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51.
In association with industry, an extensive database has been established on measurements of sea louse counts on farmed Atlantic salmon for the years 1996 to 2000 from 33 Scottish fish farms. These data include extensive counts on the sea louse species, Lepeophtheirus salmonis, at various stages of the life cycle and in particular the chalimus and mobile stages. There has been considerable speculation as to what factors might affect the abundance of sea lice, much of which is based on limited evidence. Our analyses show that there is tremendous variation in sea louse infestation patterns from year to year, whereas stock type, geographical region and coastal exposure do not appear to affect mean levels of abundance. In contrast, treatments lead to pronounced cycles of sea louse infestation with peaks and troughs at 3-week intervals, and these interventions are important if the sea louse levels on fish are to be controlled. There was no evidence of water temperature affecting the mean annual abundance of sea louse infestation. 相似文献
52.
Cryptosporidia on dairy farms and the role these farms may have in contaminating surface water supplies in the northeastern United States 总被引:12,自引:0,他引:12
The prevalence and risk factors for shedding of cryptosporidia by dairy cattle and calves and the prevalence and risk factors for cryptosporidia in surface waters associated with dairy farms were determined for a well-defined watershed in the northeastern United States. Eleven dairy farms were enrolled in the study and subjected to monthly sampling over a 6-month period. Animal-, water-, and manure-management practices were determined by survey and fecal, on-farm water, and stream samples were obtained monthly and evaluated for the presence of cryptosporidia. Ninety-one percent of the dairy farms in our study had Cryptosporidium on their premises. Fifteen percent of the sampled calves 0–3 weeks of age were shedding cryptosporidia. The risk factors for calves shedding cryptosporidia were contact between calves and frequent bedding changes. The probability of shedding cryptosporidia decreased with age. Nine percent of farm-associated stream samples were cryptosporidia-positive. The single risk factor for detecting cryptosporidia in surface water was increasing frequency of spreading of manure on fields. The probability of detecting cryptosporidia in streams decreased as 5-day cumulative precipitation increased. There were no animal-associated or barnyard-management features associated with detecting cryptosporidia in farm-impacted streams. 相似文献
53.
The objectives of this study were to characterize the glycemic and insulinemic responses of Thoroughbred broodmares fed late spring pasture only or a mixture of pasture and a high starch or low starch feed and to test hypotheses about differences in the glycemic and insulinemic effects of these dietary regimes. A group of 15 mares were divided into three treatment groups; pasture and high starch feed (PHS), pasture and low starch feed (PLS), and pasture only (PO) and maintained in these groups for 4.5 months prior to this study. These groups were maintained on a single pasture that was temporarily divided into three sections. The study protocol was conducted over two days. On day 1 the mares were fed their respective treatments and on day 2 all mares were allowed access to pasture only. On both days plasma glucose and insulin were measured in samples taken over a 7.5 h period. Baseline measurements for glucose and insulin were not different between any of the treatment groups on either day (P > 0.05). The baseline insulin concentrations of these pasture-kept mares (26.7 ± 8.3 mIU/L) were high compared to those reported from stall-kept horses. Plasma glucose and insulin on day 1 were influenced by treatment group, sample time, and an interaction between treatment and time (P < 0.05). On day 2 there was no significant influence of treatment group (P > 0.05). Glucose and insulin rose to higher (P < 0.01) peak concentrations in the PHS group on day 1 when compared to the PLS and PO groups, with no difference (P > 0.05) detected between the PLS and PO groups. These results are reflected in greater areas under the concentration-time curves for glucose and insulin in the PHS group on day 1 (P < 0.05). On day 2 there were no differences in any of the glucose and insulin characteristics for any of the treatment groups (P > 0.05). These results indicate a clear difference in the glycemic and insulinemic effect of the PHS feed compared to the PLS and PO groups. Of further interest are the glucose and insulin characteristics of these pasture-kept mares that indicate a low insulin sensitivity and high insulin secretory response. This study provides further information on factors influencing glycemic and insulinemic responses in horses. 相似文献
54.
The effects of field aging (0–28 days) and pheromone loading rate on the longevity of red rubber septa loaded with the sex
pheromone blend of the oriental fruit mothGrapholita molesta (Busck), were evaluated in North Carolina apple orchards in 2002. Separate field tests examined the influence of trap height
and pheromone loading rate of rubber septa on trap catches of adultG. molesta males in an abandoned orchard. The loss of the major pheromone component, (Z)-8-dodecenyl acetate (Z8–12:OAc), from red rubber
septa over a 4-week period exhibited a relatively constant release rate with 30, 100 and 300 μg pheromone. Trap catch was
significantly higher in pheromone traps placed in the upper canopy than in those in the lower canopy. Pheromone traps baited
with 100μg lures caught more moths compared with those loaded with 300 μg. There was no apparent relationship between pheromone
trap catch and septa age, with trap catch appearing to be primarily a function ofG. molesta population density.
http://www.phytoparasitica.org posting May 14, 2006. 相似文献
55.
Prediction of multinomial probability of land use change using a bisection decomposition and logistic regression 总被引:1,自引:1,他引:1
Land use change is an important research area in landscape ecology and urban development. Prediction of land use change (urban
development) provides critical information for making the right policies and management plans in order to maintain and improve
ecosystem and city functions. Logistic regression is a widely used method to predict binomial probabilities of land use change
when just two responses (change and no-change) are considered. However, in practice, more than two types of change are encountered
and multinomial probabilities are therefore needed. The existing methods for predicting multinomial probabilities have limits
in building multinomial probability models and are often based on improper assumptions. This is due to the lack of proper
methodology and inadequate software. In this study, a procedure has been developed for building models to predict the multinomial
probabilities of land use change and urban development. The foundation of this procedure consists of a special bisection decomposition
system for the decomposition of multiple-class systems to bi-class systems, conditional probability inference, and logistic
regression for binomial probability models. A case study of urban development has been conducted to evaluate this procedure.
The evaluation results demonstrated that different samples and bisection decomposition systems led to very similar quality
and performance in the developed multinomial probability models, which indicates the high stability of the proposed procedure
for this case study. 相似文献
56.
K Rogers G M Barrington S M Parish 《The Canadian veterinary journal. La revue veterinaire canadienne》1997,38(10):643-644
A nonhealing wound associated with a laceration in a 12-year-old llama was evaluated. Initial attempts at closure were unsuccessful and biopsy revealed scar tissue. Subsequent biopsies, 18 mo later, revealed squamous cell carcinoma with regional metastasis. This report describes squamous cell carcinoma, secondary to a traumatic wound in a llama. 相似文献
57.
Jeroen H. van Houts Siqun Wang Huiping Shi George W. Kabalka 《Wood Science and Technology》2006,40(6):437-443
The previous paper in this series demonstrates the use of a nuclear magnetic resonance (NMR) micro-imaging system to observe the movement of liquid water through small specimens (11 × 16 mm2 cross-section) of oriented strandboard (OSB) and solid wood. In the present paper, a NMR body scanner is utilized to obtain images of moisture penetration into ASTM D 1037–99 standard sized (152 × 152 mm2) thickness swelling specimens at different intervals during water soaking. As with the micro-imaging study, silicone was applied to the surfaces and edges of some of the specimens in order to observe the directional characteristics of moisture movement through OSB. Specimens with commercially applied edge sealant were also included in the study in order to observe the effectiveness of the sealant of reducing moisture penetration and thickness swelling. The presence of voids and areas of low density were shown to contribute significantly to moisture penetration into the specimens. 相似文献
58.
George I. Mantanis Jozef Martinka Charalampos Lykidis Libor Ševčík 《Wood material science & engineering》2020,15(5):303-311
ABSTRACT The objective of the work was to evaluate the efficacy of two new polyphosphate-based fire retardants (FRs) and one commercial product named Siriono® on the fire performance and physical–mechanical properties of medium density fibreboard (MDF) fabricated in the laboratory from Scots pine (Pinus sylvestris L.) wood. The fibres were treated with aqueous solutions of fire retardants, at 12% loading (dry salt on dry wood), and bonded with a melamine urea formaldehyde (MUF) adhesive. The physical and mechanical properties of panels were assessed using the European standards, whereas their fire performance was evaluated using an in-house method and the Cone calorimeter. In overall, the chemicals added enhanced the fire and smoke properties of the panels to varying degrees. Critical FR parameters such as peak heat release rate (peak HRR), total heat release (THR) and total smoke production (TSP) were significantly improved in the FR-treated panels, as exhibited in cone calorimeter tests. However, the internal bond strength of treated panels largely decreased by the addition of fire retardants, while thickness swell and water absorption negatively affected to a significant extent. In contrast, the formaldehyde release of the panels was considerably decreased at the E1 class level, with the incorporation of the polyphosphate-based additives. 相似文献
59.
We compared radiation-use efficiency of growth (epsilon;), defined as rate of biomass accumulation per unit of absorbed photosynthetically active radiation, of forest plots exposed to ambient (approximately 360 micro l l-1) or elevated (approximately 560 micro l l-1) atmospheric CO2 concentration ([CO2]). Large plots (30-m diameter) in a loblolly pine (Pinus taeda L.) plantation, which contained several hardwood species in the understory, were fumigated with a free-air CO2 enrichment system. Biomass accumulation of the dominant loblolly pines was calculated from monthly measurements of tree growth and site-specific allometric equations. Depending on the species, leaf area index (L*) was estimated by three methods: optical, allometric and litterfall. Based on the relationship between tree height and diameter during the first 3 years of exposure, we conclude that elevated [CO2] did not alter the pattern of aboveground biomass allocation in loblolly pine. There was considerable variation in L* estimates by the different methods; total L* was 18-42% lower when estimated by the optical method compared with estimates from allometric calculations, and this discrepancy was reduced when optical measurements were corrected for the non-random distribution of loblolly pine foliage. The allometric + litterfall approach revealed a seasonal maximum total L* of 6.2-7.1 with about 1/3 of the total from hardwood foliage. Elevated [CO2] had only a slight effect on L* in the first 3 years of this study. Mean epsilon; (+/- SD), calculated for loblolly pine only, was 0.49 +/- 0.05 and 0.62 +/- 0.04 g MJ-1 for trees in the ambient and elevated [CO2] plots, respectively. The 27% increase in epsilon; in response to CO2 enrichment was caused primarily by the stimulation of biomass increment, as there was only a small effect of elevated [CO2] on L* during the initial years of fumigation. Long-term increases in atmospheric [CO2] can increase epsilon; in closed-canopy forests but the absolute magnitude and duration of this increase remain uncertain. 相似文献
60.
Multi-species tree-shrub-grass riparian buffer systems have been recognized as one of the most cost-effective bioremediation
approaches to alleviate nonpoint source agricultural pollution in heavily fertilized systems. However, highly concentrated
herbicides in surface and subsurface water and shade cast by trees along the stream bank usually compromise the effectiveness
of these systems. Greenhouse trials and field lysimeter studies were conducted to evaluate the tolerance of orchard grass
(Dactylis glomerata), smooth bromegrass (Bromus inermis), tall fescue (Festuca arundinacea), timothy (Phleum pratense), and switchgrass (Panicum virgatum) ground covers to atrazine and Balance™ (isoxaflutole) plus their capacity to sequester and degrade these herbicides and
their metabolites. Their ability to remove soil nitrate was also quantified. Concentrations of atrazine, Balance™ and their
metabolites in the leachate, soil and plant samples were determined by solid phase extraction followed by high performance
liquid or gas chromatographic analyses. Distribution of the herbicides and metabolites in the system was calculated using
a mass balance approach. Herbicide bioremediation capacity of each lysimeter treatment was determined by the ratio of metabolites
to parent herbicide plus metabolites. Bioremediation of nitrate was quantified by comparing nitrate reduction rates in grass
treatments to the bare ground control. Based on this herbicide tolerance, bioremediation data and shade tolerance determined
in a previous study, it was established that switch grass, tall fescue and smooth bromegrass are good candidates for incorporation
into tree-shrub-grass riparian buffer systems designed for the bioremediation of atrazine, Balance™ and nitrate. 相似文献