14,881 research outputs found
Recent technical advances in general purpose mobile Satcom aviation terminals
A second general aviation amplitude companded single sideband (ACSSB) aeronautical terminal was developed for use with the Ontario Air Ambulance Service (OAAS). This terminal is designed to have automatic call set up and take down and to interface with the Public Service Telephone Network (PSTN) through a ground earth station hub controller. The terminal has integrated RF and microprocessor hardware which allows such functions as beam steering and automatic frequency control to be software controlled. The terminal uses a conformal patch array system to provide almost full azimuthal coverage. Antenna beam steering is executed without relying on aircraft supplied orientation information
Index to nasa tech briefs, issue number 2
Annotated bibliography on technological innovations in NASA space program
Extending device performance in photonic devices using piezoelectric properties
This study focuses on the influence of epi-layer strain and piezoelectric effects in asymmetric GaInAs/GaAlAs action regions that potentially lead to intra-cavity frequency mixing. The theoretical limits for conduction and valence band offsets in lattice-matched semiconductor structures have resulted in the deployment of non-traditional approaches such as strain compensation to extend wavelength in intersubband devices, where strain limits are related to misfit dislocation generation. Strain and piezoelectric effects have been studied and verified using select photonic device designs. Metrics under this effort also included dipole strength, oscillator strength, and offset of energy transitions, which are strongly correlated with induced piezoelectric effects. Unique photonic designs were simulated, modeled, and then fabricated using solid-source molecular beam epitaxy into photonic devices. The initial designs produce lambda wavelength, and the introduction of the piezoelectric effect resulted in lambda/2 wavelength. More importantly, this work demonstrates that the theoretical cutoff wavelength in intersubband lasers can be overcome
Characteristics of advanced hydrogen maser frequency standards
Measurements with several operational atomic hydrogen maser standards have been made which illustrate the fundamental characteristics of the maser as well as the analysability of the corrections which are made to relate the oscillation frequency to the free, unperturbed, hydrogen standard transition frequency. Sources of the most important perturbations, and the magnitude of the associated errors, are discussed. A variable volume storage bulb hydrogen maser is also illustrated which can provide on the order of 2 parts in 10 to the 14th power or better accuracy in evaluating the wall shift. Since the other basic error sources combined contribute no more than approximately 1 part in 10 to the 14th power uncertainty, the variable volume storage bulb hydrogen maser will have net intrinsic accuracy capability of the order of 2 parts in 10 to the 14th power or better. This is an order of magnitude less error than anticipated with cesium standards and is comparable to the basic limit expected for a free atom hydrogen beam resonance standard
Trapped ions in optical lattices for probing oscillator chain models
We show that a chain of trapped ions embedded in microtraps generated by an
optical lattice can be used to study oscillator models related to dry friction
and energy transport. Numerical calculations with realistic experimental
parameters demonstrate that both static and dynamic properties of the ion chain
change significantly as the optical lattice power is varied. Finally, we lay
out an experimental scheme to use the spin degree of freedom to probe the phase
space structure and quantum critical behavior of the ion chain
High-pressure versus isoelectronic doping effect on the honeycomb iridate NaIrO
We study the effect of isoelectronic doping and external pressure in tuning
the ground state of the honeycomb iridate NaIrO by combining optical
spectroscopy with synchrotron x-ray diffraction measurements on single
crystals. The obtained optical conductivity of NaIrO is discussed in
terms of a Mott insulating picture versus the formation of quasimolecular
orbitals and in terms of Kitaev-interactions. With increasing Li content ,
(NaLi)IrO moves deeper into the Mott insulating regime and
there are indications that up to a doping level of 24\% the compound comes
closer to the Kitaev-limit. The optical conductivity spectrum of single
crystalline -LiIrO does not follow the trends observed for the
series up to . There are strong indications that -LiIrO
is less close to the Kitaev-limit compared to NaIrO and closer to the
quasimolecular orbital picture. Except for the pressure-induced hardening of
the phonon modes, the optical properties of NaIrO seem to be robust
against external pressure. Possible explanations of the unexpected evolution of
the optical conductivity with isolectronic doping and the drastic change
between and are given by comparing the pressure-induced changes
of lattice parameters and the optical conductivity with the corresponding
changes induced by doping.Comment: 12 pages, 6 figures, accepted for publication in Phys. Rev.
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