bluuebunny/crossref_metadata_2025 huggingface dataset:
The Development of Balance Retraining: An Online Intervention for Dizziness in Adults Aged 50 Years and Older
Authors: Essery Rosie , Kirby Sarah , Geraghty Adam W. A. , Andersson Gerhard , Carlbring Per , Bronstein Adolfo , Little Paul , Yardley Lucy
Published: July 2015

Purpose

This article outlines the rationale and development process for an online intervention based on vestibular rehabilitation therapy (VRT). The intervention aims to assist adults aged 50 years and older to self-manage and reduce dizziness symptoms.

Method

The intervention was developed according to the person-based approach to digital intervention design focused on accommodating perspectives of target users. A prototype version of the intervention was provided to 18 adults (11 women, 7 men) aged 50 years and older with dizziness. These adults were invited to use the intervention over a 6-week period and, during this time, took part in a think-aloud session. This session sought to understand users' perceptions of how acceptable, engaging, and easy to use they found the online intervention.

Results

Users were extremely positive regarding how easy to navigate, visually appealing, and informative they found the intervention. Think-aloud sessions provided valuable data for informing small amendments to further enhance acceptability of the intervention for target users.

Conclusions

Informed by these development-phase data, a finalized version of the intervention is now being investigated in a primary care–based randomized controlled trial. Results should provide an understanding of whether VRT can be effectively—especially, cost-effectively—delivered via an online intervention to adults aged 50 years and older.
SoundSpace Online: The Development of an Online Resource About Hearing Loss
Authors: Ng Zheng Yen , Archbold Sue , Mayer Connie , Mulla Imran
Published: July 2015

Purpose

The Internet has been a growing source of health information on hearing loss, but the information provided often varies in quality, readability, and usability. Additionally, the information is provided across a wide range of domains, making access challenging to those who need it. This research forum article describes the development of a new website, SoundSpace Online (Ng, Archbold, Mayer, & Mulla, 2014), which aims to tackle these issues and bring together information and resources for all those concerned with hearing loss.

Method

The SoundSpace Online website's current developmental state was reached through the following methods: (a) discussions with a group of individuals that included experts in e-learning, education, research, and hearing loss; (b) interviews with different target groups (e.g., users, families, and professionals); and (c) collaboration with contributors.

Result

The website is structured to become a go-to resource on various topics related to hearing loss, providing accurate, comprehensive, and functional information and resources at varying levels of complexity for the intended users.

Conclusion

The literature and the range of interest have illustrated the need for an up-to-date website providing information and resources on hearing loss. Challenges include monitoring and keeping the website up to date; in this article, a plan of action is discussed. The website is currently in development, with plans for a launch in the near future.
Computer and Internet Interventions to Optimize Listening and Learning for People With Hearing Loss: Accessibility, Use, and Adherence
Authors: Ferguson Melanie , Henshaw Helen
Published: July 2015

Purpose

The aim of this research forum article was to examine accessibility, use, and adherence to computerized and online interventions for people with hearing loss.

Method

Four intervention studies of people with hearing loss were examined: 2 auditory training studies, 1 working memory training study, and 1 study of multimedia educational support.

Results

A small proportion (approximately 15%) of participants had never used a computer, which may be a barrier to the accessibility of computer and Internet-based interventions. Computer competence was not a factor in intervention use or adherence. Computer skills and Internet access influenced participant preference for the delivery method of the multimedia educational support program.

Conclusions

It is important to be aware of current barriers to computer and Internet-delivered interventions for people with hearing loss. However, there is a clear need to develop and future-proof hearing-related applications for online delivery.
Complex conjugate poles implementation in discrete‐time charge‐domain filters
Authors: Sohrabi Z. , Jannesari A.
Published: July 2015

A discrete‐time charge‐domain filter is proposed, which can realise complex conjugate poles in the transfer function of the filter. By employing a second transconductance in the feedback path of a second‐order infinite impulse response charge‐domain filter, it is proved that the filter topology is capable of implementing complex poles. This method makes charge‐sampling filters more efficient in designing frequency‐domain filters where they can be used to synthesise any type of filter structures such as Butterworth, Chebyshev and so on.
Electrically small uniplanar antenna with pattern‐agile performance
Authors: Tang Ming‐Chun , Shi Ting , Ziolkowski Richard
Published: July 2015

A novel electrically small uniplanar antenna with pattern‐agile performance is reported. It consists of a split semi‐loop connected to the ground strips of a coplanar waveguide‐fed semi‐loop antenna. The angle of its maximum directivity can be controlled simply by changing the position of the gap in the ground‐connected semi‐loop. The measured results of this behaviour are in good agreement with the simulated values. A peak realised gain of 1.93 dBi is achieved experimentally. The radiation efficiency is observed to be higher than 95% for every angle selected.
Real‐time vehicle shadow detection
Authors: Russell M. , Zou J.J. , Fang G.
Published: July 2015

In many traffic‐related applications, such as traffic management and structural health monitoring for roads, an accurate estimation of a moving vehicle's size and shape is needed before proceeding further. However, due to the presence of cast shadows, these properties cannot be obtained accurately using common object detection systems. To deal with the problem of misclassifying shadows as foreground, various methods have been introduced. Most of these methods often fail to distinguish shadow points from the foreground object when the boundary between the umbra and the object is unclear due to camouflage. A novel method for detecting moving shadows of vehicles in real‐time applications is presented. The method is based on two measurements, namely, the illumination direction and the intensity measurements in the neighbouring pixels in a scanned line. A major advantage of using image lines for classification is the ability to solve the problem associated with camouflages. Experimental results show that the proposed method is efficient in real‐time performances and has achieved higher detection rate and discrimination rate when compared with two well‐known methods.
Reduced graphene oxide and Ag wrapped TiO2 photocatalyst for enhanced visible light photocatalysis
Authors: Leong Kah Hon , Sim Lan Ching , Bahnemann Detlef , Jang Min , Ibrahim Shaliza , Saravanan Pichiah
Published: July 2015

A well-organised reduced graphene oxide (RGO) and silver (Ag) wrapped TiO2 nano-hybrid was successfully achieved through a facile and easy route. The inherent characteristics of the synthesized RGO-Ag/TiO2 were revealed through crystalline phase, morphology, chemical composition, Raman scattering, UV-visible absorption, and photoluminescence analyses. The adopted synthesis route significantly controlled the uniform formation of silver nanoparticles and contributed for the absorption of light in the visible spectrum through localized surface plasmon resonance effects. The wrapped RGO nanosheets triggered the electron mobility and promoted visible light shift towards red spectrum. The accomplishment of synergised effect of RGO and Ag well degraded Bisphenol A under visible light irradiation with a removal efficiency of 61.9%.
Preliminary experimental results of tungsten wire-array Z-pinches on primary test stand
Authors: Huang Xian-Bin , Zhou Shao-Tong , Dan Jia-Kun , Ren Xiao-Dong , Wang Kun-Lun , Zhang Si-Qun , Li Jing , Xu Qiang , Cai Hong-Chun , Duan Shu-Chao , Ouyang Kai , Chen Guang-Hua , Ji Ce , Wei Bing , Feng Shu-Ping , Wang Meng , Xie Wei-Ping , Deng Jian-Jun , Zhou Xiu-Wen , Yang Yi
Published: July 2015

The Primary Test Stand (PTS) developed at the China Academy of Engineering Physics is a 20 TW pulsed power driver, which can deliver a ∼10 MA, 70 ns rise-time (10%–90%) current to a short-circuit load and has important applications in Z-pinch driven inertial confinement fusion and high energy density physics. Preliminary results of tungsten wire-array Z-pinch experiments on PTS are presented. The load geometries investigated include 15-mm-tall cylindrical single and nested arrays with diameter ranging from 13 mm to 30 mm, consisting of 132–300 tungsten wires with 5–10 μm in diameter. Multiple diagnostics were fielded to characterize the x-ray radiation from wire-array Z pinches. The x-ray peak power (∼50 TW) and total radiated energy (∼500 kJ) were obtained from a single 20-mm-diam array with 80-ns stagnation time. The highest x-ray peak power up to 80 TW with 2.4 ns FWHM was achieved by using a nested array with 20-mm outer diameter, and the total x-ray energy from the nested array is comparable to that of single array. Implosion velocity estimated from the time-resolved image measurement exceeds 30 cm/μs. The detailed experimental results and other findings are presented and discussed.
Versatile common instrumentation for optical detection of pH and dissolved oxygen
Authors: Sardesai Neha , Rao Govind , Kostov Yordan
Published: July 2015

The recent trend toward use of disposable and miniature bioreactors requires the use of appropriate sensors. pH and dissolved oxygen (DO) are often measured using optical chemical sensors due to their small form factor and convenience in use. These sensors are often interrogated using a specialized opto-electronic transducer that is designed around the optical sensor. In this contribution, we are presenting a new class of opto-electronic transducers that are usable with several different chemical sensors without the need to switch the optics or hardware when changing the type of the chemical sensor. This allows flexibility closer to the lab-grade devices while the size is closer to a dedicated sensor. This versatile instrumentation is capable of seamlessly switching between the pH and DO measurement modes and is capable of auto recognition of the sensor type. The principle of ratiometric fluorescence is used for pH measurements, and that of fluorescence lifetime for DO measurements. An approach to obtain identical calibrations between several devices is also presented. The described hardware constitutes common instrumentation for measuring either pH or DO and has been tested in actual bioprocesses. It has been found adequate for continuous bioprocess monitoring.
Simulations of super-structure domain walls in two dimensional assemblies of magnetic nanoparticles
Authors: Jordanovic J. , Beleggia M. , Schiøtz J. , Frandsen C.
Published: July 2015

We simulate the formation of domain walls in two-dimensional assemblies of magnetic nanoparticles. Particle parameters are chosen to match recent electron holography and Lorentz microscopy studies of almost monodisperse cobalt nanoparticles assembled into regular, elongated lattices. As the particles are small enough to consist of a single magnetic domain each, their magnetic interactions can be described by a spin model in which each particle is assigned a macroscopic “superspin.” Thus, the magnetic behaviour of these lattices may be compared to magnetic crystals with nanoparticle superspins taking the role of the atomic spins. The coupling is, however, different. The superspins interact only by dipolar interactions as exchange coupling between individual nanoparticles may be neglected due to interparticle spacing. We observe that it is energetically favorable to introduce domain walls oriented along the long dimension of nanoparticle assemblies rather than along the short dimension. This is unlike what is typically observed in continuous magnetic materials, where the exchange interaction introduces an energetic cost proportional to the area of the domain walls. Structural disorder, which will always be present in realistic assemblies, pins longitudinal domain walls when the external field is reversed, and makes a gradual reversal of the magnetization by migration of longitudinal domain walls possible, in agreement with previous experimental results.
Impact of implanted phosphorus on the diffusivity of boron and its applicability to silicon solar cells
Authors: Schrof Julian , Müller Ralph , Reedy Robert C. , Benick Jan , Hermle Martin
Published: July 2015

Boron diffusivity reduction in extrinsically doped silicon was investigated in the context of a process combination consisting of BBr3 furnace diffusion and preceding Phosphorus ion implantation. The implantation of Phosphorus leads to a substantial blocking of Boron during the subsequent Boron diffusion. First, the influences of ion implantation induced point defects as well as the initial P doping on B diffusivity were studied independently. Here, it was found that not the defects created during ion implantation but the P doping itself results in the observed B diffusion retardation. The influence of the initial P concentration was investigated in more detail by varying the P implantation dose. A secondary ion mass spectrometry (SIMS) analysis of the BSG layer after the B diffusion revealed that the B diffusion retardation is not due to potential P content in the BSG layer but rather caused by the n-type doping of the crystalline silicon itself. Based on the observations the B diffusion retardation was classified into three groups: (i) no reduction of B diffusivity, (ii) reduced B diffusivity, and (iii) blocking of the B diffusion. The retardation of B diffusion can well be explained by the phosphorus doping level resulting in a Fermi level shift and pairing of B and P ions, both reducing the B diffusivity. Besides these main influences, there are probably additional transient phenomena responsible for the blocking of boron. Those might be an interstitial transport mechanism caused by P diffusion that reduces interstitial concentration at the surface or the silicon/BSG interface shift due to oxidation during the BBr3 diffusion process. Lifetime measurements revealed that the residual (non-blocked) B leads to an increased dark saturation current density in the P doped region. Nevertheless, electrical quality is on a high level and was further increased by reducing the B dose as well as by removing the first few nanometers of the silicon surface after the BBr3 diffusion.
Elastic properties and atomic bonding character in metallic glasses
Authors: Rouxel T. , Yokoyama Y.
Published: July 2015

The elastic properties of glasses from different metallic systems were studied in the light of the atomic packing density and bonding character. We found that the electronegativity mismatch (Δe−) between the host- and the major solute-elements provides a plausible explanation to the large variation observed for Poisson's ratio (ν) among metallic glasses (MGs) (from 0.28 for Fe-based to 0.43 for Pd-based MGs), notwithstanding a similar atomic packing efficiency (Cg). Besides, it is found that ductile MGs correspond to Δe− smaller than 0.5 and to a relatively steep atomic potential well. Ductility is, thus, favored in MGs exhibiting a weak bond directionality on average and opposing a strong resistance to volume change.
New developments in micro-X-ray diffraction and X-ray absorption spectroscopy for high-pressure research at 16-BM-D at the Advanced Photon Source
Authors: Park Changyong , Popov Dmitry , Ikuta Daijo , Lin Chuanlong , Kenney-Benson Curtis , Rod Eric , Bommannavar Arunkumar , Shen Guoyin
Published: July 2015

The monochromator and focusing mirrors of the 16-BM-D beamline, which is dedicated to high-pressure research with micro-X-ray diffraction (micro-XRD) and X-ray absorption near edge structure (XANES) (6-45 keV) spectroscopy, have been recently upgraded. Monochromatic X-rays are selected by a Si (111) double-crystal monochromator operated in an artificial channel-cut mode and focused to 5 μm × 5 μm (FWHM) by table-top Kirkpatrick-Baez type mirrors located near the sample stage. The typical X-ray flux is ∼5 × 108 photons/s at 30 keV. The instrumental resolution, Δq/qmax, reaches to 2 × 10−3 and is tunable through adjustments of the detector distance and X-ray energy. The setup is stable and reproducible, which allows versatile application to various types of experiments including resistive heating and cryogenic cooling as well as ambient temperature compression. Transmission XANES is readily combined with micro-XRD utilizing the fixed-exit feature of the monochromator, which allows combined XRD-XANES measurements at a given sample condition.
On the use of a weak-coupling thermostat in replica-exchange molecular dynamics simulations
Authors: Lin Zhixiong , van Gunsteren Wilfred F.
Published: July 2015

In a molecular dynamics (MD) simulation, various thermostat algorithms, including Langevin dynamics (LD), Nosé-Hoover (NH), and weak-coupling (WC) thermostats, can be used to keep the simulation temperature constant. A canonical ensemble is generated by the use of LD and NH, while the nature of the ensemble produced by WC has not yet been identified. A few years ago, it was shown that when using a WC thermostat with particular values of the temperature coupling time for liquid water at ambient temperature and pressure, the distribution of the potential energy is less wide than the canonical one. This led to an artifact in temperature replica-exchange molecular dynamics (T-REMD) simulations in which the potential energy distributions appear not to be equal to the ones of standard MD simulations. In this paper, we re-investigate this problem. We show that this artifact is probably due to the ensemble generated by WC being incompatible with the T-REMD replica-exchange criterion, which assumes a canonical configurational ensemble. We also show, however, that this artifact can be reduced or even eliminated by particular choices of the temperature coupling time of WC and the replica-exchange time period of T-REMD, i.e., when the temperature coupling time is chosen very close to the MD time step or when the exchange time period is chosen large enough. An attempt to develop a T-REMD replica-exchange criterion which is likely to be more compatible with the WC configurational ensemble is reported. Furthermore, an exchange criterion which is compatible with a microcanonical ensemble is used in total energy REMD simulations.
Geometrization conditions for perfect fluids, scalar fields, and electromagnetic fields
Authors: Krongos D. S. , Torre C. G.
Published: July 2015

Rainich-type conditions giving a spacetime “geometrization” of matter fields in general relativity are reviewed and extended. Three types of matter are considered: perfect fluids, scalar fields, and electromagnetic fields. Necessary and sufficient conditions on a spacetime metric for it to be part of a perfect fluid solution of the Einstein equations are given. Formulas for constructing the fluid from the metric are obtained. All fluid results hold for any spacetime dimension. Geometric conditions on a metric which are necessary and sufficient for it to define a solution of the Einstein-scalar field equations and formulas for constructing the scalar field from the metric are unified and extended to arbitrary dimensions, to include a cosmological constant, and to include any self-interaction potential. Necessary and sufficient conditions on a four-dimensional spacetime metric for it to be an electrovacuum and formulas for constructing the electromagnetic field from the metric are generalized to include a cosmological constant. Both null and non-null electromagnetic fields are treated. A number of examples and applications of these results are presented.
Combinatorial approach to Mathieu and Lamé equations
Authors: He Wei
Published: July 2015

Based on some recent progress on a relation between four dimensional super Yang-Mills gauge theory and quantum integrable system, we study the asymptotic spectrum of the quantum mechanical problems described by the Mathieu equation and the Lamé equation. The large momentum asymptotic expansion of the eigenvalue is related to the instanton partition function of supersymmetric gauge theories which can be evaluated by a combinatorial method. The electro-magnetic duality of gauge theory indicates that in the parameter space, there are three asymptotic expansions for the eigenvalue, and we confirm this fact by performing the Wentzel–Kramers–Brillouin (WKB) analysis in each asymptotic expansion region. The results presented here give some new perspective on the Floquet theory about periodic differential equation.
Time-resolved fast-neutron radiography of air-water two-phase flows in a rectangular channel by an improved detection system
Authors: Zboray Robert , Dangendorf Volker , Mor Ilan , Bromberger Benjamin , Tittelmeier Kai
Published: July 2015

In a previous work, we have demonstrated the feasibility of high-frame-rate, fast-neutron radiography of generic air-water two-phase flows in a 1.5 cm thick, rectangular flow channel. The experiments have been carried out at the high-intensity, white-beam facility of the Physikalisch-Technische Bundesanstalt, Germany, using an multi-frame, time-resolved detector developed for fast neutron resonance radiography. The results were however not fully optimal and therefore we have decided to modify the detector and optimize it for the given application, which is described in the present work. Furthermore, we managed to improve the image post-processing methodology and the noise suppression. Using the tailored detector and the improved post-processing, significant increase in the image quality and an order of magnitude lower exposure times, down to 3.33 ms, have been achieved with minimized motion artifacts. Similar to the previous study, different two-phase flow regimes such as bubbly slug and churn flows have been examined. The enhanced imaging quality enables an improved prediction of two-phase flow parameters like the instantaneous volumetric gas fraction, bubble size, and bubble velocities. Instantaneous velocity fields around the gas enclosures can also be more robustly predicted using optical flow methods as previously.
Perspective: Electrospray photoelectron spectroscopy: From multiply-charged anions to ultracold anions
Authors: Wang Lai-Sheng
Published: July 2015

Electrospray ionization (ESI) has become an essential tool in chemical physics and physical chemistry for the production of novel molecular ions from solution samples for a variety of spectroscopic experiments. ESI was used to produce free multiply-charged anions (MCAs) for photoelectron spectroscopy (PES) in the late 1990 s, allowing many interesting properties of this class of exotic species to be investigated. Free MCAs are characterized by strong intramolecular Coulomb repulsions, which create a repulsive Coulomb barrier (RCB) for electron emission. The RCB endows many fascinating properties to MCAs, giving rise to meta-stable anions with negative electron binding energies. Recent development in the PES of MCAs includes photoelectron imaging to examine the influence of the RCB on the electron emission dynamics, pump-probe experiments to examine electron tunneling through the RCB, and isomer-specific experiments by coupling PES with ion mobility for biological MCAs. The development of a cryogenically cooled Paul trap has led to much better resolved PE spectra for MCAs by creating vibrationally cold anions from the room temperature ESI source. Recent advances in coupling the cryogenic Paul trap with PE imaging have allowed high-resolution PE spectra to be obtained for singly charged anions produced by ESI. In particular, the observation of dipole-bound excited states has made it possible to conduct vibrational autodetachment spectroscopy and resonant PES, which yield much richer vibrational spectroscopic information for dipolar free radicals than traditional PES.
Flowing-afterglow study of electron-ion recombination of para–H3+ and ortho–H3+ ions at temperatures from 60 K to 300 K
Authors: Hejduk Michal , Dohnal Petr , Rubovič Peter , Kálosi Ábel , Plašil Radek , Johnsen Rainer , Glosík Juraj
Published: July 2015

Detailed measurements employing a combination of a cryogenic flowing afterglow with Langmuir probe (Cryo-FALP II) and a stationary afterglow with near-infrared absorption spectroscopy (SA-CRDS) show that binary electron recombination of para–H3+ and ortho–H3+ ions occurs with significantly different rate coefficients, pαbin and oαbin, especially at very low temperatures. The measurements cover temperatures from 60 K to 300 K. At the lowest temperature of 60 K, recombination of para–H3+ is at least three times faster than that of ortho–H3+ (pαbin=(1.8±0.4)×10−7cm3s−1vs.oαbin=(0−0+5)×10−8cm3s−1).
Investigating the effect of integration constants and various plasma parameters on the dynamics of the soliton in different physical plasmas
Authors: Dag̃han D. , Dönmez O.
Published: July 2015

The nonlinear dynamics and propagation of ion acoustic waves in a relativistic and ideal plasmas, which have the pressure variation of electrons and ions and degenerate electrons, are investigated using the analytic solution of KdV type equations performed applying (G′/G)-expansion and (G′/G,1/G)-expansion methods. The effects of various parameters, such as phase velocity of the ion acoustic wave, the ratio of ion temperature to electron temperature, normalized speed of light, electron and ion streaming velocities, arbitrary and integration constants, on the soliton dynamics are studied. We have found that dim and hump solitons and their amplitudes, widths and dynamics strongly depend on these plasma parameters and integration constants. The source term μ plays also a vital role in the formation of the solitons. Moreover, it is also found that the observed solitary wave solution can be excited from hump soliton to dip soliton. This dramatic change of the solitons can occur due to the various values of the integration constants and ion streaming velocities. Finally, it is important to note that the analytic solutions of the nonlinear equation, reported in this study, could be used to explain the structures of solitons in the astrophysical space and in laboratory plasmas.
Carbon nanoparticles in the radiation field of the stationary arc discharge
Authors: Shneider M. N.
Published: July 2015

The paper considers a simple theoretical model of heating the nanoparticles, depending on their size and the parameters of the radiating arc and the surrounding gas. This problem is of interest to diagnostics and modeling of the dynamics of the nanoparticles formation and their local size distribution. Heating of nanoparticles by the radiation can affect the process of synthesis. The degree of heating of the particle is determined by its geometry, which opens, apparently, additional possibilities for nonintrusive optical diagnostics.
Sculpting bespoke mountains: Determining free energies with basis expansions
Authors: Whitmer Jonathan K. , Fluitt Aaron M. , Antony Lucas , Qin Jian , McGovern Michael , de Pablo Juan J.
Published: July 2015

The intriguing behavior of a wide variety of physical systems, ranging from amorphous solids or glasses to proteins, is a direct manifestation of underlying free energy landscapes riddled with local minima separated by large barriers. Exploring such landscapes has arguably become one of statistical physics’s great challenges. A new method is proposed here for uniform sampling of rugged free energy surfaces. The method, which relies on special Green’s functions to approximate the Dirac delta function, improves significantly on existing simulation techniques by providing a boundary-agnostic approach that is capable of mapping complex features in multidimensional free energy surfaces. The usefulness of the proposed approach is established in the context of a simple model glass former and model proteins, demonstrating improved convergence and accuracy over existing methods.
Thermal stability of wurtzite Zr1−xAlxN coatings studied by in situ high-energy x-ray diffraction during annealing
Authors: Rogström L. , Ghafoor N. , Schroeder J. , Schell N. , Birch J. , Ahlgren M. , Odén M.
Published: July 2015

We study the thermal stability of wurtzite (w) structure ZrAlN coatings by a combination of in situ high-energy x-ray scattering techniques during annealing and electron microscopy. Wurtzite structure Zr1−xAlxN coatings with Al-contents from x = 0.46 to x = 0.71 were grown by cathodic arc evaporation. The stability of the w-ZrAlN phase depends on chemical composition where the higher Al-content coatings are more stable. The wurtzite ZrAlN phase was found to phase separate through spinodal decomposition, resulting in nanoscale compositional modulations, i.e., alternating Al-rich ZrAlN layers and Zr-rich ZrAlN layers, forming within the hexagonal lattice. The period of the compositional modulations varies between 1.7 and 2.5 nm and depends on the chemical composition of the coating where smaller periods form in the more unstable, high Zr-content coatings. In addition, Zr leaves the w-ZrAlN lattice to form cubic ZrN precipitates in the column boundaries.
A modified Katsumata probe—Ion sensitive probe for measurement in non-magnetized plasmas
Authors: Čada M. , Hubička Z. , Adámek P. , Olejníček J. , Kment Š. , Adámek J. , Stöckel J.
Published: July 2015

A modified Katsumata probe has been developed for measurement of ion velocity distribution function (IVDF) in technological non-magnetized plasmas. A simple construction of the modified Katsumata probe consists of adding a pair of permanent Sm-Co magnets in front of Katsumata probe. A comparative study regarding IVDF measurement in a high power impulse magnetron sputtering system operating in pure argon atmosphere by means of developed modified Katsumata probe and commercially available gridded retarding field analyzer (RFA) has been carried out. A time-resolved measurement of IVDF for two different pressures whilst other plasma conditions have been kept unchanged has revealed that the main advantage of the modified Katsumata probe compared to the RFA consists in significantly smaller angular aperture of entrance orifice of modified Katsumata probe being approximately 15° in comparison with a commercial RFA having angular aperture more than 160°. It leads in much better velocity resolution in measured IVDF since the transversal part of velocity vector is much more suppressed compared to RFA. Furthermore, the modified Katsumata probe less suffers from collisions of ions in the space charge sheath in front or inside of the probe compared to the RFA.
A Gaussian wave packet phase-space representation of quantum canonical statistics
Authors: Coughtrie David J. , Tew David P.
Published: July 2015

We present a mapping of quantum canonical statistical averages onto a phase-space average over thawed Gaussian wave-packet (GWP) parameters, which is exact for harmonic systems at all temperatures. The mapping invokes an effective potential surface, experienced by the wave packets, and a temperature-dependent phase-space integrand, to correctly transition from the GWP average at low temperature to classical statistics at high temperature. Numerical tests on weakly and strongly anharmonic model systems demonstrate that thermal averages of the system energy and geometric properties are accurate to within 1% of the exact quantum values at all temperatures.
Electronic structure of Li1+x[Mn0.5Ni0.5]1−xO2 studied by photoemission and x-ray absorption spectroscopy
Authors: Yokoyama Y. , Ootsuki D. , Sugimoto T. , Wadati H. , Okabayashi J. , Yang Xu , Du Fei , Chen Gang , Mizokawa T.
Published: July 2015

We have studied the electronic structure of Li1+x[Mn0.5Ni0.5]1−xO2 (x = 0.00 and 0.05), one of the promising cathode materials for Li ion battery, by means of x-ray photoemission and absorption spectroscopy. The results show that the valences of Mn and Ni are basically 4+ and 2+, respectively. However, the Mn3+ component in the x = 0.00 sample gradually increases with the bulk sensitivity of the experiment, indicating that the Jahn-Teller active Mn3+ ions are introduced in the bulk due to the site exchange between Li and Ni. The Mn3+ component gets negligibly small in the x = 0.05 sample, which indicates that the excess Li suppresses the site exchange and removes the Jahn-Teller active Mn3+.
Thermal transport across few-layer boron nitride encased by silica
Authors: Ni Yuxiang , Jiang Jiechao , Meletis Efstathios , Dumitricǎ Traian
Published: July 2015

Two dimensional hexagonal boron nitride (h-BN) attracted attention for use in applications. Using equilibrium molecular dynamics, we examine the phonon transport in few-layer h-BN encased by silica (SiO2). We report large interfacial thermal resistances, of about 2.2 × 10−8 m2 K W−1, which are not sensitive to the number of h-BN layers or the SiO2 crystallinity. The h-BN/SiO2 superlattices exhibit ultra-low thermal conductivities across layers, as low as 0.3 W/m K. They are structurally stable up to 2000 K while retaining the low-thermal conductivity attributes. Our simulations indicate that incorporation of h-BN layers and nanoparticles in silica could establish thermal barriers and heat spreading paths, useful for high performance coatings and electronic device applications.
Frequency-dependent ferroelectric behavior of BaMn3Ti4O14.25 at room temperature
Authors: Hossain Muhammad E. , Liu Shuangyi , O'Brien Stephen , Li Jackie
Published: July 2015

We report the activation field and selective frequency-dependent ferroelectric behavior of BaMn3Ti4O14.25 (BMT-134) at room temperature. BMT-134, a recently discovered multiferroic complex oxide, exhibits antiferromagnetic and ferroelectric behavior and belongs to the hollandite crystal class. The microstructure can be manipulated through processing conditions to prepare a nanocrystalline textured tablet. We measured polarization-electric field (P-E) hysteresis loops and strain-electric field butterfly loops as a function of frequency in order to investigate the AC dynamics of domain switching and strain behavior. Under an electric field loading condition, a clear hysteresis loop of the electric field-displacement curve is obtained at 50 Hz, indicating that room temperature ferroelectricity is attainable under the right processing conditions. When the frequency is increased to 500 Hz, the coercive field also increases, until the frequency reaches 5 kHz, at which point the electric field versus electric displacement becomes linear indicating the limit of domain switching at high frequency.
Bias-free lateral terahertz emitters—A simulation study
Authors: Granzner R. , Polyakov V. M. , Cimalla V. , Ambacher O. , Schwierz F.
Published: July 2015

The design and performance of bias-free InN-based THz emitters that exploit lateral photocurrents is studied by means of numerical simulations. We use a drift-diffusion model with adjusted carrier temperatures and mobilities. The applicability of this approach is demonstrated by a comparison with results from Monte-Carlo simulations. We consider a simple but robust lateral emitter concept using metal stripes with two different thicknesses with one of them being thin enough to be transparent for THz radiation. This arrangement can be easily multiplexed and the efficiency of this concept has already been demonstrated by experiment for GaAs substrates. In the present study, we consider InN, which is known to be an efficient photo-Dember emitter because of its superior transport properties. Our main focus is on the impact of the emitter design on the emission efficiency assuming different operation principles. Both the lateral photo-Dember (LPD) effect and built-in lateral field effects are considered. The appropriate choice of the metal stripe and window geometry as well as the impact of surface Fermi level pinning are investigated in detail, and design guidelines for efficient large area emitters using multiplexed structures are provided. We find that InN LPD emitters do not suffer from Fermi level pinning at the InN surface. The optimum emission efficiency is found for LPD emitter structures having 200 nm wide illumination windows and mask stripes. Emitter structures in which lateral electric fields are induced by the metal mask contacts can have a considerably higher efficiency than pure LPD emitters. In the best case, the THz emission of such structures is increased by one order of magnitude. Their optimum window size is 1 μm without the necessity of a partially transparent set of mask stripes.
Ti/Al/W Ohmic contacts to p-type implanted 4H-SiC
Authors: Vivona M. , Greco G. , Lo Nigro R. , Bongiorno C. , Roccaforte F.
Published: July 2015

In this work, the morphological, structural, and electrical properties of Ti/Al/W contacts to p-type implanted silicon carbide (4H-SiC) have been monitored as a function of the annealing temperature (800–1100 °C). The increase of the annealing temperature induces a transition from a rectifying to an Ohmic behavior, with a specific contact resistance of 5.8 × 10−4 Ωcm2. The electrical behavior has been correlated with the morphological and structural analyses. In particular, the transition to an Ohmic behavior was accompanied by a gradual increase of the surface roughness and by the occurrence of a reaction leading to the formation of new phases in the stack and at the interface (TiAl3, W(SiAl)2, and TiC). The presence of Al-rich protrusions penetrating in the SiC substrate was also observed. From the temperature dependence of the electrical parameters, a barrier height of 0.69 eV for this system was determined. The thermal stability of the contacts has been demonstrated for long-term (up to 100 h) thermal cycling at 400 °C.
Improved terahertz modulation using germanium telluride (GeTe) chalcogenide thin films
Authors: Gwin A. H. , Kodama C. H. , Laurvick T. V. , Coutu R. A. , Taday P. F.
Published: July 2015

We demonstrate improved terahertz (THz) modulation using thermally crystallized germanium telluride (GeTe) thin films. GeTe is a chalcogenide material that exhibits a nonvolatile, amorphous to crystalline phase change at approximately 200 °C, as well as six orders of magnitude decreased electrical resistivity. In this study, amorphous GeTe thin films were sputtered on sapphire substrates and then tested using THz time-domain spectroscopy (THz-TDS). The test samples, heated in-situ while collecting THz-TDS measurements, exhibited a gradual absorbance increase, an abrupt nonvolatile reduction at the transition temperature, followed by another gradual increase in absorbance. The transition temperature was verified by conducting similar thermal tests while monitoring electrical resistivity. THz transmittance modulation data were investigated between 10 and 110 cm−1 (0.3–3.3 THz). A peak modulation of approximately 99% was achieved at 2.3 THz with a 100 nm GeTe film on a sapphire substrate. After isolating the sapphire and the crystalline GeTe (c-GeTe) absorbance contributions, the results showed THz modulations ranging from 88.5% to 91.5% that were attributed solely to the single layer of transitioned c-GeTe. These results strongly motivate using GeTe or other chalcogenide thin films in THz modulators, filters, and metamaterial applications.
Thermal transport across carbon nanotube-graphene covalent and van der Waals junctions
Authors: Shi Jingjing , Dong Yalin , Fisher Timothy , Ruan Xiulin
Published: July 2015

Carbon nanotubes and graphene are promising materials for thermal management applications due to their high thermal conductivities. However, their thermal properties are anisotropic, and the radial or cross-plane direction thermal conductivity is low. A 3D Carbon nanotube (CNT)-graphene structure has previously been proposed to address this limitation, and direct molecular dynamics simulations have been used to predict the associated thermal conductivity. In this work, by recognizing that thermal resistance primarily comes from CNT-graphene junctions, a simple network model of thermal transport in pillared graphene structure is developed. Using non-equilibrium molecular dynamics, the resistance across an individual CNT-graphene junction with sp2 covalent bonds is found to be around 6×10−11 m2K/W, which is significantly lower than typical values reported for planar interfaces between dissimilar materials. In contrast, the resistance across a van der Waals junction is about 4×10−8 m2K/W. Interestingly, when the CNT pillar length is small, the interfacial resistance of the sp2 covalent junction is found to decrease as the CNT pillar length decreases, suggesting the presence of coherence effects. To explain this intriguing trend, the junction thermal resistance is decomposed into interfacial region and boundary components, and it is found that while the boundary resistance has little dependence on the pillar length, the interfacial region resistance decreases as the pillar length decreases. This is explained by calculating the local phonon density of states (LDOS) of different regions near the boundary. The LDOS overlap between the interfacial region and the center region of CNT increases as the pillar length decreases, leading to the decrease of interfacial region resistance. The junction resistance Rj is eventually used in the network model to estimate the effective thermal conductivity, and the results agree well with direct MD simulation data, demonstrating the effectiveness of our model.
Electrocaloric effect and luminescence properties of lanthanide doped (Na1/2Bi1/2)TiO3 lead free materials
Authors: Zannen M. , Lahmar A. , Asbani B. , Khemakhem H. , El Marssi M. , Kutnjak Z. , Es Souni M.
Published: July 2015

Polycrystalline lead-free Sodium Bismuth Titanate (NBT) ferroelectric ceramics doped with rare earth (RE) element are prepared using solid state reaction method. Optical, ferroelectric, and electrocaloric properties were investigated. The introduction of RE3+ ions in the NBT host lattice shows different light emissions over the wavelength range from visible to near infrared region. The ferroelectric P-E hysteresis loops exhibit an antiferroelectric-like character near room temperature indicating possible existence of a morphotropic phase boundary. The enhanced electrocaloric response was observed in a broad temperature range due to nearly merged phase transitions. Coexistence of optical and electrocaloric properties is very promising for photonics or optoelectronic device applications.
Effects of vacancies on luminescence of Er-doped 0.93Bi0.5Na0.5TiO3-0.07BaTiO3 ceramics
Authors: Lau Chi Man , Wu Xiao , Kwok K. W.
Published: July 2015

0.93Bi0.5Na0.5TiO3-0.07BaTiO3 ceramics doped with 0.01 mol Er3+ have been prepared and their photoluminescence (PL), ferroelectric, dielectric, and piezoelectric properties have been studied. By doping Er3+ at various sites, ceramics containing oxygen or cation vacancies have been prepared and their effects have been investigated. Ceramic containing no vacancy (i.e., doping Er3+ at the Bi3+ site) has also been prepared as a reference for the study. In addition to the reduction of the up-conversion PL emissions at 532, 547, and 660 nm, our results also reveal that oxygen vacancies can enhance, at the expense of the visible emissions, the near-infrared (1.44–1.66 μm) and mid-infrared (2.62–2.84 μm) down-conversion emissions. Similar results have also been observed for the ceramics containing cation vacancies, and the enhancement in the near-infrared emission becomes much more significant, reaching about 70% for the ceramic doped with Er3+ at the Na+ site. These should be attributed to the looping mechanism between the 4F7/2, 2H11/2, 4I9/2, and 4I11/2 levels facilitated by the cation vacancies and the efficient cross relaxations. The ceramics also exhibit reasonably good ferroelectric, dielectric, and piezoelectric properties, suggesting that they have great potential for multifunctional applications.
Quantum dots in the GaAs/AlxGa1−xAs core-shell nanowires: Statistical occurrence as a function of the shell thickness
Authors: Francaviglia Luca , Fontana Yannik , Conesa-Boj Sonia , Tütüncüoglu Gözde , Duchêne Léo , Tanasescu Mihaela B. , Matteini Federico , Fontcuberta i Morral Anna
Published: July 2015

Quantum dots (QDs) embedded in nanowires represent one of the most promising technologies for applications in quantum photonics. Self-assembled bottom-up fabrication is attractive to overcome the technological challenges involved in a top-down approach, but it needs post-growth investigations in order to understand the self-organization process. We investigate the QD formation by self-segregation in AlxGa1−xAs shells as a function of thickness and cross-section morphology. By analysing light emission from several hundreds of emitters, we find that there is a certain thickness threshold for the observation of the QDs. The threshold becomes smaller if a thin AlAs layer is pre-deposited between the GaAs nanowire core and the AlxGa1−xAs shell. Our results evidence the development of the quantum emitters during the shell growth and provide more guidance for their use in quantum photonics.
Self-limited kinetics of electron doping in correlated oxides
Authors: Chen Jikun , Zhou You , Middey Srimanta , Jiang Jun , Chen Nuofu , Chen Lidong , Shi Xun , Döbeli Max , Shi Jian , Chakhalian Jak , Ramanathan Shriram
Published: July 2015

Electron doping by hydrogenation can reversibly modify the electrical properties of complex oxides. We show that in order to realize large, fast, and reversible response to hydrogen, it is important to consider both the electron configuration on the transition metal 3d orbitals, as well as the thermodynamic stability in nickelates. Specifically, large doping-induced resistivity modulations ranging several orders of magnitude change are only observed for rare earth nickelates with small ionic radii on the A-site, in which case both electron correlation effects and the meta-stability of Ni3+ are important considerations. Charge doping via metastable incorporation of ionic dopants is of relevance to correlated oxide-based devices where advancing approaches to modify the ground state electronic properties is an important problem.
Reduced energy loss in poly(vinylidene fluoride) nanocomposites by filling with a small loading of core-shell structured BaTiO3/SiO2 nanofibers
Authors: Liu Shaohui , Xue Shuangxi , Shen Bo , Zhai Jiwei
Published: July 2015

Homogeneous ceramic-polymer nanocomposites consisting of core-shell structured BaTiO3/SiO2 nanofibers and a p oly(vinylidene fluoride) (PVDF) polymer matrix have been prepared. The correlation between the energy discharged density and interfacial polarization is studied in PVDF nanocomposites by the measurements of the discharge performance and impedance spectroscopy. According to the results of dielectric constant, breakdown strength, and complex impedance analysis, coating SiO2 layers on the surface of BaTiO3 nanofibers can block the movement of charge carriers through the nanocomposites by playing a shielding role on the charge-rich inter layer, which resulted in weak Maxwell–Wagner–Sillars interfacial polarization and thus reduces the energy loss and improved the energy discharged density of the nanocomposites. The energy discharged density in the nanocomposite with 2.5 vol. % BaTiO3/SiO2 core-shell nanofibers is 6.28 J/cm3 at 3.3 MV/cm, which is over 11.94% higher than that of nanocomposite with BaTiO3 nanofibers at the same electric field.