bluuebunny/crossref_metadata_2025 huggingface dataset:
Physiochemical and thermodynamic characterization of lipopeptide biosurfactant secreted by Bacillus tequilensis HK01
Authors: Anvari Sanam , Hajfarajollah Hamidreza , Mokhtarani Babak , Noghabi Kambiz Akbari
Published: October 2015

An extensive investigation was applied to isolate biosurfactant producing bacteria from urban waste.
Thermal stability of MnOx–CeO2 mixed oxide for soot combustion: influence of Al2O3, TiO2, and ZrO2 carriers
Authors: Ying Zhou , Chenjun Xu , Yeqing Sheng , Qiuliang Zhu , Yinfei Chen , Hanfeng Lu
Published: October 2015

MnOx–CeO2 (Mn/Ce = 0.15/0.85) mixed oxide materials supported on ZrO2, Al2O3, and TiO2 were prepared by citrate sol–gel method to prevent the CeO2-based oxide catalyst from sintering during soot combustion reaction.
Palladium-catalysed ortho-acylation of 6-anilinopurines/purine nucleosides via C–H activation
Authors: Allu Srinivasarao , Swamy K. C. Kumara
Published: October 2015

Purinyl N1-directedortho-acylation of 6-anilinopurines was achieved in the presence of [Pd]-catalyst using aldehydes/α-oxocarboxylic acids as the acylating sources.
A magnetic relaxation switching immunosensor for one-step detection of salbutamol based on gold nanoparticle–streptavidin conjugate
Authors: Chen Yiping , Xie Mengxia
Published: October 2015

A magnetic relaxation switching immunosensor based on gold nanoparticles–streptavidin conjugate for the detection of salbutamol.
Structure–property relationship in fluorene-based polymer films obtained by electropolymerization of 4,4′-(9-fluorenylidene)-dianiline
Authors: Damaceanu Mariana-Dana , Marin Luminita
Published: October 2015

For the first time, the electropolymerization of 4,4′-(9-fluorenylidene)-dianiline and physico-chemical properties of the obtained polymer films are reported.
Greatly enhanced H2S sensitivity using defect-rich titanium oxide films
Authors: Jagadale Tushar C. , Prasad Vidya , Ramgir Niranjan S. , Prajapat Champalal , Patil Uday V. , Debnath Anil , Aswal D. K. , Gupta S. K.
Published: October 2015

Defect-rich titanium oxide films revealed overlayers of chemi-sorbed oxygen, producing a significant enhancement in sensitivity towards H2S gas with greater stability, better selectivity and quicker recovery.
Palladium dispersed in three-dimensional polyaniline networks as the catalyst for hydrogen peroxide electro-reduction in an acidic medium
Authors: Guo Fen , Ye Ke , Huang Xiaomei , Gao Yinyi , Cheng Kui , Wang Guiling , Cao Dianxue
Published: October 2015

A novel Pd/polyaniline/CFC electrode is prepared by electroless deposition of palladium (Pd) onto three-dimensional polyaniline networks.
Synthesis and biological evaluation of novel fluorinated anticancer agents incorporating the indolin-2-one moiety
Authors: Wang Shuai-Yu , Wang Li-Jun , Jiang Bo , Wu Ning , Li Xiang-Qian , Luo Jiao , Wang Bao-Cheng , Zhang Ren-Shuai , Xu Qi , Shi Da-Yong
Published: October 2015

A series of novel fluorinated anticancer agents containing the indolin-2-one moiety were designed, synthesized and evaluated for their anticancer activities in vitro.
Improving supercapacitor performance of alkylated graphene nanosheets via partial fluorination on their alkyl chains
Authors: Zhao Gang , Zhao Fu-Gang , Sun Jianqing , Lu Yang , Wang Wei , Li Wei-Shi , Chen Qing-Yun
Published: October 2015

Graphene sheets modified with partially fluorinated alkyl chains showed better supercapacitor performance than alkylated analogues. The best performance was achieved with a specific capacitance of 388.0 F g−1 at 1 A g−1 and good cycling stability.
Hybrids based on transition metal phosphide (Mn2P, Co2P, Ni2P) nanoparticles and heteroatom-doped carbon nanotubes for efficient oxygen reduction reaction
Authors: Chen Kuiyong , Huang Xiaobin , Wan Chaoying , Liu Hong
Published: October 2015

Hybrids based on transition metal phosphide (Mn2P, Co2P, Ni2P) nanoparticles and heteroatom-doped carbon nanotubes were facilely synthesized, and used as efficient oxygen reduction reaction (ORR) catalysts in alkaline solution.
Transition voltages respond to synthetic reorientation of embedded dipoles in self-assembled monolayers
Authors: Kovalchuk Andrii , Abu-Husein Tarek , Fracasso Davide , Egger David A. , Zojer Egbert , Zharnikov Michael , Terfort Andreas , Chiechi Ryan C.
Published: October 2015

Transition voltages respond to the collective action of dipole moments embedded in self-assembled monolayers.
Structure of DPPC–hyaluronan interfacial layers – effects of molecular weight and ion composition
Authors: Wieland D. C. Florian , Degen Patrick , Zander Thomas , Gayer Sören , Raj Akanksha , An Junxue , Dėdinaitė Andra , Claesson Per , Willumeit-Römer Regine
Published: October 2015

Hyaluronan and phospholipids play an important role in lubrication in articular joints and provide in combination with glycoproteins exceptionally low friction coefficients.
Reversible switching of liquid crystal micro-particles in a nematic liquid crystal
Authors: Imamura Koki , Yoshida Hiroyuki , Ozaki Masanori
Published: October 2015

Reversible, electric-field-induced rotation of anisotropic micro-particles is demonstrated in a nematic liquid crystal host.
Construction of hierarchical CoS nanowire@NiCo2S4 nanosheet arrays via one-step ion exchange for high-performance supercapacitors
Authors: Zeng Wei , Zhang Guanhua , Wu Xing , Zhang Kang , Zhang Hang , Hou Sucheng , Li Chengchao , Wang Taihong , Duan Huigao
Published: October 2015

In this paper, using CoS@NiCo2S4 as an example, we report the successful design and synthesis of a novel hierarchical core/shell metal sulfide with conductive CoS on nickel foam via a facile ion exchange process.
Pushing efficiency limits for semitransparent perovskite solar cells
Authors: Ramírez Quiroz César Omar , Levchuk Ievgen , Bronnbauer Carina , Salvador Michael , Forberich Karen , Heumüller Thomas , Hou Yi , Schweizer Peter , Spiecker Erdmann , Brabec Christoph J.
Published: October 2015

Here we demonstrate a maximum AVT of 46% with an efficiency of 3.6%, which is the highest combination of efficiency and transparency for a full device stack to date.
Highly tunable plasmonic assemblies of gold nanoparticles: in-plane manipulation of plasmon coupling with nanometer precision
Authors: Zvyagina Alexandra I. , Ezhov Alexander A. , Ivanov Vladimir K. , Arslanov Vladimir V. , Kalinina Maria A.
Published: October 2015

A new facile method allows the manipulation of plasmon coupling in 2D assemblies of gold nanoparticles with a precision of nanometers.
Equivalent energy-level structures in stacked metamaterials
Authors: Liu Chuanbao , Bai Yang , Zhou Ji , Zhao Qian , Yan Yu , Li Jinxu , Su Yanjing , Qiao Lijie
Published: October 2015

For stacked metamaterials, meta-atoms act as real atoms in nature materials, whose characteristic frequency bands behave as the equivalent energy levels.
Ultra‐wideband short‐pulse power divider based on coplanar waveguide and slotline structure
Authors: Zhao Hongxin , Yang Mei
Published: October 2015

An ultra‐wideband (UWB) short‐pulse power divider with a novel structure utilising the coplanar waveguide (CPW) and the slotline transmission line is presented. The novelty of the proposed design can be manifested by that the electromagnetic energy propagates along the two slots of CPW can be naturally divided into the two slotlines of the output ports. The resistors bridging the two slotlines are applied for good isolation and return loss performance. The simulated and measured results for the fabricated prototype present an ultra‐wide frequency band from 0.65 to 7 GHz, where return loss at all the ports and the isolation between output ports are better than 10 dB. The performance of the proposed power divider is also characterised by time‐domain short pulses, which shows that the power divider is featured by very high fidelity and low dispersion for short‐pulse applications.
Quantifying operating reserves with wind power: towards probabilistic–dynamic approaches
Authors: Rahmann Claudia , Heinemann Antonia , Torres Rigoberto
Published: October 2015

In this study, the economic benefits of using a probabilistic‐dynamic approach (PDA) in the quantification of operating reserves are investigated and compared with more traditional quantification rules in power systems with high penetration levels of wind power. To do this, a comprehensive methodology to quantify different operating reserves categories within the real‐time system operation is proposed. The quantification is based on an iterative process where the total costs of the system are minimised, that is the sum of the operating costs (including the additional costs of partially loading generating units due to operating reserves) and the costs of the expected energy not supplied. The PDA considers conventional generation outages; load and wind forecast uncertainty on an hourly basis as well as load and wind variability in a 10 min time frame. The authors use the Chilean power system to demonstrate the efficiency and advantages of the proposed reserve quantification approach.
Classification of micro‐Doppler signatures of human motions using log‐Gabor filters
Authors: Tivive Fok Hing Chi , Phung Son Lam , Bouzerdoum Abdesselam
Published: October 2015

In recent years, Doppler radar has been used as a sensing modality for human gait recognition, due to its ability to operate in adverse weather and penetrate opaque obstacles. Doppler radar captures not only the speed of the target, but also the micro‐motions of its moving parts. These micro‐motions induce frequency modulations that can be used to characterise the target movements. However, a major challenge in Doppler signal processing is to extract discriminative features from the radar returns for target classification. This study presents a feature extraction method for classification of human motions from the micro‐Doppler radar signal. The proposed method applies the log‐Gabor filters at multiple spatial frequencies and orientations on a joint time–frequency representation. To achieve invariance to the target speed, features are extracted from local patches along the torso Doppler shift. Then, the (2D)2PCA (two‐directional two‐dimensional principal component analysis) method is applied to create a compact feature vector. Experimental results based on real radar data obtained from multiple human subjects demonstrate the effectiveness of the proposed approach in classifying arm motions.
On covariant Poisson brackets in classical field theory
Authors: Forger Michael , Salles Mário O.
Published: October 2015

How to give a natural geometric definition of a covariant Poisson bracket in classical field theory has for a long time been an open problem—as testified by the extensive literature on “multisymplectic Poisson brackets,” together with the fact that all these proposals suffer from serious defects. On the other hand, the functional approach does provide a good candidate which has come to be known as the Peierls–De Witt bracket and whose construction in a geometrical setting is now well understood. Here, we show how the basic “multisymplectic Poisson bracket” already proposed in the 1970s can be derived from the Peierls–De Witt bracket, applied to a special class of functionals. This relation allows to trace back most (if not all) of the problems encountered in the past to ambiguities (the relation between differential forms on multiphase space and the functionals they define is not one-to-one) and also to the fact that this class of functionals does not form a Poisson subalgebra.
Study on space charge compensation in negative hydrogen ion beam
Authors: Zhang A. L. , Peng S. X. , Ren H. T. , Zhang T. , Zhang J. F. , Xu Y. , Guo Z. Y. , Chen J. E.
Published: October 2015

Negative hydrogen ion beam can be compensated by the trapping of ions into the beam potential. When the beam propagates through a neutral gas, these ions arise due to gas ionization by the beam ions. However, the high neutral gas pressure may cause serious negative hydrogen ion beam loss, while low neutral gas pressure may lead to ion-ion instability and decompensation. To better understand the space charge compensation processes within a negative hydrogen beam, experimental study and numerical simulation were carried out at Peking University (PKU). The simulation code for negative hydrogen ion beam is improved from a 2D particle-in-cell-Monte Carlo collision code which has been successfully applied to H+ beam compensated with Ar gas. Impacts among ions, electrons, and neutral gases in negative hydrogen beam compensation processes are carefully treated. The results of the beam simulations were compared with current and emittance measurements of an H− beam from a 2.45 GHz microwave driven H− ion source in PKU. Compensation gas was injected directly into the beam transport region to modify the space charge compensation degree. The experimental results were in good agreement with the simulation results.
An atomic orbital-based formulation of analytical gradients and nonadiabatic coupling vector elements for the state-averaged complete active space self-consistent field method on graphical processing units
Authors: Snyder James W. , Hohenstein Edward G. , Luehr Nathan , Martínez Todd J.
Published: October 2015

We recently presented an algorithm for state-averaged complete active space self-consistent field (SA-CASSCF) orbital optimization that capitalizes on sparsity in the atomic orbital basis set to reduce the scaling of computational effort with respect to molecular size. Here, we extend those algorithms to calculate the analytic gradient and nonadiabatic coupling vectors for SA-CASSCF. Combining the low computational scaling with acceleration from graphical processing units allows us to perform SA-CASSCF geometry optimizations for molecules with more than 1000 atoms. The new approach will make minimal energy conical intersection searches and nonadiabatic dynamics routine for molecular systems with O(102) atoms.
Dynamics of asymmetric non-polymeric binary glass formers—A nuclear magnetic resonance and dielectric spectroscopy study
Authors: Pötzschner B. , Mohamed F. , Lichtinger A. , Bock D. , Rössler E. A.
Published: October 2015

We study a dynamically asymmetric binary glass former with the low-Tg component m-tri-cresyl phosphate (m-TCP: Tg = 206 K) and a spirobichroman derivative as a non-polymeric high-Tg component (Tg = 382 K) by means of 1H nuclear magnetic resonance (NMR), 31P NMR, and dielectric spectroscopy which allow component-selectively probing the dynamics. The entire concentration range is covered, and two main relaxation processes with two Tg are identified, Tg1 and Tg2. The slower one is attributed to the high-Tg component (α1-process), and the faster one is related to the m-TCP molecules (α2-process). Yet, there are indications that a small fraction of m-TCP is associated also with the α1-process. While the α1-relaxation only weakly broadens upon adding m-TCP, the α2-relaxation becomes extremely stretched leading to quasi-logarithmic correlation functions at low m-TCP concentrations—as probed by 31P NMR stimulated echo experiments. Frequency-temperature superposition does not apply for the α2-process and it reflects an isotropic, liquid-like motion which is observed even below Tg1, i.e., in the matrix of the arrested high-Tg molecules. As proven by 2D 31P NMR, the corresponding dynamic heterogeneities are of transient nature, i.e., exchange occurs within the distribution G(lnτα2). At Tg1 a crossover is found for the temperature dependence of (mean) τα2(T) from non-Arrhenius above to Arrhenius below Tg1 which is attributed to intrinsic confinement effects. This “fragile-to-strong” transition also leads to a re-decrease of Tg2(cm−TCP) at low concentration cm−TCP, i.e., a maximum is observed in Tg2(cm−TCP) while Tg1(cm−TCP) displays the well-known plasticizer effect. Although only non-polymeric components are involved, we re-discover essentially all features previously reported for polymer-plasticizer systems.
Kinetics of optically excited charge carriers at the GaN surface: Influence of catalytic Pt nanostructures
Authors: Winnerl Andrea , Pereira Rui N. , Stutzmann Martin
Published: October 2015

In this work, we use GaN with different deposited Pt nanostructures as a controllable model system to investigate the kinetics of photo-generated charge carriers in hybrid photocatalysts. We combine conductance and contact potential difference measurements to investigate the influence of Pt on the processes involved in the capture and decay of photo-generated charge carriers at and close to the GaN surface. We found that in the presence of Pt nanostructures the photo-excitation processes are similar to those found in Pt free GaN. However, in GaN with Pt nanostructures, photo-generated holes are preferentially trapped in surface states of the GaN covered with Pt and/or in electronic states of the Pt and lead to an accumulation of positive charge there, whereas negative charge is accumulated in localized states in a shallow defect band of the GaN covered with Pt. This preferential accumulation of photo-generated electrons close to the surface is responsible for a dramatic acceleration of the turn-off charge transfer kinetics and a stronger dependence of the surface photovoltage on light intensity when compared to a Pt free GaN surface. Our study shows that in hybrid photocatalysts, the metal nanostructures induce a spatially inhomogeneous surface band bending of the semiconductor that promotes a lateral drift of photogenerated charges towards the catalytic nanostructures.
Intrinsic surface passivation of CdTe
Authors: Reese M. O. , Perkins C. L. , Burst J. M. , Farrell S. , Barnes T. M. , Johnston S. W. , Kuciauskas D. , Gessert T. A. , Metzger W. K.
Published: October 2015

Recombination is critically limiting in CdTe devices such as solar cells and detectors, with much of it occurring at or near the surface. In this work, we explore different routes to passivate p-type CdTe surfaces without any intentional extrinsic passivation layers. To provide deeper insight into the passivation routes, we uniquely correlate a set of characterization methods: surface analysis and time-resolved spectroscopy. We study two model systems: nominally undoped single crystals and large-grain polycrystalline films. We examine several strategies to reduce surface recombination velocity. First, we study the effects of removing surface contaminants while maintaining a near-stoichiometric surface. Then we examine stoichiometric thermally reconstructed surfaces. We also investigate the effects of shifting the surface stoichiometry by both “subtractive” (wet chemical etches) and “additive” (ampoule anneals and epitaxial growth) means. We consistently find for a variety of methods that a highly ordered stoichiometric to Cd-rich surface shows a significant reduction in surface recombination, whereas a Te-rich surface has high recombination and propose a mechanism to explain this. While as-received single crystals and as-deposited polycrystalline films have surface recombination velocities in the range of 105–106 cm/s, we find that several routes can reduce surface recombination velocities to <2.5 × 104 cm/s.
The formation and structure of Olympic gels
Authors: Fischer J. , Lang M. , Sommer J.-U.
Published: October 2015

Different methods for creating Olympic gels are analyzed using computer simulations. First ideal reference samples are obtained from freely interpenetrating semi-dilute solutions and melts of cyclic polymers. The distribution of pairwise concatenations per cyclic molecule is given by a Poisson-distribution and can be used to describe the elastic structure of the gels. Several batches of linear chains decorated with different selectively binding groups at their ends are mixed in the “DNA Origami” technique and network formation is realized. While the formation of cyclic molecules follows mean field predictions below overlap of the precursor molecules, an enhanced ring formation above overlap is found that is not explained by mean field arguments. The “progressive construction” method allows to create Olympic gels with a single reaction step from a concentrated mixture of large compressed rings with a low weight fraction of short chains that are below overlap concentration. This method, however, is limited by the difficulty to obtain a sufficiently high degree of polymerization of the large rings.
Optimal conditions for opening of membrane pore by amphiphilic peptides
Authors: Kabelka Ivo , Vácha Robert
Published: October 2015

Amphiphilic peptides can interact with biological membranes and severely affect their barrier and signaling functions. These peptides, including antimicrobial peptides, can self-assemble into transmembrane pores that cause cell death. Despite their medical importance, the conditions required for pore formation remain elusive. Monte Carlo simulations with coarse-grained models enabled us to calculate the free energies of pore opening under various conditions. In agreement with oriented circular dichroism experiments, a high peptide-to-lipid ratio was found to be necessary for spontaneous pore assembly. The peptide length has a non-monotonic impact on pore formation, and the optimal length matches with the membrane thickness. Furthermore, the hydrophobicity of the peptide ends and the mutual positions of peptides on the membrane play a role.
The multiscale coarse-graining method. XI. Accurate interactions based on the centers of charge of coarse-grained sites
Authors: Cao Zhen , Voth Gregory A.
Published: October 2015

It is essential to be able to systematically construct coarse-grained (CG) models that can efficiently and accurately reproduce key properties of higher-resolution models such as all-atom. To fulfill this goal, a mapping operator is needed to transform the higher-resolution configuration to a CG configuration. Certain mapping operators, however, may lose information related to the underlying electrostatic properties. In this paper, a new mapping operator based on the centers of charge of CG sites is proposed to address this issue. Four example systems are chosen to demonstrate this concept. Within the multiscale coarse-graining framework, CG models that use this mapping operator are found to better reproduce the structural correlations of atomistic models. The present work also demonstrates the flexibility of the mapping operator and the robustness of the force matching method. For instance, important functional groups can be isolated and emphasized in the CG model.
A novel simplified Bernoulli trials collision scheme in the direct simulation Monte Carlo with intelligence over particle distances
Authors: Goshayeshi Bijan , Roohi Ehsan , Stefanov Stefan
Published: October 2015

This work deals with the development of an intelligent inter-particle collision scheme using the Direct Simulation Monte Carlo (DSMC) method. Conventional DSMC collision schemes cannot perceive collision distances by their own routines and, consequently, must rely on other techniques to provide a choice of collision pairs with a smaller inter-particle space. Here, we propose a modification of the Simplified Bernoulli Trials (SBT) scheme, called the Intelligent Simplified Bernoulli Trials (ISBT) scheme, which can create pseudo-circular subcells that reduce approximately 25%–32% of the mean collision separation distance. The ISBT scheme tries to arrange the particle indexing and collision acceptance-rejection of the SBT scheme in a way that leads to the formation of virtual clusters. These inner-cell clusters then will cause the selection of the “near-neighbor” pair, which leads to smaller mean collision separation distances. Different low- and high-speed test cases, e.g., lid-driven cavity flow, steady hypersonic flow over a two-dimensional cylinder, and Mach 15.6 nitrogen flow over a 25°–55° axisymmetric biconic, are selected to assess the accuracy and efficiency of the ISBT collision scheme.
Reconstruction of chaotic saddles by classification of unstable periodic orbits: Kuramoto-Sivashinsky equation
Authors: Saiki Yoshitaka , Yamada Michio , Chian Abraham C.-L. , Miranda Rodrigo A. , Rempel Erico L.
Published: October 2015

The unstable periodic orbits (UPOs) embedded in a chaotic attractor after an attractor merging crisis (MC) are classified into three subsets, and employed to reconstruct chaotic saddles in the Kuramoto-Sivashinsky equation. It is shown that in the post-MC regime, the two chaotic saddles evolved from the two coexisting chaotic attractors before crisis can be reconstructed from the UPOs embedded in the pre-MC chaotic attractors. The reconstruction also involves the detection of the mediating UPO responsible for the crisis, and the UPOs created after crisis that fill the gap regions of the chaotic saddles. We show that the gap UPOs originate from saddle-node, period-doubling, and pitchfork bifurcations inside the periodic windows in the post-MC chaotic region of the bifurcation diagram. The chaotic attractor in the post-MC regime is found to be the closure of gap UPOs.
Structural, thermal, and photoacoustic study of nanocrystalline Cr3Ge produced by mechanical alloying
Authors: Prates P. B. , Maliska A. M. , Ferreira A. S. , Poffo C. M. , Borges Z. V. , de Lima J. C. , de Biasi R. S.
Published: October 2015

A thermodynamic analysis of the Cr-Ge system suggested that it was possible to produce a nanostructured Cr3Ge phase by mechanical alloying. The same analysis showed that, due to low activation energies, Cr-poor crystalline and/or amorphous alloy could also be formed. In fact, when the experiment was performed, Cr11Ge19 and amorphous phases were present for small milling times. For milling times larger than 15 h these additional phases decomposed and only the nanostructured Cr3Ge phase remained up to the highest milling time used (32 h). From the differential scanning calorimetry measurements, the Avrami exponent n was obtained, indicating that the nucleation and growth of the nanostructured Cr3Ge phase may be restricted to one or two dimensions, where the Cr and Ge atoms diffuse along the surface and grain boundaries. In addition, contributions from three-dimensional diffusion with a constant nucleation rate may be present. The thermal diffusivity of the nanostructured Cr3Ge phase was determined by photoacoustic absorption spectroscopy measurements.
Nested sampling of isobaric phase space for the direct evaluation of the isothermal-isobaric partition function of atomic systems
Authors: Wilson Blake A. , Gelb Lev D. , Nielsen Steven O.
Published: October 2015

Nested Sampling (NS) is a powerful athermal statistical mechanical sampling technique that directly calculates the partition function, and hence gives access to all thermodynamic quantities in absolute terms, including absolute free energies and absolute entropies. NS has been used predominately to compute the canonical (NVT) partition function. Although NS has recently been used to obtain the isothermal-isobaric (NPT) partition function of the hard sphere model, a general approach to the computation of the NPT partition function has yet to be developed. Here, we describe an isobaric NS (IBNS) method which allows for the computation of the NPT partition function of any atomic system. We demonstrate IBNS on two finite Lennard-Jones systems and confirm the results through comparison to parallel tempering Monte Carlo. Temperature-entropy plots are constructed as well as a simple pressure-temperature phase diagram for each system. We further demonstrate IBNS by computing part of the pressure-temperature phase diagram of a Lennard-Jones system under periodic boundary conditions.
Electroforming free resistive switching memory in two-dimensional VOx nanosheets
Authors: Hota M. K. , Nagaraju D. H. , Hedhili M. N. , Alshareef H. N.
Published: October 2015

We report two-dimensional VOx nanosheets containing multi-oxidation states (V5+, V4+, and V3+), prepared by a hydrothermal process for potential applications in resistive switching devices. The experimental results demonstrate a highly reproducible, electroforming-free, low SET bias bipolar resistive switching memory performance with endurance for more than 100 cycles maintaining OFF/ON ratio of ∼60 times. These devices show better memory performance as compared to previously reported VOx thin film based devices. The memory mechanism in VOx is proposed to be originated from the migration of oxygen vacancies/ions, an influence of the bottom electrode and existence of multi-oxidation states.
Evolution of structural and dynamic heterogeneities during elastic to plastic transition in metallic glass
Authors: Zhao L. Z. , Li Y. Z. , Xue R. J. , Wang W. H. , Bai H. Y.
Published: October 2015

We investigate the evolution of microscopically localized flow under a constant applied strain in apparent elastic region of a prototypical metallic glass (MG). The distribution and evolution of energy barriers and relaxation time spectra of the activated flow units in MG with time are obtained via activation-relaxation method. The results show that the unstable nano-scale liquid-like regions acting as flow units in the glass can be activated by external stress, and their evolution with time shows a crossover from localized activation to cascade as the proportion of the flow units reaches a critical percolation value. The flow unit evolution leads to a mechanical elastic-to-plastic transition or macroscopic plastic flow. A plausible diagram involved in time, stress, and temperature is established to understand the deformations and the flow mechanisms of MGs and could provide insights on the intriguing dilemmas of glassy nature, the flow units, and their correlations with the deformation behaviors in MGs.
Self-generated zonal flows in the plasma turbulence driven by trapped-ion and trapped-electron instabilities
Authors: Drouot T. , Gravier E. , Reveille T. , Collard M.
Published: October 2015

This paper presents a study of zonal flows generated by trapped-electron mode and trapped-ion mode micro turbulence as a function of two plasma parameters—banana width and electron temperature. For this purpose, a gyrokinetic code considering only trapped particles is used. First, an analytical equation giving the predicted level of zonal flows is derived from the quasi-neutrality equation of our model, as a function of the density fluctuation levels and the banana widths. Then, the influence of the banana width on the number of zonal flows occurring in the system is studied using the gyrokinetic code. Finally, the impact of the temperature ratio Te/Ti on the reduction of zonal flows is shown and a close link is highlighted between reduction and different gyro-and-bounce-average ion and electron density fluctuation levels. This reduction is found to be due to the amplitudes of gyro-and-bounce-average density perturbations ne and ni gradually becoming closer, which is in agreement with the analytical results given by the quasi-neutrality equation.
Study of self-consistent particle flows in a plasma blob with particle-in-cell simulations
Authors: Hasegawa Hiroki , Ishiguro Seiji
Published: October 2015

The self-consistent particle flows in a filamentary coherent structure along the magnetic field line in scrape-off layer (SOL) plasma (plasma blob) have been investigated by means of a three-dimensional electrostatic particle-in-cell simulation code. The presence of the spiral current system composed of the diamagnetic and parallel currents in a blob is confirmed by the particle simulation without any assumed sheath boundary models. Furthermore, the observation of the electron and ion parallel velocity distributions in a blob shows that those distributions are far from Maxwellian due to modification with the sheath formation and that the electron temperature on the higher potential side in a blob is higher than that on the lower potential side. Also, it is found that the ions on the higher potential side are accelerated more intensively along the magnetic field line than those on the lower potential side near the edge. This study indicates that particle simulations are able to provide an exact current closure to analysis of blob dynamics and will bring more accurate prediction of plasma transport in the SOL without any empirical assumptions.
Opening the way to molecular cycloaddition of large molecules on supported silicene
Authors: Stephan Régis , Hanf Marie-Christine , Sonnet Philippe
Published: October 2015

Within density functional theory, the adsorption of the H2Pc molecule on the (3 × 3) silicene/(4 × 4) Ag(111) surface has been investigated. We observe an electronic redistribution in the central macrocycle of the H2Pc molecule and the formation of two Si − N covalent bonds between the molecule and the silicene, in agreement with a cycloaddition reaction. However, while on SiC(0001)(3 × 3) or Si(111)(3×3)R30°-boron, the H2Pc molecule remains planar, and the H2Pc molecule takes a butterfly conformation on the silicene/Ag substrate due to an electrostatic or a polarization repulsion between the molecule and the silicene. Our study opens a way to the experimental adsorption of large organic molecules on supported silicene.
The polarized interface between quadrupolar insulators: Maxwell stress tensor, surface tension, and potential
Authors: Slavchov Radomir I. , Dimitrova Iglika M. , Ivanov Tzanko
Published: October 2015

The quadrupolar Maxwell electrostatic equations predict several qualitatively different results compared to Poisson’s classical equation in their description of the properties of a dielectric interface. All interfaces between dielectrics possess surface dipole moment which results in a measurable surface potential jump. The surface dipole moment is conjugated to the bulk quadrupole moment density (the quadrupolarization) similarly to Gauss’s relation between surface charge and bulk polarization. However, the classical macroscopic Maxwell equations completely neglect the quadrupolarization of the medium. Therefore, the electrostatic potential distribution near an interface of intrinsic dipole moment can be correctly described only within the quadrupolar macroscopic equations of electrostatics. They predict that near the polarized interface a diffuse dipole layer exists, which bears many similarities to the diffuse charge layer near a charged surface, in agreement with existing molecular dynamics simulation data. It turns out that when the quadrupole terms are kept in the multipole expansion of the laws of electrostatics, the solutions for the potential and the electric field are continuous functions at the surface. A well-defined surface electric field exists, interacting with the adsorbed dipoles. This allows for a macroscopic description of the surface dipole-surface dipole and the surface dipole-bulk quadrupole interactions. They are shown to have considerable contribution to the interfacial tension—of the order of tens of mN/m! To evaluate it, the Maxwell stress tensor in quadrupolar medium is deduced, including the electric field gradient action on the quadrupoles, as well as quadrupolar image force and quadrupolar electrostriction. The dependence of the interfacial tension on the external normal electric field (the dielectrocapillary curve) is predicted and the dielectric susceptibility of the dipolar double layer is related to the quadrupolarizabilities of the bulk phases and the intrinsic polarization of the interface. The coefficient of the dielectro-Marangoni effect (surface flow due to gradient of the normal electric field) is found. A model of the Langevin type for the surface dipole moment and the intrinsic surface polarizability is presented.
Discharge regime of non-ambipolarity with a self-induced steady-state magnetic field in plasma sources with localized radio-frequency power deposition
Authors: Shivarova A. , Lishev St. , Todorov D. , Paunska Ts.
Published: October 2015

Involving the idea for the Biermann effect known from space physics as well as recent discussions on non-ambipolarity of the electron and ion fluxes in low-pressure discharges, the study builds the discharge pattern in a source with localized RF power deposition outside the region of high electron density. A vortex dc current flowing in an RF discharge and a steady-state magnetic field induced by this current govern the discharge behavior. Owing to a shift in the positions of the electron-density and plasma-potential maxima, the dc current is driven with the purpose of keeping the conservativity of the dc field in the discharge. The results present the spatial structure of a discharge in a regime of non-ambipolarity of the electron and ion fluxes, including its modifications by the magnetic field.
Discrimination of molecular thin films by surface-sensitive time-resolved optical spectroscopy
Authors: Peli Simone , Nembrini Nicola , Damin Francesco , Chiari Marcella , Giannetti Claudio , Banfi Francesco , Ferrini Gabriele
Published: October 2015

An optical discrimination technique, tailored to nanometric-sized, low optical absorbance molecular complexes adhering to thin metal films, is proposed and demonstrated. It is based on a time-resolved evanescent-wave detection scheme in conjunction with hierarchical cluster analysis and principal value decomposition. The present approach aims to differentiate among molecular films based on statistical methods, without using previous detailed knowledge of the physical mechanisms responsible for the detected signal. The technique is open to integration in lab-on-a-chip architectures and nanoscopy platforms for applications ranging from medical screening to material diagnostics.
Impact of potassium doping on the electronic structure of tetracene and pentacene: An electron energy-loss study
Authors: Roth Friedrich , Knupfer Martin
Published: October 2015

We report the doping induced changes of the electronic structure of tetracene and pentacene probed by electron energy-loss spectroscopy in transmission. A comparison between the dynamic response of undoped and potassium-intercalated tetracene and pentacene emphasizes the appearance of a new excitation feature in the former gap upon potassium addition. Interestingly, the momentum dependency of this new excitation shows a negative dispersion. Moreover, the analysis of the C 1s and K 2p core-level excitation results in a significantly lower doping level compared to potassium doped picene, a recently discovered superconductor. Therefore, the present electronic structure investigations open a new pathway to better understand the exceptional differences between acenes and phenacene and their divergent behavior upon alkali doping.
Polarization-induced Zener tunnel diodes in GaN/InGaN/GaN heterojunctions
Authors: Yan Xiaodong , Li Wenjun , Islam S. M. , Pourang Kasra , Xing Huili (Grace) , Fay Patrick , Jena Debdeep
Published: October 2015

By the insertion of thin InxGa1−xN layers into Nitrogen-polar GaN p-n junctions, polarization-induced Zener tunnel junctions are studied. The reverse-bias interband Zener tunneling current is found to be weakly temperature dependent, as opposed to the strongly temperature-dependent forward bias current. This indicates tunneling as the primary reverse-bias current transport mechanism. The Indium composition in the InGaN layer is systematically varied to demonstrate the increase in the interband tunneling current. Comparing the experimentally measured tunneling currents to a model helps identify the specific challenges in potentially taking such junctions towards nitride-based polarization-induced tunneling field-effect transistors.
White organic light-emitting diodes with 4 nm metal electrode
Authors: Lenk Simone , Schwab Tobias , Schubert Sylvio , Müller-Meskamp Lars , Leo Karl , Gather Malte C. , Reineke Sebastian
Published: October 2015

We investigate metal layers with a thickness of only a few nanometers as anode replacement for indium tin oxide (ITO) in white organic light-emitting diodes (OLEDs). The ultrathin metal electrodes prove to be an excellent alternative that can, with regard to the angular dependence and efficiency of the OLED devices, outperform the ITO reference. Furthermore, unlike ITO, the thin composite metal electrodes are readily compatible with demanding architectures (e.g., top-emission or transparent OLEDs, device unit stacking, etc.) and flexible substrates. Here, we compare the sheet resistance of both types of electrodes on polyethylene terephthalate for different bending radii. The electrical performance of ITO breaks down at a radius of 10 mm, while the metal electrode remains intact even at radii smaller than 1 mm.
Low frequency azimuthal stability of the ionization region of the Hall thruster discharge. II. Global analysis
Authors: Escobar D. , Ahedo E.
Published: October 2015

The linear stability of the Hall thruster discharge is analysed against axial-azimuthal perturbations in the low frequency range using a time-dependent 2D code of the discharge. This azimuthal stability analysis is spatially global, as opposed to the more common local stability analyses, already afforded previously (D. Escobar and E. Ahedo, Phys. Plasmas 21(4), 043505 (2014)). The study covers both axial and axial-azimuthal oscillations, known as breathing mode and spoke, respectively. The influence on the spoke instability of different operation parameters such as discharge voltage, mass flow, and thruster size is assessed by means of different parametric variations and compared against experimental results. Additionally, simplified models are used to unveil and characterize the mechanisms driving the spoke. The results indicate that the spoke is linked to azimuthal oscillations of the ionization process and to the Bohm condition in the transition to the anode sheath. Finally, results obtained from local and global stability analyses are compared in order to explain the discrepancies between both methods.
Alternating current-driven microwave loss modulation in a fluxonic metamaterial
Authors: Dobrovolskiy Oleksandr V. , Huth Michael , Shklovskij Valerij A.
Published: October 2015

We introduce a fluxonic metamaterial on the basis of nanopatterned superconducting Nb microstrips and employ it for modulation and synthesis of quantized loss levels in the lower GHz range by a sine-wave quasistatic ac drive. The nanopatterns are uniaxial nanogrooves with identical and different slope steepness, which induce a pinning potential of the washboard type for Abrikosov vortices. For the fundamental matching field, when the location of vortex rows geometrically matches the nanogrooves, the following effects are observed: The forward transmission coefficient S21(f) of the microstrips can be controllably modulated within a range of about 3 dB by the ac. For the sample with symmetric grooves, depending on the choice of the operation point in the current-voltage curve, the shape and the duty cycle of the output signal can be tuned. For the sample with asymmetric grooves, depending on the ac amplitude, a sine-to-triangular or a sine-to-rectangular pulse shape conversion is observed. The possibility of synthesizing quantized loss levels by a serial connection of the two samples with different nanopatterns is exemplified and can be used for the development of multilevel excess-loss-based fluxonic devices.
Metamaterials-based sensor to detect and locate nonlinear elastic sources
Authors: Gliozzi Antonio S. , Miniaci Marco , Bosia Federico , Pugno Nicola M. , Scalerandi Marco
Published: October 2015

In recent years, acoustic metamaterials have attracted increasing scientific interest for very diverse technological applications ranging from sound abatement to ultrasonic imaging, mainly due to their ability to act as band-stop filters. At the same time, the concept of chaotic cavities has been recently proposed as an efficient tool to enhance the quality of nonlinear signal analysis, particularly in the ultrasonic/acoustic case. The goal of the present paper is to merge the two concepts in order to propose a metamaterial-based device that can be used as a natural and selective linear filter for the detection of signals resulting from the propagation of elastic waves in nonlinear materials, e.g., in the presence of damage, and as a detector for the damage itself in time reversal experiments. Numerical simulations demonstrate the feasibility of the approach and the potential of the device in providing improved signal-to-noise ratios and enhanced focusing on the defect locations.
Voltage-controlled magnetic anisotropy in Fe|MgO tunnel junctions studied by x-ray absorption spectroscopy
Authors: Miwa Shinji , Matsuda Kensho , Tanaka Kazuhito , Kotani Yoshinori , Goto Minori , Nakamura Tetsuya , Suzuki Yoshishige
Published: October 2015

In this study, voltage-controlled magnetic anisotropy (VCMA) in Fe|MgO tunnel junctions was investigated via the magneto-optical Kerr effect, soft x-ray absorption spectroscopy, and magnetic circular dichroism spectroscopy. The Fe|MgO tunnel junctions showed enhanced perpendicular magnetic anisotropy under external negative voltage, which induced charge depletion at the Fe|MgO interface. Despite the application of voltages of opposite polarity, no trace of chemical reaction such as a redox reaction attributed to O2− migration was detected in the x-ray absorption spectra of the Fe. The VCMA reported in the Fe|MgO-based magnetic tunnel junctions must therefore originate from phenomena associated with the purely electric effect, that is, surface electron doping and/or redistribution induced by an external electric field.
Distribution of free carriers near heavily-doped epitaxial surfaces of n-type Ge(100) upon HF and HCl treatments
Authors: Park S. J. , Bolotov L. , Uchida N. , Tada T.
Published: October 2015

Carrier distributions near n-type epitaxially-grown Ge(100) surfaces with high impurity concentrations (1 × 1020 cm−3) were studied using high resolution electron energy loss spectroscopy (HREELS) upon surface treatments in aqueous solutions of HF and HCl. After surface treatments with HCl and HF, the molecular vibration modes distinctly showed either chloride or hydride terminations of Ge surfaces with negligible oxidation. The free-carrier concentration profile was inferred from the conduction band plasmon measurements as a function of the incident electron energies employing a dielectric theory simulation with a 4-layer structure and an effective electron mass of 0.02m0. A carrier-free layer of 40 and 24 Å were derived for HCl- and HF-treated Ge(100), respectively. The surface band bending was estimated to be 0.32 eV for HF-treated Ge. HCl-treated Ge surfaces showed a band bending of 0.91 eV attributed to the strong effect of the surface Cl-Ge dipole.
Investigation of the on-axis atom number density in the supersonic gas jet under high gas backing pressure by simulation
Authors: Chen Guanglong , Boldarev A. S. , Geng Xiaotao , Xu Yi , Cao Yunjiu , Mi Yiming , Zhang Xiuli , Wang Lili , Kim Dong Eon
Published: October 2015

The supersonic gas jets from conical nozzles are simulated using 2D model. The on-axis atom number density in gas jet is investigated in detail by comparing the simulated densities with the idealized densities of straight streamline model in scaling laws. It is found that the density is generally lower than the idealized one and the deviation between them is mainly dependent on the opening angle of conical nozzle, the nozzle length and the gas backing pressure. The density deviation is then used to discuss the deviation of the equivalent diameter of a conical nozzle from the idealized deq in scaling laws. The investigation on the lateral expansion of gas jet indicates the lateral expansion could be responsible for the behavior of the density deviation. These results could be useful for the estimation of cluster size and the understanding of experimental results in laser-cluster interaction experiments.