Optimal pruning for tree-structured vector quantization     

Jianhua Lin  James A. Storer  Martin Cohn 《Information processing & management》1992,28(6)

Tree-structured vector quantization (VQ) is a technique designed to represent a codebook that simplifies encoding as well as vector quantizer design. Most design algorithms for tree-structured VQ used in the past are based on heuristics that successively partition the input space. Recently, Chou, Lookabaugh and Gray proposed a tree-pruning heuristic in which a given initial tree is pruned backwards according to certain optimization criterion. We define the notion of an optimal pruned tree subject to a cost constraint and study the computational complexity of finding such an optimal tree for various cost functions. Under the assumption that all trees are equally probable, we show that, on the average, the number of pruned trees in a given tree is exponential in the number of leaves. Furthermore, we prove that finding an optimal pruned tree subject to constraints such as entropy or the expected-depth is NP-hard. However, we show that when the constraint is the number of leaves, the problem can be solved in polynomial time. We develop an algorithm to find the optimal pruned tree in O(nk) time, where n is the size of the initial tree and kis the constraint size.  相似文献   

Using the web to encourage student-generated questions in large-format introductory biology classes     

Colbert JT  Olson JK  Clough MP 《CBE life sciences education》2007,6(1):42-48

Students rarely ask questions related to course content in large-format introductory classes. The use of a Web-based forum devoted to student-generated questions was explored in a second-semester introductory biology course. Approximately 80% of the enrolled students asked at least one question about course content during each of three semesters during which this approach was implemented. About 95% of the students who posted questions reported reading the instructor's response to their questions. Although doing so did not contribute to their grade in the course, approximately 75% of the students reported reading questions posted by other students in the class. Approximately 60% of the students reported that the Web-based question-asking activity contributed to their learning of biology.  相似文献   

Teachers' education, classroom quality, and young children's academic skills: results from seven studies of preschool programs   总被引：10，自引：0，他引：10  

Early DM  Maxwell KL  Burchinal M  Alva S  Bender RH  Bryant D  Cai K  Clifford RM  Ebanks C  Griffin JA  Henry GT  Howes C  Iriondo-Perez J  Jeon HJ  Mashburn AJ  Peisner-Feinberg E  Pianta RC  Vandergrift N  Zill N 《Child development》2007,78(2):558-580

In an effort to provide high-quality preschool education, policymakers are increasingly requiring public preschool teachers to have at least a Bachelor's degree, preferably in early childhood education. Seven major studies of early care and education were used to predict classroom quality and children's academic outcomes from the educational attainment and major of teachers of 4-year-olds. The findings indicate largely null or contradictory associations, indicating that policies focused solely on increasing teachers' education will not suffice for improving classroom quality or maximizing children's academic gains. Instead, raising the effectiveness of early childhood education likely will require a broad range of professional development activities and supports targeted toward teachers' interactions with children.  相似文献   

The Art of Straying: Benjamin on Distraction and the Informal Education of the City     

Tyson E. Lewis 《Educational theory》2019,69(2):169-183

In this article, Tyson E. Lewis argues for an alternative form of educational attunement beyond attentiveness. Discourses and practices of schooling emphasize being attentive as a primary educational virtue. This emphasis casts distraction as either the negation of attention or its deterioration. In either case, distraction lacks educational use and, as such, must be overcome through the cultivation of attention. Yet this approach to the question of attention versus distraction misses how distraction contains within itself a different kind of educational potentiality, a different kind of educational attunement. In an attempt to carve out space and time for distraction, Lewis turns to the writings of Walter Benjamin who offers up a more complex view of distraction than is presently found in educational philosophy. In particular, Benjamin argues that cities are not only places of negative forms of distraction (as mere diversions), but also places for cultivating productive distraction in the form of an open and alert attunement to new ways of experiencing and perceiving the relationship between world and self. Cities, for Benjamin, become educational spaces that teach lessons in a distracted form of life, the culmination of which is the creativity expressed in what he refers to as “the art of straying.”  相似文献   

Teaching primary mathematics with challenging tasks: How should lessons be structured?     

James Russo  Sarah Hopkins 《The Journal of educational research》2019,112(1):98-109

Engaging students in a challenging (cognitively demanding) task and launching a mathematics lesson with a task before instruction are two characteristics of a reform-oriented approach to mathematics instruction often considered together. The authors systematically contrasted teaching with challenging tasks using a task-first lesson structure with that of a discussion-first lesson structure to three composite classes of first- and second-grade students (n = 73). Subsequent assessments of mathematical performance revealed that the discussion-first lesson structure was somewhat more efficacious in improving fluency performance but both structures similarly improved problem-solving performance. The findings suggest there is more than one way of incorporating challenging tasks into mathematics lessons to produce sizeable learning gains.  相似文献   

Academic identity,confidence and belonging: The role of contextualised admissions and foundation years in higher education     

Katriona O'Sullivan  Niamh Bird  James Robson  Niall Winters 《British Educational Research Journal》2019,45(3):554-575

This article presents a cross-national exploration of responses to widening participation (WP), with a specific focus on the provision of foundation year (FY) programmes and the use of contextualised admissions (CA) in selective Irish and UK institutions. There remains a dearth of research on these routes, with little understanding of the characteristics of students who utilise them, of why students use these routes and little knowledge of their effect on students’ experiences in university and their overall sense of belonging. A year-long longitudinal comparative case study design examined three alternative entry routes in two selective higher education institutions (HEIs) in England and Ireland: a well-established FY; a newly formed FY; and a CA pathway. Data were collected through a mixed-method approach. Questionnaires and in-depth focus groups were employed at fixed points with participating students in each route. Results indicated that FY students had lower levels of familial educational history and parental occupation. FY students’ sense of belonging significantly increased over the year, with students reporting increased confidence and sense of belonging due to the relationships established during the FY. CA students’ sense of belonging remained the same, with students reporting feeling different and isolated. Results indicate that while students utilising FYs may be ‘more disadvantaged’ than CA students, their experiences helped establish a sense of belonging; illustrating the need for diverse WP routes catering to a wide range of needs. Results highlight the importance of providing opportunities to develop social and bridging social capital for all non-traditional students.  相似文献   

Opportunities for educational innovations in authentic project-based learning: understanding instructor perceived challenges to design for adoption     

Rees Lewis  Daniel G.  Gerber  Elizabeth M.  Carlson  Spencer E.  Easterday  Matthew W. 《Educational technology research and development : ETR & D》2019,67(4):953-982

Educational technology research and development - Authentic project-based learning (APBL) is a highly effective way for instructors to help students learn disciplinary skills, modes of thinking,...  相似文献   

Attachment,Communication, and Relationship Functioning Among College Student Veterans and Nonveterans     

Shelley A. Riggs  Kellye S. Carver  Daniel Romero  Sandra B. Morissette  Jamie Wilson  Robyn Campbell  James McGuffin 《Journal of College Counseling》2019,22(2):110-124

This study examined attachment processes of college student veterans and nonveterans and further examined how veteran status and attachment style directly and indirectly predict relationship functioning. Results indicated that student veterans were more often dismissing in their attachment style but less often preoccupied than nonveteran students. Veteran status moderated the association between attachment style and dyadic consensus. The contributions of attachment and communication processes to overall relationship adjustment differed for student veterans and nonveterans.  相似文献   

Letter from the Editors     

Peter James Bentley  Carroll Graham 《Journal of Higher Education Policy & Management》2019,41(2):119-120

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Letter from the editors     

Peter James Bentley  Carroll Graham 《Journal of Higher Education Policy & Management》2019,41(4):359-360

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