1,416 research outputs found
Locally -homogeneous Busemann -spaces
We present short proofs of all known topological properties of general
Busemann -spaces (at present no other property is known for dimensions more
than four). We prove that all small metric spheres in locally -homogeneous
Busemann -spaces are homeomorphic and strongly topologically homogeneous.
This is a key result in the context of the classical Busemann conjecture
concerning the characterization of topological manifolds, which asserts that
every -dimensional Busemann -space is a topological -manifold. We also
prove that every Busemann -space which is uniformly locally -homogeneous
on an orbal subset must be finite-dimensional
Minimality of planes in normed spaces
We prove that a region in a two-dimensional affine subspace of a normed space
has the least 2-dimensional Hausdorff measure among all compact surfaces
with the same boundary. Furthermore, the 2-dimensional Hausdorff area density
admits a convex extension to . The proof is based on a (probably)
new inequality for the Euclidean area of a convex centrally-symmetric polygon.Comment: 10 pages, v2: minor changes according to referees' comments, to
appear in GAF
Best-First Surface Realization
Current work in surface realization concentrates on the use of general,
abstract algorithms that interpret large, reversible grammars. Only little
attention has been paid so far to the many small and simple applications that
require coverage of a small sublanguage at different degrees of sophistication.
The system TG/2 described in this paper can be smoothly integrated with deep
generation processes, it integrates canned text, templates, and context-free
rules into a single formalism, it allows for both textual and tabular output,
and it can be parameterized according to linguistic preferences. These features
are based on suitably restricted production system techniques and on a generic
backtracking regime.Comment: 10 pages, LaTeX source, one EPS figur
A Flexible Shallow Approach to Text Generation
In order to support the efficient development of NL generation systems, two
orthogonal methods are currently pursued with emphasis: (1) reusable, general,
and linguistically motivated surface realization components, and (2) simple,
task-oriented template-based techniques. In this paper we argue that, from an
application-oriented perspective, the benefits of both are still limited. In
order to improve this situation, we suggest and evaluate shallow generation
methods associated with increased flexibility. We advise a close connection
between domain-motivated and linguistic ontologies that supports the quick
adaptation to new tasks and domains, rather than the reuse of general
resources. Our method is especially designed for generating reports with
limited linguistic variations.Comment: LaTeX, 10 page
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Solar noble gases in Vigarano bulk minerals – First results of the new 'BENGEL' in-vacuo etching facility
Extract from introduction: Regolith breccias are breccias that contain solar-gas-bearing grains [1,2]. It is generally accepted that the exposure to the solar wind took place rather recently on the surface of a parent body. However, it appears possible that grains were exposed early (or obtained their solar gas load by other mechanisms) prior to accretion. Some of the solar gases in chondrites may indeed be 'primordial' [3,4]. In the CI chondrite Orgueil, the presence of solar gases is restricted to magnetite, whereas the silicates appear solar-gas-free [3]. This is difficult to reconcile in a planetary environment. The observation that solar-like gases in the unbrecciated E chondrite St. Mark's were released only upon severe etching provides further evidence for the presence of primordial solar gas [5]
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Plutonium-Xenon systematics of Angrites
Introduction: Angrites are igneous meteorites that crystallized very early in the solar system, ~10 Ma after CAIs, as also implied by the presence of now extinct short-lived radionuclides such as 53Mn, 146Sm and 244Pu [1]. Fission Xe was used to calculate 244Pu-136Xeretention ages of eucrites, relative to that of Angra dos Reis (AdoR) [2]. AdoR has an absolute Pb-Pb age of 4557.8 Ma [see 1 for ref.]. Most eucrites, being as old as angrites, experienced various parent body processes leading to ages ranging from ~20 Ma before, to ~100 Ma after AdoR [2]. Angrites, however, remained largely unaltered after differentiation. Here, we examine whether Xe isotopic characteristics
allow determining an age sequence for angrites
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The trapped heavy noble gases in recently found Martian meteorites
The composition of the trapped Ar, Kr, and Xe in the Martian meteorites Los Angeles, Say Al Uhaymir 005/008, and 094 is discussed and found to be consistent with a mixture of Martian mantle and atmosphere noble gases and terrestrial contamination
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Ancient volcanic xenon in single glass grains from the D'Orbigny angrite
We present high-sensitivity xenon data for single glass grains from the D'Orbigny angrite. These grains contain the first sample of volcanic gas from a planetary body other than the Earth and excess Xe-129 detected for the first time in angrites
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Solar noble bases in enstatite chondrites and implications for the formation of the terrestrial planets
We report evidence for tiny amounts of - most likely primordial - noble gases with solar-like elemental and isotopic composition admixed to Q-type primordial noble gases in an E chondrite. We will discuss possible implications of this finding for terrestrial planet formation
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