Electrowetting-Induced Oil Film Entrapment and Instability

We investigate the spreading at variable rate of a water drop on a smooth hydrophobic substrate in an ambient oil bath driven by electrowetting. We find that a thin film of oil is entrapped under the drop. Its thickness is described by an extension of the Landau-Levich law of dip coating that includes the electrostatic pressure contribution. Once trapped, the thin film becomes unstable under the competing effects of the electrostatic pressure and surface tension and dewets into microscopic droplets, in agreement with a linear stability analysis. Our results recommend electrowetting as an efficient experimental approach to the fundamental problem of dynamic wetting in the presence of a tunable substrate-liquid interaction

Turbulence anisotropy and the SO(3) description

We study strongly turbulent windtunnel flows with controlled anisotropy. Using a recent formalism based on angular momentum and the irreducible representations of the SO(3) rotation group, we attempt to extract this anisotropy from the angular dependence of second-order structure functions. Our instrumentation allows a measurement of both the separation and the angle dependence of the structure function. In axisymmetric turbulence which has a weak anisotropy, this more extended information produces ambiguous results. In more strongly anisotropic shear turbulence, the SO(3) description enables one to find the anisotropy scaling exponent. The key quality of the SO(3) description is that structure functions are a mixture of algebraic functions of the scale with exponents ordered such that the contribution of anisotropies diminishes at small scales. However, we find that in third-order structure functions of homogeneous shear turbulence the anisotropic contribution is always large and of the same order of magnitude as the isotropic part. Our results concern the minimum instrumentation needed to determine the parameters of the SO(3) description, and raise several questions about its ability to describe the angle dependence of high-order structure functions

Intermittency in turbulence

+168hlm.;24c

Small scale velocity jumps in shear turbulence

We measure structure functions and structures in uniformly sheared strong turbulence using an array of hot-wire velocity sensors. We find that the large-scale shear persists down to the smallest scales. There is a marked asymmetry between velocity increments measured in the shear direction, and those measured in the plane perpendicular to it. In the shear direction the scaling exponents tend to a constant, signifying the presence of small-scale cliffs. Direct evidence for those is presented by the spatial structure of the strongest velocity gradient

Determining stress during finger propagation in 2D foams

We investigate the formation of fingering patterns in a radial Hele-Shaw cell filled with quasi-two-dimensional polydisperse foam of very small liquid content. Air is used as the low-viscosity driving fluid. Using high speed imaging (up to 2000fps), we directly observe the topological rearrangements on the size scale of single bubbles at the air-foam interface. We find that the growth process of the finger can be discretized as successive elementary T1-type edge exchanges between neighboring bubbles at the interface of the advancing finger. Apart from the rate of T1 events, other statistical quantities can be determined with good spatial resolution using a coordinate system moving with the finger. Measures of local bubble anisotropy (such as the texture tensor) and connectivity are used to determine the deviatoric stress tensor in the material. The data are compared to continuum results in the viscous liquid and elastic solid limits, shedding light on the continuum behavior of foam as a viscoelastic material

TRABECULAR BONE SCORE AND DENTAL IMPLANT

The article brings in the same plan and unified views related to two different phenomena: dental implant (DI) and osteoporosis. 1. DI and osteoporosis. Successful DI depends on bone quality. One of the relative contraindications of DI is osteoporosis. However, there are studies showing that DI can be done in patients with osteoporosis. In cases of osteoporosis, success depends on the lack of previous antiosteoporotic bisphosphonate treatments. 2, Diagnosis of osteoporosis. It is based on the T-score obtained for Bone Mineral Density (BMD) in DEXA (dual X ray absortiometry) tests; they must be < -2.5. This value is the standard deviation applied to an average obtained from adults. What happens to bone quality in patients with possibly osteoporosis but with BMD > -2.5? The problem of diagnosis can be solved by a new DEXA technique: trabecular bone score.3. Trabecular bone score (TBS) is the mathematical estimation of vertebral microarhitectomy.The vertebra are formed by trabecular bone (the long bone is predominantly the cortical bone). TBS is obtained by DEXA analysis with specific software. A value < -2.5 means osteoporosis. Our data showed that through TBS analysis the prevalence of osteoporosis diagnosis increased by about 40% in patients who have BMD within the limits considered by osteopenia or normal. 4. Relationship between mandible/maxillary and trabecular bone. Mandible and the maxillary are mixed bones. At the surface it presents as a cortical bone, in depth, it presents with trabecular bone structure. The cortical bone (both of mandible & maxillary) is defined as that white structure without a trabecular pattern. The trabecular bone is that part of the mandible that is found between two cortical plates. It is appropriate to make an implant when the cortical bone is more abundant. It is also stated that the implants performed in over 60% trabecular (cancellous) bone are more efficient than those performed in less than 30% of the trabecular bone. The phenomenon arises from the fact that the trabecular bone is more metabolically active and contains more osteoblasts. TBS obtained by DEXA for the vertebrae can be surrogate for the assessment of the trabecular bone in the mandible and maxillary. 5. Drugs that improve the trabecular bone score. Following the re-analysis of the TBS-BMD difference by the TBS technique, the perception of antiosteoporotic drugs has changed. More important is to improve TBS than increase BMD. Thus, teriparatide, then denosumab, strontium, SERM, and lastly bisphosphonates would be preferentially used. Furthermore, teriparatide was the only treatment available for post-bisphosphonates jaw necrosis

Simultaneous excitation of N single colloidal quantum dots

We report on the implementation of a new microscopy device that allows us to selectively excite up to 20 quantum dots simultaneously and collect their fluorescence. We use it to excite and observe single CdSe/ZnS quantum dots, which are known to be single photon emitters at room temperature. Complex excitation timings can be realised. The microscope works in confocal mode with a resolution of 2 micrometers and a field of view of 20 micrometers. We discuss applications of our device in quantum optics (imaging with incoherent single photons) and quantum cryptography (wavelength multiplexed quantum cryptography and “multi-colour” quantum cryptography).info:eu-repo/semantics/publishe