Том 214, № 5 (2016)
- Жылы: 2016
- Мақалалар: 9
- URL: https://journals.rcsi.science/1072-3374/issue/view/14734
Article
The Length of an Extremal Network in a Normed Space: Maxwell Formula
Аннотация
In the present paper we consider local minimal and extremal networks in normed spaces. It is well known that in the case of the Euclidean space these two classes coincide and the length of a local minimal network can be found by using only the coordinates of boundary vertices and the directions of boundary edges (the Maxwell formula). Moreover, as was shown by Ivanov and Tuzhilin [15], the length of a local minimal network in the Euclidean space can be found by using the coordinates of boundary vertices and the structure of the network. In the case of an arbitrary norm there are local minimal networks that are not extremal networks, and an analogue of the formula mentioned above is only true for extremal networks; this is the main result of the paper. Moreover, we generalize the Maxwell formula for the case of extremal networks in normed spaces and give an explicit construction of norming functionals used in the formula for several normed spaces.
On the Combinatorics of Smoothing
Аннотация
Many invariants of knots rely upon smoothing the knot at its crossings. To compute them, it is necessary to know how to count the number of connected components the knot diagram is broken into after the smoothing. In this paper, it is shown how to use a modification of a theorem of Zulli together with a modification of the spectral theory of graphs to approach such problems systematically. We give an application to counting subdiagrams of pretzel knots which have one component after oriented and unoriented smoothings.
Graph-Links: Nonrealizability, Orientation, and Jones Polynomial
Аннотация
The present paper is devoted to graph-links with many components and consists of two parts. In the first part of the paper we classify vertices of a labeled graph according to the component they belong to. Using this classification, we construct an invariant of graph-links. This invariant shows that the labeled second Bouchet graph generates a nonrealizable graph-link.
In the second part of the work we introduce the notion of an oriented graph-link. We define a writhe number for the oriented graph-link and we get an invariant of oriented graph-links, the Jones polynomial, by normalizing the Kauffman bracket with the writhe number.
On Large Subgraphs with Small Chromatic Numbers Contained in Distance Graphs
Аннотация
It is proved that each distance graph on a plane has an induced subgraph with a chromatic number that is at most 4 containing over 91% of the vertices of the original graph. This result is used to obtain the asymptotic growth rate for a threshold probability that a random graph is isomorphic to a certain distance graph on a plane. Several generalizations to larger dimensions are proposed.
On the Chromatic Numbers of Integer and Rational Lattices
Аннотация
In this paper, we give new upper bounds for the chromatic numbers for integer lattices and some rational spaces and other lattices. In particular, we have proved that for any concrete integer number d, the chromatic number of ℤn with critical distance \( \sqrt{2d} \) has a polynomial growth in n with exponent less than or equal to d (sometimes this estimate is sharp). The same statement is true not only in the Euclidean norm, but also in any lp norm. Moreover, we have given concrete estimates for some small dimensions as well as upper bounds for the chromatic number of ℚpn, where by ℚp we mean the ring of all rational numbers having denominators not divisible by some prime numbers.
Weak Parities and Functorial Maps
Аннотация
We consider functorial maps and weak parities that are two equivalent descriptions of one object. Functorial maps allow one to transform knots and extend knot invariants with these transformations. We introduce maximal weak parity and calculate it for knots in a given closed oriented surface. The weak parity induce a projection from virtual knots onto classical ones.
An Invariant of Knots in Thickened Surfaces
Аннотация
In the present paper, we construct an invariant of knots in the thickened sphere with g handles dependent on 2g + 3 variables. In the construction of the invariant we use the Wirtinger presentation of the knot group and the concept of parity introduced by Manturov [9]. In the present paper, we also consider examples of knots in the thickened torus considered in [2] such that their nonequivalence is proved by using the constructed polynomial.