7,249 research outputs found
Non Binary Low Density Parity Check Codes Decoding Over Galois Field
Conventional LDPC codes have a low decoding complexity but may have high encoding complexity. The encoding complexity is typically of the order O(n2)[5]. Also high storage space may be required to explicitly store the generator matrix. For long blocknbsp lengths the storage space required would be huge. The above factors make the implementation of the Conventional LDPC codes less attractive.
These codes are usually decoded using the sum-product algorithm, which is anbsp message passing algorithm working on the Tanner graph of the code[5]. The sparseness of the parity check matrix is essential for attaining good performance with sum-product decoding. The time complexity of the sum- product algorithm is linear in code length. This property makes it possible to implement a practical decoder for long lengths.nbs
Asymptotically Optimal Approximation Algorithms for Coflow Scheduling
Many modern datacenter applications involve large-scale computations composed
of multiple data flows that need to be completed over a shared set of
distributed resources. Such a computation completes when all of its flows
complete. A useful abstraction for modeling such scenarios is a {\em coflow},
which is a collection of flows (e.g., tasks, packets, data transmissions) that
all share the same performance goal.
In this paper, we present the first approximation algorithms for scheduling
coflows over general network topologies with the objective of minimizing total
weighted completion time. We consider two different models for coflows based on
the nature of individual flows: circuits, and packets. We design
constant-factor polynomial-time approximation algorithms for scheduling
packet-based coflows with or without given flow paths, and circuit-based
coflows with given flow paths. Furthermore, we give an -approximation polynomial time algorithm for scheduling circuit-based
coflows where flow paths are not given (here is the number of network
edges).
We obtain our results by developing a general framework for coflow schedules,
based on interval-indexed linear programs, which may extend to other coflow
models and objective functions and may also yield improved approximation bounds
for specific network scenarios. We also present an experimental evaluation of
our approach for circuit-based coflows that show a performance improvement of
at least 22% on average over competing heuristics.Comment: Fixed minor typo
Review of two-dimensional materials for photocatalytic water splitting from a theoretical perspective
Two-dimensional (2D) materials have shown extraordinary performances as photocatalysts compared to their bulk counterparts. Simulations have made a great contribution to the deep understanding and design of novel 2D photocatalysts. Ab initio simulations based on density functional theory (DFT) not only show efficiency and reliability in new structure searching, but also can provide a reliable, efficient, and economic way for screening the photocatalytic property space. In this review, we summarize the recent developments in the field of water splitting using 2D materials from a theoretical perspective. We address that DFT-based simulations can fast screen the potential spaces of photocatalytic properties with the accuracy comparable to experiments, by investigating the effects of various physical/chemical perturbations. This, at last, will lead to the enhanced photocatalytic activities of 2D materials, and promote the development of photocatalysis
{Vid2Doppler}: {S}ynthesizing Doppler Radar Data from Videos for Training Privacy-Preserving Activity Recognition
Pressure-induced alpha-to-omega transition in titanium metal: A systematic study of the effects of uniaxial stress
We investigated the effects of uniaxial stress on the pressure-induced
alpha-to-omega transition in pure titanium (Ti) by means of angle dispersive
x-ray diffraction in a diamond-anvil cell. Experiments under four different
pressure environments reveal that: (1) the onset of the transition depends on
the pressure medium used, going from 4.9 GPa (no pressure medium) to 10.5 GPa
(argon pressure medium); (2) the a and w phases coexist over a rather large
pressure range, which depends on the pressure medium employed; (3) the
hysteresis and quenchability of the w phase is affected by differences in the
sample pressure environment; and (4) a short term laser-heating of Ti lowers
the alpha-to-omega transition pressure. Possible transition mechanisms are
discussed in the light of the present results, which clearly demonstrated the
influence of uniaxial stress in the alpha-to-omega transition.Comment: 16 pages, 6 figures, 1 tabl
Probing pulsar dispersion measures using the GMRT
We present the results from a novel experiment for accurate estimation of pulsar dispersion measure (1 part in 104) using the GMRT, without requiring any absolute timing information. The observations were carried out over a period of more than one year for a sample of twelve pulsars. We have used the simultaneous multi-frequency capability of the GMRT. Most of the sample pulsars studied show dispersion measure (DM) variations on time scales of weeks to months. The mean DM value for some of the pulsars show a significant discrepancy with respect to the catalog value. Pulsar B2217+47 shows a large-scale DM gradient over a one year period. For some pulsars we find small differences in the DM values obtained from different frequency combinations
Tracking pulsar dispersion measures using the giant metrewave radio telescope
In this paper, we describe a novel experiment for the accurate estimation of pulsar dispersion measures (DMs) using the Giant Metrewave Radio Telescope. This experiment was carried out for a sample of 12 pulsars, over a period of more than one year (2001 January to 2002 May) with observations about once every fortnight. At each epoch, the pulsar DMs were obtained from simultaneous dual-frequency observations, without requiring any absolute timing information. The DM estimates were obtained from both the single-pulse data streams and from the average profiles. The accuracy of the DM estimates at each epoch is ~1 part in 104 or better, making the data set useful for many different kinds of studies. The time-series of DMs shows significant variations on time-scales of weeks to months for most of the pulsars. An analysis of the mean DM values from these data shows significant deviations from catalogue values (as well as from other estimates in the literature) for some of the pulsars, with PSR B1642-03 showing the most notable differences. From our analysis results it appears that the constancy of pulsar DMs (at the level of 1 in 103 or better) cannot be taken for granted. For PSR B2217+47, we see evidence of a large-scale DM gradient over a 1-yr period, which is modelled as being due to a blob of enhanced electron density sampled by the line of sight. For some pulsars, including pulsars with fairly simple profiles such as PSR B1642-03, we find evidence for small changes in DM values for different frequency pairs of measurement, a result that needs to be investigated in detail. Another interesting result is that we find significant differences in DM values obtained from average profiles and single-pulse data
Tracking pulsar dispersion measures using the GMRT
In this paper, we describe a novel experiment for the accurate estimation of
pulsar dispersion measures using the Giant Metre-wave Radio Telescope. This
experiment was carried out for a sample of twelve pulsars, over a period of
more than one year (January 2001 to May 2002) with observations about once
every fortnight. At each epoch, the pulsar DMs were obtained from simultaneous
dual frequency observations, without requiring any absolute timing information.
The DM estimates were obtained from both the single pulse data streams and from
the average profiles. The accuracy of the DM estimates at each epoch is ~ 1
part in 10^4 or better, making the data set useful for many different kinds of
studies. The time series of DM shows significant variations on time scales of
weeks to months for most of the pulsars. A comparison of the mean DM values
from these data show significant deviations from catalog values (as well as
from other estimates in literature) for some of the pulsars, with PSR B1642-03
showing the most notable changes. From our analysis results it appears that
constancy of pulsar DMs (at the level of 1 in 10^3 or better) can not be taken
for granted. For PSR B2217+47, we see evidence for a large-scale DM gradient
over a one year period, which is modeled as being due to a blob of enhanced
electron density sampled by the line of sight. For some pulsars, including
pulsars with fairly simple profiles like PSR B1642-03, we find evidence for
small changes in DM values for different frequency pairs of measurement, a
result that needs to be investigated in detail. Another interesting result is
that we find significant differences in DM values obtained from average
profiles and single pulse data.Comment: 10 pages, 7 Postscript figures, to be published in MNRA
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