19,484 research outputs found
Efficient atomic clocks operated with several atomic ensembles
Atomic clocks are typically operated by locking a local oscillator (LO) to a
single atomic ensemble. In this article we propose a scheme where the LO is
locked to several atomic ensembles instead of one. This results in an
exponential improvement compared to the conventional method and provides a
stability of the clock scaling as with being the number
of atoms in each of the ensembles and is a constant depending on
the protocol being used to lock the LOComment: 10 pages, 8 figure
Bayesian modeling and forecasting of 24-hour high-frequency volatility: A case study of the financial crisis
This paper estimates models of high frequency index futures returns using
`around the clock' 5-minute returns that incorporate the following key
features: multiple persistent stochastic volatility factors, jumps in prices
and volatilities, seasonal components capturing time of the day patterns,
correlations between return and volatility shocks, and announcement effects. We
develop an integrated MCMC approach to estimate interday and intraday
parameters and states using high-frequency data without resorting to various
aggregation measures like realized volatility. We provide a case study using
financial crisis data from 2007 to 2009, and use particle filters to construct
likelihood functions for model comparison and out-of-sample forecasting from
2009 to 2012. We show that our approach improves realized volatility forecasts
by up to 50% over existing benchmarks.Comment: 48 pages, 7 figure
Elementary test for non-classicality based on measurements of position and momentum
We generalise a non-classicality test described by Kot et al. [Phys. Rev.
Lett. 108, 233601 (2010)], which can be used to rule out any classical
description of a physical system. The test is based on measurements of
quadrature operators and works by proving a contradiction with the classical
description in terms of a probability distribution in phase space. As opposed
to the previous work, we generalise the test to include states without
rotational symmetry in phase space. Furthermore, we compare the performance of
the non-classicality test with classical tomography methods based on the
inverse Radon transform, which can also be used to establish the quantum nature
of a physical system. In particular, we consider a non-classicality test based
on the so-called filtered back-projection formula. We show that the general
non-classicality test is conceptually simpler, requires less assumptions on the
system and is statistically more reliable than the tests based on the filtered
back-projection formula. As a specific example, we derive the optimal test for
a quadrature squeezed single photon state and show that the efficiency of the
test does not change with the degree of squeezing
Liquid phase hydrogenation of crotonaldehyde over Pt/SiO2 catalysts
The dependence of the catalytic properties of Pt/SiO2 catalysts for the hydrogenation of crotonaldehyde on the hydrogen pressure, the reaction temperature, the nature of the solvent and the presence of several additives were investigated. Strong deactivation of the catalysts mainly caused by decarbonylation of crotonaldehyde and irreversible adsorption of CO was observed. The initial activity of the deactivated catalysts is regained by oxidation of the adsorbed CO to CO2 by purging with air. The selectivity to crotylalcohol increased with increasing number of turnovers per metal site. This is explained with preferential blocking of the nonselective sites on the metal crystallites by CO and by a slow surface modification of the aging catalyst with organic deposits. The overall rate and the selectivity to the saturated aldehyde are markedly enhanced by an increase in hydrogen pressure and by a decrease in reaction temperature. The addition of modifiers such as potassium acetate, triphenylphosphine and thiophene had only little influence on the activity and the selectivity of the catalysts
Effect of glow discharge treatment of poly(acrylic acid) preadsorbed onto poly(ethylene)
In order to introduce carboxylic acid groups at the surface of poly(ethylene) (PE) films, an attempt was made to covalently link a preadsorbed layer of poly(acrylic acid) (PAAc) on a PE film by an argon or tetrafluoromethane (CF4) plasma treatment. Surface analysis was performed by XPS (X-ray photoelectron spectroscopy) and water contact angle measurements. It was shown that by treatment of a PAAc layer preadsorbed on PE with an argon or a CF4 plasma, a small amount of carboxylic acid groups was introduced at the surface. A similar amount of these groups was obtained by plasma treatment of PE films without a preadsorbed PAAc layer. A comparison of the etching rates of PAAc and PE by either an argon or a CF4 plasma, showed that PAAc is etched much faster by both types of plasmas than PE. The preadsorbed PAAc layer on PE is etched off before it could be immobilized by either an argon or a CF4 plasma treatment. Additionally the effect of treating PE films for very short times with an argon or a CF4 plasma was studied. After an induction period of approximately 0.1 s, the oxidation during the argon plasma treatment and the fluorination during the CF4 plasma treatment were proportional to the logarithm of the treatment time for time periods up to 50 s
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