Drift of Phase Fluctuations in the ABC Model

In a recent work, Bodineau and Derrida analyzed the phase fluctuations in the ABC model. In particular, they computed the asymptotic variance and, on the basis of numerical simulations, they conjectured the presence of a drift, which they guessed to be an antisymmetric function of the three densities. By assuming the validity of the fluctuating hydrodynamic approximation, we prove the presence of such a drift, providing an analytical expression for it. This expression is then shown to be an antisymmetric function of the three densities. The antisymmetry of the drift can also be inferred from a symmetry property of the underlying microscopic dynamics.     

Computational analysis of entropy generation in mixed convection flow past a vertical wavy cone

Journal of Thermal Analysis and Calorimetry - The problem of entropy generation in mixed convection flow of incompressible viscous fluid along an isothermal vertical wavy cone is investigated...     

A study of cylindrically symmetric solutions in $$f(R, \phi,X)$$ theory of gravity

The European Physical Journal C - Much theoretical effort and automatization are required to confront new physics models with experimental data for many types of particle reactions at future...     

Drop impact on surfactant films and solutions

Drops impacting on horizontal aqueous surfactant films have been analyzed using a high-speed camera. Drops of either water or aqueous surfactant solutions had a diameter of 2.4?±?0.4 mm and impacted with a velocity of 0.1 to 1.3 m/s. As surfactants, anionic sodium dodecyl sulfate and cationic cetyltrimethyl ammonium bromide were used. Pure water drops impacting on freestanding surfactant films showed coalescence, bouncing, partial bouncing, passing, and partial passing. For bouncing, the concentration of surfactant in the surfactant film must exceed the critical micelle concentration. When surfactant was added to the drop, coalescence and partial passing were suppressed. We attribute the different behavior to different hydrodynamic boundary conditions at the surface of pure water and surfactant solution, leading to different repulsive hydrodynamic forces arising when the air has to flow out of the closing gap between the two liquid surfaces. The boundary condition changes as a function of surfactant concentration from a slip to no-slip, leading to stronger hydrodynamic repulsion. In addition, estimates of the characteristic velocities show that diffusion of air into the water is slow and can only account for the very last thinning of the air gap before coalescence.     

Diffusion of isolated surface-active molecules at the air/water interface

Fluorescence correlation spectroscopy was applied to study the diffusion of isolated surface-active molecules at air/water interfaces. Rhodamine 6G was used as a surface-active fluorescent tracer. Results show that the diffusion coefficient of the Rhodamine 6G at the interface is about 2.5 times higher than in the bulk. Effects of Rhodamine 6G concentration and added SDS or CTAB surfactants have been studied. Diffusion of Rhodamine 6G at the interface is slowed down at surfactant concentration corresponding to a mean distance between molecules of 10 and 40 nm, indicating a long-range interaction.     

Fast dynamic wetting of polymer surfaces by miscible and immiscible liquids

The initial stages of spontaneous spreading of a solvent drop (toluene) on the surface of a soluble polymer (polystyrene) have been studied with a high-speed camera. For drops of 1–4 μL volume, the increase in contact radius r can be described by a power law r μ t^a r \propto {t^{\alpha }} , with the spreading exponent α = 0.50 and for the first ≈8 ms. Thereafter, the three-phase contact line was pinned leading to a macroscopic static contact angle of Θ₀ = 12–15°. The insoluble liquids ethanol (α = 0.47, Θ₀ = 0) and water (α = 0.35, Θ₀ = 90°) showed a slower spreading. We attribute the fast spreading of toluene to the strong interaction with the polymer, like in reactive wetting. The finite macroscopic contact angle indicates the formation of a ridge by softening of polystyrene due to permeated toluene and the subsequent plastic deformation by the surface tension of the liquid. This interpretation is supported by experiments on polymers grafted from a silicon wafer. Toluene completely wets polymer brush surfaces. Transport of toluene through the vapor phase plays a significant role.     

Flow structure due to hexagonal cavities and bumps on a plate surface

We present the results of flow visualization and velocity measurements on a hexagonal structured surface. Several configurations with concave and convex hexagonal structures are investigated. Each hexagonal structure is 2.7 mm deep and 33 mm wide (width between flats) and has a height to diameter ratio of 0.05 based on equivalent diameter. Considered are flow velocities 19 m/s, 24 m/s, and 27 m/s. The flow bifurcates on the leading edge of the concave configuration into two counter rotating vortices and propagates further in streamwise direction. The circulating regions are identified by the peaks in r.m.s. velocity curves. In case of concave configuration, the flow splits up into counter rotating vortical structures in a vertical plane parallel to the flow. The lower vortex rotating in the opposite direction of the flow cause the oil film fringes to drift upstream. Complex circulating regions similar to the arrangement of slices in an orange can be observed on the trailing edge of the concave hexagonal structure.     

Preparation and stereochemistry of methyl 3-(and 4)-p-chlorothiophenoxy-1-methylpiperidine-4-(and 3)-carboxylates,and cyclization to benzothiopyranopyridinones

The title piperidines were prepared by (a) methanolysis of the corresponding nitriles and (b) addition of p-chlorothiophenol to the appropriate tetrahydropyridines. Three esters were obtained with stereochemistry assigned by nmr analysis: 2 [3(a) SAr, 4(e) CO₂Me], 5 [4(e) SAr, 3(e) CO₂Me], 6 [4(a) SAr, 3(e) CO₂Me]. Compounds 2 and 6 cyclized in 70% sulfuric acid. The product structures were established by X-ray crystallography and, surprisingly, both had trans-fused rings. Compound 5 , however, did not cyclize but gave 4-(methylthio)chlorobenzene as the sole isolated product.