2,805 research outputs found
Sliding Window Spectrum Sensing for Full-Duplex Cognitive Radios with Low Access-Latency
In a cognitive radio system the failure of secondary user (SU) transceivers
to promptly vacate the channel can introduce significant access-latency for
primary or high-priority users (PU). In conventional cognitive radio systems,
the backoff latency is exacerbated by frame structures that only allow sensing
at periodic intervals. Concurrent transmission and sensing using
self-interference suppression has been suggested to improve the performance of
cognitive radio systems, allowing decisions to be taken at multiple points
within the frame. In this paper, we extend this approach by proposing a
sliding-window full-duplex model allowing decisions to be taken on a
sample-by-sample basis. We also derive the access-latency for both the existing
and the proposed schemes. Our results show that the access-latency of the
sliding scheme is decreased by a factor of 2.6 compared to the existing slotted
full-duplex scheme and by a factor of approximately 16 compared to a
half-duplex cognitive radio system. Moreover, the proposed scheme is
significantly more resilient to the destructive effects of residual
self-interference compared to previous approaches.Comment: Published in IEEE VTC Spring 2016, Nanjing, Chin
Spatial Multiplexing of QPSK Signals with a Single Radio: Antenna Design and Over-the-Air Experiments
The paper describes the implementation and performance analysis of the first
fully-operational beam-space MIMO antenna for the spatial multiplexing of two
QPSK streams. The antenna is composed of a planar three-port radiator with two
varactor diodes terminating the passive ports. Pattern reconfiguration is used
to encode the MIMO information onto orthogonal virtual basis patterns in the
far-field. A measurement campaign was conducted to compare the performance of
the beam-space MIMO system with a conventional 2-by-?2 MIMO system under
realistic propagation conditions. Propagation measurements were conducted for
both systems and the mutual information and symbol error rates were estimated
from Monte-Carlo simulations over the measured channel matrices. The results
show the beam-space MIMO system and the conventional MIMO system exhibit
similar finite-constellation capacity and error performance in NLOS scenarios
when there is sufficient scattering in the channel. In comparison, in LOS
channels, the capacity performance is observed to depend on the relative
polarization of the receiving antennas.Comment: 31 pages, 23 figure
Augmentation of Self-Interference Cancellation for Full-Duplex using NARX Neural Networks
A self-interference cancellation augmentation technique based on a NARX (Nonlinear Autoregressive Exogenous) network model is implemented and evaluated on an OFDM-based full-duplex system testbed operating at 2.4 GHz. In a comparison with the state-of-the-art polynomial models, our experimental results demonstrate the significant computational efficiency of the proposed NARX model. Specifically, the NARX model with one hidden layer reduces computations by 83.3% while achieving the same cancellation level within a bandwidth of 2 MHz
Photometric Confirmation of MACHO Large Magellanic Cloud Microlensing Events
We present previously unpublished photometry of three Large Magellanic Cloud
(LMC) microlensing events and show that the new photometry confirms the
microlensing interpretation of these events. These events were discovered by
the MACHO Project alert system and were also recovered by the analysis of the
5.7 year MACHO data set. This new photometry provides a substantial increase in
the signal-to-noise ratio over the previously published photometry and in all
three cases, the gravitational microlensing interpretation of these events is
strengthened. The new data consist of MACHO-Global Microlensing Alert Network
(GMAN) follow-up images from the CTIO 0.9 telescope plus difference imaging
photometry of the original MACHO data from the 1.3m "Great Melbourne" telescope
at Mt. Stromlo. We also combine microlensing light curve fitting with
photometry from high resolution HST images of the source stars to provide
further confirmation of these events and to show that the microlensing
interpretation of event MACHO-LMC-23 is questionable. Finally, we compare our
results with the analysis of Belokurov, Evans & Le Du who have attempted to
classify candidate microlensing events with a neural network method, and we
find that their results are contradicted by the new data and more powerful
light curve fitting analysis for each of the four events considered in this
paper. The failure of the Belokurov, Evans & Le Du method is likely to be due
to their use of a set of insensitive statistics to feed their neural networks.Comment: 29 pages with 8 included postscript figures, accepted by the
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The effect of fast and slow motor unit activation on whole-muscle mechanical performance: the size principle may not pose a mechanical paradox
The output of skeletal muscle can be varied by selectively recruiting different motor units. However, our knowledge of muscle function is largely derived from muscle in which all motor units are activated. This discrepancy may limit our understanding of in vivo muscle function. Hence, this study aimed to characterize the mechanical properties of muscle with different motor unit activation. We determined the isometric properties and isotonic force–velocity relationship of rat plantaris muscles in situ with all of the muscle active, 30% of the muscle containing predominately slower motor units active or 20% of the muscle containing predominately faster motor units active. There was a significant effect of active motor unit type on isometric force rise time (p < 0.001) and the force–velocity relationship (p < 0.001). Surprisingly, force rise time was longer and maximum shortening velocity higher when all motor units were active than when either fast or slow motor units were selectively activated. We propose this is due to the greater relative effects of factors such as series compliance and muscle resistance to shortening during sub-maximal contractions. The findings presented here suggest that recruitment according to the size principle, where slow motor units are activated first and faster ones recruited as demand increases, may not pose a mechanical paradox, as has been previously suggested.Organismic and Evolutionary Biolog
Maternal high-fat feeding in pregnancy programmes atherosclerotic lesion size in the ApoE*3 Leiden mouse
Periods of rapid growth seen during the early stages of fetal development, including cell proliferation and differentiation, are greatly influenced by the maternal environment. We demonstrate here that over-nutrition, specifically exposure to a high fat diet in utero, programmed the extent of atherosclerosis in the offspring of ApoE*3 Leiden transgenic mice. Pregnant ApoE*3 Leiden mice were fed either a control chow diet (2.8% fat, n=12) or a high-fat, moderate-cholesterol diet (MHF, 19.4% fat, n=12). Dams were fed the chow diet during the suckling period. At 28d postnatal age wild type and ApoE*3 Leiden offspring from chow or MHF-fed mothers were fed either a control chow diet (n=37) or a diet rich in cocoa butter (15%) and cholesterol (0.25%), for 14 weeks to induce atherosclerosis (n=36). Offspring from MHF-fed mothers had 1.9-fold larger atherosclerotic lesions (p<0.001). There was no direct effect of prenatal diet on plasma triglycerides or cholesterol, however transgenic ApoE*3 Leiden offspring displayed raised cholesterol when on an atherogenic diet compared to wild-type controls (p=0.031). Lesion size was correlated with plasma lipid parameters after adjustment for genotype, maternal diet and postnatal diet (R2=0.563, p<0.001). ApoE*3 Leiden mothers fed a MHF diet developed hypercholesterolemia (plasma cholesterol 2-fold higher than in chow fed mothers, p=0.011). The data strongly suggest that maternal hypercholesterolaemia programmes later susceptibility to atherosclerosis. This is consistent with previous observations in humans and animal models
Maternal high-fat feeding in pregnancy programmes atherosclerotic lesion size in the ApoE*3 Leiden mouse
Periods of rapid growth seen during the early stages of fetal development, including cell proliferation and differentiation, are greatly influenced by the maternal environment. We demonstrate here that over-nutrition, specifically exposure to a high fat diet in utero, programmed the extent of atherosclerosis in the offspring of ApoE*3 Leiden transgenic mice. Pregnant ApoE*3 Leiden mice were fed either a control chow diet (2.8% fat, n=12) or a high-fat, moderate-cholesterol diet (MHF, 19.4% fat, n=12). Dams were fed the chow diet during the suckling period. At 28d postnatal age wild type and ApoE*3 Leiden offspring from chow or MHF-fed mothers were fed either a control chow diet (n=37) or a diet rich in cocoa butter (15%) and cholesterol (0.25%), for 14 weeks to induce atherosclerosis (n=36). Offspring from MHF-fed mothers had 1.9-fold larger atherosclerotic lesions (p<0.001). There was no direct effect of prenatal diet on plasma triglycerides or cholesterol, however transgenic ApoE*3 Leiden offspring displayed raised cholesterol when on an atherogenic diet compared to wild-type controls (p=0.031). Lesion size was correlated with plasma lipid parameters after adjustment for genotype, maternal diet and postnatal diet (R2=0.563, p<0.001). ApoE*3 Leiden mothers fed a MHF diet developed hypercholesterolemia (plasma cholesterol 2-fold higher than in chow fed mothers, p=0.011). The data strongly suggest that maternal hypercholesterolaemia programmes later susceptibility to atherosclerosis. This is consistent with previous observations in humans and animal models
Pattern Transfer of Sub-10 nm Features via Tin-Containing Block Copolymers
Tin-containing block copolymers were investigated as materials for nanolithographic applications. Poly(4-trimethylstannylstyrene-block-styrene) (PSnS-PS) and poly(4-trimethylstannylstyrene-block-4-methoxystyrene) (PSnS-PMOST) synthesized by reversible addition–fragmentation chain transfer polymerization form lamellar domains with periodicities ranging from 18 to 34 nm. Thin film orientation control was achieved by thermal annealing between a neutral surface treatment and a top coat. Incorporation of tin into one block facilitates pattern transfer into SiO_2 via a two-step etch process utilizing oxidative and fluorine-based etch chemistries
Deterministic optical quantum computer using photonic modules
The optical quantum computer is one of the few experimental systems to have
demonstrated small scale quantum information processing. Making use of cavity
quantum electrodynamics approaches to operator measurements, we detail an
optical network for the deterministic preparation of arbitrarily large
two-dimensional cluster states. We show that this network can form the basis of
a large scale deterministic optical quantum computer that can be fabricated
entirely on chip.Comment: 9 pages, 10 figures, minor revision
Nonprescribed Antimicrobial Drugs in Latino Community, South Carolina
We investigated in a sample of Latinos the practices of antimicrobial drug importation and use of nonprescribed antimicrobial drugs. In interviews conducted with 219 adults, we assessed health beliefs and past and present behaviors consistent with acquiring antimicrobial drugs without a prescription in the United States. Many (30.6%) believed that antimicrobial drugs should be available in the United States without a prescription. Furthermore, 16.4% had transported nonprescribed antimicrobial drugs into the United States, and 19.2% had acquired antimicrobial agents in the United States without a prescription. A stepwise logistic regression analysis showed that the best predictors of having acquired nonprescribed antimicrobial drugs in the United States were beliefs and behavior consistent with limited regulations on such drugs. Many persons within the Latino community self-medicate with antimicrobial drugs obtained without a prescription both inside and outside the United States, which adds to the reservoir of antimicrobial drugs in the United States
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