Problem of cryogenic cooling of semiconductor switches for power convertors

Currently, in Russia and abroad there is a significant progress in the development and manufacturing of electromechanical devices based on high-temperature superconducting materials. These devices possess the specific power at liquid nitrogen cooling above 10 kW/kg. Semiconductor convertors, which normally are necessary to operate together with electromechanical converters, have the specific power not exceeding 1 kW/kg at forced cooling. Therefore, the problem of increasing of the specific power of both electromechanical and static electrical devices of mobile objects (especially at operating in the aerospace field) is very relevant. The paper is devoted to the cooling of semiconductor electronic switches for semiconductor power converters at liquid nitrogen environment. In this case the improvement of cooling efficiency leads to a significant increase of the heat-transfer factor and, as a consequence, decreasing the mass and size of the radiators, and total weight and size of the semiconductor converters. The calculations which were carried out according to the results of the experiments showed that the use of cryogenic cooling allows increasing about ~100 times the specific power of the semiconductor converters. The researches have shown that the placement of semiconductor converter in the medium of liquid nitrogen is most perspective for real application

PRIZMA predictions of in-core detection indications in the VVER-1000 reactor

The paper describes calculations which were done by the PRIZMA code(1) to predict indications of in-core rhodium detectors in the VVER-1000 reactor for some core fragments with allowance for fuel and rhodium burnout

Cardo Polybenzimidazole (PBI-O-PhT) Based Membrane Reinforced with m-polybenzimidazole Electrospun Nanofiber Mat for HT-PEM Fuel Cell Applications

The further development of high temperature polymer electrolyte membrane (HT-PEM) fuel cells largely depends on the improvement of all components of the membrane–electrode assembly (MEA), especially membranes and electrodes. To improve the membrane characteristics, the cardo-polybenzimidazole (PBI-O-PhT)-based polymer electrolyte complex doped with phosphoric acid is reinforced using an electrospun m-PBI mat. As a result, the PBI-O-PhT/es-m-PBInet · nH3PO4 reinforced membrane is obtained with hydrogen crossover values (~0.2 mA cm−2 atm−1), one order of magnitude lower than the one of the initial PBI-O-PhT membrane (~3 mA cm−2 atm−1) during HT-PEM fuel cell operation with Celtec®P1000 electrodes at 180 °C. Just as importantly, the reinforced membrane resistance was very close to the original one (65–75 mΩ cm2 compared to ~60 mΩ cm2). A stress test that consisted of 20 start–stops, which included cooling to the room temperature and heating back to 180 °C, was applied to the MEAs with the reinforced membrane. More stable operation for the HT-PEM fuel cell was shown when the Celtec®P1000 cathode (based on carbon black) was replaced with the carbon nanofiber cathode (based on the pyrolyzed polyacrylonitrile electrospun nanofiber mat). The obtained data confirm the enhanced characteristics of the PBI-O-PhT/es-m-PBInet · nH3PO4 reinforced membrane

Unique Self-Phosphorylating Polybenzimidazole of the 6F Family for HT-PEM Fuel Cell Application

High-temperature polymer-electrolyte membrane fuel cells (HT-PEMFCs) are a very important type of fuel cells since they operate at 150–200 °C, making it possible to use hydrogen contaminated with CO. However, the need to improve the stability and other properties of gas-diffusion electrodes still impedes their distribution. Self-supporting anodes based on carbon nanofibers (CNF) are prepared using the electrospinning method from a polyacrylonitrile solution containing zirconium salt, followed by pyrolysis. After the deposition of Pt nanoparticles on the CNF surface, the composite anodes are obtained. A new self-phosphorylating polybenzimidazole of the 6F family is applied to the Pt/CNF surface to improve the triple-phase boundary, gas transport, and proton conductivity of the anode. This polymer coating ensures a continuous interface between the anode and proton-conducting membrane. The polymer is investigated using CO2 adsorption, TGA, DTA, FTIR, GPC, and gas permeability measurements. The anodes are studied using SEM, HAADF STEM, and CV. The operation of the membrane–electrode assembly in the H2/air HT-PEMFC shows that the application of the new PBI of the 6F family with good gas permeability as a coating for the CNF anodes results in an enhancement of HT-PEMFC performance, reaching 500 mW/cm2 at 1.3 A/cm2 (at 180 °C), compared with the previously studied PBI-O-PhT-P polymer

Distinct Traits of Structural and Regulatory Evolutional Conservation of Human Genes with Specific Focus on Major Cancer Molecular Pathways

The evolution of protein-coding genes has both structural and regulatory components. The first can be assessed by measuring the ratio of non-synonymous to synonymous nucleotide substitutions. The second component can be measured as the normalized proportion of transposable elements that are used as regulatory elements. For the first time, we characterized in parallel the regulatory and structural evolutionary profiles for 10,890 human genes and 2972 molecular pathways. We observed a ~0.1 correlation between the structural and regulatory metrics at the gene level, which appeared much higher (~0.4) at the pathway level. We deposited the data in the publicly available database RetroSpect. We also analyzed the evolutionary dynamics of six cancer pathways of two major axes: Notch/WNT/Hedgehog and AKT/mTOR/EGFR. The Hedgehog pathway had both components slower, whereas the Akt pathway had clearly accelerated structural evolution. In particular, the major hub nodes Akt and beta-catenin showed both components strongly decreased, whereas two major regulators of Akt TCL1 and CTMP had outstandingly high evolutionary rates. We also noticed structural conservation of serine/threonine kinases and the genes related to guanosine metabolism in cancer signaling: GPCRs, G proteins, and small regulatory GTPases (Src, Rac, Ras); however, this was compensated by the accelerated regulatory evolution

Development of DNA aptamers for visualization of glial brain tumors and detection of circulating tumor cells

Here, we present DNA aptamers capable of specific binding to glial tumor cells in vitro, ex vivo, and in vivo for visualization diagnostics of central nervous system tumors. We selected the aptamers binding specifically to the postoperative human glial primary tumors and not to the healthy brain cells and meningioma, using a modified process of systematic evolution of ligands by exponential enrichment to cells; sequenced and analyzed ssDNA pools using bioinformatic tools and identified the best aptamers by their binding abilities; determined three-dimensional structures of lead aptamers (Gli-55 and Gli-233) with small-angle X-ray scattering and molecular modeling; isolated and identified molecular target proteins of the aptamers by mass spectrometry; the potential binding sites of Gli-233 to the target protein and the role of post-translational modifications were verified by molecular dynamics simulations. The anti-glioma aptamers Gli-233 and Gli-55 were used to detect circulating tumor cells in liquid biopsies. These aptamers were used for in situ, ex vivo tissue staining, histopathological analyses, and fluorescence-guided tumor and PET/CT tumor visualization in mice with xenotransplanted human astrocytoma. The aptamers did not show in vivo toxicity in the preclinical animal study. This study demonstrates the potential applications of aptamers for precise diagnostics and fluorescence-guided surgery of brain tumors.peerReviewe