Electrostatic charging of jumping droplets

With the broad interest in and development of superhydrophobic surfaces for self-cleaning, condensation heat transfer enhancement and anti-icing applications, more detailed insights on droplet interactions on these surfaces have emerged. Specifically, when two droplets coalesce, they can spontaneously jump away from a superhydrophobic surface due to the release of excess surface energy. Here we show that jumping droplets gain a net positive charge that causes them to repel each other mid-flight. We used electric fields to quantify the charge on the droplets and identified the mechanism for the charge accumulation, which is associated with the formation of the electric double layer at the droplet–surface interface. The observation of droplet charge accumulation provides insight into jumping droplet physics as well as processes involving charged liquid droplets. Furthermore, this work is a starting point for more advanced approaches for enhancing jumping droplet surface performance by using external electric fields to control droplet jumping.United States. Dept. of Energy. Office of Basic Energy Sciences (Solid-State Solar-Thermal Energy Conversion Center Award DE-FG02-09ER46577)United States. Office of Naval ResearchNational Science Foundation (U.S.) (Major Research Instrumentation Grant for Rapid Response Research (MRI- RAPID))National Science Foundation (U.S.) (Award ECS-0335765)National Science Foundation (U.S.). Graduate Research Fellowship Program (Grant 1122374

A COMPARISON OF PULLOUT STRENGTH OF PEDICULAR SCREWS BETWEEN DIFFERENT METHODS OF SCREW INSERTION IN POSTERIOR FIXATION OF THORACIC SPINE

"nPedicle screws provide rigid fixation for instabilities in the lumbar and lumbosacral spine. Anatomical consideration and potential risk of neurologic complications are the reasons to hesitate using pedicle screws in the thoracic spine. Twenty moulages similar to human vertebrae were instrumented with Cotrel-Dubousset (CD) system pedicle screw by intratransverse process, extrapedicular and intrapedicular methods and pullout strength was measured. There was statistically significant difference between three techniques. By increasing the length of screw in any method, pullout strength increased. Average pullout strength in extrapedicular technique was less than two other techniques in dynamic state. The strongest technique for screw placement was intratransverse process technique. It seems that intratransverse process technique is safe for posterior fixation of spine

Electrostatic Deformation of Liquid Surfaces by a Charged Rod and a Van de Graaff Generator

Authors of physics textbooks frequently use the deflection of a thin, vertically falling water jet by a charged balloon, 1–3 comb, 4–6 or rod 7–9 as a visually appealing and conceptually relevant example of electrostatic attraction. Nevertheless, no attempts are made to explore whether these charged bodies could cause visible deformation of a horizontal water surface. That being so, we were quite surprised when we discovered that a 19th-century French book 10 contained a drawing showing an appreciable deformation of an oil surface caused by a charged rod. When we initially tried to recreate this electrostatics demonstration, we didn't succeed in reproducing the effect with a charged rod. Despite the initial unsuccessful try, we were not discouraged and we modified the demonstration a little bit, finding that it was possible to cause visible deformations of different liquid surfaces by using a Van de Graaff generator, as we will explain later.The work on this article was started during the visit of the first author to the Universitat d'Alacant (Spain), planned within the research project Active Physics Learning Online, supported by the CONACyT (Mexico). Financial support from the Centro de Estudios Iberoamericanos Mario Benedetti