494 research outputs found
Numerical treatment of a generalized Vandermonde system of equations
AbstractA stable method is proposed for the numerical solution of a linear system of equations having a generalized Vandermonde matrix. The method is based on Gaussian elimination and establishes explicit expressions for the elements of the resulting upper triangular matrix. These elements can be computed by means of sums of exclusively positive terms. In an important special case these sums can be reduced to simple recursions. Finally the method is retraced for the case of a confluent type of generalized Vandermonde matrix
Manhattan orbifolds
We investigate a class of metrics for 2-manifolds in which, except for a
discrete set of singular points, the metric is locally isometric to an L_1 (or
equivalently L_infinity) metric, and show that with certain additional
conditions such metrics are injective. We use this construction to find the
tight span of squaregraphs and related graphs, and we find an injective metric
that approximates the distances in the hyperbolic plane analogously to the way
the rectilinear metrics approximate the Euclidean distance.Comment: 17 pages, 15 figures. Some definitions and proofs have been revised
since the previous version, and a new example has been adde
The simplicial boundary of a CAT(0) cube complex
For a CAT(0) cube complex , we define a simplicial flag complex
, called the \emph{simplicial boundary}, which is a
natural setting for studying non-hyperbolic behavior of . We compare
to the Roller, visual, and Tits boundaries of
and give conditions under which the natural CAT(1) metric on
makes it (quasi)isometric to the Tits boundary.
allows us to interpolate between studying geodesic
rays in and the geometry of its \emph{contact graph} , which is known to be quasi-isometric to a tree, and we characterize
essential cube complexes for which the contact graph is bounded. Using related
techniques, we study divergence of combinatorial geodesics in using
. Finally, we rephrase the rank-rigidity theorem of
Caprace-Sageev in terms of group actions on and
and state characterizations of cubulated groups with
linear divergence in terms of and .Comment: Lemma 3.18 was not stated correctly. This is fixed, and a minor
adjustment to the beginning of the proof of Theorem 3.19 has been made as a
result. Statements other than 3.18 do not need to change. I thank Abdul
Zalloum for the correction. See also: arXiv:2004.01182 (this version differs
from previous only by addition of the preceding link, at administrators'
request
Alpha Decay Hindrance Factors: A Probe of Mean Field Wave Functions
A simple model to calculate alpha-decay Hindrance Factors is presented. Using
deformation values obtained from PES calculations as the only input, Hindrance
Factors for the alpha-decay of Rn- and Po-isotopes are calculated. It is found
that the intrinsic structure around the Fermi surface determined by the
deformed mean field plays an important role in determining the hindrance of
alpha-decay. The fair agreement between experimental and theoretical Hindrance
Factors suggest that the wave function obtained from the energy minima of the
PES calculations contains an important part of the correlations that play a
role for the alpha-decay. The calculated HF that emerges from these
calculations render a different interpretation than the commonly assumed
n-particle n-hole picture.Comment: 7 pages, 9 figure
LINKING URBAN (STREET CANYON) MODELS WITH REGIONAL AIR QUALITY MODELS THROUGH URBAN BOUNDARY CONDITIONS
This contribution addresses the question of how detailed information from the urban canopy can be assimilated into
regional models. This detailed information concerns, among others, road transport emissions, specific exchange and turbulence
patterns in the built up canopy, and effects of roads and roughness elements on wind direction and wind speed. This information is
typically obtained from detailed street canyon models in combination with traffic emission models. In order to integrate the
dynamics of the urban canopy into regional air quality models, we propose the formulation of urban boundary conditions. The
formulation has been tested and compared with measurements for benzene and NOx in the city of Antwerp, Belgium
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