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General and selective deoxygenation by hydrogen using a reusable earth-abundant metal catalyst
Chemoselective deoxygenation by hydrogen is particularly challenging but crucial for an efficient late-stage modification of functionality-laden fine chemicals, natural products, or pharmaceuticals and the economic upgrading of biomass-derived molecules into fuels and chemicals. We report here on a reusable earth-abundant metal catalyst that permits highly chemoselective deoxygenation using inexpensive hydrogen gas. Primary, secondary, and tertiary alcohols as well as alkyl and aryl ketones and aldehydes can be selectively deoxygenated, even when part of complex natural products, pharmaceuticals, or biomass-derived platform molecules. The catalyst tolerates many functional groups including hydrogenation-sensitive examples. It is efficient, easy to handle, and conveniently synthesized from a specific bimetallic coordination compound and commercially available charcoal. Selective, sustainable, and cost-efficient deoxygenation under industrially viable conditions seems feasible. © 2019 The Authors
A theory for magnetic-field effects of nonmagnetic organic semiconducting materials
A universal mechanism for strong magnetic-field effects of nonmagnetic
organic semiconductors is presented. A weak magnetic field (less than hundreds
mT) can substantially change the charge carrier hopping coefficient between two
neighboring organic molecules when the magnetic length is not too much longer
than the molecule-molecule separation and localization length of electronic
states involved. Under the illumination of lights or under a high electric
field, the change of hopping coefficients leads also to the change of polaron
density so that photocurrent, photoluminescence, electroluminescence,
magnetoresistance and electrical-injection current become sensitive to a weak
magnetic field. The present theory can not only explain all observed features,
but also provide a solid theoretical basis for the widely used empirical
fitting formulas.Comment: 4 pages, 2 figure
Generation of Squeezing in Higher Order Hermite-Gaussian Modes with an Optical Parametric Amplifier
We demonstrate quantum correlations in the transverse plane of continuous
wave light beams by producing -4.0 dB, -2.6 dB and -1.5 dB of squeezing in the
TEM00, TEM10 and TEM20 Hermite- Gauss modes with an optical parametric
amplifier, respectively. This has potential applications in quantum information
networking, enabling parallel quantum information processing. We describe the
setup for the generation of squeezing and analyze the effects of various
experimental issues such as mode overlap between pump and seed and nonlinear
losses.Comment: 7 pages, 4 figure
A compact, multi-sensor laser scanning head for processing and monitoring micro-spot welding
In order to improve the reliability of micro-spot welding of metal parts in production such as e.g. in electron guns for TV picture tubes, real-time information about the evolution of the welding process should be available to allow on-line modification of the laser parameters. Such information can be derived from a set of sensors that are mounted on a laser-scanning head. Different sensors are used to monitor the optical fiber output power to determine the evolution of temperature during the spot welding process, to measure plasma emission and back-reflected laser light. A vision channel and a CCD camera are used to control the position of the laser spot on the parts to be processed. The compact scanning head is composed of a tip/tilt laser scanner, a collimating lens and a focusing lens. The scanner is fast steering, with a bandwidth of 700Hz, and can tilt by +/-3.5 degrees with a repeatability better than 50 mu rad. The settling time for maximum deflection is less than 10ms. The scanning lens is a newly developed focusing lens designed to replace commercial cumbersome scanning lenses such as F-theta lenses, which have large volume, weight and price. This lens is based on the well-known Cooke triplet design and guarantees a constant shape of the spot all over the scan surface and is specially well suited for high power beam delivery. The scan field achieved by the system is limited to 25mm x 25mm. The laser used for this application is a pulsed Nd:YAG laser delivered by an optical fiber to the optical head. However, the system can be adapted to different types of lasers. Laser micro-spot welding on copper substrate has been performed in the frame of the Brite-Euram project MAIL. Smaller tolerances (a factor of 2 less) on the spot diameters were obtained in the case of a sensor controlled operation compared to the case where sensor control is not used
Electronic structure of wurtzite and zinc-blende AlN
The electronic structure of AlN in wurtzite and zinc-blende phases is studied
experimentally and theoretically. By using x-ray emission spectroscopy, the Al
3p, Al 3s and N 2p spectral densities are obtained. The corresponding local and
partial theoretical densities of states (DOS), as well as the total DOS and the
band structure, are calculated by using the full potential linearized augmented
plane wave method, within the framework of the density functional theory. There
is a relatively good agreement between the experimental spectra and the
theoretical DOS, showing a large hybridization of the valence states all along
the valence band. The discrepancies between the experimental and theoretical
DOS, appearing towards the high binding energies, are ascribed to an
underestimation of the valence band width in the calculations. Differences
between the wurtzite and zinc-blende phases are small and reflect the slight
variations between the atomic arrangements of both phases
A constraint on antigravity of antimatter from precision spectroscopy of simple atoms
Consideration of antigravity for antiparticles is an attractive target for
various experimental projects. There are a number of theoretical arguments
against it but it is not quite clear what kind of experimental data and
theoretical suggestions are involved. In this paper we present straightforward
arguments against a possibility of antigravity based on a few simple
theoretical suggestions and some experimental data. The data are: astrophysical
data on rotation of the Solar System in respect to the center of our galaxy and
precision spectroscopy data on hydrogen and positronium. The theoretical
suggestions for the case of absence of the gravitational field are: equality of
electron and positron mass and equality of proton and positron charge. We also
assume that QED is correct at the level of accuracy where it is clearly
confirmed experimentally
Muonic hydrogen cascade time and lifetime of the short-lived state
Metastable muonic-hydrogen atoms undergo collisional -quenching,
with rates which depend strongly on whether the kinetic energy is above
or below the energy threshold. Above threshold, collisional
excitation followed by fast radiative
deexcitation is allowed. The corresponding short-lived component
was measured at 0.6 hPa room temperature gas pressure, with
lifetime ns (i.e.,
at liquid-hydrogen density) and population
% (per atom). In
addition, a value of the cascade time, ns, was found.Comment: 4 pages, 3 figure
From START to FINISH : the influence of osmotic stress on the cell cycle
Peer reviewedPublisher PD
Can spacetime curvature induced corrections to Lamb shift be observable?
The Lamb shift results from the coupling of an atom to vacuum fluctuations of
quantum fields, so corrections are expected to arise when the spacetime is
curved since the vacuum fluctuations are modified by the presence of spacetime
curvature. Here, we calculate the curvature-induced correction to the Lamb
shift outside a spherically symmetric object and demonstrate that this
correction can be remarkably significant outside a compact massive
astrophysical body. For instance, for a neutron star or a stellar mass black
hole, the correction is 25% at a radial distance of ,
16% at and as large as 1.6% even at , where is
the mass of the object, the Newtonian constant, and the speed of light.
In principle, we can look at the spectra from a distant compact super-massive
body to find such corrections. Therefore, our results suggest a possible way of
detecting fundamental quantum effects in astronomical observations.Comment: 13 pages, 3 figures, slight title change, clarifications and more
discussions added, version to be published in JHE
Absolute frequency measurement of the In clock transition with a mode-locked laser
The absolute frequency of the In -
clock transition at 237 nm was measured with an accuracy of 1.8 parts in
. Using a phase-coherent frequency chain, we compared the
- transition with a methane-stabilized He-Ne laser at 3.39 m
which was calibrated against an atomic cesium fountain clock. A frequency gap
of 37 THz at the fourth harmonic of the He-Ne standard was bridged by a
frequency comb generated by a mode-locked femtosecond laser. The frequency of
the In clock transition was found to be
kHz, the accuracy being limited by the uncertainty of the He-Ne laser
reference. This represents an improvement in accuracy of more than 2 orders of
magnitude on previous measurements of the line and now stands as the most
accurate measurement of an optical transition in a single ion.Comment: 3 pages, 2 figures. accepted for publication in Opt. Let
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