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11.
Electromagnetic flowprobe calibration must be done under controlled conditions similar to those encountered experimentally. This in situ calibration apparatus is simple in design, inexpensive, and provides pressure and flow conditions analogous to those found in small veins in vivo. 相似文献
12.
Using high performance liquid chromatography with electrochemical detection, whole body extracts of the bulb mite, Rhizoglyphus echinopus (Fumouze and Robin), were found to contain the biogenic amines dopamine and octopamine at concentrations of 4.3 +/- 0.6 and 2.3 +/- 1.4 ng g-1 wet weight, respectively. Adrenaline, noradrenaline, tyramine, N-methyldopamine, N-acetyldopamine, and 5-hydroxytryptamine, if present, were below the limits of detectability. This is the initial demonstration of the presence of octopamine in a mite species. 相似文献
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Anyone who has stared at a repeating wallpaper pattern, or a periodic pattern of tiles, has probably experienced the phenomenon of a false stereoscopic depth percept. This arises because of a mismatching in the two eyes of repeating elements in the pattern. The phenomenon is less likely to occur if an edge of the textured region is in view; the edge seems to fix the registration of elements. We describe here a stereogram which exemplifies this principle; it has a central, periodic region bounded on either side by edges with pre-assigned disparities. We find that the perceived depth of the central region is controlled by the edges. In certain conditions (when the period is spatially large), the edges simply impose one of the expected discrete matchings. In other conditions, however, we observe a striking phenomenon: interpolation in depth occurs between the edges, violating any possible feature-by-feature matching. 相似文献
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There are two dominant models of how stars form. Under gravitational collapse, star-forming molecular clumps, of typically hundreds to thousands of solar masses (M(o)), fragment into gaseous cores that subsequently collapse to make individual stars or small multiple systems. In contrast, competitive accretion theory suggests that at birth all stars are much smaller than the typical stellar mass (approximately 0.5M(o)), and that final stellar masses are determined by the subsequent accretion of unbound gas from the clump. Competitive accretion models interpret brown dwarfs and free-floating planets as protostars ejected from star-forming clumps before they have accreted much mass; key predictions of this model are that such objects should lack disks, have high velocity dispersions, form more frequently in denser clumps, and that the mean stellar mass should vary within the Galaxy. Here we derive the rate of competitive accretion as a function of the star-forming environment, based partly on simulation, and determine in what types of environments competitive accretion can occur. We show that no observed star-forming region can undergo significant competitive accretion, and that the simulations that show competitive accretion do so because the assumed properties differ from those determined by observation. Our result shows that stars form by gravitational collapse, and explains why observations have failed to confirm predictions of the competitive accretion model. 相似文献
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Identification of receptors for neuromedin U and its role in feeding 总被引:19,自引:0,他引:19
Howard AD Wang R Pong SS Mellin TN Strack A Guan XM Zeng Z Williams DL Feighner SD Nunes CN Murphy B Stair JN Yu H Jiang Q Clements MK Tan CP McKee KK Hreniuk DL McDonald TP Lynch KR Evans JF Austin CP Caskey CT Van der Ploeg LH Liu Q 《Nature》2000,406(6791):70-74
Neuromedin U (NMU) is a neuropeptide with potent activity on smooth muscle which was isolated first from porcine spinal cord and later from other species. It is widely distributed in the gut and central nervous system. Peripheral activities of NMU include stimulation of smooth muscle, increase of blood pressure, alteration of ion transport in the gut, control of local blood flow and regulation of adrenocortical function. An NMU receptor has not been molecularly identified. Here we show that the previously described orphan G-protein-coupled receptor FM-3 (ref. 15) and a newly discovered one (FM-4) are cognate receptors for NMU. FM-3, designated NMU1R, is abundantly expressed in peripheral tissues whereas FM-4, designated NMU2R, is expressed in specific regions of the brain. NMU is expressed in the ventromedial hypothalamus in the rat brain, and its level is significantly reduced following fasting. Intracerebroventricular administration of NMU markedly suppresses food intake in rats. These findings provide a molecular basis for the biochemical activities of NMU and may indicate that NMU is involved in the central control of feeding. 相似文献
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Van Houdt JK Nowakowska BA Sousa SB van Schaik BD Seuntjens E Avonce N Sifrim A Abdul-Rahman OA van den Boogaard MJ Bottani A Castori M Cormier-Daire V Deardorff MA Filges I Fryer A Fryns JP Gana S Garavelli L Gillessen-Kaesbach G Hall BD Horn D Huylebroeck D Klapecki J Krajewska-Walasek M Kuechler A Lines MA Maas S Macdermot KD McKee S Magee A de Man SA Moreau Y Morice-Picard F Obersztyn E Pilch J Rosser E Shannon N Stolte-Dijkstra I Van Dijck P Vilain C Vogels A Wakeling E Wieczorek D 《Nature genetics》2012,44(4):445-9, S1
18.
W. M. Kuzon Jr B. R. Pynn N. H. McKee 《Cellular and molecular life sciences : CMLS》1984,40(9):1020-1022
Summary Electromagnetic flowprobe calibration must be done under controlled conditions similar to those encountered experimentally. This in situ calibration apparatus is simple in design, inexpensive, and provides pressure and flow conditions analogous to those found in small veins in vivo.This work was supported by the Harold Tanenbaum Department of Research, Mt Sinai Hospital, Toronto, Ontario. Dr. Kuzon is supported by the Medical Research Council of Canada. 相似文献
19.
Massive stars (with mass m* > 8 solar masses Mmiddle dot in circle) are fundamental to the evolution of galaxies, because they produce heavy elements, inject energy into the interstellar medium, and possibly regulate the star formation rate. The individual star formation time, t*f, determines the accretion rate of the star; the value of the former quantity is currently uncertain by many orders of magnitude, leading to other astrophysical questions. For example, the variation of t*f with stellar mass dictates whether massive stars can form simultaneously with low-mass stars in clusters. Here we show that t*f is determined by the conditions in the star's natal cloud, and is typically about 105yr. The corresponding mass accretion rate depends on the pressure within the cloud--which we relate to the gas surface density--and on both the instantaneous and final stellar masses. Characteristic accretion rates are sufficient to overcome radiation pressure from about 100M middle dot in circle protostars, while simultaneously driving intense bipolar gas outflows. The weak dependence of t*f on the final mass of the star allows high- and low-mass star formation to occur nearly simultaneously in clusters. 相似文献
20.