How far can relaxation functions be increasing in viscoelastic problems?

It is known that when we add a viscoelastic damping to a frictional damping acting in the domain we might lose the property of exponential stability of the system. Moreover, a necessary condition for a system to be sub-exponentially stable is that the kernel itself must be sub-exponentially decaying to zero. Having this in mind, a natural question to be asked is that of when this necessary condition is also sufficient. We prove that this is the case for a fairly large class of kernels.     

The stability of learners’ choices for real-life situations to be used in mathematics

One of the efforts to improve and enhance the performance and achievement in mathematics of learners is the incorporation of life-related contexts in mathematics teaching and assessments. These contexts are normally, with good reasons, decided upon by curriculum makers, textbook authors, teachers and constructors of examinations and tests. However, little or no consideration is given to whether students prefer and find these real-life situations interesting. There is also a dearth of studies dealing explicitly with the real-life situations learners prefer to deal with in mathematics. This issue was investigated and data on students’ choices for contextual issues to be used in mathematics were collected at two time periods. The results indicate that learners’ preferences for contextual situations to be used in mathematics remained fairly stable. It is concluded that real-life issues that learners highly prefer are not normally included in the school mathematics curriculum and that there is a need for a multidisciplinary approach to develop mathematical activities which take into account the expressed preferences of learners.     

What can be done with PRA?

Let S⁺ denote system JR _° ² + AC _° ¹ in a classical second-order arithmetic, in which the induction rule is permitted to apply only to quantifier-free formulas and to _° ² -formulas not containing functional variables, while the convolution axiom is permitted to apply only to _° ¹ -formulas without functional variables. Also postulated is the closedness of the function class being examined, relative to primitive recursive operations. System, S⁺ turns out to be sufficiently rich: in it a theory of recursions and an elementary recursive analysis can be developed, a theorem on the continuity of effective operators and a theorem on cuteliminability from -deductions can be proved, and the usual analytic proofs of many number-theoretic theorems, including the prime distribution law, can be derived (with insignificant changes). (A formalization in S⁺ of the proof of Konig's lemma on paths in binary trees and of Godel's completeness theorem is described in the note.) On the other hand, the system admits of an interpretation in primitive recursive arithmetic (PRA). In particular, quantifier-free theorems in S⁺ are deducible in PRA, while theorems of form xyR(x,y) with a quantifier-free formula R have calculi R (x,(x)) with primitive recursive function , deducible in PRA. Thus, the suppressing part of operating constructive analysis can be developed already at the finite stages of the Shanin majorant hierarchy. In addition, a purely mechanical method exists for obtaining elementary number-theoretic proofs from many analytic proofs.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova Akad. Nauk SSSR, Vol. 60, pp. 93–102, 1976. Results announced September 4, 1975.     

Sensitivity of the Lanczos recurrence to Gaussian quadrature data: How malignant can small weights be?

Stability of passing from Gaussian quadrature data to the Lanczos recurrence coefficients is considered. Special attention is paid to estimates explicitly expressed in terms of quadrature data and not having weights in denominators. It has been shown that the recent approach, exploiting integral representation of Hankel determinants, implies quantitative improvement of D. Laurie’s constructive estimate.It has also been demonstrated that a particular implementation on the Hankel determinant approach gives an estimate being unimprovable up to a coefficient; the corresponding example involves quadrature data with a small but not too small weight. It follows that polynomial increase of a general case upper bound in terms of the dimension is unavoidable.     

Optimal oscillations in control models: How can constant demand lead to cyclical production?

The paper describes two methods to establish the endogenous periodic solutions in optimal control problems. One of them deals with ‘true cycles’, whereas the other one gives conditions for the existence of limit cycles. Both methods are illustrated by an example of inventory/production planning.     

Context in social simulation: why it can’t be wished away

Context is everywhere in the human social and cognitive spheres but it is often implicit and unnoticed. However, when one is involved in trying to understand and model the social and cognitive realms context becomes an important factor. This paper is an analysis of the role and effects of context on social simulation and a call for it to be squarely faced by the social simulation community. It briefly looks at some different kinds of context, and discussed the difficulty of talking about context, before looking at the “context heuristic” that seems to be used in human cognition. This allows for rich and fuzzy context recognition to be combined with crisp ‘foreground’ belief update and reasoning. Such a heuristic allows for causality to make sense, and limits the phenomena of causal spread—it is thus at the root of the modelling enterprise. This analysis is then applied to simulation modelling, considering the context of a simulation, and its ramifications, in particular, why generalisation is so hard.     

How many matrices can be spectrally balanced simultaneously?

We prove that any ? positive definite d × d matrices, M₁,...,M_?, of full rank, can be simultaneously spectrally balanced in the following sense: for any k < d such that ? ≤ \(\ell \leqslant \left\lfloor {\frac{{d - 1}}{{k - 1}}} \right\rfloor \), there exists a matrix A satisfying \(\frac{{{\lambda _1}\left( {{A^T}{M_i}A} \right)}}{{Tr\left( {{A^T}{M_i}A} \right)}} < \frac{1}{k}\) 1/k for all i, where λ₁(M) denotes the largest eigenvalue of a matrix M. This answers a question posed by Peres, Popov and Sousi ([PPS13]) and completes the picture described in that paper regarding sufficient conditions for transience of self-interacting random walks. Furthermore, in some cases we give quantitative bounds on the transience of such walks.     

How many atoms can be defined by boxes?

We study the functionb(n, d), the maximal number of atoms defined byn d-dimensional boxes, i.e. parallelopipeds in thed-dimensional Euclidean space with sides parallel to the coordinate axes. We characterize extremal interval families definingb(n, 1)=2n-1 atoms and we show thatb(n, 2)=2n ²-6n+7. We prove that for everyd, exists and . Moreover, we obtainb*(3)=8/9.     

How good can polynomial interpolation on the sphere be?

This paper explores the quality of polynomial interpolation approximations over the sphere S ^r−1⊂R ^r in the uniform norm, principally for r=3. Reimer [17] has shown there exist fundamental systems for which the norm ‖Λ _n ‖ of the interpolation operator Λ _n , considered as a map from C(S ^r−1) to C(S ^r−1), is bounded by d _n , where d _n is the dimension of the space of all spherical polynomials of degree at most n. Another bound is d _n ^1/2(λ_avg/λ_min)^1/2, where λ_avg and λ_min are the average and minimum eigenvalues of a matrix G determined by the fundamental system of interpolation points. For r=3 these bounds are (n+1)² and (n+1)(λ_avg/λ_min)^1/2, respectively. In a different direction, recent work by Sloan and Womersley [24] has shown that for r=3 and under a mild regularity assumption, the norm of the hyperinterpolation operator (which needs more point values than interpolation) is bounded by O(n ^1/2), which is optimal among all linear projections. How much can the gap between interpolation and hyperinterpolation be closed?

For interpolation the quality of the polynomial interpolant is critically dependent on the choice of interpolation points. Empirical evidence in this paper suggests that for points obtained by maximizing λ_min, the growth in ‖Λ _n ‖ is approximately n+1 for n<30. This choice of points also has the effect of reducing the condition number of the linear system to be solved for the interpolation weights. Choosing the points to minimize the norm directly produces fundamental systems for which the norm grows approximately as 0.7n+1.8 for n<30. On the other hand, ‘minimum energy points’, obtained by minimizing the potential energy of a set of (n+1)² points on S ², turn out empirically to be very bad as interpolation points.

This paper also presents numerical results on uniform errors for approximating a set of test functions, by both interpolation and hyperinterpolation, as well as by non-polynomial interpolation with certain global basis functions.

     

Dragging maintaining symmetry: can it generate the concept of inclusivity as well as a family of shapes?

This article describes a project using Design Based Research methodology to ascertain whether a pedagogical task based on a dynamic figure designed in a Dynamic Geometry Software (DGS) program could be instrumental in developing students’ geometrical reasoning. A dragging strategy which I have named ‘Dragging Maintaining Symmetry’ (DMS) was shown to be important for the making of mathematical meanings in the context of Dynamic Geometry. In particular, it encouraged students’ development of the concept of inclusive relations between shapes generated from the dynamic figure, especially the rhombus as a special case of the kites. This development was not automatic and in addition to their work with the dynamic figure the students were shown an animation of the figure under DMS. Watching the animation allowed the students to attend to the continuous nature of the changing figure and proved to be the catalyst for moving their reasoning towards perceiving inclusive relations between the rhombus and kite.     

How can histograms be useful for introducing continuous probability distributions?

ZDM – Mathematics Education - The teaching of probability has changed a great deal since the end of the last century. The development of technologies is indeed part of this evolution. In...     

On the Polynomials in Several Indeterminates Which can be Extended to Permutation Polynomial Vectors Over Z/p~lZ

Let m be a number, and f_1 (x_1 ,…,x_n ),…,f_k(x_1,…,x_n )∈ Z(x_1,…,x_n), k≤n. Iffor any(α_1,…α_k) ∈ Z~k, the congruenee systemhas just m~(n-k) solutions, then the system f_1,…,f_k is called an orthogonal system     

How regular can the boundary of a quadratic Siegel disk be?

In the family of quadratic polynomials with an irrationally indifferent fixed point, we show the existence of Siegel disks with a fine control on the degree of regularity of the linearizing map on their boundary. A general theorem is stated and proved. As a particular case, we show that in the quadratic family, there are Siegel disks whose boundaries are but not Jordan curves.

     

Does Quality of Life Have to be Quantified?

It is argued that quality of life is primarily a matter of aesthetics and that aesthetics has been ignored in the process we call "development". It is further argued that the aesthetic function has two complementary aspects: the creative and the recreative. The creative subfunction is to provide inspiration, the desire for and commitment to pursuit of ideals; the recreative subfunction is to provide satisfaction during this pursuit. The latter is based on stylistic (non-efficiency related) preferences among ways of doing things. Measurement of progress towards ideals and of stylistic satisfaction, though helpful, is not essential to development planning. It is argued that participative planning that begins with design of an ideal-state can provide those involved with an opportunity to incorporate both their ideals and their stylistic preferences into designs of the future and development of ways of bringing it about.