Hydrologic Transport of Dissolved Inorganic Carbon and Its Control on Chemical Weathering

Chemical weathering is one of the major processes interacting with climate and tectonics to form clays, supply nutrients to soil microorganisms and plants, and sequester atmospheric CO2. Hydrology and dissolution kinetics have been emphasized as factors controlling chemical weathering rates. However, the interaction between hydrology and transport of dissolved inorganic carbon (DIC) in controlling weathering has received less attention. In this paper, we present an analytical model that couples subsurface water and chemical molar balance equations to analyze the roles of hydrology and DIC transport on chemical weathering. The balance equations form a dynamical system that fully determines the dynamics of the weathering zone chemistry as forced by the transport of DIC. The model is formulated specifically for the silicate mineral albite, but it can be extended to other minerals, and is studied as a function of percolation rate and water transit time. Three weathering regimes are elucidated. For very small or large values of transit time, the weathering is limited by reaction kinetics or transport, respectively. For intermediate values, the system is transport controlled and is sensitive to transit time. We apply the model to a series of watersheds for which we estimate transit times and identify the type of weathering regime. The results suggest that hydrologic transport of DIC may be as important as reaction kinetics and dilution in determining chemical weathering rates

Efficient Refinement Checking in VCC

We propose a methodology for carrying out refinement proofs across declarative abstract models and concrete implementations in C, using the VCC verification tool. The main idea is to first perform a systematic translation from the top-level abstract model to a ghost implementation in VCC. Subsequent refinement proofs between successively refined abstract models and between abstract and concrete implementations are carried out in VCC. We propose an efficient technique to carry out these refinement checks in VCC. We illustrate our methodology with a case study in which we verify a simplified C implementation of an RTOS scheduler, with respect to its abstract Z specification. Overall, our methodology leads to efficient and automatic refinement proofs for complex systems that would typically be beyond the capability of tools such as Z/Eves or Rodin

An open extensible tool environment for Event-B

Abstract. We consider modelling indispensable for the development of complex systems. Modelling must be carried out in a formal notation to reason and make meaningful conjectures about a model. But formal modelling of complex systems is a difficult task. Even when theorem provers improve further and get more powerful, modelling will remain difficult. The reason for this that modelling is an exploratory activity that requires ingenuity in order to arrive at a meaningful model. We are aware that automated theorem provers can discharge most of the onerous trivial proof obligations that appear when modelling systems. In this article we present a modelling tool that seamlessly integrates modelling and proving similar to what is offered today in modern integrated development environments for programming. The tool is extensible and configurable so that it can be adapted more easily to different application domains and development methods.

Refinement-Based Verification of the FreeRTOS Scheduler in VCC

We describe our experience with verifying the scheduler-related functionality of FreeRTOS, a popular open-source embedded real-time operating system. We propose a methodology for carrying out refinement-based proofs of functional correctness of abstract data types in the popular code-level verifier VCC. We then apply this methodology to carry out a full machine-checked proof of the functional correctness of the FreeRTOS scheduler. We describe the bugs found during this exercise, the fixes made, and the effort involved

Food restriction reduces neurogenesis in the avian hippocampal formation

The mammalian hippocampus is particularly vulnerable to chronic stress. Adult neurogenesis in the dentate gyrus is suppressed by chronic stress and by administration of glucocorticoid hormones. Post-natal and adult neurogenesis are present in the avian hippocampal formation as well, but much less is known about its sensitivity to chronic stressors. In this study, we investigate this question in a commercial bird model: the broiler breeder chicken. Commercial broiler breeders are food restricted during development to manipulate their growth curve and to avoid negative health outcomes, including obesity and poor reproductive performance. Beyond knowing that these chickens are healthier than fully-fed birds and that they have a high motivation to eat, little is known about how food restriction impacts the animals' physiology. Chickens were kept on a commercial food-restricted diet during the first 12 weeks of life, or released from this restriction by feeding them ad libitum from weeks 7-12 of life. To test the hypothesis that chronic food restriction decreases the production of new neurons (neurogenesis) in the hippocampal formation, the cell proliferation marker bromodeoxyuridine was injected one week prior to tissue collection. Corticosterone levels in blood plasma were elevated during food restriction, even though molecular markers of hypothalamic-pituitary-adrenal axis activation did not differ between the treatments. The density of new hippocampal neurons was significantly reduced in the food-restricted condition, as compared to chickens fed ad libitum, similar to findings in rats at a similar developmental stage. Food restriction did not affect hippocampal volume or the total number of neurons. These findings indicate that in birds, like in mammals, reduction in hippocampal neurogenesis is associated with chronically elevated corticosterone levels, and therefore potentially with chronic stress in general. This finding is consistent with the hypothesis that the response to stressors in the avian hippocampal formation is homologous to that of the mammalian hippocampus

Modelación hidrogeológica de El Berrocal

Se sintetizan los principales resultados de la caracterización hidrogeológica del Berrocal. A escala regional, el régimen de flujo queda definido por la topografía. Ello conduce, en la zona de estudio, a un flujo vertical hacia abajo que queda Iocalmente afectado por diques y arroyos. Se han realizado múltiples ensayos de bombeo a diversas escalas. Si bien la conductividad media parece crecer con la escala del ensayo, este aumento resulta ser sólo aparente y es debido a que los ensayos de larga duración tienden a hacerse en las zonas más permeables. Los ensayos entre sondeos interpretados con modelos 3D que contienen las fracturas dominantes y que ajustan bien los datos, conducen a permeabilidades sorprendentemente parecidas a las obtenidas en ensayos de sondeo únicoMain results of El Berrocal hydrogeological characterization are summarized. Flow is controlled by topography at the regional scale. This leads to a vertically downwards flux at the site, which is only modified by preferential flow paths (veins) and local discharge points (La Tarica stream). A large number of hydraulic tests have been performed at different scales. A lthough representative hydraulic conductivities appear to increase with the scale of measurement, we show that such Increase is caused by the fact that long-term test are performed In the most conductive zones. When these tests were Interpreted by means of 3D models with embedded 2D fractures, which lead to good fits with measured drawdowns, estimated parameters turned out to be surprisingly close to those derived from single hole test