다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

Collinearity refers to the non independence of predictor variables, usually in a regression-type analysis. It is a common feature of any descriptive ecological data set and can be a problem for parameter estimation because it inflates the variance of regression parameters and hence potentially leads to the wrong identification of relevant predictors in a statistical model. Collinearity is a severe problem when a model is trained on data from one region or time, and predicted to another with a different or unknown structure of collinearity. To demonstrate the reach of the problem of collinearity in ecology, we show how relationships among predictors differ between biomes, change over spatial scales and through time. Across disciplines, different approaches to addressing collinearity problems have been developed, ranging from clustering of predictors, threshold-based pre-selection, through latent variable methods, to shrinkage and regularisation. Using simulated data with five predictor-response relationships of increasing complexity and eight levels of collinearity we compared ways to address collinearity with standard multiple regression and machine-learning approaches. We assessed the performance of each approach by testing its impact on prediction to new data. In the extreme, we tested whether the methods were able to identify the true underlying relationship in a training dataset with strong collinearity by evaluating its performance on a test dataset without any collinearity. We found that methods specifically designed for collinearity, such as latent variable methods and tree based models, did not outperform the traditional GLM and threshold-based pre-selection. Our results highlight the value of GLM in combination with penalised methods (particularly ridge) and threshold-based pre-selection when omitted variables are considered in the final interpretation. However, all approaches tested yielded degraded predictions under change in collinearity structure and the ‘folk lore’-thresholds of correlation coefficients between predictor variables of |r| >0.7 was an appropriate indicator for when collinearity begins to severely distort model estimation and subsequent prediction. The use of ecological understanding of the system in pre-analysis variable selection and the choice of the least sensitive statistical approaches reduce the problems of collinearity, but cannot ultimately solve them.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1600-0587.2012.07348.x

Collinearity: a review of methods to deal with it and a simulation study evaluating their performance

1. Introduction and Overview. 2. Detecting Influential Observations and Outliers. 3. Detecting and Assessing Collinearity. 4. Applications and Remedies. 5. Research Issues and Directions for Extensions. Bibliography. Author Index. Subject Index.

Regression Diagnostics: Identifying Influential Data and Sources of Collinearity

Investigation of equilibria in solution. Determination of equilibrium constants with the HYPERQUAD suite of programs.

In recent years, both industrial and academic world are focussing their attention toward the development of sustainable composites, reinforced with natural fibres. In particular, among the natural fibres (i.e. animal, vegetable or mineral) that can be used as reinforcement, the basalt ones represent the most interesting for their properties. The aim of this review is to illustrate the results of research on this topical subject. In the introduction, mechanical, thermal and chemical properties of basalt fibre have been reviewed. Moreover, its main manufacturing technologies have been described. Then, the effect of using this mineral fibre as reinforcement of different matrices as polymer (both thermoplastic and thermoset), metal and concrete has been presented. Furthermore, an overview on the application of this fibre in biodegradable matrix composites and in hybrid composites has been provided. Finally, the studies on the industrial applications of basalt fibre reinforced composites have been reviewed.

A review on basalt fibre and its composites

Influence of thermal treatment on tensile failure of basalt fibers

Crucial problems in regression modelling and their solutions

Nanocellulose coated woven jute/green epoxy composites: Characterization of mechanical and dynamic mechanical behavior

This work presents the short term creep behavior of novel treated jute fabric reinforced green epoxy composites. Jute fabric was treated with CO 2 pulsed infrared laser, ozone, enzyme and plasma. The treated jute fibers were characterized by scanning electron microscopy (SEM). Composites were prepared by hand layup method and compression molding technique. The creep and dynamic mechanical tests were performed in three-point bending mode by dynamic mechanical analyzer (DMA). The creep strain was experiential to increase with temperature. The treated composites exhibited less creep strain than untreated one at all temperatures. The best result in terms of creep deformation is presented by laser treated composite which dominantly exhibited elastic behavior rather than viscous behavior, especially at higher temperatures. The Burgers four parameters model was used to fit the experimental creep data using R statistical computing software. A good agreement between experimental data and theoretical curves were obtained. Dynamic mechanical analysis results revealed the reduction in the tangent delta peak height of treated composites, might be due to improvement in fiber/matrix interfacial adhesion. The degree of interfacial adhesion between the jute fiber and green epoxy was also anticipated using adhesion factor obtained through DMA data and laser treated composite revealed the better interlocking of fibers and matrix at the interface.

Jiří Militký

Papers

Influence of thermal treatment on tensile failure of basalt fibers

Crucial problems in regression modelling and their solutions

Nanocellulose coated woven jute/green epoxy composites: Characterization of mechanical and dynamic mechanical behavior

Comparative evaluation of fiber treatments on the creep behavior of jute/green epoxy composites

The boundary conditions for kinetic models