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排序方式: 共有125条查询结果,搜索用时 16 毫秒
101.
102.
Proxy global assessment of land degradation 总被引:3,自引:0,他引:3
Land degradation is always with us but its causes, extent and severity are contested. We define land degradation as a long-term decline in ecosystem function and productivity, which may be assessed using long-term, remotely sensed normalized difference vegetation index (NDVI) data. Deviation from the norm may serve as a proxy assessment of land degradation and improvement – if other factors that may be responsible are taken into account. These other factors include rainfall effects which may be assessed by rain-use efficiency, calculated from NDVI and rainfall. Results from the analysis of the 23-year Global Inventory Modeling and Mapping Studies (GIMMS) NDVI data indicate declining rain-use efficiency-adjusted NDVI on ca. 24% of the global land area with degrading areas mainly in Africa south of the equator, South-East Asia and south China, north-central Australia, the Pampas and swaths of the Siberian and north American taiga; 1.5 billion people live in these areas. The results are very different from previous assessments which compounded what is happening now with historical land degradation. Economic appraisal can be undertaken when land degradation is expressed in terms of net primary productivity and the resultant data allow statistical comparison with other variables to reveal possible drivers. 相似文献
103.
OBJECTIVE: To evaluate the effects on plasma cortisol concentration of a continuous infusion of a readily available steroid with equipotent glucocorticoid and mineralocorticoid effects. PROCEDURE: Plasma cortisol concentrations were measured before and regularly after hydrocortisone sodium succinate was administered as a continuous intravenous infusion over 6 h at 0.32 and 0.65 mg kg-1 h-1 to 12 healthy dogs weighing 12 to 22 kg. RESULTS: The infusion at both does rates produced significant and stable increases in plasma cortisol concentrations. The plateau concentrations produced by the large and small doeses were respectively above and below plasma cortisol concentrations likely to provide adequate glucocorticoid and mineralocorticoid activity in stressed dogs with significantly decreased adrenal function. CONCLUSION: This paper presents information regarding the changes in plasma cortisol concentrations in 12 normal dogs given an hydrocortisone sodium succinate infusion at two dose rates. The marked and continuous increase in plasma cortisol concentrations suggests a continuous HSS infusion may be a possible alternative to desoxycorticosterone acetate and dexamethasone in the treatment of acute adrenal dysfunction. 相似文献
104.
Carbon nanotube quantum resistors 总被引:1,自引:0,他引:1
The conductance of multiwalled carbon nanotubes (MWNTs) was found to be quantized. The experimental method involved measuring the conductance of nanotubes by replacing the tip of a scanning probe microscope with a nanotube fiber, which could be lowered into a liquid metal to establish a gentle electrical contact with a nanotube at the tip of the fiber. The conductance of arc-produced MWNTs is one unit of the conductance quantum G0 = 2e2/h = (12.9 kilohms)-1. The nanotubes conduct current ballistically and do not dissipate heat. The nanotubes, which are typically 15 nanometers wide and 4 micrometers long, are several orders of magnitude greater in size and stability than other typical room-temperature quantum conductors. Extremely high stable current densities, J > 10(7) amperes per square centimeter, have been attained. 相似文献
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106.
WA Snowdon 《Australian veterinary journal》1994,71(6):187-187
107.
GF Mastromonaco E Semple C Robert GJ Rho DH Betts WA King 《Reproduction in domestic animals》2004,39(6):462-467
Important differences exist between in vitro fertilized (IVF) and nuclear transfer (NT) bovine embryos. Studies have shown that although in vitro development is comparable, post-implantation survival is greatly reduced in NT embryos. In this study, we compare serum and bovine serum albumin (BSA) supplementation during oocyte maturation and embryo culture of IVF and NT embryos. In experiment 1, oocytes and embryos were randomly distributed into different treatment groups consisting of synthetic oviductal fluid (SOF) medium supplemented with either serum, fatty acid-free BSA (FAF) or fraction V BSA during maturation and/or culture to assess IVF embryo development. In experiment 2, oocytes were matured in SOF + serum or SOF + FAF and reconstructed embryos were cultured in SOF + FAF to assess NT embryo development. Among the IVF treatment groups, a greater number of blastocysts were observed in the steer serum (SER) group (IVM and IVC in SOF + serum) on day 6; however, no significant differences were seen in blastocyst development from day 8 onwards. Hatching frequencies on days 8 and 9 were significantly greater in groups with serum, with the exception of FAF (IVM and IVC in SOF + FAF) on day 9. For the NT treatment groups, the presence of serum during IVM resulted in a higher proportion of MII oocytes and increased blastocyst development and hatching rates were compared with supplementation of FAF. These results indicate that both serum and FAF provide comparable embryo development for IVF but not for NT bovine embryos. 相似文献
108.
W.E. Finch-Savage H.A. Clay S.P. Budge K.C. Dent J.P. Clarkson J.M. Whipps 《European journal of plant pathology / European Foundation for Plant Pathology》2003,109(6):615-624
The fungal pathogen Sclerotinia pseudotuberosa is a major cause of deterioration during storage of Quercus robur seeds (acorns) and along with other, mainly saprotrophic fungi, contributes to the decline of viability and vigour in the acorn population. Hot-water thermotherapy (HWT; 41 °C for 2.5 h) killed the fungal pathogen S. pseudotuberosa and prolonged the storage life of acorns. The addition of the systemic fungicide benomyl to the HWT and/or the broad-spectrum fungicide thiram as a seed dressing further enhanced the storage life of acorns. Three fungal antagonists, Coniothyrium minitans, Trichoderma sp. (KW3) and Trichoderma virens (G20), were also applied as a film-coating to acorns using a polyvinylacetate sticker achieving ca. 107–108 viable conidia per acorn. The biological treatments provided protection against infection and the spread of infection of S. pseudotuberosa and other fungi on the acorns during storage over several months. All treated and stored acorns grew normally following sowing in seedbeds. The Trichoderma species were more effective than C. minitans, with T. virens being the most effective. T. virens reduced pathogen spread from acorns infected with S. pseudotuberosa to `clean' acorns when T. virens coated infected and 'clean' acorns were mixed together. However, T. virens was less effective than HWT at preventing the proliferation of this pathogen within individual acorns that were infected before coating. A combination of HWT and subsequent coating with T. virens provided a more effective control against both S. pseudotuberosa and saprotrophic fungi than when either treatment was applied alone. 相似文献
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SUMMARY Forty cats with hyperthyroidism were treated using 200 to 300 (typically 250) mBq of orally administered 131I. Thirty-six cases (90%) were successfully treated, as assessed by resolution of clinical signs and reduction In plasma thyroxine concentrations to normal or reduced values after treatment. Although higher doses of 131I appear to be required when the radioisotope is administered orally rather than Intravenously, a less stressful administration procedure and greater availability of therapy capsules offer useful advantages for treating thyrotoxic cats. 相似文献