1,408 research outputs found
Synthesis and Bulk Properties of Oxychloride Superconductor Ca2-xNaxCuO2Cl2
Polycrystalline samples and submillimeter size single crystals of Na-doped
Ca2CuO2Cl2 have been synthesized under high pressure. A series of experiments
showed that the Na content depends not only on the pressure during the
synthesis but also on the synthesis temperature and time. From a comparison of
the Na-CCOC data with those of structurally related La214 cuprate
superconductors we concluded that chlorine at the apical site is less effective
that oxygen in supplying charge carriers to the CuO2 plans. As a result, the
coupling between the CuO2 planes is weakened, the transition temperature Tc is
reduced and the anisotropic nature is enhanced.Comment: 7 pages, 7 figures, 1 table, presenthed at the Eucas 2007 conference.
Accepted for "Journal of Physics: Conference Series (JPCS)" 2008 and European
News Forum, Issue 3 (2008
Load-Balancing for Parallel Delaunay Triangulations
Computing the Delaunay triangulation (DT) of a given point set in
is one of the fundamental operations in computational geometry.
Recently, Funke and Sanders (2017) presented a divide-and-conquer DT algorithm
that merges two partial triangulations by re-triangulating a small subset of
their vertices - the border vertices - and combining the three triangulations
efficiently via parallel hash table lookups. The input point division should
therefore yield roughly equal-sized partitions for good load-balancing and also
result in a small number of border vertices for fast merging. In this paper, we
present a novel divide-step based on partitioning the triangulation of a small
sample of the input points. In experiments on synthetic and real-world data
sets, we achieve nearly perfectly balanced partitions and small border
triangulations. This almost cuts running time in half compared to
non-data-sensitive division schemes on inputs exhibiting an exploitable
underlying structure.Comment: Short version submitted to EuroPar 201
On compatibility and improvement of different quantum state assignments
When Alice and Bob have different quantum knowledges or state assignments
(density operators) for one and the same specific individual system, then the
problems of compatibility and pooling arise. The so-called first
Brun-Finkelstein-Mermin (BFM) condition for compatibility is reobtained in
terms of possessed or sharp (i. e., probability one) properties. The second BFM
condition is shown to be generally invalid in an infinite-dimensional state
space. An argument leading to a procedure of improvement of one state
assifnment on account of the other and vice versa is presented.Comment: 8 page
Hamiltonian Determination with Restricted Access in Transverse Field Ising Chain
We propose a method to evaluate parameters in the Hamiltonian of the Ising
chain under site-dependent transverse fields, with a proviso that we can
control and measure one of the edge spins only. We evaluate the eigenvalues of
the Hamiltonian and the time-evoultion operator exactly for a 3-spin chain,
from which we obtain the expectation values of of the first spin.
The parameters are found from the peak positions of the Fourier transform of
the expectation value. There are four assumptions in our method, which are mild
enough to be satisfied in many physical systems.Comment: 15pages, 4 figure
Anisotropy of Superconducting Single Crystal SmFeAsO0.8F0.2 Studied by Torque Magnetometry
Single crystals of the oxypnictide superconductor SmFeAsO0.8F0.2 with T c≃45(1) K were investigated by torque magnetometry. The crystals of mass ≤0.1μg were grown by a high-pressure cubic anvil technique. The use of a high-sensitive piezoresistive torque sensor made it possible to study the anisotropic magnetic properties of these tiny crystals. The anisotropy parameter γ was found to be field independent, but varies strongly with temperature ranging from γ≃8 at T≲T c to γ≃23 at T≃0.4T c. This unusual behavior of γ signals unconventional superconductivit
Robust Online Hamiltonian Learning
In this work we combine two distinct machine learning methodologies,
sequential Monte Carlo and Bayesian experimental design, and apply them to the
problem of inferring the dynamical parameters of a quantum system. We design
the algorithm with practicality in mind by including parameters that control
trade-offs between the requirements on computational and experimental
resources. The algorithm can be implemented online (during experimental data
collection), avoiding the need for storage and post-processing. Most
importantly, our algorithm is capable of learning Hamiltonian parameters even
when the parameters change from experiment-to-experiment, and also when
additional noise processes are present and unknown. The algorithm also
numerically estimates the Cramer-Rao lower bound, certifying its own
performance.Comment: 24 pages, 12 figures; to appear in New Journal of Physic
Bell's Theorem from Moore's Theorem
It is shown that the restrictions of what can be inferred from
classically-recorded observational outcomes that are imposed by the no-cloning
theorem, the Kochen-Specker theorem and Bell's theorem also follow from
restrictions on inferences from observations formulated within classical
automata theory. Similarities between the assumptions underlying classical
automata theory and those underlying universally-unitary quantum theory are
discussed.Comment: 12 pages; to appear in Int. J. General System
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