bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of double-decker pulse radiolysis
Authors: Kan K. , Kondoh T. , Yang J. , Ogata A. , Norizawa K. , Yoshida Y.
Published: July 2012

Double-decker pulse radiolysis (DDPR), which utilizes double-decker electron beams, was investigated to develop a new pulse radiolysis with a high time resolution. The double-decker electron beams were generated by injecting two UV pulses into a photocathode radio-frequency gun. In the pulse radiolysis, one electron beam was used as a pump beam, and the other was converted to a probe pulse. Finally, as its first application, the DDPR was successfully used for observing solvated electrons in water, with a 10%–90% rise time of 8.6 ps.
Energetic ion loss detector on the Alcator C-Mod tokamak
Authors: Pace D. C. , Granetz R. S. , Vieira R. , Bader A. , Bosco J. , Darrow D. S. , Fiore C. , Irby J. , Parker R. R. , Parkin W. , Reinke M. L. , Terry J. L. , Wolfe S. M. , Wukitch S. J. , Zweben S. J.
Published: July 2012

A scintillator-based energetic ion loss detector has been successfully commissioned on the Alcator C-Mod tokamak. This probe is located just below the outer midplane, where it captures ions of energies up to 2 MeV resulting from ion cyclotron resonance heating. After passing through a collimating aperture, ions impact different regions of the scintillator according to their gyroradius (energy) and pitch angle. The probe geometry and installation location are determined based on modeling of expected lost ions. The resulting probe is compact and resembles a standard plasma facing tile. Four separate fiber optic cables view different regions of the scintillator to provide phase space resolution. Evolving loss levels are measured during ion cyclotron resonance heating, including variation dependent upon individual antennae.
Predicting the melting temperature of ice-Ih with only electronic structure information as input
Authors: Pinnick Eric R. , Erramilli Shyamsunder , Wang Feng
Published: July 2012

The melting temperature of ice-Ih was calculated with only electronic structure information as input by creating a problem-specific force field. The force field, Water model by AFM for Ice and Liquid (WAIL), was developed with the adaptive force matching (AFM) method by fitting to post-Hartree-Fock quality forces obtained in quantum mechanics/molecular mechanics calculations. WAIL predicts the ice-Ih melting temperature to be 270 K. The model also predicts the densities of ice and water, the temperature of maximum density of water, the heat of vaporizations, and the radial distribution functions for both ice and water in good agreement with experimental measurements. The non-dissociative WAIL model is very similar to a flexible version of the popular TIP4P potential and has comparable computational cost. By customizing to problem-specific configurations with the AFM approach, the resulting model is remarkably more accurate than any variants of TIP4P for simulating ice-Ih and water in the temperature range from 253 K and 293 K under ambient pressure.
Dynamic Monte Carlo modeling of exciton dissociation in organic donor-acceptor solar cells
Authors: Heiber Michael C. , Dhinojwala Ali
Published: July 2012

A general dynamic Monte Carlo model for exciton dissociation at a donor-acceptor interface that includes exciton delocalization and hot charge separation is developed to model the experimental behavior observed for the poly(3-hexylthiophene):fullerene system and predict the theoretical performance of future materials systems. The presence of delocalized excitons and the direct formation of separated charge pairs has been recently measured by transient photo-induced absorption experiments and has been proposed to facilitate charge separation. The excess energy of the exciton dissociation process has also been observed to have a strong correlation with the charge separation yield for a series of thiophene based polymer:fullerene systems, suggesting that a hot charge separation process is also occurring. Hot charge separation has been previously theorized as a cause for highly efficient charge separation. However, a detailed model for this process has not been implemented and tested. Here, both conceptual models are implemented into a dynamic Monte Carlo simulation and tested using a simple bilayer donor-acceptor system. We find that exciton delocalization can account for a significant reduction in geminate recombination when compared to the traditional, bound polaron pair model. In addition, the hot charge separation process could further reduce the geminate recombination, but only if the hot charge mobility is several orders of magnitude larger than the standard charge mobility.
Acoustic properties of Kel F-800 copolymer up to 85 GPa
Authors: Benjamin Ari S. , Ahart Muhtar , Gramsch Stephen A. , Stevens Lewis L. , Orler E. Bruce , Dattelbaum Dana M. , Hemley Russell J.
Published: July 2012

Acoustic properties of the fluorinated copolymer Kel F-800 were determined with Brillouin spectroscopy up to pressures of 85 GPa at 300 K. This research addresses outstanding issues in high-pressure polymer behavior, as to date the acoustic properties and equation of state of any polymer have not been determined above 20 GPa. We observed both longitudinal and transverse modes in all pressure domains, allowing us to calculate the C11 and C12 moduli, bulk, shear, and Young's moduli, and the density of Kel F-800 as a function of pressure. We found the behavior of the polymer with respect to all parameters to change drastically with pressure. As a result, we find that the data are best understood when split into two pressure regimes. At low pressures (less than ∼5 GPa), analysis of the room temperature isotherm with a semi-empirical equation of state yielded a zero-pressure bulk modulus Ko and its derivative $K_0^\prime $K0′ of 12.8 ± 0.8 GPa and 9.6 ± 0.7, respectively. The same analysis for the higher pressure data yielded values for Ko and $K_0^\prime $K0′ of 34.9 ± 1.7 GPa and 5.1 ± 0.1, respectively. We discuss this significant difference in behavior with reference to the concept of effective free volume collapse.
Explicit water molecular dynamics study of the mobility of halide ions in presence of ionene oligocations
Authors: Druchok Maksym , Lukšič Miha , Vlachy Vojko
Published: July 2012

We present explicit water molecular dynamics simulations of solutions of aliphatic 3,3- and 6,6-ionene oligocations neutralized with (i) fluoride, chloride, bromide, or iodide counterions, respectively, or (ii) with a 1:1 mixture of chloride and bromide anions in presence of a low molecular weight salt at 298 K. The SPC/E model was used to describe water molecules. Results of the simulation are presented in form of the pair distribution functions between various atoms on the ionene oligoion and counterions in solution. In addition, we were interested in the dynamics of counterions around model ionenes. We showed that counterions residing in the vicinity of the oligoion exchange rapidly with those in the bulk solution, with the frequency depending on the nature of the counterion and on the charge density of the oligoion. We calculated the average residence times of the various counterion species to the oligoions and proposed the model which divides the counterions into “free” and “bound” and calculated the fraction of “free” counterions. In the second part of the study, we investigated interaction of the sodium chloride and sodium bromide, being simultaneously present in the solution, with differently charged ionenes in water. The selectivity effect was clearly observed: bromide ions tend to replace chloride ions in the immediate vicinity of the ionene oligoions. Simulation results are discussed in light of our recent measurements of thermodynamic and transport properties of aqueous ionene solutions.
Optically engineered ultrafast pulses for controlled rotations of exciton qubits in semiconductor quantum dots
Authors: Gamouras Angela , Mathew Reuble , Hall Kimberley C.
Published: July 2012

Shaped ultrafast pulses designed for controlled-rotation (C-ROT) operations on exciton qubits in semiconductor quantum dots are demonstrated using a quantum control apparatus operating at ∼1 eV. Optimum pulse shapes employing amplitude and phase shaping protocols are implemented using the output of an optical parametric oscillator and a programmable pulse shaping system, and characterized using autocorrelation and multiphoton intrapulse interference phase scan techniques. We apply our pulse characterization results and density matrix simulations to assess the fundamental limits on the fidelity of the C-ROT operation, providing a benchmark for the evaluation of sources of noise in other quantum control experiments. Our results indicate the effectiveness of pulse shaping techniques for achieving high fidelity quantum operations in quantum dots with a gate time below 1 ps.
Compact “diode-based” multi-energy soft x-ray diagnostic for NSTX
Authors: Tritz K. , Clayton D. J. , Stutman D. , Finkenthal M.
Published: July 2012

A novel and compact, diode-based, multi-energy soft x-ray (ME-SXR) diagnostic has been developed for the National Spherical Tokamak Experiment. The new edge ME-SXR system tested on NSTX consists of a set of vertically stacked diode arrays, each viewing the plasma tangentially through independent pinholes and filters providing an overlapping view of the plasma midplane which allows simultaneous SXR measurements with coarse sub-sampling of the x-ray spectrum. Using computed x-ray spectral emission data, combinations of filters can provide fast (>10 kHz) measurements of changes in the electron temperature and density profiles providing a method to “fill-in” the gaps of the multi-point Thomson scattering system.
Hard x-ray (>100 keV) imager to measure hot electron preheat for indirectly driven capsule implosions on the NIF
Authors: Döppner T. , Dewald E. L. , Divol L. , Thomas C. A. , Burns S. , Celliers P. M. , Izumi N. , Kline J. L. , LaCaille G. , McNaney J. M. , Prasad R. R. , Robey H. F. , Glenzer S. H. , Landen O. L.
Published: July 2012

We have fielded a hard x-ray (>100 keV) imager with high aspect ratio pinholes to measure the spatially resolved bremsstrahlung emission from energetic electrons slowing in a plastic ablator shell during indirectly driven implosions at the National Ignition Facility. These electrons are generated in laser plasma interactions and are a source of preheat to the deuterium-tritium fuel. First measurements show that hot electron preheat does not limit obtaining the fuel areal densities required for ignition and burn.
Size dependent characteristics of plasma synthesized carbonaceous nanoparticles
Authors: Kovacevic Eva , Berndt Johannes , Strunskus Thomas , Boufendi Laifa
Published: July 2012

Low temperature plasmas with their strong non equilibrium character offer unique possibilities for the production of nanoparticles. This contribution deals with size dependent properties of nanoparticles synthesized in a capacitively coupled discharge operated in mixtures of argon and acetylene. X-ray absorption measurements show that the particle properties dramatically change during the growth process. For nanoparticles under 10 nm in diameter, near edge x-ray absorption fine structure spectroscopy shows a sp2 rich graphite-like material. The bonding situation changes with the increasing size of the dust particles, showing the formation of a sp2 poor mantle around the sp2 rich core. This phenomenon can be explained in terms of the nucleation and growth process of nanoparticles, i.e., due to differences in the heating of small nanoparticles (nuclei) and due to differences in the gas phase species involved in the nucleation phase and the surface growth phase.
Reactive molecular dynamics study of Mo-based alloys under high-pressure, high-temperature conditions
Authors: Vasenkov Alex , Newsome David , Verners Osvalds , Russo Michael F. , Zaharieva Roussislava , van Duin Adri C. T.
Published: July 2012

Structural metal alloys are of vital importance for a clean energy economy, but the current trial-and-error alloy development methodology is expensive and time consuming. In this study, we demonstrate the capability of the ReaxFF force field model to predict mechanical properties and provide a fully dynamic description of oxidation and sulfidation of Mo-based alloys under high-pressure, high-temperature conditions using molecular dynamics (MD) method. The advantage of the ReaxFF approach is in its ability to model the formation and breaking of chemical bonds within the quantum framework but several orders of magnitude faster than the traditional density functional theory models. ReaxFF-MD predictions were compared to the literature Mo shock compression measurements at 300 K and 1673 K in the pressure range of 0–350 Pa, and densities and Young’s modulus in the temperature range of 300–1500 K. Analysis of oxidation of Mo and Ni clusters and surface slabs showed that Mo oxidation proceeded at a significantly higher rate than the Ni oxidation and involved oxygen transport inside the metal cluster coupled to large heat release that caused extensive surface melting. The oxidation simulations of Mo3Ni clusters showed high production of Mo oxides and a low concentration of Ni-oxides in the gas phase. This was attributed to the higher chemical stability of Mo-oxide gas phase species. Modeling of H2S interactions with Mo slab demonstrated that sulfur atoms increasingly agglomerated in the surfaces layers of the slab as the simulation proceeded, diffusing deeper into the slab in their atomic forms. A combined ReaxFF Mo/Ni/C/O/N/S/H parameter set enabled us to obtain a detailed atomistic analysis of complex physical and chemical events during the combustion of a complex fuel molecule on a reactor surface.
Geometric and electronic structures of (BeO)N (N = 2–12, 16, 20, and 24): Rings, double rings, and cages
Authors: Ren Lei , Cheng Longjiu , Feng Yan , Wang Xuemei
Published: July 2012

The structure of (BeO)N clusters (N = 2–12, 16, 20, and 24) are investigated using the method combining the genetic algorithm with density function theory. Benchmark calculation indicates that THSSh functional is reliable to predict the structures of (BeO)N cluster. The global minimum structures of (BeO)N clusters are rings up to N = 5, double rings at N = 6 and 7 and cages at N ≥ 8. Besides, almost all of the structures of (BeO)N cluster are aromatic according to the NICS criterion. Adaptive natural density partitioning analysis reveals that C6, (BN)3, and (BeO)3 rings (C24 and (BeO)12 fullerenes) are similar in bonding patterns. The building-up principle of (BeO)N is different from that of covalent (BN) and ionic (LiF and MgO) clusters.
Non-monotonic, distance-dependent relaxation of water in reverse micelles: Propagation of surface induced frustration along hydrogen bond networks
Authors: Biswas Rajib , Chakraborti Tamaghna , Bagchi Biman , Ayappa K. G.
Published: July 2012

Layer-wise, distance-dependent orientational relaxation of water confined in reverse micelles (RM) is studied using theoretical and computational tools. We use both a newly constructed “spins on a ring” (SOR) Ising-type model (with Shore-Zwanzig rotational dynamics) and atomistic simulations with explicit water. Our study explores the effect of reverse micelle size and role of intermolecular correlations, compromised by the presence of a highly polar surface, on the distance (from the interface) dependence of water relaxation. The “spins on a ring” model can capture some aspects of distance dependence of relaxation, such as acceleration of orientational relaxation at intermediate layers. In atomistic simulations, layer-wise decomposition of hydrogen bond formation pattern clearly reveals that hydrogen bond arrangement of water at a certain distance away from the surface can remain frustrated due to the interaction with the polar surface head groups. This layer-wise analysis also reveals the presence of a non-monotonic slow relaxation component which can be attributed to this frustration effect and which is accentuated in small to intermediate size RMs. For large size RMs, the long time component decreases monotonically from the interface to the interior of the RMs with slowest relaxation observed at the interface.
Magnetotransport anisotropy in lattice-misfit-strained ultrathin La2/3Ca1/3MnO3 films epitaxially grown on (110)-oriented SrTiO3 and LaAlO3 substrates
Authors: Guo N. L. , Li J. , Wei Y. F. , Zhang Y. , Cui L. M. , Zhao L. , Jin Y. R. , Tian H. Y. , Deng Hui , Zhao G. P. , Zheng D. N.
Published: July 2012

(110)-Oriented manganite thin films are essential for studies on the interface effects concerning spin-polarized electron injection, especially the proximity effect with high temperature superconducting cuprates. However, due to the peculiarity of the (110) plane, an atomically smooth surface generally can only sustain up to a quite low film thickness. Therefore, anisotropy along the two crystallographically asymmetric [001] and [11¯0] in-plane directions in ultrathin (110)-oriented manganite films are worthy of a careful investigation. Here, studies on the magnetotransport anisotropy of (110)-oriented epitaxial La2/3Ca1/3MnO3 (LCMO) thin films of 20 nm thickness grown by pulsed laser deposition are reported. Both SrTiO3 (STO) and LaAlO3 (LAO) substrates were adopted to highlight the lattice-misfit-strain effects. While in LCMO/STO film, the magnetic easy axis is along the [11¯0] direction, in LCMO/LAO film the [001] direction is easier. Accordingly, the resistivity and magnetoresistance measured along the easy axes are lower. The correlation between the magnetic and transport anisotropy then has been undoubtedly demonstrated. For the LCMO films on STO, property evolutions with temperature and magnetic field are free from fine features, and thus clear and easily understood, making STO a more appropriate substrate for interface studies in (110)-oriented heterostructures.
Theoretical and experimental investigation of magnetoelectric effect for bending-tension coupled modes in magnetostrictive-piezoelectric layered composites
Authors: Hasanyan D. , Gao J. , Wang Y. , Viswan R. , Li M. , Shen Y. , Li J. , Viehland D.
Published: July 2012

In this paper, we discuss a theoretical model with experimental verification for the resonance enhancement of magnetoelectric (ME) interactions at frequencies corresponding to bending-tension oscillations. A dynamic theory of arbitrary laminated magneto-elasto-electric bars was constructed. The model included bending and longitudinal vibration effects for predicting ME coefficients in laminate bar composite structures consisting of magnetostrictive, piezoelectric, and pure elastic layers. The thickness dependence of stress, strain, and magnetic and electric fields within a sample are taken into account, as such the bending deformations should be considered in an applied magnetic or electric field. The frequency dependence of the ME voltage coefficients has obtained by solving electrostatic, magnetostatic, and elastodynamic equations. We consider boundary conditions corresponding to free vibrations at both ends. As a demonstration, our theory for multilayer ME composites was then applied to ferromagnetic-ferroelectric bilayers, specifically Metglas-PZT ones. A theoretical model is presented for static (low-frequency) ME effects in such bilayers. We also performed experiments for these Metglas-PZT bilayers and analyzed the influence of Metglas geometry (length and thickness) and Metglas/PZT volume fraction on the ME coefficient. The frequency dependence of the ME coefficient is also presented for different geometries (length, thickness) of Metglas. The theory shows good agreement with experimental data, even near the resonance frequency.
Treatment of enterococcus faecalis bacteria by a helium atmospheric cold plasma brush with oxygen addition
Authors: Chen Wei , Huang Jun , Du Ning , Liu Xiao-Di , Wang Xing-Quan , Lv Guo-Hua , Zhang Guo-Ping , Guo Li-Hong , Yang Si-Ze
Published: July 2012

An atmospheric cold plasma brush suitable for large area and low-temperature plasma-based sterilization is designed. Results demonstrate that the He/O2 plasma more effectively kills Enterococcus faecalis than the pure He plasma. In addition, the sterilization efficiency values of the He/O2 plasma depend on the oxygen fraction in Helium gas. The atmospheric cold plasma brush using a proper ratio of He/O2 (2.5%) reaches the optimum sterilization efficiency. After plasma treatment, the cell structure and morphology changes can be observed by the scanning electron microscopy. Optical emission measurements indicate that reactive species such as O and OH play a significant role in the sterilization process.
Vacancy-type defects in InxGa1–xN alloys probed using a monoenergetic positron beam
Authors: Uedono A. , Ishibashi S. , Watanabe T. , Wang X. Q. , Liu S. T. , Chen G. , Sang L. W. , Sumiya M. , Shen B.
Published: July 2012

Native defects in InxGa1–xN grown by plasma-assisted molecular beam epitaxy were probed by a monoenergetic positron beam. Doppler broadening spectra of the annihilation radiation were measured, and these were compared with results obtained using first-principles calculation. The defect concentration increased with increasing In composition x and reached the maximum at x = 0.44∼0.56. A clear correlation between the line-width of photoluminescence and the defect concentration was obtained. The major defect species detected by positron annihilation was identified as cation vacancies coupled with multiple nitrogen vacancies (VNs), and their introduction mechanism is discussed in terms of the strain energy due to bond-length/angle distortions and the suppression of the VN formation energy by neighboring In atoms.
Vibrational calculation for the HOCO radical and the cis-HOCO anion
Authors: Mladenović Mirjana
Published: July 2012

We present numerically exact vibrational transitions for trans-HOCO, cis-HOCO, and cis-HOCO− for the quartic force fields of Fortenberry et al. [J. Chem. Phys. 135, 134301 (2011)10.1063/1.3643336; Fortenberry et al. J. Chem. Phys. 135, 214303 (2011)10.1063/1.3663615], obtained by means of a computational strategy based on the discrete variable representation. Several adiabatic projection schemes have been employed to characterize the vibrational levels and to study the relevance of the intermode coupling (vibrational mixing). Our results help to clear up a large discrepancy between previously reported vibrational perturbation theory and vibrational configuration interaction predictions for the torsional frequency.
Probing the structures of neutral boron clusters using infrared/vacuum ultraviolet two color ionization: B11, B16, and B17
Authors: Romanescu Constantin , Harding Dan J. , Fielicke André , Wang Lai-Sheng
Published: July 2012

The structures of neutral boron clusters, B11, B16, and B17, have been investigated using vibrational spectroscopy and ab initio calculations. Infrared absorption spectra in the wavelength range of 650 to 1550 cm−1 are obtained for the three neutral boron clusters from the enhancement of their near-threshold ionization efficiency at a fixed UV wavelength of 157 nm (7.87 eV) after resonant absorption of the tunable infrared photons. All three clusters, B11, B16, and B17, are found to possess planar or quasi-planar structures, similar to their corresponding anionic counterparts (Bn−), whose global minima were found previously to be planar, using photoelectron spectroscopy and theoretical calculations. Only minor structural changes are observed between the neutral and the anionic species for these three boron clusters.
Chemical diffusion: Another factor affecting the magnetoresistance ratio in Ta/CoFeB/MgO/CoFeB/Ta magnetic tunnel junction
Authors: Yang Y. , Wang W. X. , Yao Y. , Liu H. F. , Naganuma H. , Sakul T. S. , Han X. F. , Yu R. C.
Published: July 2012

This letter investigates the microstructure and mean inner potential (MIP) profile of Ta/CoFeB/MgO/CoFeB/Ta magnetic tunnel junctions (MTJs) by high resolution transmission electron microscopy (HRTEM) and electron holography, respectively. The inconspicuous crystallization of MgO barrier is confirmed by HRTEM in the post-annealed sample at 250 °C. An obvious MIP difference is displayed in the Ta layers between the top and bottom of the MTJ, and elemental content difference of them is confirmed by energy dispersive spectroscopy. These results imply that the chemical diffusion can also give rise to a lower tunnel magnetoresistance ratio besides the inconspicuous crystallization of MgO barrier.
Ultrabroadband coherent electric field from far infrared to 200 THz using air plasma induced by 10 fs pulses
Authors: Matsubara Eiichi , Nagai Masaya , Ashida Masaaki
Published: July 2012

We generated an ultrabroadband infrared pulse ranging from far infrared to 200 THz through a plasma by focusing a hollow-fiber compressed intense 10-fs pulse and its second harmonic in air. We coherently detected the signal up to 100 THz with electro-optic sampling and clarified its drastic dependence on the orientation of the second harmonic crystal in a range of 100–200 THz with an HgCdTe detector. From these, we confirmed the whole frequency components originated from the AC biased plasma and were phase locked. This result opens the possibility of a pump-probe spectroscopy which covers the whole infrared range.
Analysis of noise-induced transitions from regular to chaotic oscillations in the Chen system
Authors: Bashkirtseva Irina , Chen Guanrong , Ryashko Lev
Published: July 2012

The stochastically perturbed Chen system is studied within the parameter region which permits both regular and chaotic oscillations. As noise intensity increases and passes some threshold value, noise-induced hopping between close portions of the stochastic cycle can be observed. Through these transitions, the stochastic cycle is deformed to be a stochastic attractor that looks like chaotic. In this paper for investigation of these transitions, a constructive method based on the stochastic sensitivity function technique with confidence ellipses is suggested and discussed in detail. Analyzing a mutual arrangement of these ellipses, we estimate the threshold noise intensity corresponding to chaotization of the stochastic attractor. Capabilities of this geometric method for detailed analysis of the noise-induced hopping which generates chaos are demonstrated on the stochastic Chen system.
Beating of magnetic oscillations in a graphene device probed by quantum capacitance
Authors: Tahir M. , Schwingenschlögl U.
Published: July 2012

We report the quantum capacitance of a monolayer graphene device in an external perpendicular magnetic field including the effects of Rashba spin-orbit interaction (SOI). The SOI mixes the spin up and spin down states of neighbouring Landau levels into two (unequally spaced) energy branches. In order to investigate the role of the SOI for the electronic transport, we study the density of states to probe the quantum capacitance of monolayer graphene. SOI effects on the quantum magnetic oscillations (Shubnikov de Haas and de Hass-van Alphen) are deduced from the quantum capacitance.
Note: Pneumatically modulated liquid delivery with feedback control
Authors: Field C. R. , Terray A. V. , Lubrano A. L. , Rogers D. A. , Hart S. J. , Rose-Pehrsson S. L.
Published: July 2012

We present the design and characterization of a pneumatically driven liquid delivery system using an embedded microcontroller with feedback control capable of maintaining a stable, constant flow rate over several hours of operation. Flow rates with relative standard deviations less than 1% were achieved and compared to a typical laboratory syringe pump.
A wavelength modulation system for highly sensitive absorption spectroscopy
Authors: Iwamitsu K. , Aihara S. , Shimamoto T. , Fujii A. , Akai I.
Published: July 2012

We developed a newly designed wavelength modulation (WM) system for highly sensitive absorption spectroscopy. In our system, the WM is realized by yawing an output mirror in a monochromator. In order to control an amplitude Δλ of the WM in a wide range, we employed a forced vibration of a permanent magnet driven by a magnetic field of a solenoid. Our system has an advantage of that the WM amplitude Δλ can be adjusted in extensively wide range from 0.08 nm to 11 nm only by tuning a driving frequency of the applying current to the solenoid, because we utilize a resonance phenomenon of the forced vibration for adjustment of the WM amplitude. By using our system, we measured WM absorption spectra of a Cu2O thin film and found clearly spectral structures for weak 2–4P excitonic resonances in the WM absorption spectra.
Solid debris collection for radiochemical diagnostics at the National Ignition Facility
Authors: Gostic J. M. , Shaughnessy D. A. , Moore K. T. , Hutcheon I. D. , Grant P. M. , Moody K. J.
Published: July 2012

Radiochemical analysis of post-ignition debris inside the National Ignition Facility (NIF) target chamber can help determine various diagnostic parameters associated with the implosion efficiency of the fusion capsule. This technique is limited by the ability to distinguish ablator material from other debris and by the collection efficiency of the capsule debris after implosion. Prior to designing an on-line collection system, the chemical nature and distribution of the debris inside the chamber must be determined. The focus of our current work has been on evaluating capture of activated Au hohlraum debris on passive foils (5 cm diameter, 50 cm from target center) post-shot. Preliminary data suggest that debris distribution is locally heterogeneous along the equatorial and polar line-of-sights.
Reduction of threshold voltage fluctuation in field-effect transistors by controlling individual dopant position
Authors: Hori Masahiro , Taira Keigo , Komatsubara Akira , Kumagai Kuninori , Ono Yukinori , Tanii Takashi , Endoh Tetsuo , Shinada Takahiro
Published: July 2012

To investigate the impact of only the dopant position on threshold voltage (Vth) in nanoscale field-effect transistors, we fabricated transistors with ordered dopant arrays and conventional random channel doping. Electrical measurements revealed that device performance could be enhanced by controlling the dopant position alone, despite varying dopant number according to a Poisson distribution. Furthermore, device-to-device fluctuations in Vth could be suppressed by implanting a heavier ion such as arsenic owing to the reduction of the projected ion struggling. The results of our study highlight potential improvements in device performance by controlling individual dopant positions.
Potential distribution in channel of thin-film transistors
Authors: Okamura Koshi , Hahn Horst
Published: July 2012

Channel voltages of ZnO thin-film transistors during operation are precisely probed at two trisecting positions between the source and drain electrode, which exactly corresponds to characteristic transistor events, such as carrier injection, carrier accumulation, pinch-off formation, and drain current saturation. Furthermore, a simple numerical calculation based on the gradual channel approximation and the current continuity equation reveals that the channel voltages have a non-linear potential distribution and an intrinsic but significant potential drop in the region near to the drain electrode in most of the linear regime.
Efficiency-limiting processes in Ga(NAsP)/GaP quantum well lasers
Authors: Hossain N. , Jin S. R. , Liebich S. , Zimprich M. , Volz K. , Kunert B. , Stolz W. , Sweeney S. J.
Published: July 2012

We report on the carrier recombination mechanisms in dilute nitride Ga(NAsP)/GaP quantum well lasers. Spontaneous emission measurements show that defect-related recombination in the devices is less significant compared with other GaAs-based dilute nitride lasers. From temperature dependent measurements, we find that the threshold current density, Jth is dominated by non-radiative recombination process(es), which account for at least 91% of Jth at room temperature. The characteristic temperature, T0 (T1) is measured to be ∼104 K (∼99 K) around 200 K, which drops to ∼58 K ( ∼37 K) around room temperature. Hydrostatic pressure measurements reveal a strong increase of threshold current with increasing pressure. This implies that current leakage dominates carrier recombination which is also responsible for their low T0 and T1 values at room temperature.
Directional adhesion behavior of a single elastic fiber
Authors: He L. W. , Yan S. P. , Li B. Q. , Chu J. R.
Published: July 2012

Theoretical analysis and optimum design of directional adhesion property are of great importance for developing high performance biomimetic fibrillar adhesives. In this paper, a theoretical study is made on the deformation and adhesion behavior of a single straight fiber contacting with a rigid smooth surface under the coupling effect of normal and shear forces. The influences of the fiber’s bending stiffness and slanted angle on the adhesion behavior are studied. It has been found that the coupling effect of normal and shear forces leads to directional adhesion behavior. Moreover, the detachment mode and the enhancement of the normal pull-off force with the increase of the applied shear force could be directly predicted based on the derived formulas. The stability of adhesion equilibrium states has also been determined by using the stability criterion of energy minimization. These theoretical findings are in good agreement with recent experiments qualitatively, and they are expected to be valuable for optimum design of fibrillar dry adhesives.
Strain relaxation in InGaN/GaN micro-pillars evidenced by high resolution cathodoluminescence hyperspectral imaging
Authors: Xie E. Y. , Chen Z. Z. , Edwards P. R. , Gong Z. , Liu N. Y. , Tao Y. B. , Zhang Y. F. , Chen Y. J. , Watson I. M. , Gu E. , Martin R. W. , Zhang G. Y. , Dawson M. D.
Published: July 2012

A size-dependent strain relaxation and its effects on the optical properties of InGaN/GaN multiple quantum wells (QWs) in micro-pillars have been investigated through a combination of high spatial resolution cathodoluminescence (CL) hyperspectral imaging and numerical modeling. The pillars have diameters (d) ranging from 2 to 150 μm and were fabricated from a III-nitride light-emitting diode (LED) structure optimized for yellow-green emission at ∼560 nm. The CL mapping enables us to investigate strain relaxation in these pillars on a sub-micron scale and to confirm for the first time that a narrow (≤2 μm) edge blue-shift occurs even for the large InGaN/GaN pillars (d > 10 μm). The observed maximum blue-shift at the pillar edge exceeds 7 nm with respect to the pillar centre for the pillars with diameters in the 2–16 μm range. For the smallest pillar (d = 2 μm), the total blue-shift at the edge is 17.5 nm including an 8.2 nm “global” blue-shift at the pillar centre in comparison with the unetched wafer. By using a finite element method with a boundary condition taking account of a strained GaN buffer layer which was neglected in previous simulation works, the strain distribution in the QWs of these pillars was simulated as a function of pillar diameter. The blue-shift in the QWs emission wavelength was then calculated from the strain-dependent changes in piezoelectric field, and the consequent modification of transition energy in the QWs. The simulation and experimental results agree well, confirming the necessity for considering the strained buffer layer in the strain simulation. These results provide not only significant insights into the mechanism of strain relaxation in these micro-pillars but also practical guidance for design of micro/nano LEDs.
Self-compensation limited conductivity in semi-insulating indium-doped Cd0.9Zn0.1Te crystals
Authors: Kosyachenko L. A. , Melnychuk S. V. , Maslyanchuk O. L. , Sklyarchuk V. M. , Sklyarchuk O. F. , Fiederle M. , Lambropoulos C. P.
Published: July 2012

Cd0.9Zn0.1Te:In crystals with semi-intrinsic conductivity have been investigated. Temperature dependence of their electrical characteristics shows a number of unconventional peculiarities: the thermal activation energy of conductivity is “anomalously” low (0.60–0.62 eV); the resistivity at elevated temperatures is greater than its intrinsic value for Cd0.9Zn0.1Te; the inversion of the conduction from n- to p-type occurs at a temperature slightly above 300 K, etc. The observed features are explained in terms of statistics of electrons and holes in a semiconductor containing a self-compensation complex, whose concentration is much higher than those of uncontrolled (background) impurities and defects. Comparison of the calculation results and experimental data leads to the conclusion that the donor level, which is far distant from the middle of the band gap, dominates in the conductivity of the material and its compensation is virtually complete (Na/Nd = 0.99996–0.99998) as predicted by theory.
Failure mechanism of THz GaAs photoconductive antenna
Authors: Qadri Syed B. , Wu Dong H. , Graber Benjamin D. , Mahadik Nadeemullah A. , Garzarella Anthony
Published: July 2012

We investigated the failure mechanism of THz GaAs photoconductive antenna using high resolution x-ray diffraction topography. From these studies, it was found that grain boundaries are formed during the high frequency device operation. This results in the segregation of gold at the boundaries causing electromigration of the metal between the gold micro-strips. This disrupts the photocurrents from being produced by femtosecond laser thus preventing terahertz beam generation from the photoconductive antennae leading to device failure.
Frequency-dispersive resistance of high impedance surface absorber with trapezoid-coupling pattern
Authors: Bin Zhang Hui , Heng Zhou Pei , Wei Deng Li , Liang Xie Jian , Fei Liang Di , Jiang Deng Long
Published: July 2012

Resonances of the high impedance surface (HIS) absorber with periodic trapezoid-coupling pattern were studied. The theoretical, numerical, and experimental study showed that a frequency dispersion of the equivalent resistance could break the single resonance limitation. The limitation is induced by the non-dispersive feature of the equivalent resistance in simple patterned HIS absorber. Therefore, multi-resonances originated from the trapezoid-coupling pattern effectively expanded the absorption bandwidth. The proposed absorber had a thickness reduced by 41% and a −15 dB absorption bandwidth broadened by 50% compared with Salisbury screen.
Charged droplet transportation under direct current electric fields as a cell carrier
Authors: Lee Chiun-Peng , Chang Hsien-Chih , Wei Zung-Hang
Published: July 2012

This study verifies the reliability of the cell transport through charged droplets under DC electrical fields. Over 90% cell viability can be obtained after charging and discharging for thousands of times. The high cell viability indicates that the electrical charging of a droplet barely influences the cells inside over a long working period. DC field induced AC electrical signals via droplet motion are also observed and analyzed quantitatively. The measured AC signals help us understand the charge transfer of a droplet during charging and discharging processes.
A tunable spin filter in periodic diluted magnetic semiconductor/semiconductor superlattices
Authors: Guo Yong , Shen Fei-Ruo , Chen Xin-Yi
Published: July 2012

We propose a tunable spin filter based on periodic diluted magnetic semiconductor/semiconductor (DMS/S) superlattices. It is found that periodic DMS/S superlattices can filter high efficiently not only spin-up electrons but also spin-down ones over a broad range of incident energies. The positions and widths of spin-filtering bands can be manipulated by adjusting the parameters of the superlattices or the external magnetic field. It is also found that the defect layer within the system generally leads to a strong suppression of spin-dependent transmission and makes the superlattices filter single-energy electrons. The results obtained may lead to potential applications in the field of spintronics.
Abnormal electronic transition variations of lanthanum-modified lead zironate stannate titanate ceramics near morphotropic phase boundary: A spectroscopic evidence
Authors: Chen X. , Jiang K. , Hu Z. G. , Chen X. F. , Wang G. S. , Dong X. L. , Chu J. H.
Published: July 2012

The structure-related optical response of (Pb1-1.5xLax)(Zr0.42Sn0.40Ti0.18)O3 (100x/42/40/18) ceramics with different compositions has been investigated. Based on x-ray diffraction, the phase transition from rhombohedral to tetragonal structure is revealed between compositions of x = 2.6% and 2.8% near morphotropic phase boundary (MPB). Correspondingly, abnormal spectral response in the photon energy from 1.4 to 6.1 eV is observed near MPB. Furthermore, the blue shift of the two critical points related parameters, which is obtained from fitting the reflectance spectra, indicates that the variation of electronic band structure near MPB is responsible for the anomalous behavior.
Using an Oculomotor Signature as an Indicator of Aesthetic Preference
Authors: Holmes Tim , Zanker Johannes M.
Published: July 2012

Eye movements are strongly influenced by the task given to an observer. The immediacy of such eye movements, which are difficult to control consciously, offers the potential to explore highly variable subjective evaluations, such as aesthetic preference, with reliable objective measures. We presented a variety of images in sets of 2, 4, or 8 items for different durations and analyzed oculomotor statistics such as cumulative fixation duration, refixations, and the sequence of fixations while participants searched for their preferred image, after which participants indicated their preference using a button press. The total amount of time spent looking at any image correlates with selection preference and does so increasingly well with longer presentation duration. For short presentations, the first and last fixations correlate better with image preference. All response measures become increasingly variable as the number and complexity of presented images are increased. A weighted combination of these measures can significantly improve the correlation with preference, suggesting a “signature” which could be used as a reliable indicator for task-free subjective evaluation of stimuli in visual psychophysics. Its role as an improved fitness function in visually driven evolutionary algorithms is discussed.
Predicting macrophyte states in a small temporarily open/closed estuary
Authors: Riddin T. , Adams J. B.
Published: July 2012

Temporarily open/closed estuaries (TOCEs) shift between abiotic states associated with mouth status. The aim of this study was to assess whether macrophyte states could be identified based on the dominant cover abundance of different species representative of specific habitats. A 5-year dataset of monthly macrophyte cover was assessed for the East Kleinemonde Estuary in South Africa. Three macrophyte states were identified: namely open and tidal (predominantly intertidal salt marsh); closed and low water level (predominantly salt marsh); and closed and high water level (with submerged macrophytes). The threshold water level for the change from salt marsh to submerged macrophytes was 1.6 m above mean sea level (amsl). A fourth state where macroalgae were dominant was identified for high salinity conditions (above 30 PSU). It was then possible to examine simulated water level data for different inflow scenarios to determine how often these macrophyte states occurred. Available macrophyte habitat was also calculated for different water levels using a spatial model written in Modelbuilder (ArcGIS 9.3.1). Both methods used to predict available macrophyte habitats are rapid, requiring only information on the elevation range of the main habitats, as well as present distribution and bathymetric maps. These predictive techniques are useful in the determination of the ecological water requirements of small estuaries.
Stable isotope analysis as a tool for elasmobranch conservation research: a primer for non-specialists
Authors: Shiffman D. S. , Gallagher A. J. , Boyle M. D. , Hammerschlag-Peyer C. M. , Hammerschlag N.
Published: July 2012

Many elasmobranch species are undergoing population declines on a global scale; however, implementation of effective conservation and management strategies is hindered, to a large extent, by a lack of sufficient data on diet, life history and behaviour. This work is a primer of how stable isotope analysis can be used as a cost-effective, relatively simple tool for examining resource use patterns (e.g. diet, habitat) and generating relevant data in support of science-based elasmobranch conservation and management. Specifically, isotopes can resolve the feeding niches of elasmobranchs, detect ontogenetic trophic shifts and calculate relative diet breadth of different species. Stable isotope analysis can also be employed to investigate the extent of anthropogenic impacts on diet or to infer the source of toxins affecting elasmobranchs. Additionally, this tool can be used to study migration patterns and habitat usage. Depending on the tissue analysed, this technique can also be non-lethal and minimally invasive. The limitations of stable isotope analysis are discussed, and recommendations for future work are presented.
Zinc marine biogeochemistry in seawater: a review
Authors: Sinoir Marie , Butler Edward C. V. , Bowie Andrew R. , Mongin Mathieu , Nesterenko Pavel N. , Hassler Christel S.
Published: July 2012

The interest in trace element biogeochemistry has arisen from the well demonstrated iron hypothesis that revealed the central role that iron exerts on oceanic primary and associated biogeochemical cycles. The essentiality of zinc for key biological enzymes, coupled with a nutrient-like vertical distribution with low dissolved concentrations in many marine surface waters, provided motivation to study zinc in marine systems. Laboratory studies have confirmed the importance of zinc to sustain phytoplankton growth and its influence on the composition of the phytoplankton community. However, mixed results were obtained in the field, which suggest a more subtle effect of zinc on oceanic phytoplankton growth than iron. As a consequence, consensus on its biological role, mechanisms at play or regional versus global relevance is currently lacking and highlights the need for new conceptual models of zinc in marine systems. The recent GEOTRACES program is generating new data approaches to discuss and understand further zinc behaviour in the ocean.
Reintroduction success of threatened Australian trout cod (Maccullochella macquariensis) based on growth and reproduction
Authors: Lyon Jarod P. , Todd Charles , Nicol Simon J. , MacDonald Alasdair , Stoessel Daniel , Ingram Brett A. , Barker Richard J. , Bradshaw Corey J. A.
Published: July 2012

Internationally, re-introductions of endangered species into their former ranges have largely failed. Here we assess a successful reintroduction program of the endangered trout cod (Maccullochella macquariensis) and examine factors contributing to this success. Stocking of marked fish (all stocked fish were marked) occurred between 1997 and 2006 in the Ovens River, south-eastern Australia, where trout cod were historically abundant but locally extinct by the 1980s. We found no natural recruits (i.e. from spawnings of stocked fish in the wild) over the age of six, indicating that natural recruitment started at most five years after stocking began. Of the 83 fish we examined for sexual maturity, 12 were immature, 20 were male, and 51 were female. The body length at which 50% of the population can be considered mature was 325 and 250 mm for females and males, respectively. The length at which 90% of the population was mature was 394 and 318 mm for females and males, respectively. The smallest mature female was 245 mm. Average relative fertility was 9 eggs g–1 fish weight. The results we obtained provide valuable insights into the aspects contributing to the success of reintroduction programs for endangered freshwater species.