Towards an Intrinsic Relationship between Diffusion Coefficients and Microscopic Features of Cements ?

2000 ◽  
Vol 663 ◽  
Author(s):  
P. Lovera ◽  
C. Galle ◽  
P. Le Bescop
Keyword(s):  
Diffusion Coefficients ◽  
Chemical Compounds ◽  
Water Diffusion ◽  
Mass Ratio ◽  
Microscopic Features ◽  
Long Term Behavior ◽  
Simple Modeling

ABSTRACTLong-term behavior of cemented waste packages requires the knowledge of water diffusion coefficients (water is supposed to be the main degradation agent, by solubilization of some chemical compounds). A simple modeling, based on the use of hydration code CEMHYD3D is proposed and validated for pure OPC pastes (sound or degraded) at mass ratio water / cement lying between 0.25 and 0.65. The nature of the porosity available for diffusion and the role of residual anhydrous compounds are discussed.

scholarly journals The Role of Dispersal in Interacting Patches Subject to an Allee Effect

2013 ◽  
Vol 45 (4) ◽  
pp. 1182-1197
Author(s):  
N. Lanchier
Keyword(s):  
Allee Effect ◽  
Interacting Particle Systems ◽  
Local Population ◽  
Critical Value ◽  
Initial Distribution ◽  
Interacting Particle ◽  
Strong Allee Effect ◽  
Long Term Behavior

This article is concerned with a stochastic multipatch model in which each local population is subject to a strong Allee effect. The model is obtained by using the framework of interacting particle systems to extend a stochastic two-patch model that was recently introduced by Kang and the author. The main objective is to understand the effect of the geometry of the network of interactions, which represents potential migrations between patches, on the long-term behavior of the metapopulation. In the limit as the number of patches tends to ∞, there is a critical value for the Allee threshold below which the metapopulation expands and above which the metapopulation goes extinct. Spatial simulations on large regular graphs suggest that this critical value strongly depends on the initial distribution when the degree of the network is large, whereas the critical value does not depend on the initial distribution when the degree is small. Looking at the system starting with a single occupied patch on the complete graph and on the ring, we prove analytical results that support this conjecture. From an ecological perspective, these results indicate that, upon arrival of an alien species subject to a strong Allee effect to a new area, though dispersal is necessary for its expansion, fast long-range dispersal drives the population toward extinction.

Empirical Dissolution Rate Law for the Glass R7T7 Contacting Halite- and Silica-Saturated Brines

1991 ◽  
Vol 257 ◽  
Author(s):  
B. Grambow ◽  
W. Lutze ◽  
R. Müller
Keyword(s):  
Time Dependence ◽  
Dissolution Rate ◽  
Diffusion Coefficients ◽  
Water Diffusion ◽  
Square Root ◽  
Borosilicate Glasses ◽  
Rate Law ◽  
Apparent Diffusion Coefficients ◽  
Apparent Diffusion

ABSTRACTWe report on the time dependence of release of glass constituents during static dissolution experiments with the COGEMA glass R7T7 in saline MgCl2 and NaCl dominated solutions at temperatures between 110 and 190°C. The experiments were performed at high S/V values to ensure silica saturation almost from the start of the tests. The results show a square root of time dependence indicating diffusion as rate-controlling with apparent diffusion coefficients similar to that of water diffusion in alkali silicate, borosilicate glasses or long-term weathered obsidians.

scholarly journals The Role of Dispersal in Interacting Patches Subject to an Allee Effect

2013 ◽  
Vol 45 (04) ◽  
pp. 1182-1197 ◽  
Author(s):  
N. Lanchier
Keyword(s):  
Allee Effect ◽  
Interacting Particle Systems ◽  
Local Population ◽  
Critical Value ◽  
Initial Distribution ◽  
Interacting Particle ◽  
Strong Allee Effect ◽  
Long Term Behavior

This article is concerned with a stochastic multipatch model in which each local population is subject to a strong Allee effect. The model is obtained by using the framework of interacting particle systems to extend a stochastic two-patch model that was recently introduced by Kang and the author. The main objective is to understand the effect of the geometry of the network of interactions, which represents potential migrations between patches, on the long-term behavior of the metapopulation. In the limit as the number of patches tends to ∞, there is a critical value for the Allee threshold below which the metapopulation expands and above which the metapopulation goes extinct. Spatial simulations on large regular graphs suggest that this critical value strongly depends on the initial distribution when the degree of the network is large, whereas the critical value does not depend on the initial distribution when the degree is small. Looking at the system starting with a single occupied patch on the complete graph and on the ring, we prove analytical results that support this conjecture. From an ecological perspective, these results indicate that, upon arrival of an alien species subject to a strong Allee effect to a new area, though dispersal is necessary for its expansion, fast long-range dispersal drives the population toward extinction.

scholarly journals Application of a Novel Measurement Setup for Characterization of Graphene Microelectrodes and a Comparative Study of Variables Influencing Charge Injection Limits of Implantable Microelectrodes

Sensors ◽  
2019 ◽  
Vol 19 (12) ◽  
pp. 2725 ◽  
Author(s):  
Ana Cisnal ◽  
Frank R. R. Ihmig ◽  
Juan-Carlos Fraile ◽  
Javier Pérez-Turiel ◽  
Víctor Muñoz-Martinez
Keyword(s):  
Biomedical Applications ◽  
Charge Injection ◽  
Electrochemical Characteristics ◽  
Maximum Charge ◽  
Fraunhofer Institute ◽  
Long Term Behavior ◽  
Electrochemical Evaluation

Depending on their use, electrodes must have a certain size and design so as not to compromise their electrical characteristics. It is fundamental to be aware of all dependences on external factors that vary the electrochemical characteristics of the electrodes. When using implantable electrodes, the maximum charge injection capacity (CIC) is the total amount of charge that can be injected into the tissue in a reversible way. It is fundamental to know the relations between the characteristics of the microelectrode itself and its maximum CIC in order to develop microelectrodes that will be used in biomedical applications. CIC is a very complex measure that depends on many factors: material, size (geometric and effectiveness area), and shape of the implantable microelectrode and long-term behavior, composition, and temperature of the electrolyte. In this paper, our previously proposed measurement setup and automated calculation method are used to characterize a graphene microelectrode and to measure the behavior of a set of microelectrodes that have been developed in the Fraunhofer Institute for Biomedical Engineering (IBMT) labs. We provide an electrochemical evaluation of CIC for these microelectrodes by examining the role of the following variables: pulse width of the stimulation signal, electrode geometry and size, roughness factor, solution, and long-term behavior. We hope the results presented in this paper will be useful for future studies and for the manufacture of advanced implantable microelectrodes.

scholarly journals PROBLEMS IN TRADITIONAL LANDFILLING AND PROPOSALS FOR SOLUTIONS BASED ON SUSTAINABILITY

Detritus ◽  
2020 ◽  
pp. 78-91
Author(s):  
Valentina Grossule ◽  
Rainer Stegmann
Keyword(s):  
Waste Management ◽  
Environmental Sustainability ◽  
Raw Materials ◽  
Storage Quality ◽  
Financial Investment ◽  
Critical Issues ◽  
Long Term Behavior ◽  
Technical Measures

In recent years, the Circular Economy has become the key lynchpin underlying the waste management system. However, the emphasis placed on recycling has led, on one hand, to an underestimation of the critical issues that are currently emerging so dramatically (i.e. limited recyclability of materials, instability of markets for secondary raw materials, and accumulation of contaminants present in the recycled materials), whilst on the other to neglect the inescapable role of landfill in waste management. In many cases, landfills are seen as a simple and economical means of disposing of waste, and from a political, legislative and technical viewpoint they are frequently denied the attention devoted to other engineering works, lacking adequate financial investment to cover the costs required to ensure a sustainable landfill system. Landfill should be designed and constructed in line with the principle of environmental sustainability, by adopting technical measures aimed at guaranteeing waste stability and immobilisation of contaminants over a period of less than one generation and ensuring a Final Storage Quality in equilibrium with the environment. This article summarises the concept of sustainable landfilling, identifies the technical strategies that characterise this system, describes the critical issues frequently encountered after decades of operation and proposes a series of solutions aimed to control long-term behavior.

scholarly journals From microscopic price dynamics to multidimensional rough volatility models

2021 ◽  
Vol 53 (2) ◽  
pp. 425-462
Author(s):  
Mathieu Rosenbaum ◽  
Mehdi Tomas
Keyword(s):  
Price Formation ◽  
Financial Assets ◽  
Correlation Matrices ◽  
Volatility Models ◽  
Microscopic Models ◽  
Joint Dynamics ◽  
Microscopic Features ◽  
Rough Volatility

AbstractRough volatility is a well-established statistical stylized fact of financial assets. This property has led to the design and analysis of various new rough stochastic volatility models. However, most of these developments have been carried out in the mono-asset case. In this work, we show that some specific multivariate rough volatility models arise naturally from microstructural properties of the joint dynamics of asset prices. To do so, we use Hawkes processes to build microscopic models that accurately reproduce high-frequency cross-asset interactions and investigate their long-term scaling limits. We emphasize the relevance of our approach by providing insights on the role of microscopic features such as momentum and mean-reversion in the multidimensional price formation process. In particular, we recover classical properties of high-dimensional stock correlation matrices.

Influence of fungal infection on the long-term water absorption and morphological behavior of bagasse fiber/polypropylene composites at different exposure times

2013 ◽  
Vol 20 (4) ◽  
pp. 351-357 ◽  
Author(s):  
Behzad Kord ◽  
Seyyed Khalil Hosseinihashemi ◽  
Mehdi Modirzare
Keyword(s):  
Water Absorption ◽  
Diffusion Coefficients ◽  
Water Diffusion ◽  
White Rot ◽  
Fungal Decay ◽  
Melt Mixing ◽  
Polypropylene Composites ◽  
Bagasse Fiber ◽  
Control Samples

AbstractIn this study, the effect of fungal decay on the long-term water absorption of bagasse fiber/polypropylene composites at different exposure times was studied. For this purpose, the blend composites were prepared through the melt mixing of bagasse fiber with polypropylene at 40:60% weight ratios, with 2% coupling agent for all formulations. Then, the samples were exposed to brown-rot (Coniophora puteana) and white-rot (Trametes versicolor) fungal treatments for 8, 12 and 16 weeks with the Kolle flask method. The long-term water absorptions of samples were evaluated by immersing them in water at room temperature for several weeks, and water diffusion coefficients were also calculated by evaluating the water absorption isotherms. Also, the morphology of composites was characterized using scanning electron microscopy (SEM). The results showed that the water absorption of samples was actually much higher after both types of rotting and was significantly higher than that of control samples. Also, the water absorption of white-rotted samples was higher than that of brown-rotted and control samples for all weeks of fungal exposure times. In addition, the control sample and composite after 16 weeks of exposure to white-rot fungi exhibited the lowest and highest water diffusion coefficients, respectively. The mechanism of water absorption of samples against fungal decay at different exposure times followed the kinetics of a Fickian diffusion process. Furthermore, the SEM micrographs showed that the extent of degradation increased with increasing exposure time to fungus.

scholarly journals Assessing the role of barite to control 226Ra long term behavior in McClean tailings - Saskatchewan, Canada

2021 ◽  
Author(s):  
Clémence Besançon ◽  
Paul Sardini ◽  
Sebastien Savoye ◽  
Kebbi Hughes ◽  
Hamid Mokhtari ◽  
...  
Keyword(s):  
Long Term Behavior
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