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931.
Helminth parasite eggs in low quality water represent main food safety and health hazards and are therefore important indicators used to determine whether such water can be used for irrigation. Through sedimentation helminth eggs accumulate in the sediment, however resuspension of deposited helminth eggs will lead to increased concentration of suspended eggs in the water. Our study aimed to determine the erodibility (erosion rate and erosion threshold) and settling velocity of Ascaris and Trichuris eggs as well as cohesive sediment at different time points after incorporation into the sediment. Cohesive sediment collected from a freshwater stream was used to prepare a sediment bed onto which helminth eggs were allowed to settle. The erodibility of both sediment and helminth eggs was found to decrease over time indicating that the eggs were incorporated into the surface material of the bed and that this material was stabilized through time. This interaction between eggs and bulk sediment was further manifested in an increased settling velocity of suspended eggs when sediment was present in the suspension as compared to a situation with settling in clean water. The incorporation into the sediment bed and the aggregation with sediment particles decrease the mobility of both helminth egg types. Our findings document that helminth eggs should not be viewed as single entities in water systems when modelling the distribution of eggs since both erodibility and settling velocity of eggs are determined by mobility of the sediment present in the water stream. Recalculation of the erosion threshold for helminth eggs and sediment showed that even at relatively low current velocities i.e. 0.07-0.12 m s−1 newly deposited eggs will be mobile in open irrigation channels. These environmental factors affecting resuspension must be taken into account when developing models for sedimentation of helminth eggs in different water systems. 相似文献
932.
Large Eddy Simulations (LESs) were performed for a confined rectangular liquid jet with a co-flow and compared in detail with particle image velocimetry (PIV) measurements. A finite-volume CFD library, OpenFOAM, was used to discretize and solve the filtered Navier–Stokes equation. The effects of grid resolution, numerical schemes and subgrid models on the LES results were investigated. The second and fourth order schemes gave similar performance, while the fourth order scheme costs much more computationally. Subgrid model comparison showed that the locally dynamic procedure is necessary for complex flow simulation. Model validation was performed by comparing LES data for the point-wise velocity statistics such as the mean and the root-mean-square velocity, shear stress, correlation coefficient, velocity skewness and flatness with the PIV data. In addition, LES data for the two-point spatial correlations of velocity fluctuations that provide structural information were computed and compared with PIV data. Good agreement was observed leading to the conclusion that the LES velocity field accurately captures the important characteristics of all the turbulent length scales present in the flow, from the fully resolved energy-containing eddies to the subgrid-scale dissipative eddies. 相似文献
933.
Raizman EA Wells SJ Godden SM Bey RF Oakes MJ Bentley DC Olsen KE 《Journal of dairy science》2004,87(9):2959-2966
The objective of this study was to characterize the distribution of Mycobacterium paratuberculosis (Map) in the environment of infected and uninfected Minnesota dairy farms. Eighty herds known to be infected from Minnesota's Johne's Disease Control Program (JDCP) and 28 herds known to be uninfected from Minnesota Voluntary Johne's Disease Herd Status Program (VJDHSP) were sampled. Fecal samples from up to 100 cows in each herd were cultured in pools of 5 cows. Two environmental samples were obtained from each farm from various locations. All samples were tested using bacterial culture for Map. Eighty percent of the JDCP herds had at least one positive pool. Environmental samples were cultured positive in 78% of the JDCP herds. Two (7%) of the VJDHSP herds had one positive pool, and one herd had one positive environmental sample. Environmental samples were cultured positive in cow alleyways (77% of the herds), manure storage (68%), calving area (21%), sick cow pen (18%), water runoff (6%), and postweaned calves areas (3%). There was an association between maximum level of colonies per tube from cow alleyways and manure storage and fecal pool prevalence. Herds with both areas cultured negative were estimated to have 0.3 to 4% fecal pool prevalence. Herds with both areas having a heavy load of bacteria were estimated to have 53 to 73% fecal pool prevalence. The study results indicate that targeted sampling of cow alleyways and manure storage areas appears to be an alternative strategy for herd screening and Johne's infection status assessment and for estimating herd fecal prevalence. 相似文献
934.
The grinding of a herringmeal may be both significantly too coarse and too fine for chicks. Particles falling between U.S. Sieve Series Nos. 16 and 50 (respective openings 1·19 and 0·297 mm) appeared to be best. 相似文献
935.
官旭华 Benjamin J Silk Wenkai Li Aaron T.Fleishchauer 邢学森 蒋晓清 余宏杰 Sonja J.Olsen Adam L.Cohen 《Canadian Metallurgical Quarterly》2011,22(1)
目的 肺炎是全球传染性疾病最主要的死因之一,但中国的肺炎疾病负担还知之甚少,因为很多数据资料都是以非英文文献的形式发表的.方法 系统回顾了中国大陆关于肺炎发病率与死亡率的中文和英文文献,这些研究都是具有第一手数据的研究,1985-2008年有37篇论文符合纳入标准.结果 各项研究的质量差异较大.5岁以下儿童肺炎发病率为(0.06~0.27)次/人年,肺炎死亡率为184/10万~1 223/10万人口.肺炎的发病率与死亡率随着时间稳定不变或者呈下降趋势,且农村高于城市.结论 肺炎仍然是中国儿童的主要公共卫生问题之一.肺炎发病率与死亡率估计的变化差异大.继续降低发病率与死亡率需要可靠的监测数据和新的预防措施的实施,特别是在农村等高发地区. 相似文献
936.
Du WX Olsen CW Avena-Bustillos RJ Friedman M McHugh TH 《Journal of food science》2011,76(2):M149-M155
Fruit and vegetable skins have polyphenolic compounds, terpenes, and phenols with antimicrobial and antioxidant activity. These flavoring plant essential oil components are generally regarded as safe. Edible films made from fruits or vegetables containing apple skin polyphenols have the potential to be used commercially to protect food against contamination by pathogenic bacteria. The main objective of this study was to evaluate physical properties as well as antimicrobial activities against Listeria monocytogenes, Escherichia coli O157:H7, and Salmonella enterica of apple skin polyphenols at 0% to 10% (w/w) concentrations in apple puree film-forming solutions formulated into edible films. Commercial apple skin polyphenol powder had a water activity of 0.44 and high total soluble phenolic compounds and antioxidant capacity (995.3 mg chlorogenic acid/100 g and 14.4 mg Trolox/g, respectively). Antimicrobial activities of edible film containing apple skin polyphenols were determined by the overlay method. Apple edible film with apple skin polyphenols was highly effective against L. monocytogenes. The minimum concentration need to inactive L. monocytogenes was 1.5%. However, apple skin polyphenols did not show any antimicrobial effect against E. coli O157:H7 and S. enterica even at 10% level. The presence of apple skin polyphenols reduced water vapor permeability of films. Apple skin polyphenols increased elongation of films and darkened the color of films. The results of the present study show that apple skin polyphenols can be used to prepare apple-based antimicrobial edible films with good physical properties for food applications by direct contact. 相似文献
937.
ML Sanz M Gonzlez C de Lorenzo J Sanz I Martínez‐Castro 《Journal of the science of food and agriculture》2004,84(12):1577-1584
Artisanal honey samples produced in Madrid province (central Spain) were characterised from their melissopalynological analysis, carbohydrate composition and physicochemical parameters. Melissopalynological analysis showed that Echium sp pollen appeared as the dominant palynomorph in most samples. It was also observed that many honey samples were natural blends from both nectar and honeydew botanical origins. Twenty‐five carbohydrates (glucose, fructose, 16 disaccharides and seven trisaccharides) were detected and quantified. Discriminant analysis was used to describe the variability of compositional data, which was probably associated with the different honey sources analysed (honeydew, Echium sp and other nectar plants), which in turn was related to the physiographical conditions (plain or mountain) occurring in Madrid province. Copyright © 2004 Society of Chemical Industry 相似文献
938.
Informative tests according to German standards (DIN) have been made with 3 clear logs of Pinus radiata to compare the results with European softwoods. Modulus of rupture and compression strengths (density between 0.35 and 0.66 g/cm3, mean value 0.53 g/cm3) as wells as the modulus of elasticity for small, elear specimen of Radiata pine. European pine, Spruce and Silver fire were nearly the same. Swelling and shrinkage values were not worse than those of European softwoods. The length of tracheidal ray cells in specimen of heart wood were 3.4 mm in the average. Extraction for several hours with Cyclohexan showed very different resin contents over the cross section between 0.27 and 15%. The concentration of preservative in sapwood of Pinus radiata was lower than expected. Phenol resorcind adhesive bonds of non-treated and preservative treated wood showed shear strengths parallel to the grain in the range of solid wood strengths. 相似文献
939.
940.
Research with dairy cows was to determine whether dairy cows in confinement are in poor physical condition, if programmed exercise improves physical fitness, and which physiological measures are most useful indicators of physical fitness. If maintenance of physiologic homeostasis when an animal is under a work load is a valid criterion of physical fitness, dairy cows in confinement are in poor physical condition, and physical fitness can be improved by programmed exercise. Walking cows at 4 km/h for a distance of 8 km daily for 5 days per wk for 8 wk prepartum improved their physical fitness. Useful hemic indicators of improved fitness were less increase in erythrocyte numbers and hemoglobin concentration and less decrease in oxygen tension, carbon dioxide, carbonic acid contents, and base excess than in poorly conditioned cattle under work load. Venous blood was satisfactory for these measurements. Also valued were heart and respiratory rates, except these rates being sensitive to extraneous disturbances may be less reliable. 相似文献