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1.
The coma morphology and short-term evolution was investigated of three non-periodic comets in retrograde orbits, C/2001 Q4 (NEAT), C/2002 T7 (LINEAR), and C/2003 K4 (LINEAR). All three comets display distinct coma features, which were very different from one comet to the next and remained rather constant in shape during the observational period. A single, broad feature perpendicular to the sun-tail direction dominated the coma of C/2003 K4 in all used filters (B,V,R,I), whereas the coma of Comet C/2002 T7 exhibited different features in blue and red filters. C/2001 Q4 showed rather complex coma morphology with clear short-term variability in coma brightness. Therefore, these non-periodic comets neither show a featureless coma nor any similarities of the features detected. The overall distribution of coma material was investigated from the shape of radial coma profiles averaged around the comet nucleus. For C/2001 Q4 and C/2002 T7, the slopes fitted to the linear part of these profiles are flatter in the blue than in the red, which can be explained by the presence of coma gas. For C/2003 K4 no such difference is indicated in the May observations (r = 2.3 AU), while in July (r = 1.7 AU) the profiles in the B-filter are flatter than in V, R, and I, hence gas contamination was relevant at least in the B filter. The R and I filter images were used to determine approximate Afρ values of each comet as a function of time. 相似文献
2.
抑制栉孔扇贝第一极体对受精卵染色体行为及胚胎倍性组成的影响 总被引：4，自引：0，他引：4
采用细胞松弛素B（CB）处理，栉孔扇贝（Chlamys ferreri）抑制其受精卵的第一极体（PB1），研究抑制PB1对受精卵减数分裂过程及胚胎倍性组成的影响。结果发现，抑制第一极体显著改变了受精卵的染色体行为，在第二次减数分裂过程中共发现4种典型染色体分离类型，分别是三极分离（41．7％）、二极分离（11．7％）、双二极分离（24．9％）和非同步分离（2．8％），其余的受精卵（19．0％）染色体分离行为紊乱。对4-8细胞期胚胎的倍性组成进行分析，发现处理组中含有二倍体（10．9％）、三倍体（12．5％）、四倍体（19.5％）、五倍体（12．6％）以及非整倍体（46．6％）胚胎。研究结果表明，二极分离和双二极分离分别是形成三倍体和四倍体的主要机制，而其他的染色体分离行为将主要形成非整倍体。 相似文献
3.
G. Pignata F. Patat S. Benetti S. Blinnikov W. Hillebrandt R. Kotak B. Leibundgut P. A. Mazzali P. Meikle Y. Qiu P. Ruiz-Lapuente S. J. Smartt E. Sorokina M. Stritzinger M. Stehle M. Turatto T. Marsh F. Martin-Luis N. McBride J. Mendez L. Morales-Rueda D. Narbutis R. Street 《Monthly notices of the Royal Astronomical Society》2004,355(1):178-190
4.
分析了在大规模定制下对物料清单(BOM)的新要求,提出了基于类的BOM。利用递归算法,结合PB中的数据窗口技术,实现了对BOM表的遍历,最后,对特殊BOM的生存期管理也进行了一些讨论。 相似文献
5.
6.
Douglas O. ReVelle 《Earth, Moon, and Planets》2008,102(1-4):345-356
We have developed a new approach to modeling the acoustic-gravity wave (AGW) radiation from bolide sources. This first effort
involves entry modeling of bolide sources that have available satellite data through procedures developed in ReVelle (Earth
Moon Planets 95, 441–476, 2004a; in: A. Milani, G. Valsecchi, D. Vokrouhlicky (eds) NEO Fireball Diversity: Energetics-based Entry Modeling and Analysis Techniques, Near-earth Objects: Our Celestial Neighbors
(IAU S236), 2007b). Results from the entry modeling are directly coupled to AGW production through line source blast wave theory for the initial
wave amplitude and period at (at 10 blast wave radii and perpendicular to the trajectory). The second effort involves the prediction of the formation
and or dominance of the propagation of the atmospheric Lamb, edge-wave composite mode in a viscous fluid (Pierce, J. Acoust.
Soc. Amer. 35, 1798–1807, 1963) as a function of the source energy, horizontal range and source altitude using the Lamb wave frequency that was deduced
directly during the entry modeling and that is used as a surrogate for the source energy. We have also determined that Lamb
wave production by bolides at close range decreases dramatically as either the source energy decreases or the source altitude
increases. Finally using procedures in Gill (Atmospheric-Ocean Dynamics, 1982) and in Tolstoy (Wave Propagation, 1973), we have analyzed two simple dispersion relationships and have calculated the expected dispersion for the Lamb edge-wave
mode and for the excited, propagating internal acoustic waves. Finally, we have used the above formalism to fully evaluate
these techniques for four large bolides, namely: the Tunguska bolide of June 30, 1908; the Revelstoke bolide of March 31,
1965; the Crete bolide of June 6, 2002 and the Antarctic bolide of September 3, 2004. Due to page limitations, we will only
present results in detail for the Revelstoke bolide. 相似文献
7.
On 28 December 2002, new vents opened on the flanks of Stromboli, just below the summit craters, interrupting the persistent
activity of the volcano with a 7-month-long effusive eruption. We here report on the plagioclase size distribution (PlgSD)
in lava samples collected following the chronology of the 2002–2003 eruption. Data reveal a linear PlgSD similar to that found
in samples of normal Stromboli activity, indicating that the switch from Strombolian explosive to effusive activity is not
associated with changes in texture. Nevertheless, the crystal size distribution slopes and intercepts exhibit slight sinusoidal
temporal variations that are here ascribed to a magma supply mechanism able to induce “resonance” in the crystal size distribution,
with an amplitude that depends on the supply rate. 相似文献
8.
C. Simon Jeffery 《Journal of Astrophysics and Astronomy》2005,26(2-3):261-271
Subdwarf B stars play a significant role in close binary evolution and in the hot star content of old stellar populations,
in particular in giant elliptical galaxies. While the question of their origin poses several problems for stellar evolution
theory, one of their most fascinating properties is the presence of multi-periodic 2–3 minute oscillations. Interpreting these
oscillations optimally requires the correct identification of the modes. Partial identifications can be obtained using high-speed
observations of radial velocity and colour variations. We review some of the several attempts to make such observations, most
recently with the Multi-Site Spectroscopic Telescope campaign and withULTRACAM. 相似文献
9.
Fine-grained floodplain sediments of the catastrophic 2002 flood deposited along the lower reaches of the Berounka and Vltava
Rivers, Czech Republic, were not highly contaminated with heavy metals and other toxic elements. This is due to the dominantly
mineral character of the sediments (Ctot in the range 3.97–5.01%, relatively low content of clay minerals), and due to the very high degree of contamination dilution
by eroded pre-industrial non-contaminated floodplain sediments. Despite this high degree of dilution, the influence of the
small Litavka River, draining the historical Pb–Zn–Ag Příbram ore region, is well visible. The Litavka River is one of important
sources of Pb and Zn contamination in the whole Berounka–Vltava–Labe river system. The 2002 flood sediments deposited in the
floodplain of the Berounka and Vltava Rivers show poor vertical chemical zoning, except for some components enriched in the
uppermost layer by precipitation from evaporated pore-water contained in the mud, i.e. secondary carbonate. The content of
Ccarb of the sediments (0.05–0.15%) is partly represented by this secondary carbonate, which is later leached by rainwater, and
partly by fragments of river mollusk shells. A majority of the heavy metals contained in sediments can be readily leached
by diluted acids, and to a much smaller degree by rainwater. 相似文献
10.
分析了计算机网络建设的现状及海量信息和网络环境下选择新的数据库管理工具的必要性。阐述了水文地质信息处理的重要性,介绍了PowerBuilder的特点,应用该工具设计开发了C／S模式下大连市水文地质信息管理系统。结合实例介绍了该系统的主要功能、数据流程、组织结构等。 相似文献