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.

Dual beam radar system

Abstract: Various embodiments are described herein relating to a radar system and associated methods for detecting targets in the presence of certain types of clutter. The radar system generally comprises hardware operatively configured to obtain first and second sets of radar return signals concurrently, first circuitry operatively configured to detect targets in the first and second sets of radar return signals, and second circuitry operatively configured to identify detected targets due to clutter.

A review of the state-of-the-art of oil spill fate/behavior models

Abstract: The fate and behavior of spilled oil can be affected by nine physical, chemical, and biological processes: advection, spreading, evaporation, dissolution, emulsification, dispersion, auto-...

A new in situ residual stress measurement method for a MEMS thin fixed-fixed beam structure

Abstract: A new method is described to measure the in situ residual stress state in a thin fixed-fixed beam structure used in microelectromechanical systems (MEMS). The methodology can be applied to devices at the anticipated operational and environmental temperatures. The new technique makes use of differences in the thermal expansion coefficient between the thin beam and the substrate. The residual stress distribution is determined by matching the thermal deflections from a finite element model (FEM) to measured deflections of the beam. All previous residual stress measurement methods for MEMS suspended structures reported a uniformly distributed residual stress. Experimental data coupled with the new analytical method suggests that this may not be adequate for the case of a suspended thin structure with nonplanar surface topology. A stress gradient through the thickness must be included in the determination of the stress state of the beam. The new method indicates a spatially varying residual stress distribution and is capable of de-coupling the mean stress and the stress gradient through the thickness. It was found through an extensive literature review that the quantification of the stress gradient in a thin suspended structure has never been reported. The de-coupling makes the prediction of the stress state at different temperature points possible. Details of the new method are demonstrated and discussed by the use of a capacitive radio frequency (RF) MEMS switch.

The High-mass Stellar Initial Mass Function in M31 Clusters

Abstract: We have undertaken the largest systematic study of the high-mass stellar initial mass function (IMF) to date using the optical color?magnitude diagrams (CMDs) of 85 resolved, young (), intermediate mass star clusters (103?104 M?), observed as part of the Panchromatic Hubble Andromeda Treasury program. We fit each cluster?s CMD to measure its mass function (MF) slope for stars ?2 M?. By modeling the ensemble of clusters, we find the distribution of MF slopes is best described by with a very small intrinsic scatter and no drastic outliers. This model allows the MF slope to depend on cluster mass, size, and age, but the data imply no significant dependencies within this regime of cluster properties. The lack of an age dependence suggests that the MF slope has not significantly evolved over the first ?25 Myr and provides direct observational evidence that the measured MF represents the IMF. Taken together, this analysis?based on an unprecedented large sample of young clusters, homogeneously constructed CMDs, well-defined selection criteria, and consistent principled modeling?implies that the high-mass IMF slope in M31 clusters is universal. The IMF has a slope (; statistical uncertainties) that is slightly steeper than the canonical Kroupa () and Salpeter () values, and our measurement of it represents a factor of ?20 improvement in precision over the Kroupa IMF (+1.30 ? 0.7). Using our inference model on select Milky Way (MW) and LMC high-mass IMF studies from the literature, we find and , both with intrinsic scatter of ?0.3?0.4 dex. Thus, while the high-mass IMF in the Local Group may be universal, systematics in the literature of IMF studies preclude any definitive conclusions; homogenous investigations of the high-mass IMF in the local universe are needed to overcome this limitation. Consequently, the present study represents the most robust measurement of the high-mass IMF slope to date. To facilitate practical use over the full stellar mass spectrum, we have grafted the M31 high-mass IMF slope onto widely used sub-solar mass Kroupa and Chabrier IMFs. The increased steepness in the M31 high-mass IMF slope implies that commonly used UV- and H?-based star formation rates should be increased by a factor of ?1.3?1.5 and the number of stars with masses M? is ?25% fewer than expected for a Salpeter/Kroupa IMF.