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91.
当前,我国的现代化建设事业已进入了全面发展的局面。在新的形势下,现代科学的特点不但是科学知识彼此之间的紧密联系、互相渗透。边缘科学层出不穷,而且作为知识体系的自然科学理论也同社会的其它各项事业以大跨度地结网,凝结在尘产力的基本因素之中,空前的发挥着它的社会职能。 相似文献
92.
Gregory M. Troup Yi Xie Kathleen Boesze-Battaglia Yong Huang Terry Kirk Francine Hanley Thomas N. Tulenko 《Macromolecular Symposia》2005,219(1):25-38
At least three types of cholesterol-rich membrane domains have been described in biological membranes including cholesterol rafts, membrane caveolae and crystalline cholesterol domains,. While clear biological functions have been ascribed to both rafts and caveolae, little attention has been directed to the biological consequences of cholesterol enrichment of cell membranes and the formation of cholesterol domains. Elevated blood cholesterol levels have been shown to result in the enrichment of the cell plasma membrane with cholesterol in arterial smooth muscle cells (SMC), endothelial cells (EC) and cardiac myocytes. In the early period of cholesterol feeding (within days), the cell membrane enriches with cholesterol and membrane viscosity and membrane bilayer width increase. This latter effect severely alters membrane protein function, and recent data indicates that this induces the modulation of vascular cells (SMC and EC) to the atherosclerotic phenotype. In cardiac myocytes these membrane modifications appear to induce alterations in gene expression patterns that lead to the development of a heart failure phenotype. In addition, as the cholesterol content increases, phase separation of cholesterol occurs resulting in the formation of immiscible cholesterol domains within the membrane. These domains likely initiate nucleation of cholesterol crystals which would explain the origin of “cholesterol clefts” in atherosclerotic lesions. Taken together, these membrane alterations secondary to cholesterol enrichment constitute a “membrane lesion” which contribute to the very early pathogenic events underlying major human diseases including coronary artery disease, stroke and heart failure. 相似文献
93.
Pamela L. Broaddus-Lawrence Kathleen Treole Robert B. McCabe Rose L. Allen Louise Toppin 《Journal of voice》2000,14(1):58-71
The purpose of the present study was to determine the effects of vocal hygiene education on the vocal hygiene behaviors and perceptual vocal characteristics of untrained singers. Eleven adult untrained singers served as subjects. They attended four 1-hour class sessions on vocal hygiene, including anatomy and physiology of the phonatory mechanism, vocally abusive behaviors, voice disorders commonly seen in singers, and measures to prevent voice disorders. Pre- and postinstruction surveys were used to record subjects' vocal abuses and their perceptions of their speaking and singing voice. They also rated their perceived value of vocal hygiene education. Results revealed minimal changes in vocal hygiene behaviors and perceptual voice characteristics. The subjects did report a high degree of benefit and learning, however. 相似文献
94.
It is shown that the index of a constrained critical point in the isoperimetric calculus of variations is simply related to the number of negative eigenvalues of a certain bordered operator associated with the second variation. A conjugate point theory for this bordered operator is then established. 相似文献
95.
Understanding the complex process of information spread in online social networks (OSNs) enables the efficient maximization/minimization of the spread of useful/harmful information. Users assume various roles based on their behaviors while engaging with information in these OSNs. Recent reviews on information spread in OSNs have focused on algorithms and challenges for modeling the local node-to-node cascading paths of viral information. However, they neglected to analyze non-viral information with low reach size that can also spread globally beyond OSN edges (links) via non-neighbors through, for example, pushed information via content recommendation algorithms. Previous reviews have also not fully considered user roles in the spread of information. To address these gaps, we: (i) provide a comprehensive survey of the latest studies on role-aware information spread in OSNs, also addressing the different temporal spreading patterns of viral and non-viral information; (ii) survey modeling approaches that consider structural, non-structural, and hybrid features, and provide a taxonomy of these approaches; (iii) review software platforms for the analysis and visualization of role-aware information spread in OSNs; and (iv) describe how information spread models enable useful applications in OSNs such as detecting influential users. We conclude by highlighting future research directions for studying information spread in OSNs, accounting for dynamic user roles. 相似文献
96.
Stefan Vonhoff Kathleen Piens Muriel Pipelier Christophe Braet Marc Claeyssens Andrea Vasella 《Helvetica chimica acta》1999,82(7):963-980
The lactam 16 , the hydroximolactams 8 , 20 , 23 , and 27 , and the imidazole 32 were prepared following known methods. They were tested together with the known tetrazole 35 and the hydroximolactams 2 and 36 as inhibitors of the cellobiohydrolases Cel7A and Cel6A from Trichoderma reesei. Cel7A is only weakly inhibited by these compounds. Comparing their inhibitory activity evidences the importance of occupying subsites +1 and +2. The results strongly suggest that the shape of none of the variants of the lactone-type inhibitor motif embodied by these inhibitors is complementary to the subsite −1, i. e., analogous to the transition state. Cel6A is rather strongly inhibited by the cellobiose analogues 20 , 23 , and 32 , and by the cellotriose analogue 27 . Their relative inhibitory activities evidence that binding at subsite −2 depends upon the shape of the moiety occupying subsite −1. There is only a small difference between the inhibition by the hydroximolactams 20 and 23 , which may be (partially) protonated by the catalytic acid of either anti- or syn-protonating glycosidases, and the imidazole 32 , which can only be protonated by anti-protonating glycosidases. The results strongly suggest that shape requirements must be met by glycosidase inhibitors before they can be used to characterize the proton trajectory of glycosidases. 相似文献
97.
Scott G. Summerfield Kathleen A. Cox Simon J. Gaskell 《Journal of the American Society for Mass Spectrometry》1997,8(1):25-31
Low energy collisionally activated dissociations (CAD) of doubly protonated peptides incorporating cysteic acid and arginine residues have been studied. Deuterium labeling experiments have established that loss of the elements of H2SO3 occurs with cleavage of one CH bond and transfer of the hydrogen to a neutral fragment. Prominent d-type ions were observed corresponding to cleavage at the cysteic acid residue. The analysis of structural analogs suggested that the unexpectedly low energy requirement for this process is attributable to a charge-proximal process promoted by intra-ionic interaction of the arginine and cysteic acid side chains. CAD (in the collision hexapole of a tandem quadrupole instrument) of electrospray source-formed fragment ions established that the d-type ions can form via b-type ions; there was no evidence of formation via (a n + 1) or (b n — H2SO3) ions. The equivalent d-ion was observed, albeit with lesser abundance, when the cysteic acid residue was replaced by aspartic acid, but not by glutamic acid. 相似文献
98.
Kelly K. McGrath Kyoungmi Jang Kathleen A. Robins Prof. Dong‐Chan Lee Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(16):4070-4077
Tuning electronic properties and morphologies : We report a unique design platform of n‐type organic semiconductors based on asymmetrically substituted bisphenazines that enable tuning of both electronic properties and morphologies of 1D nanostructures (see figure) by using small substituents with various sizes and electronic demands.
99.
Colette M. Castleberry Kathleen Lilleness Rachel Baldauff Patrick A. Limbach 《Journal of mass spectrometry : JMS》2009,44(8):1195-1202
The use of isotopically labeled endonuclease digestion products allows for the relative quantification of ribonucleic acids (RNAs). This approach utilizes ribonucleases such as RNase T1 to mediate the incorporation of 18O onto the 3′‐terminus of the endonuclease digestion product from a solution containing heavy water (H218O). The accuracy and precision of relative quantification are dependent on the efficiency of isotope incorporation and minimizing any possible 18O to 16O back‐exchange before or during mass spectral analysis. Here, we have investigated the stability of 18O‐labeled endonuclease digestion products to back‐exchange. In particular, the effects of pH, temperature and presence of RNase on the back‐exchange process were examined using matrix‐assisted laser desorption/ionization mass spectrometry (MALDI‐MS). We have found that back‐exchange depends on the presence of the RNase—back‐exchange was not observed once the enzyme was removed from the sample. With RNase present, at all pH values examined (from acidic to basic pH), back‐exchange was detected at incubation above room temperature. The rates and extent of back‐exchange were similar at all pH values. In contrast, back‐exchange in the presence of RNase was found to be especially sensitive to incubation temperature—at temperatures below room temperature, minimal back‐exchange was detected. However, back‐exchange increased as the incubation temperature increased. Based on these findings, appropriate sample‐handling and sample storage conditions for isotopically labeled endonuclease digestion products have been identified, and these conditions should improve the accuracy and precision of results from the relative quantification of RNAs obtained by this approach. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
100.
H.T. Banks Kathleen Holm Nathan C. Wanner Ariel Cintrn-Arias Grace M. Kepler Jeffrey D. Wetherington 《Mathematical and Computer Modelling》2009,50(7-8):959-974
We present a preliminary first-pass dynamic model for delivery of drug compounds to the lungs and heart. We use a compartmental mass-balance approach to develop a system of nonlinear differential equations for mass accumulated in the heart as a result of intravenous injection. We discuss sensitivity analysis as well as methodology for minimizing mass in the heart while maximizing mass delivered to the lungs on a first circulatory pass. 相似文献