bluuebunny/crossref_metadata_2025 huggingface dataset:
First Bloch eigenvalue in high contrast media
Authors: Briane Marc , Vanninathan Muthusamy
Published: January 2014

This paper deals with the asymptotic behavior of the first Bloch eigenvalue in a heterogeneous medium with a high contrast ɛY-periodic conductivity. When the conductivity is bounded in L1 and the constant of the Poincaré-Wirtinger weighted by the conductivity is very small with respect to ɛ−2, the first Bloch eigenvalue converges as ɛ → 0 to a limit which preserves the second-order expansion with respect to the Bloch parameter. In dimension two the expansion of the limit can be improved until the fourth-order under the same hypotheses. On the contrary, in dimension three a fibers reinforced medium combined with a L1-unbounded conductivity leads us to a discontinuity of the limit first Bloch eigenvalue as the Bloch parameter tends to zero but remains not orthogonal to the direction of the fibers. Therefore, the high contrast conductivity of the microstructure induces an anomalous effect, since for a given low-contrast conductivity the first Bloch eigenvalue is known to be analytic with respect to the Bloch parameter around zero.
Hydrogen negative ion production in a 14 GHz electron cyclotron resonance compact ion source with a cone-shaped magnetic filter
Authors: Ichikawa T. , Kasuya T. , Kenmotsu T. , Maeno S. , Nishiura M. , Shimozuma T. , Yamaoka H. , Wada M.
Published: January 2014

The plasma electrode structure of a 14 GHz ECR ion source was modified to enlarge the plasma volume of low electron temperature region. The result shows that the extracted beam current reached about 0.6 mA/cm2 with about 40 W microwave power. To investigate the correlation between the volume of the low electron temperature region and the H− current, a vacuum ultraviolet (VUV) spectrometer had been installed to observe light emission in the VUV wavelength range from the plasma. From the results of the negative ion beam current and that from VUV spectrometry, production rate of vibrationally excited hydrogen molecule seems to be enhanced by increasing the volume of low electron temperature region.
Molecular dynamics analysis on wetting and interfacial properties of water-alcohol mixture droplets on a solid surface
Authors: Surblys D. , Yamaguchi Y. , Kuroda K. , Kagawa M. , Nakajima T. , Fujimura H.
Published: January 2014

Molecular dynamics simulations of single water, water-methanol, or water-IPA (isopropyl-alcohol) mixture droplets on a solid surface were performed with various mixture ratios. An increase in alcohol fraction generally gave an increase in droplet wettability. Both methanol and IPA molecules showed a strong preference to gather at various interfaces, with methanol molecules also showing a tendency to diffuse into the droplet bulk. Specific interfacial tensions were investigated using quasi-one-dimensional simulation systems, and liquid-vapor and solid-liquid interfacial tensions were found to decrease greatly due to the presence of interfacial alcohol, while solid-vapor interfacial tensions were proved to have little influence on wettability. Young's relation was found to hold quantitatively well for both water-methanol and water-IPA droplets. The validity of using Bakker's equation on solid-liquid interfaces was also investigated, and it was shown that for tightly spaced crystal surfaces, the introduced uncertainly is small.
An improved dynamic non-equilibrium wall-model for large eddy simulation
Authors: Park George Ilhwan , Moin Parviz
Published: January 2014

A non-equilibrium wall-model based on unsteady 3D Reynolds-averaged Navier-Stokes (RANS) equations has been implemented in an unstructured mesh environment. The method is similar to that of the wall-model for structured mesh described by Wang and Moin [Phys. Fluids 14, 2043–2051 (2002)], but is supplemented by a new dynamic eddy viscosity/conductivity model that corrects the effect of the resolved Reynolds stress (resolved turbulent heat flux) on the skin friction (wall heat flux). This correction is crucial in predicting the correct level of the skin friction. Unlike earlier models, this eddy viscosity/conductivity model does not have a stress-matching procedure or a tunable free parameter, and it shows consistent performance over a wide range of Reynolds numbers. The wall-model is validated against canonical (attached) transitional and fully turbulent flows at moderate to very high Reynolds numbers: a turbulent channel flow at Reτ = 2000, an H-type transitional boundary layer up to Reθ = 3300, and a high Reynolds number boundary layer at Reθ = 31 000. Application to a separated flow over a NACA4412 airfoil operating close to maximum lift is also considered to test the performance of the wall-model in complex non-equilibrium flows.
Isentropic expansion of copper plasma in Mbar pressure range at “Luch” laser facility
Authors: Bel'kov S. A. , Derkach V. N. , Garanin S. G. , Mitrofanov E. I. , Voronich I. N. , Fortov V. E. , Levashov P. R. , Minakov D. V.
Published: January 2014

We present experimental results on thermodynamic properties of dense copper plasma in Mbar pressure range. The laser facility “Luch” with laser intensity 1014 W/cm2 is used to compress copper up to ∼8 Mbar by a strong shock wave; subsequent expansion of copper plasma into Al, Ti, Sn allows us to obtain release isentropes of copper by the impedance–matching method. A theoretical analysis and quantum simulations show that in our experiments strongly coupled quantum plasma is generated.
A rail system for circular synthetic aperture sonar imaging and acoustic target strength measurements: Design/operation/preliminary results
Authors: Kennedy J. L. , Marston T. M. , Lee K. , Lopes J. L. , Lim R.
Published: January 2014

A 22 m diameter circular rail, outfitted with a mobile sonar tower trolley, was designed, fabricated, instrumented with underwater acoustictransducers, and assembled on a 1.5 m thick sand layer at the bottom of a large freshwater pool to carry out sonar design and target scattering response studies. The mobile sonar tower translates along the rail via a drive motor controlled by customized LabVIEW software. The rail system is modular and assembly consists of separately deploying eight circular arc sections, measuring a nominal center radius of 11 m and 8.64 m arc length each,and having divers connect them together in the underwater environment. The system enables full scale measurements on targets of interest with 0.1° angular resolution over a complete 360° aperture, without disrupting target setup, and affording a level of control over target environment conditions and noise sources unachievable in standard field measurements. In recent use, the mobile cart carrying an instrumented sonar tower was translated along the rail in 720 equal position increments and acoustic backscatter data were acquired at each position. In addition, this system can accommodate both broadband monostatic and bistatic scatteringmeasurements on targets of interest, allowing capture of target signature phenomena under diverse configurations to address current scientific and technical issues encountered in mine countermeasure and unexploded ordnance applications. In the work discussed here, the circular rail apparatus is used for acoustic backscatter testing, but this system also has the capacity to facilitate the acquisition of magnetic and optical sensor data from targets of interest. A brief description of the system design and operation will be presented along with preliminary processed results for data acquired from acoustic measurements conducted at the Naval Surface Warfare Center, Panama City Division Test Pond Facility. [Work Supported by the U.S. Office of Naval Research and The Strategic Environmental Research and Development Program.]
Investigation on the comparability of the light spot hydrophone and the fiber optic hydrophone in lithotripter field measurements
Authors: Rad Abtin Jamshidi , Ueberle Friedrich , Krueger Klaus
Published: January 2014

Optical hydrophones are optimized pressure-pulse-sensors used for high-power shockwave sources, such as lithotripters. Recent investigation of Smith et al. [“A Comparison of light spot hydrophone and fiber optic probe hydrophone for lithotripter field characterization,” Rev. Sci. Instrum. 83, 014301 (2012)] show discrepancies in the negative pressure peak and tensile pulse duration regarding measurements carried out with two optical hydrophones: the Light Spot Hydrophone (LSHD) and the fiber optic hydro-phone. It was assumed that the differences arise from cavitation effects at the end-face of the LSHD glass-block and filter characteristics of the trans-impedance amplifier of the LSHD. The present study investigates the transfer-function of the LSHD. It is shown that the filter characteristics of the amplifier cause discrepancies in the rarefaction pressure pulse fraction (depending on the energy settings of the source 15 ± 2%).
A cylindrical converging shock tube for shock-interface studies
Authors: Luo Xisheng , Si Ting , Yang Jiming , Zhai Zhigang
Published: January 2014

A shock tube facility for generating a cylindrical converging shock wave is developed in this work. Based on the shock dynamics theory, a specific wall profile is designed for the test section of the shock tube to transfer a planar shock into a cylindrical one. The shock front in the converging part obtained from experiment presents a perfect circular shape, which proves the feasibility and reliability of the method. The time variations of the shock strength obtained from numerical simulation, experiment, and theoretical estimation show the desired converging effect in the shock tube test section. Particular emphasis is then placed on the problem of shock-interface interaction induced by cylindrical converging shock waves. For this purpose, membrane-less gas cylinder is adopted to form the interface between two different fluids while the laser sheet technique to visualize the flow field. The result shows that it is convenient to perform such experiments in this facility.
The virtual aeroshaping enhancement by synthetic jets with variable suction and blowing cycles
Authors: Feng Li-Hao , Wang Jin-Jun
Published: January 2014

A novel waveform modified from the standard-sinusoidal function is adopted to enhance the virtual aeroshaping effect of the synthetic jets positioned at the front stagnation point of a circular cylinder. The waveform is characterized by a control parameter, namely, the suction duty cycle factor k, which is the ratio of the time duration of the suction cycle to that of the blowing cycle. The strength of the synthetic jet vortex pair is enhanced by increasing the suction duty cycle factor. The periodic closed envelope forms upstream of the circular cylinder for k ≤ 1.00, while the quasi-steady open envelope forms for k ≥ 2.00, acting the virtual aeroshaping effect. As a result, both the statistical characteristics and the vortex dynamics of the near-wake flow field change with the suction duty cycle factor. The recirculation region downstream of the circular cylinder becomes smaller or even disappears, and thus, the drag coefficient over the circular cylinder is reduced by increasing the suction duty cycle factor to k ≥ 1.00. The statistical mean and fluctuating velocities show corresponding changes in the near wake with the different wake patterns. For k ≤ 0.50, the wake vortex shows the antisymmetric shedding mode which is similar with the natural case. For 1.00 ≤ k ≤ 2.00, the wake vortex shows the bistable state mode, where vortex sheds with symmetric or antisymmetric mode; the antisymmetric shedding mode dominates the global flow field for k = 1.00, while it is the symmetric shedding mode that dominates the flow field for k = 2.00. For k = 4.00, it shows the antisymmetric shedding mode with a shorter vortex formation length than the natural case. The above findings indicate that the virtual aeroshaping effect of the synthetic jets can be enhanced by increasing the suction duty cycle factor so as to increase the momentum coefficient while keeping other control parameters unchanged, providing us another way for effective flow control.
Essential role of catalysts (Mn, Au, and Sn) in the vapor liquid solid growth kinematics of ZnS nanowires
Authors: Rehman S. , Shehzad M. A. , Hafeez M. , Bhatti A. S.
Published: January 2014

In this paper, we demonstrate that surface energy of the catalyst is a vital parameter for the growth rate, self doping of the self assembled nanowires synthesized by employing vapor liquid solid growth technique. The synthesis of ZnS nanowires was done by selectively using three different catalysts (Mn, Au, and Sn), where Au, is the most common catalyst, was used as a reference. The distinctive difference in the growth rate was due to the surface energy of the metal alloy droplet and the interface energies, as explained theoretically using thermodynamic approach. We have found that the activation energy of diffusion of (Zn, S) species in the catalyst droplet was low in Sn (0.41 eV for Zn and 0.13 eV for S) and high in Mn (1.79 eV for Zn and 0.61 eV for S) compared to Au (0.62 eV for Zn and 0.21 eV for S) catalyzed ZnS nanostructures. The thermodynamic calculations predicted the growth rates of Sn (7.5 nm/s) catalyzed nanowires was faster than Au (5.1 nm/s) and Mn (4.6 nm/s) catalyzed ZnS nanostructures, which were in agreement with the experimental results. Finally, the location of the catalyst as dopant in the grown nanostructure was predicted and compared with experimental observations.
Formation of multi-charged ion beams by focusing effect of mid-electrode on electron cyclotron resonance ion source
Authors: Imai Youta , Kimura Daiju , Kurisu Yosuke , Nozaki Dai , Yano Keisuke , Kumakura Sho , Sato Fuminobu , Kato Yushi , Iida Toshiyuki
Published: January 2014

We are constructing a tandem type electron cyclotron resonance ion source (ECRIS) and a beam line for extracting ion beams. The ion beam is extracted from the second stage by an accel-decel extraction system with a single-hole and the ion beam current on each electrode is measured. The total ion beam current is measured by a faraday cup downstream the extraction electrodes. We measure these currents as a function of the mid-electrode potential. We also change the gap length between electrodes and perform similar measurement. The behaviors of these currents obtained experimentally against the mid-electrode potential show qualitatively good agreement with a simple theoretical consideration including sheath potential effects. The effect of mid-electrode potential is very useful for decreasing the beam loss for enhancing ion beam current extracted from ECRIS.
Note: Influence of calcium corrosion on the performance of an adjacent permeation barrier
Authors: Klumbies H. , Müller-Meskamp L. , Nehm F. , Leo K.
Published: January 2014

Organic devices have to be protected with a permeation barrier against ambient moisture since their performance is strongly reduced by contact with water. The corrosion of calcium is widely used to evaluate such permeation barriers. However, design details of the calcium corrosion test may have severe consequences for the validity and precision of the measurement results. In this work, we present such a measurement distortion caused by the direct contact between calcium and the inorganic permeation barrier. Fortunately, even a 20 nm thin interlayer of a soft material (i.e., C60) sandwiched between calcium and the barrier reestablishes the validity of the measurement. In addition, we present our latest and improved electrical calcium test layout used for this investigation.
Highly accurate spectral retardance characterization of a liquid crystal retarder including Fabry-Perot interference effects
Authors: Vargas Asticio , del Mar Sánchez-López María , García-Martínez Pascuala , Arias Julia , Moreno Ignacio
Published: January 2014

Multiple-beam Fabry-Perot (FP) interferences occur in liquid crystal retarders (LCR) devoid of an antireflective coating. In this work, a highly accurate method to obtain the spectral retardance of such devices is presented. On the basis of a simple model of the LCR that includes FP effects and by using a voltage transfer function, we show how the FP features in the transmission spectrum can be used to accurately retrieve the ordinary and extraordinary spectral phase delays, and the voltage dependence of the latter. As a consequence, the modulation characteristics of the device are fully determined with high accuracy by means of a few off-state physical parameters which are wavelength-dependent, and a single voltage transfer function that is valid within the spectral range of characterization.
Simulations of Janus droplets at equilibrium and in shear
Authors: Shardt Orest , Derksen J. J. , Mitra Sushanta K.
Published: January 2014

Janus droplets are compound droplets that consist of two adhering drops of different fluids that are suspended in a third fluid. We use the Shan-Chen lattice Boltzmann method for multicomponent mixtures to simulate Janus droplets at rest and in shear. In this simulation model, interfacial tensions are not known a priori from the model parameters and must be determined using numerical experiments. We show that interfacial tensions obtained with the Young-Laplace law are consistent with those measured from the equilibrium geometry. The regimes of adhering, separated, and engulfing droplets were explored. Two different adhesion geometries were considered for two-dimensional simulations of Janus droplets in shear. The first geometry resembles two adhering circles with small overlap. In the second geometry, the two halves are semicircular. For both geometries, the rotation rate of the droplet depends on its orientation. The width of the periodic simulation domain also affects the rotation rate of both droplet types up to an aspect ratio of 6:1 (width:height). While the droplets with the first geometry oscillated about the middle of the domain, the droplets of the second geometry did not translate while rotating. A four-pole vortex structure inside droplets of the second geometry was found. These simulations of single Janus droplets reveal complex behaviour that implies a rich range of possibilities for the rheology of Janus emulsions.
Binding energetics of substitutional and interstitial helium and di-helium defects with grain boundary structure in α-Fe
Authors: Tschopp M. A. , Gao F. , Yang L. , Solanki K. N.
Published: January 2014

The formation/binding energetics and length scales associated with the interaction between He atoms and grain boundaries in BCC α-Fe were explored. Ten different low Σ grain boundaries from the ⟨100⟩ and ⟨110⟩ symmetric tilt grain boundary systems were used. In this work, we then calculated formation/binding energies for 1–2 He atoms in the substitutional and interstitial sites (HeV, He2V, HeInt, He2Int) at all potential grain boundary sites within 15 Å of the boundary (52 826 simulations total). The present results provide detailed information about the interaction energies and length scales of 1–2 He atoms with grain boundaries for the structures examined. A number of interesting new findings emerge from the present study. For instance, the Σ3(112) twin boundary in BCC Fe possesses a much smaller binding energy than other boundaries, which corresponds in long time dynamics simulations to the ability of an interstitial He defect to break away from the boundary in simulations on the order of nanoseconds. Additionally, positive correlations between the calculated formation/binding energies of the He defects (R > 0.9) asserts that the local environment surrounding each site strongly influences the He defect energies and that highly accurate quantum mechanics calculations of lower order defects may be an adequate predictor of higher order defects. Various metrics to quantify or classify the local environment were compared with the He defect binding energies. The present work shows that the binding and formation energies for He defects are important for understanding the physics of He diffusion and trapping by grain boundaries, which can be important for modeling He interactions in polycrystalline steels.
Conduction paths in Cu/amorphous-Ta2O5/Pt atomic switch: First-principles studies
Authors: Xiao Bo , Gu Tingkun , Tada Tomofumi , Watanabe Satoshi
Published: January 2014

We have examined the structure of Cu filaments in Cu/amorphous-Ta2O5 (a-Ta2O5)/Pt atomic switch from first principles. We have found that the Cu single atomic chains are unstable during the molecular dynamics (MD) simulation and thus cannot work as conduction paths. On the other hand, Cu nanowires with various diameters are stable and can form conductive paths. In this case, the Cu-Cu bonding mainly contributes to the conductive, delocalized defect state. These make a sharp contrast with the case of single Cu chains in crystalline Ta2O5, which can be conductive paths through the alternant Cu-Ta bonding structure. A series of MD simulations suggest that even Cu nanowires with a diameter of 0.24 nm can work as conduction paths. The calculations of the transport properties of Cu/a-Ta2O5/Pt heterostructures with Cu nanowires between two electrodes further confirm the conductive nature of the Cu nanowires in the a-Ta2O5.
Phonon-mediated squeezing of the cavity field off-resonantly coupled with a coherently driven quantum dot
Authors: Zhu Jia-pei , Huang Hui , Li Gao-xiang
Published: January 2014

We theoretically propose a scheme for the quadrature squeezing of the cavity field via dissipative processes. The effects of the electron-phonon interaction (EPI) on the squeezing are investigated, where the cavity is off-resonantly coupled with a coherently driven quantum dot (QD) which is allowed to interact with an acoustic-phonon reservoir. Under certain conditions, the participation of the phonon induced by both the EPI and the off-resonant coupling of the cavity with the QD enables some dissipative processes to occur resonantly in the dressed-state basis of the QD. The cavity-mode photons emitted or absorbed during the phonon-mediated dissipative processes are correlated, thus leading to the squeezing of the cavity field. A squeezed vacuum reservoir for the cavity field is built up due to the EPI plus the off-resonant coupling between the cavity and the QD. The numerical results obtained with an effective polaron master equation derived using second-order perturbation theory indicate that, in low temperature limit, the degree of squeezing is maximal but the increasing temperature of the phonon reservoir could hinder the squeezing and degrade the degree of the squeezing of the cavity field. In addition, the presence of the photonic crystal could enhance the quadrature squeezing of the cavity field.
Physical origin of surface slip morphologies induced by regular self-organized dislocation patterns in fatigued copper single crystals
Authors: Li P. , Zhang Z. F.
Published: January 2014

In this study, the formation mechanisms of typical dislocation patterns in fatigued copper single crystals were systematically investigated and summarized. The formation of persistent slip band (PSB) ladders depends on the width of extended dislocation and the trap distance of dipole. When the actual capture distance dtrap is less than the critical capture distance dcritical, a group of relatively stable multipoles are obtained from many dipole segments, followed by the formation of the veins and PSB-ladder structures. Further evolution will bring about more and more ladder-like PSBs appearing in one local zone until 100% PSB, which is corresponding to the formation of developing deformation bands (DBs), and then the developing DBs will be converted into the well-developed DBs by merging ladder-like PSBs. After the secondary fatigue, the veins, PSB ladders, or walls can be regarded as the nucleation source of new slip bands (SBs). No matter how the surface slip morphologies change, the evolution of dislocation patterns always keeps the dynamic equilibrium and essentially reflects the constant deepening of strain localization.
Numerical analysis of droplet impact onto liquid film
Authors: Shetabivash H. , Ommi F. , Heidarinejad G.
Published: January 2014

Normal impingement of a single droplet on a thin liquid film is investigated numerically solving the axisymmetric Navier-Stokes equations. Gravity and viscosity are taken into account whereas compressibility effects are neglected. Two phases are tracked by means of volume of fluid method and adaptive mesh refinement is used to increase accuracy of the interface. Numerical results are validated both qualitatively and quantitatively using experimental measurements. Effects of gas density, gas viscosity, and film thickness on the crown behavior are studied. Influence of droplet deviation from spherical shape on the crown behavior is investigated. It is shown that increasing the gas density leads to reduction of crown radius evolution rate, while gas viscosity does not affect the rate of crown radius evolution. Development rate of crown height decreases by increasing the gas density. Reynolds number and splashing regime can change the effect of gas viscosity on the crown height evolution. Deviation of droplet from sphere can change behavior of crown completely as result of change in droplet mass center position. Difference between numerical results and experimental ones is justified using different droplet shapes.
Highly sensitive superhydrophobic Ag nanorods array substrates for surface enhanced fluorescence studies
Authors: Kumar Samir , Goel Pratibha , Singh Dhruv P. , Singh J. P.
Published: January 2014

We report a facile method to fabricate highly sensitive superhydrophobic Ag nanorods (AgNR) arrays based surface enhanced fluorescence spectroscopy (SEFS) substrates using glancing angle deposition technique at a substrate temperature of 133 K and then subsequent coating of heptadecafluoro-1-decanethiol (HDFT) molecules. The SEFS enhancement behaviour of these substrates was determined by using aqueous solution of Rhodamine 6G. The HDFT coated superhydrophobic AgNR arrays SEFS substrates exhibit more then 3-fold fluorescence signal enhancement than conventional AgNR films. These HDFT coated superhydrophobic AgNR SEFS substrates based sensors may find application for the purpose of trace analysis and biosensing.
Hard X-ray dark-field imaging with incoherent sample illumination
Authors: Endrizzi Marco , Diemoz Paul C. , Millard Thomas P. , Louise Jones J. , Speller Robert D. , Robinson Ian K. , Olivo Alessandro
Published: January 2014

We report on a non-interferometric technique enabling dark-field imaging by using incoherent illumination and two achromatic optical elements. The simultaneous retrieval of absorption and differential phase images in the hard X-ray regime is also provided. We show that three projection images are sufficient to separate three signals: absorption, differential phase, and scattering. The method is highly efficient, also in terms of the dose delivered to the sample, flexible, robust against environmental vibrations, and scalable. It can be easily implemented in laboratories and translated into commercial systems, lending itself to a wide range of applications.
Spectroscopic ellipsometry of homoepitaxial diamond multilayers and delta-doped structures
Authors: Bousquet J. , Chicot G. , Eon D. , Bustarret E.
Published: January 2014

The optimization of diamond-based unipolar electronic devices such as pseudo-vertical Schottky diodes or delta-doped field effect transistors relies in part on the sequential growth of nominally undoped (p–) and heavily boron doped (p++) layers with well-controlled thicknesses and steep interfaces. Optical ellipsometry offers a swift and contactless method to characterize the thickness, roughness, and electronic properties of semiconducting and metallic diamond layers. We report ellipsometric studies carried out on delta-doped structures and other epitaxial multilayers with various boron concentrations and thicknesses (down to the nanometer range). The results are compared with Secondary Ion Mass Spectroscopy and transport measurements.
Calculating the spontaneous magnetization and defining the Curie temperature using a positive-feedback model
Authors: Harrison R. G.
Published: January 2014

A positive-feedback mean-field modification of the classical Brillouin magnetization theory provides an explanation of the apparent persistence of the spontaneous magnetization beyond the conventional Curie temperature—the little understood “tail” phenomenon that occurs in many ferromagnetic materials. The classical theory is unable to resolve this apparent anomaly. The modified theory incorporates the temperature-dependent quantum-scale hysteretic and mesoscopic domain-scale anhysteretic magnetization processes and includes the effects of demagnetizing and exchange fields. It is found that the thermal behavior of the reversible and irreversible segments of the hysteresis loops, as predicted by the theory, is a key to the presence or absence of the “tails.” The theory, which permits arbitrary values of the quantum spin number J, generally provides a quantitative agreement with the thermal variations of both the spontaneous magnetization and the shape of the hysteresis loop.
Polarized Raman scattering of single ZnO nanorod
Authors: Yu J. L. , Lai Y. F. , Wang Y. Z. , Cheng S. Y. , Chen Y. H.
Published: January 2014

Polarized Raman scattering measurement on single wurtzite c-plane (001) ZnO nanorod grown by hydrothermal method has been performed at room temperature. The polarization dependence of the intensity of the Raman scattering for the phonon modes A1(TO), E1(TO), and E2high in the ZnO nanorod are obtained. The deviations of polarization-dependent Raman spectroscopy from the prediction of Raman selection rules are observed, which can be attributed to the structure defects in the ZnO nanorod as confirmed by the comparison of the transmission electron microscopy, photoluminescence spectra as well as the polarization dependent Raman signal of the annealed and unannealed ZnO nanorod. The Raman tensor elements of A1(TO) and E1(TO) phonon modes normalized to that of the E2high phonon mode are |a/d|=0.32±0.01, |b/d|=0.49±0.02, and |c/d|=0.23±0.01 for the unannealed ZnO nanorod, and |a/d|=0.33±0.01, |b/d|=0.45±0.01, and |c/d|=0.20±0.01 for the annealed ZnO nanorod, which shows strong anisotropy compared to that of bulk ZnO epilayer.
Electronic properties and morphology of Cu-phthalocyanine—C60 composite mixtures
Authors: Roth Friedrich , Lupulescu Cosmin , Arion Tiberiu , Darlatt Erik , Gottwald Alexander , Eberhardt Wolfgang
Published: January 2014

Phthalocyanines in combination with C60 are benchmark materials for organic solar cells. Here, we have studied the morphology and electronic properties of co-deposited mixtures (blends) of these materials forming a bulk heterojunction as a function of the concentration of the two constituents. For a concentration of 1:1 of Cu-Phthalocyanine (CuPc):C60, a phase separation into about 100 nm size domains is observed, which results in electronic properties similar to layered systems. For low C60 concentrations (10:1 CuPc:C60), the morphology, as indicated by Low-Energy Electron Microscopy images, suggests a growth mode characterized by (amorphous) domains of CuPC, whereby the domain boundaries are decorated with C60. Despite of these markedly different growth modes, the electronic properties of the heterojunction films are essentially unchanged.
Single-shot high aspect ratio bulk nanostructuring of fused silica using chirp-controlled ultrafast laser Bessel beams
Authors: Bhuyan M. K. , Velpula P. K. , Colombier J. P. , Olivier T. , Faure N. , Stoian R.
Published: January 2014

We report single-shot, high aspect ratio nanovoid fabrication in bulk fused silica using zeroth order chirp-controlled ultrafast laser Bessel beams. We identify a unique laser pulse length and energy dependence of the physical characteristics of machined structures over which nanovoids of diameter in the range 200–400 nm and aspect ratios exceeding 1000 can be fabricated. A mechanism based on the axial energy deposition of nonlinear ultrashort Bessel beams and subsequent material densification or rarefaction in fused silica is proposed, intricating the non-diffractive nature with the diffusing character of laser-generated free carriers. Fluid flow through nanochannel is also demonstrated.
Chalcogenide nanostructures: Topography, synthesis, properties, and applications
Authors: Al-Douri Y. , Hashim U.
Published: January 2014

High-quality Cadmium sulfide (CdS) nanostructures for high-efficiency optoelectronic devices were prepared at different annealing temperatures using a sol-gel spin-coating method. Atomic force microscopy and X-ray diffraction were performed to measure the structural properties of the nanostructures and calculate their bulk modulus using our model. Thermogravimetric analysis, differential thermal analysis, differential scanning calorimetry, and Fourier transform infrared, UV-Vis, and photoluminescence spectroscopies were used to investigate the thermal and optical properties of the samples. The electrical characteristics of the CdS nanostructures were analyzed to determine their gain.
On the variations of optical property and electronic structure in heavily Al-doped ZnO films during double-step growth process
Authors: Hu Q. C. , Ding K. , Zhang J. Y. , Yan F. P. , Pan D. M. , Huang F. , Chiou J. W.
Published: January 2014

We have investigated the variations of optical property and electronic structure in heavily Al-doped ZnO (AZO) films during the growth process, which were formed by first creating Zn vacancies in O2-rich atmosphere and second filling the vacancies with Zn atoms in Zn-vapor atmosphere. After the first step, the high-resistance AZO films have the same optical bandgap with nominally undoped ZnO, indicating that negligible variations in the fundamental bandgap happened to the AZO films although Al atom was incorporated into the ZnO lattice. After the second step, once free electrons were brought into the lattice by Zn-filling, the optical transition energy blueshifts due to the band-filling effect. X-ray absorption fine structure measurements suggest that Zn-filling process decreased the unoccupied states of the conduction band, but not raised the conduction band minimum.
Low-energy irradiation effects in cellulose
Authors: Polvi Jussi , Nordlund Kai
Published: January 2014

Using molecular dynamics simulations, we determined the threshold energy for creating defects as a function of the incident angle for all carbon and oxygen atoms in the cellulose monomer. Our analysis shows that the damage threshold energy is strongly dependent on the initial recoil direction and on average slightly higher for oxygen atoms than for carbon atoms in cellulose chain. We also performed cumulative bombardment simulations mimicking low-energy electron irradiation (such as TEM imaging) on cellulose. Analyzing the results, we found that formation of free molecules and broken glucose rings were the most common forms of damage, whereas cross-linking and chain scission were less common. Pre-existing damage was found to increase the probability of cross-linking.
Sub-picowatt volatile memory cell based on double-barrier tunnel junction
Authors: Han Jin-Woo , Meyyappan M.
Published: January 2014

A bistable resistor as a volatile memory is proposed. A silicon island sandwiched with a double barrier oxide tunnel junction is used as storage node. The write operations are conducted by direct tunneling. The charges are localized on one side of the two silicon-oxide interfaces, and the position of the charge is interchanged upon the polarity of the applied voltages. The bistable data states are clearly identified and all operations are performed under a voltage below 1 V and a current below 1 pA. The present device can be a promising candidate for ultra low-power capacitorless dynamic random access memory.
Performance analysis of boron nitride embedded armchair graphene nanoribbon metal–oxide–semiconductor field effect transistor with Stone Wales defects
Authors: Chanana Anuja , Sengupta Amretashis , Mahapatra Santanu
Published: January 2014

We study the performance of a hybrid Graphene-Boron Nitride armchair nanoribbon (a-GNR-BN) n-MOSFET at its ballistic transport limit. We consider three geometric configurations 3p, 3p + 1, and 3p + 2 of a-GNR-BN with BN atoms embedded on either side (2, 4, and 6 BN) on the GNR. Material properties like band gap, effective mass, and density of states of these H-passivated structures are evaluated using the Density Functional Theory. Using these material parameters, self-consistent Poisson-Schrodinger simulations are carried out under the Non Equilibrium Green's Function formalism to calculate the ballistic n-MOSFET device characteristics. For a hybrid nanoribbon of width ∼5 nm, the simulated ON current is found to be in the range of 265 μA–280 μA with an ON/OFF ratio 7.1 × 106–7.4 × 106 for a VDD = 0.68 V corresponding to 10 nm technology node. We further study the impact of randomly distributed Stone Wales (SW) defects in these hybrid structures and only 2.5% degradation of ON current is observed for SW defect density of 3.18%.
Comment on “Magnetic field mediated low-temperature resistivity upturn in electron-doped La1−xHfxMnO3 manganite oxides” [J. Appl. Phys. 112, 123710 (2012)]
Authors: Rozenberg E.
Published: January 2014

In a recent paper, Guo et al. [J. Appl. Phys. 112, 123710 (2012)] reported on characteristic features of the temperature (T) and magnetic field (H) dependences of electrical resistivity (ρ) in polycrystalline La1−xHfxMnO3 (x = 0.2 and 0.3) manganites. In particular, shallow minima were observed at some Tmin below 100 K on ρ(T) curves. Application of an external H ≤ 5 T leads first to a decrease in the Tmin value, while this value increases notably at H > 0.75 T. The authors attributed this complex behavior to competitive electron-electron interaction and Kondo-like spin dependent scattering of carriers. It is shown in the comment that such interpretation is very questionable due to the fundamental inapplicability of this approach for analysis of low-T conductivity in polycrystalline manganites. It seems that the most likely reason for the appearance of the low temperature minima on ρ(T) curves and their evolution upon field application is the well known grain boundary effects in magnetically and structurally inhomogeneous samples.
Distant optical detection of small rotations and displacements by means of chiral liquid crystals
Authors: Shibaev Petr V. , Iljin Andrey , Troisi Juliana , Reddy Kathryn
Published: January 2014

The paper describes novel chiral viscoelastic liquid crystalline mixtures and their application for the detection of small rotational displacements of two plates confining cholesteric liquid crystals (CLC). The mixtures are characterized by extremely high viscosities and stability of the selective reflection band (SRB) at ambient temperatures. Even a small rotation applied to the chiral liquid crystal (CLC) cell results in dramatic changes of the reflective properties of sandwiched CLC films. The angle and direction of rotation as well as the magnitude of CLC's shear deformation can be determined for a variety of experimental geometries, each of which is characterized by its own response function. The proposed model explains changes in the reflection spectra for different experimental geometries and relates them to the angle of rotation and magnitude of shear. The method was tested for a detection of small rotations from a distance of up to 50 m and allows for resolving small rotations of the order of fractions of degrees.
Investigation of photoluminescence of Si−O−C(−H) ceramics at an early stage of decarbonization by using high energy excitation
Authors: Narisawa Masaki , Kawai Taketoshi , Watase Seiji , Matsukawa Kimihiro , Iwase Akihiro
Published: January 2014

Si−O−C(−H) ceramics with reduced carbon contents were prepared by pyrolyzing polysiloxane particles in hydrogen at temperatures of 750, 800 and 850 °C. Under HeCd laser irradiation (325 nm), the obtained ceramics show broad spectra peaking at 400–415 nm. On the other hand, the excitation on the higher energy region by an ArF excimer laser (193 nm) induces new PL bands located at short wavelength region of 300 and 355 nm. Such high energy PL bands appear prominently in the ceramics synthesized at 750 °C, and are minor in ceramics synthesized at 800 and 850 °C.
Emergency department waiting times: do the raw data tell the whole story?
Authors: Green Janette , Dawber James , Masso Malcolm , Eagar Kathy
Published: January 2014

Objective To determine whether there are real differences in emergency department (ED) performance between Australian states and territories. Methods Cross-sectional analysis of 2009−10 attendances at an ED contributing to the Australian non-admitted patient ED care database. The main outcome measure was difference in waiting time across triage categories. Results There were more than 5.8 million ED attendances. Raw ED waiting times varied by a range of factors including jurisdiction, triage category, geographic location and hospital peer group. All variables were significant in a model designed to test the effect of jurisdiction on ED waiting times, including triage category, hospital peer group, patient socioeconomic status and patient remoteness. When the interaction between triage category and jurisdiction entered the model, it was found to have a significant effect on ED waiting times (P < 0.001) and triage was also significant (P < 0.001). Jurisdiction was no longer statistically significant (P = 0.248 using all triage categories and 0.063 using only Australian Triage Scale 2 and 3). Conclusions Although the Council of Australian Governments has adopted raw measures for its key ED performance indicators, raw waiting time statistics are misleading. There are no consistent differences in ED waiting times between states and territories after other factors are accounted for. What is known about the topic? The length of time patients wait to be treated after presenting at an ED is routinely used to measure ED performance. In national health agreements with the federal government, each state and territory in Australia is expected to meet waiting time performance targets for the five ED triage categories. The raw data indicate differences in performance between states and territories. What does this paper add? Measuring ED performance using raw data gives misleading results. There are no consistent differences in ED waiting times between the states and territories after other factors are taken into account. What are the implications for practitioners? Judgements regarding differences in performance across states and territories for triage waiting times need to take into account the mix of patients and the mix of hospitals.
Oxyhalogen–Sulfur Chemistry: Kinetics and Mechanism of Oxidation of N-Acetyl-ʟ-methionine by Aqueous Iodine and Acidified Iodate
Authors: Chipiso Kudzanai , Mbiya Wilbes , Morakinyo Moshood K. , Simoyi Reuben H.
Published: January 2014

The use of N-acetyl-l-methionine (NAM) as a bio-available source for methionine supplementation as well as its ability to reduce the toxicity of acetaminophen poisoning has been reported. Its interaction with the complex physiological matrix, however, has not been thoroughly investigated. This manuscript reports on the kinetics and mechanism of oxidation of NAM by acidic iodate and aqueous iodine. Oxidation of NAM proceeds by a two electron transfer process resulting in formation of a sole product: N-acetyl-l-methionine sulfoxide (NAMS=O). Data from electrospray ionization mass spectrometry confirmed the product of oxidation as NAMS=O. The stoichiometry of the reaction was deduced to be IO3– + 3NAM → I– + 3NAMS=O. In excess iodate, the stoichiometry was deduced to be 2IO3– + 5NAM + 2H+ → I2 + 5NAMS=O + H2O. The reaction between aqueous iodine and NAM gave a 1 : 1 stoichiometric ratio: NAM + I2 + H2O → NAMS=O + 2I– + H+. This reaction was relatively rapid when compared with that between NAM and iodate. It did, however, exhibit some auto-inhibitory effects through the formation of triiodide (I3–) which is a relatively inert electrophile when compared with aqueous iodine. A simple mechanism containing 11 reactions gave a reasonably good fit to the experimental data.
Spatiotemporal pattern of action potential firing in developing inner hair cells of the mouse cochlea
Authors: Sendin Gaston , Bourien Jérôme , Rassendren François , Puel Jean-Luc , Nouvian Régis
Published: January 2014

Significance

Sensory inner hair cells (IHCs) of the cochlea, the organ of hearing, fire action potentials during development. This presensory activity likely drives refinement of the ascending auditory pathway. Our study shows that the IHCs fire spontaneous bursts of action potentials, which tend to occur at a regular time interval and have a similar length toward the end of the first postnatal week. The spiking behavior does not depend on ATP but, rather, is modulated by the α9α10 nicotinic receptor, which is expressed by the developing IHCs. The firing pattern of the IHCs may therefore convey a temporal signature of the cochlear development to the higher auditory centers.
The Punjab paradox: understanding the failures of Diaspora engagement
Authors: Thandi Shinder Singh
Published: January 2014

Punjabi Diaspora is one of the oldest of the ‘free’ Indian regional Diasporas with a history of over 125 years. Given this long history it would not be surprising to learn that it is economically, socially and politically well positioned in its host countries. Further, although globally dispersed, it is predominantly located in the three economically advanced countries of the USA, the UK and Canada, thereby enhancing its potential to play a significant role in homeland development. Yet despite this, compared to other regional Diasporas, it continues to have a troubled, almost Janus-type relationship, with the Punjab state. This is reflected in the lack of a constructive engagement between them, with both Diaspora communities and state governments continuing to make hollow promises. The paper explores the reasons behind the failure in developing a constructive engagement, focusing on the socio-economic characteristics of the Punjabi Diaspora and the nature of Punjab’s as well as India’s outreach policies. It is argued that recent trends in the evolution of overseas Punjabi communities and nature of the economic and political environment in Punjab act as formidable barriers towards building a partnership for development. It does seem paradoxical, especially in the context of current debates on the Diaspora-development nexus, that despite being once the most prosperous state in India with a rich and vibrant Diaspora, Punjab should still continue to slide down the economic league table of Indian states.