Radar detection of phobos

Radar echoes from the martian satellite Phobos provide information about that object's surface properties at scales near the 3.5-cm observing wavelength. Phobos appears less rough than the moon at centimeter-to-decimeter scales. The uppermost few decimeters of the satellite's regolith have a mean bulk density within 20% of 2.0 g cm(-3). The radar signature of Phobos (albedo, polarization ratio, and echo spectral shape) differs from signatures measured for small, Earth-approaching objects, but resembles those of large (>/=100-km), C-class, mainbelt asteroids.     

Radar detection of the nucleus and coma of comet hyakutake

Radar observations of comet Hyakutake (C/1996 B2) made at the Goldstone Deep Space Communications Complex in California have detected echoes from the nucleus and from large grains in the inner coma. The nucleus of this bright comet was estimated to be only 2 to 3 kilometers in diameter. Models of the coma echo indicate backscatter from porous, centimeter-size grains ejected anisotropically at velocities of tens of meters per second. The radar observations suggest that a comet's activity may be a poor indicator of its size and provide evidence that large grains constitute an important component of the mass loss from a typical active comet.     

Satellite detection of effects due to increased atmospheric carbon dioxide

The use of satellites to detect climatic changes due to increased carbon dioxide was investigated. This method has several advantages over ground-based methods of monitoring climatic change. Calculations indicate that, by monitoring the outgoing longwave flux for small intervals in the 15-micrometer spectral region, changes in stratospheric temperatures due to doubled atmospheric carbon dioxide are large enough to be detected above the various sources of noise. This method can be extended to other spectral regions so that causal links between changes in outgoing longwave radiation due to other trace gases and the thermal structure of the atmosphere could be established.     

转基因作物的非预期效应及其检测

随着转基因产业的飞速发展,转基因食品的安全性逐步引起人们的广泛关注.外源基因的非预期效应可能引起转基因食品的营养成分发生改变,甚至产生一些新的毒性物质,可能对人类和动物健康以及环境形成潜在的危害,是转基因食品安全性评价的重要内容之一.由于外源基因的非预期效应具有潜在性,非预见性,因此以“实质等同性”为基础的定向评价方法很难充分考虑到由遗传修饰引起的非预期效应.文章主要阐述了转基因植物整合位点的分布和机制、转基因作物可能产生的非预期效应,以及利用基因芯片技术、蛋白质组定量分析技术、代谢组分析技术分别从mRNA水平、蛋白质水平、代谢水平上比较转基因作物和非转基因作物基因表达的差异,在食品安全评价中会是完善定向方法的补充方案,对转基因食品的安全性评价至关重要.     

相控阵天气雷达与多普勒雷达回波的对比分析

介绍相控阵天气雷达研究进展及其技术特点,并利用相控阵天气雷达和抛物面天线雷达的观测数据进行了对比分析。结果表明,相控阵天气雷达比普通雷达具有更灵活快捷的扫描能力,强度回波的分布和数值比较接近,但相控阵雷达的强回波区略强,回波细节更丰富,是探测中小尺度灾害天气系统的更理想工具。     

Radar observations of icarus

Radar observations of Icarus were made in mid-June 1968, at the time of closest approach. From the data, it is estimated that the radius is between 0.3 and 0.6 kilometer and the rotation period between 1.5 and 3.3 hours. A set of round-trip Doppler shift measurements is given.     

Radar reflectivity of titan

The present understanding of the atmosphere and surface conditions on Saturn's largest moon, Titan, including the stability of methane, and an application of thermodynamics leads to a strong prediction of liquid hydrocarbons in an ethane-methane mixture on the surface. Such a surface would have nearly unique microwave reflection properties due to the low dielectric constant. Attempts were made to obtain reflections at a wavelength of 3.5 centimeters by means of a 70-meter antenna in California as the transmitter and the Very Large Array in New Mexico as the receiving instrument. Statistically significant echoes were obtained that show Titan is not covered with a deep, global ocean of ethane, as previously thought. The experiment yielded radar cross sections normalized by the Titan disk of 0.38 +/- 0.15, 0.78 +/- 0.15, and 0.25 +/- 0.15 on three consecutive nights during which the sub-Earth longitude on Titan moved 50 degrees. The result for the combined data for the entire experiment is 0.35 +/- 0.08. The cross sections are very high, most consistent with those of the Galilean satellites; no evidence of the putative liquid ethane was seen in the reflection data. A global ocean as shallow as about 200 meters would have exhibited reflectivities smaller by an order of magnitude, and below the detection limit of the experiment. The measured emissivity at similar wavelengths of about 0.9 is somewhat inconsistent with the high reflectivity.     

Radar images of Mars

Full disk images of Mars have been obtained with the use of the Very Large Array (VLA) to map the radar reflected flux density. The transmitter system was the 70-m antenna of the Deep Space Network at Goldstone, California. The surface of Mars was illuminated with continuous wave radiation at a wavelength of 3,5 cm. The reflected energy was mapped in individual 12-minute snapshots with the VLA in its largest configuration; fringe spacings as small as 67 km were obtained. The images reveal near-surface features including a region in the Tharsis volcano area, over 2000 km in east-west extent, that displayed no echo to the very low level of the radar system noise. The feature, called Stealth, is interpreted as a deposit of dust or ash with a density less than about 0.5 gram per cubic centimeter and free of rocks larger than 1 cm across. The deposit must be several meters thick and may be much deeper. The strongest reflecting geological feature was the south polar ice cap, which was reduced in size to the residual south polar ice cap at the season of observation. The cap image is interpreted as arising from nearly pure CO(2) or H(2)O ice with a small amount of martian dust (less than 2 percent by volume) and a depth greater than 2 to 5 m. Only one anomalous reflecting feature was identified outside of the Tharsis region, although the Elysium region was poorly sampled in this experiment and the north pole was not visible from Earth.     

Phenothiazine effects on auditory signal detection in paranoid and nonparanoid schizophrenics

The differential effects of phenothiazine medication on auditory signal detection performance were compared in two types of schizophrenic subjects and in normal subjects. With increasing phenothiazine dosage a decrease in efficiency of signal detection performance occurred among nonparanoid schizophrenics and an increase in efficiency occurred among paranoid schizophrenics. These and related findings were interpreted in terms of differences in neuropsychological response and information processing characteristics in the two types of schizophrenics. The primary deficit in information processing in nonparanoid schizophrenics may be related primarily to their hypersensitivity to sensory stimuli, whereas in paranoids it may be related primarily to their impaired focusing of attention. Phenothiazines appear to decrease sensitivity to stimuli in nonparanoids but increase the ability to focus attention in paranoids. The possibility of treatment regimens which take into account the differential effects of phenothiazine medication was suggested.     

Fine-Scale Doppler Radar Observations of Tornadoes

Observations obtained with a mobile pencil-beam Doppler radar revealed many previously unresolved structures within tornadic storms and tornadoes and helped verify various aspects of conceptual models. Radar data from the parent circulations indicate the existence of spiral reflectivity bands, intense radial wind shear zones, and multiple larger-scale velocity maxima. Tornado structures observed include debris shields, clear axial (eye) regions, multiple reflectivity bands surrounding the center of the eye, and occasional reflectivity protrusions into the eye. Velocity and reflectivity data from tornado-scale circulations show evidence of axial downdrafts.     

Radar measurement of the upper atmosphere

In the last two decades large radars have proved to be powerful instruments for the measurement of the properties of the upper atmosphere. These radars were used initially to measure properties of the ionosphere by the Thomson scattering technique at heights above 100 kilometers. Careful interpretation of the power and spectrum of radar echoes yielded data on electron and ion densities and temperatures as well as on bulk motion of the ionospheric plasma, all as functions of height and time. More recent developments have made it possible to measure wind speeds and the structure of turbulence in the stratosphere and mesosphere at altitudes below 100 kilometers.     

Radar Image of Asteroid 1989 PB

Radar observations of the near-Earth asteroid 1989 PB, made shortly after its optical discovery, yield a sequence of delay-Doppler images that reveal it to consist of two distinct lobes that appear to be in contact. It seems likely that the two lobes once were separate and that they collided to produce the current "contact-binary" configuration.