3,383 research outputs found
Interaction-assisted propagation of Coulomb-correlated electron-hole pairs in disordered semiconductors
A two-band model of a disordered semiconductor is used to analyze dynamical
interaction induced weakening of localization in a system that is accessible to
experimental verification. The results show a dependence on the sign of the
two-particle interaction and on the optical excitation energy of the
Coulomb-correlated electron-hole pair.Comment: 4 pages and 3 ps figure
Tuning of structure inversion asymmetry by the -doping position in (001)-grown GaAs quantum wells
Structure and bulk inversion asymmetry in doped (001)-grown GaAs quantum
wells is investigated by applying the magnetic field induced photogalvanic
effect. We demonstrate that the structure inversion asymmetry (SIA) can be
tailored by variation of the delta-doping layer position. Symmetrically-doped
structures exhibit a substantial SIA due to impurity segregation during the
growth process. Tuning the SIA by the delta-doping position we grow samples
with almost equal degrees of structure and bulk inversion asymmetry.Comment: 4 pages 2 figure
Algorithms and literate programs for weighted low-rank approximation with missing data
Linear models identification from data with missing values is posed as a weighted low-rank approximation problem with weights related to the missing values equal to zero. Alternating projections and variable projections methods for solving the resulting problem are outlined and implemented in a literate programming style, using Matlab/Octave's scripting language. The methods are evaluated on synthetic data and real data from the MovieLens data sets
Non-universal dynamics of dimer growing interfaces
A finite temperature version of body-centered solid-on-solid growth models
involving attachment and detachment of dimers is discussed in 1+1 dimensions.
The dynamic exponent of the growing interface is studied numerically via the
spectrum gap of the underlying evolution operator. The finite size scaling of
the latter is found to be affected by a standard surface tension term on which
the growth rates depend. This non-universal aspect is also corroborated by the
growth behavior observed in large scale simulations. By contrast, the
roughening exponent remains robust over wide temperature ranges.Comment: 11 pages, 7 figures. v2 with some slight correction
Solving the Richardson equations for Fermions
Forty years ago Richardson showed that the eigenstates of the pairing
Hamiltonian with constant interaction strength can be calculated by solving a
set of non-linear coupled equations. However, in the case of Fermions these
equations lead to singularities which made them very hard to solve. This letter
explains how these singularities can be avoided through a change of variables
making the Fermionic pairing problem numerically solvable for arbitrary single
particle energies and degeneracies.Comment: 5 pages, 4 figures, submitted to Phys.Rev.
Hydrodynamics of flagellated microswimmers near free-slip interfaces
The hydrodynamics of a flagellated microorganism is investigated when
swimming close to a planar free-slip surface by means of numerical solu- tions
of the Stokes equations obtained via a Boundary Element Method. Depending on
the initial condition, the swimmer can either escape from the free-slip surface
or collide with the boundary. Interestingly, the mi- croorganism does not
exhibit a stable orbit. Independently of escape or attraction to the interface,
close to a free-slip surface, the swimmer fol- lows a counter-clockwise
trajectory, in agreement with experimental find- ings, [15]. The hydrodynamics
is indeed modified by the free-surface. In fact, when the same swimmer moves
close to a no-slip wall, a set of initial conditions exists which result in
stable orbits. Moreover when moving close to a free-slip or a no-slip boundary
the swimmer assumes a different orientation with respect to its trajectory.
Taken together, these results contribute to shed light on the hydrodynamical
behaviour of microorgan- isms close to liquid-air interfaces which are relevant
for the formation of interfacial biofilms of aerobic bacteria
Electric Dipole Moments and Polarizability in the Quark-Diquark Model of the Neutron
For a bound state internal wave function respecting parity symmetry, it can
be rigorously argued that the mean electric dipole moment must be strictly
zero. Thus, both the neutron, viewed as a bound state of three quarks, and the
water molecule, viewed as a bound state of ten electrons two protons and an
oxygen nucleus, both have zero mean electric dipole moments. Yet, the water
molecule is said to have a nonzero dipole moment strength with
. The neutron may also be said to have
an electric dipole moment strength with .
The neutron analysis can be made experimentally consistent, if one employs a
quark-diquark model of neutron structure.Comment: four pages, two figure
Network connectivity during mergers and growth: optimizing the addition of a module
The principal eigenvalue of a network's adjacency matrix often
determines dynamics on the network (e.g., in synchronization and spreading
processes) and some of its structural properties (e.g., robustness against
failure or attack) and is therefore a good indicator for how ``strongly'' a
network is connected. We study how is modified by the addition of a
module, or community, which has broad applications, ranging from those
involving a single modification (e.g., introduction of a drug into a biological
process) to those involving repeated additions (e.g., power-grid and transit
development). We describe how to optimally connect the module to the network to
either maximize or minimize the shift in , noting several applications
of directing dynamics on networks.Comment: 7 pages, 5 figure
Space-Time Approach to Scattering from Many Body Systems
We present scattering from many body systems in a new light. In place of the
usual van Hove treatment, (applicable to a wide range of scattering processes
using both photons and massive particles) based on plane waves, we calculate
the scattering amplitude as a space-time integral over the scattering sample
for an incident wave characterized by its correlation function which results
from the shaping of the wave field by the apparatus. Instrument resolution
effects - seen as due to the loss of correlation caused by the path differences
in the different arms of the instrument are automatically included and analytic
forms of the resolution function for different instruments are obtained. The
intersection of the moving correlation volumes (those regions where the
correlation functions are significant) associated with the different elements
of the apparatus determines the maximum correlation lengths (times) that can be
observed in a sample, and hence, the momentum (energy) resolution of the
measurement. This geometrical picture of moving correlation volumes derived by
our technique shows how the interaction of the scatterer with the wave field
shaped by the apparatus proceeds in space and time. Matching of the correlation
volumes so as to maximize the intersection region yields a transparent,
graphical method of instrument design. PACS: 03.65.Nk, 3.80 +r, 03.75, 61.12.BComment: Latex document with 6 fig
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