A helium flow dynamics simulation is performed along the propagation region of the plasma bullet to determine the minimum helium mole fraction value necessary to sustain its propagation. The plasma bullet launches from a plasma jet device called the ‘plasma pencil’ driven by unipolar square nanosecond high voltage pulses and propagates in the surrounding air. During its propagation, air molecules diffuse into the path/helium channel of the plasma bullet. It is found that if the ratio of air molecules to helium atoms exceeds a certain limit, the plasma bullet propagation is inhibited. In this study, the helium mole fraction limits are estimated for different operating conditions of the plasma pencil.

We demonstrate negative dielectrophoresis (DEP) trapping of particles from high-conductivity media using a novel planar microelectrode that allows electrothermal enhancement of DEP traps. DEP force and electrothermal flow motion are investigated using a scaling analysis, numerical simulations, and experiments. Results show that the DEP trapping is enhanced by lateral transport of particles toward the capture zones due to electrothermal flow, whereas DEP trapping occurred only in limited spatial ranges without the flow motion. The electrothermally enhanced DEP will broaden the limit of electrokinetic manipulations in high-conductivity media. By providing patterned trapping zones that can act as target-specific attachment/detection sites, the presented device allows development of biosensor applications for rapid detection of pathogens and other microorganisms within a practical range of buffer conductivity.

Active flow control technology is finding increasing use in aerospace applications to control flow separation and improve aerodynamic performance. In this paper we examine the characteristics of a class of fluidic actuators that are being considered for active flow control applications for a variety of practical problems. Based on recent experimental work, such actuators have been found to be more efficient for controlling flow separation in terms of mass flow requirements compared to constant blowing and suction or even synthetic jet actuators. The fluidic actuators produce spanwise oscillating jets, and therefore are also known as sweeping jets. The frequency and spanwise sweeping extent depend on the geometric parameters and mass flow rate entering the actuators through the inlet section. The flow physics associated with these actuators is quite complex and not fully understood at this time. The unsteady flow generated by such actuators is simulated using the lattice Boltzmann based solver PowerFLOW R . Computed mean and standard deviation of velocity profiles generated by a family of fluidic actuators in quiescent air are compared with experimental data. Simulated results replicate the experimentally observed trends with parametric variation of geometry and inflow conditions. Nomenclature

A microfluidic device with planar square electrodes is developed for capturing particles from high conductivity media using negative dielectrophoresis (n-DEP). Specifically, Bacillus subtilis and Clostridium sporogenes spores, and polystyrene particles are tested in NaCl solution (0.05 and 0.225 S∕m), apple juice (0.225 S∕m), and milk (0.525 S∕m). Depending on the conductivity of the medium, the Joule heating produces electrothermal flow (ETF), which continuously circulates and transports the particles to the DEP capture sites. Combination of the ETF and n-DEP results in different particle capture efficiencies as a function of the conductivity. Utilizing 20 μm height DEP chambers, "almost complete" and rapid particle capture from lower conductivity (0.05 S∕m) medium is observed. Using DEP chambers above 150 μm in height, the onset of a global fluid motion for high conductivity media is observed. This motion enhances particle capture on the electrodes at the center of the DEP chamber. The n-DEP electrodes are designed to have well defined electric field minima, enabling sample concentration at 1000 distinct locations within the chip. The electrode design also facilitates integration of immunoassay and other surface sensors onto the particle capture sites for rapid detection of target micro-organisms in the future.

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