3,648 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
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
Thermodynamics, transition dynamics, and texturing in polymer-dispersed liquid crystals with mesogens exhibiting a direct isotropic/smectic-A transition
Experimental and modeling/simulation studies of phase equilibrium and growth
morphologies of novel polymer-dispersed liquid crystal (PDLC) mixtures of PS
(polystyrene) and liquid crystals that exhibit a direct isotropic/smectic-A
(lamellar) mesophase transition were performed for PS/10CB (decyl-
cyanobiphenyl) and PS/12CB (dodecyl-cyanobiphenyl). Partial phase diagrams were
determined using polarized optical microscopy (POM) and differential scanning
calorimetry (DSC) for different compositions of both materials, determining
both phase separation (liquid/liquid demixing) and phase ordering
(isotropic/smectic-A transition) temperatures. The Flory-Huggins theory of
isotropic mixing and Maier-Saupe-McMillan theory for smectic-A liquid
crystalline ordering were used to computationally determine phase diagrams for
both systems, showing good agreement with the experimental results. In addition
to thermodynamic observations, growth morphology relations were found depending
on phase transition sequence, quench rate, and material composition. Three
stages of liquid crystal-rich domain growth morphology were observed: spherical
macroscale domain growth ("stage I"), highly anisotropic domain growth ("stage
II"), and sub-micron spheroid domain growth ("stage III"). Nano-scale structure
of spheroidal and spherocylindrical morphologies were then determined via
two-dimensional simulation of a high-order Landau-de Gennes model. Morphologies
observed during stage II growth are typical of di- rect isotropic/smectic-A
phase transitions, such as highly anisotropic "batonnets" and filaments. These
morphologies, which are found to be persistent in direct isotropic/smectic-A
PDLCs, could provide new functionality and applications for these functional
materials.Comment: First Revision, 21 pages, 11 figures, submitted to Macromolecules as
an article 17JUL200
Particle Yields and Ratios within Equilibrium and Non-Equilibrium Statistics
In characterizing the yields and ratios various of well identified particles
in the ALICE experiment, we utilize extensive {\it additive} thermal
approaches, to which various missing states of the hadron resonances are taken
into consideration, as well. Despite some non-equilibrium conditions that are
slightly driving this statistical approach away from equilibrium, the
approaches are and remain additive and extensive. Besides van der Waals
repulsive interactions (assuming that the gas constituents are no longer
point-like, i.e. finite-volume corrections taken into consideration), finite
pion chemical potentials as well as perturbations to the light and strange
quark occupation factors are taken into account. When confronting our
calculations to the ALICE measurements, we conclude that the proposed
conditions for various aspects deriving the system out of equilibrium notably
improve the reproduction of the experimental results, i.e. improving the
statistical fits, especially the finite pion chemical potential. This points
out to the great role that the non-equilibrium pion production would play, and
the contributions that the hadron resonance missing states come up with, even
when the principles of statistical extensivity and additivity aren't violated.
These results seem to propose revising the conclusions propagated by most of
the field, that the produced particles quickly reach a state of local
equilibrium leading to a collective expansion often described by fluid
dynamics. This situation seems not remaining restrictively valid, at very large
collision energies.Comment: 15 pages, 4 figures, submitted to EP
Extensive/nonextensive statistics for distributions of various charged particles produced in p+p and A+A collisions in a wide range of energies
We present a systematic study for the statistical fits of the transverse
momentum distributions of charged pions, Kaons and protons produced at energies
ranging between 7.7 and 2670 GeV to the extensive Boltzmann-Gibbs (BG) and the
nonextensive statistics (Tsallis as a special type and the generic axiomatic
nonextensive approach). We also present a comprehensive review on various
experimental parametrizations proposed to fit the transverse momentum
distributions of these produced particles. The inconsistency that the BG
approach is to be utilized in characterizing the chemical freezeout, while the
Tsallis approach in determining the kinetic freezeout is elaborated. The
resulting energy dependence of the different fit parameters largely varies with
the particle species and the degree of (non)extensivity. This manifests that
the Tsallis nonextensive approach seems to work well for p+p rather than for
A+A collisions. Drawing a complete picture of the utilization of Tsallis
statistics in modeling the transverse momentum distributions of several charged
particle produced at a wide range of energies and accordingly either disprove
or though confirm the relevant works are main advantages of this review. We
propose analytical expressions for the dependence of the fit parameters
obtained on the size of the colliding system, the energy, as well as the types
of the statistical approach applied. We conclude that the statistical
dependence of the various fit parameters, especially between Boltzmann and
Tsallis approaches could be understood that the statistical analysis ad hoc is
biased to the corresponding degree of extensivity (Boltzmann) or nonextensivity
(Tsallis). Alternatively, the empirical parameterizations, the other models,
and the generic (non)extensive approach seem to relax this biasness.Comment: 42 pages, 17 figures, IX tables, submitted to JSTA
THE EXPLOITATION OF COAL AS AN ENGINE FOR GROWTH IN EASTERN KENTUCKY - AN INPUT-OUTPUT STUDY
Resource /Energy Economics and Policy,
Negotiations for meaning in the context of a massively multiplayer online role-playing game
This study investigated negotiations for meaning as conditions for second language (L2) learning in the context of a massively multiplayer online role-playing game, World of Warcraft (WoW) (Blizzard Entertainment, 2004). Varonis and Gass’s (1985) and Smith’s (2003a) models were used to identify negotiation episodes during on-task and off-task talks among the participants while playing WoW. The participants were six non-native (NNS) and one native English speaker (NS). The NNSs were divided into two teams of three: Team 1 (T1) pre-intermediate and Team 2 (T2) upper-intermediate. The NS played the game with both teams. The study lasted for six months and resulted in 59.96 hours of recorded audio and nine hours of screen-recorded gaming sessions. Negotiation patterns were compared across the L2 proficiency levels and three different types of dyads. The results revealed that (a) T1 encountered more communication breakdowns, but T2 engaged in more negotiations, (b) T1 engaged in more complex negotiations, (c) breakdowns and negotiations occurred more during off-task talk, and (d) breakdowns were triggered more by the NS’s utterances in T1 and by NNSs’ utterances in T2. The results also showed the participants’ abundant L2 use to undertake authentically contextualized game-driven tasks, meticulous involvement in bi- and multi-lateral negotiations, and creative strategies to resolve incomprehension
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