Regulation of an Escherichia coli/mammalian chimeric carbamoyl-phosphate synthetase

Carbamoyl-phosphate synthetase (CPSase) consists of a 120-kDa synthetase domain (CPS) that makes carbamoyl phosphate from ATP, bicarbonate, and ammonia usually produced by a separate glutaminase domain. CPS is composed of two subdomains, CPS.A and CPS.B. Although CPS.A and CPS.B have specialized functions in intact CPSase, the separately cloned subdomains can catalyze carbamoyl phosphate synthesis. This report describes the construction of a 58-kDa chimeric CPSase composed of Escherichia coli CPS.A catalytic subdomains and the mammalian regulatory subdomain. The catalytic parameters are similar to those of the E. coli enzyme, but the activity is regulated by the mammalian effectors and protein kinase A phosphorylation. The chimera has a single site that binds phosphoribosyl 5'-pyrophosphate (PRPP) with a dissociation constant of 25 microM. The dissociation constant for UTP of 0.23 mM was inferred from its effect on PRPP binding. Thus, the regulatory subdomain is an exchangeable ligand binding module that can control both CPS.A and CPS.B domains, and the pathway for allosteric signal transmission is identical in E. coli and mammalian CPSase. A deletion mutant that truncates the polypeptide within a postulated regulatory sequence is as active as the parent chimera but is insensitive to effectors. PRPP and UTP bind to the mutant, suggesting that the carboxyl half of the subdomain is essential for transmitting the allosteric signal but not for ligand binding.     

Proline isomerization-independent accumulation of an early intermediate and heterogeneity of the folding pathways of a mixed alpha/beta protein, Escherichia coli thioredoxin

Oxidized Escherichia coli thioredoxin (Trx) is a small protein of 108 residues with one disulfide bond (C32-C35 essentially involved in the activity) and no prosthetic moieties, which folds into a structural motif containing a central twisted beta-sheet flanked by helices that is found in many larger proteins. The kinetics of refolding of Trx in vitro have been investigated using a newly developed active site titration assay and continuous or stopped-flow (SF) methods in conjunction with circular dichroism (CD) and fluorescence (Fl) spectroscopy. These studies revealed the presence of early folding intermediates with "molten globule or pre-molten globule" characteristics. Measurements of the ellipticity at 222 nm indicated that about 68% of the total change associated with refolding occurred during the dead time (4 ms) of the stopped-flow instrument, suggesting the formation of substantial secondary structure. The reconstruction of the far-UV CD spectrum of the burst intermediate using combined continuous and stopped-flow methods showed the formation of a defined secondary structure that contains more beta-structure than the native state. Kinetic measurements using SF far-UV CD and Fl over a wide range (0.087-6 M) of GuHCl concentrations at two temperatures (6 and 20 degreesC) demonstrated that the population formed during the 4 ms dead time contained multiple species that are stabilized mainly by hydrophobic interactions and undergo further folding along alternative pathways. One of these species leads directly and rapidly to the native state as demonstrated by active site titration, while the two others fold into a fourth intermediate that is slowly converted to the native protein. Double-jump experiments suggest that the heterogeneity in folding behavior results from proline isomerizations occurring in the unfolded state. Conversely, the accumulation of the burst intermediate does not depend on proline isomerizations.     

联合因子分析中的本征信道空间拼接方法

为了使联合因子分析适用于多种信道条件下的文本无关说话人识别,提出了一种本征信道空间的正交拼接法.在多信道条件下,可以通过混合数据法或简单拼接法估计本征信道空间,但前者存在空间掩盖,后者虽解决了空间掩盖但引入了空间重叠.本文首先证明说话人建模和测试的核心运算是斜投影,基于上述证明,通过将待拼接空间正交的方法移除了空间重叠.在NIST SRE 2008核心评测数据库上的实验表明,本文所提算法优于混合数据法和简单拼接法.     

GPU Acceleration for FEM-Based Structural Analysis

Graphic Processing Units (GPUs) have greatly exceeded their initial role of graphics accelerators and have taken a new role of co-processors for computation—heavy tasks. Both hardware and software ecosystems have now matured, with fully IEEE compliant double precision and memory correction being supported and a rich set of software tools and libraries being available. This in turn has lead to their increased adoption in a growing number of fields, both in academia and, more recently, in industry. In this review we investigate the adoption of GPUs as accelerators in the field of Finite Element Structural Analysis, a design tool that is now essential in many branches of engineering. We survey the work that has been done in accelerating the most time consuming steps of the analysis, indicate the speedup that has been achieved and, where available, highlight software libraries and packages that will enable the reader to take advantage of such acceleration. Overall, we try to draw a high level picture of where the state of the art is currently at.     

改性纳米二氧化钛光催化降解聚乙烯薄膜的研究

以硬脂酸钠改性的纳米TiO2为光催化剂,与LDPE树脂制备了nano-TiO2/PE复合薄膜.研究了该薄膜在紫外光照射条件下的降解性能,并进行了SEM、FI-IR、VHX-100数码显微镜等分析,测试了薄膜经辐照前后的力学性能、质量变化和分子量变化.研究结果表明,该薄膜在紫外光照射下降解性能明显提高,薄膜在40W、254nm的紫外光照射120h后,粘均分子量(Mη)降低27.1%,拉伸强度降低49.1%,断裂伸长率降低91.3%;照射144h后质量损失达16%(质量分数);辐照后薄膜的羰基含量升高.     

Technological windows for MIAB welding of tubes featuring original longitudinal magnetization system with peripheral solenoids

This paper presents the performances of an original longitudinal magnetization system, designed to assure the magnetic flux concentration on the tube wall. This magnetization system is made of several small peripheral solenoids disposed around each tube, parallel to the tube axis, and was used to investigate the interaction between the arc and the magnetic field in case of MIAB (Magnetically Impelled Arc Butt) welding of low carbon steel thin-walled tubes. The main research objective was the development of process parametrical windows for assuring qualitative joint achievement. Macro- and micro-structural analysis accompanies the hardness tests made on corresponding welded samples, demonstrating the operational process maps in producing sound MIAB joints. The paper also discusses the process main stages based on corresponding images resulting from process monitoring, from arc initiation to the emergence of molten metal when upsetting starts and the weld is formed.     

Determinant spreading associated with demyelination in a nonhuman primate model of multiple sclerosis

Definition of the immune process that causes demyelination in multiple sclerosis is essential to determine the feasibility of Ag-directed immunotherapy. Using the nonhuman primate, Callithrix jacchus jacchus (common marmoset), we show that immunization with myelin basic protein and proteolipid protein determinants results in clinical disease with significant demyelination. Demyelination was associated with spreading to myelin oligodendrocyte glycoprotein (MOG) determinants that generated anti-MOG serum Abs and Ig deposition in central nervous system white matter lesions. These data associate intermolecular "determinant spreading" with clinical autoimmune disease in primates and raise important issues for the pathogenesis and treatment of multiple sclerosis.     

Radiographic evaluation of complications after jejunoileal bypass surgery

A retrospective analysis of 89 patients who underwent jejunoileal bypass surgery for morbid obesity disclosed 33 complications that were detected radiographically. Intestinal obstruction (10.1% of patients), cholecystitis (5.6%), renal stones (4.5%), peptic ulcer (3.4%), megacolon (6.7%), and elongation of the small intestine with hypertrophy of the mucosal folds of the jejunum (6.7%) were diagnosed solely by radiographic means.