Energy and charge localization in irradiated DNA.

The relation between the site of energy deposition and the site of its biological action is an important question in radiobiology. Even at 77 degrees K, evidence is clear that these two sites must be separated since energy deposition is random but specific products are formed. Several processes that may contribute to this separation are: 1) hole migration and stabilization through deprotonation to give neutral oxidation product radicals; 2) electron trapping and transfer to form specific radical anions, possibly followed by protonation to give neutral reduction product radicals; and 3) recombination of spatially separated charges or radicals. These microscopic processes will be reviewed critically in an analysis using electron paramagnetic resonance spectroscopy (EPR) evidence for and against long-range transfer of energy and/or charge in frozen, hydrated DNA.     

Performance characteristics of lithium ion cells at low temperatures

The low temperature charge and discharge characteristics of experimental MCMB-Li/sub x/Ni/sub y/Co/sub 1-y/O/sub 2/ cells containing different electrolytes were investigated. The use of low ethylene carbonate (EC)-content electrolyte formulations has resulted in good discharge performance to temperatures as low as -40/spl deg/C. The effect of charge voltage and charge current upon the individual electrode potentials at low temperature was investigated using the three electrode cells (containing lithium reference electrodes). In some cases, lithium plating was observed to occur upon low temperature charge, and found to be facilitated by high charge voltages, high charge currents, and poor anode kinetics. Electrochemical characterization of the cells has helped to establish the conditions under which lithium plating can occur by providing information regarding the polarization effects present at each electrode.     

Data Quantization for Narrowband Signal Detection

In automatic radar detection, digital integration of the envelope detector outputs is often used as a good approximation to the optimum. This requires quantizing the envelope detector outputs. In this paper, quantizer structures for narrowband signal detection are considered. Quantizer characteristics are derived to optimize performance as measured by the detector efficacy?an asymptotic performance measure. Asymptotic and finite sample performance results are presented. The results obtained are not limited in their application to Gaussian noise only, although this important case is given specific consideration.     

Temporal decorrelation of X-band backscatter from wind-influencedvegetation

The temporal decorrelation characteristics of X-band radar backscatter from wind-influenced vegetation were investigated using a short-range CW radar. Radar reflectance data were gathered on various types of individual trees from a distance of approximately 30 m. The windspeed was monitored during each measurement, which lasted 5 s. The crown cover and the mean leaf area of the trees were also recorded. Autocovariance plots were generated for each measurement, from which the decorrelation time was estimated. As expected, the return signals decorrelated faster at higher wind speeds. However, the decorrelation time was also found to depend on the tree type, tree structure, and leaf cover characteristics. Measured decorrelation times for moderate winds (7-9 m/s) were often between 40-60 ms, although the lowest decorrelation time measured under these conditions was 14 ms for the Eastern Cottonwood. In lighter winds (1-4 m/s), decorrelation times were much longer, and there was substantial spread in the data     

Microprocessor smart cards with fingerprint user authentication

Due to the great increase in Information Technology (IT) systems where user authentication is needed, security in those systems relies on using PINs or passwords. During recent years, the scientific community has been trying to improve biometric techniques to be accepted as an alternative to other user authentication schemes. One of the sectors where user identity must be verified, is the identification cards sector. In fact, if great security wants to be achieved, smart cards should be used. But cardholder verification is performed using Card Holder Verification Keys (CHV-Keys), which are PIN-based. The authors are trying to integrate fingerprint verification inside a smart card, following their works in the past. The fingerprint scheme used is shown, and the work to achieve the integration inside a commercial smart card is detailed.     

AI techniques in uninhabited aerial vehicle flight

This describes the development of an application of artificial intelligence (AI) for unmanned aerial vehicle (UAV) control. The project was part of the requirements for a class in AI at NOVA Southeastern University and a beginning project at NASA Wallops Flight Facility for a resilient, robust, and intelligent UAV flight control system. A method is outlined which allows a base level application for applying an artificial intelligence method, fuzzy logic, to aspects of control logic for UAV flight. One element of UAV flight, automated altitude hold, has been implemented and preliminary results displayed.     

A global HF telecommand system for long duration balloon flights

An HF telecommand system for the control of long duration balloon flights at any point on the globe is described. The system proposed consists of a network of low-power transmitters operating at the same carrier frequency. The choice of transmitter frequency, power and location are presented. Control of the transmitters may be performed remotely by means of the public switched telephone network; an assessment of the error-rate in the system as a whole is given.     

Evaluation of light emitting diode characteristics for a space-based plant irradiation source.

Light emitting diodes (LEDs) are a promising irradiation source for plant growth in space. Improved semiconductor technology has yielded LED devices fabricated with gallium aluminum arsenide (GaAlAs) chips which have a high efficiency for converting electrical energy to photosynthetically active radiation. Specific GaAlAs LEDs are available that emit radiation with a peak wavelength near the spectral peak of maximum quantum action for photosynthesis. The electrical conversion efficiency of installed systems (micromole s-1 of photosynthetic photons per watt) of high output LEDs can be within 10% of that for high pressure sodium lamps. Output of individual LEDs were found to vary by as much as 55% from the average of the lot. LED ratings, in mcd (luminous intensity per solid angle), were found to be proportional to total photon output only for devices with the same dispersion angle and spectral peak. Increasing current through the LED increased output but also increased temperature with a consequent decrease in electrical conversion efficiency. A photosynthetic photon flux as high as 900 micromoles m-2 s-1 has been produced on surfaces using arrays with LEDs mounted 7.6 mm apart, operating as a current of 50 mA device-1 and at an installed density of approximately 17,200 lamps m-2 of irradiated area. Advantages of LEDs over other electric light sources for use in space systems include long life, minimal mass and volume and being a solid state device.     

Dust motion in Jupiter's tilted magnetic field

We outline an analytical method for studying the motion of charged dust particles that orbit an oblate planet having a tilted, offset, dipolar magnetic field. Our computed trajectories closely mimic previous numerical results; equilibrium dust potentials must be less then 10 volts or the Jovian ring would be thicker than observed. We identify several $\text{Lorentz resonances}$, where the periods of components of the Lorentz force, as seen by a reference particle moving in the equatorial plane, match the particle's orbital period; several seem to be near observed features of the Jovian ring system.