Hubble space telescope observations of comet p/shoemaker-levy 9 (1993e)

The Hubble Space Telescope observed the fragmented comet P/Shoemaker-Levy 9 (1993e) (P indicates that it is a periodic comet) on 1 July 1993. Approximately 20 individual nuclei and their comae were observed in images taken with the Planetary Camera. After subtraction of the comae light, the 11 brightest nuclei have magnitudes between approximately 23.7 and 24.8. Assuming that the geometric albedo is 0.04, these magnitudes imply that the nuclear diameters are in the range approximately 2.5 to 4.3 kilometers. If the density of each nucleus is 1 gram per cubic centimeter, the total energy deposited by the impact of these 11 nuclei into Jupiter's atmosphere next July will be approximately 4 x 10(30) ergs ( approximately 10(8) megatons of TNT). This latter number should be regarded as an upper limit because the nuclear magnitudes probably contain a small residual coma contribution. The Faint Object Spectrograph was used to search for fluorescence from OH, which is usually an excellent indicator of cometary activity. No OH emission was detected, and this can be translated into an upper limit on the water production rate of approximately 2 x 10(27) molecules per second.     

Separation and conversion dynamics of four nuclear spin isomers of ethylene

Molecules with three or more nuclei of nonzero spin exist as discrete spin isomers whose interconversion in the gas phase is generally considered improbable. We have studied the interconversion process in ethylene by creating a sample depleted in the B2u nuclear spin isomer. The separation was achieved through spatial drift of this isomer induced by resonant absorption of narrow-band infrared light. Evolution of the depleted sample revealed conversion between B2u and B3u isomers at a rate linearly proportional to pressure, with a rate constant of 5.5 (+/-0.8) x 10(-4) s(-1) torr(-1). However, almost no change was observed in the Ag isomer populations. The results suggest a spin conversion mechanism in C2H4 via quantum relaxation within the same inversion symmetry.     

Fertilization in Brassica campestris ssp. pekinensis and its duration of each stage

This paper reports the process of fertilization in Brassica campestris ssp. pekinensis and the duration of each stage. The results are as follows: (1) Pollen germinates on stigma 2–3 h after pollination. (2) 4–8 h after pollination, pollen tube grows in the style. (3) 8–14 h after pollination, pollen tube grows in the ovary and gets into the ovule via the micropyle. (4) 16 h after pollination, one sperm nucleus moves to the egg and enters it. (5) The sperm nucleus adheres to the nuclear membrane of the egg 18 h after pollination. (6) 20 h after pollination, it enters the egg nucleus and male chromatin gradually disperses and 24 h after pollination, a male nucleolus appears. A large female nucleolus and a small male nucleolus occur in the nucleus of the fertilized egg, and zygote formed. The dispersing of sperm chromatin in the egg nucleus takes about 4 h. (7) 32–34 h after pollination, the division of zygote begins. The dormancy stage of the zygote lasts for about 8–10 h. (8) The pair polar nuclei lie in the chalazal end of the egg before fertilization, which may fuse into a secondary nucleus or not. (9) 16–18 h after pollination, the sperm nucleus moves to the polar nuclei or the secondary nucleus. 18 h after pollination, the sperm nucleus adheres to the nuclear membrane of the polar nuclei or that of the secondary nucleus. (10) 20 h after pollination, the sperm nucleus enters one of the polar nuclei or the secondary nucleus and a triple fusion takes place. The process of fusion is similar to the karyogamy but faster. The dispersing of the sperm chromatin in the polar nucleus or secondary nucleus takes about 2 h. (11) 22 h after pollination, the primary endosperm nucleus formed. The female and male nucleoli cannot fuse with each other before mitotic division of the primary endosperm nucleus. (12) 24 h after pollination, the division of the primary endosperm nucleus actually takes place. __________ Translated from Acta Horticulturae Sinica, 2005, 32(5): 812–817 [译自: 园艺学报]     

交配型因子和细胞质对香菇双核体中两组成型核比例的影响

    对造成香菇原生质体单核化后两种交配型单核体比例偏离1,1分离的遗传背景进行探讨.结果表明,B因子或是与B因子连锁的因子对这种偏离有明显的影响,而A因子对此影响不明显.B因子特异性不同,与之相对应的交配型单核体出现的比例亦不同,特异性越高,其对应交配型单核体在经原生质体单核化后将以较大的比例出现.参试的2个香菇菌株中4个B因子特异性顺序为B1B>3B>4B>2.双-单杂交所形成的由受体细胞质和受体、供体细胞核组成的同质异核体经原生质体单核化裂解后均与受体交配型相同的核居多,表明受体细胞质环境对双一单杂交所得异核体裂解后的核的存活和数量起着重要作用.作为供体的2个核中只有亲和力强的那个核优先迁移到受体中,形成新的异核体,即存在先导核.先导核与B因子的亲和特异性有关,特异性越高,先导核迁移速度越快.     

Spherical bilayer vesicles of fullerene-based surfactants in water: a laser light scattering study

The low solubility of fullerenes in aqueous solution limits their applications in biology. By appropriate substitution, the fullerenes can be transformed into stabilized anions that are water soluble and can form large aggregated structures. A laser light scattering study of the association behavior of the potassium salt of pentaphenyl fullerene (Ph5C60K) in water revealed that the hydrocarbon anions Ph5C60- associate into bilayers, forming stable spherical vesicles with an average hydrodynamic radius and a radius of gyration of about 17 nanometers at a very low critical aggregation concentration of less than 10(-7) moles per liter. The average aggregation number of associated particles in these large spherical vesicles is about 1.2 x 10(4).     

HST and VLT investigations of the fragments of comet C/1999 S4 (LINEAR)

At least 16 fragments were detected in images of comet C/1999 S4 (LINEAR) taken on 5 August 2000 with the Hubble Space Telescope (HST) and on 6 August with the Very Large Telescope (VLT). Photometric analysis of the fragments indicates that the largest ones have effective spherical diameters of about 100 meters, which implies that the total mass in the observed fragments was about 2 x 10(9) kilograms. The comet's dust tail, which was the most prominent optical feature in August, was produced during a major fragmentation event, whose activity peaked on UT 22.8 +/- 0.2 July 2000. The mass of small particles (diameters less than about 230 micrometers) in the tail was about 4 x 10(8) kilograms, which is comparable to the mass contained in a large fragment and to the total mass lost from water sublimation after 21 July 2000 (about 3 x 10(8) kilograms). HST spectroscopic observations during 5 and 6 July 2000 demonstrate that the nucleus contained little carbon monoxide ice (ratio of carbon monoxide to water is less than or equal to 0.4%), which suggests that this volatile species did not play a role in the fragmentation of C/1999 S4 (LINEAR).     

The radio-frequency single-electron transistor (RF-SET): A fast and ultrasensitive electrometer

A new type of electrometer is described that uses a single-electron transistor (SET) and that allows large operating speeds and extremely high charge sensitivity. The SET readout was accomplished by measuring the damping of a 1.7-gigahertz resonant circuit in which the device is embedded, and in some ways is the electrostatic "dual" of the well-known radio-frequency superconducting quantum interference device. The device is more than two orders of magnitude faster than previous single-electron devices, with a constant gain from dc to greater than 100 megahertz. For a still-unoptimized device, a charge sensitivity of 1.2 x 10(-5) e/hertz was obtained at a frequency of 1.1 megahertz, which is about an order of magnitude better than a typical, 1/f-noise-limited SET, and corresponds to an energy sensitivity (in joules per hertz) of about 41 Planck's over 2pi.     

基于多Agent的分布式制造执行系统模型

提出了一种开放式、模块化、分布式、可配置、可集成和可维护的基于多Agent的制造执行系统(MES)模型。首先分析了制造系统中的制造执行系统域，然后提出了基于多Agent的MES模型，采用UML图表详细分析了该模型的MES功能实现，最后给出了实施的MES系统框架。该MES系统易与企业资源计划(ERP)、车间控制系统(FCS)及其他制造系统相集成。     

Hot plasma environment at jupiter: voyager 2 results

Measurements of the hot (electron and ion energies >/=20 and >/= 28 kiloelectron volts, respectively) plasma environment at Jupiter by the low-energy charged particle (LECP) instrument on Voyager 2 have revealed several new and unusual aspects of the Jovian magnetosphere. The magnetosphere is populated from its outer edge into a distance of at least approximately 30 Jupiter radii (R(J)) by a hot (3 x 10(8) to 5 x 10(8) K) multicomponent plasma consisting primarily of hydrogen, oxygen, and sulfur ions. Outside approximately 30 R(J) the hot plasma exhibits ion densities from approximately 10(-1) to approximately 10(-6) per cubic centimeter and energy densities from approximately 10(-8) to 10(-13) erg per cubic centimeter, suggesting a high beta plasma throughout the region. The plasma is flowing in the corotation direction to the edge of the magnetosphere on the dayside, where it is confined by solar wind pressure, and to a distance of approximately 140 to 160 R(J) on the nightside at approximately 0300 local time. Beyond approximately 150 R(J) the hot plasma flow changes into a "magnetospheric wind" blowing away from Jupiter at an angle of approximately 20 degrees west of the sun-Jupiter line, characterized by a temperature of approximately 3 x 10(8) K (26 kiloelectron volts), velocities ranging from approximately 300 to > 1000 kilometers per second, and composition similar to that observed in the inner magnetosphere. The radial profiles of the ratios of oxygen to helium and sulfur to helium (相似文献   

Relationship between Nuclear Volumes, Chromosome Numbers, and Relative Radiosensitivities

An inverse relationship between a volume estimated to be associated with interphase chromosomes and acute lethal exposure to x-or gamma radiation has been found in 16 plant species. The apparent differences in radiosensitivities found would seem spurious, since the estimated average energy absorbed in the nucleus per chromosome (3.6 x 10(6) ev) approaches a constant (variation less than fourfold) in spite of wide ranges of lethal exposures (0.6 to 75 kr), of nuclear volumes (43 to 1758 micro(3)), and of somatic chromosome numbers (6 to 136). The regression line obtained can be used to predict the radiosensitivities of other plant species if their nuclear volumes and chromosome numbers are known.     

Venus: density of upper atmosphere from measurements of drag on pioneer orbiter

Measurements of the changes in orbital period of the Pioneer Venus orbiter have yielded estimates of the density of the upper atmosphere of Venus at altitudes in the range from 150 to 200 kilometers. At the lower limit of this range, the density on the dayside of the terminator exhibits a temporal variation of amplitude near 4 x 10(-14) gram per cubic centimeter aboult a mean of approximately 1.4 x 10(-13) gram per cubic centimeter. The variation appears oscillatory, with a 4- to 5-day period, but barely one cycle was observed. The density on the nightside of the terminator, sampled inthe same 150-kilometer altitude range, fluctuates about a smaller mean of approximately 4 x 10(-14) gram per cubic centimeter. The density between the altitudes of 150 and 200 kilometers, sampled only on the dayside of the terminator, imply a scale height of between 15 and 20 kilometers. The interpretation of this estimate is uncertain, however, in view of the measurements at the different altitudes having been made at different times and, hence, at different values of solar phase.     

Leukemia and ionizing radiation

Leukemia in man can be induced by ionizing radiations and also occurs spontaneously. For the "average" individual in a population, the probability of developing radiation-induced leukemia is estimated to be 2 x 10(-6) per rad (unit of absorbed dose of radiation) per year. The available data from four independent sources make it likely that this estimate is valid within a factor of about 3, giving a range from 0.7 x 10(-6) to 6 x 10(-6) per rad per year. It is pointed out that 10 to 20 percent of the spontaneous incidence of leukemia (Brooklyn, 1943-52) may result from radiation from natural background sources. It is estimated that a 5- to 10-percent increase in the current spontaneous incidence of leukemia would occur if the population were to reach and maintain a body level of Sr(90) amounting to one-tenth of the "maximum permissible concentration."     

The polar ionosphere of venus near the terminator from early pioneer venus orbiter radio occultations

Fourteen profiles of electron density in the ionosphere of Venus were obtainecd by the dual-frequency radio occulation method with the Pioneer Venus orbiter between 5 and 30 December 1978. The solar zenith angles for these measurements were between about 85 degrees and 92 degrees , and the latitudes ranged from about 81 degrees to 88 degrees (ecliptic north). In addition to the expected decreasein peak electron density from about 1.5 x 10(3) to 0.5 x 10(3) per cubic centimeter with increasing solar zenith angle, a region of almost constant electron density above about 250 kilometers was observed. The ionopause height varies from about 300 to 700 kilometers and seems to be influenced by diurnal changes in solar wind conditions. The structures of the profiles are consistent with models in which O(2)(+) dominates near the ionization peak and is replaced by O(+) at higher altitudes.     

Neurons of the hypothalamus concentrate (3H)progesterone or its metabolites

Selective concentration of [(1)H]progesterone or its metabolites is observed in nuclei of neurons in certain hypothalamic regions of the guinea pig 15 minutes after injection of [1,2,6,7-(3)H]progesterone, by use of dry-mount autoradiography. Highest concentrations of progestin target neurons exist in the nucleus arcuatus, the nucleus preopticus periventricularis, and the nucleus preopticus suprachiasmaticus. Previous administration of unlabeled progesterone inhibits the nuclear concentration of radioactivity, but cortisol has no effect. Estradiol priming enhances the nuclear uptake of radioactivity. The results demonstrate the existence of progestin target sites in the hypothalamus and suggest a direct action of progestin on certain hypothalamic structures.     

日本鹌鹑睾丸的电镜观察

本文是通过透射电镜观察日本鹌鹑(Coturnix coturnix japonica)雄性生殖细胞及间质细胞的超微结构。精原细胞呈椭圆形。核圆形,异染色质少,常呈小块状,多靠近核被膜,核仁明显。染色质周围颗粒及染色质间颗粒清晰可见。线粒体有时呈空泡状,嵴短而稀疏,均匀分布于胞质中。精母细胞的异染色质散在分布于核质中,由颗粒状物质聚成团块,核仁明显。线粒体数量不多,分布情况如精原细胞。这与鸡的线粒体分布位置存有差异。粗面内质网和高尔基复合体发育良好,并可见环孔板。精子细胞核大而圆,异染色质少,呈稀疏的颗粒状分布在核被膜附近及分散于核液中。线粒体电子密度较高,内质网及高尔基复合体发育中等。间质细胞形状不规則,核仁清晰,内质网及线粒体丰富,二者有极性分布现象。线粒体嵴既有小管状,又有板层状。     

Zodiacal dust and deep-sea sediments

The recent detection of radioactive Al(26) in marine sediments has led to the conclusion that it is brought into the earth's atmosphere by micrometeorites which have been exposed, in interplanetary space, to solar high-energy protons. The Al(26) method is not precise enough to yield directly a reliable value for the mass accretion rate to the earth to better than about 3 orders of magnitude, but is sufficiently accurate to allow a crucial decision between two widely differing of interplanetary dust which have been proposed to explain observations of the zodiacal light. The two models lead to Al(26) concentrations which would differ by about 5 orders of magnitude. Thus, the presence of Al(26) is consistent with the zodiacal dust model with particles of some tens of microns rather then with submicron particles. From this model a mass accretion to the earth then be calculated which is set at 1250 (upper limit, 2500; lower limit, 250) tons per day, or 2.8 x 10(-15) g/cm(2) sec, or 4.5 x 10(11) g over the earth per This value does not depend on the flux of the solar high-energy particles, which may be uncertain by an order of magnitude or more. The presence of Al(26) supports the idea that an important fraction of the dust is stony in composition material density, and thus eliminates some more exotic dust models, as such one consisting entirely of carbon grains. We may also conclude that the accreted dust particles have been in the solar system and exposed to protons from solar high-energy particles for a time interval which is greater than a significant of the Al(26) half-life (0.74 x 10(6) years).     

Mariner 9 s-band martian occultation experiment: initial results on the atmosphere and topography of Mars

A preliminary analysis of 15 radio occultation measurements taken on the day side of Mars between 40 degrees S and 33 degrees S has revealed that the temperature in the lower 15 to 20 kilometers of the atmosphere of Mars is essentially isothermal and warmer than expected. This result, which is also confirmed by the increased altitude of the ionization peak of the ionosphere, can possibly be caused by the absorption of solar radiation by fine particles of dust suspended in the lower atmosphere. The measurements also revealed elevation differences of 13 kilometers and a range of surface pressures between 2.9 and 8.3 millibars. The floor of the classical bright area of Hellas was found to be about 6 kilometers below its western rim and 4 kilometers below the mean radius of Mars at that latitude. The region between Mare Sirenum and Solis Lacus was found to be relatively high, lying 5 to 8 kilometers above the mean radius. The maximum electron density in the ionosphere (about 1.5 x 10(5) electrons per cubic centimeter), which was found to be remarkably constant, was somewhat lower than that observed in 1969 but higher than that observed in 1965.     

小麦8539高产系统模式栽培研究

采用播期（ｘ１）、密度（ｘ２）、氮肥（ｘ３）、磷肥（ｘ４）、钾肥（ｘ５）五元二次正交旋转回归组合设计,建立小麦８５３９高产栽培优化模型ｙ＝３５６．６４－３０．３１ｘ１＋１４．２３ｘ２＋３４．０８ｘ３＋７．５６ｘ４－１８．０７ｘ１ｘ２－１３．５１ｘ１ｘ３－１８．９８ｘ１ｘ４－８．６２ｘ４ｘ５＋１０．００ｘ５２。因子水平选优,当ｘ１取－２、ｘ２取２、ｘ３取２、ｘ４取２、ｘ５取－２时,获得产量１２０８５．８ｋｇ／ｈｍ２,比各因子取０水平时,净增６７４７．０ｋｇ／ｈｍ２,增产１２５．９２％,比四川小麦历史最高产量７５７５．０ｋｇ／ｈｍ２,增产８３．３８％。这是目前粮食作物高产模式栽培中罕见的增产效益。经大田验证,模型信度均达０．９５以上,具有较好的稳定性。模型的建立,对小麦８５３９的高产栽培和四川小麦上新台阶具有重要的指导作用。     

葡萄双受精过程的形态学观察

观察了葡萄双受精过程中雌雄性核的融合。结果表明:花粉管通过珠孔穿入退化助细胞,释放出二精子;精子核接近并贴附在卵核和次生核上,二者核膜融合,精核沉入卵核及次生核,染色质松解,并与雌性核染色质融合,出现雄性核仁,两性核仁融合,形成合子及初生胚乳核。卵核完成受精较次生核晚。受精属有丝分裂前型。精核进入卵核前看到了它的核仁。少数胚囊具有两套卵器。