4,630 research outputs found
HI and OH absorption in the lensing galaxy of MG J0414+0534
We report the detection of \HI 21-cm absorption in the early-type
lensing galaxy towards MG J0414+0534 with the Green Bank Telescope. The
absorption, with total , is resolved into two strong components, probably due to the two
strongest lens components, which are separated by 0.4\arcsec. Unlike the other
three lenses which have been detected in \HI, J0414+0534 does not exhibit
strong OH absorption, giving a OH/\HI column density ratio of N_{\rm
OH}/N_{\rm HI}\lapp10^{-6} (for K, K and
). This underabundance of molecular gas may indicate
that the extreme optical--near-IR colour () along the line-of-sight
is not due to the lens. We therefore suggest that despite the strong upper
limits on molecular absorption at the quasar redshift, as traced by millimetre
lines, the extinction occurs primarily in the quasar host galaxy.Comment: Accepted by MNRAS Letters, 5 (and a bit) pages, 5 figure
High-dimensional quantum dynamics of adsorption and desorption of H at Cu(111)
We performed high-dimensional quantum dynamical calculations of the
dissociative adsorption and associative desorption of hydrogen on Cu(111). The
potential energy surface (PES) is obtained from density functional theory
calculations. Two regimes of dynamics are found, at low energies sticking is
determined by the minimum energy barrier, at high energies by the distribution
of barrier heights. Experimental results are well-reproduced qualitatively, but
some quantitative discrepancies are identified as well.Comment: 4 two column pages, revtex, 4 figures, to appear in Phys. Rev. Let
Elastic and thermodynamic properties of the shape-memory alloy AuZn
The current work reports on the elastic shear moduli, internal friction, and
the specific heat of the B2 cubic ordered alloy AuZn as a function of
temperature. Measurements were made on single-crystal and polycrystalline
samples using Resonant Ultrasound Spectroscopy (RUS), semi-adiabatic
calorimetry and stress-strain measurements. Our results confirm that this alloy
exhibits the shape-memory effect and a phase transition at 64.75 K that appears
to be continuous (second-order) from the specific heat data. It is argued that
the combination of equiatomic composition and a low transformation temperature
constrain the chemical potential and its derivatives to exhibit behavior that
lies at the borderline between that of a first-order (discontinuous) and a
continuous phase transition. The acoustic dissipation does not peak at the
transtion temperature as expected, but shows a maximum well into the
low-temperature phase. The Debye temeprature value of 219 K, obtained from the
low-temperature specific heat data is in favorable agreement with that
determined from the acoustic data (207 K) above the transition.Comment: 25 pages, 6 figures, submitted to Phys. Rev.
A Laboratory for Constraining Cosmic Evolution of the Fine Structure Constant: Conjugate 18 cm OH Lines Toward PKS 1413+135 at z=0.2467
We report the detection of the satellite 18 cm OH lines at 1612 and 1720 MHz
in the z=0.2467 molecular absorption system toward the radio source PKS
1413+135. The two OH lines are conjugate; the 1612 MHz line is seen in
absorption while the 1720 MHz line is seen in weak maser emission of equal, but
negative, optical depth. We do not detect the main 18 cm OH lines at 1667 and
1665 MHz down to 1.1 mJy rms in 4.0 km/s channels. The detected and undetected
18 cm OH lines support a scenario of radiatively pumped stimulated absorption
and emission with pumping dominated by the intraladder 119 micron line of OH,
suggesting a column density N(OH) ~= 10^15 to 10^16 cm^-2. Combined with
simultaneous HI 21 cm observations and published CO data, we apply the OH
redshifts to measurements of cosmic evolution of the fine structure constant
alpha = e^2/(hbar c). We obtain highly significant (~25 sigma) velocity offsets
between the OH and HI lines and the OH and CO lines, but measurements of
alpha-independent systematics demonstrate that the observed velocity
differences are entirely attributable to physical velocity offsets between
species rather than a change in alpha. The OH alone, in which conjugate line
profiles guarantee that both lines originate in the same molecular gas,
provides a weak constraint of Delta alpha/alpha_o = (+0.51 +/- 1.26) x 10^-5 at
z=0.2467. Higher frequency OH line detections can provide a larger lever arm on
Delta alpha and can increase precision by an order of magnitude. The OH
molecule can thus provide precise measurements of the cosmic evolution of alpha
that include quantitative constraints on systematic errors. Application of this
technique is limited only by the detectability of |tau|~0.01 OH lines toward
radio continuum sources and may be possible to z~5.Comment: AASTeX, 11 pages, 2 figures, accepted by Astrophysical Journa
Volume contraction at the Jahn-Teller transition of LaMnO
We have studied the volume collapse of LaMnO at the Jahn- Teller (JT)
transition temperature T=750 K which has recently been found in high
temperature powder x- ray and neutron diffraction experiments. We construct a
model Hamiltonian involving the pseudospin of Mn e states, the
staggered JT distortion and the volume strain coordinate. We show that the
anharmonic coupling between these primary and secondary order parameters leads
to the first order JT phase transition associated with a comparatively large
reduction of the unit cell volume of V/V 10. We explain
the temperature dependence of JT distortions and volume strain and discuss the
volume change as function of the anharmonic coupling constant. A continuous
change to a second order transition as function of model parameters is
obtained. This behaviour is also observed under Ba doping.Comment: 5 pages, 4 figure
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