264 research outputs found
Aggregation pheromone compounds of the black larder beetle Dermestes haemorrhoidalis Kuster (Coleoptera: Dermestidae)
Gas chromatography with simultaneous flame ionisation and electroantennographic detection (GCEAD) and gas chromatography with mass spectrometry analysis (GCMS) of abdominal extracts of adult male Dermestes haemorrhoidalis Kuster (Coleoptera: Dermestidae) revealed the presence of electrophysiologically and behaviourally active compounds to its conspecific males and females. Isopropyl dodecanoate (3), isopropyl (Z)-9-tetradecenoate (5), isopropyl tetradecanoate (6), isopropyl (Z)-9-hexadecenoate (7) and isopropyl hexadecanoate (8) were detected in male abdominal extracts only. Analysis of collected male headspace volatiles revealed the presence of six EAD-active compounds (3), (5), (6) and isopropyl tridecanoate (4) plus two unidentified compounds (1) and (9). Synthetic compounds (3), (4), (5), (6) and (7) showed EAD activity with antennae of both sexes in contrast to synthetic (8) which showed EAD activity with female antennae only. Male and female antennae of D. haemorrhoidalis reacted with high receptor potentials to isopropyl (Z)-9-dodecenoate (2), although this compound itself was detected in neither male nor female abdominal extracts or headspace volatiles. Petri dish bioassays indicated that male abdominal extracts and compounds (2), (3), (5) and (6) aroused and attracted conspecific male and female beetles significantly (
Exact Solution of the Gauge Symmetric p -Spin Glass Model on a Complete Graph
We consider a gauge symmetric version of the p-spin glass model on a complete graph. The gauge symmetry guarantees the absence of replica symmetry breaking and allows to fully use the interpolation scheme of Guerra (Fields Inst. Commun. 30:161, 2001) to rigorously compute the free energy. In the case of pairwise interactions (p=2), where we have a gauge symmetric version of the Sherrington-Kirkpatrick model, we get the free energy and magnetization for all values of external parameters. Our analysis also works for even p≥4 except in a range of parameters surrounding the phase transition line, and for odd p≥3 in a more restricted region. We also obtain concentration estimates for the magnetization and overlap parameter that play a crucial role in the proofs for odd p and justify the absence of replica symmetry breaking. Our initial motivation for considering this model came from problems related to communication over a noisy channel, and is briefly explaine
On the concentration of the capacity for a code division multiple access system
We prove the concentration of the capacity, in the large system limit, for a code division multiple access system over an additive white Gaussian noise channel, with Gaussian signature sequences and {\it binary input} symbols. The probabilistic tools that are used are quite powerful and could have applications in many other similar situations
Restoration Data Storage in Multi-cloud Storage Services
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Exchange of Limits: Why Iterative Decoding Works
We consider communication over binary-input memoryless output-symmetric
channels using low-density parity-check codes and message-passing decoding. The
asymptotic (in the length) performance of such a combination for a fixed number
of iterations is given by density evolution. Letting the number of iterations
tend to infinity we get the density evolution threshold, the largest channel
parameter so that the bit error probability tends to zero as a function of the
iterations.
In practice we often work with short codes and perform a large number of
iterations. It is therefore interesting to consider what happens if in the
standard analysis we exchange the order in which the blocklength and the number
of iterations diverge to infinity. In particular, we can ask whether both
limits give the same threshold.
Although empirical observations strongly suggest that the exchange of limits
is valid for all channel parameters, we limit our discussion to channel
parameters below the density evolution threshold. Specifically, we show that
under some suitable technical conditions the bit error probability vanishes
below the density evolution threshold regardless of how the limit is taken.Comment: 16 page
Polar Codes are Optimal for Lossy Source Coding
We consider lossy source compression of a binary symmetric source using polar
codes and the low-complexity successive encoding algorithm. It was recently
shown by Arikan that polar codes achieve the capacity of arbitrary symmetric
binary-input discrete memoryless channels under a successive decoding strategy.
We show the equivalent result for lossy source compression, i.e., we show that
this combination achieves the rate-distortion bound for a binary symmetric
source. We further show the optimality of polar codes for various problems
including the binary Wyner-Ziv and the binary Gelfand-Pinsker problemComment: 15 pages, submitted to Transactions on Information Theor
A Class of Transformations that Polarize Symmetric Binary-Input Memoryless Channels
A generalization of Ar\i kan's polar code construction using transformations
of the form where is an matrix is
considered. Necessary and sufficient conditions are given for these
transformations to ensure channel polarization. It is shown that a large class
of such transformations polarize symmetric binary-input memoryless channels.Comment: 7 pages, 1 figur
Exact solution for the conditional entropy of Poissonian LDPC codes over the Binary Erasure Channel
We consider communication over a binary erasure channel with low density parity check codes and optimal maximum a posteriori decoding. It is known that the problem of computing the average conditional entropy, over such code ensembles, in the asymptotic limit of large block length is closely related to computing the free energy of a mean field spin glass in the thermodynamic limit. Tentative, but explicit, formulas for these quantities have been derived thanks to the replica method (of spin glass theory) and are generally conjectured to be exact. In this contribution we show that the replica formulas are indeed exact in the case of Poissonian low density parity check ensembles. Our methods use ideas coming from the recent progress in the rigorous analysis of the Sherrington-Kirkpatrick model and their applications to the theory of error correcting codes
Polar Codes: Characterization of Exponent, Bounds, and Constructions
Polar codes were recently introduced by Ar\i kan. They achieve the capacity
of arbitrary symmetric binary-input discrete memoryless channels under a low
complexity successive cancellation decoding strategy. The original polar code
construction is closely related to the recursive construction of Reed-Muller
codes and is based on the matrix \bigl[ 1 &0 1& 1 \bigr]. It was
shown by Ar\i kan and Telatar that this construction achieves an error exponent
of , i.e., that for sufficiently large blocklengths the error
probability decays exponentially in the square root of the length. It was
already mentioned by Ar\i kan that in principle larger matrices can be used to
construct polar codes. A fundamental question then is to see whether there
exist matrices with exponent exceeding . We first show that any matrix none of whose column permutations is upper triangular
polarizes symmetric channels. We then characterize the exponent of a given
square matrix and derive upper and lower bounds on achievable exponents. Using
these bounds we show that there are no matrices of size less than 15 with
exponents exceeding . Further, we give a general construction based on
BCH codes which for large achieves exponents arbitrarily close to 1 and
which exceeds for size 16.Comment: Submitted to IEEE Transactions on Information Theory, minor update
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