She Wears the Mask

The emergence of the so-called primitive masking its way into the art world of the twentieth century brought with it an alluring mystique which intrigued numerous artists and consequently provoked its appropriation. Specifically, the tribal can be seen in the works of Pablo Picasso as he imbues the geometric facades of Afro- Iberian masks, with shamanistic powers. Upon comparison, the primal found in Picasso\u27s work adds an interesting twist to the work of the female Dadaist Hannah Hoch, who puzzles her audience both aesthetically and intellectually through her use of dense iconography

Diffusive shielding stabilizes bulk nanobubble clusters

Using molecular dynamics, we study the nucleation and stability of bulk nanobubble clusters. We study the formation, growth, and final size of bulk nanobubbles. We find that, as long as the bubble-bubble interspacing is small enough, bulk nanobubbles are stable against dissolution. Simple diffusion calculations provide an excellent match with the simulation results, giving insight into the reason for the stability: nanobubbles in a cluster of bulk nanobubbles "protect" each other from diffusion by a shielding effect

Mixed adsorption and surface tension prediction of nonideal ternary surfactant systems

To deal with the mixed adsorption of nonideal ternary surfactant systems, the regular solution approximation for nonideal binary surfactant systems is extended and a pseudo-binary system treatment is also proposed. With both treatments, the compositions of the mixed monolayer and the solution concentrations required to produce given surface tensions can be predicted based only on the gamma-LogC curves of individual surfactants and the pair interaction parameters. Conversely, the surface tensions of solutions with different bulk compositions can be predicted by the surface tension equations for mixed surfactant systems. Two ternary systems: SDS/Hyamine 1622/AEO7, composed of homogeneous surfactants, and AES/DPCl/AEO9, composed of commercial surfactants, in the presence of excess NaCl, are examined for the applicability of the two treatments. The results show that, in general, the pseudo-binary system treatment gives better prediction than the extended regular solution approximation, and the applicability of the latter to typical anionic/cationic/nonionic nonideal ternary surfactant systems seems to depend on the combined interaction parameter, $${\mathop {(\beta }\nolimits_{an}^s } + {\mathop \beta \nolimits_{cn}^s })/2 - {\mathop \beta \nolimits_{ac}^s }/4$$ : the more it deviates from zero, the larger the prediction difference. If $${\mathop {(\beta }\nolimits_{an}^s } + {\mathop \beta \nolimits_{cn}^s })/2 - {\mathop \beta \nolimits_{ac}^s }/4$$ rarr0, good agreements between predicted and experimental results can be obtained and both treatments, though differently derived, are interrelated and tend to be equivalent

Influence of water pressure dynamics and fluid flow on the streaming-potential response for unsaturated conditions

International audienceA B S T R A C T Streaming-potentials are produced by electrokinetic effects in relation to fluid flow and are used for geophysical prospecting. The aim of this study is to model streaming potential measurements for unsaturated conditions using an empirical approach. A conceptual model is applied to streaming potential measurements obtained from two drainage experiments in sand. The streaming potential data presented here show a non-monotonous behaviour with increasing water saturation, following a pattern that cannot be predicted by existing models. A model involving quasi-static and dynamic components is proposed to reproduce the streaming potential measurements. The dynamic component is based on the first time derivative of the driving pore pressure. The influence of this component is investigated with respect to fluid velocity, which is very different between the two experiments. The results demonstrate that the dynamic component is predominant at the onset of drainage in experiments with the slowest water flow. On the other hand, its influence appears to vanish with increasing drainage velocity. Our results suggest that fluid flow and water distribution at the pore scale have an important influence on the streaming potential response for unsat-urated conditions. We propose to explain this specific streaming potential response in terms of the behaviour of both rock/water interface and water/air interfaces created during desaturation processes. The water/air interfaces are negatively charged, as also observed in the case of water/rock interfaces. Both the surface area and the flow velocity across these interfaces are thought to contribute to the non-monotonous behaviour of the streaming potential coefficient as well as the variations in its amplitude. The non-monotonous behaviour of air/water interfaces created during the flow was highlighted as it was measured and modelled by studies published in the literature. The streaming potential coefficient can increase to about 10 to 40 when water saturation decreases. Such an increase is possible if the amount of water/air interfaces is increased in sufficient amount, which can be the case

Clinical and Demographic Factors Associated with COVID-19, Severe COVID-19, and SARS-CoV-2 Infection in Adults: A Secondary Cross-Protocol Analysis of 4 Randomized Clinical Trials

Importance: Current data identifying COVID-19 risk factors lack standardized outcomes and insufficiently control for confounders. Objective: To identify risk factors associated with COVID-19, severe COVID-19, and SARS-CoV-2 infection. Design, Setting, and Participants: This secondary cross-protocol analysis included 4 multicenter, international, randomized, blinded, placebo-controlled, COVID-19 vaccine efficacy trials with harmonized protocols established by the COVID-19 Prevention Network. Individual-level data from participants randomized to receive placebo within each trial were combined and analyzed. Enrollment began July 2020 and the last data cutoff was in July 2021. Participants included adults in stable health, at risk for SARS-CoV-2, and assigned to the placebo group within each vaccine trial. Data were analyzed from April 2022 to February 2023. Exposures: Comorbid conditions, demographic factors, and SARS-CoV-2 exposure risk at the time of enrollment. Main Outcomes and Measures: Coprimary outcomes were COVID-19 and severe COVID-19. Multivariate Cox proportional regression models estimated adjusted hazard ratios (aHRs) and 95% CIs for baseline covariates, accounting for trial, region, and calendar time. Secondary outcomes included severe COVID-19 among people with COVID-19, subclinical SARS-CoV-2 infection, and SARS-CoV-2 infection. Results: A total of 57692 participants (median [range] age, 51 [18-95] years; 11720 participants [20.3%] aged ≥65 years; 31058 participants [53.8%] assigned male at birth) were included. The analysis population included 3270 American Indian or Alaska Native participants (5.7%), 7849 Black or African American participants (13.6%), 17678 Hispanic or Latino participants (30.6%), and 40745 White participants (70.6%). Annualized incidence was 13.9% (95% CI, 13.3%-14.4%) for COVID-19 and 2.0% (95% CI, 1.8%-2.2%) for severe COVID-19. Factors associated with increased rates of COVID-19 included workplace exposure (high vs low: aHR, 1.35 [95% CI, 1.16-1.58]; medium vs low: aHR, 1.41 [95% CI, 1.21-1.65]; P <.001) and living condition risk (very high vs low risk: aHR, 1.41 [95% CI, 1.21-1.66]; medium vs low risk: aHR, 1.19 [95% CI, 1.08-1.32]; P <.001). Factors associated with decreased rates of COVID-19 included previous SARS-CoV-2 infection (aHR, 0.13 [95% CI, 0.09-0.19]; P <.001), age 65 years or older (aHR vs age <65 years, 0.57 [95% CI, 0.50-0.64]; P <.001) and Black or African American race (aHR vs White race, 0.78 [95% CI, 0.67-0.91]; P =.002). Factors associated with increased rates of severe COVID-19 included race (American Indian or Alaska Native vs White: aHR, 2.61 [95% CI, 1.85-3.69]; multiracial vs White: aHR, 2.19 [95% CI, 1.50-3.20]; P <.001), diabetes (aHR, 1.54 [95% CI, 1.14-2.08]; P =.005) and at least 2 comorbidities (aHR vs none, 1.39 [95% CI, 1.09-1.76]; P =.008). In analyses restricted to participants who contracted COVID-19, increased severe COVID-19 rates were associated with age 65 years or older (aHR vs <65 years, 1.75 [95% CI, 1.32-2.31]; P <.001), race (American Indian or Alaska Native vs White: aHR, 1.98 [95% CI, 1.38-2.83]; Black or African American vs White: aHR, 1.49 [95% CI, 1.03-2.14]; multiracial: aHR, 1.81 [95% CI, 1.21-2.69]; overall P =.001), body mass index (aHR per 1-unit increase, 1.03 [95% CI, 1.01-1.04]; P =.001), and diabetes (aHR, 1.85 [95% CI, 1.37-2.49]; P <.001). Previous SARS-CoV-2 infection was associated with decreased severe COVID-19 rates (aHR, 0.04 [95% CI, 0.01-0.14]; P <.001). Conclusions and Relevance: In this secondary cross-protocol analysis of 4 randomized clinical trials, exposure and demographic factors had the strongest associations with outcomes; results could inform mitigation strategies for SARS-CoV-2 and viruses with comparable epidemiological characteristics

Acides naphténiques hydrates de gaz (influence de l'interface eau/huile sur les propriétés dispersantes d'un brut acide.)

Actuellement, les compagnies pétrolières sont amenées à exploiter des gisements de bruts situés à des profondeurs sous-marines de plus en plus importantes. Dans ces conditions de production (hautes pressions et basses températures), se pose le problème du bouchage des conduites pétrolières par les hydrates de gaz, composés cristallins constitués d'eau et de gaz. Il a été montré que certains bruts asphalténiques forment des émulsions eau dans huile (E/H) stables sur plusieurs mois et évitent la formation des bouchons d'hydrate. Dans le cadre de cette thèse, les propriétés "anti-hydrates" d'un brut acide AH provenant d'Afrique de l'Ouest sont étudiées. Ce brut comporte des acides naphténiques, composés hydrocarbures de formule brute RCOOH réactifs au pH et à la salinité de la phase aqueuse. Dans un premier temps, les propriétés émulsifiantes du brut AH ont été explorés. Il a été montré que la stabilité des émulsions E/H avec ce brut provient principalement des résines lourdes et des asphaltènes. Les naphténates RCOO-, forme basique des acides naphténiques, diminuent la stabilité des émulsions E/H. L'étude du brut AH vis à vis des hydrates de gaz a montré que ce brut présente des propriétés anti-agglomérantes modérées grâce aux résines lourdes et aux asphaltènes. Par contre, les naphténates RCOO- favorisent la formation des bouchons d'hydrate. D'autre part, il a été relevé que l'agglomération des particules d'hydrate accélère la cinétique de formation des hydrates et favorise le cassage des émulsions E/H. Un mécanisme d'agglomération par contact particule/gouttelette est proposé pour interpréter ces comportements. Enfin, nous proposons un modèle des équilibres physico-chimiques des acides naphténiques dans le mélange binaire eau/brut AH, afin de transposer les résultats obtenus en laboratoire aux conditions réelles.Nowadays, the development of offshore oil production under increasing water depths (high pressures and low temperatures) has led oil companies to focus on gas hydrates risks. Hydrates are crystals containing gas and water molecules which can plug offshore pipelines. It has been shown that some asphaltenic crude oils stabilise water-in-oil emulsions (W/O) during several months and exhibit very good anti-agglomerant properties avoiding hydrate plugs formation. In this work, we have studied the anti-hydraté properties of a West African acidic crude oil called crude AH. This oil contains naphthenic acids, RCOOH hydrocarbons which are sensitive to both the pH and the salinity of the water phase. The emulsifying properties of the crude AH have firstly been explored. It has been shown that heavy resins and asphaltenes are the main compounds of the crude AH responsible for the long term stability of the W/O emulsions whereas the napthenates RCOO- lead to less stable W/O emulsions. Dealing with hydrates, the crude AH exhibits moderate anti-agglomerant properties due to the presence of heavy resins and asphaltenes. However, the naphthenates RCOO- drastically increase the formation of hydrate plugs. Moreover, it has been pointed out that hydrate particles agglomeration accelerates the kinetics of hydrate formation and enhances the water/oil separation. In order to explain these behaviours, a mechanism of agglomeration by "sticking" between a hydrate particle and a water droplet has been proposed. Finally, we have developed a model which describes the physico-chemical equilibria of the naphthenic acids in the binary system water/crude AH, in order to transpose the results obtained in the laboratory to the real oilfield conditions.PAU-BU Sciences (644452103) / SudocSudocFranceF

Application de la luminescence à l’étude des changements de structure moléculaire, avec la température, de l’éthanol vitreux ou surfondu

Lorsqu’on élève de 80 à 150 K la température de l’éthanol d’abord vitreux, puis surfondu, des changements de structure à courte distance se produisent dans le domaine de la transition vitreuse (90, 100 K) et dans celui de la nucléation (110, 130 K). Ils peuvent être décelés et précisés à partir de l’étude de la luminescence d’un colorant (ici la fluorescéine) ou d’un carbure aromatique (ici le phénanthrène d10) dissous dans l’éthanol.Dans le cas de solutions étendues de fluorescéine (10-6 g/cm3), les mouvements libérés des molécules d’éthanol se traduisent par une dépolarisation de la fluorescence directe (S* → S). Dans le cas de solutions concentrées (10-2 ML-1) de phénanthrène d10, ces mouvements entraînent des « flambées » d’intensité de la fluorescence retardée, qui résulte de l’annihilation de l’énergie électronique de deux molécules de soluté dans l’état triplet de plus basse énergie

Formation/dissociation d'hydrates de gaz en milieu poreux (effet de la capillarité sur les conditions d'équilibre P/T.)

Les hydrates de gaz sont des composés solides qui pourraient être utilisés comme indicateurs thermiques des gisements d'hydrocarbures qu'ils surplombent. Pour cela, il est nécessaire de connaître avec précision leurs conditions d'équilibre P/T en milieu poreux. Le travail rapporté dans ce mémoire est une contribution à l'étude de ces conditions. Nous avons mis au point deux montages expérimentaux. Le premier, muni d'une cellule transparente, permet de visualiser et de mesurer les conditions d'équilibre des hydrates jusqu'à 0,5 MPa. Le second, muni d'une cellule sans fenêtre, permet de mesurer les conditions d'équilibre des hydrates jusqu'à 60 MPa. Nous avons vérifié que, en l'absence de milieu poreux, l'introduction d'un tensioactif (SDS) accélère la formation des hydrates. Leurs conditions d'équilibre mesurées et calculées sont en bon accord avec les données de la littérature sur l'intervalle 0,2 0,5 MPa pour l'hydrate de propane et 3 20 MPa pour l'hydrate de méthane. Nous avons amélioré la connaissance, tant expérimentale que théorique, des conditions d'équilibre de l'hydrate de méthane entre 20 et 53 MPa. Nous avons également vérifié que seuls des milieux mésoporeux (billes de silice, argile) ont une influence sur les conditions d'équilibre des hydrates. Ils produisent des décalages vers les plus basses températures et les plus hautes pressions, d'autant plus grands que les tailles des mésopores sont plus petites. Sur la base d'un modèle de van der Waals et Platteeuw modifié, nous avons montré que les décalages mesurés peuvent être attribués à la distribution de tailles des mésopores.Gas hydrates are solid compounds that could be used as a thermal tracer for the oil or gas fields they recover. In order to do it, the P/T equilibrium conditions must be known accurately in porous medium. The work presented in this report is a contribution to the study of these conditions. Two experimental set-ups were built up. The first one, provided with a transparent cell, allows to visualize and measure equilibrium conditions of gas hydrates up to 0.5 MPa. The second one, provided with a cell without any windows, allows to measure equilibrium conditions of gas hydrates up to 60 MPa. We checked that, in a bulk system, the use of a surfactant (SDS) accelerated hydrate formation. Their equilibrium conditions, measured and calculated, were in good agreement with literature data in the ranges 0.2 0.5 MPa for propane hydrate and 3 20 MPa for methane hydrate. We determined equilibrium conditions of methane hydrate, experimentally and theoretically, between 20 and 53 MPa, which completed literature data. We also checked that only mesoporous media (silica gels, clay) had an influence on equilibrium conditions of gas hydrates. They are shifted to lower temperatures and higher pressures and the smaller the mesopores, the higher the shift. On the basis of a modified van der Waals and Platteeux model, we demonstrated that shifts depended on the pore size distribution of the mesoporous systems.PAU-BU Sciences (644452103) / SudocSudocFranceF