bluuebunny/crossref_metadata_2025 huggingface dataset:
Critical phenomena in superconductors and uniaxial antiferromagnets (Review Article)
Authors: Sirenko V. A.
Published: October 2012

This overview is inspired by the pioneering works by Eremenko et al. on the first observed similarities in the low-temperature phase formation of conventional antiferromagnets and superconductors near the critical temperature of the transition. In the development of the detected similarities, a comparison was made of the temperature dependence of the magnetic and structural properties of new anisotropic superconductors and antiferromagnets with competing order parameters (multiferroics). Common features in their critical behavior near the ordering temperature Tc are discussed.
Auto- and cross-power spectral analysis of dual trap optical tweezer experiments using Bayesian inference
Authors: von Hansen Yann , Mehlich Alexander , Pelz Benjamin , Rief Matthias , Netz Roland R.
Published: October 2012

The thermal fluctuations of micron-sized beads in dual trap optical tweezer experiments contain complete dynamic information about the viscoelastic properties of the embedding medium and—if present—macromolecular constructs connecting the two beads. To quantitatively interpret the spectral properties of the measured signals, a detailed understanding of the instrumental characteristics is required. To this end, we present a theoretical description of the signal processing in a typical dual trap optical tweezer experiment accounting for polarization crosstalk and instrumental noise and discuss the effect of finite statistics. To infer the unknown parameters from experimental data, a maximum likelihood method based on the statistical properties of the stochastic signals is derived. In a first step, the method can be used for calibration purposes: We propose a scheme involving three consecutive measurements (both traps empty, first one occupied and second empty, and vice versa), by which all instrumental and physical parameters of the setup are determined. We test our approach for a simple model system, namely a pair of unconnected, but hydrodynamically interacting spheres. The comparison to theoretical predictions based on instantaneous as well as retarded hydrodynamics emphasizes the importance of hydrodynamic retardation effects due to vorticity diffusion in the fluid. For more complex experimental scenarios, where macromolecular constructs are tethered between the two beads, the same maximum likelihood method in conjunction with dynamic deconvolution theory will in a second step allow one to determine the viscoelastic properties of the tethered element connecting the two beads.
The Thomas-Fermi model in the theory of systems of charged particles above the surface of liquid dielectrics
Authors: Lytvtnenko D. M. , Slyusarenko Yu. V. , Kirdin A. I.
Published: October 2012

A consistent theory of equilibrium states of same sign charges above the surface of liquid dielectric film located on solid substrate in the presence of external attracting constant electric field is proposed. The approach to the development of the theory is based on the Thomas-Fermi model generalized to the systems under consideration and on the variational principle. The using of self-consistent field model allows formulating a theory containing no adjustable constants. In the framework of the variational principle we obtain the self-consistency equations for the parameters describing the system: the distribution function of charges above the liquid dielectric surface, the electrostatic field potentials in all regions of the system and the surface profile of the liquid dielectric. The self-consistency equations are used to describe the phase transition associated with the formation of spatially periodic structures in the system of charges on liquid dielectric surface. Assuming the non-degeneracy of the gas of charges above the surface of liquid dielectric film the solutions of the self-consistency equations near the critical point are obtained. In the case of the symmetric phase we obtain the expressions for the potentials and electric fields in all regions of the studied system. The distribution of the charges above the surface of liquid dielectric film for the symmetric phase is derived. The system parameters of the phase transition to nonsymmetric phase – the states with a spatially periodic ordering are obtained. We derive the expression determining the period of two-dimensional lattice as a function of physical parameters of the problem – the temperature, the external attractive electric field, the number of electrons per unit of the flat surface area of the liquid dielectric, the density of the dielectric, its surface tension and permittivity, and the permittivity of the solid substrate. The possibility of generalizing the developed theory in the case of degenerate gas of like-charged particles above the liquid dielectric surface is discussed.
Characterization of informational completeness for covariant phase space observables
Authors: Kiukas J. , Lahti P. , Schultz J. , Werner R. F.
Published: October 2012

In the nonrelativistic setting with finitely many canonical degrees of freedom, a shift-covariant phase space observable is uniquely characterized by a positive operator of trace one and, in turn, by the Fourier-Weyl transform of this operator. We study three properties of such observables, and characterize them in terms of the zero set of this transform. The first is informational completeness, for which it is necessary and sufficient that the zero set has dense complement. The second is a version of informational completeness for the Hilbert-Schmidt class, equivalent to the zero set being of measure zero, and the third, known as regularity, is equivalent to the zero set being empty. We give examples demonstrating that all three conditions are distinct. The three conditions are the special cases for p = 1, 2, ∞ of a more general notion of p-regularity defined as the norm density of the span of translates of the operator in the Schatten-p class. We show that the relation between zero sets and p-regularity can be mapped completely to the corresponding relation for functions in classical harmonic analysis.
Proton conduction related electrical dipole and space charge polarization in hydroxyapatite
Authors: Horiuchi N. , Nakamura M. , Nagai A. , Katayama K. , Yamashita K.
Published: October 2012

Hydroxyapatite (HAp), well known as a biomaterial, is also known as a proton conductor. Its electrical properties are related strongly to its stability and surface properties. In particular, persistent electrical polarization related to proton conductivity of hydroxyapatite has a substantial influence on hydroxyapatite surface properties. The origins of polarizations were investigated in proton-defect-induced HAp ceramics using thermally stimulated depolarization current (TSDC) measurements. Two peaks were observed, indicating that the persistent polarization comprises polarization elements of two kinds. The TSDC response as a function of the applied electric field in polarization treatments indicated that the persistent polarization is dipole polarization and space charge polarization. The former, dipole polarization, increased continuously with increased defect concentration. The activation energies were 0.67–0.86 eV, which are comparable to proton conduction activation energy. Results show that dipole polarization consists of electrical dipoles of the defect pairs, which are formed through proton conduction. The activation energies of 1.01 ± 0.01 eV for space charge polarization are independent of the defect concentration, suggesting that these originated from protons trapped at the grain boundaries as a result of long-range proton conduction. The polarization of two different types is expected to exert different effects on the HAp surface properties.
Hydrodynamic-induced enantiomeric enrichment of self-assemblies: Role of the solid-liquid interface in chiral nucleation and seeding
Authors: Raudino Antonio , Pannuzzo Martina
Published: October 2012

A simple hydrodynamic model has been developed to explain the experimentally observed chirality selection in stirred solutions of self-assembling achiral dyes. Selection depends on the stirring direction: the dichroic signal reverses its shape in clockwise or anti-clockwise rotations. Our model investigates the possible role of the liquid-solid interface in nucleating, growing, and transferring to the bulk of chiral seeds. The nucleation step requires a double modulation of the hydrodynamic field exhibiting different velocity along two orthogonal axes. Under a series of restrictions, such a condition is easily met at the solid-liquid interface and it is dictated by the boundary conditions and geometry of stirring. In stagnant conditions, growing helices made-up of self-assembled achiral dyes have no chiral preference forming a racemic mixture that contains identical amount of right-handed (R) and left-handed (L) configurations. The application of a hydrodynamic torque (related to the velocity gradient and width of the helix) breaks down the original symmetry, a further velocity gradient perpendicular to the first one ensures, after averaging, a slightly different population of R and L conformations. The yields of the hydrodynamic-induced chirality excess are extremely tiny, hence the suggested mechanism is significant only if next chirality amplification processes are efficient. Again, hydrodynamics provides a tool for the detachment of weakly bound aggregates once they have reached a critical length. Aggregates are transported in the bulk where the ripening process goes to completion. The efficiency of the surface catalytic effect strongly depends on the aggregate-surface sticking energy, reaching a maximum at intermediate sticking energies (of order of 10 kT). Numerical estimates show that the proposed mechanism is rather efficient, giving rise to entatiomeric excesses near (but smaller than) those experimentally found.
Case study: Simulation and optimization of photovoltaic-wind-battery hybrid energy system in Taleghan-Iran using homer software
Authors: Shiroudi A. , Rashidi R. , Gharehpetian G. B. , Mousavifar S. A. , Akbari Foroud A.
Published: October 2012

In respect to increasing demand for energy in the world and limited fossil fuel resources, there is a great need for using renewable energies (REs). One of the most attractive applications of RE technology is the application of hybrid energy systems in remote areas. An alternative to overcoming the intermittence of RE sources, such as the sun and wind (are freely available and environmental friendly), is to develop the hybrid energy system where excess electrical energy could be converted and stored. These sources combined with energy storage would provide a better system reliability making it suitable for stand-alone applications. They have been integrated and worked at the Taleghan renewable energies site in Iran. The National Renewable Energy Laboratory's hybrid optimization model for electric renewables simulation software has been used to carry out the optimal design and techno-economic viability of energy system in this study. The simulation results demonstrate that for hybrid energy system is consists of 0.8 kW PV modules, two wind turbines (0.4 kW each), 2.5 kW inverter, and 8 batteries (200 Ah and 12 V). The cost of energy is 1.655 US$/kWh, whereas the initial capital required, and net present costs are, 22998 US$ and 24623 US$, respectively.
Photoisomerization for a model protonated Schiff base in solution: Sloped/peaked conical intersection perspective
Authors: Malhado João Pedro , Hynes James T.
Published: October 2012

The topographical character of conical intersections (CIs)—either sloped or peaked—has played a fundamental and important role in the discussion of the efficiency of CIs as photochemical “funnels.” Here this perspective is employed in connection with a recent study of a model protonated Schiff base (PSB) cis to trans photoisomerization in solution [Malhado et al., J. Phys. Chem. A 115, 3720 (2011)10.1021/jp106096m]. In that study, the calculated reduced photochemical quantum yield for the successful production of trans product versus cis reactant in acetonitrile solvent compared to water was interpreted in terms of a dynamical solvent effect related to the dominance, for the acetonitrile case, of S1 to S0 nonadiabatic transitions prior to the reaching the seam of CIs. The solvent influence on the quantum yield is here re-examined in the sloped/peaked CI topographical perspective via conversion of the model's two PSB internal coordinates and a nonequilibrium solvent coordinate into an effective branching space description, which is then used to re-analyze the generalized Langevin equation/surface hopping results. The present study supports the original interpretation and enriches it in terms of topographical detail.
Theoretical and experimental study of the optical absorption at longitudinal phonon or phonon-plasmon coupling mode energy: An example of GaN
Authors: Ishitani Yoshihiro
Published: October 2012

Reflectance loss of p-polarized infrared light at longitudinal optical (LO) phonon energies has been reported by Berreman. The origin of this loss has been discussed in view of the absorption by electric dipole moment by the polarization charges at the interfaces and propagation of interface polaritons. However, the existence of the absorption effect is not clear. In this issue, we take an example of GaN films with large polarization charges, and distinguish the two effects on optical spectra by theoretical and experimental analysis. It is found for the first time that the absorption by electric dipoles at the resonant energy with the LO phonon or LO phonon-plasmon coupling (LOPC) mode is identified separately from the interface polariton effect by varying the wavenumber component parallel to the interfaces by attenuated total reflectance analysis. We construct a theoretical expression of the pseudo-dielectric function of thin films around the LO phonon or LOPC mode energies, and show the quantitative proof of the existence of the absorption effect in the experimental spectra.
Regions for Brillouin seed pulse growth in relativistic laser-plasma interaction
Authors: Lehmann G. , Schluck F. , Spatschek K. H.
Published: October 2012

Parametric plasma processes received renewed interest in the context of generating ultraintense and ultrashort laser pulses up to the exawatt-zetawatt regime. For Brillouin scattering and seed pulse amplification at high intensities, the strong coupling regime is of special interest. The intensity-driven low-frequency modes depend on the amplitudes of the laser fields. It is investigated here how these modes develop in the relativistic regime. Then, a unified treatment of Raman and Brillouin processes becomes necessary. Assuming circular polarization, it is shown that with increasing intensity an overlap of the originally different Raman, Brillouin, and modulational instability branches occurs. Numerical simulations with a linearized Maxwell-fluid code confirm the analytically predicted behavior.
Anomalous behavior of epitaxial indium nano-contacts on cadmium-zinc-telluride
Authors: Ruzin A. , Sinkevich O. , Cohen-Taguri G. , Goldfarb I.
Published: October 2012

In this work, experimental characterization results of indium nano-contacts are presented. The indium nano-contacts are epitaxially grown on a two-dimensional surface of high-resistivity, n-type Cd0.9Zn0.1Te in ultra-high vacuum. The scaling effect in these contacts is systematic, but not linear. It is shown that the contacts exhibit a profoundly asymmetric behavior. It is argued that the “rectifying” behavior of these contacts is due to tunneling and that the tunneling does not necessarily imply Schottky nature.
Exchange coupled bilayer thin films with tilted out-of-plane anisotropy easy axis
Authors: Layadi A.
Published: October 2012

The ferromagnetic resonance (FMR) modes are worked out for the case of exchange coupled bilayer thin films where the anisotropy axis in the ferromagnetic film is tilted out of the plane. General formulas are obtained for the mode position, frequency and field linewidths, and intensity for an arbitrary tilt angle. The analysis is then applied for the in-plane, weak and strong perpendicular anisotropies. Analytical expressions for the magnetization curve and the FMR modes are derived. It will be shown how the exchange anisotropy field HE, the uniaxial anisotropy HK, and the magnetization angle are related to the FMR spectrum characteristics and how they can be found in a straightforward manner.
Time-domain determination of transmission in quantum nanostructures
Authors: Sullivan Dennis M. , Wilson Paul M.
Published: October 2012

The finite-difference time-domain method is being used to calculate transmission through nanoscale quantum structures. This is determined by first taking the Fourier transform of a waveform before it enters a channel and then taking the Fourier transform of the portion of the waveform that is transmitted through the channel. By storing the time-domain waveforms at the input and output, a very small total problem space is required. This is significant, because it is intended that this one-dimensional method be extended to three dimensions.
Critical behavior of two-dimensional spin systems under the random-bond six-state clock model
Authors: Wu Raymond P. H. , Lo Veng-cheong , Huang Haitao
Published: October 2012

The critical behavior of the clock model in two-dimensional square lattice is studied numerically using Monte Carlo method with Wolff algorithm. The Kosterlitz-Thouless (KT) transition is observed in the six-state clock model, where an intermediate phase exists between the low-temperature ordered phase and the high-temperature disordered phase. The bond randomness is introduced to the system by assuming a Gaussian distribution for the coupling coefficients with the mean μ=1 and different values of variance, from σ2=0.1 to σ2=3.0. An abrupt jump in the helicity modulus at the transition, which is the key characteristic of the KT transition, is verified with a stability argument. The critical temperature Tc for both pure and disordered systems is determined from the critical exponent η(Tc)=1/4. The results showed that a small amount of disorder (small σ) reduces the critical temperature of the system, without altering the nature of transition. However, a larger amount of disorder changes the transition from the KT-type into that of non-KT-type.
Tuning the binding energy of surface impurities in cylindrical GaAs/AlGaAs quantum dots by a tilted magnetic field
Authors: Zeng Zaiping , Garoufalis Christos S. , Baskoutas Sotirios , Terzis Andreas F.
Published: October 2012

Using the potential morphing method in the framework of the effective-mass approximation, we have studied theoretically the effect of a tilted magnetic field on the binding energy of surface impurities in GaAs/Al0.3Ga0.7As cylindrical quantum dots. It is found that contrary to what was expected based on the existing literature for growth-direction magnetic fields, the presence of a tilted field does not always contribute positively to the binding energy of surface impurities. The shape (aspect ratio) and size of the cylindrical QD as well as the dopant positions at the QD surface play an important role. Furthermore, we find that decrease of the QD size can reduce the sensitivity of the variation of the donor binding energy with respect to the field strength (orientation), but it cannot change its general behaviour.
The origin of 0.78 eV line of the dislocation related luminescence in silicon
Authors: Xiang Luelue , Li Dongsheng , Jin Lu , Pivac Branko , Yang Deren
Published: October 2012

In this paper, the 0.78 eV line of the dislocation related luminescence in the electron-irradiated silicon has been investigated. It is found that the 0.78 eV line only exists in float zone silicon samples, and its intensity could be largely enhanced by high temperature and long time annealing while no 0.78 eV line was found in Czochralski silicon. The activation energy of 0.78 eV line in floating-zone silicon is ∼13 meV, indicating a different nature from that of D1/D2 lines which can be ascribed to specific reconstructed dislocations which could be easily affected by point defects and temperature.
Electric-field control of CoFeB/IrMn exchange bias system
Authors: Rizwan Syed , Yu G. Q. , Zhang S. , Zhao Y. G. , Han X. F.
Published: October 2012

The electrically controlled spintronic devices based on magnetism at the interface is a key challenge today. We have studied the top sub./CoFeB/IrMn and bottom sub./IrMn/CoFeB pinned exchange bias systems as a function of electric field at room temperature deposited on the (011)-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) piezoelectric substrate. It was found that the electric-field tuning of exchange bias was very small although both the structures show good regular magnetoelectric coupling. We propose an alternative way to control the exchange bias via electric field in the multilayered structure by inserting a metallic spacer layer between exchange bias bilayer and bottom free magnetic layer, i.e., PMN-PT/CoFeB/Cu/CoFeB/IrMn. We successfully tuned the exchange bias of such multilayer structure as function of electric field at room temperature. Our results show a step forward in utilizing electrically controlled multiferroic systems for practical applications.
Effect of compositional variation on the shock wave response of bulk amorphous alloys
Authors: Jaglinski T. , Turneaure Stefan J. , Gupta Y. M.
Published: October 2012

The objective of this work was to determine how variations in composition influence the shock wave response of bulk amorphous alloys (BAAs). Toward this end, (Hf,Zr)-based bulk amorphous alloy specimens (nominal composition of (Hf0.5Zr0.5)56.7Cu15.3Ni12.5Nb5.0Al10.0Y0.5) were subjected to peak stresses of 4-16 GPa in plate impact experiments and their response was compared to a previously studied Zr-based BAA (nominal composition of Zr56.7Cu15.3Ni12.5Nb5.0Al10.0Y0.5). The (Hf,Zr)-based BAA displayed a Hugoniot elastic limit (HEL) of ∼7.4 GPa corresponding to an elastic strain of 4.3%. (Hf,Zr)-based BAAs shock compressed above the HEL exhibited distinct two wave structures, small elastic precursor relaxation, non-steady plastic waves, and strength loss. All of these features are qualitatively similar to previous observations in various Zr-based BAAs. One dimensional wave propagation simulations incorporating a strain-softening strength model, developed previously for a Zr-based BAA, showed excellent agreement between measured and simulated particle velocity histories for the (Hf,Zr)-based BAA. The only significant differences in the shock wave responses of the (Hf,Zr)-based alloy and the Zr-based alloy are elastic shock velocity and plastic shock velocity differences which are due to the different ambient densities and different elastic moduli for the two alloy compositions. These findings demonstrate that, apart from differences related to ambient density and elastic stiffness, the substitution of Hf for 50% of the Zr did not significantly alter the shock compression response of the (Hf,Zr)-based BAA as compared to the previously examined Zr-based BAA. Based on the results of this study and other relevant data in the literature, it is expected that monolithic BAAs displaying brittle quasi-static compression behavior will likely display shock compression response that is comparable to Zr-based and (Hf,Zr)-based BAAs.
Subthreshold swings below 60 mV/dec in three-terminal nanojunctions at room temperature
Authors: Müller C. R. , Worschech L. , Forchel A.
Published: October 2012

Subthreshold swings below the thermal limit of 60 mV/dec are demonstrated in a three-terminal nanojunction (TTJ) at room temperature. The T-shaped TTJ with a 50 nm wide center branch was based on a modulation-doped GaAs/AlGaAs heterostructure and was defined by electron-beam lithography and wet chemical etching. Operated as in-plane gated field-effect transistor, transistor characteristics were demonstrated. Efficient switching with subthreshold swings smaller than 40 mV/dec was observed. These findings are attributed to a dynamic gate capacitance which improves the switching properties of the device significantly.
Solvation of fullerene and fulleride ion in liquid ammonia: Structure and dynamics of the solvation shells
Authors: Rana Malay Kumar , Chandra Amalendu
Published: October 2012

Molecular dynamics simulations have been performed to investigate the solvation characteristics of neutral fullerene (\documentclass[12pt]{minimal}\begin{document}$\rm C_{60}$\end{document}C60) and charged fulleride anion (\documentclass[12pt]{minimal}\begin{document}${\rm C}_{60}^{5-}$\end{document}C605−) in liquid ammonia. Potassium ions are present as counterions in the system containing fulleride ion. In addition to solvation characteristics, dynamical properties of solvation shells are also found out for both the neutral and anionic solutes. Our results reveal the presence of a rather large solvation shell of ammonia molecules around the \documentclass[12pt]{minimal}\begin{document}$\rm C_{60}^{5-}$\end{document}C605− ion. It is found that the ammonia molecules are more closely packed in the first solvation shell of \documentclass[12pt]{minimal}\begin{document}$\rm C_{60}^{5-}$\end{document}C605− than that of \documentclass[12pt]{minimal}\begin{document}$\rm C_{60}$\end{document}C60. The distributions of ammonia molecules in the solvation shells of \documentclass[12pt]{minimal}\begin{document}$\rm C_{60}$\end{document}C60 and \documentclass[12pt]{minimal}\begin{document}$\rm C_{60}^{5-}$\end{document}C605− solutes together with hydrogen bonding characteristics of the solvent in different solvation shells are investigated. It is found that the solvation of the small counterions (\documentclass[12pt]{minimal}\begin{document}$\rm K^{+}$\end{document}K+) in liquid ammonia is affected very little by the presence of the large \documentclass[12pt]{minimal}\begin{document}$\rm C_{60}^{5-}$\end{document}C605− anion. Regarding the dynamics of ammonia in solvation shells, it is found that the residence, translational and rotational dynamics of ammonia molecules differ significantly between the solvation shells of the neutral and charged fullerene solutes, especially in the first solvation shells. The average lifetimes of ammonia-ammonia hydrogen bonds are calculated from both continuous and intermittent hydrogen bond correlation functions. The calculations of binding energies reveal that the hydrogen bonds are weaker, hence short lived in the solvation shell of \documentclass[12pt]{minimal}\begin{document}$\rm C_{60}^{5-}$\end{document}C605− compared to those in the solvation shell of neutral C60 and also in bulk liquid ammonia.
Unusual metallic behavior in nanostructured cobalt ferrite at superparamagnetic regime
Authors: Kannan R. , Rajagopan S. , Arunkumar A. , Vanidha D. , Murugaraj R.
Published: October 2012

Cobalt ferrite nanoparticles have been synthesized by coprecipitation method by varying the precipitation temperatures. The samples have been characterized by x-ray diffraction, impedance analysis, ac conductivity, dielectric, and vibrating sample magnetometer. When the average crystallite size is in the range of 2–16 nm, these compounds behave as metallic, and upon thermal activation, they become semiconducting, indicating anomalous conducting behavior. Impedance analysis reveals a metallic to semiconducting phase transition, accompanied by grain boundary effect, gradually replaced by grain contribution. Ac conductivity measurements and dielectric analysis also confirmed the transformation, when the slope changed from positive to negative as a function of temperature. Particle size independent magnetic behavior was observed in finite size limit due to site exchange of cations between tetrahedral (A) and octahedral (B) sites.
Large quasineutral electron velocity oscillations in radial expansion of an ionizing plasma
Authors: Karimov A. R. , Yu M. Y. , Stenflo L.
Published: October 2012

Radial expansion of an ionizing gas or plasma cylinder into vacuum is investigated. An exact model for the evolution of the density and velocity fields of the electrons, ions, and neutrals, including the effect of photo and electron-impact ionization on the flow characteristics is developed and solutions obtained. A quasineutral nonlinear electrostatic mode involving rapid oscillations in the electron velocity but not in the density can occur in the expanding plasma. The mode turns out to be almost unaffected by weak ionization.
Study of the plasma wave excited by intense femtosecond laser pulses in a dielectric capillary
Authors: Eremin V. , Malkov Yu. , Korolikhin V. , Kiselev A. , Skobelev S. , Stepanov A. , Andreev N.
Published: October 2012

Laser wakefield in a gas-filled capillary driven by a 1-TW femtosecond Ti:Sa laser pulse is studied experimentally by observing driving pulse spectrum modifications, which are caused by the combined action of the optical field ionization and the plasma density oscillations. Good agreement between the results of extensive numerical simulations and the experimental data allows us to estimate the accelerating gradients in the wake, which range from 5 to 10 MV/cm for typical experimental conditions.
Colloidal cluster crystallization dynamics
Authors: Beltran-Villegas Daniel J. , Sehgal Ray M. , Maroudas Dimitrios , Ford David M. , Bevan Michael A.
Published: October 2012

The crystallization dynamics of a colloidal cluster is modeled using a low-dimensional Smoluchowski equation. Diffusion mapping shows that two order parameters are required to describe the dynamics. Using order parameters as metrics for condensation and crystallinity, free energy, and diffusivity landscapes are extracted from Brownian dynamics simulations using Bayesian inference. Free energy landscapes are validated against Monte Carlo simulations, and mean first-passage times are validated against dynamic simulations. The resulting model enables a low-dimensional description of colloidal crystallization dynamics.
The Ehrenfest force field: Topology and consequences for the definition of an atom in a molecule
Authors: Pendás A. Martín , Hernández-Trujillo J.
Published: October 2012

The Ehrenfest force is the force acting on the electrons in a molecule due to the presence of the other electrons and the nuclei. There is an associated force field in three-dimensional space that is obtained by the integration of the corresponding Hermitian quantum force operator over the spin coordinates of all of the electrons and the space coordinates of all of the electrons but one. This paper analyzes the topology induced by this vector field and its consequences for the definition of molecular structure and of an atom in a molecule. Its phase portrait reveals: that the nuclei are attractors of the Ehrenfest force, the existence of separatrices yielding a dense partitioning of three-dimensional space into disjoint regions, and field lines connecting the attractors through these separatrices. From the numerical point of view, when the Ehrenfest force field is obtained as minus the divergence of the kinetic stress tensor, the induced topology was found to be highly sensitive to choice of Gaussian basis sets at long range. Even the use of large split valence and highly uncontracted basis sets can yield spurious critical points that may alter the number of attraction basins. Nevertheless, at short distances from the nuclei, in general, the partitioning of three-dimensional space with the Ehrenfest force field coincides with that induced by the gradient field of the electron density. However, exceptions are found in molecules where the electron density yields results in conflict with chemical intuition. In these cases, the molecular graphs of the Ehrenfest force field reveal the expected atomic connectivities. This discrepancy between the definition of an atom in a molecule between the two vector fields casts some doubts on the physical meaning of the integration of Ehrenfest forces over the basins of the electron density.
High contrast tandem organic light emitting devices
Authors: Ding Bao-Fu , Hou Xiao-Yuan , Alameh Kamal
Published: October 2012

A high contrast-ratio organic light emitting device (OLED) is proposed and experimentally demonstrated. The OLED is implemented by stacking two organic phase tuning (PT) layers between composite metal layers and optimizing their thicknesses. Such a tandem device can increase the current efficiency by 98%, and reduce the operating voltage by 1.04 V, in comparison to conventional high contrast OLEDs. Measured reflection spectra validate the high-contrast capability of the OLED, and demonstrate experimentally an average reflectivity of 6% under ambient light illumination. This is the lowest reflectivity reported to date for OLEDs employing organic phase tuning layers.
A holistic approach performance analysis of substrate-free focal plane array
Authors: Mao Liang , Cheng Teng , Chen Dapeng , Zhang Qingchuan
Published: October 2012

Based on a bi-material micro-cantilever thermal deformation principle, an uncooled infrared focal plane array (FPA) with optical readout has been developed from a substrate-based structure to a substrate-free structure. Infrared imaging of the substrate-free FPA indicates that this structure does not satisfy temperature-constant substrate conditions when the FPA unit size decreases from 200 μm to 60 μm. To evaluate the performance of the FPA, this paper puts forward an analytical model of heat transfer in the substrate-free FPA, by using a holistic approach and an electrical circuit analogy. The analytical model provides a fast and convenient way to calculate the temperature gray response and the response time of the substrate-free FPA. A substrate-free FPA with a unit size of 50 μm was fabricated. Infrared imaging experiments validate the model and indicate a noise equivalent temperature difference value of 170 mK has been achieved.
A clear oscillation of the interlayer exchange coupling in Co2FeAl/Cr/Co2FeAl structure with MgO capping layer
Authors: Xu Xiaoguang , Zhang Jianli , Sha Lei , Zhang Delin , Jiang Yong
Published: October 2012

We have studied the interlayer exchange coupling in Co2FeAl (CFA)/Cr/CFA/MgO multilayers via both experiments and numerical simulation. Magnetization measurement on the films shows a clear oscillation attenuation behavior with the thickness (0.6 nm < t < 10 nm) of the Cr spacer layer, and the oscillation period is about 2.1 nm. The numerical simulation demonstrates that the interlayer exchange coupling between CFA layers is 90° coupling having an oscillation behavior, which is in good agreement with the experiments. MgO capping layer is supposed to be a key factor for the clear periodic oscillation behavior in CFA/Cr/CFA trilayers.
Structure determination of thin CoFe films by anomalous x-ray diffraction
Authors: Gloskovskii Andrei , Stryganyuk Gregory , Ouardi Siham , Fecher Gerhard H. , Felser Claudia , Hamrle Jaroslav , Pištora Jaromír , Bosu Subrojati , Saito Kesami , Sakuraba Yuya , Takanashi Koki
Published: October 2012

This work reports on the investigation of structure-property relationships in thin CoFe films grown on MgO. Because of the very similar scattering factors of Fe and Co, it is not possible to distinguish the random A2 (W-type) structure from the ordered B2 (CsCl-type) structure with commonly used x-ray sources. Synchrotron radiation based anomalous x-ray diffraction overcomes this problem. It is shown that as grown thin films and 300 K post annealed films exhibit the A2 structure with a random distribution of Co and Fe. In contrast, films annealed at 400 K adopt the ordered B2 structure.
Note: Statistical errors estimation for Thomson scattering diagnostics
Authors: Maslov M. , Beurskens M. N. A. , Flanagan J. , Kempenaars M. ,   JET-EFDA Contributors
Published: October 2012

A practical way of estimating statistical errors of a Thomson scattering diagnostic measuring plasma electron temperature and density is described. Analytically derived expressions are successfully tested with Monte Carlo simulations and implemented in an automatic data processing code of the JET LIDAR diagnostic.
Exchange bias and memory effect in double perovskite Sr2FeCoO6
Authors: Pradheesh R. , Nair Harikrishnan S. , Sankaranarayanan V. , Sethupathi K.
Published: October 2012

We report on the observation of exchange bias (EB) and memory effect in double perovskite Sr2FeCoO6. Antiphase boundaries between the ferromagnetic and the antiferromagnetic regions in the disordered glassy phase are assumed as responsible for the observed effect, which reflects in the cooling field dependence and temperature evolution of exchange bias field and in training effect. The spin glass (SG) phase itself is characterized through memory, ageing, and magnetic relaxation experiments. The spin glass transition temperature, Tg, versus Hdc2/3 follows the Almeida-Thouless line yielding a freezing temperature, Tf=73K. Time-dependent magnetic relaxation studies reveal the magnetization dynamics of the underlying glassy phase in this double perovskite.
A microfluidic platform for real-time and in situ monitoring of virus infection process
Authors: Xu Na , Zhang Zhen-Feng , Wang Li , Gao Bo , Pang Dai-Wen , Wang Han-Zhong , Zhang Zhi-Ling
Published: October 2012

Microfluidic chip is a promising platform for studying virus behaviors at the cell level. However, only a few chip-based studies on virus infection have been reported. Here, a three-layer microfluidic chip with low shear stress was designed to monitor the infection process of a recombinant Pseudorabies virus (GFP-PrV) in real time and in situ, which could express green fluorescent protein during the genome replication. The infection and proliferation characteristics of GFP-PrV were measured by monitoring the fluorescence intensity of GFP and determining the one-step growth curve. It was found that the infection behaviors of GFP-PrV in the host cells could hardly be influenced by the microenvironment in the microfluidic chip. Furthermore, the results of drug inhibition assays on the microfluidic chip with a tree-like concentration gradient generator showed that one of the infection pathways of GFP-PrV in the host cells was microtubule-dependent. This work established a promising microfluidic platform for the research on virus infection.
Physical-gap-channel graphene field effect transistor with high on/off current ratio for digital logic applications
Authors: Hun Mun Jeong , Jin Cho Byung
Published: October 2012

We propose and analyze an approach to secure a high on/off current ratio in a graphene field effect transistor (FET) by introducing a physical gap along the channel rather than by attempting to open the energy bandgap of graphene. The device simulation results of the newly proposed device structure reveal highly suppressed off-state current of ∼10−9 A/μm, an on/off current ratio of more than seven orders of magnitude, and a subthreshold slope of 2.23 mV/decade more than a 20-fold reduction relative to the theoretical limitation of conventional metal-oxide-semiconductor FETs.
Enhanced carrier extraction from Ge quantum dots in Si solar cells under strong photoexcitation
Authors: Tayagaki Takeshi , Usami Noritaka , Pan Wugen , Hoshi Yusuke , Ooi Kazufumi , Kanemitsu Yoshihiko
Published: October 2012

We report studies of the carrier extraction mechanism in Si solar cells with Ge quantum dots (QDs), which enable the optical absorption of photons with energies below the band gap of the host. Photocurrent measurements revealed that the photocurrent in the QD solar cells increased superlinearly with increasing excitation intensity under strong photoexcitation, which differed greatly from the behavior of Si solar cells without Ge QDs. This nonlinear photocurrent generation indicates that the carrier extraction efficiency from QDs is enhanced under strong photoexcitation by nonlinear carrier extraction processes, such as two-step photon absorption and hot carrier generation via Auger recombination.
Introduction to the Focus Issue: Chemo-Hydrodynamic Patterns and Instabilities
Authors: De Wit A. , Eckert K. , Kalliadasis S.
Published: October 2012

Pattern forming instabilities are often encountered in a wide variety of natural phenomena and technological applications, from self-organization in biological and chemical systems to oceanic or atmospheric circulation and heat and mass transport processes in engineering systems. Spatio-temporal structures are ubiquitous in hydrodynamics where numerous different convective instabilities generate pattern formation and complex spatiotemporal dynamics, which have been much studied both theoretically and experimentally. In parallel, reaction-diffusion processes provide another large family of pattern forming instabilities and spatio-temporal structures which have been analyzed for several decades. At the intersection of these two fields, “chemo-hydrodynamic patterns and instabilities” resulting from the coupling of hydrodynamic and reaction-diffusion processes have been less studied. The exploration of the new instability and symmetry-breaking scenarios emerging from the interplay between chemical reactions, diffusion and convective motions is a burgeoning field in which numerous exciting problems have emerged during the last few years. These problems range from fingering instabilities of chemical fronts and reactive fluid-fluid interfaces to the dynamics of reaction-diffusion systems in the presence of chaotic mixing. The questions to be addressed are at the interface of hydrodynamics, chemistry, engineering or environmental sciences to name a few and, as a consequence, they have started to draw the attention of several communities including both the nonlinear chemical dynamics and hydrodynamics communities. The collection of papers gathered in this Focus Issue sheds new light on a wide range of phenomena in the general area of chemo-hydrodynamic patterns and instabilities. It also serves as an overview of the current research and state-of-the-art in the field.
A compact and efficient strontium oven for laser-cooling experiments
Authors: Schioppo M. , Poli N. , Prevedelli M. , Falke St. , Lisdat Ch. , Sterr U. , Tino G. M.
Published: October 2012

Here we describe a compact and efficient strontium oven well suited for laser-cooling experiments. Novel design solutions allowed us to produce a collimated strontium atomic beam with a flux of 1.0 × 1013 s−1 cm−2 at the oven temperature of 450 °C, reached with an electrical power consumption of 36 W. The oven is based on a stainless-steel reservoir, filled with 6 g of metallic strontium, electrically heated in a vacuum environment by a tantalum wire threaded through an alumina multi-bore tube. The oven can be hosted in a standard DN40CF cube and has an estimated continuous operation lifetime of 10 years. This oven can be used for other alkali and alkaline earth metals with essentially no modifications.
Chemical assembly and electrical characteristics of surface-rich topological insulator Bi2Se3 nanoplates and nanoribbons
Authors: Jacobs-Gedrim Robin B. , Durcan Chris A. , Jain Nikhil , Yu Bin
Published: October 2012

We demonstrate synthesis of low-dimensional, surface-rich bismuth selenide nanoplates and nanoribbons through a low-pressure chemical-vapor-deposition method. The single crystalline lattice structure, morphology, and chemical composition of the synthesized nanoplates and nanoribbons are analyzed. As-prepared samples are found to be all n-type doped. Very large surface-to-volume ratios have been achieved in these low-dimensional nanostructures, making them ideal for investigating topological insulator properties. Gate-controlled bismuth selenide nanoplate field-effect transistors are fabricated and basic electrical behavior is characterized.
A note on the reactions in the Ti-Ge system
Authors: Pelleg Joshua , Eliahu Reut , Barkai Assia , Levi George
Published: October 2012

Formations of germanides in thin films of the Ti-Ge system were investigated by XRD after furnace annealing for 1 hour. Ti6Ge5 seems to be the first phase formed while TiGe2 is the end phase with the lowest resistivity. The existence of the phase Ti5Ge3 was confirmed which forms at higher temperatures than Ti6Ge5. The presence of a thin TiO2 layer was observed by TEM. Which of the phase exists or is missed depends on composition of the constituents comprising the film, their thickness and temperature of reaction. Three phases are observed to coexist on the Ge substrate, which are Ti5Ge3, Ti6Ge5 and TiGe2. A schematic suggestion is presented for explaining the coexistence of two or more phases. The concept of formation and coexistence of two phases at lower temperatures is also proposed.
Strong coupling effects between a meta-atom and MIM nanocavity
Authors: Chen San , Liu Jianqiang , Lu Hongyang , Wang Qianjin , Zhu Yongyuan
Published: October 2012

In this paper, we investigate the strong coupling effects between a meta-atom and a metal-insulator-metal (MIM) nanocavity. By changing the meta-atom sizes, we achieve the meta-atomic electric dipole, quadrupole or multipole interaction with the plasmonic nanocavity, in which characteristic anticrossing behaviors demonstrate the occurrence of the strong coupling. The various interactions present obviously different splitting values and behaviors of dependence on the meta-atomic position. The largest Rabi-type splittings, about 360.0 meV and 306.1 meV, have been obtained for electric dipole and quadrupole interaction, respectively. We attribute the large splitting to the highly-confined cavity mode and the large transition dipole of the meta-atom. Also the Rabi-type oscillation in time domain is given.
The Sun’s oblateness appears to be constant
Authors: Schwarzschild Bertram M.
Published: October 2012

A precision measurement finds its equatorial bulge somewhat smaller than expected and seemingly unaffected by the solar cycle.
South Korea invests big in basic research
Authors: Feder Toni
Published: October 2012

Internationalizing the science community, encouraging creativity, and becoming a world research leader are the aims of an initiative in a country better known for its industry than for its science.
Physics peeks into the ballot box
Authors: Fortunato Santo , Castellano Claudio
Published: October 2012

In different countries and over time, electoral features such as statistics of candidates’ performance and turnout rates show universal behaviors. Are voters as predictable as atoms?
Multidisciplinary care: experience of patients with complex needs
Authors: Maneze Della , Dennis Sarah , Chen Huei-Yang , Taggart Jane , Vagholkar Sanjyot , Bunker Jeremy , Liaw Siaw Teng
Published: October 2012

The rapidly increasing prevalence of diabetes with its high morbidity and mortality raises the need for an integrated multidisciplinary service from health care providers across health sectors. The aim of this study was to explore the diabetic patients’ experience of multidisciplinary care, in particular their perceptions, perceived barriers and facilitators. Thirteen patients with type-2 diabetes admitted to the emergency department of a local hospital in NSW were interviewed and completed a demographic questionnaire. Results showed that patients found it inconvenient to be referred to many health professionals because of multiple physical and psychosocial barriers. Separate sets of instructions from different health professionals were overwhelming, confusing and conflicting. Lack of a dedicated coordinator of care, follow up and support for self-management from health professionals were factors that contributed to patients’ challenges in being actively involved in their care. The presence of multiple co-morbidities made it more difficult for patients to juggle priorities and ‘commitments’ to many health professionals. In addition, complex socioeconomic and cultural issues, such as financial difficulties, lack of transport and language barriers, intensified the challenge for these patients to navigate the health system independently. Few patients felt that having many health professionals involved in their care improved their diabetes control. Communication among the multidisciplinary care team was fragmented and had a negative effect on the coordination of care. The patients’ perspective is important to identify the problems they experience and to formulate strategies for improving multidisciplinary care for patients with diabetes.