Existence of optimal strategies for a fire confinement problem

We consider a class of variational problems for differential inclusions related to the control of forest fires. The area burned by the fire at time t > 0 is modeled as the reachable set for a differential inclusion ? ∈ F(x) starting from an initial set R₀. To block the fire, a barrier can be constructed progressively in time at a given speed. In this paper we prove the existence of an optimal strategy, which minimizes the value of the area destroyed by the fire plus the cost of constructing the barrier. © 2008 Wiley Periodicals, Inc.     

Compensations in the Shapley value and the compensation solutions for graph games

We consider an alternative expression of the Shapley value that reveals a system of compensations: each player receives an equal share of the worth of each coalition he belongs to, and has to compensate an equal share of the worth of any coalition he does not belong to. We give a representation in terms of formation of the grand coalition according to an ordering of the players and define the corresponding compensation vector. Then, we generalize this idea to cooperative games with a communication graph in order to construct new allocation rules called the compensation solutions. Firstly, we consider cooperative games with arbitrary graphs and construct rooted spanning trees (see Demange, J Political Econ 112:754–778, 2004) instead of orderings of the players by using the classical algorithms DFS and BFS. If the graph is complete, we show that the compensation solutions associated with DFS and BFS coincide with the Shapley value and the equal surplus division respectively. Secondly, we consider cooperative games with a forest (cycle-free graph) and all its rooted spanning trees. The compensation solution is characterized by component efficiency and relative fairness. The latter axiom takes into account the relative position of a player with respect to his component in the communication graph.     

Fractal analysis for studying the evolution of forests

Deforestation is an important phenomenon that may create major imbalances in ecosystems. In this study we propose a new mathematical analysis of the forest area dynamic, enabling qualitative as well as quantitative statements and results. Fractal dimensions of the area and the perimeter of a forest were determined using digital images. The difference between fractal dimensions of the area and the perimeter images turned out to be a crucial quantitative parameter. Accordingly, we propose a new fractal fragmentation index, FFI, which is based on this difference and which highlights the degree of compaction or non-compaction of the forest area in order to interpret geographic features. Particularly, this method was applied to forests, where large areas have been legally or illegally deforested. However, these methods can easily be used for other ecological or geographical investigations based on digital images, including deforestation of rainforests.     

Energy estimate, energy gap phenomenon, and relaxed energy for Yang-Mills functional

Concerning the Yang-Mills functional over R ⁵ ∖ {a ₁,...,a _p },we calculate its energy using geometrical term. Moreover, we may find the energy gap phenomenon with respect to the Yang-Mills energy which occurs also for harmonic mapping etc. From this, we propose to consider new functional, called relaxed energy.     

Perspectives on experimental fires in Canadian forestry research

This paper offers some insights into the field approach to conducting experimental forest fires based on two decades of experience dealing with a wide variety of fuel types, burning conditions, and resultant fire behavior. The practical aspects involved in designing a study area for an experimental burning project and its successful execution are considered as well as the methods used in the measurement of physical fire characteristics, fuel properties, and fire weather elements. On the basis of this review, several impressions emerge about the possible future requirements and emphasis in outdoor forest fire behavior research involving naturally occurring fuel complexes. Finally, the conclusion is reached that there can be no substitute for actual “hands-on” experience in observing experimental fires as a basis for understanding the behavior of free-burning fires in the forest environment resulting from planned or accidental ignitions.     

Differential inclusions and the control of forest fires

This paper introduces a new class of variational problems for differential inclusions, motivated by the control of forest fires. The area burned by the fire at time t>0 is modelled as the reachable set for a differential inclusion , starting from an initial set R₀. To block the fire, a wall can be constructed progressively in time, at a given speed. In this paper, we study the possibility of constructing a wall which completely encircles the fire. Moreover, we derive necessary conditions for an optimal strategy, which minimizes the total area burned by the fire.     

Singular sets of convex bodies and surfaces with generalized curvatures

In this paper we consider generalized surfaces with curvature measures and we study the properties of those k-dimensional subsets Σ ^k of such surfaces where the curvatures have positive density with respect to k-dimensional Hausdorff measure. Special attention is given to boundaries of convex bodies inR ³. We introduce a class of convex sets whose curvatures live only on integer dimension sets. For such convex sets we consider integral functionals depending on the curvature and the area ofK and on the curvature andH ^k of Σ ^k .     

Perfect Packings of Squares Using the Stack-Pack Strategy

Abstract. We consider the problem of packing an infinite set of square tiles into a finite number of rectangular boxes. We introduce a simple packing strategy that we call stack-pack. Using this strategy, we prove that if 1/2 < t < 2/3, then the squares of side n ^-t , for positive integers n , can be packed into some finite collection of square boxes of the same area ζ(2t) as the total area of the tiles.     

A General Approach to Gibbs Phenomenon

Gibbs phenomenon occurs for most approximations based on standard orthogonal expansions, as well as for those based on integral operators. It also occurs in interpolations and other types of approximations. We consider a general approach to approximation based on delta sequences in an attempt to better understand the concept.     

Perfect Packings of Squares Using the Stack-Pack Strategy

   Abstract. We consider the problem of packing an infinite set of square tiles into a finite number of rectangular boxes. We introduce a simple packing strategy that we call stack-pack. Using this strategy, we prove that if 1/2 < t < 2/3, then the squares of side n ^-t , for positive integers n , can be packed into some finite collection of square boxes of the same area ζ(2t) as the total area of the tiles.     

The Solution of a Free Boundary Problem Related to Environmental Management Systems

Abstract

Explicit solutions of free boundary problems are notoriously difficult to find. In this article, we consider two log-normal diffusions. One represents the level of pollution, or degradation, in some environmental area. The second models the social, political, or financial cost of the pollution. A single control parameter is considered that reduces the rate of pollution. The optimal time to implement the change in the parameter is found by explicitly solving a free boundary problem. The novelty is that the smooth pasting conditions, which are difficult to justify, are not used in the derivation.     

Edge cover by connected bipartite subgraphs

We consider the problem of covering the edge set of an unweighted, undirected graph with the minimum number of connected bipartite subgraphs (where the subgraphs are not necessarily bicliques). We show that this is an NP-hard problem, provide lower bounds through an integer programming formulation, propose several constructive heuristics and a local search, and discuss computational results. Finally, we consider a constrained variant of the problem which we show to be NP-hard, and provide an integer programming formulation for the variant.     

On the category Q-Mod

In this paper we consider the category Q-Mod of modules over a given quantale Q. The paper is motivated by constructions and results from the category of modules over a ring. We show that the category Q-Mod is monadic, consider its relation to the category Q-Top of Q-topological spaces and generalize a method of completion of partially ordered sets. Received December 20, 2005; accepted in final form December 4, 2006.     

Polynomial time algorithms for some classes of constrained nonconvex quadratic problems

In this paper we consider different classes of noneonvex quadratic problems that can be solved in polynomial time. We present an algorithm for the problem of minimizing the product of two linear functions over a polyhedron P in R ⁿ The complexity of the algorithm depends on the number of vertices of the projection of P onto the R ² space. In the worst-case this algorithm requires an exponential number of steps but its expected computational time complexity is polynomial. In addition, we give a characterization for the number of isolated local minimum areas for problems on this form.

Furthermore, we consider indefinite quadratic problems with variables restricted to be nonnegative. These problems can be solved in polynomial time if the number of negative eigenvalues of the associated symmetric matrix is fixed.     

A degenerate hyperbolic equation under Levi conditions

Abstract We consider the Cauchy problem for a second order equation of hyperbolic type. This equation degenerates in two different ways. On one hand, the coefficients have a bad behavior with respect to time: there is a blow-up phenomenon in the first time derivative of the principal part’s coefficients, that is the derivative vanishes at the time t=0. On the other hand, the equation is weakly hyperbolic and the multiplicity of the roots is not constant, but zeroes are of finite order. Here we overcome the blow-up problem and, moreover, the finitely degeneration of the Cauchy problem allows us to give an appropriate Levi condition on the lower order terms in order to get C^∞ well posedness of the Cauchy problem. Keywords: Cauchy problem, Hyperbolic equations, Levi conditions     

The classical overdetermined Serrin problem

Abstract

In this survey, we consider the classical overdetermined problem which was studied by Serrin in 1971. The original proof relies on Alexandrov’s moving plane method, maximum principles, and a refinement of Hopf’s boundary point Lemma. Since then other approaches to the same problem have been devised. Among them we consider the one due to Weinberger which strikes for the elementary arguments used and became very popular. Then we discuss also a duality approach involving harmonic functions, a shape derivative approach and a purely integral approach, all of them not relying on maximum principle. For each one, we consider pros and cons as well as some generalizations.     

A General Notion of Visibility Graphs

Abstract. We define a natural class of graphs by generalizing prior notions of visibility, allowing the representing regions and sightlines to be arbitrary. We consider mainly the case of compact connected representing regions, proving two results giving necessary properties of visibility graphs, and giving some examples of classes of graphs that can be so represented. Finally, we give some applications of the concept, and we provide potential avenues for future research in the area.     

Equational Classes of Totally Ordered Modal Lattices

A modal lattice is a bounded distributive lattice endowed with a unary operator which preserves the join-operation and the smallest element. In this paper we consider the variety CH of modal lattices that is generated by the totally ordered modal lattices and we characterize the lattice of subvarieties of CH. We also give an equational basis for each subvariety of CH.     

Global existence and stability of a nonlinear wave equation with variable-exponent nonlinearities

ABSTRACT

In this paper, we consider a nonlinear wave equation with damping and source terms of variable-exponent types. First, we use the stable-set method to prove a global result. Then, by applying an integral inequality due to Komornik, we obtain the stability result.