bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantifying Wikipedia Usage Patterns Before Stock Market Moves
Authors: Moat Helen Susannah , Curme Chester , Avakian Adam , Kenett Dror Y. , Stanley H. Eugene , Preis Tobias
Published: May 2013

Financial crises result from a catastrophic combination of actions. Vast stock market datasets offer us a window into some of the actions that have led to these crises. Here, we investigate whether data generated through Internet usage contain traces of attempts to gather information before trading decisions were taken. We present evidence in line with the intriguing suggestion that data on changes in how often financially related Wikipedia pages were viewed may have contained early signs of stock market moves. Our results suggest that online data may allow us to gain new insight into early information gathering stages of decision making.
UV-induced functionalization of poly(divinylbenzene) nanoparticlesvia efficient [2 + 2]-photocycloadditions
Authors: Ethirajan Anitha , Baeten Linny , Conradi Matthias , Ranieri Kayte , Conings Bert , Boyen Hans-Gerd , Junkers Tanja
Published: May 2013

A facile postmodification strategy for the surface functionalization of nanoparticles is presented based on [2 + 2] photoconjugation with particles made from miniemulsion polymerization of divinylbenzene.
RACK1 (receptor for activated C-kinase 1) interacts with FBW2 (F-box and WD-repeat domain-containing 2) to up-regulate GCM1 (glial cell missing 1) stability and placental cell migration and invasion
Authors: Wang Chang-Chun , Lo Hsiao-Fan , Lin Shu-Yu , Chen Hungwen
Published: May 2013

GCM1 (glial cell missing 1) is a short-lived transcription factor essential for placental development. The F-box protein, FBW2 (F-box and WD-repeat domain-containing 2), which contains five WD (tryptophan–aspartate) repeats, recognizes GCM1 and mediates its ubiquitination via the SCFFBW2 E3 ligase complex. Although the interaction between GCM1 and FBW2 is facilitated by GCM1 phosphorylation, it is possible that this interaction might be regulated by additional cellular factors. In the present study, we perform tandem-affinity purification coupled with MS analysis identifying RACK1 (receptor for activated C-kinase 1) as an FBW2-interacting protein. RACK1 is a multifaceted scaffold protein containing seven WD repeats. We demonstrate that the WD repeats in both RACK1 and FBW2 are required for the interaction of RACK1 and FBW2. Furthermore, RACK1 competes with GCM1 for FBW2 and thereby prevents GCM1 ubiquitination, which is also supported by the observation that GCM1 is destabilized in RACK1-knockdown BeWo placental cells. Importantly, RACK1 knockdown leads to decreased expression of the GCM1 target gene HTRA4 (high-temperature requirement protein A4), which encodes a serine protease crucial for cell migration and invasion. As a result, migration and invasion activities are down-regulated in RACK1-knockdown BeWo cells. The present study reveals a novel function for RACK1 to regulate GCM1 activity and placental cell migration and invasion.
Structural characterization of amorphous calcium carbonate-binding protein: an insight into the mechanism of amorphous calcium carbonate formation
Authors: Su Jingtan , Liang Xiao , Zhou Qiang , Zhang Guiyou , Wang Hongzhong , Xie Liping , Zhang Rongqing
Published: May 2013

ACC (amorphous calcium carbonate) plays an important role in biomineralization process for its function as a precursor for calcium carbonate biominerals. However, it is unclear how biomacromolecules regulate the formation of ACC precursor in vivo. In the present study, we used biochemical experiments coupled with bioinformatics approaches to explore the mechanisms of ACC formation controlled by ACCBP (ACC-binding protein). Size-exclusion chromatography, chemical cross-linking experiments and negative staining electron microscopy reveal that ACCBP is a decamer composed of two adjacent pentamers. Sequence analyses and fluorescence quenching results indicate that ACCBP contains two Ca2+-binding sites. The results of in vitro crystallization experiments suggest that one Ca2+-binding site is critical for ACC formation and the other site affects the ACC induction efficiency. Homology modelling demonstrates that the Ca2+-binding sites of pentameric ACCBP are arranged in a 5-fold symmetry, which is the structural basis for ACC formation. To the best of our knowledge, this is the first report on the structural basis for protein-induced ACC formation and it will significantly improve our understanding of the amorphous precursor pathway.
Minimal functional domains of paralogues hnRNP L and hnRNP LL exhibit mechanistic differences in exonic splicing repression
Authors: Shankarling Ganesh , Lynch Kristen W.
Published: May 2013

Understanding functional distinctions between related splicing regulatory proteins is critical to deciphering tissue-specific control of alternative splicing. The hnRNP (heterogeneous nuclear ribonucleoprotein) L and hnRNP LL (hnRNP L-like) proteins are paralogues that have overlapping, but distinct, expression patterns and functional consequences. These two proteins share high sequence similarity in their RRMs (RNA-recognition motifs), but diverge in regions outside of the RRMs. In the present study, we use an MS2-tethering assay to delineate the minimal domains of hnRNP L and hnRNP LL which are required for repressing exon inclusion. We demonstrate that for both proteins, regions outside the RRMs, the N-terminal region, and a linker sequence between RRMs 2 and 3, are necessary for exon repression, but are only sufficient for repression in the case of hnRNP LL. In addition, both proteins require at least one RRM for maximal repression. Notably, we demonstrate that the region encompassing RRMs 1 and 2 of hnRNP LL imparts a second silencing activity not observed for hnRNP L. This additional functional component of hnRNP LL is consistent with the fact that the full-length hnRNP LL has a greater silencing activity than hnRNP L. Thus the results of the present study provide important insight into the functional and mechanistic variations that can exist between two highly related hnRNP proteins.
Ferroelectric nanodomains in epitaxial PbTiO3 films grown on SmScO3 and TbScO3 substrates
Authors: Borodavka F. , Gregora I. , Bartasyte A. , Margueron S. , Plausinaitiene V. , Abrutis A. , Hlinka J.
Published: May 2013

Domain structures of 320 nm thin epitaxial films of ferroelectric PbTiO3 grown by metal-organic chemical vapor deposition technique in identical conditions on SmScO3 and TbScO3 perovskite substrates have been investigated by Raman spectroscopy and piezoresponse force microscopy techniques. Phonon frequency shifts and typical domain structure motifs are discussed. The results reveal strikingly different domain structure architecture: domain structures of the PbTiO3 film grown on SmScO3 have dominantly a-domain orientation while strongly preferential c-domain orientation was found in the PbTiO3 film grown on the TbScO3 substrate. Differences between the two cases are traced back to the film-substrate lattice mismatch at the deposition temperature.
Full field electron spectromicroscopy applied to ferroelectric materials
Authors: Barrett N. , Rault J. E. , Wang J. L. , Mathieu C. , Locatelli A. , Mentes T. O. , Niño M. A. , Fusil S. , Bibes M. , Barthélémy A. , Sando D. , Ren W. , Prosandeev S. , Bellaiche L. , Vilquin B. , Petraru A. , Krug I. P. , Schneider C. M.
Published: May 2013

The application of PhotoEmission Electron Microscopy (PEEM) and Low Energy Electron Microscopy (LEEM) techniques to the study of the electronic and chemical structures of ferroelectric materials is reviewed. Electron optics in both techniques gives spatial resolution of a few tens of nanometres. PEEM images photoelectrons, whereas LEEM images reflected and elastically backscattered electrons. Both PEEM and LEEM can be used in direct and reciprocal space imaging. Together, they provide access to surface charge, work function, topography, chemical mapping, surface crystallinity, and band structure. Examples of applications for the study of ferroelectric thin films and single crystals are presented.
Local properties of the surface layer(s) of BiFeO3 single crystals
Authors: Domingo Neus , Narvaez Jackeline , Alexe Marin , Catalan Gustau
Published: May 2013

The surface of BiFeO3 single crystals has been characterized at the local level using several AFM-based techniques. We have observed the presence of two different epilayers showing electrical and mechanical properties different from those of the bulk: a ferroelectrically “dead” outer skin of 5 nm sitting upon a subsurface layer that displays an extremely fine pattern of hierarchical self-ordered nanodomains. Based on the size of the nanodomains and applying a Kittel-like analysis, we argue that the nanotwinned region should be confined in a layer less than a micron deep. The superficial phase transition at T* = 275 °C is restricted to the outer skin layer (the “dead” layer), while the nanotwinned layer is insensitive to this transition. In view of the photovoltaic properties and spin-dependent transport of domain walls in BiFeO3, the existence of nanodomains (and thus a high density of domain walls) in bulk single crystals is likely to be relevant for understanding their functional properties.
Mapping nanoscale domain patterns in ferroelectric ceramics by atomic force acoustic microscopy and piezoresponse force microscopy
Authors: Zhou X. L. , Li F. X. , Zeng H. R.
Published: May 2013

In this paper, nanoscale domain patterns of ferroelectric ceramics were investigated by both atomic force acoustic microscopy (AFAM) and piezoresponse force microscopy (PFM). First, we applied the dual frequency resonance tracking (DFRT) technique on AFAM and realized nanoscale modulus mapping. Then we comparatively mapped the nanoscale domain patterns in a PZT ceramics using PFM, single-frequency AFAM, and DFRT AFAM in the same scanning area. Results show that PFM can give the best contrast domain patterns and is not sensitive to cantilever stiffness. In comparison, both modes of AFAM are sensitive to cantilever stiffness and can give good contrast of domains only using very stiff cantilevers. Furthermore, both modes of AFAM can map the subsurface domain structures and the grain boundaries clearly while PFM usually cannot. Based on the resonance-frequency image obtained by the DFRT AFAM, we also obtained the nanoscale modulus of the whole scanning area which may help understand the possible domain movement under mechanical or electric fields. Finally, we suggest that, to characterize the nanoscale domain properties in ferroelectrics, PFM plus resonance tracking AFAM is the best choice.
Thermal hysteresis of local instabilities in paraelectric phase of PbZr0.96Sn0.04 O3 single crystals
Authors: Jankowska-Sumara Irena , Szot Krzysztof , Majchrowski Andrzej , Roleder Krystian
Published: May 2013

Investigations of local electromechanical properties for PbZr1−xSnxO3 single crystals are a way to understand better the phase transition mechanisms in oxide perovskites with antiferroelectric phase transition. The investigations of local electromechanical studies were performed by the PEFM. The piezoelectric activity in nano-scale and weak birefringence observed in micro-scale have been found in the paraelectric phase and are a proof for theoretically predicted local instability above TC [A. Bussmann-Holder et al., Phys. Rev. B 79, 184111 (2009)]. Origin of these instabilities is analysed taking into account non-homogeneous distribution of Sn in crystal lattice, presence of extended defects and other lattice inhomogeneities. Temperature dependences and thermal hysteresis of piezo- and electrostrictive responses were compared with bulk properties.
Gaussian Lagrangian stochastic models for multi-particle dispersion
Authors: Sawford B. L. , Pope S. B. , Yeung P. K.
Published: May 2013

We have extended the “well-mixed” two-particle stochastic models for 3D Gaussian turbulence to n particles, and have performed calculations for clusters of n ⩽ 6 particles. The particle joint motions are Gaussian and are constrained by pair-wise spatial correlations. This neglects non-Gaussian properties of the two-point velocity distribution and also neglects multi-point correlations. It also takes no account of intermittency. Although the models do not predict the growth of the separation of particles in the cluster satisfactorily, we find that they do give a good representation of the shape statistics for the cluster in comparison with direct numerical simulation results. We conclude that the pair-wise spatial structure of the turbulence accounts for most of the observed characteristics of the shape of multi-particle clusters in turbulence, and that non-Gaussian and multi-point features of the turbulence are of secondary importance.
Selecting boron fullerenes by cage-doping mechanisms
Authors: Boulanger Paul , Morinière Maxime , Genovese Luigi , Pochet Pascal
Published: May 2013

So far, no boron fullerenes were synthesized: more compact sp3-bonded clusters are energetically preferred. To circumvent this, metallic clusters have been suggested by Pochet et al. [Phys. Rev. B 83, 081403(R) (2011)10.1103/PhysRevB.83.081403] as “seeds” for a possible synthesis which would topologically protect the sp2 sector of the configuration space. In this paper, we identify a basic pentagonal unit which allows a balance between the release of strain and the self-doping rule. We formulate a guiding principle for the stability of boron fullerenes, which takes the form of an isolated filled pentagon rule (IFPR). The role of metallic clusters is then reexamined. It is shown that the interplay of the IFPR and the seed-induced doping breaks polymorphism and its related problems: it can effectively select between different isomers and reduce the reactivity of the boron shells. The balance between self and exterior doping represents the best strategy for boron buckyball synthesis.
Towards the blackbox computation of magnetic exchange coupling parameters in polynuclear transition-metal complexes: Theory, implementation, and application
Authors: Phillips Jordan J. , Peralta Juan E.
Published: May 2013

We present a method for calculating magnetic coupling parameters from a single spin-configuration via analytic derivatives of the electronic energy with respect to the local spin direction. This method does not introduce new approximations beyond those found in the Heisenberg-Dirac Hamiltonian and a standard Kohn-Sham Density Functional Theory calculation, and in the limit of an ideal Heisenberg system it reproduces the coupling as determined from spin-projected energy-differences. Our method employs a generalized perturbative approach to constrained density functional theory, where exact expressions for the energy to second order in the constraints are obtained by analytic derivatives from coupled-perturbed theory. When the relative angle between magnetization vectors of metal atoms enters as a constraint, this allows us to calculate all the magnetic exchange couplings of a system from derivatives with respect to local spin directions from the high-spin configuration. Because of the favorable computational scaling of our method with respect to the number of spin-centers, as compared to the broken-symmetry energy-differences approach, this opens the possibility for the blackbox exploration of magnetic properties in large polynuclear transition-metal complexes. In this work we outline the motivation, theory, and implementation of this method, and present results for several model systems and transition-metal complexes with a variety of density functional approximations and Hartree-Fock.
A system for acoustical and optical analysis of encapsulated microbubbles at ultrahigh hydrostatic pressures
Authors: Zhushma Aleksandr , Lebedeva Natalia , Sen Pabitra , Rubinstein Michael , Sheiko Sergei S. , Dayton Paul A.
Published: May 2013

Acoustics are commonly used for borehole (i.e., oil well) imaging applications, under conditions where temperature and pressure reach extremes beyond that of conventional medical ultrasonics. Recently, there has been an interest in the application of encapsulated microbubbles as borehole contrast agents for acoustic assessment of fluid composition and flow. Although such microbubbles are widely studied under physiological conditions for medical imaging applications, to date there is a paucity of information on the behavior of encapsulated gas-filled microbubbles at high pressures. One major limitation is that there is a lack of experimental systems to assess both optical and acoustic data of micrometer-sized particles data at these extremes. In this paper, we present the design and application of a high-pressure cell designed for acoustical and optical studies of microbubbles at hydrostatic pressures up to 27.5 MPa (271 atm).
Classification of Lie point symmetries for quadratic Liénard type equation $\ddot{x}+f(x)\dot{x}^2+g(x)=0$ẍ+f(x)ẋ2+g(x)=0
Authors: Tiwari Ajey K. , Pandey S. N. , Senthilvelan M. , Lakshmanan M.
Published: May 2013

In this paper we carry out a complete classification of the Lie point symmetry groups associated with the quadratic Li\documentclass[12pt]{minimal}\begin{document}$\acute{e}$\end{document}énard type equation, \documentclass[12pt]{minimal}\begin{document}$\ddot{x} + f(x){\dot{x}}^{2} + g(x)\break = 0$\end{document}ẍ+f(x)ẋ2+g(x)=0, where f(x) and g(x) are arbitrary functions of x. The symmetry analysis gets divided into two cases, (i) the maximal (eight parameter) symmetry group and (ii) non-maximal (three, two, and one parameter) symmetry groups. We identify the most general form of the quadratic Li\documentclass[12pt]{minimal}\begin{document}$\acute{e}$\end{document}énard equation in each of these cases. In the case of eight parameter symmetry group, the identified general equation becomes linearizable as well as isochronic. We present specific examples of physical interest. For the non-maximal cases, the identified equations are all integrable and include several physically interesting examples such as the Mathews-Lakshmanan oscillator, particle on a rotating parabolic well, etc. We also analyse the underlying equivalence transformations.
Spectroscopic observation of gold-dicarbide: Photodetachment and velocity map imaging of the AuC2 anion
Authors: Visser Bradley R. , Addicoat Matthew A. , Gascooke Jason R. , Lawrance Warren D. , Metha Gregory F.
Published: May 2013

Photoelectron spectra following photodetachment of the gold dicarbide anion, ${\rm AuC}_2^ - $ AuC 2−, have been recorded using the velocity map imaging technique at several excitation wavelengths. The binding energy spectra show well-defined vibrational structure which, with the aid of computational calculations and Franck-Condon simulations, was assigned to a progression in the Au–C stretching mode, ν3. The experimental data indicate that the features in the spectrum correspond to a 2A′ ← 3A′ transition, involving states which we calculate to have bond angles ∼147° but with a low barrier to linearity.
On the strong solutions of one-dimensional Navier-Stokes-Poisson equations for compressible non-Newtonian fluids
Authors: Song Yukun , Yuan Hongjun , Chen Yang
Published: May 2013

We study the strong solutions of 1D Navier-Stokes-Poisson equations for compressible non-Newtonian fluids in bounded intervals. The model is raised from the viscous isentropic gas flow under considering an external force and the non-Newtonian gravitational force term. By using the iterative method we prove the local existence and uniqueness of strong solutions based on some compatibility condition. The main condition is that the initial density vacuum is allowed.
Insights into hydrogen bond dynamics at the interface of the charged monolayer-protected Au nanoparticle from molecular dynamics simulation
Authors: Li Yunzhi , Yang Zhen , Hu Na , Zhou Rongfei , Chen Xiangshu
Published: May 2013

The structure and dynamics properties of water molecules at the interface of the charged monolayer-protected Au nanoparticle (MPAN) have been investigated in detail by using classical molecular dynamics simulation. The simulation results demonstrated clearly that a well-defined hydration layer is formed at the interface of MPAN and a stable “ion wall” consisting of terminal ${\rm NH}_{3}^{+}$ NH 3+ groups and Cl− counterions exists at the outmost region of self-assembled monolayer (SAM) where the translational and rotational motions of water molecules slow considerably down compared to those in the bulk owing to the presence of SAM and ion wall. Furthermore, we found that the translational motions of interfacial water molecules display a subdiffusive behavior while their rotational motions exhibit a nonexponential feature. The unique behavior of interfacial water molecules around the MPAN can be attributed to the interfacial hydrogen bond (HB) dynamics. By comparison, the lifetime of ${\rm NH}_{3}^{+}$ NH 3+–Cl− HBs was found to be the longest, favoring the stability of ion wall. Meanwhile, the lifetime of H2O–H2O HBs shows an obvious increase when the water molecules approach the Au core, suggesting the enhanced H2O–H2O HBs around the charged MPAN, which is contrary to the weaken H2O–H2O HBs around the neutral MPAN. Moreover, the HB lifetimes between water molecules and the ion wall (i.e., the Cl−–H2O and ${\rm NH}_{3}^{+}$ NH 3+–H2O HBs) are much longer than that of interfacial H2O–H2O HBs, which leads to the increasing rotational relaxation time and residence time of water molecules surrounding the ion wall. In addition, the corresponding binding energies for different HB types obtained from the precise density functional theory are in excellent accordance with above simulation results. The detailed HB dynamics studied in this work provides insights into the unique behavior of water molecules at the interface of charged self-assemblies of nanoparticles as well as proteins.
Energy transfer efficiency in YF3 nanocrystals: Quantifying the Yb3+ to Tm3+ infrared dynamics
Authors: Quintanilla Marta , Núñez Nuria O. , Cantelar Eugenio , Ocaña Manuel , Cussó Fernando
Published: May 2013

In this work, we report on the determination of the infrared Yb3+ → Tm3+ energy transfer efficiency in YF3:Yb3+/Tm3+ nanocrystals through the study of Yb3+ dynamics. The obtained results are compared to those previously reported in macrocrystals to analyze possible changes related to size reduction. Luminescence lifetimes are much shorter in the nanoparticles than in bulk samples, a behavior that can be related to Yb3+ → Yb3+ migration and the enhanced surface/volume ratio of the nanoparticles. On the other hand, Yb3+ → Tm3+ energy transfer macroparameter remains unaltered, demonstrating that spectroscopic intrinsic parameters such as radiative and non-radiative probabilities are not affected by size reduction. Finally, a formula that describes Yb3+ lifetime dependence with Yb3+ and Tm3+ concentration is proposed, considering both the effects produced by migration between Yb3+ ions and energy transfer from Yb3+ to Tm3+ ions.
Quantum critical point of spin-boson model and infrared catastrophe in bosonic bath
Authors: Zheng Hang , Lü Zhiguo
Published: May 2013

An analytic ground state is proposed for the unbiased spin-boson Hamiltonian, which is non-Gaussian and beyond the Silbey-Harris ground state with lower ground state energy. The infrared catastrophe in Ohmic and sub-Ohmic bosonic bath plays an important role in determining the degeneracy of the ground state. We show that the infrared divergence associated with the displacement of the nonadiabatic modes in bath may be removed from the proposed ground state for the coupling α < αc. Then αc is the quantum critical point of a transition from non-degenerate to degenerate ground state and our calculated αc agrees with previous numerical results.
Electrical switching dynamics and broadband microwave characteristics of VO2 radio frequency devices
Authors: Ha Sieu D. , Zhou You , Fisher Christopher J. , Ramanathan Shriram , Treadway Jacob P.
Published: May 2013

Vanadium dioxide (VO2) is a correlated electron system that features a metal-insulator phase transition (MIT) above room temperature and is of interest in high speed switching devices. Here, we integrate VO2 into two-terminal coplanar waveguides and demonstrate a large resistance modulation of the same magnitude (>103) in both electrically (i.e., by bias voltage, referred to as E-MIT) and thermally (T-MIT) driven transitions. We examine transient switching characteristics of the E-MIT and observe two distinguishable time scales for switching. We find an abrupt jump in conductivity with a rise time of the order of 10 ns followed by an oscillatory damping to steady state on the order of several μs. We characterize the RF power response in the On state and find that high RF input power drives VO2 further into the metallic phase, indicating that electromagnetic radiation-switching of the phase transition may be possible. We measure S-parameter RF properties up to 13.5 GHz. Insertion loss is markedly flat at 2.95 dB across the frequency range in the On state, and sufficient isolation of over 25 dB is observed in the Off state. We are able to simulate the RF response accurately using both lumped element and 3D electromagnetic models. Extrapolation of our results suggests that optimizing device geometry can reduce insertion loss further and maintain broadband flatness up to 40 GHz.
Fabrication and characterization of strain-driven self-assembled CrN nanoislands on Cu(001)
Authors: Krukowski P. , Iimori T. , Nakatsuji K. , Yamada M. , Komori F.
Published: May 2013

Two types of square-shaped self-assembled CrN nanoislands of monoatomic layer are fabricated on the Cu(001) substrate. The island edges are commonly oriented along the ⟨110⟩ directions, and the islands locally form a two-dimensional square superstructure. The mean height is either 0.09 or 0.18 nm, and the average lateral size of the islands is 2.5 × 2.5 nm2 for the lower islands and 3.5 × 3.5 nm2 for the others. The formation of the higher CrN islands is attributed to an unconventional short-range attractive mechanism. The lower islands coexisting with the clean surface are made by the interplay between the long- and short-range interactions.
Fabricating functionally graded films with designed gradient profiles using pulsed laser deposition
Authors: Jai Won Yoo , Ki Hyungson
Published: May 2013

A novel picosecond-laser pulsed laser deposition method has been developed for fabricating functionally graded films with pre-designed gradient profiles. Theoretically, the developed method is capable of precisely fabricating films with any thicknesses and any gradient profiles by controlling the laser beam powers for the two different targets based on the film composition profiles. As an implementation example, we have successfully constructed functionally graded diamond-like carbon films with six different gradient profiles: linear, quadratic, cubic, square root, cubic root, and sinusoidal. Energy dispersive X-ray spectroscopy is employed for investigating the chemical composition along the thickness of the film, and the deposition profile and thickness errors are found to be less than 3% and 1.04%, respectively. To the best of the authors' knowledge, this is the first method for fabricating films with designed gradient profiles and has huge potential in many areas of coatings and films, including multifunctional optical films. We believe that this method is not only limited to the example considered in this study, but also can be applied to all material combinations as long as they can be deposited using the pulsed laser deposition technique.
Controlled nanostructuration of polycrystalline tungsten thin films
Authors: Girault B. , Eyidi D. , Goudeau P. , Sauvage T. , Guerin P. , Bourhis E. Le , Renault P.-O.
Published: May 2013

Nanostructured tungsten thin films have been obtained by ion beam sputtering technique stopping periodically the growing. The total thickness was maintained constant while nanostructure control was obtained using different stopping periods in order to induce film stratification. The effect of tungsten sublayers' thicknesses on film composition, residual stresses, and crystalline texture evolution has been established. Our study reveals that tungsten crystallizes in both stable α- and metastable β-phases and that volume proportions evolve with deposited sublayers' thicknesses. α-W phase shows original fiber texture development with two major preferential crystallographic orientations, namely, α-W⟨110⟩ and unexpectedly α-W⟨111⟩ texture components. The partial pressure of oxygen and presence of carbon have been identified as critical parameters for the growth of metastable β-W phase. Moreover, the texture development of α-W phase with two texture components is shown to be the result of a competition between crystallographic planes energy minimization and crystallographic orientation channeling effect maximization. Controlled grain size can be achieved for the α-W phase structure over 3 nm stratification step. Below, the β-W phase structure becomes predominant.
Magnetoresistance in magnetic nanoconstrictions: The role of structural defects
Authors: Biziere N. , Clochard M.-C. , Do Chung Pham , Wegrowe J.-E. , Viret M.
Published: May 2013

The resistance of a ferromagnetic cylindrical Ni nano-constriction has been measured as a function of the external magnetic field. Typical profiles of the resistance versus external field are observed with irreversible jumps separated by stable plateaus, showing systematic slow relaxation effects. An interpretation in terms of magnetomechanical strain at the level of the constriction is proposed. This scenario allows the slow relaxation behaviour to be understood in terms of displacement of dislocations or similar metastable structural defects.
Terahertz, optical, and Raman signatures of monolayer graphene behavior in thermally reduced graphene oxide films
Authors: Lim Juhwan , Choi Kyujin , Rani J. R. , Kim Jin-Seon , Lee Changgu , Hoon Kim Jae , Chan Jun Seong
Published: May 2013

We report on our joint spectroscopic study of the thermal reduction process of quasi-monolayer graphene oxide films grown on fused silica substrates by spin-coating. We estimate that about 65% of our film area consists of monolayer platelets of reduced graphene oxide, based on our quantitative analysis of the local atomic force microscopy topography. With thermal annealing under suitable conditions, clear signatures of monolayer graphene behavior were identified in the resonant excitonic absorption at 4.55 eV, the overall decrease in the visible-range transmission, the re-emergence of the Raman 2D band, the red-shift of the Raman G band toward the monolayer position, and the decrease in the optical sheet resistance in the terahertz range.
Understanding the stability and dynamical process of hydrogen trimers on graphene
Authors: Fei Cao Teng , Feng Huang Liang , Hong Zheng Xiao , Lai Gong Peng , Zeng Zhi
Published: May 2013

With density functional theory calculations, the performance of hydrogen trimers on graphene including the structural stability and the dynamical evolution paths is systematically investigated. The stability of the trimer is closely related with its adsorption configuration. The configurations containing ortho-dimers and para-dimers are more stable than the others. Meanwhile, other nearby hydrogen clusters have different impacts on the stability of trimers, which is determined by the competition between lattice deformation and inter-cluster electronic pairing. Atomic diffusion and desorption are proved to be very important for the dynamical evolution paths of trimers, in which all trimers are first easily changed into stable dimers and then follow the desorption of dimers. Our results have well explained the phenomena given by the scanning tunneling microscopy experiments and are helpful for the understanding of the interaction between hydrogen and graphene, and for the application of hydrogenated graphene.
Studies of electrical resistivity of an annealed Cu-Fe composite
Authors: Qu Lei , Wang Engang , Han Ke , Zuo Xiaowei , Zhang Lin , Jia Peng , He Jicheng
Published: May 2013

Cu-15 vol. % Fe composites produced by cold deformation were annealed at various temperatures for 1 h. The electrical resistivity, tensile strength, and microstructure were investigated by four-probe technique, electronic universal testing machine, and scanning electron microscopy (SEM), respectively. The Fe solubility in Cu-matrix was estimated from the saturation magnetization of the composites. The results reveal that the resistivity of impurity scattering ρimp is the main contributor to the resistivity of the Cu-Fe composites if the phonon and dislocation scattering contributions to the electrical resistivity are considered to be constants. At annealing temperatures below 500 °C, an increase of filament spacing and reduction of interface area in unit volume result in a marginal decrease of the resistivity with temperatures. Above 500 °C, the Fe solubility in Cu-matrix rapidly increases with temperature, which directly causes the increase of composites resistivity.
Ag/TiO2 nanofiber heterostructures: Highly enhanced photocatalysts under visible light
Authors: Wang Yuan , Liu Lixin , Xu Liang , Meng Chuanmin , Zhu Wenjun
Published: May 2013

Photocatalysis of TiO2 has recently drawn considerable attention, while the photoefficiency of TiO2 is limited by its large band-gap energy and usually fast electron-hole recombination. Here, we present an unconventional heterostructure of Ag nanoparticles modified TiO2 nanofibers synthesized by one-step electrospinning process, to improve the photoefficiency of TiO2 host. The efficient promotion of the visible light photocatalysis of Ag/TiO2 nanofiber heterostructures can be ascribed to the electronic excitation of Ag nanoparticles under visible light and the transfer of the electrons to TiO2 conduction band, which deeply depends on the number of Ag/TiO2 junctions and the height of Schottky barrier. The Ag/Ti molar ratio can be easily controlled by the electrospinning process and the Ag/TiO2 nanofibers with Ag/Ti molar ratio of 0.05 exhibit the highest photocatalytic activity. Simultaneously, the Ag/TiO2 nanofiber heterostructures show excellent photocatalytic stability.
Magnetic properties of the (LaMnO3)N/(SrTiO3)N atomic layer superlattices
Authors: Zhai Xiaofang , Mohapatra Chandra S. , Shah Amish B. , Zuo Jian-Min , Eckstein James N.
Published: May 2013

We studied the magnetic properties of atomic layer superlattices of (LaMnO3)N/(SrTiO3)N (N = 1,2,8) fabricated by ozone-assisted atomic layer-by-layer molecular beam epitaxy. Compared to a reference LaMnO3 thin film, the N = 8 superlattice exhibits enhanced magnetization, while the N = 1 and 2 superlattices exhibit suppressed magnetization. The onset temperature of the ferromagnetic transition is lowered in all superlattices. Moreover, the Brillouin function fits to the magnetic hysteresis curves indicate that the ground state of the superlattices consists of non-uniform spin interactions. The electric transport measurements suggest a very small variation of Mn valence (∼±0.015) that may not be enough to induce the observed large change in the magnetic property.
Development of a polar direct-drive platform for studying inertial confinement fusion implosion mix on the National Ignition Facility
Authors: Schmitt Mark J. , Bradley Paul A. , Cobble James A. , Fincke James R. , Hakel Peter , Hsu Scott C. , Krasheninnikova Natalia S. , Kyrala George A. , Magelssen Glenn R. , Montgomery David S. , Murphy Thomas J. , Obrey Kimberly A. , Shah Rahul C. , Tregillis Ian L. , Baumgaertel Jessica A. , Wysocki Frederick J. , Batha Steven H. , Stephen Craxton R. , McKenty Patrick W. , Fitzsimmons Paul , Nikroo Abbas , Wallace Russell
Published: May 2013

Experiments were performed to develop a platform for the simultaneous measurement of mix and its effects on fusion burn. Two polar direct drive implosions of all-plastic capsules were conducted for the first time on the National Ignition Facility (NIF). To measure implosion trajectory and symmetry, area image backlighting of these capsules was also employed for the first time on NIF, an advance over previous 1-D slit imaging experiments, providing detailed symmetry data of the capsules as they imploded. The implosion trajectory and low-mode asymmetry seen in the resultant radiographs agreed with pre-shot predictions even though the 700 kJ drive energy produced laser beam intensities exceeding laser-plasma instability thresholds. Post-shot simulations indicate that the capsule yield was reduced by a factor of two compared to pre-shot predictions owing to as-shot laser drive asymmetries. The pre-shot predictions of bang time agreed within 200 ps with the experimental results. The second shot incorporated a narrow groove encircling the equator of the capsule. A predicted yield reduction factor of three was not observed.
Measurement of the specific heat and determination of the thermodynamic functions of relaxed amorphous silicon
Authors: Roura P. , Taïr F. , Farjas J. , Roca i Cabarrocas P.
Published: May 2013

The specific heat, cp, of two amorphous silicon (a-Si) samples has been measured by differential scanning calorimetry in the 100–900 K temperature range. When the hydrogen content is reduced by thermal annealing, cp approaches the value of crystalline Si (c-Si). Within experimental accuracy, we conclude that cp of relaxed pure a-Si coincides with that of c-Si. This result is used to determine the enthalpy, entropy, and Gibbs free energy of defect-free relaxed a-Si. Finally, the contribution of structural defects on these quantities is calculated and the melting point of several states of a-Si is predicted.
Optical absorption and photoreflectance spectroscopy of the single-crystalline chalcopyrite semiconductor AgGaSe2
Authors: Hori Takehito , Ozaki Shunji
Published: May 2013

Optical absorption and photoreflectance (PR) spectra have been measured on the single-crystalline chalcopyrite semiconductor AgGaSe2 for light polarization perpendicular (E ⊥ c) and parallel to the c-axis (E ‖ c) at T = 15–300 K. Optical absorption measurements suggest that AgGaSe2 is a direct-gap semiconductor having an optical band gap of E0 ∼ 1.8 eV at T = 15–300 K. The temperature-dependent PR spectra are obtained at T = 20–300 K in the 1.8–2.5 eV spectral ranges. The lowest band-gap energy E0 of AgGaSe2 shows unusual temperature dependence at T ≤ 80 K. The resultant temperature coefficients dE0/dT are positive at T ≤ 70 K and negative above 70 K, and are explained by considering the effects of thermal expansion and electron-phonon interaction. The spin-orbit and crystal-field splitting parameters are also determined to be Δso = 327 meV and Δcr = −288 meV at T = 20 K, respectively.
Characterization and parametric dependencies of low wavenumber pedestal turbulence in the National Spherical Torus Experiment
Authors: Smith D. R. , Fonck R. J. , McKee G. R. , Thompson D. S. , Bell R. E. , Diallo A. , Guttenfelder W. , Kaye S. M. , LeBlanc B. P. , Podesta M.
Published: May 2013

The spherical torus edge region is among the most challenging regimes for plasma turbulence simulations. Here, we measure the spatial and temporal properties of ion-scale turbulence in the steep gradient region of H-mode pedestals during edge localized mode-free, MHD quiescent periods in the National Spherical Torus Experiment. Poloidal correlation lengths are about 10 ρi, and decorrelation times are about 5 a/cs. Next, we introduce a model aggregation technique to identify parametric dependencies among turbulence quantities and transport-relevant plasma parameters. The parametric dependencies show the most agreement with transport driven by trapped-electron mode, kinetic ballooning mode, and microtearing mode turbulence, and the least agreement with ion temperature gradient turbulence. In addition, the parametric dependencies are consistent with turbulence regulation by flow shear and the empirical relationship between wider pedestals and larger turbulent structures.
Bandgap tuning of mono- and bilayer graphene doped with group IV elements
Authors: Kaplan D. , Swaminathan V. , Recine G. , Balu R. , Karna S.
Published: May 2013

We report density functional theory band structure calculations of graphene doped with group IV elements. A bandgap as high as 2.13 eV is calculated for a single layer of graphene doped with Si while Ge and Sn doping reduce this bandgap for equal doping concentrations. Bilayers of doped graphene are also studied and it is found that the bandgap of these materials is less than that of the single layer counterparts. Finally, a transverse electric field is applied to the doped bilayers and it is found that the bandgap is inversely proportional to the electric field strength in contrast to what has been observed in the case of pristine bilayers. Carrier effective masses were calculated and in general the effective masses of electrons and holes are found to be similar.
Silicon photomultiplier device architecture with dark current improved to the ultimate physical limit
Authors: Pagano R. , Valvo G. , Sanfilippo D. , Libertino S. , Corso D. , Fallica P. G. , Lombardo S.
Published: May 2013

This paper describes a silicon photomultiplier device architecture achieving the ultimate physical limit of the dark count level. Two different structures are compared and the resulting dark count levels as a function of temperature and applied overvoltage are modelled by a 2D drift-diffusion device simulator. In the best structure, the concentration of minority carriers (electrons) approaching the depletion region from the anode side is below the concentration of holes approaching the depletion region from the cathode side. An improvement in the dark count level of a factor 50 is experimentally found, close to the ultimate physical limit.
Improved fluid simulations of radio-frequency plasmas using energy dependent ion mobilities
Authors: Greb Arthur , Niemi Kari , O'Connell Deborah , Ennis Gerard J. , MacGearailt Niall , Gans Timo
Published: May 2013

Symmetric and asymmetric capacitively coupled radio-frequency plasmas in oxygen at 40 Pa, 300 V voltage amplitude and a discharge gap of 40 mm are investigated by means of one-dimensional numerical semi-kinetic fluid modeling on the basis of a simplified reaction scheme including the dominant positive and negative ions, background gas, and electrons. An improved treatment, by accounting for the dependence of ion mobilities on E/N, is compared to the standard approach, based on using zero-field mobility values only. The charged particle dynamics as a result of direct electron impact ionization of oxygen, secondary electron release from the electrodes, the spatial distribution of all involved particles as well as impact of geometry and model modification on ion energies is analyzed and compared to independent simulations and experiments.
Note: Mobile micro-Raman analyzer integrated with a lab-on-a-chip
Authors: Li Haibo , Chen Gang , Zhang Yuxin , Geng Yijia , Gu Yuejiao , Wang Hailong , Xu Shuping , Xu Weiqing
Published: May 2013

A mobile micro-Raman microfluidic analyzer was designed and built for label-free, nondestructive, fingerprint detection of samples on microfluidic chip systems. It mainly includes an optical module (including the Raman detection system and the microscopic imaging system), 3-axis stages with step motors and other auxiliary circuits. The setup of the analyzer was designed with fully considering the characters of the microfluidics system. The experimental results prove that this microfluidics analyzer is practical and very convenient to use. This micro-Raman microfluidics analyzer with high performance to cost ratio has wide application potential in lab-on-a-chip fields as a powerful analytical tool.
Dynamics of low dimensional model for weakly relativistic Zakharov equations for plasmas
Authors: Sahu Biswajit , Pal Barnali , Poria Swarup , Roychoudhury Rajkumar
Published: May 2013

In the present paper, the nonlinear interaction between Langmuir waves and ion acoustic waves described by the one-dimensional Zakharov equations (ZEs) for relativistic plasmas are investigated formulating a low dimensional model. Equilibrium points of the model are found and it is shown that the existence and stability conditions of the equilibrium point depend on the relativistic parameter. Computational investigations are carried out to examine the effects of relativistic parameter and other plasma parameters on the dynamics of the model. Power spectrum analysis using fast fourier transform and also construction of first return map confirm that periodic, quasi-periodic, and chaotic type solution exist for both relativistic as well as in non-relativistic case. Existence of supercritical Hopf bifurcation is noted in the system for two critical plasmon numbers.
The role of an interface on Ni film removal and surface roughness after irradiation by femtosecond laser pulses
Authors: Murphy Ryan D. , Torralva Ben , Yalisove Steven M.
Published: May 2013

We have observed thin film removal from glass substrates after the irradiation of Ni films with femtosecond laser pulses in air. It was found that the material removal threshold and laser-induced morphology are dependent on film thickness. With decreasing thickness, material removal transitions from intra-film separation to removal at the Ni-glass interface. The Gaussian energy distribution of the laser pulse allows for intra-film separation in the annular region of the crater and interface separation in the center. We propose a model to explain these data as well as the observed increased surface roughness in the interfacial removal regions.
Enhanced photocurrent readout for a quantum dot qubit by bias modulation
Authors: Quilter J. H. , Coles R. J. , Ramsay A. J. , Fox A. M. , Skolnick M. S.
Published: May 2013

We demonstrate coherent control of a quantum dot exciton using photocurrent detection with a sinusoidal reverse bias. Optical control is performed at low bias, where tunneling-limited coherence times are long. Following this step, the tunneling rates are increased to remove the long-lived hole, achieving a high photocurrent signal. For a detection efficiency of 68%, electron and hole tunneling times during optical control of 200 ps and 20 ns can be achieved, compared to 120 ps and 7 ns for the constant bias case, respectively.
Low frequency plasmonic state and negative permittivity spectra of coagulated Cu granular composite materials in the percolation threshold
Authors: Tsutaoka Takanori , Kasagi Teruhiro , Yamamoto Shinichiro , Hatakeyama Kenichi
Published: May 2013

We have studied the relative complex permittivity (εr = εr′- iεr″) of copper granular composite materials containing coagulated Cu particles in the microwave range as well as the electrical conductivity. The insulator to metal transition was observed at the percolation threshold φc = 16.0 vol. %. The enhancement of permittivity in the insulating state can be described by the Effective Cluster Model. Above the percolation threshold φc, it was found that the Cu granular composites show negative permittivity spectra below a characteristic frequency f0 indicating the low frequency plasmonic state. Characteristic frequency tends to increase with particle content.
Communication: Overtone (2NH) spectroscopy of NH3–Ar
Authors: Didriche K. , Földes T. , Vanfleteren T. , Herman M.
Published: May 2013

The Π (11) ← Σ (00) 2NH (ν1+ν3) band of the NH3–Ar van der Waals complex formed in a supersonic jet expansion, with origin at 6628 cm−1 was recorded at high-resolution using cavity ring down spectroscopy. The analysis leads to upper state rotational constants and J-dependent predissociation lifetimes estimated from linewidth analysis, with a mean value about 0.6 ns.