Hurst's exponent behaviour, weak-form stock market efficiency and financial liberalization: the Tunisian case

In this paper, we test the weak-form stock market efficiency for the Tunisian stock market (TSE). Our empirical approach is founded on the analysis of the behaviour over time of the Hurst's exponent. Thus, we computed the Hurst's exponent using a “rolling sample†with a time window of 4 years. The sample data covers in daily frequency the period (January, 1997- October 2007). Since the classical R/S analysis is strongly affected by short-range dependencies both in the mean and the conditional variance of TSE daily volatility, daily stock returns were filtered using the traditional AR-GARCH(1,1) model. Our results for Hurst's and filtered Hurst's exponents behaviour analysis show a strong evidence of long-range dependence with persistent behaviour of the TSE. However, during the last two years, the filtered Hurst's exponent seems to exhibit a switching regime behaviour with alternating persistent and antipersistent behaviour but where it was somewhat close to 0.5.The nonparametric statistic approach results reveal that some TSE reforms including the launching of the Electronic quotation system on April, 1998, the fiscal regime for holdings, the security reinforcement laws, the legal protection of minority shareholder may play a role in understanding the Hurst's exponent behaviour over timefinancial reforms, long-range dependence; weak-form efficiency; Hurst's exponent; rolling sample approach.

A new kinetic model for predicting polyamide 6-6 hydrolysis and its mechanical embrittlement

PA 6-6 hydrolysis at 60, 70, 80 and 90 °C in distilled water has been studied by Fourier transform infrared spectroscopy, viscometry in molten state, differential scanning calorimetry and uniaxial tensile testing. The molar mass decreases sharply from the early periods of exposure to reach an equilibrium value of about MnE ≈ 10−11 kg mol−1 almost temperature independent. Hydrolytic chain scissions destroy the entanglement network in the amorphous phase and liberate small macromolecular segments which rearrange locally and initiate a chemicrystallisation. As expected, the embrittlement occurs at a very low conversion of the hydrolysis, in particular when the number average molar mass becomes lower than a critical value of about MnF ≈ 17 kg mol−1, i.e. very close to its initial value. A new kinetic model has been derived from the classical mechanistic scheme of reversible hydrolysis. This model describes satisfyingly all the kinetic characteristics of the reversible hydrolysis of PA 6-6 not controlled by water diffusion: decrease in molar mass, increase in crystallinity ratio and decrease in ultimate elongation, but also of other types of polyamides previously studied, such as PA 11. Moreover, when it is used as an inverse method, this model gives access to the rate constants of hydrolysis and condensation reactions. It is thus an interesting tool for elucidating structure/rate constant relationships in common families of hydrolysable polymers

Reconstructing pedigrees using probabilistic analysis of ISSR amplification

Data obtained from ISSR amplification may readily be extracted but only allows us to know, for each gene, if a specific allele is present or not. From this partial information we provide a probabilistic method to reconstruct the pedigree corresponding to some families of diploid cultivars. This method consists in determining for each individual what is the most likely couple of parent pair amongst all older individuals, according to some probability measure. The construction of this measure bears on the fact that the probability to observe the specific alleles in the child, given the status of the parents does not depend on the generation and is the same for each gene. This assumption is then justified from a convergence result of gene frequencies which is proved here. Our reconstruction method is applied to a family of 85 living accessions representing the common broom {\it Cytisus scoparius}.Comment: 5 figure

Una combinación basada en operadores OWA para la Clasificación de Género Multi-etiqueta de páginas web

This paper presents a new method for genre identification that combines homogeneous classifiers using OWA (Ordered Weighted Averaging) operators. Our method uses character n-grams extracted from different information sources such as URL, title, headings and anchors. To deal with the complexity of web pages, we applied MLKNN as a multi-label classifier, in which a web page can be affected by more than one genre. Experiments conducted using a known multi-label corpus show that our method achieves good results.En este trabajo se presenta un nuevo método para la identificación de género que combina clasificadores homogéneos utilizando OWA (promedio ponderado) Pedimos operadores. Nuestro método utiliza caracteres n-gramas extraídos de diferentes fuentes de información, tales como URL, título, encabezados y anclajes. Para hacer frente a la complejidad de las páginas web, se aplicó MLKNN como un clasificador multi-etiqueta, en el que una página web puede verse afectada por más de un género. Los experimentos llevados a cabo usando un conocido corpus multi-etiqueta muestran que nuestro método logra buenos resultados

Thermal oxidation kinetics of additive free polyamide 6-6

Thermal aging of an additive free PA 6-6 has been elucidated at 90, 100, 120, 140, 150 and 160 C in airventiled ovens by Fourier transform infrared spectrophotometry, viscosimetry in molten state and uniaxial tensile testing. Oxidation of methylene groups starts after a considerably shorter induction period but reaches a lower maximal rate than in additive free PE. Cleavage of CeN bonds constitutes the main source of chain scissions. It leads to the formation of aldehyde chain-ends and a catastrophic decrease in molar mass. Embrittlement occurs at a very low conversion ratio of the oxidation process, in particular when the concentration of aldehyde chain-ends reaches a critical value of [PH¼O]F z 5.6 10 3 mol l 1, corresponding to a critical value of the number average molar mass ofMnFz17 kg mol 1. At this stage, the entanglement network in the amorphous phase is deeply damaged. A non-empirical kinetic model has been derived from the oxidation mechanistic scheme previously established for PE, but improved by adding elementary reactions specific to polyamides such as the rapid decomposition of unstable hydroxylated amide groups. This model describes satisfyingly the main features of the thermal oxidation kinetics of PA 6-6, but also of other types of aliphatic polyamides studied previously in the literature such as: PA 6, PA 12 and PA 4-6, as long as it is not controlled by oxygen diffusion. At the same time, it confirms the existence of an universal character for the thermal oxidation kinetics of aliphatic polyamides whatever their origin, i.e. their initial molar mass, crystallinity ratio, concentration of impurities, structural irregularities, etc

Corporate Social Responsibility and its importance from the general to the hospitality sectors: A Literature Review

Corporate Social Responsibility (CSR) policy operates as the self-regulatory system in which a company observes and makes sure it is active in terms of compliance with national norms, ethical standards and the spirit of the law. Williams, Sheridan, and McLean (2019) point out that CSR is a corporate method which is aimed at leading to sustainable development by providing environmental, social and economic benefits for every stakeholder involved. With certain models, a company's implementation of CSR goes beyond compliance, and involves actions which seems to add some social betterment, beyond the benefits of the company and that which is needed by regulation. The motive is to upsurge long-run profits through shareholder trust by taking accountability for business activities, high ethical morals to decrease legal and business risk, and ensure positive public relations. According to Huda et al. (2018), CSR tactics motivate the business to have a fruitful influence on the stakeholders and environment including communities, investors, employees, and consumers. (...