bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimal sensor scheduling for state estimation over lossy channel
Authors: Sui Tianju , You Keyou , Fu Minyue
Published: August 2015

This study studies a sensor scheduling problem for the state estimation of a stochastic discrete‐time system where the measurements are to be sent from multiple sensors to a centralised estimator through a lossy channel. By adopting a carrier sense multiple access/collision avoidance (CSMA/CA) protocol, the packet loss rate of the channel increases with the number of competing sensors for data communication. To increase the channel utilisation, it requires to smartly select informative sensors to transmit their measurements. Depending on the availability of the acknowledgment (ACK) messages from the estimator, both online and offline algorithms for scheduling sensor communication are proposed to optimise the expected performance of minimum mean‐square error state estimator. Particularly, the online scheduling uses the ACK to trigger the sensor communication while the offline version adopts a random transmission framework and only decides the probability of sending measurements for each sensor in an offline manner. The optimal online scheduler is given by the solution of an integer programming, which is approximated by a practically solvable optimisation. Simulations are included to demonstrate the effectiveness of the proposed algorithms.
Performance evaluation of turbulence‐accentuated interchannel crosstalk for hybrid fibre and free‐space optical wavelength‐division‐multiplexing systems using digital pulse‐position modulation
Authors: Mbah Afamefuna M. , Walker John G. , Phillips Andrew J.
Published: August 2015

A hybrid fibre and free‐space optical communication link using digital pulse‐position modulation (DPPM) in a wavelength‐division‐multiplexing system is proposed. Such a system, which could provide a power efficient, robust and flexible solution to high‐speed access networks, is a contender for a passive optical network solution and could readily be deployed in areas with restrictions in optical fibre installation, or alternatively as a disaster recovery network. Interchannel crosstalk and atmospheric turbulence are major impairments in such a system and could combine in some cases to degrade the system. Both impairments are investigated here and the results are presented in the form of bit error probability, required optical transmission power and power penalties. Depending on the position of the interferer relative to the desired user, power penalties of about 0.2–3.0 dB for weak turbulence and above 20 dB for strong turbulence regimes are reported for bit error rate of 10−6. DPPM scheme with a coding level of 2 show about 2 dB improvements over on–off‐keying scheme.
Mastoid Obliteration with Autologous Bone in Mastoidectomy Canal Wall Down Surgery: a Literature Overview
Authors: Alves Ricardo , Cabral Junior Francisco , Fonseca Anna , Bento Ricardo
Published: August 2015

Introduction The objectives of mastoidectomy in cholesteatoma are a disease-free and dry ear, the prevention of recurrent disease, and the maintenance of hearing or the possibility to reconstruct an affected hearing mechanism. Canal wall down mastoidectomy has been traditionally used to achieve those goals with greater or lesser degrees of success. However, canal wall down is an aggressive approach, as it involves creating an open cavity and changing the anatomy and physiology of the middle ear and mastoid. A canal wall up technique eliminates the need to destroy the middle ear and mastoid, but is associated with a higher rate of residual cholesteatoma. The obliteration technics arise as an effort to avoid the disadvantages of both techniques.

Objectives Evaluate the effectiveness of the mastoid obliteration with autologous bone in mastoidectomy surgery with canal wall down for chronic otitis, with or without cholesteatoma.

Data Synthesis We analyzed nine studies of case series comprehending similar surgery techniques on 1017 total cases of operated ears in both adults and children, with at least 12 months follow-up.

Conclusion Mastoid Obliteration with autologous bone has been utilized for many years to present date, and it seems to be safe, low-cost, with low recurrence rates - similar to traditional canal wall down procedures and with greater water resistance and quality of life improvements.
The raspberry model for hydrodynamic interactions revisited. I. Periodic arrays of spheres and dumbbells
Authors: Fischer Lukas P. , Peter Toni , Holm Christian , de Graaf Joost
Published: August 2015

The so-called “raspberry” model refers to the hybrid lattice-Boltzmann and Langevin molecular dynamics scheme for simulating the dynamics of suspensions of colloidal particles, originally developed by Lobaskin and Dünweg [New J. Phys. 6, 54 (2004)], wherein discrete surface points are used to achieve fluid-particle coupling. This technique has been used in many simulation studies on the behavior of colloids. However, there are fundamental questions with regards to the use of this model. In this paper, we examine the accuracy with which the raspberry method is able to reproduce Stokes-level hydrodynamic interactions when compared to analytic expressions for solid spheres in simple-cubic crystals. To this end, we consider the quality of numerical experiments that are traditionally used to establish these properties and we discuss their shortcomings. We show that there is a discrepancy between the translational and rotational mobility reproduced by the simple raspberry model and present a way to numerically remedy this problem by adding internal coupling points. Finally, we examine a non-convex shape, namely, a colloidal dumbbell, and show that the filled raspberry model replicates the desired hydrodynamic behavior in bulk for this more complicated shape. Our investigation is continued in de Graaf et al. [J. Chem. Phys. 143, 084108 (2015)], wherein we consider the raspberry model in the confining geometry of two parallel plates.
Pattern formation in binary fluid mixtures induced by short-range competing interactions
Authors: Bores Cecilia , Lomba Enrique , Perera Aurélien , Almarza Noé G.
Published: August 2015

Molecular dynamics simulations and integral equation calculations of a simple equimolar mixture of diatomic molecules and monomers interacting via attractive and repulsive short-range potentials show the existence of pattern formation (microheterogeneity), mostly due to depletion forces away from the demixing region. Effective site-site potentials extracted from the pair correlation functions using an inverse Monte Carlo approach and an integral equation inversion procedure exhibit the features characteristic of a short-range attractive and a long-range repulsive potential. When charges are incorporated into the model, this becomes a coarse grained representation of a room temperature ionic liquid, and as expected, intermediate range order becomes more pronounced and stable.
Modeling high-temperature diffusion of gases in micro and mesoporous amorphous carbon
Authors: Ranganathan Raghavan , Rokkam Srujan , Desai Tapan , Keblinski Pawel , Cross Peter , Burnes Richard
Published: August 2015

In this work, we study diffusion of gases in porous amorphous carbon at high temperatures using equilibrium molecular dynamics simulations. Microporous and mesoporous carbon structures are computationally generated using liquid quench method and reactive force fields. Motivated by the need to understand high temperature diffusivity of light weight gases like H2, O2, H2O, and CO in amorphous carbon, we investigate the diffusion behavior as function of two important parameters: (a) the pore size and (b) the concentration of diffusing gases. The effect of pore size on diffusion is studied by employing multiple realizations of the amorphous carbon structures in microporous and mesoporous regimes, corresponding to densities of 1 g/cm3 and 0.5 g/cm3, respectively. A detailed analysis of the effect of gas concentration on diffusion in the context of these two porosity regimes is presented. For the microporous structure, we observe that predominantly, a high diffusivity results when the structure is highly anisotropic and contains wide channels between the pores. On the other hand, when the structure is highly homogeneous, significant molecule-wall scattering leads to a nearly concentration-independent behavior of diffusion (reminiscent of Knudsen diffusion). The mesoporous regime is similar in behavior to the highly diffusive microporous carbon case in that diffusion at high concentration is governed by gas-gas collisions (reminiscent of Fickian diffusion), which transitions to a Knudsen-like diffusion at lower concentration.
Multireference linearized coupled cluster theory for strongly correlated systems using matrix product states
Authors: Sharma Sandeep , Alavi Ali
Published: August 2015

We propose a multireference linearized coupled cluster theory using matrix product states (MPSs-LCC) which provides remarkably accurate ground-state energies, at a computational cost that has the same scaling as multireference configuration interaction singles and doubles, for a wide variety of electronic Hamiltonians. These range from first-row dimers at equilibrium and stretched geometries to highly multireference systems such as the chromium dimer and lattice models such as periodic two-dimensional 1-band and 3-band Hubbard models. The MPS-LCC theory shows a speed up of several orders of magnitude over the usual Density Matrix Renormalization Group (DMRG) algorithm while delivering energies in excellent agreement with converged DMRG calculations. Also, in all the benchmark calculations presented here, MPS-LCC outperformed the commonly used multi-reference quantum chemistry methods in some cases giving energies in excess of an order of magnitude more accurate. As a size-extensive method that can treat large active spaces, MPS-LCC opens up the use of multireference quantum chemical techniques in strongly correlated ab initio Hamiltonians, including two- and three-dimensional solids.
The position of deuterium in HOD—NNO as determined by structural and nuclear quadrupole coupling constants
Authors: Obenchain Daniel A. , Frank Derek S. , Novick Stewart E. , Klemperer William
Published: August 2015

Rotational spectra of the weakly bound H2O—N2O complex and its HOD—N2O isotopologue in a supersonic jet are reported. Rotational constants of the singly substituted deuterium in water and each singly substituted nitrogen-15 are presented. Combinations of isotopic data and high level ab initio calculations place the water in a similar position to those of the isoelectronic H2O—CO2 complex, with a slight tilt of the OH towards the NNO axis. The deuterium nuclear quadrupole coupling constant places the deuterium on the O—H axis quasi-parallel to the NNO axis.
Microstructural dependency of optical properties of m-plane InGaN multiple quantum wells grown on 2° misoriented bulk GaN substrates
Authors: Tang Fengzai , Barnard Jonathan S. , Zhu Tongtong , Oehler Fabrice , Kappers Menno J. , Oliver Rachel A.
Published: August 2015

A non-polar m-plane structure consisting of five InGaN/GaN quantum wells (QWs) was grown on ammonothermal bulk GaN by metal-organic vapor phase epitaxy. Surface step bunches propagating through the QW stack were found to accommodate the 2° substrate miscut towards the -c direction. Both large steps with heights of a few tens of nanometres and small steps between one and a few atomic layers in height are observed, the former of which exhibit cathodoluminescence at longer wavelengths than the adjacent m-plane terraces. This is attributed to the formation of semi-polar facets at the steps on which the QWs are shown to be thicker and have higher Indium contents than those in the adjacent m-plane regions. Discrete basal-plane stacking faults (BSFs) were occasionally initiated from the QWs on the main m-plane terraces, but groups of BSFs were frequently observed to initiate from those on the large steps, probably related to the increased strain associated with the locally higher indium content and thickness.
A new approach to the problem of bulk-mediated surface diffusion
Authors: Berezhkovskii Alexander M. , Dagdug Leonardo , Bezrukov Sergey M.
Published: August 2015

This paper is devoted to bulk-mediated surface diffusion of a particle which can diffuse both on a flat surface and in the bulk layer above the surface. It is assumed that the particle is on the surface initially (at t = 0) and at time t, while in between it may escape from the surface and come back any number of times. We propose a new approach to the problem, which reduces its solution to that of a two-state problem of the particle transitions between the surface and the bulk layer, focusing on the cumulative residence times spent by the particle in the two states. These times are random variables, the sum of which is equal to the total observation time t. The advantage of the proposed approach is that it allows for a simple exact analytical solution for the double Laplace transform of the conditional probability density of the cumulative residence time spent on the surface by the particle observed for time t. This solution is used to find the Laplace transform of the particle mean square displacement and to analyze the peculiarities of its time behavior over the entire range of time. We also establish a relation between the double Laplace transform of the conditional probability density and the Fourier-Laplace transform of the particle propagator over the surface. The proposed approach treats the cases of both finite and infinite bulk layer thicknesses (where bulk-mediated surface diffusion is normal and anomalous at asymptotically long times, respectively) on equal footing.
22.5% efficient silicon heterojunction solar cell with molybdenum oxide hole collector
Authors: Geissbühler Jonas , Werner Jérémie , Martin de Nicolas Silvia , Barraud Loris , Hessler-Wyser Aïcha , Despeisse Matthieu , Nicolay Sylvain , Tomasi Andrea , Niesen Bjoern , De Wolf Stefaan , Ballif Christophe
Published: August 2015

Substituting the doped amorphous silicon films at the front of silicon heterojunction solar cells with wide-bandgap transition metal oxides can mitigate parasitic light absorption losses. This was recently proven by replacing p-type amorphous silicon with molybdenum oxide films. In this article, we evidence that annealing above 130 °C—often needed for the curing of printed metal contacts—detrimentally impacts hole collection of such devices. We circumvent this issue by using electrodeposited copper front metallization and demonstrate a silicon heterojunction solar cell with molybdenum oxide hole collector, featuring a fill factor value higher than 80% and certified energy conversion efficiency of 22.5%.
Development of electrical-erosion instrument for direct write micro-patterning on large area conductive thin films
Authors: Álvarez Ángel Luis , Coya Carmen , García-Vélez Miguel
Published: August 2015

We have developed a complete instrument to perform direct, dry, and cost-effective lithography on conductive materials, based on localized electrical discharges, which avoids using masks or chemicals typical of conventional photolithography. The technique is considered fully compatible with substrate transport based systems, like roll-to-roll technology. The prototype is based on two piezo nano-steppers coupled to three linear micro-stages to cover a large scale operation from micrometers to centimeters. The operation mode consists of a spring probe biased at low DC voltage with respect to a grounded conductive layer. The tip slides on the target layer keeping contact with the material in room conditions, allowing continuous electric monitoring of the process, and also real-time tilt correction via software. The sliding tip leaves an insulating path (limited by the tip diameter) along the material, enabling to draw electrically insulated tracks and pads. The physical principle of operation is based in the natural self-limitation of the discharge due to material removal or insulation. The so produced electrical discharges are very fast, in the range of μs, so features may be performed at speeds of few cm/s, enabling scalability to large areas. The instrument has been tested on different conducting materials as gold, indium tin oxide, and aluminum, allowing the fabrication of alphanumeric displays based on passive matrix of organic light emitting diodes without the use of masks or photoresists. We have verified that the highest potential is achieved on graphene, where no waste material is detected, producing excellent well defined edges. This allows manufacturing graphene micro-ribbons with a high aspect ratio up to 1200:1.
Optimization of scintillation performance via a combinatorial multi-element co-doping strategy: Application to NaI:Tl
Authors: Khodyuk I. V. , Messina S. A. , Hayden T. J. , Bourret E. D. , Bizarri G. A.
Published: August 2015

A combinatorial approach where doped bulk scintillator materials can be rapidly optimized for their properties through concurrent extrinsic doping/co-doping strategies is presented. The concept that makes use of design of experiment, rapid growth, and evaluation techniques, and multivariable regression analysis, has been successfully applied to the engineering of NaI performance, a historical but mediocre performer in scintillation detection. Using this approach, we identified a three-element doping/co-doping strategy that significantly improves the material performance. The composition was uncovered by simultaneously screening for a beneficial co-dopant ion among the alkaline earth metal family and by optimizing its concentration and that of Tl+ and Eu2+ ions. The composition with the best performance was identified as 0.1% mol Tl+, 0.1% mol Eu2+, and 0.2% mol Ca2+. This formulation shows enhancement of energy resolution and light output at 662 keV, from 6.3 to 4.9%, and from 44 000 to 52 000 ph/MeV, respectively. The method, in addition to improving NaI performance, provides a versatile framework for rapidly unveiling complex and concealed correlations between material composition and performance, and should be broadly applicable to optimization of other material properties.
Role of force-constant difference in phonon scattering by nano-precipitates in PbTe
Authors: Yang Xiaolong , Carrete Jesús , Wang Zhao
Published: August 2015

We study the effect of nanoscale precipitates on lattice thermal conduction in thermoelectric PbTe using a combination of ab-initio phonon calculations and molecular dynamics. We take into account the effects of mass difference and change in force constants, and find an enhanced influence of the latter with increased precipitate concentration. As a consequence, our inclusion of the change in force constants in the calculation affords a smaller predicted optimal nano-precipitate size that minimizes the thermal conductivity. These results suggest that the phonon scattering by nanoprecipitates in thermoelectric composites could be stronger than previously thought.
The geometry of generalized force matching and related information metrics in coarse-graining of molecular systems
Authors: Kalligiannaki Evangelia , Harmandaris Vagelis , Katsoulakis Markos A. , Plecháč Petr
Published: August 2015

Using the probabilistic language of conditional expectations, we reformulate the force matching method for coarse-graining of molecular systems as a projection onto spaces of coarse observables. A practical outcome of this probabilistic description is the link of the force matching method with thermodynamic integration. This connection provides a way to systematically construct a local mean force and to optimally approximate the potential of mean force through force matching. We introduce a generalized force matching condition for the local mean force in the sense that allows the approximation of the potential of mean force under both linear and non-linear coarse graining mappings (e.g., reaction coordinates, end-to-end length of chains). Furthermore, we study the equivalence of force matching with relative entropy minimization which we derive for general non-linear coarse graining maps. We present in detail the generalized force matching condition through applications to specific examples in molecular systems.
Semicontinuous solar drying of sludge from a waste water treatment plant
Authors: Al-Otoom Awni , Äbu Al-Rub Fahmi , Mousa Hasan , Shadeed Mays
Published: August 2015

This study presents a newly developed system to utilize solar energy to dewater the sludge in a semicontinuous mode. The semicontinuous dryer mainly consists of a moving belt on which aluminum bars are fixed to hold the sludge and a fan is used to drive the air at the required speed. The effects of operating conditions, such as air velocity, belt speed, and mode of contact between the sludge and air, on the drying rate of water were investigated. The drying rate of water was measured under the effects of different operating conditions, including air velocity, belt speed, and mode of contact between the sludge and air. The experimental results proved the technical feasibility of the developed solar drying system to efficiently evaporate water. The achieved drying rates were 2.02 kg water/m2 h and 0.49 kg water/m2 h in September and February, respectively. Under a given insolation rate, a high evaporation rate is achieved at large air velocity and slow motor speed. An empirical relationship to predict the mass transfer coefficient (drying flux constant) was derived by conducting a well-designed experiment using a tray dryer. The data obtained successfully described the mass transfer coefficient expressed as JD = 15.1Re−0.72.
Elastic scattering of low energy electrons in partially ionized dense semiclassical plasma
Authors: Dzhumagulova K. N. , Shalenov E. O. , Ramazanov T. S.
Published: August 2015

Elastic scattering of electrons by hydrogen atoms in a dense semiclassical hydrogen plasma for low impact energies has been studied. Differential scattering cross sections were calculated within the effective model of electron-atom interaction taking into account the effect of screening as well as the quantum mechanical effect of diffraction. The calculations were carried out on the basis of the phase-function method. The influence of the diffraction effect on the Ramsauer–Townsend effect was studied on the basis of a comparison with results made within the effective polarization model of the Buckingham type.
A new ion cyclotron range of frequency scenario for bulk ion heating in deuterium-tritium plasmas: How to utilize intrinsic impurities in our favour
Authors: Kazakov Ye. O. , Ongena J. , Van Eester D. , Bilato R. , Dumont R. , Lerche E. , Mantsinen M. , Messiaen A.
Published: August 2015

A fusion reactor requires plasma pre-heating before the rate of deuterium-tritium fusion reactions becomes significant. In ITER, radio frequency (RF) heating of 3He ions, additionally puffed into the plasma, is one of the main options considered for increasing bulk ion temperature during the ramp-up phase of the pulse. In this paper, we propose an alternative scenario for bulk ion heating with RF waves, which requires no extra 3He puff and profits from the presence of intrinsic Beryllium impurities in the plasma. The discussed method to heat Be impurities in D-T plasmas is shown to provide an even larger fraction of fuel ion heating.
On the role of topological complexity in spontaneous development of current sheets
Authors: Kumar Sanjay , Bhattacharyya R. , Smolarkiewicz P. K.
Published: August 2015

The computations presented in this work aim to asses the importance of field line interlacing on spontaneous development of current sheets. From Parker's magnetostatic theorem, such development of current sheets is inevitable in a topologically complex magnetofluid, with infinite electrical conductivity, at equilibrium. Relevant initial value problems are constructed by superposition of two untwisted component fields, each component field being represented by a pair of global magnetic flux surface. The intensity of field line interlacing is then specified by the relative amplitude of the two superposed fields. The computations are performed by varying this relative amplitude. Also to have a direct visualization of current sheet formation, we follow the evolution of flux surfaces instead of the vector magnetic field. An important finding of this paper is in the demonstration that initial field lines having intense interlacing tend to develop current sheets which are distributed throughout the computational domain with no preference for topologically favorable sites like magnetic nulls or field reversal layers. The onsets of these current sheets are attributed to favorable contortions of magnetic flux surfaces where two oppositely directed parts of the same field line or different field lines come to close proximity. However, for less intensely interlaced field lines, the simulations indicate development of current sheets at sites only where the magnetic topology is favorable. These current sheets originate as two sets of anti-parallel complimentary field lines press onto each other.
Ion-acoustic solitons, double layers and supersolitons in a plasma with two ion- and two electron species
Authors: Olivier C. P. , Maharaj S. K. , Bharuthram R.
Published: August 2015

The polarity of ion-acoustic solitons that arise in a plasma with two (same mass, different temperature) ion species and two (different temperature) electron species is investigated. Two different fluid models are compared. The first model treats all species as adiabatic fluids, while the second model treats the ion species as adiabatic, and the electron species as isothermal. Nonlinear structures are analysed via the reductive perturbation analysis and pseudo-potential analysis. Each model supports both slow and fast ion-acoustic solitons, associated with the two (slow and fast) ion-acoustic speeds. The models support both positive and negative polarity solitons associated with the slow ion-acoustic speed. Moreover, results are in good agreement, and both models support positive and negative polarity double layers. For the fast ion-acoustic speed, the first model supports only positive polarity solitons, while the second model supports solitons of both polarity, coexistence of positive and negative polarity solitons, double layers and supersolitons. A novel feature of our analysis is the evaluation of nonlinear structures at critical number densities where polarity changes occur. This analysis shows that solitons that occur at the acoustic speed are neither a necessary nor a sufficient condition for the phenomenon of coexistence. The relationship between the existence regions of supersolitons and soliton polarity is also discussed.
Magnetohydrodynamic instability excited by interplay between a resistive wall mode and stable ideal magnetohydrodynamic modes in rotating tokamak plasmas
Authors: Aiba N. , Hirota M.
Published: August 2015

In a rotating toroidal plasma surrounded by a resistive wall, it is shown that linear magnetohydrodynamic (MHD) instabilities can be excited by interplay between the resistive wall mode (RWM) and stable ideal MHD modes, where the RWM can couple with not only a stable external kink mode but also various stable Alfvén eigenmodes that abound in a toroidal plasma. The RWM growth rate is shown to peak repeatedly as the rotation frequency reaches specific values for which the frequencies of the ideal MHD modes are Doppler-shifted to the small RWM frequency. Such destabilization can be observed even when the RWM in a static plasma is stable. A dispersion relation clarifies that the unstable mode changes from the RWM to the ideal MHD mode destabilized by wall resistivity when the rotation frequency passes through these specific values. The unstable mode is excited at these rotation frequencies even though plasma rotation also tends to stabilize the RWM from the combination of the continuum damping and the ion Landau damping.
The motion of a neutrally buoyant particle of an elliptic shape in two dimensional shear flow: A numerical study
Authors: Huang Shih-Lin , Chen Shih-Di , Pan Tsorng-Whay , Chang Chien-Cheng , Chu Chin-Chou
Published: August 2015

In this article, we investigate the motion of a neutrally buoyant particle of an elliptic shape freely moving in two dimensional shear flow by direct numerical simulation. An elliptic shape particle in shear flow, when initially being placed at the middle between two walls, either keeps rotating or has a stationary inclination angle depending on the particle Reynolds number Re=Grra2/ν, where Gr is the shear rate, ra is the semi-long axis of the elliptic particle, and ν is the kinetic viscosity of the fluid. The critical particle Reynolds number Recr for the transition from a rotating motion to a stationary orientation depends on the aspect ratio AR = rb/ra and the confined ratio K = 2ra/H, where rb is the semi-short axis of the elliptic particle and H is the distance between two walls. Although the increasing of either parameters makes an increase in Recr, the dynamic mechanism is distinct. The AR variation causes the change of geometry shape; however, the K variation influences the wall effect. The stationary inclination angle of non-rotating slender elliptic particle with smaller confined ratio seems to depend only on the value of Re − Recr. An expected equilibrium position of the particle mass center in shear flow is the centerline between two walls. When placing the particle away from the centerline initially, it migrates either toward an equilibrium height away from the middle between two walls or back to the middle depending on the confined ratio and particle Reynolds number; but for higher particle Reynolds numbers, besides the previous two positions, the elliptic particle placed close to the middle just moves parallel to the wall with a stationary orientation.
Motion of a free cylinder inside a rotating water-filled drum
Authors: Hernández R. H. , Vial A. , Barraud C.
Published: August 2015

We report experimental results on the motion and levitation of a freely to-move heavy cylinder, of constant diameter and varying mass, inside a water-filled drum rotating around its horizontal axis. The resulting flow field and the cylinder dynamics were determined with the aid of flow visualizations and particle image velocimetry methods. The spatial tracking of the inner cylinder was done with the aid of Fourier cross correlation methods. The steady bulk flow field created by the drum rotation generated forces that make the inner cylinder to counter-rotate without contact with the drum walls. Testing different cylinder masses and rotating drum frequencies has shown that there exists a range of stable spatial positions of the inner cylinder describing an angular segment inside the drum flow. The cylinder frequency can be set to zero if we increase the drum frequency beyond a threshold value. Increasing the drum frequency produces a stronger secondary flow circulation which is the key-mechanism responsible of the counter-rotating cylinder frequency. At this point, the inner cylinder levitates with a constant separation from the drum walls close to half of its diameter. Tests on heavy hollow cylinders revealed that the fluid filling the cylinder remains at rest while the cylinder was under levitation with zero rotation frequency.
Laboratory studies of nonlinear whistler wave processes in the Van Allen radiation belts
Authors: Tejero E. M. , Crabtree C. , Blackwell D. D. , Amatucci W. E. , Mithaiwala M. , Ganguli G. , Rudakov L.
Published: August 2015

Important nonlinear wave-wave and wave-particle interactions that occur in the Earth's Van Allen radiation belts are investigated in a laboratory experiment. Predominantly electrostatic waves in the whistler branch are launched that propagate near the resonance cone with measured wave normal angle greater than 85°. When the pump amplitude exceeds a threshold ∼5×10−6 times the background magnetic field, wave power at frequencies below the pump frequency is observed at wave normal angles (∼55°). The scattered wave has a perpendicular wavelength that is nearly an order of magnitude larger than that of the pump wave. Occasionally, the parametric decay of a lower hybrid wave into a magnetosonic wave and a whistler wave is simultaneously observed with a threshold of δB/B0∼7×10−7.
Formation of continuous metallic film on quartz studied by noncontact resonant ultrasound spectroscopy
Authors: Nakamura N. , Yoshimura N. , Ogi H. , Hirao M.
Published: August 2015

Dynamics of continuous film formation of metallic films on quartz substrates is studied using an electrodeless resonance method. Bare quartz is used as a substrate, and a metallic film is deposited on it. We use antenna transmission technique to measure the evolution of resonance frequencies and internal friction of the substrate during and after deposition, and the morphological transition between discontinuous islands and a continuous film is detected. By comparison with atomic force microscopy images, we confirm that the frequency drop and the internal-friction peak that appear during deposition indicate this transition. We also find that Pt film shows unexpected morphology change after deposition.
Work function contrast and energy band modulation between amorphous and crystalline Ge2Sb2Te5 films
Authors: Tong H. , Yang Z. , Yu N. N. , Zhou L. J. , Miao X. S.
Published: August 2015

The work function (WF) is of crucial importance to dominate the carrier transport properties of the Ge-Sb-Te based interfaces. In this letter, the electrostatic force microscopy is proposed to extract the WF of Ge2Sb2Te5 (GST) films with high spatial and energy resolution. The measured WF of as-deposited amorphous GST is 5.34 eV and decreases drastically after the amorphous GST is crystallized by annealing or laser illumination. A 512 × 512 array 2D-WF map is designed to study the WF spatial distribution and shows a good consistency. The WF contrast between a-GST and c-GST is ascribed to band modulation, especially the modification of electron affinity including the contribution of charges or dipoles. Then, the band alignments of GST/n-Si heterostructures are obtained based on the Anderson's rule. Due to the band modulation, the I-V characteristics of a-GST/Si heterojunction and c-GST/Si heterojunction are very different from each other. The quantitative relationship is calculated by solving the Poisson's equation, which agrees well with the I-V measurements. Our findings not only suggest a way to further understand the electrical transport properties of Ge-Sb-Te based interfaces but also provide a non-touch method to distinguish crystalline area from amorphous matrix with high spatial resolution.
Note: Improving long-term stability of hot-wire anemometer sensors by means of annealing
Authors: Lundström H.
Published: August 2015

Annealing procedures for hot-wire sensors of platinum and platinum-plated tungsten have been investigated experimentally. It was discovered that the two investigated sensor metals behave quite differently during the annealing process, but for both types annealing may improve long-term stability considerably. Measured drift of sensors both without and with prior annealing is presented. Suggestions for suitable annealing temperatures and times are given.
Intrachain exciton dynamics in conjugated polymer chains in solution
Authors: Tozer Oliver Robert , Barford William
Published: August 2015

We investigate exciton dynamics on a polymer chain in solution induced by the Brownian rotational motion of the monomers. Poly(para-phenylene) is chosen as the model system and excitons are modeled via the Frenkel exciton Hamiltonian. The Brownian fluctuations of the torsional modes were modeled via the Langevin equation. The rotation of monomers in polymer chains in solution has a number of important consequences for the excited state properties. First, the dihedral angles assume a thermal equilibrium which causes off-diagonal disorder in the Frenkel Hamiltonian. This disorder Anderson localizes the Frenkel exciton center-of-mass wavefunctions into super-localized local exciton ground states (LEGSs) and higher-energy more delocalized quasi-extended exciton states (QEESs). LEGSs correspond to chromophores on polymer chains. The second consequence of rotations—that are low-frequency—is that their coupling to the exciton wavefunction causes local planarization and the formation of an exciton-polaron. This torsional relaxation causes additional self-localization. Finally, and crucially, the torsional dynamics cause the Frenkel Hamiltonian to be time-dependent, leading to exciton dynamics. We identify two distinct types of dynamics. At low temperatures, the torsional fluctuations act as a perturbation on the polaronic nature of the exciton state. Thus, the exciton dynamics at low temperatures is a small-displacement diffusive adiabatic motion of the exciton-polaron as a whole. The temperature dependence of the diffusion constant has a linear dependence, indicating an activationless process. As the temperature increases, however, the diffusion constant increases at a faster than linear rate, indicating a second non-adiabatic dynamics mechanism begins to dominate. Excitons are thermally activated into higher energy more delocalized exciton states (i.e., LEGSs and QEESs). These states are not self-localized by local torsional planarization. During the exciton’s temporary occupation of a LEGS—and particularly a quasi-band QEES—its motion is semi-ballistic with a large group velocity. After a short period of rapid transport, the exciton wavefunction collapses again into an exciton-polaron state. We present a simple model for the activated dynamics which is in agreement with the data.
Optically switchable photonic metasurfaces
Authors: Waters R. F. , Hobson P. A. , MacDonald K. F. , Zheludev N. I.
Published: August 2015

We experimentally demonstrate an optically switchable gallium-based metasurface, in which a reversible light-induced transition between solid and liquid phases occurring in a confined nanoscale surface layer of the metal drives significant changes in reflectivity and absorption. The metasurface architecture resonantly enhances the metal's “active plasmonic” phase-change nonlinearity by an order of magnitude, offering high contrast all-optical switching in the near-infrared range at low, μW μm−2, excitation intensities.
Epitaxial growth of phase-pure ε-Ga2O3 by halide vapor phase epitaxy
Authors: Oshima Yuichi , Víllora Encarnación G. , Matsushita Yoshitaka , Yamamoto Satoshi , Shimamura Kiyoshi
Published: August 2015

Epitaxial growth of ε-Ga2O3 is demonstrated for the first time. The ε-Ga2O3 films are grown on GaN (0001), AlN (0001), and β-Ga2O3 (2¯01) by halide vapor phase epitaxy at 550 °C using gallium chloride and O2 as precursors. X-ray ω-2θ and pole figure measurements prove that phase-pure ε-Ga2O3 (0001) films are epitaxially grown on the three kinds of substrates, although some minor misoriented domains are observed. High temperature X-ray diffraction measurements reveal that the ε-Ga2O3 is thermally stable up to approximately 700 °C. The optical bandgap of ε-Ga2O3 is determined for the first time to be 4.9 eV.
Selective absorbers and thermal emitters for far-infrared wavelengths
Authors: Streyer W. , Feng K. , Zhong Y. , Hoffman A. J. , Wasserman D.
Published: August 2015

We demonstrate engineered selective absorption and subsequent selective thermal emission from sub-wavelength thickness optical structures at far-infrared (30–40 μm) wavelengths. Control over absorption/emission wavelength is demonstrated, with both polarization-dependent and -independent structures fabricated. Samples are characterized experimentally by Fourier transform infrared reflection and emission spectroscopy, and modeled using three-dimensional rigorous coupled wave analysis. The ability to design and demonstrate strong selective absorption and thermal emission from optical structures in the far-infrared offers a potential route towards low-cost sources for the exploration of Reststrahlen band frequencies.
Magnetic anisotropy of single-crystalline Mn3Sn in triangular and helix-phase states
Authors: Duan T. F. , Ren W. J. , Liu W. L. , Li S. J. , Liu W. , Zhang Z. D.
Published: August 2015

The magnetic structure and phase transitions in single-crystalline Mn3Sn with the D019 structure have been investigated by torque measurements and magnetic measurements. The results show that a triangular antiferromagnet (AFM) and a weak ferromagnet coexist above 270 K. At these temperatures, the torque measurements indicate a six-fold symmetry and another two-fold symmetry of the magnetic anisotropy. The [112¯0] direction is the lowest-energy state in the triangular configuration. At low temperatures, two AFM helix-phase states are found in an applied magnetic field (H): In one of them, the [112¯0] direction is the easiest deviation direction from the AFM state. In the other, it is the [0001] direction. The variation of the two states with temperature (T) and magnetic field is presented in an H-T phase diagram.
Manipulating waves with LEGO® bricks: A versatile experimental platform for metamaterial architectures
Authors: Celli Paolo , Gonella Stefano
Published: August 2015

In this letter, we discuss a versatile, fully reconfigurable experimental platform for the investigation of phononic phenomena in metamaterial architectures. The approach revolves around the use of 3D laser vibrometry to reconstruct global and local wavefield features in specimens obtained through simple arrangements of LEGO® bricks on a thin baseplate. The agility by which it is possible to reconfigure the brick patterns into a nearly endless spectrum of topologies makes this an effective approach for rapid experimental proof of concept, as well as a powerful didactic tool, in the arena of phononic crystals and metamaterials engineering. We use our platform to provide a compelling visual illustration of important spatial wave manipulation effects (waveguiding and seismic isolation), and to elucidate fundamental dichotomies between Bragg-based and locally resonant bandgap mechanisms.
Electric properties of La2O3/SiO2/4H-SiC MOS capacitors with different annealing temperatures
Authors: Wang Yucheng , Jia Renxu , Li Chengzhan , Zhang Yuming
Published: August 2015

In this work, we describe a rapid thermal annealing (RTA) process for the La2O3/SiO2/4H-SiC interface and investigate its effect on the material’s electrical properties. Our results indicate that the trap charge density and interface state density (Dit) are reduced as the RTA temperature increases due to the termination of residual carbon and dangling bonds. We demonstrate that the sample obtained after RTA at 500 °C has the highest breakdown electric field (Efb) (7 MV/cm) due to a decrease in the trap charge density and an improvement in the interfacial properties. However, when the RTA temperature reaches 600 °C or higher, a lower Efb value (1.2 MV/cm) is obtained due to leakage routes generated by the crystallization of La2O3. Based on our results, we conclude that the ideal choice for the RTA temperature is 500 °C.
Post-fire succession during the long-term absence of fire in coastal heathland and a test of the chronosequence survey method
Authors: Freestone Marc , Wills Timothy J. , Read Jennifer
Published: August 2015

Post-fire vegetation succession in long-unburnt heathland in south-east Australia is not well understood. In the present study we investigated temporal change in vegetation along a 37-year post-fire chronosequence in coastal heathland in the Gippsland Lakes Coastal Park, Victoria, Australia. Fourteen sites were surveyed for vegetation characteristics approximately 10 years after an initial chronosequence survey, enabling an extension of the chronosequence to cover a longer fire-free interval as well as testing predictions of declining species richness and diversity from the initial chronosequence study. Total species richness, mean species richness, mean diversity and mean evenness declined with time since fire across the 14 sites. However, only diversity (H) and evenness (E) decreased within sites as predicted in the original chronosequence study. No decrease in species richness within sites was observed. The chronosequence correctly predicted changes in species abundance but not the number of species present. Tree cover also increased, suggesting that the heathland was becoming a woodland in the long-term absence of fire. Fire history, which is an uncontrolled historical factor, provides the most likely explanation for why species richness did not decrease as predicted by the initial chronosequence. This study advocates caution in using the chronosequence method to predict species richness during post-fire succession.
Pseudoraphis spinescens (Poaceae) grasslands at Barmah Forest, Victoria, Australia: current distribution and implications for floodplain conservation
Authors: Vivian L. M. , Ward K. A. , Marshall D. J. , Godfree R. C.
Published: August 2015

Floodplain grasslands are highly productive ecosystems that are becoming increasingly degraded and fragmented because of changes to natural flood regimes. In this work, we mapped and quantified the distribution of Pseudoraphis spinescens – an ecologically important mat-forming grass – in treeless floodplain grasslands in the Barmah Forest, Victoria, Australia, across two seasons. Although P. spinescens was once widespread in the forest, there has been a decline in its extent, particularly since the Millennium Drought (2001–09) and subsequent unseasonal and prolonged La Niña-associated flooding from late 2010 to 2012. Our detailed on-ground surveys show that only 182 ha of P. spinescens grassland remain in treeless areas of Barmah Forest, representing ~12% of the total area of treeless plains and lakes. Critically, just 51 ha of the thick monospecific P. spinescens swards that were a historically important part of the floodplain vegetation was located and mapped. Although there was a small increase in the area of P. spinescens in some treeless areas following a favourable flood season in 2013–14, the boundaries of most grassland patches remained relatively stable during this period. Potential drivers of the overall decline in P. spinescens across Barmah Forest include the direct and indirect impacts of altered flood regimes, drought, and grazing pressure. Improved understanding of these drivers and their interactions, as well as the status of the seedbank, will be crucial for future management and conservation of these floodplain grasslands.
Feral cat diet and predation on endangered endemic mammals on a biodiversity hot spot (Amami–Ohshima Island, Japan)
Authors: Shionosaki Kazumi , Yamada Fumio , Ishikawa Takuya , Shibata Shozo
Published: August 2015

Context There has been concern that feral cats have negative impacts on the endangered endemic mammals of Amami-Ohshima Island, Japan, including the Amami rabbit, Pentalagus furnessi, Ryukyu long-tailed giant rat, Diplothrix legata, and Amami spiny rat, Tokudaia osimensis. However, no diet study of feral cat has been conducted to support the necessity of an urgent feasible feral-cat management for the island. Aims The aims of the present study were to analyse feral-cat diet on Amami-Ohshima Island by using scat analysis and estimate the potential predation impact of feral cats on endangered mammals on the island. Methods The diet of feral cats was studied using scat analysis. We estimated the number of prey, percentage of prey, frequency of occurrence (the percentage of scats in a sample containing a particular prey item), percentage of biomass (biomass of the same prey item divided by the total consumed biomass ×100) and daily consumed biomass (DCB). Key results Three endangered endemic mammals were the main prey species of the feral cat diet (65% of total DCB). The percentage contributions of these species on DCB were long-tailed giant rat (34.7%), Amami spiny rat (21.9%) and Amami rabbit (12%). Conclusions Mammals, especially endangered endemic mammals, were main prey species of feral cat on Amami Island. In Amami Island, where native and invasive rodents coexisted, feral cats consumed more native (56.6%) than invasive (22.2% for Rattus rattus) species. Implications Feral cats are likely to be having a significant impact on endangered endemic mammals on the island. To ensure the long-term survival of these endemic species, active management of the feral-cat population should be considered.