14,106 research outputs found
Investigation of passive atmospheric sounding using millimeter and submillimeter wavelength channels
Activities within the period from July 1, 1992 through December 31, 1992 by Georgia Tech researchers in millimeter and submillimeter wavelength tropospheric remote sensing have been centered around the calibration of the Millimeter-wave Imaging Radiometer (MIR), preliminary flight data analysis, and preparation for TOGA/COARE. The MIR instrument is a joint project between NASA/GSFC and Georgia Tech. In the current configuration, the MIR has channels at 90, 150, 183(+/-1,3,7), and 220 GHz. Provisions for three additional channels at 325(+/-1,3) and 8 GHz have been made, and a 325-GHz receiver is currently being built by the ZAX Millimeter Wave Corporation for use in the MIR. Past Georgia Tech contributions to the MIR and its related scientific uses have included basic system design studies, performance analyses, and circuit and radiometric load design, in-flight software, and post-flight data display software. The combination of the above millimeter wave and submillimeter wave channels aboard a single well-calibrated instrument will provide unique radiometric data for radiative transfer and cloud and water vapor retrieval studies. A paper by the PI discussing the potential benefits of passive millimeter and submillimeter wave observations for cloud, water vapor and precipitation measurements has recently been published, and is included as an appendix
First electrostatic probe results from Explorer 17
Electrostatic probe results from ionospheric sounding by Explorer XVII satellit
Methods for detecting flaring structures in Sagittarius A* with high frequency VLBI
The super massive black hole candidate, Sagittarius A*, exhibits variability
from radio to X-ray wavelengths on time scales that correspond to < 10
Schwarzschild radii. We survey the potential of millimeter-wavelength VLBI to
detect and constrain time variable structures that could give rise to such
variations, focusing on a model in which an orbiting hot spot is embedded in an
accretion disk. Non-imaging algorithms are developed that use interferometric
closure quantities to test for periodicity, and applied to an ensemble of
hot-spot models that sample a range of parameter space. We find that structural
periodicity in a wide range of cases can be detected on most potential VLBI
arrays using modern VLBI instrumentation. Future enhancements of mm/sub-mm VLBI
arrays including phased array processors to aggregate VLBI station collecting
area, increased bandwidth recording, and addition of new VLBI sites all
significantly aid periodicity detection. The methods described herein can be
applied to other models of Sagittarius A*, including jet outflows and
Magneto-Hydrodynamic accretion simulations.Comment: Submitted to Ap
Coherent microwave radiation emitted during the process of stimulated Raman scattering in weakly compressed hydrogen : experimental studies, together with an attempt to interpret this microwave emission
A coherent microwave radiation, concomitant with experiments of stimulated
Raman scattering (SRS) in weakly compressed hydrogen, had been observed;
qualitative and quantitative results had been obtained, and are given in this
article. .An attempt to interpret this emission on a phenomenological basis is
presented, on the basis of a model in which the influence of hydrogen molecule
anharmonicity is taken into account, leading to two main effects:1) possible
existence of an intermediate state involving a vibrationally excited
quasiparticle system, the lifetime of which should be very short (0.1-1 ps); 2)
nonlinear coupling between the Stokes light wave and the longitudinal
propagating waves associated to the quasiparticle system. Moreover, several
processes are also to be taken into account; existence of a macroscopic
longitudinal electric field, due to coulombian interactions; electrostriction
effect giving rise to a "piezoelectric" character for the quasiparticle system;
Cherenkov-type and anomalous relativistic Doppler effects. Then, the source of
the coherent microwave radiation might be the in phase quadrature part of the
longitudinal polarisation associated to the quasiparticle waves, and its
emission should appear like parametric instabilities. Concerning the SRS
process itself, an additional contribution to the Raman gain should arise from
the laser induced electro-optic effect
Far-field spectral characterization of conical emission and filamentation in Kerr media
By use of an imaging spectrometer we map the far-field ()
spectra of 200 fs optical pulses that have undergone beam collapse and
filamentation in a Kerr medium. By studying the evolution of the spectra with
increasing input power and using a model based on stationary linear asymptotic
wave modes, we are able to trace a consistent model of optical beam collapse
high-lighting the interplay between conical emission, multiple pulse splitting
and other effects such as spatial chirp.Comment: 8 pages, 9 figure
Investigation of passive atmospheric sounding using millimeter and submillimeter wavelength channels
Activities within the period from January 1, 1992 through June 30, 1992 by Georgia Tech researchers in millimeter and submillimeter wavelength tropospheric remote sensing have been centered around the integration and initial data flights of the MIR on board the NASA ER-2. Georgia Tech contributions during this period include completion of the MIR flight software and implementation of a 'quick-view' graphics program for ground based calibration and analysis of the MIR imagery. In the current configuration, the MIR has channels at 90, 150, 183 +/- 1,3,7, and 220 GHz. Provisions for three additional channels at 325 +/-1,3 and 9 GHZ have been made, and a 325-GHz receiver is currently being built by the ZAX Millimeter Wave Corporation for use in the MIR. The combination of the millimeter wave and submillimeter wave channels aboard a single well-calibrated instrument will provide the necessary aircraft radiometric data for radiative transfer and cloud and water vapor retrieval studies. A paper by the PI discussing the potential benefits of passive millimeter and submillimeter wave observations for cloud, water vapor and precipitation measurements has recently been accepted for publication (Gasiewski, 1992), and is included as Appendix A. The MIR instrument is a joint project between NASA/GSFC and Georgia Tech. Other Georgia Tech contributions to the MIR and its related scientific uses have included basic system design studies, performance analyses, and circuit and radiometric load design
Deterministic dynamics of stimulated Brillouin scattering in optical fibres
Abstract unavailable please refer to PD
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