67,641 research outputs found
Error Correction for Cooperative Data Exchange
This paper considers the problem of error correction for a cooperative data
exchange (CDE) system, where some clients are compromised or failed and send
false messages. Assuming each client possesses a subset of the total messages,
we analyze the error correction capability when every client is allowed to
broadcast only one linearly-coded message. Our error correction capability
bound determines the maximum number of clients that can be compromised or
failed without jeopardizing the final decoding solution at each client. We show
that deterministic, feasible linear codes exist that can achieve the derived
bound. We also evaluate random linear codes, where the coding coefficients are
drawn randomly, and then develop the probability for a client to withstand a
certain number of compromised or failed peers and successfully deduce the
complete message for any network size and any initial message distributions
Large financial crashes
We propose that large stock market crashes are analogous to critical points
studied in statistical physics with log-periodic correction to scaling. We
extend our previous renormalization group model of stock market prices prior to
and after crashes [D. Sornette et al., J.Phys.I France 6, 167, 1996] by
including the first non-linear correction. This predicts the existence of a
log-frequency shift over time in the log-periodic oscillations prior to a
crash. This is tested on the two largest historical crashes of the century, the
october 1929 and october 1987 crashes, by fitting the stock market index over
an interval of 8 years prior to the crashes. The good quality of the fits, as
well as the consistency of the parameter values obtained from the two crashes,
promote the theory that crashes have their origin in the collective ``crowd''
behavior of many interacting agents.Comment: 14 pages and 4 figures. To be published in Physica
Computation of correlation-induced atomic displacements and structural transformations in paramagnetic KCuF3 and LaMnO3
We present a computational scheme for ab initio total-energy calculations of
materials with strongly interacting electrons using a plane-wave basis set. It
combines ab initio band structure and dynamical mean-field theory and is
implemented in terms of plane-wave pseudopotentials. The present approach
allows us to investigate complex materials with strongly interacting electrons
and is able to treat atomic displacements, and hence structural
transformations, caused by electronic correlations. Here it is employed to
investigate two prototypical Jahn-Teller materials, KCuF3 and LaMnO3, in their
paramagnetic phases. The computed equilibrium Jahn-Teller distortion and
antiferro-orbital order agree well with experiment, and the structural
optimization performed for paramagnetic KCuF3 yields the correct lattice
constant, equilibrium Jahn-Teller distortion and tetragonal compression of the
unit cell. Most importantly, the present approach is able to determine
correlation-induced structural transformations, equilibrium atomic positions
and lattice structure in both strongly and weakly correlated solids in their
paramagnetic phases as well as in phases with long-range magnetic order.Comment: 27 pages, 11 figure
On how good DFT exchange-correlation functionals are for H bonds in small water clusters: Benchmarks approaching the complete basis set limit
The ability of several density-functional theory (DFT) exchange-correlation
functionals to describe hydrogen bonds in small water clusters (dimer to
pentamer) in their global minimum energy structures is evaluated with reference
to second order Moeller Plesset perturbation theory (MP2). Errors from basis
set incompleteness have been minimized in both the MP2 reference data and the
DFT calculations, thus enabling a consistent systematic evaluation of the true
performance of the tested functionals. Among all the functionals considered,
the hybrid X3LYP and PBE0 functionals offer the best performance and among the
non-hybrid GGA functionals mPWLYP and PBE1W perform the best. The popular BLYP
and B3LYP functionals consistently underbind and PBE and PW91 display rather
variable performance with cluster size.Comment: 9 pages including 4 figures; related publications can be found at
http://www.fhi-berlin.mpg.de/th/th.htm
Self-concatenated code design and its application in power-efficient cooperative communications
In this tutorial, we have focused on the design of binary self-concatenated coding schemes with the help of EXtrinsic Information Transfer (EXIT) charts and Union bound analysis. The design methodology of future iteratively decoded self-concatenated aided cooperative communication schemes is presented. In doing so, we will identify the most important milestones in the area of channel coding, concatenated coding schemes and cooperative communication systems till date and suggest future research directions
The impact of coffee market reforms on producer prices and price transmission
This paper evaluates the impact of coffee sector reforms during late 1980s and early 1990s on coffee growers in the main coffee producing countries. Earlier evidence suggests that the reforms increased the share of producer prices in the world price of coffee. This hypothesis is tested in the paper with the help of cointegration analysis, and the results show that in most countries the longterm producer price share has indeed increased substantially after the liberalization. Moreover, the results suggest that the reforms induced a closer cointegrating relationship between grower prices and world market prices. Finally, estimation of an error-correction model reveals that short-run transmission of price signals from the world market to domestic producers has improved, such that domestic prices adjust faster today to world price fluctuations than they did prior to the reforms. However, there is some evidence of asymmetries in the way positive and negative world price changes are transmitted to domestic markets.Payment Systems&Infrastructure,Markets and Market Access,Insurance&Risk Mitigation,Environmental Economics&Policies,Economic Theory&Research,Access to Markets,Markets and Market Access,Crops&Crop Management Systems,Environmental Economics&Policies,Economic Theory&Research
The impact of coffee market reforms on producer prices and price transmission
This paper evaluates the impact of coffee sector reforms during late 1980s and early 1990s on coffee growers in the main coffee producing countries. Earlier evidence suggests that the reforms increased the share of producer prices in the world price of coffee. This hypothesis is tested in the paper with the help of cointegration analysis, and the results show that in most countries the long-term producer price share has indeed increased substantially after the liberalization. Moreover, the results suggest that the reforms induced a closer cointegrating relationship between grower prices and world market prices. Finally, estimation of an error-correction model reveals that short-run transmission of price signals from the world market to domestic producers has improved, such that domestic prices adjust faster today to world price fluctuations than they did prior to the reforms. However, there is some evidence of asymmetries in the way positive and negative world price changes are transmitted to domestic markets.International Relations/Trade,
Cooperative medium access control based on spectrum leasing
Based on cooperative spectrum leasing, a distributed “win–win” (WW) cooperative framework is designed to encourage the licensed source node (SN) to lease some part of its spectral resources to the unlicensed relay node (RN) for the sake of simultaneously improving the SN’s achievable rate and for reducing the energy consumption (EC). The potential candidate RNs carry out autonomous decisions concerning whether to contend for a cooperative transmission opportunity, which could dissipate some of their battery power, while conveying their traffic in light of their individual service requirements. Furthermore, a WW cooperative medium-access-control (MAC) protocol is designed to implement the proposed distributed WW cooperative framework. Simulation results demonstrate that our WW cooperative MAC protocol is capable of providing both substantial rate improvements and considerable energy savings for the cooperative spectrum leasing system
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