bluuebunny/crossref_metadata_2025 huggingface dataset:
Layer number identification of intrinsic and defective multilayered graphenes up to 100 layers by the Raman mode intensity from substrates
Authors: Li Xiao-Li , Qiao Xiao-Fen , Han Wen-Peng , Lu Yan , Tan Qing-Hai , Liu Xue-Lu , Tan Ping-Heng
Published: April 2015

Raman signals from Si substrates have been used as a robust, fast and nondestructive way to probe the layer number of graphene flakes up to 100 layers.
Regioselective sulfamoylation at low temperature enables concise syntheses of putative small molecule inhibitors of sulfatases
Authors: Miller Duncan C. , Carbain Benoit , Beale Gary S. , Alhasan Sari F. , Reeves Helen L. , Baisch Ulrich , Newell David R. , Golding Bernard T. , Griffin Roger J.
Published: April 2015

An improved synthesis from d-glucosamine of a purported Sulf-2 inhibitor is described, with assay data for this compound and analogues showing only weak inhibition of Sulf-2, and sulfatases ARSA or ARSB.
Facile synthesis and stereo-resolution of chiral 1,2,3-triazoles
Authors: Shi Ye , Ye Xiaohan , Gu Qiang , Shi Xiaodong , Song Zhiguang
Published: April 2015

We describe herein the first facile synthesis of chiral triazoles through side chain functionalization.
Unique photophysical properties of 9-styryl-1,2-dihydropyrrolo[3,4-β]indolizin-3-one and its efficient synthesis via direct C–H activation
Authors: Choi Eun Joung , Park Seung Bum
Published: April 2015

A styryl Seoul-Fluor (SF) skeleton was rationally designed by introducing an olefin unit at the C-9 of 1,2-dihydropyrrolo[3,4-β]indolizin-3-one via regioselective direct C–H activation, affording average 39 nm of bathochromic shift.
Synthesis and P-glycoprotein induction activity of colupulone analogs
Authors: Bharate Jaideep B. , Batarseh Yazan S. , Wani Abubakar , Sharma Sadhana , Vishwakarma Ram A. , Kaddoumi Amal , Kumar Ajay , Bharate Sandip B.
Published: April 2015

A diprenylated acylphloroglucinol was identified as a potent P-gp inducer and showing ability to increase amyloid-beta transport across BBB, thus it is a potential anti-Alzheimer lead compound.
Organocatalytic diastereoselective synthesis of chiral decalines through the domino Claisen–Schmidt/Henry reaction
Authors: Shashank Adluri B. , Ramachary Dhevalapally B.
Published: April 2015

General and operative domino Claisen–Schmidt/Henry (CS/H) reaction has been revealed to obtain highly substituted chiral decalines in good yields with excellent ees and des by using push–pull enamine catalysis.
Ultralong mesoporous ZnO nanowires grown via room temperature self-assembly of ZnO nanoparticles for enhanced reversible storage in lithium ion batteries
Authors: Yang Hong-Jie , Lim Suh-Ciuan , He Sheng-Yan , Tuan Hsing-Yu
Published: April 2015

Template-free synthesis of ultralong mesoporous ZnO nanowires (up to 50 μm) was developed. Compared to ZnO powder, the obtained porous ZnO nanowires show enhanced reversible storage as lithium ion battery anodes.
High sulfur loaded carbon aerogel cathode for lithium–sulfur batteries
Authors: Balakumar K. , Kalaiselvi N.
Published: April 2015

Carbon aerogel, capable of performing as a conductive additive and potential host to accommodate higher sulfur content offers better polysulfide confining matrix also to exhibit appreciable electrochemical behavior with regard to 60 wt% sulfur.
Porous membranes designed from bi-phasic polymeric blends containing silver decorated reduced graphene oxide synthesized via a facile one-pot approach
Authors: Kumar S Mural Prasanna , Sharma Maya , Shukla Abhinaya , Bhadra Sambhu , Padmanabhan Babu , Madras Giridhar , Bose Suryasarathi
Published: April 2015

In this work, porous membranes were designed by selectively etching the PEO phase, by water, from a melt-mixed PE/PEO blend.
Novel chitosan-based/montmorillonite/palladium hybrid microspheres as heterogeneous catalyst for Sonogashira reactions
Authors: Zeng Minfeng , Yuan Xia , Zuo Shufeng , Qi Chenze
Published: April 2015

The objective of this study was to develop novel chitosan-based/montmorillonite/palladium (CS/MMT/Pd) hybrid microsphere catalysts with improved properties for use in Sonogashira reactions.
Fabrication of attapulgite/carbon composites from spent bleaching earth for the efficient adsorption of methylene blue
Authors: Tang Jie , Mu Bin , Zong Li , Zheng Maosong , Wang Aiqin
Published: April 2015

In this work, one-dimensional attapulgite/carbon composites were prepared by a one-step carbonization process using the residual organic matter of spent bleaching earth as a low-cost available carbon precursor.
Self-assembly of two high-nuclearity manganese calixarene-phosphonate clusters: diamond-like Mn16 and drum-like Mn14
Authors: Su Kongzhao , Jiang Feilong , Qian Jinjie , Pan Jie , Pang Jiandong , Wan Xiuyan , Hu Falu , Hong Maochun
Published: April 2015

Variation of the phosphonic acid “converts” a tetradecanuclear drum-like MnII14 cluster (1) into a hexadecanuclear diamond-like MnII16 cluster (2).
Synthesis and characterization of amino-functionalized poly(propylene carbonate)
Authors: Song Pengfei , Shang Yingqi , Chong Siying , Zhu Xiaogang , Xu Haidong , Xiong Yubing
Published: April 2015

The first synthesis of amino-functionalized poly(propylene carbonate) (PPC) by terpolymerization of carbon dioxide (CO2), propylene oxide (PO), and N,N-dibenzyl amino glycidol (DBAG) following the removal of benzyl protecting groups.
A strong charge-transfer effect in surface-enhanced Raman scattering induced by valence electrons of actinide elements
Authors: Gao Yang , Chen Lei , Dai Xing , Song Ruixia , Wang Bo , Wang Zhigang
Published: April 2015

The 6d electrons of Ac atom involved in excited transitions induce a strong CT-SERS enhancement which can be tuned by changing the conformation of pyridine-Ac@Au7 complexes.
Oxidative coupling of 2-naphthol to (R)/(S)-BINOL by MCM-41 supported Mn-chiral Schiff base complexes
Authors: Bania Kusum K. , Karunakar G. V. , Satyanarayana Lanka
Published: April 2015

Conversion of 2-naphthol toC2-symmetric BINOL is achieved in 91% ee in the presence of an Mn-Schiff base chiral catalyst supported on MCM-41.
The effect of the microstructure on the corrosion behavior of N5 superalloy in a molten (Li,Na,K)F eutectic salt
Authors: Wang Yan Li , Wang Qian , Liu Hui Jun , Zeng Chao Liu
Published: April 2015

The corrosion of structural materials in molten fluorides, influenced by the microstructure of the structural materials, is considered to be a great challenge for the development of molten salt reactors using fluorides as fuel carriers or coolants.
One-pot chemo/regio/stereoselective generation of a library of functionalized spiro-oxindoles/pyrrolizines/pyrrolidines from α-aroylidineketene dithioacetals
Authors: Dhanalakshmi Pandi , Babu Seenivasagaperumal Sriram , Thimmarayaperumal Solaimalai , Shanmugam Sivakumar
Published: April 2015

An efficient chemo/regio/stereoselective synthesis of novel and functionalized spiro-oxindole/pyrrolizine/pyrrolidine scaffolds has been achieved.
Pd-catalyzed asymmetric hydrogenation of fluorinated aromatic pyrazol-5-ols via capture of active tautomers
Authors: Chen Zhang-Pei , Chen Mu-Wang , Shi Lei , Yu Chang-Bin , Zhou Yong-Gui
Published: April 2015

Here we explore a novel strategy for asymmetric hydrogenation of aromatic pyrazol-5-olsviacapture of the active tautomers.
One-step synthesis of three-dimensional graphene/multiwalled carbon nanotubes/Pd composite hydrogels: an efficient recyclable catalyst for Suzuki coupling reactions
Authors: Song Hui-qing , Zhu Qian , Zheng Xue-jing , Chen Xing-guo
Published: April 2015

In this paper, a simple one-pot hydrothermal procedure to create three-dimensional (3D) graphene/multiwalled carbon nanotube/Pd (G/MWCNT/Pd) composite hydrogels with a unique porous nanostructure was reported.
High-performance LiMnPO4 nanorods synthesized via a facile EG-assisted solvothermal approach
Authors: Hong Ye , Tang Zilong , Wang Shitong , Quan Wei , Zhang Zhongtai
Published: April 2015

Novel LiMnPO4 nanorods with a thin thickness along the [010] direction have been synthesized by the effective regulation of the EG solvent and applied as cathode materials for lithium-ion batteries.
Subunits controlled synthesis of α-Fe2O3 multi-shelled core–shell microspheres and their effects on lithium/sodium ion battery performances
Authors: Wu Zhen-guo , Zhong Yan-jun , Liu Jie , Wu Jiao-hong , Guo Xiao-dong , Zhong Ben-he , Zhang Zhi-ye
Published: April 2015

Two kinds of Fe2O3 yolk–shell microspheres with different subunits were synthesized by a solvothermal method. The electrochemical performances of lithium and sodium ion batteries using Fe2O3 anodes were greatly affected by the distinctive subunits.
Manganese dioxide-anchored three-dimensional nitrogen-doped graphene hybrid aerogels as excellent anode materials for lithium ion batteries
Authors: Sui Zhu-Yin , Wang Caiyun , Shu Kewei , Yang Quan-Sheng , Ge Yu , Wallace Gordon G. , Han Bao-Hang
Published: April 2015

MnO2/nitrogen-doped graphene aerogels prepared via a redox process between KMnO4 and carbon demonstrate excellent electrochemical properties in Li-ion batteries.
A mussel-inspired chitooligosaccharide based multidentate ligand for highly stabilized nanoparticles
Authors: Lu Chichong , Park Min Kyu , Lu Chenxin , Lee Young Haeng , Chai Kyu Yun
Published: April 2015

A mussel-inspired poly(ethylene glycol)-grafted-chitooligosaccharide based multidentate ligand (ML) is designed for preparing robust biocompatible iron oxide nanoparticles. The successfulin vivoMRI application confirmed their suitability for biomedical applications.
Reliability of the step phase detection using inertial measurement units: pilot study
Authors: Sessa Salvatore , Zecca Massimiliano , Bartolomeo Luca , Takashima Takamichi , Fujimoto Hiroshi , Takanishi Atsuo
Published: April 2015

The use of inertial sensors for the gait event detection during a long‐distance walking, for example, on different surfaces and with different walking patterns, is important to evaluate the human locomotion. Previous studies demonstrated that gyroscopes on the shank or foot are more reliable than accelerometers and magnetometers for the event detection in case of normal walking. However, these studies did not link the events with the temporal parameters used in the clinical practice; furthermore, they did not clearly verify the optimal position for the sensors depending on walking patterns and surface conditions. The event detection quality of the sensors is compared with video, used as ground truth, according to the parameters proposed by the Gait and Clinical Movement Analysis Society. Additionally, the performance of the sensor on the foot is compared with the one on the shank. The comparison is performed considering both normal walking and deviations to the walking pattern, on different ground surfaces and with or without constraints on movements. The preliminary results show that the proposed methodology allows reliable detection of gait events, even in case of abnormal footfall and in slipping surface conditions, and that the optimal location to place the sensors is the shank.
Corrective control for transient faults with application to configuration controllers
Authors: Yang Jung‐Min , Kwak Seong Woo
Published: April 2015

A novel design methodology of corrective control is proposed for fault‐tolerance against transient faults in input/output asynchronous sequential machines. The main objective is to lessen controller complexity by proposing a structure of corrective control that employs no state observer, which is required in the former studies for input/output control of asynchronous machines. The form of the output feedback is also simplified as a unit character instead of bursts. Although the exact identification of the machine's state is infeasible, the proposed controller achieves immediate fault‐tolerance against transient faults that cause unauthorised state transitions. As a case study, the authors apply the proposed control scheme to implementing configuration controllers for space‐borne field programmable gate array with hardware redundancy in which single event upset faults may happen by the radiation effect.
Incorporating approximate rotational invariance into two‐dimensional S‐transform
Authors: Cheng Chun Hing , Pradhan Pyari Mohan , Mitchell Joseph Ross
Published: April 2015

The discrete two‐dimensional (2D) S‐transform (ST‐2D) is a space‐frequency representation that provides the local spectrum at each pixel in an image. The inherent localisation properties of the ST‐2D make it a preferred candidate for space‐frequency analysis. However, the ST‐2D is sensitive to the image rotation. This limits its use in many image processing applications such as texture analysis. This study describes the rotational sensitivity of the ST‐2D, and explains how this limits its application. To overcome these problems, a novel rotationally invariant S‐transform (RIST) is formulated, and its rotational invariance is investigated. The RIST can provide approximate rotational invariance for magnitudes and complex values over a wide range of rotation angles, but with a trade‐off of higher computation time. The RIST may be useful for many medical, scientific and industrial applications.
Proximity‐effect test for lossy wireless‐device measurements in reverberation chambers
Authors: Aan Den Toorn Joop , Remley Kate A. , Holloway Christopher L. , Ladbury John M. , Wang Chih‐Ming
Published: April 2015

The authors present a test method for quantifying and reducing systematic errors arising from antenna proximity to lossy objects in over‐the‐air performance testing of lossy large‐form‐factor wireless devices. The method determines the extent to which antenna proximity to lossy, large‐form‐factor objects influences the measured reference power transfer function. The test may be used to pre‐characterise a given chamber set‐up in terms of a minimum distance between antennas and lossy objects. They illustrate the use of the method in a total radiated power measurement of a large, commercially available, machine‐to‐machine device, where agreement to anechoic‐chamber measurements is demonstrated to within the measurement uncertainty.
Stellungnahme der Taskforce „Neurostimulation bei Schlafapnoe“ zur Stimulation der oberen Atemwege
Authors: Steffen A. , Heiser C. , Herzog M. , Bergler W. , Rothmeier N. , Maurer J.
Published: April 2015

Die Stimulation der oberen Atemwege kann als Sekundärtherapie der mindestens mittelgradigen obstruktiven Schlafapnoe als wirksame Behandlungsmethode betrachtet werden. Die atmungsgesteuerte Stimulation der oberen Atemwege (geschlossener Kreislauf; Fa. Inspire Medical Systems) weist ein hohes Evidenzniveau mit größeren Patientenkollektiven und längeren Nachbeobachtungszeiten auf, sodass die Einschätzung als sichere und effektive Therapiealternative fundiert erfolgen kann. Ob die Ergebnisse der atmungsunabhängigen Stimulation (offener Kreislauf; Fa. ImThera Medical) mit denen der atmungssynchronen vergleichbar sind, kann zum jetzigen Zeitpunkt nicht beurteilt werden. Es ist jedoch zu erwarten, dass eine erste Einschätzung hierzu nach Abschluss der Studie THN#2 möglich sein wird. Zur weiteren Optimierung beider Verfahren und zu Langzeitergebnissen sind weiterführende klinisch-wissenschaftliche Studien mit für die Verfahren jeweils unterschiedlichen Fragestellungen notwendig. Die Arbeitsgruppe Schlafmedizin der DGHNO begleitet die weitere Entwicklung mithilfe einer im Mai 2014 eigens gegründeten Taskforce „Neurostimulation bei Schlafapnoe“.
Effect of interparticle plasmon coupling and temperature on the optical properties of bimetallic composite nanoparticles with a core-shell structure
Authors: Daneshfar Nader
Published: April 2015

In this work, the optical properties of bimetal composite nanoparticles with a core-shell structure are investigated in the framework of quasi-static and Maxwell-Garnett approximation. The influence of interparticle plasmon coupling and temperature on the optical absorption of bimetallic core-shell nanoparticles is studied while the shell consists of Al and Cu particles. In fact, dependence of the optical absorption and its full width at half maximum on the dielectric constant of the core, host matrix, and embedding medium for both spherical and cylindrical bimetallic nanocomposites is shown. It was found that both the plasmonic shifting and bandwidth are dependent on the volume fraction of metal nanoparticles (filling factors) and the temperature. However, a new plasmon oscillation mode is created and observed in the spectra owing to the interparticle plasmon coupling of different metallic particles which cannot be found in a monometal nanocomposite.
Nonlinear optimals in the asymptotic suction boundary layer: Transition thresholds and symmetry breaking
Authors: Cherubini S. , De Palma P. , Robinet J.-Ch.
Published: April 2015

The effect of a constant homogeneous wall suction on the nonlinear transient growth of localized finite amplitude perturbations in a boundary-layer flow is investigated. Using a variational technique, nonlinear optimal disturbances are computed for the asymptotic suction boundary layer (ASBL) flow, defined as those finite amplitude disturbances yielding the largest energy growth at a given target time T. It is found that homogeneous wall suction remarkably reduces the optimal energy gain in the nonlinear case. Furthermore, mirror-symmetry breaking of the shape of the optimal perturbation appears when decreasing the Reynolds number from 10 000 to 5000, whereas spanwise mirror-symmetry was a robust feature of the nonlinear optimal perturbations found in the Blasius boundary-layer flow. Direct numerical simulations show that the different evolutions of the symmetric and of the non-symmetric initial perturbations are linked to different mechanisms of transport and tilting of the vortices by the mean flow. By bisecting the initial energy of the nonlinear optimal perturbations, minimal energy thresholds for subcritical transition to turbulence have been obtained. These energy thresholds are found to be 1–4 orders of magnitude smaller than those provided in the literature for other transition scenarios. For low to moderate Reynolds numbers, the energy thresholds are found to scale with Re−2, suggesting a new scaling law for transition in the ASBL.
A framework for large eddy simulation of Burgers turbulence based upon spatial and temporal statistical information
Authors: LaBryer A. , Attar P. J. , Vedula P.
Published: April 2015

We present a novel theoretical framework that has the potential not only to improve the reliability and computational efficiency of large-eddy simulation (LES) predictions for turbulent flows but also promises to address a major drawback of many existing constructs of LES, namely, inaccurate predictions for the underlying spatiotemporal structure. In our proposed framework, subgrid models are constructed based upon information that is consistent with the underlying spatiotemporal statistics of the flow. Unlike many pre-existing LES approaches, the proposed subgrid models include non-Markovian memory terms whose origins can be related to the optimal prediction formalism. These optimal subgrid models are studied within the context of the forced Burgers equation. Results indicate that the proposed models perform better than standard LES models by virtue of their ability to better preserve the underlying spatiotemporal statistical structure of the flow. Furthermore, the presence of coarse-grained temporal information in our subgrid models allows for faster simulations (resulting in about an order of magnitude reduction in computational time, in comparison to conventional LES) through the use of larger time steps.
A broadband single-chip transceiver for multi-nuclear NMR probes
Authors: Grisi Marco , Gualco Gabriele , Boero Giovanni
Published: April 2015

In this article, we present an integrated broadband complementary metal-oxide semiconductor single-chip transceiver suitable for the realization of multi-nuclear pulsed nuclear magnetic resonance (NMR) probes. The realized single-chip transceiver can be interfaced with on-chip integrated microcoils or external LC resonators operating in the range from 1 MHz to 1 GHz. The dimension of the chip is about 1 mm2. It consists of a radio-frequency (RF) power amplifier, a low-noise RF preamplifier, a frequency mixer, an audio-frequency amplifier, and fully integrated transmit-receive switches. As specific example, we show its use for multi-nuclear NMR spectroscopy. With an integrated coil of about 150 μm external diameter, a 1H spin sensitivity of about 1.5 × 1013 spins/Hz1/2 is achieved at 7 T.
Magnetic tweezers with high permeability electromagnets for fast actuation of magnetic beads
Authors: Chen La , Offenhäusser Andreas , Krause Hans-Joachim
Published: April 2015

As a powerful and versatile scientific instrument, magnetic tweezers have been widely used in biophysical research areas, such as mechanical cell properties and single molecule manipulation. If one wants to steer bead position, the nonlinearity of magnetic properties and the strong position dependence of the magnetic field in most magnetic tweezers lead to quite a challenge in their control. In this article, we report multi-pole electromagnetic tweezers with high permeability cores yielding high force output, good maneuverability, and flexible design. For modeling, we adopted a piece-wise linear dependence of magnetization on field to characterize the magnetic beads. We implemented a bi-linear interpolation of magnetic field in the work space, based on a lookup table obtained from finite element simulation. The electronics and software were custom-made to achieve high performance. In addition, the effects of dimension and defect on structure of magnetic tips also were inspected. In a workspace with size of 0.1 × 0.1 mm2, a force of up to 400 pN can be applied on a 2.8 μm superparamagnetic bead in any direction within the plane. Because the magnetic particle is always pulled towards a tip, the pulling forces from the pole tips have to be well balanced in order to achieve control of the particle’s position. Active video tracking based feedback control is implemented, which is able to work at a speed of up to 1 kHz, yielding good maneuverability of the magnetic beads.
Continuous refractive index dispersion measurement based on derivative total reflection method
Authors: Deng Zhichao , Wang Jin , Ye Qing , Sun Tengqian , Zhou Wenyuan , Mei Jianchun , Zhang Chunping , Tian Jianguo
Published: April 2015

Traditionally, continuous refractive index dispersion (CRID) measurement of materials with scattering is hard to realize. In this paper, CRID measurement based on the derivative total reflection method (CRIDM-DTRM) is proposed to measure the CRID of both absorption and scattering materials. It effectively determined the CRID of K9 glass, concentrated milk, and 0.5% methyl red solution in the 400-750 nm range with the spectral resolution of about 0.259 nm. For the first time, CRID of a scattering material is measured. CRIDM-DTRM is a useful technique in the field of RID measurement, especially for biotissues and anomalous dispersion materials.
Soft-spring wall based non-periodic boundary conditions for non-equilibrium molecular dynamics of dense fluids
Authors: Ghatage Dhairyashil , Tomar Gaurav , Shukla Ratnesh K.
Published: April 2015

Non-equilibrium molecular dynamics (MD) simulations require imposition of non-periodic boundary conditions (NPBCs) that seamlessly account for the effect of the truncated bulk region on the simulated MD region. Standard implementation of specular boundary conditions in such simulations results in spurious density and force fluctuations near the domain boundary and is therefore inappropriate for coupled atomistic-continuum calculations. In this work, we present a novel NPBC model that relies on boundary atoms attached to a simple cubic lattice with soft springs to account for interactions from particles which would have been present in an untruncated full domain treatment. We show that the proposed model suppresses the unphysical fluctuations in the density to less than 1% of the mean while simultaneously eliminating spurious oscillations in both mean and boundary forces. The model allows for an effective coupling of atomistic and continuum solvers as demonstrated through multiscale simulation of boundary driven singular flow in a cavity. The geometric flexibility of the model enables straightforward extension to nonplanar complex domains without any adverse effects on dynamic properties such as the diffusion coefficient.
Perspective: Insight into reaction coordinates and dynamics from the potential energy landscape
Authors: Wales D. J.
Published: April 2015

This perspective focuses on conceptual and computational aspects of the potential energy landscape framework. It has two objectives: first to summarise some key developments of the approach and second to illustrate how such techniques can be applied using a specific example that exploits knowledge of pathways. Recent developments in theory and simulation within the landscape framework are first outlined, including methods for structure prediction, analysis of global thermodynamic properties, and treatment of rare event dynamics. We then develop a connection between the kinetic transition network treatment of dynamics and a potential of mean force defined by a reaction coordinate. The effect of projection from the full configuration space to low dimensionality is illustrated for an atomic cluster. In this example, where a relatively successful structural order parameter is available, the principal change in cluster morphology is reproduced, but some details are not faithfully represented. In contrast, a profile based on configurations that correspond to the discrete path defined geometrically retains all the barriers and minima. This comparison provides insight into the physical origins of “friction” effects in low-dimensionality descriptions of dynamics based upon a reaction coordinate.
A parallel algorithm for step- and chain-growth polymerization in molecular dynamics
Authors: de Buyl Pierre , Nies Erik
Published: April 2015

Classical Molecular Dynamics (MD) simulations provide insight into the properties of many soft-matter systems. In some situations, it is interesting to model the creation of chemical bonds, a process that is not part of the MD framework. In this context, we propose a parallel algorithm for step- and chain-growth polymerization that is based on a generic reaction scheme, works at a given intrinsic rate and produces continuous trajectories. We present an implementation in the ESPResSo++ simulation software and compare it with the corresponding feature in LAMMPS. For chain growth, our results are compared to the existing simulation literature. For step growth, a rate equation is proposed for the evolution of the crosslinker population that compares well to the simulations for low crosslinker functionality or for short times.
Room-temperature ballistic energy transport in molecules with repeating units
Authors: Rubtsova Natalia I. , Nyby Clara M. , Zhang Hong , Zhang Boyu , Zhou Xiao , Jayawickramarajah Janarthanan , Burin Alexander L. , Rubtsov Igor V.
Published: April 2015

In materials, energy can propagate by means of two limiting regimes: diffusive and ballistic. Ballistic energy transport can be fast and efficient and often occurs with a constant speed. Using two-dimensional infrared spectroscopy methods, we discovered ballistic energy transport via individual polyethylene chains with a remarkably high speed of 1440 m/s and the mean free path length of 14.6 Å in solution at room temperature. Whereas the transport via the chains occurs ballistically, the mechanism switches to diffusive with the effective transport speed of 130 m/s at the end-groups attached to the chains. A unifying model of the transport in molecules is presented with clear time separation and additivity among the transport along oligomeric fragments, which occurs ballistically, and the transport within the disordered fragments, occurring diffusively. The results open new avenues for making novel elements for molecular electronics, including ultrafast energy transporters, controlled chemical reactors, and sub-wavelength quantum nanoseparators.
Evolution of GaAs nanowire geometry in selective area epitaxy
Authors: Bassett Kevin P. , Mohseni Parsian K. , Li Xiuling
Published: April 2015

Nanowires (NWs) grown via selective area epitaxy (SAE) show great promise for applications in next generation electronic and photonic devices, yet the design of NW-based devices can be complicated due to the complex kinetics involved in the growth process. The presence of the patterned selective area mask, as well as the changing geometry of the NWs themselves during growth, leads to non-linear growth rates which can vary significantly based on location in the mask and the NW size. Here, we present a systematic study of the evolution of GaAs NW geometry during growth as a function of NW size and pitch. We highlight a breakdown of NW uniformity at extended growth times, which is accelerated for NW arrays with larger separations. This work is intended to outline potential fundamental growth challenges in achieving desired III–V NW array patterns and uniformity via SAE.
Effective binary theory of multi-component nucleation
Authors: Kalikmanov V. I.
Published: April 2015

Classical theory of multi-component nucleation [O. Hirschfelder, J. Chem. Phys. 61, 2690 (1974)] belongs to the class of the so-called intractable problems: it requires computational time which is an exponential function of the number of components N. For a number of systems of practical interest with N > 10, the brute-force use of the classical theory becomes virtually impossible and one has to resort to an effective medium approach. We present an effective binary model which captures important physics of multi-component nucleation. The distinction between two effective species is based on the observation that while all N components contribute to the cluster thermodynamic properties, there is only a part of them which trigger the nucleation process. The proposed 2D-theory takes into account adsorption by means of the Gibbs dividing surface formalism and uses statistical mechanical considerations for the treatment of small clusters. Theoretical predictions for binary-, ternary-, and 14-component mixtures are compared with available experimental data and other models.
Formation mechanism of steep wave front in magnetized plasmas
Authors: Sasaki M. , Kasuya N. , Kobayashi T. , Arakawa H. , Itoh K. , Fukunaga K. , Yamada T. , Yagi M. , Itoh S.-I.
Published: April 2015

Bifurcation from a streamer to a solitary drift wave is obtained in three dimensional simulation of resistive drift waves in cylindrical plasmas. The solitary drift wave is observed in the regime where the collisional transport is important as well as fluctuation induced transport. The solitary drift wave forms a steep wave front in the azimuthal direction. The phase of higher harmonic modes are locked to that of the fundamental mode, so that the steep wave front is sustained for a long time compared to the typical time scale of the drift wave oscillation. The phase entrainment between the fundamental and second harmonic modes is studied, and the azimuthal structure of the stationary solution is found to be characterized by a parameter which is determined by the deviation of the fluctuations from the Boltzmann relation. There are two solutions of the azimuthal structures, which have steep wave front facing forward and backward in the wave propagation direction, respectively. The selection criterion of these solutions is derived theoretically from the stability of the phase entrainment. The simulation result and experimental observations are found to be consistent with the theoretical prediction.
Annealing effect on donor-acceptor interface and its impact on the performance of organic photovoltaic devices based on PSiF-DBT copolymer and C60
Authors: Marchiori Cleber F. N. , Yamamoto Natasha A. D. , Matos Carolina F. , Kujala Jiri , Macedo Andréia G. , Tuomisto Filip , Zarbin Aldo J. G. , Koehler Marlus , Roman Lucimara S.
Published: April 2015

In this work, poly[2,7-(9,9-bis(2-ethylhexyl)-dibenzosilole)-alt-4,7-bis(thiophen-2-yl)benzo-2,1,3-thiadiazole] (PSiF-DBT) was used as active layer in bilayer solar cell with C60 as electron acceptor. As cast devices already show reasonable power conversion efficiency (PCE) that increases to 4% upon annealing at 100 °C. Space charge limited measurements of the hole mobility (μ) in PSiF-DBT give μ ∼ 1.0 × 10−4 cm2/(V s) which does not depend on the temperature of the annealing treatment. Moreover, positron annihilation spectroscopy experiments revealed that PSiF-DBT films are well stacked even without the thermal treatment. The variations in the transport of holes upon annealing are then small. As a consequence, the PCE rise was mainly induced by the increase of the polymer surface roughness that leads to a more effective interface for exciton dissociation at the PSiF-DBT/fullerene heterojunction.
Optimal electron irradiation as a tool for functionalization of MoS2: Theoretical and experimental investigation
Authors: Karmakar Debjani , Halder Rumu , Padma N. , Abraham Geogy , Vaibhav K. , Ghosh M. , Kaur M. , Bhattacharya D. , Chandrasekhar Rao T. V.
Published: April 2015

We demonstrate the utility of electron irradiation as a tool to enhance device functionality of graphene-analogous MoS2. With the help of first-principles based calculations, vacancy-induced changes of various electronic properties are shown to be a combined result of crystal-field modification and spin-orbital coupling. A comparative theoretical study of various possible vacancy configurations both in bulk and monolayer MoS2 and related changes in their respective band-structures help us to explain plausible irradiation induced effects. Experimentally, various structural forms of MoS2 in bulk, few layered flakes, and nanocrystals are observed to exhibit important modification of their magnetic, transport, and vibrational properties, following low doses of electron irradiation. While irradiated single crystals and nanocrystals show an enhanced magnetization, transport properties of few-layered devices show a significant increase in their conductivity, which can be very useful for fabrication of electronic devices. Our theoretical calculations reveal that this increase in n-type conductivity and magnetization can be correlated with the presence of sulfur and molybdenum vacancies.
Synthesis and characterization of CoFe2O4 nanoparticles with high coercivity
Authors: Gandha Kinjal , Elkins Kevin , Poudyal Narayan , Ping Liu J.
Published: April 2015

Single crystalline CoFe2O4 nanoparticles with high coercivity were prepared via a one-step hydrothermal method. The shape and size of the nanocrystals (in the range of 20–100 nm) can be controlled by varying synthesis parameters such as the concentration of NaOH and CTAB. X-ray diffraction and Raman spectra analysis confirmed that all the as-synthesized nanoparticles have a face centered cubic spinel crystal structure. HRTEM observation of particles shows interlayer spacing 0.48 nm of (111) lattice planes. A coercive force up to 5.0 kOe and saturation magnetization of 73 emu/g was achieved at room temperature for the 40 nm CoFe2O4 nanoparticles.
Pulsed high-magnetic-field experiments: New insights into the magnetocaloric effect in Ni-Mn-In Heusler alloys
Authors: Salazar Mejía C. , Ghorbani Zavareh M. , Nayak A. K. , Skourski Y. , Wosnitza J. , Felser C. , Nicklas M.
Published: April 2015

The present pulsed high-magnetic-field study on Ni50Mn35In15 gives an extra insight into the thermodynamics of the martensitic transformation in Heusler shape-memory alloys. The transformation-entropy change, ΔS, was estimated from field-dependent magnetization experiments in pulsed high magnetic fields and by heat-capacity measurements in static fields. We found a decrease of ΔS with decreasing temperature. This behavior can be understood by considering the different signs of the lattice and magnetic contributions to the total entropy. Our results further imply that the magnetocaloric effect will decrease with decreasing temperature and, furthermore, the martensitic transition is not induced anymore by changing the temperature in high magnetic fields.
Electron acceleration by linearly polarized twisted laser pulse with narrow divergence
Authors: Vaziri Mohammad , Golshani Mojtaba , Sohaily Sozha , Bahrampour Alireza
Published: April 2015

We numerically investigate the vacuum electron acceleration by a high-intensity linearly polarized twisted laser pulse. It is shown that the inherent spiral structure of a Laguerre-Gaussian laser pulse leads to improvement in trapping and acceleration of an electron to energies of the order of GeV in the off-axis case. Also, it is demonstrated that by employing a proper choice of initial injection parameters, the high-energetic electrons with very small scattering angles can be produced.
Plasma instability in fast spherical discharge induced by a preionization
Authors: Antsiferov P. S. , Dorokhin L. A.
Published: April 2015

As it was shown earlier, fast discharge (dI/dt ∼ 1012 A/s and Imax ≈ 40 kA) in a spherical cavity (Al2O3, inner diameter 11 mm, 4 mm apertures for the current supply) filled with working gas (Ar and Xe, pressure 80 Pa), results in the formation of a plasma with the form close to spherical. The physical mechanism can be the cumulation of a convergent shock wave, which was originated near the inner surface of the discharge cavity. It was also shown for the cylindrical fast discharge that the preionization influences the dynamics of the cylindrical convergent shock wave, its evolutions becomes faster. The present work is devoted to the study of the influence of the preionization on the plasma formation in the fast discharge with spherical geometry (Ar, 80 Pa). The inductive storage with plasma erosion opening switch was used as a current driver. The spatial structure of the discharge plasma was studied by means of a pin-hole camera with the microchannel plate (MCP) detector with time gate of 5 ns. The extreme ultra violet spectra were studied by means of the grazing incidence spectrometer with the same MCP detector with time gate of 20 ns. Beside the expected effects (reduction of the spherical plasma formation time and some increase of the electron temperature), the preionization of the discharge by the current 500 A results also in the development of the plasma instabilities and destruction of the compact plasma ball in several tens of nanoseconds. Possible mechanism of the instability is discussed.
A modified method to simulate the dispersion properties of infrared nonlinear optical crystals
Authors: Xiao Ruichun , Wu Haixin , Ni Youbao , Wang Zhenyou , Huang Changbao , Qi Ming , Ge Chuanwen
Published: April 2015

This paper presents a modified method to study the dispersion properties of infrared nonlinear optical crystals, which takes advantage of the first principles calculations and oscillator model. The phonon effects play an important role in the dispersion properties, and obvious discrepancies between calculated and experimental results are found due to the lack of such effects in first principles optical property calculations. In order to compensate for such deficiency, the oscillator model was introduced. Phonon oscillator terms are added to the calculated dispersion equations, and the phonon oscillator coefficients can be obtained from first principles infrared dielectric property calculations. With the modified method, the simulated dispersion curves of GaAs, CdSiP2, AgGaS2, and ZnGeP2 crystals show excellent agreement with the experimental results.
Highly collimated monoenergetic target-surface electron acceleration in near-critical-density plasmas
Authors: Mao J. Y. , Chen L. M. , Huang K. , Ma Y. , Zhao J. R. , Li D. Z. , Yan W. C. , Ma J. L. , Aeschlimann M. , Wei Z. Y. , Zhang J.
Published: April 2015

Optimized-quality monoenergetic target surface electron beams at MeV level with low normalized emittance (0.03π mm mrad) and high charge (30 pC) per shot have been obtained from 3 TW laser-solid interactions at a grazing incidence. The 2-Dimension particle-in-cell simulations suggest that electrons are wake-field accelerated in a large-scale, near-critical-density preplasma. It reveals that a bubble-like structure as an accelerating cavity appears in the near-critical-density plasma region and travels along the target surface. A bunch of electrons are pinched transversely and accelerated longitudinally by the wake field in the bubble. The outstanding normalized emittance and monochromaticity of such highly collimated surface electron beams could make it an ideal beam for fast ignition or may serve as an injector in traditional accelerators.
Ionic polymer metal composites with polypyrrole-silver electrodes
Authors: Cellini F. , Grillo A. , Porfiri M.
Published: April 2015

Ionic polymer metal composites (IPMCs) are a class of soft active materials that are finding increasing application in robotics, environmental sensing, and energy harvesting. In this letter, we demonstrate the fabrication of IPMCs via in-situ photoinduced polymerization of polypyrrole-silver electrodes on an ionomeric membrane. The composition, morphology, and sheet resistance of the electrodes are extensively characterized through a range of experimental techniques. We experimentally investigate IPMC electrochemistry through electrochemical impedance spectroscopy, and we propose a modified Randle's model to interpret the impedance spectrum. Finally, we demonstrate in-air dynamic actuation and sensing and assess IPMC performance against more established fabrication methods. Given the simplicity of the process and the short time required for the formation of the electrodes, we envision the application of our technique in the development of a rapid prototyping technology for IPMCs.
Conditions for entangled photon emission from (111)B site-controlled pyramidal quantum dots
Authors: Juska G. , Murray E. , Dimastrodonato V. , Chung T. H. , Moroni S. T. , Gocalinska A. , Pelucchi E.
Published: April 2015

A study of highly symmetric site-controlled pyramidal In0.25Ga0.75As quantum dots (QDs) is presented. It is discussed that polarization-entangled photons can be also obtained from pyramidal QDs of different designs from the one already reported in Juska et al. [Nat. Photonics 7, 527 (2013)]. Moreover, some of the limitations for a higher density of entangled photon emitters are addressed. Among these issues are (1) a remaining small fine-structure splitting and (2) an effective QD charging under non-resonant excitation conditions, which strongly reduce the number of useful biexciton-exciton recombination events. A possible solution of the charging problem is investigated exploiting a dual-wavelength excitation technique, which allows a gradual QD charge tuning from strongly negative to positive and, eventually, efficient detection of entangled photons from QDs, which would be otherwise ineffective under a single-wavelength (non-resonant) excitation.
Low temperature magneto-dielectric measurements on BiFeO3 lightly substituted by cobalt
Authors: Ray J. , Biswal A. K. , Vishwakarma P. N.
Published: April 2015

Dielectric and magnetodielectric measurements are done on BiFe1−xCoxO3: x = 0, 0.01, and 0.02 in the temperature range 70–300 K and up to magnetic field 1.3 T. The dielectric data are well described by Haverliak–Negami expression plus an additional term for the Maxwell Wagner (MW) type relaxations, whose contribution is dominant near room temperature. The parameters obtained from the fitting of data using the above mentioned expression, suggest slowing down of relaxation and approach towards ideal Debye type relaxations, as the temperature is lowered. The dielectric relaxations obey polaronic variable range hopping model with distinct activation energies (Ea) in the extrinsic (6.67T3/4 meV) and intrinsic (2.88T3/4 meV) regions for the parent sample (x = 0), and thus a distinct transition from extrinsic to intrinsic behavior is seen at 215 K while lowering the temperature. This distinct transition is missing for Co substituted samples probably due to the extrinsic region values of Ea (3.42T3/4 meV and 2.42T3/4 meV for x = 0.01 and 0.02, respectively) comparable to that of the intrinsic region (see x = 0). The magnetodielectric measurement shows positive magnetodielectricity (MD) in the intrinsic region (T < 215 K for x = 0) and negative MD in the extrinsic region (T > 215 K for x = 0). The extrinsic region is found to be dominated by MW and magnetoresistance effects, whereas MD in intrinsic regions is due to the spin reorientation transitions. The Co substitution is found to increase the extrinsic and non-Debye contributions to dielectricity, which becomes so large that no spin reorientation transitions are seen in x = 0.02 sample. The pyroelectric active region in x = 0 is found to be dominated by the diffusive behavior having contribution of the form ω−0.5.
Interfacial bonding and electronic structure of GaN/GaAs interface: A first-principles study
Authors: Cao Ruyue , Zhang Zhaofu , Wang Changhong , Li Haobo , Xie Xinjian , Dong Hong , Liu Hui , Wang Weichao
Published: April 2015

Understanding of GaN interfacing with GaAs is crucial for GaN to be an effective interfacial layer between high-k oxides and III-V materials with the application in high-mobility metal-oxide-semiconductor field effect transistor (MOSFET) devices. Utilizing first principles calculations, here, we investigate the structural and electronic properties of the GaN/GaAs interface with respect to the interfacial nitrogen contents. The decrease of interfacial N contents leads to more Ga dangling bonds and As-As dimers. At the N-rich limit, the interface with N concentration of 87.5% shows the most stability. Furthermore, a strong band offsets dependence on the interfacial N concentration is also observed. The valance band offset of N7 with hybrid functional calculation is 0.51 eV. The electronic structure analysis shows that significant interface states exist in all the GaN/GaAs models with various N contents, which originate from the interfacial dangling bonds and some unsaturated Ga and N atoms. These large amounts of gap states result in Fermi level pinning and essentially degrade the device performance.
Femtosecond laser-induced crystallization of amorphous N-doped Ge8Sb92 films and in situ characterization by coherent phonon spectroscopy
Authors: Li Zhongyu , Hu Yifeng , Wen Ting , Zhai Jiwei , Lai Tianshu
Published: April 2015

Femtosecond laser-irradiation-induced phase change of amorphous N-doped Ge8Sb92 films is in situ studied by coherent phonon spectroscopy. We have observed that a new coherent optical phonon (COP) mode occurs as laser irradiation fluence reaches certain thresholds, indicating laser-induced phase changes. Additionally, this new phonon mode has also been verified in heat-annealing-crystallized N-doped Ge8Sb92 films, confirming the emergence of laser-irradiation-induced crystallization. By measuring the pump fluence dependence of COP dynamics in laser-crystallized N-doped Ge8Sb92 films, we found that the frequency and lifetime of COP decrease with the increasing of pump fluence, which suggests good crystallinity in laser-crystallized N-doped Ge8Sb92 films. It has also been observed that the crystallization temperature of amorphous N-doped Ge8Sb92 films increases with N-doping content. Our results indicate promising applications of N-doped Ge8Sb92 films in optical phase-change memory devices.