Viewpoint: cloud drops stick together

An imaging probe on an airplane observes the clustering of water droplets in clouds, confirming a predicted effect that is correlated with rainfall

Verifique sus conocimientos sobre técnicas de diagnóstico por la imagen en patología dental y maxilofacial

Esta entrega, que forma parte de una serie de Nursing sobre las pruebas complementarias, está dedicada a las técnicas de imagen para la exploración dental. La exploración y el diagnóstico se pueden llevar a cabo mediante diferentes modalidades diagnósticas. Las más habituales son la radiología convencional, la tomografía computarizada (TC) y la resonancia magnética (RM). Para facilitar a los profesionales de enfermería los recursos necesarios para satisfacer las demandas de información de los pacientes, es necesario un recorrido por estas técnicas, habituales en los diferentes ámbitos asistenciales. Desde el punto de vista de atención al paciente es útil poder explicar y despejar las dudas que se pudieran plantear respecto a la preparación, a la dinámica y, en general, al proceso diagnóstico

Effect of particle injection on heat transfer in rotating Rayleigh-Bénard convection

The present study attempts to change the regime transitions and heat transfer properties in rotating Rayleigh-Bénard convection by injecting ∼100-μm-diam particles in the flow. The particles start settling out of the fluid immediately after injection and separate entirely from the fluid over a period of several hours. The particles deposit on the top and bottom surfaces, forming porous layers with nonideal thermal properties, and, as expected, decrease the heat flux. The reduction in heat transfer is a result of the inability of the layers to respond rapidly enough to fluid temperature fluctuations. However, in the rotation-dominated geostrophic regime, the heat transfer normalized by its nonrotating value is higher in the presence of the particle layers than without them. Direct numerical simulations with ideal heat transfer walls indicate that the temperature fluctuations in the bulk become slower under the damping effect of rotation, in contrast with those in the boundary layers, which do not show any damping until the flow transitions to the geostrophic regime. In this regime, the dominant time scale of the near-wall fluid temperature fluctuations increases substantially as the rotation rate is increased. It is thus likely that the time response of the particle layers in relation to that of the nearby fluid improves only in the geostrophic regime, which is reflected in a relatively larger heat transfer

Exploring the geostrophic regime of rapidly rotating convection with experiments

Rapidly rotating Rayleigh-Bénard convection is studied using time-resolved particle image velocimetry and three-dimensional particle tracking velocimetry. Approaching the geostrophic regime of rotating convection, where the flow is highly turbulent and at the same time dominated by the Coriolis force, typically requires dedicated setups with either extreme dimensions or troublesome working fluids (e.g. cryogenic helium). In this study, we explore the possibilities of entering the geostrophic regime of rotating convection with classical experimental tools: a table-top conventional convection cell with a height of 0.2 m and water as the working fluid. In order to examine our experimental measurements, we compare the spatial vorticity autocorrelations with the statistics from simulations of geostrophic convection reported earlier in [D. Nieves et al., Phys. Fluids 26, 086602 (2014)]. Our findings show that we have indeed access to the geostrophic convection regime and can observe the signatures of the typical flow features reported in the aforementioned simulations

Turbulence statistics and energy budget in rotating Rayleigh-Bénard convection

The strongly-modified turbulence statistics of Rayleigh-Bénard convection subject to various rotation rates is addressed by numerical investigations. The flow is simulated in a domain with periodic boundary conditions in the horizontal directions, and confined vertically by parallel no-slip isothermal walls at the bottom and top. Steady rotation is applied about the vertical. The rotation rate, or equivalently the Rossby number Ro, is varied such that Ro ranges from 8 (no rotation) to Ro = 0.1 (strong rotation). Two different Rayleigh numbers are used, viz. Ra = 2.5 × 106 and 2.5 × 107, characterising buoyancy due to temperature differences. The Prandtl number s = 1, close to the value for air. Horizontally averaged statistics show that rotation reduces the turbulence intensity, although probability density functions clearly show that considerable (preferably cyclonic) vorticity is added to the flow by the Ekman boundary layers on the solid walls. Rotation changes the balance of the turbulent kinetic energy budget. It is found that for a range of rotation rates the buoyant production is higher than without rotation. Therefore, at appropriate rotation rates the heat flux through the fluid layer is increased relative to the non-rotating case. At sufficiently rapid rotation, however, the heat flux through the fluid layer is strongly attenuated

Numerical investigation of the combined effects of gravity and turbulence on the motion of small and heavy particles

\u3cp\u3eNumerical studies [1, 2] show that the influence of gravity and turbulence on the motion of small and heavy particles is not a simple superposition. However, in [3] it is shown that these studies may be artificially influenced by the turbulence forcing scheme. In the present study, a new numerical setup to investigate the combined effects of gravity and turbulence on the motion of small and heavy particles is presented, where the turbulence is only forced at the inflow and is advected through the domain by a mean flow velocity. Within a transition region the turbulence develops to a physical state which shares similarities with grid-generated turbulence in wind tunnels. In this flow, trajectories of about 43 million small and heavy particles are advanced in time. It is found that for a specific particle inertia the particles fall faster in a turbulent flow compared with their fall velocity in quiescent flow. Additionally, specific regions within the turbulent vortices cannot be reached by the particles as a result of the particle vortex interaction. Therewith, the particles tend to cluster outside the vortices. These results are in agreement with the theory of Dávilla and Hunt [4].\u3c/p\u3

Anisotropy in turbulent rotating convection

A simple model for many geophysical and astrophysical flows, such as oceanic deep convection and the convective outer layer of the Sun, is found in rotating Rayleigh.BéLenard convection: a horizontal fluid layer heated from below and cooled from above is rotated about a vertical axis. Three dimensionless parameters characterise this flow: the Rayleigh number Ra describes the strength of the destabilising temperature gradient, the Prandtl number relates the diffusion coefficients for heat and momentum of the fluid, and the Rossby number Ro is the ratio of buoyancy and Coriolis forces (when rotation is absent and Ro 1 for rotation-dominated flow). We investigate the effect of rotation on the flow anisotropy in turbulent convection in an upright cylinder of equal height and diameter, with experiments and numerical simulations

On the accessibility of rotating convection regimes in laboratory experimental studies

Many geophysical and astrophysical phenomena are driven by massively-turbulent, multiscale fluid dynamics. These fluid systems are often both too remote and too complex to fully grasp without employing forward models. While attempts to directly simulate geophysical systems have made important strides, such models still inhabit modest ranges of the governing parameters that cannot be extrapolated to extreme planetary settings with certainty. An alternate approach is to isolate the fundamental physics in a reduced setting. The canonical problem of rotating Rayleigh-B\'enard convection in a plane layer provides such a reduced framework. Laboratory experiments are capable of resolving broad ranges of length and time scales and are thus well-suited for reaching the extreme conditions where asymptotic behaviors distinctly manifest. In this study, we discuss how to optimize laboratory experiments toward testing asymptotically-predicted rotating convection regimes. We also discuss the limitations that arise in designing these experiments. We apply these criteria to several of the most extreme rotating convection setups to date and predict their capabilities. The achievable parameter ranges of these current and upcoming devices demonstrate that laboratory studies likely still remain on the cusp of exploring geophysically-relevant flow behaviors in rotating convection

Thermally responsive particles in Rayleigh-Bénard convection

We track particles that experience both mechanical and thermal inertia in direct numerical simulations of Rayleigh-Bénard convection (RBC), a fluid layer heated from below and cooled from above. Both particles and fluid exhibit thermal expansion. The particles have a larger thermal expansion coefficient than the fluid, such that particles become lighter than the fluid near the hot bottom plate and heavier than the fluid near the cold top plate. First we investigate how the dynamics of thermal expansion affect the distribution of particles in the RBC cell. We find a regime of viscous and thermal response times where the concentration of particles at the plates is enhanced. A particle deposited on a plate re-suspends after a characteristic residence time, that depends on the thermal response time. Now that we found a mechanism driving particles towards the plates, while also enforcing a motion back to the bulk, we include mechanical and thermal two-way coupling and investigate how thermally responsive particles affect flow structures and heat transfer in RBC. Ultimately, we want to explore the possibility to enhance heat transfer using these thermally inertial particles