1,900 research outputs found
Protein adsorption and interfacial rheology interfering in dilatational experiment
The static and dilatational response of β-lactoglobulin fibrils and native β-lactoglobulin (monomers) at water-air and water-oil interfaces (pH 2) was measured using the pendant drop method. The resulting adsorption behavior and viscoelasticity is dependent of concentration and adsorption time. The interfacial pressure of the β-lactoglobulin fibrils obtained in static measurements was 16-18 mN/m (against air) and 7 mN/m (against oil) for all concentrations. With higher concentrations, faster adsorption kinetics and slightly higher interfacial and surface pressure is achieved but did not lead to higher viscoelastic moduli. The transient saturation of the interface is similar for both the fibril solution and the monomers, however the fibril solution forms a strong viscoelastic network. To evaluate the superimposed adsorption behavior and rheological properties, the formed interfacial layer was subjected to dilatational experiments, which were performed by oscillating the surface area of the drop in sinusoidal and sawtooth (diagonal) deformation manner. The sinusoidal oscillations (time depended area deformation rate) result in a complex interfacial tension behavior against air and oil interfaces and show remarkable differences during compression and expansion as emphasized by Lissajous figures. For diagonal (constant area deformation rate) experiments, a slight bending of the interfacial tension response was observed at low frequencies emphasizing the influence of protein adsorption during rheological measurement
L^2-Betti numbers of one-relator groups
We determine the L^2-Betti numbers of all one-relator groups and all
surface-plus-one-relation groups (surface-plus-one-relation groups were
introduced by Hempel who called them one-relator surface groups). In particular
we show that for all such groups G, the L^2-Betti numbers b_n^{(2)}(G) are 0
for all n>1. We also obtain some information about the L^2-cohomology of
left-orderable groups, and deduce the non-L^2 result that, in any
left-orderable group of homological dimension one, all two-generator subgroups
are free.Comment: 18 pages, version 3, minor changes. To appear in Math. An
Resummation of Nonalternating Divergent Perturbative Expansions
A method for the resummation of nonalternating divergent perturbation series
is described. The procedure constitutes a generalization of the Borel-Pad\'{e}
method. Of crucial importance is a special integration contour in the complex
plane. Nonperturbative imaginary contributions can be inferred from the purely
real perturbative coefficients. A connection is drawn from the quantum field
theoretic problem of resummation to divergent perturbative expansions in other
areas of physics.Comment: 5 pages, LaTeX, 2 tables, 1 figure; discussion of the Carleman
criterion added; version to appear in Phys. Rev.
from decays: contour-improved versus fixed-order summation in a new QCD perturbation expansion
We consider the determination of from hadronic decays, by
investigating the contour-improved (CI) and the fixed-order (FO)
renormalization group summations in the frame of a new perturbation expansion
of QCD, which incorporates in a systematic way the available information about
the divergent character of the series. The new expansion functions, which
replace the powers of the coupling, are defined by the analytic continuation in
the Borel complex plane, achieved through an optimal conformal mapping. Using a
physical model recently discussed by Beneke and Jamin, we show that the new
CIPT approaches the true results with great precision when the perturbative
order is increased, while the new FOPT gives a less accurate description in the
regions where the imaginary logarithms present in the expansion of the running
coupling are large. With the new expansions, the discrepancy of 0.024 in
between the standard CI and FO summations is reduced to
only 0.009. From the new CIPT we predict , which practically coincides with the result of the
standard FOPT, but has a more solid theoretical basis
Monte Carlo simulation of subsurface ordering kinetics in an fcc-alloy model
Within the atom-vacancy exchange mechanism in a nearest-neighbor interaction
model we investigate the kinetics of surface-induced ordering processes close
to the (001) surface of an fcc A_3B-alloy. After a sudden quench into the
ordered phase with a final temperature above the ordering spinodal, T_f > T_sp,
the early time kinetics is dominated by a segregation front which propagates
into the bulk with nearly constant velocity. Below the spinodal, T_f < T_sp,
motion of the segregation wave reflects a coarsening process which appears to
be slower than predicted by the Lifschitz-Allen-Cahn law. In addition, in the
front-penetrated region lateral growth differs distinctly from perpendicular
growth, as a result of the special structure of antiphase boundaries near the
surface. Our results are compared with recent experiments on the subsurface
ordering kinetics at Cu_3Au (001).Comment: 10 pages, 9 figures, submitted to Phys. Rev. B, in prin
A Measurement of the Flux of Cosmic Ray Iron at 5 x 10^13 eV
We present results from the initial flight of our Balloon Air CHerenkov
(BACH) payload. BACH detects air Cherenkov radiation from cosmic ray nuclei as
coincident flashes in two optical modules. The flight (dubbed PDQ BACH) took
place on April 22, 1998 from Ft. Sumner, New Mexico. During an exposure of 2.75
hours, with a typical threshold energy for iron nuclei of 2.2
eV, we observed several events cleanly identifiable as iron group nuclei.
Analysis of the data yields a new flux measurement that is fully consistent
with that reported by other investigations.Comment: 16 pages, 7 Figures, accepted for publication in Astroparticle
Physic
Restoration of supersymmetric Slavnov-Taylor and Ward identities in presence of soft and spontaneous symmetry breaking
Supersymmetric Slavnov-Taylor and Ward identities are investigated in
presence of soft and spontaneous symmetry breaking. We consider an abelian
model where soft supersymmetry breaking yields a mass splitting between
electron and selectron and triggers spontaneous symmetry breaking, and we
derive corresponding identities that relate the electron and selectron masses
with the Yukawa coupling. We demonstrate that the identities are valid in
dimensional reduction and invalid in dimensional regularization and compute the
necessary symmetry-restoring counterterms.Comment: 35 pages, LaTeX, 9 postscript figure
Solitary magnetic perturbations at the ELM onset
Edge localised modes (ELMs) allow maintaining sufficient purity of tokamak
H-mode plasmas and thus enable stationary H-mode. On the other hand in a future
device ELMs may cause divertor power flux densities far in excess of tolerable
material limits. The size of the energy loss per ELM is determined by
saturation effects in the non-linear phase of the ELM, which at present is
hardly understood. Solitary magnetic perturbations (SMPs) are identified as
dominant features in the radial magnetic fluctuations below 100kHz. They are
typically observed close (+-0.1ms) to the onset of pedestal erosion. SMPs are
field aligned structures rotating in the electron diamagnetic drift direction
with perpendicular velocities of about 10km/s. A comparison of perpendicular
velocities suggests that the perturbation evoking SMPs is located at or inside
the separatrix. Analysis of very pronounced examples showed that the number of
peaks per toroidal turn is 1 or 2, which is clearly lower than corresponding
numbers in linear stability calculations. In combination with strong peaking of
the magnetic signals this results in a solitary appearance resembling modes
like palm tree modes, edge snakes or outer modes. This behavior has been
quantified as solitariness and correlated to main plasma parameters. SMPs may
be considered as a signature of the non-linear ELM-phase originating at the
separatrix or further inside. Thus they provide a handle to investigate the
transition from linear to non-linear ELM phase. By comparison with data from
gas puff imaging processes in the non-linear phase at or inside the separatrix
and in the scrape-off-layer (SOL) can be correlated. A connection between the
passing of an SMP and the onset of radial filament propagation has been found.
Eventually the findings related to SMPs may contribute to a future quantitative
understanding of the non-linear ELM evolution.Comment: submitted to Nuclear Fusio
Dzyaloshinskii-Moriya interaction in NaVO: a microscopic study
We present a unified account of magnetic exchange and Raman scattering in the
quasi-one-dimensional transition-metal oxide NaVO. Based on a
cluster-model approach explicit expressions for the exchange integral and the
Raman-operator are given. It is demonstrated that a combination of the
electronic-structure and the Dzyaloshinskii-Moriya interaction, allowed by
symmetry in this material, are responsible for the finite Raman cross-section
giving rise to both, one- and two-magnon scattering amplitudes.Comment: 7 pages, 1 figur
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