35,720 research outputs found
Conical scan tracking system employing a large antenna
A conical scan tracking system for tracking spacecraft and distant radio sources is described. The system detects small sinusoidal modulation in received power from a source that is off target with a frequency equal to a very low scan rate, an amplitude proportional to angular deviation of the source from the target, and a phase directly related to the direction the source is off target. The sinusoid is digitally correlated with inphase and out-of-phase scan sinusoids to obtain azimuth/elevation and hour angle/declination signals which are digitally integrated over exactly one scan period to obtain correction signals for an antenna pointing subsystem
Conical-scan tracking with the 64-m-diameter antenna at goldstone
The theory and experimental work which demonstrated the feasibility of conical-scan tracking with a 64 m diameter paraboloid antenna is documented. The purpose of this scheme is to actively track spacecraft and radio sources continuously with an accuracy superior to that obtained by manual correction of the computer driven pointing. The conical-scan implementation gives increased tracking accuracy with X-band spacecraft signals, as demonstrated in the Mariner Venus/Mercury 1973 mission. Also, the high accuracy and ease of measurement with conical-scan tracking allow evaluation of systematic and random antenna tracking errors
Criteria for generalized macroscopic and mesoscopic quantum coherence
We consider macroscopic, mesoscopic and "S-scopic" quantum superpositions of
eigenstates of an observable, and develop some signatures for their existence.
We define the extent, or size of a superposition, with respect to an
observable \hat{x}, as being the range of outcomes of \hat{x} predicted by that
superposition. Such superpositions are referred to as generalized -scopic
superpositions to distinguish them from the extreme superpositions that
superpose only the two states that have a difference in their prediction
for the observable. We also consider generalized -scopic superpositions of
coherent states. We explore the constraints that are placed on the statistics
if we suppose a system to be described by mixtures of superpositions that are
restricted in size. In this way we arrive at experimental criteria that are
sufficient to deduce the existence of a generalized -scopic superposition.
The signatures developed are useful where one is able to demonstrate a degree
of squeezing. We also discuss how the signatures enable a new type of
Einstein-Podolsky-Rosen gedanken experiment.Comment: 15 pages, accepted for publication in Phys. Rev.
Alfv\'en waves in simulations of solar photospheric vortices
Using advanced numerical magneto-hydrodynamic simulations of the magnetised
solar photosphere, including non-grey radiative transport and a non-ideal
equation of state, we analyse plasma motions in photospheric magnetic vortices.
We demonstrate that apparent vortex-like motions in photospheric magnetic field
concentrations do not exhibit "tornado"-like behaviour or a "bath-tub" effect.
While at each time instance the velocity field lines in the upper layers of the
solar photosphere show swirls, the test particles moving with the
time-dependent velocity field do not demonstrate such structures. Instead, they
move in a wave-like fashion with rapidly changing and oscillating velocity
field, determined mainly by magnetic tension in the magnetised intergranular
downflows. Using time-distance diagrams, we identify horizontal motions in the
magnetic flux tubes as torsional Alfv\'en perturbations propagating along the
nearly vertical magnetic field lines with local Alfv\'en speed.Comment: 5 pages, 4 figures, accepted to ApJ
A precision DC-potentiometer microwave insertion-loss test set
Precision dc potentiometer microwave insertion loss test set for calibrating low noise microwave receiving systems used in space communication
Tripartite entanglement from interlinked parametric interactions
We examine the tripartite entanglement properties of an optical system using
interlinked interactions, recently studied experimentally in terms
of its phase-matching properties by Bondani et al [M. Bondani, A. Allevi, E.
Gevinti, A. Agliati, and A. Andreoni, arXiv:quant-ph/0604002.]. We show that
the system does produce output modes which are genuinely tripartite entangled
and that detection of this entanglement depends crucially on the correlation
functions which are measured, with a three-mode Einstein-Podolsky-Rosen
inequality being the most sensitive.Comment: 15 pages, 5 figure
A probabilistic model of insolation for the Mojave Desert area
A discussion of mathematical models of insolation characteristics suitable for use in analysis of solar energy systems is presented and shows why such models are essential for solar energy system design. A model of solar radiation for the Mojave Desert area is presented with probabilistic and deterministic components which reflect the occurrence and density of clouds and haze, and mimic their effects on both direct and indirect radiation. Multiple comparisons were made between measured total energy received per day and the corresponding simulated totals. The simulated totals were all within 11 percent of the measured total. The conclusion is that a useful probabilistic model of solar radiation for the Goldstone, California, area of the Mojave Desert has been constructed
Unified criteria for multipartite quantum nonlocality
Wiseman and co-workers (Phys. Rev. Lett. 98, 140402, 2007) proposed a
distinction between the nonlocality classes of Bell's nonlocality, steering and
entanglement based on whether or not an overseer trusts each party in a
bipartite scenario where they are asked to demonstrate entanglement. Here we
extend that concept to the multipartite case and derive inequalities that
progressively test for those classes of nonlocality, with different thresholds
for each level. This framework includes the three classes of nonlocality above
in special cases and introduces a family of others.Comment: V2: corrected image display; V3: substantial changes including new
proofs, arguments, and result
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