17,272 research outputs found
Semiquantum key distribution using entangled states
Recently, Boyer et al. presented a novel semiquantum key distribution
protocol [M. Boyer, D. Kenigsberg, and T. Mor, Phys. Rev. Lett. 99, 140501
(2007)], by using four quantum states, each of which is randomly prepared by Z
basis or X basis. Here we present a semiquantum key distribution protocol by
using entangled states in which quantum Alice shares a secret key with
classical Bob. We also show the protocol is secure against eavesdropping.Comment: 6 page
Thermodynamic Properties of Spherically-Symmetric, Uniformly-Accelerated Reference Frames
We aim to study the thermodynamic properties of the spherically symmetric
reference frames with uniform acceleration, including the spherically symmetric
generalization of Rindler reference frame and the new kind of uniformly
accelerated reference frame. We find that, unlike the general studies about the
horizon thermodynamics, one cannot obtain the laws of thermodynamics for their
horizons in the usual approaches, despite that one can formally define an area
entropy (Bekenstein-Hawking entropy). In fact, the common horizon for a set of
uniformly accelerated observers is not always exist, even though the
Hawking-Unruh temperature is still well-defined. This result indicates that the
Hawking-Unruh temperature is only a kinematic effect, to gain the laws of
thermodynamics for the horizon, one needs the help of dynamics. Our result is
in accordance with those from the various studies about the acoustic black
holes.Comment: 8 page
Gravity waves over topographical bottoms: Comparison with the experiment
In this paper, the propagation of water surface waves over one-dimensional
periodic and random bottoms is investigated by the transfer matrix method. For
the periodic bottoms, the band structure is calculated, and the results are
compared to the transmission results. When the bottoms are randomized, the
Anderson localization phenomenon is observed. The theory has been applied to an
existing experiment (Belzons, et al., J. Fluid Mech. {\bf 186}, 530 (1988)). In
general, the results are compared favorably with the experimental observation.Comment: 15 pages, 7 figure
Pseuduscalar Heavy Quarkonium Decays With Both Relativistic and QCD Radiative Corrections
We estimate the decay rates of ,
, and ,
, by taking into account both relativistic and
QCD radiative corrections. The decay amplitudes are derived in the
Bethe-Salpeter formalism. The Bethe-Salpeter equation with a QCD-inspired
interquark potential are used to calculate the wave functions and decay widths
for these states. We find that the relativistic correction to the
ratio is negative and tends to compensate the positive contribution from
the QCD radiative correction. Our estimate gives and ,
which are smaller than their nonrelativistic values. The hadronic widths
and are then indicated accordingly to the first order
QCD radiative correction, if . The decay widths for
states are also estimated. We show that when making the assmption
that the quarks are on their mass shells our expressions for the decay widths
will become identical with that in the NRQCD theory to the next to leading
order of and .Comment: 14 pages LaTex (2 figures included
Decays of and into vector and pseudoscalar meson and the pseudoscalar glueball- mixing
We introduce a parametrization scheme for where
the effects of SU(3) flavor symmetry breaking and doubly OZI-rule violation
(DOZI) can be parametrized by certain parameters with explicit physical
interpretations. This scheme can be used to clarify the glueball-
mixing within the pseudoscalar mesons. We also include the contributions from
the electromagnetic (EM) decays of and via
. Via study of the isospin violated
channels, such as , ,
and , reasonable constraints on the EM decay
contributions are obtained. With the up-to-date experimental data for
, and , etc, we arrive at a consistent description of the mentioned
processes with a minimal set of parameters. As a consequence, we find that
there exists an overall suppression of the form factors,
which sheds some light on the long-standing " puzzle". By determining
the glueball components inside the pseudoscalar and in
three different glueball- mixing schemes, we deduce that the lowest
pseudoscalar glueball, if exists, has rather small component, and it
makes the a preferable candidate for glueball.Comment: Revised version to appear on J. Phys. G; An error in the code was
corrected. There's slight change to the numerical results, while the
conclusion is intac
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The tarantula toxin GxTx detains K+ channel gating charges in their resting conformation.
Allosteric ligands modulate protein activity by altering the energy landscape of conformational space in ligand-protein complexes. Here we investigate how ligand binding to a K+ channel's voltage sensor allosterically modulates opening of its K+-conductive pore. The tarantula venom peptide guangxitoxin-1E (GxTx) binds to the voltage sensors of the rat voltage-gated K+ (Kv) channel Kv2.1 and acts as a partial inverse agonist. When bound to GxTx, Kv2.1 activates more slowly, deactivates more rapidly, and requires more positive voltage to reach the same K+-conductance as the unbound channel. Further, activation kinetics are more sigmoidal, indicating that multiple conformational changes coupled to opening are modulated. Single-channel current amplitudes reveal that each channel opens to full conductance when GxTx is bound. Inhibition of Kv2.1 channels by GxTx results from decreased open probability due to increased occurrence of long-lived closed states; the time constant of the final pore opening step itself is not impacted by GxTx. When intracellular potential is less than 0 mV, GxTx traps the gating charges on Kv2.1's voltage sensors in their most intracellular position. Gating charges translocate at positive voltages, however, indicating that GxTx stabilizes the most intracellular conformation of the voltage sensors (their resting conformation). Kinetic modeling suggests a modulatory mechanism: GxTx reduces the probability of voltage sensors activating, giving the pore opening step less frequent opportunities to occur. This mechanism results in K+-conductance activation kinetics that are voltage-dependent, even if pore opening (the rate-limiting step) has no inherent voltage dependence. We conclude that GxTx stabilizes voltage sensors in a resting conformation, and inhibits K+ currents by limiting opportunities for the channel pore to open, but has little, if any, direct effect on the microscopic kinetics of pore opening. The impact of GxTx on channel gating suggests that Kv2.1's pore opening step does not involve movement of its voltage sensors
Electronic Structure of KFeSe from First Principles Calculations
Electronic structure and magnetic properties for iron-selenide KFeSe
are studied by first-principles calculations. The ground state is stripe-like
antiferromagnetic with calculated 2.26 magnetic moment on Fe atoms; and
the , coupling strengths are calculated to be 0.038 eV and 0.029 eV.
The states around are dominated by the Fe-3d orbitals which hybridize
noticeably to the Se-4p orbitals. While the band structure of KFeSe is
similar to a heavily electron-doped BaFeAs or FeSe system, the Fermi
surface of KFeSe is much closer to \fs11 system since the electron
sheets around is symmetric with respect to - exchange. These
features, as well as the absence of Fermi surface nesting, suggest that the
parental KFeSe could be regarded as an electron over-doped 11 system
with possible local moment magnetism.Comment: accepted by Chinese Physics Letter, to appear as Chinese Physics
Letter, Vol 28, page 057402 (2011
Chaotic Orbits in Thermal-Equilibrium Beams: Existence and Dynamical Implications
Phase mixing of chaotic orbits exponentially distributes these orbits through
their accessible phase space. This phenomenon, commonly called ``chaotic
mixing'', stands in marked contrast to phase mixing of regular orbits which
proceeds as a power law in time. It is operationally irreversible; hence, its
associated e-folding time scale sets a condition on any process envisioned for
emittance compensation. A key question is whether beams can support chaotic
orbits, and if so, under what conditions? We numerically investigate the
parameter space of three-dimensional thermal-equilibrium beams with space
charge, confined by linear external focusing forces, to determine whether the
associated potentials support chaotic orbits. We find that a large subset of
the parameter space does support chaos and, in turn, chaotic mixing. Details
and implications are enumerated.Comment: 39 pages, including 14 figure
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