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SUMMARY A decision analysis model was designed to evaluate the cost effectiveness of a vaccination program for preventing endemic or epidemic porcine parvovirus (PPV) Induced reproductive failure in a 100-sow pig herd. The results showed that the cost of vaccination was less than the cost incurred by continuing endemic PPV infection, or the cost of a severe epidemic. A long term vaccination program is a cost effective method for controlling PPV-induced reproductive failure in pig herds suffering endemic and epidemic PPV infection. 相似文献
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Jess K. Zimmerman Liza S. Comita Jill Thompson María Uriarte Nicholas Brokaw 《Landscape Ecology》2010,25(7):1099-1111
Where large disturbances do not cause landscape-wide mortality and successional change, forested ecosystems should exhibit
landscape metastability (landscape equilibrium) at a scale equal to the dominant patch size of disturbance and recovery within
the landscape. We investigated this in a 16-ha contiguous plot of subtropical wet forest in Puerto Rico, the Luquillo Forest
Dynamics Plot (LFDP), which experienced two major hurricanes during the 15-year study and has a land use history (logging
and agriculture 40 or more years hence) that differs in intensity between two areas of the plot. Using he LFDP as our “landscape,”
we studied the spatial pattern of community change through time (3–5 year intervals) by calculating community dissimilarity
between tree censuses for two size classes of trees (1 to <10 cm DBH and ≥10 cm DBH) in quadrats ranging in size from 0.010–1 ha
and for the entire landscape, i.e., plot or land use type. The point at which the decline in community dissimilarity with
quadrat size showed maximum curvature identified the dominant patch size (i.e., point of metastability). For canopy trees
≥10 cm dbh, there was no evidence that the community experienced landscape-wide successional changes in either land use type,
and we found a consistent patch size of community change around 0.1 ha (range 0.091–0.107). For the understory tree and shrub
community (1 to <10 cm dbh) there was some evidence of landscape-wide community changes over time in response to hurricane
damage, apparently driven by interactions with the dominant canopy species, whose composition varied with land use intensity,
and their species-specific susceptibility to hurricane damage. 相似文献
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During the summer of 1990 deaths, occurred in racing camels (Camelus dromedarius) associated with a specific disease syndrome. Clinical signs included pyrexia, coughing, lachrymation, oedema of the throat and submandibular region and enlargement of submandibular lymph nodes. In terminal cases nervous signs were present and sometimes there was bloody diarrhoea and vomiting. Of 480 camels at least 70 animals were affected with the disease and about 40 died. Morbidity and mortality was greater in camels recently imported. Consistent necropsy findings were extensive petechial and ecchymotic haemorrhage beneath the epicardium, endocardium and visceral pleura and in the mediastinal lymph nodes, and haemorrhagic oedema of the pharyngeal and laryngeal areas. Haemorrhages occurred more variably in abdominal organs and on the omasal and abomasal mucosa. Bronchopneumonia, omasitis and abomasitis were observed on microscopic examination, together with liver and kidney lesions of presumed toxic origin. Fungal hyphae and, occasionally, the characteristic conidial morphology of Aspergillus fumigatus were seen in sections and direct smears from lesions in the respiratory and alimentary tracts. A fumigatus was cultured from trachea, bronchi, bronchioles, lung tissue, heart blood, omasum, abomasum, ileum and submandibular lymph nodes. Whether the role of Aspergillus in the overall syndrome is primary or secondary has not been established; no other potential aetiological agent has been identified. 相似文献
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Observations were made on the abundance and survival of Haemonchus placei, Cooperia punctata and Oesophagostomum radiatum infective larvae from cattle faecal pats exposed at various times of the year in north Queensland wet tropics. Pats exposed in the hot, wet season yielded abundant larvae on herbage. In the dry season, although low numbers of infective larvae were usual, considerable numbers were produced under conditions of heavy dews on dense herbage. Irrespective of season of deposition of pats, the resulting larvae persisted generally for not longer than 10 to 12 weeks, and in large numbers for only 2 to 6 weeks. The findings suggest that prevention of contamination in the wet season, and in the dry season when light rainfalls are accompanied by heavy dews on dense herbage, will result in low levels of larval infestation on herbage. Rotational grazing in the area is suggested as a means of worm control. 相似文献
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DH Hathaway PA Gilman JW Harvey F Hill RF Howard HP Jones JC Kasher JW Leibacher JA Pintar GW Simon 《Science (New York, N.Y.)》1996,272(5266):1306-1309
Doppler velocity observations obtained by the Global Oscillation Network Group (GONG) instruments directly measure the nearly steady flows in the solar photosphere. The sun's differential rotation is accurately determined from single observations. The rotation profile with respect to latitude agrees well with previous measures, but it also shows a slight north-south asymmetry. Rotation profiles averaged over 27-day rotations of the sun reveal the torsional oscillation signal-weak, jetlike features, with amplitudes of 5 meters per second, that are associated with the sunspot latitude activity belts. A meridional circulation with a poleward flow of about 20 meters per second is also evident. Several characteristics of the surface flows suggest the presence of large convection cells. 相似文献
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