bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantitative determination of mineral types and abundances from reflectance spectra using principal components analysis
Authors: Smith Milton O. , Johnson Paul E. , Adams John B.
Published: December 2012

A procedure was developed for analyzing remote reflectance spectra, including multispectral images, that quantifies parameters such as types of mineral mixtures, the abundances of mixed minerals, and particle sizes. Principal components analysis (PCA) reduced the spectral dimensionality and allowed testing the uniqueness and validity of spectral mixing models. By analyzing variations in the overall spectral reflectance curves we identified the type of spectral mixture, quantified mineral abundances, and identified the effects of particle size. The results demonstrate an advantage in classification accuracy over classical forms of analysis that ignore effects of particle‐size or mineral‐mixture systematics on spectra. The approach is applicable to remote sensing data of planetary surfaces for quantitative determinations of mineral abundances.
The scaling of complex craters
Authors: Croft Steven K.
Published: December 2012

The empirical relation between the transient crater diameter (Dg) and final crater diameter (Dr) of complex craters and basins is estimated using cumulative terrace widths, central uplift diameters, continuous ejecta radii, and transient crater reconstructions determined from lunar and terrestrial impact structures. The ratio Dg/Dr is a power law function of Dr, decreasing uniformly from unity at the diameter of the simple‐complex crater morphology transition to about 0.5 for large multiring basins like Imbrium on the moon. The empirical constants in the Dg/Dr relation are interpreted physically to mean that the position of the final rim relative to the transient crater, and hence the extent of collapse, is controlled or greatly influenced by the properties of the zone of dissociated material produced by the impact shock. The continuity of the Dg/Dr relation over the entire spectrum of morphologic types from complex craters to multiring basins implies that the rims of all these structures form in the same tectonic environment despite morphologic differences.
Novel configuration of a myosin II transient intermediate analogue revealed by quick-freeze deep-etch replica electron microscopy
Authors: Kimori Yoshitaka , Baba Norio , Katayama Eisaku
Published: December 2012

In the present paper, we described our attempt to characterize the rough three-dimensional features of the structural analogue of the key intermediate of myosin's cross-bridge cycle. Using quick-freeze deep-etch replica electron microscopy, we observed that actin-attached myosin during in vitro sliding was bent superficially as postulated by the conventional hypothesis, but in the opposite direction of the putative pre-power-stroke configuration, as for ADP·Vi (inorganic vanadate)-bound myosin. We searched for the conformational species with a similar appearance and found that SH1–SH2 (thiols 1 and 2)-cross-linked myosin is a good candidate. To characterize such small asymmetric structures, we employed a new pattern-recognition procedure that accommodates the metal-replicated samples. In this method, the best-matched views of the target microscopic images were selected from a comprehensive set of images simulated from known atomic co-ordinates of relevant proteins. Together with effective morphological filtering, we could define the conformational species and the view angles of the catalytic domain and the lever arm cropped from averaged images of disulfide-cross-linked myosin. Whereas the catalytic domain of the new conformer closely resembled the pPDM (N,N′-p-phenylenedimaleimide)-treated, but SH2 Lys705-cross-linked, structure (PDB code 1L2O), a minor product of the same cross-linking reaction, the lever arm projected differently. Using separately determined view angles of the catalytic domain and the lever arm, we built a model of disulfide-cross-linked myosin. Further combination with the ‘displacement-mapping’ procedure enabled us to reconstruct the global three-dimensional envelope of the unusual structure whose lever arm orientation is compatible with our reports on the actin-sliding cross-bridge structure. Assuming this conformer as the structural analogue of the transient intermediate during actin sliding, the power stroke of the lever arm might accompany the reversal of the disorganized SH1 helix.
Misprocessing and functional arrest of microRNAs by miR-Pirate: roles of miR-378 and miR-17
Authors: Deng Zhaoqun , Yang Xiangling , Fang Ling , Rutnam Zina J. , Yang Burton B.
Published: December 2012

miRNAs (microRNAs) are short non-coding RNAs that can regulate gene expression in cancer development, which makes them valuable targets for therapeutic intervention. In the present study we report on an approach that can not only arrest the functions of mature miRNAs by binding to them, but it can also induce the ‘mis-processing’ of the target miRNA, producing a non-functional truncated miRNA. This approach involves generating an expression construct that produces an RNA fragment with 16 repeat sequences. The construct is named miR-Pirate (miRNA-interacting RNA-producing imperfect RNA and tangling endogenous miRNA). The transcript of the construct contained mismatches to the seed region, and thus it would not target the potential targets of the miRNA under study. The homology of the construct is sufficiently high, allowing the transcript to block miRNA functions. The functions of the construct were validated in cell cultures, in tumour formation assays and in transgenic mice stably expressing this construct. To explore the possibility of adopting this approach in gene therapy, we transfected cells with synthetic miR-Pirate and obtained the results we expected. The miR-Pirate, expressed by the construct or synthesized chemically, was found to be able to specifically pirate and silence a mature miRNA through its dual roles and thus could be clinically applied for miRNA intervention.
Construct Rigidity after Fatigue Loading in Pedicle Subtraction Osteotomy with or without Adjacent Interbody Structural Cages
Authors: Deviren Vedat , Tang Jessica A. , Scheer Justin K. , Buckley Jenni M. , Pekmezci Murat , McClellan R. Trigg , Ames Christopher P.
Published: December 2012

Introduction

Studies document rod fracture in pedicle subtraction osteotomy (PSO) settings where disk spaces were preserved above or adjacent to the PSO. This study compares the multidirectional bending rigidity and fatigue life of PSO segments with or without interbody support.

Methods

Twelve specimens received bilateral T12–S1 posterior fixation and L3 PSO. Six received extreme lateral interbody fusion (XLIF) cages in addition to PSO at L2–L3 and L3–L4; six had PSO only. Flexion-extension, lateral bending, and axial rotation (AR) tests were conducted up to 7.5 Newton-meters (Nm) for groups: (1) posterior fixation, (2) L3 PSO, (3) addition of cages (six specimens). Relative motion across the osteotomy (L2–L4) and entire fixation site (T12–S1) was measured. All specimens were then fatigue tested for 35K cycles.

Results

Regardingmultiaxial bending, there was a significant 25.7% reduction in AR range of motion across L2–L4 following addition of cages. Regarding fatigue bending, dynamic stiffness, though not significant ( p = 0.095), was 22.2% greater in the PSO + XLIF group than in the PSO-only group.

Conclusions

Results suggest that placement of interbody cages in PSO settings has a potential stabilizing effect, which is modestly evident in the acute setting. Inserting cages in a second-stage surgery remains a viable option and may benefit patients in terms of recovery but additional clinical studies are necessary to confirm this.
Strain in silicon nanowire beams
Authors: Ureña Ferran , Olsen Sarah H. , Šiller Lidija , Bhaskar Umesh , Pardoen Thomas , Raskin Jean-Pierre
Published: December 2012

In this work, strain in silicon free standing beams loaded in uniaxial tension is experimentally and theoretically investigated for strain values ranging from 0 to 3.6%. The fabrication method allows multiple geometries (and thus strain values) to be processed simultaneously on the same wafer while being studied independently. An excellent agreement of strain determined by two non-destructive characterization techniques, Raman spectroscopy and mechanical displacement using scanning electron microscopy (SEM) markers, is found for all the sample lengths and widths. The measured data also show good agreement with theoretical predictions of strain based upon continuum mechanical considerations, giving validity to both measurement techniques for the entire range of strain values. The dependence of Young's modulus and fracture strain on size has also been analyzed. The Young's modulus is determined using SEM and compared with that obtained by resonance-based methods. Both methods produced a Young's modulus value close to that of bulk silicon with values obtained by resonance-based methods being slightly lower. Fracture strain is analyzed in 40 sets of samples with different beam geometries, yielding values up to 3.6%. The increase in fracture strain with decreasing beam width is compared with previous reports. Finally, the role of the surface on the mechanical properties is analyzed using UV and visible lasers having different penetration depths in silicon. The observed dependence of Raman shift on laser wavelength is used to assess the thermal conductivity of deformed silicon.
Room-temperature ferromagnetism in Co-doped CeO2 nanospheres prepared by the polyvinylpyrrolidone-assisted hydrothermal method
Authors: Phokha Sumalin , Pinitsoontorn Supree , Maensiri Santi
Published: December 2012

Nanospheres of pure CeO2 and Co-doped CeO2 (Ce1−xCoxO2, 0.01 ≤ x ≤ 0.07) dilute magnetic oxide were prepared by hydrothermal treatment using cerium (III) nitrate, cobalt (III) nitrate, and polyvinylpyrrolidone (PVP) as a surfactant. The prepared samples were studied using x-ray diffraction (XRD), transmission electron microscopy, field-emission scanning electron microscopy (FE-SEM), and UV-Visible spectroscopy. The valence states of Ce and Co ions were determined by using x-ray absorption near edge spectroscopy. The magnetic properties of the samples were studied using vibrating sample magnetometry. The results from XRD indicated that the synthesized samples had a cubic structure without a change in the structure of CeO2 due to Co substitution. FE-SEM micrographs showed that the samples had a spherical morphology. The Co-doped CeO2 showed a red shift of the band gap energy that originates from defects caused by Co substitution. The samples of both CeO2 and Co-doped CeO2 exhibit room temperature ferromagnetism, and the saturated magnetization (Ms) increases with increasing Co content until x = 0.03 and then displays ferromagnetic loops as well as paramagnetic behavior. Oxygen vacancies have been proposed to play an important role in the magnetic properties of Co-doped CeO2.
On the streamer propagation in methane plasma discharges
Authors: Ferrara Carlo , Preda Marco , Cavallotti Carlo
Published: December 2012

The initial stages of formation and propagation of a streamer in methane at atmospheric pressure were studied using a 2-dimensional axial symmetric hydrodynamic model. The model is based on the drift diffusion approximation and exploits electron transport parameters determined using an external Boltzmann equation solver. The resulting system of equations was solved using the finite element methods and integrated in time with an Euler backward algorithm. An approach useful to alleviate the numerical difficulties determined by the steep gradients that appear on the streamer front was developed. It is based on a proper choice of the adaptation algorithm of the integration time step. Three phases in the streamer development could be identified, in agreement with analytical and numerical models reported in the literature: ionization avalanche, streamer, and shielded plasma. The properties of the three phases have been characterized analyzing the evolution in time of the most important variables characterizing the system (ion and electron densities, potential, and electric field). Finally, the influence of some operative parameters, such as inter-electrodic gap, seed electron density, and applied potential, has been investigated in order to determine how it affects the evolution of the micro-discharge, and in particular, the transition from ionization avalanche to streamer.
A hierarchical exact accelerated stochastic simulation algorithm
Authors: Orendorff David , Mjolsness Eric
Published: December 2012

A new algorithm, “HiER-leap” (hierarchical exact reaction-leaping), is derived which improves on the computational properties of the ER-leap algorithm for exact accelerated simulation of stochastic chemical kinetics. Unlike ER-leap, HiER-leap utilizes a hierarchical or divide-and-conquer organization of reaction channels into tightly coupled “blocks” and is thereby able to speed up systems with many reaction channels. Like ER-leap, HiER-leap is based on the use of upper and lower bounds on the reaction propensities to define a rejection sampling algorithm with inexpensive early rejection and acceptance steps. But in HiER-leap, large portions of intra-block sampling may be done in parallel. An accept/reject step is used to synchronize across blocks. This method scales well when many reaction channels are present and has desirable asymptotic properties. The algorithm is exact, parallelizable and achieves a significant speedup over the stochastic simulation algorithm and ER-leap on certain problems. This algorithm offers a potentially important step towards efficient in silico modeling of entire organisms.
Photonic band gaps in one-dimensional magnetized plasma photonic crystals with arbitrary magnetic declination
Authors: Zhang Hai-Feng , Liu Shao-Bin , Kong Xiang-Kun
Published: December 2012

In this paper, the properties of photonic band gaps and dispersion relations of one-dimensional magnetized plasma photonic crystals composed of dielectric and magnetized plasma layers with arbitrary magnetic declination are theoretically investigated for TM polarized wave based on transfer matrix method. As TM wave propagates in one-dimensional magnetized plasma photonic crystals, the electromagnetic wave can be divided into two modes due to the influence of Lorentz force. The equations for effective dielectric functions of such two modes are theoretically deduced, and the transfer matrix equation and dispersion relations for TM wave are calculated. The influences of relative dielectric constant, plasma collision frequency, incidence angle, plasma filling factor, the angle between external magnetic field and +z axis, external magnetic field and plasma frequency on transmission, and dispersion relation are investigated, respectively, and some corresponding physical explanations are also given. From the numerical results, it has been shown that plasma collision frequency cannot change the locations of photonic band gaps for both modes, and also does not affect the reflection and transmission magnitudes. The characteristics of photonic band gaps for both modes can be obviously tuned by relative dielectric constant, incidence angle, plasma filling factor, the angle between external magnetic field and +z axis, external magnetic field and plasma frequency, respectively. These results would provide theoretical instructions for designing filters, microcavities, and fibers, etc.
Improvement of (004) texturing by slow growth of Nd doped TiO2 films
Authors: Ali A. , Yassitepe E. , Ruzybayev I. , Ismat Shah S. , Bhatti A. S.
Published: December 2012

In this work, we present preferred (004) texturing of sputter deposited titanium dioxide (TiO2) films on glass substrates as a consequence of Nd doping at very slow growth rate. Nd concentration was varied from 0.0 to 2.0 atomic percent (at. %) in TiO2 thin films deposited under identical growth conditions, i.e., the growth rate of 0.6 Å/s and at 500 °C. At 2 at. % Nd, complete texturing along (004) plane was observed, as indicated by the X-ray diffraction analyses. Morphology of the deposited TiO2 films from pure to 2 at. % Nd doped TiO2 films showed faceted to planar growth. Visualization of electrical and structural analysis (VESTA) software revealed that the change in the morphology was due to preferential growth in (004) orientation. Raman spectroscopy highlighted the phonon confinement in the Eg mode, and a red shift was observed due to an increase in the anti-symmetry in bonding with increased Nd concentration. XPS results confirmed the variation in oxygen vacancy concentration along with the reduction of Ti and Nd valance states with the change in the dopant concentration. Our experiments confirmed that the substitution of Nd at Ti sites was responsible for texturing in (004) orientation and this was possible by growing films at a very slow rate.
Influence of nanoparticle size, loading, and shape on the mechanical properties of polymer nanocomposites
Authors: Kutvonen Aki , Rossi Giulia , Puisto Sakari R. , Rostedt Niko K. J. , Ala-Nissila Tapio
Published: December 2012

We study the influence of spherical, triangular, and rod-like nanoparticles on the mechanical properties of a polymer nanocomposite (PNC), via coarse-grained molecular dynamics simulations. We focus on how the nanoparticle size, loading, mass, and shape influence the PNC’s elastic modulus, stress at failure and resistance against cavity formation and growth, under external stress. We find that in the regime of strong polymer-nanoparticle interactions, the formation of a polymer network via temporary polymer-nanoparticle crosslinks has a predominant role on the PNC reinforcement. Spherical nanoparticles, whose size is comparable to that of the polymer monomers, are more effective at toughening the PNC than larger spherical particles. When comparing particles of spherical, triangular, and rod-like geometries, the rod-like nanoparticles emerge as the best PNC toughening agents.
Maximizing the amplitude of coherent phonons with shaped laser pulses
Authors: Shimada Toru , Frischkorn Christian , Wolf Martin , Kampfrath Tobias
Published: December 2012

We perform model calculations of coherent lattice vibrations in solids driven by ultrashort laser pulses. In order to maximize the amplitude of the coherent phonon in the time domain, an evolutionary algorithm optimizes the driving laser field. We find that only a Fourier-limited single pulse yields the maximum phonon amplitude, irrespective of the actual physical excitation mechanism (impulsive or displacive). This result is in clear contrast to the widespread intuition that excitation by a pulse train in phase with the oscillation leads to the largest amplitude of an oscillator. We rationalize this result by an intuitive model and discuss implications for other nonlinear processes such as optical rectification.
Quantum-classical path integral. I. Classical memory and weak quantum nonlocality
Authors: Lambert Roberto , Makri Nancy
Published: December 2012

We consider rigorous path integral descriptions of the dynamics of a quantum system coupled to a polyatomic environment, assuming that the latter is well approximated by classical trajectories. Earlier work has derived semiclassical or purely classical expressions for the influence functional from the environment, which should be sufficiently accurate for many situations, but the evaluation of quantum-(semi)classical path integral (QCPI) expressions has not been practical for large-scale simulation because the interaction with the environment introduces couplings nonlocal in time. In this work, we analyze the nature of the effects on a system from its environment in light of the observation [N. Makri, J. Chem. Phys. 109, 2994 (1998)] that true nonlocality in the path integral is a strictly quantum mechanical phenomenon. If the environment is classical, the path integral becomes local and can be evaluated in a stepwise fashion along classical trajectories of the free solvent. This simple “classical path” limit of QCPI captures fully the decoherence of the system via a classical mechanism. Small corrections to the classical path QCPI approximation may be obtained via an inexpensive random hop QCPI model, which accounts for some “back reaction” effects. Exploiting the finite length of nonlocality, we argue that further inclusion of quantum decoherence is possible via an iterative evaluation of the path integral. Finally, we show that the sum of the quantum amplitude factors with respect to the system paths leads to a smooth integrand as a function of trajectory initial conditions, allowing the use of Monte Carlo methods for the multidimensional phase space integral.
Switching of bound vector solitons for the coupled nonlinear Schrödinger equations with nonhomogenously stochastic perturbations
Authors: Sun Zhi-Yuan , Gao Yi-Tian , Yu Xin , Liu Ying
Published: December 2012

We investigate the dynamics of the bound vector solitons (BVSs) for the coupled nonlinear Schrödinger equations with the nonhomogenously stochastic perturbations added on their dispersion terms. Soliton switching (besides soliton breakup) can be observed between the two components of the BVSs. Rate of the maximum switched energy (absolute values) within the fixed propagation distance (about 10 periods of the BVSs) enhances in the sense of statistics when the amplitudes of stochastic perturbations increase. Additionally, it is revealed that the BVSs with enhanced coherence are more robust against the perturbations with nonhomogenous stochasticity. Diagram describing the approximate borders of the splitting and non-splitting areas is also given. Our results might be helpful in dynamics of the BVSs with stochastic noises in nonlinear optical fibers or with stochastic quantum fluctuations in Bose-Einstein condensates.
Quantum-classical path integral. II. Numerical methodology
Authors: Lambert Roberto , Makri Nancy
Published: December 2012

We present a quantum-classical methodology for propagating the density matrix of a system coupled to a polyatomic (large molecular or solvent) environment. The system is treated via a full path integral, while the dynamics of the environment is approximated in terms of classical trajectories. We obtain quantum-classical path integral (QCPI) expressions in which the trajectories can undergo transitions to other quantum states at regular time intervals, but the cumulative probability of these transitions is governed by the local strength of the state-to-state coupling as well as the magnitude of the solvent reorganization energy. If quantum effects in the coordinates of the environment are relatively weak, an inexpensive random hop approximation leads to accurate descriptions of the dynamics. We describe a systematic iterative scheme for including quantum mechanical corrections for the solvent by gradually accounting for nonlocal “quantum memory” effects. As the length of the included memory approaches the decoherence time of the environment, the iterative QCPI procedure converges to the full QCPI result. The methodology is illustrated with application to dissipative symmetric and asymmetric two-level systems.
Non-Markovianity and Clauser-Horne-Shimony-Holt (CHSH)-Bell inequality violation in quantum dissipative systems
Authors: Thilagam A. , Usha Devi A. R.
Published: December 2012

We examine the non-Markovian dynamics in a multipartite system of two initially correlated atomic qubits, each located in a single-mode leaky cavity and interacting with its own bosonic reservoir. We show the dominance of non-Markovian features, as quantified by the difference in fidelity of the evolved system with its density matrix at an earlier time, in three specific two-qubit partitions associated with the cavity-cavity and atom-reservoir density matrices within the same subsystem, and the cavity-reservoir reduced matrix across the two subsystems. The non-Markovianity in the cavity-cavity subsystem is seen to be optimized in the vicinity of the exceptional point. The Clauser-Horne-Shimony-Holt (CHSH)-Bell inequality computed for various two-qubit partitions show that high non-locality present in a specific subsystem appears in conjunction with enhanced non-Markovian dynamics in adjacent subsystems. This is in contrast to the matching existence of non-locality and quantum correlations in regions spanned by time t and the cavity decay rate, λc for select partitions. We discuss the applicability of these results to photosynthetic systems.
Phase diagrams of strained Ca1–xCexMnO3 films
Authors: Xiang P.-H. , Yamada H. , Akoh H. , Sawa A.
Published: December 2012

The transport and magnetic properties were examined of thin films of the electron-doped manganite Ca1−xCexMnO3 (CCMO; 0 ≤ x ≤ 0.1) deposited on three different single-crystalline oxide substrates: YAlO3, NdAlO3, and LaSrAlO4, which subject the films to a compressive strain, a practical lattice matching, and a tensile strain, respectively. The temperature dependence of the activation energy extracted from the resistivity–temperature curves clearly indicated the phase transitions in the CCMO films. A comparison with magnetization measurements revealed that regardless of the substrates, the temperature-driven phase transition of the CCMO films changed from the G-type antiferromagnetic transition at x = 0 to the canted antiferromagnetic transition and to the charge- and/or orbital-ordered transition, as x was increased. In the canted antiferromagnetic phase, the epitaxial strains have significant impact not only on the transport properties but also on the magnetic properties such as the spontaneous magnetization and the magnetic anisotropy, confirming that the competition between antiferromagnetic super-exchange and ferromagnetic double-exchange interactions results in the canted antiferromagnetic state in the electron-doped CCMO films. Based on the results of the transport and magnetic measurements, the temperature versus band-filling phase diagrams of the strained CCMO films on three different substrates were established.
Single-step holographic fabrication of large-area periodically corrugated metal films
Authors: Lu Mengqian , Krishna Juluri Bala , Zhao Yanhui , Jun Liu Yan , Bunning Timothy J. , Jun Huang Tony
Published: December 2012

We have developed a simple, high-throughput, and cost-effective method to fabricate one-dimensional and two-dimensional periodically corrugated silver films over centimeter scale areas. This fabrication uses a single-step holographic patterning technique with laser intensities as low as 88.8 mW/cm2 to deposit silver nanoparticles directly from solution to create gratings with periodicities of 570 nm. A dip in the transmission spectrum for these samples is observed due to certain visible wavelengths coupling to surface plasmon polaritons (SPPs) and the peak wavelength of this dip has a linear relationship with the surrounding material's refractive index (RI) with a sensitivity of 553.4 nm/RIU. The figure of merit (the ratio of refractive index sensitivity to the full width at half maximum (FWHM)) is typically in the range of 12–23. Our technique enables single-step fabrication of uniform, sub-wavelength periodic metal structures over a large area with low cost. Such sub-wavelength periodic metal structures are promising candidates as disposable sensors in applications such as affordable environmental monitoring systems and point-of-care diagnostics.
The structural and optical properties of supercontinuum emitting Si nanocrystals prepared by laser ablation in water
Authors: Alima Dana , Estrin Yevgeni , Rich Daniel H. , Bar Ilana
Published: December 2012

Laser ablation of Si(100) targets immersed in deionized water at room temperature was studied by applying the second harmonic of a ns pulsed Nd:YAG laser and by employing different methods for characterization of the resulting nanocrystals (NCs). Spontaneous Raman scattering showed first order Raman spectra of the Si NCs, which varied in their Raman shift and width. The Raman data were analyzed using a phonon confinement model, involving three-dimensional confinement and lognormal size distributions for the nanocrystallites constituting the samples, indicating the presence of particles greater than ∼2 nm diameter. High-resolution transmission electron microscopy and electron diffraction of the as-prepared samples showed NCs with diameters greater than ∼1.75 nm and quantum dots, corresponding to Si/SiOx. The optical properties of the Si NCs were studied with cathodoluminescence (CL) spectroscopy for sample temperatures in the 50–300 K range, which exhibited a supercontinuum emission ranging from the near ultraviolet to the red regions. The emission is characterized by four major emission bands, peaked at 1.88, 2.18, 2.64 and 3.44 eV, which practically remain at the same positions as the temperature is varied. These bands are assigned to excitonic recombination in the Si NCs, whose electron/hole transition energies are consistent with the quantum confinement of carriers in four size-dispersed groups of Si NCs. The influence of electron beam irradiation on the passivation of the NCs was examined, showing quenching of the CL as a function of electron-beam exposure time. This quenching is attributed to desorption of hydrogen, disruption of the NC surface passivation, and formation of nonradiative recombination channels involving surface states in the gap. The approach used in this study demonstrates the possibility of growing nano-scale Si crystals with the potential for incorporation into optoelectronic devices or for use in biomedical applications.
Laser induced fluorescence monitoring of the transport of small organic molecules in an organic vapor phase deposition system
Authors: Rolin Cedric , Vartanian Garen , Forrest Stephen R.
Published: December 2012

Laser-induced fluorescence is employed for the accurate and real-time in-situ monitoring of the concentration of organic molecules in an organic vapor phase deposition (OVPD) chamber. We investigate the transport dynamics of organic species in a hot N2 carrier gas from the evaporation source to the substrate. Based on the time-dependent concentration of organic molecules obtained from their fluorescence intensity near the substrate, we find that carrier gas transport is accurately described by Poiseuille flow. The interplay between convective and diffusive forces gives rise to dispersion of organic molecules in the carrier gas, resulting in the development of plug flow as described by Taylor-Aris theory. Retention of molecules in chamber dead volumes delays transport and introduces tailing of the concentration transients. Our study indicates how OVPD system design and operating conditions can be optimized to limit the duration of transport transients, ultimately leading to precise control over the growth of complex multilayer thin film structures.
Gas breakdown driven by L band short-pulse high-power microwave
Authors: Yang Yi-Ming , Yuan Cheng-Wei , Qian Bao-Liang
Published: December 2012

High power microwave (HPM) driven gas breakdown is a major factor in limiting the radiation and transmission of HPM. A method that HPM driven gas breakdown could be obtained by changing the aperture of horn antenna is studied in this paper. Changing the effective aperture of horn antenna can adjust the electric field in near field zone, leading to gas breakdown. With this method, measurements of air and SF6 breakdowns are carried out on a magnetically insulated transmission-line oscillators, which is capable of generating HPM with pulse duration of 30 ns, and frequency of 1.74 GHz. The typical breakdown waveforms of air and SF6 are presented. Besides, the breakdown field strengths of the two gases are derived at different pressures. It is found that the effects of air and SF6 breakdown on the transmission of HPM are different: air breakdown mainly shortens the pulse width of HPM while SF6 breakdown mainly reduces the peak output power of HPM. The electric field threshold of SF6 is about 2.4 times larger than that of air. These differences suggest that gas properties have a great effect on the transmission characteristic of HPM in gases.
Electron cyclotron emission measurements on JET: Michelson interferometer, new absolute calibration, and determination of electron temperature
Authors: Schmuck S. , Fessey J. , Gerbaud T. , Alper B. , Beurskens M. N. A. , de la Luna E. , Sirinelli A. , Zerbini M. ,   JET-EFDA Contributors
Published: December 2012

At the fusion experiment JET, a Michelson interferometer is used to measure the spectrum of the electron cyclotron emission in the spectral range 70–500 GHz. The interferometer is absolutely calibrated using the hot/cold technique and, in consequence, the spatial profile of the plasma electron temperature is determined from the measurements. The current state of the interferometer hardware, the calibration setup, and the analysis technique for calibration and plasma operation are described. A new, full-system, absolute calibration employing continuous data acquisition has been performed recently and the calibration method and results are presented. The noise level in the measurement is very low and as a result the electron cyclotron emission spectrum and thus the spatial profile of the electron temperature are determined to within ±5% and in the most relevant region to within ±2%. The new calibration shows that the absolute response of the system has decreased by about 15% compared to that measured previously and possible reasons for this change are presented. Temperature profiles measured with the Michelson interferometer are compared with profiles measured independently using Thomson scattering diagnostics, which have also been recently refurbished and recalibrated, and agreement within experimental uncertainties is obtained.
On the nature of Surface States Stark Effect at clean GaN(0001) surface
Authors: Kempisty Paweł , Krukowski Stanisław
Published: December 2012

Recently developed model allows for simulations of electric field influence on the surface states. The results of slab simulations show considerable change of the energy of quantum states in the electric field, i.e., Stark Effect associated with the surface (SSSE—Surface States Stark Effect). Detailed studies of the GaN slabs demonstrate spatial variation of the conduction and valence band energy revealing real nature of SSSE phenomenon. It is shown that long range variation of the electric potential is in accordance with the change of the energy of the conduction and valence bands. However, at short distances from GaN(0001) surface, the valence band follows the potential change while the conduction states energy is increased due to quantum overlap repulsion by surface states. It is also shown that at clean GaN(0001) surface Fermi level is pinned at about 0.34 eV below the long range projection of the conduction band bottom and varies with the field by about 0.31 eV due to electron filling of the surface states.
Large magnetic entropy and electron-phonon coupling in Gd-based metallic glass
Authors: Tang M. B. , Xia L. , Chan K. C. , Zhao J. T.
Published: December 2012

We study the magnetic entropy behavior in Gd55Al20Ni12Co10Mn3 metallic glass by magnetic susceptibility, resistivity, and specific heat at low temperatures. The Gd-based metallic glass shows metallic behavior, and a ferromagnetic to paramagnetic transition at 106 K. The ferromagnetic order assists the electron-phonon coupling, which induces the large excess magnetic entropy below Curie temperature in the Gd-based metallic glass. The results are important to understand the electron-phonon coupling behavior in disordered alloys.
Role of dynamic polar nanoregions in heterovalent perovskite relaxor: Inelastic light scattering study of ferroelectric Ti rich Pb(Zn1/3Nb2/3)O3-PbTiO3
Authors: Saidul Islam Md. , Tsukada Shinya , Chen Wenzhi , Ye Zuo-Guang , Kojima Seiji
Published: December 2012

The role of dynamic polar nanoregions (PNRs) of (1−x)Pb(Zn1/3Nb2/3)O3-xPbTiO3 (PZN-100xPT) single crystals with the PT content x = 0.15 (i.e., higher than above the morphotropic phase boundary composition x ∼ 0.09) has been investigated using inelastic light scattering. The remarkable anomaly of the longitudinal acoustic mode is clearly observed in the vicinity of the cubic-tetragonal phase transition temperature at the TC-T = 481 K. A broad central peak (CP) appears below the Burns temperature TB ∼ 700 K. Upon cooling, the relaxation time determined from the CP width clearly shows a critical slowing down when approaching TC-T in contrast with the suppressed slowing down previously observed in PZN-7PT [S. Tsukada and S. Kojima, Phys. Rev. B 78, 144106 (2008)]. These facts are due to the existence of dynamic PNRs and the disappearance of chemically ordered regions resulting from a higher PT content in the solid solution. In the cubic phase, the local symmetry breaking caused by the PNRs was observed by Raman scattering. The initial size of dynamic PNRs is about 3 nm just below TB, and it increases significantly upon cooling below the intermediate temperature T* ∼ 600 K, reaching 10 nm down to TC-T.
Rovibrational effects on NMR shieldings in a heavy-element system: XeF2
Authors: Lantto Perttu , Kangasvieri Sanna , Vaara Juha
Published: December 2012

Fully quantum-mechanical treatment of the effects of thermal rovibrational motion in a heavy-element molecule with relativistic effects is carried out for the heavy 129/131Xe and light 19F nuclear shieldings in the linear XeF2 molecule. More importantly, purely quantum-mechanical, intramolecular phenomena, the primary and secondary isotope effect on these shieldings, respectively, are treated with including both the zero-point vibrational and finite-temperature effects. While large solvent effects influence the experimental absolute shielding constants and chemical shifts (thereby making comparison of experiment and theory very difficult), they are not significant for the isotope shifts. We study the role of electron correlation at both nonrelativistic (NR) and relativistic [Breit-Pauli perturbational theory (BPPT) as well as 4-component Dirac theory] level. We obtain quantitative agreement with the nearly solvent-independent experimental 19F secondary isotope shifts. This implies a promising accuracy for our predictions of the experimentally so far non-existing primary Xe isotope shift and the temperature dependence of Xe and F chemical shifts corresponding to a low pressure gas phase. To achieve this, a combination of high-level ab initio NR shielding surface is found necessary, in the present work supplemented by relativistic corrections by density-functional theory (DFT). Large errors are demonstrated to arise due to DFT in the NR shielding surface, explaining findings in recent computational studies of heavy-element isotope shifts. Besides a high-quality property hypersurface, the inclusion of thermal effects (in addition to zero-point motion) is also necessary to compare with experimental results. The geometry dependence of the different relativistic influences on the wave function, Zeeman interaction, and hyperfine interaction, as well as their role in the temperature dependence of both the Xe and F shielding constants and their isotope shifts, are discussed. The relativistic rovibrational effects arise from the same individual contributions as previously found for the chemical shifts and shielding anisotropies. In general, the spin-orbit interactions are more sensitive to rovibrational motion than the scalar relativistic contributions. A previously suggested third-order BPPT contribution to shielding anisotropy is shown to be important for a better agreement with experiment.
Development of large volume double ring penning plasma discharge source for efficient light emissions
Authors: Prakash Ram , Vyas Gheesa Lal , Jain Jalaj , Prajapati Jitendra , Pal Udit Narayan , Chowdhuri Malay Bikas , Manchanda Ranjana
Published: December 2012

In this paper, the development of large volume double ring Penning plasma discharge source for efficient light emissions is reported. The developed Penning discharge source consists of two cylindrical end cathodes of stainless steel having radius 6 cm and a gap 5.5 cm between them, which are fitted in the top and bottom flanges of the vacuum chamber. Two stainless steel anode rings with thickness 0.4 cm and inner diameters 6.45 cm having separation 2 cm are kept at the discharge centre. Neodymium (Nd2Fe14B) permanent magnets are physically inserted behind the cathodes for producing nearly uniform magnetic field of ∼0.1 T at the center. Experiments and simulations have been performed for single and double anode ring configurations using helium gas discharge, which infer that double ring configuration gives better light emissions in the large volume Penning plasma discharge arrangement. The optical emission spectroscopy measurements are used to complement the observations. The spectral line-ratio technique is utilized to determine the electron plasma density. The estimated electron plasma density in double ring plasma configuration is ∼2 × 1011 cm−3, which is around one order of magnitude larger than that of single ring arrangement.
Delocalization error of density-functional approximations: A distinct manifestation in hydrogen molecular chains
Authors: Zheng Xiao , Liu Min , Johnson Erin R. , Contreras-García Julia , Yang Weitao
Published: December 2012

Delocalization error is one of the major sources of inaccuracy for mainstream density functional approximations and it is responsible for many of the most glaring failures. Quantitative identification of delocalization error in chemical species and analysis of its influence on calculated thermodynamic properties have remained scarce. In this work we demonstrate unambiguously the effect of delocalization error on a series of hydrogen molecular chains and elucidate the underlying relationship between the error magnitude and system geometry. This work stresses the necessity of minimizing delocalization error associated with density functional approximations.
Universality in bipartite mean field spin glasses
Authors: Genovese Giuseppe
Published: December 2012

In this work, we give a proof of universality with respect to the choice of the statistical distribution of the quenched noise, for mean field bipartite spin glasses. We use mainly techniques of spin glasses theory, as Guerra's interpolation and the cavity approach.
Proton induced quasi-monochromatic x-ray beams for soft x-ray spectroscopy studies and selective x-ray fluorescence analysis
Authors: Sokaras D. , Zarkadas Ch. , Fliegauf R. , Beckhoff B. , Karydas A. G.
Published: December 2012

We present the analytical features and performance of an x-ray spectroscopy end station of moderate energy resolution operating with proton-induced quasi-monochromatic x-ray beams. The apparatus was designed, installed and operated at the 5.5 MV Tandem VdG Accelerator Laboratory of the Institute of Nuclear Physics, N.C.S.R. “Demokritos,” Athens. The setup includes a two-level ultrahigh vacuum chamber that hosts in the lower level up to six primary targets in a rotatable holder; there, the irradiation of pure element materials—used as primary targets—with few-MeV high current (∼μA) proton beams produces intense quasi-monochromatic x-ray beams of selectable energy. In the chamber's upper level, a six-position rotatable sample holder hosts the targets considered for x-ray spectroscopy studies. The proton-induced x-ray beam, after proper collimation, is guided to the sample position whereas various filters can be also inserted along the beam's path to eliminate the backscattered protons or/and to absorb selectively components of the x-ray beam. The apparatus incorporates an ultrathin window Si(Li) spectrometer (FWHM 136 eV at 5.89 keV) coupled with low-noise electronics capable of efficiently detecting photons down to carbon Kα. Exemplary soft x-ray spectroscopy studies and results of selective x-ray fluorescence analysis are presented.
Quantum instanton calculation of rate constant for CH4 + OH → CH3 + H2O reaction: Torsional anharmonicity and kinetic isotope effect
Authors: Wang Wenji , Zhao Yi
Published: December 2012

Thermal rate constants for the title reaction are calculated by using the quantum instanton approximation within the full dimensional Cartesian coordinates. The results reveal that the quantum effect is remarkable for the reaction at both low and high temperatures, and the obtained rates are in good agreement with experimental measurements at high temperatures. Compared to the harmonic approximation, the torsional anharmonic effect of the internal rotation has a little influence on the rates at low temperatures, however, it enhances the rate by about 20% at 1000 K. In addition, the free energy barriers for the isotopic reactions and the temperature dependence of kinetic isotope effects are also investigated. Generally speaking, for the title reaction, the replacement of OH with OD will reduce the free energy barrier, while substituting D for H (connected to C) will increase the free energy barrier.
Stability of molecular dynamics simulations of classical systems
Authors: Toxvaerd Søren
Published: December 2012

The existence of a shadow Hamiltonian \documentclass[12pt]{minimal}\begin{document}$\tilde{H}$\end{document}H̃ for discrete classical dynamics, obtained by an asymptotic expansion for a discrete symplectic algorithm, is employed to determine the limit of stability for molecular dynamics (MD) simulations with respect to the time-increment h of the discrete dynamics. The investigation is based on the stability of the shadow energy, obtained by including the first term in the asymptotic expansion, and on the exact solution of discrete dynamics for a single harmonic mode. The exact solution of discrete dynamics for a harmonic potential with frequency ω gives a criterion for the limit of stability h ⩽ 2/ω. Simulations of the Lennard-Jones system and the viscous Kob-Andersen system show that one can use the limit of stability of the shadow energy or the stability criterion for a harmonic mode on the spectrum of instantaneous frequencies to determine the limit of stability of MD. The method is also used to investigate higher-order central difference algorithms, which are symplectic and also have shadow Hamiltonians, and for which one can also determine the exact criteria for the limit of stability of a single harmonic mode. A fourth-order central difference algorithm gives an improved stability with a factor of \documentclass[12pt]{minimal}\begin{document}$\sqrt{3}$\end{document}3, but the overhead of computer time is a factor of at least two. The conclusion is that the second-order “Verlet”-algorithm, most commonly used in MD, is superior. It gives the exact dynamics within the limit of the asymptotic expansion and this limit can be estimated either from the conserved shadow energy or from the instantaneous spectrum of harmonic modes.
Evolution of variable range hopping in strongly localized two dimensional electron gas at NdAlO3/SrTiO3 (100) heterointerfaces
Authors: Annadi A. , Putra A. , Srivastava A. , Wang X. , Huang Z. , Liu Z. Q. , Venkatesan T. , Ariando
Published: December 2012

We report evolution of the two-dimensional electron gas behavior at the NdAlO3/SrTiO3 heterointerfaces with varying thicknesses of the NdAlO3 overlayer. The samples with a thicker NdAlO3 show strong localizations at low temperatures and the degree of localization is found to increase with the NdAlO3 thickness. The T−1/3 temperature dependence of the sheet resistance at low temperatures and the magnetoresistance study reveal that the conduction is governed by a two-dimensional variable range hopping mechanism in this strong localized regime. We attribute this thickness dependence of the transport properties of the NdAlO3/SrTiO3 interfaces to the interface strain induced by the overlayers.