scholarly journals Longest paths in random Apollonian networks and largest r-ary subtrees of random d-ary recursive trees

2016 ◽  
Vol 53 (3) ◽  
pp. 846-856 ◽  
Author(s):  
Andrea Collevecchio ◽  
Abbas Mehrabian ◽  
Nick Wormald
Keyword(s):  
Related Result ◽  
Plane Graph ◽  
Time Step ◽  
Single Vertex ◽  
Planar Triangulation ◽  
The Face ◽  
Longest Paths ◽  
Recursive Trees ◽  
Positive Integers ◽  
Iterative Construction

AbstractLet r and d be positive integers with r<d. Consider a random d-ary tree constructed as follows. Start with a single vertex, and in each time-step choose a uniformly random leaf and give it d newly created offspring. Let 𝒯d,t be the tree produced after t steps. We show that there exists a fixed δ<1 depending on d and r such that almost surely for all large t, every r-ary subtree of 𝒯d,t has less than tδ vertices. The proof involves analysis that also yields a related result. Consider the following iterative construction of a random planar triangulation. Start with a triangle embedded in the plane. In each step, choose a bounded face uniformly at random, add a vertex inside that face and join it to the vertices of the face. In this way, one face is destroyed and three new faces are created. After t steps, we obtain a random triangulated plane graph with t+3 vertices, which is called a random Apollonian network. We prove that there exists a fixed δ<1, such that eventually every path in this graph has length less than t𝛿, which verifies a conjecture of Cooper and Frieze (2015).

scholarly journals Total Face Irregularity Strength of Grid and Wheel Graph under K-Labeling of Type (1, 1, 0)

2021 ◽  
Vol 2021 ◽  
pp. 1-16
Author(s):  
Aleem Mughal ◽  
Noshad Jamil
Keyword(s):  
Plane Graph ◽  
Plane Graphs ◽  
Wheel Graph ◽  
Wheel Graphs ◽  
The Face ◽  
Vertex Set ◽  
Positive Integers ◽  
Special Case ◽  
Irregularity Strength

In this study, we used grids and wheel graphs G = V , E , F , which are simple, finite, plane, and undirected graphs with V as the vertex set, E as the edge set, and F as the face set. The article addresses the problem to find the face irregularity strength of some families of generalized plane graphs under k -labeling of type α , β , γ . In this labeling, a graph is assigning positive integers to graph vertices, graph edges, or graph faces. A minimum integer k for which a total label of all verteices and edges of a plane graph has distinct face weights is called k -labeling of a graph. The integer k is named as total face irregularity strength of the graph and denoted as tfs G . We also discussed a special case of total face irregularity strength of plane graphs under k -labeling of type (1, 1, 0). The results will be verified by using figures and examples.

scholarly journals Numerical Analysis of Unsteady Laminar Flow past a Pentagonal Obstacle

2021 ◽  
Vol 10 (2) ◽  
pp. 968-974
Keyword(s):  
Laminar Flow ◽  
Flow Direction ◽  
Rectangular Channel ◽  
Time Frame ◽  
Two Dimensional ◽  
Fluid Inertia ◽  
Time Step ◽  
The Face ◽  
Computational Fluid Dynamics Cfd ◽  
Current Article

The current article dispenses the numerical investigation of a two dimensional unsteady laminar flow of incompressible fluid passing a regular pentagonal obstacle in an open rectangular channel. The centre of attention of this work is the comparison of drag coefficients estimated for two distinct cases based on the orientation of face and corner of an obstacle against the flow direction. The numerical results shows that the corner – oriented obstacle bring about 42% larger value of drag coefficient at Re = 500 than face – oriented obstacle. The substantial growth in the expanse of vortex behind obstacle (presented as a function of fluid inertia 25 < Re < 500) is analyzed through the contours and streamline patterns of velocity field. The two eddies in the downstream become entirely unsymmetrical at Re = 500 for both the cases, whereas; the flow separation phenomena occurs a bit earlier in the face – oriented case at Re = 250. Two dimensional Pressure – Based – Segregated solver is employed to model the governing equations written in velocity and pressure fields. The numerical simulations of unsteady flow are presented for 50 seconds time frame with time step 0.01 by using one of the best available commercial based Computational Fluid Dynamics (CFD) software, ANSYS 15.0.

On A theorem of Niven

1974 ◽  
Vol 17 (1) ◽  
pp. 109-110 ◽  
Author(s):  
Robert E. Dressler
Keyword(s):  
Positive Integer ◽  
Related Result ◽  
Positive Integers

In [3], Niven proved that for any positive integer k, the density of the set of positive integers n for which (n, (φ(n))≤k is zero (where φ is the Euler to tient function). In this paper, we prove a related result—namely if k and j are any positive integers, then the density of the set of positive integers n for which (n,σj(n))≤k is zero (where σj(n) is the sum of the jth powers of the positive divisors of n). We will borrow from Niven’s technique, but we must make some crucial modifications.

scholarly journals FOLDING EQUILATERAL PLANE GRAPHS

2013 ◽  
Vol 23 (02) ◽  
pp. 75-92 ◽  
Author(s):  
ZACHARY ABEL ◽  
ERIK D. DEMAINE ◽  
MARTIN L. DEMAINE ◽  
SARAH EISENSTAT ◽  
JAYSON LYNCH ◽  
...  
Keyword(s):  
Plane Graph ◽  
Analogous Problem ◽  
Central Vertex ◽  
Polyhedral Complex ◽  
Plane Graphs ◽  
Single Vertex ◽  
Np Completeness ◽  
Np Complete ◽  
Polyhedral Manifold

We consider two types of folding applied to equilateral plane graph linkages. First, under continuous folding motions, we show how to reconfigure any linear equilateral tree (lying on a line) into a canonical configuration. By contrast, it is known that such reconfiguration is not always possible for linear (nonequilateral) trees and for (nonlinear) equilateral trees. Second, under instantaneous folding motions, we show that an equilateral plane graph has a noncrossing linear folded state if and only if it is bipartite. Furthermore, we show that the equilateral constraint is necessary for this result, by proving that it is strongly NP-complete to decide whether a (nonequilateral) plane graph has a linear folded state. Equivalently, we show strong NP-completeness of deciding whether an abstract metric polyhedral complex with one central vertex has a noncrossing flat folded state. By contrast, the analogous problem for a polyhedral manifold with one central vertex (single-vertex origami) is only weakly NP-complete.

scholarly journals A computational method for sharp interface advection

2016 ◽  
Vol 3 (11) ◽  
pp. 160405 ◽  
Author(s):  
Johan Roenby ◽  
Henrik Bredmose ◽  
Hrvoje Jasak
Keyword(s):  
Three Dimensional ◽  
Volume Of Fluid ◽  
Accurate Estimate ◽  
Computational Method ◽  
Time Step ◽  
Face Area ◽  
The Face ◽  
Polyhedral Cells ◽  
Reconstructed Surface ◽  
Submerged Area

We devise a numerical method for passive advection of a surface, such as the interface between two incompressible fluids, across a computational mesh. The method is called isoAdvector, and is developed for general meshes consisting of arbitrary polyhedral cells. The algorithm is based on the volume of fluid (VOF) idea of calculating the volume of one of the fluids transported across the mesh faces during a time step. The novelty of the isoAdvector concept consists of two parts. First, we exploit an isosurface concept for modelling the interface inside cells in a geometric surface reconstruction step. Second, from the reconstructed surface, we model the motion of the face–interface intersection line for a general polygonal face to obtain the time evolution within a time step of the submerged face area. Integrating this submerged area over the time step leads to an accurate estimate for the total volume of fluid transported across the face. The method was tested on simple two-dimensional and three-dimensional interface advection problems on both structured and unstructured meshes. The results are very satisfactory in terms of volume conservation, boundedness, surface sharpness and efficiency. The isoAdvector method was implemented as an OpenFOAM ® extension and is published as open source.

scholarly journals Links in the complex of weakly separated collections

2020 ◽  
Vol DMTCS Proceedings, 28th... ◽  
Author(s):  
Suho Oh ◽  
David Speyer
Keyword(s):  
Short Note ◽  
Cluster Algebras ◽  
Combinatorial Objects ◽  
The Face ◽  
International Audience ◽  
Plabic Graphs ◽  
Positive Integers ◽  
Do So

International audience Plabic graphs are combinatorial objects used to study the totally nonnegative Grassmannian. Faces of plabic graphs are labeled by k-element sets of positive integers, and a collection of such k-element sets are the face labels of a plabic graph if that collection forms a maximal weakly separated collection. There are moves that one can apply to plabic graphs, and thus to maximal weakly separated collections, analogous to mutations of seeds in cluster algebras. In this short note, we show if two maximal weakly separated collections can be mutated from one to another, then one can do so while freezing the face labels they have in common. In particular, this provides a new, and we think simpler, proof of Postnikov's result that any two reduced plabic graphs with the same decorated permutations can be mutated to each other.

scholarly journals Kempe-Locking Configurations

2018 ◽  
Author(s):  
James A. Tilley
Keyword(s):  
Bipartite Graph ◽  
Systematic Search ◽  
Single Edge ◽  
Heuristic Argument ◽  
Bottom Boundary ◽  
Single Vertex ◽  
Planar Triangulation ◽  
Isomorphism Classes ◽  
Connectivity Property ◽  
Proper Subgraph

Existing proofs of the 4-color theorem succeeded by establishing an unavoidable set of reducible configurations. By this device, their authors showed that a minimum counterexample cannot exist. G.D. Birkhoff proved that a minimum counterexample must satisfy a connectivity property that is referred to in modern parlance as internal 6-connectivity. We show that a minimum counterexample must also satisfy a coloring property, one that we call Kempe-locking. We define the terms Kempe-locking configuration and fundamental Kempe-locking configuration. We provide a heuristic argument that a fundamental Kempe-locking configuration must be of low order and then perform a systematic search through isomorphism classes for such configurations. We describe a methodology for analyzing whether an arbitrary planar triangulation is Kempe-locked; it involves deconstructing the triangulation into a stack of configurations with common endpoints and then creating a bipartite graph of coloring possibilities for each configuration in the stack to assess whether certain 2-color paths can be transmitted from the configuration's top boundary to its bottom boundary. All Kempe-locked triangulations we discovered have two features in common: (1) they are Kempe-locked with respect to only a single edge, say $xy$, and (2) they have a Birkhoff diamond with endpoints $x$ and $y$ as a proper subgraph. On the strength of our various investigations, we are led to a plausible conjecture that the Birkhoff diamond is the only fundamental Kempe-locking configuration. If true, this would establish that the connectivity and coloring properties of a minimum counterexample to the 4-color theorem are incompatible. It would also point to the singular importance of a particularly elegant 4-connected triangulation of order 9 that consists of a triangle enclosing a pentagon enclosing a single vertex.

scholarly journals Bit flipping and time to recover

2016 ◽  
Vol 53 (3) ◽  
pp. 650-666 ◽  
Author(s):  
Anton Muratov ◽  
Sergei Zuyev
Keyword(s):  
Central Limit Theorem ◽  
Limit Theorem ◽  
Central Limit ◽  
Ground State ◽  
Sufficient Conditions ◽  
Return Time ◽  
Time Step ◽  
Transient Behaviour ◽  
Fractional Moments ◽  
Positive Integers

AbstractWe call `bits' a sequence of devices indexed by positive integers, where every device can be in two states: 0 (idle) and 1 (active). Start from the `ground state' of the system when all bits are in 0-state. In our first binary flipping (BF) model the evolution of the system behaves as follows. At each time step choose one bit from a given distribution P on the positive integers independently of anything else, then flip the state of this bit to the opposite state. In our second damaged bits (DB) model a `damaged' state is added: each selected idling bit changes to active, but selecting an active bit changes its state to damaged in which it then stays forever. In both models we analyse the recurrence of the system's ground state when no bits are active. We present sufficient conditions for both the BF and DB models to show recurrent or transient behaviour, depending on the properties of the distribution P. We provide a bound for fractional moments of the return time to the ground state for the BF model, and prove a central limit theorem for the number of active bits for both models.

Numbers

2018 ◽  
Author(s):  
Graham Priest
Keyword(s):  
Nineteenth Century ◽  
Middle Ages ◽  
Family Resemblance ◽  
Seventh Century ◽  
Complex Numbers ◽  
Square Root ◽  
Irrational Numbers ◽  
The Face ◽  
Definition Of ◽  
Positive Integers

Numbers are, in general, mathematical entities whose function is to express the size, order or magnitude of something or other. Historically, starting from the most basic kind of number, the positive integers (1, 2, 3,…), which appear in the earliest written records, the notion of number has been generalized and extended in several different directions – often in the face of considerable opposition. Other than the positive integers, the most venerable are the rational numbers (fractions), which were known to the Egyptians and Mesopotamians. The discovery, by Pythagorean mathematicians, that there are lengths that cannot be expressed as fractions occasioned the introduction of irrational numbers, such as the square root of 2, though the Greeks managed only a geometric understanding of these. The number zero was recognized, first in Indian mathematics, by the seventh century; the use of negative numbers evolved after this time; and complex numbers, such as the square root of −1, appeared first at the end of the Middle Ages. Infinitesimal numbers were developed by the founders of the calculus, Newton and Leibniz, in the seventeenth century (and were later to disappear from mathematics – for a time); and infinite numbers (ordinals and cardinals) were introduced by the founder of modern set theory, Cantor, in the nineteenth century. The introductions of three of these kinds of number, in particular, occasioned crises in the foundations of mathematics. The first (concerning irrational numbers) was finally resolved in the nineteenth century by the work of Cauchy and Weierstrass. The second (concerning infinitesimals) was also resolved then, by the work of Weierstrass and Dedekind. The third (concerning infinite numbers), which involves paradoxes such as Russell’s, still awaits a convincing solution. It is seemingly impossible to give a rigorous definition of what it is to be a number. The closest one can get is a family-resemblance notion, with very ill-defined boundaries.

Cohen-Macaulay type of the face poset of a plane graph

1994 ◽  
Vol 10 (2-4) ◽  
pp. 133-138
Author(s):  
Takayuki Hibi
Keyword(s):  
Plane Graph ◽  
The Face
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