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81.
Marilyn Breen 《Journal of Geometry》1980,14(2):164-173
Let A and B be closed nonempty sets in the plane with A B=R2, A B=bdry A=bdry B=C. Assume that for every m 2 points in C, at least one of the corresponding segments is in A, at least one in B. Then each of A and B is locally expressible as a union of m–1 or fewer convex sets. 相似文献
82.
In situ EXAFS has been used to examine the hydrogen effect on the selective catalytic reduction of NOx over silver/alumina catalysts. For all SCR conditions used, with or without co-reductant (H2 or CO), the catalyst structure remained the same. Significant changes in the catalyst were only found under reducing conditions. The enhanced activity found in the presence of hydrogen is thought to be due to a chemical effect and not the result of a change in the structure of the active site. 相似文献
83.
Marilyn Breen 《Archiv der Mathematik》1997,68(1):60-64
Let S be a nonempty closed, simply connected set in the plane, and let α τ; 0. If every three points of 5 see a common point of
S via paths of length at most α, then for some point s0 of S, s0 sees each point of S via such a path. That is, S is starshaped via paths of length at most α.
Supported in part by NSF grant DMS-9207019 相似文献
84.
85.
86.
87.
Marilyn Breen 《Journal of Geometry》1989,35(1-2):19-25
Let
and assume that there is a countable collection of lines {L
i
: 1 i} such that (int cl S)
and ((int cl S) S) L
i has one-dimensional Lebesgue measure zero, 1 i. Then every 4 point subset ofS sees viaS a set of positive two-dimensional Lebesgue measure if and only if every finite subset ofS sees viaS such a set. Furthermore, a parallel result holds with two-dimensional replaced by one-dimensional. Finally, setS is finitely starlike if and only if every 5 points ofS see viaS a common point. In each case, the number 4 or 5 is best possible.Supported in part by NSF grant DMS-8705336. 相似文献
88.
Marilyn Breen 《Journal of Geometry》1989,35(1-2):14-18
SetS inR
d has propertyK
2 if and only ifS is a finite union ofd-polytopes and for every finite setF in bdryS there exist points c1,c2 (depending onF) such that each point ofF is clearly visible viaS from at least one ci,i = 1,2. The following characterization theorem is established: Let
, d2. SetS is a compact union of two starshaped sets if and only if there is a sequence {S
j
} converging toS (relative to the Hausdorff metric) such that each setS
j satisfies propertyK
2. For
, the sufficiency of the condition above still holds, although the necessity fails. 相似文献
89.
Marilyn Breen 《Israel Journal of Mathematics》1985,52(1-2):140-146
Let ? be a tiling of the plane such that each tile of ? meets at most finitely many other tiles. Then exactly one of the following must occur:
- Uncountably many boundary points of ? belong to no nondegenerate edge of ?, hence ? has uncountably many singular points; or
- Every boundary point of ? belongs to a nondegenerate edge of ?, moreover, ? has no singular points.
90.
Two novel hybrid polyoxovanadates that are functionalized by (4-aminophenyl)arsonic acid ligands form upon the reduction of vanadates(V) in aqueous systems, whereby the underlying condensation reactions are influenced by the nature of the employed acid. In the presence of Cl(-) ions that derive from hydrochloric acid, a tetradecanuclear cage structure [V(IV)(14)O(16)(OH)(8)-(O(3)AsC(6)H(4)-4-NH(2))(10)](4-), whose cavity contains stabilizing halide ions and water molecules, is obtained. When nitric acid is used, a decanuclear [V(10)O(18)(O(3)AsC(6)H(4)-4-NH(2))(7)(DMF)(2)](5-) cluster can be isolated. The latter organizes into a hexagonal packing arrangement in the solid state. 相似文献