37,663 research outputs found
Carrier extraction circuit
Feedback loop extracts demodulated reference signals from IF input and feeds signal back to demodulator. Since reference signal is extracted directly from carrier, no separate reference need be transmitted. Circuit obtains coherent carrier from balanced or unbalanced four-phase signal of varying characteristics
Traffic control system and method
Frequency of carrier received by aircraft is measured and compared with reference to indicate magnitude of Doppler shift. One Doppler frequency range is selected and indicated by digital signal. Difference between frequency is offset of apparent carrier frequency transmitted by aircraft
Traffic control system and method Patent
Traffic control system for supersonic transports using synchronous satellite for data relay between vehicles and ground statio
Spontaneous radiative decay of translational levels of an atom near a dielectric surface
We study spontaneous radiative decay of translational levels of an atom in
the vicinity of a semi-infinite dielectric. We systematically derive the
microscopic dynamical equations for the spontaneous decay process. We calculate
analytically and numerically the radiative linewidths and the spontaneous
transition rates for the translational levels. The roles of the interference
between the emitted and reflected fields and of the transmission into the
evanescent modes are clearly identified. Our numerical calculations for the
silica--cesium interaction show that the radiative linewidths of the bound
excited levels with large enough but not too large vibrational quantum numbers
are moderately enhanced by the emission into the evanescent modes and those for
the deep bound levels are substantially reduced by the surface-induced red
shift of the transition frequency
Functional requirements for the man-vehicle systems research facility
The NASA Ames Research Center proposed a man-vehicle systems research facility to support flight simulation studies which are needed for identifying and correcting the sources of human error associated with current and future air carrier operations. The organization of research facility is reviewed and functional requirements and related priorities for the facility are recommended based on a review of potentially critical operational scenarios. Requirements are included for the experimenter's simulation control and data acquisition functions, as well as for the visual field, motion, sound, computation, crew station, and intercommunications subsystems. The related issues of functional fidelity and level of simulation are addressed, and specific criteria for quantitative assessment of various aspects of fidelity are offered. Recommendations for facility integration, checkout, and staffing are included
ASCA and ROSAT observations of nearby cluster cooling flows
We present a detailed analysis of the X-ray properties of the cooling flows
in a sample of nearby, X-ray bright clusters of galaxies using high-quality
ASCA spectra and ROSAT X-ray images. We demonstrate the need for multiphase
models to consistently explain the spectral and imaging X-ray data for the
clusters. The mass deposition rates of the cooling flows, independently
determined from the ASCA spectra and ROSAT images, exhibit reasonable
agreement. We confirm the presence of intrinsic X-ray absorption in the
clusters using a variety of spectral models. We also report detections of
extended m infrared emission, spatially coincident with the cooling
flows, in several of the systems studied. The observed infrared fluxes and flux
limits are in good agreement with the predicted values due to reprocessed X-ray
emission from the cooling flows. We present precise measurements of the
abundances of iron, magnesium, silicon and sulphur in the central regions of
the Virgo and Centaurus clusters. Our results firmly favour models in which a
high mass fraction (70-80 per cent) of the iron in the X-ray gas in these
regions is due to Type Ia supernovae. Finally, we present a series of methods
which may be used to measure the ages of cooling flows from the X-ray data. The
results for the present sample of clusters indicate ages of between 2.5 and 7
Gyr. If the ages of cooling flows are primarily set by subcluster merger
events, then our results suggest that in the largest clusters, mergers with
subclusters with masses of approximately 30 per cent of the final cluster mass
are likely to disrupt cooling flows.Comment: Final version. MNRAS, in press. 36 pages, 9 figs, 14 tables in MNRAS
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Symmetry analysis of crystalline spin textures in dipolar spinor condensates
We study periodic crystalline spin textures in spinor condensates with
dipolar interactions via a systematic symmetry analysis of the low-energy
effective theory. By considering symmetry operations which combine real and
spin space operations, we classify symmetry groups consistent with non-trivial
experimental and theoretical constraints. Minimizing the energy within each
symmetry class allows us to explore possible ground states.Comment: 19 pages, 4 figure
Field-induced structure transformation in electrorheological solids
We have computed the local electric field in a body-centered tetragonal (BCT)
lattice of point dipoles via the Ewald-Kornfeld formulation, in an attempt to
examine the effects of a structure transformation on the local field strength.
For the ground state of an electrorheological solid of hard spheres, we
identified a novel structure transformation from the BCT to the face-centered
cubic (FCC) lattices by changing the uniaxial lattice constant c under the hard
sphere constraint. In contrast to the previous results, the local field
exhibits a non-monotonic transition from BCT to FCC. As c increases from the
BCT ground state, the local field initially decreases rapidly towards the
isotropic value at the body-centered cubic lattice, decreases further, reaching
a minimum value and increases, passing through the isotropic value again at an
intermediate lattice, reaches a maximum value and finally decreases to the FCC
value. An experimental realization of the structure transformation is
suggested. Moreover, the change in the local field can lead to a generalized
Clausius-Mossotti equation for the BCT lattices.Comment: Submitted to Phys. Rev.
Noble gas films on a decagonal AlNiCo quasicrystal
Thermodynamic properties of Ne, Ar, Kr, and Xe adsorbed on an Al-Ni-Co
quasicrystalline surface (QC) are studied with Grand Canonical Monte Carlo by
employing Lennard-Jones interactions with parameter values derived from
experiments and traditional combining rules. In all the gas/QC systems, a
layer-by-layer film growth is observed at low temperature. The monolayers have
regular epitaxial fivefold arrangements which evolve toward sixfold
close-packed structures as the pressure is increased. The final states can
contain either considerable or negligible amounts of defects. In the latter
case, there occurs a structural transition from five to sixfold symmetry which
can be described by introducing an order parameter, whose evolution
characterizes the transition to be continuous or discontinuous as in the case
of Xe/QC (first-order transition with associated latent heat). By simulating
fictitious noble gases, we find that the existence of the transition is
correlated with the size mismatch between adsorbate and substrate's
characteristic lengths. A simple rule is proposed to predict the phenomenon.Comment: 19 pages. 8 figures. (color figures can be seen at
http://alpha.mems.duke.edu/wahyu/ or
http://www.iop.org/EJ/abstract/0953-8984/19/1/016007/
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