bluuebunny/crossref_metadata_2025 huggingface dataset:
Ratiometric detection of enzyme turnover and flavin reduction using rare-earth upconverting phosphors
Authors: Harvey Peter , Oakland Chloë , Driscoll Max D. , Hay Sam , Natrajan Louise S.
Published: February 2014

Ytterbium:thulium doped rare-earth upconversion phosphors signal the redox behaviour of flavin mononucleotide in a ratiometric manner and report on the turnover of an archetypal flavo-protein, pentaerythritol tetranitrate reductaseviaFRET modulation.
Fractionation of ‘water-soluble lignocellulose’ into C5/C6 sugars and sulfur-free lignins
Authors: Käldström Mats , Meine Niklas , Farès Christophe , Rinaldi Roberto , Schüth Ferdi
Published: February 2014

Lignocellulose undergoes deep depolymerization by mechanocatalysis, quantitatively forming ‘water-soluble lignocellulose’. The saccharification of the aqueous ‘wood solution’ at 140 °C for 1 h forms C5 and C6 sugars at high yields in addition to sulfur-free lignins.
Exploring the prominent performance of CX-4945 derivatives as protein kinase CK2 inhibitors by a combined computational study
Authors: Wang Xuwen , Pan Peichen , Li Youyong , Li Dan , Hou Tingjun
Published: February 2014

Protein kinase CK2, also known as casein kinase II, is related to various cellular events and is a potential target for numerous cancers.
Design of efficient dye-sensitized solar cells with patterned ZnO–ZnS core–shell nanowire array photoanodes
Authors: Chen Xiang , Bai Zhiming , Yan Xiaoqin , Yuan Haoge , Zhang Guangjie , Lin Pei , Zhang Zheng , Liu Yichong , Zhang Yue
Published: February 2014

The light-harvesting ability and conversion efficiency of DSSCs can be significantly improved with the use of patterned ZnO–ZnS core–shell nanowire array photoanodes.
Plant cyclopropylsterol-cycloisomerase: key amino acids affecting activity and substrate specificity
Authors: Rahier Alain , Karst Francis
Published: February 2014

The enzyme CPI (cyclopropylsterol-cycloisomerase) from the plant sterol pathway catalyses the cleavage of the 9β,19-cyclopropane ring of the 4α-methyl-cyclopropylsterol cycloeucalenol to produce the Δ8-sterol obtusifoliol. Randomly mutated plasmids carrying the Arabidopsis thaliana cpi gene were screened for inactive CPI mutant enzymes on the basis of their ability to genetically complement a Saccharomyces cerevisiae erg7 (defective in oxidosqualene cyclase) ergosterol auxotroph grown in the presence of exogenous cycloeucalenol, and led to the identification of four catalytically important residues. Site-directed mutagenesis experiments confirmed the role of the identified residues, and demonstrated the importance of selected acidic residues and a conserved G108NYFWTHYFF117 motif. The mutated isomerases were assayed both in vivo by quantification of cycloeucalenol conversion into ergosterol in erg7 cells, and in vitro by examination of activities of recombinant AtCPI (A. thaliana CPI) mutants. These studies show that Gly28, Glu29, Gly108 and Asp260 are crucial for CPI activity and that an hydroxy function at residue 113 is needed for maximal substrate affinity and CPI activity. CPI is inactive on upstream 4α,β-dimethyl-cyclopropylsterol precursors of phytosterols. The single mutation W112L generates a CPI with an extended substrate specificity, that is able to convert 4α,β-dimethyl-cyclopropylsterols into the corresponding Δ8 products. These findings provide insights into the molecular basis of CPI activity and substrate specificity.
Assembly of the TgrB1–TgrC1 cell adhesion complex during Dictyostelium discoideum development
Authors: Chen Gong , Xu Xiaoqun , Wu Xiangfu , Thomson Alexander , Siu Chi-Hung
Published: February 2014

In Dictyostelium discoideum, TgrB1 and TgrC1 are partners of a heterophilic cell-adhesion system. To investigate its assembly process, the split GFP complementation assay was used to track the oligomeric status of both proteins. The ability of TgrC1 to form cis-homodimers spontaneously was demonstrated by fluorescence complementation studies and confirmed by chemical cross-linking. In contrast, TgrB1 failed to form cis-homodimers in the absence of TgrC1. Treatment of cell aggregates with antibodies against TgrB1 or TgrC1 did not affect TgrC1 dimerization, but inhibited TgrB1 dimer formation, suggesting that TgrB1 cis-homodimerization is dependent on trans-interaction with TgrC1. When TgrB1 and TgrC1 conjugated with the complementary halves of GFP were co-expressed in cells, cis-heterodimers were not detected. However, weak FRET signals were detected in cells expressing TgrB1–RFP and TgrC1–GFP, suggesting that TgrB1 dimers and TgrC1 dimers were arranged juxtapose to each other in the adhesion complex. The results of the present study suggest that the assembly process is initiated upon trans-interaction of monomeric TgrB1 with TgrC1 homodimers on adjacent cells, which triggers the formation of TgrB1 dimers. The homodimerization of TgrB1 in turn induces the clustering of TgrB1 and TgrC1, and the coalescence of TgrB1–TgrC1 clusters results in the formation of large adhesion complexes.
Phonological Assessment and Analysis of Bilingual Preschoolers' Spanish and English Word Productions
Authors: Prezas Raúl Francisco , Hodson Barbara Williams , Schommer-Aikins Marlene
Published: February 2014

Purpose

The major purpose of this study was to examine Spanish and English phonological productions (patterns/deviations) of typically developing bilingual preschool children. Phonological scores were compared in order to determine if significant differences exist between (a) boys and girls, (b) 4- and 5-year-olds, and/or (c) their productions of Spanish and English words.

Method

Fifty-six bilingual 4- and 5-year-old children (27 boys and 29 girls) who attended Head Start programs named stimulus items for Spanish and English phonological assessment instruments that were similar in procedures and analyses.

Results

Multivariate analyses indicated no significant differences for phonological scores between boys and girls or between the 2 languages. Differences between the 4- and 5-year-olds, however, were significant, with the 5-year-olds performing better than the 4-year-olds. Liquid deviations and omissions of consonants in clusters/sequences were the most frequently occurring phonological deviations.

Conclusions

Phonological score differences between typically developing bilingual Spanish–English-speaking preschool boys and girls from similar backgrounds are not likely to be significant. Better phonological scores, however, can be expected for 5-year-olds than for 4-year-olds. Moreover, phonological deviation percentage scores of typically developing bilingual children for comparable Spanish and English assessment instruments are likely to be similar.
Inferring Speaker Attributes in Adductor Spasmodic Dysphonia: Ratings From Unfamiliar Listeners
Authors: Isetti Derek , Xuereb Linnea , Eadie Tanya L.
Published: February 2014

Purpose

To determine whether unfamiliar listeners' perceptions of speakers with adductor spasmodic dysphonia (ADSD) differ from control speakers on the parameters of relative age, confidence, tearfulness, and vocal effort and are related to speaker-rated vocal effort or voice-specific quality of life.

Method

Twenty speakers with ADSD (including 6 speakers with ADSD plus tremor) and 20 age- and sex-matched controls provided speech recordings, completed a voice-specific quality-of-life instrument (Voice Handicap Index; Jacobson et al., 1997), and rated their own vocal effort. Twenty listeners evaluated speech samples for relative age, confidence, tearfulness, and vocal effort using rating scales.

Results

Listeners judged speakers with ADSD as sounding significantly older, less confident, more tearful, and more effortful than control speakers (
p
< .01). Increased vocal effort was strongly associated with decreased speaker confidence (
r
s = .88–.89) and sounding more tearful (
r
s = .83–.85). Self-rated speaker effort was moderately related (
r
s = .45–.52) to listener impressions. Listeners' perceptions of confidence and tearfulness were also moderately associated with higher Voice Handicap Index scores (
r
s = .65–.70).

Conclusion

Unfamiliar listeners judge speakers with ADSD more negatively than control speakers, with judgments extending beyond typical clinical measures. The results have implications for counseling and understanding the psychosocial effects of ADSD.
Efficient VLSI architecture for interpolation decoding of Hermitian codes
Authors: Srivastava Shraddha , Lee Kwankyu , Popovici Emanuel
Published: February 2014

A fast, area efficient very large scale integration (VLSI) architecture is proposed for a unique decoding algorithm of Hermitian codes which was presented recently by Lee and O'Sullivan from an interpolation perspective. The algorithm iteratively computes the sent message through a majority voting procedure by using the Gröbner bases of interpolation modules. The algorithm has a regular structure which makes it suitable for VLSI implementation. The circuitry is simplified as the decoding algorithm directly gives the message word at the end of the decoding algorithm without separate steps like Chien search and Forney's formula. In terms of hardware requirements, for the widely used high rate Hermitian codes, the Lee–O'Sullivan algorithm is q times faster than Kötters algorithm with the same space complexity of O(q4). Further speed improvements can be achieved by combining the main idea of Guruswami list decoding with the Lee–O'Sullivan algorithm. In terms of hardware, the addition of this concept, will further reduce the running time of the algorithm and make the circuitry about two times faster than the original Lee–O'Sullivan algorithm. The implementation results for both the Köetter and the Lee–O'Sullivan algorithms on Xilinx Virtex‐5 shows that the proposed decoder can be operated at higher clock frequency with almost same area complexity.
Image segmentation by Dirichlet process mixture model with generalised mean
Authors: Zhang Hui , Jonathan Wu Qing Ming , Nguyen Thanh Minh
Published: February 2014

The Dirichlet process mixture model (DPMM) with spatial constraints – e.g. hidden Markov random field (HMRF) model – has been considered as an effective algorithm for image processing application. However, the HMRF model is complex and time‐consuming for implementation. A new DPMM has been introduced, where a generalised mean (GDM) is selected as the spatial constraints function. The GDM is applied not only on prior probability (and posterior probability) to incorporate local spatial information and component information, but also on conditional probability to incorporate local spatial information and observation information. The purpose of the HMRF model and GDM are the same for incorporating some spatial constraints into the system. However, compared to HMRF, GDM is easier, faster and simpler to implement. Finally, a variational Bayesian approach has been adopted for parameters estimation and model selection. Experimental results on image segmentation application demonstrate the improved performance of the proposed approach.
An approach for chest tube detection in chest radiographs
Authors: Mercan Cem Ahmet , Celebi Mustafa Serdar
Published: February 2014

It is known that overlapping tissues cause highly complex projections in chest radiographs. In addition, artificial objects, such as catheters, chest tubes and pacemakers can appear on these radiographs. It is important that the anomaly detection algorithms are not confused by these objects. To achieve this goal, the authors propose an approach to train a convolutional neural network (CNN) to detect chest tubes present on radiographs. To detect the chest tube skeleton as the final output in a better manner, non‐uniform rational B‐spline curves are used to automatically fit with the CNN output. This is the first study conducted to automatically detect artificial objects in the lung region of chest radiographs. Other automatic detection schemes work on the mediastinum. The authors evaluated the performance of the model using a pixel‐based receiver operating characteristic (ROC) analysis. Each true positive, true negative, false positive and false negative pixel is counted and used for calculating average accuracy, sensitivity and specificity percentages. The results were 99.99% accuracy, 59% sensitivity and 99.99% specificity. Therefore they obtained promising results on the detection of artificial objects.
Thermal behavior investigation of silicon-Pyrex micro heat pipe
Authors: Luo Yi , Liu Gang , Zou Liang-liang , Yu Bei-ke , Wang Xiao-dong
Published: February 2014

High heat flux is the major reason for the malfunctioning or shortened life of high-power light-emitting diodes (LEDs) or integrated circuit (IC) components. Cooling technical devices have been widely studied in recent years. A heat pipe made of silicon wafer and Pyrex 7740 has been used in the experiments. Silicon-to-Pyrex bonding is used for the visualization of the flow behavior of the working liquid in heat transfer. A thermal behavior testing system for micro heat pipes (MHPs), including a vacuum chamber, heat flux sensors and thermocouples, was designed and established. The experiments revealed the characteristics of the MEMS heat pipe in LEDs heat transfer, and the maximum equivalent thermal conductivity of the MHPs was 10.6 times that of the silicon wafer. Furthermore, the structure of MHP can be optimized based on these experimental results. They can also be the experimental basis for theoretical study of two-phase flow on the micro scale.
Uniform Ti-doped Sb2Te3 materials for high-speed phase change memory applications
Authors: Zhu Min , Wu Liangcai , Rao Feng , Song Zhitang , Ren Kun , Ji Xinglong , Song Sannian , Yao Dongning , Feng Songlin
Published: February 2014

Compared with pure Sb2Te3, Ti0.32Sb2Te3 (TST) phase change material has larger resistance ratio, higher crystallization temperature and better thermal stability. The sharp decrease in mobility is responsible for the increasing amorphous and crystalline sheet resistance. The uniform crystalline structure of TST film is very benefit for the endurance characteristic. The Set and Reset operation voltages for TST-based phase change memory device are much lower than those of conventional Ge2Sb2Te5-based one. Remarkably, the device presents extremely rapid Set operation speed (∼6 ns). Furthermore, up to 1 × 106 programming cycles are obtained with stable Set and Reset resistances.
Optical and electronic properties of mixed Ag-Au tetramer cations
Authors: Shayeghi A. , Heard C. J. , Johnston R. L. , Schäfer R.
Published: February 2014

We present experimental and theoretical studies of the optical response of mixed \documentclass[12pt]{minimal}\begin{document}${\rm Ag}_{n}{\rm Au}_{4-n}^{+}$\end{document} Ag n Au 4−n+ (n=1–3) clusters in the photon energy range ℏω = 1.9–3.5 eV. Absorption spectra are recorded by a newly built longitudinal molecular beam depletion spectroscopy apparatus providing lower limits to absolute photodissociation cross sections. The experimental data are compared to optical response calculations in the framework of long-range corrected time-dependent density functional theory with initial cluster geometries obtained by the unbiased Birmingham Cluster Genetic Algorithm coupled with density functional theory. Experiments and excited state calculations shed light on the structural and electronic properties of the mixed Ag-Au tetramer cations.
Investigation of magnetic proximity effect in Ta/YIG bilayer Hall bar structure
Authors: Yang Yumeng , Wu Baolei , Yao Kui , Shannigrahi Santiranjan , Zong Baoyu , Wu Yihong
Published: February 2014

In this work, the investigation of magnetic proximity effect was extended to Ta which has been reported to have a negative spin Hall angle. Magnetoresistance (MR) and Hall measurements for in-plane and out-of-plane applied magnetic field sweeps were carried out at room temperature. The size of the MR ratio observed (∼10−5) and its magnetization direction dependence are similar to that reported in Pt/yttrium iron garnet, both of which can be explained by the spin Hall magnetoresistance theory. Additionally, a flip of magnetoresistance polarity is observed at 4 K in the temperature dependent measurements, which can be explained by the magnetic proximity effect induced anisotropic magnetoresistance at low temperature. Our findings suggest that both magnetic proximity effect and spin Hall magnetoresistance have contribution to the recently observed unconventional magnetoresistance effect.
Development of a high dynamic range spectroscopic system for observation of neutral hydrogen atom density distribution in Large Helical Device core plasma
Authors: Fujii K. , Atsumi S. , Watanabe S. , Shikama T. , Goto M. , Morita S. , Hasuo M.
Published: February 2014

We report development of a high dynamic range spectroscopic system comprising a spectrometer with 30% throughput and a camera with a low-noise fast-readout complementary metal-oxide semiconductor sensor. The system achieves a 106 dynamic range (∼20 bit resolution) and an instrumental function approximated by a Voigt profile with Gauss and Lorentz widths of 31 and 0.31 pm, respectively, for 656 nm light. The application of the system for line profile observations of the Balmer-α emissions from high temperature plasmas generated in the Large Helical Device is also presented. In the observed line profiles, emissions are detected in far wings more than 1.0 nm away from the line center, equivalent to neutral hydrogen atom kinetic energies above 1 keV. We evaluate atom density distributions in the core plasma by analyzing the line profiles.
Translationally invariant conservation laws of local Lindblad equations
Authors: Žnidarič Marko , Benenti Giuliano , Casati Giulio
Published: February 2014

We study the conditions under which one can conserve local translationally invariant operators by local translationally invariant Lindblad equations in one-dimensional rings of spin-1/2 particles. We prove that for any 1-local operator (e.g., particle density) there exist Lindblad dissipators that conserve that operator, while on the other hand we prove that among 2-local operators (e.g., energy density) only trivial ones of the Ising type can be conserved, while all the other cannot be conserved, neither locally nor globally, by any 2- or 3-local translationally invariant Lindblad equation. Our statements hold for rings of any finite length larger than some minimal length determined by the locality of Lindblad equation. These results show in particular that conservation of energy density in interacting systems is fundamentally more difficult than conservation of 1-local quantities.
Impact of tortuous flow on bacteria streamer development in microfluidic system during filtration
Authors: Marty A. , Causserand C. , Roques C. , Bacchin P.
Published: February 2014

The way in which bacterial communities colonize flow in porous media is of importance, but basic knowledge on the dynamic of these phenomena is still missing. The aim of this work is to develop microfluidic experiments in order to progress in the understanding of bacteria capture in filters and membranes. PDMS microfluidic devices mimicking filtration processes have been developed to allow a direct dynamic observation of bacteria across 10 or 20 μm width microchannels. When filtered in such devices, bacteria behave surprisingly: Escherichia coli, Pseudomonas aeruginosa or Staphylococcus aureus accumulate in the downstream zone of the filter and form large streamers which oscillate in the flow. In this study, streamer formation is put in evidence for bacteria suspension in non nutritive conditions in less than 1 h. This result is totally different from the one observed in same system with “inert” particles or dead bacteria which are captured in the bottleneck zone and are accumulated in the upstream zone. Observations within different flow geometries (straight channels, connected channels, and staggered row pillars) show that the bacteria streamer development is influenced by the flow configuration and, particularly by the presence of tortuosity within the microchannels zone. These results are discussed at the light of 3D flow simulations. In confined systems and in laminar flow, there is secondary flow (z-velocities) superimposed to the streamwise motion (in xy plane). The presence of the secondary flow in the microsystems has an effect on the bacterial adhesion. A scenario in three steps is established to describe the formation of the streamers and to explain the positive effect of tortuous flow on the development kinetics.
A first-principles study of magnetostrictions of Fe3O4 and CoFe2O4
Authors: Odkhuu Dorj , Taivansaikhan Purev , Yun Won Seok , Hong Soon Cheol
Published: February 2014

Effects of charge ordering in the octahedral sites of Fe3O4 and CoFe2O4 on their magnetostrictions are investigated using the density functional theory plus U approach. Precise description of charge ordering was found to be crucial in determining only band-gaps of Fe3O4 and CoFe2O4, but not other physical properties such as lattice constant, magnetic moment, and magnetostriction. And Co configuration in CoFe2O4 is important in determining its magnetostriction; the most stable configuration results in substantially enhanced magnetostriction (−245 ppm), compared to that (−25 ppm) of Fe3O4, in consistent with experiments.
Dirac solutions for quaternionic potentials
Authors: De Leo Stefano , Giardino Sergio
Published: February 2014

The Dirac equation is solved for quaternionic potentials, i V0 + j W0 (\documentclass[12pt]{minimal}\begin{document}$V_{{0}}\in \mathbb {R}\,,\,\,W_{{0}}\in \mathbb {C}$\end{document}V0∈R,W0∈C). The study shows two different solutions. The first one contains particle and anti-particle solutions and leads to the diffusion, tunneling, and Klein energy zones. The standard solution is recovered taking the complex limit of this solution. The second solution, which does not have a complex counterpart, can be seen as a V0-antiparticle or |W0|-particle solution.
Peculiarities of the coherent spontaneous synchrotron radiation of dense electron bunches
Authors: Balal N. , Bratman V. L. , Savilov A. V.
Published: February 2014

In a short section of homogeneous magnetic field, quasi-plane electron bunches from linear accelerators with laser-driven photo-injectors at moderate particle energies can generate strongly directed, very short and powerful terahertz electromagnetic pulses with a broad frequency spectrum. The formulas for radiation fields, their spectra and efficiency of radiation are presented in a very simple analytical form using expressions for the fields of an arbitrary moving charged plane. The self-action and mutual interaction of thin electron layers are estimated. It is shown that the radiation with frequencies of up to (1–3) THz can be effectively generated by electrons with energies (4–6) MeV in a short and relatively weak magnetic field of (4–10) kOe.
Generalized event-chain Monte Carlo: Constructing rejection-free global-balance algorithms from infinitesimal steps
Authors: Michel Manon , Kapfer Sebastian C. , Krauth Werner
Published: February 2014

In this article, we present an event-driven algorithm that generalizes the recent hard-sphere event-chain Monte Carlo method without introducing discretizations in time or in space. A factorization of the Metropolis filter and the concept of infinitesimal Monte Carlo moves are used to design a rejection-free Markov-chain Monte Carlo algorithm for particle systems with arbitrary pairwise interactions. The algorithm breaks detailed balance, but satisfies maximal global balance and performs better than the classic, local Metropolis algorithm in large systems. The new algorithm generates a continuum of samples of the stationary probability density. This allows us to compute the pressure and stress tensor as a byproduct of the simulation without any additional computations.
Photothermal excitation setup for a modified commercial atomic force microscope
Authors: Adam Holger , Rode Sebastian , Schreiber Martin , Kobayashi Kei , Yamada Hirofumi , Kühnle Angelika
Published: February 2014

High-resolution imaging in liquids using frequency modulation atomic force microscopy is known to suffer from additional peaks in the resonance spectrum that are unrelated to the cantilever resonance. These unwanted peaks are caused by acoustic modes of the liquid and the setup arising from the indirect oscillation excitation by a piezoelectric transducer. Photothermal excitation has been identified as a suitable method for exciting the cantilever in a direct manner. Here, we present a simple design for implementing photothermal excitation in a modified Multimode scan head from Bruker. Our approach is based on adding a few components only to keep the modifications as simple as possible and to maintain the low noise level of the original setup with a typical deflection noise density of about 15 fm/\documentclass[12pt]{minimal}\begin{document}$\sqrt{\text{Hz}}$\end{document}Hz measured in aqueous solution. The success of the modification is illustrated by a comparison of the resonance spectra obtained with piezoelectric and photothermal excitation. The performance of the systems is demonstrated by presenting high-resolution images on bare calcite in liquid as well as organic adsorbates (Alizarin Red S) on calcite with simultaneous atomic resolution of the underlying calcite substrate.
Anelastic internal wave reflection and transmission in uniform retrograde shear
Authors: Eberly Lauren , Sutherland Bruce R.
Published: February 2014

We perform fully nonlinear simulations in two dimensions of a horizontally periodic, vertically localized, anelastic internal wavepacket in order to examine the effects of weak and strong nonlinearity upon wavepackets approaching a reflection level in uniform retrograde shear. Transmission, reflection, and momentum deposition are measured in terms of the horizontal momentum associated with the wave-induced mean flow. These are determined in part as they depend upon the initial wavenumber vector, \documentclass[12pt]{minimal}\begin{document}$\vec{k}=(k,m)$\end{document}k⃗=(k,m), which determines the modulational stability (if |m/k| ≳ 0.7) or instability (if |m/k| ≲ 0.7) of moderately large amplitude quasi-monochromatic internal wavepackets. Whether modulationally stable or unstable, the evolution of the wavepacket is determined by the height of the reflection level predicted by linear theory, zr, relative to the height, zΔ, at which weak nonlinearity becomes significant, and the height, \documentclass[12pt]{minimal}\begin{document}$z_b>z_\Delta$\end{document}zb>zΔ, at which linear theory predicts anelastic waves first overturn in the absence of shear. If \documentclass[12pt]{minimal}\begin{document}$z_r<z_\Delta$\end{document}zr<zΔ, the amplitude remains sufficiently small and the waves reflect as predicted by linear theory. If zr is moderately larger than \documentclass[12pt]{minimal}\begin{document}$z_\Delta$\end{document}zΔ, a fraction of the momentum associated with the wavepackets transmits past the reflection level. This is because the positive shear associated with the wave-induced mean flow can partially shield the wavepacket from the influence of the negative background shear enhancing its transmission. The effect is enhanced for weakly nonlinear modulational unstable wavepackets that narrow and grow in amplitude faster than the anelastic growth rate. However, as nonlinear effects become more pronounced, a significant fraction of the momentum associated with the wavepacket is irreversibly deposited to the background below the reflection level. This is particularly the case for modulationally unstable wavepackets, whose enhanced amplitude growth leads to overturning below the predicted breaking level. Because the growth in the amplitude envelope of modulationally stable wavepackets is retarded by weakly nonlinear effects, reflection is enhanced and transmission retarded relative to their modulationally unstable counterparts. Applications to mountain wave propagation through the stratosphere in the winter hemisphere are discussed.
K
6 carbon: A metallic carbon allotrope in sp3 bonding networks
Authors: Niu Chun-Yao , Wang Xin-Quan , Wang Jian-Tao
Published: February 2014

We identify by first-principles calculations a new cubic carbon phase in I4132 (O8) symmetry, named K6 carbon, which has a six atom primitive cell comprising sp3 hybridized C3 triangle rings. The structural stability is verified by phonon mode analysis. The calculated elastic constants show that the K6 carbon is a high ductile material with a density even lower than graphite. Electronic band and density of states calculations reveal that it is a metallic carbon allotrope with a high electronic density of states of ∼0.10 states/eV per atom at the Fermi level. These results broaden our understanding of the structural and electronic properties of carbon allotropes.
Anomalous composition-dependent dynamics of nanoconfined water in the interlayer of disordered calcium-silicates
Authors: Qomi Mohammad Javad Abdolhosseini , Bauchy Mathieu , Ulm Franz-Josef , Pellenq Roland J.-M.
Published: February 2014

With shear interest in nanoporous materials, the ultraconfining interlayer spacing of calcium–silicate–hydrate (C–S–H) provides an excellent medium to study reactivity, structure, and dynamic properties of water. In this paper, we present how substrate composition affects chemo-physical properties of water in ultraconfined hydrophilic media. This is achieved by performing molecular dynamics simulation on a set of 150 realistic models with different compositions of calcium and silicon contents. It is demonstrated that the substrate chemistry directly affects the structural properties of water molecules. The motion of confined water shows a multi-stage dynamics which is characteristic of supercooled liquids and glassy phases. Inhomogeneity in that dynamics is used to differentiate between mobile and immobile water molecules. Furthermore, it is shown that the mobility of water molecules is composition-dependent. Similar to the pressure-driven self-diffusivity anomaly observed in bulk water, we report the first study on composition-driven diffusion anomaly, the self diffusivity increases with increasing confined water density in C–S–H. Such anomalous behavior is explained by the decrease in the typical activation energy required for a water molecule to escape its dynamical cage.
Symmetry determination on Pb-free piezoceramic 0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 using convergent beam electron diffraction method
Authors: Gao Jinghui , Zhang Lixue , Xue Dezhen , Kimoto Takayoshi , Song Minghui , Zhong Lisheng , Ren Xiaobing
Published: February 2014

(1−x)(Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 (BZT-xBCT) Pb-free piezoceramic has been reported showing ultrahigh piezoelectric performance in its morphotropic phase boundary (MPB) region. However, the crystal structure characteristic for the MPB composition of BZT-xBCT is still under debate—between single orthorhombic phase and tetragonal + rhombohedral two phase mixture. In the present study, we perform the local symmetry determination on the MPB composition x = 0.5 using convergent beam electron diffraction analysis (CBED). Our CBED results from multiple zone axes suggest that there are two coexisting phases with the point group symmetries of 4 mm (tetragonal) and 3 m (rhombohedral) respectively, which agree with two phase mixture model. The strong piezoelectricity can thus be understood by considering the polarization rotation between tetragonal and rhombohedral phases by external field.
High quantum efficiency and low dark count rate in multi-layer superconducting nanowire single-photon detectors
Authors: Jafari Salim A. , Eftekharian A. , Hamed Majedi A.
Published: February 2014

In this paper, we theoretically show that a multi-layer superconducting nanowire single-photon detector (SNSPD) is capable of approaching characteristics of an ideal SNSPD in terms of the quantum efficiency, dark count, and band-width. A multi-layer structure improves the performance in two ways. First, the potential barrier for thermally activated vortex crossing, which is the major source of dark counts and the reduction of the critical current in SNSPDs is elevated. In a multi-layer SNSPD, a vortex is made of 2D-pancake vortices that form a stack. It will be shown that the stack of pancake vortices effectively experiences a larger potential barrier compared to a vortex in a single-layer SNSPD. This leads to an increase in the experimental critical current as well as significant decrease in the dark count rate. In consequence, an increase in the quantum efficiency for photons of the same energy or an increase in the sensitivity to photons of lower energy is achieved. Second, a multi-layer structure improves the efficiency of single-photon absorption by increasing the effective optical thickness without compromising the single-photon sensitivity.
Magnetic properties of Co/Pt nanoring arrays deposited on carbon nanotubes
Authors: Yoon Seungha , Ho Lee Sang , Kwak Wonyoung , Nam Chunghee , Bae Kim Won , Cho B. K.
Published: February 2014

Multiple Co/Pt bilayers were deposited on vertically aligned carbon nanotubes on an anodic aluminum oxide template. The structural and the magnetic properties of the nanoring arrays were investigated by varying the number of Co/Pt bilayers in the ranges 3–10 in multilayers with a Ta(3.0 nm)/[Co(1.0 nm)/Pt(1.5 nm)]n/Ta(1.0 nm) structure. The thickness and diameter of the nanorings increased with increasing repeat number. Compared with Co/Pt films, the Co/Pt nanoring arrays showed a larger coercivity. However, the magnetostatic interactions between the nanorings became dominant in the reversal behavior and caused a nonsquare hysteresis loop. Giant magnetoresistance structures consisting of multiple Co/Pt bilayers and a thick Cu spacer exhibited magnetization curve that were in good agreement the summation of the moments of layers with varied bilayer repetition.
Generation, transmission, and detection of terahertz photons on an electrically driven single chip
Authors: Ikushima Kenji , Ito Atsushi , Okano Shun
Published: February 2014

We demonstrate single photon counting of terahertz (THz) waves transmitted from a local THz point source through a coplanar two-wire waveguide on a GaAs/AlGaAs single heterostructure crystal. In the electrically driven all-in-one chip, quantum Hall edge transport is used to achieve a noiseless injection current for a monochromatic point source of THz fields. The local THz fields are coupled to a coplanar two-wire metal waveguide and transmitted over a macroscopic scale greater than the wavelength (38 μm in GaAs). THz waves propagating on the waveguide are counted as individual photons by a quantum-dot single-electron transistor on the same chip. Photon counting on integrated high-frequency circuits will open the possibilities for on-chip quantum optical experiments.
The surface structure of SrTiO3 at high temperatures under influence of oxygen
Authors: Hesselberth M. B. S. , van der Molen S. J. , Aarts J.
Published: February 2014

We use low energy electron microscopy to investigate the structure of the SrTiO3 (001) surface at elevated temperatures and different oxygen pressures. Upon varying the temperature between 500 °C and 900 °C in oxygen pressures ranging from 10−9 millibar to 10−4 millibar, two surface transitions are found to be present. The lower temperature (1 × 1) → (2 × 1) transition that is known to occur in ultrahigh vacuum can be reversed by increasing the oxygen pressure. At higher temperatures, we observe a (2 × 1) → disordered (1 × 1) transition which is irreversible in the experimental parameter range. The observations are expected to have a strong bearing on the growth of interface structures.
Enhancement of interfacial thermal transport by carbon nanotube-graphene junction
Authors: Bao Hua , Shao Cheng , Luo Shirui , Hu Ming
Published: February 2014

Due to the high intrinsic thermal conductivity, carbon nanotubes are very promising to serve as effective thermal interface materials for microelectronics or other cooling applications. However, the performance of carbon nanotube based thermal interface material is strongly limited by the small effective contact area and weak bonding at carbon nanotube and material interface. Here, we propose a junction structure that the carbon nanotube is bonded with a monolayer graphene, which could potentially enhance the interface thermal conductance. Molecular dynamics simulations show that the interface thermal conductance can be enhanced by at least 40% compared to direct carbon nanotube and silicon interface with strong covalent bonding, while for weak van der Waals bonding the conductance can be enhanced by almost one order of magnitude. The enhancement of thermal conductance is attributed to the efficient thermal transport between carbon nanotube and graphene, as well as the good contact between graphene and silicon surface.
Simulations of the spontaneous emission of a quantum dot near a gap plasmon waveguide
Authors: Perera Chamanei S. , Vernon Kristy C. , Mcleod Angus
Published: February 2014

In this paper, we modeled a quantum dot at near proximity to a gap plasmon waveguide to study the quantum dot-plasmon interactions. Assuming that the waveguide is single mode, this paper is concerned about the dependence of spontaneous emission rate of the quantum dot on waveguide dimensions such as width and height. We compare coupling efficiency of a gap waveguide with symmetric configuration and asymmetric configuration illustrating that symmetric waveguide has a better coupling efficiency to the quantum dot. We also demonstrate that optimally placed quantum dot near a symmetric waveguide with 50 nm × 50 nm cross section can capture 80% of the spontaneous emission into a guided plasmon mode.
Improved organic p-i-n type solar cells with n-doped fluorinated hexaazatrinaphthylene derivatives HATNA-F6 and HATNA-F12 as transparent electron transport material
Authors: Selzer Franz , Falkenberg Christiane , Hamburger Manuel , Baumgarten Martin , Müllen Klaus , Leo Karl , Riede Moritz
Published: February 2014

We study new electron transport materials (ETM) to replace the reference material C60 in p-i-n type organic solar cells. A comprehensive material characterization is performed on two fluorinated hexaazatrinaphthylene derivatives, HATNA-F6 and HATNA-F12, to identify the most promising material for the application in devices. We find that both HATNA derivatives are equally able to substitute C60 as ETM as they exhibit large optical energy gaps, low surface roughness, and sufficiently high electron mobilities. Furthermore, large electron conductivities of 3.5×10−5 S/cm and 2.0×10−4 S/cm are achieved by n-doping with 4 wt. % W2(hpp)4. HOMO levels of (7.72 ± 0.05) eV and (7.73 ± 0.05) eV are measured by ultraviolet photoelectron spectroscopy and subsequently used for estimating LUMO values of (4.2 ± 0.8) eV and (4.3 ± 0.8) eV. Both fluorinated HATNA derivatives are successfully applied in p-i-n type solar cells. Compared to identical reference devices comprising the standard material C60, the power conversion efficiency (PCE) can be increased from 2.1 % to 2.4 % by using the new fluorinated HATNA derivatives.
Interface-reaction-limited growth of thermal oxides on 4H-SiC (0001) in nanometer-thick region
Authors: Heihachiro Kikuchi Richard , Kita Koji
Published: February 2014

Growth kinetics of nanometer-thick thermal oxides on 4H-SiC (0001), Si-face, was investigated. A linear oxide growth was clearly observed in this thickness region, indicating the oxide growth is limited by interface reaction. The activation energy of the interface reaction was estimated to be 3.8 ± 0.1 eV. The rate-limiting step in this reaction was discussed from both the value of activation energy and the oxygen partial pressure dependence of the growth rate. The enhanced growth limited only to the initial <2 nm region was also observed, which is suggesting the change of the rate-limiting step for the interface reaction in the ultrathin region.
Coherent and incoherent terahertz beams measured from a terahertz photoconductive antenna
Authors: Ho Wu Dong , Graber Benjamin , Kim Christopher , Qadri S. B. , Garzarella Anthony
Published: February 2014

We have systematically measured and analyzed the terahertz beams of a photoconductive antenna fabricated on a GaAs substrate. Our data indicate that the antenna produces both coherent and incoherent terahertz beams. The former is produced largely by the plasmon, and the latter is believed to be due to the black body radiation resulting from the thermal excitations and Joule heating by both the femto-second laser and the bias voltage, applied across the electrodes of the antenna. The terahertz-beam property is greatly affected by the operating condition of the photoconductive antenna.
Communication: Rigidity of the molecular ion ${\rm H}_5^+$H5+
Authors: Fábri Csaba , Sarka János , Császár Attila G.
Published: February 2014

The fourth-age quantum chemical code GENIUSH is used for the variational determination of rotational-vibrational energy levels corresponding to reduced- and full-dimensional models of \documentclass[12pt]{minimal}\begin{document}${\rm H}_5^+$\end{document}H5+, a molecular ion exhibiting several strongly coupled large-amplitude motions. The computations are supplemented with one- and two-dimensional analytic results which help to understand the peculiar rovibrational energy-level structure computed correctly for the first time. An unusual aspect of the results is that the canonical Eckart-embedding of molecule-fixed axes, a cornerstone of the computational spectroscopy of semirigid molecules, is found to be inadequate. Furthermore, it is shown that while the 1D “active torsion” model provides proper results when compared to the full, 9D treatment, models excluding the torsion have limited physical significance. The structure of the rovibrational energy levels of \documentclass[12pt]{minimal}\begin{document}${\rm H}_5^+$\end{document}H5+ proves that this is a prototypical astructural molecule: the rotational and vibrational level spacings are of the same order of magnitude and the level structure drastically deviates from that computed via perturbed rigid-rotor and harmonic-oscillator models.
Dissipative soliton dynamics in a discrete magnetic nano-dot chain
Authors: Lee Kyeong-Dong , You Chun-Yeol , Song Hyon-Seok , Park Byong-Guk , Shin Sung-Chul
Published: February 2014

Soliton dynamics is studied in a discrete magnetic nano-dot chain by means of micromagnetic simulations together with an analytic model equation. A soliton under a dissipative system is driven by an applied field. The field-driven dissipative soliton enhances its mobility nonlinearly, as the characteristic frequency and the intrinsic Gilbert damping decrease. During the propagation, the soliton emits spin waves which act as an extrinsic damping channel. The characteristic frequency, the maximum velocity, and the localization length of the soliton are found to be proportional to the threshold field, the threshold velocity, and the initial mobility, respectively.
All-optically controlled fourth- and sixth-order fluorescence processes of Pr3+:YSO
Authors: Li Changbiao , Wang Lele , Zheng Huaibin , Lan Huayan , Lei Chengjun , Zhang Dan , Xiao Min , Zhang Yanpeng
Published: February 2014

We report all-optically controlled fourth- and sixth-order fluorescence processes with and without splitting, in a heteronuclear-like molecule system of Pr3+:YSO both in theory and experiment. We construct the asymptote among Pr3+ ions localized at different cation vacancies. By changing the frequency detuning and power of the controlling field, fluorescence signal can be controlled to switch from an enhanced peak to a suppressed dip, and vice versa. Such transition has a potential application to produce all-optical switches. The results can be well explained by a theory model based on the high-order coherent process.
Thermal emission control by evanescent wave coupling between guided mode of resonant grating and surface phonon polariton on silicon carbide plate
Authors: Ito Kota , Matsui Takayuki , Iizuka Hideo
Published: February 2014

Dielectric guided mode resonant gratings exhibit a sharp spectral and angular response of high reflectivity for propagation wave, and strong evanescent waves are excited. We show that in such a resonant grating positioned above the silicon carbide (SiC) plate, incident light is absorbed in the SiC plate via the evanescent wave coupling when the lateral wavenumber of a guided mode of the grating coincides with that of surface phonon polaritons on the SiC plate. This coupling scheme using the thermally transparent grating enables a sharp spectral and angular emission in the infrared region with capabilities of emissivity modulation and spatially asymmetric emissivity. Thermally transparent subwavelength structures electromagnetically coupled to polar material thermal bodies are crucial in enabling components for thermal emission control.
Spectrally dependent photovoltages in Schottky photodiode based on (100) B-doped diamond
Authors: Čermák Jan , Koide Yasuo , Takeuchi Daisuke , Rezek Bohuslav
Published: February 2014

Spectrally and spatially resolved photovoltages were measured by Kelvin probe force microscopy (KPFM) on a Schottky photo-diode made of a 4 nm thin tungsten-carbide (WC) layer on a 500 nm oxygen-terminated boron-doped diamond epitaxial layer (O-BDD) that was grown on a Ib (100) diamond substrate. The diode was grounded by the sideways ohmic contact (Ti/WC), and the semitransparent Schottky contact was let unconnected. The electrical potentials across the device were measured in dark (only 650 nm LED of KPFM being on), under broad-band white light (halogen lamp), UV (365 nm diode), and deep ultraviolet (deuterium lamp) illumination. Illumination induced shift of the electrical potential remains within 210 mV. We propose that the photovoltage actually corresponds to a shift of Fermi level inside the BDD channel and thereby explains orders of magnitude changes in photocurrent.
Grain boundary orientation effects on deformation of Ta bicrystal nanopillars under high strain-rate compression
Authors: Wang L. , Zhao F. , Zhao F. P. , Cai Y. , An Q. , Luo S. N.
Published: February 2014

We investigate grain boundary (GB) orientation effects on deformation of Ta bicrystal nanopillars under high strain-rate, uniaxial compression with molecular dynamics simulations. The GB is of the ⟨110⟩90° twist grain boundary type. We vary the angle between the GB normal and the loading direction (θ) in the range of 0°–90° while keeping the GB type unchanged. The GB orientation has strong effects on deformation mechanism, yield stress, failure strain, and dynamics, due to the combined effects of Schmid factors in constituent crystals and resolved shear stress on the GB plane. Single crystal plasticity and GB deformation are competing factors, and the GB-initiated deformation mechanisms (stacking faults vs. twinning, and GB sliding) depend on the local stress level around the GB. The large Schmid factors in constituent single crystals for θ=0° lead to twinning in the single crystals and the lowest yield stress; the ensuing GB deformation is achieved via stacking fault formation due to premature stress relaxation. However, nanopillar deformation in the cases of higher angles is dominated by GB deformation largely in the form of twinning, driven by enhanced stress buildup. GB-initiated deformation in the high Schmid factor nanocrystal precedes and may drive that in the low Schmid factor nanocrystal. The details of twin/stacking fault nucleation and growth/shrinking, twin-twin interaction, and twin-GB interaction are also discussed.