A numerical study of Richtmyer–Meshkov instability in continuously stratified fluids

Theory and calculations are presented for the evolution of Richtmyer–Meshkov instability in two-dimensional continuously stratified fluid layers. The initial acceleration and subsequent instability of the fluid layer are induced by means of an impulsive pressure distribution. The subsequent dynamics of the fluid layer are then calculated numerically using the incompressible equations of motion. Initial conditions representing single-scale perturbations and multiple-scale random perturbations are considered. It is found that the growth rates for Richtmyer–Meshkov instability of stratified fluid layers are substantially lower than those predicted by Richtmyer for a sharp fluid interface with an equivalent jump in density. A frozen field approximation for the early-time dynamics of the instability is proposed, and shown to approximate the initial behavior of the layer over a time equivalent to the traversal of several layer thicknesses. It is observed that the nonlinear development of the instability results in the formation of plumes of penetrating fluid. Late in the process, the initial momentum deposited by the impulse is primarily used in the internal mixing of the layer rather than in the overall growth of the stratified layer. At intermediate times, some evidence for the existence of scaling behavior in the width of the mixing layer of the instability is observed for the multiple-scale random perturbations, but not for the single-scale perturbations. The time variation of the layer thickness differs from the scaling derived using ideas of self-similarity due to Barenblatt [Non-Linear Dynamics and Turbulence, edited by G. I. Barenblatt, G. Ioos, and D. D. Joseph (Pitman, Boston, 1983), p. 48] even at low Atwood ratio, presumably because of the inhomogeneity and anisotropy due to the excitation of vortical plumes

Mixing and non-mixing local minima of the entropy contrast for blind source separation

In this paper, both non-mixing and mixing local minima of the entropy are analyzed from the viewpoint of blind source separation (BSS); they correspond respectively to acceptable and spurious solutions of the BSS problem. The contribution of this work is twofold. First, a Taylor development is used to show that the \textit{exact} output entropy cost function has a non-mixing minimum when this output is proportional to \textit{any} of the non-Gaussian sources, and not only when the output is proportional to the lowest entropic source. Second, in order to prove that mixing entropy minima exist when the source densities are strongly multimodal, an entropy approximator is proposed. The latter has the major advantage that an error bound can be provided. Even if this approximator (and the associated bound) is used here in the BSS context, it can be applied for estimating the entropy of any random variable with multimodal density.Comment: 11 pages, 6 figures, To appear in IEEE Transactions on Information Theor

Effective Approaches to Attention-based Neural Machine Translation

An attentional mechanism has lately been used to improve neural machine translation (NMT) by selectively focusing on parts of the source sentence during translation. However, there has been little work exploring useful architectures for attention-based NMT. This paper examines two simple and effective classes of attentional mechanism: a global approach which always attends to all source words and a local one that only looks at a subset of source words at a time. We demonstrate the effectiveness of both approaches over the WMT translation tasks between English and German in both directions. With local attention, we achieve a significant gain of 5.0 BLEU points over non-attentional systems which already incorporate known techniques such as dropout. Our ensemble model using different attention architectures has established a new state-of-the-art result in the WMT'15 English to German translation task with 25.9 BLEU points, an improvement of 1.0 BLEU points over the existing best system backed by NMT and an n-gram reranker.Comment: 11 pages, 7 figures, EMNLP 2015 camera-ready version, more training detail

The collective consciousness of Information Technology research: The significance and value of research projects. A. The views of IT researchers

This research seeks to reveal the different perceptual worlds in a research community, with the longterm intent of fostering increased understanding and hence collaboration. In the relatively new field of information technology (IT) research, available evidence suggests that a shared understanding of the research object or territory does not yet exist. This has led to the development of different perceptions amongst IT researchers of what constitutes significant and valuable research. A phenomenological approach is used to elicit data from a diverse range of IT researchers in semistructured interviews. This data is presented to show (1) the variation in meaning associated with the idea of significance and value and (2) the awareness structures through which participants experience significance and value. An Outcome Space represents the interrelation between those different ways of seeing, revealing a widening awareness. Five categories of ways of seeing the significance and value of research projects were found: The Personal Goals Conception, The Research Currency Conception, The Design of the Research Project Conception, The Outcomes for the Technology End User Conception and The Solving Real-World Problems Conception. These are situated within three wider perceptual boundaries: The Individual, The Research Community and Humankind. The categories are described in detail, demonstrated with participants’ quotes and illustrated with diagrams. A tentative comparison is made between this project and a similar investigation of IT professionals’ ways of seeing the significance and value of IT research projects. Finally, some recommendations for further research are made

The collective consciousness of Information Technology research: The significance and value of research projects. B. The views of IT industry professionals

This research seeks to reveal the different perceptual worlds in a research community, with the longterm intent of fostering increased understanding and hence collaboration. In the relatively new field of information technology (IT) research, available evidence suggests that a shared understanding of the research object or territory does not yet exist. This has led to the development of different perceptions amongst IT researchers of what constitutes significant and valuable research. Phenomenological methodology is used to elicit data from a diverse range of IT industry professionals in semi-structured interviews. This data is presented to show (1) the variation in meaning associated with the idea of significance and value and (2) the awareness structures through which participants experience significance and value. An Outcome Space represents the interrelation between those different ways of seeing, revealing a widening awareness. Five categories of ways of seeing the significance and value of research projects were found: The Personal Goals Conception, The Commercial Goals Conception, The Outcomes for the Technology End User Conception, The Solving Real-World Problems Conception and The Design of the Research Project Conception. These are situated within three wider perceptual boundaries: The Individual, The Enterprise and Society. The categories are described in detail, demonstrated with participants’ quotes and illustrated with diagrams. A tentative comparison is made between this project and a similar investigation of IT researchers’ ways of seeing the significance and value of IT research projects. Finally, some recommendations for further research are made

The Collective Consciousness of Information Technology Research: Ways of seeing Information Technology Research: Its Objects and Territories

The collective consciousness of effective groups of researchers is characterised by shared understandings of their research object or territory. In the relatively new field of information technology research, rapid expansion and fragmentation of the territory has led to different perceptions about what constitutes information technology research. This project explores a facet of the collective consciousness of disparate groups of researchers and lays a foundation for constructing shared research objects. Making IT researchers’ ways of seeing explicit may help us understand some of the complexities associated with inter and intra disciplinary collaboration amongst research groups, and the complexities associated with technology transfer to industry. This report analyses IT research, its objects and territories, as they are constituted by IT researchers associated with the sub-disciplines of information systems, computer science and information security. A phenomenographic approach is used to elicit data from a diverse range of IT researchers in semistructured interviews. This data is analysed to show (1) the variation in meaning associated with the idea of IT research and (2) the awareness structures through which participants experience variation in ways of seeing the object and territories of IT research. An Outcome Space represents the interrelation between different ways of seeing the territory. Eight ways of seeing IT research, its objects and territories, were found: The Technology Conception, The Information Conception, The Information and Technology Conception, The Communication Conception, The Ubiquitous Conception, The Sanctioned Conception, The Dialectic Conception and The Constructed Conception. These are described in detail and illustrated with participants’ quotes. Finally, some recommendations for further research are made

Distinct subpopulations of enteric neuronal progenitors defined by time of development, sympathoadrenal lineage markers and Mash-1-dependence

Enteric and sympathetic neurons have previously been proposed to be lineally related. We present independent lines of evidence that suggest that enteric neurons arise from at least two lineages, only one of which expresses markers in common with sympathoadrenal cells. In the rat, sympathoadrenal markers are expressed, in the same order as in sympathetic neurons, by a subset of enteric neuronal precursors, which also transiently express tyrosine hydroxylase. If this precursor pool is eliminated in vitro by complement-mediated lysis, enteric neurons continue to develop; however, none of these are serotonergic. In the mouse, the Mash-1−/− mutation, which eliminates sympathetic neurons, also prevents the development of enteric serotonergic neurons. Other enteric neuronal populations, however, including those that contain calcitonin gene related peptide are present. Enteric tyrosine hydroxylase-containing cells co-express Mash-1 and are eliminated by the Mash-1−/− mutation, consistent with the idea that in the mouse, as in the rat, these precursors generate serotonergic neurons. Serotonergic neurons are generated early in development, while calcitonin gene related peptide-containing enteric neurons are generated much later. These data suggest that enteric neurons are derived from at least two progenitor lineages. One transiently expresses sympathoadrenal markers, is Mash-1-dependent, and generates early-born enteric neurons, some of which are serotonergic. The other is Mash-1-independent, does not express sympathoadrenal markers, and generates late-born enteric neurons, some of which contain calcitonin gene related peptide

Nguyễn An Ninh’s Anti-Colonial Thought: A New Account of National Shame

A source of national shame can be the perception that one’s nation is intellectually inferior to other nations. This kind of national shame can lead not to despair but to a sense of national responsibility to engage in creative self-renewal and to create national identity from scratch. An exemplar of someone who recognized and engaged with this kind of national shame is Nguyễn An Ninh (1900–1943), an influential Vietnamese anti-colonial intellectual in French colonial Vietnam. Ninh’s account of national shame challenges existing assumptions in political theory, namely that national identity requires national pride, that national shame comes from bad actions towards outside groups, and that national responsibility means responsibility for those bad actions. Postcolonial and decolonial literature have tended to attribute any perception of inferiority on the part of the colonized to “internalized inferiority,” and to assume the existence of an indigenous “original” culture that colonizers destroy, overlooking the fact that natives themselves sometimes questioned the existence of “original” culture. Ninh shows that colonized people can be ashamed of lacking intellectual culture on their own terms and be anti-colonial at the same time

Perturbation Detection Through Modeling of Gene Expression on a Latent Biological Pathway Network: A Bayesian hierarchical approach

Cellular response to a perturbation is the result of a dynamic system of biological variables linked in a complex network. A major challenge in drug and disease studies is identifying the key factors of a biological network that are essential in determining the cell's fate. Here our goal is the identification of perturbed pathways from high-throughput gene expression data. We develop a three-level hierarchical model, where (i) the first level captures the relationship between gene expression and biological pathways using confirmatory factor analysis, (ii) the second level models the behavior within an underlying network of pathways induced by an unknown perturbation using a conditional autoregressive model, and (iii) the third level is a spike-and-slab prior on the perturbations. We then identify perturbations through posterior-based variable selection. We illustrate our approach using gene transcription drug perturbation profiles from the DREAM7 drug sensitivity predication challenge data set. Our proposed method identified regulatory pathways that are known to play a causative role and that were not readily resolved using gene set enrichment analysis or exploratory factor models. Simulation results are presented assessing the performance of this model relative to a network-free variant and its robustness to inaccuracies in biological databases