High voltage (>1kV) and high current gain (32) 4H-SiC power BJTs using Al-free ohmic contact to the base

This letter reports the design and fabrication of 4H-SiC bipolar junction transistors with both high voltage (>1kV) and high dc current gain (/spl beta/=32) at a collector current level of I/sub c/=3.83A (J/sub c/=319 A/cm/sup 2/). An Al-free base ohmic contact has been used which, when compared with BJTs fabricated with Al-based base contact, shows clearly improved blocking voltage. A specific on-resistance of 17 m/spl Omega//spl middot/cm/sup 2/ has been achieved for collector current densities up to 289 A/cm/sup 2/.     

Fracture prediction in steady ideal plastic flows

The theory of ideal plastic flows is a powerful tool for the preliminary design of metal forming operations. The present paper develops an approach to include a fracture criterion in this design procedure. The fracture criterion is based on the workability diagram and an average value of the triaxiality factor. In the case of three dimensional flows, this fracture criterion is modified which leads to mathematical advantages. It is shown that in many cases the modified criterion coincides with the original criterion. Using the proposed approach fracture initiation in drawing and extrusion processes is predicted. In particular, it is demonstrated that fracture predictions may be carried out without having the solution for stress and strain in the plastic zone (it is only necessary to know that it exists). The maximum possible area reduction with no fracture is given by the solution to a quadratic equation (in general, it might be a transcendental equation).     

Pole Placement Optimization for SISO Control System

Automation and Remote Control - We consider the control design problem for a linear time-invariant plant. A linear controller is found that minimizes some system performance index, for example, the...     

Early Lipid Raft-Related Changes: Interplay between Unilateral Denervation and Hindlimb Suspension

Muscle disuse and denervation leads to muscle atrophy, but underlying mechanisms can be different. Previously, we have found ceramide (Cer) accumulation and lipid raft disruption after acute hindlimb suspension (HS), a model of muscle disuse. Herein, using biochemical and fluorescent approaches the influence of unilateral denervation itself and in combination with short-term HS on membrane-related parameters of rat soleus muscle was studied. Denervation increased immunoexpression of sphingomyelinase and Cer in plasmalemmal regions, but decreased Cer content in the raft fraction and enhanced lipid raft integrity. Preliminary denervation suppressed (1) HS-induced Cer accumulation in plasmalemmal regions, shown for both nonraft and raft-fractions; (2) HS-mediated decrease in lipid raft integrity. Similar to denervation, inhibition of the sciatic nerve afferents with capsaicin itself increased Cer plasmalemmal immunoexpression, but attenuated the membrane-related effects of HS. Finally, both denervation and capsaicin treatment increased immunoexpression of proapoptotic protein Bax and inhibited HS-driven increase in antiapoptotic protein Bcl-2. Thus, denervation can increase lipid raft formation and attenuate HS-induced alterations probably due to decrease of Cer levels in the raft fraction. The effects of denervation could be at least partially caused by the loss of afferentation. The study points to the importance of motor and afferent inputs in control of Cer distribution and thereby stability of lipid rafts in the junctional and extrajunctional membranes of the muscle.     

hTERT-Driven Immortalization of RDEB Fibroblast and Keratinocyte Cell Lines Followed by Cre-Mediated Transgene Elimination

The recessive form of dystrophic epidermolysis bullosa (RDEB) is a crippling disease caused by impairments in the junctions of the dermis and the basement membrane of the epidermis. Using ectopic expression of hTERT/hTERT + BMI-1 in primary cells, we developed expansible cultures of RDEB fibroblasts and keratinocytes. We showed that they display the properties of their founders, including morphology, contraction ability and expression of the respective specific markers including reduced secretion of type VII collagen (C7). The immortalized keratinocytes retained normal stratification in 3D skin equivalents. The comparison of secreted protein patterns from immortalized RDEB and healthy keratinocytes revealed the differences in the contents of the extracellular matrix that were earlier observed specifically for RDEB. We demonstrated the possibility to reverse the genotype of immortalized cells to the state closer to the progenitors by the Cre-dependent hTERT switch off. Increased β-galactosidase activity and reduced proliferation of fibroblasts were shown after splitting out of transgenes. We anticipate our cell lines to be tractable models for studying RDEB from the level of single-cell changes to the evaluation of 3D skin equivalents. Our approach permits the creation of standardized and expandable models of RDEB that can be compared with the models based on primary cell cultures.     

Effects of an Ingot Smelting Method and Pressure Treatment Modes on the Structure of Deformed TiNi-Based Alloy Semi-Finished Products

Metallurgist - It is shown that the pressure treatment of titanium nickelide alloys should be carried out in two stages. At the first stage, ingots are deformed in order to transform the brittle...     

Theory of chromatography of complex cyclic polymers: eight-shaped and daisy-like macromolecules

A theory of chromatography of eight-shaped, trefoil-shaped and daisy-like polymers is developed. For a model of an ideal chain in a slit-like pore exact equations and a number of approximate formulae for the distribution coefficient K of these polymers are derived. All modes of chromatography of complex macrocycles of arbitrary molar mass in both narrow and wide pores are covered by the theory. It is shown that complex macrocycles always elute after linear polymers and rings of the same contour length. The effective chromatographic radius of eight-shaped and daisy-like macromolecules, which determines retention in size-exclusion chromatography are calculated. The increase in the retention with molar mass is predicted for all types of macrocycles at the critical interaction condition. Non-monotonous molar mass dependences of K are found at pre-critical interaction. We simulate separation of complex cyclic polymers from linear and ring precursors, discuss possibilities to separate symmetric and asymmetric eights, and speculates on the use of chromatography for separating knotted and unknotted polymer rings. According to the theory, the chromatography under the critical and pre-critical interaction conditions is expected to be especially efficient in these and similar problems. Boundary conditions for the theory and its applicability to real systems are discussed.     

超声CO激光的现状和展望(续)

介绍了200kWCW超声电子束连续CO激光器（SSCO－EIL）开环实物模型的能量和光谱特征的实验研究结果，以及增加SSCO－EIL的输出功率，谱线选择性，Q－开关激光作用的数字计算结果，同时讨论了SSCO－EIL的特性对几种激光技术效率的影响，由于激光能量利用率的增加和能量成本的降低，SSCO－EIL拥有的无与伦比的能量和特有的特征，将大大拓宽激光技术的应用领域。     

Study of hemocompatibility and endothelial cell interaction of tecoflex-based electrospun vascular grafts

Abstract

Ensuring long-term functioning and efficient endothelialization of small diameter vascular grafts (VG) is an urgent task of tissue engineering. A solution may be to use electrospun VGs prepared from blends polyurethane with gelatin and/or bivalirudin. Here, properties of 3D matrices were explored by SEM, contact angle measurements and IR spectroscopy, and their interaction with blood and endothelial cells was studied. Introduction of gelatin into matrices enhanced adhesion and proliferation of endotheliocytes and enabled adhesion of platelets, whereas bivalirudin inhibited platelet adhesion while having no negative effect on the adhesion and proliferation of endothelial cells.     

Engineering of functional supramacromolecular complexes of proteins (enzymes) using reversed micelles as matrix microreactors

The size of the inner water cavity of reversed micelles formedin a triple system ‘water-surfactant-organic solvent’can be widely varied by changing the degree of surfactant hydration.This gives grounds to use reversed micelles as matrix microreactorsfor the design of supramolecular complexes of proteins. Usingultracentrifugation analysis, it has been demonstrated thatthe oligomeric composition of various enzymes (ketoglutaratedehydrogenase, alkaline phosphatase, lactic dehydrogenase, glyceraldehyde-3-phosphatedehydrogenase) solubilized in reversed micelles of Aerosol OT[sodium bis(2-ethylehexyl)sulfosuccinate] in octane changesupon variation of the degree of hydration. An oligomeric complexforms under conditions when the radius of the micelle innercavity is big enough to incorporate this complex as a whole.At lower degrees of hydration the micelles ‘uncouple’such complexes to their components. The catalytic propertiesof various oligomeric complexes have been studied. Possibilitiesof using reversed micelles for the separation of subunits ofoligomeric enzymes under non-denaturating conditions have beendemonstrated. In particular, the isolated subunits of alkalinephosphatase, lactic dehydrogenase and glyceralde-hyde-3-phosphatedehydrogenase have been found to be active in Aerosol OT reversedmicelles. The dependences of the catalytic activity of oligomericenzymes represent saw-like curves. The maxima of the catalyticactivity observed at these curves relate to the functioningof various oligomeric forms of an enzyme. The radii of the micelleinner cavity under conditions when these maxima are observedcorrelate with the linear dimensions of the enzyme oligomericforms. Correlation of the position of a maximum with the shapeof an oligomeric complex is discussed.