Effects of heavy ions on visual function and electrophysiology of rodents: the ALTEA-MICE project.

ALTEA-MICE will supplement the ALTEA project on astronauts and provide information on the functional visual impairment possibly induced by heavy ions during prolonged operations in microgravity. Goals of ALTEA-MICE are: (1) to investigate the effects of heavy ions on the visual system of normal and mutant mice with retinal defects; (2) to define reliable experimental conditions for space research; and (3) to develop animal models to study the physiological consequences of space travels on humans. Remotely controlled mouse setup, applied electrophysiological recording methods, remote particle monitoring, and experimental procedures were developed and tested. The project has proved feasible under laboratory-controlled conditions comparable in important aspects to those of astronauts' exposure to particle in space. Experiments are performed at the Brookhaven National Laboratories [BNL] (Upton, NY, USA) and the Gesellschaft für Schwerionenforschung mbH [GSI]/Biophysik (Darmstadt, FRG) to identify possible electrophysiological changes and/or activation of protective mechanisms in response to pulsed radiation. Offline data analyses are in progress and observations are still anecdotal. Electrophysiological changes after pulsed radiation are within the limits of spontaneous variability under anesthesia, with only indirect evidence of possible retinal/cortical responses. Immunostaining showed changes (e.g. increased expression of FGF2 protein in the outer nuclear layer) suggesting a retinal stress reaction to high-energy particles of potential relevance in space.     

The low temperature organic chemistry of Titan's geofluid.

Organic chemistry on Titan and prebiotic chemistry on Earth involve the same N-containing organics: nitriles and their oligomers. Couplings of their chemistry in the three parts of Titan's geofluid (atmosphere, aerosols and surface) seem to play a key role in the organic chemical evolution of the planet. If liquid water was present on Titan, then a prebiotic chemistry, involving eutectics, similar to that of the early Earth, may have occurred. However, liquid water is currently absent and a prebiotic chemistry based only on N-organics may be evolving now on Titan. The other consequence of the low temperatures of Titan is the possible formation of organics unstable at room temperature and very reactive. So far, these compounds have not been systematically searched for in experimental studies of Titan's organic chemistry. C4N2 has already been detected on Titan. Powerful reactants in organic chemistry, CH2N2, and CH3N3, may be also present. They exhibit spectral signatures in the mid-IR strong enough to allow their detection at the 10-100 ppb level. They may be detectable on future IR spectra (ISO and Cassini) of Titan.     

High resolution imaging of objects at Ka band

A coherent wideband millimeter wave (mmW) imaging radar which operates in two different imaging modes is briefly described. The principles of two-dimensional (2-D) high resolution imaging are introduced. The image reconstruction algorithm together with image enhancement techniques are discussed. Some experiments imaging on both scaled aircraft model and full-size large scale vehicle are presented     

The sondrestrom radar and accompanying ground-based instrumentation

The Sondrestrom radar facility, funded by the NSF Upper Atmospheric Facilities Program, is operated and managed by SRI International. The facility is located on the west coast of Greenland, just north of the Arctic Circle, near 75 deg invariant magnetic latitude. The principal instrument at the facility is the incoherent scatter radar. The incoherent scatter technique allows the direct measurement of ionospheric electron number density, ion velocity, and electron and ion temperature along the radar beam. Because the radar antenna is fully steerable these parameters can be determined as functions of horizontal distance and altitude. Additional ionospheric quantities can be derived using these measured parameters. As part of the ISTP mission, the radar will measure the spatial (horizontal and altitudinal) and temporal variations of ionospheric parameters including electron density, large scale electric field. conductivity, currents, and energy input. Repetitive measurements define variations of parameters with local time, as well.     

Sunlight viewable electroluminescent displays for militaryapplication

A new advanced type of high ambient viewing AC electroluminescent display has been developed incorporating a combination of high contrast and high brightness techniques. The improvement in the contrast is achieved by a black absorption layer within the thin film structure. Improvement in the brightness is attributed to increasing the refresh rate by an order of magnitude. This can only be accomplished by an order of magnitude decrease in front electrode impedance with the use of a new metalized structure to reinforce the ITO electrodes and lower their resistance     

Carbonaceous matter in cometary dust and coma.

The analysis of carbonaceous matter in p/Halley's dust and coma via mass spectrometry of positive ions is reviewed. Dust impact generated ions were analyzed by the PUMA instrument aboard VEGA I, and coma plasma ions by the PICCA instrument aboard GIOTTO. For the organic molecules results an overall C:H:O:N ratio of 1.:1.4:0.6:0.1. Most of this polymer material can formally be understood as an aggregation of monomers C2H2, CH2O, and HCN. Special emphasis is given to possible aromatic, especially heterocyclic, and other unsaturated ions, and their importance for abiotic chemical and prebiotic evolution. Aspects of the potential heterogeneous catalysis in liquid water at the inorganic grain backbone structure found by this analysis, too, are also treated.     

The SERENDIP SETI project: new instrumentation for SETI and results of recent observations

Over the past 30 years research into the existence of extraterrestrial life has focused on attempts to detect stable narrowband radio signals emitted in the microwave portion of the radio frequency (RF) spectrum. The SERENDIP SETI group is currently conducting search operations on the world’s largest radio telescope at the Arecibo Observatory in Puerto Rico.The third generation SERENDIP system, SERENDIP III, is a 4 million channel FFT-based spectrum analyzer with 0.6 Hz frequency resolution. In this paper, we will discuss the results of our recent 3.5 year sky survey. SERENDIP looked at 95% of the sky visible from Arecibo in the 424–436 MHz range, analyzed 10¹⁴ spectral bins, and logged information on over 2.5×10⁸ signals.The fourth generation SERENDIP system expands on the SERENDIP III design. SERENDIP IV computes 2×10¹¹ operations each second, providing spectral analysis on 160 million channels in 1.7 s. We will discuss the design and use of the SERENDIP IV system and future observing plans.     

Similarity of the infrared spectrum of an Orgueil organic polymer with interstellar organic compounds in the line of sight towards IRS 7.

We present a comparison between the IR spectrum of the galactic center source IRS 7 and the spectrum of a carbonaceous polymer from the Orgueil meteorite. We have obtained an almost perfect match between the two spectra in the region between 3020-2790 cm-1, which suggests that the chemical composition of the interstellar organic matter and that of the meteorite polymer are similar or that the meteoritic polymer could be a well preserved interstellar organic molecule. Assuming that the meteoritic polymer has the same C/H ratio as these interstellar molecules, we find that 45 % of the total abundance of carbon in the line of sight toward IRS 7 is trapped in such an interstellar organic grain material.     

Interference Canceler Array with Reference Generating Loop

Adaptive arrays utilizing an internally generated reference signal to drive least mean square (LMS) weight determining loops have experienced difficulty arising from phase shifts induced by the reference generating circuits. The phenomenon observed is that the expected value of the weights oscillate in the steady state modulating the incoming signal. A scheme is reported which avoids this problem. It differs from earlier methods in that the reference generator has no infinite limiter so that the amplitude of the reference is not constant and in that one element is left unweighted. Alternative schemes were considered wherein the reference signal is drawn from all the array elements or from the weighted elements only. Only the latter is fully reported here, and is found superior. It is shown that in the presence of a desired signal and independent element noise, the processing scheme proposed produces weights whose expected values converge to a constant nonoscillatory state provided certain mild constraints are satisfied. In particular, if a cos ? ? 1, a being the gain and ? the phase shift of the filter in the reference generator, the weights converge. In addition, the steady state signal-to-noise power ratio (SNR) is determined. It is found that with a cos ? close to unity the SNR is that of an (N-1) element array coherently combined, where N is the number of elements. The SNR falls off with departures of a and ? from 1 and 0, respectively, but not drastically.     

Resolution Limits with Propagation Phase Errors

Resolution limits and corresponding optimum linear apertures are determined in the presence of phase errors. Let ?(t) be the phase aberration at position t across the aperture; it is assumed that the random process ? has a power law structure function, E{[(?(t)-?(?)]2}= c|t-?|n. Beam tilting caused by the phase error is "removed" (for each sample of ?), then resolution formulas are developed. An approximate analysis is obtained in closed form and yields an optimum resolution proportional to c1/n for O < n < 2. The exact analysis is given for Gaussian ?, and again the optimum resolution is proportional to c1/n. In applications n= 5/3 is of interest, and in the Gaussian case the best obtainable equivalent rectangle resolution is ? ?)/2? (0.975)c3/5 radians with a corresponding optimum linear aperture of 14c-3/5. When long exposures are considered, imaging without removing beam tilting is of interest, and resolution is degraded by a factor of about 2.5 for a linear aperture. Alternatively, in some applications optimum focus as well as beam tilt should be considered, in this case resolution is improved by a factor of about 1.4 (again for n= 5/3). Finally, joint (tilt corrected) optimization over aperture length and taper is treated; however, as one might expect, the use of taper offers negligible resolution improvement.