32,443 research outputs found
Transient dynamics of molecular devices under step-like pulse bias
We report first principles investigation of time-dependent current of
molecular devices under a step-like pulse.Our results show that although the
switch-on time of the molecular device is comparable to the transit time, much
longer time is needed to reach the steady state. In reaching the steady state
the current is dominated by resonant states below Fermi level. The contribution
of each resonant state to the current shows the damped oscillatory behavior
with frequency equal to the bias of the step-like pulse and decay rate
determined by the life time of the corresponding resonant state. We found that
all the resonant states below Fermi level have to be included for accurate
results. This indicates that going beyond wideband limit is essential for a
quantitative analysis of transient dynamics of molecular devices
Outflow and hot dust emission in high redshift quasars
Correlations of hot dust emission with outflow properties are investigated,
based on a large z~2 non-broad absorption lines quasar sample built from the
Wide-field Infrared Survey and the Sloan Digital Sky Survey data releases. We
use the near infrared slope and the infrared to UV luminosity ratio to indicate
the hot dust emission relative to the emission from the accretion disk. In our
luminous quasars, these hot dust emission indicators are almost independent of
the fundamental parameters, such as luminosity, Eddington ratio and black hole
mass, but moderately dependent on the blueshift and asymmetry index (BAI) and
full width at half-maximum (FWHM) of CIV lines. Interestingly, the latter two
correlations dramatically strengthen with increasing Eddington ratio. We
suggest that, in high Eddington ratio quasars, CIV regions are dominated by
outflows so the BAI and FWHM(CIV) can reliably reflect the general properties
and velocity of outflows, respectively. While in low Eddington ratio quasars,
CIV lines are primarily emitted by virialized gas so the BAI and FWHM(CIV)
become less sensitive to outflows. Therefore, the correlations for the highest
Eddington ratio quasars are more likely to represent the true dependence of hot
dust emission on outflows and the correlations for the entire sample are
significantly diluted by the low Eddington ratio quasars. Our results show that
an outflow with a large BAI or velocity can double the hot dust emission on
average. We suggest that outflows either contain hot dust in themselves or
interact with the dusty interstellar medium or torus.Comment: 14 page, 4 figures, accepted for publication in ApJ
Energy Efficiency Analysis of Heterogeneous Cache-enabled 5G Hyper Cellular Networks
The emerging 5G wireless networks will pose extreme requirements such as high throughput and low latency. Caching as a promising technology can effectively decrease latency and provide customized services based on group users behaviour (GUB). In this paper, we carry out the energy efficiency analysis in the cache-enabled hyper cellular networks (HCNs), where the macro cells and small cells (SCs) are deployed heterogeneously with the control and user plane (C/U) split. Benefiting from the assistance of macro cells, a novel access scheme is proposed according to both user interest and fairness of service, where the SCs can turn into semi- sleep mode. Expressions of coverage probability, throughput and energy efficiency (EE) are derived analytically as the functions of key parameters, including the cache ability, search radius and backhaul limitation. Numerical results show that the proposed scheme in HCNs can increase the network coverage probability by more than 200% compared with the single- tier networks. The network EE can be improved by 54% than the nearest access scheme, with larger research radius and higher SC cache capacity under lower traffic load. Our performance study provides insights into the efficient use of cache in the 5G software defined networking (SDN)
Algorithm and Architecture for Path Metric Aided Bit-Flipping Decoding of Polar Codes
Polar codes attract more and more attention of researchers in recent years,
since its capacity achieving property. However, their error-correction
performance under successive cancellation (SC) decoding is inferior to other
modern channel codes at short or moderate blocklengths. SC-Flip (SCF) decoding
algorithm shows higher performance than SC decoding by identifying possibly
erroneous decisions made in initial SC decoding and flipping them in the
sequential decoding attempts. However, it performs not well when there are more
than one erroneous decisions in a codeword. In this paper, we propose a path
metric aided bit-flipping decoding algorithm to identify and correct more
errors efficiently. In this algorithm, the bit-flipping list is generated based
on both log likelihood ratio (LLR) based path metric and bit-flipping metric.
The path metric is used to verify the effectiveness of bit-flipping. In order
to reduce the decoding latency and computational complexity, its corresponding
pipeline architecture is designed. By applying these decoding algorithms and
pipeline architecture, an improvement on error-correction performance can be
got up to 0.25dB compared with SCF decoding at the frame error rate of
, with low average decoding latency.Comment: 6 pages, 6 figures, IEEE Wireless Communications and Networking
Conference (2019 WCNC
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