13,964 research outputs found
Nonlinear lattice model of viscoelastic Mode III fracture
We study the effect of general nonlinear force laws in viscoelastic lattice
models of fracture, focusing on the existence and stability of steady-state
Mode III cracks. We show that the hysteretic behavior at small driving is very
sensitive to the smoothness of the force law. At large driving, we find a Hopf
bifurcation to a straight crack whose velocity is periodic in time. The
frequency of the unstable bifurcating mode depends on the smoothness of the
potential, but is very close to an exact period-doubling instability. Slightly
above the onset of the instability, the system settles into a exactly
period-doubled state, presumably connected to the aforementioned bifurcation
structure. We explicitly solve for this new state and map out its
velocity-driving relation
Does the continuum theory of dynamic fracture work?
We investigate the validity of the Linear Elastic Fracture Mechanics approach
to dynamic fracture. We first test the predictions in a lattice simulation,
using a formula of Eshelby for the time-dependent Stress Intensity Factor.
Excellent agreement with the theory is found. We then use the same method to
analyze the experiment of Sharon and Fineberg. The data here is not consistent
with the theoretical expectation.Comment: 4 page
The Universal Gaussian in Soliton Tails
We show that in a large class of equations, solitons formed from generic
initial conditions do not have infinitely long exponential tails, but are
truncated by a region of Gaussian decay. This phenomenon makes it possible to
treat solitons as localized, individual objects. For the case of the KdV
equation, we show how the Gaussian decay emerges in the inverse scattering
formalism.Comment: 4 pages, 2 figures, revtex with eps
Perforation of Bowel Associated with Blunt Abdominal Trauma in Children
Motor vehicle accidents remain the commonest cause of abdominal trauma in children, but there are many situations that expose the child more particularly to blunt abdominal trauma. In order to avoid unnecessary delay in diagnosis, a plan of management is proposed, based on our experience with 4 cases of abdominal trauma. The need for early diagnosis is emphasised
A Preliminary Look at the Physics Reach of a Solar Neutrino TPC: Time-Independent Two Neutrino Oscillations
This paper will discuss the physics reach of a solar neutrino TPC containing
many tons of He4 under high pressure. Particular attention is given to the LMA
and SMA solutions, which are allowed by current data, and which are
characterized by a lack of time-dependent phenomena (either summer-winter or
day-night asymmetries). In this case, the physics of neutrino masses and mixing
is all contained in the energy dependence of the electron neutrino survival
probability, (or in its reciprocal, the electron neutrino disappearance
probability).Comment: 19 pages, 12 figure
Arrested Cracks in Nonlinear Lattice Models of Brittle Fracture
We generalize lattice models of brittle fracture to arbitrary nonlinear force
laws and study the existence of arrested semi-infinite cracks. Unlike what is
seen in the discontinuous case studied to date, the range in driving
displacement for which these arrested cracks exist is very small. Also, our
results indicate that small changes in the vicinity of the crack tip can have
an extremely large effect on arrested cracks. Finally, we briefly discuss the
possible relevance of our findings to recent experiments.Comment: submitted to PRE, Rapid Communication
Phase-Field Model of Mode III Dynamic Fracture
We introduce a phenomenological continuum model for mode III dynamic fracture
that is based on the phase-field methodology used extensively to model
interfacial pattern formation. We couple a scalar field, which distinguishes
between ``broken'' and ``unbroken'' states of the system, to the displacement
field in a way that consistently includes both macroscopic elasticity and a
simple rotationally invariant short scale description of breaking. We report
two-dimensional simulations that yield steady-state crack motion in a strip
geometry above the Griffith threshold.Comment: submitted to PR
Quantum network of neutral atom clocks
We propose a protocol for creating a fully entangled GHZ-type state of
neutral atoms in spatially separated optical atomic clocks. In our scheme,
local operations make use of the strong dipole-dipole interaction between
Rydberg excitations, which give rise to fast and reliable quantum operations
involving all atoms in the ensemble. The necessary entanglement between distant
ensembles is mediated by single-photon quantum channels and collectively
enhanced light-matter couplings. These techniques can be used to create the
recently proposed quantum clock network based on neutral atom optical clocks.
We specifically analyze a possible realization of this scheme using neutral Yb
ensembles.Comment: 13 pages, 11 figure
Optical Superradiance from Nuclear Spin Environment of Single Photon Emitters
We show that superradiant optical emission can be observed from the polarized
nuclear spin ensemble surrounding a single photon emitter such as a single
quantum dot (QD) or Nitrogen-Vacancy (NV) center. The superradiant light is
emitted under optical pumping conditions and would be observable with realistic
experimental parameters.Comment: 4+ pages, 3 figures, considerably rewritten, conclusions unchanged,
accepted versio
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