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排序方式: 共有188条查询结果,搜索用时 14 毫秒
91.
Shmuel Burmil 《Landscape Research》2013,38(4):427-440
While natural processes, mainly wind and water erosion, define desert landscapes, human manipulation and use of water play important roles in defining the landscape within desert oases. The role of water in the oases of the Western Desert of Egypt is described, and it is considered how the scarcity of water affects its use. The challenge to the protection of these archetypal landscapes presented by new forms of development is identified. 相似文献
92.
It has often been claimed that SBSE uses so-called ‘embarrassingly parallel’ algorithms that will imbue SBSE applications with easy routes to dramatic performance improvements. However, despite recent advances in multicore computation, this claim remains largely theoretical; there are few reports of performance improvements using multicore SBSE. This paper shows how inexpensive General Purpose computing on Graphical Processing Units (GPGPU) can be used to massively parallelise suitably adapted SBSE algorithms, thereby making progress towards cheap, easy and useful SBSE parallelism. The paper presents results for three different algorithms: NSGA2, SPEA2, and the Two Archive Evolutionary Algorithm, all three of which are adapted for multi-objective regression test selection and minimization. The results show that all three algorithms achieved performance improvements up to 25 times, using widely available standard GPUs. We also found that the speed-up was observed to be statistically strongly correlated to the size of the problem instance; as the problem gets harder the performance improvements also get better. 相似文献
93.
94.
Eyal Baharad Jacob Goldberger Moshe Koppel Shmuel Nitzan 《Autonomous Agents and Multi-Agent Systems》2011,22(1):31-42
Given the judgments of multiple voters regarding some issue, it is generally assumed that the best way to arrive at some collective
judgment is by following the majority. We consider here the now common case in which each voter expresses some (binary) judgment
regarding each of a multiplicity of independent issues and assume that each voter has some fixed (unknown) probability of
making a correct judgment for any given issue. We leverage the fact that multiple votes by each voter are known in order to
demonstrate, both analytically and empirically, that a method based on maximum likelihood estimation is superior to the simple
majority rule for arriving at true collective judgments. 相似文献
95.
The response of incompressible fiber composites to moderate levels of out-of-plane shear and tension along the fibers is examined.
It is assumed that the phases’ constitutive behaviors depend on the first invariant of the right Cauchy–Green deformation
tensor, and in the vicinity of the reference configuration can be approximated by a two-terms Taylor series in this invariant.
A deformation field satisfying an appropriate boundary conditions on a representative cylindrical composite element is proposed,
and the resulting equilibrium equations are expanded in terms of a series. A solution, which is exact to second order in the
deformation, is determined. This solution provides accurate estimates for the local fields developing in a cylindrical composite
with Gent phases up to one third of the locking stretch ratio. The overall response predicted by this approximated quadratic
solution is found to be in agreement with corresponding results for fiber composites with Gent phases that were determined
by application of a new variational procedure and by finite-element simulation of a periodic composite. 相似文献
96.
Shmuel Hayun Amir Weizmann Moshe P. Dariel Nahum Frage 《Journal of the European Ceramic Society》2010,30(4):1007-1014
The previously reported model that accounts for the formation of the core-rim structure in reaction-bonded boron carbide composites (RBBC) is expanded and validated by additional experimental observations and by a thermodynamic analysis of the ternary B–C–Si system. The microstructure of the RBBC composites consists of boron carbide particles with a core-rim structure, β-SiC and some residual silicon. The SiC carbide particles have a polygonal shape in composites fabricated in the presence of free carbon, in contrast to the plate-like morphology when the initial boron carbide is the sole source of carbon. In the course of the infiltration process, the original B4C particles dissolve partly or fully in molten silicon, and a local equilibrium is established between boron carbide, molten silicon and SiC. Overall equilibrium in the system is achieved as a result of the precipitation of the ternary boron carbide phase B12(B,C,Si)3 at the surface of the original boron carbide particles and leads to the formation of the rim regions. This feature is well accounted for by the “stoichiometric saturation” approach, which takes into account the congruent dissolution of B4C particles. The SiC phase, which precipitates form the silicon melt adopts the β-allotropic structure and grows preferably as single plate-like particles with an {1 1 1}β habit plane. The morphology of the SiC particles is determined by the amount of carbon available for their formation. 相似文献
97.
Shai Salhov Michael Aizenshtein Natalie Froumin Shmuel Barzilai Nahum Frage 《Journal of Materials Science》2013,48(8):3173-3176
The interaction between NaCl–KCl salt of an equimolar composition and CaF2 was investigated in the 1023–1123 K temperature range. The solubility limit was determined as 2.1, 2.5, and 3.4 mol.% for 1023, 1073, and 1123 K, respectively. The linear dependence of the specific weight loss with time and the activation energy of the dissolution (124.6 ± 8.7 kJ/mol) indicate that CaF2 dissociation of the ions is the limiting stage of the process. Thermodynamic properties (partial enthalpy and entropy) of CaF2 in a dilute ternary –NaCl–KCl–CaF2 liquid solution were estimated using the values of the solubility limit and by applying a regular solution approach. 相似文献
98.
von Schneidemesser E Zhou I Stone EA Schauer JI Shpund J Brenner S Qasrawi R Abdeen Z Sarnat JA 《Environmental science & technology》2010,44(6):1911-1917
Carbonaceous aerosol concentrations and sources were compared during a year long study at two sites in East and West Jerusalem that were separated by a distance of approximately 4 km. One in six day 24-h PM(2.5) elemental and organic carbon concentrations were measured, along with monthly average concentrations of particle-phase organic compound tracers for primary and secondary organic aerosol sources.Tracer compounds were used in a chemical mass balance ICMB) model to determine primary and secondary source contributions to organic carbon. The East Jerusalem sampling site at Al Quds University experienced higher concentrations of organic carbon (OC) and elemental carbon (EC) compared to the West Jerusalem site at Hebrew University. The annual average concentrations of OC and EC at the East Jerusalem site were 5.20 and 2.19 μg m(-3), respectively, and at the West Jerusalem site were 4.03 and 1.14 μg m(-3), respectively. Concentrations and trends of secondary organic aerosol and vegetative detritus were similar at both sites, but large differences were observed in the concentrations of organic aerosol from fossil fuel combustion and biomass burning, which was the cause of the large differences in OC and EC concentrations observed at the two sites. 相似文献
99.
Some electric power markets allow bidders to specify constraints on ramp rates for increasing or decreasing power production. We show in a small example that a bidder could use an overly restrictive constraint to increase profits, and explore the cause by visualizing the feasible region from the linear program corresponding to the power auction. We propose three penalty approaches to discourage bidders from such a tactic: two based on the duality theory of linear programming (LP) and the other based on social cost differences caused by ramp constraints. We evaluate the approaches using a simplified scaled model of the California power system, with actual 2001 California demand data. 相似文献
100.
Superhydrophobic surfaces can be obtained by tailoring both the chemistry and roughness topography, mimicking the Lotus leaf characteristics. Most of the synthetic superhydrophobic surfaces reported have been composed of micro and nanoparticles (NPs) embedded in polymer‐based coatings. The particles which tailor the topography are bonded to the base polymers by weak secondary forces. Consequently, the topography integrity is highly affected by handling and surface drag making them unsuitable for long term applications. This work is focused on promoting covalent bonding between the NPs and the base polymer to obtain durable superhydrophobic surfaces. The rough topography was achieved by ultraviolet (UV) curing of SiO2 NPs containing a photoreactive benzophenone moiety in addition to methylated fumed silica NPs which can bind covalently to the polymer base coating, on UV radiation. The hydrophobic chemistry was obtained by fluoroalkylsilane top coating. Coating durability was evaluated using surface air drag and accelerated weathering conditions (UV radiation, humidity and temperature). Results indicated that the proposed approach resulted in superhydrophobic surfaces having high contact angle (>150°) and low sliding angle (<10°) with improved long term durability. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41122. 相似文献