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981.
Epithelial tissues provide the first line of defense between an organism and the environment. Disruption of this barrier leads to bacterial invasion and subsequent inflammation. This is precisely the situation existing in the human oral cavity, where tissues are constantly exposed to a variety of microbial challenges that can lead to bacterially induced periodontal diseases, and to infections of the oral mucosa by bacteria, fungi, and viruses. With the recent discoveries of host-derived peptide antibiotics in mammalian mucosal epithelium, a new line of investigation is emerging to test the hypothesis that one class of these peptides, called "beta-defensins", functions to protect the host against microbial pathogenesis at these critical, confrontational sites. In that light, impairment of beta-defensin activity has recently been implicated in chronic bacterial infections in cystic fibrosis patients. The first direct evidence of expression of defensin peptides in the oral mucosa was the identification of a novel epithelial beta-defensin in mammalian tongue. It was shown to be upregulated in inflammation, suggesting that it participates in host defense. It is theorized that epithelial cell-derived antimicrobial peptides function to keep the natural flora of micro-organisms in a steady state in different niches such as the skin, the intestines, the airway, the endocervix, and the mouth. There is now evidence indicating that normal gingival epithelial cells and tissues express two beta-defensins, hBD-1 and the newly described hBD-2. In addition, a cathelin-class antimicrobial peptide, designated LL-37 and found in human neutrophils, is also expressed in skin and gingiva. It is highly likely that these and/or other epithelial antimicrobial peptides play an important role in determining the outcome of the host-pathogen interaction at the oral mucosal barrier, and that they may have important future applications in antibiotic treatment. 相似文献
982.
983.
阐述西藏电视发射台智慧运维监控系统的实现方法.该系统实现对台站内发射机运行状态、电视节目信号源、发射播出信号以及发射台电力、环境、内外安全等进行实时监测、监控,台站各子系统出现故障时,运维监控系统能自动告警、自动切换,可以实时查询和统计各子系统的状态数据、告警数据.该系统有效提高了西藏电视发射台的工作效率和管理水平,增强了台站的指挥调度能力,更好地保障了台站的播出安全. 相似文献
984.
Placek Lida L. Pastor H. P. Hughes J. P. Bickford W. G. 《Journal of the American Oil Chemists' Society》1961,38(2):107-109
Four divinyl sulfone-eleostearate adducts were synthesized and compared with dibutyl sebacate as plastieizers for nitrile
rubber. Three of these, the adducts of methylalpha-eleostearate, its hydrogenated derivative, and that of tung oil, were found to be satisfactory primary plastieizers. The
stocks prepared from the unhydrogenated adducts were superior in plasticizing efficiency to those prepared from their hydrogenated
derivatives. The divinyl sulfone-tung oil adduct yielded a rubber which met the low-temperature flexibility requirements (−40°C.)
of the automotive industry.
One of the laboratories of the Southern Utilization Research and Development Division, Agricultural Research Services, U.S.
Department of Agriculture. 相似文献
985.
针对液体膨胀式波纹管蒸汽疏水阀排量不稳定、漏汽率高等问题,分析波纹管热动元件的热工特性.基于Riedel蒸汽压方程和气液平衡方程,建立饱和蒸汽压式波纹管热动元件的热力学模型,设计相应实验系统,进行不同参数下的实验研究.结果表明,饱和蒸汽压式波纹管热动元件伸长量是相变温度的单值函数,近似呈指数关系;采用不同混合比、刚度及填充方式,可调节疏水阀的排水过冷度. 相似文献
986.
Non-conservative changes, consisting of Y76E, Y76L, Y76Q and Y76W, have
been made to tyrosine 76, one of the key DNA binding residues in DNase I.
Normally Y76 inserts into the minor groove of DNA and makes an unusual,
hydrophobic, stacking interaction with one of the sugars. All four mutants
bind to DNA more tightly than the wild type, but cut it more slowly as
assessed by Kunitz assays. This gives a rather small decrease in the
specificity constants (Vmax/K(m)) for the hydrolysis of DNA, which is
roughly paralleled by the loss of activity towards the non-DNA small
chromophoric substrate, thymidine-3',5'-di(p- nitrophenyl)phosphate. These
non-conservative mutants, therefore, show different behaviour to Y76A and
Y76G, studied previously [Doherty A.J., Worrall A.F. and Connolly B.A.
(1995) J: Mol. Biol., 251, 366-377]. These two mutants both bind to and cut
DNA poorly, resulting in large decreases in Vmax/K(m) values. However, they
showed little reduction in rates with the chromophoric substrate. It is
likely that the altered side chains in the non-conservative mutants are
still able to interact productively with the DNA and contribute to the
observed DNA distortion that is essential for efficient catalysis. However,
these mutations disrupt the active site, most probably by interference with
the hydrogen bonded Y76-E78-H134 triad. H134 is a critical hydrolytic
residue of DNase I that is essential for catalysis. The DNA cleavage
selectivity of the Y76E, Y76L, Y76Q and Y76W mutants were little altered as
compared with the wild-type enzyme as measured using the cutting patterns
of a 160 base-pair Escherichia coli Tyr T promoter DNA fragment. This
confirms earlier observations, with Y76F, Y76A and Y76G, that showed that
this tyrosine has little role in DNA cleavage specificity.
相似文献
987.
988.
Monitoring the service condition of concrete structures requires the quantitative assessment of properties and corrosion rate
of structural steels surrounded by concrete. A multi-cell sensor system that included a reference electrode, a chloride content
sensor, a macrocell current unit and an electrical resistance measurement unit was developed. This system provided the following
important electrochemical data in the cover-zone concrete on site: open circuit potential, macrocell current from anodes to
cathode, chloride profile, concrete resistance and corrosion rate of built-in anodes. The experimental results show that the
macrocell current increases when the chloride content in concrete is higher. Thus, monitoring the chloride content is a good
method for monitoring the corrosion state. The chloride ion content and cover depth are the key factors that affect the electrical
resistance of concrete. Without considering the temperature and time, a simplified model of the instantaneous corrosion rate
of steel rebar in a concrete structure based on the measured chloride contents and concrete resistance was proposed. The test
results further prove the reliability of this simplified predicting model. 相似文献
989.
Michael Hughes Kerby C. Jones Megan E. Hums Richard A. Cairncross Victor T. Wyatt 《Journal of the American Oil Chemists' Society》2018,95(4):407-420
Fatty acid methyl esters (FAME) from waste grease usually contain higher concentrations of sulfur (S) than allowed to meet the specified quality standard for biodiesel (<15 ppm). Brown grease lipid‐derived FAME was produced and fractionated by two passes through a wiped‐film evaporator (WFE) to produce three fractions: (1) a 120 °C pass distillate, (2) a 170 °C pass distillate, and (3) a heavy residue. Solid phase extraction (SPE) was used to concentrate the S species from the distillate fractions so that they could be detected by a gas chromatography–pulsed flame photometric detector (GC–PFPD) and GC–mass spectrometry (MS). The ethyl acetate and methanol (MeOH) fractions obtained by SPE of the 120 °C WFE distillate and methyl tert‐butyl ether and acetone fractions obtained by SPE of the 170 °C WFE distillate had the highest concentration of S and were, therefore, the best candidates for GC–PFPD analysis. GC–PFPD methods were developed to separate the S species adequately enough for those peaks to be analyzed by GC–MS which matched fragmentation patterns identified by the MS chemical library as tetrahydrothiophenes, dithiolanes, and thiophenes. MS fragmentation patterns were used to identify other, larger, S‐bearing species as sulfides and disulfides cross‐linking between two FAME molecules. The results obtained from this study provide a foundation for developing effective purification methods to remove S‐containing impurities from waste grease‐derived biodiesel. 相似文献
990.
从强度安全性的角度出发,综合运用了概率密度函数联合积分法与功能密度函数积分法,整理并推导了油气悬架零部件的模糊可靠度计算公式,即应力、强度都为正态分布,隶属度函数为线性分布时的模糊可靠度计算公式;通过VB编程实现数值解的计算,可直接应用于设计计算中,以提高油气悬架的设计水平. 相似文献