It's Not Too Late to Conceptualize: Constructing a Generalized Subtraction Schema by Abstracting and Connecting Procedures

In this study, children were encouraged to abstract mathematical principles by making connections between procedures. Children from 2 sixth-grade classes (N = 58) were asked to solve and explain subtraction examples in 3 different number domains (whole numbers, fractions, and decimals), solve subtraction word problems, compare the procedures, and discuss subtraction principles. Forty percent of the children could identify procedural similarities and could abstract general subtraction principles. The rest of the children received more instruction. One group received individual abstraction and mapping instruction that encouraged them to generalize procedural steps and connect procedures. Another group received domain-specific instruction without connections between domains. The results show that following mapping instruction, children whose original instruction was mostly procedural could make connections and abstract principles, that is, construct a general subtraction schema. These children improved in conceptual knowledge and in solving transfer problems.     

The powers and pitfalls of algorithmic knowledge: a case study

This study examines one child's use of computational procedures over a period of 3 years in an urban elementary school where teachers were using a standards-based curriculum. From a sociocultural perspective, the use of standard algorithms to solve mathematical problems is viewed as a cultural tool that both enables and constrains particular practices. As this student appropriated and mastered procedures for addition, subtraction, multiplication and division, she could solve problems that involved fairly straightforward computations or where she could easily model the action to determine an appropriate computation. At the same time, her use of these algorithms, along with other readily available tools, such as her fingers or multiplication tables, constrained her ability to reflect on the tens-structure of the number system, an effect that had serious consequences for her overall mathematical achievement. The results of this study suggest that even when not directly introduced, algorithms have such strong currency that they can mediate more reform-oriented instruction.     

Analyzing the word-problem performance and strategies of students experiencing mathematics difficulty

The purpose of this study was to examine the word-problem performance and strategies utilized by 3rd-grade students experiencing mathematics difficulty (MD). We assessed the efficacy of a word-problem intervention and compared the word-problem performance of students with MD who received intervention (n = 51) to students with MD who received general education classroom word-problem instruction (n = 60). Intervention occurred for 16 weeks, 3 times per week, 30 min per session and focused on helping students understand the schemas of word problems. Results demonstrated that students with MD who received the word-problem intervention outperformed students with MD who received general education classroom word-problem instruction. We also analyzed the word-problem strategies of 30 randomly-selected students from the study to understand how students set up and solve word problems. Students who received intervention demonstrated more sophisticated word-problem strategies than students who only received general education classroom word-problem instruction. Findings suggest students with MD benefit from use of meta-cognitive strategies and explicit schema instruction to solve word problems.     

Intra-mathematical connections made by high school students in performing Calculus tasks

In this article, we report the results of research that explores the intra-mathematical connections that high school students make when they solve Calculus tasks, in particular those involving the derivative and the integral. We consider mathematical connections as a cognitive process through which a person relates or associates two or more ideas, concepts, definitions, theorems, procedures, representations and meanings among themselves, with other disciplines or with real life. Task-based interviews were used to collect data and thematic analysis was used to analyze them. Through the analysis of the productions of the 25 participants, we identified 223 intra-mathematical connections. The data allowed us to establish a mathematical connections system which contributes to the understanding of higher concepts, in our case, the Fundamental Theorem of Calculus. We found mathematical connections of the types: different representations, procedural, features, reversibility and meaning as a connection.     

Use of invented algorithms by second graders in a reform mathematics curriculum

Second-grade students in three schools were individually tested on multidigit addition and subtraction problems and solution procedures observed. The schools were all using a reform mathematics curriculum (UCSMP) with an emphasis on problem solving in broader mathematical contexts. Both contextualized and bare computation problems were included in these interviews. On all but one problem, more students used a mental procedure than used the standard written algorithms, and both methods were used with about the same degree of accuracy. Although the standard school algorithm was the only written algorithm used, a number of different mental procedures were employed by students, and choice appeared to be influenced by characteristics of the problems (magnitude of the numbers or the need for regrouping). Major differences between the three schools were found, which are linked to instruction.     

Distinguishing Features of Mechanical and Human Problem-Solving

Over the years, research in mathematical problem-solving has examined expert/novice problem-solving performance on various types of problems and subjects. In particular, DeFranco examined two groups of Ph.D. mathematicians as they solved four mathematics problems and found that although all were content experts, only one group were problem-solving experts. Based on this study, this article posits the notion that one distinguishing feature between experts and novices is that experts tend to look for special features of a problem and use algorithms only as a “fail-safe” system while novices act like “machines” relying on algorithms to solve the problems. Why? The article explores the idea that novice problem solvers learned to solve problems the way they learned proof, that is, in a formal, abstract and mechanizable way. Beliefs about proof and the culture in which it is practiced help frame a mathematician's view of the discipline and ultimately impacts classroom practice. The authors believe that current classroom instruction tends to create a culture that fosters algorithmic proficiency and a “machine-like” approach to the learning of mathematics and problem-solving. Further, they argue that mathematicians need to be aware of the distinction between knowing a proof is true and explaining why it is true. When these distinctions are appreciated and practiced during classroom instruction, then and only then will students begin to acquire the mathematical knowledge to become better problem solvers.     

The Effect of Journal Writing on Achievement in and Attitudes Toward Mathematics

A teaching experiment was conducted to investigate the effect of journal writing on achievement in and attitudes toward mathematics. Achievement variables included conceptual understanding, procedural knowledge, problem solving, mathematics school achievement, and mathematical communication. Subjects were selected from first intermediate students (11–13 years) attending the International College, Beirut, Lebanon, where either English or French is the language of mathematics instruction. The journal-writing (JW) group received the same mathematics instruction as the no-journal-writing (NJW) group, except that the JW group engaged in prompted journal writing for 7 to 10 minutes at the end of each class period, three times a week, for 12 weeks. The NJW group engaged in exercises during the same period. The results of ANCOVA suggest that journal writing has a positive impact on conceptual understanding, procedural knowledge, and mathematical communication but not on problem solving, school mathematics achievement, and attitudes toward mathematics. Gender, language of instruction, mathematics achievement level, and writing achievement level failed to interact with journal writing. Student responses to a questionnaire indicated that students found journal writing to have both cognitive and affective benefits.     

时频分析与算子代数

Gabor分析中几个著名的基本定理(如对偶原理和稠密性定理)与群表示和算子代数理论密切相连.尽管时频分析与算子代数之间的某些联系是Jon von Neumann于1930年代建立的,可是它们在近期得到广泛研究,这主要应归于小波/Gabor理论或更一般的框架理论近二十年的发展.本文将讨论过去几年得到的一些主要结果,同时也给出一些新的结果、解释和问题,我们主要考虑来源于时频分析并能反映与群表示理论存在内在联系的那些结果.特别地,针对群表示的时频分析,将详细说明抽象的对偶原理及其与算子代数理论中几个公开问题的联系.     

Teaching children to add and subtract

At a 1980 conference, leading mathematics educators synthesized previous knowledge on children's early understanding of addition and subtraction and proposed central parameters for future research in these areas form a cognitive science perspective. We have, since 1980, increased our knowledge about how children learn to add and subtract, but we need to know more about the best ways for teachers to guide children as they construct knowledge of addition and subtraction.In this article, we review several studies that focus on an enhanced role for teachers in enabling children to learn addition and subtraction. These studies describe efforts that have been made to teach children to use diagrams and mediational representations, number sentences, or algorithms and procedures. The studies report improvement in children's problem-solving performance, but the impact of the efforts described on children's conceptual understanding is less clear. Thus, we analyze this research, pose questions on the relationship of instruction to children's knowledge construction, and propose a research agenda that we believe will enable us to understand how teaching can best help children learn to add and subtract.     

To teach or not to teach algorithms

Second, third, and fourth graders in 12 classes were individually interviewed to investigate the effects of teaching computational algorithms such as those of “carrying.” Some of the children had been encouraged to invent their own procedures and had not been taught any algorithms in grades 1 and 2, or in grades 1–3. Others had been taught the conventional algorithms prescribed by textbooks. The children were asked to solve multidigit addition and multiplication problems and to explain how they got their answers. It was found that those who had not been taught any algorithms produced significantly more correct answers. If children made errors, the incorrect answers of those who had not been taught any algorithms were much more reasonable than those found in the “Algorithms” classes. It was concluded that algorithms “unteach” place value and hinder children's development of number sense.     

On Global Optimality Conditions via Separation Functions

The paper examines some axiomatic definitions of separation functions that can be employed fruitfully in the analysis of side-constrained extremum problems. A study of their general properties points out connections with abstract convex analysis and recent generalizations of Lagrangian approaches to duality and exact penalty methods. Many concrete examples are brought out.     

Generalized solution principles and out-ranking relations in multi-criteria decision-making

In this paper the abstract notion of a solution principle for multi-criteria decision-making problems is introduced as a set-valued mapping which associates to each decision problem (several) sets of potential solutions. Some modeling conditions are imposed on solution principles which relate them with binary (preference or outranking) relations; this relationship is studied, particularly, the concepts of kernel, quasi-kernel, subsolution and supercore are discussed in terms of solution principles.     

Potential theory of infinite dimensional Lévy processes

We study the potential theory of a large class of infinite dimensional Lévy processes, including Brownian motion on abstract Wiener spaces. The key result is the construction of compact Lyapunov functions, i.e., excessive functions with compact level sets. Then many techniques from classical potential theory carry over to this infinite dimensional setting. Thus a number of potential theoretic properties and principles can be proved, answering long standing open problems even for the Brownian motion on abstract Wiener space, as, e.g., formulated by R. Carmona in 1980. In particular, we prove the analog of the known result, that the Cameron-Martin space is polar, in the Lévy case and apply the technique of controlled convergence to solve the Dirichlet problem with general (not necessarily continuous) boundary data.     

Understanding multidigit whole numbers: The role of knowledge components,connections, and context in understanding regrouping 3+-digit numbers

This case study of a PST's understanding of regrouping with multidigit whole numbers in base-10 and non-base-10 contexts shows that although she seems to have all the knowledge elements necessary to give a conceptually based explanation of regrouping in the context of 3-digit numbers, she is unable to do so. This inability may be due to a lack of connections among various knowledge components (conceptual knowledge) or a lack of connections between knowledge components and context (strategic knowledge). Although she exhibited both conceptual and strategic knowledge of numbers while regrouping 2-digit numbers, her struggles in explaining regrouping 3-digit numbers in the context of the standard algorithms indicate that explaining regrouping with 3-digit is not a mere extension of doing so for 2-digit numbers. She also accepts an overgeneralization of the standard algorithms for subtraction to a time (mixed-base) context, indicating a lack of recognition of the connections between the base-10 contexts and the standard algorithms. Implications for instruction are discussed.     

Learning angles through movement: Critical actions for developing understanding in an embodied activity

Angle instruction often begins with familiar, real-world examples of angles, but the transition to more abstract ideas can be challenging. In this study, we examine 20 third and fourth grade students completing a body-based angle task in a motion-controlled learning environment using the Kinect for Windows. We present overall pre- and post-test results, showing that the task enhanced learners’ developing ideas about angles, and we describe two case studies of individual students, looking in detail at the role the body plays in the learning process. We found that the development of a strong connection between the body and the abstract representation of angle was instrumental to learning, as was exploring the space and making connections to personal experiences. The implications of these findings for developing body-based tasks are discussed.     

Using Analogies to Improve Elementary School Students' Inferential Reasoning About Scientific Concepts

Various scientific concepts were taught to students in the third through sixth grades. Some children were taught the concepts using instructional analogies. Each analogy explicitly compared the science concept to a more familiar topic. Other children received expository texts not containing analogies. Students were asked to recall the texts and to answer inference questions about the science concepts. Fourth- and sixth-grade students read the texts on their own in Experiment 1. Students who read the analogical text showed higher levels of performance on inference questions than students who received the non-analogical texts. In Experiment 2, texts were read aloud to third- and fifth-grade students. The analogical texts were read once, and the nonanalogical texts were read twice to equate the number of times students were exposed to the general principles governing the domains. As in Experiment 1, students who received the analogical texts demonstrated better inferential reasoning than students who received the non-analogical texts.     

A Shared Framework for Consequence Operations and Abstract Model Theory

In this paper we develop an abstract theory of adequacy. In the same way as the theory of consequence operations is a general theory of logic, this theory of adequacy is a general theory of the interactions and connections between consequence operations and its sound and complete semantics. Addition of axioms for the connectives of propositional logic to the basic axioms of consequence operations yields a unifying framework for different systems of classical propositional logic. We present an abstract model-theoretical semantics based on model mappings and theory mappings. Between the classes of models and theories, i.e., the set of sentences verified by a model, it obtains a connection that is well-known within algebra as Galois correspondence. Many basic semantical properties can be derived from this observation. A sentence A is a semantical consequence of T if every model of T is also a model of A. A model mapping is adequate for a consequence operation if its semantical inference operation is identical with the consequence operation. We study how properties of an adequate model mapping reflect the properties of the consequence operation and vice versa. In particular, we show how every concept of the theory of consequence operations can be formulated semantically.     

Developing Prospective Elementary Teachers' Flexibility in the Domain of Proportional Reasoning

Flexibility in the use of mathematics procedures consists of the ability to employ multiple solution methods across a set of problems, solve the same problem using multiple methods, and choose strategically from among methods so as to reduce computational demands. The purpose of this study was to characterize prospective elementary teachers' (n = 148) flexibility in the domain of proportional reasoning before formal instruction and to test the effects of two versions of an intervention that engaged prospective teachers in comparing different solutions to proportion problems. Results indicate that (a) participants exhibited limited flexibility before formal instruction, (b) the intervention led to significant gains in participants' flexibility that were retained six months after instruction, and (c) varying the source of the problem solutions that participants compared had no discernible effects on their flexibility. Implications for mathematics teacher preparation and for research on flexibility development are provided.     

The spectrum of the Hilbert space valued second derivative with general self-adjoint boundary conditions

We consider a large class of self-adjoint elliptic problems associated with the second derivative acting on a space of vector-valued functions. We present and survey several results that can be obtained by means of two different approaches to the study of the associated eigenvalues problems. The first, more general one allows to replace a secular equation (which is well known in some special cases) by an abstract rank condition. The second one, though available in general, seems to apply particularly well to a specific boundary condition, the sometimes dubbed anti-Kirchhoff condition in the literature, that arises in the theory of differential operators on graphs; it also permits to discuss interesting and more direct connections between the spectrum of the differential operator and some graph theoretical quantities, in particular some results on the symmetry of the spectrum in either case.     

Asymptotically compatible schemes for the approximation of fractional Laplacian and related nonlocal diffusion problems on bounded domains

Approximations of solutions of fractional Laplacian equations on bounded domains are considered. Such equations allow global interactions between points separated by arbitrarily large distances. Two approximations are introduced. First, interactions are localized so that only points less than some specified distance, referred to as the interaction radius, are allowed to interact. The resulting truncated problem is a special case of a more general nonlocal diffusion problem. The second approximation is the spatial discretization of the related nonlocal diffusion problem. A recently developed abstract framework for asymptotically compatible schemes is applied to prove convergence results for solutions of the truncated and discretized problem to the solutions of the fractional Laplacian problems. Intermediate results also provide new convergence results for the nonlocal diffusion problem. Special attention is paid to limiting behaviors as the interaction radius increases and the spatial grid size decreases, regardless of how these parameters may or may not be dependent. In particular, we show that conforming Galerkin finite element approximations of the nonlocal diffusion equation are always asymptotically compatible schemes for the corresponding fractional Laplacian model as the interaction radius increases and the grid size decreases. The results are developed with minimal regularity assumptions on the solution and are applicable to general domains and general geometric meshes with no restriction on the space dimension and with data that are only required to be square integrable. Furthermore, our results also solve an open conjecture given in the literature about the convergence of numerical solutions on a fixed mesh as the interaction radius increases.