265 research outputs found
Deuterium on Venus: Observations from Earth
In view of the importance of the deuterium-to-hydrogen ratio in understanding the evolutionary scenario of planetary atmospheres and its relationship to understanding the evolution of our own Earth, we undertook a series of observations designed to resolve previous observational conflicts. We observed the dark side of Venus in the 2.3 micron spectral region in search of both H2O and HDO, which would provide us with the D/H ratio in Venus' atmosphere. We identified a large number of molecular lines in the region, belonging to both molecules, and, using synthetic spectral techniques, obtained mixing ratios of 34 plus or minus 10 ppm and 1.3 plus or minus 0.2 ppm for H2O and HDO, respectively. These mixing ratios yield a D/H ratio for Venus of D/H equals 1.9 plus or minus 0.6 times 10 (exp 12) and 120 plus or minus 40 times the telluric ratio. Although the detailed interpretation is difficult, our observations confirm that the Pioneer Venus Orbiter results and establish that indeed Venus had a period in its early history in which it was very wet, perhaps not unlike the early wet period that seems to have been present on Mars, and that, in contrast to Earth, lost much of its water over geologic time
Near-infrared oxygen airglow from the Venus nightside
Groundbased imaging and spectroscopic observations of Venus reveal intense near-infrared oxygen airglow emission from the upper atmosphere and provide new constraints on the oxygen photochemistry and dynamics near the mesopause (approximately 100 km). Atomic oxygen is produced by the Photolysis of CO2 on the dayside of Venus. These atoms are transported by the general circulation, and eventually recombine to form molecular oxygen. Because this recombination reaction is exothermic, many of these molecules are created in an excited state known as O2(delta-1). The airglow is produced as these molecules emit a photon and return to their ground state. New imaging and spectroscopic observations acquired during the summer and fall of 1991 show unexpected spatial and temporal variations in the O2(delta-1) airglow. The implications of these observations for the composition and general circulation of the upper venusian atmosphere are not yet understood but they provide important new constraints on comprehensive dynamical and chemical models of the upper mesosphere and lower thermosphere of Venus
Extended Jaynes-Cummings models and (quasi)-exact solvability
The original Jaynes-Cummings model is described by a Hamiltonian which is
exactly solvable. Here we extend this model by several types of interactions
leading to a nonhermitian operator which doesn't satisfy the physical condition
of space-time reflection symmetry (PT symmetry). However the new Hamiltonians
are either exactly solvable admitting an entirely real spectrum or quasi
exactly solvable with a real algebraic part of their spectrum.Comment: 16 pages, 3 figures, discussion extended, one section adde
On realizations of nonlinear Lie algebras by differential operators
We study realizations of polynomial deformations of the sl(2,R)- Lie algebra
in terms of differential operators strongly related to bosonic operators. We
also distinguish their finite- and infinite-dimensional representations. The
linear, quadratic and cubic cases are explicitly visited but the method works
for arbitrary degrees in the polynomial functions. Multi-boson Hamiltonians are
studied in the context of these ``nonlinear'' Lie algebras and some examples
dealing with quantum optics are pointed out.Comment: 21 pages, Latex; New examples added in Sect.
A new class of non-Hermitian Hamiltonians with real spectra
We construct a new class of non-Hermitian Hamiltonians with real spectra. The
Hamiltonians possess one explicitly known eigenfunction.Comment: 6 page
The Surface Compositions of Triton, Pluto, and Charon
Neptune's satellite Triton, and the planet-satellite binary Pluto and Charon, are the most distant planetary bodies on which ices have been directly detected. Triton and Pluto have very similar dimensions and mean densities, suggesting a similar or common origin. Through earth-based spectroscopic observations in the near-infrared, solid N2, CH4, and CO have been found on both bodies, with the additional molecule C02 on Triton. N2 dominates both surfaces, although the coverage is not spatially uniform. On Triton, the CH4 and CO are mostly or entirely frozen in the N2 matrix, while CO2 may be spatially segregated. On Pluto, some CH4 and the CO are frozen in the N2 matrix, but there is evidence for additional CH4 in a pure state, perhaps lying as a lag deposit on a subsurface layer of N2. Despite their compositional and dimensional similarities, Pluto and Triton are quite different from one another in detail. Additional hydrocarbons and other volatile ices have been sought spectroscopically but not yet have been detected. The only molecule identified on Pluto's satellite Charon is solid H2O, but the spectroscopic data are of low precision and admit the presence of other ices such as CH4
The Dirac-Dowker Oscillator
The oscillator-like interaction is introduced in the equation for the
particle of arbitrary spin, given by Dirac and re-written to a matrix form by
Dowker.Comment: LaTeX file, 4pp. Preprint EFUAZ 94-0
Polynomial algebras and exact solutions of general quantum non-linear optical models I: Two-mode boson systems
We introduce higher order polynomial deformations of Lie algebra. We
construct their unitary representations and the corresponding single-variable
differential operator realizations. We then use the results to obtain exact
(Bethe ansatz) solutions to a class of 2-mode boson systems, including the
Boson-Einstein Condensate models as special cases. Up to an overall factor, the
eigenfunctions of the 2-mode boson systems are given by polynomials whose roots
are solutions of the associated Bethe ansatz equations. The corresponding
eigenvalues are expressed in terms of these roots. We also establish the
spectral equivalence between the BEC models and certain quasi-exactly solvable
Sch\"ordinger potentials.Comment: 20 pages, final version to appear in J. Phys. A: Math. Theor
Realizations of the Lie superalgebra q(2) and applications
The Lie superalgebra q(2) and its class of irreducible representations V_p of
dimension 2p (p being a positive integer) are considered. The action of the
q(2) generators on a basis of V_p is given explicitly, and from here two
realizations of q(2) are determined. The q(2) generators are realized as
differential operators in one variable x, and the basis vectors of V_p as
2-arrays of polynomials in x. Following such realizations, it is observed that
the Hamiltonian of certain physical models can be written in terms of the q(2)
generators. In particular, the models given here as an example are the
sphaleron model, the Moszkowski model and the Jaynes-Cummings model. For each
of these, it is shown how the q(2) realization of the Hamiltonian is helpful in
determining the spectrum.Comment: LaTeX file, 15 pages. (further references added, minor changes in
section 5
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