Great sand sea and selima sand sheet, eastern sahara: geochronology of desertification

The relation of playa sediments and associated archeological sites with longitudinal dunes allows estimation of ages for the two uppermost strata of the Great Sand Sea. Active dune formation corresponds with interpluvial periods of hyperaridity; dune stability corresponds with semiarid pluvial periods. Archeological sites associated with truncated paleosols in the Selima Sand Sheet suggest a similar climatic relation and indicate that the isohyets of central Sudan shifted at least 400 kilometers northward during the peak of pluvials.     

Venus: topography revealed by radar data

Surface height variations over the entire equatorial region on Venus have been estimated from extended series of measurements of interplanetary radar echo delays. Most notable is a mountainous section of about 3-kilometer peak height located at a longitude of 100 degrees (International Astronomical Union coordinate system). The eastern edge has an average inclination of about 0.5 degrees, which is unusually steep for a large-scale slope on Venus. The resolution of the radar measurements along the surface of Venus varied between about 200 and 400 kilometers with a repeatability in altitude determination generally between 200 and 500 meters. The mean equatorial radius was found to be 6050.0+/-0.5 kilometers.     

Subsurface radar sounding of the south polar layered deposits of Mars

The ice-rich south polar layered deposits of Mars were probed with the Mars Advanced Radar for Subsurface and Ionospheric Sounding on the Mars Express orbiter. The radar signals penetrate deep into the deposits (more than 3.7 kilometers). For most of the area, a reflection is detected at a time delay that is consistent with an interface between the deposits and the substrate. The reflected power from this interface indicates minimal attenuation of the signal, suggesting a composition of nearly pure water ice. Maps were generated of the topography of the basal interface and the thickness of the layered deposits. A set of buried depressions is seen within 300 kilometers of the pole. The thickness map shows an asymmetric distribution of the deposits and regions of anomalous thickness. The total volume is estimated to be 1.6 x 10(6) cubic kilometers, which is equivalent to a global water layer approximately 11 meters thick.     

Expansion and contraction of the sahara desert from 1980 to 1990

Data from polar-orbiting meteorological satellites have been used to determine the extent of the Sahara Desert and to document its interannual variation from 1980 to 1990. The Sahara Desert ranged from 8,633,000 square kilometers in 1980 to 9,982,000 square kilometers in 1984. The greatest annual north-south latitudinal movement of the southern Saharan boundary was 110 kilometers from 1984 to 1985 and resulted in a decrease in desert area of 724,000 square kilometers.     

Cretaceous sauropods from the sahara and the uneven rate of skeletal evolution among dinosaurs

Lower Cretaceous fossils from central Niger document the succession of sauropod dinosaurs on Africa as it drifted into geographic isolation. A new broad-toothed genus of Neocomian age ( approximately 135 million years ago) shows few of the specializations of other Cretaceous sauropods. A new small-bodied sauropod of Aptian-Albian age ( approximately 110 million years ago), in contrast, reveals the highly modified cranial form of rebbachisaurid diplodocoids. Rates of skeletal change in sauropods and other major groups of dinosaurs are estimated quantitatively and shown to be highly variable.     

赤水、习水沟谷地区的日照和太阳辐射状况

通过地形遮蔽图法对赤水、习水沟谷地区的日照和太阳辐射进行了测算，结果表明，该区年太阳总辐射为2466.3-2999.2Mj/m^2，较当地开阔地形站减少21%-35%，年实照时间为451.2-786.9h，较当地开阔地形站减少39%-65%，年日照百分率为10.2%-17.8%。7、8月晴朗天气多，太阳高度角大，地形遮蔽作用小，实照时间较当地开阔地形站减少35%-63%；12月阴雨天气多，太阳高度角小，地形遮蔽作用大，实照时间减少53%-84%。沟谷地区阴蔽，阳光和煦，冬暖夏凉，湿润风和，形成了喜阴湿耐阴蔽植被繁茂的小生境和旅游观光的适宜气候。     

潜流式人工湿地系统处理制胶废水小型试验

进行了潜流式人工湿地系统处理天然橡胶加工废水的小型试验.结果表明当进水pH、CODCr NH3-N平均值分别为6.85、1 523.34 mg/L、297.25 mg/L,水力负荷为0.016 m3/m2·d,水力停留时间为3 d时,湿地系统对CODCr、BOD5、NH3-N的去除率分别为90.42%、93.25%、75.37%;该系统耐冲击负荷强,出水水质稳定.湿地系统内外牧草栽培对比试验结果表明,制胶废水能促进湿地牧草的生长及品质的改善.     

Asymmetry of the acetylcholine channel revealed by quaternary anesthetics

Tissue-cultured rat myoballs were examined electrophysiologically with a suction pipette, which was used for voltage clamping and internal perfusion. The lidocaine derivative QX-314 caused a time- and membrane potentia-dependent block of acetylcholine-induced current only when applied from the extracellular membrane surface. The same compounds caused a use-dependent block of the sodium channel only from the intracellular membrane surface. These experiments demonstrate a fundamental asymmetry of the acetylcholine receptor-channel complex.     

无压局部灌溉对番茄生长发育及品质的影响研究

为了探明水分对作物的品质的调控作用,在温室大棚种植番茄采用根区局部控水无压地下灌溉和沟灌的田间对比试验。对番茄根系、生长环境、叶片蒸腾速率、气孔导度和光合速率变化,以及对不同生育期内果实品质成分的变化进行了监测分析。结果表明,与沟灌相比,无压灌溉降低了番茄的蒸腾量、减小了气孔导度和光合速率,提高了水分利用率和水分生产率;并不降低作物产量,使番茄的维生素C提高45.79%、可溶性糖提高25.86%、总糖提高34.65%。研究表明,无压灌溉通过水分调控改变了作物生长环境,维持了根冠间协调平衡比例关系,改善物品质,具有以水调质功效。研究结果揭示了番茄生命需水信号与环境信息的内在关系,为农业节水理论深入研究提供了方向。     

潜流湿地对农村生活污水中磷的净化作用

分别以香根草、芦竹和灯心草为植物构建潜流人工湿地植物床,研究其对农村生活污水中磷的净化功能。设计正交试验,分析pH值、水力负荷、碳氮比和植物4个因素对潜流人工湿地处理农村生活污水中磷的去除率的影响。结果表明,影响因素pH值、水力负荷、碳氮比、植物均对系统处理农村生活污水的除磷能力有极显著的影响(P0.01)。从单因素分析来看,当污水呈偏酸性、中性、偏碱性时,TP的平均去除率均高于90.00%,偏碱性环境下湿地对TP的去除率略高一些。水力负荷为33mm/d时,TP的平均去除率最高,达95.52%。各种植物对模拟农村生活污水中的污染物的处理能力不同,香根草和灯心草对TP的平均去除率相当,均达到94.00%以上,芦竹稍差一些,为89.94%。     

Venus: mapping the surface reflectivity by radar interferometry

The surface reflectivity of Venus obtained by radar interferometry at a wavelength of 3.8 centimeters has been mapped for a region extending approximately from -80 degrees to 0 degrees in longitude (Carpenter's definition) and from -50 degrees to +40 degrees in latitude. The map is free from the twofold range-Doppler ambiguity because the interferometer fringe pattern makes possible the separation of two points of equal range and Doppler shift. The map presents many new features and clearly delineates features already observed. Most notably, the map shows large circular regions of significantly lower reflectivity than their surroundinigs.     

Subsurface phenomena and the splashing of drops on shallow liquids

High-speed movies have been taken of the formation of the sub-surface cavity and of the Rayleigh jet formed during the splash of a drop on a shallow liquid. They show that the initial increase and subsequent decrease in the rate of rise of the jet and the maximum jet height with decreasing depth of liquid are the result of the interaction of the subsurface cavity with the solid boundary beneath the liquid. This interaction modifies considerably the pressure gradients in the liquid during the formation and collapse of the cavity.     

Solar flares, proton showers, and the space shuttle

The space shuttle era will focus renewed attention on the hazards of the space environment to human habitation. The chief unpredictable hazard for astronauts is energetic proton radiation from solar flares. In some orbits, there is no reasonable level of shielding material that will protect shuttle occupants from potentially lethal doses of radiation. The effects of a solar flare that occurred druing the first flight of the Columbia are discussed and current flare research reviewed. The emphasis is on progress made during the recent international Solar Maximum Year toward understanding the origins of proton showers.     

涝渍相随对棉花产量与品质的影响

 利用测坑试验研究了棉花花铃期涝渍相随对产量及品质的影响。结果表明 ,棉花花铃期受涝渍相随的影响很大 ,不同涝渍处理棉花产量差异显著 ;涝渍胁迫对棉花品质有一定影响 ,但处理间差异不大。通过数学模型定量分析表明 ,涝渍连续过程中涝和渍对作物的影响程度不同 ,涝对棉花产量的影响远比渍大 ,渍前受涝越严重 ,减产越严重。