98,865 research outputs found
Asymptotic Behavior of Error Exponents in the Wideband Regime
In this paper, we complement Verd\'{u}'s work on spectral efficiency in the
wideband regime by investigating the fundamental tradeoff between rate and
bandwidth when a constraint is imposed on the error exponent. Specifically, we
consider both AWGN and Rayleigh-fading channels. For the AWGN channel model,
the optimal values of and are calculated, where
is the maximum rate at which information can be transmitted over a
channel with bandwidth when the error-exponent is constrained to be
greater than or equal to Based on this calculation, we say that a sequence
of input distributions is near optimal if both and are
achieved. We show that QPSK, a widely-used signaling scheme, is near-optimal
within a large class of input distributions for the AWGN channel. Similar
results are also established for a fading channel where full CSI is available
at the receiver.Comment: 59 pages, 6 figure
Ultra High Energy Cosmic Rays: Strangelets? -- Extra dimensions, TeV-scale black holes and strange matter
The conjecture that ultra high energy cosmic rays (UHECRs) are actually
strangelets is discussed. Besides the reason that strangelets can do as cosmic
rays beyond the GZK-cutoff, another argument to support the conjecture is
addressed in this letter via the study of formation of TeV-scale microscopic
black holes when UHECRs bombarding bare strange stars. It is proposed that the
exotic quark surface of a bare strange star could be an effective
astro-laboratory in the investigations of the extra dimensions and of the
detection of ultra-high energy neutrino fluxes. The flux of neutrinos (and
other point-like particles) with energy >2.3 x 10^{20} eV could be expected to
be smaller than 10^{-26} cm^{-2}$ s^{-1} if there are two extra spatial
dimensions.Comment: accepted by Chin. Phys. Lett., or at
http://vega.bac.pku.edu.cn/~rxxu/publications/index_P.ht
Adsorption, Segregation and Magnetization of a Single Mn Adatom on the GaAs (110) Surface
Density functional calculations with a large unit cell have been conducted to
investigate adsorption, segregation and magnetization of Mn monomer on
GaAs(110). The Mn adatom is rather mobile along the trench on GaAs(110), with
an energy barrier of 0.56 eV. The energy barrier for segregation across the
trenches is nevertheless very high, 1.67 eV. The plots of density of states
display a wide gap in the majority spin channel, but show plenty of
metal-induced gap states in the minority spin channel. The Mn atoms might be
invisibl in scanning tunneling microscope (STM) images taken with small biases,
due to the directional p-d hybridization. For example, one will more likely see
two bright spots on Mn/GaAs(110), despite the fact that there is only one Mn
adatom in the system
Quakes in Solid Quark Stars
A starquake mechanism for pulsar glitches is developed in the solid quark
star model. It is found that the general glitch natures (i.e., the glitch
amplitudes and the time intervals) could be reproduced if solid quark matter,
with high baryon density but low temperature, has properties of shear modulus
\mu = 10^{30~34} erg/cm^3 and critical stress \sigma_c = 10^{18~24} erg/cm^3.
The post-glitch behavior may represent a kind of damped oscillations.Comment: 11 pages, 4 figures (but Fig.3 is lost), a complete version can be
obtained by http://vega.bac.pku.edu.cn/~rxxu/publications/index_P.htm, a new
version to be published on Astroparticle Physic
Heat transport in quantum spin chains: the relevance of integrability
We investigate heat transport in various quantum spin chains, using the
projector operator technique. We find that anomalous heat transport is linked
not to the integrability of the Hamiltonian, but to whether it can be mapped to
a model of non-interacting fermions. Our results also suggest how seemingly
anomalous transport may occur at low temperatures in a much wider class of
models.Comment: 4 pages, 2fig
An Upper Limit on Omega_matter Using Lensed Arcs
We use current observations on the number statistics of gravitationally
lensed optical arcs towards galaxy clusters to derive an upper limit on the
cosmological mass density of the Universe. The gravitational lensing statistics
due to foreground clusters combine properties of both cluster evolution, which
is sensitive to the matter density, and volume change, which is sensitive to
the cosmological constant. The uncertainties associated with the predicted
number of lensing events, however, currently do not allow one to distinguish
between flat and open cosmological models with and without a cosmological
constant. Still, after accounting for known errors, and assuming that clusters
in general have dark matter core radii of the order ~ 35 h^-1 kpc, we find that
the cosmological mass density, Omega_m, is less than 0.56 at the 95%
confidence. Such a dark matter core radius is consistent with cluster
potentials determined recently by detailed numerical inversions of strong and
weak lensing imaging data. If no core radius is present, the upper limit on
Omega_m increases to 0.62 (95% confidence level). The estimated upper limit on
Omega_m is consistent with various cosmological probes that suggest a low
matter density for the Universe.Comment: 6 pages, 3 figures. Accepted version (ApJ in press
Aqua MODIS Electronic Crosstalk on SMWIR Bands 20 to 26
Aqua MODIS Moon images obtained with bands 20 to 26 (3.66 - 4.55 and 1.36 -
1.39 m) during scheduled lunar events show evidence of electronic
crosstalk contamination of the response of detector 1. In this work, we
determined the sending bands for each receiving band. We found that the
contaminating signal originates, in all cases, from the detector 10 of the
corresponding sending band and that the signals registered by the receiving and
sending detectors are always read out in immediate sequence. We used the lunar
images to derive the crosstalk coefficients, which were then applied in the
correction of electronic crosstalk striping artifacts present in L1B images,
successfully restoring product quality.Comment: Accepted to be published in the IEEE 2017 International Geoscience &
Remote Sensing Symposium (IGARSS 2017), scheduled for July 23-28, 2017 in
Fort Worth, Texas, US
Intrinsic electron-doping in nominal "non-doped" superconducting (La,Y)CuO thin films grown by dc magnetron sputtering
The superconducting nominal "non-doped" (LYCO) thin
films are successfully prepared by dc magnetron-sputtering and in situ
post-annealing in vacuum. The best more than 13K is achieved in the
optimal LYCO films with highly pure c-axis oriented T'-type structure. In the
normal state, the quasi-quadratic temperature dependence of resistivity, the
negative Hall coefficient and effect of oxygen content in the films are quite
similar to the typical Ce-doped T'-214 cuprates, suggesting that T'-LYCO shows
the electron-doping nature like known n-type cuprates, and is not a band
superconductor as proposed previously. The charge carriers are considered to be
induced by oxygen deficiency.Comment: 5 pages, 7 figure
- …