bluuebunny/crossref_metadata_2025 huggingface dataset:
Vortex formation in starting buoyant jets at moderate Richardson numbers
Authors: Guo Hui-Fen , Gao Lei , Yu Simon C. M.
Published: November 2020

In this paper, the formation process of the leading vortex ring in positively and negatively buoyant starting jets with moderate Richardson number in the range of 0.06 < |Ri| ≤ 0.321 has been investigated numerically and theoretically. Using the similarity variables |Ri| and |Ri|2/5 for the positively and negatively buoyant starting jets, respectively, fitting equations can be obtained to predict the buoyant jet penetration rate. Based on these fitting equations, a revised circulation model is proposed by incorporating the effects of both over-pressure and buoyancy. The revised model is well consistent with the numerical results for all positively buoyant starting jets. However, for the negatively buoyant starting jets, this model can predict well only during the initial period. The over-pressure has little influence on the vortex ring characteristics of the starting jets with positive buoyancy, whereas it can significantly affect the vortex ring formation of the negatively buoyant starting jets at moderate Richardson numbers. As the positive Richardson number increases, the instabilities of the trailing shear layer occur earlier. At moderately negative Richardson numbers, a “double plume” structure (an inner sinking circular forced plume and an outer rising annular plume) can be observed. The outer negative vorticity layers develop gradually due to the baroclinic effect. Consequently, the size and strength of the leading vortex progressively decrease. As the negative Richardson number decreases, the negative vorticity layers occur earlier and grow faster.
The role of collective elasticity on activated structural relaxation, yielding, and steady state flow in hard sphere fluids and colloidal suspensions under strong deformation
Authors: Ghosh Ashesh , Schweizer Kenneth S.
Published: November 2020

We theoretically study the effect of external deformation on activated structural relaxation and aspects of the nonlinear mechanical response of glassy hard sphere fluids in the context of elastically collective nonlinear Langevin equation theory. This microscopic force-based approach describes activated relaxation as a coupled local–nonlocal event involving caging and longer range collective elasticity, with the latter becoming more important and ultimately dominant with increasing packing fraction under equilibrium conditions. The central new question we address is how this physical picture of activated relaxation, and the relative importance of local caging vs collective elasticity physics, depends on external deformation. Theoretical predictions are presented for deformation-induced enhancement of mobility, the onset of relaxation speed up at remarkably low values of stress, strain, or shear rate, apparent power law thinning of the steady state structural relaxation time and viscosity, a non-vanishing activation barrier in the shear thinning regime, an apparent Herschel–Bulkley form of the rate dependence of the steady state shear stress, exponential growth of different measures of a dynamic yield or flow stress with the packing fraction, and reduced fragility and dynamic heterogeneity under deformation. The results are contrasted with experiments and simulations, and qualitative or better agreement is found. An overarching conclusion is that deformation strongly reduces the importance of longer range collective elastic effects relative to the local caging aspect for most, but not all, physical questions, with deformation-dependent fragility and dynamic heterogeneity phenomena being qualitatively sensitive to collective elasticity. Overall, nonlinear rheology is predicted to be a more local problem than quiescent structural relaxation, albeit with deformation-modified activated processes still important.
A dynamic optical constant extraction method for thin films with structural and optical-parametric justifications
Authors: Zubair M. A. , Chowdhury M. T.
Published: November 2020

An original fitting approach grounded on dynamic n(λ) dispersion along with envelop based Connell–Lewis (C–L) relation for optical absorption was developed and implemented to extract the optical constants from experimental T(λ) spectra of thin films. Thermal-vapor-deposited chalcogenide CdSe thin films having a thickness range of ∼650–1550 nm were chosen for this purpose. The interdependence of n(λ) and k(λ) in the analytical T(λ) expression through the C–L equation partially mimics the Kramers–Kronig relation, which is a requirement for the optical constant to be physically meaningful. The average quadratic function within the measured spectral range was found to fall below 1%. On the contrary, a pronounced scattering in the relative difference spectra (∼10%) observed within a very narrow band of interference pattern was attributed to a systematic error and uncertainty in the spectral shape just above the absorption edge. The validity of the extracted optical and dimensional parameters was scrutinized in terms of microstructural and crystallographic measurements. The variation in packing density, estimated from the extracted n(λ) spectra, commensurates with the temperature evolution of microstructural features. The bathochromic shifts in the split transition energies obtained from the extracted k(λ) spectra were discussed satisfactorily in terms of the quantum threshold size effect. Although this fitting approach was applied only to a chalcogenide thin film, it is anticipated to be applicable to the other transparent thin films as well.
Photothermal characterization of biodiesel and petroleum diesel fuels—A review and perspective
Authors: Shen Jun , Michaelian Kirk H. , Gieleciak Rafal , Baesso Mauro L. , Astrath Nelson G. C. , Malacarne Luis C.
Published: November 2020

Alternative fuels hold considerable promise as substitutes for petroleum diesel fuel. As such, biodiesel is a promising renewable fuel that has been developed and tested by a number of research groups. Quality control of this transportation fuel is of great significance to its commercialization. Conventional chromatographic and spectroscopic analytical methods are most commonly used for biodiesel characterization, in some cases yielding information detail beyond that needed for the determination of biodiesel quality. By contrast, less common methods, such as photothermal techniques, are well suited to characterize a wide range of transportation fuels. The complexities of photothermal and chemical analytical techniques are roughly similar, as are the costs. Photothermal methods are based on spectroscopic and thermophysical properties of the sample, an advantage with respect to ordinary chromatography and spectroscopy techniques. Furthermore, some photothermal techniques can be adapted for remote signal detection, which can be used for in situ analysis in fuel production for inline biodiesel quality inspection and control. Therefore, an overview and outlook of the photothermal characterization is of considerable interest. In this paper, the applications of photothermal techniques in the characterization of biodiesel, petroleum diesel fuels, and their blends are reviewed. The review includes thermophysical properties and correlations for fuels, determination of blend levels, and biodiesel stability investigations. After the review, discussion and perspective are presented for future improvement of photothermal characterization and industrial applications.
Experimental visualization of sneezing and efficacy of face masks and shields
Authors: Arumuru Venugopal , Pasa Jangyadatta , Samantaray Sidhartha Sankar
Published: November 2020

In the present work, we propose and demonstrate a simple experimental visualization to simulate sneezing by maintaining dynamic similarity to actual sneezing. A pulsed jet with Reynolds number Re = 30 000 is created using compressed air and a solenoid valve. Tracer particles are introduced in the flow to capture the emulated turbulent jet formed due to a sneeze. The visualization is accomplished using a camera and laser illumination. It is observed that a typical sneeze can travel up to 25 ft in ∼22 s in a quiescent environment. This highlights that the present widely accepted safe distance of 6 ft is highly underestimated, especially under the act of a sneeze. Our study demonstrates that a three-layer homemade mask is just adequate to impede the penetration of fine-sized particles, which may cause the spreading of the infectious pathogen responsible for COVID-19. However, a surgical mask cannot block the sneeze, and the sneeze particle can travel up to 2.5 ft. We strongly recommend using at least a three-layer homemade mask with a social distancing of 6 ft to combat the transmission of COVID-19 virus. In offices, we recommend the use of face masks and shields to prevent the spreading of droplets carrying the infectious pathogen. Interestingly, an N-95 mask blocks the sneeze in the forward direction; however, the leakage from the sides and top spreads the sneeze in the backward direction up to 2 ft. We strongly recommend using the elbow or hands to prevent droplet leakage even after wearing a mask during sneezing and coughing.
Conformational properties of complexes of poly(propylene imine) dendrimers with linear polyelectrolytes in dilute solutions
Authors: Gupta Shilpa , Biswas Parbati
Published: November 2020

This study investigates the conformational properties of complexes of poly(propylene imine) dendrimers with a linear polyelectrolyte (LPE) at neutral pH in an aqueous solution via molecular dynamics simulations. Various conformational properties, such as the atomic density profile, counterion density distribution, charge distribution, cavity volume, and the static structure factor are studied as a function of the charge and chain length of the LPE. The lower generation dendrimer complexes encapsulate the shorter linear PE chains, while the longer PE chains are adsorbed on the dendrimer surface that screen the surface charge and prevent the penetration of the counterions and water molecules. However, the overall charge of the higher generation dendrimers is not neutralized by the charge of the PE chains, which results in chloride counterion penetration within the dendrimers. The adsorption of the PE chains on the dendrimers is also verified from the charge distribution of the dendrimer–PE complexes. The charge on the lower generation dendrimer complexes is overcompensated by the longer PE chains resulting in an overall negative charge on the complexes, while the PE chains do not completely neutralize the charge of the higher generation dendrimers and produce positively charged complexes. The results of the structure factor indicate a conformational transition of the dendrimer–PE complexes from a dense compact structure to an open one with an increase in the PE chain length. This transition is characterized by an increase in the cavity volume in dendrimers with an increase in the PE chain length.
Reassessing water slippage in hydrophobic nanostructures
Authors: Zuo Hong , Javadpour Farzam , Deng Shouchun , Jiang Xiaofang , Li Zhiwen , Li Haibo
Published: November 2020

Reported data of measured slip lengths in nanostructures span several orders of magnitude, from a few nanometers to tens of micrometers. Small roughness on surfaces caused by structural defects or thermal fluctuations dramatically reduces slippage. Tiny bubbles entrapped on rough surfaces can also affect slippage. We used an asymptotic solution and a high density-ratio pseudopotential lattice Boltzmann model to systematically study the drag resistance of a rough surface with attached bubbles. As bubbles nucleate and grow, drag resistance is slightly reduced until the tri-phase contact line reaches the edges of roughness, where bubbles with small angles substantially reduce drag resistance. As bubbles grow to become a continuous gas layer on the surface, the drag resistance greatly decreases. However, the interface deformation from flat to curved shape greatly hinders liquid flow, and the vortex structures cause a wave-like fluctuation in the effective slip length. This finding sheds light on the controversies of reported large variations in the slip length of super-hydrophobic surfaces in nanostructures, e.g., carbon nanotubes.
Forage biomass yield and arbuscular mycorrhizal symbiosis in a legume and C3 and C4 grasses under increasing soil phosphorus availability
Authors: Chippano Tomás , García Ileana , Cofré Noelia , Mendoza Rodolfo
Published: November 2020

Phosphorus (P) is the main limiting factor for forage production in grasslands. It is important to determine levels of available P in soil that optimise production with minimum impact on arbuscular mycorrhizal (AM) symbiosis. We investigated the effects of increasing P availability on biomass production, root morphology, AM symbiosis and P acquisition of a forage legume (Lotus tenuis), a C3 grass (Schedonorus arundinaceus) and a C4 grass (Panicum coloratum) growing on a P-deficient soil in pots with P applied at rates of 0–160 mg kg–1 dry soil. The three forage species responded strongly to addition of P, with 90% of maximum shoot growth reached at available P levels of 24.3 mg kg–1 for L. tenuis, 14.4 mg kg–1 for P. coloratum and 11.2 mg kg–1 for S. arundinaceus. Lotus tenuis and P. coloratum produced higher yields of shoot biomass than S. arundinaceus. Root dry weight was higher in the legume than in the grasses, with the root-mass fraction being lowest in P. coloratum. AM colonisation was higher in L. tenuis roots than in grass roots, and decreased with increased soil P availability, especially in grasses. Low to moderate additions of P did not affect, and could even improve, AM colonisation in L. tenuis roots. For L. tenuis, it is possible to increase forage yield while maintaining high values of AM colonisation at 10–20 mg kg–1 of available P, but for grasses, especially S. arundinaceus, it is difficult to achieve both objectives. The presence of L. tenuis in grasslands or pastures may contribute to maintaining the native AM inoculum under a wide range of soil P availability in regions such as the Salado River basin of Argentina.
Spinors of spin-one-half fields
Authors: Cahill Kevin
Published: November 2020

This paper reviews how a two-state, spin-one-half system transforms under rotations. It then uses that knowledge to explain how momentum-zero, spin-one-half annihilation and creation operators transform under rotations. The paper then explains how a spin-one-half field transforms under rotations. The momentum-zero spinors are found from the way spin-one-half systems transform under rotations and from the Dirac equation. Once the momentum-zero spinors are known, the Dirac equation immediately yields the spinors at finite momentum. The paper then shows that with these spinors, a Dirac field transforms appropriately under charge conjugation, parity, and time reversal. The paper also describes how a Dirac field may be decomposed either into two 4-component Majorana fields or into a 2-component left-handed field and a 2-component right-handed field. Wigner rotations and Weinberg’s derivation of the properties of spinors are also discussed.
Silicon Y-bifurcated microchannels etched in 25 wt% TMAH water solution
Authors: Smiljanić Milče M , Lazić Žarko , Rafajilović Milena Rašljić , Zobenica Katarina Cvetanović , Milinković Evgenija , Filipović Ana
Published: November 2020

In this study, Y-bifurcated microchannels fabricated from a {100} silicon in 25 wt% tetramethylammonium hydroxide water solution at the temperature of 80 °C have been presented and analysed. We studied the etching of acute angles with sides along the  crystallographic directions in the masking layer where 1 < n < 8. We considered symmetrical acute corners in the masking layer with respect to the <100> crystallographic directions. The angles between the appropriate  and <100> crystallographic directions were smaller than 45°. Moreover, we observed asymmetrical acute corners formed by the  and  crystallographic directions, where m ≠ n. We found that the obtained convex corners were not distorted during etching. Consequently, it is not necessary to apply convex corner compensation. These fabricated undistorted convex corners represent the angles of the bifurcations. The sidewalls of the microchannels are defined by etched planes of the {n11} and {100}families. Analytical relations were derived for the widths of the microchannels. The results enable simple and cost-effective fabrication of various complex silicon microfluidic platforms.
Rydberg transitions and photoionisation cross section of NH3
Authors: Modak Paresh , Antony Bobby
Published: November 2020

Partial photoionisation cross sections of NH3 are calculated for processes involving transitions from the ground state to 2A1 and 2E excited electronic states of the neutral target and residual ion respectively for a wide range of wavelengths using the R-matrix method. Some near threshold structures are resolved. A comparative study is reported for the lone pair 3a
1 electrons with the isoelectronic system, H2O [Modak and Antony 2020 J. Phys. B: At. Mol. Opt. Phys.
53 045202]. We observe that the lone pair of NH3 is loosely bound compared to H2O. A local rise in cross section data for 2A1 (3a
1) electronic state due to autoionisation is also observed from higher excited states. This was earlier predicted by Brion et al [Brion et al 1977 J. Elect. Spectrosc. Rel. Phenom.
12 323]. This is the first report which confirms predissociation due to the dissociative photoionisation of 2E state. A major aim of this study is to resolve Rydberg transitions above the ionisation threshold and quantify them for photoionisation rate coefficients. A recent study by Saraswathya et al [Saraswathya et al 2010 Spectrosc. Lett.
43 290] is the only reported data for few of these Rydberg transitions. These transitions are usually absent in experiments due to the difficulty in resolving narrow energy range. In this investigation, we observed Rydberg transitions above the first ionisation threshold of NH3. An autoionisation peak is also identified in the background of Rydberg transitions.
Refined analysis of current–voltage characteristics in Townsend dielectric barrier discharges in nitrogen at atmospheric pressure
Authors: Mejanes Naomi De , Profili Jacopo , Babaei Sara , Naudé Nicolas , Stafford Luc
Published: November 2020

A refined method is proposed to analyze surface spreading phenomena along the gas flow lines in plane-to-plane Townsend dielectric barrier discharges (TDBDs) in nitrogen at atmospheric pressure. Current–voltage characteristics are recorded as a function of gas residence time using a recently-developed, fragmented-electrode system and the results are analyzed using an equivalent circuit model using dielectric, gas and parasitic capacitances as adjustable parameters. The results show that the capacitance values are directly correlated to the surface spreading of the TDBD, which in turn, influences the shape of the discharge current and gas voltage curves for each half-cycle of the applied voltage. This highlights the importance of a good determination of the effective discharge surface area and therefore of the capacitance values in electrical analysis of TDBD.
Improved Na storage performance of Na3V2(PO4)3 cathode material for sodium-ion batteries by K-Cl co-doping
Authors: Hong Xianda , Liang Kang , Huang Xiaobing , Ren Yurong , Wang Haiyan
Published: November 2020

As a promising cathode material for sodium-ion batteries (SIBs), Na3V2(PO4)3 (NVP), the typical NASICON (Na super-ionic conductor)-structure cathode material, has received much attention resulting from its high working potential and excellent structural stability. However, it has always suffered from low electroconductivity, which largely limits its application in SIBs. Herein, to improve the electrochemical performance, we developed potassium and chlorine co-doped Na3V2(PO4)3/carbon particles (NKVPCl/C) using a spray-drying method combined with a calcinating process and adopted them as cathode materials for SIBs. We studied in detail how K+ and Cl− affected the electrochemical performance. The NKVPCl/C-2 particles displayed a highly initial discharge capacity of 109.6 mA h g−1 at 0.2 C, and had a superior cycling stable property (nearly 100% of initial discharge capacity after 500 cycles at 5 C). The excellent electrochemical performance of NKVPCl/C can be attributed to its higher Na+ diffusion and electron conduction, which indicates that the strategy of co-doping K-Cl is an effective tactic for improving the property of NVP in SIBs.
Validity of the effective injection barrier in organic field-effect transistors
Authors: Lee Yongjeong , Horowitz Gilles , Jung Sungyeop , Bonnassieux Yvan
Published: November 2020

The injection barrier is a key parameter that governs the charge and current density in organic field-effect transistors (OFETs). However, the energetic disorder of organic disordered semiconductors (ODSs) hinders a clear definition of the injection barrier. We study the validity of effective injection barrier at the metal/organic disordered semiconductor by means of systematic numerical simulation of OFETs in full consideration of the Gaussian density-of-states. The contact resistance from the numerical simulation and analytical model are compared to verify this procedure. By varying the Gaussian width, the effective injection barrier is validated for low degree of disorder at which the semiconductor is under non-degenerate condition. The position of Fermi level with respect to the Gaussian width distinguishes the non-degenerate and degenerate condition of ODSs, indicating clearly the range of validity of the effective injection barrier.
A method to test the coupling strength of the linear and nonlinear contributions to higher-order flow harmonics via event shape engineering
Authors: Magdy Niseem , Evdokimov Olga , Lacey Roy A
Published: November 2020

A multi-phase transport model is used to study the efficacy of shape-engineered events to delineate the degree of coupling between the linear and nonlinear contributions to the higher-order flow harmonics v
4 and v
5. The study shows that the nonlinear contributions are strongly shape-dependent while the linear contributions are shape-independent, indicating little if any, coupling between the linear and nonlinear flow coefficients. The experimental verification of such patterns could be an invaluable tool for robust extraction of the linear and mode-coupled flow coefficients, especially for beam energies where the charged particle multiplicity and the event statistics precludes the use of current methods to establish the coupling strength.
Even–even 122–138Ce isotopes shape study within CNS model
Authors: Kaim S , Azzam B Saad
Published: November 2020

The present paper concerns the study of the even–even 122–138Ce isotopes, based on the cranked Nilsson–Strutinsky model. The energy levels are calculated for these nuclei and the potential energy surfaces are represented in deformation parameters plane (ɛ
2, γ). The configurations are assigned to different bands using the best difference between calculated and observed energies. The nuclear shape evolution as function of the spin is examined and explored by two separate studies, using, respectively, the values of deformation parameters in the first study and the analysis of kinetic and dynamic moments of inertia (

J

(1) and

J

(2)) in the second one. The results of both studies are consistent.
Weak localization and weak antilocalization in doped Ge1-y
Sn
y
layers with up to 8% Sn
Authors: Weißhaupt David , Funk Hannes S , Kern Michal , Dettling Marco M. , Schwarz Daniel , Oehme Michael , Sürgers Christoph , van Slageren Joris , Fischer Inga A , Schulze Jörg
Published: November 2020

Low-temperature magnetoresistance measurements of n- and p-doped germanium–tin (Ge1-y
Sn
y
) layers with Sn concentrations up to 8% show contributions arising from effects of weak localization for n-type and weak antilocalization for p-type doped samples independent of the Sn concentration. Calculations of the magnetoresistance using the Hikami–Larkin–Nagaoka model for two-dimensional transport allow us to extract the phase-coherence length for all samples as well as the spin–orbit length for the p-type doped samples. For pure Ge, we find phase-coherence lengths as long as (349.0 ± 1.4) nm and (614.0 ± 0.9) nm for n-type and p-type doped samples, respectively. The phase-coherence length decreases with increasing Sn concentration. From the spin–orbit scattering length, we determine the spin-diffusion scattering length in the range of 20–30 nm for all highly degenerate p-type doped samples irrespective of Sn concentration. These results show that Ge1-y
Sn
y
is a promising material for future spintronic applications.
Investigation of the magnetic phase diagram of the 2D ferrimagnetic J
1–J
2 model
Authors: Wieser R
Published: November 2020

The zero-temperature phase diagram and spin dynamics of the 2D ferrimagnetic J
1–J
2 model with (S
1, S
2) = (1/2, 1) are investigated using the time-dependent cluster mean-field theory (t-CMFT). The t-CMFT enables the investigation of the quantum-mechanical as well as semi-classical phase diagram and spin dynamics by control of the entanglement. For the characterization of the ferrimagnetic system, the magnetization, the energy per atom, the cluster quantum states and the von Neumann entropy have been determined.
Black-box inhomogeneous preconditioning for self-consistent field iterations in density functional theory
Authors: Herbst Michael F , Levitt Antoine
Published: November 2020

We propose a new preconditioner based on the local density of states for computing the self-consistent problem in Kohn–Sham density functional theory. This preconditioner is inexpensive and able to cure the long-range charge sloshing known to hamper convergence in large, inhomogeneous systems such as clusters and surfaces. It is based on a parameter-free and physically motivated approximation to the independent-particle susceptibility operator, appropriate for both metals and insulators. It can be extended to semiconductors by using the macroscopic electronic dielectric constant as a parameter in the model. We test our preconditioner successfully on inhomogeneous systems containing metals, insulators, semiconductors and vacuum.
First-principles investigation on the thermoelectric performance of half-Heusler compound CuLiX(X = Se, Te)
Authors: Jia Kang , Yang Chuan-Lu , Wang Mei-Shan , Ma Xiao-Guang , Yi You-Gen
Published: November 2020

The remarkable thermoelectric performance is predicted for half-Heusler (HH) compounds of CuLiX (X = Se, Te) based on the first-principles calculation, the deformation potential (DP) theory, and semi-classical Boltzmann theory. The Slack model is employed to evaluate the lattice thermal conductivity and the result is in good agreement with the previously reported data. The results of mechanical properties demonstrate that CuLiSe is ductile but CuLiTe is brittle. The relaxation time and the carrier mobility are calculated with DP theory. The electrical and thermal conductivities are obtained by using the semi-classical Boltzmann theory based on the relaxation approximation. The Seebeck coefficient and power factor are obtained and their characters are analyzed. The dimensionless figure of merits (ZT) is obtained for the p- and n-type CuLiX. The maximum ZT of 2.65 can be achieved for n-type CuLiTe at the carrier concentration of 3.19 × 1019 cm−3 and 900 K, which indicates that this compound is a very promising candidate for the highly efficient thermoelectric materials.
Automated calibration of multiple long gauge blocks using the KRISS linear measurement system
Authors: Kim Jong-Ahn , Lee Jae Yong , Woo Jae Heun , Eom Sung Hoon , Kim Myung Soon , Kang Chu-Shik
Published: November 2020

For efficient calibration of multiple long gauge blocks (LGBs), an automatic alignment system, consisting of a multi-axis stage and an angle sensor, was developed and integrated with the Korea Research Institute of Standards and Science linear measurement system. The stage was designed to be installed in the limited space of the linear measurement system, with the ability to translate and align the linear and angular positions of LGBs. The auto-collimation angle sensor detected the tip-tilt angle of an LGB with an angular resolution of 0.11″, by image processing the intensity profile of a beam reflected from one of the measured faces of an LGB. Using this automatic alignment system, up to five LGBs were calibrated sequentially without any manual operation or thermal instability. Therefore, multiple LGBs can be calibrated in a short time with small alignment errors and under optimal thermal conditions. When four LGBs with nominal lengths of between 250 mm and 1000 mm were measured, the measurement repeatability of each LGB length was less than 22 nm, and the calibration results agreed well with those obtained by an LGB interferometer within the expanded measurement uncertainty.
A front-tracking measurement technique for in-situ columnar and equiaxed structure growth with controlled solidification
Authors: Hughes Turlough , McFadden Shaun , Robinson Anthony J
Published: November 2020

Growth rate is an important consideration in solidification as it influences features of the micro and macrostructure such as morphology and the columnar to equiaxed transition. Thus, accurately quantifying the growth rate is key to understanding the solidification process as well as verifying numerical simulations. In this work, an experimental apparatus has been developed to investigate in-situ directional solidification using a transparent analogue material, neopentyl glycol-35 wt%(D)camphor. The facility enables the control of the mushy zone growth rate as well as the imposed temperature gradient during solidification, similar to Bridgman type furnaces. Image processing techniques were developed for automated tracking of position and growth rate of the solidification front (SF) using background subtraction on photographic image sequences captured in experiments. Growth rate measurements using this technique and the traditional method (liquidus isotherm speed) have been benchmarked against manual measurements of position and growth rate. Results show that automatically tracked growth rate compares well throughout experiments with errors less than 2.7%. Contrastingly, isotherm speed was in error up to 19%. Three columnar and two equiaxed morphologies were investigated and SFs were characterised for their growth rates and thermal conditions.
Effects of charge carrier density of ZnO film used in UV sensors: difficulties in measurement and rectification method
Authors: Seeneevassen Seydiren , Kashan Mohammad Ali Mohammadzadeh , Ramakrishnan N
Published: November 2020

In this Technical Note, we demonstrate a rectification method to enable the use of zinc oxide (ZnO) films in conductometric ultraviolet (UV) sensors. The phenomenon of persistent conductivity has long impeded the employment of ZnO films as conductometric UV sensors and eventually yields photo-induced current saturation in the film. To address this problem, we propose measuring the change in current in a transient response compromising of an OFF period of 60 s followed by an ON period of 20 s. In addition, we have investigated the effects of temperature and relative humidity, and dyanamic response of the sensor for different UV intensities. The experimental result shows that this measurement technique allows the ZnO film to act as a conductometric sensor even after prolonged exposures.
Performance improvement of P3HT nanowire-based organic solar cells by interfacial morphology engineering
Authors: Kiymaz Deniz , Kiymaz Aykut , Zafer Ceylan
Published: November 2020

Poly (3-hexylthiophene-2,5-diyl) nanowires (nw-P3HT) have been a great interest for organic electronics, including organic field-effect transistors, organic photodetectors, organic photovoltaics, etc due to easy formation in the solution process. Thus both explanations of charge transport dynamics and morphology are crucial for device performance. Here we demonstrated the optoelectronic properties of the P3HT nanowires where the polymer backbones were parallel to the nanowire axis. The nanowires tended to form a bundle due to van der Waals interactions. Nanowire bundles were separated by 1,8-diiodooctane (DIO) additive for photovoltaic fabrication. The bundle separation was visualized by atomic force microscopy. The charge transfer mechanism was evaluated by electrochemical impedance spectroscopy. The electrical analysis showed that short-circuit current density (J
sc) increases to 10.74 mA cm−2 after the bundle separation. According to impedance analysis, there is a correlation between effective lifetime and DIO ratio. These findings were considered as promising results for improving the transport by forming pathways for charge carriers.
The effect of Ag atom doped Cu@CuO core–shell structure on its electronic properties and catalytic performance: a first principles study
Authors: Zhang Xiao , Zhou Xiaolong , Guo Yanxin , Li Jintao , Hu Chen , Zhang Kunhua , Wang Lihui
Published: November 2020

Density functional theory was used to study the Ag-doped Cu@CuO core–shell structure, electronic properties and catalytic properties. Similar to the undoped Cu@CuO clusters, the Ag doped clusters also retain the core–shell structure. Ag doping increases the charge transfer between surrounding O atoms and Cu atoms and reduces the potential of the core–shell structure, thereby increasing its surface activity. The study of its orbital distribution found that the doping of Ag atoms caused the interaction between the inner Cu core and the outer CuO shell, which changed the electron orbital motion inside the shell. The internal chemical stability of the core–shell material is improved. In addition, Ag atom doping accelerates the decomposition of H2O2 on Cu@CuO structure and increases its adsorption of small molecules, which indicates that Ag atom doping improves the catalytic performance of Cu@CuO structure.
Validation of a CT-based motion model with in-situ fluoroscopy for lung surface deformation estimation
Authors: Ranjbar M , Sabouri P , Mossahebi S , Sawant A , Mohindra P , Lasio G , Topoleski L D Timmie
Published: November 2020

Many surrogate-based motion models (SMMs), proposed to guide motion management in radiotherapy, are constructed by correlating motion of an external surrogate and internal anatomy during CT-simulation. Changes in this correlation define model break down. We validate a methodology that incorporates fluoroscopic (FL) images acquired during treatment for SMM construction and update. Under a prospective IRB, 4DCT scans, VisionRT (VRT) surfaces, and orthogonal FLs were collected from five lung cancer patients. VRT surfaces and two FL time-series were acquired pre- and post-treatment. A simulated annealing optimization scheme was used to estimate optimal lung deformations by maximizing the mutual information (MI) between digitally reconstructed radiographs (DRRs) of the SMM-estimated 3D images and FLs. Our SMM used partial-least-regression and was trained using the optimal deformations and VRT surfaces from the first breathing-cycle. SMM performance was evaluated using the MI score between reference FLs and the corresponding SMM or phase-assigned 4DCT DRRs. The Hausdorff distance for contoured landmarks was used to evaluate target position estimation error. For four out of five patients, two principal components approximated lung surface deformations with submillimeter accuracy. Analysis of the MI score between more than 4000 pairs of FL and DRR demonstrated that our model led to more similarity between the FL and DRR images compared to 4DCT and DRR images from a model based on an a priori correlation model. Our SMM consistently displayed lower mean and 95th percentile Hausdorff distances. For one patient, 95th percentile Hausdorff distance was reduced by 11 mm. Patient-averaged reductions in mean and 95th percentile Hausdorff distances were 3.6 mm and 7 mm for right-lung, and 3.1 mm and 4 mm for left-lung targets. FL data were used to evaluate model performance and investigate the feasibility of model update. Despite variability in breathing, use of post-treatment FL preserved model fidelity and consistently outperformed 4DCT for position estimation.
Modelling and analysis of electrical impedance myography of the lateral tongue
Authors: Schooling Chlöe N , Jamie Healey T , McDonough Harry E , French Sophie J , McDermott Christopher J , Shaw Pamela J , Kadirkamanathan Visakan , Alix James J P
Published: November 2020

Objective: Electrical impedance myography (EIM) performed on the centre of the tongue shows promise in detecting amyotrophic lateral sclerosis (ALS). Lateral recordings may improve diagnostic performance and provide pathophysiological insights through the assessment of asymmetry. However, it is not known if electrode proximity to the muscle edge, or electrode rotation, distort spectra. We evaluated this using finite element-based modelling. Approach: Nine thousand EIM from patients and healthy volunteers were used to develop a finite element model for phase and magnitude. Simulations varied electrode proximity to the muscle edge and electrode rotation. LT-Spice simulations assessed disease effects. Patient data were assessed for reliability, agreement and classification performance. Main results: No effect on phase spectra was seen if all electrodes remained in contact with the tissue. Small effects on magnitude were observed. Cole-Cole circuit simulations indicated capacitance reduced with disease severity. Lateral tongue muscle recordings in both patients and healthy volunteers were reproducible and symmetrical. Combined lateral/central tongue EIM improved disease classification compared to either placement alone. Significance: Lateral EIM tongue measurements using phase angle are feasible. Such measurements are reliable, find no evidence of tongue muscle asymmetry in ALS and improve disease classification. Lateral measurements enhance tongue EIM in ALS.
Evaluation of abrupt energy transfer among turbulent plasma structures using singular value decomposition
Authors: Sasaki M , Kobayashi T , Dendy R O , Kawachi Y , Arakawa H , Inagaki S
Published: November 2020

A method to quantify the energy transfer among turbulent structures using singular value decomposition (SVD) is presented. We apply the method to numerical turbulence data obtained from a global plasma simulation using the Hasegawa–Wakatani fluid model, in which the Kelvin–Helmholtz instability plays a dominant role. Using the SVD method, the electrostatic potential is decomposed into a background potential deformation, a zonal flow, a coherent mode and an intermittent structure. Thus there are four key structures, as distinct from the three found in conventional theory. The kinetic energy of each structure is evaluated, and the limit cycle among them is obtained. In the limit cycle, an abrupt change of the background is found to be synchronised with the period of the zonal flow. The energy transfer function of each turbulence structure, which is defined on the basis of a vorticity equation, is evaluated. This then provides physical understanding of how the limit cycle is sustained by dynamical changes in the energy transfer among structures over the its period. In addition, it is shown that the abrupt deformation of the background is caused by the non-linear self-coupling of the intermittent structure.
L-mode plasmas analyses and current ramp-up predictions for a JT-60SA hybrid scenario
Authors: Morales J , Garcia J , Giruzzi G , Artaud J-F , Piron C , Vallar M , Goodman T
Published: November 2020

In this work, L-mode analyses are performed in order to assess a modeling framework for the prediction of electron cyclotron resonant heating (ECRH) -assisted current ramp-up phases for JT-60SA tokamak hybrid scenario #4-2. We compare two turbulence transport models, CDBM and TGLF, using the integrated modeling code CRONOS. Model validation is performed on the basis of an L-mode ramp-up phase in a JET plasma, and a flat-top L-mode TCV (Tokamak a configuration variable) plasma with applied ECRH. Parameter scans in

Z

eff

and in-edge electron temperature (T

e
) are performed. Our results indicate effective prediction of the q profile in JET ramp-up if edge T

e
is properly captured. Indeed, our sensitivity scan demonstrates the strong impact of edge T

e
on q profile evolution. The results of CDBM and TGLF modeling show good agreement with the experimental measurements. With respect to a JT-60SA hybrid scenario, a significant amount of ECRH off-axis is required to maintain a q profile above unity across the entire plasma radius. Based on an analysis of power deposition location, we find that ECRH applied close to ρ = 0.33 allows a compromise between a q profile larger than unity, and high central T

e
. We evaluate two current ramp-up rates, where the fast rate is double that of the slower rate. The quantity of ECRH required for the fast ramp scenario is found to be greater by almost a factor of two than that required in the slow ramp scenario.
Fast neural Poincaré maps for toroidal magnetic fields
Authors: Burby J W , Tang Q , Maulik R
Published: November 2020

Poincaré maps for toroidal magnetic fields are routinely employed to study gross confinement properties in devices built to contain hot plasmas. In most practical applications, evaluating a Poincaré map requires numerical integration of a magnetic field line, a process that can be slow and that cannot be easily accelerated using parallel computations. We propose a novel neural network architecture, the HénonNet, and show that it is capable of accurately learning realistic Poincaré maps from observations of a conventional field-line-following algorithm. After training, such learned Poincaré maps evaluate much faster than the field-line integration method. Moreover, the HénonNet architecture exactly reproduces the primary physics constraint imposed on field-line Poincaré maps: flux preservation. This structure-preserving property is the consequence of each layer in a HénonNet being a symplectic map. We demonstrate empirically that a HénonNet can learn to mock the confinement properties of a large magnetic island by using coiled hyperbolic invariant manifolds to produce a sticky chaotic region at the desired island location. This suggests a novel approach to designing magnetic fields with good confinement properties that may be more flexible than ensuring confinement using KAM tori.
Disruption prediction using a full convolutional neural network on EAST
Authors: Guo B H , Shen B , Chen D L , Rea C , Granetz R S , Huang Y , Zeng L , Zhang H , Qian J P , Sun Y W , Xiao B J
Published: November 2020

In this study, a full convolutional neural network is trained on a large database of experimental EAST data to classify disruptive discharges and distinguish them from non-disruptive discharges. The database contains 14 diagnostic parameters from the ∼104 discharges (disruptive and non-disruptive). The test set contains 417 disruptive discharges and 999 non-disruptive discharges, which are used to evaluate the performance of the model. The results reveal that the true positive (TP) rate is ∼ 0.827, while the false positive (FP) rate is ∼0.067. This indicates that 72 disruptive discharges and 67 non-disruptive discharges are misclassified in the test set. The FPs are investigated in detail and are found to emerge due to some subtle disturbances in the signals, which lead to misjudgment of the model. Therefore, hundreds of non-disruptive discharges from training set, containing time slices of small disturbances, are artificially added into the training database for retraining the model. The same test set is used to assess the performance of the improved model. The TP rate of the improved model increases up to 0.875, while its FP rate decreases to 0.061. Overall, the proposed data-driven predicted model exhibits immense potential for application in long pulse fusion devices such as ITER.
Electron concentration in the non-luminous part of the atmospheric pressure filamentary discharge
Authors: Faltýnek J , Kudrle V , Šnírer M , Toman J , Jašek O
Published: November 2020

The non-luminous surroundings of atmospheric pressure plasma jets contain still substantial electron density which can be of practical importance, when e.g. reactant or precursor is introduced into this zone. Low signal-to-noise ratio makes the Stark broadening technique unsuitable there, and so we employed the microwave interferometry to determine the electron density during the plasma synthesis of graphene. The relatively long wavelength, tight geometry and the presence of overcritical plasma filament necessitated the use of a numerical solution of the Maxwell equations. Besides laying the groundwork of the method, the paper also discusses the importance of plasma density profile in the active filament and its surroundings. The results show that in radial distance ten times higher than a visually apparent plasma diameter, the plasma density was still around 1016–1017 m−3.
Investigation of an AlGaN-channel Schottky barrier diode on a silicon substrate with a molybdenum anode
Authors: Zhang Tao , Zhang Jincheng , Zhang Weihang , Zhang Yachao , Duan Xiaoling , Ning Jing , Hao Yue
Published: November 2020

We demonstrate an AlGaN-channel Schottky barrier diode (SBD) with a molybdenum anode that has excellent performance at high temperatures. The AlGaN-channel SBD shows a suppressed leakage current, compared to a GaN-channel SBD, and the leakage current only increases by 3.5 times when the temperature increases from 300 K to 425 K, while that of the GaN-channel SBD increases by 27.8 times. Meanwhile, the forward current also shows less degeneration at an elevated temperature. Combined with the 1 A forward current of a large-periphery device with a perimeter of 20 mm, the AlGaN-channel SBD shows great potential for use in next-generation power electronics, especially in extreme environments.
Creating 3D printed sensor systems with conductive composites
Authors: Lazarus Nathan , Bedair Sarah S
Published: November 2020

Fused filament fabrication (FFF), the printing of parts through the deposition of layers of melted thermoplastic, is one of the most widely used 3D printing processes due to its ease of use, low cost and accessibility. In this work, integration of 3D printed sensors and interconnect between embedded components into a printed part is demonstrated in an FFF process for the first time. The use of printed active materials for sensing allows interactivity with the end user through mechanisms like touch and temperature. Through dual extrusion in a low cost commercial printer, printing of both a conductive thermoplastic composite and a non-conducting filament are combined to create complex patterns. The piezoresistive and thermally responsive properties of the thermoplastic composite are used to create several different sensor modalities including a piezoresistive strain sensor, a contact switch and a resistive temperature sensor. A heated insertion technique is then developed for embedding of electrical components. The conductive thermoplastic is also used to incorporate a 3D printed circuit board in the same part, including in-line embedding within the body of the part during the printing process. The sensor performance and component embedding properties are characterized, and the process is used to print systems including relaxation oscillators and op-amp interface circuits for sensor monitoring.