A high pressure-ratio, energyfocused thermoacoustic heat engine with a tapered resonator

Heat energy with temperature difference may lead to self-excited acoustical oscillation under appropriate condition, which is called “thermoacoustic phenomenon”. The physical phenomenon was observed about two hundreds years ago. However, the research on high-energy thermoacoustic devices was begun only about a decade ago.Thermoacoustic machines use inert gases as working medium and have no moving mechanical pans; consequently they are really environment-friendly and highly reliable.The efficiencies of thermoacoustic machines are now greatly improved, close or even higher than that of conventional heat engines.     

一种无阈值压降的可重构高功率密度电荷泵

文章通过折叠浮置电容的方法实现电荷泵片上实时重构,解决了可重构电荷泵中开关路径过多以及低电压转换倍率(voltage conversion ratio,VCR)时部分电容闲置的问题,降低了电荷泵内阻,提高了功率密度,降低了输出电压纹波;在此基础上,提出新的电平转换器(level shifter,LS)来产生开关管的控制信号,以消除开关管的阈值压降;同时采用双路LS交替输出的方法,使开关管的控制信号保持适当的死区时间,减小了反向电流。文中以4阶电荷泵为例,基于TSMC CMOS 0.18μm工艺库仿真验证了上述方案的可行性,该结构可在2×、3×、4×、5×这4种VCR之间实时转换,工作电压低至金属氧化物半导体(metal oxide semiconductor,MOS)管阈值电压,空载条件下的输出电压能够达到理想值的97%以上。     

航天器短时大功率排热系统质量分析

为既能提高航天器排热能力,又能降低排热系统质量,提出了单相流体回路、蓄冷-单相流体回路、热泵单相流体回路、蓄冷热泵回路4种排热方案,计算了各方案排热能力和系统质量构成.与单相流体回路相比,在给定条件下,采用蓄冷-热泵回路可减少辐射器面积69.9%,降低排热系统质量53.5%.而蓄冷单相流体回路可减少辐射器面积56.0%,降低排热系统质量48.8%.结果表明蓄冷方案可以有效解决航天器短时大排热功率问题.     

高维热传导方程的高精度交替方向隐式方法

提出了数值求解二维和三维热传导方程的高精度交替方向隐式（ADI）方法,其空间为四阶精度、时间为二阶精度,并通过Neumann方法证明是无条件稳定的．该方法沿每个空间方向只涉及3个网格基架点,因此可以重复采用TDMA算法,大大节省了计算时间．数值实验验证了该方法的高阶精度,并与二阶的Peaceman—Rachford格式、Douglas格式及Crank—Nicolson格式进行了比较．     

基于高SBS阈值的HNLF产生高重复频率超短光脉冲

基于光纤中的四波混频(FWM)产生高重复频率超短光脉冲的原理,并为抑制光纤中的受激Brillouin散射(SBS),采用非均匀掺杂高SBS阈值非线性光纤,通过FWM对双拍频信号进行整形压缩,实验上获得了100GHz的高重复率超短光脉冲序列,进而分析了入纤功率对输出光脉冲的影响。     

高温双再生器型吸收式热变换器热力循环分析

提出一种新型以溴化锂溶液为工质的高温双再生器型吸收式热变换器（HDAHT）循环系统,该系统在高温单级吸收式热变换器循环中再生器和冷凝器之间增加了第二级再生器.HDAHT系统可以将高温废热源的温度进一步提高至有用温位.对HDAHT内各参数对系统性能系数COP的影响进行了模拟计算.计算结果表明,系统性能系数COP随着蒸发温度、低压再生器温度和溴化锂溶液中间浓度的升高而增大,随着吸收温度、高压再生器温度和溴化锂稀溶液浓度的升高而减小.在适合的操作条件下,本循环的系统性能系数COP达到了0.61,是高温单级吸收式热变换器的1.2倍.所得到的这些规律将为高温吸收式热变换器设计系统优化提供必要的理论依据.     

在索赔额相依的风险模型中的阈值分红策略

介绍了带有阈值分红的索赔额相依风险模型,给出了Gerber-Shiu罚金折现函数满足的非齐次积分微分方程及其解的分析,并给出了红利折现期望满足的齐次积分微分方程。     

高压功率LDMOS阈值电压温度系数的分析

分析了高压LDMOS在-27℃至300℃温度范围内的温度特性,并给出了阈值电压温度系数的计算公式.根据计算结果,可以得到以下结论:高压LDMOS的阈值电压温度系数在相当宽的温区内是一常数;可用温度的线性表达式来计算阈值电压温度系数;薄栅氧化层和高沟道掺杂浓度可减小高压功率LDMOS的阈值电压温度系数.     

A transglutaminase homologue as a condensation catalyst in antibiotic assembly lines

The unrelenting emergence of antibiotic-resistant bacterial pathogens demands the investigation of antibiotics with new modes of action. The pseudopeptide antibiotic andrimid is a nanomolar inhibitor of the bacterial acetyl-CoA carboxylase that catalyses the first committed step in prokaryotic fatty acid biosynthesis. Recently, the andrimid (adm) biosynthetic gene cluster was isolated and heterologously expressed in Escherichia coli. This establishes a heterologous biological host in which to rapidly probe features of andrimid formation and to use biosynthetic engineering to make unnatural variants of this important and promising new class of antibiotics. Bioinformatic analysis of the adm cluster revealed a dissociated biosynthetic assembly system lacking canonical amide synthases between the first three carrier protein domains. Here we report that AdmF, a transglutaminase (TGase) homologue, catalyses the formation of the first amide bond, an N-acyl-beta-peptide link, in andrimid biosynthesis. Hence, AdmF is a newly discovered biosynthetic enzyme that acts as a stand-alone amide synthase between protein-bound, thiotemplated substrates in an antibiotic enzymatic assembly line. TGases (enzyme class (EC) 2.3.2.13) normally catalyse the cross-linking of (poly)peptides by creating isopeptidic bonds between the gamma-carboxamide group of a glutamine side chain of one protein and various amine donors, including lysine side chains. To the best of our knowledge, the present study constitutes the first report of a TGase-like enzyme recruited for the assembly of an antibiotic. Moreover, genome mining using the AdmF sequence yielded additional TGases in unassigned natural product biosynthetic pathways. With many more microbial genomes being sequenced, such a strategy could potentially unearth biosynthetic pathways producing new classes of antibiotics.     

Identification of a potent Xenopus mesoderm-inducing factor as a homologue of activin A

The first inductive interaction in amphibian development is mesoderm induction, when a signal from the vegetal hemisphere of the blastula induces mesoderm from overlying equatorial cells. Recently, several 'mesoderm-inducing factors' (MIFs) have been discovered. These cause isolated Xenopus animal caps to form mesodermal cell types such as muscle, instead of their normal fate of epidermis. The MIFs fall into two classes. One comprises members of the fibroblast growth factor (FGF) family, and the other members of the transforming growth factor type beta (TGF-beta) family. Of the latter group, the most potent is XTC-MIF, a protein produced by Xenopus XTC cells. Here we show that XTC-MIF is the homologue of mammalian activin A. Activins modulate the release of follicle-stimulating hormone from cultured anterior pituitary cells and cause the differentiation of two erythroleukaemia cell lines. Our results indicate that these molecules may also act in early development during formation of the mesoderm.     

一类热方程扰动系统的能控性

研究了一类热方程扰动系统的能控性问题.首先得到了系统的逼近能控性;然后采用变分方法对系统线性化,再结合解映射的性质,应用推广的隐函数定理,证明系统的局部零能控性;最后给出系统零能控的结论.     

一个无可信中心的有向门限签名方案

签名只有接受者才能验证,而任何第三方只有在接受者的合作下才能验证签名的数字签名方案称之为有向签名.而在大多情况下,有向签名通常是一个人,然而当所需签名的消息代表一个群体时,就需要群体中的一部分人同意,门限签名方案就被用作解决这个问题.由于在许多特定的应用环境下,一个可被所有成员信任的可信中心并不存在,所以不需要可信中心的门限签名方案就显得很有吸引力.文章提供了一个安全有效的有向门限签名方案.     

一类热传导方程逆时反问题的数值解法

讨论一类热传导方程逆时反问题(BHCP)的数值解法.中心差分法的思想是基于对原问题只进行空间离散,转化为一个不适定的常微分方程组的初值问题,然后利用变量变换把该问题转化为一个适定的常微分方程组的初值问题,最后利用Runge-Kutta方法进行数值求解.数值结果说明了数值解与精确解吻合良好.     

含高分压不凝气体的蒸汽在分离式热管内凝结换热

设计建立了一套以水为工质的分离式热管系统实验台,系统冷凝端采用水冷套管式换热器.在此实验台基础上研究了不抽真空、有大量不凝性气体存在于分离式热管的凝结放热问题,测定了在不同的入口蒸汽温度、循环蒸汽流量、冷却水进口温度及流量条件下混合气体在圆管内凝结换热的情况,分析了这些参数对换热过程的影响.同时,还对套管内含高分压不凝性气体——空气——的水蒸汽凝结换热物理模型进行了研究,并建立了相应的数学模型.模型中除了质量守恒、动量守恒、能量守恒和界面控制方程外,还增加了流动扩散和凝结控制方程.模型结果显示蒸汽放热量与实验测定值基本吻合,偏差在8%～15%之间.     

An integral heat flux sensor with high spatial and temporal resolutions

To measure heat flux on the sharp leading edge and other surface with very small curvature radius in the wind tunnel, Hong-Ru Yu proposed a novel design of inte- gral type heat flux sensor. Compared with the traditional heat flux sensor, the integral type heat flux sensor improved spatial resolution up to an order of magnitude, and the size of the sensing elements has been minimized to 0.1 mm successfully, which satisfied the heat flux measurement requirements at R0.5 mm pointed cone stagnation point. A constantan film was used as the contact layer of the integral heat flux sensor, which was prepared by electron beam coevaporation method. The influence of sensor structure on the accuracy of measurement was analyzed using numerical calculation. The measurement results in shock wave wind tunnel indicated that the response frequency was about 100 kHz and the repeatability error was less than 10 %.     

小型压燃式发动机缸内辐射热量的实验研究

在一台小型高速单缸压燃式发动机上,利用商用辐射传感器测量了缸内辐射传热量。实验包括在变转速和变负荷情况下,缸内缸盖火力面辐射热流量的测量。研究表明,在不同的运转工况下,发动机缸内的辐射热量是变化的。负荷增加时辐射热量增加,转速增加时辐射热量减少。     

带有阈值和优先权的三队列轮询排队系统

本文研究了一个带有阈值的优先权轮询排队系统,其中队列1有最高优先权,队列2次之,队列3最低。排队系统由3个M/M/1队列和一个服务台组成,采用阈值服务策略,队列1和队列2的阈值分别为1和N,队列3无阈值。在忽略转换时间和抢占情形下,利用分析的方法,给出了3个队长的稳态联合概率分布的母函数。借助母函数,得到了平均队长和平均等待时间。     

The Markov-dependent risk model with a threshold dividend strategy

This paper studies a Markov-dependent risk model in which the claim occurrence and the claim amount are regulated by an external discrete time Markov process.Integro-differential equations in matrix form for the Gerber-Shiu discounted penalty function are presented.Then the analytical solutions to the equations are derived.Finally,in the two-state model,some numerical results are obtained when claim amount is exponentially distributed.     

A human homologue of the yeast HDEL receptor

Retention of resident proteins in the lumen of the endoplasmic reticulum is achieved in both yeast and animal cells by their continual retrieval from the cis-Golgi, or a pre-Golgi compartment. Sorting of these proteins is dependent on a C-terminal tetrapeptide signal, usually Lys-Asp-Glu-Leu (KDEL in the single letter code) in animal cells, His-Asp-Glu-Leu (HDEL) in Saccharomyces cerevisiae. There is evidence that the ERD2 gene encodes the sorting receptor that recognizes HDEL in yeast; its product is an integral membrane protein of relative molecular mass 26,000 (26K) that is not glycosylated. In contrast, Vaux et al. suggest that the mammalian KDEL receptor is a 72K glycoprotein that they detected using an anti-idiotypic antibody approach. If this were so, it would indicate a surprising divergence of the retrieval machinery between yeast and animal cells. We report here that human cells express a protein similar in sequence, size and properties to the ERD2 product, and propose that this protein is the human KDEL receptor.