20,682 research outputs found
Herpetofaunal Inventories of the National Parks of South Florida and the Caribbean: Volume III. Big Cypress National Preserve
Amphibian declines and extinctions have been documented around the world, often in protected
natural areas. Concern for this trend has prompted the U.S. Geological Survey and the National Park
Service to document all species of amphibians that occur within U.S. National Parks and to search for any
signs that amphibians may be declining. This study, an inventory of amphibian species in Big Cypress
National Preserve, was conducted from 2002 to 2003. The goals of the project were to create a
georeferenced inventory of amphibian species, use new analytical techniques to estimate proportion of
sites occupied by each species, look for any signs of amphibian decline (missing species, disease, die-offs,
and so forth.), and to establish a protocol that could be used for future monitoring efforts.
Several sampling methods were used to accomplish these goals. Visual encounter surveys and
anuran vocalization surveys were conducted in all habitats throughout the park to estimate the proportion
of sites or proportion of area occupied (PAO) by each amphibian species in each habitat. Opportunistic
collections, as well as limited drift fence data, were used to augment the visual encounter methods for
highly aquatic or cryptic species. A total of 545 visits to 104 sites were conducted for standard sampling
alone, and 2,358 individual amphibians and 374 reptiles were encountered. Data analysis was conducted
in program PRESENCE to provide PAO estimates for each of the anuran species.
All of the amphibian species historically found in Big Cypress National Preserve were detected
during this project. At least one individual of each of the four salamander species was captured during
sampling. Each of the anuran species in the preserve was adequately sampled using standard
herpetological sampling methods, and PAO estimates were produced for each species of anuran by habitat.
This information serves as an indicator of habitat associations of the species and relative abundance of
sites occupied, but it will also be useful as a comparative baseline for future monitoring efforts.
In addition to sampling for amphibians, all encounters with reptiles were documented. The
sampling methods used for detecting amphibians are also appropriate for many reptile species. These
reptile locations are included in this report, but the number of reptile observations was not sufficient to
estimate PAO for reptile species. We encountered 35 of the 46 species of reptiles believed to be present in
Big Cypress National Preserve during this study, and evidence exists of the presence of four other reptile
species in the Preserve.
This study found no evidence of amphibian decline in Big Cypress National Preserve. Although no
evidence of decline was observed, several threats to amphibians were identified. Introduced species,
especially the Cuban treefrog (Osteopilus septentrionalis), are predators and competitors with several
native frog species. The recreational use of off-road vehicles has the potential to affect some amphibian
populations, and a study on those potential impacts is currently underway. Also, interference by humans
with the natural hydrologic cycle of south Florida has the potential to alter the amphibian community.
Continued monitoring of the amphibian species in Big Cypress National Preserve is recommended.
The methods used in this study were adequate to produce reliable estimates of the proportion of sites
occupied by most anuran species, and are a cost-effective means of determining the status of their
populations
Vortices in self-gravitating disks
Vortices are believed to greatly help the formation of km sized planetesimals
by collecting dust particles in their centers. However, vortex dynamics is
commonly studied in non-self-gravitating disks. The main goal here is to
examine the effects of disk self-gravity on the vortex dynamics via numerical
simulations. In the self-gravitating case, when quasi-steady gravitoturbulent
state is reached, vortices appear as transient structures undergoing recurring
phases of formation, growth to sizes comparable to a local Jeans scale, and
eventual shearing and destruction due to gravitational instability. Each phase
lasts over 2-3 orbital periods. Vortices and density waves appear to be coupled
implying that, in general, one should consider both vortex and density wave
modes for a proper understanding of self-gravitating disk dynamics. Our results
imply that given such an irregular and rapidly changing, transient character of
vortex evolution in self-gravitating disks it may be difficult for such
vortices to effectively trap dust particles in their centers that is a
necessary process towards planet formation.Comment: to appear in the proceedings of Cool Stars, Stellar Systems and The
Sun, 15th Cambridge Workshop, St. Andrews, Scotland, July 21-25, 200
Modem design for a MOBILESAT terminal
The implementation is described of a programmable digital signal processor based system, designed for use as a test bed in the development of a digital modem, codec, and channel simulator. Code was written to configure the system as a 5600 bps or 6600 bps QPSK modem. The test bed is currently being used in an experiment to evaluate the performance of digital speech over shadowed channels in the Australian mobile satellite (MOBILESAT) project
The role of the energy equation in the fragmentation of protostellar discs during stellar encounters
In this paper, we use high-resolution smoothed particle hydrodynamics (SPH)
simulations to investigate the response of a marginally stable self-gravitating
protostellar disc to a close parabolic encounter with a companion discless
star. Our main aim is to test whether close brown dwarfs or massive planets can
form out of the fragmentation of such discs. We follow the thermal evolution of
the disc by including the effects of heating due to compression and shocks and
a simple prescription for cooling and find results that contrast with previous
isothermal simulations. In the present case we find that fragmentation is
inhibited by the interaction, due to the strong effect of tidal heating, which
results in a strong stabilization of the disc. A similar behaviour was also
previously observed in other simulations involving discs in binary systems. As
in the case of isolated discs, it appears that the condition for fragmentation
ultimately depends on the cooling rate.Comment: 9 pages, 10 figures, accepted in MNRA
Semi-Phenomenological Analysis of Dynamics of Nonlinear Excitations in One-Dimensional Electron-Phonon System
The structure of moving nonlinear excitations in one-dimensional
electron-phonon systems is studied semi-phenomenologically by using an
effective action in which the width of the nonlinear excitation is treated as a
dynamical variable. The effective action can be derived from Su, Schrieffer and
Heeger's model or its continuum version proposed by Takayama, Lin-Liu and Maki
with an assumption that the nonlinear excitation moves uniformly without any
deformation except the change of its width. The form of the action is
essentially the same as that discussed by Bishop and coworkers in studying the
dynamics of the soliton in polyacetylene, though some details are different.
For the moving excitation with a velocity , the width is determined by
minimizing the effective action. A requirement that there must be a minimum in
the action as a function of its width provides a maximum velocity. The velocity
dependence of the width and energy can be determined. The motions of a soliton
in p olyacetylene and an acoustic polaron in polydiacetylene are studied within
this formulation. The obtained results are in good agreement with those of
numerical simulations.Comment: 19 pages, LaTeX, 7 Postscript figures, to be published in J. Phys.
Soc. Jpn. vol.65 (1996) No.
The influence of chiral surface states on the London penetration depth in SrRuO
The London penetration depth for the unconventional superconductor
SrRuO is analyzed assuming an order parameter which breaks time
reversal symmetry and parity simultaneously. Such a superconducting state
possesses chiral quasiparticle states with subgap energies at the surface. We
show that these subgap states can give a significant contribution to the
low-temperature behavior of the London penetration depth yielding a
power-law even though bulk quasiparticle spectrum is gapped. The presence of
several electron bands gives rise to interband transition among the subgap
surface states and influences the properties of the surface impedance.
Furthermore, the surface states lead also to a non-linear Meissner effect.Comment: 4 pages, 1 figure, the definition of the Nambu field operator
introduced, and some typos correcte
Sea turtle nesting in the Ten Thousand Islands of Florida
Loggerhead sea turtles (Caretta caretta) nest in numerous substrate and beach
types within the Ten Thousand Islands (TTl) of southwest Florida. Nesting beach
selection was analyzed on 12 islands within this archipelago. Numerous physical
characteristics were recorded to identify the relatedness of these variables and determine
their importance for nesting beach selection in C. caretta. These variables were chosen
after evaluating the islands, conducting literature searches and soliciting personal
communications. Along transects, data were collected, on the following: height of
canopy, beach width, overall slope (beach slope and slope of offshore approach) and sand
samples analyzed for pH, percentage of water, percentage of organic content, percentage
of carbonate and particle size (8 size classes). Data on ordinal aspect of beaches and
beach length were also recorded and included in the analysis. All of the variables were
analyzed by tree regression, incorporating the nesting data into the analysis. In the TTl,
loggerheads appear to prefer wider beaches (p< 0.001; R2
= 0.56) that inherently have less
slope, and secondarily, wider beaches that have low amounts of carbonate (p< O.00 1). In
addition, C. caretta favors nest sites within or in close proximity to the supra-littoral
vegetation zone of beaches in the TTl (p< 0.001). (86 page document
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