1,265 research outputs found
The Golden Fleece; The American Century
Two one-act plays on marriage, family and the American way, directed, and performed by John Carroll students, November 20-23, 2003.https://collected.jcu.edu/plays/1134/thumbnail.jp
Analysis of defect structure in silicon. Characterization of SEMIX material. Silicon sheet growth development for the large area silicon sheet task of the low-cost solar array project
Statistically significant quantitative structural imperfection measurements were made on samples from ubiquitous crystalline process (UCP) Ingot 5848 - 13C. Important correlation was obtained between defect densities, cell efficiency, and diffusion length. Grain boundary substructure displayed a strong influence on the conversion efficiency of solar cells from Semix material. Quantitative microscopy measurements gave statistically significant information compared to other microanalytical techniques. A surface preparation technique to obtain proper contrast of structural defects suitable for quantimet quantitative image analyzer (QTM) analysis was perfected and is used routinely. The relationships between hole mobility and grain boundary density was determined. Mobility was measured using the van der Pauw technique, and grain boundary density was measured using quantitative microscopy technique. Mobility was found to decrease with increasing grain boundary density
A new theoretical paradigm to describe hysteresis, discrete memory and nonlinear elastic wave propagation in rock
International audienceThe velocity of sound in rock is a strong function of pressure, indicating that wave propagation in rocks is very nonlinear. The quasistatic elastic properties of rocks axe hysteretic, possessing discrete memory. In this paper a new theory is developed, placing all of these properties (nonlinearity, hysteresis, and memory) on equal footing. The starting point of the new theory is closer to a microscopic description of a rock than the starting point of the traditional five-constant theory of nonlinear elasticity. However, this starting point (the number density ? of generic mechanical elements in an abstract space) is deliberately independent of a specific microscopic model. No prejudice is imposed as to the mechanism causing nonlinear response in the microscopic mechanical elements. The new theory (1) relates suitable stress-strain measurements to the number density ? and (2) uses the number density ? to find the behaviour of nonlinear elastic waves. Thus the new theory provides for the synthesis of the full spectrum of elastic behaviours of a rock. Early development of the new theory is sketched in this contribution
Instability of insulating states in optical lattices due to collective phonon excitations
The role of collective phonon excitations on the properties of cold atoms in
optical lattices is investigated. These phonon excitations are collective
excitations, whose appearance is caused by intersite atomic interactions
correlating the atoms, and they do not arise without such interactions. These
collective excitations should not be confused with lattice vibrations produced
by an external force. No such a force is assumed. But the considered phonons
are purely self-organized collective excitations, characterizing atomic
oscillations around lattice sites, due to intersite atomic interactions. It is
shown that these excitations can essentially influence the possibility of atoms
to be localized. The states that would be insulating in the absence of phonon
excitations can become delocalized when these excitations are taken into
account. This concerns long-range as well as local atomic interactions. To
characterize the region of stability, the Lindemann criterion is used.Comment: Latex file, 27 pages, 1 figur
Phase field modeling of electrochemistry I: Equilibrium
A diffuse interface (phase field) model for an electrochemical system is
developed. We describe the minimal set of components needed to model an
electrochemical interface and present a variational derivation of the governing
equations. With a simple set of assumptions: mass and volume constraints,
Poisson's equation, ideal solution thermodynamics in the bulk, and a simple
description of the competing energies in the interface, the model captures the
charge separation associated with the equilibrium double layer at the
electrochemical interface. The decay of the electrostatic potential in the
electrolyte agrees with the classical Gouy-Chapman and Debye-H\"uckel theories.
We calculate the surface energy, surface charge, and differential capacitance
as functions of potential and find qualitative agreement between the model and
existing theories and experiments. In particular, the differential capacitance
curves exhibit complex shapes with multiple extrema, as exhibited in many
electrochemical systems.Comment: v3: To be published in Phys. Rev. E v2: Added link to
cond-mat/0308179 in References 13 pages, 6 figures in 15 files, REVTeX 4,
SIUnits.sty. Precedes cond-mat/030817
Linear and nonlinear modulus surfaces in stress space, from stress-strain measurements on Berea sandstone
International audienceThe elastic response of many rocks to quasistatic stress changes is highly nonlinear and hysteretic, displaying discrete memory. Rocks also display unusual nonlinear response to dynamic stress changes. A model to describe the elastic behavior of rocks and other consolidated materials is called the Preisach-Mayergoyz (PM) space model. In contrast to the traditional analytic approach to stress-strain, the PM space picture establishes a relationship between the quasistatic data and a number density of hysteretic mesoscopic elastic elements in the rock. The number density allows us to make quantitative predictions of dynamic elastic properties. Using the PM space model, we analyze a complex suite of quasistatic stress-strain data taken on Berea sandstone. We predict a dynamic bulk modulus and a dynamic shear modulus surface as a function of mean stress and shear stress. Our predictions for the dynamic moduli compare favorably to moduli derived from time of flight measurements. We derive a set of nonlinear elastic constants and a set of constants that describe the hysteretic behavior of the sandstone
A Model for Solid He: II
We propose a simple Ginzburg-Landau free energy to describe the magnetic
phase transition in solid He. The free energy is analyzed with due
consideration of the hard first order transitions at low magnetic fields. The
resulting phase diagram contains all of the important features of the
experimentally observed ph ase diagram. The free energy also yields a critical
field at which the transition from the disordered state to the high field state
changes from a first order to a second order one.Comment: This paper has been accepted for publication in Journal of Low
Temperature Physics. Use regular Tex, with the D. Eardley version of Macros
called jnl.tex. 10 pages, 4 figs available from [email protected]
Resonant steps and spatiotemporal dynamics in the damped dc-driven Frenkel-Kontorova chain
Kink dynamics of the damped Frenkel-Kontorova (discrete sine-Gordon) chain
driven by a constant external force are investigated. Resonant steplike
transitions of the average velocity occur due to the competitions between the
moving kinks and their radiated phasonlike modes. A mean-field consideration is
introduced to give a precise prediction of the resonant steps. Slip-stick
motion and spatiotemporal dynamics on those resonant steps are discussed. Our
results can be applied to studies of the fluxon dynamics of 1D
Josephson-junction arrays and ladders, dislocations, tribology and other
fields.Comment: 20 Plain Latex pages, 10 Eps figures, to appear in Phys. Rev.
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