9,846 research outputs found
Recursion Polynomials of Unfolded Sequences
Watermarking digital media is one of the important chal- lenges for information hiding. Not only the watermark must be resistant to noise and against attempts of modification, legitimate users should not be aware that it is embedded in the media. One of the techniques for watermarking is using an special variant of spread-spectrum tech- nique, called frequency hopping. It requires ensembles of periodic binary sequences with low off-peak autocorrelation and cross-correlation. Un- fortunately, they are quite rare and difficult to find. The small Kasami, Kamaletdinov, and Extended Rational Cycle constructions are versatile, because they can also be converted into Costas-like arrays for frequency hopping. We study the implementation of such ensembles using linear feedback shift registers. This permits an efficient generation of sequences and arrays in real time in FPGAs. Such an implementation requires minimal memory usage and permits dynamic updating of sequences or arrays. The aim of our work was to broaden current knowledge of sets of se- quences with low correlation studying their implementation using linear feedback shift registers. A remarkable feature of these families is their similarities in terms of implementation and it may open new way to characterize sequences with low correlation, making it easier to gener- ate them. It also validates some conjectures made by Moreno and Tirkel about arrays constructed using the method of composition.Supported by Consejería de Universidades e Investigación, Medio Ambiente y Política Social, Gobierno de Cantabria (ref. VP34
Capturing coevolutionary signals in repeat proteins
The analysis of correlations of amino acid occurrences in globular proteins
has led to the development of statistical tools that can identify native
contacts -- portions of the chains that come to close distance in folded
structural ensembles. Here we introduce a statistical coupling analysis for
repeat proteins -- natural systems for which the identification of domains
remains challenging. We show that the inherent translational symmetry of repeat
protein sequences introduces a strong bias in the pair correlations at
precisely the length scale of the repeat-unit. Equalizing for this bias reveals
true co-evolutionary signals from which local native-contacts can be
identified. Importantly, parameter values obtained for all other interactions
are not significantly affected by the equalization. We quantify the robustness
of the procedure and assign confidence levels to the interactions, identifying
the minimum number of sequences needed to extract evolutionary information in
several repeat protein families. The overall procedure can be used to
reconstruct the interactions at long distances, identifying the characteristics
of the strongest couplings in each family, and can be applied to any system
that appears translationally symmetric
RRS James Cook Cruise 30, 26 Dec 2008-30 Jan 2009. Antarctic Deep Water Rates of Export (ANDREX)
This report describes scientific activities on RRS James Cook cruise 30, “ANDREX”, westwards from 30°E and in the vicinity of latitude 60°S, between late December 2008 and late January 2009. The cruise was terminated about halfway through by a medical emergency. Hydrographic work comprised 27 CTD/LADCP stations. Water samples were captured for measurement of salinity, dissolved oxygen, inorganic nutrients, oxygen isotope fraction, chlorofluorocarbons and sulphur hexafluoride, dissolved inorganic carbon and alkalinity, helium / tritium / noble gases and radiocarbon. Underway measurements comprised navigation, currents (ADCP), meteorology, and sea surface temperature and salinity. The remainder of the hydrographic section was executed a year later on RRS James Clark Ross, cruise JR239
Quasi-Cyclic Asymptotically Regular LDPC Codes
Families of "asymptotically regular" LDPC block code ensembles can be formed
by terminating (J,K)-regular protograph-based LDPC convolutional codes. By
varying the termination length, we obtain a large selection of LDPC block code
ensembles with varying code rates, minimum distance that grows linearly with
block length, and capacity approaching iterative decoding thresholds, despite
the fact that the terminated ensembles are almost regular. In this paper, we
investigate the properties of the quasi-cyclic (QC) members of such an
ensemble. We show that an upper bound on the minimum Hamming distance of
members of the QC sub-ensemble can be improved by careful choice of the
component protographs used in the code construction. Further, we show that the
upper bound on the minimum distance can be improved by using arrays of
circulants in a graph cover of the protograph.Comment: To be presented at the 2010 IEEE Information Theory Workshop, Dublin,
Irelan
Digital quantum simulators in a scalable architecture of hybrid spin-photon qubits
Resolving quantum many-body problems represents one of the greatest
challenges in physics and physical chemistry, due to the prohibitively large
computational resources that would be required by using classical computers. A
solution has been foreseen by directly simulating the time evolution through
sequences of quantum gates applied to arrays of qubits, i.e. by implementing a
digital quantum simulator. Superconducting circuits and resonators are emerging
as an extremely-promising platform for quantum computation architectures, but a
digital quantum simulator proposal that is straightforwardly scalable,
universal, and realizable with state-of-the-art technology is presently
lacking. Here we propose a viable scheme to implement a universal quantum
simulator with hybrid spin-photon qubits in an array of superconducting
resonators, which is intrinsically scalable and allows for local control. As
representative examples we consider the transverse-field Ising model, a spin-1
Hamiltonian, and the two-dimensional Hubbard model; for these, we numerically
simulate the scheme by including the main sources of decoherence. In addition,
we show how to circumvent the potentially harmful effects of inhomogeneous
broadening of the spin systems
Effect of matrix parameters on mesoporous matrix based quantum computation
We present a solid state implementation of quantum computation, which
improves previously proposed optically driven schemes. Our proposal is based on
vertical arrays of quantum dots embedded in a mesoporous material which can be
fabricated with present technology. We study the feasibility of performing
quantum computation with different mesoporous matrices. We analyse which matrix
materials ensure that each individual stack of quantum dots can be considered
isolated from the rest of the ensemble-a key requirement of our scheme. This
requirement is satisfied for all matrix materials for feasible structure
parameters and GaN/AlN based quantum dots. We also show that one dimensional
ensembles substantially improve performances, even of CdSe/CdS based quantum
dots
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