102 research outputs found
Quality Assessment of Linked Datasets using Probabilistic Approximation
With the increasing application of Linked Open Data, assessing the quality of
datasets by computing quality metrics becomes an issue of crucial importance.
For large and evolving datasets, an exact, deterministic computation of the
quality metrics is too time consuming or expensive. We employ probabilistic
techniques such as Reservoir Sampling, Bloom Filters and Clustering Coefficient
estimation for implementing a broad set of data quality metrics in an
approximate but sufficiently accurate way. Our implementation is integrated in
the comprehensive data quality assessment framework Luzzu. We evaluated its
performance and accuracy on Linked Open Datasets of broad relevance.Comment: 15 pages, 2 figures, To appear in ESWC 2015 proceeding
Tunneling Time Distribution by means of Nelson's Quantum Mechanics and Wave-Particle Duality
We calculate a tunneling time distribution by means of Nelson's quantum
mechanics and investigate its statistical properties. The relationship between
the average and deviation of tunneling time suggests the exsistence of
``wave-particle duality'' in the tunneling phenomena.Comment: 14 pages including 11 figures, the text has been revise
Possibility of the tunneling time determination
We show that it is impossible to determine the time a tunneling particle
spends under the barrier. However, it is possible to determine the asymptotic
time, i.e., the time the particle spends in a large area including the barrier.
We propose a model of time measurements. The model provides a procedure for
calculation of the asymptotic tunneling and reflection times. The model also
demonstrates the impossibility of determination of the time the tunneling
particle spends under the barrier. Examples for delta-form and rectangular
barrier illustrate the obtained results.Comment: 8 figure
Phonon-Coupled Electron Tunneling in Two and Three-Dimensional Tunneling Configurations
We treat a tunneling electron coupled to acoustical phonons through a
realistic electron phonon interaction: deformation potential and piezoelectric,
in two or three-dimensional tunneling configurations. Making use of slowness of
the phonon system compared to electron tunneling, and using a Green function
method for imaginary time, we are able to calculate the change in the
transition probability due to the coupling to phonons. It is shown using
standard renormalization procedure that, contrary to the one-dimensional case,
second order perturbation theory is sufficient in order to treat the
deformation potential coupling, which leads to a small correction to the
transmission coefficient prefactor. In the case of piezoelectric coupling,
which is found to be closely related to the piezoelectric polaron problem,
vertex corrections need to be considered. Summing leading logarithmic terms, we
show that the piezoelectric coupling leads to a significant change of the
transmission coefficient.Comment: 17 pages, 4 figure
Current-voltage characteristic and stability in resonant-tunneling n-doped semiconductor superlattices
We review the occurrence of electric-field domains in doped superlattices
within a discrete drift model. A complete analysis of the construction and
stability of stationary field profiles having two domains is carried out. As a
consequence, we can provide a simple analytical estimation for the doping
density above which stable stable domains occur. This bound may be useful for
the design of superlattices exhibiting self-sustained current oscillations.
Furthermore we explain why stable domains occur in superlattices in contrast to
the usual Gunn diode.Comment: Tex file and 3 postscript figure
Electron transport through double quantum dots
Electron transport experiments on two lateral quantum dots coupled in series
are reviewed. An introduction to the charge stability diagram is given in terms
of the electrochemical potentials of both dots. Resonant tunneling experiments
show that the double dot geometry allows for an accurate determination of the
intrinsic lifetime of discrete energy states in quantum dots. The evolution of
discrete energy levels in magnetic field is studied. The resolution allows to
resolve avoided crossings in the spectrum of a quantum dot. With microwave
spectroscopy it is possible to probe the transition from ionic bonding (for
weak inter-dot tunnel coupling) to covalent bonding (for strong inter-dot
tunnel coupling) in a double dot artificial molecule. This review on the
present experimental status of double quantum dot studies is motivated by their
relevance for realizing solid state quantum bits.Comment: 32 pages, 31 figure
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