Compact Multi-Class Boosted Trees

Gradient boosted decision trees are a popular machine learning technique, in part because of their ability to give good accuracy with small models. We describe two extensions to the standard tree boosting algorithm designed to increase this advantage. The first improvement extends the boosting formalism from scalar-valued trees to vector-valued trees. This allows individual trees to be used as multiclass classifiers, rather than requiring one tree per class, and drastically reduces the model size required for multiclass problems. We also show that some other popular vector-valued gradient boosted trees modifications fit into this formulation and can be easily obtained in our implementation. The second extension, layer-by-layer boosting, takes smaller steps in function space, which is empirically shown to lead to a faster convergence and to a more compact ensemble. We have added both improvements to the open-source TensorFlow Boosted trees (TFBT) package, and we demonstrate their efficacy on a variety of multiclass datasets. We expect these extensions will be of particular interest to boosted tree applications that require small models, such as embedded devices, applications requiring fast inference, or applications desiring more interpretable models.Comment: Accepted for publication in IEEE Big Data 2017 http://cci.drexel.edu/bigdata/bigdata2017/AcceptedPapers.htm

Distant drums: the British Commonwealth and the approach of war, 1 October 1938 - 11 September 1939

While there has been much coverage of the influence of the British Commonwealth on the Chamberlain government's foreign policy, there has been little on the impact of European events on the dominions themselves, especially relating to the particular contexts in which they existed. Yet it is these contexts which were crucial in determining how they perceived events in Europe. This study therefore aims to consider the developing attitudes of the Australian, Canadian, New Zealand, and South African governments towards the idea of war with Germany between the Munich Settlement and Canada's declaration of war on Germany on 10 September 1939. The Irish Free State is deliberately excluded from consideration, as its circumstances were sufficiently distinct from those of the other dominions to render its inclusion meaningless, and there was consequently never any realistic prospect that it would enter the war at Britain's side, as the others did. The first chapter of this thesis examines the underlying imperatives which defined the dominions' perspectives on Europe, while succeeding ones trace the effect of the key developments in the approach of war, such as Kris.s.tallnacht and the march into Prague, on the Commonwealth's evolving views of the international situation during the eleven months after Munich. The methodology follows the Agents & Structures model laid down in M. G. Fry's 1999 article `The British Dominions & the Munich Crisis.' Sources for this study include dominion government records, the personal diaries of participants, their private correspondence & newspaper coverage of their activities, as well as the secondary literature dealing with the wider picture of the prelude to war and the Commonwealth's role within that, as outlined above

The users centered design of a new digital fluorometer

The fluorometer is the equipment used in chemical analysis laboratories, research institutes and nuclear fuel cycle companies. This equipment measures an unknown amount of uranium in ores, rivers, etc. The fluorometer functioning is based on the uranium fluorescence when submitted to the ultraviolet radiation incidence. The fluorescence is measured by an electronic optic system with optics filters, photomultiplier tube, and a current amplifier. The user centered design involvers the user in the product development in all phases of the design process. Users are not simply consulted at the beginning of the design process and evaluated the system at the end; they are treated as partners throughout the design process. The user centered design emphasizes the needs and abilities of the users and improves the usability of the equipment. The activity centered design emphasizes the development of the equipment with a deep understanding of the users activities and of the current work practices of the users. The aim of this paper is to present a methodological framework that contributes to the design and evaluation of a new digital fluorometer towards an approach related to the users and their activities. This methodological framework includes users-based testing, interviews, questionnaires, human factors standards and guidelines, the users activity analysis and users satisfaction questionnaire

Multidimensional wavelets

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mathematics, 1997.Includes bibliographical references (p. 78-82).by Thoams Colthurst.Ph.D

Fast Approximate Determinants Using Rational Functions

We show how rational function approximations to the logarithm, such as $\log z \approx (z^2 - 1)/(z^2 + 6z + 1)$, can be turned into fast algorithms for approximating the determinant of a very large matrix. We empirically demonstrate that when combined with a good preconditioner, the third order rational function approximation offers a very good trade-off between speed and accuracy when measured on matrices coming from Mat\'ern-$5/2$ and radial basis function Gaussian process kernels. In particular, it is significantly more accurate on those matrices than the state-of-the-art stochastic Lanczos quadrature method for approximating determinants while running at about the same speed.Comment: 22 pages, 17 figure

Attachment dimensions as predictors of mental health and psychosocial well-being in the transition to university

This study sought to investigate the predictive relationship that dimensions of attachment shared with an array of indicators of psychosocial well-being and mental health in a sample of students making the transition to higher education. One hundred and thirty-one students completed the Vulnerable Attachment Styles Questionnaire (VASQ) prior to enrolment in their first semester of university education. Subsequently, the students completed measures related to perceived loneliness, institutional integration, psychological need satisfaction, depressive symptoms and ways of coping during their first semester. Results suggested that higher scores in relation to the insecurity dimension of the VASQ were instrumental in predicting negative psychosocial well-being and mental health. The results discussed the key vulnerability dimensions of attachment when seeking to predict indices of psychosocial well-being and mental health

How teens learn teamwork: agentic and constructive peer processes

Teamwork is widely proclaimed as a valuable contemporary skill set. Youth programs provide distinct opportunities for young people to develop collaborative competencies. The current study examines the developmental experiences of teamwork in a residential summer camp setting. This dissertation analyzes youth’s narratives about learning collaborative skills in a service program for teens at Camp Clore. The data for this project includes 50 qualitative, semi-structured interviews with teenage participants in the Clore Corps, who ranged in age from 14 to 16. Modified grounded theory methods facilitated the use of narrative data from the youth themselves. This study examines the conscious ways teenagers learn teamwork, especially in terms of their agentic involvement in constructive processes of learning from peers. The findings address the general question of how youth learn teamwork and the grounded theorization of positive processes in youth programs. Highlighting the roles of agency and peers, the analysis illustrates the rich diversity of ways that youth learn teamwork. Youth reiterated prosocial values as they found many ways to reconcile task challenges with complex interpersonal dynamics. Two categories of learning episodes were distinguished by youth’s orientation toward their peers as they learned: Peers as People and Peers as Exemplars. Each of these sets of learning episodes received its own inductive, within-category analysis on the basis of their shared features. Youth acknowledging the human qualities of their peers was a pivotal motivation for accommodating and accepting in the Peers-as-People learning episodes. This allowed youth to restrain judgment and collaborate successfully with peers. For the Peers-as-Exemplars category, in contrast, youth actively drew on the example of their peers work and evaluated them. The evaluative processes stimulated learner’s imaginative generation of skills, attitudes, insights, and principles of teamwork. A prominent theme across both episode categories was youth’s creativity and strategy as they learned teamwork. Youth demonstrated these qualities by drawing on peers as resources and actively developing teamwork knowledge and skills. Creative and strategic choices, intentions, and courses of action and thought in youth’s teamwork constituted agency in their development. Peers’ input in learning, moreover, was not absorbed or spread via contagion; rather, youth described making use of peers’ involvement to determine their own course. The theme of creativity and strategy across episodes establishes agentic processes in conjunction with constructive peer processes, not despite or in addition to them. The contribution of this dissertation, then, sheds light on how youth learn prosocial skills in a way that is, at once, both agentic and constructively peer-driven

Authentic Biology: Student-led research and discovery in schools

Conducting cutting-edge biomedical research in schools and further education college laboratories has its challenges, but these are not insurmountable. In 2008, we established a successful cutting-edge research project into a debilitating human disease, in a secondary school environment. Here we provide a narrative describing the process behind the project, and then reflect not only on the process, but also on the benefits for school students, teachers and university researchers from engagement in such a collaborative project. We describe how, with significant financial input from a major biomedical charity, we were able to expand the initial project into Authentic Biology, a national programme of research in schools across the UK. Authentic Biology has resulted in six schools establishing their own novel research projects, mainly relating to human disease, and working in collaboration with their local university. Authentic Biology is a model for longterm school/college/university collaboration that is highly effective, productive and measurable through outcome. The challenge ahead is how to sustain the technical and financial support for such programmes