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71.
Zircaloy-4 is susceptible to stress corrosion cracking (SCC) in solutions of iodine dissolved in different alcohols (methanol, ethanol, 1-propanol, 1-butanol, 1-pentanol and 1-octanol). The crack propagation rate is known to decrease as the solvent molecular weight increases, as a consequence of steric hindrance. However, the mechanism that operates during SCC is still unknown. In the present work the effect of temperature on SCC susceptibility was evaluated in 1-butanol and 1-pentanol iodine containing solutions. The dependence of the crack growth rate with temperature follows an Arrhenius law, and the activation energy obtained from experimental data is consistent with a process controlled by volume diffusion of the active species (the iodine-alcohol complex) to the crack tip. 相似文献
72.
The phase diagram of polytetrafluoroethylene is enlarged by differential scanning calorimetry to include the concentration of hexafluoropropylene comonomer units. The two transitions near 292 and 303 K in the homopolymer move to lower temperatures and apparently become one at small concentrations. Analysis of the data yields 295 K for the temperature and 13.2 J/g for the heat of transition of an infinitely large homopolymer crystal. The heat of transition associated with the formation of a crystal defect is 0.021 eV. The qualitative features of the transition can be accounted for by a mean-field model which involves two order parameters corresponding to planar units and helix reversals. This model yields two transitions which move closer together and to lower temperatures with increasing comonomer concentration. Decreasing lamella thickness will have a qualitatively similar effect. 相似文献
73.
We develop the theory for chromatographic separation of isomers such as polycyclic aromatic hydrocarbons, polychlorinated biphenyls, dioxins, steroids, and carotenoids based on shape-selective mechanisms for either exclusion or adsorption. Block-like solute transport and retention on oriented stationary phases are modeled by a dispersed-flow chromatographic equation combined with simultaneous exclusion partitioning and shaped-based adsorption. Molecules to be separated are considered distributed continuously with respect to the shape and sorption parameters. The population balance equations of distribution kinetics provide the governing differential equations that are solved for the temporal moments of the concentration in a chromatographic column. By including dispersive mass transport effects, the model allows estimation of peak variance and HETP and is thus an improvement over theories that focus solely on retention time. The model predictions are compared with experimental data from the literature for gas chromatography. 相似文献
74.
M. T. Garcia J. Sanchez Leal I. Ribosa 《Journal of the American Oil Chemists' Society》1992,69(1):20-24
The influence of various experimental parameters on the flux of sodium dodecyl sulfate (SDS) through a collagen membrane has
been studied. The variables evaluated were donor concentration, time, temperature, pH and ionic strength. Data on the influence
of both surfactant concentration and time on surfactant diffusion through the collagen film allow one to postulate a diffusion
process mainly of the monomeric type. This diffusion mechanism based on surfactant monomers has been corroborated by studying
the effect of ionic strength. Thisin vitro technique could be a useful tool to predict the effect of diverse experimental parameters on the percutaneous absorption
of surfactants. 相似文献
75.
Benjamin D. Deacon A. Cecil Wamble 《Journal of the American Oil Chemists' Society》1954,31(7):284-287
Conclusions A procedure for the analysis of cottonseed and its products for Vitamin E has been developed and improved. The present procedure
generally gives good checks on duplicate analyses.
The Vitamin E content of whole cottonseed is somewhat more a function of variety than of locality. The 1952 crop of cottonseed
contained more Vitamin E than the 1951 crop. The two crops averaged 84 g. per ton and 68.5 g. per ton, respectively.
Most recent results show that there is no loss of Vitamin E in the storage of cottonseed or during the processing of the seed
for its oil and other products.
The hexane-soluble portion of a methanol extract of rolled or cooked cottonseed meats contains Vitamin E in concentrations
that have exceeded the values reported for wheat germ oil, the present commercial source.
A sample of commercial solvent extracted cottonseed meal was found to contain considerably less Vitamin E than hydraulic-
or screw-pressed meals.
The Vitamin E research described in this writing was conducted as a cooperative project of the Texas Engineering Experiment
Station and the Cotton Research Committee of Texas. 相似文献
76.
Richard Kotek Dong‐Wook Jung Joon Ho Kim Brent Smith Patricia Guzman Benjamin Schmidt 《应用聚合物科学杂志》2004,92(3):1724-1730
The surface alkaline hydrolysis of fibers made from poly(trimethylene terephthalate) (PTT) was studied after extruding the polymer at high spinning speeds from 2000 to 6000 m/min and heat setting in the range of temperatures from 100 to 180°C. Fiber weight loss increased with an increasing heat‐setting temperature but it was also dependent on the spinning speed. Some of the partially hydrolyzed fibers had a well‐developed, hydrophilic surface, and pore size in the range of 0.69 to 1.20 μm. The optimum reaction and morphological conditions for increasing porosity in PTT fibers depends on spinning speed and heat‐setting temperature. A temperature of 180°C is the upper limit for heat‐setting PTT filaments but seems to be the most effective for making porous fibers. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1724–1730, 2004 相似文献
77.
Tristan Allard Benjamin Nguyen Philippe Pucheral 《Distributed and Parallel Databases》2014,32(2):191-244
The goal of Privacy-Preserving Data Publishing (PPDP) is to generate a sanitized (i.e. harmless) view of sensitive personal data (e.g. a health survey), to be released to some agencies or simply the public. However, traditional PPDP practices all make the assumption that the process is run on a trusted central server. In this article, we argue that the trust assumption on the central server is far too strong. We propose Met ??P, a generic fully distributed protocol, to execute various forms of PPDP algorithms on an asymmetric architecture composed of low power secure devices and a powerful but untrusted infrastructure. We show that this protocol is both correct and secure against honest-but-curious or malicious adversaries. Finally, we provide an experimental validation showing that this protocol can support PPDP processes scaling up to nation-wide surveys. 相似文献
78.
A unique blowing-assisted electro-spinning process has been demonstrated recently to fabricate hyaluronic acid (HA) nanofibers. In this article, effects of various experimental parameters, such as air-blowing rate, HA concentration, feeding rate of HA solution, applied electric field, and type of collector on the performance of blowing-assisted electro-spinning of HA solution were investigated. With the assistance of air-blowing, the solution-feeding rate could be increased to 40 μl/min/spinneret and the applied electric field could be decreased to 2.5 kV/cm. The optimum conditions for consistent fabrication of HA (with a molecular weight of ∼3.5 million) nanofibers involved the use of an air-blowing rate of around 70 ft3/h and a concentration range between 2.5 and 2.7% (w/v) in aqueous solution. Two benign methods to fabricate water-resistant HA nanofibrous membranes without the use of reactive chemical agents were demonstrated: (a) the exposure of HA membranes in hydrochloric acid (HCl) vapor, followed by a freezing treatment at −20 °C for 20-40 days; and (b) the immersion of HA membranes in an acidic mixture of ethanol/HCl/H2O at 4 °C for 1-2 days. Although both methods could produce hydrophilic, substantially water-resistant HA nanofibrous membranes (the treated membranes could keep their shape intact in neutral water at 25 °C for about 1 week), the immersion method (6) was shown to be more versatile and effective. IR spectroscopy was used to investigate this ‘cross-linking’ mechanism in the solid HA membrane. Viscosity studies of acidic HA solutions under varying freezing conditions were also carried out. It was found that when the freezing time exceeded 8 h, the HA solution became gel-like and exhibited a large increase in the hydrogen-bond concentration. Thus, the resistance to water solubility could be due to the high density of hydrogen bonds in the solid HA membranes that were treated by the ‘freezing’ approach. 相似文献
79.
Abstract. We study an iterative filtering method to estimate frequencies of random Gaussian sinusoids in white noise. The method uses higher order crossings and takes advantage of a fixed point to guide the use of bandpass filtering in an attempt effectively to increase the signal-to-noise ratio. At each iteration the expected zero-crossing rate is estimated from independent time series. Convergence occurs with any prespecified probability less than one. 相似文献
80.
Warren A. Thomas Michael W. Kopp J. M. Sanchez 《Journal of the American Ceramic Society》1993,76(9):2175-2179
The unusual stress–strain hysteresis loop shape exhibited by ceramic-matrix composites under cyclic loading has previously been explained as a result of either strain rate dependence of the frictional shear stress or crack closure. This investigation has determined that the response is due to neither mechanism. Instead, it is proposed that a variation of interfacial shear strength occurs during each cycle. A static coefficient of friction dominates immediately after loading or unloading. A much lower dynamic coefficient of friction operates once fiber sliding begins. This dynamic coefficient appears to be very dependent on surface roughness. 相似文献