A complete and an incomplete algorithm for automated guided vehicle scheduling in container terminals

In this paper, a scheduling problem for automated guided vehicles in container terminals is defined and formulated as a Minimum Cost Flow model. This problem is then solved by a novel algorithm, NSA+, which extended the standard Network Simplex Algorithm (NSA). Like NSA, NSA+ is a complete algorithm, which means that it guarantees optimality of the solution if it finds one within the time available. To complement NSA+, an incomplete algorithm Greedy Vehicle Search (GVS) is designed and implemented. The NSA+ and GVS are compared and contrasted to evaluate their relative strength and weakness. With polynomial time complexity, NSA+ can be used to solve very large problems, as verified in our experiments. Should the problem be too large for NSA+, or the time available for computation is too short (as it would be in dynamic scheduling), GVS complements NSA+.     

Dispersion of a Plume of Volatile Aerosol

A theoretical basis and numerical schemes are presented for simulating the dispersion of a plume of volatile aerosol. For special cases where analytical solutions are possible, excellent agreement is shown between analytical and numerical solutions. It is demonstrated that the error in the numerical simulation can be reduced to any desired level. Simulation results for volatile plume dispersion under realistic atmospheric conditions are also presented.     

Mesoscale characterization of coupled hydromechanical behavior of a fractured-porous slope in response to free water-surface movement

To better understand the role of groundwater-level changes on rock-slope deformation and damage, a carbonate rock slope (30 m×30 m×15 m) was extensively instrumented for mesoscale hydraulic and mechanical measurements during water-level changes. The slope is naturally drained by a spring that can be artificially closed or opened by a water gate. In this study, a 2-h slope-dewatering experiment was analyzed. Changes in fluid pressure and deformation were simultaneously monitored, both at discontinuities and in the intact rock, using short-base extensometers and pressure gauges as well as tiltmeters fixed at the slope surface. Field data were analyzed with different coupled hydromechanical (HM) codes (ROCMAS, FLAC^3D, and UDEC).

Field data indicate that, in the faults, a 40 kPa pressure fall occurs in 2 min and induces a 0.5–31×10⁻⁶ m normal closure. Pressure fall is slower in the bedding-planes, lasting 120 min, with no normal deformation. No pressure change or deformation is observed in the intact rock. The slope surface displays a complex tilt towards the interior of the slope, with magnitudes ranging from 0.6 to 15×10⁻⁶ rad.

Close agreement with model for both slope surface and internal measurements is obtained when a high variability in slope-element properties is introduced into the models, with normal stiffnesses of k_{n_faults}=10⁻³×k_{n_bedding-planes} and permeabilities of k_{h_faults}=10³×k_{h_bedding-planes}. A nonlinear correlation between hydraulic and mechanical discontinuity properties is proposed and related to discontinuity damage. A parametric study shows that 90% of slope deformation depends on HM effects in a few highly permeable and highly deformable discontinuities located in the basal, saturated part of the slope while the remaining 10% is related to elasto-plastic deformations in the low-permeability discontinuities induced by complex stress/strain transfers from the high-permeability zones. The periodicity and magnitude of free water-surface movements cause 10–20% variations in those local stress/strain accumulations related to the contrasting HM behavior for high- and low-permeability elements of the slope. Finally, surface-tilt monitoring coupled with internal localized pressure/deformation measurements appears to be a promising method for characterizing the HM properties and behavior of a slope, and for detecting its progressive destabilization.     

Isolation of synthetic lethal mutants of ras1 in Schizosaccharomyces pombe

Ras proteins are membrane-associated guanine nucleotide-binding proteins that serve as molecular switches for signal transduction pathways in a diverse array of organisms. Various cellular factors are known to interact with Ras proteins. In order to find the novel cellular factors that are associated with Ras function, we have constructed synthetic lethal mutants of the ras1+ gene in Schizosaccharomyces pombe and used them to identify the genes that are functionally dependent on the Ras1. We first constructed S. pombe strains in which chromosomal ras1+ gene is placed under the nmt1 promoter that is regulated by thiamine. This strain shows ras1+ phenotype in the absence of thiamine, whereas it shows ras1- phenotype in the presence of thiamine. Second, we mutated the constructed strains with ultraviolet light (UV) and selected two synthetic lethal mutants that could not grow when Ras1 function was repressed (ras1-). One of the mutants, KSC3, showed a swollen cell shape, aberrant deposition of septum materials, and aberrant nuclei. The other mutant, KSC4, showed sensitivity to hyper-osmolarity when Ras1 function is absent. These mutants, however, grow normally when Ras1 is expressed (ras1+). These two novel synthetic lethal mutants of ras1 provide the means to isolate the corresponding genes that function in association with Ras1 in S. pombe. Screening of a genomic library of S. pombe complementing the mutant phenotype allowed us to identify several novel genes associated with Ras1 of S. pombe.     

Multilevel expansion of the sparse-matrix canonical grid method fortwo-dimensional random rough surfaces

Wave scattering from two-dimensional (2-D) random rough surfaces up to several thousand square wavelengths has been previously analyzed using the sparse-matrix canonical grid (SMCG) method. The success of the SMCG method highly depends on the roughness of the random surface for a given surface area. We present a multilevel expansion algorithm to overcome this limitation. The proposed algorithm entails the use of a three-dimensional (3-D) canonical grid. This grid is generated by a uniform discretization of the vertical displacement along the height (z-axis) of the rough surface in addition to the uniform sampling of the rough surface along the x-y plane. The Green's function is expanded about the 3-D canonical grid for the far interactions. The trade-off in computer memory requirements and CPU time between the neighborhood distance and the number of discretization levels along the x-axis are discussed for both perfectly electric conducting (PEC) and lossy dielectric random rough surfaces. Ocean surfaces of the Durden-Vesecky (1985) spectrum with various bandlimits are also studied     

A discussion of thermo–hydro–mechanical (THM) processes associated with nuclear waste repositories

The design of a nuclear waste repository involves modeling a complex system of physical mechanisms that operate over a long period of time. The perturbations caused by both the engineering excavation and the waste heat have to be modeled, taking into account the short and long term thermo–hydro–mechanical (THM) processes. In this paper, we discuss the approach philosophy and we comment on heterogeneity, multi-stage data needs and modeling phases.     

Studies of the angular correlation function of scattering by randomrough surfaces with and without a buried object

The discrimination of the scattered wave from an object buried in shallow ground from that of the rough surface is a difficult task with present ground penetrating radar (GPR) systems. Recently, a new approach for this classical problem has been proposed and its effectiveness has been verified. This new method is based on the angular correlation function (ACF) of the scattered wave observed at two or more different incident and scattered angle combinations. It has been shown that the angular memory signatures of rough surfaces are substantially different from those of typical man-made targets and by choosing the appropriate incident and scattered angles, the surface scattering can be minimized whereas the scattering from the target is almost unchanged. The authors present detailed numerical studies of the ACF of the scattered wave from rough surfaces with and without a buried object. To obtain the ACF, the three averaging methods: realization, frequency and angular averaging, are tested numerically. It is shown that a single random rough surface of moderate extent can exhibit memory effect by using frequency averaging. Frequency averaging with a wide bandwidth is also effective for suppressing fluctuation in ACF and is most useful for practical applications. Numerical simulations indicate that even when the ratio of scattered intensities with and without the buried object is close to unity, the corresponding ratio of ACF magnitude can be more than 10 dB. Thus, using the ACF is superior to using the radar cross section (RCS) in the detection of buried objects     

Feasibility of a one–step process for desizing,scouring, bleaching and mercerisating cotton fabrics

In this study the desizing, scouring, bleaching and slack mercerising of cotton fabric by a one–step process at different sodium hydroxide concentrations, impregnation temperatures and curing times were examined. The results indicate that when the fabrics are mercerised at lower temperature, the strength retention and colour strength are enhanced. When the sodium hydroxide concentration is increased, these properties also increase. When cotton fabrics are mercerised for 3 min at 40C and cured for 30 s at 120C, their physical properties are similar to those obtained using a conventional two–step approach.