A Finite Horizon Production Model with Variable Production Rates and Constant Demand Rate

In this paper we present a finite horizon single product single machine production problem. Demand rate and all the cost patterns do not change over time. However, end of horizon effects may require production rate adjustments at the beginning of each cycle. It is found that no such adjustments are required. The machine should be operated either at minimum speed (i.e. production rate = demand rate; shortage is not allowed), avoiding the buildup of any inventory, or at maximum speed, building up maximum inventories that are controlled by the optimal production lot size.     

Connectivity guarantees for wireless networks with directional antennas

We study a combinatorial geometric problem related to the design of wireless networks with directional antennas. Specifically, we are interested in necessary and sufficient conditions on such antennas that enable one to build a connected communication network, and in efficient algorithms for building such networks when possible.We formulate the problem by a set P of n points in the plane, indicating the positions of n transceivers. Each point is equipped with an α-degree directional antenna, and one needs to adjust the antennas (represented as wedges), by specifying their directions, so that the resulting (undirected) communication graph G is connected. (Two points p,q∈P are connected by an edge in G, if and only if q lies in p?s wedge and p lies in q?s wedge.) We prove that if α=60°, then it is always possible to adjust the wedges so that G is connected, and that α?60° is sometimes necessary to achieve this. Our proof is constructive and yields an time algorithm for adjusting the wedges, where k is the size of the convex hull of P.Sometimes it is desirable that the communication graph G contain a Hamiltonian path. By a result of Fekete and Woeginger (1997) [8], if α=90°, then it is always possible to adjust the wedges so that G contains a Hamiltonian path. We give an alternative proof to this, which is interesting, since it produces paths of a different nature than those produced by the construction of Fekete and Woeginger. We also show that for any n and ε>0, there exist sets of points such that G cannot contain a Hamiltonian path if α=90°−ε.     

NMR Spectral Patterns in Magneto-Aligned Biaxial Liquid Crystals

Unique NMR spectral patterns can be obtained from biaxially ordered smectic phases where only one of the principal axes of the time averaged nuclear spin interaction is aligned by the magnetic field. It is shown how the asymmetry parameter of the interaction can be obtained directly from edge singularities in these patterns.     

11th Annual BNL Accelerator Test Facility Program Committee and Users' Meeting

The Seventh Annual Users' Meeting of the Canadian Light Source was a great success, as the world's newest synchrotron welcomed close to 400 researchers and students from across Canada, the U.S., Europe and Australia to the University of Saskatchewan on November 17–21, 2004. The plenary session of the Users' Meeting, held November 20, was preceded by five workshops: “XAFS Analysis Using Ifeffit, Athena and Artemis,” “SR Applications in Environmental Science,” “Medical Imaging,” “Protein Crystallography,” and “Applications of Elliptically Polarized Synchrotron Radiation.” Meetings of the Beamline Advisory Committee and beamline teams were held on November 21.

After welcoming remarks by Dr. Alan Anderson, Chair of the CLS User Advisory Committee, the meeting opened with a briefing by CLS Executive Director William Thomlinson regarding the accomplishments made by the CLS over the preceding year.     

Adiabatic plasma buncher

In this paper, we present a new scheme of injection into a plasma accelerator, aimed at producing a high-quality beam while relaxing the demands on the bunch length of the injected beam. The beam dynamics in the injector, consisting of a high-voltage pulsed photodiode, is analyzed and optimized to produce a λ_p/20 long electron bunch at 2.5 MeV. This bunch is injected into a plasma wave in which it compresses down to λ_p/100, while accelerating up to 250 MeV. This simultaneous bunching and acceleration of a high-quality beam requires a proper combination of injection energy and injection phase. Preliminary results from simulations are shown to assess the potentials of the scheme     

Directional approach to gradual cover: a maximin objective

The objective of original cover location models is to cover demand within a given distance by facilities. Locating a given number of facilities to cover as much demand as possible is referred to as max-cover, and finding the minimum number of facilities required to cover all the demand is referred to as set covering. When the objective is to maximize the minimum cover of demand points, the maximin objective is equivalent to set covering because each demand point is either covered or not. The gradual (or partial) cover replaces abrupt drop from full cover to no cover by defining gradual decline in cover. Both maximizing total cover and maximizing the minimum cover are useful objectives using the gradual cover measure. In this paper we use a recently proposed rule for calculating the joint cover of a demand point by several facilities termed “directional gradual cover”. The objective is to maximize the minimum cover of demand points. The solution approaches were extensively tested on a case study of covering Orange County, California.

     

Hybrid meta-heuristics with VNS and exact methods: alication to large unconditional and conditional vertex $$$$-centre roblems

Large-scale unconditional and conditional vertex \(p\)-centre problems are solved using two meta-heuristics. One is based on a three-stage approach whereas the other relies on a guided multi-start principle. Both methods incorporate Variable Neighbourhood Search, exact method, and aggregation techniques. The methods are assessed on the TSP dataset which consist of up to 71,009 demand points with \(p\) varying from 5 to 100. To the best of our knowledge, these are the largest instances solved for unconditional and conditional vertex \(p\)-centre problems. The two proposed meta-heuristics yield competitive results for both classes of problems.     

On solving the planar k-centrum problem with Euclidean distances

This paper presents a solution procedure based on a gradient descent method for the k-centrum problem in the plane. The particular framework of this problem for the Euclidean norm leads to bisector lines whose analytical expressions are easy to handle. This allows us to develop different solution procedures which are tested on different problems and compared with existing procedures in the literature of Location Analysis. The computational analysis reports that our procedures provide better results than the existing ones for the k-centrum problem.     

First observation of the Greisen-Zatsepin-Kuzmin suppression

The High Resolution Fly's Eye (HiRes) experiment has observed the Greisen-Zatsepin-Kuzmin suppression (called the GZK cutoff) with a statistical significance of five standard deviations. HiRes' measurement of the flux of ultrahigh energy cosmic rays shows a sharp suppression at an energy of 6 x 10(19) eV, consistent with the expected cutoff energy. We observe the ankle of the cosmic-ray energy spectrum as well, at an energy of 4 x 10(18) eV. We describe the experiment, data collection, and analysis and estimate the systematic uncertainties. The results are presented and the calculation of the statistical significance of our observation is described.