1,239 research outputs found
Secrecy Wireless Information and Power Transfer in Fading Wiretap Channel
Simultaneous wireless information and power transfer (SWIPT) has recently
drawn significant interests for its dual use of radio signals to provide
wireless data and energy access at the same time. However, a challenging
secrecy communication issue arises as the messages sent to the information
receivers (IRs) may be eavesdropped by the energy receivers (ERs), which are
presumed to harvest energy only from the received signals. To tackle this
problem, we propose in this paper an artificial noise (AN) aided transmission
scheme to facilitate the secrecy information transmission to IRs and yet meet
the energy harvesting requirement for ERs, under the assumption that the AN can
be cancelled at IRs but not at ERs. Specifically, the proposed scheme splits
the transmit power into two parts, to send the confidential message to the IR
and an AN to interfere with the ER, respectively. Under a simplified three-node
wiretap channel setup, the transmit power allocations and power splitting
ratios over fading channels are jointly optimized to minimize the outage
probability for delay-limited secrecy information transmission, or to maximize
the average rate for no-delay-limited secrecy information transmission, subject
to a combination of average and peak power constraints at the transmitter as
well as an average energy harvesting constraint at the ER. Both the secrecy
outage probability minimization and average rate maximization problems are
shown to be non-convex, for each of which we propose the optimal solution based
on the dual decomposition as well as suboptimal solution based on the
alternating optimization. Furthermore, two benchmark schemes are introduced for
comparison. Finally, the performances of proposed schemes are evaluated by
simulations in terms of various trade-offs for wireless (secrecy) information
versus energy transmissions.Comment: to appear in IEEE Transactions on Vehicular Technolog
A Comprehensive Analysis of Fermi Gamma-Ray Burst Data. IV. Spectral Lag and its Relation to E p Evolution
The spectral evolution and spectral lag behavior of 92 bright pulses from 84 gamma-ray bursts observed by the Fermi Gamma-ray Burst Monitor (GBM) telescope are studied. These pulses can be classified into hard-to-soft pulses (H2S; 64/92), H2S-dominated-tracking pulses (21/92), and other tracking pulses (7/92). We focus on the relationship between spectral evolution and spectral lags of H2S and H2S-dominated-tracking pulses. The main trend of spectral evolution (lag behavior) is estimated with ( ), where E p is the peak photon energy in the radiation spectrum, t + t 0 is the observer time relative to the beginning of pulse −t 0, and is the spectral lag of photons with energy E with respect to the energy band 8–25 keV. For H2S and H2S-dominated-tracking pulses, a weak correlation between and k E is found, where W is the pulse width. We also study the spectral lag behavior with peak time of pulses for 30 well-shaped pulses and estimate the main trend of the spectral lag behavior with . It is found that is correlated with k E . We perform simulations under a phenomenological model of spectral evolution, and find that these correlations are reproduced. We then conclude that spectral lags are closely related to spectral evolution within the pulse. The most natural explanation of these observations is that the emission is from the electrons in the same fluid unit at an emission site moving away from the central engine, as expected in the models invoking magnetic dissipation in a moderately high-σ outflow
A comprehensive analysis of Fermi Gamma-Ray Burst Data: IV. Spectral lag and Its Relation to Ep Evolution
The spectral evolution and spectral lag behavior of 92 bright pulses from 84
gamma-ray bursts (GRBs) observed by the Fermi GBM telescope are studied. These
pulses can be classified into hard-to-soft pulses (H2S, 64/92),
H2S-dominated-tracking pulses (21/92), and other tracking pulses (7/92). We
focus on the relationship between spectral evolution and spectral lags of H2S
and H2S-dominated-tracking pulses. %in hard-to-soft pulses (H2S, 64/92) and
H2S-dominating-tracking (21/92) pulses. The main trend of spectral evolution
(lag behavior) is estimated with
(), where is the peak photon
energy in the radiation spectrum, is the observer time relative to the
beginning of pulse , and is the spectral lag of photons
with energy with respect to the energy band - keV. For H2S and
H2S-dominated-tracking pulses, a weak correlation between
and is found, where is the pulse width. We also study the spectral
lag behavior with peak time of pulses for 30 well-shaped pulses
and estimate the main trend of the spectral lag behavior with . It is found that is correlated with
. We perform simulations under a phenomenological model of spectral
evolution, and find that these correlations are reproduced. We then conclude
that spectral lags are closely related to spectral evolution within the pulse.
The most natural explanation of these observations is that the emission is from
the electrons in the same fluid unit at an emission site moving away from the
central engine, as expected in the models invoking magnetic dissipation in a
moderately-high- outflow.Comment: 58 pages, 11 figures, 3 tables. ApJ in pres
Symmetry dictated universal helicity redistribution of Dirac fermions in transport
Helicity is a fundamental property of Dirac fermions. Yet, how it changes in
transport processes remains largely mysterious. We uncover, theoretically, the
rule of spinor state transformation and consequently universal helicity
redistribution in two cases of transport through potentials of electrostatic
and mass types, respectively. The former is dictated by Lorentz boost and its
complex counterpart in Klein tunneling regime. The latter is governed by an
abstract rotation group we identified, which reduces to SO(2) when acting on
the plane of effective mass and momentum. This endows an extra structure
foliating the Hilbert space of Dirac spinors, establishes miraculously a
unified yet latent connection between helicity, Klein tunneling, and Lorentz
boost. Our results thus deepen the understanding of relativistic quantum
transport, and may open a new window for exotic helicity-based physics and
applications in mesoscopic systems.Comment: 6 pages, 4 figure
An FBG staged monitoring method for carbon fiber reinforced plastics composite fracture status based on modulus/strain wave coupling property
From the sensitivity of the FBG center wavelength changing with the macro-elastic modulus and the instantaneous fracture strain wave on the surface of carbon fiber reinforced plastics (CFRP) composite, we investigate the correlation between the macro-elastic modulus (the changing rate of the FBG center wavelength during the stretching process) and the fracture status of CFRP specimen. An FBG staged monitoring method based on modulus/strain wave coupling properties designed to monitor tensile fracture state of composite has been proposed. By monitoring the change of macro-elastic modulus during the stretching process, the damage state of composite in a macro perspective is obtained; when the internal damage reaches a critical state, the fracture distribution status of CFRP specimen is captured by monitoring the strain wave response induced by stress relaxation in different locations. Simulated analysis and experimental results in this paper show that the proposed FBG staged monitoring method can achieve the identification of the damage state and the breakage position of CFRP composite effectively, with a good prospect
The Protective Effects of Curcumin on Obesity-Related Glomerulopathy Are Associated with Inhibition of Wnt/ β
The present study investigated the effects of curcumin, one of the most important active ingredients of turmeric, on podocyte injury in vitro and obesity-related glomerulopathy (ORG) in vivo. Cellular experiments in vitro showed that curcumin significantly antagonized leptin-induced downregulation of the mRNA and protein expression of podocyte-associated molecules including nephrin, podocin, podoplanin, and podocalyxin. Animal experiments in vivo showed that curcumin significantly reduced the body weight, Lee’s index, abdominal fat index, urinary protein excretion, and average glomerular diameter and significantly upregulated the mRNA and protein expressions of the above podocyte-associated molecules in ORG mice. Furthermore, the experiments in vitro and in vivo both displayed that curcumin could downregulate the mRNA and protein expressions of Wnt1, Wnt2b, Wnt6, and β-catenin and upregulate the phosphorylation level of β-catenin protein in podocytes and renal tissue. In conclusion, curcumin is able to alleviate the harmful reaction of leptin on podocytes and reduce the severity of ORG. The above protective effects are associated with the inhibition of Wnt/β-catenin signaling activation in podocytes
Suppression of the multiplicity fluctuations in particle correlations
Multiplicity fluctuations play a crucial role in relativistic heavy-ion
collisions. In this work, we explore how the multiplicity fluctuations can be
effectively suppressed in the measurement of particle correlations. In
particular, through proper normalization, particle correlations can be
evaluated in a manner irrelevant to multiplicity. When the multiplicity
fluctuations are adequately extracted, Monte Carlo simulations show that the
remaining correlations possess distinct features buried in the otherwise
overwhelming fluctuations. Moreover, we argue that such a normalization scheme
naturally agrees with the multi-particle correlator, which can be evaluated
using the Q-vectors. The implications of the present study in the data analysis
are also addressed.Comment: 15 pages, 3 figure
Utilizing maximum likelihood estimator for flow analysis
We explore the possibility of evaluating flow harmonics by employing the
maximum likelihood estimator (MLE). For a given finite multiplicity, the MLE
simultaneously furnishes estimations for all the parameters of the underlying
distribution function while efficiently suppressing the variance of measures.
Also, the method provides a means to assess a specific class of mixed
harmonics, which is not straightforwardly feasible by the approaches primarily
based on particle correlations. The results are analyzed using the Wald,
likelihood ratio, and score tests of hypotheses. Besides, the resultant flow
harmonics obtained using MLE are compared with those derived using particle
correlations and event plane methods. The dependencies of extracted flow
harmonics on the multiplicity of individual events and the total number of
events are analyzed. It is shown that the proposed approach works efficiently
to deal with the deficiency in detector acceptability. Moreover, we elaborate
on a fictitious scenario where the event plane is not a well-defined quantity
in the distribution function. For the latter case, the MLE is shown to largely
perform better than the two-particle correlation estimator. In this regard, one
concludes that the MLE furnishes a meaningful alternative to the existing
approaches for flow analysis.Comment: 15 pages, 5 figures, and 8 table
Optical and Gamma-Ray Variability Behaviors of 3C 454.3 from 2006 to 2011
We present our photometric monitoring of a flat spectrum radio quasar (FSRQ)
3C 454.3 at Yunnan observatories from 2006 to 2011. We find that the optical
color of 3C 454.3 shows obvious redder-when-brighter trend, which reaches a
saturation stage when the source is brighter than 15.15 mag at V band. We
perform a simulation with multiple values of disk luminosity and spectral index
to reproduce the magnitude-color diagram. The results show that the
contamination caused by the disk radiation alone is difficult to produce the
observed color variability. The variability properties during the outburst in
December 2009 are also compared with -ray data derived from Fermi
-ray space telescope. The flux variation of these two bands follow a
linear relation with , which provides an
observational evidence for external Compton process in 3C 454.3. Meanwhile,
this flux correlation indicates that electron injection is the main mechanism
for variability origin. We also explore the variation of the flux ratio
and the detailed structures in the lightcurves, and discuss
some possible origins for the detailed variability behaviors.Comment: accepted for publication in The Astrophysical Journal, 5 figures, 2
table
- …