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.

STB Model and Transport Properties of Pyrolytic Graphites

Abstract: We propose to demonstrate that a coherent description of pyrolytic graphite (PG) layer‐plane phenomena can be based on a parabolic two‐band system with cylindrical equal‐energy surfaces. In this simple two‐band model (STB model), band overlap and effective mass must be interpreted as phenomenological parameters to be derived from experiments on highly heat‐treated pure PG. With p‐type (boron‐doped) specimens, the objective is to describe the situation from the shift of the Fermi level, on the assumption that the presence of trapping centers would not inject major perturbations in the band structure. (1) Galvanomagnetic effects: As derived from zero‐field resistivity and magnetoresistance mobility, the intrinsic carrier concentration and its variation with temperature in the range 0° to 1500°K implies that past a given graphitization stage band‐structural features may no longer be seriously affected by the size of the carbon networks. Above room temperature the carrier concentration increases almost linear...

The distance to m51

Abstract: Great investments of observing time have been dedicated to the study of nearby spiral galaxies with diverse goals ranging from understanding the star formation process to characterizing their dark matter distributions. Accurate distances are fundamental to interpreting observations of these galaxies, yet many of the best studied nearby galaxies have distances based on methods with relatively large uncertainties. We have started a program to derive accurate distances to these galaxies. Here we measure the distance to M51 - the Whirlpool galaxy - from newly obtained Hubble Space Telescope optical imaging using the tip of the red giant branch method. We measure the distance modulus to be 8.58+/-0.10 Mpc (statistical), corresponding to a distance modulus of 29.67+/-0.02 mag. Our distance is an improvement over previous results as we use a well-calibrated, stable distance indicator, precision photometry in a optimally selected field of view, and a Bayesian Maximum Likelihood technique that reduces measurement uncertainties.

The HALO network/sup TM/

Abstract: The High Altitude Long Operation Network/sup TM/ is a broadband wireless metropolitan area network, with a star topology, whose solitary hub is located in the atmosphere above the service area at an altitude higher than commercial airline traffic. The HALO/Proteus airplane is the central node of this network. It will fly at altitudes higher than 51,000 ft. The signal footprint of the network, its "Cone of Commerce", will have a diameter on the scale of 100 km. The initial capacity of the network will be on the scale of 10 Gb/s, with growth beyond 100 Gb/s. The network will serve the communications needs of each subscriber with bit rates in the multimegabit per second range. A variety of spectrum bands licensed by the FCC for commercial wireless services could provide the needed millimeter wavelength carrier bandwidth. An attractive choice for the subscriber links is the LMDS band. The airplane's fuselage can house switching circuitry and fast digital network functions. An MMW antenna array and its related components will be located in a pod suspended below the aircraft fuselage. The antenna array will produce many beams, typically more than 100. Adjacent beams will be separated in frequency. Electronic beamforming techniques can be used to stabilize the beams on the ground, as the airplane flies within its station keeping volume. For the alternative of aircraft-fixed beams, the beams will traverse over a user location, while the airplane maintains station overhead, and the virtual path will be changed to accomplish the beam-to-beam handoff. For each isolated city to be served, a fleet of three aircraft will be operated in shifts to achieve around-the-clock service. In deployments where multiple cities will be served from a common primary flight base, the fleet will be sized for allocating, on average, two aircraft per city to be served. Flight operational tactics will be steadily evolved and refined to achieve continuous presence of the node above each city. Many services will be provided, including but not limited to T1 access, ISDN access, Web browsing, high-resolution videoconferencing, large file transfers, and Ethernet LAN bridging.

Robust Detection of Ionospheric Irregularities

Abstract: The Wide Area Augmentation System (WAAS) will provide real-time differential GPS corrections and integrity information for aircraft navigation use. The most stringent application of this system will be precision approach, where the system guides the aircraft to within a few hundred feet of the ground. Precision approach operations require the use of differential ionospheric corrections. WAAS must incorporate information from reference stations to create a correction map of the ionosphere. More importantly, this map must contain confidence bounds describing the integrity of the corrections. The confidence bounds must be large enough to describe the error in the correction, but tight enough to allow the operation to proceed. The difficulty in generating these corrections is that the reference station measurements are not co-located with the aviation user measurements. For an undisturbed ionosphere over the Conterminous United States (CONUS), this is not a problem as the ionosphere is nominally well behaved. However, a concern is that irregularities in the ionosphere will decrease the correlation between the ionosphere observed by the reference stations and that seen by the user. Therefore, it is essential to detect when such irregularities may be present and adjust the confidence bounds accordingly. The approach outlined in this paper conservatively bounds the ionospheric errors even for the worst observed ionospheric conditions to date, using data sets taken from the operational receivers in the WAAS reference station network. As we progress through the current solar cycle and gather more data on the behavior of the ionosphere, many of our pessimistic assumptions will be relaxed. This will result in higher availability while maintaining full integrity.

Generalized Box–MÜller Method for Generating $q$ -Gaussian Random Deviates

Abstract: The q-Gaussian distribution is known to be an attractor of certain correlated systems and is the distribution which, under appropriate constraints, maximizes a generalization of the familiar Shannon entropy. This generalized entropy, or q-entropy, provides the basis of nonextensive statistical mechanics, a theory which is postulated as a natural extension of the standard (Boltzmann-Gibbs) statistical mechanics, and which may explain the ubiquitous appearance of heavy-tailed distributions in both natural and man-made systems. The q-Gaussian distribution is also used as a numerical tool, for example as a visiting distribution in Generalized Simulated Annealing. A simple, easy to implement numerical method for generating random deviates from a q-Gaussian distribution based upon a generalization of the well known Box-Miiller method is developed and presented. This method is suitable for a larger range of q values, -infin < q < 3, than has previously appeared in the literature, and can generate deviates from q-Gaussian distributions of arbitrary width and center. MATLAB code showing a straightforward implementation is also included.