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.

Curse of dimensionality and particle filters

Abstract: Particle filtering (PF) is a new class of algorithms to solve the nonlinear filtering problem. These PFs are very general and easy to code. The main issue with PF is the large computational complexity. In particular, for typical low dimensional tracking problems, the PF requires 2 to 6 orders of magnitude more computer throughput than the extended Kalman filter, to achieve the same accuracy. It has been asserted that the PF avoids the curse of dimensionality, but there is no formula or theorem that bounds or, approximates the computational complexity of the PF as a function of dimension (d). In this paper, we derive a simple back-of-the-envelope formula that explains why a carefully designed PF should mitigate the curse of dimensionality for certain filtering problems, but the PF does not avoid the curse of dimensionality in general. We also show experimental results which c o n f i i our simple formula. We consider this a triumph of theory. This new theory hinges on the fact that the volume of the d dimensional unit sphere is an amazingly small fraction of the volume of the d dimensional unit cube, for large d.

Phonon Scattering in Semiconductors From Thermal Conductivity Studies

Abstract: The lattice thermal conductivity of a number of semiconductors including InSb, GaAs, GaSb, CdTe, and CdS has been measured between 1.7 and 300\ifmmode^\circ\else\textdegree\fi{}K. This, together with previous work on Si and Ge, is used to investigate the validity of the relaxation time expressions for scattering of phonons by boundaries, atomic impurities and electrons, and to discuss phonon-phonon interactions and resonance scattering effects. The results indicate that the boundary scattering and isotope scattering relaxation times lead to accurate calculated values of thermal conductivity only when the materials are exceptionally pure. Structure, which has been identified as due to resonance scattering, has been observed in the data for most of the materials. Electron-phonon scattering has been noted in GaSb but the complexity of the problems make the analysis only qualitative. The maximum transverse acoustical phonon frequency may be of more significance than the Debye temperature for thermal conductivity calculations.

A vacuum packaged surface micromachined resonant accelerometer

Abstract: This paper describes the operation of a vacuum packaged resonant accelerometer subjected to static and dynamic acceleration testing. The device response is in broad agreement with a new analytical model of its behavior under an applied time-varying acceleration. Measurements include tests of the scale factor of the sensor and the dependence of the output sideband power and the noise floor of the double-ended tuning fork oscillators as a function of the applied acceleration frequency. The resolution of resonant accelerometers is shown to degrade 20 dB/decade beyond a certain characteristic acceleration corner frequency. A prototype device was fabricated at Sandia National Laboratories and exhibits a noise floor of 40 /spl mu/g//spl radic/(Hz) for an input acceleration frequency of 300 Hz.

One-time logon means and methods for distributed computing systems

Abstract: Apparatus and methods of authenticating users in a distributed networked computing system (10). The system (10) may comprise a central server (12) embodiment that includes a file (19) wherein IDs and encrypted passwords (30) are stored, or a distributed system embodiment where IDs and encrypted passwords (30) are stored in files (19) at each respective computer in the system (10). A multiple logon procedure (16) and secure transport layer protocol are used with a user's communication software and network communication software. When a user desires to use a particular computer (13), logon requests are processed by the multiple logon procedure (16) and it accesses the stored file (19) that contains the user's ID and encrypted password, decrypts the password (30), accesses the remote computer (13), and logs the user onto that computer (13). In the central server system all IDs and encrypted passwords (30) are stored on a single computer (the server (12)) that controls access to the entire distributed system (10). Once access is granted to a particular user, nonencrypted passwords (30) are transmitted to the remote computers (13), since the server (12) controls the entire system. In the distributed version, password files (19) are stored in all networked computers (13), and once a user logs on to a computer (11), if the user wishes to use services at a second computer (13), the authentication information is forwarded to the second computer (13) using the secure transport layer protocol to protect its integrity, and after receiving the authentication information, it is compared with authentication information for the same user stored in the second computer (13). If the authentication information matches, the user is logged onto the second computer (13).