<p>The magnetosphere-ionosphere (M-I) transition region is the several thousand--kilometer stretch between the cold, dense and variably resistive region of ionized atmospheric gases beginning tens of kilometers above the terrestrial surface, and the hot, tenuous, and conductive plasmas that interface with the solar wind at higher altitudes. The M-I transition region is therefore the site through which magnetospheric conditions, which are strongly susceptible to solar wind dynamics, are communicated to ionospheric plasmas, and vice versa. We systematically study the influence of geomagnetic storms on energy input, electron precipitation, and ion outflow in the M-I transition region, emphasizing the role of inertial Alfven waves both as a preferred mechanism for dynamic (instead of static) energy transfer and particle acceleration, and as a low-altitude manifestation of high-altitude interaction between the solar wind and the magnetosphere, as observed by the FAST satellite. Via superposed epoch analysis and high-latitude distributions derived as a function of storm phase, we show that storm main and recovery phase correspond to strong modulations of measures of Alfvenic activity in the vicinity of the cusp as well as premidnight. We demonstrate that storm main and recovery phases occur during ~30% of the four-year period studied, but together account for more than 65% of global Alfvenic energy deposition and electron precipitation, and more than 70% of the coincident ion outflow. We compare observed interplanetary magnetic field (IMF) control of inertial Alfven wave activity with Lyon-Fedder-Mobarry global MHD simulations predicting that southward IMF conditions lead to generation of Alfvenic power in the magnetotail, and that duskward IMF conditions lead to enhanced prenoon Alfvenic power in the Northern Hemisphere. Observed and predicted prenoon Alfvenic power enhancements contrast with direct-entry precipitation, which is instead enhanced postnoon. This situation reverses under dawnward IMF. Despite clear observational and simulated signatures of dayside Alfvenic power, the generation mechanism remains unclear. Last, we present premidnight FAST observations of accelerated precipitation that is best described by a kappa distribution, signaling a nonthermal source population. We examine the implications for the commonly used Knight Relation.

Particles can be adsorbed to liquid-fluid interface to minimize interfacial energy. The adsorbed particles interact in many ways. There has been a lot of theoretical predictions as well as experimental measurements of the interaction potential between particles confined at interfaces. Experimentally, we track multiple particles using optical microscope image processing of isolated pairs of particles and of more concentrated systems. Statistical methods were implemented to compute microparticle interaction forces from tracking data. The accuracy of different methods were tested with Monte Carlo simulation, which showed that care is needed to avoid artifacts. Our measurements confirmed the absence of significant pair-interactions among charged microparticles and liquid droplets at flat air-water interfaces. At the interface between water and a fluorocarbon, however, we observed strong interactions that cannot be explained by capillary interactions among neutral particles. Theoretically, we focused on the capillary interaction mediated by the curvature of interface. The perturbation to a cylindrical interface upon adsorption of a single spherical particle is studied first. We present an analytical model of the interfacial shape and energy upon adsorption of a single particle, and then calculate the interaction between two particles. Based on our result for a cylindrical interface, we propose a general formula for the force on a particle on a curved interface having constant mean curvature (i.e., not subject to an external forces). This study provides an important step toward understanding the interactions among interfacial particles.

We investigate the stretching and breakup of a drop freely suspended in a viscous fluid undergoing chaotic advection. Droplets stretch into filaments acted on by a complex flow history leading to exponential length increase, folding, and eventual breakup; following breakup, chaotic stirring disperses the fragments throughout the flow. These events are studied by experiments conducted in a time-periodic two-dimensional low Reynolds number chaotic flow. Studies are restricted to viscosity ratios p such that 0.01 $<$ p $<$ 2.8. The experimental results are highly reproducible and illustrate new qualitative aspects with respect to the case of stretching and breakup in linear flows. For example, breakup near folds is associated with a change of sign in stretching rate; this mode of breakup leads to the formation of rather large drops. The dominant breakup mechanism, however, is capillary wave instabilities in highly stretched filaments. Other modes of breakup, such as 'necking', 'end-pinching', and 'fold-pinching' occur as well. We find that drops in low-viscosity-ratio systems, p $<$ 1, extend relatively little, O(10$\sp1$-10$\sp2$), before they break, producing an array of uniformly spaced drops (also known as mother drops) with as many as 19 satellites and sub-satellites in between. Large drop fragments, typically the product of end-pinching and fold-pinching, may again undergo a succession of breakup events, usually about 2-4 times. Drops in systems with p $>$ 1, on the other hand, stretch substantially, O(10$\sp1$-10$\sp4$), before they break producing small fragments that rarely break again. The number of satellites in between two mother drops in these systems never exceeds 5. The experimental results are interpreted in terms of a simple model assuming that moderately extended filaments behave passively; this is an excellent approximation especially for low-viscosity-ratio drops, p $<$ 1. The dynamics of the disturbances on the surface of the extending filament, and consequently the sizes of the resulting mother drops, are computed by means of linear stability theory. The linear stability theory, however, fails to capture the evolution of the undulated filament once the large curvature around the neck region develops. Thus, we resort to a different technique, i.e., boundary integral method, to obtain the exact pinch-off location and simulate the subsequent fluid motions which lead to the formation of satellite drops. Data from 2000-3000 thousands of droplets measured in each experiment after a long time indicate that the mean drop size decreases as the viscosity ratio increases. The repetitive nature of stretching and folding, as well as the self-repeating nature of the breakup process, suggests self-similarity. We find that, indeed, upon scaling, the drop size distributions corresponding to different viscosity ratios can be collapsed into a master curve.

No description available.

A statistical equilibrium theory is developed which characterizes the large-scale coherent structures that emerge during the course of the evolution of an ideal two-dimensional magnetofluid. Macrostates are defined to be local joint probability distributions, or Young measures, on the values of the fluctuating magnetic field and velocity field at each point in the spatial domain. The most probable macrostate is found by maximizing a Kullback-Liebler entropy functional subject to constraints dictated by the conserved integrals of the ideal dynamics. This maximum entropy macrostate is, for each point in the spatial domain, a Gaussian probability distribution, whose local mean is an exact stationary solution of the evolution equations of the magnetohydrodynamic system. The predictions of the statistical equilibrium model are found to be in excellent qualitative and quantitative agreement with recent high resolution numerical simulations of turbulence in slightly dissipative two-dimensional magnetofluids.

Terahertz line-images of surfactant-stabilized dodecane(C 12 H 26 )-brine emulsions are obtained by translating the emulsified region through the focus of a terahertz time-domain spectrometer, capturing a time-domain waveform at each vertical position. From these images, relative dodecane content, emulsion size, and stability can be extracted to evaluate the efficacy of the surfactant in solvating the dodecane. In addition, the images provide insight into the dynamics of concentrated emulsions after mixing.

Single-dielectric-barrier-discharge (SDBD) plasma actuators have shown much promise as an actuator for active flow control. Proper design and optimization of plasma actuators requires a model capable of accurately predicting the induced flow for a range of geometrical and excitation parameters. A number of models have been proposed in the literature, but have primarily been developed in isolation on independent geometries, frequencies and voltages. This study presents a comparison of four popular plasma actuator models over a range of actuation parameters for three different actuator geometries typical of actuators used in the literature. The results show that the hybrid model of Lemire & Vo (2011) is the only model capable of predicting the appropriate trends of the induced velocity for different geometries. Additionally, several modifications of this model have been integrated into a new proposed model for the plasma actuator, introducing a number of improvements.

Single-dielectric-barrier-discharge (SDBD) plasma actuators have shown much promise as an actuator for active flow control. Proper design and optimization of plasma actuators requires a model capable of accurately predicting the induced flow for a range of geometrical and excitation parameters. A number of models have been proposed in the literature, but have primarily been developed in isolation on independent geometries, frequencies and voltages. This study presents a comparison of four popular plasma actuator models over a range of actuation parameters for three different actuator geometries typical of actuators used in the literature. The results show that the hybrid model of Lemire & Vo (2011) is the only model capable of predicting the appropriate trends of the induced velocity for different geometries. Additionally, several modifications of this model have been integrated into a new proposed model for the plasma actuator, introducing a number of improvements.

<p> The non-resonant heating of gases by laser irradiation and plasma formation has been under investigation since the development of 100 megawatt peak power, Q-switched, nanosecond pulse duration lasers and the commensurate discovery of laser air sparks. More recently, advances in mode-locking and chirped pulse amplification have led to commercially available 100 gigawatt peak power, femtosecond pulse duration lasers with a rapidly increasing number of applications including remote sensing, laser spectroscopy, aerodynamic flow control, and molecular tagging velocimetry and thermometry diagnostics. This work investigates local energy deposition and gas heating produced by focused, non-resonant, nanosecond and femtosecond laser pulses in the context of flow control and laser diagnostic applications. </p><p> Three types of pulse configurations were examined: single nanosecond pulses, single femtosecond pulses and a dual pulse approach whereby a femtosecond pre-ionizing pulse is followed by a nanosecond pulse. For each pulse configuration, optical and laser diagnostic techniques were applied in order to qualitatively and quantitatively measure the plasmadynamic and hydrodynamic processes accompanying laser energy deposition. Time resolved imaging of optical emission from the plasma and excited species was used to qualitatively examine the morphology and decay of the excited gas. Additionally, Thomson scattering and Rayleigh scattering diagnostics were applied towards measurements of electron temperature, electron density, gas temperature and gas density. </p><p> Gas heating by nanosecond and dual pulse laser plasmas was found to be considerably more intense than femtosecond plasmas, irrespective of pressure, while the dual pulse approach provided substantially more controllability than nanosecond pulses alone. In comparison, measurements of femtosecond laser heating showed a strong and nonlinearly dependence on focusing strength. With comparable pulse energy, measurements of maximum temperature rise ranged from 50K to 2000K for 500mm and 175mm focal length lenses, respectively. Experiments with various lens and pulse energy combinations indicated an important connection between gas heating and the phenomena of intensity clamping and self-guiding. The long-term behavior of the heated region varied considerably among pulse configurations. However, in each case, the formation of a toroidal vortex could be suppressed or enhanced depending on the variables of pressure, focusing and pulse energy.</p>

<p>The state of matter at extremely high pressures and densities is of fundamental interest to many branches of research, including planetary science, material science, condensed matter physics, and plasma physics. Matter with pressures, or energy densities, above 1 megabar (100 gigapascal) are defined as High Energy Density (HED) plasmas. They are directly relevant to the interiors of planets such as Earth and Jupiter and to the dense fuels in Inertial Confinement Fusion (ICF) experiments. To create HEDP conditions in laboratories, a sample may be compressed by a smoothly varying pressure ramp with minimal temperature increase, following the isentropic thermodynamic process. Isentropic compression of aluminum targets has been done using magnetic pressure produced by megaampere, pulsed power currents having ~ 100 ns rise times. In this research project, magnetically driven, cylindrical isentropic compression has been numerically studied. In cylindrical geometry, material compression and pressure become higher than in planar geometry due to geometrical effects. Based on a semi-analytical model for the Magnetized Liner Inertial Fusion (MagLIF) concept, a code called ?SA? was written to design cylindrical compression experiments on the 1.0 MA Zebra pulsed power generator at the Nevada Terawatt Facility (NTF). To test the physics models in the code, temporal progresses of rod compression and pressure were calculated with SA and compared with 1-D magnetohydrodynamic (MHD) codes. The MHD codes incorporated SESAME tables, for equation of state and resistivity, or the classical Spitzer model. A series of simulations were also run to find optimum rod diameters for 1.0 MA and 1.8 MA Zebra current pulses. For a 1.0 MA current peak and 95 ns rise time, a maximum compression of ~ 2.35 (~ 6.3 g/cm</p><p>3) and a pressure of ~ 900 GPa within a 100 ?m radius were found for an initial diameter of 1.05 mm. For 1.8 MA peak simulations with the same rise time, the initial diameter of 1.3 mm was optimal with ~ 3.32 (~ 9.0 g/cm</p><p>3) compression.