Non-Linear Deformations of Liquid-Liquid Interfaces Induced by Electromagnetic Radiation Pressure

The idea of working with a near-critical phase-separated liquid mixture whereby the surface tension becomes weak, has recently made the field of laser manipulation of liquid interfaces a much more convenient tool in practice. The deformation of interfaces may become as large as several tenths of micrometers, even with the use of conventional laser power. This circumstance necessitates the use of nonlinear geometrical theory for the description of surface deformations. The present paper works out such a theory, for the surface deformation under conditions of axial symmetry and stationarity. Good agreement is found with the experimental results of Casner and Delville [A. Casner and J. P. Delville, Phys. Rev. Lett. {\bf 87}, 054503 (2001); Opt. Lett. {\bf 26}, 1418 (2001); Phys. Rev. Lett. {\bf 90}, 144503 (2003)], in the case of moderate power or a broad laser beam. In the case of large power and a narrow beam, corresponding to surface deformations of about 50 micrometers or higher, the theory is found to over-predict the deformation. Possible explanations of this discrepancy are discussed.Comment: RevTeX4, 19 pages, 4 figures. Sec. IIIB rewritten, 4 new references. To appear in Phys. Rev.

CFD Wake Modelling with a BEM Wind Turbine Sub-Model

Modelling of wind farms using computational fluid dynamics (CFD) resolving the flow field around each wind turbine's blades on a moving computational grid is still too costly and time consuming in terms of computational capacity and effort. One strategy is to use sub-models for the wind turbines, and sub-grid models for turbulence production and dissipation to model the turbulent viscosity accurately enough to handle interaction of wakes in wind farms. A wind turbine sub-model, based on the Blade Momentum Theory, see Hansen (2008), has been implemented in an in-house CFD code, see Hallanger et al. (2002). The tangential and normal reaction forces from the wind turbine blades are distributed on the control volumes (CVs) at the wind turbine rotor location as sources in the conservation equations of momentum. The classical k-epsilon turbulence model of Launder and Spalding (1972) is implemented with sub-grid turbulence (SGT) model, see Sha and Launder (1979) and Sand and Salvesen (1994). Steady state CFD simulations were compared with flow and turbulence measurements in the wake of a model scale wind turbine, see Krogstad and Eriksen (2011). The simulated results compared best with experiments when stalling (boundary layer separation on the wind turbine blades) did not occur. The SGT model did improve turbulence level in the wake but seems to smear the wake flow structure. It should be noted that the simulations are carried out steady state not including flow oscillations caused by vortex shedding from tower and blades as they were in the experiments. Further improvement of the simulated velocity defect and turbulence level seems to rely on better parameter estimation to the SGT model, improvements to the SGT model, and possibly transient- instead of steady state simulations

Exploring Early Childhood Teachers\u27 Beliefs and Perceptions About the Use of Technology in the Classroom

The purpose of this qualitative study was to explore how the professional beliefs and perceptions of teachers in early childhood education (ECE) influenced their acceptance for the use of interactive technology as a learning tool for children. Eight primary grade teachers at a rural school district in Washington State were interviewed. Of the eight ECE teachers, two had no student technology use in their classrooms. The second group of two teachers had some student technology use on a weekly basis, and the last group of four teachers utilized daily student technology use in their classrooms. The sample subjects were interviewed face-to-face and asked to respond to an online survey regarding their beliefs and perceptions about the use of technology in their classroom; including technology manipulated by students such as Ipads, tablets, laptops and desktop computers. The data were looked at through the Framework Method and helped determine similarities or differences in the results. This case study focused on beliefs and practices that teachers hold, and how it influences the implementation and use of technology in the classroom concerning student’s use and experiences. This case study provides information for teachers, administration and the educational community. Recommendations for future research are discussed

Macondo-1 well oil-derived polycyclic aromatic hydrocarbons in mesozooplankton from the northern Gulf of Mexico

Copyright 2012 by the American Geophysical UnionMesozooplankton (>200 μm) collected in August and September of 2010 from the northern Gulf of Mexico show evidence of exposure to polycyclic aromatic hydrocarbons (PAHs). Multivariate statistical analysis revealed that distributions of PAHs extracted from mesozooplankton were related to the oil released from the ruptured British Petroleum Macondo-1 (M-1) well associated with the R/VDeepwater Horizon blowout. Mesozooplankton contained 0.03–97.9 ng g−1 of total PAHs and ratios of fluoranthene to fluoranthene + pyrene less than 0.44, indicating a liquid fossil fuel source. The distribution of PAHs isolated from mesozooplankton extracted in this study shows that the 2010 Deepwater Horizon spill may have contributed to contamination in the northern Gulf of Mexico ecosystem

Randall-Sundrum Model in the Presence of a Brane Bulk Viscosity

The presence of a bulk viscosity for the cosmic fluid on a single Randall-Sundrum brane is considered. The spatial curvature is assumed to be zero. The five-dimensional Friedmann equation is derived, together with the energy conservation equation for the viscous fluid. These governing equations are solved for some special cases: (i) in the low-energy limit when the matter energy density is small compared with brane tension; (ii) for a matter-dominated universe, and (iii) for a radiation-dominated universe. Rough numerical estimates, for the extreme case when the universe is at its Planck time, indicate that the viscous effect can be significant.Comment: 18 pages, RevTeX4, no figures. Discussion in Sec. III expanded; new references. To appear in Phys. Rev.

Simulation of an optically induced asymmetric deformation of a liquid-liquid interface

Deformations of liquid interfaces by the optical radiation pressure of a focused laser wave were generally expected to display similar behavior, whatever the direction of propagation of the incident beam. Recent experiments showed that the invariance of interface deformations with respect to the direction of propagation of the incident wave is broken at high laser intensities. In the case of a beam propagating from the liquid of smaller refractive index to that of larger one, the interface remains stable, forming a nipple-like shape, while for the opposite direction of propagation, an instability occurs, leading to a long needle-like deformation emitting micro-droplets. While an analytical model successfully predicts the equilibrium shape of weakly deformed interface, very few work has been accomplished in the regime of large interface deformations. In this work, we use the Boundary Integral Element Method (BIEM) to compute the evolution of the shape of a fluid-fluid interface under the effect of a continuous laser wave, and we compare our numerical simulations to experimental data in the regime of large deformations for both upward and downward beam propagation. We confirm the invariance breakdown observed experimentally and find good agreement between predicted and experimental interface hump heights below the instability threshold

The pedunculopontine tegmental nucleus - A functional hypothesis from the comparative literature

We present data from animal studies showing that the pedunculopontine tegmental nucleus-conserved through evolution, compartmentalized, and with a complex pattern of inputs and outputs-has functions that involve formation and updates of action-outcome associations, attention, and rapid decision making. This is in contrast to previous hypotheses about pedunculopontine function, which has served as a basis for clinical interest in the pedunculopontine in movement disorders. Current animal literature points to it being neither a specifically motor structure nor a master switch for sleep regulation. The pedunculopontine is connected to basal ganglia circuitry but also has primary sensory input across modalities and descending connections to pontomedullary, cerebellar, and spinal motor and autonomic control systems. Functional and anatomical studies in animals suggest strongly that, in addition to the pedunculopontine being an input and output station for the basal ganglia and key regulator of thalamic (and consequently cortical) activity, an additional major function is participation in the generation of actions on the basis of a first-pass analysis of incoming sensory data. Such a function-rapid decision making-has very high adaptive value for any vertebrate. We argue that in developing clinical strategies for treating basal ganglia disorders, it is necessary to take an account of the normal functions of the pedunculopontine. We believe that it is possible to use our hypothesis to explain why pedunculopontine deep brain stimulation used clinically has had variable outcomes in the treatment of parkinsonism motor symptoms and effects on cognitive processing. © 2016 International Parkinson and Movement Disorder Society

The dynamic stability of an unbalanced mass exciter

The dynamic stability of single- and multi-degree-of-freedom unbalanced mass exciter systems is discussed. Previous work concerning this subject by A. Sommerfield, Y. Rocard, R. Mazet, V.0. Kononenko, Y.G. Panovko and I.I. Gubanova is summarized. A single-degree-of-freedom system consisting of a linear mechanical oscillator with a rotating unbalanced mass connected rigidly to it is defined as the basic single-degree-of-freedom system. This system is mathematically equivalent to the one used by Rocard in his analysis. The differential equations of motion for the system are obtained by using Lagrange's Equations. Global stability, stability in the sense of Laplace, is proved using Liapunov's second method. Four separate local stability analyses of this system are developed, two of which assume a constant angular velocity, [omega], of the unbalanced mass and two which allow for periodic variations in [omega]. These analyses are termed zero and first order respectively. The first zero order analysis is based directly on the differential equations of motion and the zero order steady state solution. The steady state torque output of the vibration exciter motor and the steady state torque requirements of the oscillator are obtained as functions of the operating frequency. Stability is determined by examining the behavior of the system in the vicinity of the intersection points of these two functions. The second zero order analysis examines the behavior of small perturbations added to the steady state solution. The system is considered stable if these perturbations disappear with time. The first first order analysis is a perturbation type, but is based on a steady state solution which allows for periodic variations in [omega]. The second first order analysis is also based on the first order perturbed equations of motion but is a Floquet type analysis. Validity criteria for the zero and first order analyses are obtained, and the zero order region of validity is plotted graphically. A representative set of systems is analyzed numerically, and the results are presented in a figure showing the stability boundary as a function of the system parameters in non-dimensional form. Two distinct types of muIti-degree-of-freedom systems are discussed. The first consists of a single oscillator mass that is free to perform planar motion. It is shown that when an unbalanced mass exciter with a uniaxial force output is mounted on the oscillator in such a way that only one mode is excited, the problem reduces to the sing le-degree-of-freedom problem. The second system consists of a series of linear sing I e-degree -of -freedom oscillators with an unbalanced mass exciter mounted on one of them. The special case of a three oscillator system with equal masses is used to demonstrate that, for systems with widely separated resonances, the "equivalent" singIe-degree-of-freedom analysis presented by Kononenko is valid. From these results it is concluded that, in any multi-degree-of-freedom system, an "equivalent" single-degree-of-freedom analysis may be used to examine the stability of the system near any resonance as long as that particular mode is the only one which is being significantly excited. Appendices covering the details of Rocard's analysis, and of the unbalanced mass exciters designed and built at the California Institute of Technology are included

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