14,142 research outputs found
Damage-Induced Modeling of Asphalt Mixtures through Computational Micromechanics and Cohesive Zone Fracture
This paper presents a computational micromechanics modeling approach to predict damage-induced mechanical response of asphalt mixtures. Heterogeneous geometric characteristics and inelastic mechanical behavior were taken into account by introducing finite element modeling techniques and a viscoelastic material model. The modeling also includes interface fracture to represent crack growth and damage evolution. The interface fracture is modeled by using a micromechanical nonlinear viscoelastic cohesive-zone constitutive relation. Fundamental material properties and fracture characteristics were measured from simple laboratory tests and then incorporated into the model to predict rate-dependent viscoelastic damage behavior of the asphalt mixture. Simulation results demonstrate that each model parameter significantly influences the mechanical behavior of the overall asphalt mixture. Within a theoretical framework of micromechanics, this study is expected to be suitable for evaluating damage-induced performance of asphalt mixtures by measuring only material properties and fracture properties of each mix component and not by recursively performing expensive laboratory tests that are typically required for continuum damage mechanics modeling
Exploring Oxidation in the Remote Free Troposphere: Insights from Atmospheric Tomography (ATom)
Earth's atmosphere oxidizes the greenhouse gas methane and other gases, thus determining their lifetimes and oxidation products. Much of this oxidation occurs in the remote, relatively clean free troposphere above the planetary boundary layer, where the oxidation chemistry is thought to be much simpler and better understood than it is in urban regions or forests. The NASA airborne Atmospheric Tomography study (ATom) was designed to produce cross sections of the detailed atmospheric composition in the remote atmosphere over the Pacific and Atlantic Oceans during four seasons. As part of the extensive ATom data set, measurements of the atmosphere's primary oxidant, hydroxyl (OH), and hydroperoxyl (HO₂) are compared to a photochemical box model to test the oxidation chemistry. Generally, observed and modeled median OH and HO₂ agree to with combined uncertainties at the 2σ confidence level, which is ~±40%. For some seasons, this agreement is within ~±20% below 6 km altitude. While this test finds no significant differences, OH observations increasingly exceeded modeled values at altitudes above 8 km, becoming ~35% greater, which is near the combined uncertainties. Measurement uncertainty and possible unknown measurement errors complicate tests for unknown chemistry or incorrect reaction rate coefficients that would substantially affect the OH and HO₂ abundances. Future analysis of detailed comparisons may yield additional discrepancies that are masked in the median values
Two Aspects of the Mott-Hubbard Transition in Cr-doped V_2O_3
The combination of bandstructure theory in the local density approximation
with dynamical mean field theory was recently successfully applied to
VO -- a material which undergoes the f amous Mott-Hubbard
metal-insulator transition upon Cr doping. The aim of this sh ort paper is to
emphasize two aspects of our recent results: (i) the filling of the
Mott-Hubbard gap with increasing temperature, and (ii) the peculiarities of the
Mott-Hubbard transition in this system which is not characterized by a diver
gence of the effective mass for the -orbital.Comment: 2 pages, 3 figures, SCES'04 conference proceeding
Stretching Wiggly Strings
How does the amplitude of a wiggle on a string change when the string is
stretched? We answer this question for both longitudinal and transverse wiggles
and for arbitrary equation of state, {\it i.e.}, for arbitrary relation between
the tension and the energy per unit length of the string.
This completes our derivation of the renormalization of string parameters which
results from averaging out small scale wiggles on a string. The program is
presented here in its entirety.Comment: Written with ReVTeX 3.0 package. Two figures are not included.
Complete paper with postscript figures can be retrieved through anonymous ftp
@quark.phys.ufl.edu. Get /preprints/ifthep94_4.tar.gz, gunzip and tar it.
UFIFT-HEP-94-
Fault Models for Quantum Mechanical Switching Networks
The difference between faults and errors is that, unlike faults, errors can
be corrected using control codes. In classical test and verification one
develops a test set separating a correct circuit from a circuit containing any
considered fault. Classical faults are modelled at the logical level by fault
models that act on classical states. The stuck fault model, thought of as a
lead connected to a power rail or to a ground, is most typically considered. A
classical test set complete for the stuck fault model propagates both binary
basis states, 0 and 1, through all nodes in a network and is known to detect
many physical faults. A classical test set complete for the stuck fault model
allows all circuit nodes to be completely tested and verifies the function of
many gates. It is natural to ask if one may adapt any of the known classical
methods to test quantum circuits. Of course, classical fault models do not
capture all the logical failures found in quantum circuits. The first obstacle
faced when using methods from classical test is developing a set of realistic
quantum-logical fault models. Developing fault models to abstract the test
problem away from the device level motivated our study. Several results are
established. First, we describe typical modes of failure present in the
physical design of quantum circuits. From this we develop fault models for
quantum binary circuits that enable testing at the logical level. The
application of these fault models is shown by adapting the classical test set
generation technique known as constructing a fault table to generate quantum
test sets. A test set developed using this method is shown to detect each of
the considered faults.Comment: (almost) Forgotten rewrite from 200
Correlated metallic state of vanadium dioxide
The metal-insulator transition and unconventional metallic transport in
vanadium dioxide (VO) are investigated with a combination of spectroscopic
ellipsometry and reflectance measurements. The data indicates that electronic
correlations, not electron-phonon interactions, govern charge dynamics in the
metallic state of VO. This study focuses on the frequency and temperature
dependence of the conductivity in the regime of extremely short mean free path
violating the Ioffe-Regel-Mott limit of metallic transport. The standard
quasiparticle picture of charge conduction is found to be untenable in metallic
VO.Comment: 5 pages, 3 figure
Soft disks in a narrow channel
The pressure components of "soft" disks in a two dimensional narrow channel
are analyzed in the dilute gas regime using the Mayer cluster expansion and
molecular dynamics. Channels with either periodic or reflecting boundaries are
considered. It is found that when the two-body potential, u(r), is singular at
some distance r_0, the dependence of the pressure components on the channel
width exhibits a singularity at one or more channel widths which are simply
related to r_0. In channels with periodic boundary conditions and for
potentials which are discontinuous at r_0, the transverse and longitudinal
pressure components exhibit a 1/2 and 3/2 singularity, respectively. Continuous
potentials with a power law singularity result in weaker singularities of the
pressure components. In channels with reflecting boundary conditions the
singularities are found to be weaker than those corresponding to periodic
boundaries
Fermi Surface of Metallic VO from Angle-Resolved Photoemission: Mid-level Filling of Bands
Using angle resolved photoemission spectroscopy (ARPES) we report the first
band dispersions and distinct features of the bulk Fermi surface (FS) in the
paramagnetic metallic phase of the prototypical metal-insulator transition
material VO. Along the -axis we observe both an electron pocket and
a triangular hole-like FS topology, showing that both V 3 and
states contribute to the FS. These results challenge the existing
correlation-enhanced crystal field splitting theoretical explanation for the
transition mechanism and pave the way for the solution of this mystery.Comment: 5 pages, 4 figures plus supplement 12 pages, 3 figures, 1 tabl
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