Edges and Diffractive Effects in Casimir Energies

The prototypical Casimir effect arises when a scalar field is confined between parallel Dirichlet boundaries. We study corrections to this when the boundaries themselves have apertures and edges. We consider several geometries: a single plate with a slit in it, perpendicular plates separated by a gap, and two parallel plates, one of which has a long slit of large width, related to the case of one plate being semi-infinite. We develop a general formalism for studying such problems, based on the wavefunctional for the field in the gap between the plates. This formalism leads to a lower dimensional theory defined on the open regions of the plates or boundaries. The Casimir energy is then given in terms of the determinant of the nonlocal differential operator which defines the lower dimensional theory. We develop perturbative methods for computing these determinants. Our results are in good agreement with known results based on Monte Carlo simulations. The method is well suited to isolating the diffractive contributions to the Casimir energy.Comment: 32 pages, LaTeX, 9 figures. v2: additional discussion of renormalization procedure, version to appear in PRD. v3: corrected a sign error in (70

Reproductive Biology of the Green Turtle (Chelonia mydas) at Tern Island, French Frigate Shoals, Hawai'i

We monitored nesting of the green turtle (Chelonia mydas Linnaeus) on Tern Island, French Frigate Shoals, in the Northwestern Hawaiian Islands from 1986 through 1991. Egg oviposition occurred between 26 April and 20 October. Nesting peaked between mid-June and early August. Hatchlings emerged between 8 July and 27 December. Hatchling emergence peaked between mid-August and early October. Mean incubation period was 66.0 (range 53-97) days. Mean clutch size was 92.4 (range 33-150) eggs. Mean hatching success was 78.6% when averaged over success of individual nests and 81.1% when calculated as percentage of total number of eggs. Natural hatchling emergence was 71.1 %, based on percentage of total number of eggs. Live and dead hatchlings were found when nests were excavated and accounted for 10.0% of the eggs. Incubation periods tended to be longer in early and late portions of the season than in midseason, and incubation periods tended to decrease the farther inland the nest was situated from the high tide line. Maximum hatching success occurred at an incubation length of 66.7 days. Other trends indicated that nesting peaked near 5 July when conditions produced a near optimal incubation period for yielding maximum hatching success

Climate Impacts on Agriculture: Implications for Forage and Rangeland Production

Projections of temperature and precipitation patterns across the United States during the next 50 yr anticipate a 1.5 to 2°C warming and a slight increase in precipitation as a result of global climate change. There have been relatively few studies of climate change effects on pasture and rangeland (grazingland) species compared to those on crop species, despite the economic and ecological importance of the former. Here we review the literature on responses of pastureland and rangeland species to rising atmospheric CO2 and climate change (temperature and precipitation) and discuss plant and management factors likely to influence pastureland and rangeland responses to change (e.g., community composition, plant competition, perennial growth habit, seasonal productivity, and management methods). Overall, the response of pastureland and rangeland species to increased [CO2] is consistent with the general responses of C3 and C4 vegetation, although exceptions exist. Both pastureland and rangeland species may experience accelerated metabolism and advanced development with rising temperature, often resulting in a longer growing season. However, soil resources will often constrain temperature effects. In general, it is expected that increases in [CO2] and precipitation will enhance rangeland net primary production (NPP) whereas increased air temperatures will either increase or decrease NPP. Much of the uncertainty in predicting how pastureland and rangeland species will respond to climate change is due to uncertainty in future projections of precipitation, both globally and regionally. This review reveals the need for comprehensive studies of climate change impacts on pastureland and rangeland ecosystems that include an assessment of the mediating effects of grazing regimes and mutualistic relationships (e.g., plant roots-nematodes; N-fixing organisms) as well as changes in water, carbon, and nutrient cycling

Large-Scale Cryogen Systems and Test Facilities

NASA has completed initial construction and verification testing of the Integrated Systems Test Facility (ISTF) Cryogenic Testbed. The ISTF is located at Complex 20 at Cape Canaveral Air Force Station, Florida. The remote and secure location is ideally suited for the following functions: (1) development testing of advanced cryogenic component technologies, (2) development testing of concepts and processes for entire ground support systems designed for servicing large launch vehicles, and (3) commercial sector testing of cryogenic- and energy-related products and systems. The ISTF Cryogenic Testbed consists of modular fluid distribution piping and storage tanks for liquid oxygen/nitrogen (56,000 gal) and liquid hydrogen (66,000 gal). Storage tanks for liquid methane (41,000 gal) and Rocket Propellant 1 (37,000 gal) are also specified for the facility. A state-of-the-art blast proof test command and control center provides capability for remote operation, video surveillance, and data recording for all test areas

Implications of invariance of the Hamiltonian under canonical transformations in phase space

We observe that, within the effective generating function formalism for the implementation of canonical transformations within wave mechanics, non-trivial canonical transformations which leave invariant the form of the Hamilton function of the classical analogue of a quantum system manifest themselves in an integral equation for its stationary state eigenfunctions. We restrict ourselves to that subclass of these dynamical symmetries for which the corresponding effective generating functions are necessaarily free of quantum corrections. We demonstrate that infinite families of such transformations exist for a variety of familiar conservative systems of one degree of freedom. We show how the geometry of the canonical transformations and the symmetry of the effective generating function can be exploited to pin down the precise form of the integral equations for stationary state eigenfunctions. We recover several integral equations found in the literature on standard special functions of mathematical physics. We end with a brief discussion (relevant to string theory) of the generalization to scalar field theories in 1+1 dimensions.Comment: REVTeX v3.1, 13 page