Experimental study of damping properties of a composite torsion bar in the helicopter main rotor hingeless hub

The results of the experimental studies of damping characteristics of a composite torsion bar in the helicopter main rotor hingeless hub are presented. A variant of their improvement is considered.     

Recent Breakthroughs in RF Photonics for Radar Systems

Radar systems require transmission of very high purity signals. Photonics is now mature enough to achieve analog transmission with very low noise, strong immunity, and wide-bandwidth even in harsh environments. We present our recent developments of optimized optical links dedicated to radar and multifunction systems     

Two Methods of Spectral Estimation for SARSAT Signals

Search and rescue satellite aided tracking (SARSAT) depends on the processing of emergency locator transmitter (ELT) signals which are received by a satellite in low polar orbit. Since the signal from a distressed vehicle is normally immersed in a background of other ELT signals (false alarms), interference, and noise, different methods of spectral estimation can provide advantages in estimating carrier frequency. A comparison between average spectrum and minimum spectrum for several real signals is provided here.     

Numerically Efficient Calculations of Clutter Map CFAR Performance

An alternative expression for the false alarm probability ofclutter map constant false alarm rate (CFAR), as derived by Nitzberg, is suggested. The new expression converges more rapidly.     

Microdosimetric measurements of heavy ion tracks.

The biological effectiveness of radiations depends on the spatial pattern of ionizations and excitations produced by the charged particle tracks involved. Ionizations produced by both the primary ion and by energetic delta rays may contribute to the production of biologically relevant damage and to the concentration of damage which may effect the probability of repair. Although average energy concentration (dose) can be calculated using homogeneous track models, the energy is actually concentrated in small volumes containing segments of the ion and delta ray tracks. These local concentrations are studied experimentally using low pressure proportional counters, and theoretically, using Monte Carlo methods. Small volumes near an ion track may be traversed by a delta ray. If they are, the energy deposited will be similar to that produced by a single electron track in a low-energy x-ray irradiation. The probability of a delta ray interaction occurring decreases with the square of the radial distance from the track. The average energy deposited is the product of this probability and the energy deposited in an interaction. Average energy deposited calculated from measured interaction probability is in good agreement with the results of homogeneous track models.     

Distributed decision fusion using empirical estimation

The problem of optimal data fusion in multiple detection systems is studied in the case where training examples are available, but no a priori information is available about the probability distributions of errors committed by the individual detectors. Earlier solutions to this problem require some knowledge of the error distributions of the detectors, for example, either in a parametric form or in a closed analytical form. Here we show that, given a sufficiently large training sample, an optimal fusion rule can be implemented with an arbitrary level of confidence. We first consider the classical cases of Bayesian rule and Neyman-Pearson test for a system of independent detectors. Then we show a general result that any test function with a suitable Lipschitz property can be implemented with arbitrary precision, based on a training sample whose size is a function of the Lipschitz constant, number of parameters, and empirical measures. The general case subsumes the cases of nonindependent and correlated detectors.     

An experiment with an S-band radar using pulse compression andrange sidelobe suppression for meteorological measurements

A major technology barrier to the application of pulse compression for the meteorological functions required by a next generation ATC radar is range/time sidelobes which mask and corrupt observations of weak phenomena occurring near areas of strong extended meteorological scatterers. Techniques for suppressing range sidelobes are well known but without prior knowledge of the scattering medium's velocity distribution their performance degrades rapidly in the presence of Doppler. Recent investigations have presented a “doppler tolerant” range sidelobe suppression technique. The thrust of the work described herein is the extension of previous simulations to actual transmitted dispersed/coded waveforms using the S-band surveillance radar located at Rome Laboratory Surveillance Facility. The objectives of the experiment are: 1) to extend the verification of the simulation of the Doppler tolerant technique; and 2) to demonstrate that the radar transmitter, waveform generator, and receiver imperfections do not significantly degrade resolution, performance or reliability of meteorological spectral moment estimates     

Radiation situation determining the possibility of a manned flight to Mars and back.

Possible manned flights toward Mars are discussed from the viewpoint of radiation hazard. A standard situation is considered for the fast two times crossing of the Earth radiation belts. The flight to Mars is shown to be practically impossible without a special system of radiation shelters, because of the effect of penetrating galactic and solar radiations which are responsible for almost maximum permissible doses. But even in case there were radiation shelters on board the spacecraft their flights are undesirable in the periods of maximum and minimum solar activity. It would obviously be worthwhile to schedule Martian flights for intervals in between minima and maxima of 11-year cycles of solar activity when primary cosmic rays levels are considerable reduced and flare activity is not yet sufficiently high. It should be mentioned that it would not be easy to select such allowed intervals. Further studies of that aspect are discussed.     

Isotopic Criteria for Identification of Organic Carbon on Earth and Meteorites

Contrary to the often stated view, an enrichment of organic material in the light isotope is not a conclusive evidence of its life-related origin. The β¹³C - σ¹³C correlation is a special feature of biological systems. Therefore it can be used as a criterion for identification of organic carbon. A survey of the available isotopic data for organic compounds in meteorites shows that they do not comply with the β¹³C - σ¹³C correlation. The prevalence of amino and hydroxy acids in purines and sugars found in carbonaceous meteorites indicates that condensation of HCN and HCHO passed through cyanohydrin reaction, while biological evolution proceeds through formation of adenosine triphosphate (ATP). This, in addition to the isotope criterion, indicates that the organic compounds in carbonaceous chondrites are not life-related substances. This revised version was published online in August 2006 with corrections to the Cover Date.     

First estimations of the aerosol optical thickness using Langley Method at Southern Brazil (29.4°S, 53.8°W)

The first estimations of the aerosol optical thickness (AOT) using Langley Method at Southern Space Observatory (SSO) at Southern Brazil (29.4°S, 53.8°W) are presented. In addition to ozone and sulphur dioxide columns, AOT can be obtained using Brewer Spectrophotometer at specific wavelengths: 306.3, 310.1, 313.5, 316.8 and 320.1 nm. The AOT was obtained for the period from November/2002 to May/2003. Very low AOT averages were obtained, whose values were about 0.21 ± 0.03 at 306.3 nm, 0.21 ± 0.02 at 310.1 nm, 0.19 ± 0.02 at 313.5 nm, 0.20 ± 0.02 at 316.8 nm and 0.20 ± 0.02 at 320.0 nm for all period analysed. Different behaviour of AOT were obtained at two daily specific periods of aerosol accumulation, one in the afternoons from November/2002 to February/2003, caused mainly by a mild biomass burning season’s in the region and other in the mornings from March to May/2003, due the high relative humidity presented in the region studied.