Economies of Transport Density and Industrial Agglomeration

This paper develops a model of a spatial economy in which interregional trade patterns and the structure of the transport network are determined endogenously as a result of the interaction between industrial location behavior and increasing returns in transportation, in particular, economies of transport density. The traditional models assume either the structure of the transport network or industrial location patterns, and hence, they are unable to explain the interdependence of the two. It is shown that economies of transport density can be the primary source of industrial localization.

Study of the Influence of Localized Vibrational Modes in Charge Transport Properties at Nanoscale Systems.

In molecular and atomic devices the interaction between electrons and ionic vibrations has an important role in electronic transport. The electron-phonon coupling can cause the loss of the electron's phase coherence, the opening of new conductance channels and the suppression of purely elastic ones. From the technological viewpoint phonons might restrict the efficiency of electronic devices by energy dissipation, causing heating, power loss and instability. The state of the art in electron transport calculations consists in combining ab initio calculations via Density Functional Theory (DFT) with Non-Equilibrium Green's Function formalism (NEGF). In order to include electron-phonon interactions, one needs in principle to include a self-energy scattering term in the open system Hamiltonian which takes into account the effect of the phonons over the electrons and vice versa. Nevertheless this term could be obtained approximately by perturbative methods. In the First Born Approximation one considers only the first order terms of the electronic Green's function expansion. In the Self-Consistent Born Approximation, the interaction self-energy is calculated with the perturbed electronic Green's function in a self-consistent way. In this work we describe how to incorporate the electron-phonon interaction to the SMEAGOL program (Spin and Molecular Electronics in Atomically Generated Orbital Landscapes), an ab initio code for electronic transport based on the combination of DFT + NEGF. This provides a tool for calculating the transport properties of materials' specific system, particularly in molecular electronics. Preliminary results will be presented, showing the effects produced by considering the electron-phonon interaction in nanoscale devices.

The location of manufacturing firms and imperfect information in transport market

It is well know that transport charges are not symmetric: fronthaul and backhaul costs on a route may differ, because they are affected by the distribution of economic acitivities. This paper develops a two-regional general equilibrium model in which transport costs are determined endogenously as a result of a search and matching process. It is shown that economies or diseconomies of transport density emerge, depending on the search costs of transport firms and the relative importance of the possibility of backhaul transportation. It is found that the symmetry of the distribution of economic activity may break owing to economies of transport density when the additional search costs are small enough.

Fresh water-salt water density currents : a major cause of siltation in estuaries /

"April 1957."

Three-dimensional model for multi-component reactive transport with variable density groundwater flow

PHWAT is a new model that couples a geochemical reaction model (PHREEQC-2) with a density-dependent groundwater flow and solute transport model (SEAWAT) using the split-operator approach. PHWAT was developed to simulate multi-component reactive transport in variable density groundwater flow. Fluid density in PHWAT depends not on only the concentration of a single species as in SEAWAT, but also the concentrations of other dissolved chemicals that can be subject to reactive processes. Simulation results of PHWAT and PHREEQC-2 were compared in their predictions of effluent concentration from a column experiment. Both models produced identical results, showing that PHWAT has correctly coupled the sub-packages. PHWAT was then applied to the simulation of a tank experiment in which seawater intrusion was accompanied by cation exchange. The density dependence of the intrusion and the snow-plough effect in the breakthrough curves were reflected in the model simulations, which were in good agreement with the measured breakthrough data. Comparison simulations that, in turn, excluded density effects and reactions allowed us to quantify the marked effect of ignoring these processes. Next, we explored numerical issues involved in the practical application of PHWAT using the example of a dense plume flowing into a tank containing fresh water. It was shown that PHWAT could model physically unstable flow and that numerical instabilities were suppressed. Physical instability developed in the model in accordance with the increase of the modified Rayleigh number for density-dependent flow, in agreement with previous research. (c) 2004 Elsevier Ltd. All rights reserved.

Wall mediated transport in confined spaces: Exact theory for low density

We present a theory for the transport of molecules adsorbed in slit and cylindrical nanopores at low density, considering the axial momentum gain of molecules oscillating between diffuse wall reflections. Good agreement with molecular dynamics simulations is obtained over a wide range of pore sizes, including the regime of single-file diffusion where fluid-fluid interactions are shown to have a negligible effect on the collective transport coefficient. We show that dispersive fluid-wall interactions considerably attenuate transport compared to classical hard sphere theory.

Survival of Ucides cordatus (Decapoda: Ocypodidae) megalopae during transport under different conditions of density and duration

Target areas for Ucides cordatus (Linnaeus, 1763) restocking programs are often located far from the laboratory where larval rearing is developed. During translocation, the larvae are submitted to highly stressful conditions due to handling, packing, and transport activities. The aim of the present study was to assess the mortality rates of U. cordatus megalopae caused by different transportation procedures. Megalopae at loading densities of 50, 150, and 300 ind.L-1 were packed in double polyethylene 12 x 25 cm plastic bags with 200 ml of marine water at salinity 30. The bags were filled with oxygen at a proportion of 1:2 parts of water and sealed tightly. The trepidations during transport were simulated by the use of a shaker device (800 vibrations/minute) over periods of three and six hours inside a dark container. The survivorship rates of larvae after simulation were compared to those obtained in control groups, which consisted of plastic vials with megalopae at a loading density of 50 ind.L-1 maintained at rest. Immediately after the two transport simulations, there was no significant difference in survivorship between the treatments and the control. However, 24 hours after simulation some of the tested densities resulted in significantly lower survivorships. The results demonstrated that U. cordatus megalopae can tolerate six hours of shaking during transportation, at high densities with minimal mortality.

Transport properties of the transverse charge-density-wave system Fe3O2BO3

We study the transport properties of the charge-density-wave system Fe3O2BO3. ac conductivity measurements for different frequencies are presented for temperatures above and below the structural transition. dc conductivity, as a function of temperature and pressure, yields the variation of the transition temperature with external pressure. Below this transition the conductivity is thermally activated in a wide range of temperature and the gap obtained is strongly pressure dependent. The ac conductivity at sufficiently low temperatures below the transition is ascribed to the excitation of local defects associated with domain walls and which are characteristic of the one-dimensional nature of the Fe3O2BO3 system.

Oxidized low-density lipoproteins and their antibodies: Relationships with the reverse cholesterol transport and carotid atherosclerosis in adults without cardiovascular diseases

Background: Metabolic predictors and the atherogenicity of oxidized LDL (oxLDL) and the specific antibodies against oxLDL (oxLDL Ab) are unclear and controversial. Methods: In 107 adults without atherosclerotic manifestations, we measured oxLDL and oxLDL Ab, and also the activities of CETP. PLTP, lipases and the carotid intima-media thickness (cIMT). Comparisons were performed for the studied parameters between the lowest and the highest tertile of oxLDL and oxLDL Ab, and the relationships between studied variables were evaluated. Results: Subjects with higher oxLDL Ab present reduced hepatic lipase activity and borderline increased cIMT. In the highest oxLDL tertile, besides the higher levels of total cholesterol, LDL-C and apoB100, we found reduced CETP activity and higher cIMT. A significant correlation between oxLDL Ab and cIMT, independent of oxLDL, and a borderline correlation between oxLDL and cIMT independent of oxLDL Ab were found. In the multivariate analysis, apoAl was a significant predictor of oxLDL Ab, in contrast to regulation of oxLDL by apoB100, PLTP and inverse of CETP. Conclusions: In adults without atherosclerotic disease, the metabolic regulation and carotid atherosclerosis of oxLDLAb and oxLDL groups, characterized a dual trait in oxLDL Ab, as a contributor to carotid atherosclerosis, much less so than oxidized LDL, and with a modest atheroprotective role. (C) 2012 Elsevier B.V. All rights reserved.

Agglomeration and directional imbalance of freight rates : the role of density economies in the transport sector

This paper examines the conventional assumption that bilateral transport costs are symmetric. We develop an economic geography model with transport sector in which asymmetric freight rates can occur as a result of density economies. Comparing this to models without density economies, we show that agglomeration of economic activities is more likely to emerge and that multiple equilibria can emerge for some parameters. Then we show the change in its bifurcation and stability of equilibrium and conclude that economies of density in transport flows can act as an agglomeration force.

Hydrodynamics and suspended sediment transport in the Camboriú estuary - Brazil: pre jetty conditions

Estuarine hydrodynamics is a key factor in the definition of the filtering capacity of an estuary and results from the interaction of the processes that control the inlet morphodynamics and those that are acting in the mixing of the water in the estuary. The hydrodynamics and suspended sediment transport in the Camboriú estuary were assessed by two field campaigns conducted in 1998 that covered both neap and spring tide conditions. The period measured represents the estuarine hydrodynamics and sediment transport prior to the construction of the jetty in 2003 and provides important background information for the Camboriú estuary. Each field campaign covered two complete tidal cycles with hourly measurements of currents, salinity, suspended sediment concentration and water level. Results show that the Camboriú estuary is partially mixed with the vertical structure varying as a function of the tidal range and tidal phase. The dynamic estuarine structure can be balanced between the stabilizing effects generated by the vertical density gradient, which produces buoyancy and stratification flows, and the turbulent effects generated by the vertical velocity gradient that generates vertical mixing. The main sediment source for the water column are the bottom sediments, periodically resuspended by the tidal currents. The advective salt and suspended sediment transport was different between neap and spring tides, being more complex at spring tide. The river discharge term was important under both tidal conditions. The tidal correlation term was also important, being dominant in the suspended sediment transport during the spring tide. The gravitational circulation and Stokes drift played a secondary role in the estuarine transport processes.

Quantitative constraints on the transport properties of hot partonic matter from semi-inclusive single high transverse momentum pion suppression in Au plus Au collisions at root S(NN)=200 GeV

The PHENIX experiment has measured the suppression of semi-inclusive single high-transverse-momentum pi(0)'s in Au+Au collisions at root s(NN) = 200 GeV. The present understanding of this suppression is in terms of energy loss of the parent (fragmenting) parton in a dense color-charge medium. We have performed a quantitative comparison between various parton energy-loss models and our experimental data. The statistical point-to-point uncorrelated as well as correlated systematic uncertainties are taken into account in the comparison. We detail this methodology and the resulting constraint on the model parameters, such as the initial color-charge density dN(g)/dy, the medium transport coefficient <(q) over cap >, or the initial energy-loss parameter epsilon(0). We find that high-transverse-momentum pi(0) suppression in Au+Au collisions has sufficient precision to constrain these model-dependent parameters at the +/- 20-25% (one standard deviation) level. These constraints include only the experimental uncertainties, and further studies are needed to compute the corresponding theoretical uncertainties.

Transport properties of single vacancies in nanotubes

We present density of states and electronic transport calculations of single vacancies in carbon nanotubes. We confirm that the defect reconstructs into a pentagon and a nonagon, following the removal of a single carbon atom. This leads to the formation of a dangling bond. Finally, we demonstrate that care must be taken when calculating the density of states of impurities in one-dimensional systems in general. Traditional treatments of these systems using periodic boundary conditions leads to the formation of minigaps even in the limit of large unit cells.

Transport Barkhausen-like noise in uniaxially pressed Bi(1.65)Pb(0.35)Sr(2)Ca(2)Cu(3)O(10+delta) ceramic samples

We report on the detection of the transport Barkhausen-like noise (TBN) in polycrystalline samples of Bi(1.65)Pb(0.35)Sr(2)Ca(2) Cu(3)O(10+delta) (Bi-2223) which were subjected to different uniaxial compacting pressures. The transport Barkhausen-like noise was measured when the sample was subjected to an ac triangular-shape magnetic field (f similar to 1 Hz) with maximum amplitude B(max) approximate to 5.5 mT, in order to avoid the flux penetration within the superconducting grains. Analysis of the TBN signal, measured for several values of excitation current density, indicated that the applied magnetic field in which the noise signal first appears, B(a)(t(i)), is closely related to the magnetic-flux pinning capability of the material. The combined results are consistent with the existence of three different superconducting levels within the samples: (i) the superconducting grains; (ii) the superconducting clusters; and (iii) the weak-links. We finally argue that TBN measurements constitute a powerful tool for probing features of the intergranular transport properties in polycrystalline samples of high-T(c) superconductors. (C) 2010 Elsevier B.V. All rights reserved.