34,950 research outputs found
A Simplified Scheme of Estimation and Cancellation of Companding Noise for Companded Multicarrier Transmission Systems
Nonlinear companding transform is an efficient method to reduce the high peak-to-average power ratio (PAPR) of multicarrier transmission systems. However, the introduced companding noise greatly degrades the bit-error-rate (BER) performance of the companded multicarrier systems. In this paper, a simplified but effective scheme of estimation and cancellation of companding noise for the companded multicarrier transmission system is proposed. By expressing the companded signals as the summation of original signals added with a companding noise component, and subtracting this estimated companding noise from the received signals, the BER performance of the overall system can be significantly improved. Simulation results well confirm the great advantages of the proposed scheme over other conventional decompanding or no decompanding schemes under various situations
Numerical Study on Indoor Wideband Channel Characteristics with Different Internal Wall
Effects of material and configuration of the internal wall on the performance of wideband channel are investigated by using the Finite Difference Time-Domain (FDTD) method. The indoor wideband channel characteristics, such as the path-loss, Root-Mean-Square (RMS) delay spread and number of the multipath components (MPCs), are presented. The simulated results demonstrate that the path-loss and MPCs are affected by the permittivity, dielectric loss tangent and thickness of the internal wall, while the RMS delay spread is almost not relevant with the dielectric permittivity. Furthermore, the comparison of simulated result with the measured one in a simple scenario has validated the simulation study
The spectral energy distribution of galaxies at z > 2.5: Implications from the Herschel/SPIRE color-color diagram
We use the Herschel SPIRE color-color diagram to study the spectral energy
distribution (SED) and the redshift estimation of high-z galaxies. We compiled
a sample of 57 galaxies with spectroscopically confirmed redshifts and SPIRE
detections in all three bands at , and compared their average SPIRE
colors with SED templates from local and high-z libraries. We find that local
SEDs are inconsistent with high-z observations. The local calibrations of the
parameters need to be adjusted to describe the average colors of high-z
galaxies. For high-z libraries, the templates with an evolution from z=0 to 3
can well describe the average colors of the observations at high redshift.
Using these templates, we defined color cuts to divide the SPIRE color-color
diagram into different regions with different mean redshifts. We tested this
method and two other color cut methods using a large sample of 783
Herschel-selected galaxies, and find that although these methods can separate
the sample into populations with different mean redshifts, the dispersion of
redshifts in each population is considerably large. Additional information is
needed for better sampling.Comment: 17 pages, 14 figures, accepted for publication in A&
Combined fit to BaBar and Belle data on e+e- to pi+pi- psi(2S)
A combined fit is performed to the BaBar and Belle measurements of the e+e-
to pi+pi-psi(2S) cross sections for center-of-mass energy between threshold and
5.5 GeV. The resonant parameters of the Y(4360) and Y(4660) are determined. The
mass is 4355^{+9}_{-10}\pm 9 MeV/c^2 and the width is 103^{+17}_{-15}\pm 11
MeV/c^2 for the Y(4360), and the mass is 4661^{+9}_{-8}\pm 6 MeV/c^2 and the
width is 42^{+17}_{-12}\pm 6 MeV/c^2 for the Y(4660). The production of the
Y(4260) in pi+pi-psi(2S) mode is found to be at 2\sigma level, and B(Y(4260) to
pi+pi-psi(2S))\Gamma_{e+e-} is found to be less than 4.3 eV/c^2 at the 90%
confidence level, or equal to 7.4^{+2.1}_{-1.7} eV/c^2 depending on it
interferes with the Y(4360) constructively or destructively. These information
will shed light on the understanding of the nature of the Y states observed in
initial state radiation processes.Comment: 8 pages, 4 figure
Dynamical state of galaxy clusters evaluated from X-ray images
X-ray images of galaxy clusters often show disturbed structures that are
indication of cluster mergers. As a complementary to our previous work on
dynamical state of 964 clusters observed by the Chandra, we process the X-ray
images for 1308 clusters from XMM-Newton archival data, together with the
images of 22 clusters newly released by the Chandra, and evaluate their
dynamical state from these X-ray images. The concentration index , the
centroid shift , the power ratio are calculated in circular
regions with a certain radius of 500 kpc, and the morphology index is
estimated within elliptical regions adaptive to the cluster size and shape. In
addition, the dynamical parameters for 42 clusters previously estimated from
Chandra images are upgraded based on the newly available redshifts. Good
consistence is found between dynamical parameters derived from XMM-Newton and
Chandra images for the overlapped sample of clusters in the two datasets. The
dependence of mass scaling relations on dynamical state is shown by using data
of 388 clusters.Comment: 10 pages, 6 figures, 4 tables, MNRAS in pres
Hurst parameter analysis of radio pulsar timing noise
We present an analysis of timing residual (noise) of 54 pulsars obtained from
25-m radio telescope at Urumqi Observatory with a time span of 5~8 years,
dealing with statistics of the Hurst parameter. The majority of these pulsars
were selected to have timing noise that look like white noise rather than
smooth curves. The results are compared with artificial series of different
constant pairwise covariances. Despite the noise like appearance, many timing
residual series showed Hurst parameters significantly deviated from that of
independent series. We concluded that Hurst parameter may be capable of
detecting dependence in timing residual and of distinguishing chaotic behavior
from random processes.Comment: 7 pages, 3 figures, 2 tables, Submitted to MNRA
Spin transfer torques in nonlocal lateral spin valve
We report a theoretical study on the spin and electron transport in the
nonlocal lateral spin valve with non-collinear magnetic configuration. The
nonlocal magnetoresistance, defined as the voltage difference on the detection
lead over the injected current, is derived analytically. The spin transfer
torques on the detection lead are calculated. It is found that spin transfer
torques are symmetrical for parallel and antiparallel magnetic configurations,
which is different from that in conventional sandwiched spin valve.Comment: 7 papges, 5 figure
Phonon-induced dephasing of chromium colour centres in diamond
We report on the coherence properties of single photons from chromium-based
colour centres in diamond. We use field-correlation and spectral lineshape
measurements to reveal the interplay between slow spectral wandering and fast
dephasing mechanisms as a function of temperature. We show that the zero-phonon
transition frequency and its linewidth follow a power-law dependence on
temperature indicating that the dominant fast dephasing mechanisms for these
centres are direct electron-phonon coupling and phonon-modulated Coulomb
coupling to nearby impurities. Further, the observed reduction in the quantum
yield for photon emission as a function of temperature is consistent with the
opening of additional nonradiative channels through thermal activation to
higher energy states predominantly and indicates a near-unity quantum
efficiency at 4 K
- …