bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurement of the internal stress and electric field in a resonating piezoelectric transformer for high-voltage applications using the electro-optic and photoelastic effects
Authors: VanGordon James A. , Kovaleski Scott D. , Norgard Peter , Gall Brady B. , Dale Gregory E.
Published: February 2014

The high output voltages from piezoelectric transformers are currently being used to accelerate charged particle beams for x-ray and neutron production. Traditional methods of characterizing piezoelectric transformers (PTs) using electrical probes can decrease the voltage transformation ratio of the device due to the introduction of load impedances on the order of hundreds of kiloohms to hundreds of megaohms. Consequently, an optical diagnostic was developed that used the photoelastic and electro-optic effects present in piezoelectric materials that are transparent to a given optical wavelength to determine the internal stress and electric field. The combined effects of the piezoelectric, photoelastic, and electro-optic effects result in a time-dependent change the refractive indices of the material and produce an artificially induced, time-dependent birefringence in the piezoelectric material. This induced time-dependent birefringence results in a change in the relative phase difference between the ordinary and extraordinary wave components of a helium-neon laser beam. The change in phase difference between the wave components was measured using a set of linear polarizers. The measured change in phase difference was used to calculate the stress and electric field based on the nonlinear optical properties, the piezoelectric constitutive equations, and the boundary conditions of the PT. Maximum stresses of approximately 10 MPa and electric fields of as high as 6 kV/cm were measured with the optical diagnostic. Measured results were compared to results from both a simple one-dimensional (1D) model of the piezoelectric transformer and a three-dimensional (3D) finite element model. Measured stresses and electric fields along the length of an operating length-extensional PT for two different electrical loads were within at least 50 % of 3D finite element simulated results. Additionally, the 3D finite element results were more accurate than the results from the 1D model for a wider range of electrical load impedances under test.
A detailed balance analysis of conversion efficiencies limits for nanocrystal solar cells—Relating the shape of the excitonic peak to conversion efficiencies
Authors: Moore David T. , Gaskey Bernard , Robbins Andrew , Hanrath Tobias
Published: February 2014

We report the detailed balance analysis of the photovoltaic conversion efficiency of nanocrystal solar cells with discrete excitonic absorption profiles. We calculated the conversion efficiency limits of single junction, multiexciton, and tandem solar cells as a function of exciton peak energy and width. We delineate the width of the absorption spectrum in terms of the energetic width of an isolated nanocrystal and the physical width due to the nanocrystal diameter distribution in the ensemble. Our results suggest that the conversion efficiency is less strongly impacted by the ensemble distribution than by the energetic peak width.
Initial nucleation site formation due to acoustic droplet vaporization
Authors: Li David S. , Kripfgans Oliver D. , Fabiilli Mario L. , Brian Fowlkes J. , Bull Joseph L.
Published: February 2014

Acoustic droplet vaporization (ADV) is the selective vaporization of liquid microdroplets using ultrasound, resulting in gas bubbles. The ADV process has been proposed as a tool in biomedical applications such as gas embolotherapy, drug delivery, and phase-change contrast agents. Using a 7.5 MHz focused transducer, the initial gas nucleus formed in perfluorocarbon microdroplets was directly visualized using ultra-high speed imaging. The experimental results of initial nucleation site location were compared to a 2D axisymmetric linear acoustic model investigating the focal spot of the acoustic wave within the microdroplets. Results suggest a wavelength to droplet diameter dependence on nucleation site formation.
Impact of thermal annealing on bulk InGaAsSbN materials grown by metalorganic vapor phase epitaxy
Authors: Kim T. W. , Kim K. , Lee J. J. , Kuech T. F. , Mawst L. J. , Wells N. P. , LaLumondiere S. D. , Sin Y. , Lotshaw W. T. , Moss S. C.
Published: February 2014

Two different thermal annealing techniques (rapid thermal annealing (RTA) and in-situ post-growth annealing in the metalorganic vapor phase epitaxy (MOVPE) chamber) were employed to investigate their impact on the optical characteristics of double-heterostructures (DH) of InGaAsSbN/GaAs and on the performance of single-junction solar cell structures, all grown by MOVPE. We find that an optimized RTA procedure leads to a similar improvement in the photoluminescence (PL) intensity compared with material employing a multi-step optimized anneal within the MOVPE reactor. Time-resolved photoluminescence techniques at low temperature (LT) and room temperature (RT) were performed to characterize the carrier dynamics in bulk InGaAsSbN layers. Room temperature carrier lifetimes were found to be similar for both annealing methods, although the LT-PL (16 K) measurements of the MOVPE-annealed sample found longer lifetimes than the RTA-annealed sample (680 ps vs. 260 ps) for the PL measurement energy of 1.24 eV. InGaAsSbN-based single junction solar cells processed with the optimized RTA procedure exhibited an enhancement of the electrical performance, such as improvements in open circuit voltage, short circuit current, fill factor, and efficiency over solar cells subjected to the in-situ MOVPE annealing technique.
Magnetic and magnetocaloric properties of La0.85(Na1−xKx)0.15MnO3 ceramics produced by reactive spark plasma sintering
Authors: Regaieg Y. , Sicard L. , Monnier J. , Koubaa M. , Ammar-Merah S. , Cheikhrouhou A.
Published: February 2014

La0.85(Na1−xKx)0.15MnO3 (0 ≤ x ≤ 1) ceramics were synthesized from the raw La(OH)3, NaOH, KOH, and MnO2 powders using Reactive Spark Plasma Sintering. All the compounds were obtained as pure, dense, and ultrafine grained pellets. The Rietveld refinement of the X-Ray powder diffraction shows that all our synthesized samples are single phase and crystallize in the distorted rhombohedral system with R-3c space group. The thermal variation of their magnetization under a magnetic applied field of 50 mT shows a paramagnetic to ferromagnetic transition at a Curie temperature very close to room temperature. The magnetic entropy change, deduced from magnetization measurements versus magnetic applied field up to 5 T at several temperatures exhibits a maximum |ΔSM|max which slightly increases with increasing K content. The relative cooling power values, inferred from the |ΔSM| vs T peak broadening, vary slightly with the potassium content, reaching, values between 316 and 289 Jkg−1, in an applied magnetic field of 5 T, when x increases from 0 to 1. Technically, these large values make the prepared materials very promising for domestic magnetic refrigeration.
Magnetization switching detection of a single permalloy nanomagnet using magneto-transport measurements
Authors: Nguyen V. D. , Laczkowski P. , Marty A. , Notin L. , Beigné C. , Vila L. , Attané J. P.
Published: February 2014

The magnetoresistance of Permalloy (NiFe) nanomagnets is studied at room temperature. For low aspect ratios, the main contribution is the anisotropic magnetoresistance, whereas for higher aspect ratio this contribution vanishes. We show that magnon magnetoresistance measurements need to be taken into account to detect precisely the magnetization switching of a single NiFe nanomagnet of dimensions 200 × 32 × 30 nm3. Experimental results are found to be in agreement with micromagnetic simulations and we give the analytical expressions to compute this effect. The measurement of the angular dependence on the magnetization switching allows studying the magnetization reversal mode of a single nanomagnet.
Hydrogen plasma induced modification of photoluminescence from a-SiNx:H thin films
Authors: Bommali R. K. , Ghosh S. , Vijaya Prakash G. , Gao K. , Zhou S. , Khan S. A. , Srivastava P.
Published: February 2014

Low temperature (250–350 °C) hydrogen plasma annealing (HPA) treatments have been performed on amorphous hydrogenated silicon nitride (a-SiNx:H) thin films having a range of compositions and subsequent modification of photoluminescence (PL) is investigated. The PL spectral shape and peak positions for the as deposited films could be tuned with composition and excitation energies. HPA induced modification of PL of these films is found to depend on the N/Si ratio (x). Upon HPA, the PL spectra show an emergence of a red emission band for x ≤ 1, whereas an overall increase of intensity without change in the spectral shape is observed for x > 1. The emission observed in the Si rich films is attributed to nanoscale a-Si:H inclusions. The enhancement is maximum for off-stoichiometric films (x ∼ 1) and decreases as the compositions of a-Si (x = 0) and a-Si3N4 (x = 1.33) are approached, implying high density of non-radiative defects around x = 1. The diffusion of hydrogen in these films is also analyzed by Elastic Recoil Detection Analysis technique.
Direct imaging of electron recombination and transport on a semiconductor surface by femtosecond time-resolved photoemission electron microscopy
Authors: Fukumoto Keiki , Yamada Yuki , Onda Ken , Koshihara Shin-ya
Published: February 2014

Much effort has been devoted to the development of techniques to probe carrier dynamics, which govern many semiconductor device characteristics. We report direct imaging of electron dynamics on semiconductor surfaces by time-resolved photoemission electron microscopy using femtosecond laser pulses. The experiments utilized a variable-repetition-rate femtosecond laser system to suppress sample charging problems. The recombination of photogenerated electrons and the lateral motion of the electrons driven by an external electric field on a GaAs surface were visualized. The mobility was estimated from a linear relationship between the drift velocity and the potential gradient.
InGaZnO thin-film transistors with back channel modification by organic self-assembled monolayers
Authors: Xiao Peng , Lan Linfeng , Dong Ting , Lin Zhenguo , Shi Wen , Yao Rihui , Zhu Xuhui , Peng Junbiao
Published: February 2014

InGaZnO (IGZO) thin-film transistors (TFTs) with back channel modified by different kinds of self-assembled monolayers (SAMs) were fabricated. The mobility and electrical stability of the IGZO-TFTs were greatly improved after SAM-modification, owing to the good interface coupling and less water adsorption-desorption effect on the IGZO surface. Meanwhile, the octadecyltriethoxysilane (OTES) treated IGZO-TFT exhibited a higher mobility of 26.6 cm2 V−1 s−1 and better electrical stability compared to the octadecanethiol (ODT) treated one, which was attributed to the formation of a more compact and steady SAM on the IGZO surface after OTES treatment.
A full-dimensional quantum dynamical study of H2+H2 collisions: Coupled-states versus close-coupling formulation
Authors: Bohr Alex , Paolini Stephen , Forrey Robert C. , Balakrishnan N. , Stancil P. C.
Published: February 2014

Collision-induced energy transfer involving H2 molecules plays an important role in many areas of physics. Kinetic models often require a complete set of state-to-state rate coefficients for H2+H2 collisions in order to interpret results from spectroscopic observations or to make quantitative predictions. Recent progress in full-dimensional quantum dynamics using the numerically exact close-coupling (CC) formulation has provided good agreement with existing experimental data for low-lying states of H2 and increased the number of state-to-state cross sections that may be reliably determined over a broad range of energies. Nevertheless, there exist many possible initial states (e.g., states with high rotational excitation) that still remain elusive from a computational standpoint even at relatively low collision energies. In these cases, the coupled-states (CS) approximation offers an alternative full-dimensional formulation. We assess the accuracy of the CS approximation for H2+H2 collisions by comparison with benchmark results obtained using the CC formulation. The results are used to provide insight into the orientation effects of the various internal energy transfer mechanisms. A statistical CS approximation is also investigated and cross sections are reported for transitions which would otherwise be impractical to compute.
Plasmon-enhanced UV photocatalysis
Authors: Honda Mitsuhiro , Kumamoto Yasuaki , Taguchi Atsushi , Saito Yuika , Kawata Satoshi
Published: February 2014

We report plasmonic nanoparticle enhanced photocatalysis on titanium dioxide (TiO2) in the deep-UV range. Aluminum (Al) nanoparticles fabricated on TiO2 film increases the reaction rate of photocatalysis by factors as high as 14 under UV irradiation in the range of 260–340 nm. The reaction efficiency has been determined by measuring the decolorization rate of methylene blue applied on the TiO2 substrate. The enhancement of photocatalysis shows particle size and excitation wavelength dependence, which can be explained by the surface plasmon resonance of Al nanoparticles.
Hardness and incipient plasticity in silicate glasses: Origin of the mixed modifier effect
Authors: Kjeldsen Jonas , Smedskjaer Morten M. , Mauro John C. , Yue Yuanzheng
Published: February 2014

The scaling of Vickers hardness (Hv) in oxide glasses with varying network modifier/modifier ratio is manifested as either a positive or negative deviation from linearity with a maximum deviation at the ratio of about 1:1. In an earlier study [J. Kjeldsen et al., J. Non-Cryst. Solids 369, 61 (2013)], we observed a minimum of Hv in CaO/MgO sodium aluminosilicate glasses at CaO/MgO = 1:1 and postulated that this minimum is linked to a maximum in plastic flow. However, the origin of this link has not been experimentally verified. In this work, we attempt to do so by exploring the links among Hv, volume recovery ratio (VR) and plastic deformation volume (VP) under indentation, glass transition temperature (Tg), Young's modulus (E), and liquid fragility index (m) in CaO/MgO and CaO/Li2O sodium aluminosilicate glasses. We confirm the negative deviations from linearity and find that the maximum deviation (i.e., the so-called mixed modifier effect) of Hv, Tg, and m is at the modifier ratio of 1:1. These deviations increase in intensity as the total modifier concentration increases. We find a strong correlation between VP and Hv for the CaO/MgO series, implying that the minimum in Hv originates primarily from an increased shear flow in the mixed modifier glasses.
Actuating dielectric elastomers in pure shear deformation by elastomeric conductors
Authors: Wang Yin , Chen Baohong , Bai Yuanyuan , Wang Hong , Zhou Jinxiong
Published: February 2014

Pure shear experiments are commonly used to characterize dielectric elastomer (DE) material properties and to evaluate DE actuator/generator performance. It is increasingly important for many applications to replace conventional carbon grease electrodes with stretchable elastomeric conductors. We formulate a theory for DE with elastomeric conductors, synthesize transparent hydrogel as ionic conductors, and measure actuation of DE in pure shear deformation. Maximum 67% actuation strain is demonstrated. The theory agrees well with our measurement and also correlates well with reported experiments on DE with electronic conductors.
Positive temperature variation of the bandgap energy in the single-crystalline chalcopyrite semiconductor AgInS2
Authors: Ozaki Shunji , Horikoshi Yoshimichi
Published: February 2014

Optical absorption spectra have been measured on the single-crystalline chalcopyrite semiconductor AgInS2 using polarized light at T = 10–300 K. The bandgap energy Eg of AgInS2 shows unusual temperature dependence at low temperatures. The resultant temperature coefficient ∂Eg/∂T is found to be positive at T < 130 K and negative above 130 K. This result has been successfully explained by considering the effects of thermal expansion and electron–phonon interaction. The free-exciton emission of photoluminescence spectra also indicates positive temperature dependence of the peak energies at low temperatures. The exciton binding energy of AgInS2 is determined to be 26.4 meV.
Manipulation by exchange coupling in layered magnetic structures
Authors: Moskalenko M. A. , Uzdin V. M. , Zabel H.
Published: February 2014

Exchange coupling in magnetic heterostructures can be modified via introduction of additional magnetic spacer layers at the interfaces. The magnetic characteristics and the spacer layer thickness determine the functional properties of the whole system. We show that the hysteresis loop area of trilayer spring magnets with two different soft magnetic layers (s1, s2) and one hard magnetic layer (h) with the sequence s1/s2/h can be increased as compared to both bilayer structures s1/h and s2/h with the same total thickness of the soft layers and for definite thickness ratios of the soft layers and their sequences. For ferrimagnetic spin valves, the perpendicular exchange bias effect can be tuned via the thickness of non-magnetic spacer layers at the interface, which determine the exchange coupling between ferrimagnets. A simple quasi one-dimensional phenomenological model is able to describe the magnetic hysteresis of even complex layered structures and to predict optimal geometrical and magnetic parameters of such heterostructures.
Fundamental effects in nanoscale thermocapillary flow
Authors: Hun Jin Sung , Song Jizhou , Uk Chung Ha , Zhang Chenxi , Dunham Simon N. , Xie Xu , Du Frank , Kim Tae-il , Lee Jong-Ho , Huang Yonggang , Rogers John A.
Published: February 2014

When implemented on the nanoscale, material flows driven by gradients in temperature, sometimes known as thermocapillary flows, can be exploited for various purposes, including nanopatterning, device fabrication, and purification of arrays of single walled carbon nanotubes (SWNTs). Systematic experimental and theoretical studies on thermocapillary flow in thin polymer films driven by heating in individual metallic SWNT over a range of conditions and molecular weights reveal the underlying physics of this process. The findings suggest that the zero-shear viscosity is a critical parameter that dominates the dependence on substrate temperature and heating power. The experimentally validated analytical models in this study allow assessment of sensitivity to other parameters, such as the temperature coefficient of surface tension, the thermal interface conductance, and the characteristic length scale of the heated zone.
Coherent laminar and turbulent motion of toroidal vortex bundles
Authors: Wacks D. H. , Baggaley A. W. , Barenghi C. F.
Published: February 2014

Motivated by experiments performed in superfluid helium, we study numerically the motion of toroidal bundles of vortex filaments in an inviscid fluid. We find that the evolution of these large-scale vortex structures involves the generalized leapfrogging of the constituent vortex rings. Despite three dimensional perturbations in the form of Kelvin waves and vortex reconnections, toroidal vortex bundles retain their coherence over a relatively large distance (compared to their size), in agreement with experimental observations.
First-principles simulation of the optical response of bulk and thin-film α-quartz irradiated with an ultrashort intense laser pulse
Authors: Lee Kyung-Min , Min Kim Chul , Sato Shunsuke A. , Otobe Tomohito , Shinohara Yasushi , Yabana Kazuhiro , Moon Jeong Tae
Published: February 2014

A computational method based on a first-principles multiscale simulation has been used for calculating the optical response and the ablation threshold of an optical material irradiated with an ultrashort intense laser pulse. The method employs Maxwell's equations to describe laser pulse propagation and time-dependent density functional theory to describe the generation of conduction band electrons in an optical medium. Optical properties, such as reflectance and absorption, were investigated for laser intensities in the range 1010 W/cm2 to 2 × 1015 W/cm2 based on the theory of generation and spatial distribution of the conduction band electrons. The method was applied to investigate the changes in the optical reflectance of α-quartz bulk, half-wavelength thin-film, and quarter-wavelength thin-film and to estimate their ablation thresholds. Despite the adiabatic local density approximation used in calculating the exchange–correlation potential, the reflectance and the ablation threshold obtained from our method agree well with the previous theoretical and experimental results. The method can be applied to estimate the ablation thresholds for optical materials, in general. The ablation threshold data can be used to design ultra-broadband high-damage-threshold coating structures.
Efficiency of genomic DNA extraction dependent on the size of magnetic nanoclusters
Authors: Cho Hyun Ah , Hyun Min Ji , Hua Wu Jun , Woo Jang Jin , Lim Chae-Seung , Keun Kim Young
Published: February 2014

We report the efficiency of genomic DNA extraction as a function of particle size and quantity. For DNA extraction, we synthesized magnetic nanoclusters of various sizes and coated the surface of these magnetic nanoclusters with meso-2,3-dimercaptosuccinic acid. We showed that the nanoclusters had a tight particle size distribution and high crystallinity. Furthermore, we observed that the three types of magnetic nanoclusters studied exhibited ferrimagnetic behavior and that larger nanoclusters showed larger saturation magnetization values. The resultant efficiency of DNA extraction is inversely proportional to particle size in the range of nanoclusters tested, due to the fact that the surface-to-volume ratio decreases as particle size increases.
Controlled domain wall pinning in nanowires with perpendicular magnetic anisotropy by localized fringing fields
Authors: Breitkreutz Stephan , Eichwald Irina , Kiermaier Josef , Hiblot Gaspard , Csaba Gyorgy , Porod Wolfgang , Schmitt-Landsiedel Doris , Becherer Markus
Published: February 2014

A novel approach to directly control the domain wall (DW) pinning in a magnetic wire with perpendicular anisotropy is presented. Propagating DWs are blocked in a notch by the fringing fields of nearby gate magnets. Theoretical calculations of controlled DW pinning are confirmed by micromagnetic simulations. Experiments using magnetic force microscopy (MFM) and magneto-optical microscopy prove the functionality of the device. The presented structure enables to control the DW propagation in magnetic interconnects in order to store and buffer magnetic domains and hence, to directly control the signal flow in magnetic logic circuitry.
Two worlds collide: Image analysis methods for quantifying structural variation in cluster molecular dynamics
Authors: Steenbergen K. G. , Gaston N.
Published: February 2014

Inspired by methods of remote sensing image analysis, we analyze structural variation in cluster molecular dynamics (MD) simulations through a unique application of the principal component analysis (PCA) and Pearson Correlation Coefficient (PCC). The PCA analysis characterizes the geometric shape of the cluster structure at each time step, yielding a detailed and quantitative measure of structural stability and variation at finite temperature. Our PCC analysis captures bond structure variation in MD, which can be used to both supplement the PCA analysis as well as compare bond patterns between different cluster sizes. Relying only on atomic position data, without requirement for a priori structural input, PCA and PCC can be used to analyze both classical and ab initio MD simulations for any cluster composition or electronic configuration. Taken together, these statistical tools represent powerful new techniques for quantitative structural characterization and isomer identification in cluster MD.
Effect of polarization switching cycles on the dielectric response and Rayleigh constant in Pb0.4Sr0.6TiO3 thin films
Authors: Li Kui , Dong Xianlin , Rémiens Denis , Li Tao , Chen Ying , Wang Genshui
Published: February 2014

Pb0.4Sr0.6TiO3 thin films with good fatigue endurance were crystallized at low temperature compatible with the current semiconductor technology. The effect of polarization switching cycles on the ferroelectric properties, dielectric response, and Rayleigh constant in thin films were systematically investigated. The results indicated that the polarization switching improves the extrinsic dielectric response and dielectric nonlinearity of these thin films because of the dielectric response of the oxygen vacancy to the applied electric field, while shows weak effect on the intrinsic dielectric and ferroelectric response. Moreover, the Rayleigh constant showed different evolutions in the films prepared at different substrate temperatures.
Modeling of the quantum dot filling and the dark current of quantum dot infrared photodetectors
Authors: Ameen Tarek A. , El-Batawy Yasser M. , Abouelsaood A. A.
Published: February 2014

A generalized drift-diffusion model for the calculation of both the quantum dot filling profile and the dark current of quantum dot infrared photodetectors is proposed. The confined electrons inside the quantum dots produce a space-charge potential barrier between the two contacts, which controls the quantum dot filling and limits the dark current in the device. The results of the model reasonably agree with a published experimental work. It is found that increasing either the doping level or the temperature results in an exponential increase of the dark current. The quantum dot filling turns out to be nonuniform, with a dot near the contacts containing more electrons than one in the middle of the device where the dot occupation approximately equals the number of doping atoms per dot, which means that quantum dots away from contacts will be nearly unoccupied if the active region is undoped.
Determination of carrier lifetime and mobility in colloidal quantum dot films via impedance spectroscopy
Authors: Rath Arup K. , Lasanta Tania , Bernechea Maria , Diedenhofen Silke L. , Konstantatos Gerasimos
Published: February 2014

Impedance Spectroscopy (IS) proves to be a powerful tool for the determination of carrier lifetime and majority carrier mobility in colloidal quantum dot films. We employ IS to determine the carrier lifetime in PbS quantum dot Schottky solar cells with Al and we verify the validity of the technique via transient photovoltage. We also present a simple approach based on an RC model that allows the determination of carrier mobility in PbS quantum dot films and we corroborate the results via comparison with space charge limited measurements. In summary, we demonstrate the potential of IS to characterize key-to-photovoltaics optoelectronic properties, carrier lifetime, and mobility, in a facile way.
Preparation of room temperature terahertz detector with lithium tantalate crystal and thin film
Authors: Wang Jun , Gou Jun , Li Weizhi
Published: February 2014

Research on room temperature terahertz (THz) detector is essential for promoting the application of THz science and technology. Both lithium tantalate crystal (LiTaO3) and lithium tantalate thin film were used to fabricate the THz detector in this paper. Polishing process were used to reduce the thickness of LiTaO3 crystal slice by chemical mechanical polishing techniques and an improved sol-gel process was used to obtain high concentration LiTaO3 precursor solution to fabricate LiTaO3 thin film. Three dimension models of two THz detectors were set up and the temperature increasing map of two devices were simulated using finite element method. The lowest noise equivalent power value for terahertz detector using pyroelectric material reaches 6.8 × 10−9 W at 30 Hz operating frequency, which is suitable for THz imaging application.
Electrical, thermal, and species transport properties of liquid eutectic Ga-In and Ga-In-Sn from first principles
Authors: Yu Seungho , Kaviany Massoud
Published: February 2014

Using ab initio molecular dynamics, the atomic structure and transport properties of eutectic Ga-In and Ga-In-Sn are investigated. The Kubo-Greenwood (K-G) and the Ziman-Faber (Z-F) formulations and the Wiedemann-Franz (W-F) law are used for the electrical and electronic thermal conductivity. The species diffusivity and the viscosity are also predicted using the mean square displacement and the Stokes-Einstein (S-E) relation. Alloying Ga causes more disordered structure, i.e., broadening the atomic distance near the In and Sn atoms, which reduces the transport properties and the melting temperature. The K-G treatment shows excellent agreement with the experimental results while Z-F treatment formula slightly overestimates the electrical conductivity. The predicted thermal conductivity also shows good agreement with the experiments. The species diffusivity and the viscosity are slightly reduced by the alloying of Ga with In and Sn atoms. Good agreements are found with available experimental results and new predicted transport-property results are provided.
Water vapour permeability of poly(lactic acid): Crystallinity and the tortuous path model
Authors: Duan Z. , Thomas N. L.
Published: February 2014

The water vapour transmission rates (WVTR) through samples of polylactic acid of different crystallinities have been measured. Three different grades of commercial poly(lactic acid) (PLA) were used with different ratios of L-lactide and D-lactide to give a range of crystallinities from 0% to 50%. Sheets of PLA were prepared by melt compounding followed by compression moulding and annealing at different temperatures and for different times to give the range of crystallinities required. Crystallinity was measured by differential scanning calorimetry and the morphology of the samples was observed under crossed polars in a transmitted light microscope. Water vapour transmission rates through the films were measured at 38 °C and at a relative humidity of 90%. It was found that the measured values of WVTR decreased linearly with increasing crystallinity of the PLA from 0% to 50%. The results are discussed in terms of the effect of crystallinity on solubility and shown to fit the “Tortuous Path Model.” The model was also successfully used to explain published data on water permeability of polyethylene terephthalate.
New approach for absolute fluence distribution calculations in Monte Carlo simulations of light propagation in turbid media
Authors: Böcklin Christoph , Baumann Dirk , Fröhlich Jürg
Published: February 2014

A novel way to attain three dimensional fluence rate maps from Monte-Carlo simulations of photon propagation is presented in this work. The propagation of light in a turbid medium is described by the radiative transfer equation and formulated in terms of radiance. For many applications, particularly in biomedical optics, the fluence rate is a more useful quantity and directly derived from the radiance by integrating over all directions. Contrary to the usual way which calculates the fluence rate from absorbed photon power, the fluence rate in this work is directly calculated from the photon packet trajectory. The voxel based algorithm works in arbitrary geometries and material distributions. It is shown that the new algorithm is more efficient and also works in materials with a low or even zero absorption coefficient. The capabilities of the new algorithm are demonstrated on a curved layered structure, where a non-scattering, non-absorbing layer is sandwiched between two highly scattering layers.
Electro-optic precursors of critical transitions in dielectric liquids
Authors: Zhang X. , Zahn M.
Published: February 2014

Motivated by the search for approaches to non-destructive breakdown test and impurity detection in dielectric liquids, we explore the possibility of early warning of breakdown initiation in high voltage pulsed transformer oil from the data of Kerr electro-optic measurements. It is found that the light intensities near the rough surfaces of electrodes both fluctuate in repeated measurements and vary spatially in a single measurement. We show that the major cause is electrostriction which brings disturbances into optical detection. The calculated spatial variation has a strong nonlinear dependence on the applied voltage, which generates a precursory indicator of the critical transitions.
Dielectric and phonon properties of the multiferroic ferrimagnet Cu2OSeO3
Authors: Apostolova I. N.
Published: February 2014

We propose a microscopic model in order to study the multiferroic properties of Cu2OSeO3 taking into account the ferrimagnetic interaction, frustration, linear magnetoelectric (ME) coupling, and anharmonic spin-phonon interaction. We have shown that the dielectric constant and the phonon energy and damping have a kink near the magnetic phase transition TC = 58 K which disappears with increasing of an external magnetic field. This behavior is an evidence for a strong ME coupling and in qualitative agreement with the experimental data.
Probing temperature gradients within the GaN buffer layer of AlGaN/GaN high electron mobility transistors with Raman thermography
Authors: Hodges C. , Pomeroy J. , Kuball M.
Published: February 2014

We demonstrate the ability of confocal Raman thermography using a spatial filter and azimuthal polarization to probe vertical temperature gradients within the GaN buffer layer of operating AlGaN/GaN high electron mobility transistors. Temperature gradients in the GaN layer are measured by using offset focal planes to minimize the contribution from different regions of the GaN buffer. The measured temperature gradient is in good agreement with a thermal simulation treating the GaN thermal conductivity as homogeneous throughout the layer and including a low thermal conductivity nucleation layer to model the heat flow between the buffer and substrate.
Successive inverse and normal magnetocaloric effects in HoFeSi compound
Authors: Zhang H. , Sun Y. J. , Yang L. H. , Niu E. , Wang H. S. , Hu F. X. , Sun J. R. , Shen B. G.
Published: February 2014

Magnetic properties and magnetocaloric effect (MCE) of HoFeSi compound have been studied systematically. HoFeSi compound undergoes two successive magnetic phase transitions with the variation of temperature: a paramagnetic to ferromagnetic (FM) transition around TC =29 K followed by an FM to antiferromagnetic (AFM) or ferrimagnetic (FIM) transition at Tt = 20 K. The field dependence of magnetization reveals that a field-induced AFM/FIM-FM metamagnetic transition occurs below Tt with the increase in magnetic field. For a relatively low field change of 2 T, successive inverse and normal MCEs are observed and the maximum ΔSM values reach as high as 5.6 and 7.1 J/kg K around Tt and TC, respectively. This feature of successive inverse and normal MCEs in HoFeSi are suggested to be applied in some magnetic refrigerators with special designs and functions.
Microstructure of multistage annealed nanocrystalline SmCo2Fe2B alloy with enhanced magnetic properties
Authors: Jiang Xiujuan , Devaraj Arun , Balamurugan B. , Cui Jun , Shield Jeffrey E.
Published: February 2014

The microstructure and chemistry of SmCo2Fe2B melt-spun alloy after multistage annealing was investigated using high resolution transmission electron microscopy (HRTEM) and 3D atom probe tomography. The multistage annealing resulted in an increase in both the coercivity and magnetization. The presence of Sm(Co,Fe)4B (1:4:1) and Sm2(Co,Fe)17Bx (2:17:x) magnetic phases were confirmed using both techniques. Fe2B at a scale of ∼5 nm was found by HRTEM precipitating within the 1:4:1 phase after the second-stage annealing. Ordering within the 2:17:x phase was directly identified both by the presence of antiphase boundaries observed by TEM and the interconnected isocomposition surface network found in 3D atom probe results in addition to radial distribution function analysis. The variations in the local chemistry after the secondary annealing were considered pivotal in improving the magnetic properties.
Rapid microwave phase detection based on a solid state spintronic device
Authors: Yao B. M. , Fu L. , Chen X. S. , Lu W. , Bai L. H. , Gui Y. S. , Hu C.-M.
Published: February 2014

A technique for rapidly detecting microwave magnitude and phase has been developed using a spintronic device as a microwave sensor, which allows a lock-in amplifier to perform real-time microwave measurement. To demonstrate the feasibility and reliability of the proposed approach, the resonance including the amplitude and phase in a complementary electric inductive-capacitive resonator has been characterized. The results are in agreement with measurement preformed by a vector network. This sensor approach is not limited for use only with spintronic devices, but can also be used with semiconductor devices and hence offers a useful alternative to existing microwave imaging and characterization technologies.
Bandgap measurements of low-k porous organosilicate dielectrics using vacuum ultraviolet irradiation
Authors: Zheng H. , King S. W. , Ryan V. , Nishi Y. , Shohet J. L.
Published: February 2014

Vacuum ultraviolet (VUV) photoemission spectroscopy is used to investigate the effect of VUV radiation on porous organosilicate (SiCOH) dielectrics during plasma processing. By comparing photoemission spectroscopic results before and after VUV exposure, VUV irradiation with photon energies less than 9.0 eV was found to be beneficial in depleting accumulated charge in SiCOH films while VUV photons with higher energies did not have this effect. Moreover, VUV irradiation with 8.9 eV photons depletes the most charge. From this result, it can be concluded that 8.9 eV is the bandgap plus the electron affinity energy of SiCOH dielectrics.
Type-I superconductor pick-up coil in superconducting quantum interference device-based ultra-low field nuclear magnetic resonance
Authors: Hwang Seong-min , Kim Kiwoong , Kyu Yu Kwon , Lee Seong-Joo , Hyun Shim Jeong , Körber Rainer , Burghoff Martin
Published: February 2014

In ultra-low field nuclear magnetic resonance (ULF-NMR) with strong prepolarization field (Bp), type-II superconducting pick-up coils may be vulnerable to flux pinning from the strong Bp. Pick-up coils made of NbTi, Nb, and Pb were evaluated in terms of acquired NMR signal quality. The type-II pick-up coils showed degraded signals above 61 mT maximum exposure, while the Pb pick-up coil exhibited no such degradation. Furthermore, a negative counter pulse following a strong Bp was shown to follow magnetic hysteresis loop to unpin the trapped flux in the type-II pick-up coil and restore the NMR signal.
Empirical feasibility analysis of thermoelectric energy harvesting in thermally limited compact mobile computers
Authors: Khan M. A. A. , Muhtaroğlu A.
Published: February 2014

Thermoelectric (TE) generation technology was experimentally established in previous research by our group as a viable technique for energy scavenging in a large notebook computer with no significant impact to system performance. The computer under investigation was designed to have additional thermal headroom, with Central Processing Unit (CPU) temperature significantly below its maximum limit under maximum workload conditions. Yet the question remained on if and how such scavenging could be done in small, thermally limited systems, which increasingly represent a larger portion of the contemporary microelectronic products. This paper thus empirically demonstrates the feasibility of thermoelectric energy scavenging in a compact mobile system, where CPU temperature readily reaches the maximum limit as the workload activity is increased. A detailed Finite Element model is presented first for what-if studies. The simulation results from the model are then correlated with the experimental thermal characterization data from a small notebook computer. “Hotspots” as well as the plausible locations for TE integration are identified in the system through the thermal simulations, and are validated by integrating the TE module to the target system. TE power generation density has been measured as 4.27 mW/cm3 under maximum workload conditions with no impact to system performance, as measured indirectly through cooling fan speed, CPU, and integrated graphics temperatures. For a well-characterized off-the-shelf TE component of size 6.05 mm × 6.05 mm × 2.09 mm, the maximum generated power was 410.5 μW, 3.5 times more than the corresponding value measured previously in the large notebook system under the same workload. Harvested power is expected to scale with the system workload activity, and the extension of the current solution to the similar opportunistic locations within the system.
Electric-field-tunable mechanical properties of relaxor ferroelectric single crystal measured by nanoindentation
Authors: Zhou Hao , Pei Yongmao , Li Faxin , Luo Haosu , Fang Daining
Published: February 2014

Electric field dependent mechanical properties of relaxor ferroelectric material Pb(Mn1/3Nb2/3)O3-PbTiO3 are investigated with the nanoindentation technique. Giant electric-field-tunable apparent elastic modulus (up to −39%), hardness (−9% to 20%), and energy dissipation (up to −13%) are reported. Based on experimental data, a characterization method of electromechanical coupled nanoindentation is proposed. In this method, an electric field tunable scaling relationship among elastic modulus, hardness, and indentation work for ferroelectric materials can be determined. In addition, this method can be used to obtain the electric-field-dependent elastic modulus and hardness, and avoid the estimate of contact area in the Oliver-Pharr method. Finally, the different effects on elastic modulus between positive and negative electric fields can be explained by the flexoelectric effect.
Monoacetylation of Carbohydrate Diols via Transesterification with Ethyl Acetate
Authors: Liu Xuyu , Becker Bernd , Cooper Matthew A.
Published: February 2014

Monoacetylation of secondary diols in protected monosaccharides was achieved with ethyl acetate as acyl donor and sodium tert-butoxide as a base. The regioseletivity of the reaction varied depending on the substrate. This new method provides a simple, fast, and efficient method to access selectively acetylated carbohydrates that is compatible with acid-sensitive protecting groups.
Preferential retention of chromosome regions in derived synthetic wheat lines: a source of novel alleles for wheat improvement
Authors: McIntyre C. L. , Rattey A. , Kilian A. , Dreccer M. F. , Shorter R.
Published: February 2014

Synthetic hexaploid wheats (SHWs) and their synthetic derivative lines (SDLs) are being used as a means of introducing novel genetic variation into bread wheat (BW). Phenotypic information for days to flowering, height, grain weight and grain yield was collected from multiple environments for three SDL families, each with ~50 lines, and their elite BW parents. In general, the SDLs were earlier flowering and taller with larger grain size, but similar grain yield to the BWs. The three SDL families and their SHW and BW parents were genotyped using mapped DArT (diversity arrays technology) markers. Within each SDL family, SHW-specific DArT markers were used to identify SHW-derived chromosomal regions that appeared to be preferentially retained in the SDL families, as determined by retention at frequencies >0.25, the expected frequency for Mendelian segregation. Regions on chromosomes 2BS and 7BL appeared to be preferentially retained in all three SDL families, while regions on chromosomes 1AL, 1BS, 3BS, 5AS, 5BL, and 7AS were preferentially retained in two of the three SDL families. Other regions were preferentially retained in single families only, including some regions located on the D genome. Single-marker regression analysis was performed using the preferentially retained markers and identified markers and regions that were significantly associated with one or more of the four traits measured. Comparative mapping also indicates that these preferentially retained markers and chromosome regions may co-locate with previously identified QTLs for anthesis, height, grain weight and/or grain yield. Therefore, SHWs may contain novel alleles at these loci in these regions for these traits, which may provide a selective advantage to the SDLs. This approach could provide a useful method for identifying chromosomal regions of interest with potentially novel alleles for introgression for further BW improvement.
Assessing the magnitude of impact of volcanic ash deposits on Merino wool production and fibre traits in the context of a drought in North-west Patagonia, Argentina
Authors: Easdale M. H. , Sacchero D. , Vigna M. , Willems P.
Published: February 2014

Environmental variability is a key feature of arid and semiarid rangelands worldwide. Drought is one of the main sources of variation in most extensive livestock production systems in arid environments, with biophysical and socioeconomic implications. The effect of non-climatic disturbance factors, such as volcanic eruption and ash deposits, has been less documented in arid environments. The aim was to assess the magnitude of impact of volcanic ash deposits on Merino wool production and quality that took place in the context of a drought, by making a comparison along a gradient of ash deposition before and after a volcanic eruption. It was found that volcanic ash deposits in the context of a regional drought significantly affected Merino wool production and fibre quality traits in farms from North-western Patagonia, Argentina. The magnitude of the impacts differed among wool traits. It is argued that further research is needed on the impact of ash deposits on wool weights and quality, and that measures of livestock production should be included in environmental monitoring systems at regional and farm levels.
Tissue factor expression provokes escape from tumor dormancy and leads to genomic alterations
Authors: Magnus Nathalie , Garnier Delphine , Meehan Brian , McGraw Serge , Lee Tae Hoon , Caron Maxime , Bourque Guillaume , Milsom Chloe , Jabado Nada , Trasler Jacquetta , Pawlinski Rafal , Mackman Nigel , Rak Janusz
Published: February 2014

Significance

Our study shows that the clotting protein tissue factor (TF) controls the state of tumor dormancy and does so in conjunction with recruitment of inflammatory cells and blood vessels. We show that indolent glioma cells remain harmless in mice unless rendered TF positive. Our work also demonstrates the ability of TF to indirectly influence the DNA of cancer cells by facilitating gene mutations and silencing. This ability is important because injury, cardiovascular disease, or other conditions may activate the clotting system and contribute to the awakening of occult cancer cells. This understanding also may suggest a prophylactic use of blood thinners in cases where dormant cancer cells and clotting are suspected to coexist (e.g., after surgery).
Transmitochondrial mice as models for primary prevention of diseases caused by mutation in the
tRNA

Lys

gene
Authors: Shimizu Akinori , Mito Takayuki , Hayashi Chisato , Ogasawara Emi , Koba Ryusuke , Negishi Issei , Takenaga Keizo , Nakada Kazuto , Hayashi Jun-Ichi
Published: February 2014

Significance

We generated transmitochondrial mito-mice-tRNA
Lys7731
as models for precise examination of the pathogenesis and transmission profiles of mtDNA mutations in the
tRNA

Lys

genes and have obtained important information regarding primary prevention of the diseases caused by the mtDNA mutations. Although nuclear transplantation from oocytes of affected mothers into enucleated oocytes of unrelated women has been suggested, the methodology carries the technical risk of inducing nuclear abnormalities and prompts ethical concerns regarding the production of three-parent babies with normal mtDNA from unrelated oocyte donors. The current study suggests that the selection of oocytes with high proportions of normal mtDNA from affected mothers can be used to avoid these issues and therefore provides insights into mitochondrial genetics and medicine.