11,999 research outputs found
A beginner's introduction to Fukaya categories
The goal of these notes is to give a short introduction to Fukaya categories
and some of their applications. The first half of the text is devoted to a
brief review of Lagrangian Floer (co)homology and product structures. Then we
introduce the Fukaya category (informally and without a lot of the necessary
technical detail), and briefly discuss algebraic concepts such as exact
triangles and generators. Finally, we mention wrapped Fukaya categories and
outline a few applications to symplectic topology, mirror symmetry and
low-dimensional topology. This text is based on a series of lectures given at a
Summer School on Contact and Symplectic Topology at Universit\'e de Nantes in
June 2011.Comment: 42 pages, 13 figure
A custom designed density estimation method for light transport
We present a new Monte Carlo method for solving the global illumination problem in environments with general geometry descriptions and light emission and scattering properties. Current Monte Carlo global illumination algorithms are based on generic density estimation techniques that do not take into account any knowledge about the nature of the data points --- light and potential particle hit points --- from which a global illumination solution is to be reconstructed. We propose a novel estimator, especially designed for solving linear integral equations such as the rendering equation. The resulting single-pass global illumination algorithm promises to combine the flexibility and robustness of bi-directional path tracing with the efficiency of algorithms such as photon mapping
BaFe_{1.8}Co_{0.2}As_2 thin film hybrid Josephson junctions
Josephson junctions with iron pnictides open the way for fundamental
experiments on superconductivity in these materials and their application in
superconducting devices. Here, we present hybrid Josephson junctions with a
BaFe_{1.8}Co_{0.2}As_2 thin film electrode, an Au barrier and a PbIn counter
electrode. The junctions show RSJ-like current-voltage characteristics up to
the critical temperature of the counter electrode of about 7.2K. The
temperature dependence of the critical current, IC, does not show an
Ambegaokar-Baratoff behavior. Well-pronounced Shapiro steps are observed at
microwave frequencies of 10-18GHz. Assuming an excess current, I_ex, of 200
{\mu}A at 4.2K we get an effective I_C R_N product of 6 {\mu}V.Comment: submitted to Appl. Phys. Let
The Evolution of Distorted Rotating Black Holes II: Dynamics and Analysis
We have developed a numerical code to study the evolution of distorted,
rotating black holes. This code is used to evolve a new family of black hole
initial data sets corresponding to distorted ``Kerr'' holes with a wide range
of rotation parameters, and distorted Schwarzschild black holes with odd-parity
radiation. Rotating black holes with rotation parameters as high as
are evolved and analyzed in this paper. The evolutions are generally carried
out to about , where is the ADM mass. We have extracted both the
even- and odd-parity gravitational waveforms, and find the quasinormal modes of
the holes to be excited in all cases. We also track the apparent horizons of
the black holes, and find them to be a useful tool for interpreting the
numerical results. We are able to compute the masses of the black holes from
the measurements of their apparent horizons, as well as the total energy
radiated and find their sum to be in excellent agreement with the ADM mass.Comment: 26 pages, LaTeX with RevTeX 3.0 macros. 27 uuencoded gz-compressed
postscript figures. Also available at http://jean-luc.ncsa.uiuc.edu/Papers/
Submitted to Physical Review
Influence of the spreading resistance on the conductance spectrum of planar hybrid thin film SNS' junctions based on iron pnictides
To investigate the superconducting properties of iron pnictides we prepared
planar hybrid SNS' junctions in thin film technology with a pnictide base
electrode, a gold barrier layer and a lead counter electrode. Our design allows
characterization of the electrodes and the junction independently in a 4-probe
method. We show how both electrodes influence the measured spectra due to their
spreading resistance. While the Pb electrode has a constant resistance above
its , the contribution of the pnictide electrode is clearly
current-dependent and thus it needs a more advanced method to be corrected. We
present an empirical method, which is simple to apply and allows to deal with
the spreading resistance in our junctions to recalculate the actual conductance
and voltage of one junction at given temperature
Sub 20 nm Short Channel Carbon Nanotube Transistors
Carbon nanotube field-effect transistors with sub 20 nm long channels and
on/off current ratios of > 1000000 are demonstrated. Individual single-walled
carbon nanotubes with diameters ranging from 0.7 nm to 1.1 nm grown from
structured catalytic islands using chemical vapor deposition at 700 degree
Celsius form the channels. Electron beam lithography and a combination of HSQ,
calix[6]arene and PMMA e-beam resists were used to structure the short channels
and source and drain regions. The nanotube transistors display on-currents in
excess of 15 microA for drain-source biases of only 0.4 Volt.Comment: Nano Letters in pres
Influence of Josephson current second harmonic on stability of magnetic flux in long junctions
We study the long Josephson junction (LJJ) model which takes into account the
second harmonic of the Fourier expansion of Josephson current. The dependence
of the static magnetic flux distributions on parameters of the model are
investigated numerically. Stability of the static solutions is checked by the
sign of the smallest eigenvalue of the associated Sturm-Liouville problem. New
solutions which do not exist in the traditional model, have been found.
Investigation of the influence of second harmonic on the stability of magnetic
flux distributions for main solutions is performed.Comment: 4 pages, 6 figures, to be published in Proc. of Dubna-Nano2010, July
5-10, 2010, Russi
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