Breakup of liquid filaments.

Whether a thin filament of liquid separates into two or more droplets or eventually condenses lengthwise to form a single larger drop depends on the liquid's density, viscosity, and surface tension and on the initial dimensions of the filament. Surface tension drives two competing processes, pinching-off and shortening, and the relative time scales of these, controlled by the balance between capillary and viscous forces, determine the final outcome. Here we provide experimental evidence for the conditions under which a liquid filament will break up into drops, in terms of a wide range of two dimensionless quantities: the aspect ratio of the filament and the Ohnesorge number. Filaments which do not break up into multiple droplets demand a high liquid viscosity or a small aspect ratio.This work was supported by EPSRC (RG53364 and RG55605

Dynamics of wrinkling in ultrathin elastic sheets

The wrinkling of thin elastic objects provides a means of generating regular patterning at small scales in applications ranging from photovoltaics to microfluidic devices. Static wrinkle patterns are known to be governed by an energetic balance between the object's bending stiffness and an effective substrate stiffness, which may originate from a true substrate stiffness or from tension and curvature along the wrinkles. Here we investigate dynamic wrinkling, induced by the impact of a solid sphere onto an ultra-thin polymer sheet floating on water. The vertical deflection of the sheet's centre induced by impact draws material radially inwards, resulting in an azimuthal compression that is relieved by the wrinkling of the entire sheet. We show that this wrinkling is truly dynamic, exhibiting features that are qualitatively different to those seen in quasi-static wrinkling experiments. Moreover, we show that the wrinkles coarsen dynamically because of the inhibiting effect of the fluid inertia. This dynamic coarsening can be understood heuristically as the result of a dynamic stiffness, which dominates the static stiffnesses reported thus far, and allows new controls of wrinkle wavelength.Comment: 8 pages, 4 figures. Please see published version for supplementary movies and SI Appendi

Controlled cavity collapse: scaling laws of drop formation

The formation of transient cavities at liquid interfaces occurs in an immense variety of natural processes, among which the bursting of surface bubbles and the impact of a drop on a liquid pool are salient. The collapse of a surface liquid cavity is a well documented natural process that leads to the ejection of a thin and fast jet. Droplets generated through this process can be one order of magnitude smaller than the cavity's aperture, and they are consequently of interest in drop on demand inkjet applications. In this work, the controlled formation and collapse of a liquid cavity is analyzed, and the conditions for minimizing the resulting size and number of ejected drops are determined. The experimental and numerical models are simple and consist of a liquid reservoir, a nozzle plate with the discharge orifice, and a moving piston actuated by single half-sine-shaped pull-mode pulses. The size of the jetted droplet is described by a physical model resulting in a scaling law that is numerically and experimentally validatedRoyal Society (UF120319, URF\R\180016, and RGF\EA\180061)John Fell Oxford University Press Research Fund (0005176)EPSRC – UK (EP/P024173/1)Ministerio de Economía y Competitividad, Plan Estatal 2013–2016 Retos, project DPI2013-46485-C3-1-

The breakup length of harmonically stimulated capillary jets

A simple transfer function that can predict the breakup length of a pressure-modulated capillary jet is rigorously deduced from first principles. In this paper, the initial velocity modulation of a stimulated jet is given in terms of its pressure amplitude by means of a generalized Bernoulli equation, which in turn is connected to the breakup time through a two-mode linear analysis. The predicted breakup length is compared against experimental results with water jets emerging from a thin 1 mm-diameter orifice for different pressure modulations. These experiments agree better with the presented theoretical prediction than with a previously established model.Spanish Government under Contract No. FIS2011-25161Junta de Andalucía under Contract Nos. P09-FQM-4584 and P11- FQM-7919EPSRC-UK (Grant No. EP/H018913/1)Royal SocietyJohn Fell Oxford University Press (OUP) Research Fun

Self-Stimulated Capillary Jet

Inspired by Savart’s pioneering work, we study the self-stimulated dynamics of a capillary jet. The feedback loop is realized by extracting surface perturbations from a section of the jet itself via a laserphotodiode pair, whose amplified signal drives an electromechanical actuator that, in turn, produces pressure perturbations at the exit chamber. Under specific conditions, this loop establishes phase-locked stimulation regimes that overcome the otherwise random natural breakup. For each laser position along the jet, the gain of the amplifier acts as a selector across a discrete set of observable frequencies. The main observed features are explained by a linear theory that combines the transfer function of each stage in the loop. Our findings are relevant to continuous inkjet technologies for the production of equally sized droplets.Spanish Research Agency Ministerio de Ciencia e Innovación and ERDF Project PGC2018-099217-B-I0

Effect of surfactants on the splashing dynamics of drops impacting smooth substrates

We present the results of a systematic study elucidating the role that dynamic surface tension has on the spreading and splashing dynamics of surfactant-laden droplets during the impact on hydrophobic substrates. Using four different surfactants at various concentrations, we generated a range of solutions whose dynamic surface tension were characterized to submillisecond timescales using maximum bubble-pressure tensiometry. Impact dynamics of these solutions were observed by high-speed imaging with subsequent quantitative image processing to determine the impact parameters (droplet size and speed) and dynamic wetting properties (dynamic contact angle). Droplets were slowly formed by dripping to allow the surfactants to achieve equilibrium at the free surface prior to impact. Our results indicate that while only the fastest surfactants appreciably affect the maximum spreading diameter, the droplet morphology during the initial stages of spreading is different to water for all surfactant solutions studied. Moreover, we show that surfactant-laden droplets splash more easily than pure liquid (water). Based on the association of the splashing ratio to our tensiometry measurements, we are able to predict the effective surface tension acting during splashing. These results suggest that droplet splashing characteristics are primarily defined by the stretching of the equilibrated droplet free surface

New Physics searches in a low threshold scintillating argon bubble chamber measuring coherent elastic neutrino-nucleus scattering in reactors

The sensitivity to New Physics of a low threshold scintillating argon bubble chamber measuring coherent elastic neutrino-nucleus scattering in reactors is reported. Namely, light scalar mediators, sterile neutrino oscillations, unitarity violation, and non-standard interactions are studied. The results indicate that this detector could be able to set stronger constraints than current limits set by the recent COHERENT measurements. Considering the best scenario, a 100 kg detector located 30 m from a 2000 MW$_{th}$ reactor, a sterile neutrino search would cover most of the space parameter allowed from the reactor anti-neutrino anomaly fit. Unitarity violation studies could set constraints on $\alpha_{11}$ more stringent than the current oscillation experiments fit. A low threshold argon detector with very low backgrounds has the potential to explore New Physics in different scenarios and set competitive constraints

Energía eólica y paisaje. Identificación y cuantificación de paisajes afectados por instalaciones eólicas en Andalucía

Este artículo analiza la distribución territorial y paisajística de los parques eólicos en Andalucía, identificando y cuantificando las superficies afectadas por cambios paisajísticos como consecuencia de la implantación de estas infraestructuras. Ello se lleva a cabo a partir de la generación de una geodatabase de energías renovables que recoge información espacial detallada de estas infraestructuras, con un nivel de precisión hasta el momento inédito en Andalucía. El uso de las capacidades analíticas de los Sistemas de Información Geográfica permite la definición y generación de nuevos indicadores paisajísticos relacionados con las instalaciones de energía eólica, no aplicados previamente para la Comunidad Autónoma Andaluza.This article analyzes the spatial and landscape distribution of wind farms in the region of Andalusia, Spain, and identifies and quantifies the surface area affected by landscape changes resulting from the implementation of this type of infrastructure. This is done by creating a geodatabase of renewable energies that includes detailed spatial information of these infrastructures with a scale of accuracy that is unprecedented in Andalusia. By using the analytical abilities of Geographical Information Systems it has been possible to define and create new landscape indicators linked to the installation of wind farms that have not been applied previously in the Andalusian Autonomous Community

Wind power and landscape. Identification and cuantification of landscapes affected by wind power plants in Andalusía

Este artículo analiza la distribución territorial y paisajística de los parques eólicos en Anda-lucía, identificando y cuantificando las superficies afectadas por cambios paisajísticos como consecuencia de la implantación de estas infraestructuras. Ello se lleva a cabo a partir de la generación de una geodatabase de energías renovables que recoge información espacial deta-llada de estas infraestructuras, con un nivel de precisión hasta el momento inédito en Andalu-cía. El uso de las capacidades analíticas de los Sistemas de Información Geográfica permite la definición y generación de nuevos indicadores paisajísticos relacionados con las instalaciones de energía eólica, no aplicados previamente para la Comunidad Autónoma Andaluza.This article analyzes the spatial and landscape distribution of wind farms in the region of Andalusia, Spain, and identifies and quantifies the surface area affected by landscape changes resulting from the implementation of this type of infrastructure. This is done by creating a geodatabase of renewable energies that includes detailed spatial information of these infrastructures with a scale of accuracy that is unprecedented in Andalusia. By using the analytical abilities of Geographical Information Systems it has been possible to define and create new landscape indicators linked to the installation of wind farms that have not been applied previously in the Andalusian Autonomous Community