Extended-spectrum beta-lactamase-producing bacteria isolated from companion animals     

Steen SI  Webb PJ 《The Veterinary record》2007,161(20):703

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Vaccination against dog rabies in the United States.     

S Bech-Nielsen  H V Hagstad  W T Hubbert 《Journal of the American Veterinary Medical Association》1979,174(7):695-699

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Ground deposit of pesticides in relation to the cereal canopy density     

Steen Gyldenkrne  Bo J M Secher  Ebbe Nordbo 《Pest management science》1999,55(12):1210-1216

Pesticides not reaching the intended target may have negative effects on the environment and the field ecosystem. To estimate the potential ground water pollution and risk for soil-dwelling organisms it is necessary to estimate the amount of pesticide reaching the soil in different spraying situations. Literature shows that ground deposition may vary even within equal growth stages due to variations in canopy density. This paper discusses the feasibility of estimating the ground deposition of pesticides from canopy density in cereal fields. Spray experiments were carried out in wheat and barley with flat-fan nozzles of two sizes. Differences of ground deposition between the two nozzle sizes were insignificant. Adding surfactant to the spray solution significantly reduced the soil deposition in barley and in wheat cv Sleipner but not in cv Haven. A significant effect of Leaf Area Index (LAI) on ground deposition was obtained. A simple exponential model based on the LAI with an extinction coefficient of 0.48–0.50 may for many occasions satisfactorily describe the soil deposition of pesticides in cereals. Using non-destructive LAI-measurements combined with the deposition model may be useful in pesticide risk assessment on field, farm and larger regional scale and is optimising the application rate in site-specific farming. © 1999 Society of Chemical Industry  相似文献   

Factors influencing the response in intake of silage and animal performance after wilting of grass before ensiling: a review   总被引：1，自引：0，他引：1  

Wright  Gordon  Steen  & Patterson 《Grass and Forage Science》2000,55(1):1-13

This review examines the response in intake of silage and animal performance after wilting of grass before ensiling. It uses data from eighty‐five published comparisons. Initial analysis identified those variables having the greatest influence on the increase in dry‐matter (DM) intake of grass silage owing to wilting. Total water loss, drying rate of the wilted material and ammonia‐N concentration of the unwilted material were the variables most closely and positively correlated to the proportional increase in DM intake as a result of wilting, with r² values of 0·344, 0·393 and 0·240 respectively. There was little evidence of curvilinearity in any of the relationships. Stepwise regression analysis was used to identify the best multiple linear regressions for predicting the proportional increase in intake owing to wilting. Factors associated with the extent and rate of water loss in the field (total water loss and drying rate) and the quality of the unwilted material ensiled and its subsequent fermentation pattern (DM digestibility, crude protein, ammonia‐N content of unwilted silage) were the key variables in the relationship. Subsequent analysis related the increase in output of milk energy of dairy cows and liveweight gain of beef cattle to the same independent variables. This indicated that variables shown to describe the response in DM intake in the previous analysis were among those most closely related to the increases in animal performance owing to wilting of grass. To assess whether the increase in animal performance owing to wilting could be explained as a direct response to increased metabolizable energy (ME) intake of wilted compared with unwilted silages, linear relationships were derived between the increase in milk and beef production parameters and the increase in ME intake owing to wilting. From these, it was concluded that there was no clear evidence that wilting reduced the efficiency of utilization of ME in beef or dairy cattle. The present study showed that the increase in milk energy output (measured in MJ) per increase in ME intake (measured in MJ) owing to wilting was linear, with a slope of 0·19. This response from additional ME intake owing to wilting is in line with what would be anticipated when increasing ME intake by other methods.  相似文献   

Terrestrial habitat requirements of nesting freshwater turtles     

D.A. Steen  J.P. Gibbs  K.A. Buhlmann  J.L. Carr  B.W. Compton  J.D. Congdon  J.S. Doody  J.C. Godwin  K.L. Holcomb  D.R. Jackson  F.J. Janzen  G. Johnson  M.T. Jones  J.T. Lamer  T.A. Langen  M.V. Plummer  J.W. Rowe  R.A. Saumure  D.S. Wilson 《Biological conservation》2012,150(1):121-128

Because particular life history traits affect species vulnerability to development pressures, cross-species summaries of life history traits are useful for generating management guidelines. Conservation of aquatic turtles, many members of which are regionally or globally imperiled, requires knowing the extent of upland habitat used for nesting. Therefore, we compiled distances that nests and gravid females had been observed from wetlands. Based on records of > 8000 nests and gravid female records compiled for 31 species in the United States and Canada, the distances that encompass 95% of nests vary dramatically among genera and populations, from just 8 m for Malaclemys to nearly 1400 m for Trachemys. Widths of core areas to encompass varying fractions of nesting populations (based on mean maxima across all genera) were estimated as: 50% coverage = 93 m, 75% = 154 m, 90% = 198 m, 95% = 232 m, 100% = 942 m. Approximately 6–98 m is required to encompass each consecutive 10% segment of a nesting population up to 90% coverage; thereafter, ca. 424 m is required to encompass the remaining 10%. Many genera require modest terrestrial areas (<200 m zones) for 95% nest coverage (Actinemys, Apalone, Chelydra, Chrysemys, Clemmys, Glyptemys, Graptemys, Macrochelys, Malaclemys, Pseudemys, Sternotherus), whereas other genera require larger zones (Deirochelys, Emydoidea, Kinosternon, Trachemys). Our results represent planning targets for conserving sufficient areas of uplands around wetlands to ensure protection of turtle nesting sites, migrating adult female turtles, and dispersing turtle hatchlings.  相似文献   

Quantitative measurement of discoloration pigment in injured potato tissue by densitometry     

M. L. Weaver  H. A. Steen  K. N. Nilsen 《American Journal of Potato Research》1966,43(11):412-417

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Root size fractions of ryegrass and clover contribute differently to C and N inclusion in SOM     

Jim Rasmussen  Jørgen Eriksen  Erik Steen Jensen  Henning Høgh-Jensen 《Biology and Fertility of Soils》2010,46(3):293-297

Grass-clover mixtures are essential in many low-N-input cropping systems, but the importance of various root fractions for the below-ground N dynamics are not well understood. This may be due to the difficulties of studying root longevity and turnover in situ in mixtures. The present field study, investigated (1) the development in root biomass over two growing seasons and (2) the turnover of dual ¹⁵N- and ¹⁴C-labelled ryegrass and white clover root material. Litter bags containing various dual-labelled plant materials were incubated in cylinders inserted in the topsoil of a young ryegrass-clover ley. Disappearance of ¹⁴C and ¹⁵N from the litter bag material were studied for 1 year following incubation. Four times during two growing seasons, roots were divided into two classes: large roots, retained on a 1-cm sieve, and small roots, passing a 1-cm sieve but retained on a 100-µm sieve. Large root biomass increased during the two growing seasons, and small root biomass increased during the growing seasons but decreased during autumn and winter. White clover roots lost ¹⁴C and ¹⁵N almost twice as fast as ryegrass roots. The disappearance pattern of ¹⁴C and ¹⁵N from dual-labelled ryegrass and white clover roots and the C and N contents of the recovered root material indicate that large roots are determining soil C pool build-up, whereas small roots determine soil N pool build-up.  相似文献   

Evolution. Transitions from nonliving to living matter     

Rasmussen S  Chen L  Deamer D  Krakauer DC  Packard NH  Stadler PF  Bedau MA 《Science (New York, N.Y.)》2004,303(5660):963-965

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1 + 1 = 0: new math for a new age     

Steen LA 《Science (New York, N.Y.)》1984,225(4666):981

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Adaptive cluster sampling for estimation of deforestation rates   总被引：2，自引：0，他引：2  

Steen?MagnussenEmail author  Werner?Kurz  Don?G.?Leckie  Dennis?Paradine 《European Journal of Forest Research》2005,124(3):207-220

National estimates of deforestation rates may be based on a survey. Precise estimation requires an efficient design. When deforestation rates are low (<1%) large sample sizes are required with traditional sampling designs to meet a precision target. This study explores the efficiency of adaptive cluster sampling (ACS) for this estimation problem. The efficiency is assessed by simulated ACS sampling from 18,200 × 200 km populations with 78–10,742 deforestation polygons (DFP) of different shape and size and average 10-year deforestation rates between 0.2% and 1.0%. Each population is composed of four million square 1 ha population units (PU) in a regular grid. Relative root mean square errors (RMSE) of ACS were, depending on sample size, 30–50% lower than comparable errors with simple random sampling (SRS) designs. ACS achieves this advantage by adaptively adding PUs to an initial SRS sample of size n. Realized ACS sample sizes were, on average, twice the nominal size (n). Three measures of ACS efficiency indicated that the costs of adaptively increasing the sample size are critical for the effectiveness of ACS. Population effects were manifest in all estimators. Estimates of the abundance, size, and shape of DFPs will allow a prediction of these effects. Populations dominated by a few large DFPs were clearly unsuited for ACS. The performance of ACS relative to that of SRS was similar across plot sizes of 1, 10, and 40 ha. The general conclusion of this study is that the lower RMSE of ACS remains attractive when the average cost of adaptively adding a PU to the initial sample is low relative to the average cost of sampling a PU at random.  相似文献