2,892 research outputs found

    Fluid structure interaction of submerged metallic and composite plates subjected to low velocity impact loading

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    An instrumented low velocity impact rig has been used to acquire experimental data for impacts in air and underwater for both metallic and composite plates when subjected to a low velocity drop-weight impact with a 2kg steel impactor. Initial impact studies were conducted in air and then repeated for submersed conditions underwater. Experimental results are compared for all tests with numerical solutions and are found to be in good agreement. For underwater impact, the numerical model incorporates the use of a Eulerian formulation for the water with a coupled fluid-structure interaction algorithm. The effect of the water surrounding the target plates was found to reduce the peak accelerations and also reduce the overall impact duration when compared to the same impacts in air. X-Ray imagery of the composite plates also showed visibly reduced damage for the submersed test specimens. This research provides data on the impact response of metallic and composite materials, and validates numerical methodologies for use in future work on fluid-structure interactions which show strong potential for relevant industrial applications

    Evidence that the 36kb plasmid of Brachyspira hyodysenteriae contributes to virulence

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    Swine dysentery (SD) results from infection of the porcine large intestine with the anaerobic intestinal spirochaete Brachyspira hyodysenteriae. Recently the genome of virulent Australian B. hyodysenteriae strain WA1 was sequenced, and a 36. kilobase (kb) circular plasmid was identified. The plasmid contained 31 genes including six rfb genes that were predicted to be involved with rhamnose biosynthesis, and others associated with glycosylation. In the current study a set of PCRs was developed to amplify portions of nine of the plasmid genes. When used with DNA extracted from virulent strain B204, PCR products were generated, but no products were generated with DNA from avirulent strain A1. Analysis of the DNA using pulsed field gel electrophoresis (PFGE) identified a plasmid band in strains WA1 and B204, but not in strain A1. These results demonstrate that strain A1 does not contain the plasmid, and suggests that lack of the plasmid may explain why this strain is avirulent. To determine how commonly strains lacking plasmids occur, DNA was extracted from 264 Australian field isolates of B. hyodysenteriae and subjected to PCRs for three of the plasmid genes. Only one isolate (WA400) that lacked the plasmid was identified, and this absence was confirmed by PFGE analysis of DNA from the isolate and further PCR testing. To assess its virulence, 24 pigs were experimentally challenged with cultures of WA400, and 12 control pigs were challenged with virulent strain WA1 under the same conditions. Significantly fewer (P= 0.03) of the pigs challenged with WA400 became colonised and developed SD (13/24; 54%) compared to the pigs infected with WA1 (11/12; 92%). Gross lesions in the pigs colonised with WA400 tended to be less extensive than those in pigs colonised with WA1, although there were no obvious differences at the microscopic level. The results support the likelihood that plasmid-encoded genes of B. hyodysenteriae are involved in colonisation and/or disease expression

    Potential for rabies control through dog vaccination in wildlife-abundant communities of Tanzania

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    Canine vaccination has been successful in controlling rabies in diverse settings worldwide. However, concerns remain that coverage levels which have previously been sufficient might be insufficient in systems where transmission occurs both between and within populations of domestic dogs and other carnivores. To evaluate the effectiveness of vaccination targeted at domestic dogs when wildlife also contributes to transmission, we applied a next-generation matrix model based on contract tracing data from the Ngorongoro and Serengeti Districts in northwest Tanzania. We calculated corresponding values of R0, and determined, for policy purposes, the probabilities that various annual vaccination targets would control the disease, taking into account the empirical uncertainty in our field data. We found that transition rate estimates and corresponding probabilities of vaccination-based control indicate that rabies transmission in this region is driven by transmission within domestic dogs. Different patterns of rabies transmission between the two districts exist, with wildlife playing a more important part in Ngorongoro and leading to higher recommended coverage levels in that district. Nonetheless, our findings indicate that an annual dog vaccination campaign achieving the WHO-recommended target of 70% will control rabies in both districts with a high level of certainty. Our results support the feasibility of controlling rabies in Tanzania through dog vaccination

    Estimated Returns from Farms of Large, Medium and Small Size of Business in the Spring Wheat Areas of South Dakota

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    Size of farm business is recognized by all farm management investigators and by many farmers as one of the most important factors making for success or failure in farming. A moderately large size of business, doubtless is more profitable in so-called normal times than is a small sized business. Size of business in this circular is not measured in acres only, as is common in certain sections where most of the land is fertile and tillable, and most of the farms are of the same type. Size of business cannot be measured accurately, nor by a single descriptive term such as acres. It includes the area farmed the area in crop land, the amount of productive labor employed, the amount of capital used, the rate of turnover of capital, the total production and the quality of production. Size of business may be increased by employing a laborer for productive work, by increasing the numbers of livestock, by increasing yields per acre, by doing work for hire outside the farm, etc. The purpose of this circular is to discuss the relative profitableness of a selected type of farm when operated as a business of different sizes. In the discussion six hypothetical farms are used for illustration. In the first group of three, a diversified farm, which is farmed rather intensively, is shown as a business of large size, of medium size, and of small size. The same plan is used for presenting the second group, a diversified farm which is farmed rather extensively

    Estimated Returns from Operating 800 acres in the Spring Wheat Area Under Four Different Plans - A Method of Determining What to Produce

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    The relatively low prices farmers receive for their products, and the continued high costs of interest, taxes, and the products farmers buy, increase the need of study of factors which tend to give the best possible net returns from a farm business. The purpose of this circular is to discuss the relative profitableness of different enterprises on diversified farms in the Spring Wheat Area of South Dakota. The plan of the circular is to show the organization and to give the estimated returns of four farms, on each of which the enterprises are of different relative importance. Three of the farms are assumed to be 800 acres in area. The fourth farm is assumed to be 800 acres in area but the size of business is increased by placing cattle out on pasture during the summer, a practice common to the area. Each of the hypothetical farms is very similar to someone actual farm from which records were secured. These similarities include acres of crops, numbers of livestock, amounts of power and equipment used, labor used, receipts and expenses, and income. The farms selected as patterns are common types within the area

    Tractor and Horse Power in the Wheat Area of South Dakota

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    A study of farm operations and farm management was made on 48 farms in Potter county during 1930, through the method of accounts kept daily by farm operators, assisted at regular monthly intervals by a resident field agent. During 1931 thirty other farmers within the spring wheat area of the state kept records of their tractors; and a survey by visits to farmers in the same area was made in 1931 and 1932, in which additional information about tractor and horse uses, performances, and costs was secured. The results of the Potter county study are being published as preliminary reports, of which this is the second. A part of the information secured during 1931 and 1932 is included in this report for the purpose of giving more reliable standards of performance of horses and tractors. The purpose of the report is to make available information which will aid farmers in deciding under what circumstances it is the more economical to use tractors or horses or a combination of both

    Indebtedness on 48 Potter County Farms, 1930

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    A study of farm operations and farm management was made on 48 farms in Potter County, South Dakota during 1930, through the method of accounts kept by the farm operators, assisted at regular monthly intervals by a resident field man. The study was made by the Department of Agricultural Economics of the South Dakota Agricultural Experiment station. The results of the study will be published first as preliminary reports, each dealing with only one or a few phases of the study. Data supporting certain statements is omitted in this report for want of space, but in most cases will be published in later reports. This, the first report, deals with indebtedness, one of the most important problems in farm management at present. Its chief objective is to make available information that will aid farmers in financing their business in the best manner

    An Economic Study of Farms in the Spring Wheat Area of South Dakota

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    This is the first of a series of three circulars being published as progress reports of a five year study which was begun in 1930, on the economics of agriculture in the Spring Wheat Area of South Dakota. The study was started as a modified cost route in Potter County with 48 farmer cooperators keeping records, some of which were quite complete in that labor and feed records were also kept. During the first year a representative of the college lived at Gettysburg and visited the cooperators at least once each month to check on the completeness of the records and to secure additional information concerning crop and livestock practices. After the first year the project was made cooperative with the Division of Farm Management and Costs of the Bureau of Agricultural Economics, United States Department of Agriculture, and was enlarged to include 150 farmer cooperators living in seven counties of the Spring Wheat Area. Figure 1. Since 1930 the cooperators have been visited three or four times each year. The statements of this publication are based on data collected from a total of 283 records. Satisfactory records were secured from 44 cooperators in 1930, 29 in 1931, 112 in 1932, and 98 in 1933

    A comparison of center of pressure variables recorded during running in barefoot, minimalist footwear, and traditional running shoes in the female population

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    In recent years, barefoot running and running in minimalist footwear as opposed to running in traditional running shoes has increased in popularity. The influence of such footwear choices on center of pressure (COP) displacements and velocity variables linked to injuries is yet to be understood. The aim of this study was to investigate differences between COP variables, linked to injuries measured in barefoot running, a minimalist running shoe, and with traditional running shoes and conditions during running in a healthy female population. Seventeen healthy female participants were examined. Participants performed five footfalls in each footwear condition while running at 12km/h±10% over a pressure plate while COP variables were recorded at 500Hz. The results suggest that minimalist running shoe COP characteristics were similar to those of barefoot runners, with various significant differences reported in both groups compared to runners with the traditional running shoe
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