92 research outputs found
Influence of the charge carrier tunneling processes on the recombination dynamics in single lateral quantum dot molecules
We report on the charge carrier dynamics in single lateral quantum dot
molecules and the effect of an applied electric field on the molecular states.
Controllable electron tunneling manifests itself in a deviation from the
typical excitonic decay behavior which is strongly influenced by the tuning
electric field and inter-molecular Coulomb energies. A rate equation model is
developed to gain more insight into the charge transfer and tunneling
mechanisms. Non-resonant (phonon-mediated) electron tunneling which changes the
molecular exciton character from direct to indirect, and vice versa, is found
to be the dominant tunable decay mechanism of excitons besides radiative
recombination.Comment: 4 pages, 4 figure
Stiffness Changes due to Static Loading of a Brick Arch
A brick arch was loaded under laboratory conditions in three successive loading steps. No cracks were observed but reduction of natural frequencies and stiffness of the arch was experimentally documented. The stiffness was evaluated in a non-destructive test using an impact hammer and only two accelerometers. The proposed identification technique based on known experimental modal analysis theory is tailored to stiffness evaluation of masonry vaults. The results and the applied method are extensively discussed
Polarization fine-structure and enhanced single-photon emission of self-assembled lateral InGaAs quantum dot molecules embedded in a planar micro-cavity
Single lateral InGaAs quantum dot molecules have been embedded in a planar
micro-cavity in order to increase the luminescence extraction efficiency. Using
a combination of metal-organic vapor phase and molecular beam epitaxy samples
could be produced that exhibit a 30 times enhanced single-photon emission rate.
We also show that the single-photon emission is fully switchable between two
different molecular excitonic recombination energies by applying a lateral
electric field. Furthermore, the presence of a polarization fine-structure
splitting of the molecular neutral excitonic states is reported which leads to
two polarization-split classically correlated biexciton exciton cascades. The
fine-structure splitting is found to be on the order of 10 micro-eV.Comment: 14 pages, 4 figures; the following article has been submitted to
Journal of Applied Physics (29th ICPS - invited paper); after it is
published, it will be found at http://jap.aip.org
Stabilization and Consolidation of Historical Multi-Leaf Masonry
Historical masonry structures with a greater thickness can often be made as so called multi-leaf masonry with outer leaves lined with the application of some of the masonry bonding methods and with the inner leave of the so-called cast core formed by fragments of stones of different sizes that are bonded with more mortar. The load capacity, stiffness and the failure mechanism of multi-leaf masonry are influenced by the interaction of individual leaves with different deformation and physico-mechanical properties and the nature of the mutual connection of individual leaves of masonry. The performed analyses showed a significant influence of especially the cast core masonry tensile strength and the contact joint strength between the core masonry and the outer leaves
Science with a small two-band UV-photometry mission III: Active Galactic Nuclei and nuclear transients
In this review (the third in the series focused on a small two-band
UV-photometry mission), we assess possibilities for a small UV two-band
photometry mission in studying accreting supermassive black holes (SMBHs; mass
range -). We focus on the following
observational concepts: (i) dedicated monitoring of selected type-I Active
Galactic Nuclei (AGN) in order to measure the time delay between the far-UV,
the near-UV, and other wavebands (X-ray and optical), (ii) nuclear transients
including (partial) tidal disruption events and repetitive nuclear transients,
and (iii) the study of peculiar sources, such as changing-look AGN, hollows and
gaps in accretion disks, low-luminosity AGN, and candidates for
Intermediate-Mass Black Holes (IMBHs; mass range -)
in galactic nuclei. For tidal disruption events (TDEs), high-cadence UV
monitoring is crucial for distinguishing among different scenarios for the
origin of the UV emission. The small two-band UV space telescope will also
provide the information about the near- and far-UV continuum variability for
rare transients, such as repetitive partial TDEs and jetted TDEs. We also
discuss the possibilities to study and analyze sources with non-standard
accretion flows, such as AGN with gappy disks, low-luminosity active galactic
nuclei with intermittent accretion, and SMBH binaries potentially involving
intermediate-mass black holes.Comment: Submitted to Space Science Review
Conservation laws and evolution schemes in geodesic, hydrodynamic, and magnetohydrodynamic flows
Carter and Lichnerowicz have established that barotropic fluid flows are
conformally geodesic and obey Hamilton's principle. This variational approach
can accommodate neutral, or charged and poorly conducting, fluids. We show
that, unlike what has been previously thought, this approach can also
accommodate perfectly conducting magnetofluids, via the Bekenstein-Oron
description of ideal magnetohydrodynamics. When Noether symmetries associated
with Killing vectors or tensors are present in geodesic flows, they lead to
constants of motion polynomial in the momenta. We generalize these concepts to
hydrodynamic flows. Moreover, the Hamiltonian descriptions of ideal
magnetohydrodynamics allow one to cast the evolution equations into a
hyperbolic form useful for evolving rotating or binary compact objects with
magnetic fields in numerical general relativity. Conserved circulation laws,
such as those of Kelvin, Alfv\'en and Bekenstein-Oron, emerge simply as special
cases of the Poincar\'e-Cartan integral invariant of Hamiltonian systems. We
use this approach to obtain an extension of Kelvin's theorem to baroclinic
(non-isentropic) fluids, based on a temperature-dependent time parameter. We
further extend this result to perfectly or poorly conducting baroclinic
magnetoflows. Finally, in the barotropic case, such magnetoflows are shown to
also be geodesic, albeit in a Finsler (rather than Riemann) space.Comment: 23 page
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