In an expanding universe, what doesn't expand?

The expansion of the universe is often viewed as a uniform stretching of space that would affect compact objects, atoms and stars, as well as the separation of galaxies. One usually hears that bound systems do not take part in the general expansion, but a much more subtle question is whether bound systems expand partially. In this paper, a very definitive answer is given for a very simple system: a classical "atom" bound by electrical attraction. With a mathemical description appropriate for undergraduate physics majors, we show that this bound system either completely follows the cosmological expansion, or -- after initial transients -- completely ignores it. This "all or nothing" behavior can be understood with techniques of junior-level mechanics. Lastly, the simple description is shown to be a justifiable approximation of the relativistically correct formulation of the problem.Comment: 8 pages, 9 eps figure

Studies on the Crustacea of the Turks and Caicos Islands, British West Indies. V. Records of Mysids from Pine Cay, Fort George Cay, Water Cay, and Adjacent Waters

Only 2 species of mysids, Heteromysis spottei and Stygiomysis clarkei, have been previously reported from the Turks and Caicos Islands. Between 1988 and 1990, 21 species of mysids were collected from reef (to 38 m) and shallow non-reef habitats surrounding Pine Cay, Fort George Cay, and Water Cay, Turks and Caicos Islands. One species collected, Anchialina typica, is distributed throughout tropical and subtropical seas. Twelve species (Bowmaniella johnsoni, Dioptromysis paucispinosa, Heteromysis bermudensis, H. guitarti, H. mayana, Mysidium columbiae, M. gracile, M. integrum, Mysidopsis bispinulata, M. brattstromei, Parvimysis bahamensis, and Siriella chierchiae) are widely distributed throughout the subtropical and tropical waters of the Northwest Atlantic. Five species (Amathimysis serrata, A. torleivi, Heteromysis coralina, Mysidopsis mathewsoni, and Siriella chessi) are reported for only the second or third time. Three undescribed species are recognized: 2 species of Amathimysis associated with either gorgonians on reefs or grass beds and a species of Heteromysis collected from sponges on deeper reefs

The periodic standing-wave approximation: eigenspectral computations for linear gravity and nonlinear toy models

The periodic standing wave approach to binary inspiral assumes rigid rotation of gravitational fields and hence helically symmetric solutions. To exploit the symmetry, numerical computations must solve for ``helical scalars,'' fields that are functions only of corotating coordinates, the labels on the helical Killing trajectories. Here we present the formalism for describing linearized general relativity in terms of helical scalars and we present solutions to the mixed partial differential equations of the linearized gravity problem (and to a toy nonlinear problem) using the adapted coordinates and numerical techniques previously developed for scalar periodic standing wave computations. We argue that the formalism developed may suffice for periodic standing wave computations for post-Minkowskian computations and for full general relativity.Comment: 21 pages, 10 figures, RevTe

A taxonomic guide to the mysids of the South Atlantic Bight.

Following the examination of extensive collections from the National Museum of Natural History (NMNH), the Southeastern Regional Taxonomic Center (SERTC), and other regional institutions, 18 species of the family Mysidae are recognized and described from the South Atlantic Bight (Cape Lookout, North Carolina to Cape Canaveral, Florida). This report includes synonymies of previous records, as well as new species distribution records. Previous regional accounts of Metamysidopsis munda and Metamysidopsis mexicana are attributed to Metamysidopsis swifti. New regional records are established for Amathimysis brattegardi, Heteromysis beetoni, and Siriella thompsonii. Two other species tentatively identified as Amathimysis sp. (nr. serrata) and Mysidopsis sp. (cf. mortenseni) may represent new taxa. Neobathymysis renoculata is included and discussed as a potential regional species. An illustrated key to the species currently known from the South Atlantic Bight is presented. Relevant taxonomic, distributional, and ecological information is also included for each species. (PDF file contains 45 pages.

Cerebrospinal Fluid Concentrations of the Synaptic Marker Neurogranin in Neuro-HIV and Other Neurological Disorders.

Purpose of reviewThe aim of this study was to examine the synaptic biomarker neurogranin in cerebrospinal fluid (CSF) in different stages of HIV infection and in relation to what is known about CSF neurogranin in other neurodegenerative diseases.Recent findingsCSF concentrations of neurogranin are increased in Alzheimer's disease, but not in other neurodegenerative disorder such as Parkinson's disease, frontotemporal dementia, and Lewy body dementia. Adults with HIV-associated dementia have been found to have decreased levels of neurogranin in the frontal cortex, which at least to some extent, may be mediated by the proinflammatory cytokines IL-1β and IL-8. CSF neurogranin concentrations were in the same range for all groups of HIV-infected individuals and uninfected controls. This either indicates that synaptic injury is not an important part of HIV neuropathogenesis or that CSF neurogranin is not sensitive to the type of synaptic impairment present in HIV-associated neurocognitive disorders

The periodic standing-wave approximation: post-Minkowski computation

The periodic standing wave method studies circular orbits of compact objects coupled to helically symmetric standing wave gravitational fields. From this solution an approximation is extracted for the strong field, slowly inspiralling motion of black holes and binary stars. Previous work on this model has dealt with nonlinear scalar models, and with linearized general relativity. Here we present the results of the method for the post-Minkowski (PM) approximation to general relativity, the first step beyond linearized gravity. We compute the PM approximation in two ways: first, via the standard approach of computing linearized gravitational fields and constructing from them quadratic driving sources for second-order fields, and second, by solving the second-order equations as an ``exact'' nonlinear system. The results of these computations have two distinct applications: (i) The computational infrastructure for the ``exact'' PM solution will be directly applicable to full general relativity. (ii) The results will allow us to begin supplying initial data to collaborators running general relativistic evolution codes.Comment: 19 pages, 3 figures, 1 table, RevTe

Design of Pneumatic Diffuser System

During non-generation periods, leakage through the wicket gates of a hydroturbine often results in very poor quality water (low or zero dissolved oxygen) in the tailrace of the hydropower facility. Generally, the leakage rate is relatively small, usually about 5-10 cfs per turbine. A bottom-mounted diffuser system was designed based on laboratory-measured and manufacturer-supplied specifications about the gas transfer characteristics of the bubble plume generated by an 11- inch flexible head diffuser. The design criteria and the overall effectiveness of the system were evaluated in field tests at Lake Eufaula, Oklahoma. The analysis of field data is reported herein

Crustacea of the Cayman Islands, British West Indies. I. Records of Mysids from Shallow Water Non-Reef Habitats

A single species of mysid Siriella chierchiae has been previously reported from the Cayman Islands. However, between May 1995 and August 1999, 20 species of mysids were collected from shallow water non-reef habitats surrounding Grand Cayman and Little Cayman Islands. Of the species collected, one species Anchialina typica has a cosmopolitan distribution in tropical and subtropical seas. Thirteen species (Amathimysis cherados, A. gibba, Bowmaniella johnsoni, Dioptromysis paucispinosa, Heteromysis bermudensis, H. mayana, Mysidium columbiae, M. gracile, M. integrum, Mysidopsis bispinulata, M. brattstromi, Parvimysis bahamensis, Siriella chierchiae) are found widely distributed throughout the subtropical and tropical waters of the Northwest Atlantic. Four species (Heteromysis coralina, Mysidopsis mathewsoni, Siriella chessi, S. macrophthalma) previously known only from their type localities are reported, and two undescribed species of Heteromysis, one from Little Cayman Island, and one from Grand Cayman Island, are recognized