21,003 research outputs found
Determinate-state convolutional codes
A determinate state convolutional code is formed from a conventional convolutional code by pruning away some of the possible state transitions in the decoding trellis. The type of staged power transfer used in determinate state convolutional codes proves to be an extremely efficient way of enhancing the performance of a concatenated coding system. The decoder complexity is analyzed along with free distances of these new codes and extensive simulation results is provided of their performance at the low signal to noise ratios where a real communication system would operate. Concise, practical examples are provided
Triangular Antiferromagnets
In this article we review the effects of magnetic frustation in the stacked
triangular lattice. Frustration increases the degeneracy of the ground state,
giving rise to different physics. In particular it leads to unique phase
diagrams with multicritical points and novel critical phenomena. We describe
the confrontation of theory and experiment for a number of systems with
differing magnetic Hamiltonians; Heisenberg, Heisenberg with easy-axis
anisotropy, Heisenberg with easy-plane anisotropy, Ising and singlet ground
state. Interestingly each leads to different magnetic properties and phase
diagrams. We also describe the effects of ferromagnetic, rather than
antiferromagnetic, stacking and of small distortions of the triangular lattice.Comment: Review article, 36 pages, revtex, 19 figures in PS format, to appear
in Can. J. Phy
Dark matter cores all the way down
We use high resolution simulations of isolated dwarf galaxies to study the
physics of dark matter cusp-core transformations at the edge of galaxy
formation: M200 = 10^7 - 10^9 Msun. We work at a resolution (~4 pc minimum cell
size; ~250 Msun per particle) at which the impact from individual supernovae
explosions can be resolved, becoming insensitive to even large changes in our
numerical 'sub-grid' parameters. We find that our dwarf galaxies give a
remarkable match to the stellar light profile; star formation history;
metallicity distribution function; and star/gas kinematics of isolated dwarf
irregular galaxies. Our key result is that dark matter cores of size comparable
to the stellar half mass radius (r_1/2) always form if star formation proceeds
for long enough. Cores fully form in less than 4 Gyrs for the M200 = 10^8 Msun
and 14 Gyrs for the 10^9 Msun dwarf. We provide a convenient two parameter
'coreNFW' fitting function that captures this dark matter core growth as a
function of star formation time and the projected stellar half mass radius.
Our results have several implications: (i) we make a strong prediction that
if LCDM is correct, then 'pristine' dark matter cusps will be found either in
systems that have truncated star formation and/or at radii r > r_1/2; (ii)
complete core formation lowers the projected velocity dispersion at r_1/2 by a
factor ~2, which is sufficient to fully explain the 'too big to fail problem';
and (iii) cored dwarfs will be much more susceptible to tides, leading to a
dramatic scouring of the subhalo mass function inside galaxies and groups.Comment: 20 pages; 9 figures; final version to appear in MNRAS including typos
corrected in proo
Quantization effects in Viterbi decoding rate 1/n convolutional codes
A Viterbi decoder's performance loss due to quantizing data from the additive white Gaussian noise (AWGN) channel is studied. An optimal quantization scheme and branch metric calculation method are presented. The uniformly quantized channel capacity C(sub u)(q) is used to determine the smallest number of quantization bits q that does not cause a significant loss. The quantizer stepsize which maximizes C(sub u)(q) almost minimizes the decoder bit error rate (BER). However, a slightly larger stepsize is better, like the value that minimizes the Bhattacharyya bound. The range and renormalization of state metrics is analyzed, in particular for K = 15 decoders such as the Big Viterbi Decoder (BVD) for the Galileo mission. These results are required to design reduced hardware complexity Viterbi decoders with a negligible quantization loss
Kinematics of Current Region Fragmentation in Semi-Inclusive Deeply Inelastic Scattering
Different kinematical regimes of semi-inclusive deeply inelastic scattering
(SIDIS) processes correspond to different underlying partonic pictures, and it
is important to understand the transition between them. This is particularly
the case when there is sensitivity to intrinsic transverse momentum, in which
case kinematical details can become especially important. We address the
question of how to identify the current fragmentation region --- the
kinematical regime where a factorization picture with fragmentation functions
is appropriate. We distinguish this from soft and target fragmentation regimes.
Our criteria are based on the kinematic regions used in derivations of
factorization theorems. We argue that, when hard scales are of order a few
GeVs, there is likely significant overlap between different rapidity regions
that are normally understood to be distinct. We thus comment on the need to
take this into account with more unified descriptions of SIDIS, which should
span all rapidities for the produced hadron. Finally, we propose general
criteria for estimating the proximity to the current region at large Q.Comment: 9 Pages, 5 figures; minor clarifications and corrections, version
appearing in Physics Letters
Superconducting resonators as beam splitters for linear-optics quantum computation
A functioning quantum computer will be a machine that builds up, in a
programmable way, nonclassical correlations in a multipartite quantum system.
Linear optics quantum computation (LOQC) is an approach for achieving this
function that requires only simple, reliable linear optical elements, namely
beam splitters and phase shifters. Nonlinear optics is only required in the
form of single-photon sources for state initialization, and detectors. However,
the latter remain difficult to achieve with high fidelity. A new setting for
quantum optics has arisen in circuit quantum electrodynamics (cQED) using
superconducting (SC) quantum devices, and opening up the way to LOQC using
microwave, rather than visible photons. Much progress is being made in SC
qubits and cQED: high-fidelity Fock state generation and qubit measurements
provide single photon sources and detection. Here we show that the LOQC toolkit
in cQED can be completed with high-fidelity (>99.92%) linear optical elements.Comment: 4 pages, 3 figure
De novo transcriptome assembly of the amphipod Gammarus chevreuxi exposed to chronic hypoxia
publisher: Elsevier articletitle: De novo transcriptome assembly of the amphipod Gammarus chevreuxi exposed to chronic hypoxia journaltitle: Marine Genomics articlelink: http://dx.doi.org/10.1016/j.margen.2017.01.006 content_type: article copyright: © 2017 Elsevier B.V. All rights reserved
The Application of Coaching Techniques to Financial Issues
Financial coaching is emerging as a distinct approach to building personal financial capability. However, the term financial coaching refers to a wide array of interventions. This article reviews the literature in order to define financial coaching. Financial coaching includes helping individuals define financial goals, develop plans of action, and implement steps toward their goals. The coaching approach is designed to help people develop and sustain positive financial behaviors. This article also presents findings from three financial coaching field studies; the results suggest that working with a financial coach increases clients’ ability to focus on their financial goals and engage in positive financial behaviors. Despite these beneficial outcomes, the coaching field faces several challenges including a lack of practice standards and consistent outcomes measures
The Randall-Sundrum Scenario with an Extra Warped Dimension
We investigate a scenario with two four-branes embedded in six dimensions.
When the metric is periodic and compact in one of the dimensions parallel to
the branes, the value of the effective cosmological constant for the remaining
five dimensions can assume a variety of values, determined by the dependence of
the metric on the sixth dimension. The picture that emerges resembles the
Randall-Sundrum model but with an extra warped dimension that allows the usual
brane-bulk fine tuning to be satisfied without finely tuning any of the
parameters in the underlying six dimensional theory. Although the action
contains terms with four derivatives of the metric, we show that when the
branes have a finite, natural thickness, such terms have only a small effect on
the Randall-Sundrum structure. The presence of these four derivative terms also
allows a configuration that resembles that produced by a domain wall but which
results from gravity alone.Comment: 12 pages, 3 figures, requires harvmac and picte
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