714 research outputs found
Phase Diagrams for Sonoluminescing Bubbles
Sound driven gas bubbles in water can emit light pulses. This phenomenon is
called sonoluminescence (SL). Two different phases of single bubble SL have
been proposed: diffusively stable and diffusively unstable SL. We present phase
diagrams in the gas concentration vs forcing pressure state space and also in
the ambient radius vs gas concentration and vs forcing pressure state spaces.
These phase diagrams are based on the thresholds for energy focusing in the
bubble and two kinds of instabilities, namely (i) shape instabilities and (ii)
diffusive instabilities. Stable SL only occurs in a tiny parameter window of
large forcing pressure amplitude atm and low gas
concentration of less than of the saturation. The upper concentration
threshold becomes smaller with increasing forcing. Our results quantitatively
agree with experimental results of Putterman's UCLA group on argon, but not on
air. However, air bubbles and other gas mixtures can also successfully be
treated in this approach if in addition (iii) chemical instabilities are
considered. -- All statements are based on the Rayleigh-Plesset ODE
approximation of the bubble dynamics, extended in an adiabatic approximation to
include mass diffusion effects. This approximation is the only way to explore
considerable portions of parameter space, as solving the full PDEs is
numerically too expensive. Therefore, we checked the adiabatic approximation by
comparison with the full numerical solution of the advection diffusion PDE and
find good agreement.Comment: Phys. Fluids, in press; latex; 46 pages, 16 eps-figures, small
figures tarred and gzipped and uuencoded; large ones replaced by dummies;
full version can by obtained from: http://staff-www.uni-marburg.de/~lohse
Fusion yield: Guderley model and Tsallis statistics
The reaction rate probability integral is extended from Maxwell-Boltzmann
approach to a more general approach by using the pathway model introduced by
Mathai [Mathai A.M.:2005, A pathway to matrix-variate gamma and normal
densities, Linear Algebra and Its Applications}, 396, 317-328]. The extended
thermonuclear reaction rate is obtained in closed form via a Meijer's
G-function and the so obtained G-function is represented as a solution of a
homogeneous linear differential equation. A physical model for the
hydrodynamical process in a fusion plasma compressed and laser-driven spherical
shock wave is used for evaluating the fusion energy integral by integrating the
extended thermonuclear reaction rate integral over the temperature. The result
obtained is compared with the standard fusion yield obtained by Haubold and
John in 1981.[Haubold, H.J. and John, R.W.:1981, Analytical representation of
the thermonuclear reaction rate and fusion energy production in a spherical
plasma shock wave, Plasma Physics, 23, 399-411]. An interpretation for the
pathway parameter is also given.Comment: 17 pages, LaTe
Music listening in relation to recommended daily noise exposure dose and hearing problems using personal listening devices in adolescents and young adults
Objective: This systematic review aimed to explore the evidence on whether the preferred listening levels (PLLs) and durations of music listening through personal listening devices (PLDs) in adolescents and young adults exceed the current recommended 100% daily noise dose; together with the impact on hearing and possible influential factors of such listening behaviours. Design: A systematic search was conducted using multiple online bibliographic databases. Study sample: The 26 studies were included on the basis of the inclusion and exclusion criteria. Results: The results showed that up to 58.2% of participants exceeded the 100% daily noise dose, particularly in the presence of background noise. Significantly positive correlations were found among background noise levels and mean PLLs, as well as the proportion of participants exceeding the 100% daily noise dose. Moreover, significantly worse hearing thresholds were found in PLD users using audiometry, and significantly poor results in otoacoustic emission (OAE), even in the participants with self-reported ‘normal hearing’. Conclusion: It is crucial to develop appropriate standards and safe recommendations for daily music exposure dose in future studies. Providing an essential guide and effective education to adolescents and young adults will help raise awareness, increase knowledge, and consequently change attitudes and listening habits
Closing the gap in the solutions of the strong explosion problem: An expansion of the family of second-type self-similar solutions
Shock waves driven by the release of energy at the center of a cold ideal gas
sphere of initial density rho\propto r^{-omega} approach a self-similar (SLS)
behavior, with velocity \dot{R}\propto R^delta, as R->\infty. For omega>3 the
solutions are of the second-type, i.e., delta is determined by the requirement
that the flow should include a sonic point. No solution satisfying this
requirement exists, however, in the 3\leq omega\leq omega_{g}(gamma) ``gap''
(\omega_{g}=3.26 for adiabatic index gamma=5/3). We argue that second-type
solutions should not be required in general to include a sonic point. Rather,
it is sufficient to require the existence of a characteristic line r_c(t), such
that the energy in the region r_c(t)\infty,
and an asymptotic solution given by the SLS solution at r_c(t)<r<R and
deviating from it at r<r_c may be constructed. The two requirements coincide
for omega>omega_g and the latter identifies delta=0 solutions as the asymptotic
solutions for 3\leq omega\leq omega_{g} (as suggested by Gruzinov03). In these
solutions, r_c is a C_0 characteristic. It is difficult to check, using
numerical solutions of the hydrodynamic equations, whether the flow indeed
approaches a delta=0 SLS behavior as R->\infty, due to the slow convergence to
SLS for omega~3. We show that in this case the flow may be described by a
modified SLS solution, d\ln\dot{R}/d\ln R=delta with slowly varying delta(R),
eta\equiv d delta/d\ln R<<1, and spatial profiles given by a sum of the SLS
solution corresponding to the instantaneous value of delta and a SLS correction
linear in eta. The modified SLS solutions provide an excellent approximation to
numerical solutions obtained for omega~3 at large R, with delta->0 (and
eta\neq0) for 3\leq omega\leq omega_{g}. (abridged)Comment: 10 pages, 11 figures, somewhat revised, version accepted to Ap
The Self-Regulated Winds of Long Period Variable Stars
Numerical models of the extended atmospheres of long period variable or Mira
stars have shown that their winds have a very simple, power law structure when
averaged over the pulsation cycle. This structure is stable and robust despite
the pulsational wave disturbances, and appears to be strongly self-regulated.
Observational studies support these conclusions. The models also show that
dust-free winds are nearly adiabatic, with little heating or cooling. The
classical, steady, adiabatic wind solution to the hydrodynamic equations fails
to account for an extensive region of nearly constant outflow velocity. We
investigate analytic solutions which include the effects of wave pressure,
heating, and the resulting entropy changes. Wave pressure is represented by a
term like that in the Reynolds turbulence equation for the mean velocity.
Although the pressure from individual waves is modest, the waves are likely the
primary agent of self-regulation of dust-free winds. In models of dusty winds,
the gas variables also adopt a power law dependence on radius. Heating is
required at all radii to maintain this flow, and grain heating and heat
transfer to the gas are significant. Both hydrodynamic and gas/grain thermal
feedbacks transform the flow towards self-regulated forms. (Abridged)Comment: 14 pgs., 3 figures, accepted for MNRAS, 200
Disturbance of Social Hierarchy by an Invasive Species: A Gene Transcription Study
BACKGROUND: Ecological and evolutionary changes in native populations facing invasion by exotic species are increasingly reported. Recently, it has been shown that competition with exotic rainbow trout (Oncorhynchus mykiss) disrupts dominance hierarchies within groups of native Atlantic salmon (Salmo salar). The genetic and molecular actors underlying phenotypic plasticity are poorly understood. METHODOLOGY: Here, we aimed at identifying the genetic and molecular actors contributing to this plastic loss of dominance hierarchies as well as at identifying genes implicated in behaviours related to social dominance. By using microarrays, we compared the genome-wide gene transcription profiles in brains of dominant versus subordinate juvenile Atlantic salmon in presence or absence of a competitive rainbow trout. PRINCIPAL FINDINGS: Adding the trout competitor resulted in dominant and subordinate salmon being more similar, both behaviourally and at the level of brain gene transcription patterns. Genes for which transcription levels differed between dominant and subordinate salmon in the absence of exotic trout were mainly over-expressed in dominant salmon and included genes implicated in protein turnover, neuronal structural change and oxygen transport. CONCLUSIONS/SIGNIFICANCE: Our study provides one of the few examples demonstrating a close interplay between behavioural plasticity and gene transcription, therefore contributing to the understanding of the molecular mechanisms underlying these processes in an ecologically relevant context
Direct Visualization of Laser-Driven Focusing Shock Waves
Cylindrically or spherically focusing shock waves have been of keen interest
for the past several decades. In addition to fundamental study of materials
under extreme conditions, cavitation, and sonoluminescence, focusing shock
waves enable myriad applications including hypervelocity launchers, synthesis
of new materials, production of high-temperature and high-density plasma
fields, and a variety of medical therapies. Applications in controlled
thermonuclear fusion and in the study of the conditions reached in laser fusion
are also of current interest. Here we report on a method for direct real-time
visualization and measurement of laser-driven shock generation, propagation,
and 2D focusing in a sample. The 2D focusing of the shock front is the
consequence of spatial shaping of the laser shock generation pulse into a ring
pattern. A substantial increase of the pressure at the convergence of the
acoustic shock front is observed experimentally and simulated numerically.
Single-shot acquisitions using a streak camera reveal that at the convergence
of the shock wave in liquid water the supersonic speed reaches Mach 6,
corresponding to the multiple gigapascal pressure range 30 GPa
Temperature acclimatisation of swimming performance in the European Queen Scallop
The phenotypic plasticity of muscle performance and locomotory physiology allows the maintenance of essential activity capacity in the face of environmental change, and has been demonstrated in a wide phylogenetic range of eurythermal vertebrates. This study used the scallop, Aequipecten opercularis, as a model eurythermal invertebrate. Animals caught in different seasons demonstrated marked differences in their swimming performance and the relationship between, temperature and performance. When stimulated to swim at natural ranges of temperature, Winter (cold acclimatised), animals accelerated faster than autumn collected animals swimming at the same temperature (x 2 at 11degreesC) and attained higher velocities during jetting. The effects of acclimatisation were confined to the jetting phase and may be a mechanism for the maintenance of acceleration during predator-prey interactions. This is the first demonstration of the thermal acclimatisation of muscle performance in a mollusc and one of very few studies in invertebrates
Observation of critical phenomena and self-similarity in the gravitational collapse of radiation fluid
We observe critical phenomena in spherical collapse of radiation fluid. A
sequence of spacetimes is numerically computed, containing
models () that adiabatically disperse and models () that
form a black hole. Near the critical point (), evolutions develop a
self-similar region within which collapse is balanced by a strong,
inward-moving rarefaction wave that holds constant as a function of a
self-similar coordinate . The self-similar solution is known and we show
near-critical evolutions asymptotically approaching it. A critical exponent
is found for supercritical () models.Comment: 10 pages (LaTeX) (to appear in Phys. Rev. Lett.), TAR-039-UN
Self-similar imploding relativistic shock waves
Self-similar solutions to the problem of a strong imploding relativistic
shock wave are calculated. These solutions represent the relativistic
generalisation of the Newtonian Gouderley-Landau-Stanyukovich problem of a
strong imploding spherical shock wave converging to a centre. The solutions are
found assuming that the pre-shocked flow has a uniform density, and are
accurate for sufficiently large times after the formation of the shock wave.Comment: 22 pages, 4 figures. Minor corrections and a discussion of the
singular C_ characteristic added. Accepted for publication in Physics of
Fluid
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