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61.
Ageing behaviour, leading to ballistic changes, has been studied as a function of oxidizer loading in polystyrene/ammonium perchlorate solid-propellants. The ageing studies were carried out at 100 °C in air. Change in burning rate decreased as the oxidizer loading increased from 75 to 80%. The change in thermal decomposition rates both at 230 and 260 °C also decreased as the oxidizer loading in the propellants increased. The shapes of the plots of the changes in burning rate and thermal decomposition rate (230 and 260 °C) at different storage times for different oxidizer-loaded propellants seem to be exactly similar. These results lead to the conclusion that the thermal decomposition of the propellant may be responsible for bringing about the ballistic changes during the ageing process. Infrared studies of the binder portion of the aged propellant indicate that peroxide formation takes place during the course of ageing and that peroxide formation for a particular storage time and temperature increases as the loading decreases. 相似文献
62.
It is shown how the equations of a class of coupled distributed networks can be decoupled, and their transmission parameters expressed in terms of those of an equivalent scalar system. 相似文献
63.
Immunological properties of human decidual macrophages--a possible role in intrauterine immunity 总被引:2,自引:0,他引:2
Singh U Nicholson G Urban BC Sargent IL Kishore U Bernal AL 《Reproduction (Cambridge, England)》2005,129(5):631-637
Our aim was to investigate the contribution of decidual macrophages, which constitute an important immune component of the decidua in late gestation, to intrauterine defence mechanisms. Using flow cytometry we examined the ability of decidual macrophages, isolated from term decidua, to bind and phagocytose fluorescence-labelled bacterial and yeast bioparticles. We also assessed their ability to generate superoxide radicals and tumour necrosis factor-alpha following lipopolysaccharide challenge. Decidual macrophages bound bacterial and yeast particles in a dose-dependent manner, which subsequently led to phagocytosis. These macrophages also produced superoxide radicals and the pro-inflammatory cytokine TNF-alpha when challenged with bacterial lipopolysaccharides. These results suggest a role for decidual macrophages in pathogen recognition and clearance during pregnancy, and, therefore, they are likely to protect the fetus against intrauterine infections which might otherwise lead to preterm labour. 相似文献
64.
Nine cases of patients in whom intracranial infection was suspected after operation are presented. Lesions with ring enhancement were seen in all of these patients. The differentiation of enhancement, seen as a normal postoperative phenomenon, from residual neoplasia and cerebral abscess can be difficult. This can be resolved by serial and sequential-delayed CT, and thus unnecessary re-exploration may be prevented. 相似文献
65.
66.
Vitamin C kinetic degradation of strawberry juice stored under non-isothermal conditions 总被引:2,自引:0,他引:2
Strawberries are a good source of nutritional compounds and may be considered among the fruit most rich in ascorbic acid (AA). Strawberry juice is easily damaged in transit due to temperature fluctuations that may significantly reduce shelf life. In this way, the use of “best before” and “use by” dates should be reconsidered in the light of temperature variability during transport or storage. Kinetic degradation of ascorbic acid and shelf life estimation of strawberry juice stored under non-isothermal conditions was performed using a Weibullian-logistic model. A kinetic order of 1.1 was estimated as the best value to fit AA degradation under isothermal conditions and may be considered as the value for this particular medium. Moreover, the Weibullian-logistic model well fitted AA degradation under non isothermal conditions and may be used to predict shelf life under different fluctuation temperature histories. On the basis of temperature profiles considered in this paper, a retention of 46.8% and 42.7%, respectively for experimental and predicted data after 15 days were measured. Furthermore, it was showed a significant decrease of shelf life (about 5 days) for samples exposed to fluctuation temperature in comparison whit samples kept at constant temperature. 相似文献
67.
Influence of altitudinal variation on the antioxidant potential of tartar buckwheat of Western Himalaya 总被引:1,自引:0,他引:1
Garima Kishore Shashi Ranjan Anjana Pandey Sanjay Gupta 《Food science and biotechnology》2010,19(5):1355-1363
In the present work, the effect of altitudinal variations on the total phenol, flavonoid, and antioxidant potential of seeds
and hull of Tartar buckwheat collected from 15 different locations of Western Himalaya has been investigated. Methanolic and
acetonic extracts of seed and hull powder showed significantly increasing amounts of total polyphenol content, and antioxidant
potential with rising altitude. Methanolic extract of seed and hull powder were found to have significantly greater polyphenol,
and antioxidant potential as compared to acetonic extract. The methanolic seed extract of Inderdhara (3,133 m) showed the
maximum total phenolic content 1,651 μg gallic acid equivalent/50 mg of dry weight. The methanolic seed extract of Inderdhara
showed the maximum antioxidant activity (77.29±1.2%) and antiradical activity (55.5±0.5%) also. The results of this study
exhibited good correlation with total polyphenol and antioxidant potential in all the samples followed by the increasing tendency
towards rising altitude. 相似文献
68.
One class of applications envisaged for the IEEE 802.15.4 LR-WPAN (low data rate—wireless personal area network) standard
is wireless sensor networks for monitoring and control applications. In this paper we provide an analytical performance model
for a network in which the sensors are at the tips of a star topology, and the sensors need to transmit their measurements
to the hub node so that certain objectives for packet delay and packet discard are met. We first carry out a saturation throughput
analysis of the system; i.e., it is assumed that each sensor has an infinite backlog of packets and the throughput of the
system is sought. After a careful analysis of the CSMA/CA MAC that is employed in the standard, and after making a certain
decoupling approximation, we identify an embedded Markov renewal process, whose analysis yields a fixed point equation, from
whose solution the saturation throughput can be calculated. We validate our model against ns2 simulations (using an IEEE 802.15.4
module developed by Zheng [14]). We find that with the default back-off parameters the saturation throughput decreases sharply
with increasing number of nodes. We use our analytical model to study the problem and we propose alternative back-off parameters
that prevent the drop in throughput. We then show how the saturation analysis can be used to obtain an analytical model for
the finite arrival rate case. This finite load model captures very well the qualitative behavior of the system, and also provides
a good approximation to the packet discard probability, and the throughput. For the default parameters, the finite load throughput
is found to first increase and then decrease with increasing load. We find that for typical performance objectives (mean delay
and packet discard) the packet discard probability would constrain the system capacity. Finally, we show how to derive a node
lifetime analysis using various rates and probabilities obtained from our performance analysis model.
相似文献
P. M. AmeerEmail: |
69.
70.
JA Sikorski B Devadas ME Zupec SK Freeman DL Brown HF Lu S Nagarajan PP Mehta AC Wade NS Kishore ML Bryant DP Getman CA McWherter JI Gordon 《Canadian Metallurgical Quarterly》1997,43(1):43-71
MyristoylCoA: protein N-myristoyltransferase (NMT) catalyzes the cotranslational covalent attachment of a rare cellular fatty acid, myristate, to the N-terminal Gly residue of a variety of eukaryotic proteins. The myristoyl moiety is often essential for expression of the biological functions for these proteins. Attachment of C14:0 alone provides barely enough hydrophobicity to allow stable association with membranes. The partitioning of N-myrisotylproteins is therefore often modulated by "switches" that function through additional covalent or noncovalent modifications. Candida albicans, the principal cause of systemic fungal infection in immunocompromised humans, contains a single NMT gene that is essential for its viability. The functional properties of the acylCoA binding site of human and C. albicans NMT are very similar. However, there are distinct differences in their peptide binding sites. An ADP ribosylation factor (Arf) is included among the few cellular protein substrates of the fungal enzyme. Alanine scanning mutagenesis of an octapeptide derived from an N-terminal Arf sequence (GLYASKLS-NH2) disclosed that Gly1, Ser5, and Lys6 play predominant roles in binding. ALYASKLS-NH2 is an inhibitor competitive for peptide [Ki(app) = 15.3 +/- 6.4 microM] and noncompetitive for myristoylCoA. Remarkably, replacement of the N-terminal tetrapeptide with an 11-aminoundecanoyl group results in a competitive inhibitor (11-aminoundecanoyl-SKLS-NH2) that is approximately 40-fold more potent [Ki(app) = 0.40 +/- 0.03 microM] than the starting octapeptide. Removal of Leu-Ser from the C-terminus generates a competitive dipeptide inhibitor (11-aminoundecanoyl-SK-NH2) with a Ki(app) of 11.7 +/- 0.4 microM, equivalent to that of the starting octapeptide. A derivative dipeptide inhibitor containing a C-terminal N-cyclohexylethyl lysinamide moiety has the advantage of being more potent (IC50 = 0.11 +/- 0.03 microM) and resistant to digestion by cellular carboxypeptidases. Rigidifying the flexible aminoundecanoyl chain results in very potent general NMT inhibitors (IC50 = 40-50 nM). Substituting a 2-methylimidazole for the N-terminal amine and adding a benzylic alpha-methyl group with R stereochemistry to the rigidifying element produces even more potent inhibitors (IC50 = 20-50 nM) that are up to 500-fold selective for the fungal compared to human enzyme. A related less potent member of this series of compounds is fungistatic. Its growth inhibitory effects are associated with a reduction in cellular protein N-myristoylation, judged using cellular Arf as a reporter. These studies establish that NMT is a new antifungal target. 相似文献