5,020 research outputs found
Entanglement Rate for Gaussian Continuous Variable Beams
We derive a general expression that quantifies the total entanglement
production rate in continuous variable systems, where a source emits two
entangled Gaussian beams with arbitrary correlators.This expression is
especially useful for situations where the source emits an arbitrary frequency
spectrum,e.g. when cavities are involved. To exemplify its meaning and
potential, we apply it to a four-mode optomechanical setup that enables the
simultaneous up- and down-conversion of photons from a drive laser into
entangled photon pairs. This setup is efficient in that both the drive and the
optomechanical up- and down-conversion can be fully resonant.Comment: 18 pages, 6 figure
Truthful Mechanisms for Secure Communication in Wireless Cooperative System
To ensure security in data transmission is one of the most important issues
for wireless relay networks, and physical layer security is an attractive
alternative solution to address this issue. In this paper, we consider a
cooperative network, consisting of one source node, one destination node, one
eavesdropper node, and a number of relay nodes. Specifically, the source may
select several relays to help forward the signal to the corresponding
destination to achieve the best security performance. However, the relays may
have the incentive not to report their true private channel information in
order to get more chances to be selected and gain more payoff from the source.
We propose a Vickey-Clark-Grove (VCG) based mechanism and an
Arrow-d'Aspremont-Gerard-Varet (AGV) based mechanism into the investigated
relay network to solve this cheating problem. In these two different
mechanisms, we design different "transfer payment" functions to the payoff of
each selected relay and prove that each relay gets its maximum (expected)
payoff when it truthfully reveals its private channel information to the
source. And then, an optimal secrecy rate of the network can be achieved. After
discussing and comparing the VCG and AGV mechanisms, we prove that the AGV
mechanism can achieve all of the basic qualifications (incentive compatibility,
individual rationality and budget balance) for our system. Moreover, we discuss
the optimal quantity of relays that the source node should select. Simulation
results verify efficiency and fairness of the VCG and AGV mechanisms, and
consolidate these conclusions.Comment: To appear in IEEE Transactions on Wireless Communication
Infrared perfect absorber based on nanowire metamaterial cavities
An infrared perfect absorber based on gold nanowire metamaterial cavities
array on a gold ground plane is designed. The metamaterial made of gold
nanowires embedded in alumina host exhibits an effective permittivity with
strong anisotropy, which supports cavity resonant modes of both electric dipole
and magnetic dipole. The impedance of the cavity modes matches the incident
plane wave in free space, leading to nearly perfect light absorption. The
incident optical energy is efficiently converted into heat so that the local
temperature of the absorber will increase. Simulation results show that the
designed metamaterial absorber is polarization-insensitive and nearly
omnidirectional for the incident angle.Comment: 3 pages, 4 figure
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Nanowire Photoelectrochemistry.
Recent applications of photoelectrochemistry at the semiconductor/liquid interface provide a renewable route of mimicking natural photosynthesis and yielding chemicals from sunlight, water, and air. Nanowires, defined as one-dimensional nanostructures, exhibit multiple unique features for photoelectrochemical applications and promise better performance as compared to their bulk counterparts. This article reviews the use of semiconductor nanowires in photoelectrochemistry. After introducing fundamental concepts essential to understanding nanowires and photoelectrochemistry, the review considers answers to the following questions: (1) How can we interface semiconductor nanowires with other building blocks for enhanced photoelectrochemical responses? (2) How are nanowires utilized for photoelectrochemical half reactions? (3) What are the techniques that allow us to obtain fundamental insights of photoelectrochemistry at single-nanowire level? (4) What are the design strategies for an integrated nanosystem that mimics a closed cycle in artificial photosynthesis? This framework should help readers evaluate the salient features of nanowires for photoelectrochemical applications, promoting the sustainable development of solar-powered chemical plants that will benefit our society in the long run
A genome-wide transcriptional activity survey of rice transposable element-related genes
BACKGROUND: Transposable element (TE)-related genes comprise a significant portion of the gene catalog of grasses, although their functions are insufficiently characterized. The recent availability of TE-related gene annotation from the complete genome sequence of rice (Oryza sativa) has created an opportunity to conduct a comprehensive evaluation of the transcriptional activities of these potentially mobile elements and their related genes. RESULTS: We conducted a genome-wide survey of the transcriptional activity of TE-related genes associated with 15 developmental stages and stress conditions. This dataset was obtained using a microarray encompassing 2,191 unique TE-related rice genes, which were represented by oligonucleotide probes that were free from cross-hybridization. We found that TE-related genes exhibit much lower transcriptional activities than do non-TE-related genes, although representative transcripts were detected from all superfamilies of both type I and II TE-related genes. The strongest transcriptional activities were detected in TE-related genes from among the MULE and CACTA superfamilies. Phylogenetic analyses suggest that domesticated TE-related genes tend to form clades with active transcription. In addition, chromatin-level regulations through histone and DNA modifications, as well as enrichment of certain cis elements in the promoters, appear to contribute to the transcriptional activation of representative TE-related genes. CONCLUSION: Our findings reveal clear, albeit low, general transcription of TE-related genes. In combination with phylogenetic analysis, transcriptional analysis has the potential to lead to the identification of domesticated TEs with adapted host functions
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