bluuebunny/crossref_metadata_2025 huggingface dataset:
Improved basis set for low frequency plasma waves
Authors: Bellan P. M.
Published: November 2012

It is shown that the low frequency plasma wave equation can be obtained much more directly than by the previously used method of solving for the determinant of a matrix involving the three components of the electric field vector. The more direct method uses a two‐dimensional current density vector space that is precisely equivalent to the previously used three‐dimensional electric field vector space. Unlike the electric field, the current density is restricted by the quasi‐neutrality condition to a two‐dimensional vector space. Comparison with previously obtained dispersion relations is provided and a method is presented for obtaining exact analytic solutions for the three roots of the cubic dispersion relation. The commonly used kinetic Alfvén dispersion relation is shown to be valid only for near‐perpendicular propagation in a low beta plasma. It is shown that at a cross‐over point where the perpendicular wave phase velocity equals the ion acoustic velocity, the coupling between Alfvén and fast modes vanishes and the Alfvén mode reverts to its cold form even in situations where the Alfvén velocity is smaller than the electron thermal velocity. A method is prescribed by which measurement of wave electric current density completely eliminates the space‐time ambiguity previously believed to be an unavoidable shortcoming of single‐spacecraft frequency measurements.
Impacts of black carbon mixing state on black carbon nucleation scavenging: Insights from a particle‐resolved model
Authors: Ching J. , Riemer N. , West M.
Published: November 2012

This paper presents an advancement of the recently developed particle‐resolved aerosol model PartMC‐MOSAIC (Particle Monte Carlo‐Model for Simulating Aerosol Interactions and Chemistry) to investigate the impacts of mixing state on cloud droplet formation and to provide a tool for the quantification of errors in cloud properties introduced by simplifying mixing state assumptions. We coupled PartMC‐MOSAIC with a cloud parcel model. We initialized the cloud parcel simulation with hourly PartMC‐MOSAIC model output from a 48‐hour urban plume simulation. The cloud parcel model then explicitly simulated activation and condensational growth of the particles as the parcel underwent cooling at a specified rate and the particles of the aerosol population competed for water vapor. We used this capability to quantify the relative importance of size information versus composition information for the prediction of the cloud droplet number fraction, mass fraction of black carbon that is nucleation‐scavenged, cloud droplet effective radius, and relative dispersion of the droplet size distribution by introducing averaging of particle‐resolved information within prescribed bins. For the cloud droplet number fraction, both composition averaging and size‐bin averaging individually led to an error of less than 25% for all cloud parcel simulations, while averaging in both size bins and composition resulted in errors of up to 34% for the base case cooling rate of 0.5 K/min. In contrast, for the nucleation‐scavenged black carbon mass fraction, the results for size‐bin averaging tracked the reference case well, while composition averaging, with or without size‐bin averaging, led to overestimation of this quantity by up to 600%.
Interaction of long telomeric DNAs with macrocyclic hexaoxazole as a G-quadruplex ligand
Authors: Iida Keisuke , Tsubouchi Gen , Nakamura Takahiro , Majima Satoki , Seimiya Hiroyuki , Nagasawa Kazuo
Published: November 2012

The interactions of long telomeric DNAs, which mimic telomeres in living cells, with a macrocyclic hexaoxazole ligand L2H2-6OTD (2) were investigated by means of electrophoresis mobility shift assay, circular dichroism (CD) titration analysis, and DNA melting measurements.
Sign preference in ion-induced nucleation: Contributions to the free energy barrier
Authors: Keasler Samuel J. , Kim Hyunmi , Chen Bin
Published: November 2012

We have performed a series of computer simulations using the AVUS-HR approach to better understand the origin of the sign preference in ion-induced nucleation. In particular, we emphasize the importance of distinguishing between the total formation free energy of a cluster, and the nucleation free energy, which involves only those steps contributing to the free energy barrier. We have separately considered how the ion-water potential energy, the water-water potential energy, and the entropy contribute to both the cluster formation free energy, and the nucleation free energy. These simulations have shown that while the ion-water potential energies make the largest contribution to the formation free energy difference between positive and negative ions, the entropy is the contribution leading to lower nucleation free energy barriers for negative ions. The primary reason for this is the larger stable (but precritical) clusters formed around negative ions. We have further shown that the distinction between formation and nucleation free energies is of particular importance when comparing small cations with larger anions where the formation free energies can be much lower for the cationic clusters, even though the nucleation barriers are lower for the anionic clusters.
Analytic non-integrability of the Suslov problem
Authors: Mahdi Adam , Valls Claudia
Published: November 2012

In this work, we consider the Suslov problem, which consists of a rotation motion of a rigid body, whose center of mass is located at one axis of inertia, around a fixed point O in a constant gravity field restricted to a nonholonomic constraint. The integrability and non-integrability has been established by a number of authors for the nongeneric values of b = (b1, b2, b3) which is the unit vector along the line connecting the point O with the center of mass of the body. Here, we prove the analytic non-integrability for the remaining (generic) values of b.
Noncommuting local common causes for correlations violating the Clauser–Horne inequality
Authors: Hofer-Szabó Gábor , Vecsernyés Péter
Published: November 2012

In the paper, the EPR-Bohm scenario will be reproduced in an algebraic quantum field theoretical setting with locally finite degrees of freedom. It will be shown that for a set of spatially separated correlating events (projections) maximally violating the Clauser–Horne inequality there can be given a common causal explanation if commutativity is abandoned between the common cause and the correlating events. Moreover, the noncommuting common cause will be local and supported in the common past of the correlating events.
Methodological aspects of the quantum-chemical description of interface dipoles at tetrathiafulvalene/tetracyanoquinodimethane interfaces
Authors: Van Regemorter T. , Guillaume M. , Fuchs A. , Lennartz C. , Geskin V. , Beljonne D. , Cornil J.
Published: November 2012

The formation of dipoles at interfaces between organic semiconductors is expected to play a significant role in the operation of organic-based devices, though the electronic processes at their origin have still to be clearly elucidated. Quantum-chemical calculations can prove very useful to shed light on such electronic interfacial phenomena provided that a suitable theoretical approach is used. In this context, we have performed calculations on small vertical stacks of TTF-TCNQ molecules, first at the CAS-MRCI level to validate the use of single-determinantal approaches, then at the MP2 level set as a benchmark. Various density functional theory (DFT) functionals have then been applied to larger stacks, showing that long-range corrected functionals are required to reproduce MP2 results taken as benchmark. Finally, the use of periodic boundary conditions at the DFT level points to the huge impact of depolarization effects between adjacent stacks.
Studies on the effect of different solar dryers on the vitamin content of tomato (Solanum lycopersicon)
Authors: Eze J. I. , Ojike O.
Published: November 2012

Samples of tomato fruit were dried under four different conditions: open-air sun drying method and by using three different models of integral passive solar dryers which include green house solar dryer, sun-tracking solar dryer, and latitudinal box solar dryer. The fresh tomato samples and the dried samples were analysed for vitamins A, C, and E. The results showed a significant difference in the concentrations of vitamins A, C, and E between the fresh samples and the dried samples for all drying systems. While vitamin C is reduced in concentration for all dried samples, vitamins A and E are increased significantly with open-air system having the highest value in vitamin C concentration while latitudinal box dryer gives the best result in terms of vitamins A and E retention. All year round, availability of tomato could be enhanced by chipping and drying. Packaging and marketing of dried chips in small quantities could be a lucrative entrepreneurial endeavour for the business minded.
Electrostatic interactions mediated by polarizable counterions: Weak and strong coupling limits
Authors: Démery Vincent , Dean David S. , Podgornik Rudolf
Published: November 2012

We investigate the statistical mechanics of an inhomogeneous Coulomb fluid composed of charged particles with static polarizability. We derive the weak- and the strong-coupling approximations and evaluate the partition function in a planar dielectric slab geometry with charged boundaries. We investigate the density profiles and the disjoining pressure for both approximations. Comparison to the case of non-polarizable counterions shows that polarizability brings important differences in the counterion density distribution as well as the counterion mediated electrostatic interactions between charged dielectric interfaces.
Exact two-component relativistic theory for NMR parameters: General formulation and pilot application
Authors: Sun Qiming , Xiao Yunlong , Liu Wenjian
Published: November 2012

The previously proposed exact two-component (X2C) relativistic theory of nuclear magnetic resonance (NMR) parameters [Q. Sun, W. Liu, Y. Xiao, and L. Cheng, J. Chem. Phys. 131, 081101 (2009)10.1063/1.3216471] is reformulated to accommodate two schemes for kinetic balance, five schemes for magnetic balance, and three schemes for decoupling in a unified manner, at both matrix and operator levels. In addition, three definitions of spin magnetization are considered in the coupled-perturbed Kohn-Sham equation. Apart from its simplicity, the most salient feature of X2C-NMR lies in that its diamagnetic and paramagnetic terms agree individually with the corresponding four-component counterparts for any finite basis. For practical applications, five approximate schemes for the first order coupling matrix X10 and four approximate schemes for the treatment of two-electron integrals are introduced, which render the computations of X2C-NMR very much the same as those of approximate two-component approaches.
The fundamental role of quantized vibrations in coherent light harvesting by cryptophyte algae
Authors: Kolli Avinash , O’Reilly Edward J. , Scholes Gregory D. , Olaya-Castro Alexandra
Published: November 2012

The influence of fast vibrations on energy transfer and conversion in natural molecular aggregates is an issue of central interest. This article shows the important role of high-energy quantized vibrations and their non-equilibrium dynamics for energy transfer in photosynthetic systems with highly localized excitonic states. We consider the cryptophyte antennae protein phycoerythrin 545 and show that coupling to quantized vibrations, which are quasi-resonant with excitonic transitions is fundamental for biological function as it generates non-cascaded transport with rapid and wider spatial distribution of excitation energy. Our work also indicates that the non-equilibrium dynamics of such vibrations can manifest itself in ultrafast beating of both excitonic populations and coherences at room temperature, with time scales in agreement with those reported in experiments. Moreover, we show that mechanisms supporting coherent excitonic dynamics assist coupling to selected modes that channel energy to preferential sites in the complex. We therefore argue that, in the presence of strong coupling between electronic excitations and quantized vibrations, a concrete and important advantage of quantum coherent dynamics is precisely to tune resonances that promote fast and effective energy distribution.
A model for emission yield from planar photocathodes based on photon-enhanced thermionic emission or negative-electron-affinity photoemission
Authors: Sahasrabuddhe Kunal , Schwede Jared W. , Bargatin Igor , Jean Joel , Howe Roger T. , Shen Zhi-Xun , Melosh Nicholas A.
Published: November 2012

A general model is presented for electron emission yield from planar photocathodes that accounts for arbitrary cathode thickness and finite recombination velocities at both front and back surfaces. This treatment is applicable to negative electron affinity emitters as well as positive electron affinity cathodes, which have been predicted to be useful for energy conversion. The emission model is based on a simple one-dimensional steady-state diffusion treatment. The resulting relation for electron yield is used to model emission from thin-film cathodes with material parameters similar to GaAs. Cathode thickness and recombination at the emissive surface are found to strongly affect emission yield from cathodes, yet the magnitude of the effect greatly depends upon the emission mechanism. A predictable optimal film thickness is found from a balance between optical absorption, surface recombination, and emission rate.
The isotope dependence of dissociative recombination via the indirect mechanism
Authors: Pratt S. T. , Jungen Ch.
Published: November 2012

A recently derived analytic formula for the low-energy dissociative recombination of molecular ions and electrons involving capture into vibrationally excited Rydberg states provides a simple expression for the isotope dependence of the process. This expression depends only on the ratio of the relevant vibrational frequencies of the two isotopomers of interest and can therefore be evaluated even without knowledge of the dynamical parameters required to determine the recombination cross sections. The expression is used to predict the isotope dependence for a number of molecular ions and the results are compared with experiment. While the agreement with the experiment is generally quite reasonable, discrepancies may indicate a breakdown of the assumptions used to derive the cross section formula or potential inaccuracies in the experiments.
Extension of the source-sink potential (SSP) approach to multichannel quantum transport
Authors: Rocheleau Philippe , Ernzerhof Matthias
Published: November 2012

We present an extension of the single channel source-sink potential approach [F. Goyer, M. Ernzerhof, and M. Zhuang, J. Chem. Phys. 126, 144104 (2007)10.1063/1.2715932] for molecular electronic devices (MEDs) to multiple channels. The proposed multichannel source-sink potential method relies on an eigenchannel description of conducting states of the MED which are obtained by a self-consistent algorithm. We use the newly developed model to examine the transport of the 1-phenyl-1,3-butadiene molecule connected to two coupled rows of atoms that act as contacts on the left and right sides. With an eigenchannel description of the wave function in the contacts, we determined that one of the eigenchannels is effectively closed by the interference effects of the side chain. Furthermore, we provide an example where we observe a complete inversion (from bonding to antibonding and vice versa) of the transverse character of the wave function upon passage through the molecule.
The structure of N2 adsorbed on the rumpled NaCl(100) surface—A combined LEED and DFT-D study
Authors: Vogt Jochen
Published: November 2012

The structure of N2 physisorbed on the NaCl(100) single crystal surface is investigated by means of quantitative low-energy electron diffraction (LEED) in combination with dispersion corrected density functional theory (DFT-D). In the temperature range between 20 K and 45 K, a p(1 × 1) structure is observed in the LEED experiment. According to the structure analysis based on the measured diffraction spot intensity profiles, the N2 molecules are adsorbed over the topmost Na+ ions. The experimental distance of the lower nitrogen to the Na+ ion underneath is (2.55 ± 0.07) Å; the corresponding DFT-D value is 2.65 Å. The axes of the molecules are tilted (26 ± 3)° with respect to the surface normal, while in the zero Kelvin optimum structure from DFT-D, the molecules have a perpendicular orientation. The experimental monolayer heat of adsorption, deduced from a Fowler-Guggenheim kinetic model of adsorption is −(13.6 ± 1.6) kJ mol−1, including a lateral molecule-molecule interaction energy of −(2.0 ± 0.4) kJ mol−1. The zero Kelvin adsorption energy from DFT-D, including zero point energy correction, is −15.6 kJ mol−1; the molecule-molecule interaction is −2.4 kJ mol−1. While the rumpling of the NaCl(100) surface is unchanged upon adsorption of nitrogen, the best-fit root mean square thermal displacements of the ions in the topmost substrate layer are significantly reduced.
Role of B19′ martensite deformation in stabilizing two-way shape memory behavior in NiTi
Authors: Benafan O. , Padula S. A. , Noebe R. D. , Sisneros T. A. , Vaidyanathan R.
Published: November 2012

Deformation of a B19′ martensitic, polycrystalline Ni49.9Ti50.1 (at. %) shape memory alloy and its influence on the magnitude and stability of the ensuing two-way shape memory effect (TWSME) was investigated by combined ex situ mechanical experimentation and in situ neutron diffraction measurements at stress and temperature. The microstructural changes (texture, lattice strains, and phase fractions) during room-temperature deformation and subsequent thermal cycling were captured and compared to the bulk macroscopic response of the alloy. With increasing uniaxial strain, it was observed that B19′ martensite deformed by reorientation and detwinning with preferred selection of the (1¯50)M and (010)M variants, (201¯)B19′ deformation twinning, and dislocation activity. These mechanisms were indicated by changes in bulk texture from the neutron diffraction measurements. Partial reversibility of the reoriented variants and deformation twins was also captured upon load removal and thermal cycling, which after isothermal deformation to strains between 6% and 22% resulted in a strong TWSME. Consequently, TWSME functional parameters including TWSME strain, strain reduction, and transformation temperatures were characterized and it was found that prior martensite deformation to 14% strain provided the optimum condition for the TWSME, resulting in a stable two-way shape memory strain of 2.2%. Thus, isothermal deformation of martensite was found to be a quick and efficient method for creating a strong and stable TWSME in Ni49.9Ti50.1.
Influence of growth and annealing conditions on low-frequency magnetic 1/f noise in MgO magnetic tunnel junctions
Authors: Feng Jiafeng , Diao Zhu , Kurt Huseyin , Stearrett Ryan , Singh A. , Nowak Edmund R. , Coey J. M. D.
Published: November 2012

Magnetic 1/f noise is compared in magnetic tunnel junctions with electron-beam evaporated and sputtered MgO tunnel barriers in the annealing temperature range 350 - 425 °C. The variation of the magnetic noise parameter (αmag) of the reference layer with annealing temperature mainly reflects the variation of the pinning effect of the exchange-bias layer. A reduction in αmag with bias is associated with the bias dependence of the tunneling magnetoresistance. The related magnetic losses are parameterized by a phase lag ε, which is nearly independent of bias especially below 100 mV. The similar changes in magnetic noise with annealing temperature and barrier thickness for two types of MgO magnetic tunnel junctions indicate that the barrier layer quality does not affect the magnetic losses in the reference layer.
New oxyfluoride glass with high fluorine content and laser patterning of nonlinear optical BaAlBO3F2 single crystal line
Authors: Shionozaki K. , Honma T. , Komatsu T.
Published: November 2012

A new oxyfluoride glass of 50BaF2-25Al2O3-25B2O3 (mol. %) with a large fraction of fluorine, i.e., F/(F + O) = 0.4, was prepared using a conventional melt-quenching method in order to synthesize new glass-ceramics containing nonlinear optical oxyfluoride crystals. The refractive index at 632.8 nm and ultra-violet cutoff wavelength of the glass were 1.564 and ∼200 nm, respectively. Eu3+ ions in the glass showed a high quantum yield of 88% in the photoluminescence spectrum in the visible region. BaAlBO3F2 crystals (size: 50–100 nm) showing second harmonic generations were formed through the crystallization of the glass. Lines consisting of BaAlBO3F2 crystals were patterned successfully on the glass surface by laser irradiations (Yb:YVO4 laser with a wavelength of 1080 nm, laser power of 1.1 W, scanning speed of 8 μm/s). High resolution transmission electron microscope observations combined with a focused ion beam technique indicate that BaAlBO3F2 crystals are highly oriented just like a single crystal. The present study proposes that the new oxyfluoride glass and glass-ceramics prepared have a high potential for optical device applications.
Electronic, structural, and optical properties of the host and Cr-doped cadmium thioindate
Authors: Tablero C.
Published: November 2012

The cadmium thioindate spinel CdIn2S4 semiconductor has potential applications for optoelectronic devices. We present a theoretical study of the structural and optoelectronic properties of the host and of the Cr-doped ternary spinel. For the host spinel, we analyze the direct or indirect character of the energy bandgap, the change of the energy bandgap with the anion displacement parameter and with the site cation distribution, and the optical properties. The main effect of the Cr doping is the creation of an intermediate band within the energy bandgap. The character and the occupation of this band are analyzed for two substitutions: Cr by In and Cr by Cd. This band permits more channels for the photon absorption. The optical properties are obtained and analyzed. The absorption coefficients are decomposed into contributions from the different absorption channels and from the inter- and intra-atomic components.
Validation of a correction procedure for removing the optical effects from transmission spectra of thin films on substrates
Authors: Milosevic Milan , King Sean W.
Published: November 2012

Transmission spectra of thin films on double side polished substrates feature a quasi sinusoidal baseline superimposed onto the true absorption spectra of the thin film. The quasi sinusoidal baseline is due to strong interference from multiple reflections within the film and can directly affect the relative degree of the measured absorption in the film. In a previous article [S. W. King and M. Milosevic, J. Appl. Phys. 111, 073109 (2012)], we described a method for the removal of these optical effects from infrared transmission spectra. This method renormalizes the spectrum and removes modulations imprinted onto the absorption by interference fringes. Here, we use simulated spectra for a model material to explicitly validate that the proposed correction procedure accurately extracts the pure absorption coefficient of the thin film and is not an ad hoc baseline correction procedure.
Magnetic anisotropy and anomalous Hall effect of ultrathin Co/Pd bilayers
Authors: Kou Xinli , Schmalhorst Jan-Michael , Keskin Vedat , Reiss Guenter
Published: November 2012

The magnetic properties and anomalous Hall effect of ultrathin Co/Pd bilayers have been studied. The easy magnetization axis of ultrathin Co/Pd bilayers switches from perpendicular-to-plane to in-plane if the Co film thickness increases. A temperature dependent reorientation transition of the easy axis occurs when the film thickness is close to this reorientation thickness. The anomalous Hall conductivity σxy and the longitudinal conductivity σxx have been evaluated taking into account the current density in each individual layer. The obtained values are consistent with previous investigations of thick Co films. The scattering independent mechanism seems to be the dominant source of the AHE effect in our samples. However, an interfacial contribution to the anomalous Hall conductivity which has opposite sign as compared with the bulk contribution is suggested by our data.
Contamination effects on fixed-bias Langmuir probes
Authors: Steigies C. T. , Barjatya A.
Published: November 2012

Langmuir probes are standard instruments for plasma density measurements on many sounding rockets. These probes can be operated in swept-bias as well as in fixed-bias modes. In swept-bias Langmuir probes, contamination effects are frequently visible as a hysteresis between consecutive up and down voltage ramps. This hysteresis, if not corrected, leads to poorly determined plasma densities and temperatures. With a properly chosen sweep function, the contamination parameters can be determined from the measurements and correct plasma parameters can then be determined. In this paper, we study the contamination effects on fixed-bias Langmuir probes, where no hysteresis type effect is seen in the data. Even though the contamination is not evident from the measurements, it does affect the plasma density fluctuation spectrum as measured by the fixed-bias Langmuir probe. We model the contamination as a simple resistor-capacitor circuit between the probe surface and the plasma. We find that measurements of small scale plasma fluctuations (meter to sub-meter scale) along a rocket trajectory are not affected, but the measured amplitude of large scale plasma density variation (tens of meters or larger) is attenuated. From the model calculations, we determine amplitude and cross-over frequency of the contamination effect on fixed-bias probes for different contamination parameters. The model results also show that a fixed bias probe operating in the ion-saturation region is affected less by contamination as compared to a fixed bias probe operating in the electron saturation region.
Nano-faceting of Cu capping layer grown on Fe/Si (111) and its effect on magnetic anisotropy
Authors: Liu Hao-Liang , He Wei , Wu Qiong , Zhang Xiang-Qun , Yang Hai-Tao , Cheng Zhao-Hua
Published: November 2012

We represent a report on the growth and structure of Cu capping layer on ultrathin Fe films on Si (111) substrate as well as its effect on magnetic anisotropy. Cu grows as forming triangular-shaped pyramids with nano-facets and in epitaxial mode with Kurdjumov-Sachs orientation. Spin reorientation transition (SRT) from out-of-plane to in-plane of Fe films is induced by Cu capping, which is believed to be mainly affected by strain change in Fe films. Based on strain relief mechanism, rapid decrease in Cu critical thickness to induce SRT with increasing Fe underlayer thickness can be interpreted quite well.
Unloading and reloading response of shocked aluminum single crystals: Time-dependent anisotropic material description
Authors: Winey J. M. , Johnson J. N. , Gupta Y. M.
Published: November 2012

The measured unloading and reloading wave profiles in shocked metals have long been known to show deviations from the usual elastic-plastic response used to model shocked metals. To gain insight into inelastic deformation mechanisms during unloading and reloading from the shocked state and to avoid complexities associated with material heterogeneities present in polycrystalline metals, this work has focused on the shock wave response of single crystals. Here, we report on wave propagation simulations to examine the unloading and reloading response of aluminum single crystals shocked along [100], [110], and [111] orientations to 21 GPa peak stresses. The simulations utilized a dislocation dynamics based, time-dependent anisotropic material description to model shock-induced elastic-plastic deformation. The calculated profiles provide good overall agreement with measured unloading and reloading wave profiles [H. Huang and J. R. Asay, J. Appl. Phys. 101, 063550 (2007)] for all three crystal orientations and for two different peak stresses. Our single crystal simulations show that differences between the profiles calculated using simpler elastic-plastic models and the measured profiles can be understood in terms of time-dependent material inelastic response. Therefore, the general applicability of previous time-independent analysis methods to infer shear strength from unloading and reloading wave profiles is questionable. Our simulations also show that dislocation mechanisms governing the unloading response of shocked Al single crystals differ from those governing the reloading response. Overall, our findings show that a dislocation-based approach provides a useful physical description to explain unloading and reloading of shocked Al single crystals. More generally, the present work demonstrates that understanding and modeling the unloading and reloading response of shocked metals may require the incorporation of time-dependent inelastic deformation response.
Optical emission diagnostics with electric probe measurements of inductively coupled Ar/O2/Ar-O2 plasmas
Authors: Chung T. H. , Ra Kang Hae , Keun Bae Min
Published: November 2012

Physical properties of low-pressure inductively coupled argon, oxygen, and Ar-O2 mixture plasmas are investigated using optical emission spectroscopy (OES) combined with an rf-compensated Langmuir probe measurement. In each gas discharge, the electron density and the electron temperature were obtained by using the probe. The electron temperature was also obtained by OES models and compared with that measured by the probe. The electron temperature was observed to decrease with increasing power and pressure and also observed to decrease with increasing Ar content. Argon metastable densities were calculated based on an optical transition model. In Ar-O2 discharges, the dissociation fraction of O2 molecules was estimated using optical emission actinometry. The dissociation fraction was observed to increase with increasing power and Ar content.
Suppression of spin relaxation in rubrene nanowire spin valves
Authors: Alam Kazi M. , Bodepudi Srikrishna C. , Starko-Bowes Ryan , Pramanik Sandipan
Published: November 2012

We report spin valve measurements performed on vertically oriented array of amorphous rubrene (5,6,11,12-tetraphenylnaphthacene) nanowires. Compared to previously reported rubrene thin-film spin valves, rubrene nanowires exhibit significant suppression of spin relaxation. Our results indicate spin-orbit interaction to be the dominant mechanism and are consistent with recent theoretical works, which suggest spin admixture parameter as a crucial ingredient in determining spin relaxation length.
Particle deconfinement in a bent magnetic mirror
Authors: Gueroult Renaud , Fisch Nathaniel J.
Published: November 2012

Coils misalignment in a magnetic mirror can produce additional particle transport. The magnetic field non axi-symmetry is responsible for radial and longitudinal drifts in a way much similar to the neo-classical transport in a tandem mirror cell distorted by end plugs. Accordingly, a regime exhibiting large radial displacements––similar to the resonant regime in tandem mirrors––can be obtained by confining ions azimuthally, for example by means of a properly tuned radial electric field. Because of the mass dependence of the magnetic field non-homogeneity drift velocities, the azimuthal trapping is mass specific, allowing, in principle, the filtering of a specific species based on its mass.
Electrophoretic deposition onto an insulator for thin film preparation toward electronic device fabrication
Authors: Miyajima Shougo , Nagamatsu Shuichi , Pandey Shyam S. , Hayase Shuzi , Kaneto Keiichi , Takashima Wataru
Published: November 2012

An electrostatic film fabrication method utilizing the dielectric layer, entitled dielectric barrier electrophoretic deposition (DBEPD) has been proposed. We demonstrated the fabrication of uniform organic semiconductor thin film onto any kind of substrate by DBEPD. Optical absorption spectra of colloidal poly(3-hexylthiophene) (P3HT) film prepared by DBEPD exhibited the clear vibrational structure attributed to highly ordered domains. It was in contrast to the relatively disordered structure as shown in the case of P3HT film prepared by conventional electrophoretic deposition (EPD). Organic field effect transistors fabricated by each method showed similar organic field effect transistor characteristics, however, the uniformity of DBEPD film was superior to EPD film.
Can interference patterns in the reflectance spectra of GaN epilayers give important information of carrier concentration?
Authors: Zheng C. C. , Xu S. J. , Zhang F. , Ning J. Q. , Zhao D. G. , Yang H. , Che C. M.
Published: November 2012

Low-temperature reflectance spectra of a series of Si-doped GaN epilayers with different doping concentrations grown on sapphire by metal-organic chemical vapour deposition were measured. In addition to the excitonic polariton resonance structures at the band edge, interference oscillating patterns were observed in the energy region well below the band gap. The amplitudes of these oscillation patterns show a distinct dependence on the doping concentrations of the samples. From the thin-film optical interference principle, an approach connecting the amplitude of the interference oscillations and the impurity scattering was established. Good agreement between experiment and theory is achieved.
High single-spatial-mode pulsed power from 980 nm emitting diode lasers
Authors: Hempel Martin , Tomm Jens W. , Elsaesser Thomas , Bettiati Mauro
Published: November 2012

Single-spatial-mode pulsed powers as high as 13 W and 20 W in 150 and 50 ns pulses, respectively, are reported for 980 nm emitting lasers. In terms of energy, single-spatial-mode values of up to 2 μJ within 150 ns pulses are shown. In this high-power pulsed operation, the devices shield themselves from facet degradation, being the main degradation source in continuous wave (cw) operation. Our results pave the way towards additional applications while employing available standard devices, which have originally been designed as very reliable cw fiber pumps.
Silicon-based three-dimensional photonic crystal nanocavity laser with InAs quantum-dot gain
Authors: Cao Daoshe , Tandaechanurat Aniwat , Nakayama Shigeru , Ishida Satomi , Iwamoto Satoshi , Arakawa Yasuhiko
Published: November 2012

We report on the demonstration of lasing oscillation in a silicon-based three-dimensional photonic crystal nanocavity using InAs quantum dots as gain material by pulsed optical pumping at 11 K. An active layer embedding InAs quantum dots was inserted in the cavity using micromanipulation technique. The highest quality factor for silicon-based three-dimensional photonic crystal cavities (∼22 000) was achieved. We also evaluated the spontaneous emission coupling factor of the laser to be ∼0.78 by fitting the experimental light-in light-out curve with coupled rate equations. This result would pave the way to the realization of CMOS-compatible high-density three-dimensional photonic integrated circuits.
Blue 6-ps short-pulse generation in gain-switched InGaN vertical-cavity surface-emitting lasers via impulsive optical pumping
Authors: Chen Shaoqiang , Okano Makoto , Zhang Baoping , Yoshita Masahiro , Akiyama Hidefumi , Kanemitsu Yoshihiko
Published: November 2012

We report the demonstration of the picosecond-pulse lasing in blue region from an optically pumped gain-switched InGaN vertical-cavity-surface-emitting laser (VCSEL). Through 150-fs optical pulse excitations at room temperature, multimode pulse lasing with a main mode at 436.5 nm from the InGaN VCSEL was observed. The output pulse widths were measured to be as short as 9.8 ps for the total lasing spectra and 6.0 ps for the main mode. Since the obtained short pulses were still not limited by its photon lifetime of 0.7 ps or band-width of 0.8 nm, possible ways to generate even shorter pulses have been examined.
A rotary piezoelectric actuator using longitudinal and bending hybrid transducer
Authors: Liu Yingxiang , Yang Xiaohui , Chen Weishan , Liu Junkao
Published: November 2012

A rotary piezoelectric actuator using bolt-clamped type transducer with double driving feet is proposed in this study. The first-order longitudinal and fourth-order bending vibration modes are superimposed in the actuator to produce elliptical movements on the driving tips. Longitudinal PZT and bending PZT are clamped between the exponential shape horns and the flange by bolts. The vibration shape changes of the actuator are presented to give a clear explanation of its working principle. Several structural parameters of the exponential shape horn are selected and adjusted to accomplish the tuning process of the longitudinal and bending resonance frequencies. The input impedance and vibration characteristics are calculated by using FEM method; the gained results verify the feasibility of the proposed actuator. After the fabrication of a prototype, its vibration characteristics are measured by using a scanning laser Doppler vibrometer; the tested results are in good agreement with the FEM calculated results. The mechanical output performance experiments state that the prototype achieves a maximum speed of 129 r/min and a maximum torque of 1.5 Nm.
Dual mycorrhizal associations of jarrah (Eucalyptus marginata) in a nurse-pot system
Authors: Kariman Khalil , Barker Susan J. , Finnegan Patrick M. , Tibbett Mark
Published: November 2012

Jarrah (Eucalyptus marginata Donn ex Sm.) plants, like many other eucalypts, can form symbiotic associations with both arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) fungi. To study this tripartite relationship we developed a novel nurse-pot system to allow us to investigate the extent and temporal colonisation dynamics of jarrah by two AM species (Rhizophagus irregularis (Błaszk., Wubet, Renker & Buscot) C. Walker & A. Schüßler comb. nov. and Scutellospora calospora Nicol. & Gerd.) and two putative ECM species (Austroboletus occidentalis Watling & N.M. Greg. and Scleroderma sp.) and their potential effects on jarrah growth and nutrition. Our nurse-pot system, using jarrah as both the nurse plant and test plant, was developed to establish extraradical hyphal networks of both AM and ECM fungi that act as single or dual inoculum for test plants. Mycorrhizal colonisation was described and quantified, and growth and nutritional effects measured and analysed. Mycorrhizal colonisation increased with time for the test seedlings exposed to hyphae networks from S. calospora and Scleroderma sp. The nurse-pot system was effective at initiating colonisation of functioning AM or (putative) ECM systems separately but the ECM symbiosis was inhibited where a dual AM + ECM inoculum (R. irregularis and Scleroderma sp.) was present. The presence of S. calospora, A. occidentalis and Scleroderma sp. individually significantly increased the shoot biomass of seedlings compared with non-mycorrhizal controls. The two AM isolates had different physiological effects on jarrah plants. S. calospora improved growth and micronutrient uptake of jarrah seedlings whereas no positive response was observed with R. irregularis. In addition, as an interesting observation, the non-responsive AM fungus R. irregularis suppressed the ECM symbiosis in dually inoculated plants where ECM structures, positive growth response and nutritional effects were absent. When inoculated individually, ECM isolates dominated the growth response and uptake of P and other nutrients in this dual symbiotic plant. Despite the positive growth response in the A. occidentalis treatment, ECM structures were not observed in either nurse or test seedlings. From the effects of A. occidentalis on jarrah we hypothesise that this fungus forms a functional mycorrhizal-type partnership even without forming archetypal structures in and on the root.
Dereplicating nonribosomal peptides using an informatic search algorithm for natural products (iSNAP) discovery
Authors: Ibrahim Ashraf , Yang Lian , Johnston Chad , Liu Xiaowen , Ma Bin , Magarvey Nathan A.
Published: November 2012

Nonribosomal peptides are highly sought after for their therapeutic applications. As with other natural products, dereplication of known compounds and focused discovery of new agents within this class are central concerns of modern natural product-based drug discovery. Development of a chemoinformatic library-based and informatic search strategy for natural products (iSNAP) has been constructed and applied to nonribosomal peptides and proved useful for true nontargeted dereplication across a spectrum of nonribosomal peptides and within natural product extracts.
Watching a signaling protein function in real time via 100-ps time-resolved Laue crystallography
Authors: Schotte Friedrich , Cho Hyun Sun , Kaila Ville R. I. , Kamikubo Hironari , Dashdorj Naranbaatar , Henry Eric R. , Graber Timothy J. , Henning Robert , Wulff Michael , Hummer Gerhard , Kataoka Mikio , Anfinrud Philip A.
Published: November 2012

To understand how signaling proteins function, it is crucial to know the time-ordered sequence of events that lead to the signaling state. We recently developed on the BioCARS 14-IDB beamline at the Advanced Photon Source the infrastructure required to characterize structural changes in protein crystals with near-atomic spatial resolution and 150-ps time resolution, and have used this capability to track the reversible photocycle of photoactive yellow protein (PYP) following
trans
-to-
cis
photoisomerization of its
p
-coumaric acid (pCA) chromophore over 10 decades of time. The first of four major intermediates characterized in this study is highly contorted, with the pCA carbonyl rotated nearly 90° out of the plane of the phenolate. A hydrogen bond between the pCA carbonyl and the Cys69 backbone constrains the chromophore in this unusual twisted conformation. Density functional theory calculations confirm that this structure is chemically plausible and corresponds to a strained
cis
intermediate. This unique structure is short-lived (∼600 ps), has not been observed in prior cryocrystallography experiments, and is the progenitor of intermediates characterized in previous nanosecond time-resolved Laue crystallography studies. The structural transitions unveiled during the PYP photocycle include
trans
/
cis
isomerization, the breaking and making of hydrogen bonds, formation/relaxation of strain, and gated water penetration into the interior of the protein. This mechanistically detailed, near-atomic resolution description of the complete PYP photocycle provides a framework for understanding signal transduction in proteins, and for assessing and validating theoretical/computational approaches in protein biophysics.
Ion-beam irradiation, gene identification, and marker-assisted breeding in the development of low-cadmium rice
Authors: Ishikawa Satoru , Ishimaru Yasuhiro , Igura Masato , Kuramata Masato , Abe Tadashi , Senoura Takeshi , Hase Yoshihiro , Arao Tomohito , Nishizawa Naoko K. , Nakanishi Hiromi
Published: November 2012

Rice (
Oryza sativa
L.) grain is a major dietary source of cadmium (Cd), which is toxic to humans, but no practical technique exists to substantially reduce Cd contamination. Carbon ion-beam irradiation produced three rice mutants with <0.05 mg Cd⋅kg
−1
in the grain compared with a mean of 1.73 mg Cd⋅kg
−1
in the parent, Koshihikari. We identified the gene responsible for reduced Cd uptake and developed a strategy for marker-assisted selection of low-Cd cultivars. Sequence analysis revealed that these mutants have different mutations of the same gene (
OsNRAMP5
), which encodes a natural resistance-associated macrophage protein. Functional analysis revealed that the defective transporter protein encoded by the mutant
osnramp5
greatly decreases Cd uptake by roots, resulting in decreased Cd in the straw and grain. In addition, we developed DNA markers to facilitate marker-assisted selection of cultivars carrying
osnramp5
. When grown in Cd-contaminated paddy fields, the mutants have nearly undetectable Cd in their grains and exhibit no agriculturally or economically adverse traits. Because mutants produced by ion-beam radiation are not transgenic plants, they are likely to be accepted by consumers and thus represent a practical choice for rice production worldwide.
A classification of spin frustration in molecular magnets from a physical study of large odd-numbered-metal, odd electron rings
Authors: Baker Michael L. , Timco Grigore A. , Piligkos Stergios , Mathieson Jennifer S. , Mutka Hannu , Tuna Floriana , Kozłowski Piotr , Antkowiak Michał , Guidi Tatiana , Gupta Tulika , Rath Harapriya , Woolfson Robert J. , Kamieniarz Grzegorz , Pritchard Robin G. , Weihe Høgni , Cronin Leroy , Rajaraman Gopalan , Collison David , McInnes Eric J. L. , Winpenny Richard E. P.
Published: November 2012

The term “frustration” in the context of magnetism was originally used by P. W. Anderson and quickly adopted for application to the description of spin glasses and later to very special lattice types, such as the kagomé. The original use of the term was to describe systems with competing antiferromagnetic interactions and is important in current condensed matter physics in areas such as the description of emergent magnetic monopoles in spin ice. Within molecular magnetism, at least two very different definitions of frustration are used. Here we report the synthesis and characterization of unusual nine-metal rings, using magnetic measurements and inelastic neutron scattering, supported by density functional theory calculations. These compounds show different electronic/magnetic structures caused by frustration, and the findings lead us to propose a classification for frustration within molecular magnets that encompasses and clarifies all previous definitions.
Neuronal code for extended time in the hippocampus
Authors: Mankin Emily A. , Sparks Fraser T. , Slayyeh Begum , Sutherland Robert J. , Leutgeb Stefan , Leutgeb Jill K.
Published: November 2012

The time when an event occurs can become part of autobiographical memories. In brain structures that support such memories, a neural code should exist that represents when or how long ago events occurred. Here we describe a neuronal coding mechanism in hippocampus that can be used to represent the recency of an experience over intervals of hours to days. When the same event is repeated after such time periods, the activity patterns of hippocampal CA1 cell populations progressively differ with increasing temporal distances. Coding for space and context is nonetheless preserved. Compared with CA1, the firing patterns of hippocampal CA3 cell populations are highly reproducible, irrespective of the time interval, and thus provide a stable memory code over time. Therefore, the neuronal activity patterns in CA1 but not CA3 include a code that can be used to distinguish between time intervals on an extended scale, consistent with behavioral studies showing that the CA1 area is selectively required for temporal coding over such periods.
Fluctuation broadening in carbon nanotube resonators
Authors: Barnard Arthur W. , Sazonova Vera , van der Zande Arend M. , McEuen Paul L.
Published: November 2012

We simulated the behavior of suspended carbon nanotube resonators over a broad range of temperatures to explore the physics of semiflexible polymers in underdamped environments. We find that thermal fluctuations induce strong coupling between resonance modes. This effect leads to spectral fluctuations that readily account for the experimentally observed quality factors
Q
∼ 100 at 300
K
. Using a mean-field approach to describe fluctuations, we analytically calculate
Q
and frequency shifts in tensioned and buckled carbon nanotubes and find excellent agreement with simulations.