An LP-based heuristic procedure for the generalized assignment problem with special ordered sets

The generalized assignment problem with special ordered sets (GAPS2), is the problem of allocating n tasks to m time-periods, where each task must be assigned to a time-period, or shared between two consecutive time-periods. For reasonably large values of m and n the NP-hard combinatorial problem GAPS2 becomes intractable for standard mathematical programming software, hence there is a need for heuristic algorithms to solve such problems. It will be shown how an LP-based heuristic developed previously for the well-established generalized assignment problem can be modified and extended to solve GAPS2. Encouraging results, in terms of speed and accuracy, in particular when compared to an existing heuristic for GAPS2, are described.     

Development and characterization of magnetorheological polymer gels

Magnetorheological materials have been used in many applications in recent years. To develop new materials, polyurethane and silicone polymer gels were investigated. Rheology is qualitatively controlled for each system by controlling the concentration of reactants and diluents. The resulting polymers have solid, gel, or liquid states, depending on the crosslinking and dilution. The gels were characterized through kinetic analysis. Differential scanning calorimetry (DSC) was used with analysis methods to find the kinetic properties for diluted and undiluted polyurethane systems. Heat of reaction, order of reaction, preexponential constant, and activation energy were obtained from the experimental DSC data. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2733–2742, 2002     

Measurement of the temperature field induced by dynamic crack growth in Beta-C titanium

The temperature increase at the tip of a dynamically propagating crack may have a significant effect on a material's mechanical properties, and hence on its dynamic fracture toughness. In order to start to understand this phenomena, measurements of the temperature field at the tip of a dynamically growing crack in Beta-C titanium alloy were performed using a linear array of high speed infrared detectors. The results show that a maximum temperature of 450°C is reached at the crack tip. In addition, the dynamic fracture toughness was measured for crack speeds from 0 to 500 m/s. In this speed range, the toughness appears to be constant. Estimates of the crack tip energy release rate and plastic strain rate are made using analysis of the experimental data.     

Effect of pretreatments and freezing rate on the firmness of potato tissue after a freeze–thaw cycle

The texture of potato tissue after a freeze–thaw process using different freezing rates and different pretreatments was analysed, in order to select the best strategy for optimum preservation of the textural characteristics of pre‐frozen potato. Ten blanching conditions were tested and a two‐step blanching process with calcium chloride (0.07 g mL^?1) proved the most effective in protecting the tissue after a freeze–thaw process (maximum load force around 10–55% of the raw tissue, depending on potato batch, for air‐blast freezing and 20–60% for immersion freezing). Vacuum impregnation at 100 and 400 mbar, even when followed by different pre‐drying treatments to remove excess water, was very detrimental to resistance to a freeze–thaw process (maximum load force below 10% of the raw tissue for air‐blast freezing and below 20% for immersion freezing). Microstructure analysis confirmed better tissue integrity retention with ethyleneglycol immersion freezing instead of air‐freezing. Differences were found between batches with a 6‐month difference in storage time, indicating that the fresher batch was more suitable for freezing.     

Empirical efficiency and volume relationships for HPGe detectors

We have extended the empirical work of Vano et al.[1] relating the slope of the detector efficiency curve to the active volume for Ge detectors. The analysis was carried out using Monte Carlo techniques and covered a wide range of incident energies (200 keV-20 MeV) and active volumes (19.6 cm³–396 cm³). It is shown that the expression of Vano et al.[1] is only valid over the energy range 200 keV-3 MeV for active volumes <50 cm³. The upper bound decreases to 2 MeV for volumes of a few hundred cm³. The usable energy range can, however, be extended to 6 MeV by introducing higher order terms into the polynomial. Above this energy, the shape of the efficiency curve is better described by a non-linear function since linear forms fail simultaneously to fit large active volumes and high energies. We therefore propose a composite function which reduces to the form given in Vano et al. in the low energy/active volume limit. By comparison with the Monte Carlo results, it is estimated that relative efficiencies can be calculated to within 6% over the energy range 200 keV-20 MeV and active volumes 20 cm³–400 cm³. Since the largest errors occur for the smallest volumes, we recommend that for energies <3 MeV a two-fold approach be followed, i.e. using the expression of Vano et al.[1] for active volumes less than 50 cm³ and the proposed non-linear form for larger volumes. For high energy work (E > 3 MeV), we advocate the non-linear form. In this way, average errors can be kept 3%. Finally, we point out that the real power of the expression of Vano et al. lies not in predicting efficiencies, but active volumes.     

Dimensional scaling for impact cratering and perforation

The issue of generic scaling laws able to adequately predict (within better than 20%) cratering in semi-infinite targets and perforations through finite thickness targets was revisited. The approach used was to apply physical logic for hydrodynamics in a consistent manner able to account for chunky-body impacts such that the only variables needed are those directly related to known material properties for both the impactor and target. The analyses were compared and verified versus CTH hydrodynamic code calculations and existing experimental data. Comparisons with previous scaling laws were also performed to identify which (if any) were good for generic purposes. This paper is a short synopsis of the full report [1] available through the NASA Langley Research Center, LDEF Science Office.     

The relative effects of transection of the gustatory branches of the seventh and ninth cranial nerves on NaCl taste detection in rats.

Chorda tympani nerve (CT) transection in rats severely impairs NaCl taste detection. These rats can detect higher concentrations of NaCl, however, suggesting that remaining oral nerves maintain some salt sensibility. Rats were tested in a gustometer with a 2-response operant taste-detection task before and after sham surgery (n = 5), combined transection of the CT and the greater superficial petrosal nerves (GSP; 7x, n = 6), or transection of the glossopharyngeal nerve (GL; 9x, n = 4). Thresholds did not significantly change after sham surgery. Although the GL responds to NaCl and innervates nearly 60% of total taste buds, 9x surgery had no effect. However, 7x surgery increased NaCl detection threshold by ～2.5 log?? units, greater than that reported for CT transection alone. These results suggest that the GSP contributes to NaCl sensitivity in rats and also demonstrate that the GL and perhaps the superior laryngeal and lingual nerve proper can maintain some NaCl detectability at high concentrations. These findings confirm the primacy of the 7th nerve relative to the 9th nerve in sensibility of NaCl in the rat model. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Gender moderates the relationship between testosterone and marital interaction.

Higher testosterone levels are related to assertiveness and dominance. Given the relevance of those behavioral correlates to spouses' daily transactions, links between testosterone levels and marital interaction were explored among 92 newlywed couples. Marital problem-solving and social support transactions were assessed, and saliva was collected and assayed for testosterone. Whether marital behavior was related to husbands' and wives' testosterone levels was examined. The link between spouses' testosterone and their behavior was contingent on the partner's testosterone levels. Husbands exhibited more adaptive problem-solving behaviors and social support provision when husbands and wives were concordant for lower testosterone levels. In contrast, wives exhibited more adaptive support provision when spouses had discordant testosterone levels such that wives had higher levels and husbands had lower levels. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Aspects of three-dimensional constrained Delaunay meshing

Presented in this paper are the theoretical aspects of node addition to a non-convex, multiboundary mesh of tetrahedral elements as used in finite element modelling. The method used is derived from Watson¹ and Shenton and Cendes² and is extended to deal with node addition on inter-material boundaries. Several situations are identified that result in an illegal insertion polyhedron (IP), these could be caused by the ‘constrained’ nature of the mesh, adjacent objects with different material properties, or degenerate node configurations. A new Delaunay algorithm is described that checks for illegal cases of the IP and then corrects them, this checking relies on the consistent ordering of the element nodes. It is shown that a particular type of illegal IP can easily be identified and corrected using this technique. The Delaunay algorithm is then applied to automatic mesh generation, and modification to the basic Delaunay algorithm is described so that previously meshed edges and faces of the current object being meshed are not deleted during the addition of subsequent nodes. This ‘protection’ method only becomes viable by recognizing the node ordering sense of the IP faces.