L'hydrologie urbaine: nouvelles problématiques, nouvelles approches de solutions

La pratique de l'hydrologie, appliquée au milieu urbain, a beaucoup évolué depuis les années 1960. De nouveaux outils scientifiques, méthodologiques et technologiques ont été mis au point. En ce qui concerne les eaux pluviales urbaines, un changement de philosophie complet s'est produit. Aujourd'hui, des développements rapides continuent à se produire pour faire face de la meilleure manière possible aux graves problèmes qui se posent en zone urbaine : inondation et pollution du milieu naturel. Deux approches récentes illustrent ces développements : la gestion des risques et l'approche globale sur le bassin versant. Une évaluation de plus en plus précise de l'aléa et de la vulnérabilité s'avère nécessaire ainsi qu'une planification hydrologique bassin versant par bassin versant. Celle-ci devrait conduire à définir et à hiérarchiser les principaux objectifs que l'on se fixe dans les domaines du contrôle des inondations, du contrôle de l'érosion, de l'amélioration du milieu naturel et de la protection de l'environnement. Les actions à mener doivent utiliser les outils de modélisation des phénomènes hydrologiques sur les bassins versants. L'efficacité de ces approches est illustrée par un exemple pris sur le bassin versant de la rivière Beauport au Québec.Urban hydrology practice has evolved a great deal, keeping up with the evolution of urban problems. Thus, professional engineers have had to keep up with this evolution, in order to understand the effects of urbanization on the hydrological behavior of the systems for which they have to recommend best solutions. Engineers have also had to evolve from the traditional approach of a limited vision of the problem, of its extent and of its impacts on the system. A global vision of the entire system, grouping every watershed element, such as forestry, agriculture or urbanization, is necessary if one is to circumscribe the problem, to analyze it and to reach to the best long-lasting solution. This article represents a synthesis of the hydrological disturbance phenomenon caused by uncontrolled urbanization, not properly planned, which is often characterized by numerous short-term solutions, often ineffective in the context of a long-lasting approach.Examples of natural disasters caused by meteorological events are more and more frequent. Take the case of Vaison-la-Romaine, in September 1992, where the Groseau devastated the Vaison community. More recently, the 1996 summer floods in the Saguenay region, in Québec, demonstrate once more that water always tends to return to its original bed, now occupied by artificial structures. When these types of events are analyzed in detail, we notice that meteorological phenomena are not always the main cause of the disaster cause and that often part of the responsibility lies with the occurrence of human activity in the catchment. This observation shows the importance of using wisdom and humility towards these natural forces and of anticipating, during design, a "secure" passage for the inevitable flows that one day will exceed the structure capacity. Knowing all the interactions that exist in the heart of the stormwater management problems, it is risky to intervene in isolation without analyzing the impact of the action. The approach must then be global and coherent; the tool necessary for success is the stormwater master plan made on a watershed basis. The master plan allows us to properly describe the problematical elements, to identify the real causes and to optimize the location of the control solutions. It also allows us to manage the increase in stormwater due to urbanization, with the "flow set point" concept of each watercourse tributary.This article presents an application example where the global analysis approach is used and where the solution involves different interventions and developments, which, when combined, effectively treat backwater effects, flooding and erosion in the presented area. The master plan of the watershed containing this sector had already been conceived and the specific flows of each of its tributaries had been identified; the global approach method therefore allowed us to settle the local problems in the studied area while respecting the flow granted by the master plan. Finally, a floodable plain, containing marshes, completes the intervention plan by combining the restoration of certain watercourse ecological characteristics with the need for flood control. This example demonstrates the necessity and the advantages of approaching urban drainage problems at the watershed level. However, watershed management concepts lead planners and designers to deal with antagonisms: urbanization or renaturalization? Obviously, in urban areas, the return to natural conditions is impossible and the disturbances to watercourses generated by urbanization cannot all be compensated for. Rather, we must aspire to the establishment of a balanced environment by controlling inflows produced by the watershed and by supporting the system to receive them. The notion of feasibility must always occupy the thoughts of the master plan designers and planners. The credibility and the continuity of the master plan depend on all these considerations; any unrealistic flow order, on an implementation level, can compromise the balance of the management plan and its applicability, which in turn can lead to a confused plan, possibly having disastrous consequences. The ultimate consequence of the management plan is the protection of the watercourse, the development of which can be designed to meet different criteria, such as flood control, erosion control, ecological potential enhancement, etc. It is at this stage that management becomes most complex: flood control, for example, does not apply to the same type of events as erosion control. The former requires management of major hydrological events, whereas the second needs implies control of frequent flows, which are at the origin of bank undermining caused by differential volume excesses. The management scheme must then handle multiple events and multiple criteria; consequently, it becomes more complex but also grows in value and justifies itself more adequately. Furthermore, the whole question of watercourse quality, in the broad sense of the term, must be managed from a frequent-event point of view, as this yields the best physical, ecological and aesthetic image of the aquatic environment. To this effect, present efforts in the control of combined sewage network overflows can be seen as a predecessor of what will later be extended to the entire stormwater network. This whole aspect of management has not been treated in this paper, as many others are dedicated to doing so. The evolution of the situation is similar in France and in Québec; coherent watershed management must rest on clear political goals regarding environmental use, risk protection and urban development. The stormwater master plan must, permanently, become part of the water resource master plan for the whole watershed, with its objectives of flood control, erosion control and maintenance of acceptable physical-chemical and biochemical water quality, as well as assured resource use (drinking water--, hydroelectricity, agriculture, industrial waters, etc.). This water resource master plan will have to be integrated in the same way as the French Water Agencies do today, and as Québec is preparing to do so

Incidence of gallbladder lithiasis after ceftriaxone treatment

Ceftriaxone has potent activity against a broad range of Gram-positive and Gram-negative bacteria. While it is eliminated mainly by the kidney, 10-20% of the drug is eliminated in the bile and ceftriaxone salt precipitates have been described in the gallbladder of animals dosed with ceftriaxone. The purpose of the present study was to investigate the incidence of biliary lithiasis 6 and 12 months after treatment with ceftriaxone and to compare it with that in patients treated with amoxycillin/clavulanate. Biliary ultrasonography was performed at the start of treatment, at 6 months and at 12 months after the beginning of the study. One hundred patients were randomized and 74 were evaluable: 34 were given amoxycillin/clavulanate, 40 ceftriaxone. Gallbladder lithiasis developed in one patient 12 months after the amoxycillin/clavulanate treatment and in none in the ceftriaxone treatment arm. Biliary precipitate during ceftriaxone treatment was not looked for because this phenomenon was not known at the beginning of the study, but gallbladder precipitation that was seen in two patients given ceftriaxone during and at the end of treatment, respectively, resolved spontaneously. In conclusion, ceftriaxone treatment does not appear to lead to gallstone formation more often than an antibiotic that is not eliminated through the bil

Method for fabricating submicron silicide structures on silicon using a resistless electron beam lithography process

Abstract : A novel resistless lithography process using a conventional electron beam system is presented. Metallic lines with widths of less than 50 nm were produced on silicon substrates. The process is based on localized heating with a focused electron beam of thin platinum layers deposited on silicon. It is demonstrated that silicide formation occurs at the Pt-Si interface. By using a dilute solution of aqua regia, it is possible to obtain a sufficient difference in etch rates between exposed and unexposed regions of the platinum thin film to selectively remove only the unexposed areas

Magma mixing enhanced by bubble segregation

In order to explore the materials' complexity induced by bubbles rising through mixing magmas, bubble-advection experiments have been performed, employing natural silicate melts at magmatic temperatures. A cylinder of basaltic glass was placed below a cylinder of rhyolitic glass. Upon melting, bubbles formed from interstitial air. During the course of the experimental runs, those bubbles rose via buoyancy forces into the rhyolitic melt, thereby entraining tails of basaltic liquid. In the experimental run products, these plume-like filaments of advected basalt within rhyolite were clearly visible and were characterised by microCT and high-resolution EMP analyses. The entrained filaments of mafic material have been hybridised. Their post-experimental compositions range from the originally basaltic composition through andesitic to rhyolitic composition. Rheological modelling of the compositions of these hybridised filaments yield viscosities up to 2 orders of magnitude lower than that of the host rhyolitic liquid. Importantly, such lowered viscosities inside the filaments implies that rising bubbles can ascend more efficiently through pre-existing filaments that have been generated by earlier ascending bubbles. MicroCT imaging of the run products provides textural confirmation of the phenomenon of bubbles trailing one another through filaments. This phenomenon enhances the relevance of bubble advection in magma mixing scenarios, implying as it does so, an acceleration of bubble ascent due to the decreased viscous resistance facing bubbles inside filaments and yielding enhanced mass flux of mafic melt into felsic melt via entrainment. In magma mixing events involving melts of high volatile content, bubbles may be an essential catalyst for magma mixing. Moreover, the reduced viscosity contrast within filaments implies repeated replenishment of filaments with fresh end-member melt. As a result, complex compositional gradients and therefore diffusion systematics can be expected at the filament-host melt interface, due to the repetitive nature of the process. However, previously magmatic filaments were tacitly assumed to be of single-pulse origin. Consequently, the potential for multi-pulse filaments has to be considered in outcrop analyses. As compositional profiles alone may remain ambiguous for constraining the origin of filaments, and as 3-D visual evidence demonstrates that filaments may have experienced multiple bubbles passages even when featuring standard diffusion gradients, therefore, the calculation of diffusive timescales may be inadequate for constraining timescales in cases where bubbles have played an essential role in magma mixing. Data analysis employing concentration variance relaxation in natural samples can distinguish conventional single-pulse filaments from advection via multiple bubble ascent advection in natural samples, raising the prospect of yet another powerful application of this novel petrological tool

Transcriptional Basis of Mouse and Human Dendritic Cell Heterogeneity

Dendritic cells (DCs) play a critical role in orchestrating adaptive immune responses due to their unique ability to initiate T cell responses and direct their differentiation into effector lineages. Classical DCs have been divided into two subsets, cDC1 and cDC2, based on phenotypic markers and their distinct abilities to prime CD8 and CD4 T cells. While the transcriptional regulation of the cDC1 subset has been well characterized, cDC2 development and function remain poorly understood. By combining transcriptional and chromatin analyses with genetic reporter expression, we identified two principal cDC2 lineages defined by distinct developmental pathways and transcriptional regulators, including T-bet and RORgt, two key transcription factors known to define innate and adaptive lymphocyte subsets. These novel cDC2 lineages were characterized by distinct metabolic and functional programs. Extending our findings to humans revealed conserved DC heterogeneity and the presence of the newly defined cDC2 subsets in human cancer

Absolute Paleointensity Study of Miocene Tiva Canyon Tuff, Yucca Mountain, Nevada: Role of Fine‐Particle Grain‐Size Variations

Fine‐grained, Ti‐poor titanomagnetite in the ~12.7 Ma Tiva Canyon (TC) Tuff systematically increases in grain size from superparamagnetic (SP) at the flow base to single domain (SD) at a few meters height. This allows us to examine the role of grain‐size variation on paleointensity, within the transition from SP to stable SD. We present magnetic properties from two previously unreported sections of the TC Tuff, as well as Thellier‐type paleointensity estimates from the lowermost ~7.0 m of the flow. Magnetic hysteresis, frequency‐dependent susceptibility, and thermomagnetic data show that sample grain‐size distribution is dominated by SP in the lower ~3.6 m, transitioning upwards to mostly stable SD. Paleointensity results are closely tied to stratigraphic height and to magnetic properties linked to domain state. SD samples have consistent absolute paleointensity values of 28.5 ± 1.94 μT (VADM of 51.3 ZAm2) and behaved ideally during paleointensity experiments. The samples including a significant SP fraction have consistently higher paleointensities and less ideal behavior but would likely pass many traditional quality‐control tests. We interpret the SD remanence to be a primary thermal remanent magnetization but discuss the possibility of a partial thermal‐chemical remanent magnetization if microcrystal growth continued at T \u3c Tc and/or the section is affected by post‐emplacement vapor‐phase alteration. The link between paleointensity and domain state is stronger than correlations with water content or other evidence of alteration and suggests that the presence of a significant SP population may adversely impact paleointensity results, even in the presence of a stable SD fraction

Thermal Liability of Hyaloclastite in the Krafla Geothermal Reservoir, Iceland:The Impact of Phyllosilicates on Permeability and Rock Strength

Geothermal fields are prone to temperature fluctuations from natural hydrothermal activity, anthropogenic drilling practices, and magmatic intrusions. These fluctuations may elicit a response from the rocks in terms of their mineralogical, physical (i.e., porosity and permeability), and mechanical properties. Hyaloclastites are a highly variable volcaniclastic rock predominantly formed of glass clasts that are produced during nonexplosive quench-induced fragmentation, in both subaqueous and subglacial eruptive environments. They are common in high-latitude geothermal fields as both weak, highly permeable reservoir rocks and compacted impermeable cap rocks. Basaltic glass is altered through interactions with external water into a clay-dominated matrix, termed palagonite, which acts to cement the bulk rock. The abundant, hydrous phyllosilicate minerals within the palagonite can dehydrate at elevated temperatures, potentially resulting in thermal liability of the bulk rock. Using surficial samples collected from Krafla, northeast Iceland, and a range of petrographic, mineralogical, and mechanical analyses, we find that smectite dehydration occurs at temperatures commonly experienced within geothermal fields. Dehydration events at 130, 185, and 600°C result in progressive mass loss and contraction. This evolution results in a positive correlation between treatment temperature, porosity gain, and permeability increase. Gas permeability measured at 1 MPa confining pressure shows a 3-fold increase following thermal treatment at 600°C. Furthermore, strength measurements show that brittle failure is dependent on porosity and therefore the degree of thermal treatment. Following thermal treatment at 600°C, the indirect tensile strength, uniaxial compressive strength, and triaxial compressive strength (at 5 MPa confining pressure) decrease by up to 68% (1.1 MPa), 63% (7.3 MPa), and 25% (7.9 MPa), respectively. These results are compared with hyaloclastite taken from several depths within the Krafla reservoir, through which the palagonite transitions from smectite-to chlorite-dominated. We discuss how temperature-induced changes to the geomechanical properties of hyaloclastite may impact fluid flow in hydrothermal reservoirs and consider the potential implications for hyaloclastite-hosted intrusions. Ultimately, we show that phyllosilicate-bearing rocks are susceptible to temperature fluctuations in geothermal fields. © 2020 Josh Weaver et al

Phase separating binary fluids under oscillatory shear

We apply lattice Boltzmann methods to study the segregation of binary fluid mixtures under oscillatory shear flow in two dimensions. The algorithm allows to simulate systems whose dynamics is described by the Navier-Stokes and the convection-diffusion equations. The interplay between several time scales produces a rich and complex phenomenology. We investigate the effects of different oscillation frequencies and viscosities on the morphology of the phase separating domains. We find that at high frequencies the evolution is almost isotropic with growth exponents 2/3 and 1/3 in the inertial (low viscosity) and diffusive (high viscosity) regimes, respectively. When the period of the applied shear flow becomes of the same order of the relaxation time $T_R$ of the shear velocity profile, anisotropic effects are clearly observable. In correspondence with non-linear patterns for the velocity profiles, we find configurations where lamellar order close to the walls coexists with isotropic domains in the middle of the system. For particular values of frequency and viscosity it can also happen that the convective effects induced by the oscillations cause an interruption or a slowing of the segregation process, as found in some experiments. Finally, at very low frequencies, the morphology of domains is characterized by lamellar order everywhere in the system resembling what happens in the case with steady shear.Comment: 1 table and 12 figures in .gif forma