11,875 research outputs found
Shear-transformation-zone theory of plastic deformation near the glass transition
The shear-transformation-zone (STZ) theory of plastic deformation in
glass-forming materials is reformulated in light of recent progress in
understanding the roles played the effective disorder temperature and entropy
flow in nonequilibrium situations. A distinction between fast and slow internal
state variables reduces the theory to just two coupled equations of motion, one
describing the plastic response to applied stresses, and the other the dynamics
of the effective temperature. The analysis leading to these equations contains,
as a byproduct, a fundamental reinterpretation of the dynamic yield stress in
amorphous materials. In order to put all these concepts together in a realistic
context, the paper concludes with a reexamination of the experimentally
observed rheological behavior of a bulk metallic glass. That reexamination
serves as a test of the STZ dynamics, confirming that system parameters
obtained from steady-state properties such as the viscosity can be used to
predict transient behaviors.Comment: 15 pages, four figure
Dynamics of Shear-Transformation Zones in Amorphous Plasticity: Formulation in Terms of an Effective Disorder Temperature
This investigation extends earlier studies of a shear-transformation-zone
(STZ) theory of plastic deformation in amorphous solids. My main purpose here
is to explore the possibility that the configurational degrees of freedom of
such systems fall out of thermodynamic equilibrium with the heat bath during
persistent mechanical deformation, and that the resulting state of
configurational disorder may be characterized by an effective temperature. The
further assumption that the population of STZ's equilibrates with the effective
temperature allows the theory to be compared directly with experimentally
measured properties of metallic glasses, including their calorimetric behavior.
The coupling between the effective temperature and mechanical deformation
suggests an explanation of shear-banding instabilities.Comment: 29 pages, 11 figure
Evolution, Explosion and Nucleosynthesis of Core Collapse Supernovae
We present a new set of presupernova evolutions and explosive yields of
massive stars of initial solar composition (Y=0.285, Z=0.02) in the mass range
13-35 Msun. All the models have been computed with the latest version (4.97) of
the FRANEC code that now includes a nuclear network extending from neutrons to
Mo98. The explosive nucleosynthesis has been computed twice: a first one with
an hydro code and a second one following the simpler radiation dominated shock
approximation (RDA).Comment: 20 pages, 10 figures, 12 tables. Accepted for publication on Ap
The Supernova Channel of Super-AGB Stars
We study the late evolution of solar metallicity stars in the transition
region between white dwarf formation and core collapse. This includes the
super-asymptotic giant branch (super-AGB, SAGB) stars, which have massive
enough cores to ignite carbon burning and form an oxygen-neon (ONe) core. The
most massive SAGB stars have cores that may grow to the Chandrasekhar mass
because of continued shell-burning. Their cores collapse, triggering a so
called electron capture supernovae (ECSN). From stellar evolution models we
find that the initial mass range for SAGB evolution is 7.5 ... 9.25\msun. We
perform calculations with three different stellar evolution codes to
investigate the sensitivity of this mass range to some of the uncertainties in
current stellar models. The mass range significantly depends on the treatment
of semiconvective mixing and convective overshooting. To consider the effect of
a large number of thermal pulses, as expected in SAGB stars, we construct
synthetic SAGB models that include a semi-analytical treatment of dredge-up,
hot-bottom burning, and thermal pulse properties. This synthetic model enables
us to compute the evolution of the main properties of SAGB stars from the onset
of thermal pulses until the core reaches the Chandrasekhar mass or is uncovered
by the stellar wind. Thereby, we determine the stellar initial mass ranges that
produce ONe-white dwarfs and electron-capture supernovae. The latter is found
to be 9.0 ... 9.25\msun for our fiducial model, implying that electron-capture
supernovae would constitute about 4% of all supernovae in the local universe.
Our synthetic approach allows us to explore the uncertainty of this number
imposed by uncertainties in the third dredge-up efficiency and ABG mass loss
rate. We find for ECSNe a upper limit of ~20% of all supernovae (abridged).Comment: 13 pages, 16 figures, submitted to ApJ, uses emulateap
Partition-dependent framing effects in lab and field prediction markets
Many psychology experiments show that individually judged probabilities of the same event can vary depending on the partition of the state space (a framing effect called "partition-dependence"). We show that these biases transfer to competitive prediction markets in which multiple informed traders are provided economic incentives to bet on their beliefs about events. We report results of a short controlled lab study, a longer field experiment (betting on the NBA playoffs and the FIFA World Cup), and naturally-occurring trading in macro-economic derivatives. The combined evidence suggests that partition-dependence can exist and persist in lab and field prediction markets
Airborne measurements of cloud forming nuclei and aerosol particles at Kennedy Space Center, Florida
Results of airborne measurements of the sizes and concentrations of aerosol particles, ice nuclei, and cloud condensation nuclei that were taken at Kennedy Space Center, Florida, are presented along with a detailed description of the instrumentation and measuring capabilities of the University of Washington airborne measuring facility (Douglas B-23). Airborne measurements made at Ft. Collins, Colorado, and Little Rock, Arkansas, during the ferry of the B-23 are presented. The particle concentrations differed significantly between the clean air over Ft. Collins and the hazy air over Little Rock and Kennedy Space Center. The concentrations of cloud condensation nuclei over Kennedy Space Center were typical of polluted eastern seaboard air. Three different instruments were used to measure ice nuclei: one used filters to collect the particles, and the others used optical and acoustical methods to detect ice crystals grown in portable cloud chambers. A comparison of the ice nucleus counts, which are in good agreement, is presented
Athermal Shear-Transformation-Zone Theory of Amorphous Plastic Deformation I: Basic Principles
We develop an athermal version of the shear-transformation-zone (STZ) theory
of amorphous plasticity in materials where thermal activation of irreversible
molecular rearrangements is negligible or nonexistent. In many respects, this
theory has broader applicability and yet is simpler than its thermal
predecessors. For example, it needs no special effort to assure consistency
with the laws of thermodynamics, and the interpretation of yielding as an
exchange of dynamic stability between jammed and flowing states is clearer than
before. The athermal theory presented here incorporates an explicit
distribution of STZ transition thresholds. Although this theory contains no
conventional thermal fluctuations, the concept of an effective temperature is
essential for understanding how the STZ density is related to the state of
disorder of the system.Comment: 7 pages, 2 figures; first of a two-part serie
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