Windshear radar calibration: Transmitter power and receiver gain stability

An experimental windshear Doppler radar was flown on 27 occasions during a series of flight experiments in 1991. Radar calibrations were performed by the flight team to monitor the transmitter power and receiver gain from pre-flight to post-flight and from one day to another. From the recorded calibration data, the receiver gain and effective receiver system noise were calculated and tabulated, together with the transmitter power. These quantities of interest are compared for two receiver/transmitter (R/T) units and two intermediate frequency (IF) bandwidths that were tested in various modes. It was found that, in most operating modes, gain stayed within a 2.5-dB range and transmitter power stayed within a 20-watt range. R/T number 1 had 0.8 dB more gain and 1.2 dBm less noise power than R/T number 2. The 7-MHz IF bandwidth resulted in 1 dB more gain and 1 dBm less noise than the 2-MHz IF bandwidth. Depending on the R/T unit and IF bandwidth, the effective system noise power averaged between -107.3 dBm and -109.5 dBm

Lighting the Farm Home

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Puzzling out the coexistence of terrestrial planets and giant exoplanets. The 2/1 resonant periodic orbits

Hundreds of giant planets have been discovered so far and the quest of exo-Earths in giant planet systems has become intriguing. In this work, we aim to address the question of the possible long-term coexistence of a terrestrial companion on an orbit interior to a giant planet, and explore the extent of the stability regions for both non-resonant and resonant configurations. Our study focuses on the restricted three-body problem, where an inner terrestrial planet (massless body) moves under the gravitational attraction of a star and an outer massive planet on a circular or elliptic orbit. Using the Detrended Fast Lyapunov Indicator as a chaotic indicator, we constructed maps of dynamical stability by varying both the eccentricity of the outer giant planet and the semi-major axis of the inner terrestrial planet, and identify the boundaries of the stability domains. Guided by the computation of families of periodic orbits, the phase space is unravelled by meticulously chosen stable periodic orbits, which buttress the stability domains. We provide all possible stability domains for coplanar symmetric configurations and show that a terrestrial planet, either in mean-motion resonance or not, can coexist with a giant planet, when the latter moves on either a circular or an (even highly) eccentric orbit. New families of symmetric and asymmetric periodic orbits are presented for the 2/1 resonance. It is shown that an inner terrestrial planet can survive long time spans with a giant eccentric outer planet on resonant symmetric orbits, even when both orbits are highly eccentric. For 22 detected single-planet systems consisting of a giant planet with high eccentricity, we discuss the possible existence of a terrestrial planet. This study is particularly suitable for the research of companions among the detected systems with giant planets, and could assist with refining observational data.Comment: Accepted for publication in A&

Origin and continuation of 3/2, 5/2, 3/1, 4/1 and 5/1 resonant periodic orbits in the circular and elliptic restricted three-body problem

We consider a planetary system consisting of two primaries, namely a star and a giant planet, and a massless secondary, say a terrestrial planet or an asteroid, which moves under their gravitational attraction. We study the dynamics of this system in the framework of the circular and elliptic restricted TBP, when the motion of the giant planet describes circular and elliptic orbits, respectively. Originating from the circular family, families of symmetric periodic orbits in the 3/2, 5/2, 3/1, 4/1 and 5/1 mean-motion resonances are continued in the circular and the elliptic problems. New bifurcation points from the circular to the elliptic problem are found for each of the above resonances and thus, new families, continued from these points are herein presented. Stable segments of periodic orbits were found at high eccentricity values of the already known families considered as whole unstable previously. Moreover, new isolated (not continued from bifurcation points) families are computed in the elliptic restricted problem. The majority of the new families mainly consist of stable periodic orbits at high eccentricities. The families of the 5/1 resonance are investigated for the first time in the restricted three-body problems. We highlight the effect of stable periodic orbits on the formation of stable regions in their vicinity and unveil the boundaries of such domains in phase space by computing maps of dynamical stability. The long-term stable evolution of the terrestrial planets or asteroids is dependent on the existence of regular domains in their dynamical neighbourhood in phase space, which could host them for long time spans. This study, besides other celestial architectures that can be efficiently modelled by the circular and elliptic restricted problems, is particularly appropriate for the discovery of terrestrial companions among the single-giant planet systems discovered so far.Comment: Accepted for publication in Celestial Mechanics and Dynamical Astronom

Hesse Pencils and 3-Torsion Structures

This paper intends to focus on the universal property of this Hesse pencil and of its twists. The main goal is to do this as explicit and elementary as possible, and moreover to do it in such a way that it works in every characteristic different from three

Radar multipath study for rain-on-radome experiments at the Aircraft Landing Dynamics Facility

An analytical study to determine the feasibility of a rain-on-radome experiment at the Aircraft Landing Dynamics Facility (ALDF) at the Langley Research Center is described. The experiment would measure the effects of heavy rain on the transmission of X-band weather radar signals, looking in particular for sources of anomalous attenuation. Feasibility is determined with regard to multipath signals arising from the major structural components of the ALDF. A computer program simulates the transmit and receive antennas, direct-path and multipath signals, and expected attenuation by rain. In the simulation, antenna height, signal polarization, and rainfall rate are variable parameters. The study shows that the rain-on-radome experiment is feasible with regard to multipath signals. The total received signal, taking into account multipath effects, could be measured by commercially available equipment. The study also shows that horizontally polarized signals would produce better experimental results than vertically polarized signals

Archaeological Studies for the San Antonio Channel Improvement Project, including Investigations at Guenther\u27s Upper Mill (41BX342)

Under Contract No. DACW63-81-C-0022 to the Department of the Army, Corps of Engineers, Fort Worth District, the Center for Archaeological Research, The University of Texas at San Antonio, in the spring of 1981, conducted historic research and survey in the areas to be affected by the San Antonio Channel Improvement Project. In the summer of 1981, extensive archaeological testing and excavation were done to determine the extent of the structural remains on the sites of Guenther\u27s Upper Mill and the Stribling House. In the spring and summer of 1982, the Center documented the removal and replacement of the mill\u27s west wall. As a result of the investigations, it can now be affirmed that most of the foundation of the east section of the mill is still present beneath the ground. The main foundation walls are made of cut limestone and measure two feet in thickness, except for the west wall which is three feet thick. Of the other buildings at various times related to the mill, only portions of a late (ca. 1910) stone and cement foundation for the Reigler Creamery still remain in the ground. The survey revealed no other cultural resources to be affected by the project

Understanding Child Support Trends: Economic, Demographic, and Political Contributions

We use data from the Panel Study of Income Dynamics (PSID) to examine trends in child support payments over the past thirty years and to assess five different explanations for these trends: inflation, the shift to unilateral divorce, changes in marital status composition, changes in men's and women's earnings, and ineffective child support laws. We find that during the 1970s and early 1980s, three factors high inflation, increase in non-marital childbearing, and shifts to unilateral divorse--exerted downward pressure on child support payments. Throughout this time period, child support policies were weak, and average real payments declined sharply. Our findings indicate that two child support policies legislative guidelines for awards and universal wage withholding--are important for insuring child support payments. Finally, our analyses suggest that further gains in child support payments will rest with our ability to collect child support for children born to unwed parents. These children are the fastest growing group of children in the US, and they are the least likely to receive child support. To date, child support policies have been ineffective in assuring child support for never married mothers.

How Hungry is the Selfish Gene?

We examine resource allocation in step-households, in the United States and South Africa, to test whether child investments vary according to economic and genetic bonds between parent and child. We used 18 years of data from the Panel Study of Income Dynamics, and compare food expenditure by family type, holding constant household size, age composition and income. We find that in those households in which a child is raised by an adoptive, step or foster mother, less is spent on food. We cannot reject the hypothesis that the effect of replacing a biological child with a non- biological child is the same, whether the non-biological child is an adoptive, step or foster child of the mother. In South Africa, where we can disaggregate food consumption more finely, we find that when a child's biological mother is the head or spouse of the head of household, the household spends significantly more on food, in particular on milk and fruit and vegetables, and significantly less on tobacco and alcohol. The genetic tie to the child, and not any anticipated future economic tie, appears to be the tie that binds.

Effective hydrodynamic boundary conditions for microtextured surfaces

We report measurements of the hydrodynamic drag force acting on a smooth sphere falling down under gravity to a plane decorated with microscopic periodic grooves. Both surfaces are lyophilic, so that a liquid (silicone oil) invades the surface texture being in the Wenzel state. A significant decrease in the hydrodynamic resistance force as compared with that predicted for two smooth surfaces is observed. To quantify the effect of roughness we use the effective no-slip boundary condition, which is applied at the imaginary smooth homogeneous isotropic surface located at an intermediate position between top and bottom of grooves. Such an effective condition fully characterizes the force reduction measured with the real surface, and the location of this effective plane is related to geometric parameters of the texture by a simple analytical formula.Comment: 4 pages, submitted to Phys. Rev.