How Dilute are Dilute Solutions in Extensional Flows?

Submitted to J. Rheol.We investigate the concentration-dependence of the characteristic relaxation time of dilute polymer solutions in transient uniaxial elongational flow. A series of monodisperse polystyrene solutions of five different molecular weights (1.8×10^6 ≤ M ≤ 8.3×10^6 g/mol) with concentrations spanning five orders of magnitude were dissolved in two solvents of differing solvent quality (diethyl phthalate and oligomeric styrene). Optical measurements of the rate of filament thinning and the time to break-up in each fluid are used to determine the characteristic relaxation time. A lower sensitivity limit for the measurements was determined experimentally and confirmed by comparison to numerical calculations. Above this sensitivity limit we show that the effective relaxation time of moderately dilute solutions (0.01 ≤ c/c* ≤ 1) in transient extensional flow rises substantially above the fitted value of the relaxation time extracted from small amplitude oscillatory shear flow and above the Zimm relaxation time computed from kinetic theory and intrinsic viscosity measurements. This effective relaxation time exhibits a power-law scaling with the reduced concentration (c/c*) and the magnitude of the exponent varies with the thermodynamic quality of the solvent. This scaling appears to be roughly consistent to that predicted when the dynamics of the partially elongated and overlapping polymer chains are described within the framework of blob theories for semi-dilute solutions.NASA Microgravity Fluid Dynamic

Well-posedness of Hydrodynamics on the Moving Elastic Surface

The dynamics of a membrane is a coupled system comprising a moving elastic surface and an incompressible membrane fluid. We will consider a reduced elastic surface model, which involves the evolution equations of the moving surface, the dynamic equations of the two-dimensional fluid, and the incompressible equation, all of which operate within a curved geometry. In this paper, we prove the local existence and uniqueness of the solution to the reduced elastic surface model by reformulating the model into a new system in the isothermal coordinates. One major difficulty is that of constructing an appropriate iterative scheme such that the limit system is consistent with the original system.Comment: The introduction is rewritte

Long-Wavelength Instability in Surface-Tension-Driven Benard Convection

Laboratory studies reveal a deformational instability that leads to a drained region (dry spot) in an initially flat liquid layer (with a free upper surface) heated uniformly from below. This long-wavelength instability supplants hexagonal convection cells as the primary instability in viscous liquid layers that are sufficiently thin or are in microgravity. The instability occurs at a temperature gradient 34% smaller than predicted by linear stability theory. Numerical simulations show a drained region qualitatively similar to that seen in the experiment.Comment: 4 pages. The RevTeX file has a macro allowing various styles. The appropriate style is "mypprint" which is the defaul

Discrete exterior calculus (DEC) for the surface Navier-Stokes equation

We consider a numerical approach for the incompressible surface Navier-Stokes equation. The approach is based on the covariant form and uses discrete exterior calculus (DEC) in space and a semi-implicit discretization in time. The discretization is described in detail and related to finite difference schemes on staggered grids in flat space for which we demonstrate second order convergence. We compare computational results with a vorticity-stream function approach for surfaces with genus 0 and demonstrate the interplay between topology, geometry and flow properties. Our discretization also allows to handle harmonic vector fields, which we demonstrate on a torus.Comment: 21 pages, 9 figure

Whole-genome sequencing reveals host factors underlying critical COVID-19

Critical COVID-19 is caused by immune-mediated inflammatory lung injury. Host genetic variation influences the development of illness requiring critical care1 or hospitalization2,3,4 after infection with SARS-CoV-2. The GenOMICC (Genetics of Mortality in Critical Care) study enables the comparison of genomes from individuals who are critically ill with those of population controls to find underlying disease mechanisms. Here we use whole-genome sequencing in 7,491 critically ill individuals compared with 48,400 controls to discover and replicate 23 independent variants that significantly predispose to critical COVID-19. We identify 16 new independent associations, including variants within genes that are involved in interferon signalling (IL10RB and PLSCR1), leucocyte differentiation (BCL11A) and blood-type antigen secretor status (FUT2). Using transcriptome-wide association and colocalization to infer the effect of gene expression on disease severity, we find evidence that implicates multiple genes—including reduced expression of a membrane flippase (ATP11A), and increased expression of a mucin (MUC1)—in critical disease. Mendelian randomization provides evidence in support of causal roles for myeloid cell adhesion molecules (SELE, ICAM5 and CD209) and the coagulation factor F8, all of which are potentially druggable targets. Our results are broadly consistent with a multi-component model of COVID-19 pathophysiology, in which at least two distinct mechanisms can predispose to life-threatening disease: failure to control viral replication; or an enhanced tendency towards pulmonary inflammation and intravascular coagulation. We show that comparison between cases of critical illness and population controls is highly efficient for the detection of therapeutically relevant mechanisms of disease

Flow in porous media, phase behavior and ultralow interfacial tensions: mechanisms of enhanced petroleum recovery. Final technical report

A major program of university research, longer-ranged and more fundamental in approach than industrial research, into basic mechanisms of enhancing petroleum recovery and into underlying physics, chemistry, geology, applied mathematics, computation, and engineering science has been built at Minnesota. The 1982 outputs of the interdisciplinary team of investigators were again ideas, instruments, techniques, data, understanding and skilled people: forty-one scientific and engineering papers in leading journals; four pioneering Ph.D. theses; numerous presentations to scientific and technical meetings, and to industrial, governmental and university laboratories; vigorous program of research visits to and from Minnesota; and two outstanding Ph.D.'s to research positions in the petroleum industry, one to a university faculty position, one to research leadership in a governmental institute. This report summarizes the 1982 papers and theses and features sixteen major accomplishments of the program during that year. Abstracts of all forty-five publications in the permanent literature are appended. Further details of information transfer and personnel exchange with industrial, governmental and university laboratories appear in 1982 Quarterly Reports available from the Department of Energy and are not reproduced here. The Minnesota program continues in 1983, notwithstanding earlier uncertainty about the DOE funding which finally materialized and is the bulk of support. Supplemental grants-in-aid from nine companies in the petroleum industry are important, as are the limited University and departmental contributions. 839 references, 172 figures, 29 tables

Wetting hydrodynamics

Bretherton's (1961) theory of the forced, steady displacement of one fluid by another in a tube or between parallel plates is generalized to account for the effects of intermolecular forces in submicroscopically thin films and of a finite driving-fluid viscosity. The theory predicts that there are two displacement regimes, depending on capillary number μU/γ. At low speed the dynamic apparent contact angle retains its static value. If the displaced fluid perfectly wets the solid an equilibrium thin-film remains ; if not, there is not a continuous thin-film. At high speed a hydrodynamically entrained film is left behind regardless of equilibrium wetting characteristics. The entrained film thickens slightly with increasing driving-fluid viscosity. These predictions accord with experiment. In addition, evidence is presented that observed discrepancies between Bretherton's theory and measured film thicknesses are caused by the presence of surface-active impurities. Finally, implications for the submicroscopic origins of seeming slip at apparent contact lines, air entrainment in coating flows, soap-film dynamics, and the generation of mixed-wettability states in porous media are discussed.Nous généralisons la théorie de Bretherton qui décrit le déplacement stationnaire forcé d'un liquide par un autre dans un tube ou entre plaques parallèles en prenant en compte les effets des forces intermol6culaires dans les films microscopiques et la viscosité finie du fluide qui avance. La théorie prévoit deux régimes d'avancée suivant la valeur du nombre capillaire μU/γ. A faible vitesse, l'angle de contact dynamique apparent garde sa valeur statique. Si le fluide déplacé mouille parfaitement le solide, un film mince existe à l'équilibre. A grande vitesse, un film entraîné de façon hydrodynamique se forme quelles que soient les caractéristiques de mouillage à l'équilibre. L'épaisseur de ce film augmente légèrement avec la viscosité du liquide qui avance. Ces prédictions sont en accord avec l'expérience. De plus, nous montrons que les écarts entre la théorie de Bretherton et les épaisseurs de film mesurées sont dues à la présence d'impuretés tensioactives. Finalement nous discutons les implications sur l'origine microscopique du glissement effectif à la ligne de contact apparente, sur l'entraînement de l'air dans les écoulements de couchage, sur la dynamique des films de savon et sur la génération d'états mixtes de mouillage dans les milieux poreux

Interfacial tensions and phase behavior of alcohol-hydrocarbon-water-sodium chloride systems

The phase behavior and interfacial tensions of mixtures of alcohol, alkane, water, and sodium chloride that split into two or three liquid phases at 25�C are reported as a function of type of alcohol and alkane and sodium chloride concentration. The patterns of phase and tension behavior are similar to those observed with surfactant-based microemulsion systems but in a higher tension regime. The qualitative patterns of phase and tension behavior in the alcohol systems appear to be characteristic of all amphiphile-oil-brine systems, although the magnitudes of the interfacial tensions of microemulsion against oil-rich or water-rich phases can be some hundredfold smaller than the corresponding tensions of the alcohol-rich phase against oil-rich or water-rich phases. This difference appears to be a distinguishing feature of microemulsions and presumably arises from the relatively large scale of microemulsion microstructure. Microemulsions in multiphase equilibria incorporate tenfold or more water or oil than do corresponding alcohol solutions, and this argues for the topology and persistence of that microstructure. � 1987 American Chemical Society