排序方式: 共有66条查询结果,搜索用时 31 毫秒
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Jun Wang Alice Laguardia Peter John Damerell Philip Riordan Kun Shi 《科学通报(英文版)》2014,59(25):3162-3168
Information about competition between carnivore species for food within high altitude regions is limited.Data collected from the Taxkorgan Nature Reserve,China revealed important interactions between snow leopard(Panthera uncia),grey wolf(Canis lupus),red fox(Vulpes vulpes)and their prey species,including domestic livestock.Sixty-four line transects were conducted in order to identify field signs of habitat occupancy and collect scats for diet analysis.High dietary overlap was observed between all three carnivore species:snow leopard and red fox(Pianka’s index=0.96),red fox and grey wolf(Pianka’s index=0.90),snow leopard and grey wolf(Pianka’s index=0.87).Snow leopard and grey wolf showed significant predation on livestock(36.8%for snow leopard and 29.4%for grey wolf in diet composition).As a pioneering exploration of the endangered snow leopard and its relationship with other species within the alpine ecosystem under livestock grazing pressure,this study contributes a greater understanding of the relationship within carnivore guild in the Pamirs whilst providing implications for conservation planning and project implementation activities in China. 相似文献
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This study attempted to examine the importance of storeenvironment in affecting consumers'store choice deci-sion;the relative importance among the three environ-mental factors;and consumers'expectations on store en-vironment for the casual-wear chain stores in HongKong.Julie Baker's Three-category framework onstore environments namely ambient,design and socialfactors was adopted for investigation.The results indi-cated that the store environment was important in affect-ing consumers'selection of store for shopping.It alsorevealed that social factor was perceived relatively im-portant than ambient and design factors.Nine store ex-pectation dimensions were categorised and the resultdemonstrated that most respondents were concerned onthe social aspect in their expectation of having a satisfy-ing store environment. 相似文献
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Marscher AP Jorstad SG D'Arcangelo FD Smith PS Williams GG Larionov VM Oh H Olmstead AR Aller MF Aller HD McHardy IM Lähteenmäki A Tornikoski M Valtaoja E Hagen-Thorn VA Kopatskaya EN Gear WK Tosti G Kurtanidze O Nikolashvili M Sigua L Miller HR Ryle WT 《Nature》2008,452(7190):966-969
Blazars are the most extreme active galactic nuclei. They possess oppositely directed plasma jets emanating at near light speeds from accreting supermassive black holes. According to theoretical models, such jets are propelled by magnetic fields twisted by differential rotation of the black hole's accretion disk or inertial-frame-dragging ergosphere. The flow velocity increases outward along the jet in an acceleration and collimation zone containing a coiled magnetic field. Detailed observations of outbursts of electromagnetic radiation, for which blazars are famous, can potentially probe the zone. It has hitherto not been possible to either specify the location of the outbursts or verify the general picture of jet formation. Here we report sequences of high-resolution radio images and optical polarization measurements of the blazar BL Lacertae. The data reveal a bright feature in the jet that causes a double flare of radiation from optical frequencies to TeV gamma-ray energies, as well as a delayed outburst at radio wavelengths. We conclude that the event starts in a region with a helical magnetic field that we identify with the acceleration and collimation zone predicted by the theories. The feature brightens again when it crosses a standing shock wave corresponding to the bright 'core' seen on the images. 相似文献
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Iman Azimi Alice H. Bong Greta X. H. Poo Kaela Armitage Dawn Lok Sarah J. Roberts-Thomson Gregory R. Monteith 《Cellular and molecular life sciences : CMLS》2018,75(24):4525-4537
Store-operated Ca2+ entry is a pathway that is remodelled in a variety of cancers, and altered expression of the components of store-operated Ca2+ entry is a feature of breast cancer cells of the basal molecular subtype. Studies of store-operated Ca2+ entry in breast cancer cells have used non-specific pharmacological inhibitors, complete depletion of intracellular Ca2+ stores and have mostly focused on MDA-MB-231 cells (a basal B breast cancer cell line). These studies compared the effects of the selective store-operated Ca2+ entry inhibitors Synta66 and YM58483 (also known as BTP2) on global cytosolic free Ca2+ ([Ca2+]CYT) changes induced by physiological stimuli in a different breast cancer basal cell line model, MDA-MB-468. The effects of these agents on proliferation as well as serum and epidermal growth factor (EGF) induced migration were also assessed. Activation with the purinergic receptor activator adenosine triphosphate, produced a sustained increase in [Ca2+]CYT that was entirely dependent on store-operated Ca2+ entry. The protease activated receptor 2 activator, trypsin, and EGF also produced Ca2+ influx that was sensitive to both Synta66 and YM58483. Serum-activated migration of MDA-MB-468 breast cancer cells was sensitive to both store-operated Ca2+ inhibitors. However, proliferation and EGF-activated migration was differentially affected by Synta66 and YM58483. These studies highlight the need to define the exact mechanisms of action of different store-operated calcium entry inhibitors and the impact of such differences in the control of tumour progression pathways. 相似文献
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Bourdon A Minai L Serre V Jais JP Sarzi E Aubert S Chrétien D de Lonlay P Paquis-Flucklinger V Arakawa H Nakamura Y Munnich A Rötig A 《Nature genetics》2007,39(6):776-780
Mitochondrial DNA (mtDNA) depletion syndrome (MDS; MIM 251880) is a prevalent cause of oxidative phosphorylation disorders characterized by a reduction in mtDNA copy number. The hitherto recognized disease mechanisms alter either mtDNA replication (POLG (ref. 1)) or the salvage pathway of mitochondrial deoxyribonucleosides 5'-triphosphates (dNTPs) for mtDNA synthesis (DGUOK (ref. 2), TK2 (ref. 3) and SUCLA2 (ref. 4)). A last gene, MPV17 (ref. 5), has no known function. Yet the majority of cases remain unexplained. Studying seven cases of profound mtDNA depletion (1-2% residual mtDNA in muscle) in four unrelated families, we have found nonsense, missense and splice-site mutations and in-frame deletions of the RRM2B gene, encoding the cytosolic p53-inducible ribonucleotide reductase small subunit. Accordingly, severe mtDNA depletion was found in various tissues of the Rrm2b-/- mouse. The mtDNA depletion triggered by p53R2 alterations in both human and mouse implies that p53R2 has a crucial role in dNTP supply for mtDNA synthesis. 相似文献
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Toppani A Robert F Libourel G de Donato P Barres O d'Hendecourt L Ghanbaja J 《Nature》2005,437(7062):1121-1124
The signature of carbonate minerals has long been suspected in the mid-infrared spectra of various astrophysical environments such as protostars. Abiogenic carbonates are considered as indicators of aqueous mineral alteration in the presence of CO2-rich liquid water. The recent claimed detection of calcite associated with amorphous silicates in two planetary nebulae and protostars devoid of planetary bodies questions the relevance of this indicator; but in the absence of an alternative mode of formation under circumstellar conditions, this detection remains controversial. The main dust component observed in circumstellar envelopes is amorphous silicates, which are thought to have formed by non-equilibrium condensation. Here we report experiments demonstrating that carbonates can be formed with amorphous silicates during the non-equilibrium condensation of a silicate gas in a H2O-CO2-rich vapour. We propose that the observed astrophysical carbonates have condensed in H2O(g)-CO2(g)-rich, high-temperature and high-density regions such as evolved stellar winds, or those induced by grain sputtering upon shocks in protostellar outflows. 相似文献