77 research outputs found
On the Wiener Index of Orientations of Graphs
The Wiener index of a strong digraph is defined as the sum of the
distances between all ordered pairs of vertices. This definition has been
extended to digraphs that are not necessarily strong by defining the distance
from a vertex to a vertex as if there is no path from to in
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Knor, \u{S}krekovski and Tepeh [Some remarks on Wiener index of oriented
graphs. Appl.\ Math.\ Comput.\ {\bf 273}] considered orientations of graphs
with maximum Wiener index. The authors conjectured that for a given tree ,
an orientation of of maximum Wiener index always contains a vertex
such that for every vertex , there is either a -path or a
-path in . In this paper we disprove the conjecture.
We also show that the problem of finding an orientation of maximum Wiener
index of a given graph is NP-complete, thus answering a question by Knor,
\u{S}krekovski and Tepeh [Orientations of graphs with maximum Wiener index.
Discrete Appl.\ Math.\ 211].
We briefly discuss the corresponding problem of finding an orientation of
minimum Wiener index of a given graph, and show that the special case of
deciding if a given graph on edges has an orientation of Wiener index
can be solved in time quadratic in
ΠΠ·ΡΡΠ΅Π½ΠΈΠ΅ ΠΊΠΈΠ½Π΅ΡΠΈΠΊΠΈ ΡΠΎΡΠ±ΡΠΈΠΈ ΠΎΡΠ΄Π΅Π»ΡΠ½ΡΡ ΠΊΠΎΠΌΠΏΠΎΠ½Π΅Π½ΡΠΎΠ² ΠΊΠΎΠΌΠΏΠΎΠ·ΠΈΡΠ½ΠΎΠ³ΠΎ Π±ΠΈΠΎΡΠΎΡΠ±Π΅Π½ΡΠ°
Π Π΄Π°Π½Π½ΠΎΠΉ ΡΡΠ°ΡΡΠ΅ ΠΈΡΡΠ»Π΅Π΄ΡΠ΅ΡΡΡ ΠΊΠΈΠ½Π΅ΡΠΈΠΊΠ° ΡΠΎΡΠ±ΡΠΈΠΈ ΡΡΠ°Π½ΠΈΠ»-ΠΈΠΎΠ½ΠΎΠ² ΠΏΠ»Π΅ΡΠ½Π΅Π²ΡΠΌΠΈ Π³ΡΠΈΠ±Π°ΠΌΠΈ Penicillium pinophilum ΠΈ Aspergillus niger. ΠΡΡΠ»Π΅Π΄ΠΎΠ²Π°Π½ΠΈΡ ΠΏΠΎΠΊΠ°Π·Π°Π»ΠΈ ΡΡΠΎ ΡΡΠ΅ΠΏΠ΅Π½Ρ ΡΠΎΡΠ±ΡΠΈΠΈ ΠΏΠ»Π΅ΡΠ½Π΅Π²ΡΡ
Π³ΡΠΈΠ±ΠΎΠ² Aspergillus niger ΠΈΠΌΠ΅Π΅Ρ Π½Π° 3% Π±ΠΎΠ»ΡΡΡΡ ΡΡΠ΅ΠΏΠ΅Π½Ρ ΡΠΎΡΠ±ΡΠΈΠΈ ΡΡΠ°Π½Π°, ΡΠ΅ΠΌ Penicillium pinophilum . Π’Π°ΠΊ ΠΆΠ΅ ΠΈΡΡΠ»Π΅Π΄ΠΎΠ²Π°Π½ΠΈΡ ΠΏΠΎΠΊΠ°Π·Π°Π»ΠΈ, ΡΡΠΎ ΠΏΠΎΡΠ»Π΅ 12 ΡΠ°ΡΠΎΠ² ΡΠΎΡΠ±ΡΠΈΡ Π·Π°ΠΌΠ΅ΡΠ½ΠΎ ΡΠΌΠ΅Π½ΡΡΠ°Π΅ΡΡΡ ΠΈ ΠΏΠΎΡΡΠΈ ΠΎΡΡΠ°Π½Π°Π²Π»ΠΈΠ²Π°Π΅ΡΡΡ ΠΊΠ°ΠΊ Ρ ΠΎΠ΄Π½ΠΎ, ΡΠ°ΠΊ ΠΈ Ρ Π΄ΡΡΠ³ΠΎΠ³ΠΎ Π²ΠΈΠ΄Π° ΠΏΠ»Π΅ΡΠ½Π΅Π²ΡΡ
Π³ΡΠΈΠ±ΠΎΠ². This article examines the kinetics of sorption of uranyl ions by fungi Penicillium pinophilum and Aspergillus niger. Studies have shown that the degree of sorption fungi Aspergillus niger has by 3% greater uranium sorption than the Penicillium pinophilum . Studies have shown that after 12 hours of sorption decreases markedly and almost stops as one or the other kind of fungi
On Complexity of Minimum Leaf Out-branching Problem
Given a digraph , the Minimum Leaf Out-Branching problem (MinLOB) is the
problem of finding in an out-branching with the minimum possible number of
leaves, i.e., vertices of out-degree 0. Gutin, Razgon and Kim (2008) proved
that MinLOB is polynomial time solvable for acyclic digraphs which are exactly
the digraphs of directed path-width (DAG-width, directed tree-width,
respectively) 0. We investigate how much one can extend this polynomiality
result. We prove that already for digraphs of directed path-width (directed
tree-width, DAG-width, respectively) 1, MinLOB is NP-hard. On the other hand,
we show that for digraphs of restricted directed tree-width (directed
path-width, DAG-width, respectively) and a fixed integer , the problem of
checking whether there is an out-branching with at most leaves is
polynomial time solvable
Proximity, remoteness and maximum degree in graphs
The average distance of a vertex of a connected graph is the
arithmetic mean of the distances from to all other vertices of . The
proximity and the remoteness of are the minimum and the
maximum of the average distances of the vertices of , respectively.
In this paper, we give upper bounds on the remoteness and proximity for
graphs of given order, minimum degree and maximum degree. Our bounds are sharp
apart from an additive constant.Comment: 20 page
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