172,605 research outputs found
The London theory of the crossing-vortex lattice in highly anisotropic layered superconductors
A novel description of Josephson vortices (JVs) crossed by the pancake
vortices (PVs) is proposed on the basis of the anisotropic London theory. The
field distribution of a JV and its energy have been calculated for both dense
() PV lattices with distance
between PVs, and the nonlinear JV core size . It is shown that the
``shifted'' PV lattice (PVs displaced mainly along JVs in the crossing vortex
lattice structure), formed in high out-of-plane magnetic fields transforms into
the PV lattice ``trapped'' by the JV sublattice at a certain field, lower than
, where is the flux quantum, is the
anisotropy parameter and is the distance between CuO planes.
With further decreasing , the free energy of the crossing vortex lattice
structure (PV and JV sublattices coexist separately) can exceed the free energy
of the tilted lattice (common PV-JV vortex structure) in the case of with the in-plane penetration depth if the low
() or high ()
in-plane magnetic field is applied. It means that the crossing vortex structure
is realized in the intermediate field orientations, while the tilted vortex
lattice can exist if the magnetic field is aligned near the -axis and the
-plane as well. In the intermediate in-plane fields
, the
crossing vortex structure with the ``trapped'' PV sublattice seems to settle in
until the lock-in transition occurs since this structure has the lower energy
with respect to the tilted vortex structure in the magnetic field
oriented near the -plane.Comment: 15 pages, 6 figures, accepted for publication in PR
Curvilinear coordinates for full-core atoms
Curvilinear coordinates, first introduced by F. Gygi for valence-only
electronic systems within the local-density functional theory, can be used to
describe both core and valence electrons in electronic-structure calculations.
A simple and quite general coordinate transformation results in a large, yet
affordable plane-wave energy cutoff for full-core systems (e.g., about 120 Ryd
for carbon or silicon) within the local-density functional theory, and in a
reduced correlation time for full-core variational Monte Carlo calculations.
Numerical tests for isolated Li, C, and Si atoms are presented.Comment: 14 pages, 8 Postscript figures; acknowledgements and two refs. adde
Incremental Distance Transforms (IDT)
A new generic scheme for incremental implementations of distance transforms (DT) is presented: Incremental Distance Transforms (IDT). This scheme is applied on the cityblock, Chamfer, and three recent exact Euclidean DT (E2DT). A benchmark shows that for all five DT, the incremental implementation results in a significant speedup: 3.4×−10×. However, significant differences (i.e., up to 12.5×) among the DT remain present. The FEED transform, one of the recent E2DT, even showed to be faster than both city-block and Chamfer DT. So, through a very efficient incremental processing scheme for DT, a relief is found for E2DT’s computational burden
Euler-Bessel and Euler-Fourier Transforms
We consider a topological integral transform of Bessel (concentric
isospectral sets) type and Fourier (hyperplane isospectral sets) type, using
the Euler characteristic as a measure. These transforms convert constructible
\zed-valued functions to continuous -valued functions over a vector
space. Core contributions include: the definition of the topological Bessel
transform; a relationship in terms of the logarithmic blowup of the topological
Fourier transform; and a novel Morse index formula for the transforms. We then
apply the theory to problems of target reconstruction from enumerative sensor
data, including localization and shape discrimination. This last application
utilizes an extension of spatially variant apodization (SVA) to mitigate
sidelobe phenomena
Accelerated Modeling of Near and Far-Field Diffraction for Coronagraphic Optical Systems
Accurately predicting the performance of coronagraphs and tolerancing optical
surfaces for high-contrast imaging requires a detailed accounting of
diffraction effects. Unlike simple Fraunhofer diffraction modeling, near and
far-field diffraction effects, such as the Talbot effect, are captured by
plane-to-plane propagation using Fresnel and angular spectrum propagation. This
approach requires a sequence of computationally intensive Fourier transforms
and quadratic phase functions, which limit the design and aberration
sensitivity parameter space which can be explored at high-fidelity in the
course of coronagraph design. This study presents the results of optimizing the
multi-surface propagation module of the open source Physical Optics Propagation
in PYthon (POPPY) package. This optimization was performed by implementing and
benchmarking Fourier transforms and array operations on graphics processing
units, as well as optimizing multithreaded numerical calculations using the
NumExpr python library where appropriate, to speed the end-to-end simulation of
observatory and coronagraph optical systems. Using realistic systems, this
study demonstrates a greater than five-fold decrease in wall-clock runtime over
POPPY's previous implementation and describes opportunities for further
improvements in diffraction modeling performance.Comment: Presented at SPIE ASTI 2018, Austin Texas. 11 pages, 6 figure
Near-field to far-field transition of photonic crystal fibers: symmetries and interference phenomena
The transition from the near to the far field of the fundamental mode
radiating out of a photonic crystal fiber is investigated experimentally and
theoretically. It is observed that the hexagonal shape of the near field
rotates two times by pi/6 when moving into the far field, and eventually six
satellites form around a nearly gaussian far-field pattern. A semi-empirical
model is proposed, based on describing the near field as a sum of seven
gaussian distributions, which qualitatively explains all the observed phenomena
and quantitatively predicts the relative intensity of the six satellites in the
far field.Comment: 7 pages including 6 figures. Animated version of Fig. 5 is available
at http://www.crystal-fibre.com/technology/movie.gi
The death of distance: how the communications revolution will change our lives
One of the World\u27s Most Insightful Journalists writes eloquently and convincingly about the ways the communications revolution will tilt the balance between large and small, rich and poor, as it transforms many business and government decisions. This "death of distance" will be the single most important economic force shaping society over the next half century.
Describing the electronic miracles of our age in the old – fashioned format of ink on wood pulp may strike you as ironic. Put it down to the fact that, for the moment, the printed and bound book remains the most convenient way to introduce new ideas to the word. The new ideas in this book are about the many ways in which the most significant technological changes of our time will affect the next century – and your life. You will find a preview of the most important in “The Trendspotter”s Guide to New Communication” that immediately follow this preface; the rest of the book sets out to interpret and elaborate these core points
- …