22,071 research outputs found
Theoretical study of production of unique glasses in space
The potential of producing the glassy form of selected materials in the weightless, containerless nature of space processing is examined through the development of kinetic relationships describing nucleation and crystallization phenomena. Transformation kinetics are applied to a well-characterized system (SiO2), an excellent glass former (B2O3), and a poor glass former (Al2O3) by conventional earth processing methods. Viscosity and entropy of fusion are shown to be the primary materials parameters controlling the glass forming tendency. For multicomponent systems diffusion-controlled kinetics and heterogeneous nucleation effects are considered. An analytical empirical approach is used to analyze the mullite system. Results are consistent with experimentally observed data and indicate the promise of mullite as a future space processing candidate
Observations of vertical velocity power spectra with the SOUSY VHF radar
A data set taken with the SOUSY VHF radar from October 28 to November 13, 1981 was used to calculate the power spectrum of the vertical velocities directly from the vertical beam measurements. The spectral slopes for the frequency spectra have been determined out to periods of several days and have been found to have values near -1 in the troposphere and shallower slopes in the lower stratosphere. The value of -1 is in agreement with the value found by Larsen et al. (1985) and Balsley and Carter (1982) in the range from a few minutes to 1 hr
Financial frictions and the monetary transmission mechanism: theory, evidence and policy implications
This paper provides a brief survey of the role of financial frictions in the monetary transmission mechanism. After noting some of the key stylised facts that any model of the transmission mechanisms must be consistent with, we discuss both the classical interest rate channel and the credit and bank lending channels of monetary transmission. We then review the empirical evidence relating to the relative importance of these channels. Finally we consider what impact the presence of significant financial frictions might have on the conduct of monetary policy JEL Classification: E52, E58, E44bank-lending channel, credit channel, monetary policy, transmission mechanism
Logarithmic correction to scaling for multi-spin strings in the AdS_5 black hole background
We find new explicit solutions describing closed strings spinning with equal
angular momentum in two independent planes in the black hole spacetime.
These are folded strings in the radial direction and also winding
times around an angular direction. We especially consider these solutions in
the long string and high temperature limit, where it is shown that there is a
logarithmic correction to the scaling between energy and spin. This is similar
to the one-spin case. The strings are spinning, or actually orbiting around the
black hole of the black hole spacetime, similarly to solutions
previously found in black hole spacetimes.Comment: 11 pages, Final version, To appear in IJMP
Sinuosity and the affect grid: A method for adjusting repeated mood scores
Copyright @ 2012 Ammons Scientific. The article can be accessed from the links below.This article has been made available through the Brunel Open Access Publishing Fund.Sinuosity is a measure of how much a travelled pathway deviates from a straight line. In this paper, sinuosity is applied to the measurement of mood. The Affect Grid is a mood scale that requires participants to place a mark on a 9 x 9 grid to indicate their current mood. The grid has two dimensions: pleasure-displeasure (horizontal) and arousal-sleepiness (vertical). In studies where repeated measurements are required, some participants may exaggerate their mood shifts due to faulty interpretation of the scale or a feeling of social obligation to the experimenter. A new equation is proposed, based on the sinuosity measure in hydrology, a measure of the meandering of rivers. The equation takes into account an individual's presumed tendency to exaggerate and meander to correct the score and reduce outliers. The usefulness of the equation is demonstrated by applying it to Affect Grid data from another study.This article is made available through the Brunel Open Access Publishing Fund
On the Key-Uncertainty of Quantum Ciphers and the Computational Security of One-way Quantum Transmission
We consider the scenario where Alice wants to send a secret (classical)
-bit message to Bob using a classical key, and where only one-way
transmission from Alice to Bob is possible. In this case, quantum communication
cannot help to obtain perfect secrecy with key length smaller then . We
study the question of whether there might still be fundamental differences
between the case where quantum as opposed to classical communication is used.
In this direction, we show that there exist ciphers with perfect security
producing quantum ciphertext where, even if an adversary knows the plaintext
and applies an optimal measurement on the ciphertext, his Shannon uncertainty
about the key used is almost maximal. This is in contrast to the classical case
where the adversary always learns bits of information on the key in a known
plaintext attack. We also show that there is a limit to how different the
classical and quantum cases can be: the most probable key, given matching
plain- and ciphertexts, has the same probability in both the quantum and the
classical cases. We suggest an application of our results in the case where
only a short secret key is available and the message is much longer.Comment: 19 pages, 2 figures. This is a revised version of an earlier version
that appeared in the proc. of Eucrocrypt'04:LNCS3027, 200
Instantaneous Pair Theory for High-Frequency Vibrational Energy Relaxation in Fluids
Notwithstanding the long and distinguished history of studies of vibrational
energy relaxation, exactly how it is that high frequency vibrations manage to
relax in a liquid remains somewhat of a mystery. Both experimental and
theoretical approaches seem to say that there is a natural frequency range
associated with intermolecular motions in liquids, typically spanning no more
than a few hundred cm^{-1}. Landau-Teller-like theories explain how a solvent
can absorb any vibrational energy within this "band", but how is it that
molecules can rid themselves of superfluous vibrational energies significantly
in excess of these values? We develop a theory for such processes based on the
idea that the crucial liquid motions are those that most rapidly modulate the
force on the vibrating coordinate -- and that by far the most important of
these motions are those involving what we have called the mutual nearest
neighbors of the vibrating solute. Specifically, we suggest that whenever there
is a single solvent molecule sufficiently close to the solute that the solvent
and solute are each other's nearest neighbors, then the instantaneous
scattering dynamics of the solute-solvent pair alone suffices to explain the
high frequency relaxation. The many-body features of the liquid only appear in
the guise of a purely equilibrium problem, that of finding the likelihood of
particularly effective solvent arrangements around the solute. These results
are tested numerically on model diatomic solutes dissolved in atomic fluids
(including the experimentally and theoretically interesting case of I_2 in Xe).
The instantaneous pair theory leads to results in quantitative agreement with
those obtained from far more laborious exact molecular dynamics simulations.Comment: 55 pages, 6 figures Scheduled to appear in J. Chem. Phys., Jan, 199
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