6,420 research outputs found
3D simulations of self-propelled, reconstructed jellyfish using vortex methods
We present simulations of the vortex dynamics associated with the
self-propelled motion of jellyfish. The geometry is obtained from image
segmentation of video recordings from live jellyfish. The numerical simulations
are performed using three-dimensional viscous, vortex particle methods with
Brinkman penalization to impose the kinematics of the jellyfish motion. We
study two types of strokes recorded in the experiment1. The first type (stroke
A) produces two vortex rings during the stroke: one outside the bell during the
power stroke and one inside the bell during the recovery stroke. The second
type (stroke B) produces three vortex rings: one ring during the power stroke
and two vortex rings during the recovery stroke. Both strokes propel the
jellyfish, with stroke B producing the highest velocity. The speed of the
jellyfish scales with the square root of the Reynolds number. The simulations
are visualized in a fluid dynamics video.Comment: 1 page, 1 figur
Calibration of thickness-dependent k-factors for germanium X-ray lines to improve energy-dispersive X-ray spectroscopy of SiGe layers in analytical transmission electron microscopy
We show that the accuracy of energy-dispersive X-ray spectroscopy can be improved by analysing and comparing multiple lines from the same element. For each line, an effective k-factor can be defined that varies as a function of the intensity ratio of multiple lines (e.g. K/L) from the same element. This basically performs an internal self-consistency check in the quantification using differently absorbed X-ray lines, which is in principle equivalent to an absorption correction as a function of specimen thickness but has the practical advantage that the specimen thickness itself does not actually need to be measured
Formation of Low Threshold Voltage Microlasers
Vertical cavity surface emitting lasers (VCSELs) with threshold voltages of 1.7V have been fabricated. The resistance-area product in these new vertical cavity lasers is comparable to that of edge-emitting lasers, and threshold currents as low as 3 mA have been measured. Molecular beam epitaxy was used to grow n-type mirrors, a quantum well active region, and a heavily Be-doped p-contact. After contact definition and alloying, passive high-reflectivity mirrors were deposited by reactive sputter deposition of SiO2/Si3N4 to complete the laser cavity
Full characterization of a three-photon GHZ state using quantum state tomography
We have performed the first experimental tomographic reconstruction of a
three-photon polarization state. Quantum state tomography is a powerful tool
for fully describing the density matrix of a quantum system. We measured 64
three-photon polarization correlations and used a "maximum-likelihood"
reconstruction method to reconstruct the GHZ state. The entanglement class has
been characterized using an entanglement witness operator and the maximum
predicted values for the Mermin inequality was extracted.Comment: 3 pages, 3 figure
Quantum nonlocality obtained from local states by entanglement purification
We have applied an entanglement purification protocol to produce a single
entangled pair of photons capable of violating a CHSH Bell inequality from two
pairs that individually could not. The initial poorly-entangled photons were
created by a controllable decoherence that introduced complex errors. All of
the states were reconstructed using quantum state tomography which allowed for
a quantitative description of the improvement of the state after purification.Comment: 4 pages, 4 figure
Single microwave photon detection in the micromaser
High efficiency single photon detection is an interesting problem for many
areas of physics, including low temperature measurement, quantum information
science and particle physics. For optical photons, there are many examples of
devices capable of detecting single photons with high efficiency. However
reliable single photon detection of microwaves is very difficult, principally
due to their low energy. In this paper we present the theory of a cascade
amplifier operating in the microwave regime that has an optimal quantum
efficiency of 93%. The device uses a microwave photon to trigger the stimulated
emission of a sequence of atoms where the energy transition is readily
detectable. A detailed description of the detector's operation and some
discussion of the potential limitations of the detector are presented.Comment: 8 pages, 5 figure
Optimal Tableaux Method for Constructive Satisfiability Testing and Model Synthesis in the Alternating-time Temporal Logic ATL+
We develop a sound, complete and practically implementable tableaux-based
decision method for constructive satisfiability testing and model synthesis in
the fragment ATL+ of the full Alternating time temporal logic ATL*. The method
extends in an essential way a previously developed tableaux-based decision
method for ATL and works in 2EXPTIME, which is the optimal worst case
complexity of the satisfiability problem for ATL+ . We also discuss how
suitable parametrizations and syntactic restrictions on the class of input ATL+
formulae can reduce the complexity of the satisfiability problem.Comment: 45 page
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