Strajki nauczycieli i walka o to, co wspólne

To celebrate the 10th anniversary of Praktyka Teoretyczna journal, we have invited our long-lasting collaborators and comrades to reflect once again on the concept of the common and it’s possible futures by posing the following questions: a) what is the most important aspect of the current struggles for the common?; b) what are the biggest challenges for the commonist politics of the future?; and c) where in the ongoing struggles do you see a potential for scaling-up and spreading organisation based on the common? In his reply, Eric Blanc draws our attention to contemporary teachers strikes as a movement with radical potentialities that greatly exceed merely reversing the privatization process of education.Z okazji 10 urodzin Praktyki Teoretycznej zaprosiliśmy naszych wieloletnich współpracowników i towarzyszy do wspólnego rozważenia przyszłości tego, co wspólne. Poprosiliśmy ich o zmierzenie się z następującymi pytaniami: a) co jest najważniejszym aspektem współczesnych walk o to, co wspólne?; b) jakie największe wyzwania stoją w przyszłości przed polityką tego, co wspólne?; c) gdzie w ramach toczonych walk wiedziecie potencjał na rozwijanie i poszerzanie organizacji opartej na tym, co wspólne? Eric Blanc, skupiający się na przebiegu strajków nauczycieli w Stanach Zjednoczonych, zwraca naszą uwagę na radykalną potencjalność tych walk, które przyjmują postać walki o to, co wspólne

Why Family Farms Are Increasingly Using Wage Labour?

In many developed countries, the share of wage employment out of the total agricultural labour force has been increasing for the last ten years. Using data from French agricultural censuses, we present an analysis of the factors that influence households' decisions about whether to work on the family farm or to work outside, and about the use of wage labour. Studying how the effects of these factors have varied between 1988 and 2000 enables us to highlight the different mechanisms that have led to an increase in permanent wage employment during that period. In particular, we show that family labour and permanent wage labour have become nearly equivalent in 2000, whereas that was not the case in 1988.agricultural employees, farms, family labour, Labor and Human Capital, C34, C35, J22, J43,

Empirical propagation laws of intergranular corrosion defects affecting 2024 T351 alloy in chloride solutions

In the present work, a first attempt was made to determine propagation laws of intergranular corrosion defects for Al 2024 T351 in various NaCl solutions as a first step for future predictive modeling of 2024 alloy. In a first step, the effect of chloride concentration on the susceptibility to intergranular corrosion of 2024 alloy was studied using current–potential curves. In a second step, conventional immersion tests were performed in chloride-containing solutions and statistical analysis was carried out to determine the depth of the intergranular corrosion defects, depending on the chloride concentration and on the immersion time. The results were compared to those obtained by measuring the load to failure of precorroded tensile specimens versus preimmersion time in a chloride solution. The latter method was selected to measure the depth of the intergranular defects even though results showed that it was not possible to use it for chloride concentrations higher than 3 M and immersion times longer than 1200 h, considering the chloride concentrations and the durations of immersion studied in this work. Thus, empirical propagation laws are proposed for chloride contents as high as 3 M and immersion times as long as 1200 h

Intergranular Corrosion of 2024 Alloy in Chloride Solutions

Experiments were performed to determine the propagation kinetics of intergranular corrosion on 2024 aluminum alloy immersed in 1 and 3 M chloride solutions. Tests consisting of immersion in a corrosive solution followed by optical observations on sectioned samples were carried out. This method was found to be time consuming and led to a lack of reproducibility due to the random nature of the corrosion attacks. Another method proved to be more efficient; it consisted of measuring the load to failure on precorroded tensile specimens vs preimmersion time in an aggressive environment. This method was found to allow the mean depth of the corrosion defects to be determined. Further, in 1 and 3 M chloride solution, intergranular corrosion led to the formation of a nonbearing zone, the thickness of which was equal to the mean depth of the corrosion defects. This corroded zone explained the premature failure of the specimens when a uniaxial tensile stress was applied

Hydrogen embrittlement susceptibility of a high strength steel X80

The present paper deals with hydrogen embrittlement (HE) susceptibility of a high strength steel grade (X80). The respective implication of different hydrogen populations, i.e. adsorbed, dissolved in interstitial sites, trapped on dislocations and/or microstructural elements on the associated embrittlement mechanisms has been addressed through mechanical testing in high pressure of hydrogen gas at room temperature. Tensile tests at various strain rates and hydrogen pressures have been carried out. Moreover, changes of gas (hydrogen or nitrogen) during loading have been imposed in order to get critical experiments able to discriminate among the potential hydrogen embrittlement mechanisms already proposed in the literature. The results of these tests have shown that hydrogen induces several kind of damages including decohesion along ferrite/pearlite interfaces and microcracks initiations on the specimens external surface. It is shown that decohesion is not critical under the loading paths used in the present study. On the contrary, it appears that the external microcracks initiation, followed by a quasi-cleavage fracture, is responsible for the premature failure of the material in high pressure of hydrogen gas. These experimental results have been further discussed by modeling hydrogen diffusion in order to identify hydrogen populations (adsorbed, diffusible or trapped) involved in HE. It was then demonstrated that adsorbed and near surface diffusible hydrogen are mainly responsible for embrittlement

Combined Kelvin probe force microscopy and secondary ion mass spectrometry for hydrogen detection in corroded 2024 aluminium alloy

The capability of Kelvin probe force microscopy (KFM) to detect and locate hydrogen in corroded 2024 aluminium alloy was demonstrated. Hydrogen was introduced inside the 2024 alloy following a cyclic corrosion test consisting of cycles of immersion in 1 M NaCl solution followed by exposure to air at -20 °C. The combination of scanning electron microscopy, secondary ion mass spectrometry and KFM demonstrated that the grain and subgrain boundaries were preferential pathways for the short-circuit diffusion of hydrogen but also acted as a source of hydrogen diffusion in the lattice over distances of up to ten microns with non-negligible desorption when exposed to air at room temperature for 24 h

Investigation of Kelvin probe force microscopy efficiency for the detection of hydrogen ingress by cathodic charging in an aluminium alloy

Detecting and locating absorbed hydrogen in aluminium alloys is necessary for evaluating the contribution of hydrogen embrittlement to the degradation of the mechanical properties for corroded or cathodically hydrogen-charged samples. The capability of Kelvin probe force microscopy (KFM) to overcome this issue was demonstrated. Aluminium alloy samples were hydrogenated by cathodic polarisation in molten salts (KHSO4/NaHSO4.H2O). The presence of absorbed hydrogen was revealed; the affected zone depth was measured by secondary ion mass spectroscopy (SIMS) analyses and KFM measurements

Une technique d'accélération pour la compression fractale d'images

Les techniques fractales de compression d'images souffrent encore aujourd'hui de temps de codage très importants. Nous proposons ici un nouvel algorithme récursif d'optimisation, couplé à un algorithme de compression de type Jacquin. Un prédicat numérique est utilisé pour déterminer quel bloc candidat peut correspondre à un bloc initial donné, ce qui permet d'éviter des comparaisons coûteuses en temps de calcul. La méthode permet d'obtenir des accélérations considérables pour un prédicat simple comme l'inclusion d'histogrammes des niveaux de gris. Elle est de surcroît compatible avec d'autres méthodes d'accélération

Corrosion Damages Induced by Cyclic Exposure of 2024 Aluminum Alloy in Chloride-Containing Environments

This paper focuses on the influence of cyclic exposure to chloride solutions on corrosion damage morphology developed on AA2024. The influence of the temperature during the air exposure periods was studied. Cyclic corrosion tests led to enhanced global corrosion damage compared to continuous immersion tests with residual mechanical properties of corroded samples significantly lower for cyclic tests. The corrosion morphology depended on the exposure conditions. For cyclic tests with air exposure periods at room temperature (CR tests), the corrosion defects were significantly longer; for a cyclic test with air exposure periodsat -20 °C (CF tests), the propagation of corrosion defects was not promoted; however, the density of corroded grain boundaries was markedly increased. For CR samples, the corrosion damage observed was mainly explained taking into account electrochemical processes occurring at the tip of the defect which could be considered as an occluded zone characterized by a chloride-enriched electrolyte and Hþ reduction as major cathodic reaction. For CF tests, the interaction between the stresses induced by the phase transformation of the medium i.e solidification and the hydrogen enrichment of the substrate could be a possible mechanism explaining the evolution of the global mechanical properties of the corroded sample