The effect of a horizontal pressure gradient on the onset of a Darcy–Bénard convection in thermal non-equilibrium conditions

In this paper there is studied the effect of a horizontal pressure gradient on the onset of Darcy–Bénard convection in a fluid-saturated porous layer heated from below, when the fluid and solid phases are not in local equilibrium. In the context of a linearized stability analysis, the problem is transformed into an eigenvalue equation. The problem, when cast in dimensionless form, contains three parameters (the pressure gradient, the porosity-scaled conductivity ratio and the scaled inter-phase heat transfer coefficient). This problem is solved numerically by using two methods: Galerkin approach and the numerical solver dsolve from Maple and comparisons between these methods are performed. Critical values of Rayleigh number, wave number and frequency are obtained for various values of the problem parameters.     

Context-aware broadcasting approaches in mobile ad hoc networks

The aim of this paper is to compare different context-aware broadcasting approaches in mobile ad hoc networks (MANETs) and to evaluate their respective performances. Message broadcasting is one of the core challenges brought up by distributed systems and has therefore largely been studied in the context of traditional network structures, such as the Internet. With the emergence of MANETs, new broadcasting algorithms especially geared at these networks have been introduced. The goal of these broadcasting algorithms is to ensure that a maximum number of nodes deliver the broadcasted message (reliability), while ensuring that the minimum number of nodes retransmit the broadcasted message (efficiency), in order to save their resources, such as bandwidth or battery. In recent years, as more and more mobile devices have become context-aware, several broadcasting algorithms have been introduced that take advantage of contextual information in order to improve their performance. We distinguish four approaches with respect to context: (1) context-oblivious approaches, (2) network traffic-aware approaches, (3) power-aware approaches, and (4) location-aware approaches. This paper precisely aims at presenting these four different broadcasting approaches and at measuring the performance of algorithms built upon them.     

Remarks and corrections to the triangular approximations of fuzzy numbers using ��-weighted valuations

A recent paper was dedicated to find the nearest fuzzy triangular approximations of a fuzzy number by using ??-weighted valuations. We prove, by simple examples, that the results of approximations are not always triangular fuzzy numbers and that in fact they are not fuzzy sets. We give a correct solution of the problem of approximation in a more general case, and we study the properties of identity, additivity, translation invariance, scale invariance, and monotonicity of the new approximation operator.     

Comparison of numerical codes for geochemical modelling of CO2 storage in target sandstone reservoirs

Long-term containment of CO₂ and storage security depends mainly on physical and geochemical trapping mechanisms. Injected CO₂ dissolves in the formation fluid and causes a sharp decrease in pH which in turn drives the dissolution and precipitation of minerals. Geochemical modelling is an important tool to understand and predict the behaviour of CO₂ reactivity. In this paper three numerical codes, PHREEQC, GEM and TOUGHREACT, are compared with respect to brine - CO₂ - rock reactions. Formation water compositions and mineralogies of three sandstone core samples from target CO₂-storage formations were used as input for kinetic models. Mineral replacement reactions were observed when CO₂ injection was initiated in all scenarios. While PHREEQC and GEM were generally in good agreement, TOUGHREACT gave diverging predictions on two models. It is considered that the discrepancies are caused primarily by the differences in the thermodynamic databases and activity models. The uncertainties in these calculations suggest that appropriate experimental tests should be performed to validate the models, so that they can be used to make predictions at the field scale.     

Piecewise Polynomial Solutions of Aerosol Dynamic Equation

This paper presents a discretization technique for particle dynamics equation based on piecewise continuous approximations of the solution. The growth terms are re-solved using a Discontinuous Galerkin approach, and the coagulation by a collocation approach. The method fits in the general framework recently proposed by the author. The discontinuous approximation allows better representations of distributions with sharp peaks. Numerical tests reveal that accurate solutions can be obtained with a very small number of size bins. An efficient software package AeroSolve which implements the proposed algorithms was developed.     

Study on visual machine-learning on the omnidirectional transporting robot

We present a computer vision solution integrated to an omnidirectional transporting robot to perform the position tracking of multiple trays moving on its planar acrylic plate surface. The trays were designed to carry lightweight materials on top of their surface so that the mechanism could be implemented as an automated transporting system for applications that require the displacement of products and/or materials in any given space. One hurdle faced by the visual system for suitable detection was the partial occlusion of the image of a tray when placing arbitrary objects on its surface. Our strategy to overcome this challenge consisted on the implementation of machine learning algorithms, such as Support Vector Machines (SVM), using datasets of images containing trays with different occlusion patterns for fast object detection through rigorous training. The results of experimental tests validate the implementation of our proposal as a reliable approach for the object tracking of multiple trays on the robotic device, even under partial occlusion. We also studied the accuracy of the position measurements performed by our visual system with respect to the position measurements taken by the OPTITRACK motion capture system and evaluated the processing time per frame required by the software implementation.     

Optical planar waveguide for cell counting

Low cost counting of cells has medical applications in screening, military medicine, disaster medicine, and rural healthcare. In this report, we present a shallow, buried, planar waveguide fabricated by potassium ion exchange in glass that enables low-cost and rapid counting of metal-tagged objects that lie in the evanescent field of the waveguide. Laser light transmitted through the waveguide was attenuated proportionately to the presence of metal-coated microstructures fabricated from photoresist. This technology enables the low-cost enumeration of cells from blood, urine, or other biofluids.     

Effect of Ni substitute in off-stoichiometric Bi(Pb)-Sr-Ca-Cu(Ni)-O superconductor. Excess conductivity,XRD analysis and thermal behaviour

Two phases (2223 and 2212) are identified in Bi_1.8Pb_0.3Sr₂Ca₂(Cu_1-xNi_x)_3.3O_y superconductor system, sintered at 847?°C for 322?h, in partial nitrogen atmosphere. The volume fraction of 2223-phase is strongly dependent on Ni doping: 78.37% for x?=?0.002, 70.29% for x?=?0.005% and 51.13% for x?=?0.015. The unit cells of 2223 and 2212 phases were indexed as tetragonal structures, having different lattice constants. Plots of resistance versus temperature (four points method) on cooling to 77?K, evidenced that the critical temperature for the transition to the superconductor phase, T_c, is linearly decreasing from 106.21 to 93.47?K when the Ni content is varying from x?=?0.002 to x?=?0.03. From log-log plots of the excess-conductivity we calculated the cross-over temperatures between 3D and 2D dimensionality as well as from 2D to SWF (short wavelength fluctuation) behaviour, the coupling factor and the coherence length for all the samples. Thermal analysis of the resulting samples (after the last sintering) was performed by heating each sample from room temperature (RT) to 1000?°C at a rate of 10?K?min^?1 in dynamic air atmosphere (150?cm³ min^?1). A clear dependence on Ni content is seen by TG and DSC, but a relative thermal equilibrium between the two phases, 2223 and 2212, in RT-869?°C range, is observed. Strong endothermic effects (melting accompanied by small decomposition processes) begin at around 869?°C for all Ni doped samples. The results for the specific heat capacities, calculated from DSC plots, are also presented. Contribution of the crystal lattice to the estimated specific heat capacity was in conformity with the Einstein model, the Einstein temperature values being dependent on Ni content.