1,416 research outputs found
Telemetry coding study for the international magnetosphere explorers mother-daughter and heliocentric missions. Volume 1: Summary
The convolutional coding study on the IME Mother-Daughter and Heliocentric spacecraft is reported. The three major tasks involved in the study are summarized
Power spectrum analysis of staggered quadriphase-shift-keyed signals
Mathematical analysis of power spectrum of outputs from high-reliability communication system is used to determine system bandwidth. Analysis provides mathematical relationships of signal power spectrum at output of hard limiter for any type of baseband pulse input subjected only to output parameter constraints
The graceful exit in pre-big bang string cosmology
We re-examine the graceful exit problem in the pre-big bang scenario of
string cosmology, by considering the most general time-dependent classical
correction to the Lagrangian with up to four derivatives. By including possible
forms for quantum loop corrections we examine the allowed region of parameter
space for the coupling constants which enable our solutions to link smoothly
the two asymptotic low-energy branches of the pre-big bang scenario, and
observe that these solutions can satisfy recently proposed entropic bounds on
viable singularity free cosmologies.Comment: 14 pages, 6 figures, JHEP class. Added new section on the classical
correction and reference
Cosmological perturbations and the transition from contraction to expansion
We investigate both analytically and numerically the evolution of scalar
perturbations generated in models which exhibit a smooth transition from a
contracting to an expanding Friedmann universe. We find that the resulting
spectral index in the late radiation dominated universe depends on which of the
or \ variables passes regularly through the transition. The
results can be parameterized through the exponent defining the rate of
contraction of the universe. For we find that there are no stable
cases where both variables are regular during the transition. In particular,
for , we find that the resulting spectral index is close to scale
invariant if is regular, whereas it has a steep blue behavior if
is regular. We also show that as long as , perturbations arising
from the Bardeen potential remain small during contraction in the sense that
there exists a gauge in which all the metric and matter perturbation variables
are small.Comment: 30 pages, 16 figures. Version to appear in Phys. Rev. D. Slight
modifications, but no change in the conclusio
Supermanifolds - Application to Supersymmetry
Parity is ubiquitous, but not always identified as a simplifying tool for
computations. Using parity, having in mind the example of the bosonic/fermionic
Fock space, and the framework of Z_2-graded (super) algebra, we clarify
relationships between the different definitions of supermanifolds proposed by
various people. In addition, we work with four complexes allowing an invariant
definition of divergence:
- an ascending complex of forms, and a descending complex of densities on
real variables
- an ascending complex of forms, and descending complex of densities on Grass
mann variables.
This study is a step towards an invariant definition of integrals of
superfunctions defined on supermanifolds leading to an extension to infinite
dimensions. An application is given to a construction of supersymmetric Fock
spaces.Comment: to appear in the "Michael Marinov Memorial Volume
Telemetry coding study for the international magnetosphere explorers, mother/daughter and heliocentric missions. Volume 2: Final report
A convolutional coding theory is given for the IME and the Heliocentric spacecraft. The amount of coding gain needed by the mission is determined. Recommendations are given for an encoder/decoder system to provide the gain along with an evaluation of the impact of the system on the space network in terms of costs and complexity
Shuttle communications design study
The design and development of a space shuttle communication system are discussed. The subjects considered include the following: (1) Ku-band satellite relay to shuttle, (2) phased arrays, (3) PN acquisition, (4) quadriplexing of direct link ranging and telemetry, (5) communications blackout on launch and reentry, (6) acquisition after blackout on reentry, (7) wideband communications interface with the Ku-Band rendezvous radar, (8) aeroflight capabilities of the space shuttle, (9) a triple multiplexing scheme equivalent to interplex, and (10) a study of staggered quadriphase for use on the space shuttle
Operations on integral lifts of K(n)
This very rough sketch is a sequel to arXiv:1808.08587; it presents evidence
that operations on lifts of the functors K(n) to cohomology theories with
values in modules over valuation rings of local number fields, indexed by
Lubin-Tate groups of such fields, are extensions of the groups of automorphisms
of the indexing group laws, by the exterior algebras on the normal bundle to
the orbits of the group laws in the space of lifts.Comment: \S 2.0 hopefully less cryptic. To appear in the proceedings of the
2015 Nagoya conference honoring T Ohkawa. Comments very welcome
The QUEST-La Silla AGN Variability Survey
We present the characterization and initial results from the QUEST-La Silla
AGN variability survey. This is an effort to obtain well sampled optical light
curves in extragalactic fields with unique multi-wavelength observations. We
present photometry obtained from 2010 to 2012 in the XMM-COSMOS field, which
was observed over 150 nights using the QUEST camera on the ESO-Schmidt
telescope. The survey uses a broadband filter, the -band, similar to the
union of the and the filters, achieving an intrinsic photometric
dispersion of mag, and a systematic error of mag in the
zero-point. Since some detectors of the camera show significant non-linearity,
we use a linear correlation to fit the zero-points as a function of the
instrumental magnitudes, thus obtaining a good correction to the non-linear
behavior of these detectors. We obtain good photometry to an equivalent
limiting magnitude of . Studying the optical variability of X-ray
detected sources in the XMM-COSMOS field, we find that the survey is
% complete to magnitudes , and % complete to a
magnitude . The determination and parameterization of the structure
function () of the variable sources shows
that most BL AGN are characterized by and . It is
further shown that variable NL AGN and GAL sources occupying the same parameter
space in and are very likely to correspond to obscured or low
luminosity AGN. Our samples are, however, small, and we expect to revisit these
results using larger samples with longer light curves obtained as part of our
ongoing survey.Comment: Accepted for publication in Ap
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