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排序方式: 共有120条查询结果,搜索用时 15 毫秒
1.
Alexander Katsman Shalom Cohen Menachem Bamberger 《Journal of Materials Science》2007,42(16):6996-7003
This work deals with the development of Mg-based alloys with enhanced properties at elevated temperatures. This is achieved
by precipitation of binary phases such as MgZn2 and Mg2Sn during the aging of these alloys. The aim of the present work is to develop and calibrate a model for precipitation hardening
in Mg-based alloys, as different types of precipitates form simultaneously. The modified Langer-Schwartz approach, while taking
into account nucleation, growth and coarsening of the new phase precipitations, was used for the analysis of precipitates’
evolution and precipitation hardening during aging of Mg-based alloys. Two strengthening mechanisms associated with particle-dislocation
interaction (shearing and bypassing) were considered to be operating simultaneously due to particle size-distribution. Parameters
of the model, R
N
i and k
σ i
, were found by fitting of calculated densities and average sizes of precipitates with ones estimated from experiments. The
effective diffusion coefficients of phase formation processes, which determine the strengthening kinetics, were estimated
from the hardness maximum positions on the aging curves. 相似文献
2.
Partially oriented polyesters yarns (POY) were strained at different strain rates (0.03–12.00 min?1) and temperatures above and below Tg (3–92°C). Thermal retraction, density, DSC, and WAXS techniques show that strain-induced crystallization takes place by straining at temperatures above as well as below Tg. Above Tg, depending upon the strain rate, two regimes are observed: Below the strain rate of 1.5 min?1, the flow regime; the degree of crystallinity is reduced as the strain rate increases. Above the strain rate of 1.5 min?1, the strain-induced crystallization regime; the degree of crystallinity increases as the strain rate increases. Thermal retraction, stress–relaxation, and sonic modulus techniques indicate that, upon cold straining, instead of the original Tg at 65–69°C, two glass transitions occur: an upper Tg (u) and a lower Tg (l). For POY strained at 3°C and at a strain rate of 10 min?1, the values are 78°C and 37°C, respectively. The higher the strain rate and the lower the straining temperature, the large the difference between Tg (u) and Tg (l). 相似文献
3.
4.
The CALPHAD method can be applied as a tool for both alloy development and process guideline determination. In this study, two Mg alloys were designed, their process parameters derived and, using the CALPHAD method, the final results simulated. These results were later confirmed using tangible experimental methods. It was found that γ- Mg17Al12 precipitates along the grain boundaries (GB), Mg2Sn forms both along the GB and as fine precipitates in the α-Mg matrix and the addition of Ce mishmetal (MM) leads to the formation of elongated Al- rare earth (RE) precipitates along the GB. The microstructural stability at 200 °C is high, showing no decrease in microhardness for 32 days. It is shown that the CALPHAD method considerably reduces the effort of alloy design and that the reliability of the results is high. 相似文献
5.
Rachel Mika Dorin William A. Phillip Hiroaki Sai Jörg Werner Menachem Elimelech Ulrich Wiesner 《Polymer》2014
Using a combination of block copolymer self-assembly and non-solvent induced phase separation, isoporous ultrafiltration membranes were fabricated from four poly(isoprene-b-styrene-b-4-vinylpyridine) triblock terpolymers with similar block volume fractions but varying in total molar mass from 43 kg/mol to 115 kg/mol to systematically study the effect of polymer size on membrane structure. Small-angle X-ray scattering was used to probe terpolymer solution structure in the dope. All four triblocks displayed solution scattering patterns consistent with a body-centered cubic morphology. After membrane formation, structures were characterized using a combination of scanning electron microscopy and filtration performance tests. Membrane pore densities that ranged from 4.53 × 1014 to 1.48 × 1015 pores/m2 were observed, which are the highest pore densities yet reported for membranes using self-assembly and non-solvent induced phase separation. Hydraulic permeabilities ranging from 24 to 850 L m−2 h−1 bar−1 and pore diameters ranging from 7 to 36 nm were determined from permeation and rejection experiments. Both the hydraulic permeability and pore size increased with increasing molar mass of the parent terpolymer. The combination of polymer characterization and membrane transport tests described here demonstrates the ability to rationally design macromolecular structures to target specific performance characteristics in block copolymer derived ultrafiltration membranes. 相似文献
6.
Erez Weinroth Menachem Luria Avia Ben-Nun Jay Kaplan Mordechai Peleg Issac Mahrer 《Israel journal of chemistry》2006,46(1):59-68
High ozone levels are regularly measured during summer months over the inland and mountainous regions of Israel. Studies analyzing the back trajectories of air masses responsible for the high ozone levels showed that the precursors originated from the densely populated Israeli coastline. In order to better understand the contribution of those emission sources to ozone production, it is essential to have an accurate emission inventory that can be inputted into a photochemical model. The present paper describes the methods used in preparing an emission inventory for Israel based on information available and published until 1998. The source and accuracy of the data available are described. The calculations performed and the assumptions taken in order to obtain data not directly available are clarified. The sources reported in the inventory were the major polluters (power plants, oil refineries, and cement industries); industry; transportation; and biogenic sources. The pollutants studied were SO2, NOx, CO, saturated and unsaturated hydrocarbons, ethylene, isoprene, toluene, xylene, formaldehyde, and aldehydes. The inventory showed that transportation is responsible for almost the entire CO and 30% of the volatile organic compounds emitted, although transportation itself accounts for only a fifth of total fuel consumption. About 75% of the NOx emitted can be attributed to industrial sources and the remaining 25% to transportation. Model simulations using the emission inventory were performed and compared to data available from a monitoring station situated 30 km east of Tel Aviv. The results showed good agreement, validating the accuracy of the emission inventory. The present emission inventory provides an important database as input to photochemical models used in forecasting ozone levels over Israel. 相似文献
7.
8.
Itzhaq Azoulay Nataly Kucherenko Esther Nachliel Menachem Gutman Abdussalam Azem Yossi Tsfadia 《International journal of molecular sciences》2013,14(6):12675-12695
Hsp70 chaperones consist of two functional domains: the 44 kDa Nucleotide Binding Domain (NBD), that binds and hydrolyses ATP, and the 26 kDa Substrate Binding Domain (SBD), which binds unfolded proteins and reactivates them, utilizing energy obtained from nucleotide hydrolysis. The structure of the SBD of the bacterial Hsp70, DnaK, consists of two sub-domains: A β-sandwich part containing the hydrophobic cavity to which the hepta-peptide NRLLLTG (NR) is bound, and a segment made of 5 α-helices, called the “lid” that caps the top of the β-sandwich domain. In the present study we used the Escherichia coli Hsp70, DnaK, as a model for Hsp70 proteins, focusing on its SBD domain, examining the changes in the lid conformation. We deliberately decoupled the NBD from the SBD, limiting the study to the structure of the SBD section, with an emphasis on the interaction between the charges of the peptide with the residues located in the lid. Molecular dynamics simulations of the complex revealed significant mobility within the lid structure; as the structure was released from the forces operating during the crystallization process, the two terminal helices established a contact with the positive charge at the tip of the peptide. This contact is manifested only in the presence of electrostatic attraction. The observed internal motions within the lid provide a molecular role for the function of this sub-domain during the reaction cycle of Hsp 70 chaperones. 相似文献
9.
Menachem Dishon John T. Bendler George H. Weiss 《Journal of research of the National Institute of Standards and Technology》1990,95(4):433-467
The inverse transform,
g(t) = ??1(e?sβ), 0 < β < 1, is a stable law that arises in a number of different applications in chemical physics, polymer physics, solid-state physics, and applied mathematics. Because of its important applications, a number of investigators have suggested approximations to g(t). However, there have so far been no accurately calculated values available for checking or other purposes. We present here tables, accurate to six figures, of g(t) for a number of values of β between 0.25 and 0.999. In addition, since g(t), regarded as a function of β, is uni-modal with a peak occurring at t = tmax we both tabulate and graph tmax and 1/g(tmax) as a function of β, as well as giving polynomial approximations to 1/g(tmax). 相似文献
10.
The transport and deposition (adhesion) kinetics of viable Cryptosporidium parvum oocysts onto ultrapure quartz surfaces in a radial stagnation point flow system were investigated. Utilizing an optical microscope and an image-capturing device enabled real time observation of oocyst deposition behavior onto the quartz surface in solutions containing either monovalent (KCl) or divalent (CaCl2) salts. Results showed a significantly lower oocyst deposition rate in the presence of a monovalent salt compared to a divalent salt. With a monovalent salt, oocyst deposition rates and corresponding attachment efficiencies were relatively low, even at high KCl concentrations where Derjaguin-Landau-Verwey-Overbeek (DLVO) theory predicts the absence of an electrostatic energy barrier. On the other hand, in the presence of a divalent salt, oocyst deposition rates increased continuously as the salt concentration was increased over the entire range of ionic strengths investigated. The unusually low deposition rate in a monovalent salt solution is attributed to "electrosteric" repulsion between the Cryptosporidium oocyst and the quartz surface, most likely due to proteins on the oocyst surface that extend into the solution. It is further proposed that specific binding of calcium ions to the oocyst surface functional groups results in charge neutralization and conformational changes of surface proteins that significantly reduce electrosteric repulsion. 相似文献