1,156 research outputs found
Subtraction of test mass angular noise in the LISA Technology Package interferometer
We present recent sensitivity measurements of the LISA Technology Package
interferometer with articulated mirrors as test masses, actuated by
piezo-electric transducers. The required longitudinal displacement resolution
of 9 pm/sqrt[Hz] above 3 mHz has been demonstrated with an angular noise that
corresponds to the expected in on-orbit operation. The excess noise
contribution of this test mass jitter onto the sensitive displacement readout
was completely subtracted by fitting the angular interferometric data streams
to the longitudinal displacement measurement. Thus, this cross-coupling
constitutes no limitation to the required performance of the LISA Technology
Package interferometry.Comment: Applied Physics B - Lasers and Optics (2008
Interactions and screening in gated bilayer graphene nanoribbons
The effects of Coulomb interactions on the electronic properties of bilayer
graphene nanoribbons (BGNs) covered by a gate electrode are studied
theoretically. The electron density distribution and the potential profile are
calculated self-consistently within the Hartree approximation. A comparison to
their single-particle counterparts reveals the effects of interactions and
screening. Due to the finite width of the nanoribbon in combination with
electronic repulsion, the gate-induced electrons tend to accumulate along the
BGN edges where the potential assumes a sharp triangular shape. This has a
profound effect on the energy gap between electron and hole bands, which
depends nonmonotonously on the gate voltage and collapses at intermediate
electric fields. We interpret this behavior in terms of interaction-induced
warping of the energy dispersion.Comment: 6 pages, 4 figure
Edge disorder induced Anderson localization and conduction gap in graphene nanoribbons
We study the effect of the edge disorder on the conductance of the graphene
nanoribbons (GNRs). We find that only very modest edge disorder is sufficient
to induce the conduction energy gap in the otherwise metallic GNRs and to lift
any difference in the conductance between nanoribbons of different edge
geometry. We relate the formation of the conduction gap to the pronounced edge
disorder induced Anderson-type localization which leads to the strongly
enhanced density of states at the edges, formation of surface-like states and
to blocking of conductive paths through the ribbons
Electronic properties of quantum dots formed by magnetic double barriers in quantum wires
The transport through a quantum wire exposed to two magnetic spikes in series
is modeled. We demonstrate that quantum dots can be formed this way which
couple to the leads via magnetic barriers. Conceptually, all quantum dot states
are accessible by transport experiments. The simulations show Breit-Wigner
resonances in the closed regime, while Fano resonances appear as soon as one
open transmission channel is present. The system allows to tune the dot's
confinement potential from sub-parabolic to superparabolic by experimentally
accessible parameters.Comment: 5 pages, 5 figure
Precision absolute measurement and alignment of laser beam direction and position
For the construction of high-precision optical assemblies, direction and position measurement and control of the involved laser beams are essential. While optical components such as beamsplitters and mirrors can be positioned and oriented accurately using coordinate measuring machines (CMMs), the position and direction control of laser beams is a much more intriguing task since the beams cannot be physically contacted. We present an easy-to-implement method to both align and measure the direction and position of a laser beam using a CMM in conjunction with a position-sensitive quadrant photodiode. By comparing our results to calibrated angular and positional measurements we can conclude that with the proposed method, a laser beam can be both measured and aligned to the desired direction and position with 10 μrad angular and 3 μm positional accuracy
STRATEGIES AGAINST PARTICLE FOULING IN THE CHANNELS OF A MICRO HEAT EXCHANGER SUBJECT TO μPIV FLOW PATTERN MEASUREMENTS
Non-Equilibrium Dynamics of Correlated Electron Transfer in Molecular Chains
The relaxation dynamics of correlated electron transport (ET) along molecular
chains is studied based on a substantially improved numerically exact path
integral Monte Carlo (PIMC) approach. As archetypical model we consider a
Hubbard chain containing two interacting electrons coupled to a bosonic bath.
For this generalization of the ubiquitous spin-boson model, the intricate
interdependence of correlations and dissipation leads to non-Boltzmann thermal
equilibrium distributions for many-body states. By mapping the multi-particle
dynamics onto an isomorphic single particle motion this phenomenon is shown to
be sensitive to the particle statistics and due to its robustness allows for
new control schemes in designed quantum aggregates.Comment: 5 pages, 4 figure
Resonant reflection at magnetic barriers in quantum wires
The conductance of a quantum wire containing a single magnetic barrier is
studied numerically by means of the recursive Greens function technique. For
sufficiently strong and localized barriers, Fano - type reflection resonances
are observed close to the pinch-off regime. They are attributed to a
magnetoelectric vortex-type quasibound state inside the magnetic barrier that
interferes with an extended mode outside. We furthermore show that disorder can
substantially modify the residual conductance around the pinch-off regime.Comment: 7 pages, 5 figure
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