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排序方式: 共有113条查询结果,搜索用时 15 毫秒
21.
Kelly P O'Sullivan K Berry D More S Meaney W O'Callaghan E O'Brien B 《Irish veterinary journal》2009,62(1):36-42
Research has shown that total bacterial count (TBC), which is the bacterial growth per ml of milk over a fixed period of time, can be decreased by good hygiene and farm management practices. The objective of the current study was to quantify the associations between herd management factors and bulk tank TBC in Irish spring calving, grass-based dairy herds. The relationship between bulk tank TBC and farm management and infrastructure was examined using data from 400 randomly selected Irish dairy farms where the basal diet was grazed grass. Herd management factors associated with bulk tank TBC were identified using linear models with herd annual total bacterial score (i.e., arithmetic mean of the natural logarithm of bulk tank TBC) included as the dependent variable. All herd management factors were individually analysed in a separate regression model, that included an adjustment for geographical location of the farm. A multiple stepwise regression model was subsequently developed. Median bulk tank TBC for the sample herds was 18,483 cells/ml ranging from 10,441 to 130,458 cells/ml. Results from the multivariate analysis indicated that the following management practices were associated with low TBC; use of heated water in the milking parlour; participation in a milk recording scheme; and tail clipping of cows at a frequency greater than once per year. Increased level of hygiene of the parlour and cubicles were also associated with lower TBC. Herd management factors associated with bulk tank TBC in Irish grazing herds were generally in agreement with most previous studies from confinement systems of milk production. 相似文献
22.
DN Basov SI Woods AS Katz EJ Singley RC Dynes M Xu DG Hinks CC Homes M Strongin 《Science (New York, N.Y.)》1999,283(5398):49-52
Analysis of the interlayer infrared conductivity of cuprate high-transition temperature superconductors reveals an anomalously large energy scale extending up to midinfrared frequencies that can be attributed to formation of the superconducting condensate. This unusual effect is observed in a va- riety of materials, including Tl2Ba2CuO6+x, La2-xSrxCuO4, and YBa2Cu3O6.6, which show an incoherent interlayer response in the normal state. Midinfrared range condensation was examined in the context of sum rules that can be formulated for the complex conductivity. One possible interpretation of these experiments is in terms of a kinetic energy change associated with the superconducting transition. 相似文献
23.
J Christensen-Dalsgaard W Dappen SV Ajukov ER Anderson HM Antia S Basu VA Baturin G Berthomieu B Chaboyer SM Chitre AN Cox P Demarque J Donatowicz WA Dziembowski M Gabriel DO Gough DB Guenther JA Guzik JW Harvey F Hill G Houdek CA Iglesias AG Kosovichev JW Leibacher P Morel CR Proffitt J Provost J Reiter EJ Rhodes FJ Rogers IW Roxburgh MJ Thompson RK Ulrich 《Science (New York, N.Y.)》1996,272(5266):1286-1292
Data from the Global Oscillation Network Group (GONG) project and other helioseismic experiments provide a test for models of stellar interiors and for the thermodynamic and radiative properties, on which the models depend, of matter under the extreme conditions found in the sun. Current models are in agreement with the helioseismic inferences, which suggests, for example, that the disagreement between the predicted and observed fluxes of neutrinos from the sun is not caused by errors in the models. However, the GONG data reveal subtle errors in the models, such as an excess in sound speed just beneath the convection zone. These discrepancies indicate effects that have so far not been correctly accounted for; for example, it is plausible that the sound-speed differences reflect weak mixing in stellar interiors, of potential importance to the overall evolution of stars and ultimately to estimates of the age of the galaxy based on stellar evolution calculations. 相似文献
24.
25.
Influence of N and non-N salts on atmospheric methane oxidation by upland boreal forest and tundra soils 总被引:10,自引:0,他引:10
S. C. Whalen 《Biology and Fertility of Soils》2000,31(3-4):279-287
The short-term (24 h) and medium-term (30 day) influence of N salts (NH4Cl, NaNO3 and NaNO2) and a non-N salt (NaCl) on first-order rate constants, k (h–1) and thresholds (CTh) for atmospheric CH4 oxidation by homogenized composites of upland boreal forest and tundra soils was assessed at salt additions ranging to 20 μmol
g–1 dry weight (dw) soil. Additions of NH4Cl, NaNO3 and NaCl to 0.5 μmol g–1 dw soil did not significantly decrease k relative to watered controls in the short term. Higher concentrations significantly reduced k, with the degree of inhibition increasing with increasing dose. Similar doses of NH4Cl and NaCl gave comparable decreases in k relative to controls and both soils showed low native concentrations of NH4
+-N (≤1 μmol g–1dw soil), suggesting that the reduction in k was due primarily to a salt influence rather than competitive inhibition of CH4 oxidation by exogenous NH4
+-N or NH4
+-N released through cation exchange. The decrease in k was consistently less for NaNO3 than for NH4Cl and NaCl at similar doses, pointing to a strong inhibitory effect of the Cl– counter-anion. Thresholds for CH4 oxidation were less sensitive to salt addition than k for these three salts, as significant increases in CTh relative to controls were only observed at concentrations ≥1.0 μmol g–1 dw soil. Both soils were more sensitive to NaNO2 than to other salts in the short term, showing a significant decrease in k at an addition of 0.25 μmol NaNO2 g–1 dw soil that was clearly attributable to NO2
–. Soils showed no recovery from NaCl, NH4
+-N or NaNO3 addition with respect to atmospheric CH4 oxidation after 30 days. However, soils amended with NaNO2 to 1.0 μmol NaNO2 g–1 dw showed values of k that were not significantly different from controls. Recovery of CH4-oxidizing ability was due to complete oxidation of NO2
–-N to NO3
–-N. Analysis of soil concentrations of N salts necessary to inhibit atmospheric CH4 oxidation and regional rates of N deposition suggest that N deposition will not decrease the future sink strength of upland
high-latitude soils in the atmospheric CH4 budget.
Received: 30 April 1999 相似文献
26.
27.
Kovacs JJ Whalen EJ Liu R Xiao K Kim J Chen M Wang J Chen W Lefkowitz RJ 《Science (New York, N.Y.)》2008,320(5884):1777-1781
28.
Climate Change During the Last Deglaciation in Antarctica 总被引:1,自引:0,他引:1
PA Mayewski MS Twickler SI Whitlow LD Meeker Q Yang J Thomas K Kreutz PM Grootes DL Morse EJ Steig ED Waddington ES Saltzman P Whung KC Taylor 《Science (New York, N.Y.)》1996,272(5268):1636-1638
Greenland ice core records provide clear evidence of rapid changes in climate in a variety of climate indicators. In this work, rapid climate change events in the Northern and Southern hemispheres are compared on the basis of an examination of changes in atmospheric circulation developed from two ice cores. High-resolution glaciochemical series, covering the period 10,000 to 16,000 years ago, from a central Greenland ice core and a new site in east Antarctica display similar variability. These findings suggest that rapid climate change events occur more frequently in Antarctica than previously demonstrated. 相似文献
29.
A methane record from the GISP2 ice core reveals that millennial-scale variations in atmospheric methane concentration characterized much of the past 110,00 years. As previously observed in a shorter record from central Greenland, abrupt concentration shifts of about 50 to 300 parts per billion by volume were coeval with most of the interstadial warming events (better known as Dansgaard-Oeschger events) recorded in the GISP2 ice core throughout the last glacial period. The magnitude of the rapid concentration shifts varied on a longer time scale in a manner consistent with variations in Northern Hemisphere summer insolation, which suggests that insolation may have modulated the effects of interstadial climate change on the terrestrial biosphere. 相似文献
30.
Earthworm influence on carbon dioxide and nitrous oxide fluxes from an unfertilized corn agroecosystem 总被引:1,自引:0,他引:1
Alicia B. Speratti Joann K. Whalen Philippe Rochette 《Biology and Fertility of Soils》2007,44(2):405-409
Earthworms modify the soil environment through their feeding, casting, and burrowing activities, which may lead to more decomposition
and respiration in aerobic microsites and more denitrification in anaerobic microsites. The objective of this study was to
determine whether earthworms increase CO2 and N2O fluxes from an unfertilized corn agroecosystem. Earthworm populations within field enclosures (2.9 m2) were reduced by repeatedly applying carbaryl insecticide, then single and mixed populations of Lumbricus terrestris L. and Aporrectodea caliginosa (Savigny) were added. Gas samples were collected once a week for 14 weeks, from June to September 2005. Carbaryl applications
reduced, but did not eliminate earthworms from enclosures. The CO2 and N2O fluxes were affected by the sampling date, with peak gas fluxes after rainfall events. Mean CO2 and N2O fluxes during the study period tended to be greater from enclosures with added earthworms than the control (no earthworms
added), but were not significantly affected by earthworm treatments due to the low survival rate of introduced earthworms.
Better control of earthworm populations in the field is required to fully assess the impact of earthworms on CO2 and N2O fluxes from temperate agroecosystems. 相似文献