bluuebunny/crossref_metadata_2025 huggingface dataset:
Effortful Pitch Glide: A Potential New Exercise Evaluated by Dynamic MRI
Authors: Miloro Keri Vasquez , Pearson William G. , Langmore Susan E.
Published: April 2014

Purpose

The purpose of this study was to compare the biomechanics of the effortful pitch glide (EPG) with swallowing using dynamic MRI. The EPG is a combination of a pitch glide and a pharyngeal squeeze maneuver for targeting laryngeal and pharyngeal muscles. The authors hypothesized that the EPG would elicit significantly greater structural excursions of anterior hyoid, superior hyoid, hyolaryngeal approximation, laryngeal elevation, and lateral pharyngeal wall medialization compared with swallowing.

Method

Eleven healthy, young subjects with a mean age of 25 were recruited. The EPG was first taught and verified via laryngoscopy. Then 2-planar (coronal and sagittal) dynamic MRI acquisitions captured 10 repeated swallows and 3 EPGs. Kinematic analyses of minimum and maximum excursion of anatomical landmarks were calculated.

Results

Results showed a nonsignificant difference between the 2 tasks for range of excursion with all measured biomechanics except for superior hyoid, where the swallow showed significantly greater excursion. This indicated that swallowing and EPG biomechanics were comparable, lending support for the potential use of the EPG as another nonswallowing exercise.

Conclusion

Findings suggest EPG may be an effective exercise to target several important swallowing muscles, especially the long pharyngeal muscles that elevate the larynx and shorten the pharynx in swallowing.
Test–Retest Reliability of Respiratory Resistance Measured With the Airflow Perturbation Device
Authors: Gallena Sally K. , Solomon Nancy Pearl , Johnson Arthur T. , Vossoughi Jafar , Tian Wei
Published: April 2014

Purpose

In this study, the authors aimed to determine reliability of the airflow perturbation device (APD) to measure respiratory resistance within and across sessions during resting tidal (RTB) and postexercise breathing in healthy athletes, and during RTB across trials within a session in athletes with paradoxical vocal fold motion (PVFM) disorder.

Method

Prospective, repeated-measures design. The APD measured respiratory resistance during 3 baseline assessments in 24 teenage female athletes, 12 with and 12 without PVFM. Control athletes provided data at rest and following a customized exercise challenge during each of 3 sessions. Intraclass correlation coefficient (ICC) analysis assessed strength of relationships, and repeated-measures analysis of variance assessed differences across trials and sessions.

Results

ICC analyses confirmed strong correlations across RTB trials for inspiratory, expiratory, and mean respiratory resistance in both groups. Inspiratory resistance decreased ~5% between sessions for control participants; expiratory and mean respiratory resistances were stable. Data from control athletes across sessions and following rigorous exercise were strongly correlated when taken at comparable intervals.

Conclusions

APD-measured respiratory resistance, including separate assessments for the inspiratory and expiratory phases, has strong test–retest reliability during RTB and after exercising. This suggests that the APD is a useful measurement tool for the assessment of airway function in patients suspected of having PVFM.
Tip‐sensitive fibre‐optic Bragg grating ultrasonic hydrophone for measuring high‐intensity focused ultrasound fields
Authors: Wang D.H. , Jia Ping Gang , Ma Z.G. , Xie L.F. , Liang Q.B.
Published: April 2014

A tip‐sensitive fibre‐optic Bragg grating ultrasonic hydrophone (TSFBGUH) with high spatial resolution for measuring high‐intensity focused ultrasound (HIFU) fields is reported. When measuring a HIFU field, the sensitive axis of the TSFBGUH with a flexible fibre‐optic sensor holder should be in parallel with the acoustic axis of the HIFU transducer to ensure the measured ultrasound impinges on the tip of the TSFBGUH. The TSFBGUH system has been established and tested. The experimental results show that the acoustic pressure sensitivity of the TSFBGUH system is about 31.3 mV/MPa within the measurement range of 10 MHz and the noise equivalent pressure is about 10.4 kPa.
Failure mechanism for input buffer under CDM test
Authors: Kao Tzu‐Cheng , Hung Chung‐Yu , Lee Jian‐Hsing , Lien Chen‐Hsin , Chiu Chien‐Wei , Lo Kuo‐Hsuan , Su Hung‐Der , Weng Wu‐Te
Published: April 2014

The influence of the body layout on the charged device model (CDM) failure site and the robustness of the input buffer is explored. The failure analysis results confirm that the gate oxide is damaged. The failure site can be moved from the region above the channel to the overlap region between the source and the gate once the body layout is cut from a ring into a small segment, providing direct evidence demonstrating that the CDM current flows through the gate oxide via the body and the source of the transistor, since both connect to the Vss bus line. Otherwise, changing the body layout of the input buffer transistor does not vary the failure location.
GF(2n) bit‐parallel squarer using generalised polynomial basis for new class of irreducible pentanomials
Authors: Xiong Xi , Fan Haining
Published: April 2014

Explicit formulae and complexities of bit‐parallel GF(2n) squarers for a new class of irreducible pentanomials xn + xn−1 + xk + x + 1, where n is odd and 1 < k < (n − 1)/2 are presented. The squarer is based on the generalised polynomial basis of GF(2n). Its gate delay matches the best results, whereas its XOR gate complexity is n + 1, which is only about two thirds of the current best results.
5.8 GHz propagation of low‐height wireless links in sea port scenario
Authors: Reyes‐Guerrero J.C. , Mariscal L.A.
Published: April 2014

Experimental fading measurements were performed in Cadiz Bay, Spain, for a variety of operational scenarios over the sea at the unlicensed 5.8 GHz frequency band. Measurements are based on continuous wave (CW) transmissions with both the transmitter and the receiver installed in typical low‐height maritime platforms, such as oceanographic buoys, military ships and boats. Based on the measurements, large‐scale and small‐scale fading statistics are characterised by cumulative distribution functions (CDFs) and key wireless channel parameters are estimated and discussed. Results show, first, that large‐scale fading can be modelled using classical log‐normal path‐loss models and, secondly, that small‐scale fading statistics fits the extreme value distribution (EVD) function when they are expressed in decibel units. This study can be used for practical planning of wireless communications in maritime applications and as an experimental basis for further simulation works.
Cascaded Brillouin fibre lasers coupled to unitravelling carrier photodiodes for narrow linewidth terahertz generation
Authors: Ducournau G. , Bacquet D. , Szriftgiser P. , Pavanello F. , Peytavit E. , Zaknoune M. , Beck A. , Lampin J.‐F.
Published: April 2014

Narrow linewidth terahertz (THz) generation using a cascaded Brillouin fibre laser structure and a unitravelling carrier photodiode is investigated. Using two distributed feedback lasers separated by > 1 THz with 1 MHz initial linewidth, the use of the cascaded Brillouin laser greatly increases the linewidth reduction factor compared to a single Brillouin laser structure. The linewidth of the realised THz source is found to be < 100 Hz at 1014.7 GHz without the use of any active stabilisation of the laser cavity or any microwave reference.
Design of frequency‐interleaved ADC with mismatch compensation
Authors: Qiu L. , Zheng Y.J. , Siek L.
Published: April 2014

A frequency‐interleaving‐based multichannel analogue‐to‐digitial converter (ADC) with mismatch compensation is presented, which is immune from the time skew problem that exist in the time‐interleaved ADC. The channel mismatches, such as bandwidth mismatch, gain mismatch, offset mismatch and filter bank mismatch, are addressed and modelled in the reconstruction optimisation. A prototype of a four‐channel 1 GS/s 12 bit frequency‐interleaved ADC (FI‐ADC) is designed to demonstrate the mismatch compensation. Simulation results show that the mismatches in the FI‐ADC can be compensated effectively.
High swing PLL charge pump with current mismatch reduction
Authors: Joram N. , Wolf R. , Ellinger F.
Published: April 2014

A compensated charge pump for use in phase‐locked loops (PLLs) is presented, which reaches several of the desired design goals for this type of circuit. The measured mismatch between the source and sink currents is below 2.1% for a large output voltage headroom of 83.3% of the supply, while still having a high output resistance of 140 kΩ. This behaviour is reached with a novel dual compensation method. The circuit was implemented in a 180 nm CMOS technology using a 3 V supply.
On power minimisation and SNR maximisation of distributed beamforming in cooperative communication systems
Authors: Baleshan T. , Jayalath A.D.S. , Coetzee J.C.
Published: April 2014

A comparison of relay power minimisation subject to received signal‐to‐noise ratio (SNR) at the receiver and SNR maximisation subject to the total transmitted power of relays for a typical wireless network with distributed beamforming is presented. It is desirable to maximise receiver quality‐of‐service (QoS) and also to minimise the cost of transmission in terms of power. Hence, these two optimisation problems are very common and have been addressed separately in the literature. It is shown that SNR maximisation subject to power constraint and power minimisation subject to SNR constraint yield the same results for a typical wireless network. It proves that either one of the optimisation approaches is sufficient.
Distance fluctuation of a single molecule in Lennard-Jones liquid based on generalized Langevin equation and mode coupling theory
Authors: Li Ping , Dong Yunhong , Zhao Nanrong , Hou Zhonghuai
Published: April 2014

Distance fluctuation of a single molecule, modeled as an idealized bead-spring chain, dissolved in a Lennard-Jones liquid is studied by using a multidimensional generalized Langevin equation, where the friction kernel ζ(t) is calculated from the kinetic mode coupling theory (MCT). Temporal behavior of the distance autocorrelation function shows three typical regimes of time dependence, starting with a constant, followed by a power law of t−α, and finally an exponential decay. Particular attentions are paid to the time span of the power law regime, which corresponds to anomalous subdiffusion behavior, and the MCT framework enables us to investigate thoroughly how this regime depends on microscopic details such as the bead-to-solvent mass ratio MR, chain spring frequency ω, and the chain length N. Interestingly, the exponent α is robust to be 1/2 against the change of these parameters, although the friction kernel ζ(t) shows nontrivial dependence on time. In addition, we find that the starting time of the power-law region t1 scales with Γ−1, with Γ = 4ω2/ζ0 where ζ0 is the zero-frequency friction which decreases rapidly with increasing bead mass. On the other hand, the ending time t2 is not sensitive to varying ω or ζ0, but it increases with N rapidly before it reaches a constant for N larger than some threshold value. Our work may provide a unified strategy starting from the microscopic level to understand the anomalous subdiffusive behavior regarding large scale conformational change of polymers or proteins.
Semi-classical properties of Berezin–Toeplitz operators with $\mathscr {C}^k$Ck-symbol
Authors: Barron Tatyana , Ma Xiaonan , Marinescu George , Pinsonnault Martin
Published: April 2014

We obtain the semi-classical expansion of the kernels and traces of Toeplitz operators with \documentclass[12pt]{minimal}\begin{document}$\mathscr {C}^k$\end{document}Ck-symbol on a symplectic manifold. We also give a semi-classical estimate of the distance of a Toeplitz operator to the space of self-adjoint and multiplication operators.
Linear stability analysis of thin liquid film flow over a heterogeneously heated substrate
Authors: Tiwari Naveen , Awasthi Anmol , Davis Jeffrey M.
Published: April 2014

The linear stability of a thin film of volatile liquid flowing over a surface with embedded, regularly spaced heaters is investigated. The temperature gradients at the upstream edges of the heaters induce gradients in surface tension that create a pronounced non-uniformity in the film profile due to the formation of capillary ridges. The Governing equations for the evolution of the film thickness are derived within the lubrication approximation, and three important parameters that affect the dynamics and stability of the film are identified. The computed two-dimensional, steady solutions for the local film thickness reveal that due to evaporation there is a slight change in the height of capillary ridge at subsequent heaters downstream. Using a linear stability analysis, it is shown that, as for a single heater, the film is susceptible to two types of instabilities. A rivulet instability leads to spanwise-periodic rivulets, and an oscillating thermocapillary instability leads to streamwise, time-periodic oscillations in the film thickness. The critical Marangoni number is calculated for both types of instability for a range of parameter values. The effect of the number of heaters, heater width, and gap between the heaters on the critical Marangoni number is computed and analyzed. For small evaporation rates and less volatile films, the presence of multiple heaters has almost no noticeable effect on the film stability. For larger evaporation rates and more volatile films, additional heaters decrease the Marangoni number at instability onset. The destabilizing effect of multiple heaters is sensitive to the heater geometry and spacing. Furthermore, the limitations of streamwise periodic boundary conditions for analyzing the stability of such flows are discussed. Computations on the transient and nonlinear growth of perturbations are also presented and indicate that the results of eigenanalysis are physically determinant.
A diagrammatic kinetic theory of density fluctuations in simple liquids in the overdamped limit. I. A long time scale theory for high density
Authors: Pilkiewicz Kevin R. , Andersen Hans C.
Published: April 2014

Starting with a formally exact diagrammatic kinetic theory for the equilibrium correlation functions of particle density and current fluctuations for a monatomic liquid, we develop a theory for high density liquids whose interatomic potential is continuous and has a strongly repulsive short ranged part. We assume that interparticle collisions via this short ranged part of the potential are sufficient to randomize the velocities of the particles on a very small time scale compared with the fundamental time scale defined as the particle diameter divided by the mean thermal velocity. When this is the case, the graphical theory suggests that both the particle current correlation functions and the memory function of the particle density correlation function evolve on two distinct time scales, the very short time scale just mentioned and another that is much longer than the fundamental time scale. The diagrams that describe the motion on each of these time scales are identified. When the two time scales are very different, a dramatic simplification of the diagrammatic theory at long times takes place. We identify an irreducible memory function and a more basic function, which we call the irreducible memory kernel. This latter function evolves on the longer time scale only and determines the time dependence of the density and current correlation functions of interest at long times. In Paper II, a simple one-loop approximation for the irreducible memory kernel is used to calculate correlation functions for a Lennard-Jones fluid at high density and a variety of temperatures.
A diagrammatic kinetic theory of density fluctuations in simple liquids in the overdamped limit. II. The one-loop approximation
Authors: Pilkiewicz Kevin R. , Andersen Hans C.
Published: April 2014

A diagrammatic kinetic theory of density fluctuations in simple dense liquids at long times, described in Paper I, is applied to a high density Lennard-Jones liquid to calculate various equilibrium time correlation functions. The calculation starts from the general theory and makes two approximations. (1) The general diagrammatic expression for an irreducible memory kernel is approximated using a one-loop approximation. (2) The generalized Enskog projected propagator, which is required for the calculation, is approximated using a simple kinetic model for the hard sphere memory function. The coherent intermediate scattering function (CISF), the longitudinal current correlation function (LCCF), the transverse current correlation function (TCCF), the incoherent intermediate scattering function (IISF), and the incoherent longitudinal current correlation function are calculated and compared with simulation results for the Lennard-Jones liquid at high density. The approximate theoretical results are in good agreement with the simulation data for the IISF for all wave vectors studied and for the CISF and LCCF for large wave vector. The approximate results are in poor agreement with the simulation data for the CISF, LCCF, and TCCF for small wave vectors because these functions are strongly affected by hydrodynamic fluctuations at small wave vector that are not well described by the simple kinetic model used. The possible implications of this approach for the study of liquids are discussed.
Paper-based ultracapacitors with carbon nanotubes-graphene composites
Authors: Li Jian , Cheng Xiaoqian , Sun Jianwei , Brand Cameron , Shashurin Alexey , Reeves Mark , Keidar Michael
Published: April 2014

In this paper, a paper-based ultracapacitors were fabricated by the rod-rolling method with the ink of carbon nanomaterials, which were synthesized by arc discharge under various magnetic conditions. Composites of carbon nanostructures, including high-purity single-walled carbon nanotubes (SWCNTs) and graphene flakes were synthesized simultaneously in a magnetically enhanced arc. These two nanostructures have promising electrical properties and synergistic effects in the application of ultracapacitors. Scanning electron microscope, transmission electron microscope, and Raman spectroscopy were employed to characterize the properties of carbon nanostructures and their thin films. The sheet resistance of the SWCNT and composite thin films was also evaluated by four-point probe from room temperature to the cryogenic temperature as low as 90 K. In addition, measurements of cyclic voltammetery and galvanostatic charging/discharging showed the ultracapacitor based on composites possessed a superior specific capacitance of up to 100 F/g, which is around three times higher than the ultracapacitor entirely fabricated with SWCNT.
Comparison of erythrocyte dynamics in shear flow under different stress-free configurations
Authors: Cordasco Daniel , Yazdani Alireza , Bagchi Prosenjit
Published: April 2014

An open question that has persisted for decades is whether the cytoskeleton of a red blood cell is stress-free or under a stress. This question is important in the context of theoretical modeling of cellular motion under a flowing condition where it is necessary to make an assumption about the stress-free state. Here, we present a 3D numerical study to compare the cell dynamics in a simple shear flow under two different stress-free states, a biconcave discocyte representing the resting shape of the cell, and a nearly spherical oblate shape. We find that whether the stress-free states make a significant difference or not depends on the viscosity of the suspending medium. If the viscosity is close to that of blood plasma, the two stress-free states do not show any significant difference in cell dynamics. However, when the suspending medium viscosity is well above that of the physiological range, as in many in vitro studies, the shear rate separating the tank-treading and tumbling dynamics is observed to be higher for the biconcave stress-free state than the spheroidal state. The former shows a strong shape oscillation with repeated departures from the biconcave shape, while the latter shows a nearly stable biconcave shape. It is found that the cell membrane in the biconcave stress-free state is under a compressive stress and a weaker bending force density, leading to a periodic compression of the cell. The shape oscillation then leads to a higher energy barrier against membrane tank-tread leading to an early transition to tumbling. However, if the cells are released with a large off-shear plane angle, the oscillations can be suppressed due to an azimuthal motion of the membrane along the vorticity direction leading to a redistribution of the membrane points and lowering of the energy barrier, which again results in a nearly similar behavior of the cells under the two different stress-free states. A variety of off-shear plane dynamics is observed, namely, rolling, kayaking, precession, and a new dynamics termed “hovering.” For the physiological viscosity range, the shear-plane tumbling appears to be relatively less common, while the rolling is observed to be more stable.
Resummed thermodynamic perturbation theory for bond cooperativity in associating fluids with small bond angles: Effects of steric hindrance and ring formation
Authors: Marshall Bennett D. , Haghmoradi Amin , Chapman Walter G.
Published: April 2014

In this paper we develop a thermodynamic perturbation theory for two site associating fluids which exhibit bond cooperativity (system energy is non-pairwise additive). We include both steric hindrance and ring formation such that the equation of state is bond angle dependent. Here, the bond angle is the angle separating the centers of the two association sites. As a test, new Monte Carlo simulations are performed, and the theory is found to accurately predict the internal energy as well as the distribution of associated clusters as a function of bond angle.
Integrated patch and slot array antenna for terahertz quantum cascade lasers at 4.7 THz
Authors: Bonzon C. , Benea Chelmus I. C. , Ohtani K. , Geiser M. , Beck M. , Faist J.
Published: April 2014

Our work presents a slot and a patch array antenna at the front facet of a 4.7 THz quantum cascade laser as extractor, decreasing the facet reflectivity down to 2.6%. The resulting output power increases by a factor 2 and the slope efficiency by a factor 4. The simulated and the measured far-fields are in good agreement.
Density functional calculations for structural, electronic, and magnetic properties of gadolinium-oxide clusters
Authors: Yuan H. K. , Chen H. , Tian C. L. , Kuang A. L. , Wang J. Z.
Published: April 2014

Gadolinium-oxide clusters in various sizes and stoichiometries have been systematically studied by employing the density functional theory with the generalized gradient approximation. The clusters in bulk stoichiometry are relatively more stable and their binding energies increase with the increasing size. Stoichiometric (Gd2O3)n clusters of n = 1–3 prefer cage-like structures, whereas the clusters of n = 4–30 prefer compact structures layered by wedge-like units and exhibit a rough feature toward the bulk-like arrangement with small disorders of atomic positions. The polyhedral-cages analogous to carbon-fullerenes are stable isomers yet not the minimum energy configurations. Their stabilities can be improved by embedding one oxygen atom or a suitable cage to form core-shell configurations. The mostly favored antiferromagnetic couplings between adjacent Gd atoms are nearly degenerated in energy with their ferromagnetic couplings, resulting in super-paramagnetic characters of gadolinium-oxide clusters. The Ruderman-Kittel-Kasuya-Yosida (RKKY)-type mechanism together with the superexchange-type mechanism plays cooperation role for the magnetic interactions in clusters. We present, as a function of n, calculated binding energies, ionization potential, electron affinity, and electronic dipole moment.
Combining low-energy electron microscopy and scanning probe microscopy techniques for surface science: Development of a novel sample-holder
Authors: Cheynis F. , Leroy F. , Ranguis A. , Detailleur B. , Bindzi P. , Veit C. , Bon W. , Müller P.
Published: April 2014

We introduce an experimental facility dedicated to surface science that combines Low-Energy Electron Microscopy/Photo-Electron Emission Microscopy (LEEM/PEEM) and variable-temperature Scanning Probe Microscopy techniques. A technical challenge has been to design a sample-holder that allows to exploit the complementary specifications of both microscopes and to preserve their optimal functionality. Experimental demonstration is reported by characterizing under ultrahigh vacuum with both techniques: Au(111) surface reconstruction and a two-layer thick graphene on 6H-SiC(0001). A set of macros to analyze LEEM/PEEM data extends the capabilities of the setup.
Misfit layered Ca3Co4O9 as a high figure of merit p-type transparent conducting oxide film through solution processing
Authors: Aksit M. , Kolli S. K. , Slauch I. M. , Robinson R. D.
Published: April 2014

Ca3Co4O9 thin films synthesized through solution processing are shown to be high-performing, p-type transparent conducting oxides (TCOs). The synthesis method is a cost-effective and scalable process that consists of sol-gel chemistry, spin coating, and heat treatments. The process parameters can be varied to produce TCO thin films with sheet resistance as low as 5.7 kΩ/sq (ρ ≈ 57 mΩ cm) or with average visible range transparency as high as 67%. The most conductive Ca3Co4O9 TCO thin film has near infrared region optical transmission as high as 85%. The figure of merit (FOM) for the top-performing Ca3Co4O9 thin film (151 MΩ−1) is higher than FOM values reported in the literature for all other solution processed, p-type TCO thin films and higher than most others prepared by physical vapor deposition and chemical vapor deposition. Transparent conductivity in misfit layered oxides presents new opportunities for TCO compositions.
Dynamics symmetries of Hamiltonian system on time scales
Authors: Peng Keke , Luo Yiping
Published: April 2014

In this paper, the dynamics symmetries of Hamiltonian system on time scales are studied. We study the symmetries and quantities based on the calculation of variation and Lie transformation group. Particular focus lies in: the Noether symmetry leads to the Noether conserved quantity and the Lie symmetry leads to the Noether conserved quantity if the infinitesimal transformations satisfy the structure equation. As the new application of result, at end of the article, we give a simple example of Noether symmetry and Lie symmetry on time scales.
Influence of electric fields on the structure and structure transition of water confined in a carbon nanotube
Authors: Qian Zhenyu , Fu Zhaoming , Wei Guanghong
Published: April 2014

Our previous work demonstrated that liquid water can freeze continuously into either pentagonal or helical solid-like ice nanotubes in a single-walled carbon nanotube (SWCNT) with a tube diameter of 1.2 nm, depending on the strengths of an external electric (E) field applied along the tube axis. In this study, the structure and the structure transition behavior of water confined in a wider SWCNT (diameter = 1.31 nm) under the influence of E-fields are investigated by molecular dynamics simulations using the TIP4P model for water at atmospheric pressure. We find that confined water can freeze into three different polygonal (including hexagonal, heptagonal, and mixed hexagonal-heptagonal) ice nanotubes through a first-order phase transition at lower E (<0.75 V/nm), while form a helical ice nanotube encapsulating a helical water nanoline through a continuous phase transition at higher E (1.0 < E < 2.0 V/nm), different from the phase transition behavior of water in a SWCNT with a diameter = 1.2 nm. The populations of the three different polygonal ice nanotubes are modulated by both temperature and electric field. In addition, an E-induced discontinuous solid-solid phase transition between polygonal and helical ice nanotubes is observed at low temperature (T < 230 K) with a significant electric hysteresis loop of 1.0 V/nm. Finally, we present a rich phase diagram of confined water as a function of temperature and electric field, in which the boundaries of the first-order phase transition at lower E and the continuous phase transition at higher E are connected by a connecting line which corresponds to the hysteresis region.
First-principles study on the interaction of nitrogen atom with α–uranium: From surface adsorption to bulk diffusion
Authors: Su Qiulei , Deng Huiqiu , Ao Bingyun , Xiao Shifang , Li Xiaofan , Chen Piheng , Hu Wangyu
Published: April 2014

Experimental studies of nitriding on uranium surfaces show that the modified layers provide considerable protection against air corrosion. The bimodal distribution of nitrogen is affected by both its implantation and diffusion, and the diffusion of nitrogen during implantation is also governed by vacancy trapping. In the present paper, nitrogen adsorption, absorption, diffusion, and vacancy trapping on the surface of and in the bulk of α–uranium are studied with a first-principles density functional theory approach and the climbing image nudged elastic band method. The calculated results indicate that, regardless of the nitrogen coverage, a nitrogen atom prefers to reside at the hollow1 site and octahedral (Oct) site on and below the surface, respectively. The lowest energy barriers for on-surface and penetration diffusion occur at a coverage of 1/2 monolayer. A nitrogen atom prefers to occupy the Oct site in bulk α–uranium. High energy barriers are observed during the diffusion between neighboring Oct sites. A vacancy can capture its nearby interstitial nitrogen atom with a low energy barrier, providing a significant attractive nitrogen-vacancy interaction at the trapping center site. This study provides a reference for understanding the nitriding process on uranium surfaces.
Effective shear modulus of piezoelectric film embedded with square nano-fibers under anti-plane shear waves
Authors: Huang Ming-Juan , Fang Xue-Qian , Zhao Xing , Liu Jin-Xi , Feng Wen-Jie
Published: April 2014

For piezoelectric films, the surface/interface energy around the nano-fibers plays an important role in predicting the overall properties. Square nano-fibers are very popular in piezoelectric films. This paper presents the size-dependent dynamic effective elastic modulus of piezoelectric films under anti-plane shear waves. The average electro-elastic field resulting from the randomly distributed nano-fibers is solved by applying the effective field method. To express the coupling fields in the effective field, the mapping method and wave function expansion method are introduced. The closed-form solution of piezoelectrically stiffened shear modulus with respect to the shape and volume fraction of fibers and surface/interface properties is obtained. The interacting effect of surface/interface and square shape of nano-fibers is examined.
Nonlinear development of the two-plasmon decay instability in three dimensions
Authors: Vu H. X. , DuBois D. F. , Russell D. A. , Myatt J. F. , Zhang J.
Published: April 2014

Most recent experiments on the excitation of the two plasmon-decay (TPD) instability involve a three-dimensional (3D) array of overlapping laser beams. Our recent two dimensional (2D) simulations suggested that Langmuir cavitation and collapse are important nonlinear saturation mechanisms for TPD. There are important quantitative differences in the Langmuir collapse process in 2D and 3D. To address these and other issues, we have developed a 3D Zakharov code. It has been applied to study the evolution of TPD from absolute instabilities (arising from 3D laser geometries) to the nonlinear state (J. Zhang et al., Phys. Rev. Lett. (submitted)). The present paper concentrates on the nonlinear saturated state excited by the collective action of two crossed laser beams with arbitrary polarizations. Remarkable agreement between 3D and 2D simulations is found for several averaged physical quantities when the beams are polarized in their common plane. As in the previous 2D simulations, we find: (a) the collective, initially convectively unstable triad modes dominate after a sub-picosecond burst, (b) Langmuir cavitation and collapse are important nonlinearities, and (c) that the statistics of intense cavitons are characteristic of a Gaussian random process. The 3D steady-state saturated Langmuir energy level is about 30% higher than in 2D. The auto-correlation functions of the Langmuir envelope field and of the low-frequency electron density field yield the spatial shape of the strongest collapsing cavitons which are 3D ellipsoids whose orientation depends on the laser polarizations. This tilting of the caviton's strongest electric field direction away from the normal to the target surface is a major new 3D result. This tilting may deflect the hot electron flux and thereby mitigate target preheat.
Whistler wave generation by non-gyrotropic, relativistic, electron beams
Authors: Skender M. , Tsiklauri D.
Published: April 2014

Particle-in-cell code, EPOCH, is used for studying features of the wave component evident to propagate backwards from the front of the non-gyrotropic, relativistic beam of electrons injected in the Maxwellian, magnetised background plasma with decreasing density profile. According to recent findings presented in Tsiklauri [Phys. Plasmas 18, 052903 (2011)], Schmitz and Tsiklauri [Phys. Plasmas 20, 062903 (2013)], and Pechhacker and Tsiklauri [Phys. Plasmas 19, 112903 (2012)], in a 1.5-dimensional magnetised plasma system, the non-gyrotropic beam generates freely escaping electromagnetic radiation with properties similar to the Type-III solar radio bursts. In this study, the backwards propagating wave component evident in the perpendicular components of the electromagnetic field in such a system is presented for the first time. Background magnetic field strength in the system is varied in order to prove that the backwards propagating wave's frequency, prescribed by the whistler wave dispersion relation, is proportional to the specified magnetic field. Moreover, the identified whistlers are shown to be generated by the normal Doppler-shifted relativistic resonance. Large fraction of the energy of the perpendicular electromagnetic field components is found to be carried away by the whistler waves, while a small but sufficient fraction is going into L- and R-electromagnetic modes.
Negative differential resistance devices by using N-doped graphene nanoribbons
Authors: Huang Jing , Wang Weiyi , Li Qunxiang , Yang Jinlong
Published: April 2014

Recently, extensive efforts have been devoted to the investigations of negative differential resistance (NDR) behavior in graphene. Here, by performing fully self-consistent density functional theory calculations combined with non-equilibrium Green's function technique, we investigate the transport properties of three molecules from conjugated molecule, one-dimension alkane chain, and single molecule magnet, which are sandwiched between two N-doped zigzag and armchair graphene nanoribbons (GNRs). We observe robust NDR effect in all examined molecular junctions including benzene, alkane, and planar four-coordinated Fe complex. Through the analyses of the calculated electronic structures and the bias-dependent transmission coefficients, we find that the narrow density of states of N-doped GNRs and the bias-dependent effective coupling between the discrete frontier molecular orbitals and the subbands of N-doped GNRs are responsible for the observed NDR phenomenon. These theoretical findings imply that N-doped GNRs hold great potential for building NDR devices based on various molecules.
Simulation and analysis of grating-integrated quantum dot infrared detectors for spectral response control and performance enhancement
Authors: Oh Kim Jun , Ku Zahyun , Krishna Sanjay , Kang Sang-Woo , Jun Lee Sang , Chul Jun Young , Urbas Augustine
Published: April 2014

We propose and analyze a novel detector structure for pixel-level multispectral infrared imaging. More specifically, we investigate the device performance of a grating-integrated quantum dots-in-a-well photodetector under backside illumination. Our design uses 1-dimensional grating patterns fabricated directly on a semiconductor contact layer and, thus, adds a minimal amount of additional effort to conventional detector fabrication flows. We show that we can gain wide-range control of spectral response as well as large overall detection enhancement by adjusting grating parameters. For small grating periods, the spectral responsivity gradually changes with parameters. We explain this spectral tuning using the Fabry–Perot resonance and effective medium theory. For larger grating periods, the responsivity spectra get complicated due to increased diffraction into the active region, but we find that we can obtain large enhancement of the overall detector performance. In our design, the spectral tuning range can be larger than 1 μm, and, compared to the unpatterned detector, the detection enhancement can be greater than 92% and 148% for parallel and perpendicular polarizations. Our work can pave the way for practical, easy-to-fabricate detectors, which are highly useful for many infrared imaging applications.
The influence of an ITER-like wall on disruptions at JET
Authors: de Vries P. C. , Baruzzo M. , Hogeweij G. M. D. , Jachmich S. , Joffrin E. , Lomas P. J. , Matthews G. F. , Murari A. , Nunes I. , Pütterich T. , Reux C. , Vega J. ,   JET-EFDA Contributors
Published: April 2014

In order to preserve the integrity of large tokamaks such as ITER, the number of disruptions has to be limited. JET has operated previously with a low frequency of disruptions (i.e., disruption rate) of 3.4% [P. C. de Vries et al., Nucl. Fusion 51, 053018 (2011)]. The start of operations with the new full-metal ITER-like wall at JET showed a marked rise in the disruption rate to 10%. A full survey was carried out to identify the root causes, the chain-of-events and classifying each disruption, similar to a previous analysis for carbon-wall operations. It showed the improvements made to avoid various disruption classes, but also indicated those disruption types responsible for the enhanced disruption rate. The latter can be mainly attributed to disruptions due to too high core radiation but also due to density control issues and error field locked modes. Detailed technical and physics understanding of disruption causes is essential for devising optimized strategies to avoid or mitigate these events.
Hydrodynamic instability growth and mix experiments at the National Ignition Facility
Authors: Smalyuk V. A. , Barrios M. , Caggiano J. A. , Casey D. T. , Cerjan C. J. , Clark D. S. , Edwards M. J. , Frenje J. A. , Gatu-Johnson M. , Glebov V. Y. , Grim G. , Haan S. W. , Hammel B. A. , Hamza A. , Hoover D. E. , Hsing W. W. , Hurricane O. , Kilkenny J. D. , Kline J. L. , Knauer J. P. , Kroll J. , Landen O. L. , Lindl J. D. , Ma T. , McNaney J. M. , Mintz M. , Moore A. , Nikroo A. , Parham T. , Peterson J. L. , Petrasso R. , Pickworth L. , Pino J. E. , Raman K. , Regan S. P. , Remington B. A. , Robey H. F. , Rowley D. P. , Sayre D. B. , Tipton R. E. , Weber S. V. , Widmann K. , Wilson D. C. , Yeamans C. B.
Published: April 2014

Hydrodynamic instability growth and its effects on implosion performance were studied at the National Ignition Facility [G. H. Miller, E. I. Moses, and C. R. Wuest, Opt. Eng. 443, 2841 (2004)]. Implosion performance and mix have been measured at peak compression using plastic shells filled with tritium gas and containing embedded localized carbon-deuterium diagnostic layers in various locations in the ablator. Neutron yield and ion temperature of the deuterium-tritium fusion reactions were used as a measure of shell-gas mix, while neutron yield of the tritium-tritium fusion reaction was used as a measure of implosion performance. The results have indicated that the low-mode hydrodynamic instabilities due to surface roughness were the primary culprits for yield degradation, with atomic ablator-gas mix playing a secondary role. In addition, spherical shells with pre-imposed 2D modulations were used to measure instability growth in the acceleration phase of the implosions. The capsules were imploded using ignition-relevant laser pulses, and ablation-front modulation growth was measured using x-ray radiography for a shell convergence ratio of ∼2. The measured growth was in good agreement with that predicted, thus validating simulations for the fastest growing modulations with mode numbers up to 90 in the acceleration phase. Future experiments will be focused on measurements at higher convergence, higher-mode number modulations, and growth occurring during the deceleration phase.
Twofold Andreev reflections and coherent transport in ferromagnetic semiconductor/d-wave superconductor/ferromagnetic semiconductor double tunneling junctions
Authors: Tao Y. C. , Li Z. P. , Ji T. T. , Liu S. Y. , Di Y. S.
Published: April 2014

Coherent transport in a ferromagnetic semiconductor (FS)/d-wave superconductor (SC)/FS structure with {110} interfaces is studied by extending Bogoliubov-de Gennes equation into eight components, in which the interband coupling of heavy and light hole bands in the FS, the strengths of potential scattering at the interfaces, and the mismatches in the effective mass and Fermi vector between the FS and SC are taken into account. Twofold Andreev reflections exist due to the existence of two bands in the FS, in which the incident hole and the two Andreev-reflected electrons, belonging to the different spin subbands, form twofold spin-singlet pairing states near the FS/SC interface. It is shown that due to the interplay of the SC with unconventional d-wave pairing symmetry and FS, the differential conductance and tunneling magnetoresistance exhibit an abundant dependence on not only the interband coupling in the FS but also the strengths of potential scattering at the interfaces. More importantly, the properties are found to be quite different from those in the FS/s-wave SC/FS structure with conventional pairing symmetry for the SC.
The rigorous wave optics design of diffuse medium reflectors for photovoltaics
Authors: Lin Albert , Ming Fu Sze , Kai Zhong Yan , Wei Tseng Chi , Yu Chen Po , Ping Ju Nyan
Published: April 2014

Recently, diffuse reflectors are being incorporated into solar cells, due to the advantage of no metallic absorption loss, higher reflectance, decent light scattering property by embedded TiO2 scatterers, and the ease of fabrication. Different methods have been employed to analyze diffuse reflectors, including Monte Carlo method, N-flux method, and a one-dimensional approximation based on semi-coherent optics, and the calculated reflectance is around 80% by these methods. In this work, rigorous wave optics solution is used, and it is shown that the reflectance for diffuse medium mirrors can actually be as high as >99% over a broad spectral range, provided the TiO2 scatterer geometry is properly optimized. The bandwidth of diffuse reflectors is un-achievable by other dielectric mirrors such as distributed Bragg reflectors or high index contrast grating mirror, using the same index contrast. Finally, it is promisingly found that even if the distribution of TiO2 is random, the wide-band reflection can still be achieved for the optimized TiO2 geometry. Initial experimental result is included in the supplementary material which shows the high feasibility of diffuse medium mirrors for solar cells.
Phase-gradient gap-plasmon metasurface based blazed grating for real time dispersive imaging
Authors: Huang Yuewang , Zhao Qiancheng , Kalyoncu Salih K. , Torun Rasul , Lu Yumeng , Capolino Filippo , Boyraz Ozdal
Published: April 2014

Dispersive Fourier transform imaging is a powerful technique in achieving ultrafast imaging of wide areas. However, system power efficiency is often limited by dispersive components. Here, we demonstrate that a gap-plasmon metasurface (GPM) based blazed grating can be used in dispersive imaging applications to achieve higher power efficiency than conventional gratings. A sub-wavelength GPM-based grating at telecommunication wavelengths has been designed and fabricated. 75.6% power efficiency with ∼0.4°/10 nm spatial dispersion has been measured for TE polarized waves at normal incidence. The fabricated device has been tested in a wide area real-time dispersive imaging system and <300 μm spatial resolution has been demonstrated experimentally.
Band alignment and interfacial structure of ZnO/Si heterojunction with Al2O3 and HfO2 as interlayers
Authors: Lu Hong-Liang , Yang Ming , Xie Zhang-Yi , Geng Yang , Zhang Yuan , Wang Peng-Fei , Sun Qing-Qing , Ding Shi-Jin , Wei Zhang David
Published: April 2014

Energy band alignment of ZnO/Si heterojunction with thin interlayers Al2O3 and HfO2 grown by atomic layer deposition has been studied using x-ray photoelectron spectroscopy. The valence band offsets of ZnO/Al2O3 and ZnO/HfO2 heterojunctions have been determined to be 0.43 and 0.22 eV, respectively. Accordingly, the band alignment ZnO/Si heterojunction is then modified to be 0.34 and 0.50 eV through inserting a thin Al2O3 and HfO2 layer, respectively. The feasibility to tune the band structure of ZnO/Si heterojunction by selecting a proper interlayer shows great advantage in improving the performance of the ZnO-based optoelectronic devices.
Summary of recent experiments on focusing of target-normal-sheath-accelerated proton beam with a stack of conducting foils
Authors: Ni P. A. , Alexander N. , Barnard J. J. , Lund S. M.
Published: April 2014

We present a summary of recent experiments on focusing of laser target-normal-sheath-accelerated (TNSA) proton beam with a stack of thin conducting foils. The experiments were performed using the Phelix laser (GSI-Darmstadt) and the Titan laser, Lawrence Livermore National Laboratory. The phenomena consistent with self-collimation (or weak self-focusing) of TNSA protons were experimentally observed for the first time at the Phelix laser user facility, in a specially engineered structure ("lens") consisting of a stack of 300 thin aluminum foils separated by 50 μm vacuum gaps. Follow up experiments using the Titan laser obtained results consistent with the collimation/focusing observed in the initial experiments using the Phelix. The Titan experiments employed improved, 25 μm- and 50 μm-gap targets and the new fine mesh diagnostic. All the experiments were carried out in a “passive environment,” i.e., no external fields were applied, and no neutralization plasma or injection of secondary charged particles was imposed. A plausible interpretation of the observed phenomena is that the combination of magnetic self-pinch forces generated by the beam current together with the simultaneous reduction of the repulsive electrostatic forces due to the conducting foils inhibits radial expansion of the beam.
Generation and transportation mechanisms for two-dimensional hole gases in GaN/AlGaN/GaN double heterostructures
Authors: Nakajima Akira , Liu Pucheng , Ogura Masahiko , Makino Toshiharu , Kakushima Kuniyuki , Nishizawa Shin-ichi , Ohashi Hiromichi , Yamasaki Satoshi , Iwai Hiroshi
Published: April 2014

The electrical properties of two-dimensional hole gases (2DHGs) in GaN/AlGaN/GaN double heterostructures were investigated. The layers were grown on sapphire substrates and a high-quality bulk GaN substrate. The coexistence of 2DHG and 2D electron gases on both sides of the AlGaN layer was confirmed by Hall effect measurements at 80–460 K. It was also verified that the 2DHGs were generated by negative polarization at the undoped GaN/AlGaN interface, which did not have a doped Mg acceptor. It was also demonstrated that the 2DHG density could be controlled by varying the AlGaN layer thickness and was inversely related to the 2DHG mobility. The measured relation indicated that the 2DHG mobility is mainly limited by phonon scatterings at around room temperature. As a result, the maximum 2DHG mobility of 16 cm2/Vs at 300 K was achieved with a density of 1 × 1013 cm−2.