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20 Feb 2012

Volume 100, Issue 8, Articles (08xxxx)

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Appl. Phys. Lett. 100, 082401 (2012); http://dx.doi.org/10.1063/1.3684972 (4 pages)

Elizabeth Rapoport and Geoffrey S. D. Beach
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Enhancement of ion generation in femtosecond ultraintense laser-foil interactions by defocusing

M. H. Xu, Y. T. Li, D. C. Carroll, P. S. Foster, S. Hawkes, S. Kar, F. Liu, K. Markey, P. McKenna, M. J. V. Streeter, C. Spindloe, Z. M. Sheng, C.-G. Wahlström, M. Zepf, J. Zheng, et al.

Appl. Phys. Lett. 100, 084101 (2012); http://dx.doi.org/10.1063/1.3688027 (4 pages)

Online Publication Date: 21 February 2012

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A simple method to enhance ion generation with femtosecond ultraintense lasers is demonstrated experimentally by defocusing laser beams on target surface. When the laser is optimally defocused, we find that the population of medium and low energy protons from ultra-thin foils is increased significantly while the proton cutoff energy is almost unchanged. In this way, the total proton yield can be enhanced by more than 1 order, even though the peak laser intensity drops. The depression of the amplified spontaneous emission (ASE) effect and the population increase of moderate-energy electrons are believed to be the main reasons for the effective enhancement.
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52.25.Tx Emission, absorption, and scattering of particles
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
78.45.+h Stimulated emission

Micronucleus formation induced by dielectric barrier discharge plasma exposure in brain cancer cells

Nagendra K. Kaushik, Hansup Uhm, and Eun Ha Choi

Appl. Phys. Lett. 100, 084102 (2012); http://dx.doi.org/10.1063/1.3687172 (4 pages) | Cited 6 times

Online Publication Date: 22 February 2012

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Induction of micronucleus formation (cytogenetic damage) in brain cancer cells upon exposure of dielectric barrier discharge plasma has been investigated. We have investigated the influence of exposure and incubation times on T98G brain cancer cells by using growth kinetic, clonogenic, and micronucleus formation assay. We found that micronucleus formation rate directly depends on the plasma exposure time. It is also shown that colony formation capacity of cells has been inhibited by the treatment of plasma at all doses. Cell death and micronucleus formation are shown to be significantly elevated by 120 and 240 s exposure of dielectric barrier discharge plasma.
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87.53.Bn Dosimetry/exposure assessment
87.17.-d Cell processes

The vibration dipole: A time reversed acoustics scheme for the experimental localisation of surface breaking cracks

Bart Van Damme, Koen Van Den Abeele, and Olivier Bou Matar

Appl. Phys. Lett. 100, 084103 (2012); http://dx.doi.org/10.1063/1.3690043 (3 pages) | Cited 2 times

Online Publication Date: 23 February 2012

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A combination of time reversed acoustics and nonlinear elastic wave spectroscopy techniques is introduced to localize surface breaking defects in a non-destructive manner. Reciprocal time reversal is applied at two neighbouring positions in order to create a vibration dipole with high amplitudes. At surface breaking cracks, nonlinear elastic effects are triggered by the shear forces due to induced friction of the crack interfaces. By mapping the nonlinearity generated by the vibration dipole over the sample surface, the position of a surface breaking crack can be visualized. The technique is tested on an industrial steel sample containing a closed crack.
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68.35.Gy Mechanical properties; surface strains
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.mt Cracks
62.30.+d Mechanical and elastic waves; vibrations

Tin doped indium oxide core—TiO2 shell nanowires on stainless steel mesh for flexible photoelectrochemical cells

Jun Hong Noh, Bo Ding, Hyun Soo Han, Ju Seong Kim, Jong Hoon Park, Sang Baek Park, Hyun Suk Jung, Jung-Kun Lee, and Kug Sun Hong

Appl. Phys. Lett. 100, 084104 (2012); http://dx.doi.org/10.1063/1.3684805 (4 pages) | Cited 3 times

Online Publication Date: 23 February 2012

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Photoanode architecture is built on highly conductive tin doped indium oxide (ITO) nanowires (NWs) on a flexible stainless steel mesh (SSM). ITO nanowires were coated with the atomic layer deposition grown TiO2 layer and the photoelectrochemical performance of the stainless steel mesh based photoanode were examined as a function of wire-length and shell-thickness. The photoanode consisting of 20 μm-long nanowire core and 36 nm thick shell increased the photocurrent of the testing cell by 4 times, compared to a reference cell. This enhanced photochemical activity is attributed to higher light harvesting efficiency of nanowire arrays and suppressed charge recombination of core-shell structure.
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81.07.Gf Nanowires
81.16.-c Methods of micro- and nanofabrication and processing
82.45.Fk Electrodes
72.40.+w Photoconduction and photovoltaic effects

Electron emission mechanism during the nanosecond high-voltage pulsed discharge in pressurized air

D. Levko, S. Yatom, V. Vekselman, and Ya. E. Krasik

Appl. Phys. Lett. 100, 084105 (2012); http://dx.doi.org/10.1063/1.3689010 (4 pages)

Online Publication Date: 23 February 2012

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A comparison between the results of x-ray absorption spectroscopy of runaway electrons (RAEs) generated during nanosecond timescale high-voltage (HV) gas discharge and the simulated attenuation of the x-ray flux produced by the runaway electron spectrum calculated using particle-in-cell numerical modeling of such a type of discharge is presented. The particle-in-cell simulation considered the field and explosive emissions (EEs) of the electrons from the cathode. It is shown that the field emission is the dominant emission mechanism for the short-duration (<2.5 ns) high-voltage pulses, while for the long-duration (>5 ns) high-voltage pulses, the explosive emission is likely to play a significant role.
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52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.65.Rr Particle-in-cell method
52.80.Qj Explosions; exploding wires
52.25.Fi Transport properties

Oscillation of the magnetic moment in modulated martensites in Ni2MnGa studied by ab initio calculations

Nan Xu, Jean-Marc Raulot, Zongbin Li, Jing Bai, Yudong Zhang, Xiang Zhao, Liang Zuo, and Claude Esling

Appl. Phys. Lett. 100, 084106 (2012); http://dx.doi.org/10.1063/1.3690054 (4 pages) | Cited 3 times

Online Publication Date: 24 February 2012

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We have revealed the oscillations in the distribution of the magnetic moments in modulated martensites in Ni2MnGa ferromagnetic shape memory alloy, by first-principles density-functional calculations. It is demonstrated that the oscillation of Ni magnetic moment that depends on the atomic shuffling in the superstructure dominates the distribution of the total magnetic moment per Ni2MnGa unit. The structure change-associated total magnetic moment has been found to increase for Ni2MnGa unit from the cubic austenite to the tetragonal nonmodulated (NM) martensite through the monoclinic modulated martensites.
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75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Cc Other ferromagnetic metals and alloys
81.30.Kf Martensitic transformations
81.40.Lm Deformation, plasticity, and creep
62.20.fg Shape-memory effect; yield stress; superelasticity
64.70.kd Metals and alloys

Measuring plasma turbulence using low coherence microwave radiation

D. R. Smith

Appl. Phys. Lett. 100, 084107 (2012); http://dx.doi.org/10.1063/1.3690922 (3 pages)

Online Publication Date: 24 February 2012

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Low coherence backscattering (LCBS) is a proposed diagnostic technique for measuring plasma turbulence and fluctuations. LCBS is an adaptation of optical coherence tomography, a biomedical imaging technique. Calculations and simulations show LCBS measurements can achieve centimeter-scale spatial resolution using low coherence microwave radiation. LCBS measurements exhibit several advantages over standard plasma turbulence measurement techniques including immunity to spurious reflections and measurement access in hollow density profiles. Also, LCBS is scalable for 1-D profile measurements and 2-D turbulence imaging.
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52.70.Gw Radio-frequency and microwave measurements
52.25.Gj Fluctuation and chaos phenomena
52.35.Ra Plasma turbulence
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