDP growth and inflation change on the profitability of sample of 4179 European commercial banks for the period between 2011 and 2015. The input data were obtained from the Orbis Focus and the World Bank databases. The determinants were used to construct two models with ROAA and ROAE as a proxies and regression analysis using between groups panel approach was conducted. It has been found that growing economy impacts banks’ profitability positively. It has been robustly confirmed that management efficiency, product diversification, market concentration and inflation result in decreased profitability. The operational size has been found to be negatively linked to changes in net results but was confirmed only with ROAA model. Similarly, statistically significant results with regard to liquidity were found only for ROAA model and the correlation was positive. The strong negative impact of market concentration on profitability is an interesting finding allowing for further exploration of reasons for this unexpected vector of correlation

Influence of Lipid Oxidization on Structures and Functions of Biological Membranes

The primary aim of this thesis is to clarify how the structures and functions of biological membranes are influenced by the oxidative damage mediated by free radicals. As a precisely defined model systems, artificially reconstituted lipid membranes (Langmuir monolayers, vesicles, supported membranes, multilamellar membranes) incorporating two oxidized phospholipids bearing aldehyde or carboxyl groups at the end of truncated sn-2 acyl chains were fabricated. By the combination of various experimental methods, the generic impact of chain oxidization on physical characteristics of membranes (e.g. lateral cooperativity, fine-structures perpendicular to membrane planes, electrostatics) and the specific interactions of oxidized phospholipids with EO6 peptides and acute immune response proteins was investigated. In the first step, the influence of oxidized phospholipids (OxPL) on the thermodynamics and electrostatics were investigated using Langmuir film balance at the air-water interface. The pressure-area (π-A) isotherms and surface potential (Δψ-A) measurements implied that both OxPLs lead to a decrease in the isothermal compression modulus. In fact, surface potential measurements suggest changes in the orientation of oxidized moieties that decrease the lateral cooperativity. Further increase in the fraction of oxidized lipids resulted in the loss of molecules into bulk water, which seems consistent with the destabilization of cell membranes under oxidative stresses. In the second step, the impact of lipid oxidization on the electrostatics of membranes was examined by the combination of high-energy specular X-ray reflectivity (XRR) and grazing-incidence X-ray fluorescence (GIXF). The scattering length density profiles reconstructed from XRR results suggested that both OxPL leads to membrane thinning, which seems plausible from the decrease in the lateral cooperativity suggested by Langmuir isotherms. GIXF offers an unique possibility to localize specific target elements within Å accuracy, suggesting that the binding affinity (Ca2+ > Cs+ > K+) could be interpreted in terms of the solvation entropy (Hofmeister series). Further, the impact of oxidization on the vertical structural ordering of vertically stacked membrane models was investigated by off-specular neutron scattering. A decreased lamellar periodicity d indicated that incorporation of OxPL into the membrane displace water molecules from the inter-membrane region due to the reorientation of oxidized moieties. In the third step, the combination of experimental techniques was utilized to shed light on specific interactions of OxPLs with peptides and proteins; C-reactive protein that is characteristic for the acute immune responses and monoclonal antibody EO6 to oxidized lipids. Following the fundamental characterization of membrane-protein interactions using isothermal titration calorimetry (ITC) and dynamic light scattering (DLS) of vesicle suspensions, in addition to XRR, GIXF, off-specular neutron scattering, dual waveguide polarization interferometry (DPI) was used to monitor the changes in thickness, refractive index, and the optical anisotropy (birefringence) of lipid membranes simultaneously. Furthermore, the specific binding of EO6 was verified from the fluorescence imaging of glioblastoma multiforme cells undergoing apoptosis, where a clear accumulation of OxPLs could be identified in apoptotic blebs. The obtained results demonstrated that the combination of well defined membrane models and unique physical techniques is a powerful tool to shed a new quantitative light on the generic and specific impacts of lipid oxidization on the lateral cooperativity, vertical fine-structures, electrostatics, and specific interactions in inflammation and apoptosis

Effects of the Phase Locked Loop on the Stability of a Voltage Source Converter in a Weak Grid Environment

Distributed generation is characterized as a form of generation that is not directly connected to the bulk transmission grid. It is usually connected via power electronic devices if it is a renewable resource, in this case in the form of a voltage source converter (VSC) operating as an inverter (converting DC-to-AC). The grid impedance connected to the VSC has an influence on its stability and control performance. By looking at the output impedance of the VSC, the stability can be determined in relation to the impedance of the grid connection. A number of parameters influence the output impedance of a VSC, one of those being the control scheme used and the phase-locked loop (PLL) contained within it. The control parameters of the PLL can be adjusted to manipulate the location of the calculated poles and zeros of the open loop output impedance of the VSC. These parameters are the gains of the loop filter, Kp and Ki. Under certain short circuit ratio (SCR) values, having large PLL gain parameters can cause the VSC to become unstable. While a large SCR will be unaffected by the PLL gains, a smaller SCR is more susceptible to PLL gains that are too large. By accounting for the effects of the PLL in the output impedance, it can be found what PLL gains are considered too large for certain SCR values. A large enough grid impedance can destabilize the VSC and, therefore, cause the renewable generation to be disconnected and unused. Ideally, the output impedance of the VSC will be large. This work analyzes the effect of the PLL on the output impedance of the VSC and ultimately the stability and control performance based on different grid impedances

Bystander effects of nitric oxide in cellular models of anti-tumor photodynamic therapy

Tumor cells exposed to stress-inducing radiotherapy or chemotherapy can send signals to non- or minimally exposed bystander cells. Bystander effects of ionizing radiation are well established, but little is known about such effects in non-ionizing photodynamic therapy (PDT). Our previous studies revealed that several cancer cell types upregulate inducible nitric oxide synthase (iNOS) and nitric oxide (NO) after a moderate 5-aminolevulinic acid (ALA)-based PDT challenge. The NO signaled for cell resistance to photokilling as well as greater growth, migration and invasion of surviving cells. Based on this work, we hypothesized that diffusible NO produced by PDT-targeted cells in a tumor might elicit pro-growth/migration responses in non-targeted bystander cells. In the present study, we tested this using a novel approach, in which ALA-PDT-targeted human cancer cells on culture dishes (prostate PC3, breast MDA-MB-231, glioma U87, or melanoma BLM) were initially segregated from non-targeted bystanders via impermeable silicone-rimmed rings. Several hours after LED irradiation, rings were removed, and both cell populations analyzed for various post-hν responses. For a moderate and uniform level of targeted cell killing by PDT (~25%), bystander proliferation and migration were both enhanced. Enhancement correlated with iNOS/NO upregulation in surviving targeted cells in the following order: PC3 > MDA-MB-231 > U87 > BLM. If occurring in an actual tumor PDT setting and not suppressed (e.g., by iNOS activity or transcription inhibitors), then such effects could compromise treatment efficacy or even stimulate disease progression if PDT’s anti-tumor potency is not great enough