1,368 research outputs found
Double Greedy Algorithms: Reduced Basis Methods for Transport Dominated Problems
The central objective of this paper is to develop reduced basis methods for
parameter dependent transport dominated problems that are rigorously proven to
exhibit rate-optimal performance when compared with the Kolmogorov -widths
of the solution sets. The central ingredient is the construction of
computationally feasible "tight" surrogates which in turn are based on deriving
a suitable well-conditioned variational formulation for the parameter dependent
problem. The theoretical results are illustrated by numerical experiments for
convection-diffusion and pure transport equations. In particular, the latter
example sheds some light on the smoothness of the dependence of the solutions
on the parameters
From West to East and Back Again: Faith, Doubt and Education in Hermann Hesse's Later Work
This paper examines Hermann Hesse’s penultimate novel, The Journey to the East, from an educational point of view. Hesse was a man of the West who turned to the idea of ‘the East’ in seeking to understand himself and his society. While highly critical of elements of Western modernism, Hesse nonetheless viewed ‘the East’ through Western lenses and drew inspiration from other Western thinkers. At the end of The Journey to the East, the main character, H.H., believes he has found the solution to his despair. This paper argues that he has not, at least not in the fullest sense Hesse came to see was possible. H.H. relies too heavily on faith and abandons reason too quickly in seeking to become ‘absorbed’ into the Other he regards as his higher self. An answer to H.H.’s existential angst can be found in Hesse’s final novel, The Glass Bead Game, where educational growth through the development of a critical, questioning, inquiring attitude is a central theme
Multilevel Preconditioning of Discontinuous-Galerkin Spectral Element Methods, Part I: Geometrically Conforming Meshes
This paper is concerned with the design, analysis and implementation of
preconditioning concepts for spectral Discontinuous Galerkin discretizations of
elliptic boundary value problems. While presently known techniques realize a
growth of the condition numbers that is logarithmic in the polynomial degrees
when all degrees are equal and quadratic otherwise, our main objective is to
realize full robustness with respect to arbitrarily large locally varying
polynomial degrees degrees, i.e., under mild grading constraints condition
numbers stay uniformly bounded with respect to the mesh size and variable
degrees. The conceptual foundation of the envisaged preconditioners is the
auxiliary space method. The main conceptual ingredients that will be shown in
this framework to yield "optimal" preconditioners in the above sense are
Legendre-Gauss-Lobatto grids in connection with certain associated anisotropic
nested dyadic grids as well as specially adapted wavelet preconditioners for
the resulting low order auxiliary problems. Moreover, the preconditioners have
a modular form that facilitates somewhat simplified partial realizations. One
of the components can, for instance, be conveniently combined with domain
decomposition, at the expense though of a logarithmic growth of condition
numbers. Our analysis is complemented by quantitative experimental studies of
the main components.Comment: 41 pages, 11 figures; Major revision: rearrangement of the contents
for better readability, part on wavelet preconditioner adde
Optimized imaging using non-rigid registration
The extraordinary improvements of modern imaging devices offer access to data
with unprecedented information content. However, widely used image processing
methodologies fall far short of exploiting the full breadth of information
offered by numerous types of scanning probe, optical, and electron
microscopies. In many applications, it is necessary to keep measurement
intensities below a desired threshold. We propose a methodology for extracting
an increased level of information by processing a series of data sets
suffering, in particular, from high degree of spatial uncertainty caused by
complex multiscale motion during the acquisition process. An important role is
played by a nonrigid pixel-wise registration method that can cope with low
signal-to-noise ratios. This is accompanied by formulating objective quality
measures which replace human intervention and visual inspection in the
processing chain. Scanning transmission electron microscopy of siliceous
zeolite material exhibits the above-mentioned obstructions and therefore serves
as orientation and a test of our procedures
Hysteresis, Avalanches, and Noise: Numerical Methods
In studying the avalanches and noise in a model of hysteresis loops we have
developed two relatively straightforward algorithms which have allowed us to
study large systems efficiently. Our model is the random-field Ising model at
zero temperature, with deterministic albeit random dynamics. The first
algorithm, implemented using sorted lists, scales in computer time as O(N log
N), and asymptotically uses N (sizeof(double)+ sizeof(int)) bits of memory. The
second algorithm, which never generates the random fields, scales in time as
O(N \log N) and asymptotically needs storage of only one bit per spin, about 96
times less memory than the first algorithm. We present results for system sizes
of up to a billion spins, which can be run on a workstation with 128MB of RAM
in a few hours. We also show that important physical questions were resolved
only with the largest of these simulations
Экранное трубчатое многопараметровое вихретоковое устройство
Рассмотрено экранное трубчатое многопараметровое устройство, с помощью которого определяются четыре параметра ферромагнитной трубы: относительная магнитная проницаемость µrt, удельное электрическое сопротивление Pt, температура трубы t и коэффициент затухания магнитного поля в трубчатом изделии ht.The screen tubular mnogoparametrovoe device is considered, which four parameters of ferromagnetic pipe are determined by: relative permeance µrt, specific electric resistance Pt, temperature of pipe of t and coefficient of fading of the magnetic field in tubular good of ht
Extended Molecular Gas in the Nearby Starburst Galaxy Maffei 2
We present a 9'x9' fully-sampled map of the CO J=1-0 emission in the nearby
starburst galaxy Maffei 2 obtained at the Five College Radio Astronomy
Observatory. The map reveals previously known strong CO emission in the central
starburst region as well as an extended asymmetric distribution with bright CO
lines at the ends of the bar and in a feature at the north-east edge of the
molecular disk. This northern feature, proposed previously to be an interacting
companion galaxy, could be a dwarf irregular galaxy, although the CO data are
also consistent with the feature being simply an extension of one of the spiral
arms. We estimate the total molecular gas mass of Maffei 2 to be (1.4-1.7)x10^9
Mo or ~3-4% of its dynamical mass. Adopting the recently determined lower value
for the CO-to-H2 conversion factor in the central region, our data lead to the
surprising result that the largest concentrations of molecular gas in Maffei 2
lie at the bar ends and in the putative dwarf companion rather than in the
central starburst. A gravitational stability analysis reveals that the extended
disk of Maffei 2 lies above the critical density for star formation; however,
whether the central region is also gravitationally unstable depends both on the
details of the rotation curve and the precise value of the CO-to-H2 conversion
factor in this region.Comment: accepted to ApJ (Sept 10 2004 issue
Electron tomography at 2.4 {\AA} resolution
Transmission electron microscopy (TEM) is a powerful imaging tool that has
found broad application in materials science, nanoscience and biology(1-3).
With the introduction of aberration-corrected electron lenses, both the spatial
resolution and image quality in TEM have been significantly improved(4,5) and
resolution below 0.5 {\AA} has been demonstrated(6). To reveal the 3D structure
of thin samples, electron tomography is the method of choice(7-11), with
resolutions of ~1 nm^3 currently achievable(10,11). Recently, discrete
tomography has been used to generate a 3D atomic reconstruction of a silver
nanoparticle 2-3 nm in diameter(12), but this statistical method assumes prior
knowledge of the particle's lattice structure and requires that the atoms fit
rigidly on that lattice. Here we report the experimental demonstration of a
general electron tomography method that achieves atomic scale resolution
without initial assumptions about the sample structure. By combining a novel
projection alignment and tomographic reconstruction method with scanning
transmission electron microscopy, we have determined the 3D structure of a ~10
nm gold nanoparticle at 2.4 {\AA} resolution. While we cannot definitively
locate all of the atoms inside the nanoparticle, individual atoms are observed
in some regions of the particle and several grains are identified at three
dimensions. The 3D surface morphology and internal lattice structure revealed
are consistent with a distorted icosahedral multiply-twinned particle. We
anticipate that this general method can be applied not only to determine the 3D
structure of nanomaterials at atomic scale resolution(13-15), but also to
improve the spatial resolution and image quality in other tomography
fields(7,9,16-20).Comment: 27 pages, 17 figure
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