Tsallisian Gravity and Cosmology

In this paper, we adopt the Verlinde hypothesis on the origin of gravity as the consequence of the tendency of systems to increase their entropy and employ the Tsallis statistics. Thereinafter, modifications to the Newtonian second law of motion, its gravity, and radial velocity profile are studied. In addition, and in a classical framework, the corresponding cosmology and also its ability in describing the inflationary phases are investigated.

Evaporating droplets on oil-wetted surfaces: Suppression of the coffee-stain effect

The evaporation of suspension droplets is the underlying mechanism in many surface-coating and surface-patterning applications. However, the uniformity of the final deposit suffers from the coffee-stain effect caused by contact line pinning. Here, we show that control over particle deposition can be achieved through droplet evaporation on oil-wetted hydrophilic surfaces. We demonstrate by flow visualization, theory, and numerics that the final deposit of the particles is governed by the coupling of the flow field in the evaporating droplet, the movement of its contact line, and the wetting state of the thin film surrounding the droplet. We show that the dynamics of the contact line can be tuned through the addition of a surfactant, thereby controlling the surface energies, which then leads to control over the final particle deposit. We also obtain an analytical expression for the radial velocity profile which reflects the hindering of the evaporation at the rim of the droplet by the nonvolatile oil meniscus, preventing flow toward the contact line, thus suppressing the coffee-stain effect. Finally, we confirm our physical interpretation by numerical simulations that are in qualitative agreement with the experiment.

Rediscovering the Galactic outer disk with LAMOST data

From the derived stellar density profile using LAMOST giant stars, we find that the Galactic disk does not show truncation or break, but smoothly transit to the halo from 19 kpc. The scale length of the outer disk is only 1.6 ± 0.1 kpc, substantially smaller than previous results. This implies that the shapes of the inner and outer disk are different. Meanwhile, the disk flaring is not only found in older populations, but also in younger population. Moreover, the vertical oscillations of the disk are identified in a wide range or R from 8 to 14 kpc. We also find that the velocity dispersion profile as a function of the Galactocentric radius is flat with scale length of 26.3 ± 3.2 kpc. We confirm that the radial velocity profile in outer disk is significantly affected by asymmetric motion. The bar with either a slower or a faster pattern speed can induce the similar radial asymmetric motion.

Large-Eddy Simulation of Roll Vortices in a Hurricane Boundary Layer

For the last decade, horizontal roll vortices have been often observed in hurricane boundary layers (HBLs). In this study, a large-eddy simulation is performed to explore the formation mechanism of the horizontal roll vortices and their significance in a near-neutrally stratified HBL at 40 km (R40) and 100 km (R100) from the center of the hurricane. Results are examined through turbulence statistics and empirical orthogonal function (EOF) analysis. The EOF analysis and budgets of turbulent kinetic energy demonstrate that an inflection-point instability in the radial velocity profile is responsible for the roll vortices with horizontal wavelengths of 1.5–2.4 km in the HBL both for R40 and R100. The roll vortices for R40 are nearly aligned with the gradient wind, while those for R100 are oriented slightly to the left of that wind. Also the horizontal distributions of velocity fluctuations suggest the presence of streaklike structures at horizontal intervals of several hundred meters near the ground surface. Internal gravity waves, Kelvin–Helmholtz waves, and entrainments occur above the HBL and are partly coupled with the roll vortices in the HBL, implying an enhancement of vertical transports of momentum and other quantities between the HBL and the free atmosphere.

Effect of Viscosity on the Separation Ability of a Hydrocyclone

On bases of numerical simulation and theoretical analysis, two cases of media, water and slurry (a kind of pseudoplastic power-law fluids), were used in the same hydrocyclone under the same operating condition. The Compare results show that the effect of the medium viscosity on the radial-velocity profile is slight; on the other hand, the effect of the media viscosity on the tangential-velocity profiles is important. The increase of the media viscosity produces not only the increase of the viscous resistance but also the steep reducing of the peak value of tangential-velocity profiles, which means that the inward viscous force loading upon the particles are enforced, on the other hand , the outward centrifugal force loading on the particles reduces greatly. The increase of the media viscosity leads to the great decrease of the separation ability of a hydrocyclone.

New analytic solutions for wave propagation in flexible, tapered vessels with reference to mammalian arteries

Novel, closed-form, analytic solutions for the pressure and velocity fields are derived for the linear problem of wave propagation inside a tapered flexible vessel of conical shape. It is shown that pressure and velocity can be written in terms of Bessel functions of orders $1/ 3$ and $4/ 3$ respectively. An expression is also derived that quantifies the effect of the cone angle on the wave propagation velocity. The analytic solutions are general and valid for tube variations at any length scale in relation to the wavelength of the wave. In other words, the requirement that the changes in vessel properties with distance should take place over a length scale large compared to the wavelength of the wave, is not employed or needed. This is the basic condition for the application of WKB theory to tapered vessels. However, this condition is not satisfied in pressure pulses propagating in mammalian arteries. The general expressions derived in this paper are directly applicable to the cardiovascular system of mammals. It is further shown that the presented solution naturally tends to the asymptotic WKB solution when the assumptions of the theory are applied to the general expressions. An explicit formula is provided for the time-averaged energy flux of the wave that shows clearly the effect of the continuous reflection of the wave from the vessel wall. Viscous effects are incorporated by coupling the derived analytic solution with the radial velocity profile of Womersley. The results are compared with full nonlinear fluid–structure interaction simulations and very good agreement is found (maximum differences are ${\ensuremath{\sim} }1\hspace{0.167em} \% $ and 1.6 % for area-averaged pressure and velocity respectively, and 4–6 % for local velocity values).

Flowing liquid crystal simulating the Schwarzschild metric

We show how to simulate the equatorial section of the Schwarzschild metric through a flowing liquid crystal in its nematic phase. Inside a liquid crystal in the nematic phase, a traveling light ray feels an effective metric, whose properties are linked to perpendicular and parallel refractive indexes, n o and n e respectively, of the rod-like molecule of the liquid crystal. As these indexes depend on the scalar order parameter of the liquid crystal, the Beris-Edwards hydrodynamic theory is used to connect the order parameter with the velocity of a liquid crystal flow at each point. This way we calculate a radial velocity profile that simulates the equatorial section of the Schwarzschild metric, in the region outside of Schwarzschild’s radius, in the nematic phase of the liquid crystal. In our model, the higher flow velocity can be on the order of some meters per second.