Nonequilibrium plasmas driven by submicrosecond high voltage pulses have been proven to produce high-energy electrons, which in turn lead to enhanced ionization and excitations. Here, we describe a device capable of launching a cold plasma plume in the surrounding air. This device, "the plasma pencil," is driven by few hundred nanosecond wide pulses at repetition rates of a few kilohertz. Correlation between current-voltage characteristics and fast photography shows that the plasma plume is in fact a small bulletlike volume of plasma traveling at unusually high velocities. A model based on photoionization is used to explain the propagation kinetics of the plasma bullet under low electric field conditions.

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Certain complex phenotypes appear repeatedly across diverse species due to processes of evolutionary conservation and convergence. In some contexts like developmental body patterning, there is increased appreciation that common molecular mechanisms underlie common phenotypes; these molecular mechanisms include highly conserved genes and networks that may be modified by lineage-specific mutations. However, the existence of deeply conserved mechanisms for social behaviors has not yet been demonstrated. We used a comparative genomics approach to determine whether shared neuromolecular mechanisms could underlie behavioral response to territory intrusion across species spanning a broad phylogenetic range: house mouse (Mus musculus), stickleback fish (Gasterosteus aculeatus), and honey bee (Apis mellifera). Territory intrusion modulated similar brain functional processes in each species, including those associated with hormone-mediated signal transduction and neurodevelopment. Changes in chromosome organization and energy metabolism appear to be core, conserved processes involved in the response to territory intrusion. We also found that several homologous transcription factors that are typically associated with neural development were modulated across all three species, suggesting that shared neuronal effects may involve transcriptional cascades of evolutionarily conserved genes. Furthermore, immunohistochemical analyses of a subset of these transcription factors in mouse again implicated modulation of energy metabolism in the behavioral response. These results provide support for conserved genetic "toolkits" that are used in independent evolutions of the response to social challenge in diverse taxa.genetic hotspot | NF-κB signaling | brain metabolism | aggression S imilar phenotypes can have a shared molecular basis, even among distantly related species (1-3). This phenomenon has been observed for an array of traits, including morphological adaptations like coat color or wing patterning, rapid adaptations like drug resistance, and artificially selected phenological traits like flowering time (reviewed in ref. 2). Shared molecular mechanisms can arise convergently as a result of de novo mutations at genetic hotspots (2) or as a result of conservation. Both of these processes result in "genetic toolkits" or genes that are repeatedly used over evolutionary time to give rise to similar phenotypes (3). The phenomenon of genetic toolkits challenges fundamental notions about evolutionary convergence, conservation, and the origins of biodiversity.The role of genetic toolkits in shaping behavioral phenotypes is unclear (4, 5). Behaviors are typically polygenic (6) and they show great nuance and plasticity within a species, raising the possibility that cross-species similarities in behavior are superficial. Social behaviors in particular present a challenge to the genetic toolkit concept: these behaviors are critical to survival and reproductive success, but across species there is significant variation in the contexts for an...

The roles of various plasma agents in the inactivation of bacteria have recently been investigated. However, up to now, the effect of the charged particles on the inactivation of bacteria is not well understood. In this paper, an atmospheric pressure plasma jet device, which generates a cold plasma plume carrying a peak current of 300 mA, is used to investigate the role of the charged particles in the inactivation process. It is found that the charged particles play a minor role in the inactivation process when He/N2(3%) is used as working gas. On the other hand, when He/O2(3%) is used, the charged particles are expected to play an important role in the inactivation of bacteria. Further analysis shows that the negative ions O2− might be the charged particles that are playing the role. Besides, it is found that the active species, including O, O3, and metastable state O2∗, can play a crucial role in the inactivation of the bacteria. However, the excited He∗, N2 C Π3u, and N2+ B Σ2u+ have no significant direct effect on the inactivation of bacteria. It is also concluded that heat and UV play no or minor role in the inactivation process.

A single electrode room-temperature atmospheric pressure plasma plume generated between a high-voltage electrode and the surrounding room air is reported. The plasma plume has a peak current of about 360mA. This is highest current carried by a room-temperature plasma plume ever reported. The rotational and vibrational temperature of the plasma plume is about 300 and 2950K, respectively. Emission spectra show that excited species, such as O, OH, N2+, etc., are present in the plasma plume.

Summary: A device capable of generating a relatively long cold plasma plume has recently been developed. The advantages of this device are: plasma controllability and stability, room temperature and atmospheric pressure operation, and low power consumption. These features are what is required from a plasma source to be used reliably in material processing applications, including the biomedical applications. In this communication we describe the device and we present evidence that it can be used successfully to inactivate Escherechia coli in a targeted fashion. More recent experiments have shown that this device inactivates other bacteria also, but these will be reported in the future.Photograph of a He plasma plume launched out of the plasma pencil.magnified imagePhotograph of a He plasma plume launched out of the plasma pencil.

Nonequilibrium, atmospheric pressure discharges are rapidly becoming an important technological component in material processing applications. Amongst their attractive features is the ability to achieve enhanced gas phase chemistry without the need for elevated gas temperatures. To further enhance the plasma chemistry, pulsed operation with pulse widths in the nanoseconds range has been suggested. We report on a specially designed, dielectric barrier discharge based diffuse pulsed discharge and its electrical characteristics. Two current pulses corresponding to two consecutive discharges are generated per voltage pulse. The second discharge, which occurs at the falling edge of the voltage pulse, is induced by the charges stored on the electrode dielectric during the initial discharge. Therefore, the power supplied to ignite the first discharge is partly stored to later ignite a second discharge when the applied voltage decays. This process ultimately leads to a much improved power transfer to the plasma.

A numerical and experimental study of plasma jet propagation in a low-temperature, atmospheric-pressure, helium jet in ambient air is presented. A self-consistent, multi-species, two-dimensional axially symmetric plasma model with detailed finite-rate chemistry of helium-air mixture composition is used to provide insights into the propagation of the plasma jet. The obtained simulation results suggest that the sheath forms near the dielectric tube inner surface and shields the plasma channel from the tube surface. The strong electric field at the edge of the dielectric field enhances the ionization in the air mixing layer; therefore, the streamer head becomes ring-shaped when the streamer runs out of the tube. The avalanche-to-streamer transition is the main mechanism of streamer advancement. Penning ionization dominates the ionization reactions and increases the electrical conductivity of the plasma channel. The simulation results are supported by experimental observations under similar discharge conditions.