Numerical models for 2D free boundary analysis of groundwater in slopes stabilized by drain trenches

AbstractA numerical model for 2D free boundary analysis of groundwater in slopes stabilized by drain trenches has been developed. It consists of a front-tracking method (based on an original way of adapting the space derivatives), very effective in saving calculation time respect to classical fix-grid methods. The method analyses the trenches effect inside slopes in which the soils above the water table are partially saturated, for which a boundary can be recognized between the saturated domain (water table) and the unsaturated one (above the water table). In this case pore pressure lowering, due to trenches, can be analyzed considering the progressively reduction of the saturated domain. This approach efficiently solves the problem of fixing hydraulic boundary conditions on the sides of the trenches. Results have been compared with those obtained by a fix-grid method, observing difference less than 0.14%. Applying the method, the capability of drain trenches to control the effect of heavy rainfalls has been investigated, calculating (during the transient process of water table lowering) limit values of water recharge for which water table keeps on constant

SURVEY, DIAGNOSTICS, MONITORING METHODOLOGY AND DIGITAL TWIN FOR THE CONSERVATION OF THE FACADE OF THE CHURCH OF SANTA MARIA DI NAZARETH IN VENICE

This contribution aims to illustrate the experimental research linked to the restoration concluded in 2018 for the conservation of the façade of the Santa Maria di Nazareth church in Venice and the ongoing monitoring methodology for the evaluation of its conservation state over time. The baroque façade is unique in Venice as it is entirely made of Carrara marble, a limestone with a saccharoid structure which has proved over the centuries unsuitable for the aggressive lagoon climate, given the complex architectural conformation and the unfavourable environmental conditions in which the façade is inserted.The state of conservation of the marble at the beginning of the last worksite showed widespread and worrying degradation in many parts, especially in the more protruding ones: in fact, the stone surface reached detachment and pulverization by simple contact. The ultimate goal was to achieve a compatible and retractable conservative restoration for a possible improvement of the conservative results over time and also to facilitate an effective retrieval of scientific data in case of future interventions. With this aim, once the construction site was completed, a survey campaign with the purpose of reproducing a digital twin through 3D modelling was planned, to monitor the façade to have an exhaustive knowledge of the possible vulnerabilities present, with the involvement of the VIDE laboratory of IUAV University of Venice. A data acquisition protocol has been developed for the preservation of cultural heritage, thus guaranteeing an uninterrupted knowledge of the material degradation and of the structural situation.</p

Microbial colonization of anaerobic biofilms: a mathematical model

A 1-D mathematical model for analysis and prediction of microbial colonization of anaerobic multispecies biofilms for methane production is presented. The model combines the related processes of hydrolysis, acidogenesis, acetogenesis, methanogenesis and takes into account phenomena of substrate reaction and diffusion, biomass growth, detachment and, in particular, the colonization of new species from bulk liquid to biofilm. The colonization phenomenon is initiated by planktonic cells, present in the bulk liquid but not initially in the biofilm, which thanks to the characteristic porous structure of biofilm matrix, may enter the channels and establish where they find favorable growth conditions. The model consists of a free boundary value problem where the biofilm growth process is governed by nonlinear hyperbolic PDEs and substrate dynamics are dominated by semilinear parabolic PDEs. The transport of colonizing bacteria from the bulk liquid to the biofilm is modelled by using a diffusionreaction equation, where the reaction term represents the loss of planktonic bacteria due to their establishment within the biofilm. The method of characteristics is used for numerical purposes. The model is based on the biological framework of ADM1 and has been applied to simulate microbial competition and evaluate the influence of substrate diffusion on microbial stratification. Specific scenarios have been simulated describing the effect of colonization of motile bacteria into an established anaerobic biofilm

Is the astronomical forcing a reliable and unique pacemaker for climate? A conceptual model study

There is evidence that ice age cycles are paced by astronomical forcing, suggesting some kind of synchronisation phenomenon. Here, we identify the type of such synchronisation and explore systematically its uniqueness and robustness using a simple paleoclimate model akin to the van der Pol relaxation oscillator and dynamical system theory. As the insolation is quite a complex quasiperiodic signal involving different frequencies, the traditional concepts used to define synchronisation to periodic forcing are no longer applicable. Instead, we explore a different concept of generalised synchronisation in terms of (coexisting) synchronised solutions for the forced system, their basins of attraction and instabilities. We propose a clustering technique to compute the number of synchronised solutions, each of which corresponds to a different paleoclimate history. In this way, we uncover multistable synchronisation (reminiscent of phase- or frequency-locking to individual periodic components of astronomical forcing) at low forcing strength, and monostable or unique synchronisation at stronger forcing. In the multistable regime, different initial conditions may lead to different paleoclimate histories. To study their robustness, we analyse Lyapunov exponents that quantify the rate of convergence towards each synchronised solution (local stability), and basins of attraction that indicate critical levels of external perturbations (global stability). We find that even though synchronised solutions are stable on a long term, there exist short episodes of desynchronisation where nearby climate trajectories diverge temporarily (for about 50 kyr). (...)Comment: 22 pages, 18 figure

The restorative role of annexin A1 at the blood–brain barrier

Annexin A1 is a potent anti-inflammatory molecule that has been extensively studied in the peripheral immune system, but has not as yet been exploited as a therapeutic target/agent. In the last decade, we have undertaken the study of this molecule in the central nervous system (CNS), focusing particularly on the primary interface between the peripheral body and CNS: the blood–brain barrier. In this review, we provide an overview of the role of this molecule in the brain, with a particular emphasis on its functions in the endothelium of the blood–brain barrier, and the protective actions the molecule may exert in neuroinflammatory, neurovascular and metabolic disease. We focus on the possible new therapeutic avenues opened up by an increased understanding of the role of annexin A1 in the CNS vasculature, and its potential for repairing blood–brain barrier damage in disease and aging

Mathematical modeling of the competition between sulfate reducing, acetoclastic and methanogenic bacteria within multispecies biofilms

Increasing anthropogenic activity has contributed to local imbalances in the natural sulfur cycle, leading to serious environmental problems. Industrial wastewater containing sulfate has contributed to this sulfur imbalance. Biological sulfate reducing processes that involve a bacterial biomass attached to media (biofilm), represent an attractive solution to the problem. The advantage of bacteria disposing in a biofilm is very important in an environmental industrial application, as the bacteria in the biofilm, different from suspended bacteria, cannot be washed out with the water flow. This allows to retain the biomass within the reactor and therefore to operate at shorter hydraulic retention time (HRT),and higher biomass concentration . Biological sulfate reduction in anaerobic fixed growth reactors has been investigated extensively at lab-scale. Under anaerobic conditions dissimilatory sulfate reducing bacteria use sulfate as a terminal electron acceptor for the degradation of organic compounds. In this anaerobic process, sulfate is reduced to sulfide by the action of sulfate reducing bacteria (SRB), which have the ability of coupling the oxidation of organic matter (electron donor) to the reduction of sulfate (electron acceptor) and depend on hydrolytic and fermentative bacteria that degrade complex organic matter. A major problem of sulfate-reducing fixed-growth reactors is the formation of undesired bacteria species which compete for space and substrate in the biofilm with SRB. This work presents a mathematical model able to simulate the physical, chemical and biological processes prevailing in a sulfate reducing biofilm under dynamic conditions. The proposed model includes sulfate reduction by complete and incomplete SRB; COD (lactate) removal by sulfate reduction and by acetogenic bacteria; acetate consumption via methanogenesis. The method of characteristics is used for the numerical resolution of the model equations. In particular the effect of the COD/SO42- ratio and the effect of different simulation times on the reactor performances in terms of bacterial species distribution and substrate diffusion trends in the biofilm have been assessed

Dynamic modeling of sulfate reducing biofilms

The paper presents a mathematical model able to simulate the physical, chemical and biological processes prevailing in a sulfate reducing biofilm under dynamic conditions. A mathematical modeling approach for microbial growth and decay is proposed. Complete oxidizers sulfate reducing bacteria, incomplete oxidizers sulfate reducing bacteria and acetate degraders are the microbial groups taken into account in the model. The proposed model is able to simulate the competition among the bacteria growing in the biofilm. The method of characteristics is introduced for the numerical process. As in the qualitative analysis of solutions, where it was first presented, this method seems to be a powerful tool in this situation also. The model has been applied to simulate the sulfate reduction process in a biofilm for several purposes. In particular the effect of the ratio and the effect of different simulation times on the reactor performances in terms of volume fraction of bacterial species and substrate diffusion trends in biofilm have been assessed