bluuebunny/crossref_metadata_2025 huggingface dataset:
Derivative couplings and analytic gradients for diabatic states, with an implementation for Boys-localized configuration-interaction singles
Authors: Fatehi Shervin , Alguire Ethan , Subotnik Joseph E.
Published: September 2013

We demonstrate that Boys-localized diabatic states do indeed exhibit small derivative couplings, as is required of quasidiabatic states. In doing so, we present a general formalism for calculating derivative couplings and analytic gradients for diabatic states. We then develop additional equations specific to the case of Boys-localized configuration-interaction singles (CIS)—in particular, the analytic gradient of the CIS dipole matrix—and we validate our implementation against finite-difference results. In a forthcoming paper, we will publish additional algorithmic and computational details and apply our method to the Closs energy-transfer systems as a further test of the validity of Boys-localized diabatic states.
Intramolecular photoelectron diffraction in the gas phase
Authors: Ueda K. , Miron C. , Plésiat E. , Argenti L. , Patanen M. , Kooser K. , Ayuso D. , Mondal S. , Kimura M. , Sakai K. , Travnikova O. , Palacios A. , Decleva P. , Kukk E. , Martín F.
Published: September 2013

We report unambiguous experimental and theoretical evidence of intramolecular photoelectron diffraction in the collective vibrational excitation that accompanies high-energy photoionization of gas-phase CF4, BF3, and CH4 from the 1s orbital of the central atom. We show that the ratios between vibrationally resolved photoionization cross sections (v-ratios) exhibit pronounced oscillations as a function of photon energy, which is the fingerprint of electron diffraction by the surrounding atomic centers. This interpretation is supported by the excellent agreement between first-principles static-exchange and time-dependent density functional theory calculations and high resolution measurements, as well as by qualitative agreement at high energies with a model in which atomic displacements are treated to first order of perturbation theory. The latter model allows us to rationalize the results for all the v-ratios in terms of a generalized v-ratio, which contains information on the structure of the above three molecules and the corresponding molecular cations. A fit of the measured v-ratios to a simple formula based on this model suggests that the method could be used to obtain structural information of both neutral and ionic molecular species.
The nature of superfluidity and Bose-Einstein condensation: From liquid 4He to dilute ultracold atomic gases (Review Article)
Authors: Vilchynskyy S. I. , Yakimenko A. I. , Isaieva K. O. , Chumachenko A. V.
Published: September 2013

We present a brief overview of crucial historical stages in creation of superfluidity theory and of the current state of the microscopic theory of superfluid 4He. We pay special attention to the role of Bose-Einstein condensates (BECs) in understanding of physical mechanisms of superfluidity and identification of quantum mechanical structure of 4He superfluid component below λ-point, in particular—the possibility that at least two types of condensates may appear and coexist simultaneously in superfluid 4He. In this context we discuss the properties of the binary mixtures of BECs and types of excitations, which may appear due to intercomponent interaction in such binary mixtures of condensates. We also discuss current status of investigations of persistent currents in toroidal optical traps and present an outlook of our recent findings on this subject.
Formation of superfluid liquid pocket in aerogel and its solidification by cooling
Authors: Matsuda H. , Ochi A. , Isozaki R. , Nomura R. , Okuda Y.
Published: September 2013

Formation of superfluid liquid pockets of 4He surrounded by 4He crystals were observed in an aerogel of 96% porosity. The liquid pockets did not crystallize by application of pressure but crystallized via avalanche by cooling below a particular temperature. The crystallization by cooling was also observed when crystals occupied a smaller portion of the aerogel. Driving force for the crystallization by cooling and possible mass transport process are discussed.
Observation of superfluidity in two- and one-dimensions
Authors: Wada Nobuo , Hieda Mitsunori , Toda Ryo , Matsushita Taku
Published: September 2013

Even though there is no long-range-ordered state of a superfluid in dimensions lower than the three-dimension (3D) such as bulk 4He liquid, superfluidity has been observed for flat 4He films in 2D and recently for nanotubes of 4He in 1D by the torsional oscillator method. In the 2D state, in addition to the superfluid below the 2D Kosterlitz–Thouless transition temperature TKT, superfluidity is also observed in a normal fluid state above TKT, which depends strongly on the measurement frequency and the system size. In the 1D state of the nanotubes, superfluidity is directly observed as a frequency shift in the torsional oscillator experiment. Some calculations suggest a superfluidity of a 1D Bose fluid with a finite length, where thermal excitations of 2π–phase winding play the main role for superfluid onset of each tube. Dynamics of the 1D superfluidity is also suggested by observing the dissipation in the torsional oscillator experiment.
Time-resolved broadband Raman spectroscopies: A unified six-wave-mixing representation
Authors: Dorfman Konstantin E. , Fingerhut Benjamin P. , Mukamel Shaul
Published: September 2013

Excited-state vibrational dynamics in molecules can be studied by an electronically off-resonant Raman process induced by a probe pulse with variable delay with respect to an actinic pulse. We establish the connection between several variants of the technique that involve either spontaneous or stimulated Raman detection and different pulse configurations. By using loop diagrams in the frequency domain, we show that all signals can be described as six wave mixing which depend on the same four point molecular correlation functions involving two transition dipoles and two polarizabilities and accompanied by a different gating. Simulations for the stochastic two-state-jump model illustrate the origin of the absorptive and dispersive features observed experimentally.
Estimation of diffusion anisotropy in microporous crystalline materials and optimization of crystal orientation in membranes
Authors: Gounaris Chrysanthos E. , First Eric L. , Floudas Christodoulos A.
Published: September 2013

The complex nature of the porous networks in microporous materials is primarily responsible for a high degree of intracrystalline diffusion anisotropy. Although this is a well-understood phenomenon, little attention has been paid in the literature with regards to classifying such anisotropy and elucidating its effect on the performance of membrane-based separation systems. In this paper, we develop a novel methodology to estimate full diffusion tensors based on the detailed description of the porous network geometry through our recent advances for the characterization of such networks. The proposed approach explicitly accounts for the tortuosity and complex connectivity of the porous framework, as well as for the variety of diffusion regimes that may be experienced by a guest molecule while it travels through the different localities of the crystal. Results on the diffusion of light gases in silicalite demonstrate good agreement with results from experiments and other computational techniques that have been reported in the literature. A comprehensive computational study involving 183 zeolite frameworks classifies these structures in terms of a number of anisotropy metrics. Finally, we utilize the computed diffusion tensors in a membrane optimization model that determines optimal crystal orientations. Application of the model in the context of separating carbon dioxide from nitrogen demonstrates that optimizing crystal orientation can offer significant benefit to membrane-based separation processes.
Charge transport in desolvated DNA
Authors: Wolter Mario , Elstner Marcus , Kubař Tomáš
Published: September 2013

The conductivity of DNA in molecular junctions is often probed experimentally under dry conditions, but it is unclear how much of the solvent remains attached to the DNA and how this impacts its structure, electronic states, and conductivity. Classical MD simulations show that DNA is unstable if the solvent is removed completely, while a micro-hydrated system with few water molecules shows similar charge transport properties as fully solvated DNA does. This surprising effect is analyzed in detail by mapping the density functional theory-based electronic structure to a tight-binding Hamiltonian, allowing for an estimate of conductivity of various DNA sequences with snapshot-averaged Landauer's approach. The characteristics of DNA charge transport turn out to be determined by the nearest hydration shell(s), and the removal of bulk solvent has little effect on the transport.
Electromagnetic boundary conditions in multipole theory
Authors: de Lange O. L. , Raab R. E.
Published: September 2013

Multipole expansions for the macroscopic charge and current densities in a dielectric half-space involve a hierarchy of singular functions comprising the Dirac delta function and its derivatives. For these, Maxwell's differential equations yield corresponding singular expansions of the macroscopic electromagnetic fields E and B, and the response fields D and H, together with their boundary conditions (in terms of macroscopic multipole moment densities) at a dielectric–vacuum (or dielectric–dielectric) interface. Explicit results are obtained up to electric octopole–magnetic quadrupole order. These show that published expressions for boundary conditions are incomplete beyond electric dipole order, due to an invalid assumption concerning two-dimensional behaviour at the interface. The effect of this on studies of certain reflection effects for anisotropic media is detailed. Comparison of the differential theory with the standard integral formulation shows that, beyond electric dipole order, the latter is incomplete and redundant.
Very low field magnetic resonance imaging with spintronic sensors
Authors: Herreros Q. , Dyvorne H. , Campiglio P. , Jasmin-Lebras G. , Demonti A. , Pannetier-Lecoeur M. , Fermon C.
Published: September 2013

A very low field magnetic resonance imaging (MRI) setup based on magnetoresistive-superconducting mixed sensors is presented. A flux transformer is used to achieve coupling between the sample to image and the mixed sensor. The novel detector was implemented in a spin echo MRI experiment, exposing the mixed sensor to RF pulses without use of any RF switch. The performance of the novel detector is given in terms of signal-to-noise ratio and is compared with classical tuned coils.
A first-principles study of ZnO polar surface growth: Adsorption of ZnxOy clusters
Authors: Wang Zhunzhun , Pan Nan , Li Zhenyu , Yang Jinlong
Published: September 2013

Adsorption of ZnxOy (x + y = 1–6) clusters on ZnO (000 ± 1) polar surfaces is studied systematically via density function theory (DFT) calculations. Different adsorption behaviors are predicted for these two surfaces. On the (0001)-Zn surface, O atoms adsorb on hollow sites at the initial stage. Then Zn atoms come in, and the stable structure becomes bulk-like for some specific clusters. On the (000$\overline 1$1¯)-O surface, Zn cluster adsorption leads to stable cage structures formed by pulling substrate O out. In clusters with both Zn and O, O atoms avoid directly bonding with the surface, and no energetically favorable bulk-like structure is found. On the basis of the prediction of these surface adsorption behaviors, experimentally observed growth rate and surface roughness differences on these two polar surfaces can be understood.
Spin waves in the B-phase of superfluid 3He in confined cylindrical geometry
Authors: Benningshof O. W. B. , Jochemsen R.
Published: September 2013

We describe experiments on superfluid 3He in a cylinder of 1 mm in diameter. This geometry causes the preferred orientation of the n-vector in the superfluid B-phase to be locally different, resulting in a curved configuration across the sample. Exclusive to our experiment is the observation that we succeeded in obtaining a texture which is metastable and unchanged in our pressure and temperature ranges, most likely because the experiment is performed at low pressures and low magnetic fields. As this texture can be considered as a potential for spin waves, we had the unique opportunity to study spin waves for several pressures in exactly the same texture. Our geometry causes this texture potential to be nearly quadratic, allowing an analytic solution of the theory which can be compared to our experimental results. As predicted we find the intensities of all spin wave modes more or less equal. Increasing the pressure shows a gradual increase in the number of spin wave modes in our cell. Finally we were able to cause a transition from the metastable to the predicted stable texture, concluding unexpectedly that the metastable texture is realized if the growing (or cooling) speed is sufficiently slow.
Theory of structure and thermodynamic function of liquid 4He (Review Article)
Authors: Vakarchuk I. O. , Pastukhov V. S. , Prytula R. O.
Published: September 2013

A new method of calculation of the density matrix of a many-boson system is proposed. The calculation of thermodynamic and structure functions at finite temperatures based on density matrix of Bose liquid is made. The structure factor of liquid 4He at T = 0 K is used as an input information for numerical calculation instead of the interatomic potential. We found a good agreement of the calculated quantities with experimental data.
Small-angle scattering of neutrons on normal and superfluid liquid helium
Authors: Tsipenyuk Yu. M. , Kirichek O. , Petrenko O.
Published: September 2013

Experiments on small-angle scattering of neutrons on liquid helium at temperatures of 1.0–5 K at the ISIS pulsed neutron source (England) are reported. Detailed measurements of the angular distribution of the scattered neutrons reveal a significant change in the temperature dependence of the second moment of the pairwise correlation function (the first derivative of the angular distribution for small scattering angles). At high temperatures the angular distribution of the scattered neutrons follows the classical description for small-angle scattering, but at temperatures below the λ-point, quantum mechanical behavior is observed (scattering of neutrons on quantum fluctuations). It is confirmed experimentally that over the entire temperature range the neutron scattering cross section at zero angle is determined by classical thermodynamic fluctuations in the density.
Proton transfer and the diffusion of H+ and OH− ions along water wires
Authors: Lee Song Hi , Rasaiah Jayendran C.
Published: September 2013

Hydrogen and hydroxide ion transport in narrow carbon nanotubes (CNTs) of diameter 8.1 Å and lengths up to 582 Å are investigated by molecular dynamics simulations using a dissociating water model. The diffusion coefficients of the free ions in an open chain are significantly larger than in periodically replicated wires that necessarily contain D or L end defects, and both are higher than they are in bulk water. The free hydroxide ion diffuses faster than the free hydronium ion in short CNTs, unlike diffusion in liquid water, and both coefficients increase and converge to nearly the same value with increasing tube length. The diffusion coefficients of the two ions increase further when the tubes are immersed in a water reservoir and they move easily out of the tube, suggesting an additional pathway for proton transport via OH− ions in biological channels.
Analysis of non-spherical particle transport in complex internal shear flows
Authors: Feng Y. , Kleinstreuer C.
Published: September 2013

Focusing on ellipsoidal particles of different aspect ratios, the motion characteristics, including critical angle and stable vs. unstable rotational periods, are computationally analyzed in developing and fully developed tubular flows. As an application of particle transport and deposition, the one-way coupled Euler-Lagrange method enhanced by Euler's rotation equations is then employed to simulate laminar-turbulent flow in a subject-specific lung-airway model. First, to gain some basic insight into the dynamics of non-spherical particles, tubular flow is considered where the trajectories of ellipsoidal fibers with randomly initialized incidence angles were released at different inlet-plane positions, computed and visualized. Local and overall particle deposition results are compared between spheres, ellipsoidal fibers, and sphere-equivalent particles for which a revised Stokes diameter was developed. Concerning non-spherical particle transport and deposition in a subject-specific respiratory system, the validated computer simulation model provides realistic and accurate particle-deposition results. Specifically, slender non-spherical particles (i.e., those with higher aspect ratios) are potentially more harmful than thicker ones due to their ability to penetrate into deeper lung regions when somewhat aligned with the major flow field. Furthermore, non-spherical particle deposition is enhanced as the breathing rate increases.
Crystallization in glassy suspensions of hard ellipsoids
Authors: Dorosz Sven , Schilling Tanja
Published: September 2013

We have carried out computer simulations of overcompressed suspensions of hard monodisperse ellipsoids and observed their crystallization dynamics. The system was compressed very rapidly in order to reach the regime of slow, glass-like dynamics. We find that, although particle dynamics become sub-diffusive and the intermediate scattering function clearly develops a shoulder, crystallization proceeds via the usual scenario: nucleation and growth for small supersaturations, spinodal decomposition for large supersaturations. In particular, we compared the mobility of the particles in the regions where crystallization set in with the mobility in the rest of the system. We did not find any signature in the dynamics of the melt that pointed towards the imminent crystallization events.
Effective potentials for representing polymers in melts as chains of interacting soft particles
Authors: Clark A. J. , McCarty J. , Guenza M. G.
Published: September 2013

This paper outlines the derivation of an analytical pair potential in a coarse grained description of polymer melts where each chain is represented as a collection of soft spheres. Each particle is located at the center of mass of a polymer subchain, while the polymer is divided into an arbitrary number of identical chain subsections, each comprised of a large number of monomers. It is demonstrated that the soft effective pair potentials acting between these center-of-mass sites is described by a soft repulsive region at separation distances less than the average size of each coarse grained unit and a long repulsive tail, with a small attractive component. The attractive component is located at a length scale beyond the size of the coarse grained unit and its form varies with the level of interpenetration between the coarse-grained units. Consistent with numerically derived potentials, it is found that the short range features of the potential dominate the liquid structure, while the long-tail features dominate the virial-route thermodynamics of the system. It follows that the accurate determination of the effective potential in both short and large separation distances is relevant for ensuring structural and thermodynamic consistency in the coarse-grained description of the macromolecular liquid. It is further shown that due to the sensitivity of thermodynamic properties to the large-scale features of the potential, which are irrelevant to the reproducibility of structural correlations, the determination of thermodynamically accurate potentials by numerical optimization of structure alone is not a reliable strategy in the high-density regime for high levels of coarse-graining.
Static stability of menisci in detached Bridgman growth
Authors: Mazuruk K. , Volz M. P.
Published: September 2013

A static stability analysis is performed for the menisci that form above the crystal-crucible gap during detached Bridgman growth. The sign of the second variation of the potential energy against admissible meniscus shape perturbations is considered as the stability criterion. Parameters governing the stability are the pressure differential across the meniscus, the Bond number, the crystal radius, the growth angle between the crystal and melt, and the contact angle between the melt and the crucible. The effects on stability of confined gases adjacent to the meniscus are also examined. Axisymmetric as well as non-axisymmetric perturbations are investigated. Axisymmetric perturbation modes require coupling to the meniscus that exists at the top of the melt to ensure melt volume preservation. Both rough and microscopically smooth interior crucible surfaces, corresponding to pinned and unpinned states, are considered. Pinning extends the parameter range over which menisci are stable. The symmetry of the least stable perturbation mode depends on the Bond number and whether the menisci are pinned. For Bond numbers equal to zero, corresponding to zero gravity conditions, all menisci are statically stable.
An atom trap trace analysis system for measuring krypton contamination in xenon dark matter detectors
Authors: Aprile E. , Yoon T. , Loose A. , Goetzke L. W. , Zelevinsky T.
Published: September 2013

We have developed an atom trap trace analysis (ATTA) system to measure Kr in Xe at the part per trillion (ppt) level, a prerequisite for the sensitivity achievable with liquid xenon dark matter detectors beyond the current generation. Since Ar and Kr have similar laser cooling wavelengths, the apparatus has been tested with Ar to avoid contamination prior to measuring Xe samples. A radio-frequency plasma discharge generates a beam of metastable atoms which is optically collimated, slowed, and trapped using standard magneto-optical techniques. Based on the measured overall system efficiency of 1.2 × 10−8 (detection mode), we expect the ATTA system to reach the design goal sensitivity to ppt concentrations of Kr in Xe in <2 h.
Conductance spectrum and superconducting gap structures observed in c-axis FeSe0.46Te0.54/Au junctions
Authors: Shen Y. T. , Li Y. S. , Lin K. C. , Wu M. K. , Chi C. C.
Published: September 2013

The electric transport properties of superconducting c-axis FeSe0.46Te0.54/Au (S/N) junctions, fabricated using pulsed laser deposition, have been investigated in the temperature range of 2 K to the superconducting transition temperature Tc (∼ 13.5 K) and in the presence of applied magnetic fields from 0 to 9 T. A large zero bias conductance peak has always been observed in every conductance spectrum of several batches of junctions. In addition, we have found several gap-like features. Using the extended BTK theory with the currently favored nodeless S±-wave symmetry, our conductance spectrum can be reproduced quite well in the low bias range with Δ1 = 4 meV and Δ2 = 6 meV at 2 K. However, the experimental conductance spectrum is substantially below the one calculated in the high bias range. Furthermore, there is a conductance minimum at approximately 20 meV, which may be the reason for the discrepancy.
The influence of particle shape on magnetoresistance effect of two-dimensional metal-semiconductor composites
Authors: Xu Jie , Wang Guodong , Li Shandong , Shao Weiquan , Zhang Xinni
Published: September 2013

The magnetoresistance (MR) effect of the two-dimensional (2D) metal-semiconductor composites is investigated theoretically as a function of the magnetic field, the particle shape and the area fraction of the metal particles. It is interestingly found that the particles' shape is a principal factor for the MR of the composites in the strong magnetic field. There is a critical value of the elliptical particle semi-axial ratio, Mc, at which the composites have the most remarkable MR effect. The magnetic field dependence of the MR will transform from the saturated to linear dependence in the strong magnetic field when M is decreased to a value less then Mc. Besides, it is found that there is a critical value for the metal particles area fraction, fc, at which the composites also have the most remarkable MR effect. The critical values, Mc and fc, imply the macrostructure in the composite has the maximum disorder. An appropriate value of M and controlling the excess metal particles is necessary for the larger MR value. At last, the theoretical results on the MR are compared with the available experimental data and a good agreement is found.
Deconvolving the temporal response of photoelectric x-ray detectors for the diagnosis of pulsed radiations
Authors: Zou Shiyang , Song Peng , Guo Liang , Pei Wenbing
Published: September 2013

Based on the conjugate gradient method, a simple algorithm is presented for deconvolving the temporal response of photoelectric x-ray detectors (XRDs) to reconstruct the resolved time-dependent x-ray fluxes. With this algorithm, we have studied the impact of temporal response of XRD on the radiation diagnosis of hohlraum heated by a short intense laser pulse. It is found that the limiting temporal response of XRD not only postpones the rising edge and peak position of x-ray pulses but also smoothes the possible fluctuations of radiation fluxes. Without a proper consideration of the temporal response of XRD, the measured radiation flux can be largely misinterpreted for radiation pulses of a hohlraum heated by short or shaped laser pulses.
Tuning of character of the N–O bond in HONO from covalent to protocovalent by different types of intramolecular interactions
Authors: Shishkina Svitlana V. , Slabko Anzhelika I. , Berski Slawomir , Latajka Zdzislaw , Shishkin Oleg V.
Published: September 2013

Quantum-chemical calculations of the H–O–N=O molecule in the equilibrium and transition states and the complexes of the HONO with BH3, study of the intramolecular interactions using NBO theory, and investigation of the electron distribution on the basis of topological analysis of the ELF function clearly indicate the influence of the n–π* conjugation and n–σ* hyperconjugation interactions on a par with exchange repulsion of lone pairs the character of the N–O bond. It is shown that repulsion between lone pairs of oxygen and nitrogen atoms causes the elongation of the N–O bond only but character of this bond remains covalent. The interaction between lone pair of the terminal oxygen atom and antibonding orbital of the N–O bond (n–σ* hyperconjugation) coincides with influence of repulsion and reinforces it changing the character of the N–O bond from covalent to protocovalent. In contrary, the n–π* conjugation interaction between lone pairs of the bridged oxygen atom and π-orbital of the N=O double bond leads to the strengthening of the N–O bond making it more covalent.
A theoretical model for anisotropic multiferroics
Authors: Wang Shuling , Li Ruixue , Fu Hua-Hua , Ding Linjie , Yao Kailun
Published: September 2013

We propose a theoretical model for anisotropic multiferroics, which are one-dimensional charge transfer magnets. By means of Green's function theory, ferroelectric and magnetic properties are studied. It is found that the anisotropy not only plays an important role on the ferroelectric phase transition but also enhances the ferroelectric polarization. Under different anisotropy, the phase diagram and temperature dependence of the magnetic susceptibility and dielectric constant are also presented. It reveals that the transition temperature increases as anisotropy ascends, which is attributed to the energy gap. These results put forward a way to enhance the ferroelectric phase transition temperature.
Fabrication of a high-aspect-ratio sub-micron tool using a cathode coated with stretched-out insulating layers
Authors: Zeng Yongbin , Wang Yufeng , Qu Ningsong , Zhu Di
Published: September 2013

This paper describes a method for preparing a high-aspect-ratio sub-micron tool using a cathode coated with stretched-out insulating layers and a straight reciprocating motion applied at the anode via the liquid membrane electrochemical machining (ECM). Simulation results indicate that the application of a cathode coated with stretched-out insulating layers is beneficial for the localization of ECM. Moreover, a mathematical model was derived to estimate the final average diameter of the fabricated tools. Experiments were conducted to verify the versatility and feasibility of the proposed method and its mathematical model. It was observed that the calculated and the experimental results are in good agreement with each other. A sub-micron tool with an average diameter 140.8 nm and an aspect ratio up to 50 was fabricated using the proposed method.
KOTOBUKI-1 apparatus for cryogenic coherent X-ray diffraction imaging
Authors: Nakasako Masayoshi , Takayama Yuki , Oroguchi Tomotaka , Sekiguchi Yuki , Kobayashi Amane , Shirahama Keiya , Yamamoto Masaki , Hikima Takaaki , Yonekura Koji , Maki-Yonekura Saori , Kohmura Yoshiki , Inubushi Yuichi , Takahashi Yukio , Suzuki Akihiro , Matsunaga Sachihiro , Inui Yayoi , Tono Kensuke , Kameshima Takashi , Joti Yasumasa , Hoshi Takahiko
Published: September 2013

We have developed an experimental apparatus named KOTOBUKI-1 for use in coherent X-ray diffraction imaging experiments of frozen-hydrated non-crystalline particles at cryogenic temperature. For cryogenic specimen stage with small positional fluctuation for a long exposure time of more than several minutes, we here use a cryogenic pot cooled by the evaporation cooling effect for liquid nitrogen. In addition, a loading device is developed to bring specimens stored in liquid nitrogen to the specimen stage in vacuum. The apparatus allows diffraction data collection for frozen-hydrated specimens at 66 K with a positional fluctuation of less than 0.4 μm and provides an experimental environment to easily exchange specimens from liquid nitrogen storage to the specimen stage. The apparatus was developed and utilized in diffraction data collection of non-crystalline particles with dimensions of μm from material and biological sciences, such as metal colloid particles and chloroplast, at BL29XU of SPring-8. Recently, it has been applied for single-shot diffraction data collection of non-crystalline particles with dimensions of sub-μm using X-ray free electron laser at BL3 of SACLA.
Magnetostrictive contribution to Poisson ratio of galfenol
Authors: Paes V. Z. C. , Mosca D. H.
Published: September 2013

In this work we present a detailed study on the magnetostrictive contribution to Poisson ratio for samples under applied mechanical stress. Magnetic contributions to strain and Poisson ratio for cubic materials were derived by accounting elastic and magneto-elastic anisotropy contributions. We apply our theoretical results for a material of interest in magnetomechanics, namely, galfenol (Fe1−xGax). Our results show that there is a non-negligible magnetic contribution in the linear portion of the curve of stress versus strain. The rotation of the magnetization towards [110] crystallographic direction upon application of mechanical stress leads to an auxetic behavior, i.e., exhibiting Poisson ratio with negative values. This magnetic contribution to auxetic behavior provides a novel insight for the discussion of theoretical and experimental developments of materials that display unusual mechanical properties.
Communication: Protein dynamical transition vs. liquid-liquid phase transition in protein hydration water
Authors: Schirò Giorgio , Fomina Margarita , Cupane Antonio
Published: September 2013

In this work, we compare experimental data on myoglobin hydrated powders from elastic neutron scattering, broadband dielectric spectroscopy, and differential scanning calorimetry. Our aim is to obtain new insights on the connection between the protein dynamical transition, a fundamental phenomenon observed in proteins whose physical origin is highly debated, and the liquid-liquid phase transition (LLPT) possibly occurring in protein hydration water and related to the existence of a low temperature critical point in supercooled water. Our results provide a consistent thermodynamic/dynamic description which gives experimental support to the LLPT hypothesis and further reveals how fundamental properties of water and proteins are tightly related.
High-resolution mass spectrometer for liquid metal ion sources
Authors: Wortmann Martin , Ludwig Arne , Meijer Jan , Reuter Dirk , Wieck Andreas D.
Published: September 2013

Recently, a mass spectrometer for liquid metal ion sources (LMIS) has been built and set into operation. This device uses an E × B-filter as mass dispersive element and provides sufficient resolution to analyse the emission of clusters from LMIS to much higher mass ranges (>2000 amu) than commercially available mass filters for focused ion beam systems. It has also been shown that for small masses the composition of clusters from different isotopes can be resolved. Furthermore, a rather high fluence of monodisperse clusters in the range of 106–107 clusters/s can be achieved with this setup. This makes it a promising tool for the preparation of mass selected clusters. In this contribution, theoretical considerations as well as technical details and the results of first measurements are presented.
Physics and model of strengthening by parallel stacking faults
Authors: Jian W. W. , Cheng G. M. , Xu W. Z. , Koch C. C. , Wang Q. D. , Zhu Y. T. , Mathaudhu S. N.
Published: September 2013

We have recently reported that parallel stacking faults (SFs) can tremendously increase the strength of a magnesium alloy. The strengthening is found to increase linearly with the reciprocal of the mean SF spacing, d. In this study we analyze dislocation interactions with SFs, and then propose a physics-based model to explain the observed relationship between yield strength and SFs spacing. Similar to the empirical Hall-Petch relationship for grain size, it is expected that this strengthening mechanism will hold true for a variety of materials engineered with parallel spaced stacking faults over a wide range of fault spacing.
Electron cyclotron harmonic resonances in high-frequency heating of the ionosphere
Authors: Kuo Spencer P.
Published: September 2013

Electron acceleration by upper hybrid waves under cyclotron harmonic resonance interaction is studied. Theory is formulated; the analytical solutions in the second and fourth harmonic cyclotron resonance cases are obtained, and in the third harmonic case, a first order differential equation governing the evolution of the electron energy is derived. The theory is applied for explaining the generation of artificial ionization layers observed in high-frequency (HF) ionospheric heating experiments. The upper hybrid waves are assumed to be excited parametrically by the O-mode HF heating wave. As the decay mode is the lower hybrid wave, the excited upper hybrid waves have wavelengths ranging from 0.25 to 0.5 m, which are short enough to effectively incorporate the finite Larmour radius effect for the harmonic cyclotron resonance interactions as well as have a frequency bandwidth of about 20 kHz, which provides an altitude region of about 10 km for continuous harmonic cyclotron resonance interaction between electrons and descending waves in the slightly inhomogeneous geomagnetic field. The numerical results on electron acceleration show that electron fluxes with energies larger than 14 eV are generated in the three harmonic cases. These energetic electrons cause impact ionizations, which are descending to form artificial ionization layers at the bottom of the ionospheric F region.
Alternative hot spot formation techniques using liquid deuterium-tritium layer inertial confinement fusion capsules
Authors: Olson R. E. , Leeper R. J.
Published: September 2013

The baseline DT ice layer inertial confinement fusion (ICF) ignition capsule design requires a hot spot convergence ratio of ∼34 with a hot spot that is formed from DT mass originally residing in a very thin layer at the inner DT ice surface. In the present paper, we propose alternative ICF capsule designs in which the hot spot is formed mostly or entirely from mass originating within a spherical volume of DT vapor. Simulations of the implosion and hot spot formation in two DT liquid layer ICF capsule concepts—the DT wetted hydrocarbon (CH) foam concept and the “fast formed liquid” (FFL) concept—are described and compared to simulations of standard DT ice layer capsules. 1D simulations are used to compare the drive requirements, the optimal shock timing, the radial dependence of hot spot specific energy gain, and the hot spot convergence ratio in low vapor pressure (DT ice) and high vapor pressure (DT liquid) capsules. 2D simulations are used to compare the relative sensitivities to low-mode x-ray flux asymmetries in the DT ice and DT liquid capsules. It is found that the overall thermonuclear yields predicted for DT liquid layer capsules are less than yields predicted for DT ice layer capsules in simulations using comparable capsule size and absorbed energy. However, the wetted foam and FFL designs allow for flexibility in hot spot convergence ratio through the adjustment of the initial cryogenic capsule temperature and, hence, DT vapor density, with a potentially improved robustness to low-mode x-ray flux asymmetry.
Study of electron trapping by a transversely ellipsoidal bubble in the laser wake-field acceleration
Authors: Cho Myung-Hoon , Kim Young-Kuk , Hur Min Sup
Published: September 2013

We present electron trapping in an ellipsoidal bubble which is not well explained by the spherical bubble model by [Kostyukov et al., Phys. Rev. Lett. 103, 175003 (2009)]. The formation of an ellipsoidal bubble, which is elongated transversely, frequently occurs when the spot size of the laser pulse is large compared to the plasma wavelength. First, we introduce the relation between the bubble size and the field slope inside the bubble in longitudinal and transverse directions. Then, we provide an ellipsoidal model of the bubble potential and investigate the electron trapping condition by numerical integration of the equations of motion. We found that the ellipsoidal model gives a significantly less restrictive trapping condition than that of the spherical bubble model. The trapping condition is compared with three-dimensional particle-in-cell simulations and the electron trajectory in test potential simulations.
Experimental observation of one-dimensional quantum holographic imaging
Authors: Song Xin-Bing , Xu De-Qin , Wang Hai-Bo , Xiong Jun , Zhang Xiangdong , Cao De-Zhong , Wang Kaige
Published: September 2013

We report the experimental observation of quantum holographic imaging of one-dimensional object with entangled photon pairs, generated in a spontaneous parametric down-conversion process. The signal photons play both roles of “object wave” and “reference wave” in holography but are recorded by a point detector providing only encoding information, while the idler photons travel freely and are locally manipulated with spatial resolution. The holographic image is formed by the two-photon correlation measurement, although both the signal and idler beams are incoherent. Three types of quantum holography schemes are analyzed according to the detection regime of the signal photons.
Transmission surface plasmon resonance microscopy
Authors: Loison Olivier , Fort Emmanuel
Published: September 2013

We present a microscopy technique to image minute variations of optical properties at the interface of a metallic thin-film. This technique is based on an original transmission configuration of surface plasmon resonance sensors. It combines high diffraction-limited lateral resolution with unaltered refractive index sensitivity. Transmitted light is obtained by using near-field transducers positioned at the metal/dielectric interface to probe the propagative surface plasmon dispersion curve. This label-free technique can find applications in highly multiplexed molecular sensing or full-field surface microscopy. As an example, we show tomography images of silica nanometric patterns.
Large hole spin anticrossings in InAs/GaAs double quantum dots
Authors: Rajadell F. , Climente J. I. , Planelles J.
Published: September 2013

We show that hole states in InAs/GaAs double quantum dots can exhibit spin anticrossings of up to 1 meV, according to simulations with a three dimensional Burt-Foreman Hamiltonian including strain and piezoelectric fields. The spin mixing originates in the valence band spin-orbit interaction plus the spatial symmetry breaking arising from misalignment between the dots and piezoelectric potential. The values we report are in better agreement with experiments than previous theoretical estimates and yield good prospects for efficient hole spin control.
Structural difference between near interface oxides grown on Si and C faces of 4H-SiC characterized by infrared spectroscopy
Authors: Hirai Hirohisa , Kita Koji
Published: September 2013

Thermal oxides on 4H-SiC (0001) (Si-face) and (0001¯) (C-face) grown at 1100 °C were characterized by Fourier transform infrared spectroscopy attenuated total reflection method. For the films thicker than 5 nm on both faces, the structure of oxide was almost the same as that of the thermal oxide on silicon irrespective of film thickness. For the films thinner than 3 nm, structural transition regions were observed near the interface on both faces, and structural difference was also clearly detected between the oxides in those transition regions on (0001) and on (0001¯) faces.
Color-tunable and high-efficiency organic light-emitting diode by adjusting exciton bilateral migration zone
Authors: Liu Shengqiang , Wu Ruofan , Huang Jiang , Yu Junsheng
Published: September 2013

A voltage-controlled color-tunable and high-efficiency organic light-emitting diode (OLED) by inserting 16-nm N,N′-dicarbazolyl-3,5-benzene (mCP) interlayer between two complementary emitting layers (EMLs) was fabricated. The OLED emitted multicolor ranging from blue (77.4 cd/A @ 6 V), white (70.4 cd/A @ 7 V), to yellow (33.7 cd/A @ 9 V) with voltage variation. An equivalent model was proposed to reveal the color-tunable and high-efficiency emission of OLEDs, resulting from the swing of exciton bilateral migration zone near mCP/blue-EML interface. Also, the model was verified with a theoretical arithmetic using single-EML OLEDs to disclose the crucial role of mCP exciton adjusting layer.
Biased interface between solid ion conductor LiBH4 and lithium metal: A first principles molecular dynamics study
Authors: Ikeshoji Tamio , Ando Yasunobu , Otani Minoru , Tsuchida Eiji , Takagi Shigeyuki , Matsuo Motoaki , Orimo Shin-ichi
Published: September 2013

We use first-principles molecular dynamics to study the electrochemical solid-solid interface between lithium metal and lithium electrolyte LiBH4. An external bias is applied by using an effective screening medium. We observe large polarization in the LiBH4, because the lithium cations in LiBH4 are shifted more on one side of the double-well potential of Li+. This results in a large potential drop in the interface region and a large double-layer capacity corresponding to ca. 70 μF/cm2. H-coordination to the Li atoms plays an important role in the charge-transfer reaction and ion transfer.
Ultrafast transient spectroscopy and photoluminescence properties of V2O5 nanowires
Authors: Othonos Andreas , Christofides Constantinos , Zervos Matthew
Published: September 2013

The properties of V2O5 semiconductor nanowires have been investigated using ultrashort transient absorption spectroscopy in conjunction with time resolved photoluminescence. Femtosecond pulse excitation has been utilized to generate non equilibrium carrier densities above the band edge of the Nanowires (NWs), and non-degenerate pump probe techniques have been employed to follow carrier relaxation through the conduction band and defects states located within the band gap of the semiconductor NWs. Photoluminescence revealed three relaxation mechanisms with time constants ranging from a single to tens of ns providing evidence of the importance of radiative and non-radiative decay channels associated with states within the nanowires.
Tunable magnetization and spin transfer induced by electric field in magnetic ultrathin BiFeO3 layer
Authors: Feng Hong-Jian
Published: September 2013

First-principles density-functional theory calculations show that switching of magnetization by 90° can be achieved in BiFeO3 ultrathin film by applying external electric field. Spin-up carriers appear to the surface with positive field while spin-down ones to the negative field surface, arising from the redistribution of Fe-t2g orbital. The half-metallic behavior of Fe-3 d states in the surface of rhombohedral phase film makes it a promising candidate for antiferromagnetic/ferromagnetic bilayer heterostructure possessing electric field tunable ferromagnetic magnetization reversal and opens a new way towards designing spintronic multiferroics. The interface exchange-bias effect in this BiFeO3/ferromagnetic bilayer is mainly driven by the Fe-t2g orbital reconstruction, as well as spin transferring and rearrangement.
Surface depletion effects in semiconducting nanowires having a non-uniform radial doping profile
Authors: Calahorra Yonatan , Ritter Dan
Published: September 2013

Doping profile has a significant effect on nanowire (NW) electrostatics, an effect that is expected to influence NW contact and transport properties. Herein, the electrostatic potential of nanowires (NWs) of non-uniform radial doping is calculated by two means: depletion approximation and a numerical calculation. Two profiles are considered: linear and exponential, corresponding to shallow and abrupt distributions; the results are compared to planar systems with similar doping profiles, and to uniformly doped NW systems. For a given average doping distribution, a non-uniform doping profile results in significantly lower carrier concentrations, an effect which intensifies with doping non-uniformity. Furthermore, in some cases, band diagrams obtained for the exponential doping profile vary greatly from any uniform doping, indicating that unique properties are expected for such NWs.
Nanophotonic luminescent solar concentrators
Authors: Rousseau I. , Wood V.
Published: September 2013

We investigate the connection between photonic local density of states and luminescent solar concentrator (LSC) performance in two manufacturable nanocavity LSC structures: a bilayer slab and a slab photonic crystal. Finite-difference time-domain electromagnetic simulations show that the waveguided luminescence photon flux can be enhanced up to 30% for the photonic crystal design over a conventional LSC operating in the ray optic limit, assuming the same number of excited lumophores. Further photonic engineering could realize an increase of up to one order of magnitude in the flux of waveguided luminescence.