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961.
Watson DM Bohac CJ Hull C Forrest WJ Furlan E Najita J Calvet N d'Alessio P Hartmann L Sargent B Green JD Kim KH Houck JR 《Nature》2007,448(7157):1026-1028
Class 0 protostars, the youngest type of young stellar objects, show many signs of rapid development from their initial, spheroidal configurations, and therefore are studied intensively for details of the formation of protoplanetary disks within protostellar envelopes. At millimetre wavelengths, kinematic signatures of collapse have been observed in several such protostars, through observations of molecular lines that probe their outer envelopes. It has been suggested that one or more components of the proto-multiple system NGC 1333-IRAS 4 (refs 1, 2) may display signs of an embedded region that is warmer and denser than the bulk of the envelope. Here we report observations that reveal details of the core on Solar System dimensions. We detect in NGC 1333-IRAS 4B a rich emission spectrum of H2O, at wavelengths 20-37 microm, which indicates an origin in extremely dense, warm gas. We can model the emission as infall from a protostellar envelope onto the surface of a deeply embedded, dense disk, and therefore see the development of a protoplanetary disk. This is the only example of mid-infrared water emission from a sample of 30 class 0 objects, perhaps arising from a favourable orientation; alternatively, this may be an early and short-lived stage in the evolution of a protoplanetary disk. 相似文献
962.
The entire surface membrane of denervated skeletal muscle is sensitive to the neuromuscular transmitter, acetylcholine (ACh), whereas in innervated muscle only the junctional area is sensitive. It has been proposed that this difference is due to a 'trophic' effect exerted by ACh in innervated muscle to keep the extrajunctional regions of the surface membrane insensitive to its depolarising action. Several studies have demonstrated an agonist-induced potentiation of ACh sensitivity, followed by desensitisation, at the endplate region of normal muscles. The potentiation has been attributed to a cooperative action of ACh on the receptors. Desensitisation of the extrajunctional regions of denervated muscles by ACh has also been described. We now provide evidence that the transmitter itself potentiates the ACh contracture and depolarisation responses of the denervated muscles of the rat in vitro and that it produces this effect by increasing the number of available ACh receptors on the surface membrane. 相似文献
963.
Omar K. Matar Panagiota Angeli Geoffrey F. Hewitt E. Susana Pérez de Ortiz 《清华大学学报》2006,11(2):202-206
Introduction Liquid-liquid dispersions in agitated vessels are fre-quently used in the chemical industry for conducting operations such as solvent extraction and heterogene-ous reactions. In liquid-liquid two-phase flow systems, usually consisting of an a… 相似文献
964.
Polarographic behaviour of polycytidylic acid and its double-stranded complex with polyinosinic acid
E. Paleček 《Cellular and molecular life sciences : CMLS》1969,25(1):13-14
Zusammenfassung Es ergibt sich, dass die Polyzytidylsäure unter dem neutralen pH eine polarographische Reduktionswelle ähnlich der Welle der denaturierten Desoxyribonukleinsäure gewährt. Zur Bestimmung der Polyzytidylsäure mit der «ersten Kurve» genügt bereits 1/10g des Stoffes. Im Komplex der Polyzytidylsäure mit Polyinosinsäure ist die Reduzierbarkeit der Polyzytidylsäure eliminiert. 相似文献
965.
Rajalakshmi Nambiar Russell E. McConnell Matthew J. Tyska 《Cellular and molecular life sciences : CMLS》2010,67(8):1239-1254
Cells build plasma membrane protrusions supported by parallel bundles of F-actin to enable a wide variety of biological functions,
ranging from motility to host defense. Filopodia, microvilli and stereocilia are three such protrusions that have been the
focus of intense biological and biophysical investigation in recent years. While it is evident that actin dynamics play a
significant role in the formation of these organelles, members of the myosin superfamily have also been implicated as key
players in the maintenance of protrusion architecture and function. Based on a simple analysis of the physical forces that
control protrusion formation and morphology, as well as our review of available data, we propose that myosins play two general
roles within these structures: (1) as cargo transporters to move critical regulatory components toward distal tips and (2)
as mediators of membrane-cytoskeleton adhesion. 相似文献
966.
967.
Davila S Furu L Gharavi AG Tian X Onoe T Qian Q Li A Cai Y Kamath PS King BF Azurmendi PJ Tahvanainen P Kääriäinen H Höckerstedt K Devuyst O Pirson Y Martin RS Lifton RP Tahvanainen E Torres VE Somlo S 《Nature genetics》2004,36(6):575-577
Mutations in PRKCSH, encoding the beta-subunit of glucosidase II, an N-linked glycan-processing enzyme in the endoplasmic reticulum (ER), cause autosomal dominant polycystic liver disease. We found that mutations in SEC63, encoding a component of the protein translocation machinery in the ER, also cause this disease. These findings are suggestive of a role for cotranslational protein-processing pathways in maintaining epithelial luminal structure and implicate noncilial ER proteins in human polycystic disease. 相似文献
968.
DDT in human milk 总被引:1,自引:0,他引:1
969.
中朝板块北缘志留纪海岛的发现 总被引:2,自引:0,他引:2
在内蒙古达尔罕茂明安联合旗北部巴特敖包地区发现了志留纪的海岸带及其底栖无脊椎动物化石(层孔虫、日射与床板珊瑚等),证实当时该地发育一个位于中朝古板块北缘大陆棚上的小海岛,将其命名为巴特岛.该岛的基部由奥陶纪火成岩组成,长、短轴分别为610和200m,现今呈北东-南西向延伸.志留纪罗德洛世(距今约420Ma)的地层围绕该岛分布,产状向四周倾状.巴特岛的南缘(背风)发育皮壳状生物,栖息在火成岩顶面并被 相似文献
970.
Faults in brittle rock are shear fractures formed through the interaction and coalescence of many tensile microcracks. The geometry of these microcracks and their surrounding elastic stress fields control the orientation of the final shear fracture surfaces. The classic Coulomb-Mohr failure criterion predicts the development of two conjugate (bimodal) shear planes that are inclined at an acute angle to the axis of maximum compressive stress. This criterion, however, is incapable of explaining the three-dimensional polymodal fault patterns that are widely observed in rocks. Here we show that the elastic stress around tensile microcracks in three dimensions promotes a mutual interaction that produces brittle shear planes oriented obliquely to the remote principal stresses, and can therefore account for observed polymodal fault patterns. Our microcrack interaction model is based on the three-dimensional solution of Eshelby, unlike previous models that employed two-dimensional approximations. Our model predicts that shear fractures formed by the coalescence of interacting mode I cracks will be inclined at a maximum of 26 degrees to the axes of remote maximum and intermediate compression. An improved understanding of brittle shear failure in three dimensions has important implications for earthquake seismology and rock-mass stability, as well as fluid migration in fractured rocks. 相似文献