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Solubility of multifunctional associating molecules: measurements and thermodynamic modeling

Queimada, António; Mota, Fátima; Pinho, Simão; Macedo, Eugénia A.
Fonte: Instituto Politécnico de Bragança Publicador: Instituto Politécnico de Bragança
Tipo: Conferência ou Objeto de Conferência
ENG
Relevância na Pesquisa
45.77%
Numerous molecules in the pharmaceutical, food and chemical industries present complex chemical structures with different functional group substitutions. Many of these groups such as amine carboxyl and hydroxyl can form hydrogen bonds To adequately describe the phase equilibria 01 these complex chemicals, models able to take into account association effects are required. Sufi, for modal development and evaluation, experimental data on some representative systems are needed. In this work, new experimental measurements and literature data were combined lo develop a methodology lo modal the phase equilibria of phenolic acids using the Cubic-plus-Association (CPA) equation of state. A comparison with The UNIQUAC activity coefficient model is also presented. Within the different classes of multifunctional associating molecules, phenolic compounds, due to their chemical and biological importance, are among the most important. Apart from being starting materials for many chemical syntheses, there is also huge evidence that some phenolic compounds have beneficial effects on human health.

UM ESTUDO SOBRE MÉTODOS DE CÁLCULO E MEDIDAS EXPERIMENTAIS DE PARÂMETROS CINÉTICOS EM SISTEMAS SUBCRÍTICOS ACIONADOS POR FONTE; A STUDY OF CALCULATION METHODOLOGY AND EXPERIMENTAL MEASUREMENTS OF THE KINETIC PARAMETERS FOR SOURCE DRIVEN SYSTEMS

Lee, Seung Min
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 17/04/2009 PT
Relevância na Pesquisa
45.82%
Este trabalho apresenta um estudo teórico sobre a cinética de reatores focando à metodologia de cálculo e às medidas experimentais dos chamados parâmetros cinéticos para sistemas subcríticos acionados por fontes. São apresentadas, por motivo de comparação, duas metodologias de cálculo dos parâmetros cinéticos: a metodologia baseada no formalismo de Dulla, e a clássica. O objetivo é mostrar a dependência desses parâmetros com o grau de subcriticalidade e a perturbação. Foram considerados um sistema rápido e um térmico, ambos de tipo placa e de meio homogêneo. O modelo utilizado foi de difusão e as soluções foram obtidas usando o método de expansão, considerando 1 grupo de energia e 1 família de precursores para o sistema rápido, e 2 grupos de energia e 1 família de precursores para o sistema térmico. São apresentadas, também, descrições dos principais métodos de medidas experimentais dos parâmetros cinéticos, i.e., métodos estáticos e de fonte pulsada, visando levantar a discussão sobre a compatibilidade desses método na região de subcriticalidade; This work presents a theoretical study of reactor kinetics focusing on the methodology of calculation and the experimental measurements of the so-called kinetic parameters. A comparison between the methodology based on the Dulla´s formalism and the classical method is made. The objective is to exhibit the dependence of the parameters on subcriticality level and perturbation. Two different slab type systems were considered: thermal one and fast one...

Monitoring in precision metal drilling process using multi-sensors and neural network

Cruz, Carlos Eduardo Dorigatti; De Aguiar, Paulo Roberto; Machado, Álisson Rocha; Bianchi, Eduardo Carlos; Contrucci, João Gabriel; Neto, Frederico Castro
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 151-158
ENG
Relevância na Pesquisa
45.72%
This paper presents a new method to estimate hole diameters and surface roughness in precision drilling processes, using coupons taken from a sandwich plate composed of a titanium alloy plate (Ti6Al4V) glued onto an aluminum alloy plate (AA 2024T3). The proposed method uses signals acquired during the cutting process by a multisensor system installed on the machine tool. These signals are mathematically treated and then used as input for an artificial neural network. After training, the neural network system is qualified to estimate the surface roughness and hole diameter based on the signals and cutting process parameters. To evaluate the system, the estimated data were compared with experimental measurements and the errors were calculated. The results proved the efficiency of the proposed method, which yielded very low or even negligible errors of the tolerances used in most industrial drilling processes. This pioneering method opens up a new field of research, showing a promising potential for development and application as an alternative monitoring method for drilling processes. © 2012 Springer-Verlag London Limited.

Amorphous solar modules simulation and experimental results: effect of shading

Melício, Rui; Fialho, Luis; Mendes, Victor; Figueiredo, João; Collares-Pereira, Manuel
Fonte: SPRINGER Publicador: SPRINGER
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
45.66%
This paper focuses on the modeling of PV systems by the five parameters model, consisting on a current controlled generator, single-diode, a shunt and series resistances. An assessment for the identification of the parameters is used requiring data on open circuit, maximum power and short circuit tests. A simulation of a photovoltaic system on a parallel of two series connected amorphous solar modules under the effect of partial shading is presented. The estimated parameters are validated by a comparison with experimental measurements on photovoltaic modules.

Mechanosensitive Channel MscS in the Open State: Modeling of the Transition, Explicit Simulations, and Experimental Measurements of Conductance

Anishkin, Andriy; Kamaraju, Kishore; Sukharev, Sergei
Fonte: The Rockefeller University Press Publicador: The Rockefeller University Press
Tipo: Artigo de Revista Científica
Publicado em /07/2008 EN
Relevância na Pesquisa
45.8%
Mechanosensitive channels of small conductance (MscS) are ubiquitous turgor pressure regulators found in many walled cells and some intracellular organelles. Escherichia coli MscS acting as a tension-activated osmolyte release valve shows a nonsaturable conductance (1.2 nS in a 39 mS/cm electrolyte) and weak preference for anions. Pursuing the transition pathways in this channel, we applied the extrapolated motion protocol (cycles of displacements, minimizations, and short simulations) to the previously generated compact resting conformation of MscS. We observed tilting and straightening of the kinked pore-forming TM3 helices during the barrel expansion. Extended all-atom simulations confirmed the stability of the open conformation in the bilayer. A 53° spontaneous axial rotation of TM3s observed after equilibration increased the width and polarity of the pore allowing for stable voltage-independent hydration and presence of both cations and anions throughout the pore. The resultant open state, characterized by a pore 1.6 nm wide, satisfied the experimental conductance and in-plane expansion. Applied transmembrane electric field (±100 to ±200 mV) in simulations produced a flow of both K+ and Cl−, with Cl− current dominating at higher voltages. Electroosmotic water flux strongly correlated with the chloride current (∼8 waters per Cl−). The selectivity and rectification were in agreement with the experimental measurements performed in the same range of voltages. Among the charged residues surrounding the pore...

Characterization of scatter in cone-beam CT breast imaging: Comparison of experimental measurements and Monte Carlo simulation

Chen, Yu; Liu, Bob; O’Connor, J. Michael; Didier, Clay S.; Glick, Stephen J.
Fonte: American Association of Physicists in Medicine Publicador: American Association of Physicists in Medicine
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
45.83%
It is commonly understood that scattered radiation in x-ray computed tomography (CT) degrades the reconstructed image. As a precursor to developing scatter compensation methods, it is important to characterize this scatter using both empirical measurements and Monte Carlo simulations. Previous studies characterizing scatter using both experimental measurements and Monte Carlo simulations have been reported in diagnostic radiology and conventional mammography. The emerging technology of cone-beam CT breast imaging (CTBI) differs significantly from conventional mammography in the breast shape and imaging geometry, aspects that are important factors impacting the measured scatter. This study used a bench-top cone-beam CTBI system with an indirect flat-panel detector. A cylindrical phantom with equivalent composition of 50% fibroglandular and 50% adipose tissues was used, and scatter distributions were measured by beam stop and aperture methods. The GEANT4-based simulation package GATE was used to model x-ray photon interactions in the phantom and detector. Scatter to primary ratio (SPR) measurements using both the beam stop and aperture methods were consistent within 5% after subtraction of nonbreast scatter contributions and agree with the low energy electromagnetic model simulation in GATE. The validated simulation model was used to characterize the SPR in different CTBI conditions. In addition...

On the Development of the Convective Boundary Layer in a Shear-Free Thermally Forced Stably Stratified Fluid Setting: a 2D and 3D Experimental Investigation Using Image Analysis Techniques Coupled with Temperature Measurements

DORE, VALENTINA
Fonte: La Sapienza Universidade de Roma Publicador: La Sapienza Universidade de Roma
Tipo: Tese de Doutorado
EN
Relevância na Pesquisa
35.93%
The motion of buoyancy driven plumes is, on all scales, the most common heat and momentum transfer mechanism in geophysical flows, well known as Free Convection. Similarly, density stratification due to heating inequalities is also an ordinary scenario in nature. Free Convection phenomenon coupled with a density stratified fluid setting leads to the so-called Penetrative Free Convection (PFC). When a fluid, in static equilibrium, is stably stratified a thermal forcing can produce an unstable configuration ensuing internal waves formation of increasing amplitude. If the perturbation is strong enough, it can definitely erode the initial stratification and cause the motion of turbulent buoyant updrafts, dome-shaped, compensated by denser downdrafts. The entrainment phenomenon occurring at the interface between the turbulent and non-turbulent region justifies the penetrative feature of convection and causes the non linear growth of the Convective Boundary Layer (CBL) of well mixed fluid against the adjacent stably stratified region. In addition to the wide engineering applications, the environmental impact mostly motivates PFC studies. The upper lakes and oceans, under calm conditions, usually exhibit a continuous, moderately stable density distribution. Turbulent convective flow can be generated both by the free-surface cooling and wind shear-stress...

EXPERIMENTAL AND NUMERICAL STUDY OF MULTI- PHASE FLOW IN A COAXIAL AIR JET

Payne, GRAHAM
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado
EN; EN
Relevância na Pesquisa
45.82%
The ultimate goal of this work was to optimize a polymer flame deposition process by developing an experimentally verified numerical model of it. This process consisted of injecting a polymer powder into an air/propane flame where the powder was heated enough to soften it before it was projected on to a substrate to provide a protective coating. Intermediate goals towards the final goal were identified. This thesis was based on four papers with each paper reporting the results of the work on an intermediate goal. The first paper reported on work with the turbulent coaxial air jet created by shutting off the flow of propane and polymer particles to the torch head. Experimental measurements of the flow field were compared to the results of numerical simulations using different Reynolds Average Navier Stokes (RANS) models. The k-ε realizable model provided the best agreement with the axial velocity measurements, but all the RANS models predicted a recirculation zone immediately downstream of the central jet that did not exist. The next paper described two phase flow created by the introduction of polymer particles into the air stream to the central air jet. A sheet of laser light and high speed digital imaging were used to determine the particle velocities...

Plastic deformation of rough rolling contact: An experimental and numerical investigation

BERTHE, Laurent; SAINSOT, p; LUBRECHT, A.A; BAIETTO, M.C
Fonte: Elsevier Publicador: Elsevier
EN
Relevância na Pesquisa
45.77%
Quantifying the surface roughness evolution in contacts is a crucial step in the fatigue prediction process. Surfaces are initially conditioned by the running-in process and later altered by surface fatigue. The aim of this study is to understand and predict the evolution of the micro-geometry in the first few over-rolling cycles. Numerical predictions are validated by experiments. A major difficulty in understanding surface degradation is the measurement of the surface roughness evolution at the relevant scales. A twin disc micro-test rig, called μMag, was specially designed for this kind of analysis. The μMag allows the “in situ” observation of changes in the disc surface during interrupted tests, thus avoiding dismounting the specimens, which is a major cause of inaccuracy. The new method also maintains the relative position of the two discs. The precision of the measurements allows one to use the initial surface micro-geometry as input for the numerical contact calculation. Thus, the plastic deformation of the surfaces can be measured during the first cycles and compared to the numerical prediction. Results show a very good agreement between numerical predictions and experimental measurements.

A new model of fluid flow to determine pressure balance characteristics

WONGTHEP, Padipat; RABAULT, Thierry; NOGUERA, Ricardo; SARRAF, Christophe
Fonte: IOP Publidhing Publicador: IOP Publidhing
EN
Relevância na Pesquisa
45.72%
Some projects such as the EUROMET project 463 have underlined the lack of agreement between experimental measurements and calculations by the finite element method (FEM), used to determine the piston fall rate of a high-pressure balance used in primary standards. This is significant because the piston fall rate is an essential parameter to characterize experimentally the mean gap between the piston and the cylinder and to determine the effective area (A p) at each pressure (p) point. By improving the method used to estimate the piston fall rate it is possible to improve the determination of the gap, the effective area and consequently the pressure distortion coefficient. One possible cause of the lack of agreement between the calculated and measured piston fall rates could be inappropriate modelling of the fluid flow. In fact, the former quasi-1D Stokes model assimilates the gap between the piston and the cylinder as formed by two parallel walls, which is an approximation. In addition, the velocity of the piston wall was neglected. In order to evaluate the influence of this model, the equations of the fluid flow are modified and are presented in this paper. Equations that were defined in a parallel-plane model are defined in an annular gap model. In addition to this...

Characterization of coating processes in Moiré Diffraction Gratings for strain measurements

Ribeiro, J.E.; Lopes, H.; Carmo, J.P.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
45.91%
This paper analyses the influence of the coating process in the optical efficiency of replicated Moire´ Diffraction Gratings (MDGs), which are applied on real field applications for measuring both the surface displacements and strains. The Moire´ diffraction technique is an experimental full-field, non-contact and high resolution optical method, which can reveal to be very useful in extreme harsh environments. The optical efficiency of the replicated MDGs plays an important role in the quality of the experimental measurements. Two processes were used to obtain the metallic coatings: sputtering and aluminum vaporization. A good coatings quality with high optical efficiency was achieved for both processes (e.g., 17%–28%). However, for the replicated gratings a slight decrease in the optical efficiency was found(e.g., 14%–21%). The MDGs were successfully used for the experimental measurements of displacement and strains in a single lap joint. The measurements also showed that high quality of measurements allowed the identification of unbounded regions.

Experimental measurements and modelling of thermophysical properties of glycols; Medição experimental e modelação das propriedades termofísicas de glicóis

Fonseca, Cristofe Henrique Gonçalves
Fonte: Universidade de Aveiro Publicador: Universidade de Aveiro
Tipo: Dissertação de Mestrado
ENG
Relevância na Pesquisa
55.83%
Apesar da sua grande importância e necessidade nos diferentes setores industriais, verifica-se ainda um défice significativo de dados fidedignos relativos às propriedades termofísicas de glicóis para uma ampla gama de temperaturas e pressões. Este trabalho tem como objetivo superar essa lacuna, avaliando as propriedades termofísicas de glicóis e glymes. Para tal, as medições experimentais de densidade, viscosidade e do índice de refração foram realizados na gama de temperaturas (288,15-373,15) K e à pressão atmosférica. Relativamente ao conjunto de compostos estudados, juntamente com os dados disponíveis na literatura, os dados obtidos experimentalmente permitiram avaliar o efeito da estrutura molecular dos compostos nas propriedades em estudo, nomeadamente, o tamanho da cadeia, o número de grupos funcionais e o efeito da substituição dos grupos terminais. A segunda parte do trabalho focou-se na otimização de modelos teóricos, com a finalidade de descrever as propriedades termofísicas da família de compostos em estudo. A Equação de Estado do tipo SAFT, nomeadamente a soft-SAFT EoS, foi aplicada na descrição dos dados experimentais. Novos parâmetros moleculares foram encontrados, ajustando a pressão de vapor e densidade de cada composto aos dados propostos pelo soft-SAFT. Para além de o modelo possibilitar descrever os dados obtidos experimentalmente...

Experimental and theoretical characterization of a Hall thruster plume

Azziz, Yassir, 1979-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 230 p.
ENG
Relevância na Pesquisa
35.98%
Despite the considerable flight heritage of the Hall thruster, the interaction of its plume with the spacecraft remains an important integration issue. Because in-flight data fully characterizing the plume in the space environment are currently unavailable, laboratory measurements are often used to understand plasma expansion and thereby minimize adverse plume-spacecraft interactions. However, experimental measurements obtained in ground facilities do not properly capture the wide angle plume effects most important for plume-spacecraft interactions because of the high background pressure of the laboratory environment. This research describes a method to determine the in-orbit plume divergence of a Hall thruster from laboratory measurements and characterizes the plasma properties of the in-orbit plume. Plume measurements were taken with a Faraday probe and a Retarding Potential Analyzer at various background pressures to correlate changes in current density and ion energy distribution with changes in pressure. Results showed that current density increases linearly with background pressure at any given angle. This linear relationship was used to extrapolate laboratory measurements to zero background pressure, the in-orbit condition. Measurements from the Faraday probe and the Retarding Potential Analyzer were compared to ensure consistency. The effect of discharge voltage on plume divergence was also investigated. Measurements from both probes revealed that plume divergence decreases with an increase in discharge voltage. Hall thruster plume expansion was also characterized using a numerical plume simulation. Comparison of plume simulation results for in-orbit conditions to extrapolated current density at zero pressure demonstrated good agreement.; (cont.) However...

A Comparison of Full-Scale Experimental Measurements and Computational Predictions of the Transom-Stern Wave of the R/V Athena I

Wyatt, Donald C.; Fu, Thomas C.; Taylor, Genevieve L.; Terrill, Eric J.; Xing, Tao; Bhushan, Shanti; O'Shea, Thomas T.; Dommermuth, Douglas G.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 07/10/2014
Relevância na Pesquisa
45.72%
Full-scale experimental measurements and numerical predictions of the wave-elevation topology behind a transom-sterned vessel, the R/V Athena I, are compared and assessed in this paper. The mean height, surface roughness (RMS), and spectra of the breaking stern-waves were measured in-situ by a LIDAR sensor over a range of ship speeds covering both wet- and dry-transom operating conditions. Numerical predictions for this data set from two Office of Naval Research (ONR) supported naval-design codes, NFA and CFDship-Iowa-V.4, have been performed. Initial comparisons of the LIDAR data to the numerical predictions at 5.4 m/s (10.5 kts), a wet-transom condition, are presented. This work represents an ongoing effort on behalf of the ONR Ship Wave Breaking and Bubble Wake program, to assess, validate, and improve the capability of Computational Fluid Dynamics (CFD) to predict full-scale ship-generated wave fields.; Comment: 15 pages, 27th Symposium on Naval Hydrodynamics, Seoul, Korea, 5-10 October 2008

A Comparison of Model-Scale Experimental Measurements and Computational Predictions for a Large Transom-Stern Wave

Drazen, David A.; Fullerton, Anne M.; Fu, Thomas C.; Beale, Kristine L. C.; O'Shea, Thomas T.; Brucker, Kyle A.; Dommermuth, Douglas G.; Wyatt, Donald C.; Bhushan, Shanti; Carrica, Pablo M.; Stern, Fred
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 07/10/2014
Relevância na Pesquisa
45.82%
The flow field generated by a transom stern hull form is a complex, broad-banded, three-dimensional system marked by a large breaking wave. This unsteady multiphase turbulent flow feature is difficult to study experimentally and simulate numerically. Recent model-scale experimental measurements and numerical predictions of the wave-elevation topology behind a transom-sterned hull form, Model 5673, are compared and assessed in this paper. The mean height, surface roughness (RMS), and spectra of the breaking stern-waves were measured by Light Detection And Ranging (LiDAR) and Quantitative Visualization (QViz) sensors over a range of model speeds covering both wet- and dry-transom operating conditions. Numerical predictions for this data set from two Office of Naval Research (ONR) supported naval-design codes, Numerical Flow Analysis (NFA) and CFDship-Iowa-V.4, have been performed. Comparisons of experimental data, including LiDAR and QViz measurements, to the numerical predictions for wet-transom and dry transom conditions are presented and demonstrate the current state of the art in the simulation of ship generated breaking waves. This work is part of an ongoing collaborative effort as part of the ONR Ship Wave Breaking and Bubble Wake program...

Calculation of the ultracold neutron upscattering loss probability in fluid walled storage bottles using experimental measurements of the thermomechanical properties of Fomblin

Lamoreaux, S. K.; Golub, R.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
45.86%
We present experimental measurements of the properties of a liquid "Fomblin" surface obtained by the quasielastic scattering of laser light. The properties include the surface tension and viscosity as a function of temperature. The results are compared to the measurements of the bulk fluid properties. We then calculate the upscattering rate of ultracold neutrons (UCN) from thermally excited surface capillary waves on the liquid surface and compare the results to experimental measurements of the UCN lifetime in Fomblin fluid-walled UCN storage bottles, and show that the excess loss rate for UCN energies near the Fomblin potential can be explained. The rapid temperature dependence of the Fomblin storage lifetime is explained by our analysis.; Comment: 25 pages, 13 figures; 2nd version corrects several errors

Towards the experimental clarification of quarkonium polarization

Faccioli, Pietro; Lourenco, Carlos; Seixas, Joao; Woehri, Hermine K.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 14/06/2010
Relevância na Pesquisa
35.9%
We highlight issues which are often underestimated in the experimental analyses on quarkonium polarization: the relation between the parameters of the angular distributions and the angular momentum composition of the quarkonium, the importance of the choice of the reference frame, the interplay between observed decay and production kinematics, and the consequent influence of the experimental acceptance on the comparison between experimental measurements and theoretical calculations. Given the puzzles raised by the available experimental results, new measurements must provide more detailed information, such that physical conclusions can be derived without relying on model-dependent assumptions. We describe a frame-invariant formalism which minimizes the dependence of the measurements on the experimental acceptance, facilitates the comparison with theoretical calculations, and probes systematic effects due to experimental biases. This formalism is a direct and generic consequence of the rotational invariance of the dilepton decay distribution and is independent of any assumptions specific to particular models of quarkonium production. The use of this improved approach, which exploits the intrinsic multidimensionality of the problem, will significantly contribute to a faster progress in our understanding of quarkonium production...

Constraint on the CKM angle alpha from the experimental measurements of CP violation in B_d^0 --> pi^+ pi^- decay

Lü, Cai-Dian; Xiao, Zhenjun
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
45.72%
In this paper, we study and try to find the constraint on the CKM angle alpha from the experimental measurements of CP violation in B_d^0 --> pi^+ pi^- decay, as reported very recently by BaBar and Belle Collaborations. After considering uncertainties of the data and the ratio r of penguin over tree amplitude, we found that strong constraint on both the CKM angle alpha and the strong phase delta can be obtained from the measured CP asymmetries S_{pi pi} and A_{pi pi}: (a) the ranges of 87 degrees <= alpha <= 131 degrees and 36 degrees <= delta <= 144 degrees are allowed by 1 sigma of the averaged data for r = 0.31; (b) for Belle's result alone, the limits on alpha and delta are 104 degrees <= alpha <= 139 degrees and 42 degrees <= delta <= 138 degrees for 0.32 <= r <= 0.41; and (c) the angle alpha larger than 90 degrees is preferred.; Comment: Revtex, 17 pages with 6 ps/eps figure files, new Babar data Reported at ICHEP 2002 considered

Modelling Washboard Road: from experimental measurements to linear stability analysis

Percier, Baptiste; Manneville, Sébastien; Taberlet, Nicolas
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
45.72%
When submitted to the repeated passages of vehicles unpaved roads made of sand or gravel can develop a ripply pattern known as washboard or corrugated road. We propose a stability analysis based on experimental measurements of the force acting on a blade (or plow) dragged on a circular sand track and show that a linear model is sufficient to describe the instability near onset. The relation between the trajectory of the plow and the profile of the sand bed left after its passage is studied experimentally. The various terms in the expression of the lift force created by the flow of granular material on the plow are determined up to first order by imposing a sinusoidal trajectory to the blade on an initially flat sand bed, as well as by imposing a horizontal trajectory on an initially rippled sand bed. Our model recovers all the previously observed features of washboard road and accurately predicts the most unstable wavelength near onset as well as the critical velocity for the instability.; Comment: 9 pages, 10 figures

Channel modelling for MIMO systems; Modelos de canal para sistemas MIMO

Mota, Susana de Jesus
Fonte: Universidade de Aveiro Publicador: Universidade de Aveiro
Tipo: Tese de Doutorado
ENG
Relevância na Pesquisa
45.78%
Systems equipped with multiple antennas at the transmitter and at the receiver, known as MIMO (Multiple Input Multiple Output) systems, offer higher capacities, allowing an efficient exploitation of the available spectrum and/or the employment of more demanding applications. It is well known that the radio channel is characterized by multipath propagation, a phenomenon deemed problematic and whose mitigation has been achieved through techniques such as diversity, beamforming or adaptive antennas. By exploring conveniently the spatial domain MIMO systems turn the characteristics of the multipath channel into an advantage and allow creating multiple parallel and independent virtual channels. However, the achievable benefits are constrained by the propagation channel’s characteristics, which may not always be ideal. This work focuses on the characterization of the MIMO radio channel. It begins with the presentation of the fundamental results from information theory that triggered the interest on these systems, including the discussion of some of their potential benefits and a review of the existing channel models for MIMO systems. The characterization of the MIMO channel developed in this work is based on experimental measurements of the double-directional channel. The measurement system is based on a vector network analyzer and a two-dimensional positioning platform...