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A moving time-resolved particle image velocimetry (MTRPIV) system was designed to measure the turbulent boundary layer (TBL). The combination of time-resolved particle image velocimetry and a translational moving system enables the MTRPIV to track the coherent structures with a long period and high temporal resolution. Based on the MTRPIV, the time-evolving of coherent structures within the TBL was measured and analyzed. The observation of the large-scale sweep collision with ejection shows that the strong collision causes the large-scale high- and low-speed coherent structures to break down. The time-evolving process of the hairpin packets shows that the low-speed fluid mass under the hairpin vortices is important for the generation of a whole hairpin packet. The small-scale low-speed structures increase their spatial scales by merging so that the independent hairpin vortices can be organized by merged larger-scale structures. The shear layer exceeding the length of 0.7–0.8 δ (δ is thickness of TBL) or 350–400 υ U τ υUτ (υ and Uτ denote the kinematic viscosity and friction velocity, respectively) is unstable, and it will roll-up to generate a hairpin vortex. In the hairpin packet growth process, the inclination angle of the hairpin packet decreases from ∼13° to 8° in a time duration of 120 υ Uτ2 υ Uτ, and the underlying low-speed fluid is elongated and then split. The analysis of the uniform momentum zones (UMZs) shows that the topmost UMZ has a relatively stable wall-normal position and convection speed. The lower UMZ is quasi-periodically generated and tends to move upward to merge with the upper UMZs. The hairpin packets impact the lower UMZs by inducing large-scale low-speed fluid mass to modulate the probability density function distribution of instantaneous streamwise velocity. The evolution of UMZs with velocity less than 0.5U∞ (U∞ denotes the free-stream velocity) is the result of the interaction of large- and small-scale streamwise fluctuation velocity. [ABSTRACT FROM AUTHOR]

Non-equilibrium atmospheric pressure plasma jet (APPJ) is a cold plasma source that promises various innovative applications. The influence of Penning effect on the formation, propagation, and other physical properties of the plasma bullets in APPJ remains a debatable topic. By using a 10 cm wide active electrode and a frequency of applied voltage down to 0.5 Hz, the Penning effect caused by preceding discharges can be excluded. It was found that the Penning effect originating in a preceding discharge helps build a conductive channel in the gas flow and provide seed electrons, thus the discharge can be maintained at a low voltage which in turn leads to a smaller propagation speed for the plasma bullet. Photographs from an intensified charge coupled device reveal that the annular structure of the plasma plume for He is irrelevant to the Penning ionization process arising from preceding discharges. By adding NH3 into Ar to introduce Penning effect, the originally filamentous discharge of Ar can display a rather extensive plasma plume in ambient as He. These results are helpful for the understanding of the behaviors of non-equilibrium APPJs generated under distinct conditions and for the design of plasma jet features, especially the spatial distribution and propagation speed, which are essential for application. [ABSTRACT FROM AUTHOR]

Interplay of discharge and gas flow in the atmospheric pressure plasma jets generated with three different discharge modes [N. Jiang, A. L. Ji, and Z. X. Cao, J. Appl. Phys. 106, 013308 (2009); N. Jiang, A. L. Ji, and Z. X. Cao, J. Appl. Phys. 108, 033302 (2010)] has been investigated by simultaneous photographing of both plasma plumes and gas flows in the ambient, with the former being visualized by using an optical schlieren system. Gas flow gains a forward momentum from discharge except for the case of overflow jets at smaller applied voltages. Larger applied voltage implies an elongated plasma jet only for single-electrode mode; for dielectric barrier discharge jet the plume length maximizes at a properly applied voltage. These findings can help understand the underlying processes, and are useful particularly for the economic operation of tiny helium plasma jets and jet arrays. [ABSTRACT FROM AUTHOR]

With a proper combination of applied voltage and the width of ground electrode, atmospheric pressure plasma jets extending beyond the ground electrode, whether it sits on the downstream or the upstream side, can be equally obtained with a dielectric barrier discharge setup, which can be ascribed to the overflow of deposited charges [J. Appl. Phys. 106, 013308 (2009)]. Here, we show that, by using narrower ground electrodes, such an overflow jet can be successfully launched at a much reduced voltage (down to below 10 kV). Moreover, by using transparent and triadic ground electrodes, development of charge overflow beneath the ground electrode was temporally and spatially resolved. Temporal evolution of discharge currents measured on the severed ground electrode helps establish the propagation dynamics of discharges along the dielectric surface beneath ground electrode, and also reinforces the conception that the streamer’s head is in connection to the active electrode via a conducting channel. A small propagation velocity of 3.3×103 m/s was measured for the “overflow” jet inside the dielectric tube. The availability of such overflow jets is enormously advantageous concerning their application to living bodies, to which the high voltage at active electrode is lethally dangerous. [ABSTRACT FROM AUTHOR]

Experimental electron energy-loss spectroscopy of O K edge in CaAl2O4 has been studied in this work. The near edge fine structure of the O K edge has been interpreted with the aid of theoretical calculations in the ground-state approximation. It reveals that the features near the threshold are associated with the coordination of Ca polyhedra. Time-resolved electron energy-loss spectroscopy of O K edge further confirms that the selective elimination of high-order coordinated Ca by electron irradiation results in a threshold shift of the O K edge. [ABSTRACT FROM AUTHOR]

Experimental electron energy-loss spectroscopy of O K edge in CaAl2O4 has been studied in this work. The near edge fine structure of the O K edge has been interpreted with the aid of theoretical calculations in the ground-state approximation. It reveals that the features near the threshold are associated with the coordination of Ca polyhedra. Time-resolved electron energy-loss spectroscopy of O K edge further confirms that the selective elimination of high-order coordinated Ca by electron irradiation results in a threshold shift of the O K edge. [ABSTRACT FROM AUTHOR]

An electrostatic field-adapted molecular fractionation with conjugated caps (EFA-MFCC) approach is implemented for treating macromolecules with several charge centers. The molecular fragmentation is performed in an “electrostatic field,” which is described by putting point charges on charge centers, directly affecting the Hamiltonians of both fragments and conjugated caps. So the present method does not need truncation during the calculation of electrostatic interactions. Our test calculations on a series of charged model systems and biological macromolecules using the HF and B3LYP methods have demonstrated that this approach is capable of describing the electronic structure with accuracy comparable to other fragment-based methods. The EFA-MFCC approach is an alternative way for predicting the total energies of charged macromolecules with acyclic, loop, and intersectional loop structures and interaction energies between two molecules. [ABSTRACT FROM AUTHOR]

The effects of high-energy (100 keV) electron irradiation have been observed in a heavy-metal fluoride glass using in situ time-resolved electron energy loss spectroscopy in a scanning transmission electron microscope. Formation of F2 has been observed. The irradiation-induced changes of configuration and composition are discussed based on the evolution of the near-edge fine structures of F K edge. We suggest that the high sensitivity to electron irradiation is due to the existence of nonbridging F in heavy-metal fluoride glasses so that is there is a tendency of the electron irradiation to eliminate nonbridging F in the irradiated region. [ABSTRACT FROM AUTHOR]

Examines the binding energy and annihilation rate of positronium hydride (PsH) using the diffusion quantum Monte Carlo method. Background information of PsH; Importance of three-body clusters in electron-positron systems; Distance of annihilating particles at the time of annihilation.

In this work, single particle dispersion was analyzed for a bacterial turbulence by retrieving the virtual Lagrangian trajectory via numerical integration of the Lagrangian equation. High-order displacement functions were calculated for cases with and without mean velocity effect. The two-regime power-law behavior for short and long time evolutions was identified experimentally, which was separated by the Lagrangian integral time. For the case with the mean velocity effect, the experimental Hurst numbers were determined to be 0.94 and 0.97 for short and long time evolutions, respectively. For the case without the mean velocity effect, the values were 0.88 and 0.58. Moreover, very weak intermittency correctionwas detected.All measured Hurst numbers were above 1/2, the value of the normal diffusion, which verifies the super-diffusion behavior of living fluid. This behavior increases the efficiency of bacteria to obtain food. [ABSTRACT FROM AUTHOR]

Turbulent flows over a superhydrophobic surface and a smooth surface have been measured and studied by particle image velocimetry technology at Reθ = 990. The Reynolds shear stress distributions over the two surfaces are significantly different. Specifically, for the superhydrophobic surface, the Reynolds shear stress is suppressed in the near-wall region (y/δ < 0.3, δ is the boundary layer thickness) and increases in the outer region (0.3 < y/δ < 0.5), which forms a second peak of the Reynolds shear stress curve. Evolutions of hairpin vortexes are analyzed to interpret differences in the Reynolds shear stress, based on some comparisons in the low-speed streaks and Q2/Q4 (ejection/sweep) events. The results show that, in the near wall region, the turbulent coherent structures (low-speed streaks and hairpin vortex) over the superhydrophobic surface are more stable and flat, due to the suppression in the strength and the lifting effect of the hairpin vortex. In the outer region, the superhydrophobic surface lifts the hairpin vortex away from the wall with a value of 0.14δ in our experiment, which makes the Q4 events occur further from the wall and contribute less to skin friction. [ABSTRACT FROM AUTHOR]

We propose a synthesis method to design a 90° bent fair circular waveguide TE01 mode transition based on the non-uniform rational B-spline technique. The transition by this method has advantages of small geometry, high transmission with wide band and high profile fairness. An example of design of such a transition is presented. The simulation shows that the transition exhibits a transmission as high as 99.3% at the central frequency 35 GHz and has a bandwidth of 16.7% when keeping the transmission over 95%. Furthermore, the profile is extremely fair, which meets the requirements to decrease the geometry errors between actual device and its design, to reduce the machining difficulty in the machining process. The hot test data indicate that good transmission of the TE01 mode is obtained. [ABSTRACT FROM AUTHOR]

This paper presents a compact fractal and meander delay line. The introduced fractal and meander microstructure results in remarkably increase in delay time. The proposed asymmetrical microstructures show shielding effects, leading to a much weaker forward coupling between adjacent fractal and meander delay lines. The weakened forward coupling brings about a compact size and small return loss. A fractal and meander delay line is fabricated with high-temperature superconducting thin films and measured at 75 K, which achieved extremely low insertion loss. The measured results are consistent with simulation results. [ABSTRACT FROM AUTHOR]

Valence electron energy-loss spectroscopy is used to investigate the plasmon excitations of ultrathin SrTiO3 sandwiched between amorphous Si and crystalline Si. Two plasmon excitations were observed, one at 15.8 eV and the other at 28.7 eV. Our calculations, based on dielectric-function theory, suggest that the former peak originates from the coupling of the Si layers and is related to the geometry of the structure, and the latter peak results from the SrTiO3 bulk plasmon after a redshift. Our findings demonstrate the value of valence electron energy-loss spectroscopy in detecting a local change in the effective electron mass. [ABSTRACT FROM AUTHOR]

We show, using spatially resolved energy loss spectroscopy in a transmission electron microscopy (TEM), that GeO2 and GeO2–SiO2 glasses are extremely sensitive to high energy electrons. Ge nanoparticles can be precipitated in GeO2 glasses efficiently by the high-energy electron beam of a TEM. This is relevant to TEM characterization of luminescent Ge nanoparticles in silicate glasses, which may produce artificial results. [ABSTRACT FROM AUTHOR]

In this letter, we report precipitation of nanometer scale Zn crystalline particles in Zn borosilicate glass induced by 100 keV electron irradiation. Nanometer Zn crystalline particles precipitate rapidly in the glass under high intensity electron irradiation. A double ionization mechanism is proposed in interpretation of the formation of Zn particles. Thermal effects are less important than ionization interactions. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]