bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimal integral sliding mode control for a class of uncertain discrete‐time systems
Authors: Sun Nana , Niu Yugang , Chen Bei
Published: July 2013

This paper considers the problem of sliding mode control for a class of uncertain discrete‐time systems. Firstly, an optimal control law for the nominal system is derived to satisfy linear quadratic performance index. And then, an optimal integral sliding surface is designed to ensure the robustness for sliding dynamics. By combining with the discrete reaching law, the existence condition of the sliding mode is proved, and the bandwidth of the quasi‐sliding mode is given. It is shown that the present method utilizes a lower control gain to attain stronger robustness and eliminate the chattering. Finally, illustrative simulation results are provided. Copyright © 2013 John Wiley & Sons, Ltd.
Mechanical behavior of porous polysiloxane with micropores interconnected by microchannels
Authors: Hong Yifeng , Yao Donggang
Published: July 2013

A microsphere templating process was recently developed for fabrication of open‐cell porous elastomer. The material contained a unique cocontinuous structure having micropores interconnected by microchannels. In this work, a follow‐up study was conducted to investigate the mechanical behavior of such porous materials. Polysiloxane was chosen as a model material. The deformation characteristics and mechanical properties of the porous elastomer under tension and compression were then studied. For both tensile and compressive tests, the mechanical properties measured were found to largely deviate from those calculated by the additive rule assuming affine deformation. This nonaffine mechanics was further verified by microscopic observations. Cyclic loading and unloading tests were also performed to study the hysteresis of the material. In comparison with the solid elastomer, the hysteresis of the porous elastomer was considerably higher and more sensitive to the strain rate. An attempt was further made to fit the stress‐strain curve using existing hyperelastic models, and the results showed that the Arruda–Boyce model, in general, fit both the solid and porous polysiloxane very well. POLYM. ENG. SCI., 54:1512–1522, 2014. © 2013 Society of Plastics Engineers
A Geosynchronous Radiation‒belt Electron Empirical Prediction (GREEP) model
Authors: Kellerman A. C. , Shprits Y. Y. , Turner D. L.
Published: July 2013

Accurate forecast models of the near‒Earth radiation belt environment are of great importance to satellite operators and engineers, as the charged particles can be damaging to satellite hardware. The A Geosynchronous Radiation‒belt Electron Empirical Prediction (GREEP) model is presented in this study and utilized to predict the daily average of 1.8–3.5 MeV relativistic electron fluxes at Geostationary Earth Orbit (GEO), based upon propagated solar wind velocity (Vsw) and solar wind number density (n) measurements. The occurrence distributions of Vsw and n are used to normalize the distribution of flux with Vsw and n, respectively. A power law fit is applied to each probability distribution function, and the fitted values are dynamically combined with recent flux measurements from GEO and with fluxes from previous solar rotations to predict the future radiation belt environment at GEO. The model outperforms recent models in terms of forecast score for 1 day predictions, and it is found that the distribution of flux as a function of Vsw generally provides better predictions during the descending phase of the solar cycle than the distribution of flux as a function of density. The latter performs better near solar maximum. The GREEP model performs best in terms of forecast score also during the declining phase, and it provides further evidence of the importance of solar wind velocity in controlling high‒energy electron flux. During the descending phase, relativistic fluxes are typically the highest, and thus most damaging to spaceborne equipment, and pose a greater risk to humans in space.
Event‐related potentials affected by spatial frequencies of background visual pattern during a cognitive task
Authors: Kato Kazuo , Miura Osamu , Shikoda Arimitsu , Kuroki Tomohiro , Ishikawa Atsuo , Kobayashi Tetsuo
Published: July 2013

Spatial variation in luminance, which is one of the most important attributes of a visual image, may cause characteristic reactions in higher order brain functions. We aim to characterize the event‐related potentials (ERPs) associated with a cognitive task (simple addition) in terms of how they are influenced by the spatial frequencies of the background visual pattern. We use vertically striped visual stimuli with embedded numbers (0–9) and different spatial frequency characteristics (white noise, 1/f, 1/f2, and 1/f3). The subjects are instructed to perform two tasks: an addition task that involved adding numbers presented as visual stimuli, and a reference task wherein the numbers were not added. In ERPs averaged over four types of visual stimuli for the addition task, positive components peaking at latencies of 182 ms in the central and frontal areas and 360 ms in the parietal area are observed, and significant differences are found between ERPs for the addition and reference tasks. In the addition task, the 182‐ms latency component shows a larger positive amplitude for 1/f3 compared with other stimuli in the right parietal‐occipital‐temporal area (P4, T6, O2), and the 360‐ms latency component tends to show a larger positive amplitude for 1/f compared with other stimuli in the parietal‐central area (C3, P3, Pz). We conclude that spatial frequency characteristics influence ERPs associated with the retrieval of arithmetic data and certain neural activities that accompany simple forms of addition. © 2013 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.
Cross‐sectional area calculation for arbitrary shape in the image using star algorithm with Green's theorem
Authors: Esmaile Maher F. , Marhaban Mohammad H. , Mahmud Rozi , Saripan M. I.
Published: July 2013

Calculation of the cross‐sectional area is an important diagnostic tool in medical imaging modality. Curvature points arrangement (CPA) is an important step in the calculation, where the Star algorithm had been shown to be effective in segmenting the carotid artery. The algorithm however works under the assumption of circular or ellipsoid shapes, and the ability to determine its center of gravity is done by exploiting the features of equi‐space diameter of the circle. In this paper, a method of calculation of the cross‐sectional area of an arbitrary shape is discussed. The Star algorithm is modified to arrange the points of the object's edge through the CPA process in order to form a simple closed curve. Several rays are emanated from a point inside the region of interest with different angles to the far points within the segmented area. The cross‐sectional area is then calculated by using Green's theorem. To validate the concepts, several regular shaped images with different noise types (Gaussian, speckles, and salt and pepper) and ultrasound images are used in the experiments. The result shows that this method can calculate the cross‐sectional area with negligible error for an arbitrary object within the image and with different types of noises. © 2013 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.
Cardiac assessment in fetuses with right‐sided congenital diaphragmatic hernia: case–control study
Authors: DeKoninck P. , Richter J. , Van Mieghem T. , Van Schoubroeck D. , Allegaert K. , De Catte L. , Deprest J. A.
Published: July 2013

Objective

To evaluate cardiac anatomy and function in fetuses with right‐sided congenital diaphragmatic hernia (RCDH), and to compare these values with those of normal controls.

Methods

Fetal echocardiography was performed in 17 consecutive cases with isolated RCDH and 17 gestational age‐matched controls. Two‐dimensional measurements included ventricular and outflow tract diameters. Doppler ultrasound was used to measure the flow pattern in the ductus venosus and over the pulmonary and aortic valves, right and left ventricular myocardial performance index and the E/A wave ratio over the atrioventricular valves. Stroke volume, cardiac output and shortening fraction were calculated.

Results

Median gestational age at evaluation was 27.4 (interquartile range, 24.4–28.9) weeks. RCDH cases had a significantly smaller right ventricle and pulmonary valve diameter. Furthermore, stroke volume and cardiac output from the right ventricle were lower than in controls. Myocardial contractility, however, appeared normal.

Conclusions

Despite significantly reduced right ventricular dimensions and cardiac output, cardiac contractility was normal in a cohort of fetuses with RCDH. Copyright © 2013 ISUOG. Published by John Wiley & Sons Ltd.
Infantile exposure to lead and late‐age cognitive decline: Relevance to AD
Authors: Bihaqi Syed Waseem , Bahmani Azadeh , Subaiea Gehad M. , Zawia Nasser H.
Published: July 2013

Background

Early‐life lead (Pb) exposure induces overexpression of the amyloid beta precursor protein and its amyloid beta product in older rats and primates. We exposed rodents to Pb during different life span periods and examined cognitive function in old age and its impact on biomarkers associated with Alzheimer's disease (AD).

Methods

Morris, Y, and the elevated plus mazes were used. Western blot, quantitative polymerase chain reaction (qPCR), and enzyme‐linked immunosorbent assay were used to study the levels of AD biomarkers.

Results

Cognitive impairment was observed in mice exposed as infants but not as adults. Overexpression of AD‐related genes (amyloid beta precursor protein and β‐site amyloid precursor protein cleaving enzyme 1) and their products, as well as their transcriptional regulator—specificity protein 1 (Sp1)—occurred only in older mice with developmental exposure to Pb.

Conclusions

A window of vulnerability to Pb neurotoxicity exists in the developing brain that can influence AD pathogenesis and cognitive decline in old age.
Drops walking on a vibrating bath: towards a hydrodynamic pilot-wave theory
Authors: Moláček Jan , Bush John W. M.
Published: July 2013

We present the results of a combined experimental and theoretical investigation of droplets walking on a vertically vibrating fluid bath. Several walking states are reported, including pure resonant walkers that bounce with precisely half the driving frequency, limping states, wherein a short contact occurs between two longer ones, and irregular chaotic walking. It is possible for several states to arise for the same parameter combination, including high- and low-energy resonant walking states. The extent of the walking regime is shown to be crucially dependent on the stability of the bouncing states. In order to estimate the resistive forces acting on the drop during impact, we measure the tangential coefficient of restitution of drops impacting a quiescent bath. We then analyse the spatio-temporal evolution of the standing waves created by the drop impact and obtain approximations to their form in the small-drop and long-time limits. By combining theoretical descriptions of the horizontal and vertical drop dynamics and the associated wave field, we develop a theoretical model for the walking drops that allows us to rationalize the limited extent of the walking regimes. The critical requirement for walking is that the drop achieves resonance with its guiding wave field. We also rationalize the observed dependence of the walking speed on system parameters: while the walking speed is generally an increasing function of the driving acceleration, exceptions arise due to possible switching between different vertical bouncing modes. Special focus is given to elucidating the critical role of impact phase on the walking dynamics. The model predictions are shown to compare favourably with previous and new experimental data. Our results form the basis of the first rational hydrodynamic pilot-wave theory.
Axisymmetric propagating vortices in centrifugally stable Taylor–Couette flow
Authors: Hoffmann C. , Altmeyer S. , Heise M. , Abshagen J. , Pfister G.
Published: July 2013

We present numerical as well as experimental results of axisymmetric, axially propagating vortices appearing in counter-rotating Taylor–Couette flow below the centrifugal instability threshold of circular Couette flow without additional externally imposed forces. These propagating vortices are periodically generated by the shear flow near the Ekman cells that are induced by the non-rotating end walls. These axisymmetric vortices propagate into the bulk towards mid-height, where they get annihilated by rotating, non-propagating defects. These propagating structures appear via a supercritical Hopf bifurcation from axisymmetric, steady vortices, which have been discovered recently in centrifugally stable counter-rotating Taylor–Couette flow (Abshagen et al., Phys. Fluids, vol. 22, 2010, 021702). In the nonlinear regime of the Hopf bifurcation, contributions of non-axisymmetric modes also appear.
The structure of sidewall boundary layers in confined rotating Rayleigh–Bénard convection
Authors: Kunnen R. P. J. , Clercx H. J. H. , van Heijst G. J. F.
Published: July 2013

Turbulent rotating convection is usually studied in a cylindrical geometry, as this is its most convenient experimental realization. In our previous work (Kunnen et al., J. Fluid Mech., vol. 688, 2011, pp. 422–442) we studied turbulent rotating convection in a cylinder with the emphasis on the boundary layers. A secondary circulation with a convoluted spatial structure has been observed in mean velocity plots. Here we present a linear boundary-layer analysis of this flow, which leads to a model of the circulation. The model consists of two independent parts: an internal recirculation within the sidewall boundary layer, and a bulk-driven domain-filling circulation. Both contributions exhibit the typical structure of the Stewartson boundary layer near the sidewall: a sandwich structure of two boundary layers of typical thicknesses ${E}^{1/ 4} $ and ${E}^{1/ 3} $, where $E$ is the Ekman number. Although the structure of the bulk-driven circulation may change considerably depending on the Ekman number, the boundary-layer recirculation is present at all Ekman numbers in the range $0. 72\times 1{0}^{- 5} \leq E\leq 5. 76\times 1{0}^{- 5} $ considered here.
Smart failure insensitive routing: smart failure insensitive routing to enhance resource utilisation and robustness
Authors: Kamrul Islam Mohammad , Ouédraogo Ihsen Aziz , Oki Eiji
Published: July 2013

As the Internet takes an increasingly central role in the authors communications infrastructure, the slowness of routing convergence after network failure is becoming a significant problem in the current link‐state‐based routing protocol. There is an alternative approach, which is to compute backup routes that allow the failure to be repaired locally by the routers that detect the failure without informing other routers of the failure immediately. Failure insensitive routing (FIR) adopts this approach, in which packet forwarding is based on not only the destination but also the link it arrives from. However, FIR faces two problems. First, a packet may travel an unnecessary path, which degrades resource utilisation efficiency. Second, FIR may fail to set a re‐route path even though an active path is available. This study proposes a resilient routing scheme that avoids these two problems by enhancing FIR. It is named smart FIR (S‐FIR). Upon failure, S‐FIR employs a backup routing table based on the unexpected link from which a packet arrives so that subsequent packets can be forwarded to a different next hop to avoid roll back, whereas the original FIR forwards every packet based on the current working routing table. Numerical results indicate that S‐FIR reduces the path length significantly, compared with the original FIR. In addition, in case of any link failure, S‐FIR is proven to guarantee that any packet reaches its destination as long as there is a valid path. S‐FIR provides more robust routing than FIR.
Caching efficiency of information‐centric networking
Authors: Liu Wai‐Xi , Yu Shun‐Zheng , Gao Ying , Wu Wei‐Tao
Published: July 2013

In‐network caching leveraged in information‐centric networking (ICN) is one key difference between ICN and the current Internet. Taken into account the complexity and practicality of technology, cooperatively in‐network caching is yet so far. However, caching efficiency of current uncooperative caching scheme is disappointing. Network coding is considered as the most promising information theoretic approach to improve performance in current Internet. The authors’ previous work has proposed information‐centric networking built network coding (ICN‐NC). In this study, the authors will prove that ICN‐NC can also improve caching efficiency besides network performance. First, a theoretical model is proposed to evaluate caching efficiency of ICN and ICN‐NC, and compare the caching efficiency between ICN and ICN‐NC both analytically and by simulations. Then effect of different parameters on caching efficiency, such as file size, copy size and probability of replacement etc., are also extensively researched. Furthermore, the authors formulate the overall caching efficiency as a multi‐objective optimisation problem with constraints, and then Pareto optimal set to achieve an optimal allocation of network‐wide caching is obtained.
Rectal sensation function rebuilding based on optimal wavelet packet and support vector machine
Authors: Jiang Enyu , Zan Peng , Zhu Xiaojin , Liu Jinding , Shao Yong
Published: July 2013

Rectal sensation function rebuilding method based on optimal wavelet packet (OWP) and support vector machine (SVM) is proposed for rectal sensation loss caused by anal incontinence. By analysing human rectum characteristics, high‐amplitude propagated contractions in rectal contractions are used to indicate an urge to defecate. Rectal pressure feature is extracted using OWP based on Davies‐Bouldin criterion. Normalised mean and energy of optimal bases coefficients are taken as feature vector. Rectal sensation prediction model is trained based on SVM whose parameters are optimised by particle swarm optimisation. Then the trained model is used to predict the urge to defecate. Meanwhile, contrast analysis of prediction accuracy of defecation intension using methods based on feedforward neural networks and SVM based on different kernel functions are given in this study. The prediction accuracy of the optimised SVM is compared with SVM using different kernel functions. Experiment results show that the proposed method is advantageous to rebuild patients’ rectal sensation.
Estimation of a normal process variance from measurements with large round‐off errors
Authors: Diamanta Benson‐Karhi , Ellite Dvir‐Harcabi , Itai Regev , Edna Schechtman
Published: July 2013

Measurements are sometimes affected by excessively large round‐off errors. Small rounding‐off may safely be ignored for purposes of statistical inference however large rounding‐off may have an effect. The importance of the round‐off (δ) is determined by the ratio between the standard deviation σ and the instrument's scale step h, δ = σ/h. In this study, the authors estimate σ when δ is small (δ < 0.5) using a variant of the method of moments (MoM). The MoM estimators are compared with the maximum‐likelihood estimators (MLE), using simulation. The authors find that the MoM can improve the estimation in terms of mean‐square error and bias, especially under circumstances where the MLE method is not accurate or cannot provide a solution.
Analysis of pre‐processing techniques when using validation methods in computational electromagnetic simulations
Authors: Jauregui Ricardo , Ventosa Oriol , Silva Ferran , Kunze Marco
Published: July 2013

In computational electromagnetic simulations, most validation methods have been developed to quantify the similarity of two datasets, making them an objective tool for test engineers to discuss data on a similar basis. However, these methods do not always agree with the expert's opinion. The main problem when a validation method is used, is not taking into account the ‘pre‐processing’ required by the expert to analyse a particular characteristic in the comparison. In this study, two different pre‐processing techniques are used to show the influence they have on the results of the validation methods in relation to the opinion of the expert.
Frequency domain sensing system using random modulation pre‐integrator
Authors: Zhao Yijiu , Wang Houjun , Zhuang Xiaoyan , Dai Zhijian , Wu Hao
Published: July 2013

A major challenge in wideband analog signal processing is the requirement for very high sampling rate. The emerging compressed sensing (CS) theory makes processing wideband signal at its information rate possible if the signal has a sparse representation in a certain space. This study introduces a frequency domain sensing system based on CS. First, the proposed system employs a random demodulator to sensing the signal in frequency domain and an integrator to compress the signal. Second, the incoherence between the proposed measurement matrix and the sparse representation basis is proved mathematically. Different from the conventional analog‐to‐information conversion, the integrator of the system does not need to be reset after each acquisition. Experimental results indicate that, for spectrally sparse signal, the system is able to recover analog waveform at a high equivalent sampling rate from a small number of low‐speed samples.
A geometrical parametrization of C1′-C5′ RNA ribose chemical shifts calculated by density functional theory
Authors: Suardíaz Reynier , Sahakyan Aleksandr B. , Vendruscolo Michele
Published: July 2013

It has been recently shown that NMR chemical shifts can be used to determine the structures of proteins. In order to begin to extend this type of approach to nucleic acids, we present an equation that relates the structural parameters and the 13C chemical shifts of the ribose group. The parameters in the equation were determined by maximizing the agreement between the DFT-derived chemical shifts and those predicted through the equation for a database of ribose structures. Our results indicate that this type of approach represents a promising way of establishing quantitative and computationally efficient analytical relationships between chemical shifts and structural parameters in nucleic acids.
Reliable modeling of the electronic spectra of realistic uranium complexes
Authors: Tecmer Paweł , Govind Niranjan , Kowalski Karol , de Jong Wibe A. , Visscher Lucas
Published: July 2013

We present an EOMCCSD (equation of motion coupled cluster with singles and doubles) study of excited states of the small [UO2]2+ and [UO2]+ model systems as well as the larger UVIO2(saldien) complex. In addition, the triples contribution within the EOMCCSDT and CR-EOMCCSD(T) (completely renormalized EOMCCSD with non-iterative triples) approaches for the [UO2]2+ and [UO2]+ systems as well as the active-space variant of the CR-EOMCCSD(T) method—CR-EOMCCSd(t)—for the UVIO2(saldien) molecule are investigated. The coupled cluster data were employed as benchmark to choose the “best” appropriate exchange–correlation functional for subsequent time-dependent density functional (TD-DFT) studies on the transition energies for closed-shell species. Furthermore, the influence of the saldien ligands on the electronic structure and excitation energies of the [UO2]+ molecule is discussed. The electronic excitations as well as their oscillator dipole strengths modeled with TD-DFT approach using the CAM-B3LYP exchange–correlation functional for the [UVO2(saldien)]− with explicit inclusion of two dimethyl sulfoxide molecules are in good agreement with the experimental data of Takao et al. [Inorg. Chem. 49, 2349 (2010)10.1021/ic902225f].
Alfvén wave collisions, the fundamental building block of plasma turbulence. II. Numerical solution
Authors: Nielson K. D. , Howes G. G. , Dorland W.
Published: July 2013

This paper presents the numerical verification of an asymptotic analytical solution for the nonlinear interaction between counterpropagating Alfvén waves, the fundamental building block of astrophysical plasma turbulence. The analytical solution, derived in the weak turbulence limit using the equations of incompressible MHD, is compared to a nonlinear gyrokinetic simulation of an Alfvén wave collision. The agreement between these methods signifies that the incompressible solution satisfactorily describes the essential dynamics of the nonlinear energy transfer, even under the weakly collisional plasma conditions relevant to many astrophysical environments.
Alfvén wave collisions, the fundamental building block of plasma turbulence. III. Theory for experimental design
Authors: Howes G. G. , Nielson K. D. , Drake D. J. , Schroeder J. W. R. , Skiff F. , Kletzing C. A. , Carter T. A.
Published: July 2013

Turbulence in space and astrophysical plasmas is governed by the nonlinear interactions between counterpropagating Alfvén waves. Here, we present the theoretical considerations behind the design of the first laboratory measurement of an Alfvén wave collision, the fundamental interaction underlying Alfvénic turbulence. By interacting a relatively large-amplitude, low-frequency Alfvén wave with a counterpropagating, smaller-amplitude, higher-frequency Alfvén wave, the experiment accomplishes the secular nonlinear transfer of energy to a propagating daughter Alfvén wave. The predicted properties of the nonlinearly generated daughter Alfvén wave are outlined, providing a suite of tests that can be used to confirm the successful measurement of the nonlinear interaction between counterpropagating Alfvén waves in the laboratory.
Consensus for the Fip35 folding mechanism?
Authors: Berezovska Ganna , Prada-Gracia Diego , Rao Francesco
Published: July 2013

Recent advances in computational power and simulation programs finally delivered the first examples of reversible folding for small proteins with an all-atom description. But having at hand the atomistic details of the process did not lead to a straightforward interpretation of the mechanism. For the case of the Fip35 WW-domain where multiple long trajectories of 100 μs are available from D. E. Shaw Research, different interpretations emerged. Some of those are in clear contradiction with each other while others are in qualitative agreement. Here, we present a network-based analysis of the same data by looking at the local fluctuations of conventional order parameters for folding. We found that folding occurs through two major pathways, one almost four times more populated than the other. Each pathway involves the formation of an intermediate with one of the two hairpins in a native configuration. The quantitative agreement of our results with a state-of-the-art reaction coordinate optimization procedure as well as qualitative agreement with other Markov-state-models and different simulation schemes provides strong evidence for a multiple folding pathways scenario with the presence of intermediates.
Role of mass on the stability of flag/flags in uniform flow
Authors: Tian Fang-Bao
Published: July 2013

The interaction between flag/flags and fluid is studied numerically and the time-average flow in the wake is analyzed. It is found that a zero-mass flag in uniform flow can not exhibit sustained flapping which only occurs when the mass is involved, while multiple zero-mass flags with small separation settle into sustained flapping state. Furthermore, the nonzero mass is an essential condition for flag/flags to establish the sustained flapping in the case of convectively instable wake, while it is an unnecessary condition for the case of the absolutely instable wake.
On the formulation of new explicit conditions for steepness from a former result of N.N. Nekhoroshev
Authors: Schirinzi Gabriella , Guzzo Massimiliano
Published: July 2013

The application of the Nekhoroshev theorem to many problems arising in different fields of Physics and Astronomy depends on a non-degeneracy property, called steepness, that a suitable Hamiltonian approximation must satisfy. Since steepness is implicitly defined, we have the problem of recognizing whether a given function is steep or not. For this purpose, we here consider some sufficient conditions for steepness provided by Nekhoroshev in 1979, based on the solvability of a collection of systems depending on the number n of degrees of freedom, the derivatives of the function up to a certain order r, and some auxiliary parameters. These conditions are really explicit only for r = 2, corresponding to quasi-convexity , and for r = 3. Instead, for r ⩾ 4, the conditions are implicit, since they require an elaborate computation of the closure of a certain set. In this paper, we first revisit Nekhoroshev's result and we show that the number of parameters in the collections of systems can be suitably reduced. Then, we show that for r = 4 Nekhoroshev's result is interesting only for n = 2, 3, and 4, and in these cases we find explicit conditions for steepness which are formulated in a purely algebraic form.
Shielding effect and wakefield pattern of a moving test charge in a non-Maxwellian dusty plasma
Authors: Ali S. , Khan S.
Published: July 2013

By using the Vlasov-Poisson equations, we calculate an expression for the electrostatic potential caused by a test charge in an unmagnetized non-Maxwellian dusty plasma, whose constituents are the superthermal hot-electrons, the mobile cold-electrons with a neutralizing background of cold ions, and charge fluctuating isolated dust grains. The superthermality effects due to hot electrons not only modify the dielectric constant of the electron-acoustic waves but also significantly affect the electrostatic potential. The latter can be decomposed into the Debye-Hückel and oscillatory wake potentials. Analytical and numerical results reveal that the Debye-Hückel and wakefield potentials converge to the Maxwellian case for large values of superthermality parameter. Furthermore, the plasma parameters play a vital role in the formation of shielding and wakefield pattern in a two-electron temperature plasma. The present results should be important for laboratory and space dusty plasmas, where hot-electrons can be assumed to follow the non-Maxwellian distribution function.
Extending high-finesse cavity techniques to the far-infrared
Authors: Alligood DePrince Bridget , Rocher Blithe E. , Carroll Anne M. , Widicus Weaver Susanna L.
Published: July 2013

Sensitive spectroscopic techniques involving high-finesse Fabry-Perot resonators are widely used in the microwave and near-infrared spectral regimes, but hardware limitations have hindered their extension to far-infrared wavelengths. While there is no theoretical limit to the frequency region where cavity-enhanced techniques are practical, the sensitivity of these methods does depend explicitly on the availability of highly reflective optics and, in the case of cavity ringdown spectroscopy, sufficiently fast detectors. Here, we describe a novel high-finesse cavity that uses wire-grid polarizers as the reflective surfaces. Quality factors on the order of 105 are achieved at 250 GHz. Based on the optimized cavity design, we investigate the feasibility of extending the cavity ringdown technique to far-infrared wavelengths. With the present commercially available technology, we find spectrometer performance to be limited by both the available optics and detectors. With a 120 cm cavity and a detector response time of ∼500 ns, we predict a minimum detectable absorption coefficient, αmin, on the order of 10−7 cm−1. Given the sensitivity and noise requirements for the ringdown measurements, faster and more sensitive detectors are needed before implementation of the spectrometer is practical or offers any significant advances to existing methods at far-infrared wavelengths.
Single shot time stamping of ultrabright radio frequency compressed electron pulses
Authors: Gao M. , Jiang Y. , Kassier G. H. , Dwayne Miller R. J.
Published: July 2013

We demonstrate a method of time-stamping Radio Frequency compressed electron bunches for Ultrafast Electron Diffraction experiments in the sub-pC regime. We use an in-situ ultra-stable photo-triggered streak camera to directly track the time of arrival of each electron pulse and correct for the timing jitter in the radio frequency synchronization. We show that we can correct for timing jitter down to 30 fs root-mean-square with minimal distortion to the diffraction patterns, and performed a proof-of-principle experiment by measuring the ultrafast electron-phonon coupling dynamics of silicon.
Induced polarized state in intentionally grown oxygen deficient KTaO3 thin films
Authors: Mota D. A. , Romaguera-Barcelay Y. , Tkach A. , Pérez de la Cruz J. , Vilarinho P. M. , Tavares P. B. , Agostinho Moreira J. , Almeida A.
Published: July 2013

Deliberately oxygen deficient potassium tantalate thin films were grown by RF magnetron sputtering on Si/SiO2/Ti/Pt substrates. Once they were structurally characterized, the effect of oxygen vacancies on their electric properties was addressed by measuring leakage currents, dielectric constant, electric polarization, and thermally stimulated depolarization currents. By using K2O rich KTaO3 targets and specific deposition conditions, KTaO3−δ oxygen deficient thin films with a K/Ta = 1 ratio were obtained. Room temperature X-ray diffraction patterns show that KTaO3−δ thin films are under a compressive strain of 2.3% relative to KTaO3 crystals. Leakage current results reveal the presence of a conductive mechanism, following the Poole-Frenkel formalism. Furthermore, dielectric, polarization, and depolarization current measurements yield the existence of a polarized state below Tpol ∼ 367 °C. A Cole-Cole dipolar relaxation was also ascertained apparently due to oxygen vacancies induced dipoles. After thermal annealing the films in an oxygen atmosphere at a temperature above Tpol, the aforementioned polarized state is suppressed, associated with a drastic oxygen vacancies reduction emerging from annealing process.
Optimizing terahertz surface plasmons of a monolayer graphene and a graphene parallel plate waveguide using one-dimensional photonic crystal
Authors: Hajian H. , Soltani-Vala A. , Kalafi M.
Published: July 2013

Through analytical calculations, the transverse magnetic surface plasmon (SP) dispersion relations for a monolayer graphene and a graphene parallel-plate waveguide (PPWG) in the presence of a one-dimensional photonic crystal (1D PC) as a substrate and a symmetric/asymmetric cladding medium are obtained. For the monolayer graphene case, we show that the presence of the 1D PC leads to significant modification in propagation length (PL) and localization length (LL) of THz SPs, as compared with the SPs of monolayer graphene on SiO2 substrate. And the SPs with largest PL and small LL, named as optimized SPs, could be supported when the 1D PC is used only as a substrate. For the graphene PPWG case with the plate separation “D” (here, 10 nm≤D≤1 μm), in addition to support of typical upper and lower branches of coupled THz SPs, presence of the 1D PC leads to support of an extra branch when 10 nm≪D≤1 μm. Moreover, as far as supporting optimized 0–2 THz SPs are concerned, the case in which the graphene PPWG with D = 1 μm is sandwiched between two symmetric 1D PC could be the best candidate. Whereas the graphene PPWG on the 1D PC, with D = 10 nm, supports optimized SPs in a frequency range from 2 to 4.5 THz. Therefore, using 1D PC improves the capability of monolayer graphene and also graphene PPWG for sensing and waveguide applications in THz frequencies.
Improvement in resistive switching of Ba-doped BiFeO3 films
Authors: Vagadia Megha , Ravalia Ashish , Solanki P. S. , Choudhary R. J. , Phase D. M. , Kuberkar D. G.
Published: July 2013

We investigate the resistive switching behavior of Ba-doped BiFeO3 (BBFO) films grown on single crystalline SrTi0.99Nb0.01O3 substrates. Observation of diode like I-V behavior and reduction in VC with Ba-content in BBFO films have been understood in the context of modifications in its energy band diagram. Also, I-V curves exhibit hysteresis which has been explained on the basis of migration and recombination of oxygen vacancies under field conditions. Furthermore, increment in Ba-content improves the retention property and ON/OFF switching ratio in BFO films which makes them suitable for applications in switching devices.
Asymmetric interface temperature during vapor bubble growth
Authors: Diana A. , Castillo M. , Steinberg T. , Brutin D.
Published: July 2013

We investigate the nucleation, growth, and detachment of single vapor bubbles at the interface microscale. Shear flow is used to investigate pool and convective boiling situations using visible and infrared visualizations. We determine a threshold Reynolds number for the onset of asymmetric interfacial temperatures. Below this threshold, bubble growth is geometrically and thermally symmetric, while above, bubbles no longer grow thermally symmetrically. This is explained by the dominance of convective heat transfer removal over viscous effects at the bubble interface. We experimentally demonstrate asymmetric interfacial temperature profiles that should be taken into account for future bubble growth modeling.
Origin of radiation tolerance in 3C-SiC with nanolayered planar defects
Authors: Ishimaru Manabu , Zhang Yanwen , Shannon Steven , Weber William J.
Published: July 2013

We have recently found that the radiation tolerance of SiC is highly enhanced by introducing nanolayers of stacking faults and twins [Y. Zhang et al., Phys. Chem. Chem. Phys. 14, 13429 (2012)]. To reveal the origin of this radiation resistance, we used in situ transmission electron microscopy to examine structural changes induced by electron beam irradiation in 3C-SiC containing nanolayers of (111) planar defects. We found that preferential amorphization, when it does occur, takes place at grain boundaries and at (1¯11) and (11¯1) planar defects. Radiation-induced point defects, such as interstitials and vacancies, migrate two-dimensionally between the (111) planar defects, which probably enhances the damage recovery.
Pure and Li-doped NiTiH: Potential anode materials for Li-ion rechargeable batteries
Authors: Qian Zhao , De Sarkar Abir , Adit Maark Tuhina , Jiang Xue , Deshpande Mrinalini D. , Bououdina Mohamed , Ahuja Rajeev
Published: July 2013

Pure and Li-doped NiTiH hydrides have been explored for their potential applications as anode materials for Li-ion batteries using density functional theory. The diffusion of Li-ion through pure NiTiH lattice has revealed a big enhancement at 600 K with the diffusion coefficient estimated to be 2.3 × 10−10 m2 s−1 or so. The most thermodynamically stable Li-doped NiTiH material has been ascertained, which evidently shows enhanced electrochemical capacity and a minor increase in voltage and unit-cell volume with respect to pure NiTiH.
Experimental evidence for cm propagation lengths of long-range guided terahertz radiation by thin layers of water
Authors: Sczech Robert , Stock Daniel , Bornemann Rainer , Haring Bolívar Peter
Published: July 2013

Terahertz waves can be guided with low losses along thin layers of a strongly absorbing medium embedded in a dielectric. By means of end-fire coupling experiments, we demonstrate the polarization dependent excitation, propagation, and detection of this loss-guided mode, demonstrating long propagation lengths for terahertz radiation along thin water films. Broadband frequency and time resolved analysis using transmission terahertz time domain spectroscopy are performed. A theoretical model is used to isolate the coupled mode from co-propagating spurious modes. Hereby, experimental propagation lengths in the cm range are demonstrated, 2–3 orders of magnitude above the intrinsic propagation length in bulk water.
Investigation of the resistance switching in Au/SrTiO3:Nb heterojunctions
Authors: Wang Y. H. , Zhao K. H. , Shi X. L. , Xie G. L. , Huang S. Y. , Zhang L. W.
Published: July 2013

The electric properties of as-prepared and annealed Au/SrTiO3:Nb heterojunctions are comparatively investigated. The former junction has hysteretic current-voltage and apparent capacitance-voltage characteristics, showing significant resistance switching effects. The latter behaves like a conventional semiconductor Schottky contact with negligible resistance switching phenomena. Based on the equivalent circuit analysis, we demonstrated that the hysteresis of the measured apparent capacitance-voltage relation of the as-prepared junction is caused by the leakage resistance. Its real junction capacitance is not hysteretic and independent on the resistance states, following the ideal Schottky model. Our results suggest that during the resistance switching, the Schottky barrier profile is kept unchanged, and the conductive filaments play a vital role.
Effect of indium composition on carrier escape in InGaN/GaN multiple quantum well solar cells
Authors: Choi Sang-Bae , Shim Jae-Phil , Kim Dong-Min , Jeong Hoon-Il , Jho Young-Dahl , Song Young-Ho , Lee Dong-Seon
Published: July 2013

The influence of indium composition on carrier escape was studied considering recombination in InGaN/GaN multiple quantum well solar cells with indium compositions of 17% and 25%. Competition between tunneling and recombination turned out to act as a crucial role for the short-circuit current density (Jsc) and fill factor (FF). To enhance the Jsc and the FF, the tunneling-dominant carrier decay rather than recombination is required in the operating range of the solar cells which is possible by optimizing the band structures for a shorter tunneling time and by improving the crystalline quality for a longer recombination time.
Mechanism of positive bias stress-assisted recovery in amorphous-indium-gallium-zinc-oxide thin-film transistors from negative bias under illumination stress
Authors: Um Jae Gwang , Mativenga Mallory , Jang Jin
Published: July 2013

We have analyzed the effect of applying positive bias stress (PBS) to amorphous-indium-gallium-zinc-oxide (a-IGZO) thin-film transistors (TFTs) immediately after applying negative bias under illumination stress (NBIS). By monitoring TFT current-voltage and capacitance-voltage characteristics, we found that PBS facilitates the recovery process. NBIS results in positive charge trapping at the active-layer/gate-insulator interface and the formation of shallow donors in the bulk a-IGZO when neutral oxygen vacancies are ionized by hole capture. In addition to the release of trapped positive charges from the active-layer/gate-insulator interface during the PBS-assisted recovery, ionized oxygen vacancies are neutralized by electron capture and relax back to their original deep levels—well below EF.
AlP/GaP distributed Bragg reflectors
Authors: Emberger Valentin , Hatami Fariba , Ted Masselink W. , Peters Sven
Published: July 2013

Distributed Bragg reflectors with high reflectivity bands centered at wavelengths from 530 to 690 nm (green to red) based on AlP/GaP quarter-wave stacks are prepared on (001)GaP using gas-source molecular-beam epitaxy. Additionally, the complex refractive index of AlP is measured using spectroscopic ellipsometry within the range of 330–850 nm in order to facilitate an accurate reflector design. Structures consisting of 15 quarter-wave stacks reach a peak reflectance between 95% and 98%, depending on the spectral position of the maximum.
Lower poling thresholds and enhanced Pockels coefficients in nanoparticle-polymer composites
Authors: Rose Alec , Latterman Ryan , Smith David R. , Sullivan Philip
Published: July 2013

We investigate computationally the electromagnetic response of composite media made from high-aspect ratio nanoparticle arrays. The shape and local ordering of the nanoparticles can be used to both confine and enhance the local electric fields induced in response to static and propagating fields. When such nanoparticle arrays are hybridized with electrooptic polymers and subjected to a poling field, we show that the nanoparticles can enable variant tensor orientations and lower poling thresholds. From an effective medium perspective, we find that the Pockels coefficients of the nanoparticle-polymer composites can be enhanced by more than an order of magnitude.
Exchange magnetic field torques in YIG/Pt bilayers observed by the spin-Hall magnetoresistance
Authors: Vlietstra N. , Shan J. , Castel V. , Ben Youssef J. , Bauer G. E. W. , van Wees B. J.
Published: July 2013

The effective field torque of an yttrium-iron-garnet (YIG) film on the spin accumulation in an attached platinum (Pt) film is measured by the spin-Hall magnetoresistance (SMR). As a result, the magnetization direction of a ferromagnetic insulating layer can be measured electrically. Experimental transverse and longitudinal resistances are well described by the theoretical model of SMR in terms of the direct and inverse spin-Hall effect, for different Pt thicknesses [3, 4, 8, and 35 nm]. Adopting a spin-Hall angle of Pt θSH=0.08, we obtain the spin diffusion length of Pt (λ=1.1±0.3 nm) as well as the real (Gr=(7±3)×1014 Ω−1m−2) and imaginary part (Gi=(5±3)×1013 Ω−1m−2) of the spin-mixing conductance and their ratio (Gr/Gi=16±4).
Neutrino oscillations in a turbulent plasma
Authors: Mendonça J. T. , Haas F.
Published: July 2013

A new model for the joint neutrino flavor and plasma oscillations is introduced, in terms of the dynamics of the neutrino flavor polarization vector in a plasma background. Fundamental solutions are found for both time-invariant and time-dependent media, considering slow and fast variations of the electron plasma density. The model is shown to be described by a generalized Hamiltonian formalism. In the case of a broad spectrum of electron plasma waves, a statistical approach indicates the shift of both equilibrium value and frequency oscillation of flavor coherence, due to the existence of a turbulent plasma background.
Spherical ion oscillations in a positive polarity gridded inertial-electrostatic confinement device
Authors: Bandara R. , Khachan J.
Published: July 2013

A pulsed, positive polarity gridded inertial electrostatic confinement device has been investigated experimentally, using a differential emissive probe and potential traces as primary diagnostics. Large amplitude oscillations in the plasma current and plasma potential were observed within a microsecond of the discharge onset, which are indicative of coherent ion oscillations about a temporarily confined excess of recirculating electron space charge. The magnitude of the depth of the potential well in the established virtual cathode was determined using a differential emissive Langmuir probe, which correlated well to the potential well inferred from the ion oscillation frequency for both hydrogen and argon experiments. It was found that the timescale for ion oscillation dispersion is strongly dependent on the neutral gas density, and weakly dependent on the peak anode voltage. The cessation of the oscillations was found to be due to charge exchange processes converting ions to high velocity neutrals, causing the abrupt de-coherence of the oscillations through an avalanche dispersion in phase space.
On-chip filter bank spectroscopy at 600–700 GHz using NbTiN superconducting resonators
Authors: Endo A. , Sfiligoj C. , Yates S. J. C. , Baselmans J. J. A. , Thoen D. J. , Javadzadeh S. M. H. , van der Werf P. P. , Baryshev A. M. , Klapwijk T. M.
Published: July 2013

We experimentally demonstrate the principle of an on-chip submillimeter wave filter bank spectrometer, using superconducting microresonators as narrow band-separation filters. The filters are made of NbTiN/SiNx/NbTiN microstrip line resonators, which have a resonance frequency in the range of 614-685 GHz, two orders of magnitude higher in frequency than what is currently studied for use in circuit quantum electrodynamics and photodetectors. The frequency resolution of the filters decreases from 350 to 140 with increasing frequency, most likely limited by dissipation of the resonators.