105,447 research outputs found
Color identification testing device
Testing device, which determines ability of a technician to identify color-coded electric wires, is superior to standard color blindness tests. It tests speed of wire selection, detects partial color blindness, allows rapid testing, and may be administered by a color blind person
Constraints to the Masses of Brown Dwarf Candidates from the Lithium Test
We present intermediate dispersion (0.7-2.2 \AA ~pix) optical
spectroscopic observations aimed at applying the ``Lithium Test'' to a sample
of ten brown dwarf candidates located in the general field, two in young open
clusters, and two in close binaries. We find evidence for strong Li depletion
in all of them, and thus infer lower mass limits of 0.065~M, depending
only slightly (0.005~M) on the interior models. None of the field
brown dwarf candidates in our sample appears to be a very young (age
~10~yr) substellar object. For one of the faintest proper motion
Pleiades members known (V=20.7) the Li test implies a mass greater than
0.08~M, and therefore it is not a brown dwarf. From our spectra
we estimate spectral types for some objects and present measurements of Halpha
emission strengths and radial velocities. Finally, we compare the positions in
the H-R diagram of our sample of brown dwarf candidates with the theoretical
region where Li is expected to be preserved (Substellar Lithium Region). We
find that certain combinations of temperature calibrations and evolutionary
tracks are consistent with the constraints imposed by the observed Li depletion
in brown dwarf candidates, while others are not.Comment: 20 pp.; 4 figs, available under request; plain LaTeX, ApJ in press,
OACatania-94-00
The effects of isometric work on heart rate, blood pressure, and net oxygen cost
Isometric exercise effects on heart rate, blood pressure, and net oxygen cos
Ages, Distances, and the Initial Mass Functions of Stellar Clusters
We provide a review of the current status of several topics on the ages,
distances, and mass functions of open clusters, with a particular emphasis on
illuminating the areas of uncertainty. Hipparcos has obtained parallaxes for
nearby open clusters that have expected accuracies much better than has been
previously achievable. By using the lithium depletion boundary method and
isochrone fitting based on much improved new theoretical evolutionary models
for low mass stars, it is arguable that we will soon have have much better age
scales for clusters and star-forming regions. With improved optical and near-IR
cameras, we are just now beginning to extend the mass function of open clusters
like the Pleiades into the regime below the hydrogen burning mass limit.
Meanwhile, observations in star-forming regions are in principle capable of
identifying objects down to of order 10 Jupiter masses.Comment: 13 pages, including 3 embedded figures (4 EPS files). To appear in
"11th Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun," ed. R.
J. Garcia Lopez, R. Rebolo, and M. R. Zapatero Osori
Recommended from our members
Free atmospheric CO2 enrichment increased above ground biomass but did not affect symbiotic N2-fixation and soil carbon dynamics in a mixed deciduous stand in Wales
Through increases in net primary production (NPP), elevated CO2 is hypothesizes to increase the amount of plant litter entering the soil. The fate of this extra carbon on the forest floor or in mineral soil is currently not clear. Moreover, increased rates of NPP can be maintained only if forests can escape nitrogen limitation. In a Free atmospheric CO2 Enrichment (FACE) experiment near Bangor, Wales, 4 ambient CO2 and 4 FACE plots were planted with patches of Betula pendula, Alnus glutinosa and Fagus sylvatica on a former arable field. Four years after establishment, only a shallow L forest floor litter layer had formed due to intensive bioturbation. Total soil C and N contents increased irrespective of treatment and species as a result of afforestation. We could not detect an additional C sink in the soil, nor were soil C stabilization processes affected by FACE. We observed a decrease of leaf N content in Betula and Alnus under FACE, while the soil C/N ratio decreased regardless of CO2 treatment. The ratio of N taken up from the soil and by N2-fixation in Alnus was not affected by FACE. We infer that increased nitrogen use efficiency is the mechanism by which increased NPP is sustained under elevated CO2 at this site
Turbulent Cooling Flows in Molecular Clouds
We propose that inward, subsonic flows arise from the local dissipation of
turbulent motions in molecular clouds. Such "turbulent cooling flows" may
account for recent observations of spatially extended inward motions towards
dense cores. These pressure-driven flows may arise from various types of
turbulence and dissipation mechanisms. For the example of MHD waves and
turbulence damped by ion-neutral friction, sustained cooling flow requires that
the outer gas be sufficiently turbulent, that the inner gas have marginal
field-neutral coupling, and that this coupling decrease sufficiently rapidly
with increasing density. These conditions are most likely met at the transition
between outer regions ionized primarily by UV photons and inner regions ionized
primarily by cosmic rays. If so, turbulent cooling flows can help form dense
cores, with speeds faster than expected for ambipolar diffusion. Such motions
could reduce the time needed for dense core formation and could precede and
enhance the motions of star-forming gravitational infall.Comment: To appear ApJL, Nov.10, 4 ApJ style pages, Postscrip
Welding of commercial base plates is investigated
Investigation of aluminum alloy welds reveals that the combinations of metallic elements with hydrogen are not capable of producing weld porosity themselves, rather they tend to increase the amount of porosity only in the presence of arc contamination by water vapor
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