Crack formation and prevention in colloidal drops

Crack formation is a frequent result of residual stress release from colloidal films made by the evaporation of colloidal droplets containing nanoparticles. Crack prevention is a significant task in industrial applications such as painting and inkjet printing with colloidal nanoparticles. Here, we illustrate how colloidal drops evaporate and how crack generation is dependent on the particle size and initial volume fraction, through direct visualization of the individual colloids with confocal laser microscopy. To prevent crack formation, we suggest use of a versatile method to control the colloid-polymer interactions by mixing a nonadsorbing polymer with the colloidal suspension, which is known to drive gelation of the particles with short-range attraction. Gelation-driven crack prevention is a feasible and simple method to obtain crack-free, uniform coatings through drying-mediated assembly of colloidal nanoparticlesopen0

Intravenous alteplase for stroke with unknown time of onset guided by advanced imaging: systematic review and meta-analysis of individual patient data

Background: Patients who have had a stroke with unknown time of onset have been previously excluded from thrombolysis. We aimed to establish whether intravenous alteplase is safe and effective in such patients when salvageable tissue has been identified with imaging biomarkers. Methods: We did a systematic review and meta-analysis of individual patient data for trials published before Sept 21, 2020. Randomised trials of intravenous alteplase versus standard of care or placebo in adults with stroke with unknown time of onset with perfusion-diffusion MRI, perfusion CT, or MRI with diffusion weighted imaging-fluid attenuated inversion recovery (DWI-FLAIR) mismatch were eligible. The primary outcome was favourable functional outcome (score of 0–1 on the modified Rankin Scale [mRS]) at 90 days indicating no disability using an unconditional mixed-effect logistic-regression model fitted to estimate the treatment effect. Secondary outcomes were mRS shift towards a better functional outcome and independent outcome (mRS 0–2) at 90 days. Safety outcomes included death, severe disability or death (mRS score 4–6), and symptomatic intracranial haemorrhage. This study is registered with PROSPERO, CRD42020166903. Findings: Of 249 identified abstracts, four trials met our eligibility criteria for inclusion: WAKE-UP, EXTEND, THAWS, and ECASS-4. The four trials provided individual patient data for 843 individuals, of whom 429 (51%) were assigned to alteplase and 414 (49%) to placebo or standard care. A favourable outcome occurred in 199 (47%) of 420 patients with alteplase and in 160 (39%) of 409 patients among controls (adjusted odds ratio [OR] 1·49 [95% CI 1·10–2·03]; p=0·011), with low heterogeneity across studies (I2=27%). Alteplase was associated with a significant shift towards better functional outcome (adjusted common OR 1·38 [95% CI 1·05–1·80]; p=0·019), and a higher odds of independent outcome (adjusted OR 1·50 [1·06–2·12]; p=0·022). In the alteplase group, 90 (21%) patients were severely disabled or died (mRS score 4–6), compared with 102 (25%) patients in the control group (adjusted OR 0·76 [0·52–1·11]; p=0·15). 27 (6%) patients died in the alteplase group and 14 (3%) patients died among controls (adjusted OR 2·06 [1·03–4·09]; p=0·040). The prevalence of symptomatic intracranial haemorrhage was higher in the alteplase group than among controls (11 [3%] vs two [<1%], adjusted OR 5·58 [1·22–25·50]; p=0·024). Interpretation: In patients who have had a stroke with unknown time of onset with a DWI-FLAIR or perfusion mismatch, intravenous alteplase resulted in better functional outcome at 90 days than placebo or standard care. A net benefit was observed for all functional outcomes despite an increased risk of symptomatic intracranial haemorrhage. Although there were more deaths with alteplase than placebo, there were fewer cases of severe disability or death. Funding: None

Viscoelastic dewetting of a polymer film on a liquid substrate

The Dewetting of thin polymer films (60–300 nm) on a non-wettable liquid substrate has been studied in the vicinity of their glass transition temperature. In our experiment, we observe a global contraction of the film while its thickness remains uniform. We show that, in this case, the strain corresponds to simple extension, and we verify that it is linear with the stress applied by the surface tension. This allows direct measurement of the stress/strain response as a function of time, and thus permits the measurement of an effective compliance of the thin films. It is, however, difficult to obtain a complete viscoelastic characterization, as the short time response is highly dependant on the physical age of the sample. Experimental results underline the effects of residual stress and friction when dewetting is analyzed on rigid substrates

Pattern formation during the drying of a colloidal suspension

Receding contact lines of colloidal suspensions are studied in the presence of drying, inside Hele-Shaw cells. At high velocity the contact line movement is continuous and the particle deposition is uniform. At small velocity, a periodic pinning-unpinning of the contact line is observed leading to a patterning of the substrate. We focused on the correlation between the deposition pattern and the pinning force that grows during the pinning. Our results strongly indicate that this pinning force is proportional to the macroscopic slope of the deposit and accounted by a simple capillary balance

Physical aging of glassy PMMA/toluene films: Influence of drying/swelling history

Gravimetry experiments in a well-controlled environment have been performed to investigate aging for a glassy PMMA/toluene film. The temperature is constant and the control parameter is the solvent vapor pressure above the film (i.e. the activity). Several experimental protocols have been used, starting from a high activity where the film is swollen and rubbery and then aging the film at different activities below the glass transition. Desorption and resorption curves have been compared for the different protocols, in particular in terms of the softening time, i.e. the time needed by the sample to recover an equilibrium state at high activity. Non-trivial behaviors have been observed, especially at small activities (deep quench). A model is proposed, extending the Leibler-Sekimoto approach to take into account the structural relaxation in the glassy state, using the Tool formalism. This model well captures some of the observed phenomena, but fails in describing the specific kinetics observed when aging is followed by a short but deep quench

Axisymmetric Drainage in Hydrophobic Porous Media Micromodels

We present studies of axisymmetric drainage in two-dimensional micromodels of porous media using up to date microfabrication and image analysis methods. Drainage of model oil by aqueous solutions is studied at low capillary numbers (Ca) typically encountered during oil recovery operations. We use two types of oil-wet micromodels: one is based on a deposition method for creating a random monolayer of micronic glass beads, while the other is made using computer generated random networks etched in glass using wet-lithography. Both models have a central injection scheme and a radial geometry, resulting in a continuous variation of the capillary number during the course of drainage. We first carry out an analysis of experiments at global micromodel scale using computer based image analysis coupled with flow rates and pressure drop measurements. Basic relevant parameters such as permeability, porosity of the micromodel and residual oil in place after waterflooding are extracted. We then take advantage of the ease of observation in transparent micromodels to investigate the drainage phenomenon at local scale. Local saturation and front width are measured as a function of the local capillary number. Interestingly, because of the radial flow geometry, our experiments allow a continuous plotting of the micromodels capillary desaturation curve on several decades. As expected but never precisely observed, all points of various experiments collapse on a single capillary desaturation curve for a given micromodel. However, we observe dissimilar behaviors between the two types of micromodels. We discuss this phenomenon in light of the pore scale geometrical differences between the two models

Tonks-Frenkel instability in electrolyte under high-frequency AC electric fields

The instability of an electrolyte surface to a high-frequency, 10 to 200kHz, electric field, normal to the interface is investigated theoretically. From a practical viewpoint, such a high frequency leads to the absence of undesired electrochemical reactions and provides an additional control parameter. The theory of unsteady electric double layer by Barrero and Ramos is exploited. At such a high frequency, which is much larger than the eigenfrequency of the mechanical system, the nonlinear mechanical term does not “feel” the fast part of the Coulomb force, but it feels its slower component. In fact, the system behaves as if the electric field were a DC field. The observed instability is qualitatively close to the Tonks-Frenkel instability. The problem of the linear stability of the 1D quiescent stationary solution is solved analytically. For the important limiting cases, simple analytical formulas are derived. The linear stability analysis is complemented by the DNS of the full nonlinear system of equations with broadband low-amplitude white-noise initial conditions. After a transition period, the linear instability mechanism filters out the broad spectrum except for a narrow band near the maximum growth rate in rather good agreement with the linear stability analysis. If the external field is large enough, the nonlinear evolution results in coherent structures with sharp tips resembling to a Taylor cone. An evaluation of the cone angle for different conditions gives its value of about 30° to 60° , which is smaller than the angle of 98.6° for DC field and qualitatively corresponds to the experiments (L.Y. Yeo et al., Phys. Rev. Lett. 92, 133902 (2004)) for the high-frequency AC field and to the theoretical evaluation of the AC Taylor cones in E.A. Demekhin et al., Phys. Rev. E 84, 035301(R) (2011)

Discussion. troisième journée

DISCUSSION — 3nd day. The third day of the seminar chaired by Mr. Mascard was devoted to "Man's Adaption". At the outset Mr. Mascard proposed the debates should bear directly on the two main questions arising out of this subject — procedures for personnel affiliation and professional improvement or recycling. Messrs. Meyers and Denkovic then briefly presented their reports and made some additional remarks. Mr. Meyers voiced his uneasiness in treating such a subject, in view of certain considerations: one, because he is among the few participants who practice, and two, because of the methods employed. Having employed a vocabulary for numerous questionnaires which was adapted to the countries, he feared that more fundamental realities were hidden behind certain responses. In addition, since the French reply was returned late, he was concerned that an important effort with regard to perfecting skills, existing outside the traditional structures, might have been neglected. He also questioned the choice of the methods destined to correct the effects of regulations for training and selection which tend to become sclerotic in most countries. He observed the absence of cohesion in the measures taken; for, although greater flexibility is indispensable in the face of new needs, defined doctrine and policy are equally necessary. It is to be feared namely, in the case of perfecting skills that good intentions obscure general policy. Mr. Denkovic first drew attention to the role of civil service in the socialist countries and elucidated its main features: searching for the general interest, guarantying citizens' rights, establishing a set standard of living. He then briefly resumed the principles governing the choice of civil servants and the different factors taken into consideration for appointment to a given post. The problems touched upon in this general report were developed in the course of the debate by the participants of other socialist countries. Hence, Messrs. Starosciak, Stjepanovic, Popovic, Kostadinov and Vintu supplied details concerning the systems in vigor in Poland, Yugoslavia, Bulgaria and Rumania respectively and answered numerous questions from the floor. Messrs. Schnur and Siedentopf gave examples of the solutions applied in Federal Germany. As for France, Messrs. Bodiguel, de Baecque and Bocognano each presented the topic of the day from a different angle. Mr. Bodiguel described a study on the career of graduates from the National School of Administration, questioning the role and importance of political influence in the promotion of civil servants. In his opinion there is an undeniable influence, which although it cannot be evaluated with precisions, would not be as important as it is sometimes said to be. Mr. Mascard underlined the interest surrounding the question of political influence and its basic importance in the socialist countries. Mr. Rybicki indicated that at a certain period (during the years following the installation of the socialist regime) political influence was the determining factor in Poland. Mr. de Baecque examined the possibilities of adaptation and perfection in civil service, the impediment constituted by security of employment and the inherent risks of inadaptation. He favored adapting civil servants to their employment through the creation of enlarged corps and the establishment of equilibrium between initial training (often costly) and on-the-job training. Mr. Bocognano made a brief inventory of the different methods for recycling within the administration, with which he has experimented, exposing their advantages and disadvantages. In conclusion Mr. Rybicki stated his satisfaction to note that knowledge of judicial, administrative and political problems had progressed in the European countries during the course of the past years. Explaining practices does not suffice, they must also be subjected to influence and improvement. Unity in Marxist principles does not solve practical problems. He therefore, considered that a general discussion between different socialist countries would be desirable. He also expressed his satisfaction with the atmosphere in which the seminar had taken place. Mr. Molitor insisted there should have been more time to discuss the very broad and varied questions brought up during the seminar. He suggested that in the future topics should be more limited in scope and that the manner in which they were to be treated should be set forth in advance. Mr. Bauchet, after having recalled the importance of Administrative Science, proposed the participation of the C.N.R.S. in future studies. He also approved the multiplication, of direct personal contact, the organization of specialized round tables and furthering the publication of studies relative to this field. Y. FORTINLa troisième journée du colloque, présidée par M. Mascard, a pour thème « l'adaptation des hommes ». Dès le départ, M. Mascard suggère que les débats portent directement sur les deux grandes questions soulevées par ce sujet: les procédures de recrutement du personnel et les procédures de perfectionnement et de recyclage. M. Meyers et M. Denkovic présentent ensuite brièvement leurs rapports et formulent quelques remarques complémentaires. M. Meyers fait part d'inquiétudes qu'il éprouve après avoir traité le sujet qui lui a été proposé : inquiétudes de climat, car il est l'un des rares praticiens participant au colloque, inquiétudes de méthode aussi, car il a employé un vocabulaire propre pour les questionnaires envoyés à de nombreux pays et a le sentiment que des réalités plus fondamentales se cachent derrière les réponses. De plus, la France ayant tardé à répondre, il craint d'avoir négligé un mouvement de perfectionnement important existant en dehors des structures prévues. S'interrogeant par ailleurs sur le choix des moyens destinés à corriger les effets des règles de formation et de sélection qui, dans la plupart des pays, ont tendance à se scléroser, il relève l'absence de cohésion des mesures prises, car s'il est indispensable d'introduire plus de souplesse afin de faire face à des besoins nouveaux, il semble également souhaitable de pouvoir insérer cette démarche dans une certaine doctrine et une certaine politique. Il est à craindre, en matière de perfectionnement notamment, que les bonnes intentions n'aient pris de vitesse une politique d'ensemble. M. Denkovic insiste tout d'abord sur le rôle de la fonction publique dans les pays socialistes et en trace les grandes lignes : la recherche de l'intérêt général, la garantie des droits des citoyens, l'établissement d'un niveau de vie déterminé. Puis, il résume brièvement les principes sur lesquels repose le choix des fonctionnaires et les différents éléments dont il est tenu compte lors de leur nomination à un poste déterminé. Les problèmes abordés dans ce rapport général sont développés au cours des débats par les participants des différents pays socialistes. Ainsi MM. Starosciak, Stjepanovic, Popovic, Kostadinov, Vintu, apportent des précisions sur les systèmes adoptés par la Pologne, la Yougoslavie, la Bulgarie, la Roumanie et les questions qui n'ont pas manqué de s'y poser. MM. Schnur et Siedentopf illustrent par des exemples les solutions retenues par l'Allemagne fédérale. Quant à la France, MM. Bodiguel, de Baecque et Bocognano présentent sous des éclairages différents le thème retenu pour cette dernière séance du colloque. M. Bodiguel communique le résultat d'une étude portant sur la carrière des anciens élèves de 1'E.N.A. et s'interroge notamment sur le rôle et l'importance de l'influence politique sur la promotion des fonctionnaires. Il estime que, si elle n'est pas niable, elle demeure néanmoins difficile à évaluer avec précision et serait inférieure à ce qu'on a pu dire parfois. M. Mascard souligne l'intérêt de cette question et rappelle que l'aspect politique est, en ce domaine fondamental dans les pays socialistes. M. Rybicki indique qu'à une certaine époque (dans les années qui ont suivi l'instauration d'un régime socialiste) ce critère a été déterminant en Pologne. M. de Baecque examine pour sa part les possibilités d'adaptation et de perfectionnement des fonctionnaires, le frein constitué par la sécurité de l'emploi, les risques inhérents à l'inadaptation. Il suggère de favoriser l'adaptation des fonctionnaires à leur emploi en créant des corps aussi larges que possible et souhaite qu'un équilibre entre une formation initiale (souvent coûteuse) et la formation en cours de carrière, soit recherché. M. Bocognano fait un bref inventaire des différents moyens utilisés par l'administration en matière de recyclage, qu'il a eu l'occasion d'expérimenter, et expose leurs avantages et leurs inconvénients. M. Rybicki, en conclusion, fait part de sa satisfaction de constater que la connaissance des problèmes juridiques, administratifs et politiques, a progressé au cours des dernières années dans les pays européens. Il ne s'agit plus seulement d'expliquer la pratique, mais aussi de l'influencer, de l'améliorer. L'unité des principes marxistes n'apporte pas de solution aux problèmes pratiques. Une discussion commune entre les différents pays socialistes s'avère donc souhaitable. Il se félicite également de l'atmosphère dans laquelle s'est déroulé le colloque. M. Molitor insiste sur la nécessité de prolonger ces journées au cours desquelles des questions très différentes et très vastes ont été abordées. Il faudrait pour des rencontres ultérieures déterminer des thèmes plus limités et préciser la manière dont ils seront traités. M. Bauchet, après avoir rappelé l'importance de la science administrative, propose d'apporter l'aide du C.N.R.S. à des recherches ultérieures en favorisant la multiplication des contacts directs personnels, l'organisation de tables rondes spécialisées et en développant la publication d'études relatives à ce domaine. Y. FORTINMeyers François, Denkovic Dragos, Bodiguel Jean-Luc, Schnur Roman, Mascard Jean, De Baecque Francis, Siedentopf H. Discussion. troisième journée. In: Revue d'études comparatives Est-Ouest, vol. 6, 1975, n°3. La recherche administrative en Europe. pp. 263-289

Sclérose en plaques et grossesse [Multiple sclerosis and pregnancy]

International audienceThe question of pregnancy in patients with multiple sclerosis is regularly raised due to the prevalence of the disease in middle age women. The multiple sclerosis think tank (Groupe de Réflexion sur la Sclérose en Plaques [GRESEP]) decided to develop recommendations on this issue, with consideration to both the impact of multiple sclerosis on pregnancy, and that of pregnancy on the disease. As with topics of previous works, the formal expert consensus method was used. The working group was composed of hospital-based and private practice neurologists. The reading group was composed of neurologists, anaesthetists and obstetricians. Each recommendation is presented with the relevant level of consensus