bluuebunny/crossref_metadata_2025 huggingface dataset:
A multi-view time-domain non-contact diffuse optical tomography scanner with dual wavelength detection for intrinsic and fluorescence small animal imaging
Authors: Lapointe Eric , Pichette Julien , Bérubé-Lauzière Yves
Published: July 2012

We present a non-contact diffuse optical tomography (DOT) scanner with multi-view detection (over 360°) for localizing fluorescent markers in scattering and absorbing media, in particular small animals. It relies on time-domain detection after short pulse laser excitation. Ultrafast time-correlated single photon counting and photomultiplier tubes are used for time-domain measurements. For light collection, seven free-space optics non-contact dual wavelength detection channels comprising 14 detectors overall are placed around the subject, allowing the measurement of time point-spread functions at both excitation and fluorescence wavelengths. The scanner is endowed with a stereo camera pair for measuring the outer shape of the subject in 3D. Surface and DOT measurements are acquired simultaneously with the same laser beam. The hardware and software architecture of the scanner are discussed. Phantoms are used to validate the instrument. Results on the localization of fluorescent point-like inclusions immersed in a scattering and absorbing object are presented. The localization algorithm relies on distance ranging based on the measurement of early photons arrival times at different positions around the subject. This requires exquisite timing accuracy from the scanner. Further exploiting this capability, we show results on the effect of a scattering hetereogenity on the arrival time of early photons. These results demonstrate that our scanner provides all that is necessary for reconstructing images of small animals using full tomographic reconstruction algorithms, which will be the next step. Through its free-space optics design and the short pulse laser used, our scanner shows unprecedented timing resolution compared to other multi-view time-domain scanners.
Special singularity function for continuous part of the spectral data in the associated eigenvalue problem for nonlinear equations
Authors: Vakhnenko V. O. , Parkes E. J.
Published: July 2012

The procedure for finding the solutions of the Vakhnenko-Parkes equation by means of the inverse scattering method is described. The continuous spectrum is taken into account in the associated eigenvalue problem. The suggested special form of the singularity function for continuous part of the spectral data gives rise to the multi-mode solutions. The sufficient conditions are proved in order that these solutions become real functions. The interaction of the N periodic waves is studied. The procedure is illustrated by considering a number of examples.
Operator extensions theory model for electromagnetic field–electron interaction
Authors: Popov I. Yu.
Published: July 2012

A model of the point-like interaction between the classical electromagnetic field and the quantum electron is suggested. It is based on the theory of self-adjoint extensions of symmetric operators in the Pontryagin and Hilbert spaces. The shift of the electron eigenvalues due to the electromagnetic field influence is obtained.
Double tangent extension method and first integrals
Authors: Lazrag Lanouar
Published: July 2012

We consider systems of ordinary differential equations and present a new method of finding first integrals called Double tangent extension method. We apply it to study the integrability by quadratures of differential systems with homogeneous polynomials right hand sides. Some new cases of integrability with two, three, and four degrees of freedom are found.
On the effects of lateral gauge misalignment in shocked targets
Authors: Appleby-Thomas G. J. , Hazell P. J. , Wood D. C. , Wilgeroth J. M. , Leighs J. A.
Published: July 2012

Plate-impact experiments have been used to interrogate the influence of gauge alignment on the shock response of wire-element lateral manganin stress gauges in PMMA and aluminium targets. Embedded gauges were progressively rotated relative to the target impact face. Peak stress and lateral gauge rise-times were found be proportional (negatively and positively, respectively) to the resolved angle of the embedded gauge element. However, lateral stress gradients behind the shock were found to be relatively insensitive to gauge alignment. In addition, investigation of the effects of release arrival showed no connection to either peak stress or behaviour behind the shock.
GaAs nanowire Schottky barrier photovoltaics utilizing Au–Ga alloy catalytic tips
Authors: Han Ning , Wang Fengyun , Yip SenPo , Hou Jared J. , Xiu Fei , Shi Xiaoling , Hui Alvin T. , Hung TakFu , Ho Johnny C.
Published: July 2012

Single GaAs nanowire photovoltaic devices were fabricated utilizing rectifying junctions in the Au–Ga catalytic tip/nanowire contact interface. Current-voltage measurements were performed under simulated Air Mass 1.5 global illumination with the best performance delivering an overall energy conversion efficiency of ∼2.8% for a nanowire of 70 nm in diameter. As compared with metal contacts directly deposited on top of the nanowire, this nanoscale contact is found to alleviate the well-known Fermi-level pinning to achieve effective formation of Schottky barrier responsible for the superior photovoltaic response. All these illustrate the potency of these versatile nanoscale contact configurations for future technological device applications.
Effective work functions for the evaporated metal/organic semiconductor contacts from in-situ diode flatband potential measurements
Authors: Zhou Mi , Png Rui-Qi , Khong Siong-Hee , Sivaramakrishnan Sankaran , Zhao Li-Hong , Chua Lay-Lay , Friend Richard H. , Ho Peter K. H.
Published: July 2012

The diode built-in potentials (Vbi) of several polymer organic semiconductor (OSC) thin films [(2,5-dialkoxy-substituted poly(p-phenylenevinylene), poly(9,9-dialkylfluorene), poly(9,9-dialkylfluorene-alt-phenylene(N-phenyl)iminophenylene), and poly(9,9-dialkylfluorene-alt-benzothiadiazole)] sandwiched between p-doped poly(3,4-ethylenedioxythiophene) (PEDT:PSSH) and evaporated metal contacts have been measured by bias-dependent electromodulated absorption (EA) spectroscopy of the Stark-shifted π–π* band. From these values and the vacuum-level offsets at the PEDT:PSSH contacts evaluated by sub-gap EA spectroscopy, the following effective work functions for the buried evaporated metal contacts have been obtained: Al 3.4 ± 0.1, Ag 3.7 ± 0.1, Au 4.4 ± 0.1, and Ca 2.4 ± 0.1 eV. These work functions are smaller than those of the “clean” metal surfaces by up to 0.8 eV, and are substantially independent of the OSC in the absence of charge transfer.
Note: Compact helical pulse forming line for the generation of longer duration rectangular pulse
Authors: Sharma Surender Kumar , Deb P. , Sharma Archana , Shukla R. , Prabaharan T. , Adhikary B. , Shyam A.
Published: July 2012

The helical pulsed forming line (PFL) can generate longer duration rectangular pulse in a smaller length. A compact PFL using helical water line is designed and experimentally investigated. The impedance of the helical PFL is 22 Ω. The compactness is achieved in terms of reduction in length of the PFL by a factor of 5.5 using helical water PFL as compared to coaxial water PFL of same length. The helical PFL was pulsed charged to 200 kV using a high voltage pulse transformer in 4.5 μs and discharged into the matched 22 Ω resistive load through a self-breakdown pressurized spark gap switch. The rectangular voltage pulse of 100 kV, 260 ns (FWHM) is measured across the load. The effect of reduction in water temperature on the pulse width is also studied experimentally. The increase in pulse width up to 7% more is observed by reducing the temperature of the deionized water to 5 °C. It will further reduce the length of the PFL and make the system small for compact pulsed power drivers.
High energy resolution five-crystal spectrometer for high quality fluorescence and absorption measurements on an x-ray absorption spectroscopy beamline
Authors: Llorens Isabelle , Lahera Eric , Delnet William , Proux Olivier , Braillard Aurélien , Hazemann Jean-Louis , Prat Alain , Testemale Denis , Dermigny Quentin , Gelebart Frederic , Morand Marc , Shukla Abhay , Bardou Nathalie , Ulrich Olivier , Arnaud Stéphan , Berar Jean-François , Boudet Nathalie , Caillot Bernard , Chaurand Perrine , Rose Jérôme , Doelsch Emmanuel , Martin Philippe , Solari Pier Lorenzo
Published: July 2012

Fluorescence detection is classically achieved with a solid state detector (SSD) on x-ray absorption spectroscopy (XAS) beamlines. This kind of detection however presents some limitations related to the limited energy resolution and saturation. Crystal analyzer spectrometers (CAS) based on a Johann-type geometry have been developed to overcome these limitations. We have tested and installed such a system on the BM30B/CRG-FAME XAS beamline at the ESRF dedicated to the structural investigation of very dilute systems in environmental, material and biological sciences. The spectrometer has been designed to be a mobile device for easy integration in multi-purpose hard x-ray synchrotron beamlines or even with a laboratory x-ray source. The CAS allows to collect x-ray photons from a large solid angle with five spherically bent crystals. It will cover a large energy range allowing to probe fluorescence lines characteristic of all the elements from Ca (Z = 20) to U (Z = 92). It provides an energy resolution of 1–2 eV. XAS spectroscopy is the main application of this device even if other spectroscopic techniques (RIXS, XES, XRS, etc.) can be also achieved with it. The performances of the CAS are illustrated by two experiments that are difficult or impossible to perform with SSD and the complementarity of the CAS vs SSD detectors is discussed.
High-efficiency cross-beam magnetic electron-impact source for improved miniature Mattauch-Herzog mass spectrometer performance
Authors: Hadjar O. , Fowler W. K.
Published: July 2012

We describe a newly designed cross-beam magnetic electron-impact ion source (CBM-EI). We demonstrate its superiority in comparison with a conventional source (CB-EI) when used with a commercial miniature sector-field-type, non-scanning mass spectrometer featuring Mattauch-Herzog geometry (MH-MS) and a permanent sector-field magnet. This paper clearly shows the value of the CBM-EI for enhancing MH-MS sensitivity. Unlike secondary electron-multiplier type detectors, the pixelated detector (IonCCD™) used in the commercial MH-MS has no gain. The MH-MS/IonCCD system is therefore challenged to compete with time-of-flight and quadrupole MS systems due to their higher ion transmissions and detector gains. Using the new CBM-EI, we demonstrate an instrument sensitivity increase of 20-fold to 100-fold relative to the CB-EI-equipped instrument. This remarkable signal increase by the simple addition of the magnet assembly arises from the magnet-induced gyromotion of the thermionic electrons, which vastly increases the effective path length of the electrons through the ionization region, and the collimated nature of the electron flux, which optimizes the ion transmission through the 100-μm object slit of the MH-MS. Some or all of the realized sensitivity increase may be exchanged for an increase in resolution and/or mass range through the use of a narrower object slit, or for a reduction in ion-source pressure to limit quenching. The CBM-EI should facilitate development of a differentially pumped ion source to extend the lifetime of the filament, especially in otherwise intractable applications associated with oxidizing and corrosive samples.
On the influence of the architecture of poly(ethylene glycol)-based thermoresponsive polymers on cell adhesion
Authors: Uhlig Katja , Boysen Björn , Lankenau Andreas , Jaeger Magnus , Wischerhoff Erik , Lutz Jean-François , Laschewsky André , Duschl Claus
Published: July 2012

Thermoresponsive polymer surface coatings are a promising tool for cell culture applications. They allow for a mild way of cell detachment that preserves the activity of membrane proteins—a prerequisite for reliable cell analysis. To enlarge the application range of these coatings to cells with different adhesion properties, we synthesized various novel poly(ethylene glycol)-based thermoresponsive polymers and describe how (i) their chemical structure and (ii) their surface density affect their efficiency. In order to quantify the influence of both factors, the time for cell spreading and rounding efficiency were observed. As a result, efficiency of cell rounding, which is closely correlated to cell detachment, is less affected by both factors than the time needed for cell spreading. This time can effectively be adjusted by the molecular architecture which includes the length of the polymer backbone and the side chains. Based on this work, recommendations are given for future optimization of functionality of thermoresponsive polymer coatings for cell culture applications.
DNA capture-probe based separation of double-stranded polymerase chain reaction amplification products in poly(dimethylsiloxane) microfluidic channels
Authors: Khodakov Dmitriy , Thredgold Leigh , Lenehan Claire E. , Andersson Gunther G. , Kobus Hilton , Ellis Amanda V.
Published: July 2012

Herein, we describe the development of a novel primer system that allows for the capture of double-stranded polymerase chain reaction (PCR) amplification products onto a microfluidic channel without any preliminary purification stages. We show that specially designed PCR primers consisting of the main primer sequence and an additional “tag sequence” linked through a poly(ethylene glycol) molecule can be used to generate ds-PCR amplification products tailed with ss-oligonucleotides of two forensically relevant genes (amelogenin and human c-fms (macrophage colony-stimulating factor) proto-oncogene for the CSF-1 receptor (CSF1PO). Furthermore, with a view to enriching and eluting the ds-PCR products of amplification on a capillary electrophoretic-based microfluidic device we describe the capture of the target ds-PCR products onto poly(dimethylsiloxane) microchannels modified with ss-oligonucleotide capture probes.
Diagnosing radiative shocks from deuterium and tritium implosions on NIF
Authors: Pak A. , Divol L. , Weber S. , Döppner T. , Kyrala G. A. , Kilne J. , Izumi N. , Glenn S. , Ma T. , Town R. P. , Bradley D. K. , Glenzer S. H.
Published: July 2012

During the recent ignition tuning campaign at the National Ignition Facility, layered cryogenic deuterium and tritium capsules were imploded via x-ray driven ablation. The hardened gated x-ray imager diagnostic temporally and spatially resolves the x-ray emission from the core of the capsule implosion at energies above ∼8 keV. On multiple implosions, ∼200–400 ps after peak compression a spherically expanding radiative shock has been observed. This paper describes the methods used to characterize the radial profile and rate of expansion of the shock induced x-ray emission.
Streaked x-ray spectrometer having a discrete selection of Bragg geometries for Omega
Authors: Millecchia M. , Regan S. P. , Bahr R. E. , Romanofsky M. , Sorce C.
Published: July 2012

The streaked x-ray spectrometer (SXS) is used with streak cameras [D. H. Kalantar, P. M. Bell, R. L. Costa, B. A. Hammel, O. L. Landen, T. J. Orzechowski, J. D. Hares, and A. K. L. Dymoke-Bradshaw, in 22nd International Congress on High-Speed Photography and Photonics, edited by D. L. Paisley and A. M. Frank (SPIE, Bellingham, WA, 1997), Vol. 2869, p. 680] positioned with a ten-inch manipulator on OMEGA [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)]10.1016/S0030-4018(96)00325-2 and OMEGA EP [L. J. Waxer et al., Presented at CLEO/QELS 2008, San Jose, CA, 4–9 May 2008 (Paper JThB1)] for time-resolved, x-ray spectroscopy of laser-produced plasmas in the 1.4- to 20-keV photon-energy range. These experiments require measuring a portion of this photon-energy range to monitor a particular emission or absorption feature of interest. The SXS relies on a pinned mechanical reference system to create a discrete set of Bragg reflection geometries for a variety of crystals. A wide selection of spectral windows is achieved accurately and efficiently using this technique. It replaces the previous spectrometer designs that had a continuous Bragg angle adjustment and required a tedious alignment calibration procedure. The number of spectral windows needed for the SXS was determined by studying the spectral ranges selected by OMEGA users over the last decade. These selections are easily configured in the SXS using one of the 25 discrete Bragg reflection geometries and one of the six types of Bragg crystals, including two curved crystals.
Effect of catalyst nanoparticle size on growth direction and morphology of InN nanowires
Authors: Ji Xu , Cheng Shuang , Hu Hairong , Li Huajun , Wu Zhiguo , Yan Pengxun
Published: July 2012

Au-assisted growth of InN nanowires (NWs) was accomplished by a simple chemical vapor deposition system. The as-prepared InN NWs exhibit two morphologies with different growth directions: periodic NWs (PNWs) and smooth NWs (SNWs) along <0001> and $ <\!\! 11\bar 20\! >$<112¯0>, respectively. The PNWs with crinoids morphology resulted when larger Au particles (∼40 nm in diameter) were used, while the SNWs with smooth sidewalls were obtained when smaller Au particles (∼10 nm in diameter) served as the collector. Furthermore, the mechanism of this growth behavior was discussed in terms of the effect of catalyst nanoparticle size.
Dark current in multilayer stabilized amorphous selenium based photoconductive x-ray detectors
Authors: Frey Joel B. , Belev George , Tousignant Olivier , Mani Habib , Laperriere Luc , Kasap Safa O.
Published: July 2012

We report on experimental results which show that the dark current in n-i-p structured, amorphous selenium films is independent of i-layer thickness in samples with consistently thick blocking layers. We have observed, however, a strong dependence on the n-layer thickness and positive contact metal chosen. These results indicate that the dominant source of the dark current is carrier injection from the contacts and any contribution from carriers thermally generated in the bulk of the photoconductive layer is negligible. This conclusion is supported by a description of the dark current transients at different applied fields by a model which assumes only carrier emission over a Schottky barrier. This model also predicts that while hole injection is initially dominant, some time after the application of the bias, electron injection may become the dominant source of dark current.
Elemental and magnetic sensitive imaging using x-ray excited luminescence microscopy
Authors: Rosenberg R. A. , Zohar S. , Keavney D. , Divan R. , Rosenmann D. , Mascarenhas A. , Steiner M. A.
Published: July 2012

We demonstrate the potential of x-ray excited luminescence microscopy for full-field elemental and magnetic sensitive imaging using a commercially available optical microscope, mounted on preexisting synchrotron radiation (SR) beamline end stations. The principal components of the instrument will be described. Bench top measurements indicate that a resolution of 1 μm or better is possible; this value was degraded in practice due to vibrations and/or drift in the end station and associated manipulator. X-ray energy dependent measurements performed on model solar cell materials and lithographically patterned magnetic thin film structures reveal clear elemental and magnetic signatures. The merits of the apparatus will be discussed in terms of conventional SR imaging techniques.
Nonlinear finite amplitude torsional vibrations of cantilevers in viscous fluids
Authors: Aureli Matteo , Pagano Christopher , Porfiri Maurizio
Published: July 2012

In this paper, we study torsional vibrations of cantilever beams undergoing moderately large oscillations within a quiescent viscous fluid. The structure is modeled as an Euler-Bernoulli beam, with thin rectangular cross section, under base excitation. The distributed hydrodynamic loading experienced by the vibrating structure is described through a complex-valued hydrodynamic function which incorporates added mass and fluid damping elicited by moderately large rotations. We conduct a parametric study on the two dimensional computational fluid dynamics of a pitching rigid lamina, representative of a generic beam cross section, to investigate the dependence of the hydrodynamic function on the governing flow parameters. As the frequency and amplitude of the oscillation increase, vortex shedding and convection phenomena increase, thus resulting into nonlinear hydrodynamic damping. We derive a handleable nonlinear correction to the classical hydrodynamic function developed for small amplitude torsional vibrations for use in a reduced order nonlinear modal model and we validate theoretical results against experimental findings.
Light attenuation experiments on double diffusive plumes and fountains
Authors: Sutherland Bruce R. , Lee Brace , Ansong Joseph K.
Published: July 2012

By adapting the method of light attenuation to the study of axisymmetric disturbances, we examine the structure of forced plumes and fountains whose buoyancy is set by salinity and/or temperature differences between the turbulent flow and the otherwise stationary ambient. The attenuation measurements are used to infer the statistically steady-state density as a function of radius and height. These compare well with in situ measurements of density taken from a conductivity-temperature probe that repeatedly traversed the centreline of the plume. The theory for forced plumes also agrees well with the centreline density profile. The radial structure of plumes and fountains near the source is found to correspond well to a Gaussian profile, although the standard deviation is found to increase moderately faster with height than spreading rates reported in the existing literature. This is attributed in part to averaging biases resulting from light attenuating through transient eddies. In most experiments, hot and salty fountains reached a steady state height consistent with existing semi-empirical theories for fountains with just one diffusive component. However, if the density of the hot and salty fluid near the source is close to, but moderately larger than, that of the ambient, over time, the fountain is observed to increase progressively in height. This occurs presumably as a consequence of heat diffusion at the top of the fountain making the ambient above it increasingly buoyant relative to the negative buoyancy associated with less diffusive salt.
Frequency-dependence of large-signal properties in lead-free piezoceramics
Authors: Dittmer Robert , Jo Wook , Aulbach Emil , Granzow Torsten , Rödel Jürgen
Published: July 2012

The dependence of large signal properties of (1−x)(0.81Bi1/2Na1/2TiO3-0.19Bi1/2K1/2TiO3)-xBi(Zn1/2Ti1/2)O3 with x = 0.02, 0.03, and 0.04 on the measurement frequency was investigated for a wide range of frequencies from 0.1 Hz to 100 Hz. A significant frequency dispersion in the characteristic parameters representatively maximum and coercive values was denoted. On extension with the temperature dependent dielectric permittivity measurement, it was shown that the observed frequency dependence is primarily correlated with the dynamics of field-induced phase transition from a relaxor state to a long-range ferroelectric state. Increasing the substitutional disorder introduced by Bi(Zn1/2Ti1/2)O3 addition was demonstrated to pronounce the frequency dependence. It was proposed that the change be due to the increase in random fields and consequent dominance of ergodicity, based on the frequency-dependent hysteresis measurements at an elevated temperature above so-called induced-ferroelectric-to-relaxor transition temperature.
Effects of internal strain and external pressure on electronic structures and optical transitions of self-assembled InxGa1−xAs/GaAs quantum dots: An experimental and theoretical study
Authors: Wen Yuan , Yang Mou , Xu S. J. , Qin L. , Shen Z. X.
Published: July 2012

The optical emissive transitions from the ground and excited states of the self-assembled InxGa1−xAs/GaAs quantum dots (QDs) at room temperature were experimentally measured as a function of the external hydrostatic pressure by means of the confocal micro-photoluminescence technique. The ground state transition is very weak under zero external pressure and the photoluminescence is dominant by the excited state transition. However, the intensity of the ground state transition monotonically increases with increasing the external pressure and eventually become the dominant transition. Their pressure coefficients (PCs) were determined to be 6.8 and 7.1 meV/kbar, respectively, which were astonishingly smaller than those of GaAs bulk and the InGaAs/GaAs reference quantum well. The emission peak from the higher order excited states had a much smaller PC (∼0.5 meV/kbar). The influence of the built-in strain and external hydrostatic pressure on the electronic structures and optical transitions of various InxGa1−xAs/GaAs QDs was theoretically investigated by using the eight-band k·p method. Good agreement between the theoretical and experimental results was achieved, firmly revealing that the internal built-in strain in the dot system is mainly responsible for the experimental findings.
Energy distribution and quantum yield for photoemission from air-contaminated gold surfaces under ultraviolet illumination close to the threshold
Authors: Hechenblaikner Gerald , Ziegler Tobias , Biswas Indro , Seibel Christoph , Schulze Mathias , Brandt Nico , Schöll Achim , Bergner Patrick , Reinert Friedrich T.
Published: July 2012

The kinetic energy distributions of photo-electrons emitted from gold surfaces under illumination by UV-light close to the threshold (photon energy in the order of the material work function) are measured and analyzed. Samples are prepared as chemically clean through Ar-ion sputtering and then exposed to atmosphere for variable durations before quantum yield measurements are performed after evacuation. During measurements, the bias voltage applied to the sample is varied and the resulting emission current measured. Taking the derivative of the current-voltage curve yields the energy distribution which is found to closely resemble the distribution of total energies derived by DuBridge for emission from a free electron gas. We investigate the dependence of distribution shape and width on electrode geometry and contaminant substances adsorbed from the atmosphere, in particular, to water and hydro-carbons. Emission efficiency increases initially during air exposure before diminishing to zero on a timescale of several hours, whilst subsequent annealing of the sample restores emissivity. A model fit function, in good quantitative agreement with the measured data, is introduced which accounts for the experiment-specific electrode geometry and an energy dependent transmission coefficient. The impact of large patch potential fields from contact potential drops between sample and sample holder is investigated. The total quantum yield is split into bulk and surface contributions which are tested for their sensitivity to light incidence angle and polarization. Our results are directly applicable to model parameters for the contact-free discharge system onboard the Laser Interferometer Space Antenna (LISA) Pathfinder spacecraft.
On the accuracy of frozen density embedding calculations with hybrid and orbital-dependent functionals for non-bonded interaction energies
Authors: Laricchia S. , Fabiano E. , Sala F. Della
Published: July 2012

We analyze the accuracy of the frozen density embedding (FDE) method, with hybrid and orbital-dependent exchange-correlation functionals, for the calculation of the total interaction energies of weakly interacting systems. Our investigation is motivated by the fact that these approaches require, in addition to the non-additive kinetic energy approximation, also approximate non-additive exact-exchange energies. Despite this further approximation, we find that the hybrid/orbital-dependent FDE approaches can reproduce the total energies with the same accuracy (about 1 mHa) as the one of conventional semi-local functionals. In many cases, thanks to error cancellation effects, hybrid/orbital-dependent approaches yield even the smallest error. A detailed energy-decomposition investigation is presented. Finally, the Becke-exchange functional is found to reproduce accurately the non-additive exact-exchange energies also for non-equilibrium geometries. These performances are rationalized in terms of a reduced-gradient decomposition of the non-additive exchange energy.
Adhesion layer-bottom electrode interaction during BaxSr1−xTiO3 growth as a limiting factor for device performance
Authors: Löffler Markus , Vorobiev Andrei , Zeng Lunjie , Gevorgian Spartak , Olsson Eva
Published: July 2012

Changes in bottom electrode morphology and adhesion layer composition upon deposition of BaxSr1−xTiO3 (BSTO) at elevated temperatures have been found, which have a negative impact on acoustic wave resonator device performance. The difference between nominal and actual adhesion layer composition are explained by grain boundary diffusion of Ti or W and their oxidation by in-diffusing oxygen, which leads to an increased interface roughness between the Pt bottom electrode and the BSTO. It is shown, that room-temperature deposited TiO2 diffusion barriers fail to protect against Ti oxidation and diffusion. Also W adhesion layers are prone to this phenomenon, which limits their ability to act as high temperature resistant adhesion layers for bottom electrodes for ferroelectric thin films.
Complete polarization analysis of high energy soft x-rays by combining a multilayer phase retarder with crystal analyzer
Authors: Wang H. , Dhesi S. S. , Maccherozzi F. , Sawhney K. J. S.
Published: July 2012

We demonstrate a complete polarization analysis of soft x-rays with an energy of 1.1 keV using a free-standing W/B4C multilayer phase retarders and a beryl crystal analyzer. The W/B4C multilayer exhibits five times increase in transmission over that previously reported. The beryl crystal proves to be a suitable analyzer for the polarization analysis with a 10% s-component of reflectivity resulting in an extinction ratio close to 0.002 at 1.1 keV. The combination of multilayer phase retarders and crystal analyzers should open up the field of the soft x-ray polarization analysis in the energy range between 1 keV and 2 keV.
Femtosecond laser-induced periodic surface structures on silica
Authors: Höhm S. , Rosenfeld A. , Krüger J. , Bonse J.
Published: July 2012

The formation of laser-induced periodic surface structures (LIPSS) on two different silica polymorphs (single-crystalline synthetic quartz and commercial fused silica glass) upon irradiation in air with multiple linearly polarized single- and double-fs-laser pulse sequences (τ = 150 fs pulse duration, λ = 800 nm center wavelength, temporal pulse separation Δt < 40 ps) is studied experimentally and theoretically. Two distinct types of fs-LIPSS [so-called low-spatial-frequency LIPSS (LSFL) and high-spatial-frequency LIPSS (HSFL)] with different spatial periods and orientations were identified. Their appearance was characterized with respect to the experimental parameters peak laser fluence and number of laser pulses per spot. Additionally, the “dynamics” of the LIPSS formation was addressed in complementary double-fs-pulse experiments with varying delays, revealing a characteristic change of the LSFL periods. The experimental results are interpreted on the basis of a Sipe-Drude model considering the carrier dependence of the optical properties of fs-laser excited silica. This new approach provides an explanation of the LSFL orientation parallel to the laser beam polarisation in silica—as opposed to the behaviour of most other materials.
Hydrogen adsorbed in a metal organic framework-5: Coupled translation-rotation eigenstates from quantum five-dimensional calculations
Authors: Matanović Ivana , Belof Jonathan L. , Space Brian , Sillar Kaido , Sauer Joachim , Eckert Juergen , Bačić Zlatko
Published: July 2012

We report rigorous quantum five-dimensional (5D) calculations of the coupled translation-rotation (T-R) eigenstates of a H2 molecule adsorbed in metal organic framework-5 (MOF-5), a prototypical nanoporous material, which was treated as rigid. The anisotropic interactions between H2 and MOF-5 were represented by the analytical 5D intermolecular potential energy surface (PES) used previously in the simulations of the thermodynamics of hydrogen sorption in this system [Belof et al., J. Phys. Chem. C 113, 9316 (2009)10.1021/jp901988e]. The global and local minima on this 5D PES correspond to all of the known binding sites of H2 in MOF-5, three of which, α-, β-, and γ-sites are located on the inorganic cluster node of the framework, while two of them, the δ- and ε-sites, are on the phenylene link. In addition, 2D rotational PESs were calculated ab initio for each of these binding sites, keeping the center of mass of H2 fixed at the respective equilibrium geometries; purely rotational energy levels of H2 on these 2D PESs were computed by means of quantum 2D calculations. On the 5D PES, the three adjacent γ-sites lie just 1.1 meV above the minimum-energy α-site, and are separated from it by a very low barrier. These features allow extensive wave function delocalization of even the lowest translationally excited T-R eigenstates over the α- and γ-sites, presenting significant challenges for both the quantum bound-state calculations and the analysis of the results. Detailed comparison is made with the available experimental data.
Gibbs free energy approach to the prediction of melting points of isolated, supported, and embedded nanoparticles
Authors: Luo Wenhua , Hu Wangyu , Su Kalin , Li Kemin
Published: July 2012

By means of the thermodynamic and thermophysical properties of bulk materials, the Gibbs free energies for isolated, supported, and embedded nanoparticles were obtained and used to elucidate the sized-dependent melting phenomenon of the nanoparticles. To account for the substrate effect upon the melting point of nanoparticles, the interfacial energy of binary immiscible systems was studied in detail. It was found that the interfacial energy of a binary immiscible system including carbon can be replaced almost entirely by the contribution from carbon; thus, the reason why the melting model of isolated nanoparticles can be applied to research the melting of the supported nanoparticles was clarified. Moreover, a new approach to achieving the diameter of the smallest crystalline nanoparticles was proposed based on the melting behavior of embedded nanoparticles.
Spin-sensitive distribution of electromagnetic field via spin-orbit interaction in structured metamaterials
Authors: Guo Qing-Hua , Kang Ming , Li Teng-Fei , Cui Hai-Xu , Gu Bing , Chen Jing , Wang Hui-Tian
Published: July 2012

We investigate the spin-sensitive distribution of electromagnetic (EM) field from a kind of defective inhomogeneous anisotropic metamaterial, with azimuthally distributed subwavelength rectangular holes within a distribution angle of Φ<2π. This structure supports the spin-orbit interaction in the optical angular momentum, induced by the Pancharatnam-Berry phase from the manipulation of the spin states of polarization. Spin-sensitive distributions of electric field intensity, spin states of polarization, and transverse energy flow in the transmitted EM field are investigated. Importance of this investigation and the possible applications are discussed.
Optical generation and detection of gigahertz-frequency longitudinal and shear acoustic waves in liquids: Theory and experiment
Authors: Klieber Christoph , Pezeril Thomas , Andrieu Stéphane , Nelson Keith A.
Published: July 2012

We describe an adaptation of picosecond laser ultrasonics tailored for study of GHz-frequency longitudinal and shear acoustic waves in liquids. Time-domain coherent Brillouin scattering is used to detect multicycle acoustic waves after their propagation through variable thickness liquid layers into a solid substrate. A specialized optical pulse shaping method is used to generate sequences of pulses whose repetition rate determines the acoustic frequency. The measurements reveal the viscoelastic liquid properties and also include signatures of the optical and acoustic cavities formed by the multilayer sample assembly. Modeling of the signals allows their features to be distinguished so that liquid properties can be extracted reliably. Longitudinal and shear acoustic wave data from glycerol and from the silicon oil DC704 are presented.
A novel particle time of flight diagnostic for measurements of shock- and compression-bang times in D3He and DT implosions at the NIF
Authors: Rinderknecht H. G. , Johnson M. Gatu , Zylstra A. B. , Sinenian N. , Rosenberg M. J. , Frenje J. A. , Waugh C. J. , Li C. K. , Sèguin F. H. , Petrasso R. D. , Rygg J. R. , Kimbrough J. R. , MacPhee A. , Collins G. W. , Hicks D. , Mackinnon A. , Bell P. , Bionta R. , Clancy T. , Zacharias R. , Döppner T. , Park H. S. , LePape S. , Landen O. , Meezan N. , Moses E. I. , Glebov V. U. , Stoeckl C. , Sangster T. C. , Olson R. , Kline J. , Kilkenny J.
Published: July 2012

The particle-time-of-flight (pTOF) diagnostic, fielded alongside a wedge range-filter (WRF) proton spectrometer, will provide an absolute timing for the shock-burn weighted ρR measurements that will validate the modeling of implosion dynamics at the National Ignition Facility (NIF). In the first phase of the project, pTOF has recorded accurate bang times in cryogenic DT, DT exploding pusher, and D3He implosions using DD or DT neutrons with an accuracy better than ±70 ps. In the second phase of the project, a deflecting magnet will be incorporated into the pTOF design for simultaneous measurements of shock- and compression-bang times in D3He-filled surrogate implosions using D3He protons and DD-neutrons, respectively.
High, magnetic field independent critical currents in (Ba,K)Fe2As2 crystals
Authors: Fang L. , Jia Y. , Chaparro C. , Sheet G. , Claus H. , Kirk M. A. , Koshelev A. E. , Welp U. , Crabtree G. W. , Kwok W. K. , Zhu S. , Hu H. F. , Zuo J. M. , Wen H.-H. , Shen B.
Published: July 2012

Each discovery of a new high temperature superconductor drives the expectation that advanced engineering of materials defect structures will enable effective vortex pinning and high values of the electrical current density. Here, we demonstrate that single crystals of the iron-based superconductor Ba0.6K0.4Fe2As2 with Tc = 37.5 K can accommodate an unprecedented large concentration of strong-pinning defects in the form of discontinuous nm-sized nanorods with no degradation of the superconducting transition temperature. At a temperature of 5 K, we find a critical current density of 5 MA/cm2 that is magnetic field independent in fields up to 7 T.
Enhancement of the thermoelectric properties in doped FeSb2 bulk crystals
Authors: Wang Kefeng , Hu Rongwei , Warren John , Petrovic C.
Published: July 2012

Kondo insulator FeSb2 with large Seebeck coefficient would have potential in thermoelectric applications in cryogenic temperature range if it had not been for large thermal conductivity κ. Here we studied the influence of different chemical substitutions at Fe and Sb site on thermal conductivity and thermoelectric effect in high quality single crystals. At 5% of Te doping at Sb site, thermal conductivity is suppressed from ∼250 W/Km in undoped sample to about 8 W/Km. However, Cr and Co doping at Fe site suppresses thermal conductivity more slowly than Te doping, and even at 20% Cr/Co doping the thermal conductivity remains ∼30 W/Km. The analysis of different contributions to phonon scattering indicates that the giant suppression of κ with Te is due to the enhanced point defect scattering originating from the strain field fluctuations. In contrast, Te-doping has small influence on the correlation effects and then for small Te substitution the large magnitude of the Seebeck coefficient is still preserved, leading to the enhanced thermoelectric figure of merit (ZT ∼0.05 at ∼100 K) in Fe(Sb0.9Te0.1)2.
Infrared spectroscopy of HOCl embedded in superfluid helium nanodroplets: Probing the dynamical response of the solvent
Authors: Raston Paul L. , Kelloway Donald D. , Jäger Wolfgang
Published: July 2012

The rotationally resolved depletion spectrum of hypochlorous acid embedded in helium nanodroplets in the 2.8 μm region is reported. The narrow a-type lines are asymmetrically skewed in the direction of the band origin, and an analysis of their line shapes based on the chirped damped oscillator function introduced by van Staveren and Apkarian [J. Chem. Phys. 133, 054506 (2010).10.1063/1.3469816] yields a response time of the helium solvent of 1 ns. The b-type lines are much broader due to the greater number of droplet states available for relaxation of the excited rotational states.
The photodissociation dynamics of the ethyl radical, C2H5, investigated by velocity map imaging
Authors: Steinbauer Michael , Giegerich Jens , Fischer Kathrin H. , Fischer Ingo
Published: July 2012

The photodissociation dynamics of the ethyl radical C2H5 has been investigated by velocity map imaging. Ethyl was produced by flash pyrolysis from n-propyl nitrite and excited to the $\~A$Ã 2A′ (3s) Rydberg state around 250 nm. The energetically most favorable reaction channel in this wavelength region is dissociation to C2H4 (ethene) + H. The H-atom dissociation products were ionized in a [1+1′] process via the 1s-2p transition. The observed translational energy distribution is bimodal: A contribution of slow H-atoms with an isotropic angular distribution peaks at low translational energies. An expectation value for the fraction of excess energy released into translation of ⟨fT⟩ = 0.19 is derived from the data, typical for statistical dissociation reactions. In addition, a fast H-atom channel is observed, peaking around 1.8 eV. The latter shows an anisotropic distribution with β = 0.45. It originates from a direct dissociation process within less than a rotational period. Time-delay scans with varying extraction voltages indicate the presence of two rates for the formation of H-atoms. One rate with a sub-nanosecond time constant is associated with H-atoms with large translational energy; a second one with a time constant on the order of 100 ns is associated with H-atoms formed with low translational energy. The data confirm and extend those from previous experiments and remove some inconsistencies. Possible mechanisms for the dissociation are discussed in light of the new results as well as previous ones.
Scaling range of velocity and passive scalar spectra in grid turbulence
Authors: Lee S. K. , Benaissa A. , Djenidi L. , Lavoie P. , Antonia R. A.
Published: July 2012

Isotropic velocity and scalar fluctuations are closely approximated by slightly stretching a heated grid flow through a short (1.36:1) contraction. The heating is such that temperature serves as a passive scalar, and the velocity/scalar time scale ratio is about one. At small values of Taylor microscale Reynolds number (10 < Rλ < 102), the spectrum of the temperature fluctuations has a more discernible scaling range than the spectrum of the velocity fluctuations. The scaling-range exponent for the thermal spectrum, mθ, exhibits a power-law function of Rλ and tends to the Kolmogorov value of 5/3 more rapidly than that for the velocity spectrum, mu. Both mθ and mu are closer to the Kolmogorov value with the contraction than with no contraction. The trends for the present measurements supplemented with previously published data for larger Rλ (>102) indicate that, to obtain a 5/3 scaling range, Rλ must exceed 103. The ratio (5/3 + mu)/mθ is approximately 2, in close conformity with the proposal of Danaila and Antonia [“Spectrum of a passive scalar in moderate Reynolds number homogeneous isotropic turbulence,” Phys. Fluids 21, 111702 (2009)10.1063/1.3264881].
Critical magnetic number in the magnetohydrodynamic Rayleigh-Taylor instability
Authors: Wang Yanjin
Published: July 2012

We study the two-phase free boundary problem for the equations of magnetohydrodynamics in an infinite slab, where the fluids are assumed to be incompressible, viscous, and of zero resistivity. We work in Lagrangian coordinates so as to rewrite the Lorentz force in terms of the fluid flow map. The equations admit a steady-state solution with the upper fluid heavier than the lower fluid, which makes the system susceptible to the Rayleigh-Taylor instability. We study the stabilizing effect of the magnetic field on solutions to the equations obtained by linearizing around this steady-state solution. We identity the critical magnetic number |B|c by a variational problem. When the magnetic field $\bar{B}$B¯ is vertical in 2D or 3D and when $\bar{B}$B¯ is horizontal in 2D we prove that the linear system is stable when $|\bar{B}|\ge |B|_c$|B¯|≥|B|c and is unstable when $|\bar{B}|<|B|_c$|B¯|<|B|c. Moreover, for $|\bar{B}|<|B|_c$|B¯|<|B|c the vertical $\bar{B}$B¯ stabilizes a low frequency interval while the horizontal $\bar{B}$B¯ stabilizes a high frequency interval, and the growth rate of growing modes is bounded.
Simultaneous detection of Raman scattering and near-infrared photoluminescence in one imaging microscope
Authors: Stürzl Ninette , Lebedkin Sergei , Peng Fei , Li Yan , Hennrich Frank , Kappes Manfred M.
Published: July 2012

We describe a microscope which allows simultaneous acquisition of Raman and near-infrared photoluminescence (NIR-PL) spectra and images. The instrument comprises an appropriately modified commercial Raman microscope, utilizes 785 nm excitation laser, and includes two detection channels for Raman and PL within the spectral ranges of ∼787–1000 nm (∼40–2700 cm−1 Raman shift) and ∼1050–1600 nm, respectively. The configuration can however be easily adapted for other excitation wavelengths and detection ranges. The possibility to simultaneously measure both Raman and NIR-PL spectra – exactly at the same sample locations - can be useful for various applications, for instance, for the characterisation of single-walled carbon nanotubes.
In situ measurement of alternating current magnetic susceptibility of Pd–hydrogen system for determination of hydrogen concentration in bulk
Authors: Akamaru Satoshi , Hara Masanori , Matsuyama Masao
Published: July 2012

An alternating current magnetic susceptometer for use as a hydrogen gauge for hydrogen-storage materials was designed and developed. The experimental system can simultaneously measure the hydrogen equilibrium pressure and the magnetic susceptibility of metal hydrides. The background voltage of the susceptometer was stabilized for a long period of time, without any adjustments, by attaching an efficient compensation circuit. The performance of the susceptometer at a static hydrogen concentration was demonstrated by measuring the magnetic susceptibility of a Pd–hydrogen system under equilibrium conditions. The in situ measurement of the magnetic susceptibility of Pd during hydrogen absorption was carried out using the susceptometer. Since the in situ magnetic susceptibility obtained at a lower initial hydrogen pressure agreed with the magnetic susceptibility measured at a static hydrogen concentration, the susceptometer could be used to determine the hydrogen concentration in Pd in situ. At a higher initial hydrogen pressure, enhancement of the magnetic susceptibility was observed at the beginning of hydrogen absorption because the magnetic moments induced by the large temporary strain generated in the Pd affected the magnetic susceptibility.