833 research outputs found
Compilation of detection sensitivities in thermal-neutron activation
Detection sensitivities of the chemical elements following thermal-neutron activation have been compiled from the available experimental cross sections and nuclear properties and presented in a concise and usable form. The report also includes the equations and nuclear parameters used in the calculations
Portable, high intensity isotopic neutron source provides increased experimental accuracy
Small portable, high intensity isotopic neutron source combines twelve curium-americium beryllium sources. This high intensity of neutrons, with a flux which slowly decreases at a known rate, provides for increased experimental accuracy
The spectroscopic evolution of the symbiotic star AG Draconis. I.The O VI Raman, Balmer, and helium emission line variations during the outburst of 2006-2008
AG Dra is one of a small group of low metallicity S-type symbiotic binaries
with K-type giants that undergoes occasional short-term outbursts of unknown
origin. Our aim is to study the behavior of the white dwarf during an outburst
using the optical Raman lines and other emission features in the red giant
wind. The goal is to determine changes in the envelope and the wind of the
gainer in this system during a major outburst event and to study the coupling
between the UV and optical during a major outburst. Using medium and high
resolution groundbased optical spectra and comparisons with archival and
spectra, we study the evolution of the Raman O VI features and the
Balmer, He I, and He II lines during the outburst from 2006 Sept. through 2007
May and include more recent observations (2009) to study the subsequent
evolution of the source. The O VI Raman features disappeared completely at the
peak of the major outburst and the subsequent variation differs substantially
from that reported during the previous decade. The He I and He II lines, and
the Balmer lines, vary in phase with the Raman features but there is a
double-valuedness to the He I 6678, 7065 relative to the O VI Raman 6825\AA\
variations in the period between 2006-2008 that has not been previously
reported. The variations in the Raman feature ratio through the outburst
interval are consistent with the disappearance of the O VI FUV resonance wind
lines from the white dwarf and of the surrounding O ionized region
within the red giant wind provoked by the expansion and cooling of the white
dwarf photosphere.Comment: 10 pages, 15 figs. A&A (in press, accepted for publication
23/11/2009
Multiwalled carbon nanotube: Luttinger liquid or not?
We have measured IV-curves of multiwalled carbon nanotubes using end
contacts. At low voltages, the tunneling conductance obeys non-Ohmic power law,
which is predicted both by the Luttinger liquid and the
environment-quantum-fluctuation theories. However, at higher voltages we
observe a crossover to Ohm's law with a Coulomb-blockade offset, which agrees
with the environment-quantum-fluctuation theory, but cannot be explained by the
Luttinger-liquid theory. From the high-voltage tunneling conductance we
determine the transmission line parameters of the nanotubes.Comment: RevTeX, 4 pages, 2 EPS-figures, submitted to Phys. Rev. Let
Effect of quantum noise on Coulomb blockade in normal tunnel junctions at high voltages
We have investigated asymptotic behavior of normal tunnel junctions at
voltages where even the best ohmic environments start to look like RC
transmission lines. In the experiments, this is manifested by an exceedingly
slow approach to the linear behavior above the Coulomb gap. As expected on the
basis of the quantum theory taking into account interaction with the
environmental modes, better fits are obtained using 1/sqrt{V}- than 1/V-
dependence for the asymptote. These results agree with the horizon picture if
the frequency-dependent phase velocity is employed instead of the speed of
light in order to determine the extent of the surroundings seen by the
junction.Comment: 9 pages, 4 figures, submitted to Phys. Rev.
The spectroscopic evolution of the symbiotic-like recurrent nova V407 Cygni during its 2010 outburst. I. The shock and its evolution
On 2010 Mar 10, V407 Cyg was discovered in outburst, eventually reaching V< 8
and detected by Fermi. Using medium and high resolution ground-based optical
spectra, visual and Swift UV photometry, and Swift X-ray spectrophotometry, we
describe the behavior of the high-velocity profile evolution for this nova
during its first three months. The peak of the X-ray emission occurred at about
day 40 with a broad maximum and decline after day 50. The main changes in the
optical spectrum began at around that time. The He II 4686A line first appeared
between days 7 and 14 and initially displayed a broad, symmetric profile that
is characteristic of all species before day 60. Low-excitation lines remained
comparatively narrow, with v(rad,max) of order 200-400 km/s. They were
systematically more symmetric than lines such as [Ca V], [Fe VII], [Fe X], and
He II, all of which showed a sequence of profile changes going from symmetric
to a blue wing similar to that of the low ionization species but with a red
wing extended to as high as 600 km/s . The Na I D doublet developed a broad
component with similar velocity width to the other low-ionization species. The
O VI Raman features were not detected. We interpret these variations as
aspherical expansion of the ejecta within the Mira wind. The blue side is from
the shock penetrating into the wind while the red wing is from the low-density
periphery. The maximum radial velocities obey power laws, v(rad,max) t^{-n}
with n ~ 1/3 for red wing and ~0.8 for the blue. (truncated)Comment: Accepted for publication, A&A (submitted: 9 Oct 2010; accepted: 1 Dec
2010) in press; based on data obtained with Swift, Nordic Optical Telescope,
Ondrejov Observatory. Corrected typo, Fermi?LAT detection was at energies
above 100 MeV (with thanks to C. C. Cheung
The rhodium, silver and indium content of some chondritic meteorites
By neutron activation analysis the rhodium, silver and indium content of five chondritic meteorites has been determined. The average data are 0.186 and 0.094 p.p.m. for rhodium and silver. The upper limit for the indium content is 0.001 p.p.m. The values for rhodium and silver are in fair agreement with the data estimated by and ; the indium values, however, are lower by a factor of 100 or more.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/32432/1/0000514.pd
High Mass Triple Systems: The Classical Cepheid Y Car
We have obtained an HST STIS ultraviolet high dispersion Echelle mode
spectrum the binary companion of the double mode classical Cepheid Y Car. The
velocity measured for the hot companion from this spectrum is very different
from reasonable predictions for binary motion, implying that the companion is
itself a short period binary. The measured velocity changed by 7 km/ s during
the 4 days between two segments of the observation confirming this
interpretation. We summarize "binary" Cepheids which are in fact members of
triple system and find at least 44% are triples. The summary of information on
Cepheids with orbits makes it likely that the fraction is under-estimated.Comment: accepted by A
Tunneling between two Luttinger liquids with long range interaction
The non linear charge transfer through a tunnel junction between two
Luttinger systems is studied for repulsive, finite range interaction between
electrons on the same, V_{11}, and on different,V_{12}, sides of the junction.
Features of the Coulomb blockade effect are observed if V_{12}=0. We predict a
novel interaction induced enhancement of the current if V_{12}>0. When
V_{12}=V_{11}, the current is suppressed at small bias, but the ``charging
energy'', obtained from the asymptotic behavior at high bias voltage, vanishes.Comment: 4 pages, RevTeX, to be published in Physical Review B (Brief Report
Re II and Other Exotic Spectra in HD 65949
Powerful astronomical spectra reveal an urgent need for additional work on
atomic lines, levels, and oscillator strengths. The star HD 65949 provides some
excellent examples of species rarely identified in stellar spectra. For
example, the Re II spectrum is well developed, with 17 lines between 3731 and
4904 [A], attributed wholly or partially to Re II. Classifications and
oscillator strengths are lacking for a number of these lines. The spectrum of
Os II is well identified. Of 14 lines attributed wholly or partially to Os II,
only one has an entry in the VALD database. We find strong evidence that Te II
is present. There are NO Te II lines in the VALD database. Ru II is clearly
present, but oscillator strengths for lines in the visual are lacking. There is
excellent to marginal evidence for a number of less commonly identified
species, including Kr II, Nb II, Sb II, Xe II, Pr III, Ho III, Au II, and Pt II
(probably Pt-198), to be present in the spectrum of HD 65949. The line Hg II at
3984 [A] is of outstanding strength, and all three lines of Multiplet 1 of Hg I
are present, even though the surface temperature of HD 65949 is relatively
high. Finally, we present the case of an unidentified, 24 [mA], line at 3859.63
[A], which could be the same feature seen in magnetic CP stars. It is typically
blended with a putative U II line used in cosmochronology.Comment: ASOS9 Poster (Lund, Sweden, August 2007), to be published in Journal
of Physics: Conference Series (JPCS), 6 pages 1 figur
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