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311.
Sthefane D’ávila Camilla Medeiros Tércia Vargas Cristiane Lafetá Furtado Mendonça 《Journal of Natural History》2018,52(23-24):1551-1569
In the present study, we aimed to characterize the life history of the land snail Subulina octona integrating information on life-history traits and morphology. We also compared the histology of the free-oviduct and spermoviduct of ovoviviparous and egg-retaining species of subulinids. We considered as ovoviviparous the species in which the complete embryonic development as well as egg hatching occurs inside the parent’s body and, at the end of this process, the parent releases juveniles instead of eggs. We considered as egg-retaining the species in which a great part of the embryonic development takes place inside the parent’s body and the eggs laid contain well-developed embryos. The results showed that the free-oviduct of both ovoviviparous and egg-retaining species shows a histological arrangement that confers greater strength to its walls and is probably related to egg retention. The wall of the spermoviduct is formed by pseudostratified columnar epithelium, with cell apical processes (probably cilia), and by underlying secretory cells. In gravid egg-retaining snails, the eggshells appear in close contact with the secretory cells of the spermoviduct. This fact suggests that these cells play a role in eggshell formation. The present study is the first account for histological features of S. octona, Allopeas gracile and Allopeas micra. The life history of S. octona is a combination of long lifespan, early sexual maturity, indeterminate growth and egg retention. Egg retention limits the number of young that can be produced in one reproductive event. However, the reproductive strategy adopted by S. octona, associating egg retention and K-strategism, compensates this cost of retaining eggs, because the reproductive success may be enhanced as a result of the higher survival of juveniles and the possibility of performing several reproductive events during the year. 相似文献
312.
313.
Timm Schubert Corinna Gleiser Peter Heiduschka Christoph Franz Kerstin Nagel-Wolfrum Ayse Sahaboglu Nicole Weisschuh Gordon Eske Karin Rohbock Norman Rieger François Paquet-Durand Bernd Wissinger Uwe Wolfrum Bernhard Hirt Wibke Singer Lukas Rüttiger Ulrike Zimmermann Marlies Knipper 《Cellular and molecular life sciences : CMLS》2015,72(20):3953-3969
314.
碳酸盐岩缝洞型油藏产水机理及控水措施研究 总被引:2,自引:0,他引:2
塔河油田4区奥陶系油藏是典型的复杂碳酸盐岩油藏。油藏开发进入高含水之后,油井产液量急剧降低,油井出水问题已经成为该油田开发的突出问题,严重制约着油田采收率。以塔河油田4区主力缝洞单元S65与S48为研究对象,在归纳出缓慢出水型、突发上升型、间歇出水型等3种产水类型油井基础上,利用地震、钻井、测井等资料,结合生产动态特征进一步分析3种类型油井的产水机理。据此提出合理、有效的控水措施:缓慢出水型油井在单元低部位注水保持能量;突发上升型油井应考虑堵水、上返高部位侧钻;间歇出水型油井考虑关井压锥,堵水控制水窜范围和规模。措施效果明显,可指导该类油藏高效开发。 相似文献
315.
我国低渗透气藏产气量在天然气总产量中所占比例越来越大,研究低渗透气藏的形成机理及形成过程是非常必要的。四川盆地上三叠统须家河组二段是重要的含气层位,但由于其储层具有非均质性强、且具低孔低渗的特点,不仅储层预测难度大,而且开发的效果也差。因此需要研究其形成过程,提高储层预测精度以改善开发效果。以储层岩石学特征、孔隙类型及分布特征、胶结物充填次序及充填时间等研究为基础,定时、定量地研究孔隙的整个演化历史,描述了孔隙在不同历史阶段的大小及变化原因,从而再现了储层形成历史,为下一步须二段气藏有效储层的预测与有效开发打下基础。 相似文献
316.
Thöne CC de Ugarte Postigo A Fryer CL Page KL Gorosabel J Aloy MA Perley DA Kouveliotou C Janka HT Mimica P Racusin JL Krimm H Cummings J Oates SR Holland ST Siegel MH De Pasquale M Sonbas E Im M Park WK Kann DA Guziy S García LH Llorente A Bundy K Choi C Jeong H Korhonen H Kubànek P Lim J Moskvitin A Muñoz-Darias T Pak S Parrish I 《Nature》2011,480(7375):72-74
Long γ-ray bursts (GRBs) are the most dramatic examples of massive stellar deaths, often associated with supernovae. They release ultra-relativistic jets, which produce non-thermal emission through synchrotron radiation as they interact with the surrounding medium. Here we report observations of the unusual GRB 101225A. Its γ-ray emission was exceptionally long-lived and was followed by a bright X-ray transient with a hot thermal component and an unusual optical counterpart. During the first 10 days, the optical emission evolved as an expanding, cooling black body, after which an additional component, consistent with a faint supernova, emerged. We estimate its redshift to be z = 0.33 by fitting the spectral-energy distribution and light curve of the optical emission with a GRB-supernova template. Deep optical observations may have revealed a faint, unresolved host galaxy. Our proposed progenitor is a merger of a helium star with a neutron star that underwent a common envelope phase, expelling its hydrogen envelope. The resulting explosion created a GRB-like jet which became thermalized by interacting with the dense, previously ejected material, thus creating the observed black body, until finally the emission from the supernova dominated. An alternative explanation is a minor body falling onto a neutron star in the Galaxy. 相似文献
317.
Chapman HN Fromme P Barty A White TA Kirian RA Aquila A Hunter MS Schulz J DePonte DP Weierstall U Doak RB Maia FR Martin AV Schlichting I Lomb L Coppola N Shoeman RL Epp SW Hartmann R Rolles D Rudenko A Foucar L Kimmel N Weidenspointner G Holl P Liang M Barthelmess M Caleman C Boutet S Bogan MJ Krzywinski J Bostedt C Bajt S Gumprecht L Rudek B Erk B Schmidt C Hömke A Reich C Pietschner D Strüder L Hauser G Gorke H Ullrich J Herrmann S Schaller G Schopper F Soltau H Kühnel KU Messerschmidt M 《Nature》2011,470(7332):73-77
X-ray crystallography provides the vast majority of macromolecular structures, but the success of the method relies on growing crystals of sufficient size. In conventional measurements, the necessary increase in X-ray dose to record data from crystals that are too small leads to extensive damage before a diffraction signal can be recorded. It is particularly challenging to obtain large, well-diffracting crystals of membrane proteins, for which fewer than 300 unique structures have been determined despite their importance in all living cells. Here we present a method for structure determination where single-crystal X-ray diffraction 'snapshots' are collected from a fully hydrated stream of nanocrystals using femtosecond pulses from a hard-X-ray free-electron laser, the Linac Coherent Light Source. We prove this concept with nanocrystals of photosystem I, one of the largest membrane protein complexes. More than 3,000,000 diffraction patterns were collected in this study, and a three-dimensional data set was assembled from individual photosystem I nanocrystals (~200?nm to 2?μm in size). We mitigate the problem of radiation damage in crystallography by using pulses briefer than the timescale of most damage processes. This offers a new approach to structure determination of macromolecules that do not yield crystals of sufficient size for studies using conventional radiation sources or are particularly sensitive to radiation damage. 相似文献
318.
319.
R_3Co单晶制备方法的研究 总被引:1,自引:1,他引:0
本文对单晶的生长条件进行了研究,用Brigdman方法成功地制备了R3Co单晶试料,为进一步研究其物性提供了必要的条件. 相似文献
320.