1,652 research outputs found
Quantum anholonomies in time-dependent Aharonov-Bohm rings
Anholonomies in eigenstates are studied through time-dependent variations of
a magnetic flux in an Aharonov-Bohm ring. The anholonomies in the eigenenergy
and the expectation values of eigenstates are shown to persist beyond the
adiabatic regime. The choice of the gauge of the magnetic flux is shown to be
crucial to clarify the relationship of these anholonomies to the eigenspace
anholonomy, which is described by a non-Abelian connection in the adiabatic
limit.Comment: 6 pages. Fixed typ
On acoustic propagation in three-dimensional rectangular ducts with flexible walls and porous linings
This is the post-print version of the Article. The official published version can be accessed from the links below - Copyright @ 2012 Acoustical Society of AmericaThe focus of this article is toward the development of hybrid analytic-numerical mode-matching methods for model problems involving three-dimensional ducts of rectangular cross-section and with flexible walls. Such methods require first closed form analytic expressions for the natural fluid-structure coupled waveforms that propagate in each duct section and second the corresponding orthogonality relations. It is demonstrated how recent theory [Lawrie, Proc. R. Soc. London, Ser. A 465, 2347–2367 (2009)] may be extended to a wide class of three-dimensional ducts, for example, those with a flexible wall and a porous lining (modeled as an equivalent fluid) or those with a flexible internal structure, such as a membrane (the “drum-like” silencer). Two equivalent expressions for the eigenmodes of a given duct can be formulated. For the ducts considered herein, the first ansatz is dependent on the eigenvalues/eigenfunctions appropriate for wave propagation in the corresponding two-dimensional flexible-walled duct, whereas the second takes the form of a Fourier series. The latter offers two advantages: no “root-finding” is involved and the method is appropriate for ducts in which the flexible wall is orthotropic. The first ansatz, however, provides important information about the orthogonality properties of the three-dimensional eigenmodes
Dual contribution to amplification in the mammalian inner ear
The inner ear achieves a wide dynamic range of responsiveness by mechanically
amplifying weak sounds. The enormous mechanical gain reported for the mammalian
cochlea, which exceeds a factor of 4,000, poses a challenge for theory. Here we
show how such a large gain can result from an interaction between amplification
by low-gain hair bundles and a pressure wave: hair bundles can amplify both
their displacement per locally applied pressure and the pressure wave itself. A
recently proposed ratchet mechanism, in which hair-bundle forces do not feed
back on the pressure wave, delineates the two effects. Our analytical
calculations with a WKB approximation agree with numerical solutions.Comment: 4 pages, 4 figure
Dielectric function of the semiconductor hole liquid: Full frequency and wave vector dependence
We study the dielectric function of the homogeneous semiconductor hole liquid
of p-doped bulk III-V zinc-blende semiconductors within random phase
approximation. The single-particle physics of the hole system is modeled by
Luttinger's four-band Hamiltonian in its spherical approximation. Regarding the
Coulomb-interacting hole liquid, the full dependence of the zero-temperature
dielectric function on wave vector and frequency is explored. The imaginary
part of the dielectric function is analytically obtained in terms of
complicated but fully elementary expressions, while in the result for the real
part nonelementary one-dimensional integrations remain to be performed. The
correctness of these two independent calculations is checked via Kramers-Kronig
relations.
The mass difference between heavy and light holes, along with variations in
the background dielectric constant, leads to dramatic alternations in the
plasmon excitation pattern, and generically, two plasmon branches can be
identified. These findings are the result of the evaluation of the full
dielectric function and are not accessible via a high-frequency expansion. In
the static limit a beating of Friedel oscillations between the Fermi wave
numbers of heavy and light holes occurs.Comment: 16 pages, 11 figures included. Update: Minor additions and
adjustments, published versio
Note on the derivative of the hyperbolic cotangent
In a letter to Nature (Ford G W and O'Connell R F 1996 Nature 380 113) we
presented a formula for the derivative of the hyperbolic cotangent that differs
from the standard one in the literature by an additional term proportional to
the Dirac delta function. Since our letter was necessarily brief, shortly after
its appearance we prepared a more extensive unpublished note giving a detailed
explanation of our argument. Since this note has been referenced in a recent
article (Estrada R and Fulling S A 2002 J. Phys. A: Math. Gen. 35 3079) we
think it appropriate that it now appear in print. We have made no alteration to
the original note
Dielectric function of the semiconductor hole gas
We study the dielectric function of the homogeneous hole gas in p-doped
zinc-blende III-V bulk semiconductors within random phase approximation with
the valence band being modeled by Luttinger's Hamiltonian in the spherical
approximation. In the static limit we find a beating of Friedel oscillations
between the two Fermi momenta for heavy and light holes, while at large
frequencies dramatic corrections to the plasmon dispersion occur.Comment: 4 pages, 1 figure included. Version to appear in Europhys. Let
Design Analysis of Corridors-in-the-Sky
Corridors-in-the-sky or tubes is one of new concepts in dynamic airspace configuration. It accommodates high density traffic, which has similar trajectories. Less air traffic controllers workload is expected than classic airspaces, thus, corridors-in-the-sky may increase national airspace capacity and reduce flight delays. To design corridors-in-the-sky, besides identifying their locations, their utilization, altitudes, and impacts on remaining system need to be analyzed. This paper chooses one tube candidate and presents analyses of spatial and temporal utilization of the tube, the impact on the remaining traffic, and the potential benefit caused by off-loading the traffic from underlying sectors. Fundamental issues regarding to the benefits have been also clarified. Methods developed to assist the analysis are described. Analysis results suggest dynamic tubes in terms of varied utilizations during different time periods. And it is found that combined lane options would be a good choice to lower the impact on non-tube users. Finally, it shows significant reduction of peak aircraft count in underlying sectors with only one tube enabled
Excitation of stellar p-modes by turbulent convection: 1. Theoretical formulation
Stochatic excitation of stellar oscillations by turbulent convection is
investigated and an expression for the power injected into the oscillations by
the turbulent convection of the outer layers is derived which takes into
account excitation through turbulent Reynolds stresses and turbulent entropy
fluctuations. This formulation generalizes results from previous works and is
built so as to enable investigations of various possible spatial and temporal
spectra of stellar turbulent convection. For the Reynolds stress contribution
and assuming the Kolmogorov spectrum we obtain a similar formulation than those
derived by previous authors. The entropy contribution to excitation is found to
originate from the advection of the Eulerian entropy fluctuations by the
turbulent velocity field. Numerical computations in the solar case in a
companion paper indicate that the entropy source term is dominant over Reynold
stress contribution to mode excitation, except at high frequencies.Comment: 14 pages, accepted for publication in A&
The Effect Of Delay Times On The Optimal Velocity Traffic Flow Behavior
We have numerically investigated the effect of the delay times and
of a mixture of fast and slow vehicles on the fundamental diagram of
the optimal velocity model. The optimal velocity function of the fast cars
depends not only on the headway of each car but also on the headway of the
immediately preceding one. It is found that the small delay times have almost
no effects, while, for sufficiently large delay time the current
profile displays qualitatively five different forms depending on ,
and the fractions and of the fast and slow cars
respectively. The velocity (current) exhibits first order transitions at low
and/or high densities, from freely moving phase to the congested state, and
from congested state to the jamming one respectively accompanied by the
existence of a local minimal current. Furthermore, there exist a critical value
of above which the metastability and hysteresis appear. The
spatial-temporal traffic patterns present more complex structur
Dynamics of a disordered, driven zero range process in one dimension
We study a driven zero range process which models a closed system of
attractive particles that hop with site-dependent rates and whose steady state
shows a condensation transition with increasing density. We characterise the
dynamical properties of the mass fluctuations in the steady state in one
dimension both analytically and numerically and show that the transport
properties are anomalous in certain regions of the density-disorder plane. We
also determine the form of the scaling function which describes the growth of
the condensate as a function of time, starting from a uniform density
distribution.Comment: Revtex4, 5 pages including 2 figures; Revised version; To appear in
Phys. Rev. Let
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