Efeitos do tratamento superficial da sílica ativa com soluções de ácidos nítrico e fosfórico em propriedades do concreto

The addition of active silica potentially improves the quality of concrete due to its high reactivity and pore refinement effect. The reactivity of silica is likely related to its charge density. Variations in surface charge alter the reactivity of the material consequently affecting the properties of concrete. The present study aimed at investigating variations in the charge density of silica as a function of acid treatments using nitric or phosphoric acid and different pH values (2.0, 4.0 and 6.0). Effects on concrete properties including slump, mechanical strength, permeability and chloride corrosion were evaluated. To that end, a statistical analysis was carried out and empirical models that correlate studied parameters (pH, acid and cement) with concrete properties were established. The quality of the models was tested by variance analysis. The results revealed that the addition of silica was efficiency in improving the properties of concrete, especially the electrochemical parameters. The addition of silica treated using nitric acid at pH = 4.0 displayed the best cement performance including highest strength, reduced permeability and lowest corrosion current

Self-handicapping tendencies, coping, and anxiety responses among athletes

Objectives: Four studies examined relationships between self-handicapping tendencies and reactions to two different yet potentially stressful sport situations (i.e., dealing with a performance slump and emotional reaction prior to competition). Design: Retrospective and prospective cross-sectional survey. Methods: For studies 1 and 2, participants were 65 male athletes (mean age=20.45) and 141 male and female athletes (mean age=21.5), respectively. Participants in study 1 completed the Self-handicapping Scale (SHS) and slump-related coping was assessed using the Coping Inventory for Stressful Situations (CISS). Participants in study 2 completed the SHS and slump-related coping was assessed using the modified Ways of Coping in Sport Scale (WCSS). For studies 3 and 4, participants were 220 male athletes (mean age=22.60) and 120 male and female athletes (mean age=34.75), respectively. Participants from both studies completed the SHS and emotions prior to competition were assessed using the Competitive State Anxiety Inventory (CSAI-2). Results: Data from study 1 showed that self-handicapping tendencies were related to emotive-oriented coping. CISS emotion scale scores accounted for 25% of the variance in SHS scores. Data from study 2 showed that self-handicapping tendencies were related to denial/avoidance and wishful thinking subscale scores of the WCSS. Together these two variables accounted for 11% of the variance in SHS scores. Data from studies 3 and 4 showed positive relations between self-handicapping tendencies and cognitive state-anxiety. Cognitive state-anxiety accounted for 8% of the variance in SHS scores in study 3 and 12% of the variance in SHS scores in study 4. Conclusions: Results from studies 1 and 2 demonstrate that self-handicapping tendencies are related to general and specific emotion coping strategies when dealing with a slump. Results from studies 3 and 4 show that self-handicapping tendencies are related to precompetitive cognitive state-anxiety.

DESLAZAMIENTOS EN LA CUENCA DEL RIO BANANO, UNA CONSECUENCIA DEL TERREMOTO DE ABRIL DE 1991

En la región Caribe algunas cuencas se vieron afectadas en su comportamiento hidrológico, como consecuencia del terremoto de abril de 1991.Un ejemplo evidente de lo anterior es la cuenca del rio Banano, que es la fuente principal del agua potable para la provincia de Limón, y que se presenta un comportamiento de rio aluvial acelerado como consecuencia de cerca de 40 millones de m3 de material deslizado. Los deslizamientos  característicos en la cuenca son deslizamientos de roca (rockslide), aunque puede observarse uno de tipo rotacional (rotational slump); además existen flujos de detritos ( debris flow). Este comportamiento acelerado origina inundaciones en poblados como Aguas Zarcas, Quitaría, Beverly; Polonia, Bomba y María Luisa. Con el fin de minimizar las consecuencias de estas inundaciones se establece una zonificación de áreas inundables para la parte baja de la cuenca en tres clases. Además, en la cuenca se registra un aporte significativo de material en suspensión, lo cual podrá alterar la posibilidad del agua. ABSTRACTThe April 1991 earthquake in Costa Rica caused changes in the hydrological characteristics of several watersheds in the Caribbean region of country.Evidence of these changes was observer in the rio Banano, the principal source of potable water for the province de Limon. The behavior of the alluvial river accelerated as a consequence of nearly 40 million cubic meters of material that moved within the watershed as a result of the earthquake. The characteristical landslides were rockslides, althoung rotational slump and debris flow slides were also observed. The accelerated hydrological changes in the river have caused flooding in populated areas such as Aguas Zarcas, Quitará, Beverly, Polonia, Bomba and Maria Luisa. In order to minimize the consequences of the flooding, the lower part of the watershed was classified in three categories according to flooding susceptibility.The river has also shown an increase in suspended material, which could affect the potability of the water.