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1.
A. Kučinskas 《Astrophysics and Space Science》1997,251(1-2):231-234
We have calculated terminal gas outflow velocities from the circumstellar shells of the AGB stars. Our results confirm that,
in case of the stationary dust driven winds, the dynamics of the outflow is governed essentially by the dust properties and
stellar luminosities, while only marginally by other stellar parameters. Although being far from comprehensive, our calculations
also indicate that the dust driven winds may only occur in cool, luminous, low mass objects.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
2.
Karel Kučera 《Studia Geophysica et Geodaetica》1966,10(4):411-421
Summary In [1] the author has put forward a three-direction method, a general way of adjustment of angular observations in incomplete
sets by the method of extending into angular combinations, and the definition of mean weightP
*. In this article the question is dealt with as a whole. In the three-direction methods>3 triangulation directions are measured in direction triplets 123, 234, 345,… …,s12, while in the method of measuring single angles at the station they are measured in angles 12, 23, 34, 45, …,s1. The advantage of transition from angles to direction triplets rests, besides in saving 31% of pointings, above all in certain
possibility of elimination of the horizontal refraction, which follows from this. The treatise of the relation between the
method of measurement and the refraction is not included into this article, as it would go beyond its scope. The fact that
adjusted directions, with the exception of the stations having four directions, are not of equal weight, is proper not only
to the three-direction method. The non-equality of weights is even more conspicuous in the method of measuring single angles
at the station, and it appears already at the stations having four directions. In author's view the homogeneity of observation
elements is more important than the homogeneity of weights from the point of view of adjustment at the station; therefore
the direction triplets ought not to exist abreast with the angles in one programme, and especially the number of observations
ought to be constant at one station with adjusted direction of homogeneous mean weight in the net.
This transition from angles to direction triplets could also provoke a comment that simultaneous visibility of three adjoining
directions occurs less often than of two such directions. The author adds to this that nowadays the causes of this phenomenon,
following from unsuitable technique, must be eliminated. It is just air limpidity that ought to define the visibility, not
unsufficient or everywhere equal intensity of light of reflectors, or too long sides of the triangulation net. Recent approach
to this problem requires simultaneous visibility of all directions during most of the days of observation. In connection with
the out-of=date technique, the methods of angular observation often have one unfavourable character: they are the cause of
the accumulation of observations of “always visible” directions. The supposed merit of angles thus turns into their imperfection.
Адрес: Politickych vězňů 12, Praha 1-Nové Město 相似文献
Адрес: Politickych vězňů 12, Praha 1-Nové Město 相似文献
3.
首次提出用石笋中稳定同位素记录重建由降雨量和降水气团同位素组成所反映的古气候历史,从而为研究高分辨率的古季风气候信息开辟了新的途径。利用Hendy准则、洞穴温度、研究区水系的δ18OH2O值以及温度公式,证实了同位素分析结果的可靠性,CaCO3-H2O之间存在同位素平衡分馏。对采自石花洞的石笋样品进行了分辨率约为25a的δ18O和δ13C的分析测量,从而得到3000a以来,北京地区古气候和古环境的变化信息 相似文献
4.
During the 1999 Chi-Chi, Taiwan earthquake, many sand boiling phenomena were observed in central Taiwan, which caused severe ground settlement and structure damages. According to the installed accelerograms, the peak ground surface horizontal accelerations in the liquefaction-affected areas range from 774.42 to 121.3 gal. The writers carried out an extensive investigation of soil liquefaction in this earthquake. In this paper, we present results of the CPT exploration and post-earthquake liquefaction analysis. Two hundred and seventy five (275) cone penetration test data were collected from the liquefaction-affected areas, and 46 liquefaction case histories and 88 non-liquefaction case histories were derived that can be used to evaluate the accuracy of existing liquefaction evaluation models. In addition, the strength of the liquefied soils after earthquake and the implication of its liquefaction potential in the future event are discussed. 相似文献
5.
6.
Milan Rieder Miroslav Huka Dagmar Kučerová Luděk Minařík Jiří Obermajer Pavel Povondra 《Contributions to Mineralogy and Petrology》1970,27(2):131-158
Compositions of natural lithium-iron micas are approximated best by the sidero-phyllite-polylithionite join. These micas contain little or no magnesium and manganese. Their octahedral sheets contain close to two trivalent cations (mainly aluminum) in small crystallographic sites and a variable quantity of lithium and R+2 (mainly iron) in large sites. Octahedral vacancies are situated mostly in large sites. Lithium and R+2 approach a 44 replacement relationship in micas with octahedral occupancy close to six. Lithium and fluorine show a good positive correlation (small excess of fluorine over lithium), which indicates a crystallochemical association between them. There is a less distinct positive correlation between lithium and R+4.Based on simplifications, a calculation shows that about two-thirds of octahedral vacancies are caused by substitutions within the octahedral sheet, one-third, by tetrahedral substitutions. Different methods of calculating the crystallochemical formula yield slightly different numbers of octahedral vacancies, but do not affect the mica's position in plots of physical parameters against composition. If a crystallochemical formula is calculated from analysis of a mica contaminated with quartz, topaz, or feldspar, the apparent number of octahedral vacancies increases; such a formula exhibits unusual behavior in composition plots. 相似文献
7.
Summary As regards the concept of complete weight p with which an observed quantity (e.g., the direction of theA–G net) should enter the net adjustment, according to Eq.(1), apart from the fundamental weight p
0
), determined by the number of repetitions, it should also contain the time parameter pt according to Eq.(11), where c>1 is a constant, and t is the number of days of observation, and also the refraction factor pr according to Eqs(17, 18), where q is the structural weight of the direction. The condition for being able to determine pr with the directions is observation by means of the three-directional vertex method[2], because it is not possible to localize lateral refraction by angular methods. The theory of complete weight is in favour of observations with a high fundamental weight p
0
which automatically yield higher values of t, and also of pt. The introduction of the complete weight into the experimental directional net in Fig. 2 caused the mean value of the uneliminated refraction error to decrease from 0.24 to 0.12, the mean square error of the adjusted direction being 0.17. The value of the constant c was investigated and the method of determining the parameter pr was derived also for lengths measured electro-optically. Mention is made of the effect of complete weights on the length adjustment of a net in[6]. 相似文献
8.
Teh-Lung Ku Shangde Luo Tim K. Lowenstein Jianren Li Ronald J. Spencer 《Quaternary Research》1998,50(3):261-275
Uranium-series dating on a 186-m core (DV93-1) drilled from Badwater Basin in Death Valley, California, and on calcareous tufas from nearby strandlines shows that Lake Manly, the lake that periodically flooded Death Valley during the late Pleistocene, experienced large fluctuations in depth and chemistry over the last 200,000 yr. Death Valley has been occupied by a long-standing deep lake, perennial shallow saline lakes, and a desiccated salt pan similar to the modern valley floor. The average sedimentation rate of about 1 mm/yr for core DV93-1 was punctuated by episodes of more-rapid accumulation of halite. Arid conditions similar to the modern conditions prevailed during the entire Holocene and between 120,000 and 60,000 yr B.P. From 35,000 yr B.P. to the beginning of the Holocene, a perennial saline lake existed, over 70 m at its deepest. A much deeper and longer lasting perennial Lake Manly existed from about 185,000 to 128,000 yr B.P., with water depths reaching about 175 m, if not 330 m. This lake had two significant “dry” excursions of 102–103yr duration about 166,000 and 146,000 yr B.P., and it began to shrink to the point of halite precipitation between 128,000 and 120,000 yr B.P. The two perennial lake periods correspond to marine oxygen isotopic stages (OIS) 2 and 6. Based on the shoreline tufa ages, we do not rule out the possible existence 200,000 yr ago of yet a third perennial lake comparable in size to the OIS 6 lake. The234U/238U data suggest that U in tufa owes its origin mainly to Ca-rich springs fed by groundwater that emanated along lake shorelines in southern Death Valley, and that an increase of this spring-water input relative to the river-water input apparently occurred during OIS 6. 相似文献
9.
δ18O of a stalagmite collected from Shihua Cave, 50 km southwest of Beijing is analyzed. The uppermost 2 cm was sampled at about
3-year intervals by a computer-controlled microsampling device. A total of 133 samples were analyzed, covering the last 480
years. A comparison of the δ18O record with the instrumentally recorded precipitation in Beijing and Tianjin back to 1840 AD shows that high precipitation
correlates with negative δ18O peaks. The long-term δ18O trend records temperature changes. Between 1620 and 1900 AD, the temperature was cooler than the average value for the 480-year
record, corresponding to the Little Ice Age. Temperatures warmer than the average prevailed during 1520–1620 and 1900—present.
Superimposed on the long-term trend are about 14 δ18O cycles of 30–40-year periodicity, with wet periods centered around 1985, 1955, 1910, 1880, 1840, 1800, 1760, 1730, 1690,
1660, 1630, 1600, 1560 and 1530 AD.
Project supported by the National Natural Science Foundation of China (Grant No. 9615875). 相似文献
10.
The isotopic compositions of oxygen and carbon and trace concentrations of magnesium and strontium in speleothems formed in
limestone caves respond to climate changes outside the caves. Measurements of these properties on a stalagmite from Shihua
Cave near Beijing, China, allowed reconstruction of the regional changes in precipitation, temperature and nature of vegetation.
Over the last ∼ 500 years, there were fourteen precipitation cycles with a periodicity of 30–40 years, which may well reflect
fluctuations in the strength of the East Asian summer monsoons reaching northeastern China. Relative to the mean temperature
of this time interval, the period 1620–1900 AD was cold and periods 1520–1620 and 1900–1994 were warm. Over the last ∼ 3000-years,
about eight wet/cool-dry/warm climatic cycles of 300–400 years duration occurred, the latest wet/cool half cycle corresponding
to the Little Ice Age. The δ13C record registers the anthropogenic activities of fossil fuel CO2 combustion in recent decades and regional deforestation between 13 and 16 centuries when Beijing was bustling with palatial
constructions and being developed into the world’s most populated city. 相似文献