790 research outputs found
The Impact of Current and Future Metrication Trends Upon Construction Uses of Forest Products1
Universal Multifractality in Quantum Hall Systems with Long-Range Disorder Potential
We investigate numerically the localization-delocalization transition in
quantum Hall systems with long-range disorder potential with respect to
multifractal properties. Wavefunctions at the transition energy are obtained
within the framework of the generalized Chalker--Coddington network model. We
determine the critical exponent characterizing the scaling behavior
of the local order parameter for systems with potential correlation length
up to magnetic lengths . Our results show that does not
depend on the ratio . With increasing , effects due to classical
percolation only cause an increase of the microscopic length scale, whereas the
critical behavior on larger scales remains unchanged. This proves that systems
with long-range disorder belong to the same universality class as those with
short-range disorder.Comment: 4 pages, 2 figures, postsript, uuencoded, gz-compresse
Excitation of Small Quantum Systems by High-Frequency Fields
The excitation by a high frequency field of multi--level quantum systems with
a slowly varying density of states is investigated. A general approach to study
such systems is presented. The Floquet eigenstates are characterized on several
energy scales. On a small scale, sharp universal quasi--resonances are found,
whose shape is independent of the field parameters and the details of the
system. On a larger scale an effective tight--binding equation is constructed
for the amplitudes of these quasi--resonances. This equation is non--universal;
two classes of examples are discussed in detail.Comment: 4 pages, revtex, no figure
Behaviour of three charged particles on a plane under perpendicular magnetic field
We consider the problem of three identical charged particles on a plane under
a perpendicular magnetic field and interacting through Coulomb repulsion. This
problem is treated within Taut's framework, in the limit of vanishing center of
mass vector , which corresponds to the strong magnetic
field limit, occuring for example in the Fractional Quantum Hall Effect. Using
the solutions of the biconfluent Heun equation, we compute the eigenstates and
show that there is two sets of solutions. The first one corresponds to a system
of three independent anyons which have their angular momenta fixed by the value
of the magnetic field and specified by a dimensionless parameter , the ratio of , the magnetic length, over , the Bohr
radius. This anyonic character, consistent with quantum mechanics of identical
particles in two dimensions, is induced by competing physical forces. The
second one corresponds to the case of the Landau problem when .
Finally we compare these states with the quantum Hall states and find that the
Laughlin wave functions are special cases of our solutions under certains
conditions.Comment: 15 pages, 3 figures, Accepeted in JP
Spektrum der zirkulierenden Schilddrüsenhormone und ihrer Jodderivate im menschlichen Blut. Zur Problematik ihrer Darstellung und Identifikation
Peer Reviewe
Quasiparticle transport equation with collision delay. II. Microscopic Theory
For a system of non-interacting electrons scattered by neutral impurities, we
derive a modified Boltzmann equation that includes quasiparticle and virial
corrections. We start from quasiclassical transport equation for
non-equilibrium Green's functions and apply limit of small scattering rates.
Resulting transport equation for quasiparticles has gradient corrections to
scattering integrals. These gradient corrections are rearranged into a form
characteristic for virial corrections
Mobility gap in fractional quantum Hall liquids: Effects of disorder and layer thickness
We study the behavior of two-dimensional electron gas in the fractional
quantum Hall regime in the presence of finite layer thickness and correlated
disordered potential. Generalizing the Chern number calculation to many-body
systems, we determine the mobility gaps of fractional quantum Hall states based
on the distribution of Chern numbers in a microscopic model. We find excellent
agreement between experimentally measured activation gaps and our calculated
mobility gaps, when combining the effects of both disordered potential and
layer thickness. We clarify the difference between mobility gap and spectral
gap of fractional quantum Hall states and explain the disorder-driven collapse
of the gap and the subsequent transitions from the fractional quantum Hall
states to insulator.Comment: 13 pages, 8 figure
On the Electromagnetic Response of Charged Bosons Coupled to a Chern-Simons Gauge Field: A Path Integral Approach
We analyze the electromagnetic response of a system of charged bosons coupled
to a Chern-Simons gauge field. Path integral techniques are used to obtain an
effective action for the particle density of the system dressed with quantum
fluctuations of the CS gauge field. From the action thus obtained we compute
the U(1) current of the theory for an arbitrary electromagnetic external field.
For the particular case of a homogeneous external magnetic field, we show that
the quantization of the transverse conductivity is exact, even in the presence
of an arbitrary impurity distribution. The relevance of edge states in this
context is analyzed. The propagator of density fluctuations is computed, and an
effective action for the matter density in the presence of a vortex excitation
is suggested.Comment: LaTex file, 27 pages, no figure
Superconducting Topological Fluids in Josephson Junction Arrays
We argue that the frustrated Josephson junction arrays may support a
topologically ordered superconducting ground state, characterized by a
non-trivial ground state degeneracy on the torus. This superconducting quantum
fluid provides an explicit example of a system in which superconductivity
arises from a topological mechanism rather than from the usual Landau-Ginzburg
mechanism.Comment: 4 page
Design, development and deployment of a hand/wrist exoskeleton for home-based rehabilitation after stroke - SCRIPT project
YesChanges in world-wide population trends have provided new demands for new technologies in areas
such as care and rehabilitation. Recent developments in the the field of robotics for neurorehabilitation
have shown a range of evidence regarding usefulness of these technologies as a tool to augment
traditional physiotherapy. Part of the appeal for these technologies is the possibility to place a
rehabilitative tool in one’s home, providing a chance for more frequent and accessible technologies
for empowering individuals to be in charge of their therapy.
Objective: this manuscript introduces the Supervised Care and Rehabilitation Involving Personal
Tele-robotics (SCRIPT) project. The main goal is to demonstrate design and development steps
involved in a complex intervention, while examining feasibility of using an instrumented orthotic
device for home-based rehabilitation after stroke.
Methods: the project uses a user-centred design methodology to develop a hand/wrist
rehabilitation device for home-based therapy after stroke. The patient benefits from a dedicated
user interface that allows them to receive feedback on exercise as well as communicating with
the health-care professional. The health-care professional is able to use a dedicated interface
to send/receive communications and remote-manage patient’s exercise routine using provided
performance benchmarks. Patients were involved in a feasibility study (n=23) and were instructed to
use the device and its interactive games for 180 min per week, around 30 min per day, for a period of
6 weeks, with a 2-months follow up. At the time of this study, only 12 of these patients have finished
their 6 weeks trial plus 2 months follow up evaluation.
Results: with the “use feasibility” as objective, our results indicate 2 patients dropping out due
to technical difficulty or lack of personal interests to continue. Our frequency of use results indicate
that on average, patients used the SCRIPT1 device around 14 min of self-administered therapy a day.
The group average for the system usability scale was around 69% supporting system usability.
Conclusions: based on the preliminary results, it is evident that stroke patients were able to use the
system in their homes. An average of 14 min a day engagement mediated via three interactive games
is promising, given the chronic stage of stroke. During the 2nd year of the project, 6 additional games
with more functional relevance in their interaction have been designed to allow for a more variant context for interaction with the system, thus hoping to positively influence the exercise duration.
The system usability was tested and provided supporting evidence for this parameter. Additional
improvements to the system are planned based on formative feedback throughout the project and
during the evaluations. These include a new orthosis that allows a more active control of the amount
of assistance and resistance provided, thus aiming to provide a more challenging interaction.This work has been partially funded under Grant FP7-ICT-288698(SCRIPT) of the European Community Seventh Framework Programme
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