bluuebunny/crossref_metadata_2025 huggingface dataset:
Ultrasound Visual Feedback Treatment and Practice Variability for Residual Speech Sound Errors
Authors: Preston Jonathan L. , McCabe Patricia , Rivera-Campos Ahmed , Whittle Jessica L. , Landry Erik , Maas Edwin
Published: August 2014

Purpose

The goals were to (a) test the efficacy of a motor-learning-based treatment that includes ultrasound visual feedback for individuals with residual speech sound errors and (b) explore whether the addition of prosodic cueing facilitates speech sound learning.

Method

A multiple-baseline, single-subject design was used, replicated across 8 participants. For each participant, 1 sound context was treated with ultrasound plus prosodic cueing for 7 sessions, and another sound context was treated with ultrasound but without prosodic cueing for 7 sessions. Sessions included ultrasound visual feedback as well as non-ultrasound treatment. Word-level probes assessing untreated words were used to evaluate retention and generalization.

Results

For most participants, increases in accuracy of target sound contexts at the word level were observed with the treatment program regardless of whether prosodic cueing was included. Generalization between onset singletons and clusters was observed, as was generalization to sentence-level accuracy. There was evidence of retention during posttreatment probes, including at a 2-month follow-up.

Conclusion

A motor-based treatment program that includes ultrasound visual feedback can facilitate learning of speech sounds in individuals with residual speech sound errors.

Supplemental Material

https://doi.org/10.23641/asha.6170471
Effects of Hand Gestures on Auditory Learning of Second-Language Vowel Length Contrasts
Authors: Hirata Yukari , Kelly Spencer D. , Huang Jessica , Manansala Michael
Published: August 2014

Purpose

Research has shown that hand gestures affect comprehension and production of speech at semantic, syntactic, and pragmatic levels for both native language and second language (L2). This study investigated a relatively less explored question: Do hand gestures influence auditory learning of an L2 at the segmental phonology level?

Method

To examine auditory learning of phonemic vowel length contrasts in Japanese, 88 native English-speaking participants took an auditory test before and after one of the following 4 types of training in which they (a) observed an instructor in a video speaking Japanese words while she made syllabic-rhythm hand gesture, (b) produced this gesture with the instructor, (c) observed the instructor speaking those words and her moraic-rhythm hand gesture, or (d) produced the moraic-rhythm gesture with the instructor.

Results

All of the training types yielded similar auditory improvement in identifying vowel length contrast. However, observing the syllabic-rhythm hand gesture yielded the most balanced improvement between word-initial and word-final vowels and between slow and fast speaking rates.

Conclusions

The overall effect of hand gesture on learning of segmental phonology is limited. Implications for theories of hand gesture are discussed in terms of the role it plays at different linguistic levels.
Density optimisation of generator matrices of quasi‐cyclic low‐density parity‐check codes and their rank analysis
Authors: Zhang Mu , Huang Qin , Wang Zulin , Yuan Shuai , Liu Zhe
Published: August 2014

The efficient encoding of quasi‐cyclic (QC) low‐density parity‐check (LDPC) codes is based on generator matrices in systematic‐circulant (SC) form. The cost of the encoders of QC‐LDPC codes mainly depends on the number of non‐zero entries in the SC generator matrices. This study introduces a novel construction of SC generator matrices based on matrix transformations via Galois Fourier transform. By revealing the structure of SC generator matrices in the transform domain, an algorithm is proposed to reduce the density of the generator matrices of QC‐LDPC codes. Furthermore, a tight upper bound on ranks of QC matrices is derived. Based on the bound, rank distributions of parity‐check matrices and generator matrices in the transform domain illustrate the efficiency of the proposed algorithm. Simulation results show that the density of their SC generator matrices can be significantly decreased with moderate computational complexity.
Analysis and modelling of a novel compact rectenna for indoor applications
Authors: Yadav Rakesh Kumar , Das Sushrut , Yadava Ram Lal
Published: August 2014

Rectenna can be used for remotely charging the rechargeable batteries, commonly used for powering wireless sensors in buildings, with the help of a dedicated RF source. However, in such a process, the effective path loss reduces the RF power level on rectenna which lowers the RF‐to‐DC conversion efficiency of the system. This study therefore focuses on the design and analysis of an efficient integrated rectifier‐antenna (rectennas) for indoor applications. In this proposed study, first a pentagonal antenna is designed at 5 GHz using Ansoft HFSS simulation. The obtained results show that the antenna resonates at two more frequencies, 10.7 and 14.2 GHz, other than the designed frequency. In order to eliminate the signals received by the antenna at these frequencies, a low‐pass filter cornered around 5 GHz is designed and integrated with the antenna. As a result, the integrated structure reveals a return loss of around 15 dB at 5 GHz. Next for rectification purpose, a Schottky diode is characterised at 5 GHz. The proposed antenna structure is then matched to the optimal complex impedance of the diode circuit. Consequently the RF–DC conversion efficiency of the rectenna is found to be 46%.
Finite‐time energy‐to‐peak filtering for Markov jump repeated scalar non‐linear systems with packet dropouts
Authors: Shen Hao , Wu Zheng‐Guang , Park Ju H.
Published: August 2014

This study is concerned with the finite‐time energy‐to‐peak filtering problem for Markov jump repeated scalar non‐linear systems with packet dropouts. The packet dropout phenomenon occurs in a random way and is modelled by a stochastic variable satisfying the Bernoulli distribution. The purpose of the study is to design a filter such that the resulting filtering error system is stochastically finite‐time bounded, and a prescribed energy‐to‐peak performance level is achieved over a finite time interval. By using the mode‐dependent diagonally dominant Lyapunov function approach, some strict linear matrix inequality‐based conditions are established for the existence of an admissible filter, and a corresponding explicit parameterisation of such a filter is obtained. Finally, a numerical example with simulation is presented to demonstrate the effectiveness of our proposed approach.
Policy to cope with deadlocks and livelocks for flexible manufacturing systems using the max′‐controlled new smart siphons
Authors: Li Shaoyong , An Aimin , Wu Hongmei , Hou Caiqin , Cai Ying , Han Xilian , Wang Ying
Published: August 2014

Both deadlocks and livelocks can result in the serious problems in running process of a flexible manufacturing system (FMS). This study proposes an iterative control policy for an FMS modelled with Petri nets on the basis of a combination of revised mixed integer programming and the concept of max′‐controlled siphon, which can not only solve the smart siphons associated with deadlocks and livelocks in Petri nets directly, but also make them max′‐controlled. Accordingly, an original Petri net system with deadlocks and livelocks can be turned into the live controlled one with a simple structure, and meanwhile no smart siphons can be found in it. It lays foundations for further analysis and control on deadlocks and livelocks. Compared with the existing methods in the literature, the proposed one is more general and effective. A theoretical analysis and several examples are given to demonstrate its efficiency and practical potentials.
Decomposition approach to exponential synchronisation for a class of non‐linear singularly perturbed complex networks
Authors: Cai Chenxiao , Wang Zidong , Xu Jing , Alsaedi Ahmed
Published: August 2014

This study is concerned with the globally exponential synchronisation problem for a class of non‐linear singularly perturbed complex networks where all nodes possess the same structure and properties. The addressed global synchronisation problem is converted into the one for two lower‐order sub‐networks, namely, a non‐linear slow sub‐network and a linear fast sub‐network, which are obtained by using the classical singular perturbation decomposition method. The network topology is directed and weighted, which means that the coupling configuration matrix is allowed to be asymmetric. By using the Lyapunov functional method and the Kronecker product technique, sufficient conditions are obtained under which the synchronisation is achieved, respectively, for the two sub‐networks and the original complex network. These conditions can be easily verified by using the semi‐definite programming method. A numerical example is finally simulated to validate the theoretical results and the effectiveness of the proposed synchronisation scheme.
Efficient image sharpening and denoising using adaptive guided image filtering
Authors: Pham Cuong Cao , Jeon Jae Wook
Published: August 2014

Enhancing the sharpness and reducing the noise of blurred, noisy images are crucial functions of image processing. Widely used unsharp masking filter‐based approaches suffer from halo‐artefacts and/or noise amplification, while noise‐ and halo‐free adaptive bilateral filtering (ABF) is computationally intractable. In this study, the authors present an efficient sharpening algorithm inspired by guided image filtering (GF). The author's proposed adaptive GF (AGF) integrates the shift‐variant technique, a part of ABF, into a guided filter to render crisp and sharpened outputs. Experiments showed the superiority of their proposed algorithm to existing algorithms. The proposed AGF sharply enhances edges and textures without causing halo‐artefacts or noise amplification, and it is efficiently implemented using a fast linear‐time algorithm.
Locally principal component analysis based on L1‐norm maximisation
Authors: Lin Guanyou , Tang Nianzu , Wang Haixian
Published: August 2014

Locally principal component analysis (LPCA) is a popular method of dimensionality reduction, which takes locality of data points into account. In this study, by using the L1‐norm instead of the L2‐norm in LPCA, the authors introduce a new formulation of LPCA based on the L1‐norm maximisation, referred to as LPCA‐L1. Compared with the conventional L2‐norm LPCA, the proposed LPCA‐L1 approach is more robust to outliers. Experiments of classification and recognition on the UCI, Yale and ORL data sets confirm the effectiveness of the proposed method.
Local brightness adaptive image colour enhancement with Wasserstein distance
Authors: Wang Liqian , Xiao Liang , Liu Hongyi , Wei Zhihui
Published: August 2014

Colour image enhancement is an important preprocessing phase of many image analysis tasks such as image segmentation, pattern recognition and so on. This study presents a new local brightness adaptive variational model using Wasserstein distance for colour image enhancement. Under the perceptually inspired variational framework, the proposed energy functional consists of an improved contrast energy term and a Wasserstein dispersion energy term. To better adjust image dynamic range, the authors propose a local brightness adaptive contrast energy term using the average brightness of image local patch as the local brightness indicator. To restore image true colours, a Wasserstein distance‐based dispersion energy term is used to measure the statistical similarity between the original image and the enhanced image. The proposed energy functional is minimised by using a gradient descent algorithm. Two objective measures are used to quantitatively measure the enhancement quality. Experimental results demonstrate the efficiency of the proposed model for removing colour cast and haze, enhancing contrast, recovering details and equalising low key images.
Exploring the heavy goods vehicle fleet behaviour through simulations: notes from the German toll system
Authors: Pfitzinger Bernd , Macos Dragan , Jestädt Thomas
Published: August 2014

The automatic German toll system is both a software‐intensive system – relying on the on‐board units to collect the toll charges due – and a socio‐technical system – the user can influence the system behaviour. The overall dynamic system behaviour emerges both from the technical implementation of the system and the users’ interaction with the system limiting the effectiveness of common software engineering practices. Simulations are an additional tool to reduce the operational risks and to improve the performance of system development projects. We have developed a realistic microscopic discrete event simulation model of the automatic tolling processes to simulate the overall system behaviour at a scale of 1:1. Taking this model our research investigates the effect of the HGV fleet behaviour on the dynamic system behaviour. To that end the system simulation model is accompanied by a separate model of the HGV driving patterns.
Compact slot antenna for wireless local area network 2.4/5.2/5.8 GHz applications
Authors: Sim Chow‐Yen‐Desmond , Shih Yuan‐Kai , Chang Ming‐Hsuan
Published: August 2014

This investigation presents a compact (30 × 30 mm2) microstrip‐fed slot antenna design for dualband wireless local area network (2.4 / 5.2 / 5.8 GHz) applications. Two dissimilar inverted L‐shaped slots and a mushroom‐shaped slot were loaded into the antenna. By feeding these slots with a microstrip‐fed line that was analogous to a sling hook, three resonant modes were excited at exactly 2.44, 5.25 and 5.8 GHz, which formed lower and upper operating bands with 10 dB bandwidths of 5.67 and 25.14%, respectively. The process of designing the proposed antenna is explicitly shown, and parametric studies were carried out by simulation. Typical experimental measurements were also conducted and compared with the simulated results.
Phase‐steered fixed beams in one and two‐dimensional scan space for substrate‐integrated radar and radio systems at 60 GHz
Authors: Guntupalli Ajay Babu , Wu Ke
Published: August 2014

In this work, one‐dimensional (1D) and 2D scan phased array antennas for 60 GHz radio communication and radar sensing systems are proposed, studied and experimentally validated in the substrate‐integrated waveguide technology. A linearly polarised phased array with 1D scanned beams in the first part of this study and a right‐hand circularly polarised (CP) array with 2D scanned beams in the second part are presented and discussed in detail. In the demonstrated 1D phased array, dielectric rod antenna is used as radiating elements to form 1 × 4 linear array and then a planar Butler matrix is integrated along with the array to obtain phase‐steered beams. In the 2D phased array, CP radiating elements are used to form 2 × 4 array and then a folded Butler matrix is used to feed the CP array. Simulated and measured characteristics of these two phased array antenna radiation parameters are compared. The proposed phased arrays can be integrated into 60 GHz and other millimetre‐wave radar and radio systems as an integrated antenna front‐end.
Reduced functional dependence graphs
Authors: Xu Xiaoli , Thakor Satyajit , Guan Yong Liang
Published: August 2014

Functional dependence graph (FDG) is an important class of directed graph that captures the functional dependence relationships of a set of random variables and it is frequently used in characterising network coding capacity bounds. Since the computational complexity of such bounds usually grows exponentially with the order of the FDG, it is desirable to find an FDG with the smallest size possible. To this end, some systematic graph reduction techniques are introduced in this study. The first reduction technique is performed on the original networks, where ‘non‐essential’ edges are identified and eliminated. This is equivalent to node reduction in the corresponding FDG. Besides, the authors show that certain edges in the FDG may also be removed without affecting the functional dependence relationships of the random variables. The removal of the edges in the FDG may create new opportunities to reduce the order of the FDG. It is proved that the reduced FDGs give the same network coding capacity region/bounds as that obtained by using the original FDGs and yet much less computation is required.
Throughput‐based rate adaptation algorithm for IEEE 802.11 vehicle networks
Authors: Ilori Ayoade , Tang Zuoyin , He Jianhua , Li Yue
Published: August 2014

A key problem with IEEE 802.11 technology is adaptation of the transmission rates to the changing channel conditions, which is more challenging in vehicular networks. Although rate adaptation problem has been extensively studied for static residential and enterprise network scenarios, there is little work dedicated to the IEEE 802.11 rate adaptation in vehicular networks. Here, the authors are motivated to study the IEEE 802.11 rate adaptation problem in infrastructure‐based vehicular networks. First of all, the performances of several existing rate adaptation algorithms under vehicle network scenarios, which have been widely used for static network scenarios, are evaluated. Then, a new rate adaptation algorithm is proposed to improve the network performance. In the new rate adaptation algorithm, the technique of sampling candidate transmission modes is used, and the effective throughput associated with a transmission mode is the metric used to choose among the possible transmission modes. The proposed algorithm is compared to several existing rate adaptation algorithms by simulations, which shows significant performance improvement under various system and channel configurations. An ideal signal‐to‐noise ratio (SNR)‐based rate adaptation algorithm in which accurate channel SNR is assumed to be always available is also implemented for benchmark performance comparison.
Reducing the power consumption of hose‐model networks with bundled links
Authors: Ba Seydou , Ouédraogo Ihsen Aziz , Oki Eiji
Published: August 2014

Given the exponential growth in telecommunication networks, more and more attention is being paid to their share in the global energy consumption. Reducing networks’ power consumption has become a major concern. However, the often over‐provisioned wired core network is still overlooked. In core networks, pairs of routers are typically connected by multiple physical cables that form one logical bundled link participating in the intra‐domain routing protocol. To reduce the energy consumption of core networks with bundled cables, the authors propose a scheme to deactivate the maximum possible number of cables, and associated equipment, while considering hose‐model traffic. A similar approach has been presented for the pipe model, where the exact traffic matrix is assumed to be known. Owing to traffic uncertainty, however, it is difficult for network operators to have exact knowledge of the traffic matrix. This traffic uncertainty can be avoided by using the hose model, which specifies only the upper bounds of the egress/ingress traffic from/to a node. They introduce a mixed integer linear problem formulation that yields the optimal solution and a more practical and near optimal heuristic algorithm for large networks. The author's performance evaluation results show that it offers up to 50% power reduction.
Angle-specific transparent conducting electrodes with metallic gratings
Authors: Rivolta N. X. A. , Maes B.
Published: August 2014

Transparent conducting electrodes, which are not made from indium tin oxide, and which display a strong angular dependence are useful for various technologies. Here, we introduce a tilted silver grating that combines a large conductance with a strong and angle-specific transmittance. When the light incidence angle matches the tilt angle of the grating, transmittance is close to the maximum along a very broadband range. We explain the behavior through simulations that show in detail the plasmonic and interference effects at play.
Magnetic properties of Sm-Co thin films grown on MgO(100) deposited from a single alloy target
Authors: Verhagen T. G. A. , Boltje D. B. , van Ruitenbeek J. M. , Aarts J.
Published: August 2014

We have grown epitaxial Sm-Co thin films by sputter deposition from a single alloy target with a nominal SmCo5 composition on Cr(100)-buffered MgO(100) single-crystal substrates. By varying the Ar gas pressure, we can change the composition of the film from a SmCo5-like to a Sm2Co7-like phase. The composition, crystal structure, morphology, and magnetic properties of these films have been determined using Rutherford Backscattering, X-ray diffraction, and magnetization measurements. We find that we can grow films with, at room temperature, coercive fields as high as 3.3 T, but with a remanent magnetization which is lower than can be expected from the texturing. This appears to be due to the Sm content of the films, which is higher than expected from the content of the target, even at the lowest possible sputtering pressures. Moreover, we find relatively large variations of film properties using targets of nominally the same composition. At low temperatures, the coercive fields increase, as expected for these hard magnets, but in the magnetization, we observe a strong background signal from the paramagnetic impurities in the MgO substrates.
Monte-Carlo simulation of noise in hard X-ray Transmission Crystal Spectrometers: Identification of contributors to the background noise and shielding optimization
Authors: Thfoin I. , Reverdin C. , Hulin S. , Szabo C. I. , Bastiani-Ceccotti S. , Batani D. , Brambrink E. , Koenig M. , Duval A. , Leboeuf X. , Lecherbourg L. , Rossé B. , Morace A. , Santos J. J. , Vaisseau X. , Fourment C. , Giuffrida L. , Nakatsutsumi M.
Published: August 2014

Transmission crystal spectrometers (TCS) are used on many laser facilities to record hard X-ray spectra. During experiments, signal recorded on imaging plates is often degraded by a background noise. Monte-Carlo simulations made with the code GEANT4 show that this background noise is mainly generated by diffusion of MeV electrons and very hard X-rays. An experiment, carried out at LULI2000, confirmed that the use of magnets in front of the diagnostic, that bent the electron trajectories, reduces significantly this background. The new spectrometer SPECTIX (Spectromètre PETAL à Cristal en TransmIssion X), built for the LMJ/PETAL facility, will include this optimized shielding.
Fringe jump analysis and implementation of polarimetry on the ASDEX Upgrade DCN interferometer
Authors: Mlynek A. , Casali L. , Ford O. , Eixenberger H. ,   ASDEX Upgrade Team
Published: August 2014

The ASDEX Upgrade tokamak is equipped with a 5-channel DCN interferometer with a probing wavelength of 195 μm. Up to now, phase measurement and density calculation have been accomplished by hard-wired phase counting electronics. Meanwhile, a fast digitizer has been installed which acquires the raw signals. That way, the various causes of counting errors by integer multiples of 2π, so-called fringe jumps, can be analyzed, and phase reconstruction schemes based on digital signal processing can be developed. In addition, a prototype polarimeter setup has been installed on one channel and allows for measurement of the Faraday rotation experienced by the probing beam.
Controlling orbital-selective Kondo effects in a single molecule through coordination chemistry
Authors: Tsukahara Noriyuki , Minamitani Emi , Kim Yousoo , Kawai Maki , Takagi Noriaki
Published: August 2014

Iron(II) phthalocyanine (FePc) molecule causes novel Kondo effects derived from the unique electronic structure of multi-spins and multi-orbitals when attached to Au(111). Two unpaired electrons in the dz2 and the degenerate dπ orbitals are screened stepwise, resulting in spin and spin+orbital Kondo effects, respectively. We investigated the impact on the Kondo effects of the coordination of CO and NO molecules to the Fe2+ ion as chemical stimuli by using scanning tunneling microscopy (STM) and density functional theory calculations. The impacts of the two diatomic molecules are different from each other as a result of the different electronic configurations. The coordination of CO converts the spin state from triplet to singlet, and then the Kondo effects completely disappear. In contrast, an unpaired electron survives in the molecular orbital composed of Fe dz2 and NO 5σ and 2π* orbitals for the coordination of NO, causing a sharp Kondo resonance. The isotropic magnetic response of the peak indicates the origin is the spin Kondo effect. The diatomic molecules attached to the Fe2+ ion were easily detached by applying a pulsed voltage at the STM junction. These results demonstrate that the single molecule chemistry enables us to switch and control the spin and the many-body quantum states reversibly.
Many-body effect in ion binding to RNA
Authors: Zhu Yuhong , Chen Shi-Jie
Published: August 2014

Ion-mediated electrostatic interactions play an important role in RNA folding stability. For a RNA in a solution with higher Mg2+ ion concentration, more counterions in the solution can bind to the RNA, causing a strong many-body coupling between the bound ions. The many-body effect can change the effective potential of mean force between the tightly bound ions. This effect tends to dampen ion binding and lower RNA folding stability. Neglecting the many-body effect leads to a systematic error (over-estimation) of RNA folding stability at high Mg2+ ion concentrations. Using the tightly bound ion model combined with a conformational ensemble model, we investigate the influence of the many-body effect on the ion-dependent RNA folding stability. Comparisons with the experimental data indicate that including the many-body effect led to much improved predictions for RNA folding stability at high Mg2+ ion concentrations. The results suggest that the many-body effect can be important for RNA folding in high concentrations of multivalent ions. Further investigation showed that the many-body effect can influence the spatial distribution of the tightly bound ions and the effect is more pronounced for compact RNA structures and structures prone to the formation of local clustering of ions.
On energy conservation in extended magnetohydrodynamics
Authors: Kimura Keiji , Morrison P. J.
Published: August 2014

A systematic study of energy conservation for extended magnetohydrodynamic models that include Hall terms and electron inertia is performed. It is observed that commonly used models do not conserve energy in the ideal limit, i.e., when viscosity and resistivity are neglected. In particular, a term in the momentum equation that is often neglected is seen to be needed for conservation of energy.
Coherence imaging of scrape-off-layer and divertor impurity flows in the Mega Amp Spherical Tokamak (invited)
Authors: Silburn S. A. , Harrison J. R. , Howard J. , Gibson K. J. , Meyer H. , Michael C. A. , Sharples R. M.
Published: August 2014

A new coherence imaging Doppler spectroscopy diagnostic has been deployed on the UK’s Mega Amp Spherical Tokamak for scrape-off-layer and divertor impurity flow measurements. The system has successfully obtained 2D images of C III, C II, and He II line-of-sight flows, in both the lower divertor and main scrape-off-layer. Flow imaging has been obtained at frame rates up to 1 kHz, with flow resolution of around 1 km/s and spatial resolution better than 1 cm, over a 40° field of view. C III data have been tomographically inverted to obtain poloidal profiles of the parallel impurity flow in the divertor under various conditions. In this paper we present the details of the instrument design, operation, calibration, and data analysis as well as a selection of flow imaging results which demonstrate the diagnostic's capabilities.
A radial collimator for a time-of-flight neutron spectrometer
Authors: Stone M. B. , Niedziela J. L. , Loguillo M. J. , Overbay M. A. , Abernathy D. L.
Published: August 2014

We have engineered and installed a radial collimator for use in the scattered beam of a neutron time-of-flight spectrometer at a spallation neutron source. The radial collimator may be used with both thermal and epithermal neutrons, reducing the detected scattering intensity due to material outside of the sample region substantially. The collimator is located inside of the sample chamber of the instrument, which routinely cycles between atmospheric conditions and cryogenic vacuum. The oscillation and support mechanism of the collimator allow it to be removed from use without breaking vacuum. We describe here the design and characterization of this radial collimator.
Bi-directional Alfvén cyclotron instabilities in the mega-amp spherical tokamak
Authors: Sharapov S. E. , Lilley M. K. , Akers R. , Ayed N. Ben , Cecconello M. , Cook J. W. S. , Cunningham G. , Verwichte E. ,   MAST Team
Published: August 2014

Alfvén cyclotron instabilities excited by velocity gradients of energetic beam ions were investigated in MAST experiments with super-Alfvénic neutral beam injection over a wide range of toroidal magnetic fields from ∼0.34 T to ∼0.585 T. In MAST discharges with high magnetic field, a discrete spectrum of modes in the sub-cyclotron frequency range is excited toroidally propagating counter to the beam and plasma current (toroidal mode numbers n < 0). At lower magnetic field ≤0.45 T, a discrete spectrum of Compressional Alfvén Eigenmodes (CAEs) with n > 0 arises, in addition to the modes with n < 0. At lowest magnetic fields, the CAEs with n > 0 become dominant, they are observed in frequency range from ∼250 kHz for n=1 to ∼3.5 MHz for n=15, well above the on-axis ion cyclotron frequency (∼2.5 MHz). The data is interpreted in terms of normal and anomalous Doppler resonances modified by magnetic drift terms due to inhomogeneity and curvature of the magnetic field. A Hall MHD model is applied for computing the eigenfrequencies and the spatial mode structure of CAEs and a good agreement with the experimental frequencies is found.
Large-eddy simulation of turbulent cavitating flow in a micro channel
Authors: Egerer Christian P. , Hickel Stefan , Schmidt Steffen J. , Adams Nikolaus A.
Published: August 2014

Large-eddy simulations (LES) of cavitating flow of a Diesel-fuel-like fluid in a generic throttle geometry are presented. Two-phase regions are modeled by a parameter-free thermodynamic equilibrium mixture model, and compressibility of the liquid and the liquid-vapor mixture is taken into account. The Adaptive Local Deconvolution Method (ALDM), adapted for cavitating flows, is employed for discretizing the convective terms of the Navier-Stokes equations for the homogeneous mixture. ALDM is a finite-volume-based implicit LES approach that merges physically motivated turbulence modeling and numerical discretization. Validation of the numerical method is performed for a cavitating turbulent mixing layer. Comparisons with experimental data of the throttle flow at two different operating conditions are presented. The LES with the employed cavitation modeling predicts relevant flow and cavitation features accurately within the uncertainty range of the experiment. The turbulence structure of the flow is further analyzed with an emphasis on the interaction between cavitation and coherent motion, and on the statistically averaged-flow evolution.
Dissociative chemisorption of methane on metal surfaces: Tests of dynamical assumptions using quantum models and ab initio molecular dynamics
Authors: Jackson Bret , Nattino Francesco , Kroes Geert-Jan
Published: August 2014

The dissociative chemisorption of methane on metal surfaces is of great practical and fundamental importance. Not only is it the rate-limiting step in the steam reforming of natural gas, the reaction exhibits interesting mode-selective behavior and a strong dependence on the temperature of the metal. We present a quantum model for this reaction on Ni(100) and Ni(111) surfaces based on the reaction path Hamiltonian. The dissociative sticking probabilities computed using this model agree well with available experimental data with regard to variation with incident energy, substrate temperature, and the vibrational state of the incident molecule. We significantly expand the vibrational basis set relative to earlier studies, which allows reaction probabilities to be calculated for doubly excited initial vibrational states, though it does not lead to appreciable changes in the reaction probabilities for singly excited initial states. Sudden models used to treat the center of mass motion parallel to the surface are compared with results from ab initio molecular dynamics and found to be reasonable. Similar comparisons for molecular rotation suggest that our rotationally adiabatic model is incorrect, and that sudden behavior is closer to reality. Such a model is proposed and tested. A model for predicting mode-selective behavior is tested, with mixed results, though we find it is consistent with experimental studies of normal vs. total (kinetic) energy scaling. Models for energy transfer into lattice vibrations are also examined.
Electromagnetic nonlinear gyrokinetics with polarization drift
Authors: Duthoit F.-X. , Hahm T. S. , Wang Lu
Published: August 2014

A set of new nonlinear electromagnetic gyrokinetic Vlasov equation with polarization drift and gyrokinetic Maxwell equations is systematically derived by using the Lie-transform perturbation method in toroidal geometry. For the first time, we recover the drift-kinetic expression for parallel acceleration [R. M. Kulsrud, in Basic Plasma Physics, edited by A. A. Galeev and R. N. Sudan (North-Holland, Amsterdam, 1983)] from the nonlinear gyrokinetic equations, thereby bridging a gap between the two formulations. This formalism should be useful in addressing nonlinear ion Compton scattering of intermediate-mode-number toroidal Alfvén eigenmodes for which the polarization current nonlinearity [T. S. Hahm and L. Chen, Phys. Rev. Lett. 74, 266 (1995)] and the usual finite Larmor radius effects should compete.
Convective radial energy flux due to resonant magnetic perturbations and magnetic curvature at the tokamak plasma edge
Authors: Marcus F. A. , Beyer P. , Fuhr G. , Monnier A. , Benkadda S.
Published: August 2014

With the resonant magnetic perturbations (RMPs) consolidating as an important tool to control the transport barrier relaxation, the mechanism on how they work is still a subject to be clearly understood. In this work, we investigate the equilibrium states in the presence of RMPs for a reduced MHD model using 3D electromagnetic fluid numerical code with a single harmonic RMP (single magnetic island chain) and multiple harmonics RMPs in cylindrical and toroidal geometry. Two different equilibrium states were found in the presence of the RMPs with different characteristics for each of the geometries used. For the cylindrical geometry in the presence of a single RMP, the equilibrium state is characterized by a strong convective radial thermal flux and the generation of a mean poloidal velocity shear. In contrast, for toroidal geometry, the thermal flux is dominated by the magnetic flutter. For multiple RMPs, the high amplitude of the convective flux and poloidal rotation are basically the same in cylindrical geometry, but in toroidal geometry the convective thermal flux and the poloidal rotation appear only with the islands overlapping of the linear coupling between neighbouring poloidal wavenumbers m, m – 1, and m + 1.
Active surfaces: Ferrofluid-impregnated surfaces for active manipulation of droplets
Authors: Khalil Karim S. , Mahmoudi Seyed Reza , Abu-dheir Numan , Varanasi Kripa K.
Published: August 2014

Droplet manipulation and mobility on non-wetting surfaces is of practical importance for diverse applications ranging from micro-fluidic devices, anti-icing, dropwise condensation, and biomedical devices. The use of active external fields has been explored via electric, acoustic, and vibrational, yet moving highly conductive and viscous fluids remains a challenge. Magnetic fields have been used for droplet manipulation; however, usually, the fluid is functionalized to be magnetic, and requires enormous fields of superconducting magnets when transitioning to diamagnetic materials such as water. Here we present a class of active surfaces by stably impregnating active fluids such as ferrofluids into a textured surface. Droplets on such ferrofluid-impregnated surfaces have extremely low hysteresis and high mobility such that they can be propelled by applying relatively low magnetic fields. Our surface is able to manipulate a variety of materials including diamagnetic, conductive and highly viscous fluids, and additionally solid particles.
Pilot-wave hydrodynamics in a rotating frame: Exotic orbits
Authors: Oza Anand U. , Wind-Willassen Øistein , Harris Daniel M. , Rosales Rodolfo R. , Bush John W. M.
Published: August 2014

We present the results of a numerical investigation of droplets walking on a rotating vibrating fluid bath. The drop's trajectory is described by an integro-differential equation, which is simulated numerically in various parameter regimes. As the forcing acceleration is progressively increased, stable circular orbits give way to wobbling orbits, which are succeeded in turn by instabilities of the orbital center characterized by steady drifting then discrete leaping. In the limit of large vibrational forcing, the walker's trajectory becomes chaotic, but its statistical behavior reflects the influence of the unstable orbital solutions. The study results in a complete regime diagram that summarizes the dependence of the walker's behavior on the system parameters. Our predictions compare favorably to the experimental observations of Harris and Bush [“Droplets walking in a rotating frame: from quantized orbits to multimodal statistics,” J. Fluid Mech. 739, 444–464 (2014)].
Note: Sub-Kelvin refrigeration with dry-coolers on a rotating system
Authors: Oguri S. , Ishitsuka H. , Choi J. , Kawai M. , Tajima O.
Published: August 2014

We developed a cryogenic system on a rotating table that achieves sub-Kelvin conditions. The cryogenic system consists of a helium sorption cooler and a pulse tube cooler in a cryostat mounted on a rotating table. Two rotary-joint connectors for electricity and helium gas circulation enable the coolers to be operated and maintained with ease. We performed cool-down tests under a condition of continuous rotation at 20 rpm. We obtained a temperature of 0.23 K with a holding time of more than 24 h, thus complying with catalog specifications. We monitored the system's performance for four weeks; two weeks with and without rotation. A few-percent difference in conditions was observed between these two states. Most applications can tolerate such a slight difference. The technology developed is useful for various scientific applications requiring sub-Kelvin conditions on rotating platforms.
The electrically and magnetically controllable random laser from dye-doped liquid crystals
Authors: Ye Lihua , Liu Bo , Zhao Chong , Wang Yan , Cui Yiping , Lu Yanqing
Published: August 2014

The electrically and magnetically controllable random laser from dye-doped liquid crystals (LCs) was studied. The rubbing-alignment of the polyimide in the LC cell influenced the threshold voltage and the response time of the electrically controllable random laser. When the applied electric field was increased, the response time of the random laser decreased. The magnetically controllable random laser was studied in the hollow fiber structure, of which the response time was less than 1 s.
Effect of oxygen doping in microcrystalline SiGe p-i-n solar cells
Authors: Bidiville A. , Matsui T. , Kondo M.
Published: August 2014

The effect of doping with oxygen the microcrystalline silicon-germanium absorber layer of single-junction p-i-n solar cells has been studied. In parallel, the absorber layer quality was measured by depositing absorber layers directly on glass and measuring their electrical properties. By doping the absorber layer with the optimum oxygen concentration (about 1.4×1019 cm−3), an increase in short-circuit current density of almost 4 mA/cm2 was achieved in 3 μm thick p-i-n solar cell. This effect is attributed to the oxygen doping compensating the space charges caused by the germanium dangling bonds rather than the direct defect passivation, as no drastic change in layer quality was measured.
Coplanar waveguide based ferromagnetic resonance in ultrathin film magnetic nanostructures: Impact of conducting layers
Authors: Głowiński H. , Schmidt M. , Gościańska I. , Ansermet J-Ph. , Dubowik J.
Published: August 2014

We report broadband ferromagnetic resonance measurements based on a coplanar waveguide (CPW) of ultrathin magnetic film structures that comprise in-plane/out-of-plane decoupled layers deposited on nonmagnetic buffer layers of various thickness and diverse sheet resistance values. We show that the excitation of the fundamental mode can be enhanced up to 10 times in the structures deposited on buffer layers with a low sheet resistance compared to what it is in the structures deposited on thin or weakly conducting buffer layers. The results are analyzed in terms of shielding of the electromagnetic field of CPW by the conducting buffer layers.
A slip model for rarefied gas flows above a moving surface with mass transfer
Authors: Wu Lin
Published: August 2014

A slip velocity boundary condition for rarefied gas flows above a moving surface with net mass transfer in-between is derived from kinetic theory. Tangential momentum transfer rate contribution from mass transfer of gas molecules at a moving surface is discovered to introduce an additional gas slip velocity, which is linearly proportional to the mass transfer rate and the average tangential velocity of gas molecules entering/leaving the gas flow domain through the surface. The mass transfer induced gas slip velocity component is very different from the previously studied slip velocity component due to velocity shearing. A generalized lubrication equation for rarefied gas flow is obtained from the derived slip velocity boundary condition. The slip velocity boundary condition and the lubrication equation are suitable for rarefied gas flows at arbitrary Knudsen number with mass transfer on bounding surfaces. Mass transfer such as evaporation/condensation and its induced gas slip velocity at moving surfaces are demonstrated to be able to significantly change gas flow pressure and velocity profiles, and thus have a dominant effect on micro/nanoscale gas flows with non-negligible mass transfer on bounding surfaces.
Communication: On nucleation statistics in small systems
Authors: Shneidman Vitaly A.
Published: August 2014

Non-stationary random formation of stable nuclei from a small metastable system is considered. Distribution of waiting times to observe the first nucleus is examined, and it is shown that the steady-state nucleation rate is given by inverse of the standard deviation, which is independent of the post-critical size n where the nucleus is detected. The mean time, on the other hand, is n-sensitive and contains additional information on transient nucleation and growth effects. The method is applied to Monte Carlo data on nucleation in a cold two-dimensional Ising ferromagnet with Metropolis dynamics, where nucleation rates obtained earlier from low-temperature cluster expansions can provide a strict independent test.
Structure determination of the intermediate phase of PbSe using experiments and calculations
Authors: Li Yanchun , Li Gong , Lin Chuanlong , Li Xiaodong , Liu Jing
Published: August 2014

The pressure-induced structure transitions of PbSe were investigated at pressures up to 50 GPa in diamond anvil cells using synchrotron powder and single-crystal X-ray diffraction methods. A phase transition from the initial NaCl-type structure to an intermediate phase was observed at 4.8 GPa, followed by another phase transition to a CsCl-type structure at 19.5 GPa, which is in agreement with previous reports. In addition, the NaCl-type, Pnma, Cmcm, and CsCl-type structures of PbSe were investigated using density functional theory calculations. Based on the experiments and calculations, the intermediate phase has Pnma symmetry rather than Cmcm symmetry, as has been previously suggested. Some of the diffraction peaks of the Pnma phase were broad in the high-pressure experiments, but were determined to be single diffraction peaks rather than the overlap of multiple peaks by different experimental methods. The Pnma and Cmcm structures of PbSe were compared. It was found that two structures were very similar, and it was difficult to distinguish one power diffraction pattern from the other.
Time-domain response of atomically thin MoS2 nanomechanical resonators
Authors: van Leeuwen R. , Castellanos-Gomez A. , Steele G. A. , van der Zant H. S. J. , Venstra W. J.
Published: August 2014

We measure the energy relaxation rate of single- and few-layer molybdenum disulphide (MoS2) nanomechanical resonators by detecting the resonator ring-down. Recent experiments on these devices show a remarkably low quality (Q)-factor when taking spectrum measurements at room temperature. The origin of the low spectral Q-factor is an open question, and it has been proposed that besides dissipative processes, frequency fluctuations contribute significantly to the resonance line-width. The spectral measurements performed thus far however, do not allow one to distinguish these two processes. Here, we use time-domain measurements to quantify the dissipation. We compare the Q-factor obtained from the ring-down measurements to those obtained from the thermal noise spectrum and from the frequency response of the driven device. In few-layer and single-layer MoS2 resonators, the two are in close agreement, which demonstrates that the spectral line-width in MoS2 membranes at room temperature is limited by dissipation, and that excess spectral broadening plays a negligible role.
Strongly localized modes in one-dimensional defect-free magnonic quasicrystals
Authors: Chen C. H. , Qiu R. Z. , Chang C. H. , Hsueh W. J.
Published: August 2014

Signal storage in magnonic quasicrystals using a slow spin-wave mode, rather than the quasinormal mode of traditional periodic magnonic crystals, is proposed, which is analogous to the slow light mode in the field of optics. Compared to traditional materials, richer and more wavelength-selective sharp resonances are achieved using the quasicrystals with a fewer number of layers, because of the peculiar fractal transmission spectra of quasicrystals. The number of sharp resonance and the quality factor for the sharp resonances in the transmission spectra also increases as the generation order of the magnonic quasicrystal increases. This generic nature allows the storage of signals using spin wave, for a wide range of quasiperiodic systems.