Cargo ships routing and scheduling: Survey of models and problems

When a ship costs thousands of dollars per day, significant savings can be achieved by proper fleet routing and scheduling. In contrast to vehicle scheduling, relatively little work has been done in ship routing and scheduling. This paper discusses briefly the differences between vehicle and ship routing and scheduling and the reasons for the low attention to ship scheduling in the past. The various modes of operation of cargo ships are described and a classification scheme for ship routing and scheduling models and problems is proposed. A review of ship routing, scheduling and related models is provided. The review is broken down into the following categories: transportation system models, liner operations, tramp shipping, industrial operations and other models. Finally, recent trends in ship scheduling, shortcomings in existing models and requirements from realistic models are discussed.     

Cooperative dynamics in two dimensions

We report results from molecular dynamics simulations of cooperative motion in a quasi-two-dimensional system of colloid particles. We find that the onset of the deviation of the single-particle displacement distribution from Gaussian form starts in the liquid phase and extends, with increasing magnitude, through the hexatic phase into the crystalline phase. The time for which the deviation is maximum increases exponentially with the density. As the density increases toward the hexatic phase a third dynamical relaxation mode emerges. We argue that the collective motion is generated by superpositions of instantaneous normal mode vibrations, with lifetimes that increase with the density, along paths with strong bond-orientation correlation.     

Formation of electrically active clusterized neural networks

Ordinarily, in vitro neurons self-organize into homogeneous networks of single neurons linked by dendrites and axons. We show that under special conditions they can also self-organize into neuronal clusters, which are linked by bundles of axons. Multielectrode array measurement reveals that the clusterized networks are also electrically active and exhibit synchronized bursting events similar to those observed in the homogeneous networks. From time-lapse recording, we deduced the features required for the neuronal clusterized versus homogeneous self-organization and developed a simple model for testing their validity.     

Coating Platinum Nanoparticles with Methyl Radicals: Effects on Properties and Catalytic Implications

It was recently reported that the reaction of methyl radicals with Pt⁰ nanoparticles (NPs), prepared by the reduction of Pt(SO₄)₂ with NaBH₄, is fast and yields as the major product stable (Pt⁰‐NPs)?(CH₃)_n and as side products, in low yields, C₂H₆, C₂H₄, and some oligomers. We decided to study the effect of this coating on the properties of the Pt⁰‐NPs. The results show that the coating can cover up to 75 % of the surface Pt⁰ atoms. The rate constant of the reaction, k( ^. CH₃+Pt⁰‐NPs), decreases with the increase in the surface coverage, leading to competing reaction paths in the solution, which gradually become dominant, affecting the composition of the products. The methyl coating also affects the zeta potential, the UV spectra, and the electrocatalytic reduction of water in the presence of the NPs. Thus, the results suggest that binding alkyl radicals to Pt⁰ surfaces might poison the NPs catalytic activity. When the Pt⁰‐NPs are prepared by the reduction of a different precursor salt, PtCl₆^2?, nearly no C₂H₄ and oligomers are formed and the methyl coating covers a larger percentage of the surface Pt⁰ atoms. The difference is attributed to the morphology of the Pt⁰‐NPs: those prepared from Pt(SO₄)₂ are twinned nanocrystals, whereas those prepared from PtCl₆^2? consist mostly of single crystals. Thus, the results indicate that the side products, or most of them at least, are formed on the twinned Pt⁰ nanocrystal edges created between (111) facets. In addition, the results show that Pt⁰‐NPs react very differently compared with other noble metals, for example, Au⁰ and Ag⁰; this difference is attributed in part to the difference in the bond strength, (M⁰‐NP)?CH₃, and should be considered in heterogeneous catalytic processes involving alkyl radicals as intermediates.     

Scale-dependent Macroscopic Balance Equations Governing Transport Through Porous Media: Theory and Observations

A theory is developed providing a rational framework for spatial scale- dependent fluid’s flow and heat transfer, and mass of a component migrating with it through porous media. Introducing the assumption of a non-Brownian type motion and referring to asymptotic expansion in powers of a small defined parameter, we develop a novel approach associated with macroscopic balance equations obtained by averaging over a Representative Elementary Volume (REV). We prove that these equations can be decomposed into a primary part that refers to the REV length scale and a secondary part valid at a length scale smaller than that of the corresponding REV length. Further to our previous development, we obtain two general forms of the primary and secondary macroscopic balance equations. One is based on the assumption that the advective flux of the extensive quantity is dominant over that of the dispersive flux, whereas the other disregards this assumption. Moreover we also introduce the primary and secondary macroscopic forms for the fluid heat- transfer equation. Considering a Newtonian fluid, the resulting primary Navier–Stokes equation can vary from a nonlinear wave equation to a drag-dominant equation at the fluid–solid interface (Darcy’s law). The secondary momentum balance equation describes a wave equation governing the concurrent propagation of the intensive momentum and the dispersive momentum flux, deviating from their corresponding average terms. The primary macroscopic fluid heat-transfer equation accounts for advective and dispersive heat fluxes and the secondary macroscopic heat-transfer equation involves the simultaneous advection of heat deviating from its corresponding intensive average quantity. The primary macroscopic solute mass balance equation accounts for advection and hydrodynamic dispersion. The secondary macroscopic component mass balance equation is in the form of pure advection governing migration of the deviation from the average component concentration. At this stage, we focus on establishing the viability of the developed theory. We do this by arguing that field observations of motion at small spatial scales are coherent with the hyperbolic characteristics of the secondary balance equations. Field observations under natural gradient flow conditions show excessive high concentration (average of 50 mg/L) of colloids under land irrigated by sewage effluents. We argue that this displacement of condensed colloidal parcels manifests the theoretical findings for the smaller spatial scale. Further evidence show the accumulation of particles moving behind the front of an emitted shockwave. We consider this as an experimental proof reinforcing the argument that colloidal migration is subject to the action of a shockwave in the fluid and pure advection transport, governed by the respective suggested hyperbolic macroscopic balance equations of fluid momentum and component mass at the smaller spatial scale.     

Prediction and correlations of some delayed neutron precursor yields for certain actinide nuclides

In this paper some predictions about some delayed neutron precursor yields are presented. The predictions are applied for certain actinides with some special interest in the nuclear energy field. The predictions are based on correlations which might be related to the cluster structure of the nucleus.     

Dissecting entropic coiling and poor solvent effects in protein collapse

The early events in protein collapse and folding are guided by the protein's elasticity. The contributions of entropic coiling and poor solvent effects like hydrophobic forces to the elastic response of proteins are currently unknown. Using molecular simulations of stretched ubiquitin in comparison with models of proteins as entropic chains, we find a surprisingly high stiffness of the protein backbone, reflected by a persistence length of 1.2 nm, which is significantly reduced by hydrophobic forces acting between protein side chains to an apparent persistence length of 0.3-0.6 nm frequently observed in single-molecule stretching experiments. Thus, the poor solvent conditions of a protein in water lead to a protein compaction much beyond the coiling of an entropic chain and thereby allow a protein to appear softer than when using good solvents.     

How does a dipolar Bose-Einstein condensate collapse?

We emphasize that the macroscopic collapse of a dipolar Bose-Einstein condensate in a pancake-shaped trap occurs through local density fluctuations, rather than through a global collapse to the trap center. This hypothesis is supported by a recent experiment in a chromium condensate.     

Effect of interface traps on Debye thickness semiconductor films

The presence of the boundary interface trapping states and their role in determining the properties of Debye thickness thin semiconductor films, are demonstrated experimentally, using PbTe films deposited on mica. These charged states could not be observed earlier and be studied directly, because of the screening by the relatively high carrier density of the ordinary PbTe. Thin, Debye length thickness, PbTe films with a high concentration of interface trapping centers, possess an extraordinary high resistance. In this case the thermostimulated capacitor discharge method can be successfully applied to determine the energy of these levels, their carrier capture cross-sections and their donor- or acceptor-like character. The experimental results and theoretical calculations are discussed.