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排序方式: 共有640条查询结果,搜索用时 15 毫秒
631.
Barraud-Lange V Chalas Boissonnas C Serres C Auer J Schmitt A Lefèvre B Wolf JP Ziyyat A 《Reproduction (Cambridge, England)》2012,144(1):53-66
Spermatozoa undergo regulation of their functions along their lifespan through exchanges via vesicles or interactions with epithelial cells, in the epididymis, in the seminal fluid and in the female genital tract. Two different ways of oocyte membrane transfer to spermatozoa have been described: trogocytosis and exosomes. We here report an analysis of in vitro exchanges between the membranes of unfertilised oocytes and capacitated spermatozoa. We showed that optimum conditions are fulfilled when unfertilised oocytes interact with acrosome-reacted spermatozoa, a scenario mimicking the events occurring when the fertilising spermatozoon is inside the perivitelline space. Although CD9 tetraspanin is an essential molecule for fertilisation, exosome and trogocytosis transfer persists in Cd9-null oocytes in spite of their dramatic fusion failure. These exchanges are CD9 tetraspanin independent. We also confirm that mice sperm express CD9 tetraspanin and that when Cd9-null oocytes were inseminated with sperm covered with oocyte membrane materials, including CD9 tetraspanin, no rescue of the oocytes' fertilisability could be obtained. Thus, the existence of two ways of exchange between gametes during fertilisation suggests that these events could be of a physiological importance in this process. 相似文献
632.
Dejnabadi H Jolles BM Casanova E Fua P Aminian K 《IEEE transactions on bio-medical engineering》2006,53(7):1385-1393
A new method of estimating lower limbs orientations using a combination of accelerometers and gyroscopes is presented. The model is based on estimating the accelerations of ankle and knee joints by placing virtual sensors at the centers of rotation. The proposed technique considers human locomotion and biomechanical constraints, and provides a solution to fusing the data of gyroscopes and accelerometers that yields stable and drift-free estimates of segment orientation. The method was validated by measuring lower limb motions of eight subjects, walking at three different speeds, and comparing the results with a reference motion measurement system. The results are very close to those of the reference system presenting very small errors (Shank: rms = 1.0, Thigh: rms = 1.6 degrees) and excellent correlation coefficients (Shank: r = 0.999, Thigh: r = 0.998). Technically, the proposed ambulatory system is portable, easily mountable, and can be used for long-term monitoring without hindrance to natural activities. Finally, a gait analysis tool was designed to visualize the motion data as synthetic skeletons performing the same actions as the subjects. 相似文献
633.
Anne Ziegler Brigitte Gillet Jean-Claude Belœil Jean-Paul Macher Michel Décorps Jean-François Nédelec 《Magma (New York, N.Y.)》2002,14(1):45-49
The purpose of this study was to acquire a localized 2D (two-dimensional)1H correlation spectrum, in a volume of interest reasonably small, and within an experiment time compatible with clinical applications.
A modified PRESS technique has been used. The last 180° pulse of the PRESS sequence has been converted into a 90° pulse for
both refocusing and coherence transfer. 2D correlation spectroscopy was performed on healthy volunteers in a clinical magnet,
at 3 T. within 34 min, for a voxel size of 27 cm3 This result makes it possible to consider clinical applications.
This work was presented at the 1999 ESMRMB meeting (Sevilla, Spain). 相似文献
634.
Melter feed viscosity during conversion to glass: Comparison between low‐activity waste and high‐level waste feeds 下载免费PDF全文
Tongan Jin Jaehun Chun Derek R. Dixon Dongsang Kim Jarrod V. Crum Charles C. Bonham Bradley J. VanderVeer Carmen P. Rodriguez Brigitte L. Weese Michael J. Schweiger Albert A. Kruger Pavel Hrma 《Journal of the American Ceramic Society》2018,101(5):1880-1891
During nuclear waste vitrification, a melter feed (a slurry mixture of a nuclear waste and various glass forming and modifying additives) is charged into the melter where undissolved refractory constituents are suspended together with evolved gas bubbles from complex reactions. Knowledge of flow properties of various reacting melter feeds is necessary to understand their unique feed‐to‐glass conversion processes occurring within a floating layer of melter feed called a cold cap. The viscosity of two low‐activity waste (LAW) melter feeds were studied during heating and correlated with volume fractions of undissolved solid phase and gas phase. In contrast to the high‐level waste (HLW) melter feed, the effects of undissolved solid and gas phases play comparable roles and are required to represent the viscosity of LAW melter feeds. This study can help bring physical insights to feed viscosity of reacting melter feeds with different compositions and foaming behavior in nuclear waste vitrification. 相似文献
635.
Christian Mielke Doris Pospiech Justus Kuhnigk Andreas Korwitz Hartmut Komber Ricardo Bernhardt Nico Krebs Regine Boldt Holger Ruckdäschel Brigitte Voit 《大分子材料与工程》2023,308(10):2300281
The interest in bio-based alternatives to classical polyesters such as poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT) is steadily growing to achieve a more sustainable approach to polymer materials. In this study, PBT/poly(butylene furanoate) (PBF) blends are prepared, characterized and extrusion foamed. PBF as a bio-based polyester offers two advantages. The ecological footprint of the material is reduced, and additionally, it can be used in Diels-Alder reactions at the blend surface to support fusion of the foamed beads. The blending behavior of the polyesters is investigated using samples prepared in a microcompounder, particularly focused on the miscibility of the blends and transesterification reactions. The blends are thermodynamically immiscible but show a certain degree of transesterification according to nuclear magnetic resonance (NMR) spectroscopy. The morphology of blend beads produced by an extrusion foaming process is analyzed regarding their cell density, cell size distribution, and open-cell content. It is shown that PBF has a positive effect on the bead foam morphology. The use of a bifunctional linker designed for chemical fusion of the bead surfaces allows to obtaining of molded parts, in contrast to beads containing pure PBT. 相似文献
636.
Wenzel SC Kunze B Höfle G Silakowski B Scharfe M Blöcker H Müller R 《Chembiochem : a European journal of chemical biology》2005,6(2):375-385
The myxobacterium Stigmatella aurantiaca DW4/3-1 harbours an astonishing variety of secondary metabolic gene clusters, at least two of which were found by gene inactivation experiments to be connected to the biosynthesis of previously unknown metabolites. In this study, we elucidate the structures of myxochromides S1-3, novel cyclic pentapeptide natural products possessing unsaturated polyketide side chains, and identify the corresponding biosynthetic gene locus, made up of six nonribosomal peptide synthetase modules. By analyzing the deduced substrate specificities of the adenylation domains, it is shown that module 4 is most probably skipped during the biosynthetic process. The polyketide synthase MchA harbours only one module and is presumably responsible for the formation of the variable complete polyketide side chains. These data indicate that MchA is responsible for an unusual iterative polyketide chain assembly. 相似文献
637.
In honeybees, the cuticular hydrocarbon profiles are partly genetically based and differ between subfamilies, which suggests that they might be used by the workers as labels for subfamily recognition. This ability could potentially form the basis for nepotistic conflicts between subfamilies that would be detrimental to the inclusive fitness of the colony. Here we have compared the subfamily hydrocarbon profiles of 5-day-old workers maintained in isolation with those kept in their parental colony. We demonstrate that the cuticular hydrocarbon profiles tend to be less distant between most subfamilies within the hive compared with those held in isolation. The main consequence of this partial homogenization of the majority of subfamily signatures may result in a reduction of the number of recognizable subfamilies in the colony. Nevertheless, a few subfamilies retain very distinct cuticular hydrocarbon profiles. 相似文献
638.
Christoph Heß Brigitte Hartmann M. Dieter Lechner Wolfgang Nierling Christian Seidel Werner‐Michael Kulicke 《Starch - St?rke》2007,59(9):423-429
Crosslinked carboxymethyl starch (CMS) was synthesized from potato starch in a single‐step procedure with mono‐ (MCA) and dichloroacetic acid (DCA), using the well‐known Williamson reaction. The products varied in their degree of substitution DS (average number of carboxymethyl groups per monomer unit) and crosslinker ratio Fz (number of crosslinker molecules offered per monomer unit). After neutralizing and removal of the formed salt, one part of the synthesized CMS networks was pre‐swollen in water in an additional purification step in order to wash out unlinked, soluble polymer chains. The rest of the product remained unwashed. Different swelling experiments were performed with the two samples, before being dried and ground. Both, the Free Swelling Capacity (FSC) and the Absorption Capacity Under Mechanical Load (AUL) of the hydrogels were strongly influenced by chemically unlinked CMS chains that were only physically entangled in the network structure. These mobile polymer segments were responsible for a significant weight loss of the swollen, unwashed hydrogels over the course of time. Rheological oscillatory experiments showed that, in order to achieve comparable values for the storage and loss moduli (G′ and G′′), the polymer content of an unwashed hydrogel had to be more than twice as high as that of the corresponding purified product. By using a special rheological test procedure with a cyclic temperature program, the long‐term stability of CMS gels could be measured and verified. 相似文献
639.
DSC thermograms of cassava starch granules heated at two intermediate moisture contents of 35 and 45% of the total weight (w.t.) reveal the existence of two endothermic steps in their progressive disorganization. Structural changes have been studied by combining polarized light microscopy and electron microscopy (scanning and transmission electron microscopy). An instability of starch granule behaviour, both at granular and crystalline levels is observed at each treatment temperature. As temperature and moisture content increase, the loss of birefringence was observed in an increasing number of granules, suggesting that there is a competition of granules for water. The loss of birefringence initiates first at the hilum and is associated with the formation of cavities in the central region of the granules, showing that the disorganization first affects the less organized areas of the granule. In limited water content conditions, the radial extension of the central cavity towards the granule surface is not observed. The limited crystalline disorganization which is restricted to the inner part of the granule does not allow either a major swelling of granules or an extensive leaching of macromolecules out of granules. Increasing temperatures progressively induced the loss of granular integrity and the development of an homogeneous matrix. These structural changes are in agreement with the cooperative disorganization model of starch crystallites following which the crystalline disorganization is facilitated by the presence of water or by the plasticization of the amorphous regions connected to these crystallites. 相似文献
640.
By means of Perot Fabry Velocimetry (PFV) we recorded material velocities generated by an intense shock wave (P > 70 kbar) in pure nitromethane. Our experiments show that nitromethane does not behave according to the Campbell-Travis model for detonation in liquid explosives. We do not find any evidence for a so-called superdetonation, which would start behind and overtake the pressure shock wave. Our recordings of material velocities show a behavior of the liquid explosive very similar to that of solid polycrystalline explosives and are compatible with the heterogeneous decomposition scheme. 相似文献