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171.
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
172.
Ronald E. Rice 《The Information Society》2005,21(4):285-299
This study summarizes prior reviews of new media and Internet research, and the growth of the term Internet in academic publications and online newsgroups. It then uses semantic network analysis to summarize the interests and concepts of an interdisciplinary group of Internet researchers, as represented by session titles and paper titles and abstracts from the 2003 and 2004 Association of Internet Researchers conferences. In both years, the most frequent words appearing in the paper abstracts included Internet, online, community, social, technology, and research. The 2003 papers emphasized topics such as the social analysis/research of online/Internet communication, community, and information, with particular coverage of access, individuals, groups, digital media, culture; role and process in e-organizations; and world development. The 2004 papers emphasized topics such as access; news and social issues; the role of individuals in communities; user-based studies; usage data; and blogs, women, and search policy, among others. 相似文献
173.
Berent GP Kelly RR Aldersley S Schmitz KL Khalsa BK Panara J Keenan S 《Journal of deaf studies and deaf education》2007,12(1):8-24
Focus-on-form English teaching methods are designed to facilitate second-language learners' noticing of target language input, where "noticing" is an acquisitional prerequisite for the comprehension, processing, and eventual integration of new grammatical knowledge. While primarily designed for teaching hearing second-language learners, many focus-on-form methods lend themselves to visual presentation. This article reports the results of classroom research on the visually based implementation of focus-on-form methods with deaf college students learning English. Two of 3 groups of deaf students received focus-on-form instruction during a 10-week remedial grammar course; a third control group received grammatical instruction that did not involve focus-on-form methods. The 2 experimental groups exhibited significantly greater improvement in English grammatical knowledge relative to the control group. These results validate the efficacy of visually based focus-on-form English instruction for deaf students of English and set the stage for the continual search for innovative and effective English teaching methodologies. 相似文献
174.
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
175.
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
176.
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
177.
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
178.
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
179.
180.