Cellular network configuration with co-channel and adjacent-channel interference constraints

Design of cellular networks has drawn much recent interest from the OR scientific community. A challenging issue is the handling of channel interference constraints. Co-channel interference occurs when the same channel is reused within a threshold distance. Adjacent-channel interference occurs when two channels with adjacent or nearby frequencies are used in the same cell tower. We present a mathematical programming formulation for this channel allocation problem with both types of interference constraints—it also includes decisions on location of cell towers. Our focus is on the special case where a cell tower and/or channel can interfere with at most two other towers/channels. By establishing theoretical properties for channel allocation amongst towers under this circumstance, we develop an efficient solution procedure. An iteration of the procedure uses a heuristic to locate the cell towers, then allocates the channels to the towers using a polynomial-time algorithm, and finally improves this allocation using a simulated annealing procedure. The iterative steps are embedded within an external simulated annealing method. This nested simulated annealing procedure provides encouraging computational results compared to a standard commercial solver like ILOG CPLEX 8.1. The major contribution of the work is the simultaneous consideration of co-channel and adjacent-channel interference constraints.     

Mesostructured mixed Mo–V–Nb oxides for propane ammoxidation

Mesostructured Mo–V–Nb mixed oxide phases were prepared by reacting inorganic precursors in the presence of cationic, anionic and alkylamine surfactants. The occurrence of these mesostructured phases was explained in part by charge-matching considerations at the inorganic–organic interface. Other interactions, such as covalent bonding between the surfactant headgroup and metal atoms, could direct the self-assembly process. Despite of the limited thermal stability of the mesophases, the air-calcined phases were catalytically active and selective for propane ammoxidation to acrylonitrile and acetonitrile. The selectivities to acrylonitrile and acetonitrile were as high as 26 and 49 mol%, respectively, at 66% propane conversion.     

Knudsen diffusion through ZIF-8 membranes synthesized by secondary seeded growth

Herein we demonstrate the synthesis of ZIF-8 membranes via secondary seeded growth on tubular stainless steel porous supports. The membranes were characterized and evaluated for the separation of CO₂/N₂ and N₂/CH₄ gas mixtures. The adsorbate polarizability correlated with the adsorption capacity on ZIF-8, and the amounts of gases adsorbed were in the order: CO₂ > CH₄ > N₂. The CO₂/N₂ separation selectivity’s for the ZIF-8 membranes were close to the Knudsen selectivity, suggesting that Knudsen diffusion through non-ZIF pores dominated the separation. On the other hand, the separation selectivity’s for N₂/CH₄ were slightly higher than the Knudsen selectivity, indicating that the flow contribution from the ZIF pores favored the transport of N₂ over CH₄.     

Adsorption Microcalorimeter and its Software: Design for the Establishment of Parameters Corresponding to Different Models of Adsorption Isotherms

Abstract

This work describes an adsorption microcalorimeter design for the characterization of porous solids and some of the results obtained with this equipment with activated carbons. Software was developed in order to calculate the corresponding parameters of gas and vapour adsorption in this type of solid, as described by different adsorption models. The results obtained with the software were compared to those previously reported in the quoted bibliography.     

Structure-function validation of high lysine analogs of {alpha}-hordothionin designed by protein modeling

Cereal grains and legume seeds, which are key protien sourcesfor the vegetarian diet, are generally deficient in essentialamino acids. Maize, in particular, is deficient in lysine. Theinherent lack of lysine-rich protiens in maize has necessitatedthe search for heterologous protiens enriched in this aminoacid, the isolation of the corresponding gene and its ultimateintroduction into maize through plant transformation techniques.However, a rate-limiting step to this strategy has been theavailability of plant-derived lysine-rich protiens. An appealingsolution to the problem is to artificially increase the lysinecontent of a given protein by mutating appropriate residuesto lysine. Here, we expound this strategy, starting with theprotein hordothionin that is derived from barley seeds andconsists of five lysine residues in a total of 45 amino acids(11 % lysine). To facilitate rational substitutions, the 3-Dstructure of the protein has been determined by homology modelingwith crambin. based on this model, we have identified surfaceresidues amenable to substitution with lysine. Furthermore,the acceptability of the mutations has been validated throughthe syntheses and characterization of the derivatives. To thisend, our approach has permitted the creation of a modified -hordothionin protein that has a lysine content of 27 % andretains the antifungal activity of the wild-type protein.     

BCS temperature-dependent superconducting energy gap in domain boundaries of melt-textured YBa2Cu3O7

Attenuation and velocity measurements in low magnetic fields in the superconducting state of a melt-textured sample of YBa₂Cu₃O₇ are reported. Changes in both attenuation and relative velocitydv/v are observed at the penetration fieldH _c1 of its domain boundaries. The change indv/v atH _c1 appears to be proportional to the repulsive force between vortices. The change in atH _c1 may be produced by a relaxation process involving superconducting quasiparticles in the vicinity of the normal core of the vortices. Analysis of the relaxation time associated with this process yields a temperature-dependent energy gap which follows the BCS dependence. The relaxation time associated with the process is about 10^–11 sec.     

Priority-based assignment and routing of a fleet of unmanned combat aerial vehicles

This paper considers the strategic routing of a fleet of unmanned combat aerial vehicles (UCAVs) to service a set of predetermined targets from a prior surveillance mission. Targets are characterized by their priority or importance level, and minimum and maximum service levels that, respectively, represent the lower bound of munitions for destruction and upper bound of munitions to limit collateral damage. Additional constraints to be respected are the payload capacities of the (possibly heterogeneous) UCAV fleet and the range based on fuel capacity and payload transported. The vital aspect of this paper is the integrated optimal utilization of available resources—weaponry and flight time—while allocating targets to UCAVs and sequencing them to maximize service to targets based on their criticality.