689 research outputs found
The spatial distribution of cavitation induced acoustic emission, sonoluminescence and cell lysis in the field of a shock wave lithotripter
This study examines the spatial distribution of various properties attributed to the cavitation field generated by a shock wave lithotripter. These properties include acoustic emission and sonoluminescence, which result from violent bubble collapse, and the degree of cell lysis in vitro, which appears to be related to cavitation. The acoustic emission detected with a 1 MHz, 12 cm diameter focused hydrophone occurs in two distinct bursts. The immediate signal is emitted from a small region contained within the 4 MPa peak negative pressure contour. A second, delayed, burst is emitted from a region extending further along the beam axis. The delay between these two bursts has also been mapped, and the longest delay occurs at positions close to the regions of maximum peak negative pressure. Sonoluminescence from both single and multiple shocks occurs in a broader region than the acoustic emission but the measurement technique does not allow time resolution of the signal. Cell lysis occurs in a relatively small region that correlates closely with the immediate acoustic emission for a shock propagating in a gelatine solution
Thermodynamics of non-local materials: extra fluxes and internal powers
The most usual formulation of the Laws of Thermodynamics turns out to be
suitable for local or simple materials, while for non-local systems there are
two different ways: either modify this usual formulation by introducing
suitable extra fluxes or express the Laws of Thermodynamics in terms of
internal powers directly, as we propose in this paper. The first choice is
subject to the criticism that the vector fluxes must be introduced a posteriori
in order to obtain the compatibility with the Laws of Thermodynamics. On the
contrary, the formulation in terms of internal powers is more general, because
it is a priori defined on the basis of the constitutive equations. Besides it
allows to highlight, without ambiguity, the contribution of the internal powers
in the variation of the thermodynamic potentials. Finally, in this paper, we
consider some examples of non-local materials and derive the proper expressions
of their internal powers from the power balance laws.Comment: 16 pages, in press on Continuum Mechanics and Thermodynamic
The Massive Multi-flavor Schwinger Model
QED with N species of massive fermions on a circle of circumference L is
analyzed by bosonization. The problem is reduced to the quantum mechanics of
the 2N fermionic and one gauge field zero modes on the circle, with nontrivial
interactions induced by the chiral anomaly and fermions masses. The solution is
given for N=2 and fermion masses (m) much smaller than the mass of the U(1)
boson with mass \mu=\sqrt{2e^2/\pi} when all fermions satisfy the same boundary
conditions. We show that the two limits m \go 0 and L \go \infty fail to
commute and that the behavior of the theory critically depends on the value of
mL|\cos\onehalf\theta| where \theta is the vacuum angle parameter. When the
volume is large \mu L \gg 1, the fermion condensate is
-(e^{4\gamma} m\mu^2 \cos^4\onehalf\theta/4\pi^3)^{1/3} or $-2e^\gamma m\mu L
\cos^2 \onehalf\theta /\pi^2 for mL(\mu L)^{1/2} |\cos\onehalf\theta| \gg 1 or
\ll 1, respectively. Its correlation function decays algebraically with a
critical exponent \eta=1 when m\cos\onehalf\theta=0.Comment: 16 pages, latex, uses epsf.sty; replaced with latex src
Induced Universal Properties and Deconfinement
We propose a general strategy to determine universal properties induced by a
nearby phase transition on a non-order parameter field. A general
renormalizable Lagrangian is used, which contains the order parameter and a
non-order parameter field, and respects all the symmetries present. We
investigate the case in which the order parameter field depends only on space
coordinates and the case in which this field is also time dependent. We find
that the spatial correlators of the non-order parameter field, in both cases,
are infrared dominated and can be used to determine properties of the phase
transition. We predict a universal behavior for the screening mass of a generic
singlet field, and show how to extract relevant information from such a
quantity. We also demonstrate that the pole mass of the non-order parameter
field is not infrared sensitive. Our results can be applied to any continuous
phase transition. As an example we consider the deconfining transition in pure
Yang-Mills theory, and show that our findings are supported by lattice data.
Our analysis suggests that monitoring the spatial correlators of different
hadron species, more specifically the derivatives of these, provides an
efficient and sufficient way to experimentally uncover the deconfining phase
transition and its features.Comment: Added computational details and improved the text. The results are
unchange
Observers in an accelerated universe
If the current acceleration of our Universe is due to a cosmological
constant, then a Coleman-De Luccia bubble will nucleate in our Universe. In
this work, we consider that our observations could be likely in this framework,
consisting in two infinite spaces, if a foliation by constant mean curvature
hypersurfaces is taken to count the events in the spacetime. Thus, we obtain
and study a particular foliation, which covers the existence of most observers
in our part of spacetime.Comment: revised version, accepted in EPJ
Recommended from our members
Estimates of energy fluence at the focal plane in beams undergoing neutralized drift compression
The authors estimate the energy fluence (energy per unit area) at the focal plane of a beam undergoing neutralized drift compression and neutralized solenoidal final focus, as is being carried out in the Neutralized Drift Compression Experiment (NDCX) at LBNL. In these experiments, in order to reach high beam intensity, the beam is compressed longitudinally by ramping the beam velocity (i.e. introducing a velocity tilt) over the course of the pulse, and the beam is transversely focused in a high field solenoid just before the target. To remove the effects of space charge, the beam drifts in a plasma. The tilt introduces chromatic aberrations, with different slices of the original beam having different radii at the focal plane. The fluence can be calculated by summing the contribution from the various slices. They develop analytic formulae for the energy fluence for beams that have current profiles that are initially constant in time. They compare with envelope and particle-in-cell calculations. The expressions derived are useful for predicting how the fluence scales with accelerator and beam parameters
QED and String Theory
We analyze the D9-D9bar system in type IIB string theory using Dp-brane
probes. It is shown that the world-volume theory of the probe Dp-brane contains
two-dimensional and four-dimensional QED in the cases with p=1 and p=3,
respectively, and some applications of the realization of these well-studied
quantum field theories are discussed. In particular, the two-dimensional QED
(the Schwinger model) is known to be a solvable theory and we can apply the
powerful field theoretical techniques, such as bosonization, to study the
D-brane dynamics. The tachyon field created by the D9-D9bar strings appears as
the fermion mass term in the Schwinger model and the tachyon condensation is
analyzed by using the bosonized description. In the T-dualized picture, we
obtain the potential between a D0-brane and a D8-D8bar pair using the Schwinger
model and we observe that it consists of the energy carried by fundamental
strings created by the Hanany-Witten effect and the vacuum energy due to a
cylinder diagram. The D0-brane is treated quantum mechanically as a particle
trapped in the potential, which turns out to be a system of a harmonic
oscillator.
As another application, we obtain a matrix theory description of QED using
Taylor's T-duality prescription, which is actually applicable to a wide variety
of field theories including the realistic QCD. We show that the lattice gauge
theory is naturally obtained by regularizing the matrix size to be finite.Comment: 33 pages, Latex, 4 figures, a reference adde
Reconstruction of field theory from excitation spectra of defects
We show how to reconstruct a field theory from the spectrum of bound states
on a topological defect. We apply our recipe to the case of kinks in 1+1
dimensions with one or two bound states. Our recipe successfully yields the
sine-Gordon and field theories when suitable bound state
spectra are assumed. The recipe can also be used to globally reconstruct the
inflaton potential of inflationary cosmology if the inflaton produces a
topological defect. We discuss how defects can provide ``smoking gun'' evidence
for a class of inflationary models.Comment: 10 pages, 4 figures. Included proof (Appendix B) that wall
fluctuation potentials have supersymmetric form. Added reference
Staggered versus overlap fermions: a study in the Schwinger model with
We study the scalar condensate and the topological susceptibility for a
continuous range of quark masses in the Schwinger model with
dynamical flavors, using both the overlap and the staggered discretization. At
finite lattice spacing the differences between the two formulations become
rather dramatic near the chiral limit, but they get severely reduced, at the
coupling considered, after a few smearing steps.Comment: 15 pages, 7 figures, v2: 1 ref corrected, minor change
Semileptonic form factors - a model-independent approach
We demonstrate that the B->D(*) l nu form factors can be accurately predicted
given the slope parameter rho^2 of the Isgur-Wise function. Only weak
assumptions, consistent with lattice results, on the wavefunction for the light
degrees of freedom are required to establish this result. We observe that the
QCD and 1/m_Q corrections can be systematically represented by an effective
Isgur-Wise function of shifted slope. This greatly simplifies the analysis of
semileptonic B decay. We also investigate what the available semileptonic data
can tell us about lattice QCD and Heavy Quark Effective Theory. A rigorous
identity relating the form factor slope difference rho_D^2-rho_A1^2 to a
combination of form factor intercepts is found. The identity provides a means
of checking theoretically evaluated intercepts with experiment.Comment: 18 pages, Revtex, 4 postscript figures, uses epsfig.st
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