4,021 research outputs found
Micromechanics of high temperature deformation and failure
The micromechanics of the constitutive behavior of elastoplastic materials at high temperatures was examined. The experimental work focused on the development of microscopic defects in superalloys (Waspaloy), especially the formation of voids at grain boundary carbides, and slip induced surface cracks within grains upon cyclic loading at high temperatures. The influence of these defects on the life expectancy of the material was examined. The theoretical work consists of two parts: (1) analytical description of the mechanisms that lead to defects observed experimentally; and (2) development of macroscopic elastoplastic nonlinear constitutive relations based on mechanical modeling
Deformation and Failure of Amorphous Solidlike Materials
Since the 1970's, theories of deformation and failure of amorphous, solidlike
materials have started with models in which stress-driven, molecular
rearrangements occur at localized flow defects via "shear transformations".
This picture is the basis for the modern theory of "shear transformation zones"
(STZ's), which is the focus of this review. We begin by describing the
structure of the theory in general terms and by showing several applications,
specifically: interpretation of stress-strain measurements for a bulk metallic
glass, analysis of numerical simulations of shear banding, and the use of the
STZ equations of motion in free-boundary calculations. In the second half of
this article, we focus for simplicity on what we call an "athermal" model of
amorphous plasticity, and use that model to illustrate how the STZ theory
emerges within a systematic formulation of nonequilibrium thermodynamics.Comment: 28 pages, 4 figures, submitted to Annual Reviews of Condensed Matter
Physic
Hadronic Equation of State and Speed of Sound in Thermal and Dense Medium
The equation of state and speed of sound squared are
studied in grand canonical ensemble of all hadron resonances having masses
GeV. This large ensemble is divided into strange and non-strange
hadron resonances and furthermore to pionic, bosonic and femionic sectors. It
is found that the pions represent the main contributors to and other
thermodynamic quantities including the equation of state at low
temperatures. At high temperatures, the main contributions are added in by the
massive hadron resonances. The speed of sound squared can be calculated from
the derivative of pressure with respect to the energy density, , or from the entropy-specific heat ratio, . It is
concluded that the physics of these two expressions is not necessarily
identical. They are distinguishable below and above the critical temperature
. This behavior is observed at vanishing and finite chemical potential. At
high temperatures, both expressions get very close to each other and both of
them approach the asymptotic value, . In the HRG results, which are only
valid below , the difference decreases with increasing the temperature and
almost vanishes near . It is concluded that the HRG model can very well
reproduce the results of the lattice quantum chromodynamics (QCD) of and , especially at finite chemical potential. In
light of this, energy fluctuations and other collective phenomena associated
with the specific heat might be present in the HRG model. At fixed
temperatures, it is found that is not sensitive to the chemical
potential.Comment: 19 pages, 6 figures with 13 eps graph
Analysis of organisational climate to improve the adequacy of primary health care in the State of Kuwait
This study covers two areas of contribution to the knowledge, firstly it tried to investigate rigourously the relationships of a number of factors believed that they may affect the climate perception, classified into three types to arrive to prove a hypothesis of the important role that qualification and personal factors play in shaping the climate perception, this is in contrast with situational factors. Secondly, the study tries to recluster the items of a wide-range applied scale for the measurement of climate named HAY in order to overcome the cross-cultural differences between the Kuwaiti and the American society, and to achieve a modified dimensions of climate for a civil service organisation in Kuwait. Furthermore, the study attempts to carry out a diagnostic test for the climate of the Ministry of Public Health in Kuwait, aiming to diagnose the perceived characteristics of the MoPH organisation, and suggests a number of areas to be given attention if an improvement is to be introduced. The study used extensively the statistical and the computer facilities to make the analysis more representing the field data, on the other hand this study is characterised by the very highly responsive rate of the main survey which would affect the findings reliability. Three main field studies are included, the first one was to conduct the main questionnaire where the second was to measure the "should be" climate by the experts of MoPH using the DELPHI technique, and the third was to conduct an extensive meeting with the very top management team in MoPH. Results of the first stage were subject to CLUSTER analysis for the reconstruction of the HAY tool, whereas comparative analysis was carried on between the results of the second and third stages on one side, the first from the other
Energy Efficiency Prediction using Artificial Neural Network
Buildings energy consumption is growing gradually and put away around 40% of total energy use. Predicting heating and cooling loads of a building in the initial phase of the design to find out optimal solutions amongst different designs is very important, as ell as in the operating phase after the building has been finished for efficient energy. In this study, an artificial neural network model was designed and developed for predicting heating and cooling loads of a building based on a dataset for building energy performance. The main factors for input variables are: relative compactness, roof area, overall height, surface area, glazing are a, wall area, glazing area distribution of a building, orientation, and the output variables: heating and cooling loads of the building. The dataset used for training are the data published in the literature for various 768 residential buildings. The model was trained and validated, most important factors affecting heating load and cooling load are identified, and the accuracy for the validation was 99.60%
Eigenvalue bounds for a class of singular potentials in N dimensions
The eigenvalue bounds obtained earlier [J. Phys. A: Math. Gen. 31 (1998) 963]
for smooth transformations of the form V(x) = g(x^2) + f(1/x^2) are extended to
N-dimensions. In particular a simple formula is derived which bounds the
eigenvalues for the spiked harmonic oscillator potential V(x) = x^2 +
lambda/x^alpha, alpha > 0, lambda > 0, and is valid for all discrete
eigenvalues, arbitrary angular momentum ell, and spatial dimension N.Comment: 10 pages (plain tex with 2 ps figures). J.Phys.A:Math.Gen.(In Press
System Level Evaluation of Innovative Coded MIMO-OFDM Systems for Broadcasting Digital TV
Single-frequency networks (SFNs) for broadcasting digital TV is a topic of theoretical and practical interest for future broadcasting systems. Although progress has been made in the characterization of its description, there are still considerable gaps in its deployment with MIMO technique. The contribution of this paper is multifold. First, we investigate the possibility of applying a space-time (ST) encoder between the antennas of two sites in SFN. Then, we introduce a 3D space-time-space block code for future terrestrial digital TV in SFN architecture. The proposed 3D code is based on a double-layer structure designed for intercell and intracell space time-coded transmissions. Eventually, we propose to adapt a technique called effective exponential signal-to-noise ratio (SNR) mapping (EESM) to predict the bit error rate (BER) at the output of the channel decoder in the MIMO systems. The EESM technique as well as the simulations results will be used to doubly check the efficiency of our 3D code. This efficiency is obtained for equal and unequal received powers whatever is the location of the receiver by adequately combining ST codes. The 3D code is then a very promising candidate for SFN architecture with MIMO transmission
Spectra generated by a confined softcore Coulomb potential
Analytic and approximate solutions for the energy eigenvalues generated by a
confined softcore Coulomb potentials of the form a/(r+\beta) in d>1 dimensions
are constructed. The confinement is effected by linear and harmonic-oscillator
potential terms, and also through `hard confinement' by means of an
impenetrable spherical box. A byproduct of this work is the construction of
polynomial solutions for a number of linear differential equations with
polynomial coefficients, along with the necessary and sufficient conditions for
the existence of such solutions. Very accurate approximate solutions for the
general problem with arbitrary potential parameters are found by use of the
asymptotic iteration method.Comment: 17 pages, 2 figure
Memory of the Unjamming Transition during Cyclic Tiltings of a Granular Pile
Discrete numerical simulations are performed to study the evolution of the
micro-structure and the response of a granular packing during successive
loading-unloading cycles, consisting of quasi-static rotations in the gravity
field between opposite inclination angles. We show that internal variables,
e.g., stress and fabric of the pile, exhibit hysteresis during these cycles due
to the exploration of different metastable configurations. Interestingly, the
hysteretic behaviour of the pile strongly depends on the maximal inclination of
the cycles, giving evidence of the irreversible modifications of the pile state
occurring close to the unjamming transition. More specifically, we show that
for cycles with maximal inclination larger than the repose angle, the weak
contact network carries the memory of the unjamming transition. These results
demonstrate the relevance of a two-phases description -strong and weak contact
networks- for a granular system, as soon as it has approached the unjamming
transition.Comment: 13 pages, 15 figures, soumis \`{a} Phys. Rev.
Evaluation of the Performance of Waterproof Perimeter Barriers : Numerical and Physical Models
Fil: Capdevila, Julio A. Universidad Nacional de Córdoba. Facultad de Arquitectura, Urbanismo y Diseño; Argentina.Fil: Zanni, Enrique. Universidad Nacional de Córdoba. Facultad de Arquitectura, Urbanismo y Diseño; Argentina.Fil: Nasser, José J. Universidad Nacional de Córdoba. Facultad de Arquitectura, Urbanismo y Diseño; Argentina.Collapsible soils cover a great part of Córdoba city in Argentina. Loessian soil is formed by silt and sand particles with clay bridges, generating macropores susceptible to collapse upon wetting under load. Those structures that are superficially supported on this type of soils are susceptible of suffering damage because of soil wetting. Some actions can be taken to prevent the effect of this phenomenon, such as trays for pipes, storm drains, deeper foundations and perimetral sidewalks. At present, there is no literature about the design or hydraulic behavior of perimetral sidewalks. In this paper different types of barriers are going to be implemented in numerical and physical models. The purpose is to analyze and evaluate the barriers performance to avoid supporting soil wetting and settlement of foundations due to soil collapse. In this sense, a shallow foundation prototype was constructed and different perimetral barriers were materialized. A design rainfall was applied over the model. Simultaneously, this prototype was implemented in a finite element software to validate numerical results with physical ones. The characterization of the materials that constitute the proposed barriers and foundation soil are carried out to the numerical models. Obtained results allow making the evaluation of performance of the different implemented barriers validating the numerical model results and making some recommendations for the proper design of waterproof perimeter barriers.http://www.seipub.org/scea/PaperInfo.aspx?ID=18325info:eu-repo/semantics/publishedVersionFil: Capdevila, Julio A. Universidad Nacional de Córdoba. Facultad de Arquitectura, Urbanismo y Diseño; Argentina.Fil: Zanni, Enrique. Universidad Nacional de Córdoba. Facultad de Arquitectura, Urbanismo y Diseño; Argentina.Fil: Nasser, José J. Universidad Nacional de Córdoba. Facultad de Arquitectura, Urbanismo y Diseño; Argentina.Diseño Arquitectónic
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