25,006 research outputs found
A condition for isotopic approximation
In this note, we show that if two surfaces in are homeomorphic, then a simple and purely topological condition is sufficient to ensure the existence of an isotopy between them. When the surfaces are connected, the condition is merely that one surface is contained in some topological thickening of the other and separates the two boundary components of that thickening. The proof of this result is based on basic 3-manifold topology
HERA high events as indications of excited leptons with weak isotopic spin 3/2
The H1 and ZEUS anomalous events are interpreted as being due to the
production and the decay of excited leptons , which correspond to spin 1/2
resonances of the first generation lepton doublet () with W triplet.
This assumption is supported by considering of Bethe-Salpeter equation in the
ladder approximation with anomalous triple gauge boson vertex. The solution
with weak isospin is shown to exist for zero mass state, that means
M_EEWEW\lambda \simeq 0.5$. Isotopic relations for
different channels are presented as a tool for checking the interpretation.Comment: 8 pages, latex, no figure
Continuous rational maps into spheres
Let X be a compact nonsingular real algebraic variety. We prove that if a
continuous map from X into the unit p-sphere is homotopic to a continuous
rational map, then, under certain assumptions, it can be approximated in the
compact-open topology by continuous rational maps. As a byproduct, we also
obtain some results on approximation of smooth submanifolds by nonsingular
subvarieties.Comment: To appear in Mathematische Zeitschrif
Shock-Wave Heating Model for Chondrule Formation: Prevention of Isotopic Fractionation
Chondrules are considered to have much information on dust particles and
processes in the solar nebula. It is naturally expected that protoplanetary
disks observed in present star forming regions have similar dust particles and
processes, so study of chondrule formation may provide us great information on
the formation of the planetary systems.
Evaporation during chondrule melting may have resulted in depletion of
volatile elements in chondrules. However, no evidence for a large degree of
heavy-isotope enrichment has been reported in chondrules. In order to meet this
observed constraint, the rapid heating rate at temperatures below the silicate
solidus is required to suppress the isotopic fractionation.
We have developed a new shock-wave heating model taking into account the
radiative transfer of the dust thermal continuum emission and the line emission
of gas molecules and calculated the thermal history of chondrules. We have
found that optically-thin shock waves for the thermal continuum emission from
dust particles can meet the rapid heating constraint, because the dust thermal
emission does not keep the dust particles high temperature for a long time in
the pre-shock region and dust particles are abruptly heated by the gas drag
heating in the post-shock region. We have also derived the upper limit of
optical depth of the pre-shock region using the radiative diffusion
approximation, above which the rapid heating constraint is not satisfied. It is
about 1 - 10.Comment: 58 pages, including 5 tables and 15 figures, accepted for publication
in The Astrophysical Journa
Complete Subdivision Algorithms, II: Isotopic Meshing of Singular Algebraic Curves
Given a real valued function f(X,Y), a box region B_0 in R^2 and a positive
epsilon, we want to compute an epsilon-isotopic polygonal approximation to the
restriction of the curve S=f^{-1}(0)={p in R^2: f(p)=0} to B_0. We focus on
subdivision algorithms because of their adaptive complexity and ease of
implementation. Plantinga and Vegter gave a numerical subdivision algorithm
that is exact when the curve S is bounded and non-singular. They used a
computational model that relied only on function evaluation and interval
arithmetic. We generalize their algorithm to any bounded (but possibly
non-simply connected) region that does not contain singularities of S. With
this generalization as a subroutine, we provide a method to detect isolated
algebraic singularities and their branching degree. This appears to be the
first complete purely numerical method to compute isotopic approximations of
algebraic curves with isolated singularities
Isotopic Equivalence from Bezier Curve Subdivision
We prove that the control polygon of a Bezier curve B becomes homeomorphic
and ambient isotopic to B via subdivision, and we provide closed-form formulas
to compute the number of iterations to ensure these topological
characteristics. We first show that the exterior angles of control polygons
converge exponentially to zero under subdivision.Comment: arXiv admin note: substantial text overlap with arXiv:1211.035
Some conjectures on continuous rational maps into spheres
Recently continuous rational maps between real algebraic varieties have
attracted the attention of several researchers. In this paper we continue the
investigation of approximation properties of continuous rational maps with
values in spheres. We propose a conjecture concerning such maps and show that
it follows from certain classical conjectures involving transformation of
compact smooth submanifolds of nonsingular real algebraic varieties onto
subvarieties. Furthermore, we prove our conjecture in a special case and obtain
several related results.Comment: arXiv admin note: text overlap with arXiv:1403.512
Predicting scattering properties of ultracold atoms: adiabatic accumulated phase method and mass scaling
Ultracold atoms are increasingly used for high precision experiments that can
be utilized to extract accurate scattering properties. This calls for a
stronger need to improve on the accuracy of interatomic potentials, and in
particular the usually rather inaccurate inner-range potentials. A boundary
condition for this inner range can be conveniently given via the accumulated
phase method. However, in this approach one should satisfy two conditions,
which are in principle conflicting, and the validity of these approximations
comes under stress when higher precision is required. We show that a better
compromise between the two is possible by allowing for an adiabatic change of
the hyperfine mixing of singlet and triplet states for interatomic distances
smaller than the separation radius. A mass scaling approach to relate
accumulated phase parameters in a combined analysis of isotopically related
atom pairs is described in detail and its accuracy is estimated, taking into
account both Born-Oppenheimer and WKB breakdown. We demonstrate how numbers of
singlet and triplet bound states follow from the mass scaling.Comment: 14 pages, 9 figure
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