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.

The ngc 300 transient: an alternative method for measuring progenitor masses

Abstract: We present an alternative technique for measuring the precursor masses of transient events in stars undergoing late stage stellar evolution. We use the well-established techniques of stellar population modeling to age-date the stars surrounding the site of the recent transient event in NGC 300 (NGC 300 OT2008-1). The surrounding stars must share a common turnoff mass with the transient, since almost all stars form in stellar clusters that remain physically associated for periods longer than the lifetime of the most massive stars. We find that the precursor of NGC 300 OT2008-1 is surrounded by stars that formed in a single burst between 8 and 13 Myr ago, with 70% confidence. The transient was therefore likely to be due to a progenitor whose mass falls between the main sequence turnoff mass (12-17 M{sub sun}) and the maximum stellar mass (16-25 M{sub sun}) found for isochrones bounding this age range. We characterize the general applicability of this technique in identifying precursor masses of historic and future transients and supernovae (SNe), noting that it requires neither precursor imaging nor sub-arcsecond accuracy in the position of the transient. It is also based on the well-understood physics of the main sequence, and thus may bemore » a more reliable source of precursor masses than fitting evolutionary tracks to precursor magnitudes. We speculate that if the progenitor mass is {approx}>17 M {sub sun}, there may be a connection between optical transients such as NGC 300 OT2008-1 and the missing type II-P SNe, known as the 'red supergiant problem'.« less

Losses in GaAs microstrip

Abstract: Newly measured data for the loss of microstrip on 4 mil GaAs from DC to 40 GHz are presented. These data were taken from transmission measurements of lightly coupled, multiple-half-wave-length resonators. A comparison of the loss data with the predicted losses from three popular CAE (computer-aided engineering) tools is provided. The loss models provided by two out of three software vendors agree fairly well with measured data through 40 GHz. Since the measured loss roughly follows a square-law frequency relationship through 20 GHz, it should be possible to adjust the loss below this frequency and above 1 GHz by modifying the resistivity of the conductor in the simulator. >

Multi-mode laser oscillator with large intermode spacing

Abstract: A laser crystal (25) having a relatively short optical length functions as a seed laser (1) and simultaneously establishes the wide separation between longitudinal modes. Pulsed operation causes multiple longitudinal modes to co-exist before competition acts to extinguish modes. The seed laser (1) is isolated from the relatively higher peak power output beam (4). Further, the injection seeded slave resonator (6) optical cavity length is adjusted by mechanical, electromechanical and/or electro-optical component(s) to harmonize the slave resonator optical cavity to the seed laser (1) optical cavity. A number of widely separated longitudinal modes are simultaneously output as a pulsed, high optical quality beam having a broad frequency range, short temporal coherence, and stable simultaneous operation of the several modes.

Plastic Encapsulated Microelectronics; Materials, Processes, Quality, Reliability, and Application

Abstract: Plastic Packaging Materials Manufacturing Processes Assembly Onto Printed Wiring Boards Packing and Handling Failure Mechanisms, Sites, and Modes Quality Assurance Qualification and Accelerated Testing Defect Analysis Techniques Trends and Challenges Glossary Index.