4,183 research outputs found
Petrology of some oceanic island basalts: PRIMELT2.XLS software for primary magma calculation
PRIMELT2.XLS software is introduced for calculating primary magma composition and mantle potential temperature (TP) from an observed lava composition. It is an upgrade over a previous version in that it includes garnet peridotite melting and it detects complexities that can lead to overestimates in TP by >100°C. These are variations in source lithology, source volatile content, source oxidation state, and clinopyroxene fractionation. Nevertheless, application of PRIMELT2.XLS to lavas from a wide range of oceanic islands reveals no evidence that volatile-enrichment and source fertility are sufficient to produce them. All are associated with thermal anomalies, and this appears to be a prerequisite for their formation. For the ocean islands considered in this work, TP maxima are typically ~1450–1500°C in the Atlantic and 1500–1600°C in the Pacific, substantially greater than ~1350°C for ambient mantle. Lavas from the Galápagos Islands and Hawaii record in their geochemistry high TP maxima and large ranges in both TP and melt fraction over short horizontal distances, a result that is predicted by the mantle plume model
A simple approach to the correlation of rotovibrational states in four-atomic molecules
The problem of correlation between quantum states of four-atomic molecules in
different geometrical configurations is reviewed in detail. A general, still
simple rule is obtained which allows one to correlate states of a linear
four-atomic molecule with those of any kind of non-linear four-atomic molecule.Comment: 16 pages (+8 figures), Postscript (ready to print!
Changes of vibrational lifetimes with minor structural modification of small polyatomic molecules
Substantial changes of population lifetimes of CH-stretching modes are observed when two atoms are exchanged in CH2=CCl2 to form trans CHCl=CHCl and when three deuterons are substituted in C6H6 to form 1,3,5.-C6H3D3. The measured lifetimes are in good agreement with estimates based on Fermi resonance-mixing which is inferred from infrared and Raman spectra
Optimal Topological Test for Degeneracies of Real Hamiltonians
We consider adiabatic transport of eigenstates of real Hamiltonians around
loops in parameter space. It is demonstrated that loops that map to nontrivial
loops in the space of eigenbases must encircle degeneracies. Examples from
Jahn-Teller theory are presented to illustrate the test. We show furthermore
that the proposed test is optimal.Comment: Minor corrections, accepted in Phys. Rev. Let
On-chip spectroscopy with thermally-tuned high-Q photonic crystal cavities
Spectroscopic methods are a sensitive way to determine the chemical
composition of potentially hazardous materials. Here, we demonstrate that
thermally-tuned high-Q photonic crystal cavities can be used as a compact
high-resolution on-chip spectrometer. We have used such a chip-scale
spectrometer to measure the absorption spectra of both acetylene and hydrogen
cyanide in the 1550 nm spectral band, and show that we can discriminate between
the two chemical species even though the two materials have spectral features
in the same spectral region. Our results pave the way for the development of
chip-size chemical sensors that can detect toxic substances
A geometrical approach to the dynamics of spinor condensates I: Hydrodynamics
In this work, we derive the equations of motion governing the hydrodynamics
of spin-F spinor condensates. We pursue a description based on standard
physical variables (total density and superfluid velocity), alongside 2F
`spin-nodes': unit vectors that describe the spin F state, and also exhibit the
point-group symmetry of a spinor condensate's mean-field ground state. The
hydrodynamic equations of motion consist of a mass continuity equation, 2F
Landau-Lifshitz equations for the spin-nodes, and a modified Euler equation. In
particular, we provide a generalization of the Mermin-Ho relation to spin one,
and find an analytic solution for the skyrmion texture in the incompressible
regime of a spin-half condensate. These results exhibit a beautiful geometrical
structure that underlies the dynamics of spinor condensates.Comment: 12 pages. First paper in two-part serie
A joint time-dependent density-functional theory for excited states of electronic systems in solution
We present a novel joint time-dependent density-functional theory for the
description of solute-solvent systems in time-dependent external potentials.
Starting with the exact quantum-mechanical action functional for both electrons
and nuclei, we systematically eliminate solvent degrees of freedom and thus
arrive at coarse-grained action functionals which retain the highly accurate
\emph{ab initio} description for the solute and are, in principle, exact. This
procedure allows us to examine approximations underlying popular embedding
theories for excited states. Finally, we introduce a novel approximate action
functional for the solute-water system and compute the solvato-chromic shift of
the lowest singlet excited state of formaldehyde in aqueous solution, which is
in good agreement with experimental findings.Comment: 11 page
Theoretical study of molecular electronic excitations and optical transitions of C60
We report results on ab initio calculations of excited states of the
fullerene molecule by using configuration interaction (CI) approach with singly
excited determinants (SCI). We have used both the experimental geometry and the
one optimized by the density functional method and worked with basis sets at
the cc-pVTZ and aug-cc-pVTZ level. Contrary to the early SCI semiempirical
calculations, we find that two lowest electron
optical lines are situated at relatively high energies of ~5.8 eV (214 nm) and
~6.3 eV (197 nm). These two lines originate from two transitions: from HOMO to (LUMO+1) () and from (HOMO--1)
to LUMO (). The lowest molecular excitation, which is the level, is found at ~2.5 eV. Inclusion of doubly excited determinants
(SDCI) leads only to minor corrections to this picture. We discuss possible
assignment of absorption bands at energies smaller than 5.8 eV (or
larger than 214 nm).Comment: 6 pages, 1 figure, 9 Table
Distributed Relay Protocol for Probabilistic Information-Theoretic Security in a Randomly-Compromised Network
We introduce a simple, practical approach with probabilistic
information-theoretic security to mitigate one of quantum key distribution's
major limitations: the short maximum transmission distance (~200 km) possible
with present day technology. Our scheme uses classical secret sharing
techniques to allow secure transmission over long distances through a network
containing randomly-distributed compromised nodes. The protocol provides
arbitrarily high confidence in the security of the protocol, with modest
scaling of resource costs with improvement of the security parameter. Although
some types of failure are undetectable, users can take preemptive measures to
make the probability of such failures arbitrarily small.Comment: 12 pages, 2 figures; added proof of verification sub-protocol, minor
correction
Detection of interstellar CH_3
Observations with the Short Wavelength Spectrometer (SWS) onboard the {\it
Infrared Space Observatory} (ISO) have led to the first detection of the methyl
radical in the interstellar medium. The branch at 16.5
m and the (0) line at 16.0 m have been unambiguously detected
toward the Galactic center SgrA. The analysis of the measured bands gives a
column density of (8.02.4) cm and an excitation
temperature of K. Gaseous at a similarly low excitation
temperature and are detected for the same line of sight. Using
constraints on the column density obtained from and
visual extinction, the inferred abundance is
. The chemically related
molecule is not detected, but the pure rotational lines of are seen
with the Long Wavelength Spectrometer (LWS). The absolute abundances and the
and ratios are inconsistent with published
pure gas-phase models of dense clouds. The data require a mix of diffuse and
translucent clouds with different densities and extinctions, and/or the
development of translucent models in which gas-grain chemistry, freeze-out and
reactions of with polycyclic aromatic hydrocarbons and solid
aliphatic material are included.Comment: 2 figures. ApJL, Accepte
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