The suitability of various spacecraft for future space applications missions

The Space Applications Advisory Committee (SAAC) of NASA's Advisory Council was asked by the Associate Administrator for Space Science and Applications to consider the most suitable future means for accomplishing space application missions. To comply with this request, SAAC formed a Task Force whose report is contained in this document. In their considerations, the Task Force looked into the suitability of likely future spacecraft options for supporting various types of application mission payloads. These options encompass a permanent manned space station, the Space Shuttle operating in a sortie mode, unmanned platforms that integrate a wide variety of instruments or other devices, and smaller free fliers that accommodate at most a few functions. The Task Force also recognized that the various elements could be combined to form a larger space infrastructure. This report summarizes the results obtained by the Task Force. It describes the approach utilized, the findings and their analysis, and the conclusions

Measurements of Static and Total Pressure Throughout the Transonic Speed Range as Obtained from an Airspeed Head Mounted on a Freely Falling Body

No abstract availabl

Eigen modes for the problem of anomalous light transmission through subwavelength holes

We show that the wide-spread concept of optical eigen modes in lossless waveguide structures, which assumes the separation on propagating and evanescent modes, fails in the case of metal-dielectric structures, including photonic crystals. In addition to these modes, there is a sequence of new eigen-states with complex values of the propagation constant and non-vanishing circulating energy flow. The whole eigen-problem ceases to be hermitian because of changing sign of the optical dielectric constant. The new anomalous modes are shown to be of prime importance for the description of the anomalous light transmission through subwavelength holes.Comment: 5 pages, 4 figure

PHYLOGENY OF ACRIDOCARPUS-BRACHYLOPHON (MALPIGHIACEAE): IMPLICATIONS FOR TERTIARY TROPICAL FLORAS AND AFROASIAN BIOGEOGRAPHY

A major tenet of African Tertiary biogeography posits that lowland rainforest dominated much of Africa in the late Cretaceous and was replaced by xeric vegetation as a response to continental uplift and consequent widespread aridification beginning in the late Paleogene. The aridification of Africa is thought to have been a major factor in the extinction of many African humid-tropical lineages, and in the present-day disparity of species diversity between Africa and other tropical regions. This primarily geologically based model can be tested with independent phylogenetic evidence from widespread African plant groups containing both humid- and xeric-adapted species. We estimated the phylogeny and lineage divergence times within one such angiosperm group, the acridocarpoid clade (Malpighiaceae), with combined ITS, ndhF , and trnL-F data from 15 species that encompass the range of morphological and geographic variation within the group. Dispersal-vicariance analysis and divergence-time estimates suggest that the basal acridocarpoid divergence occurred between African and Southeast Asian lineages approximately 50 million years ago (mya), perhaps after a southward ancestral retreat from high-latitude tropical forests in response to intermittent Eocene cooling. Dispersion of Acridocarpus from Africa to Madagascar is inferred between approximately 50 and 35 mya, when lowland humid tropical forest was nearly continuous between these landmasses. A single dispersal event within Acridocarpus is inferred from western Africa to eastern Africa between approximately 23 and 17 mya, coincident with the widespread replacement of humid forests by savannas in eastern Africa. Although the spread of xeric environments resulted in the extinction of many African plant groups, our data suggest that for others it provided an opportunity for further diversification.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72798/1/j.0014-3820.2002.tb00165.x.pd

The benefits of organic farming for biodiversity

Previous studies suggest widespread positive responses of biodiversity to organic farming. Many of these studies, however, have been small-scale. This project tested the generality of habitat and biodiversity differences between matched pairs of organic and non-organic farms containing cereal crops in lowland England on a large-scale across a range of taxa including plants, insects, birds and bats. The extent of both cropped and un-cropped habitats together with their composition and management on a range of scales were also compared. Organic farms was likely to favour higher levels of biodiversity and indeed organic farms tended to support higher numbers of species and overall abundance across most taxa. However, the magnitude of the response differed strikingly; plants showed stronger and more consistent responses than other taxa. Some, but not all, differences in biodiversity between systems appear to be a consequence of differences in habitat quantity

Revised Relativistic Hydrodynamical Model for Neutron-Star Binaries

We report on numerical results from a revised hydrodynamic simulation of binary neutron-star orbits near merger. We find that the correction recently identified by Flanagan significantly reduces but does not eliminate the neutron-star compression effect. Although results of the revised simulations show that the compression is reduced for a given total orbital angular momentum, the inner most stable circular orbit moves to closer separation distances. At these closer orbits significant compression and even collapse is still possible prior to merger for a sufficiently soft EOS. The reduced compression in the corrected simulation is consistent with other recent studies of rigid irrotational binaries in quasiequilibrium in which the compression effect is observed to be small. Another significant effect of this correction is that the derived binary orbital frequencies are now in closer agreement with post-Newtonian expectations.Comment: Submitted to Phys. Rev.

Relativistic Charged Spheres II: Regularity and Stability

We present new results concerning the existence of static, electrically charged, perfect fluid spheres that have a regular interior and are arbitrarily close to a maximally charged black-hole state. These configurations are described by exact solutions of Einstein's field equations. A family of these solutions had already be found (de Felice et al., 1995) but here we generalize that result to cases with different charge distribution within the spheres and show, in an appropriate parameter space, that the set of such physically reasonable solutions has a non zero measure. We also perform a perturbation analysis and identify the solutions which are stable against adiabatic radial perturbations. We then suggest that the stable configurations can be considered as classic models of charged particles. Finally our results are used to show that a conjecture of Kristiansson et al. (1998) is incorrect.Comment: revtex, 13 pages. five EPS figures. Accepted by CQ