Mössbauer study of iron ore from El Hobo,Huila, Colombia

Iron ore from the El Hobo municipality located in the Huila department in Colombia (2^°35^′7^″N 75^°13^′27^″E) was studied by Mössbauer spectroscopy. The material was quite inhomogeneous, consisting of light brown and dark brown concretions of up to about a centimeter in size, and a sandy fraction. Mössbauer spectra at ambient temperature and at 4.2 K were taken of the two kinds of concretions and the sandy fraction. The concretions contain iron mainly as goethite with only a few percent of hematite. The sandy fraction contains goethite and hematite in roughly equal amounts and a minor fraction of divalent iron that splits magnetically at 4.2 K and may be an impure kind of siderite.     

Joint assessment of responses of biomonitors to airborne nickel and vanadium through nuclear and non-nuclear techniques

This study deals with the influence of the exposure conditions on biological uptake, by looking into concentrations of Ni and V in lichen thalli and tree bark after continuous and discontinuous field trials at littoral sites impacted by anthropogenic emissions. Biomonitors were assessed by k ₀-INAA and AAS. Correlations at Sines are more apparent than at Viana or Lisboa. When data from all sites are pooled, V shows correlations for practically every situation while Ni shows none, which may indicate a dissimilar uptake mechanism for each element. At Sines, V/Ni ratios reach values that comply with emissions from oil-related industries.     

Optimization methodology assessment for the inlet velocity profile of a hydraulic turbine draft tube: part II—performance evaluation of draft tube model

Computational Fluids Dynamics (CFD) tools guide engineers and designers to estimate the performance of new designs. However, a CFD analysis can be very time-consuming depending mainly on the grid size and domain complexity. Thus, this paper aims to describe the tools used to evaluate and compare the performance of different 3D draft tube models for reducing the time-effort needed in an optimization procedure. The results presented here, are the second part of an overall research to establish a global optimization methodology to improve the performance of an hydraulic draft tube through the inlet velocity profile. Previously, three steps of optimization methodology to minimize the energy losses were studied: the inlet velocity profile parameterization, the numerical optimization set-up and the objective function validation. In the latter step, a global optimization method called Multi Island Genetic Algorithm (MIGA) was considered, which requires a large number of iterations before producing a reliable result. This step is able to identify an efficient inlet velocity profile to minimize the energy losses through the draft tube model. However, each iteration is expensive in terms of computational time due to the need for 3D Navier–Stokes (NS) computations to evaluate each profile’s fitness. Thus, in this work the methodology attempts to accelerate the optimization process with accurate results. In order to achieve the goal, the grid size of the 3D draft tube model was minimized, resulting in a much lower computational cost. Specifically, the draft tube calculations were performed on a sequence of five different grids each having approximately twice the number of elements compared to the previous. The measurements of the sensitivity of the draft tube performance quantities to the change of the inlet velocity parameters during the process showed that, in spite of the numerical difference between its performance, the results have the same tendency. Consequently, the 3D draft tube numerical model with a minimal grid size, is reliable and left record of its capabilities for being integrated in the optimization process.     

Bianchi–Bäcklund transforms and dressing actions,revisited

We characterize Bianchi–Bäcklund transformations of surfaces of positive constant Gauss curvature in terms of dressing actions of the simplest type on the space of harmonic maps.     

Consecutive customer losses in oscillating GIX/M//n systems with state dependent services rates

We address the probability that k or more Consecutive Customer Losses take place during a busy period of a queue, the so-called k-CCL probability, for oscillating GI ^X /M//n systems with state dependent services rates, also denoted as GI ^X /M(m)−M(m)//n systems, in which the service rates oscillate between two forms according to the evolution of the number of customers in the system. We derive an efficient algorithm to compute k-CCL probabilities in these systems starting with an arbitrary number of customers in the system that involves solving a linear system of equations. The results derived are illustrated for specific sets of parameters.     

Consecutive customer losses in regular and oscillating <Emphasis Type=Italic>M</Emphasis><Superscript><Emphasis Type=Italic>X</Emphasis></Superscript>/<Emphasis Type=Italic>G</Emphasis>/1/<Emphasis Type=Italic>n</Emphasis> systems

We derive fast recursions to compute the probability that k or more consecutive customer losses take place during a busy period of a queue, the so called k-CCL probability, for regular and oscillating M ^X /G/1/n systems.     

Optimizing the periodic pick-up of raw materials for a manufacturer of auto parts

We describe a solution procedure for a special case of the periodic vehicle routing problem (PVRP). Operation managers at an auto parts manufacturer in the north of Spain described the optimization problem to the authors. The manufacturer must pick up parts (raw material) from geographically dispersed locations. The parts are picked up periodically at scheduled times. The problem consists of assigning a pickup schedule to each of its supplier’s locations and also establishing daily routes in order to minimize total transportation costs. The time horizon under consideration may be as long as 90 days. The resulting PVRP is such that the critical decision is the assignment of locations to schedules, because once this is done, the daily routing of vehicles is relatively straightforward. Through extensive computational experiments, we show that the metaheuristic procedure described in this paper is capable of finding high-quality solutions within a reasonable amount of computer time. Our main contribution is the development of a procedure that is more effective at handling PVRP instances with long planning horizons when compared to those proposed in the literature.     

Wettability of carbon nanofiber layers on nickel foils

Carbon nanofiber (CNF) layers have been directly synthesized on nickel foils by chemical vapor deposition at 450°C using different H(2) concentrations and reaction times. The addition of 5% H(2) produces thicker, rougher and more porous CNF layers than when 1% H(2) is used. The roughness and porosity increases with reaction time when 5%, 10% or 20% H(2) are used; however, this effect is less pronounced when 1% H(2) is used. CNFs are 50-55 nm in diameter and have a fishbone type structure. We have studied the influence of CNF layer thickness, porosity and surface roughness on the interaction with water by measuring the contact angle. The water wetting properties of the samples are more significantly influenced by the CNF layer thickness than both surface roughness and porosity. When the CNF layer is thicker than ca. 20 μm, the surface is hydrophobic and the contact angle increases with surface roughness and porosity. When the CNF layer is thinner than ca. 20 μm, the surface is hydrophilic and the contact angle decreases with increasing surface roughness and porosity. This behavior is attributed to penetration of water, making contact with the hydrophilic C layer between the CNF layer and the foil.     

Disentangling the reaction mechanisms of weakly bound nuclei

Complete and incomplete fusion cross sections for the ⁹Be + ¹⁴⁴Sm reaction have been measured at near-barrier energies, using the delayed X-ray detection technique. At above-barrier energies these show a suppression of complete fusion for this weakly bound projectile on an intermediate mass target. The suppression factor, attributed to ⁹Be break-up, was deduced from a comparison of complete fusion yields with coupled-channels calculations, and appears consistent with measured incomplete fusion product yields. At ∼10%, it is considerably smaller than the value of ∼30% previously found for a ²⁰⁸Pb target. Simultaneous measurements of elastic and inelastic scattering permit a clearer picture of the reaction mechanisms.     

Three-dimensional vortex visualization in stratified spin-up

Abstract  

We present the results of three-dimensional time-dependent numerical simulations of incremental spin-up of a thermally stratified fluid. The fluid inside a vertical cylindrical container of radius R and height 2H is water characterized by the kinematic viscosity ν and thermal diffusivity κ. Initially, its density (temperature) varies linearly with height and is characterized by a constant buoyancy frequency N, which is proportional to the density gradient. The system undergoes an abrupt change in the rotation rate from its initial value Ω_i, when the fluid is in a solid-body rotation state, to the final value Ω_f. The aim of this contribution is to show the formation of columnar vortices in a high Rossby number spin-up flow.