bluuebunny/crossref_metadata_2025 huggingface dataset:
Exploring Mbar shock conditions and isochorically heated aluminum at the Matter in Extreme Conditions end station of the Linac Coherent Light Source (invited)
Authors: Fletcher L. B. , Lee H. J. , Barbrel B. , Gauthier M. , Galtier E. , Nagler B. , Döppner T. , LePape S. , Ma T. , Pak A. , Turnbull D. , White T. , Gregori G. , Wei M. , Falcone R. W. , Heimann P. , Zastrau U. , Hastings J. B. , Glenzer S. H.
Published: August 2014

Recent experiments performed at the Matter in Extreme Conditions end station of the Linac Coherent Light Source (LCLS) have demonstrated the first spectrally resolved measurements of plasmons from isochorically heated aluminum. The experiments have been performed using a seeded 8-keV x-ray laser beam as a pump and probe to both volumetrically heat and scatter x-rays from aluminum. Collective x-ray Thomson scattering spectra show a well-resolved plasmon feature that is down-shifted in energy by 19 eV. In addition, Mbar shock pressures from laser-compressed aluminum foils using velocity interferometer system for any reflector have been measured. The combination of experiments fully demonstrates the possibility to perform warm dense matter studies at the LCLS with unprecedented accuracy and precision.
High-Tc Phase of PrO0.5F0.5BiS2 single crystal induced by uniaxial pressure
Authors: Fujioka Masaya , Nagao Masanori , Denholme Saleem J. , Tanaka Masashi , Takeya Hiroyuki , Yamaguchi Takahide , Takano Yoshihiko
Published: August 2014

We demonstrated a pressure-induced phase transition from a low-Tc phase (3.5 K) to a high-Tc phase (8.7 K) in single crystalline PrO0.5F0.5BiS2. The high-Tc phase is easily observed even at 0.7 GPa by uniaxial pressure obtained from a geometric effect of a single crystal with an extremely thin thickness. For this phase transition, superconducting anisotropy and the coherence length along the c axis change from γ = 20 to 9.3 and from ξc = 0.56 to 0.71 nm, respectively. It is suggested that a shrinkage in the c lattice constant by applied uniaxial pressure enhances the three dimensionality in the superconducting state.
Spatio-temporal and modal analysis of unsteady fluctuations in a high-subsonic base flow
Authors: Schrijer F. F. J. , Sciacchitano A. , Scarano F.
Published: August 2014

The high-subsonic flow over an axisymmetric backward facing step is investigated at a Mach number of 0.7, with high-speed particle image velocimetry operating at acquisition frequency up to 20 kHz to resolve the time dependent behavior of the separated flow in the longitudinal plane. The statistical flow properties such as the approaching boundary layer thickness, mean and fluctuating velocity field and shear layer growth are quantified. It is found that the shear layer growth is nearly linear up to x/D = 0.6; downstream this location, the reattachment surface influences the shear layer growth rate, causing it to decrease. The visualization of the high-speed measurements shows a quasi-cyclic behavior of the separated region characterized by a fluctuation of the flow reattachment location. The growing and shrinking of the separated region is accompanied by large-scale fluctuations that dominate the flow motions and the momentum exchange across the shear layer. The analysis of the large-scale fluctuations based on proper orthogonal decomposition (POD) of the velocity field indicates that the separated region exhibits pulsating behaviour as associated to the highest energy mode. The second and third modes are approximately in phase quadrature and can be associated to the growth of large azimuthal vortices that undulate the shear layer approaching the mean reattachment location. Conditional averaging of the data indicates that the second/third mode is associated to either the entrainment of high momentum fluid or ejection of low momentum fluid from the separated region depending on the phase. The high-speed measurements enable the spectral analysis of the velocity; the power spectral density of the POD time coefficients for the first three modes is evaluated. The first mode associated to pulsatile growth and collapse of the separated region yields a dominant frequency at StrD = 0.13 (f = 585 Hz) while the second mode features a broader frequency distribution in the range from 1 to 3 kHz (0.22 < StrD < 0.67) with a distinguishable peak at StrD = 0.4. The dynamical correlation between these two modes shows that time derivative of the first mode temporal coefficient and second mode coefficient are strongly correlated. This suggests that the entrainment of high momentum fluid into the separated region is responsible for the wake growth phenomenon.
Mesodynamics with implicit degrees of freedom
Authors: Lin Keng-Hua , Holian Brad Lee , Germann Timothy C. , Strachan Alejandro
Published: August 2014

Mesoscale phenomena—involving a level of description between the finest atomistic scale and the macroscopic continuum—can be studied by a variation on the usual atomistic-level molecular dynamics (MD) simulation technique. In mesodynamics, the mass points, rather than being atoms, are mesoscopic in size, for instance, representing the centers of mass of polycrystalline grains or molecules. In order to reproduce many of the overall features of fully atomistic MD, which is inherently more expensive, the equations of motion in mesodynamics must be derivable from an interaction potential that is faithful to the compressive equation of state, as well as to tensile de-cohesion that occurs along the boundaries of the mesoscale units. Moreover, mesodynamics differs from Newton's equations of motion in that dissipation—the exchange of energy between mesoparticles and their internal degrees of freedom (DoFs)—must be described, and so should the transfer of energy between the internal modes of neighboring mesoparticles. We present a formulation where energy transfer between the internal modes of a mesoparticle and its external center-of-mass DoFs occurs in the phase space of mesoparticle coordinates, rather than momenta, resulting in a Galilean invariant formulation that conserves total linear momentum and energy (including the energy internal to the mesoparticles). We show that this approach can be used to describe, in addition to mesoscale problems, conduction electrons in atomic-level simulations of metals, and we demonstrate applications of mesodynamics to shockwave propagation and thermal transport.
Clamping-induced changes of domain morphology in 88%Pb(Zn1/3Nb2/3)O3-12%PbTiO3
Authors: Chang L.-W. , Nagarajan V. , Okatan M. B. , Gregg J. M.
Published: August 2014

Domain microstructures in single crystal lamellae of 88%Pb(Zn1/3Nb2/3)O3-12%PbTiO3 (cut from bulk using focused ion beam milling) have been mapped using both piezoresponse force microscopy and transmission electron microscopy. Dramatic changes from mottled microstructures typical of relaxors to larger scale domains typical of ferroelectrics have been noted. Stresses associated with substrate clamping are suspected as the cause for the transition from short- to long-range polar order, akin to effects induced by cation ordering achieved by thermal quenching.
Piezoelectric and piezomagnetic force microscopies of multiferroic BiFeO3-LiMn2O4 heterostructures
Authors: Eshghinejad Ahmad , Liang Wen-I. , Chen Qian Nataly , Ma Feiyue , Liu Yuanming , Xie Shuhong , Chu Ying-Hao , Li Jiangyu
Published: August 2014

BiFeO3-LiMn2O4 (BFO-LMO) heterostructures were fabricated via pulsed laser deposition, and their ferroelectric and ferromagnetic properties were probed by magnetic force microscopy (MFM), piezoresponse force microscopy (PFM), and the newly developed piezomagnetic force microscopy (PmFM). MFM imaging shows no clear distinction between BFO and LMO phases, while PFM and PmFM mappings clearly distinguish LMO nanopillars from BFO matrix. Linear piezoelectric and piezomagnetic responses have been observed in both phases, with the effects more prominent in BFO. The strong piezomagnetic response in BFO is believed to arise from Mn doping, while piezoelectric-like response of LMO is attributed to ionic activities as well as vertical geometry of the heterostructure. The limitation of global excitation of PmFM is also discussed.
Local polar structure and multiferroic properties of (1−x)Bi0.9Dy0.1FeO3−xPbTiO3 solid solution
Authors: Zhuang Jian , Wu Hua , Ren Wei , Ye Zuo-Guang
Published: August 2014

The multiferroic (1–x)[0.9BiFeO3–0.1DyFeO3]–xPbTiO3 (BDF–xPT) solid solution with compositions around the morphotropic phase boundary (x = 0.25, 0.28, 0.31, 0.34, and 0.37) has been synthesized in the form of ceramics. The phase symmetry, microstructure, ferroelectricity, piezoresponse, and ferromagnetic properties have been characterized by various techniques. It is found that, with increasing content of lead titanate from x = 0.25 to x = 0.37, the grain size increases and the ferroelectric property is improved. The ferroelectric performance is further enhanced by the introduction of an excess amount (2%) of TiO2 or by sintering in oxygen atmosphere, which reduces the leakage. The local polar structure is imaged by piezoresponse force microscopy. Both the out-of-plane and in-plane images reveal distinct ferroelectric domain structures, with the amplitude and the average domain size decreasing with the increase of lead titanate amount. Compared with the (1–x)BiFeO3–xPbTiO3 binary solid solution of about the same concentration of PT, the magnetic properties are enhanced in BDF–xPT due to the presence of dysprosium, as demonstrated by the ferromagnetic hysteresis loops displayed at room temperature and at 10 K, but the remnant magnetization decreases with increasing PT content. The simultaneous presence of ferroelectricity and ferromagnetism entitles the BDF–xPT solid solution a room-temperature multiferroic material.
Nanoscale characterization of β-phase HxLi1−xNbO3 layers by piezoresponse force microscopy
Authors: Manzo Michele , Denning Denise , Rodriguez Brian J. , Gallo Katia
Published: August 2014

We investigate a non-destructive approach for the characterization of proton exchanged layers in LiNbO3 with sub-micrometric resolution by means of piezoresponse force microscopy (PFM). Through systematic analyses, we identify a clear correlation between optical measurements on the extraordinary refractive index and PFM measurements on the piezoelectric d33 coefficient. Furthermore, we quantify the reduction of the latter induced by proton exchange as 83 ± 2% and 68 ± 3% of the LiNbO3 value, for undoped and 5 mol. % MgO-doped substrates, respectively.
Quantification of electromechanical coupling measured with piezoresponse force microscopy
Authors: Lepadatu Serban , Stewart Mark , Cain Markys G.
Published: August 2014

Here, we study the piezoresponse of epitaxial ferroelectric samples excited through top electrode structures with conductive tips in the global excitation mode and compare these results to displacement values obtained using artifact-free laser Doppler vibrometry (LDV) measurements. Substrate bending modes are studied using finite element simulations and LDV measurements and found to be negligible for top electrode diameters below 100 μm. The effect of electrostatic forces on the piezoresponse measurements is analyzed and methods for minimizing these are discussed. Using a resistive tip-electrode contact mode, the piezoresponse measurements are found to be in good agreement with values obtained from calibrations, providing a link between nanometer scale piezoresponse measurements and quantitative LDV measurements.
Domain growth and domain wall roughness along different directions in LiNbO3 single crystal
Authors: Du Yingchao , Bo Huifeng , Kan Yi , Jin Yaming , Lu Xiaomei , Xu Tingting , Xiao Shuyu , Yue Chen , Huang Fenzheng , Zhu Jinsong
Published: August 2014

Linear domains are grown along two different directions (x and y) in z-cut LiNbO3 single crystal by piezoresponse force microscope. Compared with linear domains along x direction, those along y direction possess larger average domain width, higher regularity and lower roughness exponent. These results indicate that domain growth along y direction is more favorable in LiNbO3, which are attributed to the smaller energy of Y domain walls and the layer-by-layer step growth of the hexagonal domains.
Effect of thermal annealing on ferroelectric domain structures in poly(vinylidene-fluoride-trifluorethylene) Langmuir-Blodgett thin films
Authors: Xiao Z. , Hamblin J. , Poddar Shashi , Ducharme Stephen , Paruch P. , Hong X.
Published: August 2014

We report a piezo-response force microscopy study of the effect of thermal annealing on ferroelectric domain structures in 6 to 20 monolayer (11 to 36 nm) polycrystalline poly(vinylidene-fluoride-trifluorethylene) thin films prepared using the Langmuir-Blodgett approach. Stripe-shape domains have been created at room temperature and subjected to thermal annealing at progressively higher temperatures up to the ferroelectric Curie temperature TC of approximately 110 °C. The static configuration of the domain walls exhibits no appreciable temperature dependence after thermal annealing, with the domain-wall roughness exponent ζ ranging from 0.4 to 0.5. Above 80 °C, we observed spontaneous polarization reversal at randomly scattered local sites in both polarization states. The number of domain nucleation centers increases rapidly as a function of temperature. We compared the thermally driven domain formation in ferroelectric polymers with those observed in ferroelectric oxides and attributed the difference to the distinct mechanisms for domain formation in these two systems.
Temperature dependence of the local piezoresponse in (K,Na)NbO3-based ceramics with large electromechanical strain
Authors: Gobeljic Danka , Shvartsman Vladimir V. , Wang Ke , Yao Fangzhou , Li Jing-Feng , Jo Wook , Rödel Jürgen , Lupascu Doru C.
Published: August 2014

We report on temperature dependence of local electromechanical properties of lead-free (K,Na)NbO3-based ceramics that macroscopically manifests a large temperature-insensitive strain. Piezoresponse force microscopy reveals the particular role of the orthorhombic-tetragonal phase transition, where a reconstruction of the domain structure occurs and local piezoelectric response shows a peak value. A good quantitative agreement between temperature dependences of the local and previously reported macroscopic small-signal piezoelectric coefficients is observed. An influence of the polymorphic phase transition on polarization switching kinetics was revealed.
Experimental observations on the links between surface perturbation parameters and shock-induced mass ejection
Authors: Monfared S. K. , Oró D. M. , Grover M. , Hammerberg J. E. , LaLone B. M. , Pack C. L. , Schauer M. M. , Stevens G. D. , Stone J. B. , Turley W. D. , Buttler W. T.
Published: August 2014

We have assembled together our ejecta measurements from explosively shocked tin acquired over a period of about ten years. The tin was cast at 0.99995 purity, and all of the tin targets or samples were shocked to loading pressures of about 27 GPa, allowing meaningful comparisons. The collected data are markedly consistent, and because the total ejected mass scales linearly with the perturbations amplitudes they can be used to estimate how much total Sn mass will be ejected from explosively shocked Sn, at similar loading pressures, based on the surface perturbation parameters of wavelength and amplitude. Most of the data were collected from periodic isosceles shapes that approximate sinusoidal perturbations. Importantly, however, we find that not all periodic perturbations behave similarly. For example, we observed that sawtooth (right triangular) perturbations eject more mass than an isosceles perturbation of similar depth and wavelength, demonstrating that masses ejected from irregular shaped perturbations cannot be normalized to the cross-sectional areas of the perturbations.
The role of non-equilibrium fluxes in the relaxation processes of the linear chemical master equation
Authors: de Oliveira Luciana Renata , Bazzani Armando , Giampieri Enrico , Castellani Gastone C.
Published: August 2014

We propose a non-equilibrium thermodynamical description in terms of the Chemical Master Equation (CME) to characterize the dynamics of a chemical cycle chain reaction among m different species. These systems can be closed or open for energy and molecules exchange with the environment, which determines how they relax to the stationary state. Closed systems reach an equilibrium state (characterized by the detailed balance condition (D.B.)), while open systems will reach a non-equilibrium steady state (NESS). The principal difference between D.B. and NESS is due to the presence of chemical fluxes. In the D.B. condition the fluxes are absent while for the NESS case, the chemical fluxes are necessary for the state maintaining. All the biological systems are characterized by their “far from equilibrium behavior,” hence the NESS is a good candidate for a realistic description of the dynamical and thermodynamical properties of living organisms. In this work we consider a CME written in terms of a discrete Kolmogorov forward equation, which lead us to write explicitly the non-equilibrium chemical fluxes. For systems in NESS, we show that there is a non-conservative “external vector field” whose is linearly proportional to the chemical fluxes. We also demonstrate that the modulation of these external fields does not change their stationary distributions, which ensure us to study the same system and outline the differences in the system's behavior when it switches from the D.B. regime to NESS. We were interested to see how the non-equilibrium fluxes influence the relaxation process during the reaching of the stationary distribution. By performing analytical and numerical analysis, our central result is that the presence of the non-equilibrium chemical fluxes reduces the characteristic relaxation time with respect to the D.B. condition. Within a biochemical and biological perspective, this result can be related to the “plasticity property” of biological systems and to their capabilities to switch from one state to another as is observed during synaptic plasticity, cell fate determination, and differentiation.
On the mathematical and geometrical structure of the determining equations for shear waves in nonlinear isotropic incompressible elastodynamics
Authors: Saccomandi Giuseppe , Vitolo Raffaele
Published: August 2014

Using the theory of 1 + 1 hyperbolic systems we put in perspective the mathematical and geometrical structure of the celebrated circularly polarized waves solutions for isotropic hyperelastic materials determined by Carroll [Acta Mechanica 3, 167–181 (1967)]. We show that a natural generalization of this class of solutions yields an infinite family of linear solutions for the equations of isotropic elastodynamics. Moreover, we determine a huge class of hyperbolic partial differential equations having the same property of the shear wave system. Restricting the attention to the usual first order asymptotic approximation of the equations determining transverse waves we provide the complete integration of this system using generalized symmetries.
Local random quantum circuits: Ensemble completely positive maps and swap algebras
Authors: Zanardi Paolo
Published: August 2014

We define different classes of local random quantum circuits (L-RQC) and show that (a) statistical properties of L-RQC are encoded into an associated family of completely positive maps and (b) average purity dynamics can be described by the action of these maps on operator algebras of permutations (swap algebras). An exactly solvable one-dimensional case is analyzed to illustrate the power of the swap algebra formalism. More in general, we prove short time area-law bounds on average purity for uncorrelated L-RQC and infinite time results for both the uncorrelated and correlated cases.
A setup for simultaneous measurement of infrared spectra and light scattering signals: Watching amyloid fibrils grow from intact proteins
Authors: Li Yang , Maurer Jürgen , Roth Andreas , Vogel Vitali , Winter Ernst , Mäntele Werner
Published: August 2014

A setup for the simultaneous measurement of mid-infrared spectra and static light scattering is described that can be used for the analysis of the formation of nanoscale and microscopic aggregates from smaller molecules to biopolymers. It can be easily integrated into sample chambers of infrared spectrometers or combined with laser beams from tunable infrared lasers. Here, its use for the analysis of the formation of amyloid fibrils from intact proteins is demonstrated. The formation of amyloid fibrils or plaques from proteins is a widespread and pathogenetic relevant process, and a number of diseases are caused and correlated with the deposition of amyloid fibrils in cells and tissues. The molecular mechanisms of these transformations, however, are still unclear. We report here the simultaneous measurement of infrared spectra and static light scattering for the analysis of fibril formation from egg-white lysozyme. The transformation of the native form into non-native forms rich in β-sheet structure is measured by analysis of the amide I spectral region in the infrared spectra, which is sensitive for local structures. At the same time, light scattering signals at forward direction as well as the forward/backward ratio, which are sensitive for the number of scattering centers and their approximate sizes, respectively, are collected for the analysis of fibril growth. Thermodynamic and kinetic parameters as well as mechanistic information are deduced from the combination of the two complementary techniques.
X-ray area backlighter development at the National Ignition Facility (invited)
Authors: Barrios M. A. , Regan S. P. , Fournier K. B. , Epstein R. , Smith R. , Lazicki A. , Rygg R. , Fratanduono D. E. , Eggert J. , Park H.-S. , Huntington C. , Bradley D. K. , Landen O. L. , Collins G. W.
Published: August 2014

1D spectral imaging was used to characterize the K-shell emission of Z ≈ 30–35 and Z ≈ 40–42 laser-irradiated foils at the National Ignition Facility. Foils were driven with up to 60 kJ of 3ω light, reaching laser irradiances on target between 0.5 and 20 × 1015 W/cm2. Laser-to-X-ray conversion efficiency (CE) into the Heα line (plus satellite emission) of 1.0%–1.5% and 0.15%–0.2% was measured for Z ≈ 30–32 and Z ≈ 40–42, respectively. Measured CE into Heα (plus satellite emission) of Br (Z = 35) compound foils (either KBr or RbBr) ranged between 0.16% and 0.29%. Measured spectra are compared with 1D non-local thermodynamic equilibrium atomic kinetic and radiation transport simulations, providing a fast and accurate predictive capability.
Dissociation of H2 on carbon doped aluminum cluster Al6C
Authors: Yang Huihui , Zhang Yan , Chen Hongshan
Published: August 2014

The dissociation of H2 molecule is the first step for chemical storage of hydrogen, and the energy barrier of the dissociation is the key factor to decide the kinetics of the regeneration of the storage material. As a light element, aluminum is an important candidate component for storage materials with high gravimetric density. This paper investigates the adsorption and dissociation of H2 on carbon doping aluminum cluster Al6C. The study shows that doping carbon into aluminum cluster can significantly change the electronic structure and increase the stability. Al6C has a few stable isomers with close energies and their structures are quite flexible. The molecular adsorption of H2 on Al6C is very weak, but the H2 molecule can be dissociated easily on this cluster. The stable product of the dissociated adsorption is searched and the different paths for the dissociation are investigated. During the dissociation of H2, the structure of the cluster adjusts accordingly, and strong orbital interaction between the hydrogen and the cluster occurs. The calculated energy barrier for the dissociation is only 0.30 eV, which means the dissociation can take place at moderate temperatures.
Extended-range grazing-incidence spectrometer for high-resolution extreme ultraviolet measurements on an electron beam ion trap
Authors: Beiersdorfer P. , Magee E. W. , Brown G. V. , Hell N. , Träbert E. , Widmann K.
Published: August 2014

A high-resolution grazing-incidence grating spectrometer has been implemented on the Livermore electron beam ion traps for performing very high-resolution measurements in the soft x-ray and extreme ultraviolet region spanning from below 10 Å to above 300 Å. The instrument operates without an entrance slit and focuses the light emitted by highly charged ions located in the roughly 50 μm wide electron beam onto a cryogenically cooled back-illuminated charge-coupled device detector. The measured line widths are below 0.025 Å above 100 Å, and the resolving power appears to be limited by the source size and Doppler broadening of the trapped ions. Comparisons with spectra obtained with existing grating spectrometers show an order of magnitude improvement in spectral resolution.
Edge impurity rotation profile measurement by using high-resolution ultraviolet/visible spectrometer on J-TEXT
Authors: Cheng Z. F. , Luo J. , Wang Z. J. , Zhang Z. P. , Zhang X. L. , Hou S. Y. , Cheng C. , Li Z. , Zhuang G.
Published: August 2014

An upgrade of the edge rotation diagnostic system is achieved by increasing the number of viewing channels to 17 on J-TEXT tokamak. With the upgrade, the spatial resolution reaches 1 cm. The bulk plasma is used as the calibration light source. And the toroidal velocity profile of C V (carbon V) at edge region is obtained by using a spatial deconvolution technique. The valid measurement region is at ρ = 0.6–0.9, corresponding to the emitting region of C V. The preliminary experimental results express that the velocity of plasma may have a zero point near ρ = 0.85.
Ab initio potential energy surface for methane and carbon dioxide and application to vapor-liquid coexistence
Authors: Pai Sung Jin , Bae Young Chan
Published: August 2014

A six-dimensional intermolecular potential energy surface for a rigid methane (CH4) and carbon dioxide (CO2) dimer was developed from the counterpoise-corrected supermolecular approach at the CCSD(T) level of theory. A total of 466 grid points distributed to 46 orientations were calculated from the complete basis set limit extrapolation based on up to aug-cc-pVQZ basis set. A modified site-site pair potential function was proposed for rapid representation of the high level ab initio calculations. A nonadditive three-body interaction was represented by the Axilrod-Teller-Muto expression for mixtures with the polarizability and the London dispersion constant of each molecule. Second to fourth virial coefficients of CH4 and CO2 mixtures were calculated using both the Mayer sampling Monte Carlo method and the present potential functions. The virial equation of state derived from these coefficients was used to predict the pVT values and showed good agreement with experimental data below 200 bar at 300 K. The vapor-liquid coexistence curves of pure CH4, CO2 and their mixtures were presented with the aid of Gibbs ensemble Monte Carlo simulations. The predicted tie lines agreed with the experimental data within the uncertainties up to near the critical point.
Analytic derivative couplings for spin-flip configuration interaction singles and spin-flip time-dependent density functional theory
Authors: Zhang Xing , Herbert John M.
Published: August 2014

We revisit the calculation of analytic derivative couplings for configuration interaction singles (CIS), and derive and implement these couplings for its spin-flip variant for the first time. Our algorithm is closely related to the CIS analytic energy gradient algorithm and should be straightforward to implement in any quantum chemistry code that has CIS analytic energy gradients. The additional cost of evaluating the derivative couplings is small in comparison to the cost of evaluating the gradients for the two electronic states in question. Incorporation of an exchange-correlation term provides an ad hoc extension of this formalism to time-dependent density functional theory within the Tamm-Dancoff approximation, without the need to invoke quadratic response theory or evaluate third derivatives of the exchange-correlation functional. Application to several different conical intersections in ethylene demonstrates that minimum-energy crossing points along conical seams can be located at substantially reduced cost when analytic derivative couplings are employed, as compared to use of a branching-plane updating algorithm that does not require these couplings. Application to H3 near its D3h geometry demonstrates that correct topology is obtained in the vicinity of a conical intersection involving a degenerate ground state.
The exponential decay of solutions and traveling wave solutions for a modified Camassa–Holm equation with cubic nonlinearity
Authors: Wu Xinglong , Guo Boling
Published: August 2014

The present paper is devoted to the study of persistence properties, infinite propagation, and the traveling wave solutions for a modified Camassa–Holm equation with cubic nonlinearity. We first show that persistence properties of the solution to the equation provided the initial datum is exponential decay and the initial potential satisfies a certain sign condition. Next, we get the infinite propagation if the initial datum satisfies certain compact conditions, while the solution to Eq. (1.1) instantly loses compactly supported, the solution has exponential decay as |x| goes to infinity. Finally, we prove Eq. (1.1) has a family traveling wave solutions.
Statistical classification of flow morphology in rapidly rotating Rayleigh-Bénard convection
Authors: Nieves David , Rubio Antonio M. , Julien Keith
Published: August 2014

In rapidly rotating convection four flow regimes with distinct characteristics have been identified via simulations of asymptotically reduced equations as a function of a reduced Rayleigh number RaE4/3 and Prandtl number σ (K. Julien, A. Rubio, I. Grooms, and E. Knobloch, “Statistical and physical balances in low Rossby number Rayleigh-Bénard convection,” Geophys. Astrophys. Fluid Dyn. 106, 392–428 (2012)). In each regime the flow organizes, with varying intensity, into coherent vertical structures. The identified morphologies, in order of increasing RaE4/3, consist of the cellular regime, the convective Taylor column regime, the plume regime, and a regime characterized by geostrophic turbulence. Presently, physical limitations on laboratory experiments and spatio-temporal resolution challenges on direct numerical simulations of the incompressible Navier-Stokes equations inhibit an exhaustive analysis of the flow morphology in the rapid rotating limit. In this paper the flow morphologies obtained from simulations of the reduced equations are investigated from a statistical perspective. We utilize auto- and cross-correlations of temporal and spatial signals that synthesize experimental data obtained from thermistor measurements or particle image velocimetry. We show how these statistics can be employed in laboratory experiments to (i) identify transitions in the flow morphology, (ii) capture the radial profiles of coherent structures, and (iii) extract transport properties of these structures. These results provide a foundation for comparison and a measure for understanding the extent to which rotationally constrained regime has been accessed by laboratory experiments and direct numerical simulations.
A quantum quasi-harmonic nonlinear oscillator with an isotonic term
Authors: Rañada Manuel F.
Published: August 2014

The properties of a nonlinear oscillator with an additional term kg/x2, characterizing the isotonic oscillator, are studied. The nonlinearity affects to both the kinetic term and the potential and combines two nonlinearities associated to two parameters, κ and kg, in such a way that for κ = 0 all the characteristics of the standard isotonic system are recovered. The first part is devoted to the classical system and the second part to the quantum system. This is a problem of quantization of a system with position-dependent mass of the form m(x) = 1/(1 − κx2), with a κ-dependent non-polynomial rational potential and with an additional isotonic term. The Schrödinger equation is exactly solved and the (κ, kg)-dependent wave functions and bound state energies are explicitly obtained for both κ < 0 and κ > 0.
Instabilities in the boundary layer over a permeable, compliant wall
Authors: Pluvinage Franck , Kourta Azeddine , Bottaro Alessandro
Published: August 2014

Local linear stability of swept and unswept incompressible boundary layers developing over compliant, fluid-saturated, porous plates is considered in the limit of small permeability. The analysis is meant to yield preliminary indications on the possible stabilization induced on the flow's hydrodynamic and hydroelastic modes by poroelastic media, such as those occurring in many natural and technological settings. As far as hydrodynamic modes are concerned, the main stabilizing effect is that of compliance, which however couples weakly to low-frequency crossflow modes. Permeability plays a damping role on hydroelastic modes, which here take the form of travelling wave flutter instabilities. The passive control of instabilities through poroelastic coatings specifically designed to selectively exploit the effect of compliance and/or permeability is a subject worthy of future research efforts.
On the oscillator realization of conformal U(2, 2) quantum particles and their particle-hole coherent states
Authors: Calixto M. , Pérez-Romero E.
Published: August 2014

We revise the unireps. of U(2, 2) describing conformal particles with continuous mass spectrum from a many-body perspective, which shows massive conformal particles as compounds of two correlated massless particles. The statistics of the compound (boson/fermion) depends on the helicity h of the massless components (integer/half-integer). Coherent states (CS) of particle-hole pairs (“excitons”) are also explicitly constructed as the exponential action of exciton (non-canonical) creation operators on the ground state of unpaired particles. These CS are labeled by points Z (2 × 2 complex matrices) on the Cartan-Bergman domain \documentclass[12pt]{minimal}\begin{document}$\mathbb {D}_4=U(2,2)/U(2)^2$\end{document}D4=U(2,2)/U(2)2, and constitute a generalized (matrix) version of Perelomov U(1, 1) coherent states labeled by points z on the unit disk \documentclass[12pt]{minimal}\begin{document}$\mathbb {D}_1=U(1,1)/U(1)^2$\end{document}D1=U(1,1)/U(1)2. First, we follow a geometric approach to the construction of CS, orthonormal basis, U(2, 2) generators and their matrix elements and symbols in the reproducing kernel Hilbert space \documentclass[12pt]{minimal}\begin{document}$\mathcal {H}_\lambda (\mathbb {D}_4)$\end{document}Hλ(D4) of analytic square-integrable holomorphic functions on \documentclass[12pt]{minimal}\begin{document}$\mathbb {D}_4$\end{document}D4, which carries a unitary irreducible representation of U(2, 2) with index \documentclass[12pt]{minimal}\begin{document}$\lambda \in \mathbb {N}$\end{document}λ∈N (the conformal or scale dimension). Then we introduce a many-body representation of the previous construction through an oscillator realization of the U(2, 2) Lie algebra generators in terms of eight boson operators with constraints. This particle picture allows us for a physical interpretation of our abstract mathematical construction in the many-body jargon. In particular, the index λ is related to the number 2(λ − 2) of unpaired quanta and to the helicity h = (λ − 2)/2 of each massless particle forming the massive compound.
Sampling microcanonical ensembles of trajectories using harmonic approximation in internal coordinates
Authors: Rybkin Vladimir V. , Ekström Ulf
Published: August 2014

In this paper, we modify quasiclassical harmonic sampling of microcanonical ensembles of trajectories by using the curvilinear internal coordinates. The harmonic approximation in the curvilinear normal coordinates provides a more realistic description of the PES than in the conventional rectilinear ones at finite displacements. Therefore, the sampling of vibrations in the internal coordinates significantly improves the quality of the sampling in a block-box fashion, providing more realistic displacements and reducing the errors in the potential energy. In particular, the sampling of large-amplitude torsion vibrations, which is non-realistic in the Cartesian modes, becomes accurate or acceptable in the curvilinear modes.
Description of the prototype diagnostic residual gas analyzer for ITER
Authors: Younkin T. R. , Biewer T. M. , Klepper C. C. , Marcus C.
Published: August 2014

The diagnostic residual gas analyzer (DRGA) system to be used during ITER tokamak operation is being designed at Oak Ridge National Laboratory to measure fuel ratios (deuterium and tritium), fusion ash (helium), and impurities in the plasma. The eventual purpose of this instrument is for machine protection, basic control, and physics on ITER. Prototyping is ongoing to optimize the hardware setup and measurement capabilities. The DRGA prototype is comprised of a vacuum system and measurement technologies that will overlap to meet ITER measurement requirements. Three technologies included in this diagnostic are a quadrupole mass spectrometer, an ion trap mass spectrometer, and an optical penning gauge that are designed to document relative and absolute gas concentrations.
Magnetic diagnostics for equilibrium reconstructions with eddy currents on the lithium tokamak experiment
Authors: Schmitt J. C. , Bialek J. , Lazerson S. , Majeski R.
Published: August 2014

The Lithium Tokamak eXperiment is a spherical tokamak with a close-fitting low-recycling wall composed of thin lithium layers evaporated onto a stainless steel-lined copper shell. Long-lived non-axisymmetric eddy currents are induced in the shell and vacuum vessel by transient plasma and coil currents and these eddy currents influence both the plasma and the magnetic diagnostic signals that are used as constraints for equilibrium reconstruction. A newly installed set of re-entrant magnetic diagnostics and internal saddle flux loops, compatible with high-temperatures and lithium environments, is discussed. Details of the axisymmetric (2D) and non-axisymmetric (3D) treatments of the eddy currents and the equilibrium reconstruction are presented.
Selective metal-organic chemical vapor deposition growth of high quality GaAs on Si(001)
Authors: Guo W. , Date L. , Pena V. , Bao X. , Merckling C. , Waldron N. , Collaert N. , Caymax M. , Sanchez E. , Vancoille E. , Barla K. , Thean A. , Eyben P. , Vandervorst W.
Published: August 2014

High quality GaAs is selectively grown in 40 nm width Shallow Trench Isolation patterned structures. The patterned wafers have a V-shape Si (111) surface obtained by Tetramethylammonium hydroxide etching. By employing a SiCoNi™ pre-epi clean and two-step growth procedure (low temperature buffer and high temperature main layer), defects are effectively confined at the trench bottom, leaving a dislocation-free GaAs layer at the upper part. The high crystal quality is confirmed by transmission electron microscopy. Scanning spreading resistance microscopy indicates a high resistance of GaAs. The process conditions and GaAs material quality are highly compatible with Si technology platform.
Multicycle rapid thermal annealing optimization of Mg-implanted GaN: Evolution of surface, optical, and structural properties
Authors: Greenlee Jordan D. , Feigelson Boris N. , Anderson Travis J. , Tadjer Marko J. , Hite Jennifer K. , Mastro Michael A. , Eddy Charles R. , Hobart Karl D. , Kub Francis J.
Published: August 2014

The first step of a multi-cycle rapid thermal annealing process was systematically studied. The surface, structure, and optical properties of Mg implanted GaN thin films annealed at temperatures ranging from 900 to 1200 °C were investigated by Raman spectroscopy, photoluminescence, UV-visible spectroscopy, atomic force microscopy, and Nomarski microscopy. The GaN thin films are capped with two layers of in-situ metal organic chemical vapor deposition -grown AlN and annealed in 24 bar of N2 overpressure to avoid GaN decomposition. The crystal quality of the GaN improves with increasing annealing temperature as confirmed by UV-visible spectroscopy and the full widths at half maximums of the E2 and A1 (LO) Raman modes. The crystal quality of films annealed above 1100 °C exceeds the quality of the as-grown films. At 1200 °C, Mg is optically activated, which is determined by photoluminescence measurements. However, at 1200 °C, the GaN begins to decompose as evidenced by pit formation on the surface of the samples. Therefore, it was determined that the optimal temperature for the first step in a multi-cycle rapid thermal anneal process should be conducted at 1150 °C due to crystal quality and surface morphology considerations.
Molecular doping and tuning threshold voltage in 6,13-bis(triisopropylsilylethynyl)pentacene/polymer blend transistors
Authors: Belasco James , Mohapatra Swagat K. , Zhang Yadong , Barlow Stephen , Marder Seth R. , Kahn Antoine
Published: August 2014

Precise control of the electrical characteristics of organic field-effect transistors is essential for their use in integrated circuits. In addition to the mobility, the threshold voltage, Vth, is a key parameter to control for proper circuit operation. In this work, we demonstrate the controlled tuning of Vth of solution-processed, small-molecule, organic semiconductor transistors via molecular doping of the solution at multiple different doping levels.
Modeling the electrical transport in epitaxial undoped and Ni-, Cr-, and W-doped TiO2 anatase thin films
Authors: Kneiß Max , Jenderka Marcus , Brachwitz Kerstin , Lorenz Michael , Grundmann Marius
Published: August 2014

Electrical transport in undoped and Ni-, Cr-, and W-doped TiO2 thin films on SrTiO3(001) is modelled either with the sum of two thermally activated processes with exponential temperature dependence of conductivity, or with the sum of three-dimensional Mott variable-range hopping (VRH) and an activated process with low activation energy. The latter is interpreted for both models as small polaron hopping (<θD/4). According to reduced chi-square values, the double activated model is superior for data of higher ordered films grown at 540 and 460 °C. For lower growth temperature, VRH plus activated conductivity fits partly better. For all dopants, n-type conductivity is observed.
Infrared luminescence for real time ionizing radiation detection
Authors: Veronese Ivan , Mattia Cristina De , Fasoli Mauro , Chiodini Norberto , Mones Eleonora , Cantone Marie Claire , Vedda Anna
Published: August 2014

Radio-luminescence (RL) optical fiber sensors enable a remote, punctual, and real time detection of ionizing radiation. However, the employment of such systems for monitoring extended radiation fields with energies above the Cerenkov threshold is still challenging, since a spurious luminescence, namely, the “stem effect,” is also generated in the passive fiber portion exposed to radiation. Here, we present experimental measurements on Yb-doped silica optical fibers irradiated with photon fields of different energies and sizes. The results demonstrate that the RL of Yb3+, displaying a sharp emission line at about 975 nm, is free from any spectral superposition with the spurious luminescence. This aspect, in addition with the suitable linearity, reproducibility, and sensitivity properties of the Yb-doped fibers, paves the way to their use in applications where an efficient stem effect removal is required.
Surface magnetism of the carbon foam: An ab-initio theoretical study
Authors: Yu Guodong , Jiang Liwei , Zheng Yisong
Published: August 2014

By means of ab-initio calculations, we study the surface magnetism of carbon foam, a carbon allotrope constructed by both the sp2 and sp3 hybridized carbon atoms. It is found that the sp3-terminated surface and sp2-terminated surface with hydrogen saturation (sp2H) have the antiferromagnetic and ferromagnetic ground states, respectively. And the corresponding phase transition temperatures of these two surfaces are estimated to exceed 100 K. In addition, the magnetic moment of the sp2H surface can be effectively modulated by strain. More interestingly, at the level of generalized gradient approximation, as the lattice are stretched, a bulk bandgap will open. And in such a bandgap, the sp2H surface states can form spin polarized Dirac cones at K(K′) point. Thus, in the vicinity of the Fermi level, only the electron with a specific spin behaves like a Dirac Fermion.
Industrial Nationalism versus European Partnerships: An Analysis of State-Led Franco—German Interfirm Linkages
Authors: Trouille Jean-Marc
Published: August 2014

This paper examines the impact of state intervention in French—German interfirm linkages and discusses the implications of conflicting national interests for the furthering of single market integration. It demonstrates that, despite initial success in launching large-scale cross-border alliances in strategic sectors, France and Germany have remained divided by their own industrial nationalism. It argues that their respective attitudes towards industrial policy are less contradictory than would appear at first sight, but that transcending industrial nationalism by Europeanising the notion of economic patriotism would be an essential precondition for a more efficient EU-wide industrial policy within a better integrated internal market.
Fiscal Policy and Crowding Out in Developing Asia
Authors: Hur Seok-Kyun , Mallick Sushanta , Park Donghyun
Published: August 2014

Fiscal stimulus programs have contributed substantially to developing Asia's faster and stronger-than-expected recovery from the global financial crisis. This may lead to political pressures for greater use of countercyclical fiscal policy in the postcrisis period. However, the countercyclical effectiveness of fiscal policy depends critically on the extent to which it crowds out private investment and consumption. In the medium term, the use of fiscal policy to promote rebalancing toward domestic demand may require a moderate fiscal expansion. The extent of crowding out will impinge upon the effectiveness of such fiscal expansion in boosting domestic demand. In this paper we perform empirical analysis on both cross-country panel data and country-specific time-series data to investigate crowding out in the region. Overall, our empirical evidence is decidedly mixed, with no clear evidence of either crowding out or crowding in. The evidence fails to provide compelling support for greater use of fiscal policy for countercyclical purposes. In the context of rebalancing, fiscal expansion will not, in and of itself, contribute to a more balanced demand and output structure. That would require using fiscal policy to help remove structural impediments to private consumption and investment.
Underqualification as an Opportunity for Low-Educated Workers
Authors: Hamersma Marije , Edzes Arjen , van Dijk Jouke
Published: August 2014

Improving the labor market position of low-educated workers is one of the most important goals of regional labor market policy. Underqualification, meaning holding a job at a higher level than expected based on one's formal education, can be—under certain conditions—a favorable position from both an individual and a policy perspective. In this study we used repeated cross-sections of data about Dutch workers from 1996 to 2006 to relate the chances of underqualification to personal, firm, and labor market characteristics. Briefly, we found that, for low-educated workers, firm and personal characteristics are more important than regional characteristics in explaining underqualification. Higher regional unemployment rates lower the chances of being underqualified. Working in smaller firms or firms with many high-skilled jobs has a strong positive effect on the chances of attaining higher level jobs, while working in firms with many highly educated workers lowers these chances. Women and nonnatives are less often underqualified, whereas older workers are more often underqualified. Gaining more insight into the determinants of underqualification is important for developing more effective policy measures that aim to improve the labor market position of the most vulnerable groups in the labor market.