13,326 research outputs found
A review of residual stress analysis using thermoelastic techniques
Thermoelastic Stress Analysis (TSA) is a full-field technique for experimental stress analysis
that is based on infra-red thermography. The technique has proved to be extremely effective for
studying elastic stress fields and is now well established. It is based on the measurement of the
temperature change that occurs as a result of a stress change. As residual stress is essentially a
mean stress it is accepted that the linear form of the TSA relationship cannot be used to
evaluate residual stresses. However, there are situations where this linear relationship is not
valid or departures in material properties due to manufacturing procedures have enabled
evaluations of residual stresses. The purpose of this paper is to review the current status of
using a TSA based approach for the evaluation of residual stresses and to provide some
examples of where promising results have been obtained
Search for correlation effects in linear chains of trapped ions
We report a precise search for correlation effects in linear chains of 2 and
3 trapped Ca+ ions. Unexplained correlations in photon emission times within a
linear chain of trapped ions have been reported, which, if genuine, cast doubt
on the potential of an ion trap to realize quantum information processing. We
observe quantum jumps from the metastable 3d 2D_{5/2} level for several hours,
searching for correlations between the decay times of the different ions. We
find no evidence for correlations: the number of quantum jumps with separations
of less than 10 ms is consistent with statistics to within errors of 0.05%; the
lifetime of the metastable level derived from the data is consistent with that
derived from independent single-ion data at the level of the experimental
errors 1%; and no rank correlations between the decay times were found with
sensitivity to rank correlation coefficients at the level of |R| = 0.024.Comment: With changes to introduction. 5 pages, including 4 figures. Submitted
to Europhys. Let
Optimal Computation of Avoided Words
The deviation of the observed frequency of a word from its expected
frequency in a given sequence is used to determine whether or not the word
is avoided. This concept is particularly useful in DNA linguistic analysis. The
value of the standard deviation of , denoted by , effectively
characterises the extent of a word by its edge contrast in the context in which
it occurs. A word of length is a -avoided word in if
, for a given threshold . Notice that such a word
may be completely absent from . Hence computing all such words na\"{\i}vely
can be a very time-consuming procedure, in particular for large . In this
article, we propose an -time and -space algorithm to compute all
-avoided words of length in a given sequence of length over a
fixed-sized alphabet. We also present a time-optimal -time and
-space algorithm to compute all -avoided words (of any
length) in a sequence of length over an alphabet of size .
Furthermore, we provide a tight asymptotic upper bound for the number of
-avoided words and the expected length of the longest one. We make
available an open-source implementation of our algorithm. Experimental results,
using both real and synthetic data, show the efficiency of our implementation
Lignin-First Fractionation of Softwood Lignocellulose Using a Mild Dimethyl Carbonate and Ethylene Glycol Organosolv Process
A mild lignin-first acidolysis process (140 °C, 40 min) was developed using the benign solvent dimethyl carbonate (DMC) and ethylene glycol (EG) as a stabilization agent/solvent to produce a high yield of aromatic monophenols directly from softwood lignocellulose (pine, spruce, cedar, and Douglas fir) with a depolymerization efficiency of 77–98 %. Under the optimized conditions (140 °C, 40 min, 400 wt % EG and 2 wt % H2SO4 to pinewood), up to 9 wt % of the aromatic monophenol was produced, reaching a degree of delignification in pinewood of 77 %. Cellulose was also preserved, as evidenced by a 85 % glucose yield after enzymatic digestion. An in-depth analysis of the depolymerization oil was conducted by using GC-MS, HPLC, 2 D-NMR, and size-exclusion chromatography, which provided structural insights into lignin-derived dimers and oligomers and the composition of the sugars and derived molecules. Mass balance evaluation was performed
Surface plasmon modes and the Casimir energy
We show the influence of surface plasmons on the Casimir effect between two
plane parallel metallic mirrors at arbitrary distances. Using the plasma model
to describe the optical response of the metal, we express the Casimir energy as
a sum of contributions associated with evanescent surface plasmon modes and
propagative cavity modes. In contrast to naive expectations, the plasmonic
modes contribution is essential at all distances in order to ensure the correct
result for the Casimir energy. One of the two plasmonic modes gives rise to a
repulsive contribution, balancing out the attractive contributions from
propagating cavity modes, while both contributions taken separately are much
larger than the actual value of the Casimir energy. This also suggests
possibilities to tailor the sign of the Casimir force via surface plasmons.Comment: 4 pages, 3 figures, revtex
Thermodynamic Scaling of the Viscosity of Van Der Waals, H-Bonded, and Ionic Liquids
Viscosities and their temperature, T, and volume, V, dependences are reported
for 7 molecular liquids and polymers. In combination with literature viscosity
data for 5 other liquids, we show that the superpositioning of relaxation times
for various glass-forming materials when expressed as a function of TV^g, where
the exponent g is a material constant, can be extended to the viscosity. The
latter is usually measured to higher temperatures than the corresponding
relaxation times, demonstrating the validity of the thermodynamic scaling
throughout the supercooled and higher T regimes. The value of g for a given
liquid principally reflects the magnitude of the intermolecular forces (e.g.,
steepness of the repulsive potential); thus, we find decreasing g in going from
van der Waals fluids to ionic liquids. For strongly H-bonded materials, such as
low molecular weight polypropylene glycol and water, the superpositioning
fails, due to the non-trivial change of chemical structure (degree of
H-bonding) with thermodynamic conditions.Comment: 16 pages 7 figure
Lichens of six vernal pools in Acadia National Park, ME, USA
Whereas lichen-habitat relations have been well-documented globally, literature on lichens of vernal pools is scant. We surveyed six vernal pools at Acadia National Park on Mount Desert Island, Maine, USA for their lichen diversity. Sixty-seven species were identified, including seven species that are new reports for Acadia National Park: Fuscidea arboricola, Hypogymnia incurvoides, Lepraria finkii, Phaeographis inusta, Ropalospora viridis, Usnea flammea, and Violella fucata. Five species are considered uncommon or only locally common in New England: Everniastrum catawbiense, Hypogymnia krogiae, Pseudevernia cladonia, Usnea flammea, and Usnea merrillii. This work represents the first survey of lichens from vernal pools in Acadia National Park and strongly suggests that previous efforts at documenting species at the Park have underestimated its species diversity. More work should be conducted to determine whether a unique assemblage of lichens occurs in association with this unique habitat type
The statistical mechanics of a polygenic characterunder stabilizing selection, mutation and drift
By exploiting an analogy between population genetics and statistical
mechanics, we study the evolution of a polygenic trait under stabilizing
selection, mutation, and genetic drift. This requires us to track only four
macroscopic variables, instead of the distribution of all the allele
frequencies that influence the trait. These macroscopic variables are the
expectations of: the trait mean and its square, the genetic variance, and of a
measure of heterozygosity, and are derived from a generating function that is
in turn derived by maximizing an entropy measure. These four macroscopics are
enough to accurately describe the dynamics of the trait mean and of its genetic
variance (and in principle of any other quantity). Unlike previous approaches
that were based on an infinite series of moments or cumulants, which had to be
truncated arbitrarily, our calculations provide a well-defined approximation
procedure. We apply the framework to abrupt and gradual changes in the optimum,
as well as to changes in the strength of stabilizing selection. Our
approximations are surprisingly accurate, even for systems with as few as 5
loci. We find that when the effects of drift are included, the expected genetic
variance is hardly altered by directional selection, even though it fluctuates
in any particular instance. We also find hysteresis, showing that even after
averaging over the microscopic variables, the macroscopic trajectories retain a
memory of the underlying genetic states.Comment: 35 pages, 8 figure
Scalar Casimir densities for cylindrically symmetric Robin boundaries
Wightman function, the vacuum expectation values of the field square and the
energy-momentum tensor are investigated for a massive scalar field with general
curvature coupling parameter in the region between two coaxial cylindrical
boundaries. It is assumed that the field obeys general Robin boundary
conditions on bounding surfaces. The application of a variant of the
generalized Abel-Plana formula allows to extract from the expectation values
the contribution from single shells and to present the interference part in
terms of exponentially convergent integrals. The vacuum forces acting on the
boundaries are presented as the sum of self-action and interaction terms. The
first one contains well-known surface divergences and needs a further
renormalization. The interaction forces between the cylindrical boundaries are
finite and are attractive for special cases of Dirichlet and Neumann scalars.
For the general Robin case the interaction forces can be both attractive or
repulsive depending on the coefficients in the boundary conditions. The total
Casimir energy is evaluated by using the zeta function regularization
technique. It is shown that it contains a part which is located on bounding
surfaces. The formula for the interference part of the surface energy is
derived and the energy balance is discussed.Comment: 22 pages, 5 figure
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