18,427 research outputs found
AMPHIBIAN DISTRIBUTION IN THE GEORGIA SEA ISLANDS: IMPLICATIONS FROM THE PAST AND FOR THE FUTURE
We summarized amphibian distributions for 12 coastal islands in Georgia, USA. Occurrence among islands was correlated with life history traits, habitats, island size, distance to other islands, and island geological age. Speciesâ distributions were determined from published literature. Island sizes and vegetation types were derived from 2011 Georgia Department of Natural Resources habitat maps, which included both federal and state vegetation classification systems. Species occurring on more islands tended to have greater total reproductive output (i.e., life span >4 years, and annual egg production >1,000 eggs) and adults had tolerance of brackish environs. Larger islands had greatÂer area of freshwater wetlands, predominantly short hydroperiod (<6 months). Species tied to long hydroperiod wetlands (>6 months) were more restricted in their distribution across islands. Overall, larger islands supported more species, but the correlation was weaker for geologically younger HoÂlocene islands (age <11,000 years). While Euclidean distance between islands does not necessarily preclude inter-island dispersal, inhospitable habitat for amphibians (brackish tidal marshes and creeks interspersed with wide rivers) suggests that inter-island dispersal is very limited. The paucity of recent occurrence data for amphibians in this dynamic coastal region, let alone standardized annual moniÂtoring data, hinders efforts to model speciesâ vulnerability in a region susceptible to sea level rise and development pressure. The most common survey method, standardized amphibian vocal surveys, will detect Anuran reproductive efforts, but is unlikely to ascertain if breeding was successful or to detect salamanders. While it will not replace actual population data, consideration of critical life-history traits and breeding habitat availability can be used to direct management to support long-term species perÂsistence in changing environs. Even common amphibians in coastal conservation areas of Georgia are vulnerable to increasing population isolation caused by unsuitable habitat
Synthesis of calculational methods for design and analysis of radiation shields for nuclear rocket systems
Eight computer programs make up a nine volume synthesis containing two design methods for nuclear rocket radiation shields. The first design method is appropriate for parametric and preliminary studies, while the second accomplishes the verification of a final nuclear rocket reactor design
Discovery of kilogauss magnetic fields in three DA white dwarfs
We have detected longitudinal magnetic fields between 2 and 4 kG in three (WD
0446790, WD 1105048, WD 2359434) out of a sample of 12 normal DA white
dwarfs by using optical spectropolarimetry done with the VLT Antu 8 m telescope
equipped with FORS1. With the exception of 40 Eri B (4 kG) these are the first
positive detections of magnetic fields in white dwarfs below 30 kG. Although
suspected, it was not clear whether a significant fraction of white dwarfs
contain magnetic fields at this level. These fields may be explained as fossil
relics from magnetic fields in the main-sequence progenitors considerably
enhanced by magnetic flux conservation during the shrinkage of the core. A
detection rate of 25 % (3/12) may indicate now for the first time that a
substantial fraction of white dwarfs have a weak magnetic field. This result,
if confirmed by future observations, would form a cornerstone for our
understanding on the evolution of stellar magnetic fields.
Keywords: stars: white dwarfs - stars: magnetic fields - stars: individual:
WD0446-790, WD1105-048, WD2359-434Comment: 15 pages, 7 figures, Astronomy and Astrophysics, in pres
Phase-resolved far-ultraviolet HST spectroscopy of the peculiar magnetic white dwarf RE J0317-853
We present phase resolved FUV HST FOS spectra of the rapidly rotating, highly
magnetic white dwarf RE J0317-853. Using these data, we construct a new model
for the magnetic field morphology across the stellar surface. From an expansion
into spherical harmonics, we find the range of magnetic field strengths present
is 180-800MG. For the first time we could identify an absorption feature
present at certain phases at 1160A as a ``forbidden'' 1s_0 -> 2s_0 component,
due to the combined presence of an electric and magnetic field.Comment: 15 pages including 4 figures. Accepted for publication in ApJ Letter
Debating a testosterone "sex gap"
Sex dimorphism of testosterone (T) in elite athletes was at the center of a recent case at the "Supreme Court of Sport", the Court of Arbitration for Sport in Switzerland, after teenage Indian sprinter Dutee Chand challenged a sports policy regulating competition eligibility of women with naturally high T. The idea of a "sex gap" in T is a cornerstone of this policy (1). Policymakers infer that men's higher T is the "one factor [that] makes a decisive difference" between men's and women's athletic performances (2) âso they claim that women with naturally high T unfairly enjoy a "massive androgenic advantage" over other women athletes (2). Yet there's an emerging scientific debate about whether the sex gap in T applies to elite athletes
An astronomical search for evidence of new physics: Limits on gravity-induced birefringence from the magnetic white dwarf RE J0317-853
The coupling of the electromagnetic field directly with gravitational gauge
fields leads to new physical effects that can be tested using astronomical
data. Here we consider a particular case for closer scrutiny, a specific
nonminimal coupling of torsion to electromagnetism, which enters into a
metric-affine geometry of space-time. We show that under the assumption of this
nonminimal coupling, spacetime is birefringent in the presence of such a
gravitational field. This leads to the depolarization of light emitted from
extended astrophysical sources. We use polarimetric data of the magnetic white
dwarf to set strong constraints on the essential coupling
constant for this effect, giving k^2 \lsim (19 {m})^2 .Comment: Statements about Moffat's NGT modified. Accepted for publication in
Phys.Rev.
Investigation of a laser Doppler velocimeter system to measure the flow field around a large scale V/STOL aircraft in ground effect
The flow field measured around a hovering 70 percent scale vertical takeoff and landing (V/STOL) aircraft model is described. The velocity measurements were conducted with a ground based laser Doppler velocimeter. The remote sensing instrumentation and experimental tests of the velocity surveys are discussed. The distribution of vertical velocity in the fan jet and fountain; the radial velocity in the wall jet and the horizontal velocity along the aircraft underside are presented for different engine rpms and aircraft height above ground. Results show that it is feasible to use a mobile laser Doppler velocimeter to measure the flow field generated by a large scale V/STOL aircraft operating in ground effect
Orbital Characteristics of the Subdwarf-B and F V Star Binary EC~20117-4014(=V4640 Sgr)
Among the competing evolution theories for subdwarf-B (sdB) stars is the
binary evolution scenario. EC~20117-4014 (=V4640~Sgr) is a spectroscopic binary
system consisting of a pulsating sdB star and a late F main-sequence companion
(O'Donoghue et al. 1997), however the period and the orbit semi-major axes have
not been precisely determined. This paper presents orbital characteristics of
the EC 20117-4014 binary system using 20 years of photometric data. Periodic
Observed minus Calculated (O-C) variations were detected in the two highest
amplitude pulsations identified in the EC 20117-4014 power spectrum, indicating
the binary system's precise orbital period (P = 792.3 days) and the
light-travel time amplitude (A = 468.9 s). This binary shows no significant
orbital eccentricity and the upper limit of the eccentricity is 0.025 (using 3
as an upper limit). This upper limit of the eccentricity is the lowest
among all wide sdB binaries with known orbital parameters. This analysis
indicated that the sdB is likely to have lost its hydrogen envelope through
stable Roche lobe overflow, thus supporting hypotheses for the origin of sdB
stars. In addition to those results, the underlying pulsation period change
obtained from the photometric data was = 5.4 (0.7)
d d, which shows that the sdB is just before the end of the
core helium-burning phase
A Meta-Analysis of Procedures to Change Implicit Measures
Using a novel technique known as network meta-analysis, we synthesized evidence from 492 studies (87,418 participants) to investigate the effectiveness of procedures in changing implicit measures, which we define as response biases on implicit tasks. We also evaluated these proceduresâ effects on explicit and behavioral measures. We found that implicit measures can be changed, but effects are often relatively weak (|ds| \u3c .30). Most studies focused on producing short-term changes with brief, single-session manipulations. Procedures that associate sets of concepts, invoke goals or motivations, or tax mental resources changed implicit measures the most, whereas procedures that induced threat, affirmation, or specific moods/emotions changed implicit measures the least. Bias tests suggested that implicit effects could be inflated relative to their true population values. Procedures changed explicit measures less consistently and to a smaller degree than implicit measures and generally produced trivial changes in behavior. Finally, changes in implicit measures did not mediate changes in explicit measures or behavior. Our findings suggest that changes in implicit measures are possible, but those changes do not necessarily translate into changes in explicit measures or behavior
A 150MG magnetic white dwarf in the cataclysmic variable RX J1554.2+2721
We report the detection of Zeeman-split Lalpha absorption pi and sigma+ lines
in the far-ultraviolet Hubble Space Telescope/Space Telescope Imaging
Spectrograph spectrum of the magnetic cataclysmic variable RX J1554.2+2721.
Fitting the STIS data with magnetic white dwarf model spectra, we derive a
field strength of B~144MG and an effective temperature of 17000K<Teff<23000K.
This measurement makes RX J1554.2+2721 only the third cataclysmic variable
containing a white dwarf with a field exceeding 100MG. Similar to the other
high-field polar AR UMa, RX J1554.2+2721 is often found in a state of feeble
mass transfer, which suggests that a considerable number of high-field polars
may still remain undiscovered.Comment: 4 pages, accepted for ApJ Letter
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