10,020 research outputs found
Dynamic Failure in Amorphous Solids via a Cavitation Instability
The understanding of dynamic failure in amorphous materials via the
propagation of free boundaries like cracks and voids must go beyond elasticity
theory, since plasticity intervenes in a crucial and poorly understood manner
near the moving free boundary. In this Letter we focus on failure via a
cavitation instability in a radially-symmetric stressed material, set up the
free boundary dynamics taking both elasticity and visco-plasticity into
account, using the recently proposed athermal Shear Transformation Zone theory.
We demonstrate the existence (in amorphous systems) of fast cavitation modes
accompanied by extensive plastic deformations and discuss the revealed physics.Comment: 4 pages, 4 figure
Conductance Characteristics between a Normal Metal and a Superconductor Carrying a Supercurrent
The low-temperature conductance (G) characteristics between a normal metal
and a clean superconductor (S) carrying a supercurrent parallel to the
interface is theoretically investigated. Increasing causes lowering and
broadening of (1) coherence peaks of s-wave S, and d-wave S at (100) contact,
(2) midgap-states-induced zero-bias conductance peak for d-wave S at (110)
contact, and (3) Andreev-reflection-induced enhancement of within the gap
near the metallic-contact limit. Novel features found include a current-induced
central peak and a three-humped structure at intermediate barrier strength,
etc.Comment: 4 pages, 4 figure
Analysis of Clumps in Molecular Cloud Models: Mass Spectrum, Shapes, Alignment and Rotation
Observations reveal concentrations of molecular line emission on the sky,
called ``clumps,'' in dense, star-forming molecular clouds. These clumps are
believed to be the eventual sites of star formation. We study the
three-dimensional analogs of clumps using a set of self-consistent,
time-dependent numerical models of molecular clouds. The models follow the
decay of initially supersonic turbulence in an isothermal, self-gravitating,
magnetized fluid. We find the following. (1) Clumps are intrinsically triaxial.
This explains the observed deficit of clumps with a projected axis ratio near
unity, and the apparent prolateness of clumps. (2) Simulated clump axes are not
strongly aligned with the mean magnetic field within clumps, nor with the
large-scale mean fields. This is in agreement with observations. (3) The clump
mass spectrum has a high-mass slope that is consistent with the Salpeter value.
There is a low-mass break in the slope at \sim 0.5 \msun, although this may
depend on model parameters including numerical resolution. (4) The typical
specific spin angular momentum of clumps is . This is larger than the median specific angular momentum of binary
stars. Scaling arguments suggest that higher resolution simulations may soon be
able to resolve the scales at which the angular momentum of binary stars is
determined.Comment: 14 pages, 13 figures, to appear in 2003 July 20 Ap
Advances in cellular and molecular predatory biology of Bdellovibrio bacteriovorus six decades after discovery
Since its discovery six decades ago, the predatory bacterium Bdellovibrio bacteriovorus has sparked recent interest as a potential remedy to the antibiotic resistance crisis. Here we give a comprehensive historical overview from discovery to progressive developments in microscopy and molecular mechanisms. Research on B. bacteriovorus has moved from curiosity to a new model organism, revealing over time more details on its physiology and fascinating predatory life cycle with the help of a variety of methods. Based on recent findings in cryo-electron tomography, we recapitulate on the intricate molecular details known in the predatory life cycle including how this predator searches for its prey bacterium, to how it attaches, grows, and divides all from within the prey cell. Finally, the newly developed B. bacteriovorus progeny leave the prey cell remnants in the exit phase. While we end with some unanswered questions remaining in the field, new imaging technologies and quantitative, systematic advances will likely help to unravel them in the next decades
Taking Stock: A report from the UK Teacher Education Network for sustainable development (ESD) /global citizenship (GC) - survey on provision for ESD/GC in initial teacher education in the UK
In 2009-10, the UK Teacher Education (TE) Network for Education for Sustainable Development and Global Citizenship (ESDGC) developed and implemented anemail survey to explore how teacher educators approach ESDGC in their courseprovision. The survey aimed to establish the pattern of Teacher Educationprovision for sustainable development/global citizenship across the UK in primaryand secondary so as to work with colleagues to support and develop provision in amore consistent form. It was sent to all Heads of Education in all English highereducation providers and to named contacts in Scotland, Northern Ireland andWales. It was also sent to all School - Centred Initial Teacher Training (SCITTs).By June 2010, 32 responses had been received from 27 providers. Researchers atthe Development Education Research Centre (DERC) were commissioned to workwith the Network Management Team at the Centre for Cross Curricular Initiatives(CCCI) to analyse the data and produce this report
Non-Markovian Fermionic Stochastic Schr\"{o}dinger Equation for Open System Dynamics
In this paper we present an exact Grassmann stochastic Schr\"{o}dinger
equation for the dynamics of an open fermionic quantum system coupled to a
reservoir consisting of a finite or infinite number of fermions. We use this
stochastic approach to derive the exact master equation for a fermionic system
strongly coupled to electronic reservoirs. The generality and applicability of
this Grassmann stochastic approach is justified and exemplified by several
quantum open system problems concerning quantum decoherence and quantum
transport for both vacuum and finite-temperature fermionic reservoirs. We show
that the quantum coherence property of the quantum dot system can be profoundly
modified by the environment memory.Comment: 10.5 pages, 3 figure
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