774 research outputs found
Sound radiation of 3 MHz driven gas bubbles
The sound radiation of 3 MHz acoustically driven air bubbles in liquid is
analysed with respect to possible applications in second harmonic ultrasound
diagnostics devices, which have recently come into clinical use. In the forcing
pressure amplitude P_a = 1-10 atm and ambient radius R_0 = 0.5-5 \mu m
parameter domain a narrow regime around the resonance radius R_0 \sim 1-1.5 \mu
m and relatively modest P_a \sim 2-2.5 atm is identified in which optimal sound
yield in the second harmonic is achieved while maintaining spherical stability
of the bubble. For smaller P_a and larger R_0 hardly any sound is radiated; for
larger P_a bubbles become unstable towards non-spherical shape oscillations of
their surface. The computation of these instabilities is essential for the
evaluation of the optimal parameter regime. A region of slightly smaller R_0
and P_a \sim 1-3 atm is best suited to achieve large ratios of the second
harmonic to the fundamental intensity. Spherical stability is guaranteed in the
suggested regimes for liquids with an enhanced viscosity compared to water,
such as blood.Comment: 19 pages, 10 low resolution ps-figures; higher resolution figures can
be retrieved from http://staff-www.uni-marburg.de/~hilgenfe/hires.htm
Analysis of Rayleigh-Plesset dynamics for sonoluminescing bubbles
Recent work on single bubble sonoluminescence (SBSL) has shown that many
features of this phenomenon, especially the dependence of SBSL intensity and
stability on experimental parameters, can be explained within a hydrodynamic
approach. More specifically, many important properties can already be derived
from an analysis of bubble wall dynamics. This dynamics is conveniently
described by the Rayleigh-Plesset (RP) equation. In this work we derive
analytical approximations for RP dynamics and subsequent analytical laws for
parameter dependences. These results include (i) an expression for the onset
threshold of SL, (ii) an analytical explanation of the transition from
diffusively unstable to stable equilibria for the bubble ambient radius
(unstable and stable sonoluminescence), and (iii) a detailed understanding of
the resonance structure of the RP equation. It is found that the threshold for
SL emission is shifted to larger bubble radii and larger driving pressures if
surface tension is enlarged, whereas even a considerable change in liquid
viscosity leaves this threshold virtually unaltered. As an enhanced viscosity
stabilizes the bubbles against surface oscillations, we conclude that the ideal
liquid for violently collapsing, surface stable SL bubbles should have small
surface tension and large viscosity, although too large viscosity (>40 times
the viscosity of water) will again preclude collapses.Comment: 41 pages, 21 eps and ps figures; LaTeX stylefiles replaced because
the PostScript file produced at the archive had misplaced and misscaled
figure
Apoptosis of moving, non-orthogonal basis functions in many-particle quantum dynamics
Due to the exponential increase of the numerical effort with the number of
degrees of freedom, moving basis functions have a long history in quantum
dynamics. In addition, spawning of new basis functions is routinely applied.
Here we advocate the opposite process: the programmed removal of motional
freedom of selected basis functions. This is a necessity for converged
numerical results with respect to the size of a non-orthogonal basis, because
generically two or more states approach each other too closely early on,
rendering unstable the matrix inversion, required to make the equations of
motion explicit. Applications to the sub-Ohmic spin-boson model as well as to
polaron dynamics in a Holstein molecular crystal model demonstrate the power of
the proposed methodology.Comment: 10 pages, 6 figure
Implementation of an Integrated Thermal Building Model for Investigations of Heat Flows
A model of the building heating system, consisting of energy source, a distributed automatic control system, elements of individual heating unit and heating system is designed. Application Simulink of mathematical package Matlab is selected as a platform for the model. There are the specialized application Simscape libraries in aggregate with a wide range of Matlab mathematical tools allow to apply the "acausal" modeling concept. Implementation the "physical" representation of the object model gave improving the accuracy of the models
Modification of aluminum alloy surface properties by wave-long laser texturing
Change of the static contact angle (SCA) of 10 [mu]L distilled water droplet on laser textured aluminium alloy (AMG-6) substrates was studied. The texture was deposited by a laser system based on a fiber laser. An increase in the power of laser radiation is found to lead to a decrease in the SCA measured on the first day after texturing. Change of dispersion and polar surface energy components of textured substrates is determined. Under the influence of the environment, the surface properties of AMG-6 change with time. SCA increased and reached stable state on the twentieth day after texturing
Bitemporal Support for Business Process Contingency Management
Modern organisations are increasingly moving from traditional monolithic business systems to environments where more and more tasks are outsourced to third party providers. Therefore, processes must operate in an open and dynamic environment in which the management of time plays a crucial role. Handling time, however, remains a challenging issue yet to be fully addressed. Traditional processing systems only consider business events in a single time dimension, but are unable to handle bitemporal events: events in two time dimensions. Recently, backend systems have started to provide increased support for handling
bitemporal events, but these enhanced capabilities have not been carried through to business process management systems. In this paper, we consider the possible relationships that exist between bitemporal properties
of events and we show how these relationships affect a business process. In addition, we demonstrate how bitemporal events can be handled to prevent certain undesired effects on the business process
Exploring systemic RNA interference in insects: a genome-wide survey for RNAi genes in Tribolium
Tribolium resembles C. elegans in showing a robust systemic RNAi response, but does not have C. elegans-type RNAi mechanisms; insect systemic RNAi probably uses a different mechanism
Glueball-Like Screening Masses in Pure SU(3) at Finite Temperatures
We investigate the finite-temperature excitation spectrum in the gluon sector
of pure gauge theory through measurements of screening masses in
correlations of loop operators. We develop the classification of such operators
under the symmetry group of the `-slice'. In the confined phase of the
theory, we find that the spectrum dynamically realises the zero temperature
symmetries. We observe a large thermal shift of the glueball mass. In
the deconfined phase, the spectrum distinguishes between operators coupling to
electrically and magnetically polarised gluon fields. The former yields a
screening mass equal to the Wilson-line screening mass; the latter, a method
for the measurement of the magnetic mass in the high-temperature limit.Comment: 20 pages, LaTeX file, no figures or macros. HLRZ 61/93, BI-TP 93/49,
FSU-SCRI-93-10
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