23,575 research outputs found
On-board processing for future satellite communications systems: Satellite-Routed FDMA
A frequency division multiple access (FDMA) 30/20 GHz satellite communications architecture without on-board baseband processing is investigated. Conceptual system designs are suggested for domestic traffic models totaling 4 Gb/s of customer premises service (CPS) traffic and 6 Gb/s of trunking traffic. Emphasis is given to the CPS portion of the system which includes thousands of earth terminals with digital traffic ranging from a single 64 kb/s voice channel to hundreds of channels of voice, data, and video with an aggregate data rate of 33 Mb/s. A unique regional design concept that effectively smooths the non-uniform traffic distribution and greatly simplifies the satellite design is employed. The satellite antenna system forms thirty-two 0.33 deg beam on both the uplinks and the downlinks in one design. In another design matched to a traffic model with more dispersed users, there are twenty-four 0.33 deg beams and twenty-one 0.7 deg beams. Detailed system design techniques show that a single satellite producing approximately 5 kW of dc power is capable of handling at least 75% of the postulated traffic. A detailed cost model of the ground segment and estimated system costs based on current information from manufacturers are presented
Universality in one-dimensional fermions at finite temperature: Density, pressure, compressibility, and contact
We present finite-temperature, lattice Monte Carlo calculations of the
particle number density, compressibility, pressure, and Tan's contact of an
unpolarized system of short-range, attractively interacting spin-1/2 fermions
in one spatial dimension, i.e., the Gaudin-Yang model. In addition, we compute
the second-order virial coefficients for the pressure and the contact, both of
which are in excellent agreement with the lattice results in the low-fugacity
regime. Our calculations yield universal predictions for ultracold atomic
systems with broad resonances in highly constrained traps. We cover a wide
range of couplings and temperatures and find results that support the existence
of a strong-coupling regime in which the thermodynamics of the system is
markedly different from the noninteracting case. We compare and contrast our
results with identical systems in higher dimensions.Comment: 6 pages, 7 figures; improved, published versio
Flight test and evaluation of Omega navigation in a general aviation aircraft. Volume 2: Appendices
Detailed documentation for each flight of the Omega Flight Evaluation study is presented, including flight test description sheets and actual flight data plots. Computer programs used for data processing and flight planning are explained and the data formats utilized by the Custom Interface Unit are summarized
Near Infrared Spectroscopic Monitoring During Cardiopulmonary Exercise Testing Detects Anaerobic Threshold
Cardiopulmonary exercise testing (CPET) provides assessment of the integrative responses involving the pulmonary, cardiovascular, and skeletal muscle systems. Application of exercise testing remains limited to children who are able to understand and cooperate with the exercise protocol. Near-infrared spectroscopy (NIRS) provides a noninvasive, continuous method to monitor regional tissue oxygenation (rSO2). Our specific aim was to predict anaerobic threshold (AT) during CPET noninvasively using two-site NIRS monitoring. Achievement of a practical noninvasive technology for estimating AT will increase the compatibility of CPET. Patients without structural or acquired heart disease were eligible for inclusion if they were ordered to undergo CPET by a cardiologist. Data from 51 subjects was analyzed. The ventilatory anaerobic threshold (VAT) was computed on VCO2 and respiratory quotient post hoc using the standard V-slope method. The inflection points of the regional rSO2 time-series were identified as the noninvasive regional NIRS AT for each of the two monitored regions (cerebral and kidney). AT calculation made using an average of kidney and brain NIRS matched the calculation made by VAT for the same patient. Two-site NIRS monitoring of visceral organs is a predictor of AT
Meander, Folding and Arch Statistics
The statistics of meander and related problems are studied as particular
realizations of compact polymer chain foldings. This paper presents a general
discussion of these topics, with a particular emphasis on three points: (i) the
use of a direct recursive relation for building (semi) meanders (ii) the
equivalence with a random matrix model (iii) the exact solution of simpler
related problems, such as arch configurations or irreducible meanders.Comment: 82 pages, uuencoded, uses harvmac (l mode) and epsf, 26+7 figures
include
Stability of Inhomogeneous Superstructures from Renormalized Mean-field Theory of the t--J Model
Using the t--J model (which can also include Coulomb repulsion) and the
``plain vanilla'' renormalized mean-field theory of Zhang et al. (1988),
stability of inhomogeneous 4a x 4a superstructures as those observed in
cuprates superconductors around hole doping 1/8 is investigated. We find a
non-uniform 4a x 4a bond order wave involving simultaneously small (~ 10^-2 t)
inhomogeneous staggered plaquette currents as well as a small charge density
modulation similar to pair density wave order. On the other hand, no supersolid
phase involving a decoupling in the superconducting particle-particle channel
is found.Comment: 4 page
Basic Representations of A_{2l}^(2) and D_{l+1}^(2) and the Polynomial Solutions to the Reduced BKP Hierarchies
Basic representations of A_{2l}^(2) and D_{l+1}^(2) are studied. The weight
vectors are represented in terms of Schur's -functions. The method to get
the polynomial solutions to the reduced BKP hierarchies is shown to be
equivalent to a certain rule in Maya game.Comment: January 1994, 11 page
Ultrahigh Transmission Optical Nanofibers
We present a procedure for reproducibly fabricating ultrahigh transmission
optical nanofibers (530 nm diameter and 84 mm stretch) with single-mode
transmissions of 99.95 0.02%, which represents a loss from tapering of
2.6 10 dB/mm when normalized to the entire stretch. When
controllably launching the next family of higher-order modes on a fiber with
195 mm stretch, we achieve a transmission of 97.8 2.8%, which has a loss
from tapering of 5.0 10 dB/mm when normalized to the
entire stretch. Our pulling and transfer procedures allow us to fabricate
optical nanofibers that transmit more than 400 mW in high vacuum conditions.
These results, published as parameters in our previous work, present an
improvement of two orders of magnitude less loss for the fundamental mode and
an increase in transmission of more than 300% for higher-order modes, when
following the protocols detailed in this paper. We extract from the
transmission during the pull, the only reported spectrogram of a fundamental
mode launch that does not include excitation to asymmetric modes; in stark
contrast to a pull in which our cleaning protocol is not followed. These
results depend critically on the pre-pull cleanliness and when properly
following our pulling protocols are in excellent agreement with simulations.Comment: 32 pages, 10 figures, accepted to AIP Advance
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