1,510 research outputs found
Measurements of HO2 chemical kinetics with a new detection method
Research for the period from December 1, 1985 to May 31, 1986 is discussed, i.e., the reaction rate constant of HO2+O3 has been measured with a discharge-flow-tube apparatus. The HO2 radical was detected by the OH(A-X) photofragment emission produced from photodissociative excitation of HO2 at 147 nm. In the meantime, the optical emissions produced by the vacuum ultraviolet excitation of chemical species in the flow tube were investigated and used to examine the possibility for their interference with the HO2 detection. The research results are summarized below
Quantitative studies for photoabsorption and fluorescence of HCl
Photoabsorption and fluorescence cross sections of HCl are investigated in the wavelength region between 105 to 220 nm. The oscillator strengths of discrete structures at wavelengths shorter than 130 nm are measured
OH(A-X) fluorescence from photodissociative excitation of HO2 at 157.5 nm
The OH(A-X) fluorescence from photodissociative excitation of HO2 by F2 laser photons (157.5 nm) was observed and compared with the OH fluorescence spectra of H2O2 and the O2+CH3OH mixture. The rotational population distributions of OH(A) were obtained from the fluorescence spectra. The most populated levels are J = 4 for photodissociative excitation of HO2, J = 20 for H2O2, and J = 21 for the O2+CH3OH mixture. The fluorescence from the gas mixture is attributed to the O + H recombination for which the atoms are produced from photodissociation of parent molecules
Influence of Random Internal Fields on the Tunneling of OH Defects in NaCl Crystals
Alkali halide crystals doped with certain impurity ions show a low
temperature behaviour, which differs significantly from that of pure crystals.
The origin of these characteristic differences are tunneling centers formed by
atomic or molecular impurity ions. We have investigated the dielectric
susceptibility of hydroxyl ions in NaCl crystals at very low concentrations
(below 30 ppm), where interactions are believed to be negligible. We find that
the temperature dependence of the susceptibility is noticeably different from
what one would expect for isolated defects in a symmetric environment. We
propose that the origin of these deviations are random internal strains arising
from imperfections of the host crystal. We will present the experimental data
and a theoretical model which allows a quantitative understanding on a
microscopic basis.Comment: 3 pages 3 figures, REVTeX, submitted to the proceedings of the
PHONONS 2001 conferenc
Can Geometric Test Probe the Cosmic Equation of State ?
Feasibility of the geometric test as a probe of the cosmic equation of state
of the dark energy is discussed assuming the future 2dF QSO sample. We examine
sensitivity of the QSO two-point correlation functions, which are theoretically
computed incorporating the light-cone effect and the redshift distortions, as
well as the nonlinear effect, to a bias model whose evolution is
phenomenologically parameterized. It is shown that the correlation functions
are sensitive on a mean amplitude of the bias and not to the speed of the
redshift evolution. We will also demonstrate that an optimistic geometric test
could suffer from confusion that a signal from the cosmological model can be
confused with that from a stochastic character of the bias.Comment: 11 pages, including 3 figures, accepted for publication in ApJ
Where Are the Baryons? II: Feedback Effects
Numerical simulations of the intergalactic medium have shown that at the
present epoch a significant fraction (40-50%) of the baryonic component should
be found in the (T~10^6K) Warm-Hot Intergalactic Medium (WHIM) - with several
recent observational lines of evidence indicating the validity of the
prediction. We here recompute the evolution of the WHIM with the following
major improvements: (1) galactic superwind feedback processes from galaxy/star
formation are explicitly included; (2) major metal species (O V to O IX) are
computed explicitly in a non-equilibrium way; (3) mass and spatial dynamic
ranges are larger by a factor of 8 and 2, respectively, than in our previous
simulations. Here are the major findings: (1) galactic superwinds have dramatic
effects, increasing the WHIM mass fraction by about 20%, primarily through
heating up warm gas near galaxies with density 10^{1.5}-10^4 times the mean
density. (2) the fraction of baryons in WHIM is increased modestly from the
earlier work but is ~40-50%. (3) the gas density of the WHIM is broadly peaked
at a density 10-20 times the mean density, ranging from underdense regions to
regions that are overdense by 10^3-10^4. (4) the median metallicity of the WHIM
is 0.18 Zsun for oxygen with 50% and 90% intervals being (0.040,0.38) and
(0.0017,0.83).Comment: 44 pages, 17 figures, high res version at
http://www.astro.princeton.edu/~cen/baryonII.ps.g
The Gravitational Lensing in Redshift-space Correlation Functions of Galaxies and Quasars
The gravitational lensing, as well as the velocity field and the cosmological
light-cone warp, changes the observed correlation function of high-redshift
objects. We present an analytical expression of 3D correlation function,
simultaneously including those three effects. When two objects are separated
over several hundreds Mpc along a line of sight, the observed correlation
function is dominated by the effect of gravitational lensing rather than the
intrinsic clustering. For a canonical lambda-CDM model, the lensing signals in
the galaxy-galaxy and galaxy-QSO correlations are beyond noise levels in
large-scale redshift surveys like the Sloan Digital Sky Survey.Comment: 10 pages, 1 figure, submitted to ApJ
Imaging Simulations of the Sunyaev-Zel'dovich Effect for ALMA
We present imaging simulations of the Sunyaev-Zel'dovich effect of galaxy
clusters for the Atacama Large Millimeter/submillimeter Array (ALMA) including
the Atacama Compact Array (ACA). In its most compact configuration at 90GHz,
ALMA will resolve the intracluster medium with an effective angular resolution
of 5 arcsec. It will provide a unique probe of shock fronts and relativistic
electrons produced during cluster mergers at high redshifts, that are hard to
spatially resolve by current and near-future X-ray detectors. Quality of image
reconstruction is poor with the 12m array alone but improved significantly by
adding ACA; expected sensitivity of the 12m array based on the thermal noise is
not valid for the Sunyaev-Zel'dovich effect mapping unless accompanied by an
ACA observation of at least equal duration. The observations above 100 GHz will
become excessively time-consuming owing to the narrower beam size and the
higher system temperature. On the other hand, significant improvement of the
observing efficiency is expected once Band 1 is implemented in the future.Comment: 16 pages, 12 figures. Accepted for publication in PASJ. Note added in
proof is include
Self-trapped states and the related luminescence in PbCl crystals
We have comprehensively investigated localized states of photoinduced
electron-hole pairs with electron-spin-resonance technique and
photoluminescence (PL) in a wide temperature range of 5-200 K. At low
temperatures below 70 K, holes localize on Pb ions and form
self-trapping hole centers of Pb. The holes transfer to other trapping
centers above 70 K. On the other hand, electrons localize on two Pb ions
at higher than 50 K and form self-trapping electron centers of Pb.
From the thermal stability of the localized states and PL, we clarify that
blue-green PL band at 2.50 eV is closely related to the self-trapped holes.Comment: 8 pages (10 figures), ReVTEX; removal of one figure, Fig. 3 in the
version
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