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.

Deformation associated with the 1997 eruption of Okmok volcano, Alaska

Abstract: [1] Okmok volcano, located on Umnak Island in the Aleutian chain, Alaska, is the most eruptive caldera system in North America in historic time. Its most recent eruption occurred in 1997. Synthetic aperture radar interferometry shows deflation of the caldera center of up to 140 cm during this time, preceded and followed by inflation of smaller magnitude. The main part of the observed deformation can be modeled using a pressure point source model. The inferred source is located between 2.5 and 5.0 km beneath the approximate center of the caldera and ∼5 km from the eruptive vent. We interpret it as a central magma reservoir. The preeruptive period features inflation accompanied by shallow localized subsidence between the caldera center and the vent. We hypothesize that this is caused by hydrothermal activity or that magma moved away from the central chamber and toward the later vent. Since all historic eruptions at Okmok have originated from the same cone, this feature may be a precursor that indicates an upcoming eruption. The erupted magma volume is ∼9 times the volume that can be accounted for by the observed preeruptive inflation. This indicates a much longer inflation interval than we were able to observe. The observation that reinflation started shortly after the eruption suggests that inflation spans the whole time interval between eruptions. Extrapolation of the average subsurface volume change rate is in good agreement with the long-term eruption frequency and eruption volumes of Okmok.

Two-Way Synchronization for Coordinated Multicell Retrodirective Downlink Beamforming

Abstract: Coordinated multicell downlink transmission has recently been proposed as a technique that can enable spectrally efficient communication in cellular networks. By coordinating downlink transmissions, the base stations in a cellular system can transmit such that signals from multiple base stations arrive coherently at a mobile. One approach to coordinated multicell downlink transmission is to have the mobiles estimate the downlink channel state information (CSI) and feed the CSI back to the base stations for precoding. This paper proposes a different approach based on retrodirectivity and channel reciprocity. The primary advantage of this approach is that there is no need for CSI estimation or feedback by the mobiles. A tradeoff, however, is that the base stations must be synchronized to within a small fraction of a carrier period. A new two-way base station synchronization protocol is proposed to facilitate coordinated multicell coherent retrodirective downlink transmission techniques. An analysis of the statistical properties of the estimation errors in the two-way synchronization protocol and the resulting power gain of a multicell retrodirective downlink beamformer using this protocol is provided. Numerical examples are also presented characterizing the performance of multicell retrodirective downlink beamforming in a system using two-way base station synchronization. The numerical results demonstrate that near-ideal multicell downlink beamforming performance can be achieved with low synchronization overhead.

Optically assisted Internet routing using arrays of novel dynamically reconfigurable FBG-based correlators

Abstract: As routing tables in core Internet routers grow to exceed 100,000 entries, it is becoming essential to develop methods to reduce the lookup time required to forward packets toward their destinations. In this paper, we employ a bank of novel thermally tuned fiber-Bragg-grating-based optical correlators to construct an "optical bypass" to accelerate conventional electronic Internet routers. The correlators are configured as a routing table cache that can quickly determine the destination port for a fraction of the incoming traffic by examining only a subset of the bits in an IP packet's 32-bit destination address. We also demonstrate a novel multiwavelength correlator based on fiber Bragg grating that can simultaneously recognize the header bits on multiple wavelengths for use in wavelength-division-multiplexed (WDM) systems. Using the optical bypass, routing table lookup times are reduced by an order of magnitude from microseconds to nanoseconds and are limited only by the speed of the optical switch.

Series resonant converter having a resonant snubber

Abstract: A fixed frequency, series resonant converter having a resonant snubber comprising an inductor and capacitor connected across a tank circuit of the converter. An optimum amount of inductance in the resonant snubber minimizes the degree of "shoot-thru," or conduction through a body-diode within a transistor switch of the converter caused by ringing, which allows for nearly sinusoidal current to be provided to a full bridge high voltage rectifier enabling the power converter to operate at a higher frequency. An alternate embodiment applies the resonant snubber only across a selected transistor switch.

System for measuring the effect of bearing errors in an active device

Abstract: Disclosed herein are apparatus and methods for measuring error associated with the rotation of bearings (50) used within a pointing device (11) on board a space-based platform. The apparatus includes inductive, or “eddy current,” proximity sensors (1000) adapted for measuring the positioning of bearing components. The apparatus also includes processing capabilities (1010) for receiving data from the proximity sensors (1000), and producing compensation data. The compensation data is used in one of various techniques for correcting errors in the angular measurement or pointing of the device (11). The techniques disclosed herein include conducting an initial calibration of the proximity sensors (1000) and generating calibration data. Once in active use, sensor measurements are combined with calibration data to produce compensation data. Ongoing measurements may be used to update the calibration data as necessary.