The stability of the viscous shock profiles of the burgers’ equation with a fourth order viscosity

We establish the stability of the viscous shock profiles of the Burgers' equation with fourth order viscosity in a weighted Sobolev space. In the course of our investigation, we develop a new method for dealing with the continuous spectrum of certain types of ordinary and partial differential operators in Hilbert spaces. This method allows us to get results in spaces that are related to L² rather than forcing us to work in spaces related to L^∞.     

The flow of a combustible mixture with a Chapman–Jouguet detonation wave around a cone

The flow around a circular cone under conditions of Chapman–Jouguet (CJ) self-sustaining detonation is investigated in the classical formulation of an infinitely thin detonation wave (DW) in an inviscid and non-heat conducting combustible mixture. Such conditions for flow around a cone are remarkable in several respects. In 1959, Chernyi and Kvashnina had already shown that, for supersonic flows of a combustible mixture around a cone, CJ detonation, as in the case of a wedge, is not only possible for a strictly fixed cone angle (the “CJ” angle) but also for angles smaller than this (including a zero angle, that is, when there is no cone). In the case of flow around a wedge with an angle that is less than the corresponding CJ angle, a centred rarefaction wave that turns the supersonic flow in the required direction borders on the CJ DW. In the case of a cone, a conical rarefaction flow also borders on the CJ DW. However, if, in the plane case, a uniform supersonic flow adjoins the centred rarefaction wave along its boundary C⁺-characteristic then the conical rarefaction flow is bounded by a conical shock wave (SW), bordered up to the surface of the cone by a conical compression flow. Only for a zero cone angle does the SW degenerate into the C⁺-characteristic and the conical compression flow degenerates into a uniform supersonic flow. The configuration obtained in the general case became the first example of a self-similar solution with two SW of “one family” (the first of them is the DW) diverging from a single point. The results of calculations carried out in this paper with the construction of streamlines and the characteristics of the two families give a fairly complete representation of the above mentioned features of the flows considered.     

Analysis of Velázquez’s solution to the mean curvature flow with a type II singularity

Velázquez in 1994 used the degree theory to show that there is a perturbation of Simons’ cone, starting from which the mean curvature flow develops a type II singularity at the origin. He also showed that under a proper time-dependent rescaling of the solution around the origin, the rescaled flow converges in the C⁰ sense to a minimal hypersurface which is tangent to Simons’ cone at infinity. In this paper, we prove that the rescaled flow actually converges locally smoothly to the minimal hypersurface, which appears to be the singularity model of the type II singularity. In addition, we show that the mean curvature of the solution blows up near the origin at a rate which is smaller than that of the second fundamental form.     

Analytical solutions for pipe flow of a fourth grade fluid with Reynold and Vogel’s models of viscosities

In this paper, the steady incompressible flow of a fourth grade fluid down a vertical cylinder with variable viscosity and heat transfer analysis are considered. The governing equations of motion of fourth grade fluid in cylindrical coordinates have been derived. The complete analytic solutions of momentum and energy equations have been obtained by homotopy analysis method (HAM). The entropy generation number for two cases of viscosities namely (i) Reynold’s model and (ii) Vogel’s model have also been computed. The results are compared with the available finite difference and perturbation solutions of third grade fluid. At the end the pressure gradient for the fourth grade fluid has also been calculated.     

Optimal sequencing of a set of positive numbers with the variance of the sequence’s partial sums maximized

We consider the problem of sequencing a set of positive numbers. We try to find the optimal sequence to maximize the variance of its partial sums. The optimal sequence is shown to have a nice structure. It is interesting to note that the symmetric problem which aims at minimizing the variance of the same partial sums is proved to be NP-complete in the literature.     

Solutions of SPDE’s Associated with a Stochastic Flow

Potential Analysis - We consider the following stochastic partial differential equation, $$begin{array}{@{}rcl@{}} &&dY_{t} = L^{ast} Y_{t} dt + A^{ast} Y_{t} cdot dB_{t}...     

Combinatorics of the subshift associated with Grigorchuk’s group

We study combinatorial properties of the subshift induced by the substitution that describes Lysenok’s presentation of Grigorchuk’s group of intermediate growth by generators and relators. This subshift has recently appeared in two different contexts: on the one hand, it allowed embedding Grigorchuk’s group in a topological full group, and on the other hand, it was useful in the spectral theory of Laplacians on the associated Schreier graphs.     

Where there’s a Will there’s a way – the research of Will Light

This paper describes the work of Will Light, who died on December 8th, 2002. It highlights his contributions in the study of minimal norm projections, tensor product approximation (including the convergence of the Diliberto–Straus algorithm), proximinality, radial and ridge function approximation, both via quasi-interpolation and interpolation. My aim is not only to describe the impact of Wills work, but also to convey some of his impact as a person.     

Fractal and multifractal analysis of the rise of oxygen in Earth’s early atmosphere

The rise of oxygen in Earth’s atmosphere that occurred 2.4–2.2 billion years ago is known as the Earth’s Great Oxidation, and its impact on the development of life on Earth has been profound. Thereafter, the increase in Earth’s oxygen level persisted, though at a more gradual pace. The proposed underlying mathematical models for these processes are based on physical parameters whose values are currently not well-established owing to uncertainties in geological and biological data. In this paper, a previously developed model of Earth’s atmosphere is modified by adding different strengths of noise to account for the parameters’ uncertainties. The effects of the noise on the time variations of oxygen, carbon and methane for the early Earth are investigated by using fractal and multifractal analysis. We show that the time variations following the Great Oxidation cannot properly be described by a single fractal dimension because they exhibit multifractal characteristics. The obtained results demonstrate that the time series as obtained exhibit multifractality caused by long-range time correlations.     

Modeling the interaction of an electromagnetic field with a two-dimensional surface in the framework of symanzik’s approach

Symanzik’s approach to the construction of models for the interaction between quantum fields and macroobjects allows finding the general form of the action functional with a Chern-Simons potential up to an arbitrary dimensionless constant; it is used to describe the interaction of a material surface with the electromagnetic field. We discuss results obtained in static models of such a type. We also consider a simple dynamic model of the interaction of a massless scalar field with moving planes.     

Lower bounds for the scalar curvature of noncompact gradient solitons of List’s flow

In this paper, we show that a noncompact gradient shrinking soliton to the List flow has at most quadratic decay for ${S = R-\alpha_n| \nabla \varphi|^2}$ . Moreover, we prove a similar result for certain noncompact gradient steady solitons to the List flow. These generalize the results of Chow et al. [4].     

Bolzano’s Argument for the Existence of Substances: a Formalization with Two Types of Predication

The topic of our analysis is the argument for the existence of substances given by Bernard Bolzano in Athanasia (1827), where he essentially employs two ontological categories: substance and adherence. Bolzano considers the real and conditioned Inbegriff of all adherences, which are wirklich and nicht selbst bestehen. He claims that the formed collection is dependent on something external and non-adherential, which therefore is a substance. Bolzano’s argumentation turns out to be structurally similar to his argument for the existence of God from Lehrbuch der Religionswissenschaft (1834), but in each of these reasonings, we find different plausible interpretations of the key concept “Inbegriff”. The latter argumentation refers to the mereological totality of existentially conditioned objects. We propose the explication of the Bolzanian Inbegriff of all adherences using two types of predication: we consider its extension as composed of certain intensional counterparts of adherences. In our approach, we use a fragment of the theory of abstract objects formulated by E. Zalta (1983), describing two different relations between individuals and properties: extensional exemplification and intensional encoding. We put our reconstruction in a wider context of Bolzano’s ontology, formulating the needed axioms with two primitive predicates of second order ... is an adherence, ... is conditioned by something real as well as the conditionally introduced first order predicate constant \(\mathfrak {In}\) for Inbegriff of all adherential ideas. Finally, we sketch a model for our theory.     

Using Haken’s subordination principle to analyze wave processes in a nonlinear system with diffusion

Haken’s subordination principle is applied to reduce a reaction–diffusion system to a wave equation. We explain the nature of the wave processes that have been previously analyzed numerically in a nonlinear distributed economic model.     

Differential Harnack inequalities for heat equations with potentials under the Bernhard List’s flow

In the paper we prove some differential Harnack inequalities for positive solutions of heat equations with potentials when the metric is evolving by the Bernhard List??s flow. We also give some applications of these inequalities.     

Maslov’s canonical operator,Hörmander’s formula,and localization of the Berry-Balazs solution in the theory of wave beams

For three-dimensional Schrödinger equations, we study how to localize exact solutions represented as the product of an Airy function (Berry-Balazs solutions) and a Bessel function and known as Airy-Bessel beams in the paraxial approximation in optics. For this, we represent such solutions in the form of Maslov’s canonical operator acting on compactly supported functions on special Lagrangian manifolds. We then use a result due to Hörmander, which permits using the formula for the commutation of a pseudodifferential operator with Maslov’s canonical operator to “move” the compactly supported amplitudes outside the canonical operator and thus obtain effective formulas preserving the structure based on the Airy and Bessel functions. We discuss the influence of dispersion effects on the obtained solutions.     

Two-dimensional Coulomb scattering of a quantum particle: Wave functions and Green’s functions

We solve the problem of the propagation of a charged quantum particle in a two-dimensional plane embedded in the three-dimensional coordinate space. We consider scattering of this particle by a stable Coulomb center situated in the same plane. We study the wave function of this particle, its Green’s function, and all radial components of these functions. We derive uniform majorant bounds on absolute values of these functions and find the wave function representation in terms of regular radial Coulomb functions and the scattering amplitude representation via partial phases. We obtain integral representations of the Greens’s function and all its radial components.     

On a sheaf-theoretic version of the Witt’s decomposition theorem. A Lagrangian perspective

The approach to a counterpart, in Abstract Geometric Algebra, that is, Geometric Algebra via sheaves of modules, of the classical Witt’s decomposition theoremis based on the axiomatization of the classical context, which however leads to the formulation of a specific subcategory of the category of sheaves of modules: the full subcategory of convenient sheaves of modules. Convenient sheaves of modules turn out, by the very essence of the matter at hand, to be of further importance as far as the setting of results leading to the sheaf-theoretic aspect of several forms of the Witt’s theorem is concerned. Further versions of the Witt’s theorem are still to be treated elsewhere.      

Free algebras of a unary variety with Mal’tsev’s operation that satisfies the Pixley conditions

In this paper we consider the variety V P of algebras with one unary and one ternary operation p that satisfies the Pixley identities, provided that operations are permutable. We describe the structure of a free algebra of the variety V P and study the structure of unary reducts of free algebras. We prove the solvability of the word problem in free algebras and the uniqueness of a free basis; we also describe groups of automorphisms of free algebras. Similar results are obtained for free algebras of a subvariety of the variety V P defined by the identities p(p(x, y, z), y, z) = p(x, y, z) and p(x, y, p(x, y, z)) = p(x, y, z).