Periodica Mathematica Hungarica - For a given integer $$k\ge 1$$ , a graph G with at least 2k vertices is called k-path-pairable, if for any set of k disjoint pairs of vertices, $$s_i,t_i$$ ,... 相似文献
Platinum is a catalyst of choice in scientific investigations and technological applications, which are both often carried out in the presence of oxygen. Thus, a fundamental understanding of platinum’s (electro)catalytic behavior requires a detailed knowledge of the structure and degree of oxidation of platinum surfaces in operando. ReaxFF reactive force field calculations of the surface energies for structures with up to one monolayer of oxygen on Pt(111) reveal four stable surface phases characterized by pure adsorbate, high‐ and low‐coverage buckled, and subsurface‐oxygen structures, respectively. These structures and temperature programmed desorption (TPD) spectra simulated from them compare favorably with and complement published scanning tunneling microscopy (STM) and TPD experiments. The surface buckling and subsurface oxygen observed here influence the surface oxidation process, and are expected to impact the (electro)catalytic properties of partially oxidized Pt(111) surfaces. 相似文献
In PET, α-methyl amino acids can play a dual role: a) precursors of neurotransmitters analogues for the study of neurodegenerative
diseases; b) non-metabolised analogues of proteinogenic amino acids for the study of amino acids uptake into normal and cancer
cells. The difference in the uptake rates during a PET scan could visualise cancer cells in a human body. Clinical applications
of such amino acids are strongly limited due to their poor availability. For the synthesis of α-[11C]methyl-tryptohan, an industrial procedure was adopted. All attempts to prepare enantiomerically pure α-[11C]methylated tyrosine failed. We carried out [11C]methylation of metalocomplex synthons derived from protected DOPA or tyrosine. Individual diastereomers were successfully
separated by preparative HPLC, diluted with excess of water and extracted on C18 cartridges. Optimisation of the procedure followed by hydrolysis of the complexes and purification of the enantiomers of
α-[11C]methylDOPA and α-[11C]methyltyrosine is underway. 相似文献
Related to Chvátal's famous conjecture stating that every 2-tough graph is hamiltonian, we study the relation of toughness and hamiltonicity on special classes of graphs.
First, we consider properties of graph classes related to hamiltonicity, traceability and toughness concepts and display some algorithmic consequences. Furthermore, we present a polynomial time algorithm deciding whether the toughness of a given split graph is less than one and show that deciding whether the toughness of a bipartite graph is exactly one is coNP-complete.
We show that every
split graph is hamiltonian and that there is a sequence of non-hamiltonian split graphs with toughness converging to
. 相似文献
Suppose that a connected graph G has n vertices and m edges, and each edge is contained in some triangle of G. Bounds are established here on the minimum number tmin(G) of triangles that cover the edges of G. We prove that ?(n - 1)/2? ? tmin(G) with equality attained only by 3-cactii and by strongly related graphs. We obtain sharp upper bounds: if G is not a 4-clique, then. The triangle cover number tmin(G) is also bounded above by Γ(G) = m - n + c, the cyclomatic number of a graph G of order n with m edges and c connected components. Here we give a combinatorial proof for tmin(G) ? Γ(G) and characterize the family of all extremal graphs satisfying equality. 相似文献
The transversal number, packing number, covering number and strong stability number of hypergraphs are denoted by τ, ν, ϱ
and α, respectively. A hypergraph family t is called τ-bound (ϱ-bound) if there exists a “binding function”f(x) such that τ(H)≦f(v(H)) (ϱ(H)≦f(α(H))) for allH ∈ t. Methods are presented to show that various hypergraph families are τ-bound and/or ϱ-bound. The results can be applied
to families of geometrical nature like subforests of trees, boxes, boxes of polyominoes or to families defined by hypergraph
theoretic terms like the family where every subhypergraph has the Helly-property. 相似文献
A weighted hypergraph is a hypergraph
H = (V, E) with a weighting function
, where
R is the set of reals. A
multiset S V generates a partial hypergraph
HS with edges
, where both the
cardinality
and the total weight
w(S) are counted with multiplicities of
vertices in S. The
transversal number of H is
represented by (H). We prove the following: there
exists a function f(n) such that, for any weighted
n-Helly hypergraph
H, (HB) 1, for all multisets
BV if and only if
(HA) 1, for all multisets
AV with
. We provide lower and
upper bounds for f(n) using a link between indecomposable
hypergraphs and critical weighted n-Helly hypergraphs.* On leave from Computing and Automation Research
Institute, Hungarian Academy of Sciences. 相似文献
The right order of magnitude for the maximal number of vertices in an r-uniform τ-critical hypergraph H is achieved by obtaining an upper bound of O(τ(H)r?1). 相似文献