Modeling microscopic swimmers at low Reynolds number

We employ three numerical methods to explore the motion of low Reynolds number swimmers, modeling the hydrodynamic interactions by means of the Oseen tensor approximation, lattice Boltzmann simulations and multiparticle collision dynamics. By applying the methods to a three bead linear swimmer, for which exact results are known, we are able to compare and assess the effectiveness of the different approaches. We then propose a new class of low Reynolds number swimmers, generalized three bead swimmers that can change both the length of their arms and the angle between them. Hence we suggest a design for a microstructure capable of moving in three dimensions. We discuss multiple bead, linear microstructures and show that they are highly efficient swimmers. We then turn to consider the swimming motion of elastic filaments. Using multiparticle collision dynamics we show that a driven filament behaves in a qualitatively similar way to the micron-scale swimming device recently demonstrated by Dreyfus et al.Comment: 12 pages, 10 figure

Pasture Improvement Costs and Returns

Much of Iowa\u27s permanent pasture is declining in productivity because of overgrazing, inroads made by brush and other factors. An unimproved pasture like that at right provides poor growth of desirable grasses and legumes and permits weeds to grow instead

The Case for Participatory Evaluation

Participatory evaluation is presented as an extension of the stakeholder-based model with a focus on enhancing evaluation utilization through primary users’ increased depth and range of participation in the applied research process. The approach is briefly described and then justified from theoretical and empirical bases. The literature on organizational learning provides theoretical support for participatory evaluation stemming primarily from the view that knowledge is socially constructed and cognitive systems and memories are developed and shared by organization members. Twenty-six recent empirical studies were found to support an organizational learning justification of the model. Studies were classified into one of six emergent categories: conceptions of use; effects of participation on the use of research; effects of participation on the use of disseminated knowledge; effects of research training; school-university partnerships; and internal evaluation. Requirements of organizations and evaluators and an agenda for research are discussed

Raising Dairy Calves

The average age at which the dairy cow In the United States either dies, Is butchered, becomes a non·breeder, or for some other reason ceases to be a producer, Is six years. To many this figure may appear low, for cows are sometimes productive at ten or twelve years and even at fifteen or sixteen years and older. These cases of exceptlonal longevity are notable and they appear to be numerous, but the number of cows which die previous to th~lr sixth year Is far greater. Studies of many herds, of both grades and purebreds, under all conditions, thruout the country, confirm the statement that the productive life of the average cow terminates when she 111 six years old. Dairy heifers become producers when two years old and thus their average production period continues for four years. There are In this country approximately 24,000,000 dairy cows; one-fourth, or 6,000,000, drop out of production each year and must he replaced. It Is safe to assume that 18,000,000 calves are born annually; probably one·half of them are bulls and from the remaining 9,000,000 heifer calves must come the two·year old heifers to replace the 6,000,000 discarded cows

Comparative study of design: application to Engineering Design

A recent exploratory study examines design processes across domains and compares them. This is achieved through a series of interdisciplinary, participative workshops. A systematic framework is used to collect data from expert witnesses who are practising designers across domains from engineering through architecture to product design and fashion, including film production, pharmaceutical drugs, food, packaging, graphics and multimedia and software. Similarities and differences across domains are described which indicate the types of comparative analysis we have been able to do from our data. The paper goes further and speculates on possible lessons for selected areas of engineering design which can be drawn from comparison with processes in other domains. As such this comparative design study offers the potential for improving engineering design processes. More generally it is a first step in creating a discipline of comparative design which aims to provide a new rich picture of design processes

Hubble Space Telescope Planetary Camera Images of NGC 1316

We present HST Planetary Camera V and I~band images of the central region of the peculiar giant elliptical galaxy NGC 1316. The inner profile is well fit by a nonisothermal core model with a core radius of 0.41" +/- 0.02" (34 pc). At an assumed distance of 16.9 Mpc, the deprojected luminosity density reaches \sim 2.0 \times 10^3 L_{\sun} pc$^{-3}$. Outside the inner two or three arcseconds, a constant mass-to-light ratio of $\sim 2.2 \pm 0.2$ is found to fit the observed line width measurements. The line width measurements of the center indicate the existence of either a central dark object of mass 2 \times 10^9 M_{\sun}, an increase in the stellar mass-to-light ratio by at least a factor of two for the inner few arcseconds, or perhaps increasing radial orbit anisotropy towards the center. The mass-to-light ratio run in the center of NGC 1316 resembles that of many other giant ellipticals, some of which are known from other evidence to harbor central massive dark objects (MDO's). We also examine twenty globular clusters associated with NGC 1316 and report their brightnesses, colors, and limits on tidal radii. The brightest cluster has a luminosity of 9.9 \times 10^6 L_{\sun} ($M_V = -12.7$), and the faintest detectable cluster has a luminosity of 2.4 \times 10^5 L_{\sun} ($M_V = -8.6$). The globular clusters are just barely resolved, but their core radii are too small to be measured. The tidal radii in this region appear to be $\le$ 35 pc. Although this galaxy seems to have undergone a substantial merger in the recent past, young globular clusters are not detected.Comment: 21 pages, latex, postscript figures available at ftp://delphi.umd.edu/pub/outgoing/eshaya/fornax

Economic efficiency in pasture production and improvement in southern Iowa

Pasture crops provide an important source of income on most Corn Belt farms. On some farms of the Corn Belt, such as in southern Iowa, resources are such that income depends largely or entirely on pastures for livestock production. On these farms, earnings and the level of living of farm families may be raised measurably through better pasture improvement and management. Research in the last few decades has led to discoveries which many persons think can greatly increase returns from pasture crops. New grass and legume species and varieties have appeared which out yield older ones; they are hardier and better adapted to the weather conditions of the area. Techniques of production have been developed which increase yields and reduce risks and costs of pasture production. Farm magazines, newspapers, the extension services of state colleges, and various state and federal agencies have encouraged more widespread adoption of improved pasture practices. Many persons see, in the improved practices, an opportunity for expanding pasture acreage without reducing income

Optimum allocation of resources between pasture improvement and other opportunities on southern Iowa farms

Pasture land represents an important portion of the total land in southern Iowa. One opportunity for increasing resource productivity and farm incomes in this part of the state is to invest capital in pasture improvement. Experiments show that capital invested in pasture improvement and renovation, and the livestock to utilize the increased forage production, can greatly increase the value of products produced on land unadapted to continuous cropping; yields of forage and livestock products can be increased as much as threefold. However, the practices of improving and renovating pastures are proceeding at a slow rate. One reason suggested is capital limitations. Most farmers operate with limited funds. Accordingly, if they are to make greatest profits, they must use each dollar, acre and labor hour where it will bring the greatest return. The question is not so much whether pasture improvement and renovation is profitable; but whether it is more profitable than alternative uses of scarce capital and labor. For example, pasture improvement may cost $5 per year and return$8 In the same period. It is profitable in this sense: Each $1 In costs returns$1.60 in sales. However, if the same $1 invested in fertilizer for crops or in hogs returns$1.80, pasture improvement should not be included in the farming plan until these more profitable opportunities have been fully exploited. It should, of course, be included before other investments which return less than $1.60