bluuebunny/crossref_metadata_2025 huggingface dataset:
Gyrokinetic simulations of zonal flows and ion temperature gradient turbulence in HL-2A ITB plasmas
Authors: Xu J. Q. , Peng X. D. , Hao G. Z. , Chen W. , Li J. Q. , Qu H. P. , Li J. C. , Ren G. Z. , He X. X. , Li Y. G.
Published: January 2022

The characteristics of zonal flows (ZFs) in ion temperature gradient (ITG) turbulence during the formation of internal transport barrier (ITB) have been investigated by nonlinear gyrokinetic simulations for the HL-2A tokamak experiment. The turbulent ion heat transport and zonal flow dynamics are investigated in the local turbulence limit for a neutral beam heated L-mode plasma. Linear stability analyses have shown that the maximum growth rate, γmax, is decreased across the whole confinement region during the formation of ITB although the critical parameter, ηi, is increased, which is identified to be due to the stabilizing of ITG with an increased ion-to-electron temperature ratio τ. The entropy generated by ion heat flux is significantly decreased together with the enhanced ZF amplitude and reduced ion heat transport when ITB has been fully developed, especially the modes with intermediate radial wavenumbers, implying that the long and medium radial scale turbulences are strongly suppressed by the ZF shear. Meanwhile, the long-range correlation and relative energy of the self-generated ZF are increased while the turbulent energy is decreased when ITB is triggered, indicating that the ZF gains more energy from background turbulence. It is found that the ratio between τ and ηi is a key parameter in determining the ZF shearing rate ωE×BZF and γmax. The value of ωE×BZF>γmax occurs around τ/ηi > 1.4, which is suggested to be responsible for the reduction of ion heat transport and hence the ITB formation.
The dynamics of an axisymmetric turbulent jet in ambient turbulence interpreted from the passive scalar field statistics
Authors: Sahebjam Rana , Kohan Khashayar F. , Gaskin Susan
Published: January 2022

The effect of approximately homogeneous isotropic turbulence on the dynamics of an axisymmetric turbulent jet (Re = 10 600 and 5800) in an ambient with a negligible mean flow is interpreted from the statistics of the passive scalar field. The ambient turbulence is generated by a random jet array and scalar concentrations are measured in orthogonal cross sections of the jet using planar laser-induced fluorescence. Statistics of the scalar field of the jet in a turbulent ambient are compared to those in a quiescent ambient, using classical Eulerian averages and those conditioned on the jet centroid. A two-region model for the jet structure in ambient turbulence is proposed based on the centroidal statistics. Following the developing region of the jet, the ambient turbulence disrupts the jet structure, due to modulation of the jet interface, meandering of the jet by large eddies, and entrainment of the turbulent ambient fluid, resulting in a faster concentration decay and reduced entrainment compared to the quiescent ambient. Further downstream, once the ambient turbulence has destroyed the jet, only molecular and turbulent diffusion modify the scalar concentrations. The regions' relative lengths depend primarily on the relative turbulence intensity (ξ) between the ambient and the jet, as assessed using centroidal analysis, which removes the effect of the relative length scale (l) on the jet behavior in the turbulent ambient. The centroidal scalar statistics reveal self-similarity and self-preservation in mean scalar properties before jet breakup, which occurs abruptly once ξ> 0.5. The smaller scales of ambient turbulence modulate the jet boundary and, when entrained, lead to a wider range of centerline concentrations and root mean square concentrations, which are hypothesized to increase local concentration gradients within the jet and reduce jet mixing.
Random growth scale-free networked models with an identical degree distribution and a tunable assortativity index
Authors: Luo Xudong , Ma Fei , Xu Wentao
Published: January 2022

In this work, we propose two kinds of graphic operations by using triangle configuration, based on which we establish a family of random growth networked models G(t;p) where notations t and p represent time step and probability parameter, respectively. By studying some fundamental structural parameters both analytically and numerically, we show that (1) all the realizations G(t;p) follow the same power-law degree distribution with exponent γ=2+ln⁡3/ln⁡2 regardless of probability p and thus have scale-free feature; (2) each model G(t;p) has a relatively high clustering coefficient; and (3) while network G(t;1) has a small average path length, it is not a unique model possessing small-world property mainly because its diameter D(t;1) does not reach the theoretical lower bound. Next, we make use of assortativity index R to quantify the tendency of forming connection between vertices and observe that (1) model G(t;0) exhibits disassortative mixing because the corresponding index R(t;0) is non-positive, and (2) model G(t;1) is in the opposite direction. As a result, we demonstrate that random model G(t;p) has a tunable quantity R(t;p) controlled by probability p. In addition, we exactly determine the total number of spanning trees of deterministic models G(t;1) and G(t;0) and also calculate the entropy of spanning trees.
All-optical microwave feedback oscillator with atomic cell resonator
Authors: Boudot R. , Abdel Hafiz M. , Petersen M. , Calosso C. E. , Rubiola E.
Published: January 2022

We report the demonstration of an all-optical self-sustained cell-based microwave feedback oscillator. In this scheme, a microwave resonance, optically induced in a buffer-gas filled vapor cell resonator through coherent population trapping (CPT), is detected by a fast photodiode, amplified, and used to drive back, through a frequency divider, a Mach–Zehnder electro-optic modulator in a sustaining loop configuration. The total gain and phase of the system was measured in an open-loop configuration with a network analyzer. In good agreement with values predicted by the Leeson effect, the CPT feedback oscillator demonstrates an absolute phase noise of −24 dB rad2/Hz at 1 Hz offset frequency, compatible with a fractional frequency stability of 8 × 10−12 at 1 s, and a phase noise floor of −112 dB rad2/Hz, limited by the low microwave power available at the photodiode output. The amplitude noise of the oscillator shows a comparable noise floor and, for offset frequencies lower than 200 Hz, a 1/f dependence, due to the presence of the frequency divider in the loop.
Molecular reorganization energy in quantum-dot cellular automata switching
Authors: Pidaparthi Subhash S. , Lent Craig S.
Published: January 2022

We examine the impact of the intrinsic molecular reorganization energy on switching in two-state quantum-dot cellular automata cells. Switching a bit involves an electron transferring between charge centers within the molecule. This, in turn, causes the other atoms in the molecule to rearrange their positions in response. We capture this in a model that treats the electron motion quantum-mechanically but the motion of nuclei semiclassically. This results in a non-linear Hamiltonian for the electron system. Interaction with a thermal environment is included by solving the Lindblad equation for the time-dependent density matrix. The calculated response of a molecule to the local electric field shows hysteresis during switching when the sweep direction is reversed. The relaxation of neighboring nuclei increases the localization of the electron, which provides an intrinsic source of enhanced bistability and single-molecule memory. This comes at the cost of increased power dissipation.
A resistive-anode based position-sensitive Rydberg atom detector
Authors: Jones A. C. L. , Moxom J. , Fuentes-Garcia M. , Cecchini G. G. , Membreno E. E. , Roeder E. E. , Mills A. P.
Published: January 2022

We describe here the development and characterization of a position-sensitive detector for Rydberg atom experiments. The detector builds on an earlier design that field-ionized incident Rydberg positronium (Ps) atoms and then electrostatically focused the freed positrons onto a micro-channel plate (MCP) detector without the use of a position sensitive anode. In this design, pulses from the MCP are deposited onto a resistive anode, providing a means of measuring the incident particles’ x, y positions. The first detector constructed utilized a pair of MCPs in a chevron configuration and was used to observe the focusing of Rydberg Ps atoms from an electrostatic mirror. A second detector, developed for use in a measurement of the 1S–2S interval of Ps, incorporates three MCPs in a Z-stack configuration to produce larger pulses. Using a UV-induced signal, we have characterized the performance of the assembled detectors, finding a spatial resolution of ∼1.4 mm for the largest induced pulses and for pulse widths of ∼7–10 ns FWHM; pulse times can be resolved to better than 1 ns. The Ps induced signal is anticipated to yield pulses ∼5 times larger, which are expected to achieve a spatial resolution of <1 mm. Appropriate lenses could make possible applications involving either imaging a large area or magnifying a small area of the incident Ps spatial distribution.
Modeling defect mediated color-tunability in LEDs with Eu-doped GaN-based active layers
Authors: Austin Hayley J. , Mitchell Brandon , Timmerman Dolf , Tatebayashi Jun , Ichikawa Shuhei , Fujiwara Yasufumi , Dierolf Volkmar
Published: January 2022

Color tunability from red to orange to yellow has been demonstrated in GaN-based LED devices with Eu-doped GaN layers as the active region. Under current injection, this is achieved by varying the current density and the pulse conditions. The underlying mechanism behind this color tunability is a redistribution of energy among the 5DJ states of a Eu3+ ion. This energy shuffling is facilitated by a local defect that has been neglected in previous modeling work. Including this defect allows for a quantitative prediction of the relative time-averaged populations of the Eu3+ ion's 5D0 and 5D1 states. Extracting, from experimental results, the red and yellow/green emission spectra due to radiative transitions from the respective levels and mixing them allows the overall chromaticity of the emission to be determined for varied excitation conditions. In addition, the model allows us to determine the optimal injection conditions to maximize the gamut of color tunability while minimizing power consumption. These simulations pave the way for practical, systematic color tuning from a single-contact pixel.
Effects of exercise on flow characteristics in human carotids
Authors: He Xinyi , Yang Xiaolei
Published: January 2022

Carotid is one of the focal regions prone to atherosclerosis. Previous studies have shown that hemodynamics plays an important role in the initiation and formation of atherosclerosis plaques. In this work, we numerically investigate the flow patterns in two carotids with different flares and proximal curvatures under inflows from three age groups with/without exercise. The simulation results show that the effects of exercising on the carotid flow and wall shear stress are different at different time instants and for different age groups. As for the oscillatory shear index, exercise does not have significant effects. The effects of inflow waveforms on the reversed flow volume are also examined. For the carotid C1 with low flare and high proximal curvature, it is found that exercising increases and decreases the reversed flow volume for young and senior people, respectively. For middle-aged people, on the other hand, the reversed flow volume is increased and decreased in the middle of the sinus and near the bifurcation, respectively, for the carotid C1. For the carotid C2 with high flare and low curvature, on the other hand, it is found that exercising increases the reversed flow volume for all age groups. This work suggests that the effects of exercise on atherosclerosis should be evaluated by fully considering patient-specific geometries and ages.
Energy density balance during shock wave implosion in water
Authors: Chefranov Sergey G. , Krasik Yakov E. , Rososhek Alexander
Published: January 2022

Analytical modeling of the evolution of cylindrical and spherical shock waves (shocks) during an implosion in water is presented for an intermediate range of convergence radii. This range of radii was observed in experiments when the exploding wire expansion dynamics does not influence on shock propagation, but not yet described by well-known self-similar solutions. The model is based on an analysis of the change in pressure and kinetic energy density as well as on the corresponding fluxes of internal and kinetic energy densities behind the shock front. It shows that the spatial evolution of the shock velocity strongly depends on the initial compression, the adiabatic index of water, and the geometry of convergence. The model also explains the transition to a rapid like a self-similar increase in the shock velocity at only a certain radius of the shock that is observed in experiments. The dependence of the threshold radius, where the shock implosion follows the power law (quasi self-similarity), on the initial compression is determined. It is stated that in the entire range of the shock radii, the internal and kinetic energy density fluxes are equal, which agrees with known experimental data.
Water drop impacts on regular micropillar arrays: The impact region
Authors: Broom Matheu , Willmott Geoff R.
Published: January 2022

A liquid drop impact on to a rough solid typically produces an “impact region,” which is an area of fully wetted surface smaller than or equal to the projected area of the drop. Here, high-speed photography is used to study the size and symmetry of this impact region and microbubbles within it for water drop impacts on regular square arrays of hydrophobic micropillars. Outcomes are most strongly influenced by pillar pitch and impact Weber number (We), and there is an apparent transition from vertical to more horizontal wetting near the edge of the projected area of the falling drop. The impact region size is well described by energetic and pinning transition analyses, but profound asymmetries are observed, indicating the influence and superposition of cross-flows for gas and liquid escape. Zipping of the liquid–air interface between pillars during later stages of drop spreading is also studied. The surfaces have 20 μm wide polydimethylsiloxane pillars of circular or square cross section. Variations in array pitch (40–80 μm) and height (15–30 μm) are systematically investigated using droplets of diameter 2.51 ± 0.04 mm over the range 50< We < 250. The geometric regularity of these surfaces could give rise to technological applications, but the results are also relevant to the many natural and industrial processes in which liquid drops impact upon dry surfaces with micrometer scale roughness.
Photon-induced degradation of InGaN-based LED in open-circuit conditions investigated by steady-state photocapacitance and photoluminescence
Authors: Caria Alessandro , De Santi Carlo , Buffolo Matteo , Meneghesso Gaudenzio , Zanoni Enrico , Meneghini Matteo
Published: January 2022

Degradation of InGaN–GaN LEDs has been the subject of intense investigations in the past few years. While current- and temperature-induced degradation processes have been described, the impact of photon-induced degradation has not been investigated in detail in the literature. This paper aims at improving the understanding of the mechanisms responsible for the degradation of the InGaN subject to high photon densities by stressing the devices under a high-intensity laser beam in open-circuit conditions (i.e., in the absence of external current). We analyzed the degradation by means of electrical, optical, and deep-level characterization techniques. First, we demonstrate the existence of optically induced degradation processes in GaN LEDs: from photoluminescence measurements, we observed a decrease in the luminescence after stress, more prominent in the region irradiated during stress. Second, we ascribe this effect to a decrease in internal quantum efficiency due to the generation of non-radiative defects within the active region. Third, by steady-state photocapacitance measurements, we reveal the presence of a shallow level with an energy of EC–2.2 eV, which can be ascribed to gallium vacancies and its complexes with oxygen and nitrogen and can be related to the increase in yellow luminescence.
Bound photoinduced giant spin polaron in EuTe
Authors: Henriques A. B. , van Kooten S. C. P. , Abramof E. , Rappl P. H. O. , Galgano G. D.
Published: January 2022

Previously, we showed that at low temperatures and very low excitation powers, EuTe displays band-edge photoluminescence with a well-resolved phonon structure, the so-called MX0 band, which is associated with the recombination of giant spin polarons (SPs) of magnetic moments of several hundred Bohr magnetons. Here, we investigate the MX0 band both experimentally and by Monte Carlo simulations. Results indicate that the SPs are bound to defects, with a localization energy of 0.29 eV. The density of defects harboring the SPs is estimated to be 4.3×1015 cm−3.
Enhanced performance of tandem plunging airfoils with an asymmetric pitching motion
Authors: Chen Zhe , Li Xiong , Chen Long
Published: January 2022

The flapping wings or fins in an in-line arrangement are a common scene in flocks and schools, as well as flying creatures with multiple pairs of wings, e.g., dragonflies. Conventional studies on these topics are underpinned by tandem plunging airfoils in either a vertical or a declined stroke plane. The former model mostly considers a symmetrical pitching motion, and the latter model fails to separate the effect of the asymmetric pitching from that of the declined incoming flow. However, our study focuses on the tandem airfoils with vertical plunging and asymmetric pitching in a horizontal freestream and, therefore, explains the effects of asymmetric pitching on tandem plunging airfoils. Using numerical methods, the aerodynamic performance and vortical structures of the tandem airfoils are examined, and the effects of the non-zero geometric angle of attack (α0), phase angles in the plunging and pitching motion (φ and θ), and inter-foil spacing (G/c) are discussed. Our results show that the tandem arrangement is beneficial to enhance the propulsion thrust while retaining the lifting capacity of the airfoil at a non-zero α0. The effects of φ and G/c are coupled since they both determine the interaction between the hind airfoil and the leading-edge vortex in the wake and the out-of-phase mode is suggested for the tandem airfoils at G/c = 1 to enhance both lift and thrust. For a tandem airfoil with in-phase mode, the optimal G/c is around 1.5 to 2. Moreover, the asymmetric pitching of the in-phase plunging airfoils should be synchronized to retain the enhanced performance.
Reconstructing Rayleigh–Bénard flows out of temperature-only measurements using nudging
Authors: Agasthya Lokahith , Clark Di Leoni Patricio , Biferale Luca
Published: January 2022

Nudging is a data assimilation technique that has proved to be capable of reconstructing several highly turbulent flows from a set of partial spatiotemporal measurements. In this study, we apply the nudging protocol on the temperature field in a Rayleigh–Bénard convection system at varying levels of turbulence. We assess the global, as well as scale by scale, success in reconstructing the flow and the transition to full synchronization while varying both the quantity and quality of the information provided by sparse measurements either on the Eulerian or Lagrangian domain. We assess the statistical reproduction of the dynamic behavior of the system by studying the spectra of the nudged fields as well as the correct prediction of heat transfer properties as measured by the Nusselt number. Furthermore, we analyze the results in terms of the complexity of solutions at various Rayleigh numbers and discuss the more general problem of predicting all state variables of a system given partial or full measurements of only one subset of the fields, in particular, temperature. This study sheds new light on the correlation between the velocity and temperature in thermally driven flows and on the possibility to control them by acting on the temperature only.
Extension of the Balbi fire spread model to include the field scale conditions of shrubland fires
Authors: Chatelon François Joseph , Balbi Jacques Henri , Cruz Miguel G. , Morvan Dominique , Rossi Jean Louis , Awad Carmen , Frangieh Nicolas , Fayad Jacky , Marcelli Thierry
Published: January 2022

The ‘Balbi model’ is a simplified rate of fire spread model aimed at providing computationally fast and accurate simulations of fire propagation that can be used by fire managers under operational conditions. This model describes the steady-state spread rate of surface fires by accounting for both radiation and convection heat transfer processes. In the present work the original Balbi model developed for laboratory conditions is improved by addressing specificities of outdoor fires, such as fuel complexes with a mix of live and dead materials, a larger scale and an open environment. The model is calibrated against a small training dataset (n = 25) of shrubland fires conducted in Turkey. A sensitivity analysis of model output is presented and its predictive capacity against a larger independent dataset of experimental fires in shrubland fuels from different regions of the world (Europe, Australia, New Zealand and South Africa) is tested. A comparison with older versions of the model and a generic empirical model is also conducted with encouraging results. The improved model remains physics-based, faster than real time and fully predictive.
Cellular homologs of the double jelly-roll major capsid proteins clarify the origins of an ancient virus kingdom
Authors: Krupovic Mart , Makarova Kira S. , Koonin Eugene V.
Published: January 2022

Significance

Viruses are the most abundant biological entities on Earth and ubiquitous parasites of cellular life forms. The general scenario for the origin of viruses involves evolution from nonviral replicators, such as plasmids and transposons, via recruitment of host proteins for virion formation. One of the most common virion core components, the double jelly-roll major capsid protein of a broad variety of viruses with double-stranded DNA genomes, so far has been thought to represent a virus innovation. However, we present evidence, obtained by protein structure comparison, that this type of virus capsid protein also evolved from a cellular ancestor, a distinct family of carbohydrate-active enzymes. These findings reinforce the chimeric scenario of virus origin.
Task design in online one-to-one classes with young learners
Authors: Thorburn Ross
Published: January 2022

This study investigated how effective four tasks were in supporting meaningful spoken language production between young learners and their teachers. The context of the study, online one-to-one lessons, is commonplace but largely unresearched. Transcripts from seventeen teacher-student dyads using four tasks were analysed using conversation analysis. These were then coded and the number of instances of meaningful communication counted. The number of instances of pushed output and negotiation of meaning were also noted. The most successful task was an open opinion-gap task, which motivated the young learners. Crucially, the task outcome (a plan of a shopping centre) allowed learners to check their teachers had understood them. Teacher misunderstandings gave learners opportunities to take control of the discourse and negotiate meaning. Aspects of task design which impeded meaningful communication included sentence stems, which resulted in drill-like interactions. Task topics familiar to learners but unfamiliar to teachers hindered meaningful communication. Also, tasks located near the end of a lesson sequence tended to result in less meaningful communication than those nearer the start.
Mixing Catalan, English and Spanish on WhatsApp
Authors: Pérez-Sabater Carmen
Published: January 2022

The purpose of this study is to examine language choice, language alternation and code-switching practices in
Instant Messaging (IM). Specifically, this article presents the results from an analysis of the written conversations of a
specific community formed by Valencian adults fluent in English. Taking a computer-mediated, discourse-centred ethnographic
approach to online discourse, the study has shown that, in this specific trilingual online community of language teachers,
language choice and the choice of a specific written variety is intimately related to audience. The group members mix Catalan,
English and Spanish regularly, their language choice and code-switching strategies serving to establish in-group solidarity,
familiarity and lessen face-threatening acts. Switches to English, sometimes followed by a switch to Catalan, are usually employed
for humorous word play. Interestingly, the case study exemplifies how the use of a certain language may be highly correlated to
ideological and political considerations.
Sex Segregation and the Participation of Transgender Adults in Recreational Sport in British Columbia, Canada
Authors: Nguyen Tung
Published: January 2022

The lack of a formal policy on transgender participation in recreational sport results in transgender people struggling alone with stigmatization. Recreational sport guidelines identify inclusion as an imperative in recreational sport participation, yet they have failed to lay out the means to achieve it. Considering this issue and opportunity, the purpose of this case study is to determine how transgender adults’ participation in recreational sport in British Columbia (BC), Canada is informed by their experiences with sex-based segregation structures in recreational sport and, secondly, to inform an enhanced and intentional change in transgender-inclusive policies and practices in terms of sex-based segregation structures in recreational sport in BC, Canada.

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© Tung Nguyen 2022
Exploring the Case Beijing 798 Arts District Demonstrates the Power of Cultural and Creative Industry
Authors: Lihui Wu
Published: January 2022

Introduction

The success of the 798 Arts District stems from the grassroots movement initiated by the artists and non-profit institutes. They challenged the authorities, who intended to carry out the demolition of the 798 Arts District, to preserve the cultural heritage of that area and shift power to the people. The 798 Arts District can serve as a model of sustainability for other arts districts or redevelopment projects in urban areas.
Microstructure and mechanical properties of W-10 wt-%Ta alloys prepared by spark plasma sintering
Authors: Liu Wenyang , Huang Yufeng , Wang Yao , Zhang Yong , Duan Xinyun , Liu Wensheng , Ma Yunzhu
Published: January 2022

The brittleness of tungsten (W) is a key factor that affects the preparation and application of high-performance tungsten alloys. Tantalum (Ta), which can form a complete solid solution with tungsten, was expected to improve its dislocation mobility and toughness. In the W-10 wt-%Ta alloys prepared by spark plasma sintering, the amount of Ta solid dissolved in tungsten increased gradually upon increasing the sintering temperature. The compressive strength of W-10 wt-%Ta alloys first increased and then decreased by increasing the sintering temperature. The solid solution of tantalum constructed a large number of defects and edge dislocations in the tungsten structure. This result is surprising because plastic flows are generally controlled by screw dislocations in Body-Centered Cubic (BCC) metals and dilute alloys.
Manipulating magnetic and magnetoresistive properties by oxygen vacancy complexes in GCMO thin films
Authors: Beiranvand A , Liedke M O , Haalisto C , Lähteenlahti V , Schulman A , Granroth S , Palonen H , Butterling M , Wagner A , Huhtinen H , Paturi P
Published: January 2022

The effect of in situ annealing is investigated in Gd0.1Ca0.9MnO3 (GCMO) thin films in oxygen and vacuum atmospheres. We show that the reduction of oxygen content in GCMO lattice by vacuum annealing induced more oxygen complex vacancies in both subsurface and interface regions and larger grain domains when compared with the pristine one. Consequently, the double exchange interaction is suppressed and the metallic-ferromagnetic state below Curie temperature turned into spin-glass insulating state. In contrast, the magnetic and resistivity measurements show that the oxygen treatment increases ferromagnetic phase volume, resulting in greater magnetization (M
S) and improved magnetoresistivity properties below Curie temperature by improving the double exchange interaction. The threshold field to observe the training effect is decreased in oxygen treated film. In addition, the positron annihilation spectroscopy analysis exhibits fewer open volume defects in the subsurface region for oxygen treated film when compared with the pristine sample. These results unambiguously demonstrate that the oxygen treated film with significant spin memory and greater magnetoresistance can be a potential candidate for the future memristor applications.
Electroosmotic modulated unsteady squeezing flow with temperature-dependent thermal conductivity, electric and magnetic field effects
Authors: Prakash J , Tripathi Dharmendra , Bég O Anwar , Sharma Ravi Kumar
Published: January 2022

Modern lubrication systems are increasingly deploying smart (functional) materials. These respond to various external stimuli including electrical and magnetic fields, acoustics, light etc. Motivated by such developments, in the present article unsteady electro-magnetohydrodynamics squeezing flow and heat transfer in a smart ionic viscous fluid intercalated between parallel plates with zeta potential effects is examined. The proposed mathematical model of problem is formulated as a system of partial differential equations (continuity, momenta and energy). Viscous dissipation and variable thermal conductivity effects are included. Axial electrical distribution is also addressed. The governing equations are converted into ordinary differential equations via similarity transformations and then solved numerically with MATLAB software. The transport phenomena are scrutinized for both when the plates move apart or when they approach each other. Also, the impact of different parameters such squeezing number, variable thermal conductivity parameter, Prandtl number, Hartmann number, Eckert number, zeta potential parameter, electric field parameter and electroosmosis parameter on the axial velocity and fluid temperature are analysed. For varied intensities of applied plate motion, the electro-viscous effects derived from electric double-capacity flow field distortions are thoroughly studied. It has been shown that the results from the current model differ significantly from those achieved by using a standard Poisson–Boltzmann equation model. Axial velocity acceleration is induced with negative squeeze number (plates approaching, S < 0) in comparison to that of positive squeeze number (plates separating, S > 0). Velocity enhances with increasing electroosmosis parameter and zeta potential parameter. With rising values of zeta potential and electroosmosis parameter, there is a decrease in temperatures for U
e > 0 for both approaching i.e. squeezing plates (S < 0) and separating (S > 0) cases. The simulations provide novel insights into smart squeezing lubrication with thermal effects and also a solid benchmark for further computational fluid dynamics investigations.
Rotation included 3-axis scanning free-space measurement and curvature compensation for electromagnetic evaluation of leading-edge and curved stealth structures
Authors: Din Salah Ud , Hyun Jong-Min , Son Dae-Sung , Lee Jung-Ryul
Published: January 2022

Since the last decade, stealth technology has been developing at a much higher speed with much research going on to evaluate the properties of radar absorbing structures (RASs) and scattering parameters of the developed stealth structures at different phases of practical use. A vector network analyzer plays an important role in RAS performance evaluation of stealth structures. Different scientists have used closed cell measurement techniques utilizing coaxial cables and waveguides to evaluate RAS materials at high accuracy, while others have used free-space measurement techniques utilizing radiating antennas to evaluate the RAS performance of larger stealth structures without damaging the specimen. All these conventional evaluation systems can scan a single point at a time. A scanning free-space measurement (SFM) system was an initial step toward automated scanning of large stealth structures. This system was capable of scanning 1000 mm × 1000 mm flat structures using raster scanning with two linear stages. However, the two-dimensional SFM was not applicable to leading-edge and cylindrical structures, and the signal-to-noise ratio (SNR) is highly affected by the specimen curvature. In this paper, a 3-axis scanning free-space measurement (3-axis SFM) system was developed. The system has two linear stages and a rotational stage for raster scanning of the specimen. The system performance was checked by scanning cylindrical RAS specimens with a radius of 100 mm. The results were then compared to the SFM system, which showed that the SNR of the 3-axis SFM is quite high compared to the SFM system. A coordinate-based scanning algorithm was also developed for 3-axis SFM to ensure a fixed interval scan of complex geometrically shaped specimens, such as wing leading edges, at lower incident angles. The algorithm achieved a zero-degree incident angle scan with ±1 degree of accuracy for the NACA-M3 symmetrical leading-edge specimen. Different scan parameters and results are visualized in the developed graphical user interface software. Finally, the inspected results were curvature-compensated to obtain the actual RAS performance of the specimen. The accuracy of the geometry-based perfect electric conductor (PEC) reflection-loss prediction algorithm was further improved by adding a stand-off distance effect and more specimen curvature data to the algorithm. The accuracy of the algorithm was verified by comparing the predicted PEC results to the measured PEC results of the corresponding specimen.
Laser ultrasonic scanning for detection of damage in copper pipelines using blind compressive sensing and the adjacent area difference coefficient
Authors: Hong Xiaobin , Huang Liuwei , Liufu Yonghong , Wang Zixin , Zhang Bin , Liu Yuan
Published: January 2022

Due to its good thermal conductivity and corrosion resistance, copper has become a common material for transmission pipelines. It is necessary to detect the early signs of damage in copper pipelines effectively and quickly. Laser ultrasound scanning is a non-contact and non-destructive damage identification method, which can realize high-precision, non-contact detection. At the same time, with the progress of internet technology, traditional damage testing has begun to use advanced technologies such as the internet of things and cloud computing to promote an upgrade of the testing industry from an offline industry to an online industry. However, obtaining a large amount of wavefield vibration data is time consuming. In this paper, we present a laser ultrasonic scanning cloud platform damage detection method for copper pipelines based on alternating learning blind compressive sensing (BCS) and the adjacent area difference coefficient (AADC); this approach can improve real-time performance and detection accuracy. First, the damage detection method is introduced in detail. BCS is used to compress the laser scanning signal at the data acquisition terminal, and then transmitted to a data processing cloud platform for reconstruction. Copper pipeline damage imaging is realized by taking the AADC value of each detection point as the pixel value. The simulated detection data of the copper pipeline are then obtained through a finite element model, and the weighted vectors of the AADC are determined by a genetic algorithm. Finally, experimental data are used to verify the effectiveness of this method, and the experimental results are analyzed and discussed. The AADC and other distance damage imaging methods are compared. The results demonstrate that this method can compress the wavefield data to 13% of the original data, and the detection of crack damage is realized.
Operando XRD studies on Bi2MoO6 as anode material for Na-ion batteries
Authors: Brennhagen Anders , Cavallo Carmen , Wragg David S. , Vajeeston Ponniah , Sjåstad Anja O. , Koposov Alexey Y. , Fjellvåg Helmer
Published: January 2022

Based on the same rocking-chair principle as rechargeable Li-ion batteries, Na-ion batteries are promising solutions for energy storage benefiting from low-cost materials comprised of abundant elements. However, despite the mechanistic similarities, Na-ion batteries require a different set of active materials than Li-ion batteries. Bismuth molybdate (Bi2MoO6) is a promising NIB anode material operating through a combined conversion/alloying mechanism. We report an operando x-ray diffraction (XRD) investigation of Bi2MoO6-based anodes over 34 (de)sodiation cycles revealing both basic operating mechanisms and potential pathways for capacity degradation. Irreversible conversion of Bi2MoO6 to Bi nanoparticles occurs through the first sodiation, allowing Bi to reversibly alloy with Na forming the cubic Na3Bi phase. Preliminary electrochemical evaluation in half-cells versus Na metal demonstrated specific capacities for Bi2MoO6 to be close to 300 mAh g−1 during the initial 10 cycles, followed by a rapid capacity decay. Operando XRD characterisation revealed that the increased irreversibility of the sodiation reactions and the formation of hexagonal Na3Bi are the main causes of the capacity loss. This is initiated by an increase in crystallite sizes of the Bi particles accompanied by structural changes in the electronically insulating Na–Mo–O matrix leading to poor conductivity in the electrode. The poor electronic conductivity of the matrix deactivates the Na
x
Bi particles and prevents the formation of the solid electrolyte interface layer as shown by post-mortem scanning electron microscopy studies.
X-ray CT adaptation based on a 2D–3D deformable image registration framework using simulated in-room proton radiographies
Authors: Palaniappan Prasannakumar , Meyer Sebastian , Rädler Martin , Kamp Florian , Belka Claus , Riboldi Marco , Parodi Katia , Gianoli Chiara
Published: January 2022

The aim of this work is to investigate in-room proton radiographies to compensate realistic rigid and non-rigid transformations in clinical-like scenarios based on 2D–3D deformable image registration (DIR) framework towards future clinical implementation of adaptive radiation therapy (ART). Monte Carlo simulations of proton radiographies (pRads) based on clinical x-ray CT of a head and neck, and a brain tumor patients are simulated for two different detector configurations (i.e. integration-mode and list-mode detectors) including high and low proton statistics. A realistic deformation, derived from cone beam CT of the patient, is applied to the treatment planning CT. Rigid inaccuracies in patient positioning are also applied and the effect of small, medium and large fields of view (FOVs) is investigated. A stopping criterion, as desirable in realistic scenarios devoid of ground truth proton CT (pCT), is proposed and investigated. Results show that rigid and non-rigid transformations can be compensated based on a limited number of low dose pRads. The root mean square error with respect to the pCT shows that the 2D–3D DIR of the treatment planning CT based on 10 pRads from integration-mode data and 2 pRads from list-mode data is capable of achieving comparable accuracy (∼90% and >90%, respectively) to conventional 3D–3D DIR. The dice similarity coefficient over the segmented regions of interest also verifies the improvement in accuracy prior to and after 2D–3D DIR. No relevant changes in accuracy are found between high and low proton statistics except for 2 pRads from integration-mode data. The impact of FOV size is negligible. The convergence of the metric adopted for the stopping criterion indicates the optimal convergence of the 2D–3D DIR. This work represents a further step towards the potential implementation of ART in proton therapy. Further computational optimization is however required to enable extensive clinical validation.
Cesium seeding for effective electron transpiration cooling in hypersonic flows
Authors: Sahu Rupali , Tropina Albina , Andrienko Daniil , Miles Richard
Published: January 2022

The concept of electron transpiration cooling (ETC) uses thermionic emission of electrons from a low work function material to cool surfaces in hypersonic flight. A theoretical estimate of the emission current is given by the Richardson–Dushman equation. In hypersonic flights, the emission current can deviate from this estimate as the ambient air is partially ionized and a plasma sheath forms near the surface. Depending on the sheath structure, the emission current can be enhanced by the Schottky effect, or could be reduced by the space charge effects. In this study, we present a theoretical analysis of ETC of the leading-edge surface of a hypersonic vehicle, considering the transpiration of liquid cesium through a porous tungsten material. A part of the transpired cesium is adsorbed on the surface, which lowers the emitter work function, while the rest is evaporated due to high surface temperatures. Both the effects provide substantial cooling. The evaporated cesium is ionized in the ambient air, which alters the plasma conductivity and reduces space charge effects. The effect of individual fields of ionized species near the surface is found to be negligible. Cesium transpiration is found to eliminate the requirement for an applied surface potential and enable stable operation at surface temperatures below 2000 K.
Electrical devices based on hybrid membranes with mechanically and magnetically controllable, resistive, capacitive and piezoelectric properties
Authors: Bica Ioan , Anitas Eugen Mircea
Published: January 2022

Cotton fabric based membranes containing carbonyl iron microparticles with and without barium titanate nanoparticles (nBaTiO3) are fabricated. The hybrid membranes (hMs) are inserted between two copper electrodes, reinforced with glass fiber and epoxy resin. The resulted assembly is introduced in a silicone rubber sheath, and plane electrical devices (EDs) are obtained. Here, it is shown that using nBaTiO3, the EDs are characterized by resistive, capacitive and piezoelectric functions which have the property of being controllable in a field of mechanical forces, in a magnetic field or a combinations of the two. This is revealed by measuring the electrical resistance, capacitance and voltage at the output terminals of the devices. The electric voltage generator property of the devices is conferred by the presence of nBaTiO3. These effects allow us to conclude that the hMs offer the possibility of manufacturing low-cost and ecological EDs for various applications such as vibration, magnetic field and mechanical deformations sensors, electric generators etc.
Engineering the radiative dynamics of thermalized excitons with metal interfaces
Authors: Chen Grace H , Li David Z , Butcher Amy , High Alexander A , Chang Darrick E
Published: January 2022

As a platform for optoelectronic devices based on exciton dynamics, monolayer transition metal dichalcogenides (TMDCs) are often placed near metal interfaces or inside planar cavities. While the radiative properties of point dipoles at metal interfaces has been studied extensively, those of excitons, which are delocalized and exhibit a temperature-dependent momentum distribution, lack a thorough treatment. Here, we analyze the emission properties of excitons in TMDCs near planar metal interfaces and explore their dependence on exciton center-of-mass momentum, transition dipole orientation, and temperature. Defining a characteristic energy scale k
B
T
c = (ℏk)2/2m (k being the radiative wavevector and m the exciton mass), we find that at temperatures T ≫ T
c and low densities where the momentum distribution can be characterized by Maxwell–Boltzmann statistics, the modified emission rates (normalized to free space) behave similarly to point dipoles. This similarity in behavior arises due to the broad nature of wavevector components making up the exciton and point dipole emission. On the other hand, the narrow momentum distribution of excitons for T < T
c can result in significantly different emission behavior as compared to point dipoles. These differences can be further amplified by considering excitons with a Bose Einstein distribution at high phase space densities, such as in a condensate phase. We find suppression or enhancement of emission relative to the point dipole case by several orders of magnitude. These insights can help optimize the performance of optoelectronic devices that incorporate 2D semiconductors near metal electrodes and can inform future studies of exciton radiative dynamics at low temperatures. Additionally, these studies show that nanoscale optical cavities are a viable pathway to generating long-lifetime exciton states in TMDCs.
Physical Agents Quality Index (PAQI): application in a University Campus
Authors: Graziuso G , Francavilla A B , Mancini S , Guida M , Guarnaccia C
Published: January 2022

Among the most common techniques and methodologies for the analysis of the exposure to polluting agents, the definition of environmental indexes represents a very useful tool able to describe the status of the environment quantitatively and qualitatively. In this perspective a general Physical Agents Quality Index (PAQI) describing the status of an environment in terms of presence of different physical pollutants was developed by authors in a previous work. In this paper the PAQI concept is extended from a punctual idea to a spatial analysis and a practical application in order to evaluate the potentiality of the index on a visual map is discussed. In particular, the PAQI visual map of the Campus of the University of Salerno (Italy) was redacted. The results are presented and lay down the basis for further improvements in the visual mapping and also in the calibration of the calculation of the index.
Open-source software tools for strategic noise mapping: a case study
Authors: Graziuso G , Francavilla A B , Mancini S , Guarnaccia C
Published: January 2022

Currently, the European Union has adopted a series of measures to combat noise problems, focusing on some key indicators, such as the daily and night level of noise. Among the possible actions to manage environmental noise, there are the creation of noise maps and the adoption of action plans. Noise maps are, usually, produced by modelling and simulating data relating to traffic and various activities of an area. However, in some cases, these input data are not available or it is not possible to include all noise sources in the models used, causing difficulties in the prediction and analysis of the environmental impacts of noise. In this paper, starting from the analysis of open-source software tools for data collection, noise modelling and mapping, i.e. Openstreet Map, Noise Modelling and QGIS, based on free and public licenses, a methodology for the creation of noise maps will be presented. Finally, the outputs of the application of the methodology to the city centre of the Municipality of Nocera Inferiore, in south Italy, will be the creation of noise maps characterized by the spatial representation of the main standard noise indicators.