31,239 research outputs found
Monte Carlo simulations of copolymers at homopolymer interfaces: Interfacial structure as a function of the copolymer density
By means of extensive Monte Carlo simulations of the bond fluctuation model,
we study the effect of adding AB diblock copolymers on the properties of an
interface between demixed homopolymer phases. The parameters are chosen such
that the homopolymers are strongly segregated, and the whole range of copolymer
concentrations in the two phase coexistence region is scanned. We compare the
``mushroom'' regime, in which copolymers are diluted and do not interact with
each other, with the ``wet brush'' regime, where copolymers overlap and
stretch, but are still swollen by the homopolymers. A ``dry brush'' regime is
never entered for our choice of chain lengths. ``Intrinsic'' profiles are
calculated using a block analysis method introduced by us in earlier work. We
discuss density profiles, orientational profiles and contact number profiles.
In general, the features of the profiles are similar at all copolymer
concentrations, however, the profiles in the concentrated regime are much
broader than in the dilute regime. The results compare well with
self-consistent field calculations.Comment: to appear in J. Chem. Phy
Taxation and Market Power
We analyze the incidence and welfare e¤ects of unit sales taxes in experimental monopoly and Bertrand markets. We nd, in line with economic theory, that rms with no market power are able to shift a high share of a tax burden on to consumers, independent of whether buyers are automated or human players. In monopoly markets, a monopolist bears a large share of the burden of a tax increase. With human buyers, however, this share is smaller than with automated buyers as the presence of human buyers constrains the pricing behavior of a monopolist.tax incidence;monopoly;Bertrand competition;experiment
Interaction-induced Renormalization of Andreev Reflection
We analyze the charge transport between a one-dimensional weakly interacting
electron gas and a superconductor within the scaling approach in the basis of
scattering states. We derive the renormalization group equations, which fully
account for the intrinsic energy dependence due to Andreev reflection. A strong
renormalization of the corresponding reflection phase is predicted even for a
perfectly transparent metal-superconductor interface. The interaction-induced
suppression of the Andreev conductance is shown to be highly sensitive to the
normal state resistance, providing a possible explanation of experiments with
carbon-nanotube/superconductor junctions by Morpurgo et al. [Science 286, 263
(2001)].Comment: 4 pages, 2 figure
Lorentz invariance violation and charge (non--)conservation: A general theoretical frame for extensions of the Maxwell equations
All quantum gravity approaches lead to small modifications in the standard
laws of physics which lead to violations of Lorentz invariance. One particular
example is the extended standard model (SME). Here, a general phenomenological
approach for extensions of the Maxwell equations is presented which turns out
to be more general than the SME and which covers charge non--conservation
(CNC), too. The new Lorentz invariance violating terms cannot be probed by
optical experiments but need, instead, the exploration of the electromagnetic
field created by a point charge or a magnetic dipole. Some scalar--tensor
theories and higher dimensional brane theories predict CNC in four dimensions
and some models violating Special Relativity have been shown to be connected
with CNC and its relation to the Einstein Equivalence Principle has been
discussed. Due to this upcoming interest, the experimental status of electric
charge conservation is reviewed. Up to now there seem to exist no unique tests
of charge conservation. CNC is related to the precession of polarization, to a
modification of the --Coulomb potential, and to a time-dependence of the
fine structure constant. This gives the opportunity to describe a dedicated
search for CNC.Comment: To appear in Physical Review
Electronic properties of disordered corner-sharing tetrahedral lattices
We have examined the behaviour of noninteracting electrons moving on a
corner-sharing tetrahedral lattice into which we introduce a uniform (box)
distribution, of width W, of random on-site energies. We have used both the
relative localization length and the spectral rigidity to analyze the nature of
the eigenstates, and have determined both the mobility edge trajectories as a
function of W, and the critical disorder, Wc, beyond which all states are
localized. We find (i) that the mobility edge trajectories (energies Ec vs.
disorder W) are qualitatively different from those found for a simple cubic
lattice, and (ii) that the spectral rigidity is scale invariant at Wc and thus
provides a reliable method of estimating this quantity -- we find Wc/t=14.5. We
discuss our results in the context of the metal-to-insulator transition
undergone by LiAlyTi{2-y}O4 in a quantum site percolation model that also
includes the above-mentioned Anderson disorder, and show that the effects
produced by Anderson disorder are far less important than those produced by
quantum site percolation, at least in the determination of the doping
concentration at which the metal-to-insulator transition is predicted to occur
Combined cerebellar and bilateral cervical posterior spinal artery stroke demonstrated on MRI
Combined cerebellar and spinal ischemic stroke is a rare, critical condition. We report a patient with combined cerebellar and bilateral posterolateral cervical spinal cord infarction due to bilateral stenosis of the vertebral arteries. MRI is the method of choice for imaging this condition; diffusion-weighted imaging of the spinal cord gives reliable results
Taxation and Market Power
We analyze the incidence and welfare e¤ects of unit sales taxes in experimental monopoly and Bertrand markets. We nd, in line with economic theory, that rms with no market power are able to shift a high share of a tax burden on to consumers, independent of whether buyers are automated or human players. In monopoly markets, a monopolist bears a large share of the burden of a tax increase. With human buyers, however, this share is smaller than with automated buyers as the presence of human buyers constrains the pricing behavior of a monopolist.
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