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11.
Marilyn Breen 《Israel Journal of Mathematics》1974,17(4):347-349
LetS be a closed, simply connected subset of the plane,J a line segment (or a one-pointed set),J⊂S. If for every three points ofS there is a point ofJ seeing at least two of these points viaS, thenS is a union of two starshaped sets. IfJ⊈S or ifS is not simply connected, the result fails. 相似文献
12.
Marilyn Breen 《Journal of Geometry》1987,28(2):103-110
Let S be an arbitrary set in R2. Every three points of cl S are clearly visible via S from a common point of cl S if and only if each bounded subset of S may be extended to a starlike set in S. When this occurs, set S is expressible as an increasing union of starlike sets. 相似文献
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14.
Marilyn Breen 《Periodica Mathematica Hungarica》2014,68(1):45-53
Let $\mathcal K$ be a finite family of orthogonal polytopes in $\mathbb R^d$ such that, for every nonempty subfamily $\mathcal K^\prime $ of $\mathcal K, \cap \{K : K$ in $\mathcal K^\prime \}$ , if nonempty, is a finite union of boxes whose intersection graph is a tree. Assume that every $d + 1$ (not necessarily distinct) members of $\mathcal K$ meet in a (nonempty) staircase starshaped set. Then $S \equiv \cap \{ K : K$ in $\mathcal K\}$ is nonempty and staircase starshaped. 相似文献
15.
Michael Breen 《Semigroup Forum》1992,44(1):129-132
The principal ideals in the semigroup of binary relations on a finite set X form a partially ordered set under inclusion.
When the cardinality of the set X is increased by one, some of the covering relations present in the original set will be
preserved and some will not. This article describes the difference. 相似文献
16.
17.
An examination of published 31P NMR spectral data for aliphatic phosphorus compounds has revealed that chain lengthening and branching effects on the chemical shift can be interpreted in terms similar to those used for 13C and 15N shifts. For six families of phosphorus compounds, a β-carbon substituent was shown to deshield phosphorus, while a γ-carbon caused shielding. The effects are additive, and good agreement was obtained between 31P shifts calculated with the appropriate constants and the experimental values. Shielding by γ-carbon is indicative of the operation of a steric influence on 31P chemical shifts, not heretofore articulated. The γ-effect is also useful in explaining the unusually large shielding found in six-membered cyclic phosphines. 相似文献
18.
The reaction of OH with acetylene was studied in a discharge flow system at room temperature. OH was generated by the reaction of atomic hydrogen with NO2 and was monitored throughout the reaction using ESR spectroscopy. Mass-spectrometric analysis of the reaction products yielded the following results: (1) less than 3 molecules of OH were consumed, and less than 2 molecules of H2O were formed for every molecule of acetylene that reacted; (2) CO was identified as the major carbon-containing product; (3) NO, formed in the generation of OH, reacted with a reaction intermediate to give among other products N2O. These observations placed severe limitations on the choice of a reaction mechanism. A mechanism containing the reaction OH + C2H2 → HC2O + H2 better accounted for the experimental results than one involving the abstraction reaction OH + C2H2 → C2H + H2O. The rate constant for the initial reaction was measured as 1.9 ± 0.6 × 10?13 cm3 molecule?1 sec?1. 相似文献
19.
Communications in Mathematical Physics - We develop a rigorous semiclassical expansion to compute the radius of convergence of the Borel transform for the pressure in (φ4)2 field theory. This... 相似文献
20.
Marilyn Breen 《Israel Journal of Mathematics》1976,24(3-4):211-216
LetS be a closedm-convex subset of the plane,m≧2,Q the set of points of local nonconvexity ofS, with convQ ⊆S. If there is some pointp in [(bdryS) ∩ (kerS)] ∼Q, thenS is a union ofm−1 closed convex sets. The result is best possible for everym. 相似文献