Characterization and snubbing of a bidirectional MCT in a resonant ac link converter

The MOS-Controlled Thyristor (MCT) is emerging as a powerful switch that combines the better characteristics of existing power devices. A study of switching stresses on an MCT switch under zero voltage resonant switching is presented. The MCT is used as a bidirectional switch in an ac/ac pulse density modulated inverter for induction motor drive. Current and voltage spikes are observed and analyzed with variations in the timing of the switching. Different snubber circuit configurations are under investigation to minimize the effect of these transients. The results will be extended to study and test the MCT switching in a medium power (5 hp) induction motor drive

Study of switching transients in high frequency converters

As the semiconductor technologies progress rapidly, the power densities and switching frequencies of many power devices are improved. With the existing technology, high frequency power systems become possible. Use of such a system is advantageous in many aspects. A high frequency ac source is used as the direct input to an ac/ac pulse-density-modulation (PDM) converter. This converter is a new concept which employs zero voltage switching techniques. However, the development of this converter is still in its infancy stage. There are problems associated with this converter such as a high on-voltage drop, switching transients, and zero-crossing detecting. Considering these problems, the switching speed and power handling capabilities of the MOS-Controlled Thyristor (MCT) makes the device the most promising candidate for this application. A complete insight of component considerations for building an ac/ac PDM converter for a high frequency power system is addressed. A power device review is first presented. The ac/ac PDM converter requires switches that can conduct bi-directional current and block bi-directional voltage. These bi-directional switches can be constructed using existing power devices. Different bi-directional switches for the converter are investigated. Detailed experimental studies of the characteristics of the MCT under hard switching and zero-voltage switching are also presented. One disadvantage of an ac/ac converter is that turn-on and turn-off of the switches has to be completed instantaneously when the ac source is at zero voltage. Otherwise shoot-through current or voltage spikes can occur which can be hazardous to the devices. In order for the devices to switch softly in the safe operating area even under non-ideal cases, a unique snubber circuit is used in each bi-directional switch. Detailed theory and experimental results for circuits using these snubbers are presented. A current regulated ac/ac PDM converter built using MCT's and IGBT's is evaluated

Reconstruction of the two-dimensional gravitational potential of galaxy clusters from X-ray and Sunyaev-Zel'dovich measurements

The mass of galaxy clusters is not a direct observable, nonetheless it is commonly used to probe cosmological models. Based on the combination of all main cluster observables, that is, the X-ray emission, the thermal Sunyaev-Zel'dovich (SZ) signal, the velocity dispersion of the cluster galaxies, and gravitational lensing, the gravitational potential of galaxy clusters can be jointly reconstructed. We derive the two main ingredients required for this joint reconstruction: the potentials individually reconstructed from the observables and their covariance matrices, which act as a weight in the joint reconstruction. We show here the method to derive these quantities. The result of the joint reconstruction applied to a real cluster will be discussed in a forthcoming paper. We apply the Richardson-Lucy deprojection algorithm to data on a two-dimensional (2D) grid. We first test the 2D deprojection algorithm on a $\beta$-profile. Assuming hydrostatic equilibrium, we further reconstruct the gravitational potential of a simulated galaxy cluster based on synthetic SZ and X-ray data. We then reconstruct the projected gravitational potential of the massive and dynamically active cluster Abell 2142, based on the X-ray observations collected with XMM-Newton and the SZ observations from the Planck satellite. Finally, we compute the covariance matrix of the projected reconstructed potential of the cluster Abell 2142 based on the X-ray measurements collected with XMM-Newton. The gravitational potentials of the simulated cluster recovered from synthetic X-ray and SZ data are consistent, even though the potential reconstructed from X-rays shows larger deviations from the true potential. Regarding Abell 2142, the projected gravitational cluster potentials recovered from SZ and X-ray data reproduce well the projected potential inferred from gravitational-lensing observations. (abridged)Comment: accepted for publication in the journal A&

Первопроходец середины ХХ века

Story of the course of life and scientific achievements of well-known Russian glaciologist and specialist in permafrost studies Boris Vtyurin.Рассказывается о жизненном пути и научных достижениях известного российского мерзлотоведа и гляциолога Бориса Ивановича Втюрина, входящего в своё девяностолети

Performance-efficient architecture for free-viewpoint 3DTV receiver

This paper presents algorithmic and architectural solutions for a free-viewpoint 3DTV receiver system. We describe our rendering algorithm and evaluate performance-related challenges in mapping of the algorithm on a receiver board of which the architecture is outlined. It is found that the required processing load exceeds the provisioning of dual Virtex5 FPGAs. We develop several mapping optimizations to fit the rendering algorithm into a platform

Preventing Pseudomonas aeruginosa and Chromobacterium violaceum infections by anti-adhesion-active components of edible seeds

<p>Abstract</p> <p>Background</p> <p><it>Pseudomonas aeruginosa </it>adhesion to animal/human cells for infection establishment involves adhesive proteins, including its galactose- and fucose-binding lectins PA-IL (LecA) and PA-IIL (LecB). The lectin binding to the target-cell receptors may be blocked by compatible glycans that compete with those of the receptors, functioning as anti-adhesion glycodecoys. The anti-adhesion treatment is of the utmost importance for abrogating devastating antibiotic-resistant <it>P. aeruginosa </it>infections in immunodeficient and cystic fibrosis (CF) patients. This strategy functions in nature in protecting embryos and neonates. We have shown that PA-IL, PA-IIL, and also CV-IIL (a PA-IIL homolog produced in the related pathogen <it>Chromobacterium violaceum</it>) are highly useful for revealing natural glycodecoys that surround embryos in diverse avian eggs and are supplied to neonates in milks and royal jelly. In the present study, these lectins were used as probes to search for seed embryo-protecting glycodecoys.</p> <p>Methods</p> <p>The lectin-blocking glycodecoy activities were shown by the hemagglutination-inhibition test. Lectin-binding glycoproteins were detected by Western blotting with peroxidase-labeled lectins.</p> <p>Results</p> <p>The present work reports the finding - by using PA-IL, PA-IIL, and CV-IIL - of rich glycodecoy activities of low (< 10 KDa) and high MW (> 10 kDa) compounds (including glycoproteins) in extracts of cashew, cocoa, coffee, pumpkin, and tomato seeds, resembling those of avian egg whites, mammal milks, and royal jelly.</p> <p>Conclusions</p> <p>Edible seed extracts possess lectin-blocking glycodecoys that might protect their embryos from infections and also might be useful for hampering human and animal infections.</p

The distinct stellar-to-halo mass relations of satellite and central galaxies: Insights from the IllustrisTNG simulations

We study the stellar-to-halo mass relation (SHMR) for central and satellite galaxies with total dynamical masses above 1010.5 M⊙ using the suite of cosmological magnetohydrodynamical simulations IllustrisTNG. In particular, we quantify environmental effects on satellite populations from TNG50, TNG100, and TNG300 located within the virial radius of group- and clusterlike hosts with total masses of 1012-15.2 M⊙. At fixed stellar mass, the satellite SHMR exhibits a distinct shift towards lower dynamical mass compared to the SHMR of centrals. Conversely, at fixed dynamical mass, satellite galaxies appear to have larger stellar-to-total mass fractions than centrals by up to a factor of a few. The systematic deviation from the central SHMR is larger for satellites in more massive hosts, at smaller cluster-centric distances, with earlier infall times, and that inhabits higher local density environments; moreover, it is in place already at early times (z 2). Systematic environmental effects might contribute to the perceived galaxy-to-galaxy variation in the measured SHMR when galaxies cannot be separated into satellites and centrals. The SHMR of satellites exhibits a larger scatter than centrals (by up to ∼0.8 dex), over the whole range of dynamical mass. The shift of the satellite SHMR results mostly from tidal stripping of their dark matter, which affects satellites in an outside-in fashion: The departure of the satellite SHMR from the centrals' relation diminishes for measurements of dynamical mass in progressively smaller apertures. Finally, we provide a family of fitting functions for the SHMR predicted by IllustrisTNG

Формирование зонной диаграммы фотонных и фононных кристаллов

Досліджено зонні особливості вхідних імпедансних характеристик необмежених і обмежених фотонного та фононного кристалів (Ф(н)К). Взаємним порівнянням залежностей коефіцієнта відбиття обмежених Ф(н)К і активної складової вхідного імпедансу необмежених Ф(н)К проаналізовано формування зонної діаграми обмеженими Ф(н)К. В результаті аналізу залежності параметрів заборонених зон обмежених Ф(н)К від кількості шарів проаналізовано степінь наближення параметрів зонної діаграми обмежених Ф(н)К до параметрів зонної діаграми необмежених Ф(н)К.Inroduction. Photon and phonon crystals are crystal structures, which just like the crystals, are characterized by zone spectral properties. The purpose of the article is to research the input impedance characteristics and formation features of the photon and phonon crystals’ zone diagrams. Impedance model and properties of unlimited crystal structure. The expressions for input impedance of unlimited one-dimensional crystal structure for waves of different nature are presented. The relationships of physical properties of the crystal structure and the mathematical features of the expressions are investigated. Impedance characteristics of photon and phonon unlimited crystals. The dependences of active and reactive components of photon and phonon unlimited crystal’s input impedance with layers of different thickness are shown. Input impedance characteristics of photon and phonon limited crystals. The dependences of active and reactive components of limited photon and phonon crystal’s input impedance are given. The conditions for waves resonant passing through photon and phonon crystals are obtained. Reflection coefficient characteristics of photon and phonon crystals. The formation of the limited photon and phonon crystal’s zone diagrams is analyzed by mutual comparison of limited photon and phonon crystal’s reflection characteristic and active component of unlimited photon and phonon crystal’s input impedance characteristics. The approximation degree of limited photon and phonon crystal’s zone diagram parameters to the unlimited photon and phonon crystal’s zone diagram parameters is quantitatively analyzed. Conclusions. The conditions for waves resonant passing through photon and phonon crystals is formulated and features of photon and phonon crystal’s zone diagram formation is investigated.Исследованы зонные особенности входных импедансных характеристик неограниченных и ограниченных фотонного и фононного кристаллов (Ф(н)К). Взаимным сравнением зависимостей коэффициента отражения ограниченных Ф(н)К и активной составляющей входного импеданса неограниченных Ф(н)К проанализировано формирование зонной диаграммы ограниченными Ф(н)К. В результате анализа зависимости параметров запрещенных зон ограниченных Ф(н)К от числа слоев проанализирована степень приближения параметров зонной диаграммы ограниченных Ф(н)К к параметрам зонной диаграммы неограниченных Ф(н)К