590 research outputs found
On the relation between Phi(1,2) and Phi(1,5) perturbed minimal models
We consider the RSOS S-matrices of the Phi(1,5) perturbed minimal models
which have recently been found in the companion paper [hep-th/9604098]. These
S-matrices have some interesting properties, in particular, unitarity may be
broken in a stronger sense than seen before, while one of the three classes of
Phi(1,5) perturbations (to be described) shares the same Thermodynamic Bethe
Ansatz as a related Phi(1,2) perturbation. We test these new S-matrices by the
standard Truncated Conformal Space method, and further observe that in some
cases the BA equations for two particle energy levels may be continued to
complex rapidity to describe (a) single particle excitations and (b) complex
eigenvalues of the Hamiltonian corresponding to non-unitary S-matrix elements.
We make some comments on identities between characters in the two related
models following from the fact that the two perturbed theories share the same
breather sector.Comment: LaTeX, 23 pages, 12 figures. Substantial revision of introductory
section, new discussion of complex eigenvalues and non-unitary S-matrice
Kinetic considerations of the strength of oriented solids
Kinetics of mechanical strength of oriented and stressed solids based on statistical absolute reaction rate theor
Theoretical studies of the kinetics of mechanical unfolding of cross-linked polymer chains and their implications for single molecule pulling experiments
We have used kinetic Monte Carlo simulations to study the kinetics of
unfolding of cross-linked polymer chains under mechanical loading. As the ends
of a chain are pulled apart, the force transmitted by each crosslink increases
until it ruptures. The stochastic crosslink rupture process is assumed to be
governed by first order kinetics with a rate that depends exponentially on the
transmitted force. We have performed random searches to identify optimal
crosslink configurations whose unfolding requires a large applied force
(measure of strength) and/or large dissipated energy (measure of toughness). We
found that such optimal chains always involve cross-links arranged to form
parallel strands. The location of those optimal strands generally depends on
the loading rate. Optimal chains with a small number of cross-links were found
to be almost as strong and tough as optimal chains with a large number of
cross-links. Furthermore, optimality of chains with a small number of
cross-links can be easily destroyed by adding cross-links at random. The
present findings are relevant for the interpretation of single molecule force
probe spectroscopy studies of the mechanical unfolding of load-bearing
proteins, whose native topology often involves parallel strand arrangements
similar to the optimal configurations identified in the study
Synthesis of solvent-modified epoxies via Chemically Induced Phase Separation: A new approach towards void toughening of epoxies
Summary: The fracture toughness has been investigated with single edge notched bending specimens in solvent-modified epoxies, which were prepared via the Chemically Induced Phase Separation technique. The generation of a controlled morphology with liquid droplets in the micrometer range leads to a substantial increase in the fracture energy of nearly 400% compared to the non-modified epoxy network. The critical stress intensity factor of these highly crosslinked thermosets does not vary significantly. These results demonstrate the general potential of the Chemically Induced Phase Separation technique to prepare porous thermosets, thus combining increased toughness with lowered densit
Molecfit: A general tool for telluric absorption correction II. Quantitative evaluation on ESO-VLT X-Shooter spectra
Context: Absorption by molecules in the Earth's atmosphere strongly affects
ground-based astronomical observations. The resulting absorption line strength
and shape depend on the highly variable physical state of the atmosphere, i.e.
pressure, temperature, and mixing ratio of the different molecules involved.
Usually, supplementary observations of so-called telluric standard stars (TSS)
are needed to correct for this effect, which is expensive in terms of telescope
time. We have developed the software package molecfit to provide synthetic
transmission spectra based on parameters obtained by fitting narrow ranges of
the observed spectra of scientific objects. These spectra are calculated by
means of the radiative transfer code LBLRTM and an atmospheric model. In this
way, the telluric absorption correction for suitable objects can be performed
without any additional calibration observations of TSS. Aims: We evaluate the
quality of the telluric absorption correction using molecfit with a set of
archival ESO-VLT X-Shooter visible and near-infrared spectra. Methods: Thanks
to the wavelength coverage from the U to the K band, X-Shooter is well suited
to investigate the quality of the telluric absorption correction with respect
to the observing conditions, the instrumental set-up, input parameters of the
code, the signal-to-noise of the input spectrum, and the atmospheric profiles.
These investigations are based on two figures of merit, I_off and I_res, that
describe the systematic offsets and the remaining small-scale residuals of the
corrections. We also compare the quality of the telluric absorption correction
achieved with moelcfit to the classical method based on a telluric standard
star. (Abridged)Comment: Acc. by A&A; Software available via ESO:
http://www.eso.org/sci/software/pipelines/skytools
Time dependent mechanical strength of oriented media
Time dependent mechanical strength of fully oriented solid
A note on W_{2,s} strings
BRST operators for two-dimensional theories with spin-2 and spin-
currents, generalising the BRST operator of Thierry-Mieg, have previously
been obtained. The construction was based on demanding nilpotence of the BRST
operators, making no reference to whether or not an underlying algebra
exists. In this paper, we analyse the known cases (, 4, 5 and 6), showing
that the two BRST operators are associated with the algebra, and
that two of the four BRST operators are associated with the
algebra. We discuss the cohomology of all the known higher-spin BRST operators,
the Weyl symmetry of their physical states, and their relation with certain
minimal models. We also obtain the BRST operator for the case .Comment: 12 pages, CTP TAMU-8/94, LZU-TH-94/0
Molecfit: A general tool for telluric absorption correction. I. Method and application to ESO instruments
Context: The interaction of the light from astronomical objects with the
constituents of the Earth's atmosphere leads to the formation of telluric
absorption lines in ground-based collected spectra. Correcting for these lines,
mostly affecting the red and infrared region of the spectrum, usually relies on
observations of specific stars obtained close in time and airmass to the
science targets, therefore using precious observing time. Aims: We present
molecfit, a tool for correcting for telluric absorption lines based on
synthetic modelling of the Earth's atmospheric transmission. Molecfit is
versatile and can be used with data obtained with various ground-based
telescopes and instruments. Methods: Molecfit combines a publicly available
radiative transfer code, a molecular line database, atmospheric profiles, and
various kernels to model the instrument line spread function. The atmospheric
profiles are created by merging a standard atmospheric profile representative
of a given observatory's climate, of local meteorological data, and of
dynamically retrieved altitude profiles for temperature, pressure, and
humidity. We discuss the various ingredients of the method, its applicability,
and its limitations. We also show examples of telluric line correction on
spectra obtained with a suite of ESO Very Large Telescope (VLT) instruments.
Results: Compared to previous similar tools, molecfit takes the best results
for temperature, pressure, and humidity in the atmosphere above the observatory
into account. As a result, the standard deviation of the residuals after
correction of unsaturated telluric lines is frequently better than 2% of the
continuum. Conclusion: Molecfit is able to accurately model and correct for
telluric lines over a broad range of wavelengths and spectral resolutions.
(Abridged)Comment: 18 pages, 13 figures, 5 tables, accepted for publication in Astronomy
and Astrophysic
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