Решение задач управления при алмазно-искровом шлифовании сверхтвёрдых материалов

Представлено решение задачи управления, когда по требуемой чертежом шероховатости определяются различные сочетания режимов обработки, которые гарантируют получения необходимого качества поверхности. Результаты исследования проверены при обработке сверхтвёрдых материалов методом алмазно-искрового шлифования.Presented the solution to management tasks, when required by the drawing of roughness are determined by various combinations of processing modes, which guarantee obtaining the necessary surface quality. The study tested the processing of superhard materials by diamond–spark grinding

n-Type Doping of Vapor–Liquid–Solid Grown GaAs Nanowires

In this letter, n-type doping of GaAs nanowires grown by metal–organic vapor phase epitaxy in the vapor–liquid–solid growth mode on (111)B GaAs substrates is reported. A low growth temperature of 400°C is adjusted in order to exclude shell growth. The impact of doping precursors on the morphology of GaAs nanowires was investigated. Tetraethyl tin as doping precursor enables heavily n-type doped GaAs nanowires in a relatively small process window while no doping effect could be found for ditertiarybutylsilane. Electrical measurements carried out on single nanowires reveal an axially non-uniform doping profile. Within a number of wires from the same run, the donor concentrations ND of GaAs nanowires are found to vary from 7 × 1017 cm-3 to 2 × 1018 cm-3. The n-type conductivity is proven by the transfer characteristics of fabricated nanowire metal–insulator-semiconductor field-effect transistor devices

Pregnane X Receptor and Yin Yang 1 Contribute to the Differential Tissue Expression and Induction of CYP3A5 and CYP3A4

The hepato-intestinal induction of the detoxifying enzymes CYP3A4 and CYP3A5 by the xenosensing pregnane X receptor (PXR) constitutes a key adaptive response to oral drugs and dietary xenobiotics. In contrast to CYP3A4, CYP3A5 is additionally expressed in several, mostly steroidogenic organs, which creates potential for induction-driven disturbances of the steroid homeostasis. Using cell lines and mice transgenic for a CYP3A5 promoter we demonstrate that the CYP3A5 expression in these organs is non-inducible and independent from PXR. Instead, it is enabled by the loss of a suppressing yin yang 1 (YY1)-binding site from the CYP3A5 promoter which occurred in haplorrhine primates. This YY1 site is conserved in CYP3A4, but its inhibitory effect can be offset by PXR acting on response elements such as XREM. Taken together, the loss of YY1 binding site from promoters of the CYP3A5 gene lineage during primate evolution may have enabled the utilization of CYP3A5 both in the adaptive hepato-intestinal response to xenobiotics and as a constitutively expressed gene in other organs. Our results thus constitute a first description of uncoupling induction from constitutive expression for a major detoxifying enzyme. They also suggest an explanation for the considerable tissue expression differences between CYP3A5 and CYP3A4

InP based double heterojunction bipolar transistorwith carbon doped GaAsSb:C base grown by LP-MOVPE

We present the growth of highly carbon doped GaAsSb on InP substrate with LP-MOVPE and nitrogen carrier gas.Carbon doped GaAsSb lattice matched on InP are of pronounced interest for high speed double heterostructure bipolar transistors (DHBTs).We observed a significant effect of the nitrogen carrier gas on the growth behaviour which results in lower distribution coefficients.A linear doping behaviour with small CBr4 flows up to p=4 x 10 19 cm-3 can be observed and first realized DHBT structures shown fT and fmax values of 100 GHz and 60GHz, respectively

Mechanism of Current Gain increase of Heterostructure Bipolar Transistors Passivated by Low-Temperature Deposited SiNx

The graded base InGaAs//InP heterostructure bipolar transistors (HBTs)were passivated by the low-temperature plasma deposited iNx .The current gain was found to increase after the passivation.The study of the Gummel plots shows that the passivation results in the reduction of both the collector current and base current,while the decrease of the base current is more significant.This causes the increase of the current gain.Nitrogen plasma treatment results in the increase of the current gain,while Silane plasma treatment results in a small reduction of the current gain.The influence of the plasmas of the two sources on the HBTs ’ performance are investigated..In- situ ellipsometer study showed that at the initial state of SiNx deposition,the SiNx deposition rate was zero,and nitrogen plasma has strong effects on the passivation of HBTs and results in the increase of the current gain. surface recombination,these cause the increase of the base current and the decrease of current gain

InP-BASED HBT with graded InGaAlAs BASE layer grown by LP-MOVPE

A compositionally graded InGaAlAs:C base layer is inserted in an InP-based HBT grown by LP-MOVPE with a novel non-gaseous source configuration. Due to the addition of 6% Al the active hole concentration in the HBT base layer, deduced from Hall measurements, is increased from 1.5 10 19 to 3.8 10 19 cm -3 . Moreover, an In-grading within the base layer results in an intrinsic electric field of about 5.4 kV/cm. A high dc current gain of β = 35 is provided at a high p-type doping level. First HBT devices exhibit a current gain cut-off frequency of fT = 117 GHz and an unilateral gain cut-off frequency of 90 GHz (not de-embedded)

A New Noise Model of HFET with Special Emphasis on Gate-Leakage

A new temperature noise model, including the influence of a gate-leakage current on the noise performance of a microwave HFET, is presented. Based on an extended small-signal equivalent circuit of the HFET and three equivalent noise temperatures the noise model allows the exact prediction of the four noise parameters in a wide frequency range. The validity of the new model is demonstrated by noise measurements at room temperature. It is shown that the three equivalent noise temperatures are frequency independent and that one of them (T/sub p/) especially represents the noise contribution caused by the gate-current I/sub G/. The advantages of the new model are clearly demonstrated in comparison with a well established temperature noise model