共查询到20条相似文献,搜索用时 15 毫秒
1.
Summary The diffraction of a spherical acoustic wave from the juncture of pressure release (soft) and locally reacting (absorbing)
half-planes in a fluid moving at subsonic velocity is examined. This consideration is important because the point sources
are regarded as better substitutes for real sources than line sources/plane waves. The integral representation of the field
is obtained using integral transforms and the Wiener-Hopf technique. The factorization of the kernel function in the Wiener-Hopf
functional equation is accomplished. The analytic solution of the integrals is obtained by employing asymptotic methods and
the far field is presented. The effect of the Mach number is shown explicitly on the diffracted field. 相似文献
2.
A three-dimensional (3D) spherical acoustic cloak is designed using an acoustic layered system, which can hide an object from
the detection of acoustic wave in arbitrary direction. The cloak is constructed from multilayered concentric spherical shells
filled with homogeneous isotropic materials. Based on spherical wave expansion method, we confirm that significant low-reflection,
acoustic-shadow-reducing, and wavefront-bending effects in 3D space can be achieved by the proposed cloak. The angle distribution
of the scattered wave is further evaluated by the far-field scattering pattern. In addition, the cloak is demonstrated to
work efficiently in a wide bandwidth in which the cloaking efficiency decreases with increasing frequency. This study may
be helpful to design high-performance 3D acoustic cloaks for broadband acoustic waves in all incidence directions. 相似文献
3.
Summary A time domain numerical procedure is presented for a simulation of acoustic-wave phenomena. The technique is an adaptation
of the finite-difference time domain (FDTD) approach usually applied to model electromagnetic waves. Simple illustrations
of propagation in a nondissipative, infinite, homogeneous medium are provided. In scattering by a soft target the interior
fields show that for an acoustically denser target the wave penetrates the target with a magnitude greater than the incident-wave
amplitude. Also, the interior acoustic pressure field consists of a pair of high-pressure bands sandwiching a low-pressure
band. 相似文献
4.
Acoustic plane progressive waves incident on a sphere immersed in a nonviscous fluid exert a steady force acting along the
direction of wave motion. It is shown here that when an elastic gold sphere is coated with a polymer-type (polyethylene) viscoelastic
layer, this force becomes a force of attraction in the long wavelength limit. Kinetic, potential and Reynolds stress energy
densities are defined and evaluated with and in the absence of absorption in the layer. Without absorption, the mechanical
energy density counteracts the Reynolds stress energy density, which causes a repulsive force. However, in the case of absorption,
the attractive force is predicted to be a physical consequence of a mutual contribution of both the mechanical and the Reynolds
stress energy densities. This condition provides an impetus for further designing acoustic tweezers operating with plane progressive
waves as well as fabricating polymer-coated gold particles for specific biophysical and biomedical applications. 相似文献
5.
Dao-Jun Liu Ying-Li Zhang Xin-Zhou Li 《The European Physical Journal C - Particles and Fields》2009,60(3):495-500
We generalize the field theory of the global monopole to the Dirac–Born–Infeld (DBI) field and investigate the gravitational
property of a DBI global monopole in four-dimensional spherically symmetric spacetime. The coupled equations for the metric
and the DBI scalar field are solved asymptotically and numerically. It is found that, just as for a canonical global monopole,
the gravitational effect of the DBI global monopole is equivalent to that of a deficit solid angle in the metric plus a negative
mass at the origin. However, compared with a canonical global monopole, for the same false vacuum and symmetry-breaking scale,
a DBI global monopole has a relatively smaller core and a larger absolute value of effective mass. Thus, it can yield a larger
deflect angle when the light is passing by. Especially, when the scale of the warp factor is small enough, the effective mass
of a DBI global monopole does not depend apparently on the value of the false vacuum, which is qualitatively different from
that of a canonical global monopole. 相似文献
6.
Güneş Tanir Niyazi Meriç Hüseyin Aytekin Şeref Okuducu 《Czechoslovak Journal of Physics》2004,54(9):941-946
In the dating studies of old samples using the Infrared Stimulated Luminescence (IRSL), the validity of the curve-fitting
employed is of critical importance. So, in this study, a new fitting procedure was suggested for obtaining the age of the
old geological sample. IRSL technique was applied using multiple-aliquot procedure to feldspar isolated from sample. The paleodose
results obtained, using linear and polynomial fitting, were (67.98±2) Gy, (30.49±2) Gy and 322.03 Gy from the suggested fitting
procedure. After application of this procedure the age was found to be 551.4 ka.
This work was supported by Karaelmas University under the project numbered 98-101-009-01. 相似文献
7.
Absorption of an acoustic wave in a colloidal solution via two mechanisms: due to viscous friction in the liquid and due to energy dissipation on nanoparticles is studied. The dependence of the imaginary part of the wave vector on the frequency is estimated in both cases. It is shown that in typical colloidal solutions, the first absorption mechanism dominates at low frequencies, and the second one, at higher, ultrasonic frequencies. 相似文献
8.
The so-called anticlassical approximation for solutions of the radial Schrödinger equation with rapidly varying potentialsU(r) for which ¦(kU)–1
dU/dr¦ 1 is worked out. With the diffuseness as a small parameter and using the method of matched asymptotic expansions the regular and irregular wave functions for the Woods-Saxon potential well with Coulomb and centrifugal barrier are obtained. The penetration factor and the reduced width are also deduced and used to express the resonance width.Communicated by X. Campi 相似文献
9.
N. Combe J. R. Huntzinger J. Morillo 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,68(1):47-58
We theoretically study the propagation of sound waves in GaAs/AlAs superlattices focusing on periodic modes in the vicinity
of the band gaps. Based on analytical and numerical calculations, we show that these modes are the product of a quickly oscillating
function times a slowly varying envelope function. We carefully study the phase of the envelope function compared to the surface
of a semi-infinite superlattice. Especially, the dephasing of the superlattice compared to its surface is a key parameter.
We exhibit two kind of modes: Surface Avoiding and Surface Loving Modes whose envelope functions have their minima and respectively
maxima in the vicinity of the surface. We finally consider the observability of such modes. While Surface Avoiding Modes have
experimentally been observed [Phys. Rev. Lett. 97, 1224301 (2006)], we show that Surface Loving Modes are likely to be observable and we discuss the achievement of such experiments.
The proposed approach could be easily transposed to other types of wave propagation in unidimensional semi-infinite periodic
structures as photonic Bragg mirror. 相似文献
10.
Wei Liao 《The European Physical Journal C - Particles and Fields》2008,57(4):763-768
We consider the non-standard matter effect in flavor conversion of neutrinos crossing the core of the Earth. We show that
oscillations of core-crossing neutrinos with E≳0.5 GeV can well be described by first order perturbation theory. We show that due to the non-standard matter effect a varying
chemical composition in the Earth can modify the neutrino flavor conversion by 100%. The effects of CP violating phases in
non-standard neutral current interactions are emphasized in particular. 相似文献
11.
12.
S. A. Bass C. Hartnack H. Stöcker W. Greiner 《Zeitschrift für Physik A Hadrons and Nuclei》1995,352(2):171-174
We present a microscopic calculation of neutronsqueeze-out in relativistic heavy ion collisions at beam energies betweeen 400 and 1000 MeV/nucleon. After demonstrating the importance of the correct isospin treatment for the neutron to proton ratio, our main emphasis is put on the investigation of the properties of neutronsqueeze-out. Thesqueeze-out ratio increases monotonously with the transverse momentum of the neutrons. This ratio is independent of the incident beam energy if plotted versusp
t
/p
proj
. Most importantly, we observe a strong dependence on the nuclear equation of state and momentum dependent interaction.Supported by GSI, BMFT and DFG 相似文献
13.
The measurement of fast protons and neutrons emitted after antiproton annihilation at rest on238U and63Cu reveals a large neutron/proton ratioR. Its value for63Cu is larger than expected from the conventional model of intranuclear pion rescattering. A value ofR essentially constant over the whole range of mass number, from12C up to238U, is also announced by the experimentalists. It is shown that, on the contrary, the conventional scheme predicts a regular increase ofR with mass number. Alternative explanations of the effect are looked for. Within the usual scheme, an excess of negative pions, leading to more emitted neutrons, is not compatible with final pion multiplicities. The influence of meson resonances on the neutron/proton ratio is considered, as well as the possible occurrence of annihilations on two nucleons. They cannot warrant an increase ofR at low mass targets sufficient to explain a constant value over the whole range of target masses. 相似文献
14.
Stefan Gmuca 《Zeitschrift für Physik A Hadrons and Nuclei》1992,342(4):387-392
The results of the modern relativistic Dirac-Brueckner calculations of nuclear matter are parametrized in terms of the relativistic- mean-field theory with scalar and vector nonlinear selfinteractions. It is shown that the inclusion of the isoscalar vector-meson quartic selfinteraction is essential for obtaining a proper density dependence of the vector potential in the mean-field model. The obtained mean-field parameters represent a simple parametrization of effective interaction in nuclear matter. This interaction may be used in the mean-field studies of the structure of finite nuclei without the introduction of additional free parameters.This work was supported in part by the Grant Agency of the Slovak Academy of Sciences under Grant No. GA SAV-517/1991. 相似文献
15.
Toluene laser-induced fluorescence (LIF) emission spectra were acquired in an optical engine with excitation at 248 nm. Toluene
was homogeneously seeded in pure nitrogen and air which were used as intake gases. Data were acquired during the compression
phase without ignition leading to simultaneous increases in temperature and pressure from 20°C and 1 bar to 500°C and 23.6 bar.
Compared to LIF emission spectra at high temperature and atmospheric pressure reported in the literature, the toluene-LIF
emission signal shifts to longer wavelengths when temperature and pressure increase simultaneously, whereas the spectrally
integrated emission intensity is slightly affected by the pressure level. 相似文献
16.
M. Kutschera 《Zeitschrift für Physik A Hadrons and Nuclei》1994,348(4):263-265
There exists profound discrepancy in the high density behaviour of the nuclear symmetry energy obtained in realistic variational many-body (VMB) calculations and in relativistic mean-field (RMF) calculations. While the symmetry energy decreases to negative values in the former approach it increases monotonically in the latter one. The origin of this discrepancy is discussed and it is argued that VMB prediction is more reliable. It is shown that vanishing of the symmetry energy implies proton-neutron separation instability in dense matter.This work was partially supported by KBN grants 2 0204 91 01 and 2 0054 91 01. 相似文献
17.
Z. Y. Pan R. S. Rawat J. J. Lin T. Zhang P. Lee T. L. Tan S. V. Springham 《Applied Physics A: Materials Science & Processing》2009,96(4):1027-1033
The effects of the different number (1, 2 and 3) of H+ ion irradiation shots on pulsed laser deposited FePt thin films, using pulsed plasma focus device, are investigated. The
FePt thin films were exposed to energetic H+ ions in a plasma focus device at a fixed distance of 4 cm from the top of central electrode. It was deduced that single shot
ion irradiation based transient thermal treatment induces an effect similar to the conventional annealing at 400°C. Well-separated
nanoparticles are formed, and the significant enhancement of the coercivity, by about two orders of magnitude, at a lower
annealing temperature of 400°C has been observed in the single shot ion irradiated samples. The increase of plasma focus ion
irradiation shots lead to the amorphorization in irradiated FePt samples due to excessive energy transfer causing more defects
and lattice distortion, and a decreasing coercivity trend in irradiated and annealed samples are observed due to reduction
in the texture coefficient of magnetic easy axis (001) orientation fct phase. 相似文献
18.
V. N. Fetisov L. Majling J. Žofka R. A. Eramzhyan 《Zeitschrift für Physik A Hadrons and Nuclei》1991,339(3):399-407
A new set of the shell-model two-particle potential parameters,S
,S
N
andT forp-shell hypernuclei is proposed. The set is consistent with the available data on the excited levels of
7
Li,
9
Be,
10
B,
12
B and
p
O. The classification of low lying states and-transitions in the 1p-shell hypernuclei is discussed in terms of the {s
4
p
n*s
:JT} configurations. The feasibility for the excited bound states and for the-transitions to be observed in the spin-flip and non spin-flip single-nucleon reactions is examined in detail.The authors are indebted to R.E. Chrien for information on the experimental results [21] before publication. 相似文献
19.
In this paper, we consider dense stars with configurations expected from the SU(3)C×SU(2)W× U(1) standard model of strong and electroweak interactions. Following a recent suggestion that strange matter, a form of (uds) quark matter, may be the true ground state of hadronic matter, we investigate the prospect for the existence of dense stars consisting partially, or entirely, of strange matter by comparing the relative stability between neutron matter and strange matter. It is found that the restriction on the maximum star mass holds in all cases, including a pure strange star, a pure neutron star, and a neutron star with a quark core. It is also found that the choice of both the bag constantB and the strong coupling constant s has a decisive effect on the relative stability between strange matter and neutron matter. For currently accepted values of (B, s), anA= dense starcannot consist entirely,nor partially, of strange matter. Nevertheless, such conclusion may be subject to change if corrections ofO (
s
2
) or other effects are taken into account. Finally, we use the framework of Tolman, Oppenheimer, and Volkoff to analyze two cases of boson stars: gluon stars and stars consisting of massive scalar particles (massive bosons). It is found that, in the case of gluon stars, the presence of the bag constant in the QCD vacuum yields results very similar to that found in quark stars. On the other hand, soliton stars consisting of massive bosons exist if there is some background pressure which plays the role similar to the bag constant for lowering the matter pressure. The stability problem for both gluon stars and soliton stars is briefly discussed. 相似文献
20.
Fabrizio Nesti 《The European Physical Journal C - Particles and Fields》2009,59(3):723-729
It is shown how the Lorentz and standard-model gauge groups can be unified by using algebraic spinors of the standard four-dimensional
Clifford algebra, in left–right symmetric fashion. This defines a framework of unification with gravity and generates exactly
a standard-model family of fermions, while a Pati–Salam unification group emerges, at the Planck scale, where (chiral) gravity
decouples. We show that this low-energy broken phase emerges from the VEV of extended vierbein fields, which at this stage
are assumed to be dynamically generated from a theory in the fully symmetric phase valid beyond the Planck scale (and whose
consistency and dynamics is thus yet to be assessed) providing thus a geometrical and group-theoretical framework for the
unification and breaking. At low energy, on the other hand, it is intriguing to find, as a remnant of this unification, new
isospin-triplet spin-two particles that may naturally lie at the weak scale, providing a striking signal at the LHC. 相似文献