26,449 research outputs found
Performance of binary block codes at low signal-to-noise ratios
The performance of general binary block codes on an unquantized additive white Gaussian noise (AWGN) channel at low signal-to-noise ratios is considered. Expressions are derived for both the block error and the bit error probabilities near the point where the bit signal-to-noise ratio is zero. These expressions depend on the global geometric structure of the code, although the minimum distance still seems to play a crucial role. Examples of codes such as orthogonal codes, biorthogonal codes, the (24,12) extended Golay code, and the (15,6) expurgated BCH code are discussed. The asymptotic coding gain at low signal-to-noise ratios is also studied
A correlative study of SSC's, interplanetary shocks, and solar activity
A total of 93 SSC's were examined during the four year period from 1968 to 1971 at and near the peak of the solar activity cycle. Of the 93 SSC's 81 could be associated with solar activity, such as solar flares and radio bursts of Type II and Type IV. The mean propagation speeds of these flare-associated events ranged from 400 to 1000 km/sec with an average speed of 600-700 km/sec. Disturbances associated with 48 of the SSC's have been studied in detail using the corresponding interplanetary (IP) magnetic field, and plasma data when they were available. It was found that 41 of the 48 disturbances corresponded to IP shock waves, and the remaining seven events were tangential discontinuities. Thirty percent of the IP shocks had thick structure (i.e. the magnetic field jump across the shock occurred over a distance much greater than 50 proton Larmor radii). Also given is a statistical study of the gross geometry of a typical or average shock surface based on multiple spacecraft sightings and their relative orientation with respect to the solar flare. It is suggested that a typical shock front propagating out from the sun at l AU has a radius of curvature on the order of l AU. Also given are some general properties of oblique IP flare-shocks
Thermodynamic properties of compounds of biochemical interest in aqueous solution. A survey of thermodynamic properties of the compounds of the elements CHNOPS Progress report
Thermodynamic properties of compounds of biochemical interest in aqueous solutio
Non-Gaussian Covariance of CMB B-modes of Polarization and Parameter Degradation
The B-mode polarization lensing signal is a useful probe of the neutrino mass
and to a lesser extent the dark energy equation of state as the signal depends
on the integrated mass power spectrum between us and the last scattering
surface. This lensing B-mode signal, however, is non-Gaussian and the resulting
non-Gaussian covariance to the power spectrum cannot be ignored as correlations
between B-mode bins are at a level of 0.1. For temperature and E-mode
polarization power spectra, the non-Gasussian covariance is not significant,
where we find correlations at the 10^{-5} level even for adjacent bins. The
resulting degradation on neutrino mass and dark energy equation of state is
about a factor of 2 to 3 when compared to the case where statistics are simply
considered to be Gaussian. We also discuss parameter uncertainties achievable
in upcoming experiments and show that at a given angular resolution for
polarization observations, increasing the sensitivity beyond a certain noise
value does not lead to an improved measurement of the neutrino mass and dark
energy equation of state with B-mode power spectrum. For Planck, the resulting
constraints on the sum of the neutrino masses is ~ 0.2 eV and on the dark
energy equation of state parameter we find, sigma_w ~ 0.5.Comment: 11 pages, 5 figures, minor changes, submitted to PR
Torus Models of the Outer Disc of the Milky Way using LAMOST Survey Data
With a sample of 48,161 K giant stars selected from the LAMOST DR 2
catalogue, we construct torus models in a large volume extending, for the first
time, from the solar vicinity to a Galactocentric distance of kpc,
reaching the outskirts of the Galactic disc. We show that the kinematics of the
K giant stars match conventional models, e.g. as created by Binney in 2012, in
the Solar vicinity. However such two-disc models fail if they are extended to
the outer regions, even if an additional disc component is utilised. If we
loosen constraints in the Sun's vicinity, we find that an effective thick disc
model could explain the anti-centre of the MW. The LAMOST data imply that the
sizes of the Galactic discs are much larger, and that the outer disc is much
thicker, than previously thought, or alternatively that the outer structure is
not a conventional disc at all. However, the velocity dispersion
of the kinematically thick disc in the best-fitting model is about 80 km
s and has a scale parameter for an exponential distribution
function of kpc. Such a height is strongly rejected by
current measurements in the solar neighbourhood, and thus a model beyond
quasi-thermal, two or three thin or thick discs is required.Comment: 11 pages, 7 figures and 3 tables, Accepted for publication in MNRA
On C*-algebras related to constrained representations of a free group
We consider representations of the free group on two generators such
that the norm of the sum of the generators and their inverses is bounded by
. These -constrained representations determine a C*-algebra
for each . We prove that these C*-algebras form a
continuous bundle of C*-algebras over and calculate their K-groups.Comment: 9 page
Exclusive Lambda_b -> Lambda l^+ l^- decay in two Higgs doublet model
Rare Lambda_b -> Lambda l^+ l^- decay is investigated in framework of general
two Higgs doublet model, in which a new source of CP violation exists (model
III). The polarization parameter, CP asymmetry and decay width are calculated.
It is shown that CP asymmetry is a very sensitive tool for establishing model
III.Comment: 16 pages, 3 figures, LaTeX formatte
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