5,378 research outputs found

    Frequency translating phase conjugation circuit for active retrodirective antenna array

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    An active retrodirective antenna array which has central phasing from a reference antenna element through a "tree" structured network of transmission lines utilizes a number of phase conjugate circuits (PCCs) at each node and a phase reference regeneration circuit (PRR) at each node except the initial node. Each node virtually coincides with an element of the array. A PCC generates the exact conjugate phase of an incident signal using a phase locked loop which combines the phases in an up converter, divides the sum by 2 and mixes the result with the phase in a down converter for phase detection. The PRR extracts the phase from the conjugate phase. Both the PCC and the PRR are not only exact but also free from mixer degeneracy

    Arc protection system for high-power RF amplifiers

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    Protective system prevents damage or destruction of high-power RF amplifiers by arcs which may occur in output transmission line. Advantages of system are listed

    Active retrodirective arrays for SPS beam pointing

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    The basic requirement of the SPS beam pointing system is that it deliver a certain amount of S-band (lambda = 12.5 cm) power to a 9.6 km diameter receiving rectenna on the ground. The power is transmitted from a 1.0 km diameter antenna array on the SPS, which is, for a rectenna at about plus or minus 40 deg. latitude, some 37.5x10 to the 6th power km distant. At the present time ARA's appear to be the best bet to realize this very stringent beam pointing requirement. An active retrodirective array (ARA) transmits a beam towards the apparent source of an illuminating signal called the pilot. The array produces, not merely reflects, RF power. Retrodirectivity is achieved by retransmitting from each element of the array a signal whose phase is the "conjugate" of that received by the element. Phase conjugate circuits and pointing errors in ARA's are described. Results obtained using a 2-element X-band ARA and an 8-element S-band ARA are included

    Effects of uncertainty on manual tracking performance

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    Transient phenomena and target acquisition modes associated with interrupted observations during ground-to-air AA tracking were investigated. Using a two-axes control stick, the subjects tracked a computer-generated airplane image on a CRT display. The airplane image excuted a low-level straight pass. At certain pseudo-random times during each 25-second run, the screen was blanked for a period of one second. When the target image reappeared, the subjects reacquired it and continued tracking, attempting to minimize vector RMS error for the entire run (including the blanked period). The results reveal an increase both in tracking error and in error variance during the blanked period, only when the target disappears while in the crossover region. Blanking at other times effected increased variance but had no effect on the mean error. A blanking period just before crossover produced an increase lag while a blanking just after crossover resulted in a lead and thus made the error curve more symmetric

    The Determinants of Education-Job Match among Canadian University Graduates

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    This study uses data from the Follow-up of Graduates Survey – Class of 2000, to look at the determinants of education-job match among Canadian university graduates. From a public policy perspective, the question of education-job match is relevant given the substantial investment society puts into its postsecondary institutions, and the role devoted to human capital in economic development. Our results indicate that one graduate out of three (35.1%) is in a job that is not closely related to his or her education. The most important result is that demographic and socioeconomic characteristics (gender and family background) do not significantly affect the match. On the other hand, education characteristics strongly influence match, with field specific programs (such as "Health sciences" and "Education") having the highest likelihood of obtaining an education-job match. In addition, the level of education (i.e. graduates with a postgraduate degree vs. a bachelor degree), as well as good grades, strongly affect the match. Employment characteristics also affect the match, but to a mixed extent, with certain characteristics, such as industry, as well as working full-time (vs. part time) affecting the match to a strong extent, while others, such as the permanence of employment, as well as the method used to obtain employment, not having a significant effect on match.Canada, university graduates, education-job match, Follow-up of Graduates Survey

    Some basic properties of infinite dimensional Hamiltonian systems

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    We consider some fundamental properties of infinite dimensional Hamiltonian systems, both linear and nonlinear. For exemple, in the case of linear systems, we prove a symplectic version of the teorem of M. Stone. In the general case we establish conservation of energy and the moment function for system with symmetry. (The moment function was introduced by B. Kostant and J .M. Souriau). For infinite dimensional systems these conservation laws are more delicate than those for finite dimensional systems because we are dealing with partial as opposed to ordinary differential equations

    Polarized Scattering in the Vicinty of Galaxies

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    Some bright cD galaxies in cluster cooling flows have Thomson optical depths exceeding 0.01. A few percent of their luminosity is scattered and appears as diffuse polarized emission. We calculate the scattering process for different geometric combinations of luminosity sources and scattering media. We apply our results to galaxies, with and without active nuclei, immersed in cooling flows. We model observations of NGC 1275 and M87 (without active nuclei) in the presence of sky and galactic background fluxes which hinder the measurement of the scattered light at optical wavelengths. Current instruments are unable to detect the scattered light from such objects. However, when a galaxy has an active nucleus of roughly the same luminosity as the remainder of the galaxy in V, both the total and polarized scattered intensity should observable on large scales (5--30kpc), meaning intensity levels greater than 1% of the background level. For typical AGN and galaxy spectral distributions, the scattering is most easily detected at short (U) wavelengths. We point out that a number of such cases will occur. We show that the radiation pattern from the central nuclear region can be mapped using the scattering. We also show that the scattered light can be used to measure inhomogeneities in the cooling flow.Comment: 29 pages of TEX, 14 figs, CRSR-1046, in ApJ Nov 20, 199
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