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.

Probabilities for Radiative and Nonradiative Decay of Er 3 + in La F 3

Abstract: The rates of radiative and nonradiative decay were determined for several excited states of ${\mathrm{Er}}^{3+}$ in La${\mathrm{F}}_{3}$ from calculated spontaneous emission probabilities and measured lifetimes. Electric-dipole, magnetic-dipole, and electric-quadrupole transition probabilities were evaluated using intermediate coupled states derived from computer diagonalization of the combined spin-orbit and electrostatic energy matrix. The required spin-orbit and Racah parameters for La${\mathrm{F}}_{3}$: ${\mathrm{Er}}^{3+}$ were obtained from a least-squares fit of experimental and theoretical energy levels. The probabilities for electric-dipole transitions were calculated using the theory of Judd and Ofelt; the phenomenological parameters needed in this approach were derived from measurements of integrated absorption coefficients. By comparing the total calculated radiative lifetimes and the observed lifetimes, the probabilities for nonradiative decay from nine different excited states were determined. The probability of nonradiative decay was found to be very dependent upon the proximity of lower energy levels, which for the levels investigated ranged from approximately 1600 to 6000 ${\mathrm{cm}}^{\ensuremath{-}1}$, and hence upon the number of phonons required to conserve energy. The rates of nonradiative transitions corresponding to the simultaneous emission of as many as five phonons were found to make significant contributions to the lifetimes of fluorescent states of rare earths in La${\mathrm{F}}_{3}$.

On-demand multicast routing protocol in multihop wireless mobile networks

Abstract: An ad hoc network is a dynamically reconfigurable wireless network with no fixed infrastructure or central administration. Each host is mobile and must act as a router. Routing and multicasting protocols in ad hoc networks are faced with the challenge of delivering data to destinations through multihop routes in the presence of node movements and topology changes. This paper presents the On-Demand Multicast Routing Protocol (ODMRP) for wireless mobile and hoc networks. ODMRP is a mesh-based, rather than a conventional tree-based, multicast scheme and uses a forwarding group concept; only a subset of nodes forwards the multicast packets via scoped flooding. It applies on-demand procedures to dynamically build routes and maintain multicast group membership. ODMRP is well suited for ad hoc wireless networks with mobile hosts where bandwidth is limited, topology changes frequently, and power is constrained. We evaluate ODMRP performance with other multicast protocols proposed for ad hoc networks via extensive and detailed simulation.

Mania-like behavior induced by disruption of CLOCK.

Abstract: Circadian rhythms and the genes that make up the molecular clock have long been implicated in bipolar disorder. Genetic evidence in bipolar patients suggests that the central transcriptional activator of molecular rhythms, CLOCK, may be particularly important. However, the exact role of this gene in the development of this disorder remains unclear. Here we show that mice carrying a mutation in the Clock gene display an overall behavioral profile that is strikingly similar to human mania, including hyperactivity, decreased sleep, lowered depression-like behavior, lower anxiety, and an increase in the reward value for cocaine, sucrose, and medial forebrain bundle stimulation. Chronic administration of the mood stabilizer lithium returns many of these behavioral responses to wild-type levels. In addition, the Clock mutant mice have an increase in dopaminergic activity in the ventral tegmental area, and their behavioral abnormalities are rescued by expressing a functional CLOCK protein via viral-mediated gene transfer specifically in the ventral tegmental area. These findings establish the Clock mutant mice as a previously unrecognized model of human mania and reveal an important role for CLOCK in the dopaminergic system in regulating behavior and mood.

Characterization of Frequency Stability

Abstract: Consider a signal generator whose instantaneous output voltage V(t) may be written as V(t) = [V 0 + ??(t)] sin [2??v 0 t + s(t)] where V 0 and v 0 are the nominal amplitude and frequency, respectively, of the output. Provided that ??(t) and ??(t) = (d??/(dt) are sufficiently small for all time t, one may define the fractional instantaneous frequency deviation from nominal by the relation y(t) - ??(t)/2??v o A proposed definition for the measure of frequency stability is the spectral density S y (f) of the function y(t) where the spectrum is considered to be one sided on a per hertz basis. An alternative definition for the measure of stability is the infinite time average of the sample variance of two adjacent averages of y(t); that is, if y k = 1/t ??? tk+r = y(t k ) y(t) dt where ?? is the averaging period, t k+1 = t k + T, k = 0, 1, 2 ..., t 0 is arbitrary, and T is the time interval between the beginnings of two successive measurements of average frequency; then the second measure of stability is ?? y 2(??) ??? (y k+1 - y k )2/2 where denotes infinite time average and where T = ??. In practice, data records are of finite length and the infinite time averages implied in the definitions are normally not available; thus estimates for the two measures must be used. Estimates of S y (f) would be obtained from suitable averages either in the time domain or the frequency domain.