Structure-function studies of an IGF-I analogue that can be chemically cleaved to a two-chain mini-IGF-I

The structure and biological activities of two disulphide isomersof a C-region deletion mutant of insulin-like growth factor-I(IGF-I) which has an Asn–Gly link engineered at the junctionof the A- and B-regions were studied before and after chemicalcleavage. Circular dichroism (CD) spectra and binding affinityto IGF binding protein 3 (IGFBP3) indicated that the treatmentwith hydroxylamine did not disrupt the overall tertiary foldof the hormones. Cleavage restored some binding affinity forthe IGF-I receptor in both isomers and weakly restored the abilityto stimulate incorporation of tritiated thymidine into DNA inNIH 3T3 fibroblasts transfected with the human IGF-I receptor.Cleavage also restored metabolic capacity, as measured by theability of the isomers to promote lipogenesis in isolated ratadipocytes through the insulin receptor. These results are consistentwith the theory that binding of IGF-I to the IGF-I receptorrequires a conformational change similar to that involved ininsulin binding the insulin receptor. The weak affinity forthe IGF-I receptor after cleavage is consistent with the beliefthat residues in the C-region interact with the IGF-I receptor.This structural difference between insulin and IGF-I gives eacha higher binding affinity for its own receptor.     

Synthesis of Ultrahigh-Temperature Si–B–C–N Ceramic from Polymeric Waste Gas

A "green" route to ultrahigh-temperature Si–B–C–N ceramic from vacuum-degassing waste gas of polyborosilazane {B[C₂H₄Si(CH₃)NH]₃} _n (T2-1) has been developed. After gas-to-gel transformation, an amorphous ceramic Si_5.3B_1.0C₁₉N_3.7 was derived from the gel by dehydrocoupling and polymer-to-ceramic transformation. The ceramic started to form a nanostructure at 1700°C and resisted thermal degradation up to 2200°C in argon. This suggests that vacuum-degassing waste gases of polymer precursors may be perfect raw materials for various advanced ceramics.     

Polymer-Derived SiOC/ZrO2 Ceramic Nanocomposites with Excellent High-Temperature Stability

Polymer-derived SiOC/ZrO₂ ceramic nanocomposites have been prepared using two synthetic approaches. A commercially available polymethylsilsesquioxane (MK Belsil PMS) was filled with nanocrystalline zirconia particles in the first approach. The second method involved the addition of zirconium tetra( n -propoxide), Zr(OⁿPr)₄, as zirconia precursor to polysilsesquioxane. The prepared materials have been subsequently cross-linked and pyrolyzed at 1100°C in argon atmosphere to provide SiOC/ZrO₂ ceramics. The obtained SiOC/ZrO₂ materials were characterized by means of X-ray diffraction, elemental analysis, Raman spectroscopy as well as transmission electron microscopy. Furthermore, annealing experiments at temperatures from 1300° to 1600°C have been performed. The annealing experiments revealed that the incorporation of ZrO₂ into the SiOC matrix remarkably increases the thermal stability of the composites with respect to crystallization and decomposition at temperatures exceeding 1300°C. The results obtained within this study emphasize the enormous potential of polymer-derived SiOC/ZrO₂ composites for high-temperature applications.     

基于有限元法的汽车变速器齿轮与轴承优化

采埃孚集团开发和生产了种类繁多的传动齿轮。对于齿轮的优化和可靠设计,有限元法是尤为适合的。而且,这种方法能容易集成于采埃孚的程序系统。本文展示了在开发过程中如何运用该方法进行齿轮优化。此外,文中多处演示了齿轮和轴承之间的相互作用。这也是采埃孚集团致力于开发轴承计算的原因。文中实例展现了如何优化滚动轴承以达到理想的齿轮接触印痕。当然,这些优化方法也适用于传动齿轮。     

Induced seismicity associated with Enhanced Geothermal Systems

Enhanced Geothermal Systems (EGS) have the potential to make a significant contribution to the world energy inventory. One controversial issue associated with EGS, however, is the impact of induced seismicity or microseismicity, which has been the cause of delays and threatened cancellation of at least two EGS projects worldwide. Although microseismicity has in fact had few (or no) adverse physical effects on operations or on surrounding communities, there remains public concern over the amount and magnitude of the seismicity associated with current and future EGS operations. The primary objectives of this paper are to present an up-to-date review of what is already known about the seismicity induced during the creation and operation of EGS, and of the gaps in our knowledge that, once addressed, should lead to an improved understanding of the mechanisms generating the events. Several case histories also illustrate a number of technical and public acceptance issues. We conclude that EGS-induced seismicity need not pose a threat to the development of geothermal energy resources if site selection is carried out properly, community issues are handled adequately and operators understand the underlying mechanisms causing the events. Induced seismicity could indeed prove beneficial, in that it can be used to monitor the effectiveness of EGS operations and shed light on geothermal reservoir processes.     

驱动步进电机的双通道音频放大器

虽然单绕线双极步进电机比较贵,但它们能在额定物理尺寸下提供很强的转矩.但是.进步电机两个绕组的每一个都需要8个驱动晶体管,并在H桥路结构中连接成4个一组.每个晶体管都必须承受过载和短路状况并迅速从中恢复,因此驱动器必须包含复杂庞大的分立元件保护电路.     

Smart Staff Recruiting

The genius of President Obama is his ability to make smart people work harder. Surely every manager wants to aspire to this ability, but first he must find smart staff. The objective of this article is to help readers better prepare to recruit smart people to work for them. An ideal IT staff member should have a computer science background or equivalent education. He or she should possess both technical and people skills. In identifying proper strengths from candidates' application material, we must be mindful of the subtle nuances. Sometimes, what hasn't been said is more important than what has. We need to be mindful that talking to a reference can usually give a more accurate assessment about an applicant than a written recommendation. We also need to be mindful that smart people in general prefer working with a boss who is more collegial than authoritative.     

Dissolution of Alumina, Sintering, and Crystallization in Glass Ceramic Composites for LTCC

Sintering and microstructure evolution of alkali-free calcium–alumo–borosilicate glass/α-Al₂O₃ composites (mean particle size ca. 2 μm) for low-temperature cofired ceramics were studied during heating at 5 K/min by heating microscopy, thermal analysis (DTA), X-ray diffraction (XRD), and electron microscopy (SEM). Composites fully densify at ≈830°C, not essentially influenced by the dissolution of alumina and glass crystallization. Thus wollastonite, as first crystalline phase, was detectable at 840°C. Above 900°C, a pronounced crystallization of anorthite is evident, reaching 60 wt% at 1050°C. Rietveld analyses of XRD data revealed that anorthite precipitates at the expenses of alumina, which declines from ≈33 to <10 wt%, and wollastonite, which fully declines from its maximum of ≈19 wt%. Based on XRD, we discuss the evolution of crystal mass fractions, the residual glass composition, the glass viscosity, and the effective shear viscosity of the composites under study during heating.     

Mass Transport in the Presence of Internal Defect Reactions—Concept of Conservative Ensembles: IV, Tracer Diffusion and Intercorrelation with Chemical Diffusion and Ion Conductivity

The tracer diffusion coefficient is analyzed for the case in which internal ionization equilibria have to be considered, using the concept of conservative ensembles. The relationships of the tracer diffusion coefficient with other phenome-nological parameters, viz., the chemical diffusion coefficient and the diffusion coefficient derived from the ionic conductivity, as well as with the defect diffusivities are given. The importance of mobile partially ionized or neutral defects is highlighted. In this respect the formulation of the tracer diffusion as an ambipolar diffusion of the different isotopes is helpful.