286 research outputs found
Three level atom optics in dipole traps and waveguides
An analogy is explored between a setup of three atomic traps coupled via
tunneling and an internal atomic three-level system interacting with two laser
fields. Within this scenario we describe a STIRAP like process which allows to
move an atom between the ground states of two trapping potentials and analyze
its robustness. This analogy is extended to other robust and coherent transport
schemes and to systems of more than a single atom. Finally it is applied to
manipulate external degrees of freedom of atomic wave packets propagating in
waveguides.Comment: 14 pages, 6 figures; submitted to special issue 'Quantum Control of
Light and Matter' of Optics Communication
Quantum theory of a polarization phase-gate in an atomic tripod configuration
We present the quantum theory of a polarization phase-gate that can be
realized in a sample of ultracold rubidium atoms driven into a tripod
configuration. The main advantages of this scheme are in its relative
simplicity and inherent symmetry. It is shown that the conditional phase shifts
of order can be attained.Comment: X International Conference on Quantum Optics, Minsk, Belaru
An Eulerian Immersed Boundary Method for flow simulations over stationary and moving rigid bodies
The fluid flow over bodies with complex geometry has been the subject of research of many scientists and widely explored experimentally and numerically. The present study proposes an Eulerian Immersed Boundary Method for flows simulations over stationary or moving rigid bodies. The proposed method allows the use of Cartesians Meshes. Here, two-dimensional simulations of fluid flow over stationary and oscillating circular cylinders were used for verification and validation. Four different cases were explored: the flow over a stationary cylinder, the flow over a cylinder oscillating in the flow direction, the flow over a cylinder oscillating in the normal flow direction, and a cylinder with angular oscillation. The time integration was carried out by a classical 4th order Runge-Kutta scheme, with a time step of the same order of distance between two consecutive points in x direction. High-order compact finite difference schemes were used to calculate spatial derivatives. The drag and lift coefficients, the lock-in phenomenon and vorticity contour plots were used for the verification and validation of the proposed method. The extension of the current method allowing the study of a body with different geometry and three-dimensional simulations is straightforward. The results obtained show a good agreement with both numerical and experimental results, encouraging the use of the proposed method
Coherent population trapping in two-electron three-level systems with aligned spins
The possibility of coherent population trapping in two electron states with
aligned spins (ortho-system) is evidenced. From the analysis of a three-level
atomic system containing two electrons, and driven by the two laser fields
needed for coherent population trapping, a conceptually new kind of
two-electron dark state appears. The properties of this trapping are studied
and are physically interpreted in terms of a dark hole, instead of a dark
two-electron state. This technique, among many other applications, offers the
possibility of measuring, with subnatural resolution, some superposition-state
matrix-elements of the electron-electron correlation that due to their time
dependent nature are inaccesible by standard measuring procedures.Comment: 10 pages and 4 figure
An Eulerian Immersed Boundary Method for flow simulations over stationary and moving rigid bodies
A proposal for an optical implementation of a universal quantum phase gate
Large optical nonlinearities occurring in a coherently prepared atomic system are shown to produce phase shifts of order pi. Such an effect may be observed in ultracold rubidium atoms where it could be feasibly exploited toward the realization of a polarization phase gate
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The favorable kinetics and balance of nebivolol-stimulated nitric oxide and peroxynitrite release in human endothelial cells
Background: Nebivolol is a third-generation beta-blocker used to treat hypertension. The vasodilation properties of nebivolol have been attributed to nitric oxide (NO) release. However, the kinetics and mechanism of nebivolol-stimulated bioavailable NO are not fully understood. Methods: Using amperometric NO and peroxynitrite (ONOO-) nanosensors, β3-receptor (agonist: L-755,507; antagonists: SR59230A and L-748,337), ATP efflux (the mechanosensitive ATP channel blocker, gadolinium) and P2Y-receptor (agonists: ATP and 2-MeSATP; antagonist: suramin) modulators, superoxide dismutase and a NADPH oxidase inhibitor (VAS2870), we evaluated the kinetics and balance of NO and ONOO- stimulated by nebivolol in human umbilical vein endothelial cells (HUVECs). NO and ONOO- were measured with nanosensors (diameter ~ 300 nm) placed 5 ± 2 μm from the cell membrane and ATP levels were determined with a bioluminescent method. The kinetics and balance of nebivolol-stimulated NO and ONOO- were compared with those of ATP, 2-MeSATP, and L-755,507. Results: Nebivolol stimulates endothelial NO release through β3-receptor and ATP-dependent, P2Y-receptor activation with relatively slow kinetics (75 ± 5 nM/s) as compared to the kinetics of ATP (194 ± 10 nM/s), L-755,507 (108 ± 6 nM/s), and 2-MeSATP (105 ± 5 nM/s). The balance between cytoprotective NO and cytotoxic ONOO- was expressed as the ratio of [NO]/[ONOO-] concentrations. This ratio for nebivolol was 1.80 ± 0.10 and significantly higher than that for ATP (0.80 ± 0.08), L-755,507 (1.08 ± 0.08), and 2-MeSATP (1.09 ± 0.09). Nebivolol induced ATP release in a concentration-dependent manner. Conclusion: The two major pathways (ATP efflux/P2Y receptors and β3 receptors) and several steps of nebivolol-induced NO and ONOO- stimulation are mainly responsible for the slow kinetics of NO release and low ONOO-. The net effect of this slow kinetics of NO is reflected by a favorable high ratio of [NO]/[ONOO-] which may explain the beneficial effects of nebivolol in the treatment of endothelial dysfunction, hypertension, heart failure, and angiogenesis
DCDB Wintermute: Enabling Online and Holistic Operational Data Analytics on HPC Systems
As we approach the exascale era, the size and complexity of HPC systems
continues to increase, raising concerns about their manageability and
sustainability. For this reason, more and more HPC centers are experimenting
with fine-grained monitoring coupled with Operational Data Analytics (ODA) to
optimize efficiency and effectiveness of system operations. However, while
monitoring is a common reality in HPC, there is no well-stated and
comprehensive list of requirements, nor matching frameworks, to support
holistic and online ODA. This leads to insular ad-hoc solutions, each
addressing only specific aspects of the problem.
In this paper we propose Wintermute, a novel generic framework to enable
online ODA on large-scale HPC installations. Its design is based on the results
of a literature survey of common operational requirements. We implement
Wintermute on top of the holistic DCDB monitoring system, offering a large
variety of configuration options to accommodate the varying requirements of ODA
applications. Moreover, Wintermute is based on a set of logical abstractions to
ease the configuration of models at a large scale and maximize code re-use. We
highlight Wintermute's flexibility through a series of practical case studies,
each targeting a different aspect of the management of HPC systems, and then
demonstrate the small resource footprint of our implementation.Comment: Accepted for publication at the 29th ACM International Symposium on
High-Performance Parallel and Distributed Computing (HPDC 2020
On the computation of zone and double zone diagrams
Classical objects in computational geometry are defined by explicit
relations. Several years ago the pioneering works of T. Asano, J. Matousek and
T. Tokuyama introduced "implicit computational geometry", in which the
geometric objects are defined by implicit relations involving sets. An
important member in this family is called "a zone diagram". The implicit nature
of zone diagrams implies, as already observed in the original works, that their
computation is a challenging task. In a continuous setting this task has been
addressed (briefly) only by these authors in the Euclidean plane with point
sites. We discuss the possibility to compute zone diagrams in a wide class of
spaces and also shed new light on their computation in the original setting.
The class of spaces, which is introduced here, includes, in particular,
Euclidean spheres and finite dimensional strictly convex normed spaces. Sites
of a general form are allowed and it is shown that a generalization of the
iterative method suggested by Asano, Matousek and Tokuyama converges to a
double zone diagram, another implicit geometric object whose existence is known
in general. Occasionally a zone diagram can be obtained from this procedure.
The actual (approximate) computation of the iterations is based on a simple
algorithm which enables the approximate computation of Voronoi diagrams in a
general setting. Our analysis also yields a few byproducts of independent
interest, such as certain topological properties of Voronoi cells (e.g., that
in the considered setting their boundaries cannot be "fat").Comment: Very slight improvements (mainly correction of a few typos); add DOI;
Ref [51] points to a freely available computer application which implements
the algorithms; to appear in Discrete & Computational Geometry (available
online
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