61 research outputs found
Towards Tuning-Free Minimum-Volume Nonnegative Matrix Factorization
Nonnegative Matrix Factorization (NMF) is a versatile and powerful tool for
discovering latent structures in data matrices, with many variations proposed
in the literature. Recently, Leplat et al.\@ (2019) introduced a minimum-volume
NMF for the identifiable recovery of rank-deficient matrices in the presence of
noise. The performance of their formulation, however, requires the selection of
a tuning parameter whose optimal value depends on the unknown noise level. In
this work, we propose an alternative formulation of minimum-volume NMF inspired
by the square-root lasso and its tuning-free properties. Our formulation also
requires the selection of a tuning parameter, but its optimal value does not
depend on the noise level. To fit our NMF model, we propose a
majorization-minimization (MM) algorithm that comes with global convergence
guarantees. We show empirically that the optimal choice of our tuning parameter
is insensitive to the noise level in the data
The effect of cold work on the transformation kinetics and texture of a zirconium alloy during fast thermal cycling
Determinants Influencing Entrepreneurial Intention in Hanoi, Vietnam
This research employed survey data from 204 students between two groups of economics and technical majors in Hanoi city for assessing the impact levels of determinants on entrepreneurial intention. The results show that a number of determinants including Need for achievement, Self-efficacy, and Instrumental readiness have positive impacts on student’s entrepreneurial intention. Besides, this study is also to create a basis for comparative students among different economics and technical majors, work exoperience, and gender. These findings are the basis to recommend policies and solutions to promote entrepreneurship movement in Vietnam. Keywords: Entrepreneurial intention, need for achievement, self-efficacy, instrumental readiness. DOI: 10.7176/EJBM/12-15-10 Publication date:May 31st 2020
Cold Creep of Titanium: Analysis of stress relaxation using synchrotron diffraction and crystal plasticity simulations
There is a long standing technological problem in which a stress dwell during
cyclic loading at room temperature in Ti causes a significant fatigue life
reduction. It is thought that localised time dependent plasticity in soft
grains oriented for easy plastic slip leads to load shedding and an increase in
stress within a neighbouring hard grain poorly oriented for easy slip.
Quantifying this time dependent plasticity process is key to successfully
predicting the complex cold dwell fatigue problem. This work uses a novel
approach of in situ synchrotron X-ray diffraction during stress relaxation
tests, to quantify the time dependent plasticity. Measured lattice strains from
multiple lattice families (21 diffraction rings) were compared with simulated
lattice strains from crystal plasticity finite element (CPFE) simulations. The
prism slip parameters were found to show stronger strain rate sensitivity
compared to basal slip, and this has a significant effect on stress
redistribution to hard grain orientations during cold creep
Probabilistic Schema Covering
Schema covering is the process of representing large and complex schemas by easily comprehensible common objects. This task is done by identifying a set of common concepts from a repository called concept repository and generating a cover to describe the schema by the concepts. Traditional schema covering approach has two shortcomings: it does not model the uncertainty in the covering process, and it requires user to state an ambiguity constraint which is hard to define. We remedy this problem by incorporating probabilistic model into schema covering to generate probabilistic schema cover. The integrated probabilities not only enhance the coverage of cover results but also eliminate the need of defining the ambiguity parameter. Both probabilistic schema covering and traditional schema covering run on top of a concept repository. Experiments on real-datasets show the competitive performance of our approach
Bootstrapping Uncertainty in Schema Covering
Schema covering is the process of representing large and complex schemas by easily comprehensible common objects. This task is done by identifying a set of common concepts from a repository called concept repository and generating a cover to describe the schema by the concepts. Traditional schema covering approach has two shortcomings: it does not model the uncertainty in the covering process, and it requires user to state an ambiguity constraint which is hard to define. We remedy this problem by incorporating probabilistic model into schema covering to generate probabilistic schema cover. The integrated probabilities not only enhance the coverage of cover results but also eliminate the need of defining the ambiguity parameter. Experiments on real-datasets show the competitive performance of our approach
IMPROVEMENT OF CO2 PURIFYING SYSTEM BY PHOTOCATALYST FOR APPLICATION IN MICROALGAE CULTURE TECHNOLOGY
By reactive grinding method Vanadium-doped rutile TiO2 nanoparticle material was obtained with an average particle size of 20‐40nm, the Brunauer–Emmet–Teller (BET) specific surface area about 20 m2g−1 and it absorbed strongly in the UV region and increased at the visible wavelength of 430 – 570 nm. This study focused on the improvement of exhaust gas treatment from coal-fired flue gas of the traditional adsorption-catalysis system (Modular System for Treating Flue Gas - MSTFG) by using the V2O5/TiO2 Rutile as photocatalyst. The results showed that integrating both catalytic systems mentioned above increased the gas treatment efficiency: CO from 77 % to over 98 %, NOx from 50 % to 93 %, SO2 was absent as opposed to the input gas component. Also it showed that V2O5/TiO2 Rutile integrated with MSTFG has got high efficiency of CO treatment, also secured the high obtained CO2 concentration as a valuable carbon source for microagal mass culture as well as saving energy and simplifying devices
An in-situ synchrotron diffraction study of stress relaxation in titanium:Effect of temperature and oxygen on cold dwell fatigue
There is a long-standing technological problem in which a stress dwell during cyclic loading at room temperature in Ti causes a drastic fatigue life reduction. To better understand the material characteristics that control or exacerbate this behaviour, evaluation of the time dependent plasticity of the main prismatic and basal slip systems is critical. Incorporating the influence of operating temperatures and common alloying elements on cold dwell fatigue will be beneficial for future alloy design to address this problem. In this work, characterisation of the time dependent plastic behaviour of two commercially pure titanium samples (grade 1 and grade 4) with different oxygen content at 4 different temperatures (room temperature, 75 , 145 and 250 ) was performed during stress relaxation using synchrotron X-ray diffraction. Key parameters that govern the dislocation motion were determined for the major prismatic and basal slip systems as a function of temperature and oxygen content by calibrating a crystal plasticity finite element model with the measured lattice strain relaxation responses. From the temperatures assessed, 75 was found to be the worst-case scenario, where the macroscopic plastic strain accumulation was significant during a relaxation cycle due to the greatest activity of both prism and basal slip systems. As the temperature increases, the contribution of thermal energy becomes greater than mechanical energy for dislocation glide. Oxygen was found to have a stronger strengthening effect on prism slip over basal slip, through a significant change in their respective critical resolved shear stresses. This effect becomes more significant in high oxygen content commercially pure Ti
- …