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排序方式: 共有2322条查询结果,搜索用时 15 毫秒
61.
Mora-Gutierrez A Farrell HM Attaie R McWhinney VJ Wang C 《The Journal of dairy research》2007,74(3):356-366
Bovine and caprine milks have a similar overall gross composition, but vary considerably in the ratios of their casein components. These differences cause significant changes in the ability of caseins to bind and stabilize calcium (Ca). It might be expected that these in vitro variations, which are thought to be due to differences in casein phosphopeptides (CPP) content, could lead to in vivo differences in the digestion and absorption of Ca. To test this hypothesis three milks with different casein ratios [bovine (B), caprine high in alphas1-casein (CH) and caprine low in alphas1-casein (CL)] were compared with regard to Ca absorption and deposition in growing male rats. For comparison, each milk was Ca-fortified (BCa-milk, CHCa-milk, and CLCa-milk) and CPP, prepared by enzymatic hydrolysis from the respective caseins (extrinsic CPP), were added to both native and Ca-milks. The effects of added CPP (extrinsic) could then be compared with intrinsic CPP released from the gastrointestinal digestion of caseins. Total gastric Ca was sampled at 15, 30 and 60 min after ingestion. No differences were found among the native milks with or without CPP, but the Ca from all Ca-milks (regardless of casein type) appeared to clear the stomach more rapidly and this was enhanced by the extrinsic CPP. The total intestinal Ca was not different among the native milks+/-CPP, however, it rose more rapidly with Ca fortification, and was higher at 30 min for all CPP-Ca-milks. At 60 min the total intestinal Ca level fell for the CPP-Ca-milks while all others continued to rise. These observations suggest that the CPP in Ca-milks enhance gastric clearance and uptake from the intestine. Ca availability from BCa-milk, CHCa-milk, and CLCa-milk with and without CPP was estimated by both plasma and femur uptake of 45Ca. Ca availability was enhanced at 5 h in the plasma in each case by added CPP. In all cases CPP stimulated Ca availability in the femur, but the CL-CPP was higher (P<0.05) than that of either CH-CPP or B-CPP (extrinsic CPP). Based on the results of this study we can conclude that the addition of CPP will have beneficial effect on the absorption of Ca in growing rats from CaCO3 added to bovine and caprine milks. 相似文献
62.
Harold N. Evin Gary Jacobs Javier Ruiz-Martinez Uschi M. Graham Alan Dozier Gerald Thomas Burtron H. Davis 《Catalysis Letters》2008,122(1-2):9-19
Doping Pt/ceria catalysts with the Group 1 alkali metals was found to lead to an important weakening of the C–H bond of formate
and methoxy species. This was demonstrated by a shift to lower wavenumbers of the formate and methoxy ν(CH) vibrational modes
by DRIFTS spectroscopy. Li and Na-doped Pt/ceria catalysts were tested relative to the undoped catalyst for low temperature
water–gas shift and methanol steam reforming using a fixed bed reactor and exhibited higher catalytic activity. Steaming of
formate and methoxy species pre-adsorbed on the catalyst surface during in-situ DRIFTS spectroscopy suggested that the species
were more reactive for dehydrogenation steps in the catalytic cycle for the Li and Na-doped catalysts relative to undoped
Pt/ceria. However, with increasing atomic number over the series of alkali-doped catalysts, the stability of a fraction of
the carbonate species was found to increase. This was observed during TPD-MS measurements of the adsorbed CO2 probe molecule by a systematic increase of a high temperature peak for a fraction of the CO2 desorbed. This result indicates that alkali-doping is an optimization problem—that is, while improving the dehydrogenation
rates of methoxy and formate species, the carbonate intermediate stability increases, making it difficult to liberate the
CO2. Infrared spectroscopy results of CO adsorbed on Pt and ceria suggest that the alkali dopant is located on, and electronically
modifies, both the Pt and ceria components. The results not only lend further support to the role that methoxy and formate
species play as intermediates in the catalytic mechanisms, but also provide a path forward for improving rates by means other
than resorting to higher noble metal loadings. 相似文献
63.
New catalytic materials were prepared by depositing nanoparticles of 35 different metals as well as their select binary combinations on Al2O3, CeO2, SiO2, TiO2, and ZrO2 supports. Nanoparticles were synthesized by high-throughput pulsed laser ablation (PLA). Catalytic materials were then screened for their selectivities towards the synthesis propylene oxide (PO) from propylene and oxygen using array channel microreactors at 1 atm and 300, 333, and 367 °C. A gas hourly space velocity (GHSV) of 20,000 h?1 was used at the feed gas composition of 20% O2, 20% C3H6 and the balance He. Initial screening experiments resulted in the discovery of SiO2 supported Cr, Mn, Cu, Ru, Pd, Ag, Sn, and Ir as the most promising leads for PO synthesis. Subsequent experiments pointed to bimetallic Cu-on-Mn/SiO2, for which the PO yields increased several fold over single metal catalysts. For multimetallic materials, the sequence of deposition of the active metals was shown to have a significant effect on the resulting catalytic activity and selectivity. 相似文献
64.
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66.
Hester Reid K.; Delaney Harold D.; Campbell William 《Canadian Metallurgical Quarterly》2011,79(2):215
Objective: To evaluate the effectiveness of a web-based protocol, ModerateDrinking.com (MD; www.moderatedrinking.com) combined with use of the online resources of Moderation Management (MM; www.moderation.org) as opposed to the use of the online resources of MM alone. Method: We randomly assigned 80 problem drinkers to either the experimental or control group with follow-ups at 3, 6, and 12 months. Results: Seventy-five participants (94%) had outcome data at 1 or more follow-up points, and 59 participants (73%) were assessed at all 3 follow-ups. Comparing baseline measures to the average outcomes at follow-ups indicated a significant overall reduction in both groups in alcohol-related problems and consumption variables. Compared with the control group, the experimental group had better outcomes on percent days abstinent. There was an interaction between intensity of drinking at baseline and treatment in determining outcomes assessing drinking. Less heavy drinkers in the experimental group had better outcomes on log mean blood alcohol content (BAC) per drinking day compared with the control group. Heavier drinkers did not differentially benefit from the MD program on this measure. Mixed model analyses in general corroborated these outcomes. Conclusion: The outcome data provide partial evidence for the effectiveness of the MD web application combined with MM, compared with the effectiveness of the resources available online at MM by themselves. (PsycINFO Database Record (c) 2011 APA, all rights reserved) 相似文献
67.
68.
Harold Weiss 《EDPACS》2013,47(11):1-9
Abstract In spite of an ambiguous standard with regard to definition, spyware is one of the most challenging problems confronting the information technology (IT) community in terms of privacy violations. This problem is magnified in the business arena. Despite the increasing technical endeavors made toward spyware mitigation, no panacea exists for spyware control and management, which is now becoming a serious business strategic issue. This article focuses on the vicious side of spyware. A framework is proposed to identify five involved parties for spyware management and control along with respective recommendations to cope with spyware pervasion. 相似文献
69.
Because of the relative ease to modify, functionalize, and synthesize polysiloxanes, these compounds offer interesting possibilities to greatly influence the properties of a catalytic system. These potentials are illustrated with three catalytic systems. In the first system, siloxane nanocages are shown to exhibit confinement effects by strongly modifying the protonation affinity of internal amine groups and by changing the activity and product selectivity in a reaction catalyzed by these groups. In the second example, the length of the siloxane backbone of a bis(pyridyl)siloxane ligand is shown to be critical both in stabilizing a Pd acetate complex catalyst in selective oxidation of benzyl alcohol, and in determining the dependence of the reaction rate on the pyridyl concentration in the reaction mixture. In the third example, polysiloxanes are shown to be useful in the preparation of a supported Pd catalyst in which the metal loading and particle size can be independently controlled. 相似文献
70.
The Stirling space power machine incorporates a linear alternator to generate electrical power. The alternator is a reciprocating device that is driven by a solar or nuclear-powered Stirling engine. The power piston and cylinder are made of titanium 6A1–4V (Ti6–4) alloy, and are designed to be lubricated by a hydrodynamically-generated gas film. Rubbing occurs during starts and stops and there is the possibility of an occasional high speed rub. Since titanium is known to have a severe galling tendency in sliding contacts, a “backup,” self-lubricating coating on the cylinder and/or the piston is needed. This report describes the results of a research program to study the lubrication of Ti6–4 with the following chromium carbide based materials: plasma-sprayed PS212 coatings and sintered PM212 counterfaces. Program objectives are to achieve adherent coatings on Ti6–4 and to measure the friction and wear characteristics of the following sliding combinations under conditions simulative of the Stirling-driven space power linear alternator: Ti6–4/Ti6–4 baseline, Ti6–4/PS212-coated Ti6–4, and PS212-coated Ti6–4/PM212. 相似文献