bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effect of a Surface Combat Swimming Training Program on Swimming Performance
Authors: Kostoulas Ioannis D. , Kounalakis Stylianos N. , Toubekis Argyris G. , Kaniadakis Antonios , Karagiannis Anastasios , Mavraganis Dimitrios , Karatrantou Konstantina , Gerodimos Vassilis
Published: March 2021

In this study the effect of a surface combat swimming (sCS) training program on performance in freestyle swimming and sCS was examined. Forty-five officer cadets were divided into three equivalent groups: a control group (CG), a group that was trained only with a swimsuit and fins (SF), and a group that was trained with combat uniform and equipment (UE). Groups SF and UE followed a 60-min training program with sCS for 4 weeks, 4 times per week. Before and after the training program all groups performed 4×50 and 400-m freestyle swimming, 250-m sCS with a uniform and equipment, 350-m with a swimsuit and fins, and 300-m with a swimsuit. The UE group showed improved performance in 4×50-m (mean±SD 14±9 s) and in 250-m sCS (24±14 s) (p<0.01). Both the SF group and the UE group improved in 300-m sCS, in 350-m sCS and in 400-m freestyle (p<0.05). We conclude that the training adaptations seemed to be specific, not only with regard to the activity performed, but also in terms of the actual conditions of an operation, which also include equipment.
A Simple and Efficient Synthesis of Fused Benzo[b]thiophene Derivatives
Authors: Fisyuk Alexander S. , Ulyankin Evgeny B. , Kostyuchenko Anastasia S. , Chernenko Sergey A. , Bystrushkin Mikhail O. , Samsonenko Anna L. , Shatsauskas Anton L.
Published: March 2021

A new approach to the synthesis of fused benzothiophene derivatives was developed based on iodine-promoted photocyclization of 4,5-diaryl-substituted thiophenes obtained in three steps from commercially­ available compounds. Comparative analysis showed that photochemical cyclization is a more efficient method for the preparation of fused benzo[b]thiophene derivatives, compared to oxidative coupling of 4,5-diaryl-substituted thiophenes in the presence of iron(III) chloride and palladium-catalyzed intramolecular arylation. This new approach provides an efficient synthesis of functionally substituted naphtho[2,1-b:3,4-b′]dithiophenes, phenanthro[9,10-b]thiophenes, benzo[1,2-b:3,4-b′:6,5-b′′]trithiophenes, as well as new fused heterocycles containing a pyridine ring and/or a carbazole moiety.
Designer Cranioplasty at Budget Prices: A Novel Use of 3D Printing Technology
Authors: Yerragunta Thirumal , Kanala Reddy Ramanadha , Yerramneni Vamsi Krishna , Kolpakawar Swapnil , Rangan Vasundhara
Published: March 2021

Background Cranioplasty using synthetic materials for restoration of the exact shape of the skull has always remained a challenge until the development of 3D printing technology. However, the high-cost of available 3D printed implants limits their extensive use.

Objectives To study the effectiveness of a low-cost, 3D-printed template for molding the polymethyl methacrylate (PMMA) (bone cement) in order to achieve exact contours of the skull specific to each patient.

Materials and Methods 10 cranioplasties have been performed between July 2018 to December 2019 in a variety of craniotomy defects using bone cement flaps shaped using custom-made molds. The mold was 3D-printed and based on each patient’s CT images in digital imaging and communications in medicine (DICOM). Miniplates and screws were used to fix the flap. Postoperatively, clinical and radiological evaluation were done to assess patient satisfaction and accuracy of contour achieved.

Results Patient satisfaction as well as accuracy of contouring, as seen on postoperative CT scans, were excellent. There were no notable complications on follow-up.

Conclusion PMMA cranioplasty flap, contoured using a 3D-printed mold, is a very cost-effective alternative for restoration of skull contour for various craniotomy defects.

Polymethyl methacrylate (PMMA) molded to form the exact shape of lost calvarium using 3D printed plastic templates is a smart and economical solution.
Central Auditory Processing and Cognitive Functions in Children
Authors: Back Nadja Cristina Furtado , Crippa Ana Chrystina de Souza , Riechi Tatiana Izabelle Jaworski de Sá , Pereira Liliane Desgualdo
Published: March 2021

Introduction Nowadays, there is no consensus on whether central auditory processing disorder is a primary or a secondary deficit to other cognitive deficits. A better understanding of the association between cognitive functions and central auditory skills may help elucidate this dilemma.

Objective To investigate possible associations between auditory abilities and cognitive functions in schoolchildren.

Methods Fifty-eight schoolchildren, aged between 8 years and 0 months old and 11 years and 11 months old, who underwent the following tests: masking level difference, gaps in noise, pitch pattern sequence test, dichotic digits test, sustained auditory attention ability test, Wechsler intelligence scale for children – IV, junior Hayling test, five digits test, and behavior rating inventory of executive function.

Results Significant correlations were found between the hearing ability of temporal resolution and executive functions, temporal ordering/sequencing, binaural integration and separation, and sustained auditory attention, operational memory, inhibitory control, and cognitive flexibility; binaural integration was also associated with intelligence. The statistically significant positive correlation found between the ability of binaural interaction and the components of emotional control and behavior regulation of the behavior rating inventory of executive function was unexpected.

Conclusion The associations identified reinforce the complexity of the tasks involved in the evaluation of central auditory processing and the need for multidisciplinary evaluation for the differential diagnosis of auditory processing disorder. Confirmation of the presence or absence of comorbidities between different disorders allows directing the therapeutic behaviors and reducing the impact of possible auditory and/or cognitive deficits in the different daily life situations of children.
A metamaterial lens based on transformation optics for horizontal radiation of OAM vortex waves
Authors: Yi Jianjia , Shi Zhe , Li Die , Liu Chenchen , Sun Haoxiang , Zhu Lina , Chen Xiaoming , Burokur Shah Nawaz
Published: March 2021

Vortex electromagnetic waves carrying orbital angular momentum (OAM) have been widely discussed for potential applications in wireless communications. Belonging to the Laguerre–Gaussian beams family, such type of waves present a hollow conical shape and divergence characteristics along with a directional radiation. In this paper, an innovative method to produce omnidirectional OAM beams based on spatial transformation is proposed at microwave frequencies. As a proof-of-concept demonstration, a lens with omnidirectional radiation in the horizontal plane is designed and simulated with an incident vortex beam carrying the OAM mode l = +2. The designed lens can be potentially implemented with an all-dielectric medium showing a gradient permittivity distribution. Furthermore, the proposed lens presents good performances over a wide operational bandwidth spanning from 8 to 17 GHz. By converting the directional beam to an omnidirectional one, the proposed method opens the door to the potential development of microwave vortex antenna systems.
Coexistence of turbulence regimes in the Texas Helimak
Authors: Pereira F. A. C. , Toufen D. L. , Guimarães-Filho Z. O. , Caldas I. L. , Viana R. L. , Gentle K. W.
Published: March 2021

The turbulence of magnetically confined plasmas usually presents high-density pulses with short duration known as bursts. In the Texas Helimak, it is possible to suppress bursts in a broader region by applying a negative electrostatic bias. However, an almost unchanged burst rate persists in a region far from the location where bias is applied. We investigate the turbulence transition that occurs from the burst suppressed region to the burst dominated region by analyzing data from Langmuir probes in the whole radial extension of the machine. We find that such turbulence transition can be understood as an alternation of two different turbulent regimes, with the probability of being in each regime depending on the radial position. One regime, named as burst-free regime, consists of only Gaussian fluctuations and the other, named as bursty turbulent regime, is a train of pulses with double exponential temporal profiles, exponential amplitude distribution, and random occurring instants. This succession between burst-free and bursty turbulent regimes influences the equilibrium parameters.
Impact of numerical hydrodynamics in turbulent mixing transition simulations
Authors: Grinstein F. F. , Pereira F. S.
Published: March 2021

Underresolved simulations are unavoidable in high Reynolds (Re) and Mach (Ma) number turbulent flow applications at scale. Implicit large-Eddy simulation (ILES) often becomes the effective strategy to capture the dominating effects of convectively driven flow instabilities. We evaluate the impact of three distinct numerical strategies in simulations of transition and turbulence decay with ILES: the Harten–Lax–van Leer (HLL) Riemann solver applying Strang splitting and a Lagrange-plus-Remap formalism to solve the directional sweep—denoted split; the Harten–Lax–Van Leer-Contact (HLLC) Riemann solver using a directionally unsplit strategy and parabolic reconstruction—denoted unsplit; and the HLLC Riemann solver using unsplit and a low-Ma correction (LMC)—denoted unsplit*. Three case studies are considered: (1) a shock tube problem prototyping shock-driven turbulent mixing, (2) the Taylor–Green Vortex (TGV) prototyping transition to turbulence, and, (3) an homogeneous isotropic turbulence (HIT) case, focusing on the impact of discretization on transition and decay from fixed well-characterized initial conditions. Significantly more accurate predictions are provided by the unsplit schemes, in particular, when augmented with the LMC. For given resolution, only the unsplit schemes predict the turbulent mixing transition after reshock observed in the shock tube experiments. Relevant comparisons of ILES based on Euler and Navier–Stokes equations addressing potential occurrence of low-Re regimes in the applications are presented. Unsplit* schemes are instrumental in allowing to capture the spatial development of the TGV flow and its validation at prescribed Re with significantly less resolution. HIT analysis confirms higher simulated turbulence Re and increased small-scale content associated with the unsplit discretizations.
Hydroelastic response of an ice sheet with a lead to a moving load
Authors: Xue Y. Z. , Zeng L. D. , Ni B. Y. , Korobkin A. A. , Khabakhpasheva T. I.
Published: March 2021

The hydroelastic symmetric response of a floating ice sheet caused by a pressure moving either in the ice lead or on the infinite ice sheet with a crack (a lead of zero width) is investigated. The ice sheet is modeled as a viscoelastic thin plate. The water is of constant depth. The flow under the ice is potential and linear. A boundary integral method (BIM) for the flow under the ice is combined with the finite difference method for the ice plate with free-free edge conditions to solve the coupled problem of linear hydroelasticity. Numerical results for deflections and stress distributions are shown to agree well with the available results by others. The proposed approach can be applied to problems with different edge conditions and different positions of the load with respect to the lead. The ice responses are studied with respect to the speed of the load. The speed can be subcritical, critical, and supercritical with respect to the critical speed for a floating infinite elastic plate. The speeds of the load, which provide maximum deflection, maximum stress, and maximum wave-making resistance, are determined. All these speeds are different and greater than the critical speed for an infinite elastic plate. The effect of the ice thickness, lead width, and load properties on these speeds is discussed.
Electronic structure modulation of MoS2 by substitutional Se incorporation and interfacial MoO3 hybridization: Implications of Fermi engineering for electrocatalytic hydrogen evolution and oxygen evolution
Authors: Parija Abhishek , Zaheer Wasif , Cho Junsang , Alivio Theodore E. G. , Fakra Sirine C. , Al-Hashimi Mohammed , Prendergast David , Banerjee Sarbajit
Published: March 2021

The design of earth-abundant electrocatalysts that can facilitate water splitting at low overpotentials, provide high current densities, and enable prolonged operational lifetimes is central to the production of sustainable fuels. The distinctive atomistic and electronic structure characteristics of the edges of MoS2 imbue high reactivity toward the hydrogen evolution reaction. MoS2 is nevertheless characterized by significantly high overpotentials as compared to platinum. Here, we demonstrate that modulation of the electronic structure of MoS2 through interfacial hybridization with MoO3 and alloying of selenium on the anion sublattice allows for systematic lowering of the conduction band edge and raising of the valence band edge, respectively. The former promotes enhanced electrocatalytic activity toward hydrogen evolution, whereas the latter promotes enhanced activity toward the oxygen evolution reaction. Such alloyed heterostructures prepared by sol-gel reactions and hydrothermal selenization expose a high density of edge sites. The alloyed heterostructures exhibit low overpotential, high current density, high turnover frequency, and prolonged operational lifetime. The mechanistic origins of catalytic activity have been established based on electronic structure calculations and x-ray absorption and emission spectroscopy probes of electronic structure, which suggest that interfacial hybridization at the MoO3 interface yields low-lying conduction band states that facilitate hydrogen adsorption. In contrast, shallow Se 4p-derived states give rise to a raised effective valence band maximum, which facilitates adsorption of oxygen intermediates and engenders a low overpotential for the oxygen evolution reaction. The findings illustrate the use of electronic structure modulation through interfacial hybridization and alloying to systematically improve electrocatalytic activity.
Subgrid-scale helicity equation model for large-eddy simulation of turbulent flows
Authors: Qi Han , Li Xinliang , Yu Changping
Published: March 2021

A new one-equation eddy-viscosity model based on subgrid-scale (SGS) helicity is introduced in this paper for large-eddy simulation (LES) of turbulent flows. First, the governing equation of SGS helicity is deduced from the incompressible Navier–Stokes equations, and it reflects the transfer of the small-scale helicity that has been filtered out. We deduce a certain functional relation between the eddy viscosity and SGS helicity based on the kinetic energy and helicity spectra in the homogeneous and isotropic helical turbulence. For improving the accuracy, each unclosed term in the governing equation of SGS helicity is modeled independently, and the coefficients of these unclosed terms are constants or are determined dynamically. The new one-equation eddy-viscosity model is first tested and validated in the simulation of the homogeneous and isotropic helical turbulence. The a priori tests from the direct numerical simulation of forced homogeneous and isotropic turbulence show that the energy and helicity fluxes exhibit scale invariance in the inertial subrange. Additionally, the a posteriori tests demonstrate that the constant-coefficient and dynamic SGS helicity equation models can predict both the energy and helicity spectra more precisely than the common SGS models. For the LES of channel flow, the SGS helicity equation model can accurately predict the mean velocity, the turbulent stress, and the viscous shear stress and supply more abundant flow structures than the compared SGS model under the same grid resolution.
Superspinglass state in functionalized zeolite 5A-maghemite nanoparticles
Authors: Ramos-Guivar Juan A. , Passamani Edson Caetano , Litterst Jochen
Published: March 2021

The structural, vibrational, and magnetic properties of maghemite nanoparticles functionalized with zeolite type 5A and synthesized by coprecipitation were studied in detail. Crystallite and particle sizes were determined and discussed based on the polydispersity index. Its value of 0.4 has suggested the presence of a broad particle distribution with particle sizes between 3 and 20 nm. Three samples were successfully functionalized either before or after the formation of the maghemite nanoparticles. Infrared studies have shown that the functionalization has occurred by hydrated surface groups present in the zeolite type 5A surface, which have favored strong bindings and highly concentrated regions of maghemite nanoparticles. From the temperature dependence of the hyperfine magnetic field obtained by Mössbauer spectroscopy, the effective magnetocrystalline anisotropy constants of the three nanohybrids were determined. They are one order of magnitude higher than for the bulk counterpart, and there is evidence for strong interparticle interactions for the three studied nanohybrids. These strong magnetic interactions of the nanoparticles in the zeolite framework have favored a superspinglass-like behavior for all samples with transition temperatures located at 74 and 208 K, as confirmed by AC susceptibility measurements.
High-performance vibration power generation using polycrystalline Fe–Co-based alloy due to large inverse magnetostrictive effect
Authors: Inoue S. , Okada T. , Fujieda S. , Osanai F. , Hashi S. , Ishiyama K. , Suzuki S. , Seino S. , Nakagawa T. , Yamamoto T. A.
Published: March 2021

The magnetic flux density change ΔB caused by the inverse magnetostrictive effect is key for achieving high-performance vibration power generation. As the magnetization curve of the polycrystalline Fe–47.6 at. % Co–2.3 at. % V (Fe–Co–V) alloy became easier to magnetize by applying tensile stresses, the value of ΔB estimated from the magnetization curves depended significantly on magnetic fields. Hence, the vibration power generation of a U-shaped unimorph device using a polycrystalline Fe–Co–V alloy core was demonstrated under various bias magnetic fields. As a result of bias magnetic field adjustment, the open-circuit voltage induced by the vibration of the device improved to ∼7.0 V. Such superior performance is attributable to a large ΔB of 1.1 T in the Fe–Co–V alloy core. Therefore, adjustment of bias magnetic fields is essential for obtaining large ΔB in Fe–Co–V alloys, which are promising inverse magnetostrictive materials for high-performance vibration power generation.
Binary alloy solidification and freckle formation: Effect of shrinkage induced flow on solutal instability and macro-segregation
Authors: Monde Aniket D. , Shrivastava Amit , Jakhar Amman , Chakraborty Prodyut R.
Published: March 2021

Freckle formation during directional solidification of binary alloy is a well-researched subject area. However, the influence of shrinkage induced flow (SIF) on freckling phenomena is barely reported. The focus of this work is to investigate this effect during bottom-up solidification of binary alloys. A fixed grid-based numerical scheme involving volume averaging of conserved parameters is proposed. The solidification geometry under consideration is a two-dimensional mold cavity with a central riser allowing continuous melt flow into the cavity. Model validation is obtained against existing numerical results involving directional solidification of Al-4.1 wt. % Cu alloy. However, heavier solute (Cu) rejection in the melt during solidification renders the validation case study devoid of freckling phenomena. The postvalidation investigations involve bottom up solidification of Al-30 wt. % Mg alloy with lighter solute (Mg) rejection, leading to solutal instability and freckle formation. The effect of SIF on solutal instability, channel formation, and overall macro-segregation is investigated. The intensity of SIF hinges on both cooling condition and opening size. The penetration depth of SIF into the solidification domain gives rise to either early or late onset of solutal instability. SIF penetration depth till the melt domain adjacent to the mushy layer promotes early onset of solutal instability. However, SIF penetration into the mushy layer itself triggers redistribution of solute-rich melt inside this layer, leading to delayed onset of solutal instability. Since the macro-segregation is a direct consequence of advection of solute inside and adjacent to the mushy region, the influence of SIF is manifested by unprecedented macro-segregation pattern.
1/2-BPS vortex strings in N=2 supersymmetric U(1)N gauge theories
Authors: Gudnason Sven Bjarke , Eto Minoru , Nitta Muneto
Published: March 2021

Strings in N=2 supersymmetric U(1)N gauge theories with N hypermultiplets are studied in the generic setting of an arbitrary Fayet–Iliopoulos triplet of parameters for each gauge group and an invertible charge matrix. Although the string tension is generically of a square-root form, it turns out that all existing Bogomol’nyi–Prasad–Sommerfield solutions have a tension that is linear in the magnetic fluxes, which, in turn, are linearly related to the winding numbers. The main result is a series of theorems establishing three different kinds of solutions of the so-called constraint equations, which can be pictured as orthogonal directions to the magnetic flux in SU(2)R space. We further prove for all cases that a seemingly vanishing Bogomol’nyi bound cannot have solutions. Finally, we write down the most general vortex equations in both master form and Taubes-like form. Remarkably, the final vortex equations essentially look Abelian in the sense that there is no trace of the SU(2)R symmetry in the equations after the constraint equations have been solved.
Eulerian–Lagrangian modeling of cough droplets irradiated by ultraviolet–C light in relation to SARS-CoV-2 transmission
Authors: D'Alessandro V. , Falone M. , Giammichele L. , Ricci R.
Published: March 2021

It is well known that several viruses, as well as SARS-CoV-2, can be transmitted through airborne diffusion of saliva micro-droplets. For this reason, many research groups have devoted their efforts in order to gain new insight into the transport of fluids and particles originated from human respiratory tracts. This paper aims to provide a contribution to the numerical modeling of saliva droplets' diffusion produced by coughing. It is worth noting that droplets' diameters of interest in this work are such that represent typical emission during a cough. Aerosolization effects are neglected since emitted droplets' diameters are greater than 10 µm. In particular, the well-known problem around the safety distance to be held for avoiding virus transmission in the absence of external wind is further investigated. Thus, new indices capable of evaluating the contamination risk are introduced, and the possibility to inactivate virus particles by means of an external ultraviolet-C (UV-C) radiation source is studied. For this purpose, a new model which takes into account biological inactivation deriving from UV-C exposure in an Eulerian–Lagrangian framework is presented.
Using approximate inertial manifold approach to model turbulent non-premixed combustion
Authors: Akram Maryam , Raman Venkat
Published: March 2021

The theory of inertial manifolds (IM) is used to develop reduced-order models of turbulent combustion. In this approach, the dynamics of the system are tracked in a low-dimensional manifold determined in situ without invoking laminar flame structures or statistical assumptions about the underlying turbulent flow. The primary concept in approximate IM (AIM) is that slow dominant dynamical behavior of the system is confined to a low-dimension manifold, and fast dynamics respond to the dynamics on the IM instantaneously. Decomposition of slow/fast dynamics and formulation of an AIM is accomplished by only exploiting the governing equations. Direct numerical simulation (DNS) of initially non-premixed fuel–air mixtures developing in forced isotropic turbulence have been carried out to investigate the proposed model. Reaction rate parameters are varied to allow for varying levels of extinction and reignition. The AIM performance in capturing different flame behaviors is assessed both a priori and a posteriori. It is shown that AIM captures the dynamics of the flames including extinction and reignition. Moreover, AIM provides scalar dissipation rate, mixing time for reactive scalars, and closures for nonlinear terms without any additional modeling. The AIM formulation is found promising and provides a new approach to modeling turbulent combustion.
Dynamic mode decomposition analysis of the common research model with adjoint-based gradient optimization
Authors: Wu PeiLi , Wang PeiYan , Gao HangShan
Published: March 2021

Aerodynamic shape refinement optimization for passenger aircraft is difficult and requires a significant workload. The adjoint-based gradient optimization method can quickly find local optimal solutions based on the initial shape in these types of problems. The optimization model of the common research model for the drag coefficient minimization and wing thickness constraints with a large-scale grid is established, and the drag coefficient is reduced by 10.2 counts while maintaining the lift coefficient. The stress-blended eddy simulation is used for unsteady simulations, and the optimized configuration can effectively eliminate oscillations in the middle of the upper wing surface. The spanwise flow is reduced and the pressure response on the wing surface is due primarily to shock chordal motion. For aerodynamic analyses with similar shapes, the dynamic mode decomposition (DMD) analysis shows that the upper wing surface mode amplitudes and spanwise instability modes of the optimized design are weaker, and the fluctuations of the pressure are more stable. Therefore, DMD is suitable for refined shape optimization analyses.
Thermocapillary instability and wave formation on a viscous film flowing down an inclined plane with linear temperature variation: Effect of odd viscosity
Authors: Mukhopadhyay Sanghasri , Mukhopadhyay Asim
Published: March 2021

Thermocapillary instability and formation of waves for a thin viscous falling film with broken time-reversal-symmetry have been discussed in this present study. The film is flowing over a flat, rigid inclined plate with linear temperature variation. The presence of the odd part of the Cauchy stress tensor with odd viscosity coefficient brings new characteristics in thin film flow. The nonlinear evolution model, which tracks the free surface formation for this problem, has been developed using classical long-wave expansion method. Due to the presence of odd viscosity in the liquid, the evolution equation modified significantly. Both spatial and temporal analysis for linear stability has been performed along with the investigation of weakly nonlinear waves, leading the free-surface equation into the famous Kuramoto–Sivashinsky equation. Periodic stationary wave solutions of the full evolution equation confirm the existence of two significant wave families, γ1 and γ2, which are discussed in detail. Formation of the dynamical system and study of different bifurcation analysis and phases diagrams are also studied. The spatiotemporal evolution of the model has been analyzed numerically for different values of the odd viscosity parameter and Marangoni number. The odd viscosity gives stabilizing effect while the increase in Marangoni number increases the instability.
Linear stability analysis of liquid jet exposed to subsonic crossflow with heat and mass transfer
Authors: Liu Luhao , Fu Qingfei , Yang Lijun
Published: March 2021

A linear temporal stability analysis of liquid jets exposed to subsonic crossflow with heat and mass transfer is reported in this paper. The effect of heat and mass transfer at the interface was represented by an existing heat flux ratio of the conduction heat flux to the evaporation heat flux. A new model, describing the physical processes of heat and mass transfer at the interface, was established to solve mathematical difficulties occurring with the heat and mass transfer effect on a cylindrical jet. The model revealed that, when the density ratio was relatively small, the enhancement of heat and mass transfer stabilized the liquid jet for both breakup modes. The coupling effects of heat and mass transfer and density ratio on the instability features also showed that sensitivity of growth rate to heat and mass transfer was linked to density ratio. The maximum growth rate decreased noticeably with the introduction of heat and mass transfer when the density ratio was close to zero. The effects of flow parameters, such as velocity ratio, on the instability features were also studied.
Least energy sign-changing solutions for a class of Schrödinger–Poisson system on bounded domains
Authors: Khoutir Sofiane
Published: March 2021

This paper is concerned with the Schrödinger–Poisson system −Δu + ϕu = λu + μ|u|2u and −Δϕ = u2 setting on a bounded domain Ω⊂R3 with smooth boundary and λ,μ∈R being parameters. By using variational techniques in combination with the nodal Nehari manifold method, we show the existence of μ̄>0 such that for all (λ,μ)∈(−∞,λ1)×(μ̄,+∞), the above system has one least energy sign-changing solution, where λ1 > 0 is the first eigenvalue of −Δ,H01(Ω). The results of this paper are complementary to those in Alves and Souto [Z. Angew. Math. Phys. 65, 1153–1166 (2014)].
Stability assessment on sinusoidal roughness elements for crossflow-transition control
Authors: Ide Yuki , Hirota Makoto , Tokugawa Naoko
Published: March 2021

In this work, we numerically investigate the effectiveness of sinusoidal roughness elements (SREs), which have been proposed by our group to delay crossflow boundary layer transition. First, an ideal control scenario was identified by several stability analysis solvers, and receptivity to stationary vortices behind conventional cylindrical discrete roughness elements (DREs) and SREs was simulated by means of direct numerical simulation (DNS). The critical heights of the two devices were next assessed with DNS. In a flow condition relevant to civil transport aircraft, it was found that the height of an SRE for control could be increased up to approximately 0.33 mm before flows became susceptible to tripping, whereas for a cylindrical DRE it was near to 0.13 mm. This finding illustrates that by the introduction of a high-initial amplitude subdominant vortex, SREs are better at suppressing amplification of the most dominant vortex. To investigate a predictive secondary N-factor (Ntr.) and associated instability mechanisms, we then carried out a bi-local analysis for flows past the critical SREs. The results revealed that there exist many unstable high-frequency secondary modes, Ntr. was approximately 8.4, and that the critical mode at the onset of transition belonged to a type-y mode at 275 kHz. This value of Ntr. was close to those reported by previous studies and also to that of the critical stationary mode at the primary stage.
Spin crossover phenomenon in a three-dimensional cyanido-bridged FeII–MoIV assembly
Authors: Kawabata Shintaro , Nakabayashi Koji , Imoto Kenta , Ohkoshi Shin-ichi
Published: March 2021

We report a spin crossover material based on a cyanido-bridged FeII–MoIV assembly, FeII2[MoIV(CN)8](1-(3-pyridyl)ethanol)8⋅4H2O. This compound has a cubic crystal structure in the Ia3¯d space group and is composed of a three-dimensional cyanido-bridged FeII–MoIV coordination network with one crystallographic FeII site. It exhibits incomplete spin crossover, because 21% of the high-spin FeII sites (S = 2) changes to low-spin FeII sites (S = 0) in the temperature range between 200 and 50 K. Thermal hysteresis is not observed. Such an incomplete and gradual spin crossover is attributed to the elastic frustration between the high-spin and the low-spin FeII sites (e.g., alternating arrangement such as –HS–LS–HS–LS–).
Electronic and optical properties of fluorinated graphene within many-body Green’s function framework
Authors: Wang Kangli , Shao Jingjing , Paulus Beate
Published: March 2021

In this article, a systematic examination of the electronic and optical properties of partially fluorinated graphene is presented. In order to capture a large variety of fluorination degrees and configurations, different sizes of the supercell combining with various degrees of fluorination are considered. On top of periodic density functional theory, the G0W0 method and the G0W0Γ method within many-body Green’s function framework are employed. Including the description of electron–hole interactions, the optical spectra based on the Bethe–Salpeter equation are calculated. Two-sided fluorination with compact fluorination arrangements is energetically most favorable. The fluorination degree has a determined impact on the bandgap value in the system, while the fluorination pattern strongly influences the characteristics of the bands in the electronic structures. Depending on the polarization of the applied electromagnetic field, the optical absorption spectra of the same structure could vary significantly. These interesting results suggest the potential applications of partially fluorinated graphene as optoelectronic materials.
Actinium-225 production with an electron accelerator
Authors: Diamond W. T. , Ross C. K.
Published: March 2021

There has been growing clinical evidence of the value of targeted alpha therapy for the treatment of several cancers. The work has been slowed by the lack of availability of the key alpha emitting isotopes, especially Ac-225. It can be produced by photonuclear reaction, Ra-226(γ,n)Ra-225. The Ra-225 decays via beta-decay to Ac-225 with a half-life of 14.9 days. This paper will provide a technical description of radium targets and a target chamber that would be capable of producing a yield of about 148 GBq (4 Ci) of Ra-225 from a 10-day irradiation of 1 g of radium segmented into two to four separate encapsulated targets at a beam power of 20 kW. These targets could be milked at least three times, yielding nearly 148 GBq (4 Ci) of Ac-225. There is also a description of a method to reduce the activity of co-produced Ac-227 to values less than a few parts per million of the activity of Ac-225. The Monte Carlo code Fluka has been used to model the yields of Ra-225 and support the design concept to reduce the production of Ac-227. It has also been used to model the experimental results by Maslov et al. [Radiochemistry 48(2), 195–197 (2006)] to provide reasonable confidence in the cross section value used by the code.
Electron generation and multiplication at the initial stage of nanosecond breakdown in water
Authors: Zhang Xuewei , Shneider Mikhail N.
Published: March 2021

Electrical breakdown of liquid dielectrics under nanosecond pulsed high voltage has been investigated extensively in the last decade. Prior studies have focused on either experimental characterization of the breakdown process and discharge plasma or formulation/verification of the electrostrictive cavitation mechanism of the breakdown initiation. There remain knowledge gaps toward a clear physical picture of how the first plasma is generated in a region saturated by nanoscale cavities created by electrostrictive forces in inhomogeneous fields at the nanosecond timescale. Initial plasma results from the multiplication of primary electrons that gain energy collisionlessly in the cavities to cause collisional ionization of water molecules on the cavity walls. This paper quantitatively discusses the possible sources of primary electrons that seed the plasma discharge. Electron detachment from hydroxide is shown to be the most probable and sustainable electron source. Using numerical modeling, this study demonstrates the plausibility of an electron multiplication mechanism involving two neighboring cavities. The drift of hydrated electrons from one cavity to the next is the rate-limiting step and sets the minimum electric field requirement. This work will inform subsequent experimental studies and have implications in various applications such as plasma sources in biomedical applications, cavitation study, and insulation of pulsed power equipment.
Deviation from universal dielectric response in CaCu3Ti4O12
Authors: Zhang Zaiyuan , Li Yongqiang , Xing Hongbin , Chen Zhichao , Chen Kai , Wang Ying , Chen Cai , Liu Junming , Zhu Jinsong
Published: March 2021

Giant-permittivity CaCu3Ti4O12 has been modeled by nature at an atomic or electronic scale. Notably, the relation between the imaginary part of the complex dielectric value and the frequency of the applied A.C. electric field is found to deviate from the universal dielectric response in the frame of classic mechanics. Only the deviation is elucidated based on the model, and thus, a clue to quantum dielectric physics appears.
Life history of
Authors: da Silva Charlene , Attwood Colin G. , Wintner Sabine P. , Wilke Chris G. , Winker Henning , Smale Malcolm J. , Kerwath Sven E.
Published: March 2021

Mustelus mustelus from the Langebaan Marine Protected Area (LMPA) has been largely protected from fishing activities for the past 30 years; therefore, its biology represents those of an unfished stock. The reproductive biology, diet, growth and maturity of M. mustelus was studied in the Langebaan Lagoon region in the south-western Cape Coast of South Africa between 2007 and 2009. In total, 217 sharks (females: 381–1734 mm total length (TL); males: 467–1267 mm TL) were examined. Sharks in the Bay represented the largest specimens among six regions, globally. Female parturition, ovulating and mating occurred between November and December after a gestation period of 10–11 months. No ontogenetic shift in diet was evident, with the diet predominantly consisting of the following three species of crustaceans; Hymenosoma orbiculare, Upogebia africana and Callichirus kraussi. The von Bertalanffy growth parameters for combined sexes were L∞ = 1594 mm TL, k = 0.15 year–1, t0 = –2.01 year (n = 95). Possible age over-estimation was investigated using micro-computed tomography, which highlighted the existence of false check marks. This study indicated that the LMPA represents a pupping, nursery and feeding ground as well as a refuge area for the largest and oldest recorded smoothhound sharks globally, emphasising its importance in spatial conservation of this species.
Evidence of a liquid–liquid transition in a glass-forming ionic liquid
Authors: Harris Matthew A. , Kinsey Thomas , Wagle Durgesh V. , Baker Gary A. , Sangoro Joshua
Published: March 2021

Significance

The liquid–liquid transition (LLT) in a single-component liquid reflects changes in the liquid structure on the molecular level. In the case of ionic liquids (ILs), a hierarchical liquid structure is present due to charge-alternation constraints and segregation of nonpolar alkyl chains. We present experimental evidence of structural reorganization in a glass-forming IL corresponding to an LLT. The change in liquid structure correlates to changes in the dynamics and dielectric properties of the IL, which may be useful for potential applications.
Understanding context in computer-mediated communication
Authors: Liang Jennifer Yameng
Published: March 2021

With unprecedented transformations taking place in the landscape of what to say and how we mean, interactions in
the digital age take on various new forms of doing and being. To make sense of “what it is that
is going on” requires an understanding of the context wherein the computer-mediated communications take place. Focusing on a
burgeoning online video commenting discourse in mainland China called Danmaku (a media feature that projects
viewer comments onto the video, like a ‘bullet curtain’), the present study applies the schematic construct of
context of situation and its paradigmatic representation developed in Systemic Functional Linguistics to a functionally-driven
discussion of Danmaku context. Drawing on a corpus of comments from 18 well-received videos on Bilibili.com (a major Danmaku site in mainland China), the study provides a
fine-grained analysis that highlights emergent technological and semiotic variables in the Danmaku Mode, such as anonymity,
invisibility, dynamicity, and pseudo-synchronicity. It then discusses how these variables mediate the properties of Field and
Tenor and further impinge upon the experiential and interpersonal meanings made in Danmaku communication. The analysis also
highlights the carnivalesque nature of Danmaku which makes it an increasingly popular social media platform in mainland
China.
A study on multi-GNSS phase-only positioning
Authors: Khodabandeh A , Zaminpardaz S , Nadarajah N
Published: March 2021

The global navigation satellite systems (GNSS) carrier phase measurements form the basis of high-precision satellite positioning. These measurements are often accompanied by their code counterparts to enable one to compute single-epoch ambiguity-resolved positioning solutions. To avoid unwanted code modelling errors, such as code multipath, one may opt for a phase-only solution and take recourse to carrier phase measurements of two successive epochs. In this paper we study the ambiguity resolution performance of a dual-epoch phase-only model, upon which the unknown positioning parameters are assumed to be completely unlinked in time. With the aid of closed-form analytical results, it is investigated how ambiguity resolution performs when dealing with high-rate phase data. It is thereby shown that multi-GNSS integration makes near real-time centimetre-level phase-only positioning possible. Our analytical analysis is supported by means of numerical results.
In silico muscle volume conduction study validates in vivo measurement of tongue volume conduction properties using a user tongue array depressor
Authors: Luo Xuesong , Sanchez Benjamin
Published: March 2021

Objective. Electrophysiological assessment of the tongue volume conduction properties (VCPs) using our novel multi-electrode user tongue array (UTA) depressor has the promise to serve as a biomarker in patients with bulbar dysfunction. However, whether in vivo data collected using the UTA depressor accurately reflect the tongue VCPs remains unknown. Approach. To address this question, we performed in silico simulations of the depressor with an accurate anatomical tongue finite element model (FEM) using healthy human tongue VCP values, namely the conductivity and the relative permittivity, in the sagittal plane (i.e. longitudinal direction) and axial and coronal planes (i.e. transverse directions). We then established the relationship between tongue VCP values simulated from our model to measured human data. Main results. Experimental versus simulated tongue VCP values including their spatial variation were in good agreement with differences well within the variability of the experimental results. Tongue FEM simulations corroborate the feasibility of our UTA depressor in assessing tongue VCPs. Significance. The UTA depressor is a new non-invasive and safe tool to measure tongue VCPs. These electrical properties reflect the tongue’s ionic composition and cellular membrane integrity and could serve as a novel electrophysiological biomarker in neurological disorders affecting the tongue.
A programmable origami-inspired webbed gripper
Authors: Wang Chunlong , Guo Hongwei , Liu Rongqiang , Yang Hui , Deng Zongquan
Published: March 2021

Origami-inspired design is becoming an innovative approach to create functional mechanisms with a variety of attractive features including scalability, programmability and simplicity. This paper presents the design of a webbed-foot-inspired gripper by employing a novel origami webbing structure, which is generated by strategically integrating several elementary Miura-ori and waterbomb-ori modules. The grasping behaviour of the proposed webbed gripper can be accustomed through rearranging the 2D crease pattern of the origami webbing by taking advantage of shape and kinematic programmability for each elementary module. And based on the rigid panels and joints, a comprehensive quantitative approach to achieve specific grasping performance is performed in terms of closed extendable configuration and enclose input angle. The origami webbing can be fabricated from a single flat paper sheet and deploy along a straight path symmetrically together with supporting skeletons. A sample webbed gripper activated with cables is designed to exhibit potential applications, and primary experimental work focusing on object grasping capability is carried out. The results demonstrate the feasibility and practicability of the origami-inspired webbed gripper design, and numerous novel origami webbing structures can be developed based on this construction strategy.
Detailed design and life prediction methodology of novel SMA actuated repeatable launch locking protective device (RLLPD) for magnetically suspended flywheel (MSFW)
Authors: Rao Zhixiang , Yan Xiaojun , Zhang Xiaoyong , Jiang Jun
Published: March 2021

This paper proposes a detailed design of a novel bias shape memory alloy (SMA) actuated repeatable launch locking protective device (RLLPD) for the magnetically suspended flywheel (MSFW) during the launching state. The proposed SMA actuated RLLPD consists of two bias SMA-spring actuators. One is designed to realize locking/unlocking and the other is intended for triggering. Besides, self-locking blocks are employed to ensure that the MSFW can be safely locked under the vibration of the launching process. Considering the locking method by compressing the flywheel against the mechanical bearing, there are at least three or four locking points to maintain the balance and enhance the locking reliability of the flywheel. Additionally, a force amplifying linkage mechanism is employed using one bias SMA-spring actuator to actuate the movement of two clamps, further reducing the total weight of the RLLPD and amplifying the locking strength. Furthermore, the recovery envelope curve which represents the recovery ability of SMA wire under various spring rate is proposed and computed using thermodynamics constitutive model. Simulation results indicate that the recovery envelope curve coincides with the austenite unloading curve. The thermodynamics constitutive model of SMA considering functional fatigue is utilized to calculate the evolution rate of functional fatigue of SMA wire in the RLLPD. The functional fatigue evolution rate computation algorithm and results are presented. After the design and simulation, a prototype of the locking device is fabricated and tested. According to the performance results, the SMA-actuated locking device can release a preload up to 1000 N. The simulation and experimental results indicate that the life cycle of the locking device is more than 50 times.