Cell sensitivity to gravity

Cultures of human lymphocytes exposed in microgravity to the mitogen concanavalin A showed less than 3 percent of the activation of ground controls. This result supports the hypothesis, based on simulations at low g and experiments at high g, that microgravity depresses whereas high gravity enhances cell proliferation rates. The effects of gravity are particularly strong in cells undergoing differentiation.     

Lunar gravity analysis from long-term effects

The global lunar gravity field was determined from a weighted least squares analysis of the averaged classical element of the five Lunar Orbiters.The observed-minus-computed residuals have been reduced by a factor of 10 from a previously derived gravity field.The values of the second-degree zonal and sectorial harmonics are compatible with those derived from libration data.     

高效重力式精选设备的研制

介绍了作者研制的高效重力式精选机的基本结构、作业原理和技术特点。重点描述了振动工作台、工作台驱振装置及其倾角调节装置等关键部件的总体配置与系统设计。该机的驱振装置采用浮动式传动设计,自平衡效果好,可有效减少整机震动,降低噪音;风系采用6台风机同轴横向组配,并配备导风、匀风装置提高工作台面各区域风量适应性和均匀性。小麦种子精选试验检测结果表明:其实际生产率为12.5 t/h,获选率99.1%,有害杂草籽清除率100%,除轻杂率92%,净度99.6%,破损率0.02%,除重杂率90%,粉尘浓度8 mg/m3,噪声82 dB(A)。     

Venus: radar determination of gravity potential

We describe a method for the determination of the gravity potential of Venus from multiple-frequency radar measurements. The method is based on the strong frequency dependence of the absorption of radio waves in Venus' atmosphere. Comparison of the differing radar reflection intensities at several frequencies yields the height of the surface relative to a reference pressure contour; combination with measurements of round-trip echo delays allows the pressure, and hence the gravity potential contour, to be mapped relative to the mean planet radius. Since calibration data from other frequencies are unavailable, the absorption-sensitive Haystack Observatory data have been analyzed under the assumption of uniform surface reflectivity to yield a gravity equipotential contour for the equatorial region and a tentative upper bound of 6 x 10(-4) on the fractional difference of Venus' principal equatorial moments of inertia. The minima in the equipotential contours appear to be associated with topographic minima.     

Lunar gravity: the first farside map

A global lunar gravity field has been determined from data on the long-term motion of the Apollo 15 and Apollo 16 subsatellites and Lunar Orbiter 5. The nearside gravity map resolves major mascon basins and, in general, is in excellent agreemnent with the results of Muller and Sjogren. The farside gravity map is characterized by broad positive gravity in the highland regions with interspersed, localized, negative anomalies corresponding to major ringed basins. A comparison between global gravity and topography indicates that a thicker farside crust could be responsible for these gravitational differences between the two lunar hemispheres.     

Materials: tribology experiment in zero gravity

A tribology experiment in zero gravity was performed during the orbital flight of Spacelab 1 to study the motion of liquid lubricants over solid surfaces. The absence of a significant gravitational force facilitates studies of the motion of liquid lubricants over solid surfaces as controlled by interfacial and capillary forces. Observations were made of phenomena associated with the liquid on one solid surface and also with the liquid between a pair of closely spaced surfaces. Typical photographic records obtained on Spacelab 1 are described.     

5XZ-5型重力式精选机的研制

研制了5XZ-5型重力式精选机,介绍了其基本结构和工作过程,重点描述了振动工作台、传动系统、风机系统3个关键工作部件的设计、原理和主要工作参数及其调节。该机的振动系统采用等惯量反向配置设计,风机系统采用多台离心风机同轴横向组配,并配有风量调节装置。小麦种子精选试验检测结果表明,其实际生产率为5.1 t/h,获选率98.8%,有害杂草籽清除率100%,除轻杂率90%,净度99.6%,破损率0.06%,除重杂率85%,粉尘浓度8 mg/m3,噪声84 dB(A)。     

Bilateral symmetry in chick embryo determination by gravity

The determination of bilateral symmetry of chick blastodiscs occurring during the second half of the uterine period is only indirectly caused by the intrauterine rotation of the egg. As a result of this rotation the blastodisc is forced into an oblique position and the force of gravity affects the symmetrization process. The same result may be artificially achieved, without rotation, by forcing the blastodisc into an oblique position.     

Blake outer ridge: development by gravity tectonics

A continuous seismic profile across the Blake Outer Ridge reveals clear evidence of a structural origin for the ridge. A ridge core separates distinctive regions of structure east and west of the crest and does not support a theory of depositional origin. The presence of horizon A continuously beneath the ridge rules out faulting or folding involving basement rocks. Gravity tectonics are suggested as the mechanism for formation of the ridge after the deposition of the sediments above horizon A.     

Lunar gravity: preliminary estimates from lunar orbiter

Tracking data fromt the lunar orbiters have been analyzed for information regarding Moon's gravity field. These preliminary results include values of a set of harmonic coefficients throlugh degree 4 in the tesserals and degree 8 in the zonals. Implications regarding Moon's mass distribution are discltssed: one implicationt is that Moon is nearly homogeneous.     

Moving visual scenes influence the apparent direction of gravity

When an observer views a wide-angled display rotating around his line of sight, he both feels his body tilted and sees a vertical straight edge tilted opposite to the moving stimulus. Displacement of the perceived vertical increases with stimulus speed to reach a maximum (averaging 15 degrees) at 30 degrees per second.     

基于改进粒子群算法的重力坝断面优化研究

【目的】将改进粒子群算法用于重力坝断面的优化计算,为重力坝的优化设计提供支持。【方法】针对传统粒子群算法(PSO)中线性递减的惯性权重极易导致算法陷入局部极值的不足,提出一种改进的粒子群算法(Improved PSO),该算法利用三角函数的相关性质改进惯性权重(w)随时间的动态变化模式,以使惯性权重值在算法的初期保持较大取值,然后逐渐递减而在算法的末期保持较小取值,从而提高粒子群算法的全局搜索能力,增强算法的收敛性能。编制基于改进粒子群算法的重力坝断面优化设计计算程序,对某水利枢纽工程的非溢流重力坝断面进行优化计算分析,并与遗传算法和标准粒子群算法的计算结果进行比较。【结果】采用改进粒子群算法得到的非溢流重力坝的最优断面面积为5 147.3 m~2,而采用标准粒子群算法(SPSO)得到的非溢流重力坝的最优断面面积为5 416.5m~2,前者较后者减小9.45%,极大地提高了经济性;采用改进的粒子群算法得到最优解需要计算15步,而采用标准粒子群算法得到最优解需要计算22步,粒子群算法收敛速度提高了31.8%。通过2种算法计算结果的对比,表明改进的粒子群算法不仅能得到更好的优化结果,而且保持了较快的收敛速度。【结论】改进粒子群算法可以用于大型水利工程结构的优化计算与设计。     

A free-fall determination of the newtonian constant of gravity

Recent determinations of the Newtonian constant of gravity have produced values that differ by nearly 40 times their individual error estimates (more than 0.5%). In an attempt to help resolve this situation, an experiment that uses the gravity field of a one-half metric ton source mass to perturb the trajectory of a free-falling mass and laser interferometry to track the falling object was performed. This experiment does not suspend the test mass from a support system. It is therefore free of many systematic errors associated with supports. The measured value was G = (6.6873 +/- 0. 0094) x 10(-11) m3 kg-1 sec-2.     

Measurements of time-variable gravity show mass loss in Antarctica

Using measurements of time-variable gravity from the Gravity Recovery and Climate Experiment satellites, we determined mass variations of the Antarctic ice sheet during 2002-2005. We found that the mass of the ice sheet decreased significantly, at a rate of 152 +/- 80 cubic kilometers of ice per year, which is equivalent to 0.4 +/- 0.2 millimeters of global sea-level rise per year. Most of this mass loss came from the West Antarctic Ice Sheet.