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La transición hacia el uso del papel para la enseñanza de la escritura en las escuelas elementales públicas en México no fue sencilla. Al finalizar el siglo XIX, se había cuestionado el uso de las pizarras por el riesgo que representaban para la salud, pues muchas veces los estudiantes borraban sus escritos con saliva y el material con el que estaban fabricadas no siempre guardaba las especificaciones necesarias, además el ruido al escribir era insoportable. En cambio, el papel, desde el punto de vista higiénico, pedagógico y estético, fue considerado un material superior frente a la dureza de la pizarra, el brillo de la superficie y la poca precisión que se obtenía en el trazo de las letras. Derivado de este planteamiento, se vislumbró seriamente la posibilidad de la adopción de papel en las escuelas oficiales. Sin embargo, este material era escaso y muy caro. Hacia el cambio de siglo, sólo dos fábricas de papel podían surtir a las escuelas y era necesario que abarataran el precio, que el sistema de distribución garantizara el abastecimiento y que el suministro fuera continuo. Este artículo analiza el inicio del proceso de reconversión de una tecnología para la enseñanza como era la pizarra por el papel. Analizo el gasto que significó y cómo esta modificación fue resultado de una multiplicidad de relaciones sociales, culturales, económicas y políticas que se entrecruzaron para dar una nueva configuración del tiempo, el ruido y los valores establecidos en el salón de clases. The transition to the use of paper in public elementary schools in Mexico was not easy. At the end of the nineteenth century, the use of slates had been questioned due to the health risk they represented since students often erased their writing with saliva and the material with which the slates were made did not always meet the necessary specifications. On the other hand, paper, from a hygienic, pedagogical and aesthetic point of view, was considered a superior material compared to the hardness of the slate, the shine of the surface and the lack of precision obtained in the tracing of the letters. Derived from this approach, the possibility of changing materials in official schools was seriously envisioned. However, the paper represented a very high cost. Only two paper mills could supply the schools and it was necessary to lower the price, and guarantee the supply by enhancing the distribution system. This article analyses the beginning of the conversion process of a technology for learning to write such as the slate for paper. I analyse the expense that it meant for the authorities and families, how the change was the result of a multiplicity of social, cultural, economic and political relations that intersected to give a new configuration of time, noise and established values in the classroom. [ABSTRACT FROM AUTHOR]

Abstract The subgrade crushed-rocks of Gonghe-Yushu (Gongyu) Expressway in Qinghai Province are seriously weathered, resulting in a series of pavement diseases. Among the weathered crushed-rocks, the weathering degree of slate is particularly serious, and its physical and mechanical properties, weathering resistance and applicability are not clear. Therefore, this paper takes the slate in the subgrade crushed-rocks of Gongyu Expressway as the research object, and drills the core of the slate rock block to make a cylindrical standard sample, and uniaxial and triaxial compression tests, nuclear magnetic resonance tests, and electron probe micro-analysis tests were performed on it within 50 freeze–thaw cycles (FTC) under saturated conditions. According to the test results, the mass, longitudinal wave velocity, and strength of the slate specimens all decrease with the increase of the number of FTC, the cohesion $$({\text{C}})$$ ( C ) increases first and then decreases, and the change trend of internal friction angle (φ) is completely opposite to the cohesion. The FTC has an expansion effect on the pores of the slate specimens, and the microstructure of the rock particles on the specimen’s surface is removed and becomes smooth. The results of mechanical tests are used in the Hoek–Brown (H-B) strength criterion, and a unified expression of the H-B criterion suitable for slate in permafrost regions is established. The above conclusions can provide some construction reference and maintenance of high-grade highways in cold regions.

Using over 20,000 electoral slates from municipal elections in the Czech Republic, we document that in proportional representation electoral systems political parties rank candidates on the slates systematically according to their valence, measured by educational attainment, and intra-party value, measured by political donations and membership. The observed patterns are consistent with market mechanisms where the party leaders benefit from the valence and intra-party value of candidates and offer slate positions (i.e. the probability of winning a mandate) in exchange. We show that candidates with high valence and those who possess more intra-party value are placed in better-ranked positions, despite the fact that candidates with more intra-party value, conditional on observables, tend to receive relatively fewer votes than candidates with low intra-party value. We further show that as a party expects to hold more council seats, the share of their candidates with higher intra-party value increases. [ABSTRACT FROM AUTHOR]

Slate typically possesses a pronounced layered structure and tends to soften when exposed to water, leading to numerous detrimental effects on the construction of related underground projects. In this study, X-ray diffraction (XRD) analysis was first performed to investigate the mineral composition of the typical slate from Changsha, China. Then, uniaxial and triaxial compression tests under varying bedding angles (i.e., 0°, 30°, 45°, 60°, and 90°) and moisture levels (i.e., dry state, natural state, and saturated state) were conducted to explore the anisotropy characteristics and susceptibility to water-induced softening of the slate. The results reveal that: (1) The exposure of slate to water exacerbates the deterioration of its layered structure, making it more prone to shear failure along the bedding planes. Furthermore, the energy released during shear-slip damage is reduced, which is macroscopically manifested by the decrease in slate brittleness and the increase in plasticity. (2) The slate's compressive strength, elastic modulus, and cohesion vary in a U-shaped pattern with the increase in bedding angles. However, Poisson's ratio and internal friction angle are slightly affected by the bedding angle and water content, which do not exhibit a clear variation pattern. (3) In addition, the formulations for strength and stiffness predictions of slate were also discussed in this study. The results show that the modified Hoek–Brown criterion characterizes the uniaxial and triaxial compressive strengths of slate more accurately, and the generalized Hooke's Law more effectively predicts the elastic modulus. [ABSTRACT FROM AUTHOR]