777 research outputs found
Identification and properties of molecular systems of potential use in solar-pumped lasers
The concepts and computational tools of theortical chemistry are used to investigate molecular properties needed in direct solar-pumped lasers. Compounds of the type RR'CXY, with R and R' organic groups, and X and Y halide atoms were identified as likely candidates because of their highly enhanced absorption coefficients over compounds with a single halide atom. The use of a combination of vibrational excitation followed by electronic excitation to enhance quantum yields at certain wavelengths is indicated. A self-consistent eikonal approximation to state-to-state transitions was tested for CH3I and is useful for other problems involving electronic energy and charge transfer. An approach to calculate potential energy surfaces and transition dipoles was developed which is based on the generation of eigenstates of the nonrelativisitc Hamiltonian followed by incorporation of the spin-orbit coupling by configuration interaction
Baryogenesis from the Kobayashi-Maskawa Phase
The Standard Model fulfills the three Sakharov conditions for baryogenesis.
The smallness of quark masses suppresses, however, the CP violation from the
Kobayashi-Maskawa phase to a level that is many orders of magnitude below what
is required to explain the observed baryon asymmetry. We point out that if, as
a result of time variation in the Yukawa couplings, quark masses were large at
the time of the electroweak phase transition, then the Kobayashi-Maskawa
mechanism could be the source of the asymmetry. The Froggatt-Nielsen mechanism
provides a plausible framework where the Yukawa couplings could all be of order
one at that time, and settle to their present values before nucleosynthesis.
The problems related to a strong first order electroweak phase transition may
also be alleviated in this framework. Our scenario reveals a loophole in the
commonly held view that the Kobayashi-Maskawa mechanism cannot be the dominant
source of CP violation to play a role in baryogenesis.Comment: 4 page
Measurement of one-particle correlations and momentum distributions for trapped 1D gases
van Hove's theory of scattering of probe particles by a macroscopic target is
generalized so as to relate the differential cross section for atomic ejection
via stimulated Raman transitions to one-particle momentum-time correlations and
momentum distributions of 1D trapped gases. This method is well suited to
probing the longitudinal momentum distributions of 1D gases in situ, and
examples are given for bosonic and fermionic atoms.Comment: 4 pages, 2 .eps figure
Fluxes and distribution of dissolved iron in the eastern (sub-) tropical North Atlantic Ocean
Aeolian dust transport from the Saharan/Sahel desert regions is considered the dominant external input of iron (Fe) to the surface waters of the eastern (sub-) tropical North Atlantic Ocean. To test this hypothesis, we investigated the sources of dissolved Fe (DFe) and quantified DFe fluxes to the surface ocean in this region. In winter 2008, surface water DFe concentrations varied between <0.1 nM and 0.37 nM, with an average of 0.13 ± 0.07 nM DFe (n = 194). A strong correlation between mixed layer averaged concentrations of dissolved aluminum (DAl), a proxy for dust input, and DFe indicated dust as a source of DFe to the surface ocean. The importance of Aeolian nutrient input was further confirmed by an increase of 0.1 nM DFe and 0.05 ?M phosphate during a repeat transect before and after a dust event. An exponential decrease of DFe with increasing distance from the African continent, suggested that continental shelf waters were a source of DFe to the northern part of our study area. Relatively high Fe:C ratios of up to 3 × 10?5 (C derived from apparent oxygen utilization (AOU)) indicated an external source of Fe to these African continental shelf waters. Below the wind mixed layer along 12°N, enhanced DFe concentrations (>1.5 nM) correlated positively with apparent oxygen utilization (AOU) and showed the importance of organic matter remineralization as an DFe source. As a consequence, vertical diffusive mixing formed an important Fe flux to the surface ocean in this region, even surpassing that of a major dust event
Non-Local Effects of Multi-Trace Deformations in the AdS/CFT Correspondence
The AdS/CFT correspondence relates deformations of the CFT by "multi-trace
operators" to "non-local string theories". The deformed theories seem to have
non-local interactions in the compact directions of space-time; in the gravity
approximation the deformed theories involve modified boundary conditions on the
fields which are explicitly non-local in the compact directions. In this note
we exhibit a particular non-local property of the resulting space-time theory.
We show that in the usual backgrounds appearing in the AdS/CFT correspondence,
the commutator of two bulk scalar fields at points with a large enough distance
between them in the compact directions and a small enough time-like distance
between them in AdS vanishes, but this is not always true in the deformed
theories. We discuss how this is consistent with causality.Comment: 24 pages, 6 figures, 2 appendices. v2: added reference
Relativistic Turbulence: A Long Way from Preheating to Equilibrium
We study, both numerically and analytically, the development of equilibrium
after preheating. We show that the process is characterised by the appearance
of Kolmogorov spectra and the evolution towards thermal equilibrium follows
self-similar dynamics. Simplified kinetic theory gives values for all
characteristic exponents which are close to what is observed in lattice
simulations. The resulting time for thermalization is long, and temperature at
thermalization is low, eV in the simple
inflationary model. Our results allow a straightforward generalization to
realistic models.Comment: 4 pages, 3figures, LaTe
Me, My Selfie, and I:The Relations Between Selfie Behaviors, Body Image, Self-Objectification, and Self-Esteem in Young Women
Due to the enormous popularity of social networking sites (SNSs), online and offline social lives seem inextricably linked, which raises concerns for how SNS use relates to psychological health. Similarly, the omnipresence of selfies on SNSs-a form of appearance-related exposure-raises concerns regarding psychological health. This study aimed to investigate the relationships between body image, self-objectification, self-esteem, and various selfie behaviors among young women (N = 179). We hypothesized that a worsened body image (i.e., higher body dissatisfaction or lower body appreciation), higher levels of self-objectification, and lower self-esteem would precede greater engagement in selfie behaviors. Structural equation modeling showed that body appreciation is associated with greater engagement in selfie selection and deliberate posting, and that self-objectification is related to greater engagement in all selfie behaviors assessed. In support of our proposed model, a reversed model was also tested that showed poorer results. These findings suggest that body image may serve not only as an outcome of SNS use but also as a motive preceding selfie behaviors
"Holey Sheets" - Pfaffians and Subdeterminants as D-brane Operators in Large N Gauge Theories
In the AdS/CFT correspondence, wrapped D3-branes (such as "giant gravitons")
on the string theory side of the correspondence have been identified with
Pfaffian, determinant and subdeterminant operators on the field theory side. We
substantiate this identification by showing that the presence of pairs of such
operators in a correlation function of a large N gauge theory naturally leads
to a modified 't Hooft expansion including also worldsheets with boundaries.
This happens independently of supersymmetry or conformal invariance.Comment: 39 pages, 10 figures, harvma
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