Raytheon

About: Raytheon is a company organization based out in Waltham, Massachusetts, United States. It is known for research contribution in the topics: Signal & Antenna (radio). The organization has 15290 authors who have published 18973 publications receiving 300052 citations.

Inhomogeneous Broadening of Ferromagnetic Resonance Lines

Abstract: A general theory of ferromagnetic resonance is developed assuming that the local, effective magnetic field is inhomogeneous. The scattering processes induced by the inhomogeneity may be classified as "primary" processes (which couple the uniform mode to nonuniform modes) and "secondary" processes (which couple nonuniform modes). In previous work only the primary processes were taken into account. The effect of secondary processes upon the susceptibility is calculated in the present paper. A perturbation series for the complex, effective resonant frequency of the uniform mode is derived. It is shown that the important terms of this infinite series can in part be generated by a self-consistency condition for the complex effective resonant frequency of spin waves. An approximate solution of this self-consistency condition is derived. Applied to polycrystals with cubic crystal structure, the theory predicts a linewidth of $\ensuremath{\simeq}2.07\frac{{{H}_{a}}^{2}}{4\ensuremath{\pi}{M}_{0}}$ for spherical samples and ${H}_{a}\ensuremath{\ll}4\ensuremath{\pi}{M}_{0}$ but $\ensuremath{\simeq}0.87{H}_{a}$ for ${H}_{a}\ensuremath{\gtrsim}4\ensuremath{\pi}{M}_{0}$. Here ${H}_{a}$ is the anisotropy field and ${M}_{0}$ the saturation magnetization. The off-resonance absorption is characterized by the existence of a "strong absorption" region. When the intrinsic damping of the spin waves is assumed to approach zero the absorption goes to zero in the exterior of this region but to a finite value in its interior. If the Fourier spectrum of the inhomogeneity has significant components only at long wavelength and the inhomogeneity is weak, the strong absorption region coincides with the dc field interval in which the signal frequency is degenerate with resonant frequencies of long-wavelength spin waves. With increasing inhomogeneity, the width of the strong absorption region increases by approximately twice the width of the resonance line.

Simple method of measuring drift-mobility profiles in thin semiconductor films

Abstract: A simple method of measuring drift-mobility profiles in semiconductor films is described. It is based on the low-frequency measurement of the transconductance and gate capacitance of an f.e.t. structure as a function of gate bias. Drift mobilities of 4000 to 5000 cm2/Vs have been measured on n-type GaAs films with 1016 to 1017 cm-3 doping levels.

Autonomous Space Flight System and Planetary Lander for Executing a Discrete Landing Sequence to Remove Unknown Navigation Error, Perform Hazard Avoidance and Relocate the Lander and Method

Abstract: An autonomous unmanned space flight system and planetary lander executes a discrete landing sequence including performing an initial velocity braking maneuver to remove velocity at altitude, coasting during which the planet surface is imaged and correlated to reference maps to estimate cross-track and along-track navigation errors and one or more lateral braking maneuvers are performed to reduce cross-track navigation error, and performing a terminal velocity braking maneuver(s) to reduce the along-track braking maneuver and remove the remainder of the velocity just prior to landing. A bi-propellant propulsion system provides a very high T/M ratio, at least 15:1 per nozzle. Short, high T/M divert maneuvers provide the capability to remove cross-track navigation error efficiently up to the maximum resolution of the reference maps. Short, high T/M terminal velocity braking maneuver(s) provide the capability to remove along-track navigation error to a similar resolution and remove the remaining velocity in a very short time window, approximately 3-15 seconds prior to touchdown. The propulsive efficiency frees up mass which can be allocated to a fuel to remove the unknown navigation errors, perform hazard avoidance and/or relocate the lander by flying it to another site or be allocated to additional payload.

Flexible and programmable delta-sigma analog signal converter

Abstract: Processing apparatus is provided that directly samples and quantizes a complex envelope of a bandlimited waveform centered at a predetermined carrier frequency. An oversampling delta-sigma modulator 1 samples and quantizes the input signal to a single bit data stream. A serial-to-parallel converter converts the single bit data stream into a parallel bit stream. A digital decimation filter digitally filters the parallel bit stream to produce an estimate of the baseband in-phase and quadrature components of the input signal. In-phase and quadrature video filters generate in-phase and quadrature samples that are output from the analog signal converter. A controller 26 and a plurality of digital-to-analog converters 25 are used to center noise shaping nulls of the delta-sigma modulator around the carrier frequency. The controller sets the spacing between nulls of the serial-to-parallel converter to maximize the signal-to-noise ratio of the analog signal. The controller controls the decimation filter to set the sample times of thereof to sample the carrier in quadrature so that the coefficients are programmed to form a bandpass filter at the carrier frequency and programs the coefficients of the video filters to form bandpass filters at the decimated carrier frequency.

EVOLUTION of THERMALLY PULSING ASYMPTOTIC GIANT BRANCH STARS. V. CONSTRAINING the MASS LOSS and LIFETIMES of INTERMEDIATE-MASS, LOW-METALLICITY AGB STARS

Abstract: Thermally-Pulsing Asymptotic Giant Branch (TP-AGB) stars are relatively short lived (less than a few Myr), yet their cool effective temperatures, high luminosities, efficient mass-loss and dust production can dramatically effect the chemical enrichment histories and the spectral energy distributions of their host galaxies. The ability to accurately model TP-AGB stars is critical to the interpretation of the integrated light of distant galaxies, especially in redder wavelengths. We continue previous efforts to constrain the evolution and lifetimes of TP-AGB stars by modeling their underlying stellar populations. Using Hubble Space Telescope (HST) optical and near-infrared photometry taken of 12 fields of 10 nearby galaxies imaged via the ACS Nearby Galaxy Survey Treasury and the near-infrared HST/SNAP follow-up campaign, we compare the model and observed TP-AGB luminosity functions as well as the number ratio of TP-AGB to red giant branch stars. We confirm the best-fitting mass-loss prescription, introduced by Rosenfield et al. 2014, in which two different wind regimes are active during the TP-AGB, significantly improves models of many galaxies that show evidence of recent star formation. This study extends previous efforts to constrain TP-AGB lifetimes to metallicities ranging -1.59 < [Fe/H] < -0.56 and initial TP-AGB masses up to ~ 4 Msun, which include TP-AGB stars that undergo hot-bottom burning.