Construction of a real-world bilevel linear programming model of the highway network design problem

The formulation of the highway network design problem (NDP) as a bilevel linear program (BLP) allows more realistic solutions taking into account the reaction of users to improvements made by the system. In this paper, a conceptual framework for the optimization of investments in inter-regional highway networks in developing countries is proposed. The model is applied to the Tunisian network using actual data. Considerable effort was expended to make the implementation as realistic as possible, taking into consideration travel times, operating costs, accident costs, improvement costs, conservation laws, and effects of intra-regional flows. A new formulation allowing the incorporation of any improvement cost functions, including non-convex and non-concave functions, is introduced.     

Selective adaptation to frequency-modulated tones: evidence for an information-processing channel selectively sensitive to frequency changes.

Exposure to an FM tone elevates FM threshold but not AM threshold. This holds for a wide range of frequency deviations (delta F = +/- 0.4 Hz- +/- 30 Hz at least) provided that modulation frequency is low (fm = 2 Hz), but if fm is somewhat higher (e.g., 8 Hz) the finding only holds for small frequency deviations. FM threshold can rise with time up to an adapting duration of at least 1200 s, through this buildup depends on frequency deviation. Exposure to an AM tone elevates AM threshold, but not FM threshold, over a wide range of modulation depths (at least m = 5%--50%). Quasi-FM (QFM) adapting tones resemble FM adapting tones in their effects upon FM and AM sensitivities, even though QFM and AM adapting tones have identical power spectra. Exposure to a pure tone produces no difference between FM and AM threshold elevations. These data can be explained if the human auditory pathway contains separate information-processing channels for AM and FM signals whose sensitivities do not overlap even with suprathreshold stimuli. We suppose that the FM channel (but not the AM channel) is sensitive to changing differences (or ratios) between signals from different sites along the basilar membrane.     

Scheduling programs with repetitive projects: A comparison of a simulated annealing,a genetic and a pair-wise swap algorithm

We address the problem of scheduling in programs involving the production of multiple units of the same product. Our study was motivated by a construction program for fast naval patrol boats. Other applications of this problem include procurement of multiple copies of aircraft, spacecraft, and weapon systems. In this problem we must decide how many units of the product to assign to each of a number of available crews (individuals, teams, subcontractors, etc.). These types of problems are characterized by two potentially conflicting considerations: 1) the need to complete each unit by its contractual due date, and 2) learning effects. Because of the first consideration, there is a tendency to use multiple crews for simultaneous production, so that meeting due dates is assured. However, the second consideration encourages assigning many units to a single crew so that learning effects are maximized. We study this scheduling problem with two different penalty cost structures and develop models for both versions. The models trade-off the penalty associated with late deliveries and the savings due to learning (and possibly incentive payments for early completion). We discuss different heuristic algorithms — simulated annealing, a genetic algorithm, and a pair-wise swap heuristic — as well as an exhaustive search to determine a baseline for comparisons. Our computational results show that the pair-wise swap algorithm is the most efficient solution procedure for these models.     

Evidence for an isomeric 3/2- state in 53Co

The fragmentation of a 550MeV/u primary beam of ⁵⁸Ni on a ⁹Be target has been used to measure time- and energy-correlated γ decays following the implantation of event-by-event discriminated secondary fragments into a ⁹Be stopper plate. A new isomeric γ decay with T _1/2 = 14( ) ns and E _γ = 646.2(2) keV is observed and attributed to the decay of the yrast 3/2^- state in ⁵³ ₂₇Co₂₆ . This short-lived isomeric state has been populated by means of nuclear reactions during the stopping process of the secondary fragments. The experimental findings are discussed in the framework of large-scale spherical shell model calculations in conjunction with isospin symmetry-breaking residual interactions for the A = 53 , T _z = ±1/2 mirror nuclei ⁵³Co and ⁵³Fe .     

Resistivity anisotropy and charge density wave in 2H - NbSe2 and 2H - TaSe2

The in-plane and out-of-plane resistivities of both 2H-TaSe₂ and 2H-NbSe₂ were determined down to 10 K. For both compounds, the resistivity anisotropy shows notably a slope change at temperatures where a CDW transition is expected to occur. On the other hand, for both compounds the resistivity anisotropy at the lowest temperature of measurement is much greater than expected by the Lawrence–Doniach model, which relates the critical magnetic field anisotropy to the normal state resistivity anisotropy for 3D-anisotropic superconductors.     

Progress in direct-drive inertial confinement fusion research at the laboratory for laser energetics

Direct-drive inertial confinement fusion (ICF) is expected to demonstrate high gain on the National Ignition Facility (NIF) in the next decade and is a leading candidate for inertial fusion energy production. The demonstration of high areal densities in hydrodynamically scaled cryogenic DT or D₂ implosions with neutron yields that are a significant fraction of the “clean” 1-D predictions will validate the ignition-equivalent direct-drive target performance on the OMEGA laser at the Laboratory for Laser Energetics (LLE). This paper highlights the recent experimental and theoretical progress leading toward achieving this validation in the next few years. The NIF will initially be configured for X-ray drive and with no beams placed at the target equator to provide a symmetric irradiation of a direct-drive capsule. LLE is developing the “polar-direct-drive” (PDD) approach that repoints beams toward the target equator. Initial 2-D simulations have shown ignition. A unique “Saturn-like” plastic ring around the equator refracts the laser light incident near the equator toward the target, improving the drive uniformity. LLE is currently constructing the multibeam, 2.6-kJ/beam, petawatt laser system OMEGA EP. Integrated fast-ignition experiments, combining the OMEGA EP and OMEGA Laser Systems, will begin in FY08.     

Role of hot-electron preheating in the compression of direct-drive imploding targets with cryogenic D2 ablators

The compression of direct-drive, spherical implosions is studied using cryogenic D2 targets on the 60-beam, 351-nm OMEGA laser with intensities ranging from approximately 3x10(14) to approximately 1x10(15) W/cm2. The hard-x-ray signal from hot electrons generated by laser-plasma instabilities increases with laser intensity, while the areal density decreases. Mitigating hot-electron production, by reducing the laser intensity to approximately 3x10(14) W/cm2, results in areal density of the order of approximately 140 mg/cm2, in good agreement with 1D simulations. These results will be considered in future direct-drive-ignition designs.