bluuebunny/crossref_metadata_2025 huggingface dataset:
Computertomografische Auswertung von humanen Unterkiefern hinsichtlich der Schichtstärke und Knochendichte der Kortikalis
Authors: Markwardt J. , Meißner H. , Weber A. , Laniado M. , Reitemeier B.
Published: October 2012

Ziel: Der Einsatz funktionsstabiler individueller Implantate zur Überbrückung von Unterkieferdefekten mit Kontinuitätstrennung setzt eine stabile Fixierung unter besonderer Nutzung der Kortikalis der Knochenstümpfe voraus.

Material und Methoden: Es wurden 5 Schnittebenen von 100 Computertomografien polytraumatisierter Patienten zur Messung der Kortikalisschichtstärke und der Knochendichte des Unterkiefers herangezogen. Zur Verfügung standen die CT-Aufnahmen von 28 weiblichen und 72 männlichen Probanden im Alter von 12 – 86 Jahren mit unterschiedlicher Bezahnung des Unterkiefers.

Ergebnisse: Die computertomografische Auswertung von humanen Unterkiefern hinsichtlich der Schichtstärke der Kortikalis ergab, dass der Unterkieferrand im Bereich des horizontalen Astes die Positionen mit den größten Schichtstärken im gesamten Unterkiefer aufweist. Die größten Mediane der Kortikalisschichtstärke befinden sich im Bereich der Molaren und Prämolaren am Unterrand des Unterkiefers in der 6-Uhr-Position, im Molarenbereich in der vestibulär-kranialen 10-Uhr-Position und in der Kinnregion lingual-kaudal in 4-Uhr-Position. Die Messungen der Knochendichte ergaben den höchsten Wert in 8-Uhr-Position (vestibulär kaudal) in der Molarenregion, sowohl bei den Männern als auch bei Frauen.

Schlussfolgerung: Vorliegende Durchschnittswerte der Knochendichte und der Kortikalisschichtstärke verschiedener Regionen des Unterkiefers unter Berücksichtigung des Alters, des Geschlechts und der Bezahnung können eine maßgebliche Hilfe für die Wahl der Lokalisation einer sicheren Fixierung von individuellen Implantaten im Bereich der Oberflächenschicht des Unterkiefers mittels Schrauben oder ähnlichen Fixierungselementen sein.
Elasticity of diamond at high pressures and temperatures
Authors: Núñez Valdez Maribel , Umemoto Koichiro , Wentzcovitch Renata M.
Published: October 2012

We combine density functional theory within the local density approximation, the quasiharmonic approximation, and vibrational density of states to calculate single crystal elastic constants, and bulk and shear moduli of diamond at simultaneous high pressures and temperatures in the ranges of 0–500 GPa and 0–4800 K. Comparison with experimental values at ambient pressure and high temperature shows an excellent agreement with our first-principles results validating our method. We show that the anisotropy factor of diamond increases to 40% at high pressures and becomes temperature independent.
Simultaneous measurement of local longitudinal and transverse wave velocities, attenuation, density, and thickness of films by using point-focus ultrasonic spectroscopy
Authors: Ju Bing-Feng , Bai Xiaolong , Chen Jian
Published: October 2012

This paper presents an ultrasonic technique for simultaneous determination of the complete set of acoustical and geometrical properties of a film or a thin layer in a stratified material embedded between two known materials using point-focus ultrasonic spectroscopy, which provides a high lateral resolution. The theoretical model of the two-dimensional spectrum Rt(θ,ω) of the stratified material is calculated as a function of six parameters of the unknown layer: longitudinal and transverse velocities cl, ct, attenuation αl, αt, density ρ, and thickness h, which fully determined the properties of the film. The experimental spectrum Re(θ,ω) can be measured by V(z,t) technique. A two-step algorithm is presented to decompose the searching process of parameters from one six-dimensional to two three-dimensional spaces. The sensitivity of the two-dimensional spectrum to individual properties and its stability against experimental noise are studied. The full set properties of a 250 μm thick stainless steel film and a 930 μm thick SiO2 thin layer of a three layered stratified material immersed in water are determined. The proposed technique used a point-focus transducer, which makes the setup simple and reliable. It allows measurement of the local properties of the film and enables precision material characterization.
On-chip stress relaxation testing method for freestanding thin film materials
Authors: Coulombier M. , Guisbiers G. , Colla M.-S. , Vayrette R. , Raskin J.-P. , Pardoen T.
Published: October 2012

A stress relaxation method for freestanding thin films is developed based on an on-chip internal stress actuated microtensile testing set-up. The on-chip test structures are produced using microfabrication techniques involving cleaning, deposition, lithography, and release. After release from the substrate, the test specimens are subjected to uniaxial tension. The applied load decays with the deformation taking place during relaxation. This technique is adapted to strain rates lower than 10−6/s and permits the determination of the strain rate sensitivity of very thin films. The main advantage of the technique is that the relaxation tests are simultaneously performed on thousands of specimens, pre-deformed up to different strain levels, for very long periods of time without monopolizing any external mechanical loading equipment. Proof of concept results are provided for 205-nm-thick sputtered AlSi0.01 films and for 350-nm-thick evaporated Pd films showing unexpectedly high relaxation at room temperature.
Micropropulsion and microrheology in complex fluids via symmetry breaking
Authors: Pak On Shun , Zhu LaiLai , Brandt Luca , Lauga Eric
Published: October 2012

Many biological fluids have polymeric microstructures and display non-Newtonian rheology. We take advantage of such nonlinear fluid behavior and combine it with geometrical symmetry-breaking to design a novel small-scale propeller able to move only in complex fluids. Its propulsion characteristics are explored numerically in an Oldroyd-B fluid for finite Deborah numbers while the small Deborah number limit is investigated analytically using a second-order fluid model. We then derive expressions relating the propulsion speed to the rheological properties of the complex fluid, allowing thus to infer the normal stress coefficients in the fluid from the locomotion of the propeller. Our simple mechanism can therefore be used either as a non-Newtonian micro-propeller or as a micro-rheometer.
Mechanical and thermal behaviors of nitrogen-doped Zr-Cu-Al-Ag-Ta––An alternative class of thin film metallic glass
Authors: Chen Pao-Sheng , Chen Hsien-Wei , Duh Jenq-Gong , Lee Jyh-Wei , Shian-Ching Jang Jason
Published: October 2012

Super-plasticity and nano-scale surface roughness make thin film metallic glass (TFMG) a candidate for master mold of micro/nano imprint technique. Meanwhile, better mechanical properties of TFMG undoubtedly expand the life time of master mold. In this study, nitrogen is doped into Zr-based TFMG to exhibit the hardness higher than 10 GPa. Different from elements used to be doped into metallic glass, the role of nitrogen atoms plays in metallic glass is distinct and vital owing to its strong electronegativity. From the correlation of thermal and mechanical behavior, the role and effect of nitrogen in Ta-Zr-Cu-Al-Ag TFMG is discussed and proposed.
Rattler model of the boson peak at silica surfaces
Authors: Steurer Wolfram , Tosatti Erio
Published: October 2012

Recent experiments unveiled two new aspects of the low-energy excitation spectrum of silica glass—commonly termed as the “boson peak” region. The first is that at low temperature the silica surface exhibits a different, softer boson peak than the bulk. The second is a giant thermal blueshift of the surface boson peak frequency causing it to cross and overcome the bulk peak with increasing temperature. Here we present a simple lattice model that reproduces this behavior in all its aspects. Each site consists of rigid tetrahedral units softly connected so as to be able to rotate anharmonically as “rattlers” in their cages. As shown by simulations, the model dynamics exhibits a boson-like peak, which has lower frequency at the surface where rattlers have a weaker restoring force. Upon heating however the larger angular freedom of surface units allows them to rattle more than in the bulk, leading to a steeper frequency increase similar to experiment.
Spin-wave modes and band structure of rectangular CoFeB antidot lattices
Authors: Lenk Benjamin , Abeling Nils , Panke Jelena , Münzenberg Markus
Published: October 2012

We present an investigation of rectangular antidot lattices in a CoFeB film. Magnonic band structures are numerically calculated, and band gaps are predicted which shift in frequency by 0.9 GHz when rotating the external field from the long to the short axis of the unit cell. We demonstrate by time-resolved experiments that magnonic dipolar surface modes are split in frequency by 0.6 GHz which agrees well with the theoretical prediction. These findings provide the basis for directional spin-wave filtering with magnonic devices.
Heredity of medium-range order structure from melts to amorphous solids
Authors: Bai Y. W. , Bian X. F. , Lv X. Q. , Pan S. P. , Qin J. Y. , Qin X. B. , Hu L. N.
Published: October 2012

A medium-range order (MRO) structure characterized by the pre-peaks in the structure factor S(Q) curves of typical glass-forming Au55Cu25Si20 melt has been detected using the high temperature x-ray diffractometer. Combining the ab initio molecular dynamics simulations and the experiments, we explore and discuss the structure of the MRO cluster. During the rapid solidification, some structural information carried by the MRO structure is inherited from the melt to the amorphous solid, which promotes the glass formation. Through the comparison of microstructures between amorphous and crystal phases, we also discuss the heredity mechanism.
Entropic vs. elastic models of fragility of glass-forming liquids: Two sides of the same coin?
Authors: Sen Sabyasachi
Published: October 2012

The two most influential atomistic models that have been proposed in the literature to explain the temperature dependent activation energy of viscous flow of a glass-forming liquid, i.e., its fragility, are the configurational entropy model of Adam and Gibbs [J. Chem. Phys. 43, 139 (1965)10.1063/1.1696442] and the elastic “shoving” model of Dyre et al. [J. Non-Cryst. Solids 352, 4635 (2006)10.1016/j.jnoncrysol.2006.02.173]. Here we demonstrate a qualitative equivalence between these two models starting from the well-established general relationships between the interatomic potentials, elastic constants, structural rearrangement, and entropy in amorphous materials. The unification of these two models provides important predictions that are consistent with experimental observations and shed new light into the problem of glass transition.
Analysis of below-threshold efficiency characteristics of InGaN-based blue laser diodes
Authors: Ryu Han-Youl , Jun Choi Won , Jeon Ki-Seong , Kang Min-Goo , Choi Yunho , Lee Jeong-Soo
Published: October 2012

In this study, we investigate the below-threshold emission characteristics of InGaN-based blue laser diodes (LDs) emitting at 442 nm to study the efficiency droop effects in InGaN LDs. From the measurement of spontaneous emission in the LD, it is observed that the peak efficiency appears at a current density of ∼20 A/cm2 and the efficiency at the threshold current density of ∼2.3 kA/cm2 are reduced to ∼47% of the peak efficiency. The measured spontaneous emission characteristics are analyzed using the carrier rate equation model, and the peak internal quantum efficiency is found to be ∼75% using the fit of the measured efficiency curve. In addition, the Auger recombination coefficient of the measured InGaN blue LD is found to be 10−31–10−30 cm6/s, which is somewhat lower than that reported for InGaN-based blue light-emitting diodes. It is discussed that low dislocation density and uniform current injection in quantum wells may have resulted in the low Auger recombination coefficient of InGaN LDs.
Thermal and mechanical response of [0001]-oriented GaN nanowires during tensile loading and unloading
Authors: Jung Kwangsub , Cho Maenghyo , Zhou Min
Published: October 2012

Molecular dynamics simulations are carried out to investigate the thermal and mechanical responses of GaN nanowires with the [0001] orientation and hexagonal cross sections to tensile loading and unloading. The thermal conductivity of the nanowires at each deformed state is calculated using the Green-Kubo approach with quantum correction. The thermal conductivity is found to be dependent on the strain induced by tensile loading and unloading. Phase transformations are observed in both the loading and unloading processes. Specifically, the initially wurtzite-structured (WZ) nanowires transform into a tetragonal structure (TS) under tensile loading and revert to the WZ structure in the unloading process. In this reverse transformation from TS to WZ, transitional states are observed. In the intermediate states, the nanowires consist of both TS regions and WZ regions. For particular sizes, the nanowires are divided into two WZ domains by an inversion domain boundary (IDB). The thermal conductivity in the intermediate states is approximately 30% lower than those in the WZ structure because of the lower phonon group velocity in the intermediate states. Significant effects of size and crystal structure on mechanical and thermal behaviors are also observed. Specifically, as the diameter increases from 2.26 to 4.85 nm, the thermal conductivity increases by 30%, 10%, and 50%, respectively, for the WZ, WZ-TS, and WZ-IDB structured wires. However, change in conductivity is negligible for TS-structured wires as the diameter changes. The different trends in thermal conductivity appear to result from changes in the group velocity which is related to the stiffness of the wires and surface scattering of phonons.
Tunable graphene-based polarizer
Authors: Bludov Yu. V. , Vasilevskiy M. I. , Peres N. M. R.
Published: October 2012

It is shown that an attenuated total reflection structure containing a graphene layer can operate as a tunable polarizer of the electromagnetic radiation. The polarization of the reflected electromagnetic wave is controlled by adjusting the voltage applied to graphene via external gate, as demonstrated for the cases of linearly and circularly polarized incident radiation. The mechanism is based on the resonant coupling of p-polarized waves to the surface plasmon-polaritons in graphene. The presented calculations show that, at resonance, the reflected wave is almost 100% s-polarized.
Annealing studies of heteroepitaxial InSbN on GaAs grown by molecular beam epitaxy for long-wavelength infrared detectors
Authors: Patra Nimai C. , Bharatan Sudhakar , Li Jia , Iyer Shanthi
Published: October 2012

We report the effect of annealing on the structural, vibrational, electrical, and optical properties of heteropepitaxially grown InSbN epilayers on GaAs substrate by molecular beam epitaxy for long-wavelength infrared detector applications. As-grown epilayers exhibited high N incorporation in the both substitutional and interstitial sites, with N induced defects as evidenced from high resolution x-ray diffraction, secondary ion mass spectroscopy, and room temperature (RT) micro-Raman studies. The as-grown optical band gap was observed at 0.132 eV (∼9.4 μm) and the epilayer exhibited high background carrier concentration at ∼1018 cm−3 range with corresponding mobility of ∼103 cm2/Vs. Ex situ and in situ annealing at 430 °C though led to the loss of N but improved InSb quality due to effective annihilation of N related defects and other lattice defects attested to enhanced InSb LO phonon modes in the corresponding Raman spectra. Further, annealing resulted in the optical absorption edge red shifting to 0.12 eV (∼10.3 μm) and the layers were characterized by reduced background carrier concentration in the ∼1016 cm−3 range with enhanced mobility in ∼104 cm2/Vs range.
Photoelectron spectroscopy of unsupported bismuth clusters: Size related effects of metallic properties
Authors: Mikkelä M.-H. , Tchaplyguine M. , Urpelainen S. , Jänkälä K. , Björneholm O. , Huttula M.
Published: October 2012

Evolution of metallic properties of free and initially neutral nanoscale Bi clusters has been studied using synchrotron radiation excited photoelectron spectroscopy. The 4f and 5d core as well as the valence levels have been probed. The cross-level analysis indicates metallic properties in Bi clusters in the observed size range from 0.5 nm to 1.4 nm. The behavior of the core-level and valence binding energies as a function of cluster size has been observed to be smooth and relatively consistent. Valence responses for the largest clusters have their shape and width similar to those of the polycrystalline solid Bi.
Equity dimensions of micro-generation: A whole systems approach
Authors: Adams C. , Taylor P. , Bell S.
Published: October 2012

Micro-generation represents one technology ready option for making the low carbon transition. Energy choices we make in the present have implications for future generations. Existing methods for formulating energy policy and assessing the suitability of micro-generation technology often concentrate upon a subset of issues relating to specific economic criteria or policy targets or on one technology, but often fail to adopt a whole systems approach or consider present or future equity issues. Important factors are often overlooked leading to poorly implemented policy or unsatisfactory technology deployment. There is a clear need for a process or assessment methodology that focuses upon equity while making choices relating to micro or small-scale generation projects. This paper describes an integrated whole systems methodology developed heuristically by a wide range of interdisciplinary stakeholders for use by groups of decision makers when assessing the equity aspects of micro-generation projects. The paper discusses the desirable attributes that this type of assessment should have and outlines the merits of the whole systems approach. Steps taken to develop, test, and refine the methodology using case studies are discussed. The equity issues arising from each case study are examined in wider context by quantifying the impact micro or small-scale generation could have within English households of varying age and tenure in a range of settings including a real community case study. This provides a snapshot of where equity issues manifest themselves and considers the numbers of households they affect. Using the methodology and focusing upon equity has allowed recommendations to be made that could inform future energy policy.
Diagnostics of underwater electrical wire explosion through a time- and space-resolved hard x-ray source
Authors: Sheftman D. , Shafer D. , Efimov S. , Gruzinsky K. , Gleizer S. , Krasik Ya. E.
Published: October 2012

A time- and space-resolved hard x-ray source was developed as a diagnostic tool for imaging underwater exploding wires. A ∼4 ns width pulse of hard x-rays with energies of up to 100 keV was obtained from the discharge in a vacuum diode consisting of point-shaped tungsten electrodes. To improve contrast and image quality, an external pulsed magnetic field produced by Helmholtz coils was used. High resolution x-ray images of an underwater exploding wire were obtained using a sensitive x-ray CCD detector, and were compared to optical fast framing images. Future developments and application of this diagnostic technique are discussed.
Mixing atoms and coarse-grained beads in modelling polymer melts
Authors: di Pasquale Nicodemo , Marchisio Daniele , Carbone Paola
Published: October 2012

We present a simple hybrid model for macromolecules where the single molecules are modelled with both atoms and coarse-grained beads. We apply our approach to two different polymer melts, polystyrene and polyethylene, for which the coarse-grained potential has been developed using the iterative Boltzmann inversion procedure. Our results show that it is possible to couple the two potentials without modifying them and that the mixed model preserves the local and the global structure of the melts in each of the case presented. The degree of resolution present in each single molecule seems to not affect the robustness of the model. The mixed potential does not show any bias and no cluster of particles of different resolution has been observed.
Uranyl ion interaction at the water/NiO(100) interface: A predictive investigation by first-principles molecular dynamic simulations
Authors: Sebbari Karim , Roques Jérôme , Domain Christophe , Simoni Eric
Published: October 2012

The behavior of the UO22+ uranyl ion at the water/NiO(100) interface was investigated for the first time using Born-Oppenheimer molecular dynamic simulations with the spin polarized DFT + U extension. A water/NiO(100) interface model was first optimized on a defect-free five layers slab thickness, proposed as a reliable surface model, with an explicit treatment of the solvent. Water molecules are adsorbed with a well-defined structure in a thickness of about 4 Å above the surface. The first layer, adsorbed on nickel atoms, remains mainly in molecular form but can partly dissociate at 293 K. Considering low acidic conditions, a bidentate uranyl ion complex was characterized on two surface oxygen species (arising from water molecules adsorption on nickel atoms) with $d_{{\rm U{-}O}_{adsorption}}\break = 2.39$dU−Oadsorption=2.39 Å. This complex is stable at 293 K due to iono-covalent bonds with an estimated charge transfer of 0.58 electron from the surface to the uranyl ion.
Transmission projective synchronization of multi-systems with non-delayed and delayed coupling via impulsive control
Authors: Sun Junwei , Shen Yi , Zhang Guodong
Published: October 2012

This paper mainly investigates the transmission projective synchronization of multi systems with non-delayed and delayed coupling via impulsive control. Based on the stability analysis of impulsive differential equation, the control laws and updating laws are designed to realize the transmission projective synchronization. Some criteria and corollaries are derived for the transmission projective synchronization among multi-systems. Numerical examples are presented to verify the effectiveness and correctness of the synchronization within a desired scaling factor. For the multi-systems synchronization model, it seems to have more valuable than the usual one drive system and one response system synchronization model.
A rapid reflectance-difference spectrometer for real-time semiconductor growth monitoring with sub-second time resolution
Authors: Núñez-Olvera O. , Balderas-Navarro R. E. , Ortega-Gallegos J. , Guevara-Macías L. E. , Armenta-Franco A. , Lastras-Montaño M. A. , Lastras-Martínez L. F. , Lastras-Martínez A.
Published: October 2012

We report on a rapid, 32-channel reflectance-difference (RD) spectrometer with sub-second spectra acquisition times and ΔR/R sensitivity in the upper 10−4 range. The spectrometer is based on a 50 kHz photo-elastic modulator for light polarization modulation and on a lock-in amplifier for signal harmonic analysis. Multichannel operation is allowed by multiplexing the 32 outputs of the spectrometer into the input of the lock-in amplifier. The spectrometer spans a wavelength range of 230 nm that can be tuned to cover E1 and E1 + Δ1 transitions for a number of III–V semiconductors at epitaxial growth temperatures, including GaAs, InAs, AlAs, and their alloys. We present two examples of real-time measurements to demonstrate the performance of the RD spectrometer, namely, the evolution of the RD spectrum of GaAs (001) annealed at 500 °C and the time-dependent RD spectrum during the first stages of the epitaxial growth of In0.3Ga0.7As on GaAs (001) substrates.
Study of mechanisms and factors that influence the formation of vortical wake of a heaving airfoil
Authors: Zheng Z. C. , Wei Z.
Published: October 2012

A two-dimensional numerical study is performed to investigate the relation between the direction of a deflected wake and the vortex pairing mechanisms. The deflection angle can be correlated with two effective phase velocities defined to represent the trends of symmetry breaking and symmetry holding, respectively. The deflection angle increases with the strength of the vortex pairs, which is associated with the heaving amplitude, frequency, and the free stream Reynolds number. Furthermore, not only the influence of Strouhal number but also those of the two heaving motion components – amplitude and frequency – are studied individually under different Reynolds numbers. The study shows that the deflection angle consistently increases with the difference between the symmetry-breaking phase velocity and symmetry-holding phase velocity.
A novel synchronization scheme with a simple linear control and guaranteed convergence time for generalized Lorenz chaotic systems
Authors: Chuang Chun-Fu , Sun Yeong-Jeu , Wang Wen-June
Published: October 2012

In this study, exponential finite-time synchronization for generalized Lorenz chaotic systems is investigated. The significant contribution of this paper is that master-slave synchronization is achieved within a pre-specified convergence time and with a simple linear control. The designed linear control consists of two parts: one achieves exponential synchronization, and the other realizes finite-time synchronization within a guaranteed convergence time. Furthermore, the control gain depends on the parameters of the exponential convergence rate, the finite-time convergence rate, the bound of the initial states of the master system, and the system parameter. In addition, the proposed approach can be directly and efficiently applied to secure communication. Finally, four numerical examples are provided to demonstrate the feasibility and correctness of the obtained results.
Instability of a backward-facing step flow modified by stationary streaky structures
Authors: Boiko A. V. , Dovgal A. V. , Sorokin A. M.
Published: October 2012

The present paper deals with small amplitude velocity oscillations at laminar boundary layer separation behind a backward-facing step on a flat plate. The focus is the effect of a spatially periodic stationary disturbance of the nominally 2D basic configuration on the linear instability of the separated shear layer. Nonstationary perturbations of the mean flow which is modulated by roughness elements spaced along the step are examined through wind-tunnel tests and stability calculations. Noteworthy is flow destabilization in the presence of streaks behind the line of separation.
Band alignment of vanadium oxide as an interlayer in a hafnium oxide-silicon gate stack structure
Authors: Zhu Chiyu , Kaur Manpuneet , Tang Fu , Liu Xin , Smith David J. , Nemanich Robert J.
Published: October 2012

Vanadium oxide (VO2) is a narrow band gap material (Eg = 0.7 eV) with a thermally induced insulator-metal phase transition at ∼343 K and evidence of an electric field induced transition at T < 343 K. To explore the electronic properties of VO2, a sandwich structure was prepared with a 2 nm VO2 layer embedded between an oxidized Si(100) surface and a 2 nm hafnium oxide (HfO2) layer. The layer structure was confirmed with high resolution transmission electron microscopy. The electronic properties were characterized with x-ray and ultraviolet photoemission spectroscopy, and the band alignment was deduced on both n-type and p-type Si substrates. The valence band offset between VO2 and SiO2 is measured to be 4.0 eV. The valence band offset between HfO2 and VO2 is measured to be ∼3.4 eV. The band relation developed from these results demonstrates the potential for charge storage and switching for the embedded VO2 layer.
Direct measurement of grain boundary enthalpy of cubic yttria-stabilized zirconia by differential scanning calorimetry
Authors: Quach Dat V. , Castro Ricardo H. R.
Published: October 2012

A straight-forward set of experiments using differential scanning calorimetry was used to obtain the average grain boundary enthalpy at high temperatures for 10 mol. % yttria-stabilized zirconia (10YSZ) by exploiting the heat of grain growth on nanograined dense samples consolidated by spark plasma sintering. The heat of grain growth was measured and correlated with the quantified microstructure evolution during the process. The average grain boundary enthalpy of 10YSZ was found to be 1.00 ± 0.29 J m−2 for the temperature range 900–1300 °C. Comparing this result with room temperature data in the literature, small temperature dependence of the grain boundary enthalpy could be found outside the experimental uncertainties in both experiments.
Hot-carrier trap-limited transport in switching chalcogenides
Authors: Piccinini Enrico , Cappelli Andrea , Buscemi Fabrizio , Brunetti Rossella , Ielmini Daniele , Rudan Massimo , Jacoboni Carlo
Published: October 2012

Chalcogenide materials have received great attention in the last decade owing to their application in new memory systems. Recently, phase-change memories have, in fact, reached the early stages of production. In spite of the industrial exploitation of such materials, the physical processes governing the switching mechanism are still debated. In this paper, we work out a complete and consistent model for transport in amorphous chalcogenide materials based on trap-limited conduction accompanied by carrier heating. A previous model is here extended to include position-dependent carrier concentration and field, consistently linked by the Poisson equation. The results of the new model reproduce the experimental electrical characteristics and their dependences on the device length and temperature. Furthermore, the model provides a sound physical interpretation of the switching phenomenon and is able to give an estimate of the threshold condition in terms of the material parameters, a piece of information of great technological interest.
A metamaterial antenna with frequency-scanning omnidirectional radiation patterns
Authors: Xu He-Xiu , Wang Guang-Ming , Qi Mei-Qing , Xu Zhi-Ming
Published: October 2012

A metamaterial antenna exhibiting simultaneously omnidirectional radiation and leaky-wave characteristics is proposed based on a two-dimensional transmission line (TL) made of complementary split ring resonators and capacitive gaps. The backward-wave propagation is demonstrated based on the dispersion characteristics provided by the generic TL theory and full-wave eigenmode analysis. Numerical and experimental results indicate that the frequency-scanning leaky-wave radiation is realized in E-plane, whereas omnidirectional radiation (parallel to H-plane) with considerable antenna gain directs from backward to broadside. The unique dispersion diagram and equivalent long monopole give rise to these abnormal physical phenomena.
Regulation of DNA conformations and dynamics in flows with hybrid field microfluidics
Authors: Ren Fangfang , Zu Yingbo , Kumar Rajagopalan Kartik , Wang Shengnian
Published: October 2012

Visualizing single DNA dynamics in flow provides a wealth of physical insights in biophysics and complex flow study. However, large signal fluctuations, generated from diversified conformations, deformation history dependent dynamics and flow induced stochastic tumbling, often frustrate its wide adoption in single molecule and polymer flow study. We use a hybrid field microfluidic (HFM) approach, in which an electric field is imposed at desired locations and appropriate moments to balance the flow stress on charged molecules, to effectively regulate the initial conformations and the deformation dynamics of macromolecules in flow. With λ-DNA and a steady laminar shear flow as the model system, we herein studied the performance of HFM on regulating DNA trapping, relaxation, coil-stretch transition, and accumulation. DNA molecules were found to get captured in the focused planes when motions caused by flow, and the electric field were balanced. The trapped macromolecules relaxed in two different routes while eventually became more uniform in size and globule conformations. When removing the electric field, the sudden stretching dynamics of DNA molecules exhibited a more pronounced extension overshoot in their transient response under a true step function of flow stress while similar behaviors to what other pioneering work in steady shear flow. Such regulation strategies could be useful to control the conformations of other important macromolecules (e.g., proteins) and help better reveal their molecular dynamics.
A method to observe fast dynamic space charge in thin dielectric films
Authors: Zheng Feihu , Lin Chen , Liu Chuandong , An Zhenlian , Lei Qingquan , Zhang Yewen
Published: October 2012

A method is proposed to observe the fast dynamic space charge in thin dielectric film within hundreds of nanoseconds. The method is based on measuring the transient current when a polarized sample is short-circuited. The transient short-circuit current shows damped oscillating feature. For polarized dielectric films, the initial period of damped oscillating current is partly determined by the applied electric field intensity and then the subsequent periods rapidly decrease with the oscillating cycles. The phenomena were demonstrated to be due to space charge formation and fast discharge procedure of space charge by stepwise heat treatment based experiments.
Single photon adiabatic wavelength conversion
Authors: Preble Stefan , Cao Liang , Elshaari Ali , Aboketaf Abdelsalam , Adams Donald
Published: October 2012

Adiabatic wavelength conversion is experimentally demonstrated at a single photon power-level using an integrated silicon ring resonator. This approach allows conversion of a photon to arbitrary wavelengths with no energy or phase matching constraints. The conversion is inherently low-noise and efficient with greater than 10% conversion efficiencies for wavelength changes up to 0.5 nm, more than twenty times the resonators line-width. The observed wavelength change and efficiency agrees well with theory and bright coherent light demonstrations. These results will enable integrated quantum optical wavelength conversion for application ranging from wavelength-multiplexed quantum networks to frequency bin entanglement.
Inclusion of diamagnetic drift effect in the matching method using finite-width inner region for stability analysis of magnetohydrodynamic modes
Authors: Furukawa M. , Tokuda S.
Published: October 2012

A matching method using a finite-width inner region is extended for stability analysis of magnetohydrodynamic mode including diamagnetic drift effect. The inclusion of the diamagnetic drift effect is accomplished by a newly developed ordering scheme in the outer region. The ordering scheme enables us to derive a hierarchy of generalized Newcomb equations. Higher-order equations give us correction of outer solution due to the diamagnetic drift effect as well as inertia and resistivity. By this correction, the accuracy of the dispersion relation is improved. Several numerical results are presented to demonstrate good performance of the matching method. Dropping the diamagnetic drift effect in the outer region leads to less accurate results.
An electromagnetic theory of turbulence driven poloidal rotation
Authors: McDevitt C. J. , Gürcan Ö. D.
Published: October 2012

An electromagnetic theory of turbulence driven poloidal rotation is developed with particular emphasis on understanding poloidal rotation in finite-β plasmas. A relation linking the flux of polarization charge to the divergence of the total turbulent stress is derived for electromagnetic gyrokinetic modes. This relation is subsequently utilized to derive a constraint on the net electromagnetic turbulent stress exerted on the poloidal flow. Various limiting cases of this constraint are considered, where it is found that electromagnetic contributions to the turbulent stress may either enhance or reduce the net turbulent stress depending upon the branch of turbulence excited.
Observed transition from Richtmyer-Meshkov jet formation through feedout oscillations to Rayleigh-Taylor instability in a laser target
Authors: Aglitskiy Y. , Karasik M. , Velikovich A. L. , Serlin V. , Weaver J. L. , Kessler T. J. , Nikitin S. P. , Schmitt A. J. , Obenschain S. P. , Metzler N. , Oh J.
Published: October 2012

Experimental study of hydrodynamic perturbation evolution triggered by a laser-driven shock wave breakout at the free rippled rear surface of a plastic target is reported. At sub-megabar shock pressure, planar jets manifesting the development of the Richtmyer-Meshkov-type instability in a non-accelerated target are observed. As the shock pressure exceeds 1 Mbar, an oscillatory rippled expansion wave is observed, followed by the “feedout” of the rear-surface perturbations to the ablation front and the development of the Rayleigh-Taylor instability, which breaks up the accelerated target.
Nanoscale surface roughness affects low Reynolds number flow: Experiments and modeling
Authors: Jaeger R. , Ren J. , Xie Y. , Sundararajan S. , Olsen M. G. , Ganapathysubramanian B.
Published: October 2012

Most micro-channel fabrication strategies generate nano-to-micro-scale, stochastic surface roughness. This inherent stochasticity can potentially be harnessed to direct microfluidic operations such as self-cleaning behavior and localized mixing. This work investigates the effect of stochastic nanoscale roughness on low to moderate Reynolds number Newtonian flow using concurrent modeling and experiments. We fabricate a microscopic channel with tailored hydrofluoric-acid-etched rough surfaces. Optical profilometry and micro-particle-image-velocimetry (micro-PIV) are used to characterize the surface roughness and flow field and is integrated with direct numerical simulation that resolves effects of nanoscale roughness. Results indicate that nanoscale roughness causes flow perturbations that extend up to the mid-plane and is insensitive to flow-rates.
Generation of residual energy in the turbulent solar wind
Authors: Gogoberidze G. , Chapman S. C. , Hnat B.
Published: October 2012

In situ observations of the fluctuating solar wind flow show that the energy of magnetic field fluctuations always exceeds that of the kinetic energy, and therefore the difference between the kinetic and magnetic energies, known as the residual energy, is always negative. The same behaviour is found in numerical simulations of magnetohydrodynamic turbulence. We study the dynamics of the residual energy for strong, anisotropic, critically balanced magnetohydrodynamic turbulence using the eddy damped quasi-normal Markovian approximation. Our analysis shows that for stationary critically balanced magnetohydrodynamic turbulence, negative residual energy will always be generated by nonlinear interacting Alfvén waves. This offers a general explanation for the observation of negative residual energy in solar wind turbulence and in the numerical simulations.
A quantum dot rolled-up microtube directional coupler
Authors: Bhowmick Sishir , Heo Junseok , Bhattacharya Pallab
Published: October 2012

A rolled-up microtube directional coupler made of twin microtubes is demonstrated. The microtube is made of a InGaAs/GaAs strained bilayer and InAs self-organized quantum dots are inserted in the GaAs layer. The input and coupled microtubes have length and outer diameter of ∼50 and 6 μm, respectively. The coupling characteristics have been analyzed by the three-dimensional finite difference time domain method. The coupling characteristics have also been measured with isopropyl alcohol, instead of air, as the surrounding media to demonstrate the potential of the device as a sensor.
Molecular beam epitaxy growth of GaAsBi/GaAs/AlGaAs separate confinement heterostructures
Authors: Fan Dongsheng , Zeng Zhaoquan , Hu Xian , Dorogan Vitaliy G. , Li Chen , Benamara Mourad , Hawkridge Michael E. , Mazur Yuriy I. , Yu Shui-Qing , Johnson Shane R. , Wang Zhiming M. , Salamo Gregory J.
Published: October 2012

GaAsBi/GaAs/AlGaAs separate confinement heterostructures are grown using an asymmetric temperature profile due to the low optimal growth temperature of GaAsBi; the bottom AlGaAs barrier is grown at 610 °C, while the GaAsBi quantum well and the top AlGaAs barrier are grown at 320 °C. Cross-sectional transmission electron microscopy and room temperature photoluminescence measurements indicate that this approach results in samples with excellent structural and optical properties. The high quality of the low temperature AlGaAs barrier is attributed to the presence of Bi on the surface as indicated by a (1 × 3) surface reconstruction persisting throughout the low temperature growth.
Evaluation and modeling of lanthanum diffusion in TiN/La2O3/HfSiON/SiO2/Si high-k stacks
Authors: Essa Z. , Gaumer C. , Pakfar A. , Gros-Jean M. , Juhel M. , Panciera F. , Boulenc P. , Tavernier C. , Cristiano F.
Published: October 2012

In this study, TiN/La2O3/HfSiON/SiO2/Si gate stacks with thick high-k (HK) and thick pedestal oxide were used. Samples were annealed at different temperatures and times in order to characterize in detail the interaction mechanisms between La and the gate stack layers. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) measurements performed on these samples show a time diffusion saturation of La in the high-k insulator, indicating an La front immobilization due to LaSiO formation at the high-k/interfacial layer. Based on the SIMS data, a technology computer aided design (TCAD) diffusion model including La time diffusion saturation effect was developed.
Broadband sound absorption by lattices of microperforated cylindrical shells
Authors: García-Chocano Victor M. , Cabrera Suitberto , Sánchez-Dehesa José
Published: October 2012

Absorption of broadband noise by sonic crystals consisting of microperforated cylindrical shells is proposed and experimentally demonstrated. The theoretical study has been performed in the framework of multiple scattering method, where a model for the T matrix of the microperforated shells has been developed. It has been predicted an extraordinary broadband sound absorption that is explained in terms of the multiple scattering phenomena occurring at the surfaces of the absorptive units—the microperforated panels. Our proposal has been supported by experiments performed on a structure consisting of 3 rows of cylindrical shells 3 meters height.
Primary energy dependence of secondary electron emission from graphene adsorbed on Ni(111)
Authors: Riccardi P. , Cupolillo A. , Pisarra M. , Sindona A. , Caputi L. S.
Published: October 2012

We measured energy distribution and yields of electrons emitted from graphene adsorbed on a Ni(111) surface under the impact of 200–1200 eV electrons. The adsorption of graphene results in significant changes of the spectra of emitted electrons but not of the total emission yields. The electronic structure of the graphitic overlayer determines the final states of excited electrons transported by collision cascade from the bulk of the substrate.
Integrated optofluidic index sensor based on self-trapped beams in LiNbO3
Authors: Chauvet M. , Al Fares L. , Guichardaz B. , Devaux F. , Ballandras S.
Published: October 2012

We show that self-trapped beams can form in structured monolithic lithium niobate chips. In particular, they are observed to be unaffected when crossing few hundred microns wide gaps. The technique is employed to fabricate an index sensor constituted of a buried circular optical waveguide crossing a fluidic channel in a lithium niobate substrate. Fluidic channels are realized by precision dicing while the optical waveguides are induced by photorefractive beam self-trapping controlled by the pyroelectric effect. The self-aligning property of this latter waveguides provides a simple fabrication technique of an integrated sensor that accurately measures the refractive index of transparent liquids.
Carrier escape mechanism dependence on barrier thickness and temperature in InGaN quantum well solar cells
Authors: Lang J. R. , Young N. G. , Farrell R. M. , Wu Y.-R. , Speck J. S.
Published: October 2012

The properties of quantum well carrier escape were studied by varying barrier thicknesses in InGaN/GaN multi-quantum well solar cell devices. The dependence of the photocurrent on applied bias and temperature exhibited properties indicative of the quantum well carrier escape mechanisms of thermionic emission and tunneling, with tunneling dominating for thin barriers and high fields. Simulations using a self-consistent drift-diffusion and Schrödinger solver with analytical formulas extracted carrier escape lifetimes. By employing sufficiently thin barriers, it was found that escape lifetimes can be made small compared to recombination lifetimes, leading to high internal quantum efficiency.
The importance of recruitment patterns versus reproductive output in the persistence of a short-range endemic shrub in a highly fragmented landscape of south-western Australia
Authors: Gibson Neil , Yates Colin , Byrne Margaret , Langley Margaret , Thavornkanlapachai Rujiporn
Published: October 2012

Calothamnus quadrifidus subsp. teretifolius A.S.George & N.Gibson is a short-range endemic shrub whose habitat has been greatly reduced by clearing for agriculture. Reproductive output was high in all populations sampled, although there were large differences among populations in fruit set, the number of seeds per fruit and seed germination. These traits showed no relationship to population size, degree of isolation, or fragment size, which contrasts strongly with the patterns found in a widespread congener. Demographic studies in remnants with an intact understorey showed stable adult populations with continuous seedling recruitment. In contrast, there was consistent widespread failure of seedling and juvenile recruitment in degraded roadside remnants that also showed significant mortality of reproductive adults. In these degraded remnants, recruitment failure appears to be the primary cause of species decline.
The Influence of Water and Metal Ions on the Transport Properties of Trihexyl(tetradecyl)phosphonium Chloride
Authors: Bayley Paul M. , Novak Jan , Khoo Timothy , Britton Melanie M. , Howlett Patrick C. , Macfarlane Douglas R. , Forsyth Maria
Published: October 2012

A recent study indicated that the water-saturated ionic liquid (IL) trihexyl(tetradecyl)phosphonium chloride ([P6,6,6,14][Cl]) provided a viable electrolyte for a Mg-air battery. However, there is limited literature on the properties of IL-water mixtures as battery electrolytes. The physical properties of [P6,6,6,14][Cl] were studied with the addition of both water and metal salts (MgCl2 and LiCl) using conductivity and self-diffusion coefficient measurements. The conductivity of the samples at low water concentrations is surprisingly enhanced by the addition of the metal salt, contrary to lithium IL electrolytes. It was also found that the conductivity of the IL was increased by an order of magnitude by saturation with water. NMR diffusion measurements were used to probe the behaviour of both the cation and the water in the mixtures. It was found that the addition of metal salts to the water-saturated [P6,6,6,14][Cl] did not affect the transport properties of the water or cation.