20,267 research outputs found
Symmetry and nonexistence of positive solutions for fractional systems
This paper is devoted to study the nonexistence results of positive solutions
for the following fractional Hnon system \begin{eqnarray*}\left\{
\begin{array}{lll}
&(-\triangle)^{\alpha/2}u=|x|^av^p,~~~&x\in R^n,
&(-\triangle)^{\alpha/2}v=|x|^bu^q,~~~ &x\in R^n,
&u\geq0, v\geq 0,
\end{array}
\right. \end{eqnarray*} where , , , ,
. Using a direct method of moving planes, we prove non-existence of
positive solution in the subcritical case
Nonadiabatic geometric rotation of electron spin in a quantum dot by 2Pi hyperbolic secant pulses
In this paper, the geometric and dynamic phase components of overall phase
induced by 2{\pi} hyperbolic secant pulses in a quantum dot is analyzed. The
dependence of two phase components on the ratio of the Rabi frequency to the
detuning is investigated. Numerical results indicate that only for one resonant
pulse the induced overall phase is purely the geometric phase. With other
values of the ratio the overall phase consists of a nonzero dynamic part. The
effect of spin precession to decrease the dynamic phase is characterized and
discussed by analytical and numerical techniques. Utilizing the symmetry
relations of the phases, a scheme to eliminate the dynamic phase by multipulse
control is proposed. By choosing the proper parameter for each pulse, the
dynamic phases induced by different pulses cancel out. The total pure geometric
phase varies from -{\pi} to {\pi}, which realizes the arbitrary geometric
rotation of spin. Average fidelity is calculated and the effects of magnetic
field and decay of the trion state are compared and discussed. The results show
the crucial role of weak magnetic field for high fidelity (above 99.3%).Comment: 7 pages, 8 figures, 1 tabl
Towards practical high-speed high dimensional quantum key distribution using partial mutual unbiased basis of photon's orbital angular momentum
Quantum Key Distribution (QKD) guarantees the security of communication with
quantum physics. Most of widely adopted QKD protocols currently encode the key
information with binary signal format---qubit, such as the polarization states.
Therefore the transmitted information efficiency of the quantum key is
intrinsically upper bounded by 1 bit per photon. High dimensional quantum
system is a potential candidate for increasing the capacity of single photon.
However, due to the difficulty in manipulating and measuring high dimensional
quantum systems, the experimental high dimensional QKD is still at its infancy.
Here we propose a sort of practical high-speed high dimensional QKD using
partial mutual unbiased basis (PMUB) of photon's orbital angular momentum
(OAM). Different from the previous OAM encoding, the high dimensional Hilbert
space we used is expanded by the OAM states with same mode order, which can be
extended to considerably high dimensions and implemented under current state of
the art. Because all the OAM states are in the same mode order, the coherence
will be well kept after long-distance propagation, and the detection can be
achieved by using passive linear optical elements with very high speed. We show
that our protocol has high key generation rate and analyze the anti-noise
ability under atmospheric turbulence. Furthermore, the security of our protocol
based on PMUB is rigorously proved. Our protocol paves a brand new way for the
application of photon's OAM in high dimensional QKD field, which can be a
breakthrough for high efficiency quantum communications.Comment: Comments are welcom
Shot cutoff timescales in different spectral states of Cygnus X-1
We investigate the shot cutoff timescale evolutions during different spectral
states in the black hole binary Cygnus X-1 with the recently proposed w
spectral analysis technique. For low energy shots, their cutoff timescale
decreases from the low state to intermediate state, and to high state
monotonically. However in the high energy range, where shots are believed to be
reprocessed in the hot corona, timescales are almost the same for different
spectral states. A linear correlation is found between the energy spectrum
photon index and the shot cutoff timescale at low energies. Both narrow and
broad iron Kalpha lines are distinguished from timing analysis, providing
dynamical evidence that broad and narrow iron lines originate respectively at
small and large radii of the accretion disk. Possible mechanisms for state
transitions and accretion flow geometry in accreting stellar mass black holes
are discussed.Comment: accepted for publication in ApJ
Model-independent determination of curvature parameter by using and data pair from BAO measurement
We present a model-independent determination of the curvature parameter
by using the Hubble parameter and angular diameter distance
from the recent baryon acoustic oscillation (BAO) measurements. Each
and pair from a BAO measurement can constrain a curvature
parameter. The accuracy of the curvature measurement improves with increased
redshift of and data. By using the and pair
derived from BAO Lyman forest measurement at , the
is confined to be -0.050.06, which is consistent with the curvature
constrained by the nine-year WMAP data only.
Considering future BAO meausurements, at least one order of magnitude
improvement of this curvature measurement could be expected.Comment: 5 pages, 3 figures. Accepted for publication in ApJ
Design and performance of an absolute gas refractometer based on quasi-synthetic wavelength method
We present a refractometer which is capable of measuring the refractive index
of gas with an unambiguous range of 1.000395 and uncertainty of 3.1E-8 at 633
nm absolutely. The measurement range is extended by means of a group of vacuum
tubes according to the principle of quasi-synthetic wavelength (QSW) method.
The basic principle of the QSW method and the design of the gas refractometer
are presented in detail. The performance of the refractometer has been verified
by the measurement of dry air, nitrogen gas and ambient air under different
environmental situations. The gas-filling or pumping process is not needed
during the measurement, so that we can complete a measurement within 70
seconds. Comparing with previous ones, the refractometer reported here has
integrated virtues of large unambiguous range, fast speed, high accuracy, and a
simple instrumentation design.Comment: 12 pages,7 figure
Control excitation and coherent transfer in a dimer
In this article, the processes of energy absorption and coherent transfer in
a dimer is studied. The dimer includes two two-level pigments --- donor and
acceptor, where donor is assumed being excited by a control pulse in the time
domain. We investigate the dynamics of probability that the acceptor is in the
excited state and the total efficiency of energy absorption and transfer under
different temporal shape of control pulse. Quantum concurrence of the dimer is
also discussed
Super sub-wavelength patterns in photon coincidence detection
High-precision measurements implemented by means of light is desired in all
fields of science. However, light is a wave and Rayleigh criterion gives us a
diffraction limitation in classical optics which restricts to get arbitrary
high resolution. Sub-wavelength interference has a potential application in
lithography to beat the classical Rayleigh limit of resolution. We carefully
study the second-order correlation theory to get the physics behind
sub-wavelength interference in photon coincidence detection. A Young's
double-slit experiment with pseudo-thermal light is carried out to test the
second-order correlation pattern. The result shows that when different scanning
ways of two point detectors are chosen, one can get super sub-wavelength
interference patterns. We then give a theoretical explanation to this
surprising result, and find this explanation is also suitable for the result by
using entangled light. Furthermore, we discuss the limitation of this kind of
super sub-wavelength interference patterns in quantum lithography.Comment: 5 pages, 5 figures, comments are welcom
Far-Infrared Spectroscopy of Cationic Polycyclic Aromatic Hydrocarbons: Zero Kinetic Energy Photoelectron Spectroscopy of Pentacene Vaporized from Laser Desorption
The distinctive set of infrared (IR) emission bands at 3.3, 6.2, 7.7, 8.6,
and 11.3{\mu}m are ubiquitously seen in a wide variety of astrophysical
environments. They are generally attributed to polycyclic aromatic hydrocarbon
(PAH) molecules. However, not a single PAH species has yet been identified in
space, as the mid-IR vibrational bands are mostly representative of functional
groups and thus do not allow one to fingerprint individual PAH molecules. In
contrast, the far-IR (FIR) bands are sensitive to the skeletal characteristics
of a molecule, hence they are important for chemical identification of unknown
species.
With an aim to offer laboratory astrophysical data for the Herschel Space
Observatory, Stratospheric Observatory for Infrared Astronomy, and similar
future space missions, in this work we report neutral and cation FIR
spectroscopy of pentacene (C_22H_14), a five-ring PAH molecule. We report three
IR active modes of cationic pentacene at 53.3, 84.8, and 266{\mu}m that may be
detectable by space missions such as the SAFARI instrument on board SPICA.
In the experiment, pentacene is vaporized from a laser desorption source and
cooled by a supersonic argon beam. We have obtained results from two-color
resonantly enhanced multiphoton ionization and two-color zero kinetic energy
photoelectron (ZEKE) spectroscopy. Several skeletal vibrational modes of the
first electronically excited state of the neutral species and those of the
cation are assigned, with the aid of ab initio and density functional
calculations.Comment: 27 pages, 5 figures, 4 tables; published in Ap
Eclipse: Practicability Beyond kNN and Skyline
The nearest neighbor (NN) query is a fundamental problem in databases.
Given a set of multidimensional data points and a query point, NN returns
the nearest neighbors based on a scoring function such as weighted sum
given an attribute weight vector. However, the attribute weight vector can be
difficult to specify in practice. Skyline returns the points including all
possible nearest neighbors without requiring the exact attribute weight vector
or a scoring function but the number of returned points can be prohibitively
large for practical use.
In this paper, we propose a novel \emph{eclipse} definition which provides a
more flexible and customizable definition than the classic NN and skyline.
In eclipse, users can specify a range of attribute weights and control the
number of returned points. We show that both NN and skyline are
instantiations of eclipse. To compute eclipse points, we propose a baseline
algorithm with time complexity of , and an improved time transformation-based algorithm by transforming the eclipse
problem to the skyline problem, where is the number of points and is
the number of dimensions. Furthermore, we propose a novel index-based algorithm
utilizing duality transform with much better efficiency. The experimental
results on the real NBA dataset and the synthetic datasets demonstrate the
effectiveness and efficiency of our eclipse algorithms
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