1,286 research outputs found

    Locality-aware parallel block-sparse matrix-matrix multiplication using the Chunks and Tasks programming model

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    We present a method for parallel block-sparse matrix-matrix multiplication on distributed memory clusters. By using a quadtree matrix representation, data locality is exploited without prior information about the matrix sparsity pattern. A distributed quadtree matrix representation is straightforward to implement due to our recent development of the Chunks and Tasks programming model [Parallel Comput. 40, 328 (2014)]. The quadtree representation combined with the Chunks and Tasks model leads to favorable weak and strong scaling of the communication cost with the number of processes, as shown both theoretically and in numerical experiments. Matrices are represented by sparse quadtrees of chunk objects. The leaves in the hierarchy are block-sparse submatrices. Sparsity is dynamically detected by the matrix library and may occur at any level in the hierarchy and/or within the submatrix leaves. In case graphics processing units (GPUs) are available, both CPUs and GPUs are used for leaf-level multiplication work, thus making use of the full computing capacity of each node. The performance is evaluated for matrices with different sparsity structures, including examples from electronic structure calculations. Compared to methods that do not exploit data locality, our locality-aware approach reduces communication significantly, achieving essentially constant communication per node in weak scaling tests.Comment: 35 pages, 14 figure

    Understanding China’s New Assertiveness - A Dyadic Study of China’s Rise, its Goals and Implications

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    Since the financial crisis in 2008-2009 China has shown a new assertiveness internationally, contradicting Deng Xiaoping’s earlier strategies of China to lay low internationally and develop economically. This new assertiveness is an often-discussed subject and is often connected to the Chinese rise and a presumed pursuit of regional hegemony in South East Asia, rejected by Chinese officials. This paper aims on studying China’s new assertiveness on both a systemic international politics level and on foreign policy level to understand what drives this new assertiveness. Graham T. Allison used three explanatory models to examine the decision-making during the Cuban Missile Crises, and I have adapted his three models to China’s behaviour in South East Asia and complemented them with e.g. factors that affect decision-making and contemporary theories of hegemony. Using this method gave me the opportunity to challenge the notion of a Chinese pursuit of hegemony since the case of China contained several anomalies compared to the theoretical framework, which instead points to an All-under-Heaven system emphasized by Chinese officials and scholars. The new assertiveness is explained mainly trough enhanced militarism, PLA influence and capacity, kept non-confrontational through e.g. Confucianism and Deng-ist advocates

    Optimization Based Control Strategy for Energy Efficient Decelerations in an Automobile Cruise Controller

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    With global warming and increased uncertainty about future vehicle fuel supply, the need for fuel efficient vehicles is growing. In this Master Thesis, design and implementation of a control strategy for fuel efficient deceleration is presented. The resulting deceleration controller, implemented in Embedded Matlab and Simulink, provides autonomous deceleration functionality to a vehicle cruise controller. Deceleration patterns are produced through online optimization of a cost function comprising fuel consumption and time loss. The cost function is calculated based on navigation information for the predicted driving path, which is also used to detect upcoming deceleration situations. The potential for fuel savings is estimated through simulation, and experiences from tentative driving tests are presented. The optimization approach proves to yield flexibility in balancing fuel savings versus time loss, while being fast enough to be run online as a prototype function in a test vehicle. The deceleration optimizer function could either be used in its current form in future cruise controllers, or as a tool for development of simplified deceleration strategies

    Feeling ready and always more to learn : students’ journeys towards becoming a professional nurse

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    Background: Well-educated competent professional nurses are needed to ensure sustainable healthcare systems and reduce health inequalities. Nursing is a global profession, and the requirements and competences vary between regions regarding both education and professional requirements. The Swedish nursing program contains both theoretical education and practical training, to prepare the students for working life. The learning process is affected by several factors, for example, learning environment, learning activities and feelings, so called academic emotions. Since students' experiences vary in relation to different learning activities and over time data was collected longitudinally to follow their development throughout the whole nursing program. Aim: The aim of this thesis was to contribute to a deeper knowledge and understanding about nursing students’ experiences of learning activities and the process of developing professional identity during higher education in the field of nursing. Methods: All students (n=459) starting the nursing program from August 2015 to January 2017 were invited to participate. The data collection started in August 2015 and was completed in January 2020. Data was collected via interviews at four occasions (n=286), and at 42 measurement (n=2,947) points using Contextual Activity Sampling System, CASS (Lachmann et al., 2012; Muukkonen et al., 2008). Study I was a mixed methods study including 126 semi-structured individual interviews and 158 CASS-questionnaires collected at the start of the program. The interviews were analysed using qualitative content analysis and the questionnaires with descriptive statistics. Study II was a longitudinal qualitative study using 136 semi-structured individual interviews performed at four stages, analysed using longitudinal content analysis. Study III was a longitudinal prospective study using 2,947 CASS-questionnaires collected throughout the program, analysed with descriptive statistics. In this study, the students’ academic positive emotions (determination; enthusiasm; interest), negative emotions (irritation; nervousness; anxiety) and their perceived challenge and competence related to their current learning activity were analysed. Study IV was a parallel mixed method study including 68 RIPLS questionnaires and 34 semi-structured individual interviews analysed with descriptive statistics, paired sample T-test, and qualitative content. Results: In Study I the findings from the interviews were summarized in the overarching theme: Making a difference if managing to become a professional nurse, from the seven main categories in the three domains Conceptions; Expectations; and Doubts. The selfrated questionnaires revealed emotions of high ambition and motivation. The ratings of negative emotions correlated with the fears and worries about uncertainty expressed in interviews. In Study II the overarching theme: Ready but not fully trained was summarized from the four main categories: Anticipation; Prepared for internship; Deepened understanding; and Insight. The students deemed that working as a professional nurse requires continuously learning and improvement and underlined in the final interview that there will always be more to learn. Study III revealed that the students experienced high positive academic emotions combined with low negative emotions when first entering clinical practice in the third semester, upon completion of clinical practice in the fourth semester and while writing their bachelor thesis in the fifth semester. Optimal experience during clinical practice was reported by 21 percent in semester three to five, and by 34 percent in semester six. The students’ reported low positive emotions and high negative emotions during theoretical courses in medical science and in research methodology preparing for writing their thesis. The negative emotions reported during the thesis preparation period shifted to more positive emotions during the time of writing it. While when writing the bachelor thesis, 29 percent experienced flow compared to 13 percent during the preparatory course. In Study IV the students’ reported learning styles and their attitudes to interprofessional collaboration were analysed. The findings indicated that 64.7 percent had a predominantly concrete learning style while 35.3 percent were predominantly reflective. No significant results were found regarding relationships between learning styles and attitudes to interprofessional learning. The theme Well-functioning teams improve patients’ outcome and working environment was summarized from the four main categories: Amazing when it’s functional; Deepened insight of care; Increased quality of care; and Understanding own profession. Conclusion: During the education, emotions experienced by students varied during the various learning activities. They started their education with a vision of making a difference. In the first academic year they developed a solid theoretical basis and were eager to enter internship to transform their knowledge into practice and to gain clinical experience. When entering clinical practice, students witnessed of a reality that did not always correspond with what they had been taught. At the time of graduation, students felt ready to join the workforce and stressed that there is always more to learn. These findings reveal a gap between theoretical and practical education that needs to be addressed

    Canonical density matrix perturbation theory

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    Density matrix perturbation theory [Niklasson and Challacombe, Phys. Rev. Lett. 92, 193001 (2004)] is generalized to canonical (NVT) free energy ensembles in tight-binding, Hartree-Fock or Kohn-Sham density functional theory. The canonical density matrix perturbation theory can be used to calculate temperature dependent response properties from the coupled perturbed self-consistent field equations as in density functional perturbation theory. The method is well suited to take advantage of sparse matrix algebra to achieve linear scaling complexity in the computational cost as a function of system size for sufficiently large non-metallic materials and metals at high temperatures.Comment: 21 pages, 3 figure
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