Frequency translating phase conjugation circuit for active retrodirective antenna array

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

Active retrodirective arrays for SPS beam pointing

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

Arc protection system for high-power RF amplifiers

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

Effects of uncertainty on manual tracking performance

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

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

Extending the domain of validity of the Lagrangian approximation

We investigate convergence of Lagrangian Perturbation Theory (LPT) by analyzing the model problem of a spherical homogeneous top-hat in an Einstein-deSitter background cosmology. We derive the formal structure of the LPT series expansion, working to arbitrary order in the initial perturbation amplitude. The factors that regulate LPT convergence are identified by studying the exact, analytic solution expanded according to this formal structure. The key methodology is to complexify the exact solution, demonstrate that it is analytic and apply well-known convergence criteria for power series expansions of analytic functions.This analysis fully explains the previously reported observation that LPT fails to predict the evolution of an underdense, open region beyond a certain time. It also implies the existence of other examples, including overdense, closed regions, for which LPT predictions should also fail. We show that this is indeed the case by numerically computing the LPT expansion in these problematic cases. The formal limitations to the validity of LPT expansion are considerably more complicated than simply the first occurrence of orbit crossings as is often assumed. Evolution to a future time generically requires re-expanding the solution in overlapping domains that ultimately link the initial and final times, each domain subject to its own convergence criterion. We demonstrate that it is possible to handle all the problematic cases by taking multiple steps (LPT re-expansion). We characterize how the leading order numerical error for a solution generated by LPT re- expansion varies with the choice of Lagrangian order and of time step size. Convergence occurs when the Lagrangian order increases and/or the time step size decreases in a simple, well-defined manner. We develop a recipe for time step control for LPT re-expansion based on these results.Comment: 40 pages, 24 figures. Abstract abbreviated. Accepted for publication in MNRAS. Updated version with minor comments from referee incorporate

Some basic properties of infinite dimensional Hamiltonian systems

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

An Investigation of Philadelphia's Youth Aid Panel: A Community-Based Diversion Program for First-Time Youthful Offenders

The formal justice system currently does not have the resources to effectively deal with nonviolent first-time offending youth, oftentimes leaving them with little punishment aside from a criminal record. This report offers a close examination of Philadelphia's Youth Aid Panels (YAP), which seeks to provide alternative sentencing for this high-risk population through the collaboration of volunteer community members, victims, parent(s)/guardian and a law enforcement official. YAP offers victims a better sense of restitution while also providing the youth with the real opportunity to reintegrate into society without a record. Our initial exploratory evaluation shows promising results, and we offer a several recommendations to strengthen YAP programs