An Analysis of the Performance of the Oscillating Limiter Driven by FM Signals Corrupted by Noise

The behavior of the oscillating limiter (OL) driven by FM signals is surveyed, and its performance with signal corrupted by noise is investigated. For high values of the carrier-to-noise ratio (CNR), if the frequency deviation of the signal is small in comparison with the locking range of the OL, it is calculated, and experimentally verified, that a system OL discriminator is equivalent to a system bandpass limiter discriminator followed by a linear network whose frequency response has been specified. When the frequency deviation is not so small, the baseband noise power increases with it; a formula is given that allows the calculation of this power when the signal is such that the circuit operates in quasistationary fashion. For low values of the CNR, a mathematical analysis presents unsurmountable difficulties. However, heuristic argumentation leads to an interpretation of the operation of the OL in the threshold region, which is substantiated by an experimental investigation. The results of this paper enable a comparative evaluation of a system OL discriminator and a system bandpass limiter discriminator, to which the former reduces when the feedback path in the OL is open.     

Artificial gravity

NASA's Artificial Gravity program consists of a team of researchers from Wyle Laboratories, NASA Johnson Space Center, and the University of Texas Medical Branch (UTMB). The short-radius centrifuge (SRC), built by Wyle Laboratories, will be integrated with UTMB's conducted bedrest studies, which mimic the detrimental effects of weightlessness (or microgravity). Bedrest subjects will be spun on the SRC at various accelerations and for various time periods, while being monitored medically. Parameters such as bone loss, muscle atrophy, balance control, and oxygen consumption will then be compared in order to research ways of mitigating the impact on astronauts' physiology. Other potential benefits from these studies extend to population groups on Earth, such as bedridden patients.     

Families of periodic solutions to Hamiltonian systems: Nonsymmetrical periodic solutions for a planar restricted three-body problem

A monodromy matrix calculated at a single arbitrary point of the periodic solution to a Hamiltonian system allows one to obtain both the direction of continuation for the family of solutions of the first (in Poincarés sense) kind and the multiplicity and direction of branching for periodic solutions of the second kind. In case of resonances 1 : 1 and 1 : 2 one needs to take into account the structure of elementary divisors of the monodromy matrix. Using the planar circular restricted three-body problem as an example, the infiniteness of the process of branching for a nonintegrable system and its finiteness for an integrable system are demonstrated. It is proved that periodic solutions of both first and second kinds which are obtained by continuation of symmetric periodic solutions of a restricted problem are also symmetric. The only exception is the case of resonance 1 : 1 and two second-order cells of the monodromy matrix in the Jordanian form. In this case, all periodic solutions of the second kind turned out to be nonsymmetrical. Examples of the families of nonsymmetrical periodic solutions are given.__________Translated from Kosmicheskie Issledovaniya, Vol. 43, No. 2, 2005, pp. 88–110.Original Russian Text Copyright © 2005 by Kreisman.     

Thoracic sonography for pneumothorax: the clinical evaluation of an operational space medicine spin-off

The recent interest in the use of ultrasound (US) to detect pneumothoraces after acute trauma in North America was initially driven by an operational space medicine concern. Astronauts aboard the International Space Station (ISS) are at risk for pneumothoraces, and US is the only potential medical imaging available. Pneumothoraces are common following trauma, and are a preventable cause of death, as most are treatable with relatively simple interventions. While pneumothoraces are optimally diagnosed clinically, they are more often inapparent even on supine chest radiographs (CXR) with recent series reporting a greater than 50% rate of occult pneumothoraces. In the course of basic scientific investigations in a conventional and parabolic flight laboratory, investigators familiarized themselves with the sonographic features of both pneumothoraces and normal pulmonary ventilation. By examining the visceral–parietal pleural interface (VPPI) with US, investigators became confident in diagnosing pneumothoraces. This knowledge was subsequently translated into practice at an American and a Canadian trauma center. The sonographic examination was found to be more accurate and sensitive than CXR (US 96% and 100% versus US 74% and 36%) in specific circumstances. Initial studies have also suggested that detecting the US features of pleural pulmonary ventilation in the left lung field may offer the ability to exclude serious endotracheal tube malpositions such as right mainstem and esophageal intubations. Applied thoracic US is an example of a clinically useful space medicine spin-off that is improving health care on earth.     

Gravity and perceptual stability during translational head movement on earth and in microgravity

We measured the amount of visual movement judged consistent with translational head movement under normal and microgravity conditions. Subjects wore a virtual reality helmet in which the ratio of the movement of the world to the movement of the head (visual gain) was variable. Using the method of adjustment under normal gravity 10 subjects adjusted the visual gain until the visual world appeared stable during head movements that were either parallel or orthogonal to gravity. Using the method of constant stimuli under normal gravity, seven subjects moved their heads and judged whether the virtual world appeared to move “with” or “against” their movement for several visual gains. One subject repeated the constant stimuli judgements in microgravity during parabolic flight. The accuracy of judgements appeared unaffected by the direction or absence of gravity. Only the variability appeared affected by the absence of gravity. These results are discussed in relation to discomfort during head movements in microgravity.     

COSAC onboard Rosetta: a bioastronomy experiment for the short-period comet 67P/Churyumov-Gerasimenko

The COSAC (Cometary Sampling and Composition Experiment) onboard the Rosetta mission is a combined gas chromatograph (GC)-mass spectrometer (MS). It is situated on Philae, the lander of the mission, which is intended to land on the nucleus of comet 67P/Churyumov- Gerasimenko. The purpose of the experiment is to analyze the volatile fraction of soil samples retrieved by a drill. For investigation, the samples will be pyrolysed, and the emanating gases fed into a GC, into an MS, or the combination of both. In the first part of this paper, the bioastronomical relevance of such measurements is outlined. In the second part the details of the hardware and its performance are described.     

A search for chiral signatures on Mars

It is thought that the chiral molecules of living material can induce circular polarization in light at levels much higher than expected from abiotic processes. We therefore obtained high quality imaging circular polarimetry of the martian surface during the favorable opposition of 2003 to seek evidence of anomalous optical activity. We used two narrow-band filters covering 43% of the martian surface, 15% of it in-depth. With polarization noise levels <0.1% (4.3 upper limits 0.2-0.3%) and spatial resolution 210 km, we did not find any regions of circular polarization. When data were averaged over the observed face of the planet, we did see a small non-zero circular polarization 0.02%, which may be due to effects associated with the opposition configuration though it is at the limit of the instrumental capability. Our observations covered only a small fraction of parameter space, so although we obtained a null result, we cannot exclude the presence of optical activity at other wavelengths, in other locations, or at higher spatial resolution.     

Cross Sections and Radar Equation for Nonlinear Scatterers

The nonlinear system concepts of nonlinear transfer functions are extended to nonlinear cross sections which may be used to quantitatively describe the characteristics of a nonlinear scatter. The concept of nonlinear cross sections is used to generalize the radar equation for nonlinear scattering objects.