1,862 research outputs found
Research and development of cells with bellows controlled electrolyte levels Final progress report, May 11, 1965 - Apr. 1, 1966
Control of electrolyte level in sealed Ni-Cd and Ag-Cd cells with bellows actio
Research and development on cells with bellows controlled electrolyte levels progress report no. 3, dec. 10, 1964 - may 10, 1965
Control of electrolyte level in nickel-cadmium cells with metal and plastic bellow
Speech Communication
Contains research objectives and reports on three research projects.U. S. Air Force (Electronics Systems Division) under Contract AF 19(628)-5661National Institutes of Health (Grant 2 RO1 NB-04332-06)Joint Services Electronics Programs (U. S. Army, U.S. Navy, and U. S. Air Force) under Contract DA 28-043-AMC-02536(E
Magnetic and Metal-Insulator Transitions in beta-Na0.5CoO2 and gamma-K0.5CoO2 -NMR and Neutron Diffraction Studies-
Co-oxides beta-Na0.5CoO2 and gamma-K0.5CoO2 have been prepared by the Na
de-intercalation from alpha-NaCoO2 and by the floating-zone method,
respectively. It has been found that successive phase transitions take place at
temperatures Tc1 and Tc2 in both systems. The appearance of the internal
magnetic field at Tc1 with decreasing temperature T indicates that the
antiferromagnetic order exists at T < Tc1, as in gamma-Na0.5CoO2. For
beta-Na0.5CoO2, the transition temperatures and the NMR parameters determined
from the data taken for magnetically ordered state are similar to those of
gamma-Na0.5CoO2, indicating that the difference of the stacking ways of the
CoO2 layers between these systems do not significantly affect their physical
properties. For gamma-K0.5CoO2, the quantitative difference of the physical
quantities are found from those of beta- and gamma-Na0.5CoO2. The difference
between the values of Tci (i = 1 and 2) of these systems might be explained by
considering the distance between CoO2 layers.Comment: 8 pages, 14 figures, 1 Tabl
Characterization of the hot Neptune GJ 436b with Spitzer and ground-based observations
We present Spitzer Space Telescope infrared photometry of a secondary eclipse
of the hot Neptune GJ436b. The observations were obtained using the 8-micron
band of the InfraRed Array Camera (IRAC). The data spanning the predicted time
of secondary eclipse show a clear flux decrement with the expected shape and
duration. The observed eclipse depth of 0.58 mmag allows us to estimate a
blackbody brightness temperature of T_p = 717 +- 35 K at 8 microns. We compare
this infrared flux measurement to a model of the planetary thermal emission,
and show that this model reproduces properly the observed flux decrement. The
timing of the secondary eclipse confirms the non-zero orbital eccentricity of
the planet, while also increasing its precision (e = 0.14 +- 0.01). Additional
new spectroscopic and photometric observations allow us to estimate the
rotational period of the star and to assess the potential presence of another
planet.Comment: Accepted for publication in A&A on 11/09/2007; 7 pages, 6 figure
The Exemplar T8 Subdwarf Companion of Wolf 1130
We have discovered a wide separation (188.5") T8 subdwarf companion to the
sdM1.5+WD binary Wolf 1130. Companionship of WISE J200520.38+542433.9 is
verified through common proper motion over a ~3 year baseline. Wolf 1130 is
located 15.83 +/- 0.96 parsecs from the Sun, placing the brown dwarf at a
projected separation of ~3000 AU. Near-infrared colors and medium resolution
(R~2000-4000) spectroscopy establish the uniqueness of this system as a
high-gravity, low-metallicity benchmark. Although there are a number of
low-metallicity T dwarfs in the literature, WISE J200520.38+542433.9 has the
most extreme inferred metallicity to date with [Fe/H] = -0.64 +/- 0.17 based on
Wolf 1130. Model comparisons to this exemplar late-type subdwarf support it
having an old age, a low metallicity, and a small radius. However, the
spectroscopic peculiarities of WISE J200520.38+542433.9 underscore the
importance of developing the low-metallicity parameter space of the most
current atmospheric models.Comment: Accepted to ApJ on 05 September 2013; 33 pages in preprint format, 8
figures, 3 table
Detecting Planets Around Very Low Mass Stars with the Radial Velocity Method
The detection of planets around very low-mass stars with the radial velocity
method is hampered by the fact that these stars are very faint at optical
wavelengths where the most high-precision spectrometers operate. We investigate
the precision that can be achieved in radial velocity measurements of low mass
stars in the near infrared (nIR) Y-, J-, and H-bands, and we compare it to the
precision achievable in the optical. For early-M stars, radial velocity
measurements in the nIR offer no or only marginal advantage in comparison to
optical measurements. Although they emit more flux in the nIR, the richness of
spectral features in the optical outweighs the flux difference. We find that
nIR measurement can be as precise than optical measurements in stars of
spectral type ~M4, and from there the nIR gains in precision towards cooler
objects. We studied potential calibration strategies in the nIR finding that a
stable spectrograph with a ThAr calibration can offer enough wavelength
stability for m/s precision. Furthermore, we simulate the wavelength-dependent
influence of activity (cool spots) on radial velocity measurements from optical
to nIR wavelengths. Our spot simulations reveal that the radial velocity jitter
does not decrease as dramatically towards longer wavelengths as often thought.
The jitter strongly depends on the details of the spots, i.e., on spot
temperature and the spectral appearance of the spot. Forthcoming nIR
spectrographs will allow the search for planets with a particular advantage in
mid- and late-M stars. Activity will remain an issue, but simultaneous
observations at optical and nIR wavelengths can provide strong constraints on
spot properties in active stars.Comment: accepted by ApJ, v2 accepted revision with new precision
calculations, abstract abride
Larval dispersal in a changing ocean with an emphasis on upwelling regions
Dispersal of benthic species in the sea is mediated primarily through small, vulnerable larvae that must survive minutes to months as members of the plankton community while being transported by strong, dynamic currents. As climate change alters ocean conditions, the dispersal of these larvae will be affected, with pervasive ecological and evolutionary consequences. We review the impacts of oceanic changes on larval transport, physiology, and behavior. We then discuss the implications for population connectivity and recruitment and evaluate life history strategies that will affect susceptibility to the effects of climate change on their dispersal patterns, with implications for understanding selective regimes in a future ocean. We find that physical oceanographic changes will impact dispersal by transporting larvae in different directions or inhibiting their movements while changing environmental factors, such as temperature, pH, salinity, oxygen, ultraviolet radiation, and turbidity, will affect the survival of larvae and alter their behavior. Reduced dispersal distance may make local adaptation more likely in well-connected populations with high genetic variation while reduced dispersal success will lower recruitment with implications for fishery stocks. Increased dispersal may spur adaptation by increasing genetic diversity among previously disconnected populations as well as increasing the likelihood of range expansions. We hypothesize that species with planktotrophic (feeding), calcifying, or weakly swimming larvae with specialized adult habitats will be most affected by climate change. We also propose that the adaptive value of retentive larval behaviors may decrease where transport trajectories follow changing climate envelopes and increase where transport trajectories drive larvae toward increasingly unsuitable conditions. Our holistic framework, combined with knowledge of regional ocean conditions and larval traits, can be used to produce powerful predictions of expected impacts on larval dispersal as well as the consequences for connectivity, range expansion, or recruitment. Based on our findings, we recommend that future studies take a holistic view of dispersal incorporating biological and oceanographic impacts of climate change rather than solely focusing on oceanography or physiology. Genetic and paleontological techniques can be used to examine evolutionary impacts of altered dispersal in a future ocean, while museum collections and expedition records can inform modern-day range shifts
A T8.5 Brown Dwarf Member of the Xi Ursae Majoris System
The Wide-field Infrared Survey Explorer has revealed a T8.5 brown dwarf (WISE
J111838.70+312537.9) that exhibits common proper motion with a
solar-neighborhood (8 pc) quadruple star system - Xi Ursae Majoris. The angular
separation is 8.5 arc-min, and the projected physical separation is about 4000
AU. The sub-solar metallicity and low chromospheric activity of Xi UMa A argue
that the system has an age of at least 2 Gyr. The infrared luminosity and color
of the brown dwarf suggests the mass of this companion ranges between 14 and 38
Jupiter masses for system ages of 2 and 8 Gyr respectively.Comment: AJ in press, 12 pages LaTeX with 6 figures. More astrometric data and
a laser guide star adaptive optics image adde
The First Ultra-cool Brown Dwarf Discovered by the Wide-field Infrared Survey Explorer
We report the discovery of the first new ultra-cool brown dwarf (BDs) found with the Wide-field Infrared Survey
Explorer (WISE). The object’s preliminary designation is WISEPC J045853.90+643451.9. Follow-up spectroscopy
with the LUCIFER instrument on the Large Binocular Telescope indicates that it is a very late-type T dwarf with a
spectral type approximately equal to T9. Fits to an IRTF/SpeX 0.8–2.5 μm spectrum to the model atmospheres of
Marley and Saumon indicate an effective temperature of approximately 600 K as well as the presence of vertical
mixing in its atmosphere. The new BD is easily detected by WISE, with a signal-to-noise ratio of ~36 at 4.6 μm.
Current estimates place it at a distance of 6–10 pc. This object represents the first in what will likely be hundreds of
nearby BDs found by WISE that will be suitable for follow-up observations, including those with the James Webb
Space Telescope. One of the two primary scientific goals of the WISE mission is to find the coolest, closest stars to
our Sun; the discovery of this new BD proves that WISE is capable of fulfilling this objective
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