Dispersion of biased swimming microorganisms in a fluid flowing through a tube

Classical Taylor-Aris dispersion theory is extended to describe the transport of suspensions of self-propelled dipolar cells in a tubular flow. General expressions for the mean drift and effective diffusivity are determined exactly in terms of axial moments, and compared with an approximation a la Taylor. As in the Taylor-Aris case, the skewness of a finite distribution of biased swimming cells vanishes at long times. The general expressions can be applied to particular models of swimming microorganisms, and thus be used to predict swimming drift and diffusion in tubular bioreactors, and to elucidate competing unbounded swimming drift and diffusion descriptions. Here, specific examples are presented for gyrotactic swimming algae.Comment: 20 pages, 4 figures. Published version available at http://rspa.royalsocietypublishing.org/content/early/2010/02/09/rspa.2009.0606.short?rss=

Future scientific exploration of Taurus-Littrow

The Apollo 17 site was surveyed with great skill and the collected samples have been studied thoroughly (but not completely) in the 20 years since. Ironically, the success of the field and sample studies makes the site an excellent candidate for a return mission. Rather than solving all the problems, the Apollo 17 mission provided a set of sophisticated questions that can be answered only by returning to the site and exploring further. This paper addresses the major unsolved problems in lunar science and points out the units at the Apollo 17 site that are most suitable for addressing each problem. It then discusses how crucial data can be obtained by robotic rovers and human field work. I conclude that, in general, the most important information can be obtained only by human exploration. The paper ends with some guesses about what we could have learned at the Apollo 17 site from a fairly sophisticated rover capable of in situ analyses, instead of sending people

The lunar environment and its effect on optical astronomy

The Moon's geologic environment features: (1) gravity field one-sixth that of Earth; (2) sidereal rotation period of 27.3 days; (3) surface with greater curvature than Earth's surface (a chord along a 10 km baseline would have a bulge of 7.2 m); (4) seismically and tidally stable platform on which to make astronomical observations (most moonquakes have magnitudes of 1 to 2 on the Richter scale, within the earth's seismic noise, resulting in ground motions only 1 nm); (5) tenuous atmosphere (the total mass at night is only 10(exp 4) kg) that has an optical depth of 10(exp -6) and does not cause wind induced stresses and vibrations on structures; (6) large diurnal temperature variation (100 to 385 K in equatorial regions), which telescopes must be designed to withstand; (7) weak magnetic field, ranging from 3 to 330 x 10(exp -9) T, compared to 3 x 10(exp -5) T on Earth at the equator; (8) surface exposed to radiation, the most dangerous of which are high energy (1 to 100 Mev) particles resulting from solar flares; (9) high flux of micrometeorites which are not slowed down from their cosmic velocities because of the lack of air (data indicate that microcraters greater than 10 microns across will form at the rate of 3000/sq m/yr); (10) regolith 2 to 30 m thick which blankets the entire lunar surface (this layer is fine-grained (average grain sizes range from 40 to 268 microns), has a low density (800 to 1000 kg/cu m in the upper few mm, rising to 1500 to 1800 kg/cu m at depths of 10 to 20 cm), is porous (35 to 45 pct), cohesive (0.1 to 1.0 kN/sq m), and has a low thermal diffusivity (0.7 to 1.0 x 110-8 sq m/sec); about 29 pct of the regolith is less than 20 micron in size (this dust could pose a hazard to optical telescopes); (11) rubbly upper several hundred meters in which intact bedrock is uncommon, especially in the lunar highlands; and (12) craters with diameter-to-depth ratios of 5 if fresh and less than km across (larger and eroded craters have diameter-to-depth ratios greater than 5)

Geological considerations for lunar telescopes

The geological features of the Moon that may be advantageous for astronomical observations are listed and described. The Moon's geologic environment offers wondrous opportunities for astronomy and presents fascinating challenges for engineers designing telescope facilities on the lunar surface. The geologic nature of the stark lunar surface and the Moon's tenuous atmosphere are summarized. The Moon as a stable platform is described as is its atmosphere, surface temperatures, its magnetic field, its regolith, and its crater morphologies

Funding for voluntary sector infrastructure: a case study analysis

This paper outlines the policy context for grant-making to voluntary sector infrastructure organisations, and describes a qualitative research programme undertaken in the UK in which a detailed study of 20 such grants were investigated from multiple perspectives in terms of their perceived impact after the projects had finished. The grants were selected on tightly determined stratification criteria, from a large pool of grants for voluntary sector infrastructure work made by the Community Fund (one of the distributors of funds to “good causes” from the UK National Lottery). Particular emphasis was placed in the study on assessing the impact on other voluntary and community organisations likely to benefit from the support given to infrastructure organisations. The paper concludes that in general terms, grant-making for voluntary sector infrastructure is an effective way of supporting the voluntary and community sector more generally, although there are important lessons both for funders and for grant-recipients to improve the effectiveness of grant-making in this field