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排序方式: 共有134条查询结果,搜索用时 420 毫秒
1.
Lorna Tapper-Jones Simon A Smail Roisin Pill Robert Harvard Davis 《BMJ (Clinical research ed.)》1988,296(6626):908-909
Russell et al have shown that the compliance of patients can be enhanced by general practitioners'' providing them with written materials.'' We examined what educational materials for patients were used by general practitioners and where the materials came from. 相似文献
2.
Yves Roisin 《Zoomorphology》1988,107(6):339-347
Summary The existence of a worker caste in Prorhinotermes inopinatus was determined with the help of biometrical analyses and morphological observations. No dichotomy between alate and worker lines was detected among the young larval instars. Mandible sclerotization and wear show that the larvae become active by the fourth instar in mature colonies, and by the third in incipient ones. Prothoracic finger-shaped expansions characterize the most dependent larval instars. The antennal structure is the best feature for distinguishing late instars. The developmental schema is very flexible: the late larvae of stages 5 to 8 (at least) can give rise to wing-padded nymphs, to the next larval instar, to presoldiers, or most likely to neotenic reproductives as well; the wing-padded individuals (nymphs) normally moult direct to alates, but they can also undergo a regression of their wing pads and revert to worker-like individuals or differentiate into soldiers or neotenics. Slight variations in alate size and antennal morphology result from their origin in different larval instars. Whole-colony censuses revealed that the major part of the colony's work force is composed of pseudergates, i.e. late larvae that do not follow the most direct pathway to the alate. The pseudergates of Prohinotermes do not constitute a distinct worker caste irreversibly diverted from the alate developmental pathway. For this reason the caste system of Prorhinotermes is analogous to that of the Kalotermitidae and Termopsidae and much more primitive than those of the other Rhinotermitidae so far studied, Reticulitermes, Schedorhinotermes and Coptotermes.Contribution No. 139 from King Léopold III Biological Station, Laing Island, Papua New GuineaSenior research assistant of the National Fund for Scientific Research, Belgium 相似文献
3.
Donatella Zona Peter M. Lafleur Koen Hufkens Beniamino Gioli Barbara Bailey George Burba Eugénie S. Euskirchen Jennifer D. Watts Kyle A. Arndt Mary Farina John S. Kimball Martin Heimann Mathias Göckede Martijn Pallandt Torben R. Christensen Mikhail Mastepanov Efrén López-Blanco Albertus J. Dolman Roisin Commane Charles E. Miller Josh Hashemi Lars Kutzbach David Holl Julia Boike Christian Wille Torsten Sachs Aram Kalhori Elyn R. Humphreys Oliver Sonnentag Gesa Meyer Gabriel H. Gosselin Philip Marsh Walter C. Oechel 《Global Change Biology》2023,29(5):1267-1281
Long-term atmospheric CO2 concentration records have suggested a reduction in the positive effect of warming on high-latitude carbon uptake since the 1990s. A variety of mechanisms have been proposed to explain the reduced net carbon sink of northern ecosystems with increased air temperature, including water stress on vegetation and increased respiration over recent decades. However, the lack of consistent long-term carbon flux and in situ soil moisture data has severely limited our ability to identify the mechanisms responsible for the recent reduced carbon sink strength. In this study, we used a record of nearly 100 site-years of eddy covariance data from 11 continuous permafrost tundra sites distributed across the circumpolar Arctic to test the temperature (expressed as growing degree days, GDD) responses of gross primary production (GPP), net ecosystem exchange (NEE), and ecosystem respiration (ER) at different periods of the summer (early, peak, and late summer) including dominant tundra vegetation classes (graminoids and mosses, and shrubs). We further tested GPP, NEE, and ER relationships with soil moisture and vapor pressure deficit to identify potential moisture limitations on plant productivity and net carbon exchange. Our results show a decrease in GPP with rising GDD during the peak summer (July) for both vegetation classes, and a significant relationship between the peak summer GPP and soil moisture after statistically controlling for GDD in a partial correlation analysis. These results suggest that tundra ecosystems might not benefit from increased temperature as much as suggested by several terrestrial biosphere models, if decreased soil moisture limits the peak summer plant productivity, reducing the ability of these ecosystems to sequester carbon during the summer. 相似文献
4.
Jennifer D. Watts Mary Farina John S. Kimball Luke D. Schiferl Zhihua Liu Kyle A. Arndt Donatella Zona Ashley Ballantyne Eugénie S. Euskirchen Frans-Jan W. Parmentier Manuel Helbig Oliver Sonnentag Torbern Tagesson Janne Rinne Hiroki Ikawa Masahito Ueyama Hideki Kobayashi Torsten Sachs Daniel F. Nadeau John Kochendorfer Marcin Jackowicz-Korczynski Anna Virkkala Mika Aurela Roisin Commane Brendan Byrne Leah Birch Matthew S. Johnson Nima Madani Brendan Rogers Jinyang Du Arthur Endsley Kathleen Savage Ben Poulter Zhen Zhang Lori M. Bruhwiler Charles E. Miller Scott Goetz Walter C. Oechel 《Global Change Biology》2023,29(7):1870-1889
Arctic-boreal landscapes are experiencing profound warming, along with changes in ecosystem moisture status and disturbance from fire. This region is of global importance in terms of carbon feedbacks to climate, yet the sign (sink or source) and magnitude of the Arctic-boreal carbon budget within recent years remains highly uncertain. Here, we provide new estimates of recent (2003–2015) vegetation gross primary productivity (GPP), ecosystem respiration (Reco), net ecosystem CO2 exchange (NEE; Reco − GPP), and terrestrial methane (CH4) emissions for the Arctic-boreal zone using a satellite data-driven process-model for northern ecosystems (TCFM-Arctic), calibrated and evaluated using measurements from >60 tower eddy covariance (EC) sites. We used TCFM-Arctic to obtain daily 1-km2 flux estimates and annual carbon budgets for the pan-Arctic-boreal region. Across the domain, the model indicated an overall average NEE sink of −850 Tg CO2-C year−1. Eurasian boreal zones, especially those in Siberia, contributed to a majority of the net sink. In contrast, the tundra biome was relatively carbon neutral (ranging from small sink to source). Regional CH4 emissions from tundra and boreal wetlands (not accounting for aquatic CH4) were estimated at 35 Tg CH4-C year−1. Accounting for additional emissions from open water aquatic bodies and from fire, using available estimates from the literature, reduced the total regional NEE sink by 21% and shifted many far northern tundra landscapes, and some boreal forests, to a net carbon source. This assessment, based on in situ observations and models, improves our understanding of the high-latitude carbon status and also indicates a continued need for integrated site-to-regional assessments to monitor the vulnerability of these ecosystems to climate change. 相似文献
5.
Ghosts derived from bovine chromaffin granules have a 32Pi-ATP exchange activity which is associated with the H+ pump of that membrane. This activity was low when compared to bacteria, chloroplasts or submitochondrial particles, but had similar properties (Km for ATP and Pi, ATP/Mg2+ ratio, pH profile, inhibition by dicyclohexylcarbodiimide and tributyltin) to the ATPase from above membranes. The 32Pi-ATP exchange activity was solubilized by cholate/octylglucoside mixtures. The soluble extract was lipid depleted by ammonium sulfate fractionation and partially purified by sucrose gradient centrifugation. The purified preparation was reconstituted with phospholipids by freeze-thawing. The reconstituted vesicles had a 32Pi-ATP exchange sensitive to dicyclohexylcarbodiimide and trybutyltin and an ATPase with a sensitivity to the inhibitors which varied with the reconstitution conditions. The α- and β-subunits of F1-ATPase were major components of the preparation. 相似文献
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7.
The ATP-ADP exchange activity previously described in a membrane farction of Escherichia coli appeared after a cold osmotic shock according to Neu and Heppel ((1965) J. Biol. Chem. 240, 3685--3692) in the shock fluid. Membranes derived from shocked cells had no activity. The enzyme responsible for this activity has been purified 125-fold and catalyzed the transfer of a phosphoryl radical from ribonucleosidetriphosphates (NTPs) to ribonucleosidediphosphates (NDPs); this is, therefore, a non-specific nucleosidediphosphate kinase (ATP:nucleosidediphosphate phosphotransferase, EC 2.7.4.6). The activity required the presence of a divalent cation, Mg2+, Mn2+ or Ca2+ at a unity mol/mol ratio of nucleotide for maximal activation. The enzyme exhibited simple saturation kinetics with respect to the phosphate donor but inhibition by excess substrate was observed upon increasing phosphate acceptor. The kinetics of the reaction indicated an ordered bi-molecular ping-pong reaction mechanism. Differential heat sensitivity of the enzyme whether it is heated alone with ATP, ADP or Mg2+ opens possibilities to study different enzyme-substrate complexes. 相似文献
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9.
Goodman Gidona Meredith Anna Girling Simon Rosell Frank Campbell-Palmer Roisin 《EcoHealth》2016,13(1):139-144
Recent advances in noninvasive detection methods for mycobacterial infection in primates create new opportunities for exploring the epidemiology of tuberculosis in free-living species. Chimpanzees (Pan troglodytes schweinfurthii) and baboons (Papio anubis) in Gombe National Park, Tanzania, were screened for infection with pathogens of the Mycobacterium tuberculosis Complex using Fecal IS6110 PCR; none was positive. This study demonstrates the feasibility of large-scale mycobacterial screening in wild primates. 相似文献
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