199,900 research outputs found
A dual frequency microstrip antenna for Ka band
For fixed satellite communication systems at Ka band with downlink at 17.7 to 20.2 GHz and uplink at 27.5 to 30.0 GHz, the focused optics and the unfocused optics configurations with monolithic phased array feeds have often been used to provide multiple fixed and multiple scanning spot beam coverages. It appears that a dual frequency microstrip antenna capable of transmitting and receiving simultaneously is highly desirable as an array feed element. This paper describes some early efforts on the development and experimental testing of a dual frequency annular microstrip antenna. The antenna has potential application for use in conjunction with a monolithic microwave integrated circuit device as an active radiating element in a phased array of phased array feeds. The antenna is designed to resonate at TM sub 12 and TM sub 13 modes and tuned with a circumferential microstrip ring to vary the frequency ratio. Radiation characteristics at both the high and low frequencies are examined. Experimental results including radiating patterns and swept frequency measurements are presented
Voyager cartography
The Jovian and Saturnian satellites are being mapped at several scales from Voyager 1 and 2 data. The maps are especially formatted color mosaics, controlled photomosaics, and airbrush maps. At 1:5,000,000 scale, mapping of Io, Europa, and Ganymede is complete. At 1:15,000,000 scale, mapping of Io and Europa is complete, and mapping of Ganymede is approximately complete. A controlled mosaic of Rhea has been compiled as a Digital Image Model (DIM) in the same format as is being used for Mars. The mosaic is being formatted for publication as a two-sheet set (Lambert Azimuthal Equal Area, Mercator, and Polar Stereographic projections). Magnetic tape copies of the DIM have been distributed to regional Planetary Image Facilities and other interested users. The DIM has a scale of 1/16 degree/pixel, corresponding to approximately 833 m/pixel on Rhea. Details of the status of the various map series are reported quarterly to Planetary Geology Principal Investigators
Quantum-mechanical wavepacket transport in quantum cascade laser structures
We present a viewpoint of the transport process in quantum cascade laser
structures in which spatial transport of charge through the structure is a
property of coherent quantum-mechanical wavefunctions. In contrast, scattering
processes redistribute particles in energy and momentum but do not directly
cause spatial motion of charge.Comment: 6 pages, 5 figures included in tex, to appear in Physical Review
Development of advanced avionics systems applicable to terminal-configured vehicles
A technique to add the time constraint to the automatic descent feature of the existing L-1011 aircraft Flight Management System (FMS) was developed. Software modifications were incorporated in the FMS computer program and the results checked by lab simulation and on a series of eleven test flights. An arrival time dispersion (2 sigma) of 19 seconds was achieved. The 4 D descent technique can be integrated with the time-based metering method of air traffic control. Substantial reductions in delays at today's busy airports should result
Evaluation of a spacecraft nitrogen generator
A research and development program was successfully completed towards the development of a method of generating nitrogen for cabin leakage makeup aboard space vehicles. The nitrogen generation concept used liquid hydrazine as the stored form of nitrogen. This reduced tankage and expendables weight associated with high pressure gaseous and cryogenic liquid nitrogen storage. The hydrazine was catalytically dissociated to yield a mixture of nitrogen and hydrogen. The latter was separated to provide the makeup nitrogen. The hydrogen will be used in the reduction of metabolic carbon dioxide
Deterministic entanglement of ions in thermal states of motion
We give a detailed description of the implementation of a Molmer-Sorensen
gate entangling two Ca+ ions using a bichromatic laser beam near-resonant with
a quadrupole transition. By amplitude pulse shaping and compensation of
AC-Stark shifts we achieve a fast gate operation without compromising the error
rate. Subjecting different input states to concatenations of up to 21
individual gate operations reveals Bell state fidelities above 0.80. In
principle, the entangling gate does not require ground state cooling of the
ions as long as the Lamb-Dicke criterion is fulfilled. We present the first
experimental evidence for this claim and create Bell states with a fidelity of
0.974(1) for ions in a thermal state of motion with a mean phonon number of
=20(2) in the mode coupling to the ions' internal states.Comment: 18 pages, 9 figures (author name spelling corrected
On the Path-Integral Derivation of the Anomaly for the Hermitian Equivalent of the Complex -Symmetric Quartic Hamiltonian
It can be shown using operator techniques that the non-Hermitian
-symmetric quantum mechanical Hamiltonian with a "wrong-sign" quartic
potential is equivalent to a Hermitian Hamiltonian with a positive
quartic potential together with a linear term. A naive derivation of the same
result in the path-integral approach misses this linear term. In a recent paper
by Bender et al. it was pointed out that this term was in the nature of a
parity anomaly and a more careful, discretized treatment of the path integral
appeared to reproduce it successfully. However, on re-examination of this
derivation we find that a yet more careful treatment is necessary, keeping
terms that were ignored in that paper. An alternative, much simpler derivation
is given using the additional potential that has been shown to appear whenever
a change of variables to curvilinear coordinates is made in a functional
integral.Comment: LaTeX, 12 pages, no figure
Chiral symmetry patterns of excited mesons with the Coulomb-like linear confinement
The spectrum of mesons in a model where the only interaction is a
linear Coulomb-like instantaneous confining potential is studied. The
single-quark Green function as well as the dynamical chiral symmetry breaking
are obtained from the Schwinger-Dyson (gap) equation. Given the dressed quark
propagator, a complete spectrum of "usual" mesons is obtained from the
Bethe-Salpeter equation. The spectrum exhibits restoration of chiral and
symmetries at large spins and/or radial excitations. This property is
demonstrated both analytically and numerically. At large spins and/or radial
excitations higher degree of degeneracy is observed, namely all states with the
given spin fall into reducible representations that combine all possible chiral multiplets with the
given and . The structure of the meson wave functions as well as the
form of the angular and radial Regge trajectories are investigated.Comment: 1. Order of references has been changed and one reference has been
added; 2. A short discussion of nonrelativistic and semirelativistic quark
models has been added in the conclusion part on referee's request. To appear
in Phys. Rev.
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