The Kissing Triangles: The Aesthetics of Mathematical Discovery

Papert's (1978) appeal to reconsider the power and possibilities of the aesthetic in mathematics learning is often ignored in mathematics education research. This paper begins with the premise, put forth by Dewey (1934), that the aesthetic structures many dimensions of inquiry and experience. In the same way that using particular paintings, musical compositions, or even everyday experiences has been instrumental to attempts by philosophers to understand the aesthetic dimensions of meaning and experience in artistic domains, I propose that analysing a particular encounter with mathematics may help reveal the nature and role of the often nebulous responses of elegance, beauty, and `fit' to which mathematicians lay claim in their mathematical activity. To achieve this, I draw on and adapt the defining features of the aesthetic character of experience set forth by the aesthetician Beardsley (1982). This, in turn, sheds light on the role thataesthetics can play in mathematical inquiry and experience, and provides initial categories and conjectures that can be used to investigate the potential roles of aesthetics in mathematics learning contexts.This revised version was published online in September 2005 with corrections to the Cover Date.     

ON HYPERBOLIC TIME DISCOUNTING IN EXHAUSTIBLE RESOURCE MODELS: AN APPLICATION TO WORLD OIL RESOURCES

ABSTRACT. Recent research on discounting in long term economic models involves hyperbolic discounting, in which the marginal discount rate shrinks as time passes. To investigate hyperbolic discounting and exhaustible resource allocation, this work develops a discrete‐time world oil model and model solution procedure, then uses the model to examine the consequences of adopting conventional (constant annual) discounting when hyperbolic discounting is appropriate, of adopting one hyperbolic discount rate path when a different hyperbolic path is appropriate, and of adopting hyperbolic discounting when conventional discounting is appropriate. Five conventional and two hyperbolic discount rate paths are considered. One hyperbolic path is that used by Nordhaus and Boyer [2000]; the other is that recommended by Weitzman [2001]. The generality of the findings is also assessed.     

Index Heuristics for Multiclass M/G/1 Systems with Nonpreemptive Service and Convex Holding Costs

We consider the optimal service control of a multiclass M/G/1 queueing system in which customers are served nonpreemptively and the system cost rate is additive across classes and increasing convex in the numbers present in each class. Following Whittle's approach to a class of restless bandit problems, we develop a Langrangian relaxation of the service control problem which serves to motivate the development of a class of index heuristics. The index for a particular customer class is characterised as a fair charge for service of that class. The paper develops these indices and reports an extensive numerical investigation which exhibits strong performance of the index heuristics for both discounted and average costs.     

用于强磁场的快响应真空规的研制进展

研制了能在强磁场、强干扰环境下工作的快响应真空电离规(快规),用于对HL 2A装置偏滤器室和等离子体附近的中性粒子密度和通量进行原位测量。介绍了快规的结构、工作原理、设计要点以及实验结果。在无磁场的情况下,快规对气体压强的测量范围为6.4×10-6～0.15Pa,在1×10-5～0.15Pa范围内,快规收集极离子流与发射电子流之比与气压保持良好线性关系;在0 15T的磁场下,快规的规管常数未发生显著变化,在规管对称轴与磁力线的夹角小于15o时,规管常数的变化小于10%。     

A time‐accurate pseudo‐compressibility approach based on an unstructured hybrid finite volume technique applied to unsteady turbulent premixed flame propagation

A preconditioning approach based on the artificial compressibility formulation is extended to solve the governing equations for unsteady turbulent reactive flows with heat release, at low Mach numbers, on an unstructured hybrid grid context. Premixed reactants are considered and a flamelet approach for combustion modelling is adopted using a continuous quenched mean reaction rate. An overlapped cell‐vertex finite volume method is adopted as a discretisation scheme. Artificial dissipation terms for hybrid grids are explicitly added to ensure a stable, discretised set of equations. A second‐order, explicit, hybrid Runge–Kutta scheme is applied for the time marching in pseudo‐time. A time derivative of the dependent variable is added to recover the time accuracy of the preconditioned set of equations. This derivative is discretised by an implicit, second‐order scheme. The resulting scheme is applied to the calculation of an infinite planar (one‐dimensional) turbulent premixed flame propagating freely in reactants whose turbulence is supposed to be frozen, homogeneous and isotropic. The accuracy of the results obtained with the proposed method proves to be excellent when compared to the data available in the literature. Copyright © 2004 John Wiley & Sons, Ltd.     

Polyelectrolyte complexes. VI. Polycation structure,polyanion molar mass,and polyion concentration effects on complex nanoparticles based on poly(sodium 2‐acrylamido‐2‐methylpropanesulfonate)

The formation and characterization of some interpolyelectrolyte complex (IPEC) nanoparticles based on poly(sodium 2‐acrylamido‐2‐methylpropanesulfonate) (NaPAMPS), as a function of the polycation structure, polyanion molar mass, and polyion concentration, were followed in this work. Poly(diallyldimethylammonium chloride) and two polycations (PCs) containing (N,N‐dimethyl‐2‐hydroxypropyleneammonium chloride) units in the backbone (PCA₅ and PCA₅D₁) were used as starting polyions. The complex stoichiometry, (n^?/n⁺)_iso, was pointed out by optical density at 500 nm (OD₅₀₀), polyelectrolyte titration, and dynamic light scattering. IPEC nanoparticle sizes were influenced by the polycation structure and polyanion molar mass only before the complex stoichiometry, which was higher for the more hydrophilic polycations (PCA₅ and PCA₅D₁) and for a higher NaPAMPS molar mass, and were almost independent of these factors after that, at a flow rate of the added polyion of about 0.28 mL × (mL PC)^?1 × h^?1. The IPEC nanoparticle sizes remained almost constant for more than 2 weeks, both before and after the complex stoichiometry, at low concentrations of polyions. NIPECs as stable colloidal dispersions with positive charges in excess were prepared at a ratio between charges (n^?/n⁺) of 0.7, and their storage colloidal stability, as a function of the polycation structure and polyion concentration (from 0.8 to ca. 7.8 mmol/L), was demonstrated. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2495–2505, 2004     

Viscoelastic behavior of polypropylene/nitrile rubber thermoplastic elastomer blends: Application of Kerner's models for reactively compatibilized and dynamically vulcanized systems

The viscoelastic properties of binary blends of nitrile rubber (NBR) and isotactic polypropylene (PP) of different compositions have been calculated with mean‐field theories developed by Kerner. The phase morphology and geometry have been assumed, and experimental data for the component polymers over a wide temperature range have been used. Hashin's elastic–viscoelastic analogy principle is used in applying Kerner's theory of elastic systems for viscoelastic materials, namely, polymer blends. The two theoretical models used are the discrete particle model (which assumes one component as dispersed inclusions in the matrix of the other) and the polyaggregate model (in which no matrix phase but a cocontinuous structure of the two is postulated). A solution method for the coupled equations of the polyaggregate model, considering Poisson's ratio as a complex parameter, is deduced. The viscoelastic properties are determined in terms of the small‐strain dynamic storage modulus and loss tangent with a Rheovibron DDV viscoelastometer for the blends and the component polymers. Theoretical calculations are compared with the experimental small‐strain dynamic mechanical properties of the blends and their morphological characterizations. Predictions are also compared with the experimental mechanical properties of compatibilized and dynamically cured 70/30 PP/NBR blends. The results computed with the discrete particle model with PP as the matrix compare well with the experimental results for 30/70, 70/30, and 50/50 PP/NBR blends. For 70/30 and 50/50 blends, these predictions are supported by scanning electron microscopy (SEM) investigations. However, for 30/70 blends, the predictions are not in agreement with SEM results, which reveal a cocontinuous blend of the two. Predictions of the discrete particle model are poor with NBR as the matrix for all three volume fractions. A closer agreement of the predicted results for a 70/30 PP/NBR blend and the properties of a 1% maleic anhydride modified PP or 3% phenolic‐modified PP compatibilized 70/30 PP/NBR blend in the lower temperature zone has been observed. This may be explained by improved interfacial adhesion and stable phase morphology. A mixed‐cure dynamically vulcanized system gave a better agreement with the predictions with PP as the matrix than the peroxide, sulfur, and unvulcanized systems. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1417–1432, 2004     

Relationship between the dynamic softening transition and wet sliding friction of elastomer compounds

For properly chosen elastomer compounds, thermorheological characterization is combined with an examination of the variation of the wet sliding friction with temperature. A conceptual argument leads to the assumption that the wet sliding friction should maximize at the energy dissipation peak associated with the dynamic softening transition at a characteristic frequency determined by the sliding speed and the effective smallest surface asperity scale. The dynamic softening transition is characterized with the peak in tan δ/G′ⁿ, where tan δ is the loss tangent, G′ is the elastic modulus, and n is a constant between 0 and 1. The William–Landel–Ferry transform is uncritically applied for extrapolating the position of the peak in tan δ/G′ⁿ at high frequencies. Even based on the criterion of tan δ, the results obtained on a concrete surface indicate that the effective smallest asperity scale is of order of 100 μm. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2467–2478, 2004     

Piecewise Deterministic Markov Control Processes with Feedback Controls and Unbounded Costs

The control of piecewise-deterministic processes is studied where only local boundedness of the data is assumed. Moreover the discount rate may be zero. The value function is shown to be solution to the Bellman equation in a weak sense; however the solution concept is strong enough to generate optimal policies. Continuity and compactness conditions are given for the existence of nonrelaxed optimal feedback controls.     

Dynamic boundary stabilization of a Reissner–Mindlin plate with Timoshenko beam

This paper is concerned with well‐posedness results for a mathematical model for the transversal vibrations of a two‐dimensional hybrid elastic structure consisting of a rectangular Reissner–Mindlin plate with a Timoshenko beam attached to its free edge. The model incorporates linear dynamic feedback controls along the interface between the plate and the beam. Classical semigroup methods are employed to show the unique solvability of the coupled initial‐boundary‐value problem. We also show that the energy associated with the system exhibits the property of strong stability. Copyright © 2004 John Wiley & Sons, Ltd.