The Power of Randomization: Distributed Submodular Maximization on Massive Datasets

A wide variety of problems in machine learning, including exemplar clustering, document summarization, and sensor placement, can be cast as constrained submodular maximization problems. Unfortunately, the resulting submodular optimization problems are often too large to be solved on a single machine. We develop a simple distributed algorithm that is embarrassingly parallel and it achieves provable, constant factor, worst-case approximation guarantees. In our experiments, we demonstrate its efficiency in large problems with different kinds of constraints with objective values always close to what is achievable in the centralized setting

Crack growth modelling: enriched continuum vs. discrete models

Failure in quasi-brittle materials usually appears in the form of narrow bands called fracture process zones, where all inelastic deformation takes place, while the surrounding bulk material outside those areas typically unloads elastically. This localised nature of failure is the main source of size effects in these materials, since the width of the fracture process zone is a material property that does not scale with the size of the material volume. An adequate description of localised failure and associated size effects requires both size and behaviour of the fracture process zone and neighbouring material to be properly taken into account. In this study, we present two alternative approaches for modelling localised failure and simulating fracture propagation using finite element methods. In the first approach, an embedded crack appears at a constitutive level by enriching the kinematics of constitutive models, while in the second one this is done at the finite element level using cohesive interface elements. The advantages and shortcomings of both are presented through one numerical example on the failure of fibre-reinforced composite materials

A New Framework for Distributed Submodular Maximization

A wide variety of problems in machine learning, including exemplar clustering, document summarization, and sensor placement, can be cast as constrained submodular maximization problems. A lot of recent effort has been devoted to developing distributed algorithms for these problems. However, these results suffer from high number of rounds, suboptimal approximation ratios, or both. We develop a framework for bringing existing algorithms in the sequential setting to the distributed setting, achieving near optimal approximation ratios for many settings in only a constant number of MapReduce rounds. Our techniques also give a fast sequential algorithm for non-monotone maximization subject to a matroid constraint

A cell-based smoothed finite element method for kinematic limit analysis

This paper presents a new numerical procedure for kinematic limit analysis problems, which incorporates the cell-based smoothed finite element method with second-order cone programming. The application of a strain smoothing technique to the standard displacement finite element both rules out volumetric locking and also results in an efficient method that can provide accurate solutions with minimal computational effort. The non-smooth optimization problem is formulated as a problem of minimizing a sum of Euclidean norms, ensuring that the resulting optimization problem can be solved by an efficient second-order cone programming algorithm. Plane stress and plane strain problems governed by the von Mises criterion are considered, but extensions to problems with other yield criteria having a similar conic quadratic form or 3D problems can be envisaged

Avec Orima - Designing the brand identity

The thesis is a document in building the brand image for the authors’ own start-up Avec Orima. It is motivated by the need to take the company from the planning stage to the next very first step of implementing the business – designing the company’s brand identity. The thesis focused on the process of designing the brand identity. The process began with analysing the company and Finnish target market to have the insights on what the company stands for and wants to achieve. The study then continued to examine the competition in Finnish market and identify the points of differences, in order to establish the brand positioning. Upon understanding the Avec Orima brand and what it stands for, the thesis study integrated the brand identity strategy with design skills to create the basic elements of Avec Orima’s visual brand identity – logotype, typography, colours, look and feel, and imagery. Using a sample of 57 people, the authors collected data from a survey. Also, data from market research was presented. As predicted, the results justify the authors’ points on the existing behaviours, trends and rising demands in Finnish market. The authors conclude that, despite a limitation in existing customer behaviours at the moment, there are rising awareness and demand for such a service provider like Avec Orima. This conclusion is the foundation for all further studies, which are based on theoretical data, in defining the company, then brand positioning and brand identity design

Semi-active suspension control problem: some new results using an LPV /H ∞ state feedback input constrained control

International audience— The semi-active suspension control problem faces the challenge of the dissipativity constraints of the semi-active dampers. This induces some compromises (actuator saturation, comfort, road holding...) which need to be taken into account in the control design step. In this paper, a state feedback input constrained control problem for LPV systems is considered with H ∞ performance objective. Stabilization conditions based on the Finsler's Lemma are derived in order to ensure the stability in the presence of the input saturation, and to attenuate the disturbance effects. To this aim, two different Lyapunov functions are used. For the stability analysis, a generalized sector condition for LPV systems is applied to treat the nonlinearity caused by the actuator saturation. The considered performance objective regards the reduction of L 2 gain from the disturbance to the controlled output. The LPV controller is computed from the solution of LMIs considering a polytopic representation for the LPV closed-loop system. These theoretical results are applied to a semi-active suspension system where the dissipativity conditions of the semi-active dampers are recast as saturation conditions on the control inputs. The comfort criteria is used as a performance objective in this study. Some simulation results are presented in order to illustrate the effectiveness of the proposed approach

Inner retinal inhibition shapes the receptive field of retinal ganglion cells in primate

The centre-surround organisation of receptive fields is a feature of most retinal ganglion cells (RGCs) and is critical for spatial discrimination and contrast detection. Although lateral inhibitory processes are known to be important in generating the receptive field surround, the contribution of each of the two synaptic layers in the primate retina remains unclear. Here we studied the spatial organisation of excitatory and inhibitory synaptic inputs onto ON and OFF ganglion cells in the primate retina. All RGCs showed an increase in excitation in response to stimulus of preferred polarity. Inhibition onto RGCs comprised two types of responses to preferred polarity: some RGCs showed an increase in inhibition whilst others showed removal of tonic inhibition. Excitatory inputs were strongly spatially tuned but inhibitory inputs showed more variable organisation: in some neurons they were as strongly tuned as excitation, and in others inhibitory inputs showed no spatial tuning. We targeted one source of inner retinal inhibition by functionally ablating spiking amacrine cells with bath application of tetrodotoxin (TTX). TTX significantly reduced the spatial tuning of excitatory inputs. In addition, TTX reduced inhibition onto those RGCs where a stimulus of preferred polarity increased inhibition. Reconstruction of the spatial tuning properties by somatic injection of excitatory and inhibitory synaptic conductances verified that TTX-mediated inhibition onto bipolar cells increases the strength of the surround in RGC spiking output. These results indicate that in the primate retina inhibitory mechanisms in the inner plexiform layer sharpen the spatial tuning of ganglion cells. © 2013 The Physiological Society

Production et utilisation des amidons de manioc dans les villages métiers du delta du fleuve rouge

Au Vietnam, différentes échelles de valorisation de l'amidon de manioc coexistent, à savoir : l'extraction d'amidon des racines et ses utilisations ultérieures dans les filières alimentaires et pharmaceutiques. Une étude diagnostique réalisée dans les villages métiers du delta du fleuve rouge, a montré qu'il existait à cette échelle, de nombreuses utilisations de l'amidon de manioc et de ses produits dérivés. Toutefois, une évaluation de la qualité des amidons pourra être réalisée pour mieux comprendre les modes d'utilisation de ces produits tout au long de l'année. (Résumé d'auteur

Market returns to acquirers of substantial assets

Does poor post-acquisition performance characterise firms that make non-M&A acquisitions? We investigate the wealth effects of substantial asset acquisitions (i.e. acquisitions that cost over $10 million) on acquiring firms' shareholders. We find significant abnormal positive market reaction to asset acquisition announcements and, contrary to findings for firms undertaking M&As, the acquiring firms perform exceptionally well post-acquisition. Our findings are robust to the research method weaknesses common to many studies of long-term performance and we control for free-cash-flow as well. Our results contradict the hubris hypothesis of acquisitions and lend weight to the argument that the auction-style process that characterizes corporate takeover bids contributes to overpayment