1,012 research outputs found
Bounds on universal quantum computation with perturbed 2d cluster states
Motivated by the possibility of universal quantum computation under noise
perturbations, we compute the phase diagram of the 2d cluster state Hamiltonian
in the presence of Ising terms and magnetic fields. Unlike in previous analysis
of perturbed 2d cluster states, we find strong evidence of a very well defined
cluster phase, separated from a polarized phase by a line of 1st and 2nd order
transitions compatible with the 3d Ising universality class and a tricritical
end point. The phase boundary sets an upper bound for the amount of
perturbation in the system so that its ground state is still useful for
measurement-based quantum computation purposes. Moreover, we also compute the
local fidelity with the unperturbed 2d cluster state. Besides a classical
approximation, we determine the phase diagram by combining series expansions
and variational infinite Projected entangled-Pair States (iPEPS) methods. Our
work constitutes the first analysis of the non-trivial effect of few-body
perturbations in the 2d cluster state, which is of relevance for experimental
proposals.Comment: 7 pages, 4 figures, revised version, to appear in PR
A posteriori error estimates for elliptic problems in two and three space dimensions
Let be the exact solution of a given selfadjoint elliptic boundary value problem, which is approximated by some , being a suitable finite-element space. Efficient and reliable a posteriors estimates of the error , measuring the (local) quality of , play a crucial role in termination criteria and in the adaptive refinement of the underlying mesh. A well-known class of error estimates can be derived systematically by localizing the discretized defect problem by using domain decomposition techniques. In this paper, we provide a guideline for the theoretical analysis of such error estimates. We further clarify the relation to other concepts. Our analysis leads to new error estimates, which are specially suited to three space dimensions. The theoretical results are illustrated by numerical computations
Concepts of flywheels for energy storage using autostable high-T(sub c) superconducting magnetic bearings
A flywheel for energy storage using autostable high-T(sub c) superconducting magnetic bearings has been built. The rotating disk has a total weight of 2.8 kg. The maximum speed is 9240 rpm. A process that allows accelerated, reliable and reproducible production of melt-textured superconducting material used for the bearings has been developed. In order to define optimum configurations for radial and axial bearings, interaction forces in three dimensions and vertical and horizontal stiffness have been measured between superconductors and permanent magnets in different geometries and various shapes. Static as well as dynamic measurements have been performed. Results are being reported and compared to theoretical models
Texture of superconducting YBaCuO-cylinders and their levitation force repulsing an inducting permanent magnet
Convergence of simple adaptive Galerkin schemes based on h − h/2 error estimators
We discuss several adaptive mesh-refinement strategies based on (h − h/2)-error estimation. This class of adaptivemethods is particularly popular in practise since it is problem independent and requires virtually no implementational overhead. We prove that, under the saturation assumption, these adaptive algorithms are convergent. Our framework applies not only to finite element methods, but also yields a first convergence proof for adaptive boundary element schemes. For a finite element model problem, we extend the proposed adaptive scheme and prove convergence even if the saturation assumption fails to hold in general
Effect of chemical disorder on NiMnSb investigated by Appearance Potential Spectroscopy: a theoretical study
The half-Heusler alloy NiMnSb is one of the local-moment ferromagnets with
unique properties for future applications. Band structure calculations predict
exclusively majority bands at the Fermi level, thus indicating {100%} spin
polarization there. As one thinks about applications and the design of
functional materials, the influence of chemical disorder in these materials
must be considered. The magnetization, spin polarization, and electronic
structure are expected to be sensitive to structural and stoichiometric
changes. In this contribution, we report on an investigation of the
spin-dependent electronic structure of NiMnSb. We studied the influence of
chemical disorder on the unoccupied electronic density of states by use of the
ab-initio Coherent Potential Approximation method. The theoretical analysis is
discussed along with corresponding spin-resolved Appearance Potential
Spectroscopy measurements. Our theoretical approach describes the spectra as
the fully-relativistic self-convolution of the matrix-element weighted,
orbitally resolved density of states.Comment: JPD submitte
Finite-Element Discretization of Static Hamilton-Jacobi Equations Based on a Local Variational Principle
We propose a linear finite-element discretization of Dirichlet problems for
static Hamilton-Jacobi equations on unstructured triangulations. The
discretization is based on simplified localized Dirichlet problems that are
solved by a local variational principle. It generalizes several approaches
known in the literature and allows for a simple and transparent convergence
theory. In this paper the resulting system of nonlinear equations is solved by
an adaptive Gauss-Seidel iteration that is easily implemented and quite
effective as a couple of numerical experiments show.Comment: 19 page
FIBS: A Generic Framework for Classifying Interval-based Temporal Sequences
We study the problem of classifying interval-based temporal sequences
(IBTSs). Since common classification algorithms cannot be directly applied to
IBTSs, the main challenge is to define a set of features that effectively
represents the data such that classifiers can be applied. Most prior work
utilizes frequent pattern mining to define a feature set based on discovered
patterns. However, frequent pattern mining is computationally expensive and
often discovers many irrelevant patterns. To address this shortcoming, we
propose the FIBS framework for classifying IBTSs. FIBS extracts features
relevant to classification from IBTSs based on relative frequency and temporal
relations. To avoid selecting irrelevant features, a filter-based selection
strategy is incorporated into FIBS. Our empirical evaluation on eight
real-world datasets demonstrates the effectiveness of our methods in practice.
The results provide evidence that FIBS effectively represents IBTSs for
classification algorithms, which contributes to similar or significantly better
accuracy compared to state-of-the-art competitors. It also suggests that the
feature selection strategy is beneficial to FIBS's performance.Comment: In: Big Data Analytics and Knowledge Discovery. DaWaK 2020. Springer,
Cha
Капитальный ремонт магистрального газопровода «НГПЗ – Парабель» на участке 227-254 км
Объектом исследования является магистральный газопровод Ду 1000 протяженностью 26,267км. Цель работы – выбор эффективного способа выполнения работ по капитальному ремонту магистрального газопровода. Проведены расчеты толщины стенки трубы, трубопровод на прочность и устойчивость. Рассмотрена разработка траншеи, сварочно-монтажные работы, прокладка, ликвидации разрывов, проведение испытания, мероприятия по охране труда и безопасности строительства, охране окружающей среды, технико-экономическая часть. Было предложено выполнять укладку нового трубопровода параллельно существующему, силами КТП. На основании выполненных расчетов на прочность было рекомендовано увеличения толщины стенки.The object of study is (are) the main gas pipeline DN 1000 with a length of 26,267 km. Purpose – the choice of effective method of execution of works on capital repair of the trunk gas pipeline. The calculations of wall thickness, tubing for strength and stability. Describes the development of a trench, welding and installation works, laying, bridging the gaps, running the test, measures on labor protection and building safety, environmental, technical and economic part. It was proposed to carry out laying a new pipeline parallel to the existing, by the CTU. On the basis of the calculations for strength, it was recommended that increasing the thickness of the wall
Habitat-based density models of pack-ice seal distribution in the southern Weddell Sea, Antarctica
Climate variability and changes in sea ice dynamics have caused several ice-obligate or krill-dependent populations of marine predators to decline, eliciting concern about their demographic persistence and the indirect ecological consequences that predator depletions may have on marine ecosystems. Pack-ice seals are dominant ice-obligate predators in the Antarctic marine ecosystem, but there is considerable uncertainty about their abundance and population trends. We modelled the density and distribution of pack-ice seals as a function of environmental covariates in the southern Weddell Sea, Antarctica. Our density surface modelling approach used data from aerial surveys of pack-ice seals collected in the 2013/14 austral summer. Crabeater seals Lobo don carcinophaga, the most numerous pack-ice seal we observed, occurred at the highest densities in areas with extensive sea ice near the continental shelf break, but were almost absent in areas of similar sea ice concentration in the southern extent of the Weddell Sea. The highest densities of Weddell seals Leptonychotes weddelli, which were less abundant than crabeater seals within the pack-ice habitat, were predicted to occur over the continental shelf, near the shelf break. The distribution of both seal species broadly corresponded with the distribution and relative abundance of their main prey (Antarctic krill Euphausia superba and Antarctic silverfish Pleuragramma antarctica) obtained from concurrent ecosystem surveys. Ross seals Ommatophoca rossii and leopard seals Hydrurga leptonyx were not detected at all and are apparently rare within the southern Weddell Sea. These results can contribute to biodiversity assessments in the context of marine protected area planning in this region of the Southern Ocean
- …