Chordal Decomposition in Rank Minimized Semidefinite Programs with Applications to Subspace Clustering

Semidefinite programs (SDPs) often arise in relaxations of some NP-hard problems, and if the solution of the SDP obeys certain rank constraints, the relaxation will be tight. Decomposition methods based on chordal sparsity have already been applied to speed up the solution of sparse SDPs, but methods for dealing with rank constraints are underdeveloped. This paper leverages a minimum rank completion result to decompose the rank constraint on a single large matrix into multiple rank constraints on a set of smaller matrices. The re-weighted heuristic is used as a proxy for rank, and the specific form of the heuristic preserves the sparsity pattern between iterations. Implementations of rank-minimized SDPs through interior-point and first-order algorithms are discussed. The problem of subspace clustering is used to demonstrate the computational improvement of the proposed method.Comment: 6 pages, 6 figure

Evaluación de las Prestaciones de una Red WiMAX Móvil en un Escenario de Alta Movilidad

The aim of this paper is to evaluate the performance of mobile WiMAX technology for users in a highly mobility scenario for an operating frequency of 3.5 GHz. By utilizing a modified version of the extended Erceg’s propagation model, based on the introduction of Rayleigh fading due to multipath, we have calculated the received desired power and the interference power to obtain the statistical signal-to-interference-plusnoise rate (as a function of mean value and variance of cochannel interference) and the user throughput. A rural scenario composed of a transmitting base station and users in moving vehicles along a cell sector is proposed. The obtained results about coverage and throughput have been simulated by a tool built in MATLA

Heavy ion irradiation damage in Zr3(Al0.9Si0.1)C2 MAX phase

© 2020 Elsevier B.V. A Zr3(Al0.9Si0.1)C2 MAX phase-based ceramic with 22 wt.% ZrC and 10 wt.% Zr5Si3 has been irradiated with 52 MeV I9+ ions at room temperature, achieving a maximum dose of 8 displacements per atom (dpa). The response of this MAX phase-rich material to irradiation has been studied using scanning electron microscopy, transmission electron microscopy and X-ray diffraction techniques. Post-irradiation examination of the material revealed a number of crystalline changes to the MAX phase. At low doses, Zr3(Al0.9Si0.1)C2 maintained a high degree of crystallinity, while at the highest doses, its degree of crystallinity was reduced significantly. A number of radiation-induced phase transformations were observed, including the decomposition of Zr3(Al0.9Si0.1)C2 into ZrC and other phases, and the formation of β-Zr3(Al,Si)C2, a MAX phase with a rearranged stacking sequence. Microstructural examination revealed that the majority of the extended defects in Zr3(Al0.9Si0.1)C2 lie in the (0001) basal planes. Analysis of X-ray diffraction profiles after heat treating the 8 dpa-irradiated material for 1 h at 300 °C and at 600 °C showed that there were only subtle changes to the profiles relative to that of the 8 dpa-irradiated material which had not been heat treated. Overall, the experimental results of this study show that the Zr3(Al0.9Si0.1)C2 MAX phase responds less well to irradiation relative to other MAX phases irradiated with high energy heavy ions at room temperature

High temperature creep of 20 vol.% SiC-HfB2 UHTCs up to 2000 °C

High temperature compressive creep of SiC-HfB2 UHTCs up to 2000 °C has been studied. Microstructural analysis after deformation reveals formation of new phases in the Hf-B-Si and Hf-B-Si-C systems, which are responsible for the poor creep resistance. RE oxide additions have a negative effect reducing the creep resistance of SiC-HfB2 UHTCs. A simplistic analysis for the required creep resistance is described, indicating that only SiC-HfB2 UHTCs could withstand re-entry conditions for 5 min in a single use. However, RE oxide addition to SiC-HfB2 UHTCs does not provide the required creep resistance for them to be candidate materials for hypersonic applications

Diffusion-driven superplasticity in ceramics: Modeling and comparison with available data

The discovery of superplasticity in ceramics polycrystals led to debates about whether or not earlier models developed for metallic polycrystals can apply to these systems. In particular, all existing models require some mobility of lattice or grain-boundary dislocations whereas such activity is not observed in most ceramic systems. A model is presented that accounts for the occurrence of superplasticity in the absence of dislocation motion. It is based on a mechanism of grain-boundary sliding by pure-shear motion under stationary conditions, which is accommodated by lattice or grain-boundary diffusion. The prediction of this model regarding the temperature dependences of the stress exponent and of the effective activation energy are found in agreement with experimental results and literature data on five ceramic systems where dislocation activity could not be recorded: -SiAlON polycrystals, Al-doped SiC polycrystals, nanocrystalline MgO, yttria-tetragonal zirconia polycrystals, and alumina ceramics polycrystal

The spanish equality law and the gender balance in the evaluation committees: an opportunity for women’s promotion in higher education

Despite advances in gender policy and equality laws in the twenty-first century, women are still a minority in the full professor category in Europe. Some measures establish gender quotas to balance gatekeeper positions, which will supposedly pave the way to make women’s integration into senior higher education positions easier. In Spain, Organic Act 3/20071 of 22 March on effective equality between women and men launched progressive norms governing gender issues, and the Spanish Science and Technology Act (2011) incorporated measures to promote effective equality in academic institutions. This paper evaluates how Spanish evaluation agencies’ compliance with implementing gender balance has affected the composition of evaluation committees and its impact on the advancement of women in science. Findings reveal some positive figures on women’s representation in recent decades, even though gender-balanced committees do not show any clear evidence of causing this effect. There seems to be no correlation between gender-balanced committees and women’s success rates, suggesting intermediate variables affect women’s low participation in competitive submissions. It explores several factors concerning two agencies’ evaluation procedures, such as formality and transparency, direct/multiple gatekeeping processes, the influence of epistemic cultures, cohorts and confidence of female candidates.Postprint (author's final draft

How to diagnose equal opportunities between women and men in organizations

Gender equality is now a matter that concerns all European countries. Despite the great effort made by governments and the progress of laws, gender discrimination still exists in family, social, cultural, political and economic spheres. Even today, it is rare to find women at the top level in companies. The path to equal opportunities is long and the only way to improve the situation is by means of appropriate equal opportunities plans. An essential part of the process of designing and implementing such action plans involves diagnosing the situation in a company. In this paper, an innovative indicator model is proposed. A review of numerous international private and public equal opportunities plans led to the design of a model to carry out a diagnose to identify all areas that could be corrected or improved by implementing specific measures, leading the company to deliver real equal opportunities policies. The indicator model is designed for the present historical context, though it is flexible enough to be adapted to each age and situation. The indicator model, which is original, will help companies carrying out one of the most important and essential parts of the process of designing and implementing and equal opportunities plan. Moreover, taking the indicator model companies ensure that all the relevant features are coveredPeer Reviewe