8,858 research outputs found
Tandem Olefin Metathesis/Oxidative Cyclization: Synthesis of Tetrahydrofuran Diols from Simple Olefins
A tandem olefin metathesis/oxidative cyclization has been developed to synthesize 2,5-disubstituted tetrahydrofuran (THF) diols in a stereocontrolled fashion from simple olefin precursors. The ruthenium metathesis catalyst is converted into an oxidation catalyst in the second step and is thus responsible for both catalytic steps. The stereochemistry of the 1,5-diene intermediate can be controlled through the choice of catalyst and the type of metathesis conducted. This olefin stereochemistry then controls the THF diol stereochemistry through a highly stereospecific oxidative cyclization
Coil system for plasmoid thruster
A coil system for a plasmoid thruster includes a bias coil, a drive coil and field coils. The bias and drive coils are interleaved with one another as they are helically wound about a conical region. A first field coil defines a first passage at one end of the conical region, and is connected in series with the bias coil. A second field coil defines a second passage at an opposing end of the conical region, and is connected in series with the bias coil
Conductance fluctuations and boundary conditions
The conductance fluctuations for various types for two-- and
three--dimensional disordered systems with hard wall and periodic boundary
conditions are studied, all the way from the ballistic (metallic) regime to the
localized regime. It is shown that the universal conductance fluctuations (UCF)
depend on the boundary conditions. The same holds for the metal to insulator
transition. The conditions for observing the UCF are also given.Comment: 4 pages RevTeX, 5 figures include
Optical to near-infrared transmission spectrum of the warm sub-Saturn HAT-P-12b
We present the transmission spectrum of HAT-P-12b through a joint analysis of
data obtained from the Hubble Space Telescope Space Telescope Imaging
Spectrograph (STIS) and Wide Field Camera 3 (WFC3) and Spitzer, covering the
wavelength range 0.3-5.0 m. We detect a muted water vapor absorption
feature at 1.4 m attenuated by clouds, as well as a Rayleigh scattering
slope in the optical indicative of small particles. We interpret the
transmission spectrum using both the state-of-the-art atmospheric retrieval
code SCARLET and the aerosol microphysics model CARMA. These models indicate
that the atmosphere of HAT-P-12b is consistent with a broad range of
metallicities between several tens to a few hundred times solar, a roughly
solar C/O ratio, and moderately efficient vertical mixing. Cloud models that
include condensate clouds do not readily generate the sub-micron particles
necessary to reproduce the observed Rayleigh scattering slope, while models
that incorporate photochemical hazes composed of soot or tholins are able to
match the full transmission spectrum. From a complementary analysis of
secondary eclipses by Spitzer, we obtain measured depths of
and at 3.6 and 4.5 m, respectively, which are
consistent with a blackbody temperature of K and indicate
efficient day-night heat recirculation. HAT-P-12b joins the growing number of
well-characterized warm planets that underscore the importance of clouds and
hazes in our understanding of exoplanet atmospheres.Comment: 25 pages, 19 figures, accepted for publication in AJ, updated with
proof correction
Spatially resolved simulation of a radio frequency driven micro atmospheric pressure plasma jet and its effluent
Radio frequency driven plasma jets are frequently employed as efficient
plasma sources for surface modification and other processes at atmospheric
pressure. The radio-frequency driven micro atmospheric pressure plasma jet
(APPJ) is a particular variant of that concept whose geometry allows
direct optical access. In this work, the characteristics of the APPJ
operated with a helium-oxygen mixture and its interaction with a helium
environment are studied by numerical simulation. The density and temperature of
the electrons, as well as the concentration of all reactive species are studied
both in the jet itself and in its effluent. It is found that the effluent is
essentially free of charge carriers but contains a substantial amount of
activated oxygen (O, O and O). The simulation results are
verified by comparison with experimental data
Two phase transitions in the fully frustrated model
The fully frustrated model on a square lattice is studied by means of
Monte Carlo simulations. A Kosterlitz-Thouless transition is found at , followed by an ordinary Ising transition at a slightly
higher temperature, . The non-Ising exponents reported by
others, are explained as a failure of finite size scaling due to the screening
length associated with the nearby Kosterlitz-Thouless transition.Comment: REVTEX file, 8 pages, 5 figures in uuencoded postscrip
An Exactly Solvable Model of N Coupled Luttinger Chains
We calculate the exact Green function of a special model of N coupled
Luttinger chains with arbitrary interchain hopping t_{perp}. The model is
exactly solvable via bosonization if the interchain interaction does not fall
off in the direction perpendicular to the chains. For any finite N we find
Luttinger liquid behavior and explicitly calculate the anomalous dimension
gamma^(N). However, the Luttinger liquid state does not preclude coherent
interchain hopping. We also show that gamma^(N) -> 0 for N -> infinity, so that
in the limit of infinitely many chains we obtain a Fermi liquid.Comment: accepted for publication in Phys. Rev.
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