Various theoretical frameworks in concept construction and how to move forward as a field: A commentary to Pegg and Tall

This paper first summarises and discusses Pegg and Tall's (2005) fundamental cycle model of conceptual construction from action to object and its relationship to other theories. Then the paper compares this with another model of different psychological theories of learning mathematics and discusses how these models can either be merged or complement each other. This leads to a general discussion about the problem of having many different theories and fashions. how knowledge grows and accumulates, and if there is a unifying theory to be found. The paper concludes that the development of metatheories, such as in the work of Pegg and Tall, is necessary rather than uncritical complementarism.     

The generalized doubling construction and formal concept analysis

Presented by R. Freese.     

A study on the method of fundamental solutions using an image concept

In this paper, both analytical and semi-analytical solutions for Green’s functions are obtained by using the image method which can be seen as a special case of method of fundamental solutions (MFS). The image method is employed to solve the Green’s function for the annular, eccentric and half-plane Laplace problems. In addition, an analytical solution is derived for the fixed-free annular case. For the half-plane problem with a circular hole and an eccentric annulus, semi-analytical solutions are both obtained by using the image concept after determining the strengths of two frozen image points and a free constant by matching boundary conditions. It is found that two frozen images terminated at the two focuses in the bipolar coordinates for the problems with two circular boundaries. A boundary value problem of an eccentric annulus without sources is also considered. Error distribution is plotted after comparing with the analytical solution derived by Lebedev et al. using the bipolar coordinates. The optimal locations for the source distribution in the MFS are also examined by using the image concept. It is observed that we should locate singularities on the two focuses to obtain better results in the MFS. Besides, whether the free constant is required or not in the MFS is also studied. The results are compared well with the analytical solutions.     

On the approximability of the minimum strictly fundamental cycle basis problem

We consider the problem of finding a strictly fundamental cycle basis of minimum weight in the cycle space associated with an undirected connected graph G, where a nonnegative weight is assigned to each edge of G and the total weight of a basis is defined as the sum of the weights of all the cycles in the basis. Several heuristics have been proposed to tackle this NP-hard problem, which has some interesting applications. In this paper we show that this problem is APX-hard, even when restricted to unweighted graphs, and hence does not admit a polynomial-time approximation scheme, unless P=NP. Using a recent result on the approximability of lower-stretch spanning trees (Elkin et al. (2005) [7]), we obtain that the problem is approximable within O(log²nloglogn) for arbitrary graphs. We obtain tighter approximability bounds for dense graphs. In particular, the problem restricted to complete graphs admits a polynomial-time approximation scheme.     

超排卵周期中卵泡不同反应组钙粘素的表达研究

目的研究超排卵周期中卵巢不同反应组患者的卵泡液E-cadherin、N-cadherin、雌二醇、孕酮的表达及相互关系.方法对70例因输卵管、男性因素不孕患者行体外受精-胚胎移植,按取卵时卵泡发育数目不同分为低反应组、高反应组及正常反应组.用ELISA法及CL法分别测定各组卵泡液中E-cadherin、N-cadherin、雌二醇、孕酮水平,并作比较分析.结果高反应组N-cadherin显著高于正常反应组(P<0.05).低反应组E-cadherin显著高于正常反应组(P<0.05).低反应组FSH用量明显高于正常反应组及高反应组(P<0.05),且与E-cadherin呈正相关.高反应组雌二醇水平明显高于其余各组(P<0.05),低反应组孕酮水平明显高于其余各组(P<0.05).结论高反应组患者卵泡群发可能与卵泡局部N-cadherin的高表达有关,而低反应组卵泡发育受阻可能与高E-cadherin水平有关,使卵泡对FSH反应性降低并有黄素化倾向.     

On the construction of odd cycle systems

Three obvious necessary conditions for the existence of a k-cycle system of order n are that if n > 1 then n ? k, n is odd, and 2k divides n(n ? 1). We show that if these necessary conditions are sufficient for all n satisfying k ? n < 3k then they are sufficient for all n. In particular, there exists a 15-cycle system of order n if and only if n ≡ 1, 15, 21, or 25 (mod 30), and there exists a 21-cycle system of order n if and only if n ≡ 1, 7, 15, or 21 (mod 42), n ≠ 7. 15.     

On the cotangent cohomology of rational surface singularities with almost reduced fundamental cycle

We prove dimension formulas for the cotangent spaces T ¹ and T ² for a class of rational surface singularities by calculating a correction term in the general dimension formulas. We get that it is zero if the dual graph of the rational surface singularity X does not contain a particular type of configurations, and this generalizes a result of Theo de Jong stating that the correction term c (X ) is zero for rational determinantal surface singularities. In particular our result implies that c (X ) is zero for Riemenschneiders quasi‐determinantal rational surface singularities, and this also generalizes results for quotient singularities. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Theories of Mathematics Education: A global survey of theoretical frameworks/trends in mathematics education research

In this article we survey the history of research on theories in mathematics education. We also briefly examine the origins of this line of inquiry, the contribution of Hans-Georg Steiner, the activities of various international topics groups and current discussions of theories in mathematics education research. We conclude by outlining current positions and questions addressed by mathematics education researchers in the research forum on theories at the 2005 PME meeting in Melbourne, Australia.     

The fundamental theorem of mutual insurance

The essence of mutual insurance is the notion that re-distributing risk in a pool of risks is more beneficial than taking the risk alone. Interpreting ‘more beneficial’ as an increase in utility and considering sequences of exchangeable risks, we are able to formalize this notion from the policyholder’s perspective and demonstrate its validity for various alternative preference functionals (e.g., expected utility, Choquet expected utility, and distortion risk measures). To obtain this result, we exploit that for a sequence of exchangeable risks the corresponding sequence of arithmetical averages is a reversed martingale.We conclude that pooling risks is fundamental for understanding the mechanisms of insurance because it favourably affects the utility of policyholders, and we refer to this phenomenon as the ‘utility-improving effect of risk pooling’. Moreover, we demonstrate that the utility of the policyholder is (strictly) increasing with the size of the risk pool.     

The fundamental duality of partially ordered sets

The representation of partially ordered sets by subsets of some set such that specified joins (meets) are taken to unions (intersections) suggests two categories, that of partially ordered sets with specified joins and meets, and that of sets equipped with suitable collections of subsets, and adjoint contravariant functors between them. This, in turn, induces a duality including, among several others, the two Stone Dualities and that between spatial locales and sober spaces.     

The fundamental group of a unitary orbit

The unitary orbit of a complex n × n matrix A is simply connected if and only if the portion of the commutant {A} which resides in the special unitary group is path connected.     

The fundamental progroupoid of a general topos

It is well known that the category of covering projections (that is, locally constant objects) of a locally connected topos is equivalent to the classifying topos of a strict progroupoid (or, equivalently, a localic prodiscrete groupoid), the fundamental progroupoid, and that this progroupoid represents first degree cohomology. In this paper we generalize these results to an arbitrary topos. The fundamental progroupoid is now a localic progroupoid, and cannot be replaced by a localic groupoid. The classifying topos is no longer a Galois topos. Not all locally constant objects can be considered as covering projections. The key contribution of this paper is a novel definition of covering projection for a general topos, which coincides with the usual definition when the topos is locally connected. The results in this paper were presented in a talk at the Category Theory Conference, Vancouver, July 2004.