Landscape and water in the oases of Egypt's western desert

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.     

GPGPU test suite minimisation: search based software engineering performance improvement using graphics cards

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.     

Distilling the wisdom of crowds: weighted aggregation of decisions on multiple issues

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.     

Out-of-plane shear of fiber composites at moderate stretch levels

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.     

Microstructural evolution during the infiltration of boron carbide with molten silicon

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.     

Dissolution kinetics and solubility limit of CaF2 in molten KCl–NaCl salt

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.     

Spatial variability of carbonaceous aerosol concentrations in East and West Jerusalem

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.     

Can we prevent the gaming of ramp constraints?

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.