864 research outputs found
Internal tension in a collapsed polymer under shear flow and the connection to enzymatic cleavage of von Willebrand factor
By means of Brownian hydrodynamics simulations we show that the tension
distribution along the contour of a single collapsed polymer in shear flow is
inhomogeneous and above a threshold shear rate exhibits a double-peak
structure when hydrodynamic interactions are taken into account. We argue that
the tension maxima close to the termini of the polymer chain reflect the
presence of polymeric protrusions. We establish the connection to shear-
induced globule unfolding and determine the scaling behavior of the maximal
tensile forces and the average protrusion length as a function of shear rate,
globule size, and cohesive strength. A quasi-equilibrium theory is employed in
order to describe the simulation results. Our results are used to explain
experimental data for the shear-sensitive enzymatic degradation of von
Willebrand factor
Spontaneous spin polarization in doped semiconductor quantum wells
We calculate the critical density of the zero-temperature, first-order
ferromagnetic phase transition in n-doped GaAs/AlGaAs quantum wells. We find
that the existence of the ferromagnetic transition is dependent upon the choice
of well width. We demonstrate rigorously that this dependence is governed by
the interplay between different components of the exchange interaction and that
there exists an upper limit for the well width beyond which there is no
transition. We predict that some narrow quantum wells could exhibit this
transition at electron densities lower than the ones that have been considered
experimentally thus far. We use a screened Hartree-Fock approximation with a
polarization-dependent effective mass, which is adjusted to match the critical
density predicted by Monte Carlo calculations for the two-dimensional electron
gas.Comment: Submitted to Eur. Phys. Journal
ICONGETM v1.0 – flexible NUOPC-driven two-way coupling via ESMF exchange grids between the unstructured-grid atmosphere model ICON and the structured-grid coastal ocean model GETM
Two-way model coupling is important for representing the mutual interactions and feedbacks between atmosphere and ocean dynamics. This work presents the development of the two-way coupled model system ICONGETM, consisting of the atmosphere model ICON and the ocean model GETM. ICONGETM is built on the latest NUOPC coupling software with flexible data exchange and conservative interpolation via ESMF exchange grids. With ICON providing a state-of-the-art kernel for numerical weather prediction on an unstructured mesh and GETM being an established coastal ocean model, ICONGETM is especially suited for high-resolution studies. For demonstration purposes the newly developed model system has been applied to a coastal upwelling scenario in the central Baltic Sea
On the c-axis optical reflectivity of layered cuprate superconductors
Using a conventional BCS -- Fermi liquid model we calculate the c-axis
optical reflectivity of the layered high temperature cuprate superconductors by
obtaining the finite temperature dynamical dielectric function in a microscopic
self-consistent gauge invariant formalism. We get good semi-quantitative
agreement with all the existing experimental data by using the measured normal
state resistivities as the input parameters in obtaining the c-axis
hopping amplitude and the normal state level broadening in our microscopic
calculation.Comment: 10 pages, 6 figures, 1 table gzipped tar fil
Disorder and chain superconductivity in YBa_2Cu_3O_{7-\delta}
The effects of chain disorder on superconductivity in YBa_2Cu_3O_{7-\delta}
are discussed within the context of a proximity model. Chain disorder causes
both pair-breaking and localization. The hybridization of chain and plane
wavefunctions reduces the importance of localization, so that the transport
anisotropy remains large in the presence of a finite fraction of
oxygen vacancies. Penetration depth and specific heat measurements probe the
pair-breaking effects of chain disorder, and are discussed in detail at the
level of the self-consistent T-matrix approximation. Quantitative agreement
with these experiments is found when chain disorder is present.Comment: 4 pages, 2 figures, submitted to PRB rapid communication
Combined potential and spin impurity scattering in cuprates
We present a theory of combined nonmagnetic and magnetic impurity scattering
in anisotropic superconductors accounting for the momentum-dependent impurity
potential. Applying the model to the d-wave superconducting state, we obtain a
quantitative agreement with the initial suppression of the critical temperature
due to Zn and Ni substitutions as well as electron irradiation defects in the
cuprates. We suggest, that the unequal pair-breaking effect of Zn and Ni may be
related to a different nature of the magnetic moments induced by these
impurities.Comment: 5 pages, 3 tables, RevTex, to be published in Phys. Rev.
Antiferromagnetic Interactions and the Superconducting Gap Function
Spin-fluctuation-mediated superconductivity is conventionally associated with
d_{x^2-y^2} pairing. We show that a generalized model of antiferromagnetic spin
fluctuations in three dimensions may also yield a state with formal ``s-wave''
(A_{1g}) symmetry but with line nodes at k_z \approx \pm \pi / 2c. We study
this new state within both BCS and Eliashberg theories using a realistic band
structure and find that it is more stable than the d_{x^2-y^2} (B_{1g}) state
over a wide range of parameters. Thus, models of spin-fluctuation-mediated
superconductivity must consider both possibilities on an equal footing.Comment: 4 pages, RevTeX with psfig, 2 PostScript figures included in
compressed form, one color PostScript figure available by request to
[email protected] or [email protected]. Minor changes and updated
references from original postin
Theory for Dynamical Short Range Order and Fermi Surface Volume in Strongly Correlated Systems
Using the fluctuation exchange approximation of the one band Hubbard model,
we discuss the origin of the changing Fermi surface volume in underdoped
cuprate systems due to the transfer of occupied states from the Fermi surface
to its shadow, resulting from the strong dynamical antiferromagnetic short
range correlations. The momentum and temperature dependence of the quasi
particle scattering rate shows unusual deviations from the conventional Fermi
liquid like behavior. Their consequences for the changing Fermi surface volume
are discussed. Here, we investigate in detail which scattering processes
might be responsible for a violation of the Luttinger theorem. Finally, we
discuss the formation of hole pockets near half filling.Comment: 5 pages, Revtex, 4 postscript figure
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