bluuebunny/crossref_metadata_2025 huggingface dataset:
Combination Therapy Targeting Akt and Mammalian Target of Rapamycin Improves Functional Outcome after Controlled Cortical Impact in Mice
Authors: Park Juyeon , Zhang Jimmy , Qiu Jianhua , Zhu Xiaoxia , Degterev Alexei , Lo Eng H , Whalen Michael J
Published: September 2011

Akt and mammalian target of rapamycin (mTOR) are both activated after traumatic brain injury (TBI), however complex interplay between the two hampers deciphering their functional implications in vivo. We examined the effects of single and combination inhibitors of Akt/mTOR in a mouse controlled cortical impact (CCI) model. Following CCI, phospho-Akt-473 (p-Akt) and -S6 ribosomal protein (p-S6RP), a downstream substrate of mTOR, were increased in cortical and hippocampal brain homogenates ( P<0.05 versus sham). At 24 hours, p-S6RP was detected in neurons and was robustly induced in microglia and astrocytes in injured hippocampus. In vivo activity of Akt and mTOR inhibitors administered separately was confirmed by reduced expression of p-GSK3β ( P<0.01) or p-S6RP ( P<0.05), respectively, after CCI. Importantly, administration of Akt and mTOR inhibitors together (but not of either alone) improved postinjury motor ( P=0.02) and cognitive deficits (hidden platform trials, P=0.001; probe trials, P<0.05), decreased propidium iodide-positive cells in CA1 and CA3 ( P<0.005), and unexpectedly increased p-GSK3β in hippocampus. Although the roles of Akt and mTOR in the pathogenesis of TBI remain to be fully elucidated, dual inhibition of Akt and mTOR may have therapeutic potential for TBI.
DNA‐damaging drug‐induced apoptosis sensitized by N‐myc in neuroblastoma cells
Authors: Li Tai , Wang Lin , Ke Xiao‐Xue , Gong Xue‐Yang , Wan Jian‐Hua , Hao Xiang‐wei , Xu Man , Xiang Zonghuai , Cui Zhao‐Bo , Cui Hongjuan
Published: September 2011

Neuroblastoma is one of the most common solid tumours in children (8–10% of all malignancies). Over 22% of cases have N‐myc amplification associated with aggressively growing neuroblastomas. Oncogene‐induced sensitization of cells to apoptosis is an important mechanism for suppression of tumorigenesis. Tumour suppressors often play a critical role in linking oncogenes to apoptotic machinery. For example, activated p53 then targets both intrinsic and extrinsic pathways to promote apoptosis through transcription‐dependent and ‐independent mechanisms. Understanding of the involved mechanisms has important clinical implications. We have employed DNA‐damaging drug‐induced apoptosis sensitized by oncogene N‐myc as a model. DNA damaging drugs trigger high levels of p53, leading to caspase‐9 activation in neuroblastoma cells. Inactivation of p53 protects cells from drug‐triggered apoptosis sensitized by N‐myc. These findings thus define a molecular pathway for mediating DNA‐damaging drug‐induced apoptosis sensitized by oncogene, and suggest that inactivation of p53 or other components of this apoptotic pathway may confer drug resistance in neuroblastoma cells. The data also suggests that inactivation of apoptotic pathways through co‐operating oncogenes may be necessary for the pathogenesis of neuroblastoma with N‐myc amplification.
Exploring the free energy surfaces of clusters using reconnaissance metadynamics
Authors: Tribello Gareth A. , Cuny Jérôme , Eshet Hagai , Parrinello Michele
Published: September 2011

A new approach is proposed for exploring the low-energy structures of small to medium-sized aggregates of atoms and molecules. This approach uses the recently proposed reconnaissance metadynamics method [G. A. Tribello, M. Ceriotti, and M. Parrinello. Proc. Natl. Acad. Sci. U.S.A. 107(41), 17509 (2010)10.1073/pnas.1011511107] in tandem with collective variables that describe the average structure of the coordination sphere around the atoms/molecules. We demonstrate this method on both Lennard-Jones and water clusters and show how it is able to quickly find the global minimum in the potential energy surface, while exploring the finite temperature free energy surface.
Characterization of lattice defects by x-ray absorption spectroscopy at the Zn K-edge in ferromagnetic, pure ZnO films
Authors: Haug J. , Chassé A. , Dubiel M. , Eisenschmidt Ch. , Khalid M. , Esquinazi P.
Published: September 2011

Ferromagnetic, pure ZnO films were grown on Al2O3 substrates at various nitrogen pressures (0.01–1.0 mbar) and investigated with x-ray diffraction (XRD) and x-ray absorption spectroscopy. According to XRD data, the crystalline films were composed of crystallites of approximately 50 nm in size, oriented with respect to the substrates, and the lattice spacings show slight deviations with respect to single-crystalline ZnO of wurtzite structure. The parameters determined by XRD agree with those determined by extended x-ray absorption fine structure, except for the sample grown at the lowest N2 pressure of 0.01 mbar, which was attributed to deviations from the ZnO single crystals. The results for the ZnO films grown at 0.1 to 1.0 mbar partial N2 pressure indicate wurtzite unit cells compressed along the c axis. The x-ray absorption near-edge structure (XANES) spectra exhibited a strong dependence on the x-ray polarization and on nitrogen partial pressure, which was explained by the increase in the concentration of defects with nitrogen partial pressure and by interface or grain boundary effects. First-principles calculations using multiple-scattering formalism suggested that the XANES spectra changes were because of increasing Zn vacancy concentration with increasing nitrogen pressure. The results indicated that Zn vacancy defects play a significant role in the ferromagnetism of these films.
Deuterium analysis in zircaloy using ps laser-induced low pressure plasma
Authors: Marpaung Alion Mangasi , Lie Zener Sukra , Niki Hideaki , Kagawa Kiichiro , Fukumoto Ken-ichi , Ramli Muliadi , Abdulmadjid Syahrun Nur , Idris Nasrullah , Hedwig Rinda , Tjia May On , Pardede Marincan , Suliyanti Maria Margaretha , Jobiliong Eric , Kurniawan Koo Hendrik
Published: September 2011

An experimental study on picosecond laser induced plasma spectroscopy of a zircaloy sample with low-pressure surrounding helium gas has been carried out to demonstrate its potential applicability to three-dimensional quantitative micro-analysis of deuterium impurities in zircaloy. This was achieved by adopting the optimal experimental condition ascertained in this study, which is specified as 7 mJ laser energy, 1.3 kPa helium pressure, and 50 μs measurement window, and which was found to result in consistent D emission enhancement. Employing these operational parameters, a linear calibration line exhibiting a zero intercept was obtained from zircaloy-4 samples doped with various concentrations of D impurity, regarded as surrogates for H impurity. An additional measurement also yielded a detection limit of about 10 μg/g for D impurity, well below the acceptable threshold of damaging H concentration in zircaloy. Each of these measurements was found to produce a crater size of only 25 μm in diameter, promising its application for performing less-destructive measurements. The result of this study has thus paved the way for conducting a further experiment with hydrogen-doped zircaloy samples and the further technical development of a three-dimensional quantitative micro-analysis of detrimental hydrogen impurity in zircaloy vessels used in nuclear power plants.
Determination of Rashba and Dresselhaus spin-orbit fields
Authors: Maiti Santanu K.
Published: September 2011

Determination of Rashba and Dresselhaus spin-orbit interaction strengths in a particular sample remains a challenge even today. In this article, we investigate the possibilities of measuring the absolute values of these interaction strengths by calculating persistent charge and spin currents in a mesoscopic ring. Our numerical results can be verified experimentally.
Point contact Andreev spectroscopy of epitaxial Co2FeSi Heusler alloys on GaAs (001)
Authors: Lehmann Hauke , Scholtyssek Jan M. , Herrmann Claudia , Herfort Jens , Merkt Ulrich , Meier Guido
Published: September 2011

The predicted half-metallicity of Co2FeSi in combination with its high Curie temperature of above 980 K makes this Heusler alloy interesting for spinelectronics. Thin Co2FeSi films are grown by molecular-beam epitaxy on GaAs (001) with a close lattice match. We present a study of point-contact measurements on different films, varying in thickness between 18 nm and 48 nm and in substrate temperature during deposition between 100 °C and 300 °C. Transport spin polarizations at the Fermi level are determined from differential conductance curves obtained by point-contact Andreev-reflection spectroscopy. A maximum transport spin polarization of about 60% is measured for a 18 nm thin Co2FeSi film grown at 200 °C.
Theoretical and experimental study of Raman spectra of pre-perovskite PbTiO3
Authors: Ni Li-Hong , Liu Yong , Ren Zhao-Hui , Li Xiang , Xu Gang , Song Chen-Lu , Han Gao-Rong
Published: September 2011

The assignment of microscopic Raman spectra on powdered samples of pre-perovskite PbTiO3 (space group I4/m) has been established according to the correspondence between the experimental and theoretical frequency and relative intensity data. We find no giant longitudinal-optical (LO) and transverse-optical (TO) splittings in pre-perovskite PbTiO3. In contrast to conventional perovskite, the largest pre-perovskite LO-TO splitting comes from its stiffest Au mode instead of from its softest mode. The pre-perovskite’s Born effective charges, dielectric tensors, and infrared frequencies are also calculated to determine its lattice dynamics and optical properties, and compared with the conventional perovskite PbTiO3. The results provide invaluable information for use in further research on PbTiO3 phase transition.
A simple and efficient solar cell parameter extraction method from a single current-voltage curve
Authors: Zhang Chunfu , Zhang Jincheng , Hao Yue , Lin Zhenhua , Zhu Chunxiang
Published: September 2011

In this work, a simple and efficient method for the extraction of all the parameters of a solar cell from a single current-voltage (I-V) curve under the constant illumination level is proposed. With the help of the Lambert W function, the explicit analytic expression for I is obtained. By reducing the number of the parameters, the expression for I only depends on the ideality factor n, the series resistance Rs, and the shunt resistance Rsh. This analytic expression is directly used to fit the experimental data and extract the device parameters. This simple solar cell parameter extraction method can be directly applied for all kinds of solar cells whose I-V characteristics follow the single-diode model. The parameters of various solar devices including silicon solar cells, silicon solar modules, dye-sensitized solar cells, and organic solar cells with standalone, tandem, and multi-junction structures have been successfully extracted by using our proposed method.
Intermittent synchronization in a network of bursting neurons
Authors: Park Choongseok , Rubchinsky Leonid L.
Published: September 2011

Synchronized oscillations in networks of inhibitory and excitatory coupled bursting neurons are common in a variety of neural systems from central pattern generators to human brain circuits. One example of the latter is the subcortical network of the basal ganglia, formed by excitatory and inhibitory bursters of the subthalamic nucleus and globus pallidus, involved in motor control and affected in Parkinson’s disease. Recent experiments have demonstrated the intermittent nature of the phase-locking of neural activity in this network. Here, we explore one potential mechanism to explain the intermittent phase-locking in a network. We simplify the network to obtain a model of two inhibitory coupled elements and explore its dynamics. We used geometric analysis and singular perturbation methods for dynamical systems to reduce the full model to a simpler set of equations. Mathematical analysis was completed using three slow variables with two different time scales. Intermittently, synchronous oscillations are generated by overlapped spiking which crucially depends on the geometry of the slow phase plane and the interplay between slow variables as well as the strength of synapses. Two slow variables are responsible for the generation of activity patterns with overlapped spiking, and the other slower variable enhances the robustness of an irregular and intermittent activity pattern. While the analyzed network and the explored mechanism of intermittent synchrony appear to be quite generic, the results of this analysis can be used to trace particular values of biophysical parameters (synaptic strength and parameters of calcium dynamics), which are known to be impacted in Parkinson’s disease.
Spatially resolved measurement of high doses in microbeam radiation therapy using samarium doped fluorophosphate glasses
Authors: Okada Go , Morrell Brian , Koughia Cyril , Edgar Andy , Varoy Chris , Belev George , Wysokinski Tomasz , Chapman Dean , Kasap Safa
Published: September 2011

The measurement of spatially resolved high doses in microbeam radiation therapy has always been a challenging task, where a combination of high dose response and high spatial resolution (microns) is required for synchrotron radiation peaked around 50 keV. The x-ray induced Sm3+ → Sm2+ valence conversion in Sm3+ doped fluorophosphates glasses has been tested for use in x-ray dosimetry for microbeam radiation therapy. The conversion efficiency depends almost linearly on the dose of irradiation up to ∼5 Gy and saturates at doses exceeding ∼80 Gy. The conversion shows strong correlation with x-ray induced absorbance of the glass which is related to the formation of phosphorus-oxygen hole centers. When irradiated through a microslit collimator, a good spatial resolution and high “peak-to-valley” contrast have been observed by means of confocal photoluminescence microscopy.
Influence of surface defects in ZnO thin films on its biosensing response characteristic
Authors: Saha Shibu , Gupta Vinay
Published: September 2011

Highly c-axis oriented zinc oxide (ZnO) thin films deposited by rf magnetron sputtering under varying processing pressure (20–50 mT) in a reactive gas mixture of argon and oxygen were studied for biosensing application. The as-deposited ZnO thin films were in a state of compressive stress having defects related to interstitial Zn and antisite oxygen. Glucose oxidase has been chosen as the model enzyme in the present study and was immobilized on the surface of ZnO thin films deposited on indium tin oxide coated Corning Glass substrate. The studies reveal a correlation between the biosensing characteristic and the presence of defects in the ZnO films. The ZnO films deposited under high pressure (50 mT) are found to be more sensitive for biosensing application due to availability of more surface area for effective immobilization of biomolecules and exhibits a suitable microenvironment with good electron transfer characteristic. The obtained results highlight the importance of desired microstate besides availability of suitable native defects in the ZnO thin film for exhibiting enhanced biosensing response.
Nanostructured electrodes for organic bulk heterojunction solar cells: Model study using carbon nanotube dispersed polythiophene-fullerene blend devices
Authors: Nam Chang-Yong , Wu Qin , Su Dong , Chiu Chien-yang , Tremblay Noah J. , Nuckolls Colin , Black Charles T.
Published: September 2011

We test the feasibility of using nanostructured electrodes in organic bulk heterojunction solar cells to improve their photovoltaic performance by enhancing their charge collection efficiency and thereby increasing the optimal active blend layer thickness. As a model system, small concentrations of single wall carbon nanotubes are added to blends of poly(3-hexylthiophene): [6,6]-phenyl-C61-butyric acid methyl ester in order to create networks of efficient hole conduction pathways in the device active layer without affecting the light absorption. The nanotube addition leads to a 22% increase in the optimal blend layer thickness from 90 nm to 110 nm, enhancing the short circuit current density and photovoltaic device efficiency by as much as ∼10%. The associated incident-photon-to-current conversion efficiency for the given thickness also increases by ∼10% uniformly across the device optical absorption spectrum, corroborating the enhanced charge carrier collection by nanostructured electrodes.
Influence of net doping, excess carrier density and annealing on the boron oxygen related defect density in compensated n-type silicon
Authors: Rougieux F. E. , Lim B. , Schmidt J. , Forster M. , Macdonald D. , Cuevas A.
Published: September 2011

In this study, we present experimental data regarding the concentration of the boron-oxygen complex in compensated n-type silicon when subjected to illumination. We find that the defect density is independent of the net dopant concentration and is strongly dependent on the minority carrier concentration during illumination. We show that annealing at temperatures in the range 500 °C to 700 °C permanently reduces the defect density possibly via a decrease in the oxygen dimer concentration.
Spin dependence of electron effective masses in InGaAs/InAlAs quantum well
Authors: Wei L. M. , Gao K. H. , Liu X. Z. , Zhou W. Z. , Cui L. J. , Zeng Y. P. , Yu G. , Yang R. , Lin T. , Shang L. Y. , Guo S. L. , Dai N. , Chu J. H. , Austing D. G.
Published: September 2011

The effective masses for spin-up and spin-down electrons of a partially spin-polarized Fermi liquid are theoretically expected to be different. We extract the spin-up and spin-down effective masses from magnetotransport measurements at different temperatures for a two-dimensional electron gas in an In0.65Ga0.35As/In0.52Al0.48As quantum well exhibiting zero-field spin splitting. We apply two analytical methods, one involving the simultaneous fitting of fast Fourier transform (FFT) spectra and the other involving inverse FFT analysis. Both methods confirm that the effective masses for spin-up and spin-down are different, consistent with theoretical expectations.
Accurate evaluation of Ge metal—insulator—semiconductor interface properties
Authors: Taoka Noriyuki , Ikeda Keiji , Mizubayashi Wataru , Morita Yukinori , Migita Shinji , Ota Hiroyuki , Takagi Shinichi
Published: September 2011

To accurately evaluate the Ge metal-insulator-semiconductor (MIS) interface trap density (Dit) by employing the conventional method for Si MIS capacitors on Ge MIS capacitors, we have investigated the impact of majority and minority carrier responses on C-V curves and/or the energy distributions of Dit. It is found that the high-frequency C-V curve, which does not include the majority carrier response with interface traps, cannot be obtained near room temperature (RT) even at 1 MHz. Therefore, to accurately evaluate the Dit values using the Terman method, the C-V curve has to be measured at an appropriate temperature. Furthermore, in the conductance method, evaluations by the model including the narrow bandgap effects are needed to obtain accurate Dit of the Ge MIS interface near RT. Through such accurate evaluation, the interface properties with different kinds of interfacial layers have been investigated. Although the GeO2/Ge interface has a low Dit and a fixed oxide charge density, the total charged center density contributing to surface potential fluctuation is larger than those for the GeOx/Ge and GeOxNy/Ge interfaces. These results suggest that the evaluation methods of the Ge MIS interface taking into account the appropriate carrier responses is quite important to obtain accurate Ge MIS interface properties.
Zero field splitting of the chalcogen diatomics using relativistic correlated wave-function methods
Authors: Rota J.-B. , Knecht S. , Fleig T. , Ganyushin D. , Saue T. , Neese F. , Bolvin H.
Published: September 2011

The spectrum arising from the (π*)2 configuration of the chalcogen dimers, namely, the X21, a2, and b0+ states, is calculated using wave-function theory based methods. Two-component (2c) and four-component (4c) multireference configuration interaction (MRCI) and Fock-space coupled cluster (FSCC) methods are used as well as two-step methods spin-orbit complete active space perturbation theory at 2nd order (SO-CASPT2) and spin-orbit difference dedicated configuration interaction (SO-DDCI). The energy of the X21 state corresponds to the zero-field splitting of the ground state spin triplet. It is described with high accuracy by the 2- and 4-component methods in comparison with experiment, whereas the two-step methods give about 80% of the experimental values. The b0+ state is well described by 4c-MRCI, SO-CASPT2, and SO-DDCI, but FSCC fails to describe this state and an intermediate Hamiltonian FSCC ansatz is required. The results are readily rationalized by a two-parameter model; Δε, the π* spinor splitting by spin-orbit coupling and K, the exchange integral between the \documentclass[12pt]{minimal}\begin{document}$\pi _{1}^{*}$\end{document}π1* and the \documentclass[12pt]{minimal}\begin{document}$\pi _{-1}^{*}$\end{document}π−1* spinors with, respectively, angular momenta 1 and −1. This model holds for all systems under study with the exception of Po2.
Two-dimensional analysis to improve the output stress in ferromagnetic shape memory alloys
Authors: He Y. J. , Chen X. , Moumni Z.
Published: September 2011

Most existing experiments investigating the martensite-variants reorientation (switching) of ferromagnetic shape memory alloys (FSMA) are in a simple 1D condition: An axial compressive stress and a transverse magnetic field. To obtain field-induced variant switching, however, the compressive stress (output stress) is limited by a small blocking stress (<10 MPa, mainly governed by the materials’ magnetic anisotropic energy). In this paper, to overcome the stress limit, we suggest using the materials in two-dimensional (2D) configurations: Two (axial and transverse) compressive stresses and a magnetic field. Based on a 2D magneto-mechanical energy analysis, it is found that only the difference between the two stresses is limited; each of the two stresses can be larger than the blocking stress. The energy analysis is also incorporated into the field-stress phase diagrams (including hysteretic effect) to study the variant switching in different loading paths: rotating/non-rotating field-induced strain and field-assisted superelasticity. Properly setting the two stresses can control the switching parameters (field magnitude and rotation angle) and the variants’ time fractions in cyclic loadings, which provide much flexibility of FSMA applications. Our 2D energy analysis can be easily reduced to 1D case, where the theoretical predictions of the switching stresses/fields/angles agree with the existing experiments.
A quantum reaction dynamics study of the translational, vibrational, and rotational motion effects on the HD + ${\rm H}_3^+$H3+ reaction
Authors: Meng Fanbin , Wang Tingting , Wang Dunyou
Published: September 2011

Time-dependent, quantum reaction dynamics wavepacket approach is employed to investigate the impacts of the translational, vibrational, and rotational motion on the \documentclass[12pt]{minimal}\begin{document}${\rm HD} + {\rm H}_3^+$\end{document} HD +H3+ → H2D+ + H2 reaction using the Xie-Braams-Bowman potential energy surface [Z. Xie, B. J. Braams, and J. M. Bowman, J. Chem. Phys. 122, 224307 (2005)]10.1063/1.1927529. We treat this five atom reaction with a seven-degree-of-freedom model by fixing one Jacobi and one torsion angle related to \documentclass[12pt]{minimal}\begin{document}${\rm H}_3^+$\end{document}H3+ at the lowest saddle point geometry of the potential energy surface. The initial state selected reaction probabilities show that the rotational excitations of H+-H2 greatly enhance the reactivity with the reaction probabilities increased double at high rotational states compared to the ground state. However, the vibrational excitations of \documentclass[12pt]{minimal}\begin{document}${\rm H}_3^+$\end{document}H3+ hinder the reactivity. The ground state reaction probability shows no reaction threshold for this exoergic reaction, and as the translational energy increases, the reaction probability decreases. Furthermore, reactive resonances and zero point energy play very important roles on the reaction dynamics. The obtained integral cross section has the character of an exoergic reaction without a threshold: it decreases with the translational energy increasing. The calculated thermal rate constants using this seven-degree-of-freedom model are in agreement with a later experiment measurement.
Hydrogen bonded structure and dynamics of liquid-vapor interface of water-ammonia mixture: An ab initio molecular dynamics study
Authors: Chakraborty Debashree , Chandra Amalendu
Published: September 2011

We have carried out ab initio molecular dynamics simulations of a liquid-vapor interfacial system consisting of a mixture of water and ammonia molecules. We have made a detailed analysis of the structural and dynamical properties of the bulk and interfacial regions of the mixture. Among structural properties, we have looked at the inhomogeneous density profiles of water and ammonia molecules, hydrogen bond distributions, orientational profiles, and also vibrational frequency distributions of bulk and interfacial molecules. It is found that the interfacial molecules show preference for specific orientations so as to form water-ammonia hydrogen bonds at the interface with ammonia as the acceptor. The structure of the system is also investigated in terms of inter-atomic voids present in the system. Among the dynamical properties, we have calculated the diffusion, orientational relaxation, hydrogen bond dynamics, and vibrational spectral diffusion in bulk and interfacial regions. It is found that the diffusion and orientation relaxation of the interfacial molecules are faster than those of the bulk. However, the hydrogen bond lifetimes are longer at the interface which can be correlated with the time scales found from the decay of frequency time correlations.
Anomalous diffusion governed by a fractional diffusion equation and the electrical response of an electrolytic cell
Authors: Santoro P. A. , de Paula J. L. , Lenzi E. K. , Evangelista L. R.
Published: September 2011

The electrical response of an electrolytic cell in which the diffusion of mobile ions in the bulk is governed by a fractional diffusion equation of distributed order is analyzed. The boundary conditions at the electrodes limiting the sample are described by an integro-differential equation governing the kinetic at the interface. The analysis is carried out by supposing that the positive and negative ions have the same mobility and that the electric potential profile across the sample satisfies the Poisson's equation. The results cover a rich variety of scenarios, including the ones connected to anomalous diffusion.
Chiral hide-and-seek: Retention of enantiomorphism in laser-induced nucleation of molten sodium chlorate
Authors: Ward Martin R. , Copeland Gary W. , Alexander Andrew J.
Published: September 2011

We report the observation of non-photochemical laser-induced nucleation (NPLIN) of sodium chlorate from its melt using nanosecond pulses of light at 1064 nm. The fraction of samples that nucleate is shown to depend linearly on the peak power density of the laser pulses. Remarkably, we observe that most samples are nucleated by the laser back into the enantiomorph (dextrorotatory or levorotatory) of the solid prior to melting. We do not observe a significant dependence on polarization of the light, and we put forward symmetry arguments that rule out an optical Kerr effect mechanism. Our observations of retention of chirality can be explained by decomposition of small amounts of the sodium chlorate to form sodium chloride, which provide cavities for retention of clusters of sodium chlorate even 18 °C above the melting point. These clusters remain sub-critical on cooling, but can be activated by NPLIN via an isotropic polarizability mechanism. We have developed a heterogeneous model of NPLIN in cavities, which reproduces the experimental data using simple physical data available for sodium chlorate.
Effect of applied stress tensor anisotropy on the electromechanically driven complex dynamics of void surfaces in metallic thin films
Authors: Sfyris Georgios I. , Rauf Gungor M. , Maroudas Dimitrios
Published: September 2011

We present a systematic computational analysis of the complex, electromechanically driven surface dynamics of voids in thin films of face-centered cubic metals for 〈100〉-oriented film planes characterized by four-fold symmetry of surface diffusional anisotropy. The voids are located at an edge of the metallic thin film, and the film is subjected simultaneously to an external electric field and an anisotropic biaxial tensile stress. Our analysis is based on self-consistent dynamical simulations of driven void surface morphological response according to a well-validated, two-dimensional, and fully nonlinear model. We examine thoroughly the effects of the anisotropic mechanical loading on the morphological evolution of the electromigration-driven void surface and the resulting asymptotic states of the surface morphological response. We have found supercritical Hopf-bifurcation transitions from stable steady to stable time-periodic states. For such films and over the range of electromechanical conditions examined, the only possible stable asymptotic states are either time-periodic states characterized by a single period of oscillation or steady states without any change in the void shape. We have determined the stability domain boundaries of the various asymptotic states and their dependence on the anisotropy of the applied stress tensor. The loading anisotropy has significant effects on the stability domain boundaries, but it does not introduce any more complex void dynamics in 〈100〉-oriented films than that under isotropic mechanical loading.
Structure of solvent-free grafted nanoparticles: Molecular dynamics and density-functional theory
Authors: Chremos Alexandros , Panagiotopoulos Athanassios Z. , Yu Hsiu-Yu , Koch Donald L.
Published: September 2011

The structure of solvent-free oligomer-grafted nanoparticles has been investigated using molecular dynamics simulations and density-functional theory. At low temperatures and moderate to high oligomer lengths, the qualitative features of the core particle pair probability, structure factor, and the oligomer brush configuration obtained from the simulations can be explained by a density-functional theory that incorporates the configurational entropy of the space-filling oligomers. In particular, the structure factor at small wave numbers attains a value much smaller than the corresponding hard-sphere suspension, the first peak of the pair distribution function is enhanced due to entropic attractions among the particles, and the oligomer brush expands with decreasing particle volume fraction to fill the interstitial space. At higher temperatures, the simulations reveal effects that differ from the theory and are likely caused by steric repulsions of the expanded corona chains.
Decoupling charge transport from the structural dynamics in room temperature ionic liquids
Authors: Griffin Philip , Agapov Alexander L. , Kisliuk Alexander , Sun Xiao-Guang , Dai Sheng , Novikov Vladimir N. , Sokolov Alexei P.
Published: September 2011

Light scattering and dielectric spectroscopy measurements were performed on the room temperature ionic liquid (RTIL) [C4mim][NTf2] in a broad temperature and frequency range. Ionic conductivity was used to estimate self-diffusion of ions, while light scattering was used to study structural relaxation. We demonstrate that the ionic diffusion decouples from the structural relaxation process as the temperature of the sample decreases toward Tg. The strength of the decoupling appears to be significantly lower than that expected for a supercooled liquid of similar fragility. The structural relaxation process in the RTIL follows well the high-temperature mode coupling theory (MCT) scenario. Using the MCT analysis we estimated the dynamic crossover temperature in [C4mim][NTf2] to be Tc ∼ 225 ± 5 K. However, our analysis reveals no sign of the dynamic crossover in the ionic diffusion process.
An instrument for the investigation of actinides with spin resolved photoelectron spectroscopy and bremsstrahlung isochromat spectroscopy
Authors: Yu S.-W. , Tobin J. G. , Chung B. W.
Published: September 2011

A new system for spin resolved photoelectron spectroscopy and bremsstrahlung isochromat spectroscopy has been built and commissioned at Lawrence Livermore National Laboratory for the investigation of the electronic structure of the actinides. Actinide materials are very toxic and radioactive and therefore cannot be brought to most general user facilities for spectroscopic studies. The technical details of the new system and preliminary data obtained therein will be presented and discussed.
Correlation between resistance-change effect in transition-metal oxides and secondary-electron contrast of scanning electron microscope images
Authors: Kinoshita K. , Yoda T. , Kishida S.
Published: September 2011

Conductive atomic-force microscopy (C-AFM) writing is attracting attention as a technique for clarifying the switching mechanism of resistive random-access memory by providing a wide area filled with filaments, which can be regarded as one filament with large radius. The writing area on a nickel-oxide (NiO) film formed by conductive atomic-force microscopy was observed by scanning electron microscope, and a correlation between the contrast in a secondary-electron image (SEI) and the resistance written by C-AFM was revealed. In addition, the dependence of the SEI contrast on the beam accelerating voltage (Vaccel) suggests that the resistance-change effect occurs near the surface of the NiO film. As for the effects of electron irradiation and vacuum annealing on the C-AFM writing area, it was shown that the resistance-change effect is caused by exchange of oxygen with the atmosphere at the surface of the NiO film. This result suggests that the low-resistance and high-resistance areas are, respectively, p-type Ni1+δO (δ < 0) and insulating (stoichiometric) or n-type Ni1+δO (δ ≥ 0).
Higher order diffusion Monte Carlo propagators for linear rotors as diffusion on a sphere: Development and application to O2@Hen
Authors: Mella Massimo
Published: September 2011

Exploiting the theoretical treatment of particles diffusing on corrugated surfaces and the isomorphism between the “particle on a sphere” and a linear molecule rotation, a new diffusion kernel is introduced to increase the order of diffusion Monte Carlo (DMC) simulations involving linear rotors. Tests carried out on model systems indicate the superior performances of the new rotational diffusion kernel with respect to the simpler alternatives previously employed. In particular, it is evidenced a second order convergence toward exact results with respect to the time step of dynamical correlation functions, a fact that guarantees an identical order for the diffusion part of the DMC projector. The algorithmic advantages afforded by the latter are discussed, especially with respect to the “a posteriori” and “on the fly” extrapolation schemes. As a first application to the new algorithm, the structure and energetics of O2@Hen (n = 1–40) clusters have been studied. This was done to investigate the possible cause of the quenching of the reaction between O2 and Mg witnessed upon increasing the size of superfluid He droplets used as a solvent. With the simulations on O2 indicating a strong localization in the cluster core, the behaviour as a function of n is ascribed to the extremely fluxional comportment of Mg@Hen, which dwells far from the droplet center, albeit being solvated, when n is large.
Response to “Comment on ‘Isotope effects in liquid water by infrared spectroscopy. IV. No free OH groups in liquid water’” [J. Chem. Phys. 135, 117101 (2011)]
Authors: Max Jean-Joseph , Chapados Camille
Published: September 2011

The original infrared spectra in the OH stretch region that Riemenschneider and Ludwig (thereafter, RL) have obtained for pure water and aqueous salt solutions are very similar to what we have previously reported [J.-J. Max and C. Chapados, J. Chem. Phys. 115, 6803 (2001)]. In our 2010 paper, we claimed that “free” OH is not present in pure liquid water. The difference spectra from the salt solutions and pure water spectrum give small negative components situated near 3655 cm−1. Because this position is in the range where free OH groups should absorb RL assigned the negative peaks to free OH removed from pure water. That is, RL consider that pure liquid water contains free OH groups which are removed in the salt solutions. Obviously, the removal of all free OH present in pure water will produce maximum negative intensities in the difference spectra. In this response, we present unpublished difference spectra between several salt solutions and pure water where negative peaks are higher than that claimed by RL for pure water. Since this is impossible it demonstrates that the assignment proposed by RL to free OH is incorrect. The negative peaks come from the difference between large components that differ a little between salt solutions and pure water [J.-J. Max and C. Chapados, J. Chem. Phys. 115, 6803 (2001)]. Recall that the ionized salts do not absorb but perturb the surrounding water molecules.
Gas density perturbations induced by a pulsed optical lattice
Authors: Lilly Taylor , Ketsdever Andrew , Cornella Barry , Quiller Trey , Gimelshein Sergey
Published: September 2011

A complimentary experimental and numerical investigation on density perturbations formed in molecular nitrogen by pulsed optical lattices was conducted. Experimental results on the effect of laser intensity and gas pressure on the magnitude of induced density perturbations from the free-molecular through continuum regimes using a coherent Rayleigh-Brillouin scattering technique are presented. The investigation further verifies the use of the direct simulation Monte Carlo method, extended to include the non-resonant optical dipole force, as a robust tool for the prediction of laser modification to a neutral gas.
High efficiency switching using graphene based electron “optics”
Authors: Sajjad Redwan N. , Ghosh Avik W.
Published: September 2011

We demonstrate a way to open a gate-tunable transmission gap across graphene p-n junction by introducing an additional barrier in the middle that replaces Klein tunneling with regular tunneling, allowing us to modulate current by several orders of magnitude. The gap arises by angularly sorting electrons by their longitudinal energy and filtering out the hottest, normally incident electrons with the tunnel barrier, and the rest through total internal reflection. Using analytical and atomistic numerical studies, we show that the barrier causes graphene p-n junction act as a metamaterial with metal-insulator transition and overcome the KTln10/decade limit for subthreshold conduction.
Molecular motions in glass-rubber transition region in polyisobutylene investigated by two-dimensional correlation dielectric relaxation spectroscopy
Authors: Wang Xiaoan , Huang G. S. , Wu J. R. , Nie Y. J. , He X. J. , Xiang K. W.
Published: September 2011

In this letter, we report the first study of the molecular relaxation dynamics in the glass-rubber transition region in polyisobutylene by 2D correlation dielectric relaxation spectroscopy (2DC-DRS). With the help of the high resolution and high sensitivity of 2DC-DRS, it is also the first time to observe and locate the positions of the Rouse modes and sub-Rouse modes in type-B polymers in the dielectric spectrum. 2DC-DRS was also applied to compare the temperature dependences of different molecular motions. Moreover, 2DC-DRS has been demonstrated as a powerful tool for studying the molecular motions with different time/length scales.
Kelvin probe force microscopy characterization of TiO2 (110)-supported Au clusters
Authors: Jing Chung Hong , Yurtsever Ayhan , Sugimoto Yoshiaki , Abe Masayuki , Morita Seizo
Published: September 2011

We present a combined non-contact atomic force microscopy and Kelvin probe force microscopy (KPFM) investigation of the structural and electrical properties of Au nanoclusters on a TiO2 model-oxide surface at room temperature. The KPFM images reveal an increase in the local contact potential difference (LCPD) of Au clusters with respect to the supporting TiO2 surface. Variation of the LCPD shift with a broad range of tip-cluster distances verifies that the obtained KPFM images are not a cause of the topographic artifacts. Based on the LCPD shift, both in the distance-dependent bias spectroscopy and KPFM images, we provide new evidence supporting the charge transfer formation from the surface to the Au cluster. We attribute the increment of the LCPD over an Au cluster site to the presence of surface dipoles, created by the charge transfer, pointing towards the substrate.
Rectifying and negative differential resistance behaviors of a functionalized Tour wire: The position effects of functional groups
Authors: Kwong Gordon , Zhang Zhenhua , Pan Jinbo
Published: September 2011

Based on Tour wire, we construct four D-π-A molecular devices with different positional functional groups, in an attempt to explore the position effects of functional groups on their electronic transport properties and to show that some interesting physical phenomena can emerge by only varying the position of functional groups. The first-principles calculations demonstrate that the position of functional groups can affect the rectifying behaviors (rectification direction and ratio) significantly and determines whether or not the negative differential resistance (NDR) can be observed as well as the physical origin of the NDR phenomenon.
Natural band alignments of InN/GaN/AlN nanorod heterojunctions
Authors: Kuo Cheng-Tai , Chang Kai-Kuen , Shiu Hung-Wei , Liu Chia-Rong , Chang Lo-Yueh , Chen Chia-Hao , Gwo Shangjr
Published: September 2011

Valence band alignments of wurtzite III-nitride semiconductor heterojunctions are investigated using cross-sectional scanning photoelectron microscopy and spectroscopy on the nonpolar side-facet of a vertically −c-axis-aligned heterostructure nanorod array. The nonpolar measurement geometry and near fully relaxed lattice structure allow for the determination of “natural” band alignments without the influence of spontaneous and piezoelectric polarization fields. The valence band offsets of InN/GaN, GaN/AlN, and InN/AlN are measured to be 0.8 ± 0.1, 0.6 ± 0.1, and 1.4 ± 0.1 eV, respectively. These results are in good agreement with previous data for heteroepitaxial films and obey the expected transitivity rule.
High domain wall magneto-resistance in amorphous TbFeCo wires
Authors: Li Songtian , Amagai Taro , Liu Xiaoxi , Morisako Akimistu
Published: September 2011

By introducing artificial pinning sites to locally modify coercivity in perpendicularly magnetized TbFeCo wires, strip domains were constructed without expense of specimen damage. The construction of strip domains with well-defined shape and controllable number enables a determination of magneto-resistance contributing from singe domain wall. Contrast to crystalline materials, a rather high domain wall magneto-resistance ratio near 20% was found at room temperature, indicating the amorphous TbFeCo is a potential candidate for spintronic devices.
A micropillar for cavity optomechanics
Authors: Kuhn A. G. , Bahriz M. , Ducloux O. , Chartier C. , Le Traon O. , Briant T. , Cohadon P.-F. , Heidmann A. , Michel C. , Pinard L. , Flaminio R.
Published: September 2011

We have designed a micromechanical resonator suitable for cavity optomechanics. We have used a micropillar geometry to obtain a high-frequency mechanical resonance with a low effective mass and a very high quality factor. We have coated a 60-μm diameter low-loss dielectric mirror on top of the pillar and are planning to use this micromirror as part of a high-finesse Fabry-Perot cavity to laser cool the resonator down to its quantum ground state and to monitor its quantum position fluctuations by quantum-limited optical interferometry.
Large magnetoresistance and metamagnetic transition in PrGa
Authors: Chen J. , Zheng X. Q. , Dong Q. Y. , Sun J. R. , Shen B. G.
Published: September 2011

The magnetic phase transition and the magnetoresistance (MR) in bulk intermetallic PrGa compound are investigated experimentally. Two successive magnetic transitions, ferromagnetic (FM)-antiferromagnetic (AFM) transition and AFM-paramagnetic transition, are observed at T1 = 28 K and T2 = 36 K, respectively. It is found that the PrGa compound exhibits a field-induced metamagnetic transition from AFM to FM state and a considerable change in lattice constants in a temperature range of 28-36 K. Accompanied with the AFM-FM transition, a negative MR occurs, and the maximal MR values are ∼30% and ∼34% at 28 K under the fields of 1 T and 5 T, respectively.
In-plane magnetic anisotropy dependence of critical current density, Walker field and domain-wall velocity in a stripe with perpendicular anisotropy
Authors: Roy P. E. , Wunderlich J.
Published: September 2011

Current and field-induced domain wall motion in a perpendicular material system having a tuneable magnetocrystalline in-plane anisotropy constant is micromagnetically simulated. It is shown that it is possible to significantly modulate critical current densities, Walker fields, and thus the domain wall velocity. In addition, suggestions that may help in determining the non-adiabatic spin transfer torque term are shown.
Fabrication of nanometer scale gaps for thermo-tunneling devices
Authors: Tanielian M. H. , Greegor R. B. , Nielsen J. A. , Parazzoli C. G.
Published: September 2011

We report a fabrication approach for making nanometer wide gaps between two planar metallic electrodes, which can be utilized for the formation of thermo-tunneling devices. The technique is a three dimensional variant of the electromigration techniques used for creating nanometer sized gaps on planar surfaces. The gap is formed by applying a low level voltage between two parallel electrodes, each deposited on separate wafers that have been bonded together. I-V and thermal characterization of the gap show very good agreement with modeling results, indicating a tunneling gap on the order of 0.5-1 nm.
Temperature-dependent photoluminescence properties of porous silicon nanowire arrays
Authors: He Haiping , Liu Chao , Sun Luwei , Ye Zhizhen
Published: September 2011

Luminescent porous silicon nanowire arrays are prepared through metal-assisted chemical etching. Photoluminescence (PL) and cathodoluminescence (CL) reveal that both the nanowire arrays and individual nanowire exhibit intense orange emission around 1.9 eV at room temperature. The emission linewidth increases monotonously and significantly with decreasing temperature. Combined with PL decay measurements, the results indicate that there are two transitions contributing to the broad emission at low temperatures. In addition, negative thermal quenching of the PL intensity due to surface states is observed. A multi-level transition model is proposed to interpret the experimental results.