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21.
Since 1999, ESA has conducted a number of system studies and technological developments to support the European and Canadian industry in the definition of a Satellite UMTS (S-UMTS) component development strategy, identifying critical technological areas and promoting S-UMTS demonstrations. In particular, the MUSIC project has successfully demonstrated advanced digital signal processing techniques to mitigate CDMA interference in spread-spectrum receivers, thus increasing the capacity and/or quality of service of a wireless communication network. The low-complexity solution for interference mitigation investigated and developed in the project is particularly suited for being implemented in mobile terminals.  相似文献   
22.
The Department of Defense (DoD) has funded a dazzling array of “high tech” solutions for many of the problems facing our military forces. Many of these “solutions” have been effective for long range mass destruction but have not been applicable for the close-in hand-to-hand combat that is on our streets. Our goal at the Hughes AET Center has been to convert “high tech” DoD capabilities into cost effective tools to help law enforcement agencies do their jobs better. Surveillance systems presently used by law enforcement officers make extensive use of television, infrared and other Line-of-Sight (LOS) surveillance systems. However, these systems cannot tell what is happening on the other side of a wall, behind bushes, around the corner, in the dark or through a dense fog. A new sensor has been developed that uses technology developed by the DoD for missile warhead fuzing. This small, light weight, low power “Radar” is based upon the fact that radio waves can penetrate nonmetallic materials. This new surveillance capability can help provide information about what is in a wall, ceiling or floor or on the other side of a door or concrete wall. Real field scenarios are used in this paper to show how this radar works and how field users can tell if someone is moving inside a building, even from remote locations  相似文献   
23.
A simple fiber-optic radar calibration target is described. Its operation is based on a wideband fiber, a laser transmitter that is directly modulated by the down-converted radar signal and an optical diode receiver recovering said signal. Further up-conversion having a common local oscillator with the first mixer ensures fidelity of the calibration return. Measured useful bandwidth exceeds 200 MHz and practically any radar RF frequency can be handled when suitable mixers are employed. Amplifiers can be added to the down-converted path as desired to compensate for the fiber loss. Modulation and LO sweep provide easy ways of introducing artificial fluctuations and Doppler frequencies. Particularly pulsed radars are readily tested with the proposed scheme as no restrictions are posed by the radar's TR-switch delays.  相似文献   
24.
The microwave landing system (MLS) transmits angle, data, andrange information for use by airborne receivers. In this paper, theintegrity of the data functions is analyzed in terms of the probabilityof undetected errors remaining in the data. The data format andintegrity requirements were derived from the MLS standards andguidance material defined by the International Civil Aviation Organization (ICAO). Results show that the performancerequirements can be met by: 1) averaging the received data bits ofseveral samples of the same word using a majority voting;2) reducing the bit error rate at the output of the receiver'sdecoder; and 3) a combination of the above techniques.  相似文献   
25.
In cells irradiation by heavy ions has been hypothesized to produce microlesions, regions of local damage. In cell membranes this damage is thought to manifest itself in the form of holes. The primary evidence for microlesions comes from morphological studies of cell membranes, but this evidence is still controversial, especially since holes also have been observed in membranes of normal, nonirradiated, cells. However, it is possible that damage not associated with histologically discernable disruptions may still occur. In order to resolve this issue, we developed a system for detecting microlesions based on liposomes filled with fluorescent dye. We hypothesized that if microlesions form in these liposomes as the result of irradiation, then the entrapped dye will leak out into the surrounding medium in a measurable way. Polypropylene vials containing suspensions of vesicles composed of either dipalmitoyl phosphatidylcholine, or a combination of egg phosphatidylcholine and cholesterol were irradiated at the Brookhaven National Laboratory using 56Fe ions at 1 GeV/amu. In several cases we obtained a significant loss of the entrapped dye above the background level. Our results suggest that holes may form in liposomes as the result of heavy ion irradiation, and that these holes are large enough to allow leakage of cell internal contents that are at least as large as a 1 nm diameter calcein molecule.  相似文献   
26.
Resistance to canavanine was studied in haploid yeast after exposure to heavy ions (argon to uranium) of energies between 1 and 10 MeV/u covering a LET-range up to about 10000 keV/micrometer. Mutations were found in all instances but the induction cross sections increased with ion energy. This is taken to mean that the contribution of penumbra electrons plays an important role. The probability to recover surviving mutants is highest if the cell is not directly hit by the particle. The experiments demonstrate that the geometrical dimensions of the target cell nucleus as well as its sensitivity in terms of survival have a critical influence on mutation induction with very heavy ions.  相似文献   
27.
Because activities in space necessarily involve chronic exposure to a heterogeneous charged particle radiation field it is important to assess the influence of dose-rate and the possible modulating role of heavy particle fragmentation on biological systems. Using the well-studied cataract model, mice were exposed to plateau 600 MeV/amu 56Fe ions either as acute or fractionated exposures at total doses of 5 - 504 cGy. Additional groups of mice received 20, 360 and 504 cGy behind 50 mm of polyethylene, which simulates body shielding. The reference radiation consisted of 60Co gamma radiation. The animals were examined by slit lamp biomicroscopy over their three year life spans. In accordance with our previous observations with heavy particles, the cataractogenic potential of the 600 MeV/amu 56Fe ions was greater than for low-LET radiation and increased with decreasing dose relative to gamma-rays. Fractionation of a given dose of 56Fe ions did not reduce the cataractogenicity of the radiation compared to the acute regimen. Fragmentation of the beam in the polyethylene did not alter the cataractotoxicity of the ions, either when administered singly or in fractions.  相似文献   
28.
Potential Martian soil components relevant to exobiology include water, organic matter, evaporites, clays, and oxides. These materials are also resources for human expeditions to Mars. When found in particular combinations, some of these materials constitute diagnostic paleobiomarker suites, allowing insight to be gained into the probability of life originating on Mars. Critically important to exobiology is the method of data analysis and data interpretation. To that end we are investigating methods of analysis of potential biomarker and paleobiomarker compounds and resource materials in soils and rocks pertinent to Martian geology. Differential thermal analysis coupled with gas chromatography is shown to be a highly useful analytical technique for detecting this wide and complex variety of materials.  相似文献   
29.
A relatively simple method is presented which eliminates previously reported (Oct. 1985) erratic estimation performance associated with Cartesian formulations of the extended Kalman filter (EKF) for the 2D angle-only emitter location problem. The technique is based on an initialization procedure which combines a priori probability density function (pdf) information with single measurement a posteriori pdf information in a manner which is more efficient than the EKF. Simulation results are presented which demonstrate the utility of the technique as compared with a previously offered modified gain EKF  相似文献   
30.
Stars in their late stages of evolution often shed matter in the form of a cool wind which is molecular in composition. These winds are a major source of replenishment of the interstellar gas and dust, so they furnish a large part of the raw materials for new generations of stars and planets. The chemistry of the circumstellar envelope depends strongly on the photospheric abundances of the elements, especially C and O. If C/O > 1, a rich organic chemistry is observable in the microwave and mm-wavelength emission lines of the reactions products. This paper reviews the observational evidence for the presence of organic molecules and their formation pathways in circumstellar envelopes, with special emphasis on rotational spectra at microwave and millimeter wavelengths.  相似文献   
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