bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrostatic potential of a uniformly charged triangle in barycentric coordinates
Authors: Kim U-Rae , Han Wooyong , Jung Dong-Won , Lee Jungil , Yu Chaehyun
Published: April 2021

We compute the electrostatic potential of a uniformly charged triangle. Barycentric coordinates are employed to express the field point, the parametrization of the surface integral, and the gradient operator. The resultant analytic expression for the electrostatic potential is expressed in terms of the side lengths of the triangle, the altitude of the field point from the plane in which the triangle is placed, and the barycentric coordinates of the field point relative to the triangle. Our results are in good agreement with available numerical results. The asymptotic behavior of the analytic expression is investigated in special limits that satisfy known values. The resultant analytic expressions for the asymptotic regions are useful in improving the numerical convergence at boundaries. As an application, we provide a strategy to compute the electrostatic potential of a uniformly charged polygon. The electrostatic potential of a uniformly charged rectangle is considered as a simple example that agrees with a previous result. Appendices provide a complete set of integral tables that are necessary to evaluate the double integral over the barycentric coordinates, an explicit parametrization of the gradient operator in the barycentric coordinates, and useful coordinate-transformation rules between the barycentric and Cartesian coordinates.
Bouncing in an oscillatory gravitational field
Authors: Martin J L , Strange P
Published: April 2021

We apply the time-dependent supersymmetry methods of Bagrov, Samsonov and Shekoyan to the Schrödinger equation for a quantum bouncer. A new family of potentials, that correspond to the linear gravitational potential with a small oscillatory component superimposed upon it, is produced. Both the frequency and amplitude of the oscillatory part can be controlled and the corresponding eigenfunctions are found. These solutions are explored and basic observables are calculated. In particular we examine how motion in such a potential can be distinguished from motion in a linear gravitational field. We also point out some pedagogical aspects of this project.
An Integrative 3D printing method for rapid additive manufacturing of a capacitive force sensor
Authors: Liu G D , Wang C H , Jia Z L , Wang K X
Published: April 2021

With the rapid development of the three-dimensional printing (3D printing) technique, several electronic devices have been fabricated by 3D printing. Compared with the traditional micro electromechanical system (MEMS) manufacturing processes, the 3D printing technique provides a convenient method to meet the customers’ personalized demands. However, the applications of 3D printing are restricted by the electrically insulating properties of the commonly used polymers. Besides, additional alignment and assembling processes are still indispensable to fabricate the MEMS devices with geometrically complex structures using the conventional 3D printers. In order to solve these problems, an integrative 3D printing approach for rapid manufacturing is presented in this paper. With a triple-extruder 3D printer, the electrically insulating polylactic acid (PLA) filament, the electrically conductive PLA filament, and the soluble high impact polystyrene filament can be printed alternately in the 3D printing process. As an application of the method, a capacitive force sensor with a relatively complex suspended beam-plate structure was fabricated in a one-step 3D printing process without using any additional metallization process, unloading–reloading filament process, alignment process, and assembling process. With a good dynamic performance, the 3D printed force sensor was used to monitor human’s blood pulse. The results show that the integrative 3D printing method has potential to meet the emerging requirement for manufacturing of MEMS devices for personalized applications.
Design, analysis and fabrication of the CPW resonator loaded by DGS and MEMS capacitors
Authors: Han Ke , Liu Yibin , Guo Xubing , Jiang Zhuoxi , Ye Nijun , Wang Peiming
Published: April 2021

In this paper, an analytical method of resonant frequency, tuning range, the effective relative dielectric constant, and characteristic impedance is proposed, which is for coplanar waveguide (CPW) resonator loaded by defected ground structure (DGS) and micro-electromechanical systems (MEMS) capacitors. The analytical solution is achieved by an employing equivalent method. The resonant frequency, tuning range, and effective relative dielectric constant are obtained by the analytical solution. For verifying the effectiveness of the proposed method, a CPW tunable bandstop filter (BSF) with DGS and MEMS capacitors is designed, simulated, and fabricated, results show good effectiveness of the proposed analysis method. By changing the height of the MEMS beam with the actuation voltage, the designed BSF can switch the center frequency among three states (i.e. 18.5 GHz, 18.2 GHz, 17.5 GHz, respectively), and fractional bandwidth is changed as well (i.e. 37.8%, 45.6%, 49.5%, respectively).
Micromachining of polymers using atmospheric pressure inductively coupled helium plasma localized by a scanning nanopipette probe microscope
Authors: Toda Shun , Nakazawa Kenta , Ogino Akihisa , Shimomura Masaru , Iwata Futoshi
Published: April 2021

We developed a local irradiation system for atmospheric pressure inductively coupled plasma (ICP) using a quartz capillary nozzle (nanopipette) with a sub-micrometer diameter tip aperture for fine processing of material surface. Using this system, a polymethyl methacrylate (PMMA) film coated on a glass substrate was etched at the micrometer scale. Fine etching was achieved by the ICP localized by the nanopipette precisely placed near the surface, using the positioning capability of a homemade scanning probe microscope. The locally etched surface of the PMMA film was confirmed by imaging immediately after the etching process by scanning the nanopipette. For quantitative evaluation, the topographical image of the same location of the surface was then acquired using an atomic force microscope. The etching rate of the ICP was 20 times higher than that of the low-frequency atmospheric pressure plasma jet. The depth of the etched holes increased with increasing applied power and irradiation time and decreasing irradiation distance. In addition, line groove patterning with sub-micrometer width was successfully achieved. The proposed system is expected to be used in various applications such as processing and repairing of microdevices.
Magnetic skyrmions generation and control in FePt nanoparticles through shape and magnetocrystalline anisotropy variation: a finite elements method micromagnetic simulation study
Authors: Stavrou Vasileios D , Gergidis Leonidas N
Published: April 2021

Magnetic skyrmions created during magnetization reversal in cylindrical, reuleaux and polygon-based magnetic nanoparticles with perpendicular magnetocrystalline anisotropy (MCA) similar to that of partially chemically ordered FePt were studied using finite elements method micromagnetic simulations. Néel chiral stripes, horseshoe, labyrinth skyrmionic textures along with multiple skyrmions were unveiled in different systems generated by the variation of the MCA magnitude and the nanoparticles geometrical shape. These skyrmionic textures under certain conditions can be stable in a range of external magnetic fields and for different MCA values. Simulations revealed the inherent relation of skyrmionic states with nanoparticle geometry and the energy differences between successive external field values observed during the magnetization reversal process. Energetical transitions from non-skyrmionic to skyrmionic and from skyrmionic to different skyrmionic states were quantified and associated with the individual anisotropy, exchange and demagnetization energy contributions for the nanoparticles studied. Finally, the diameters of Néel type skyrmions created through the nanoparticle shape variation were reported for different MCA and external magnetic field values.
Ce–Dy substituted barium hexaferrite nanoparticles with large coercivity for permanent magnet and microwave absorber application
Authors: Todkar G B , Kunale R A , Kamble R N , Batoo Khalid M , Ijaz M F , Imran A , Hadi M , Raslan E H , Shirsath Sagar E , Kadam R H
Published: April 2021

M-type barium hexaferrites (BaM) with the substitution of Ce–Dy ions were synthesized using the sol-gel auto-ignition method. The prepared materials were explored for their application as a permanent magnet and microwave absorbing material. The structural properties, phase evaluation, micro-strain, morphological analysis, magnetic behaviour, microwave absorbing properties and optical properties were studied by employing various techniques. The structural parameters and phase identification obtained by Rietveld refinement confirmed the formation of an M-type hexaferrite structure for pure BaM, whereas Ce–Dy substitution induced secondary phases of cubic CeO2 and ortho DyFeO3. Crystallite size obtained from Williamson–Hall plots increased from 27.1 nm to 30.8 nm with the introduction of Ce–Dy ions in BaM. The nanocrystalline nature of the prepared samples was confirmed using scanning and transmission electron microscopy techniques. Fourier transform infrared spectra of all the samples were recorded in the wavenumber range of 400–4000 cm−1 and also supported the x-ray diffraction findings by confirming the formation of samples with hexaferrite structures. Coercivity of the BaM hexaferrites improved from 4430 to 5721 Oe with the Ce–Dy substitution. A Ce–Dy substituted BaM hexaferrite sample of 3 mm thickness showed a maximum reflection loss of −16.3 dB around 16.7 GHz. Permittivity and permeability studies were carried out to understand the microwave absorption behaviour.
FAMOUS: a fast instrumental and computational pipeline for multiphoton microscopy applied to 3D imaging of muscle ultrastructure
Authors: Lefort Claire , Chalvidal Mathieu , Parenté Alexis , Blanquet Véronique , Massias Henri , Magnol Laetitia , Chouzenoux Emilie
Published: April 2021

We present a new instrumental and computational pipeline named FAMOUS: fast algorithm for three-dimensional (3D) multiphoton microscopy of biomedical structures. This pipeline rests on a MPM strategy combined with an original 3D post-processing computational approach. In the present work, FAMOUS approach is devoted to the 3D imaging of the myosin assembly of the ultrastructure of a whole striated skeletal muscle unsliced. Raw recordings of second harmonic generation (SHG) from myosin and instrumental point-spread functions (PSF) are led simultaneously all along the unsliced muscle depth. This procedure highlights a space-variant distortion of the PSF and the SHG signals, and an optical degradation of the axial resolution increasing with imaging depth resulting from the optical heterogeneity of the muscle structure. A 3D mathematical modelling of the PSF, relying on the recent FIGARO method, evaluates and models the depth-variant evolution of the optical distortions. Then, the fast image deblurring algorithm BD3MG is employed to correct those non-stationary distortions all along the sample, thanks to a sounded regularized inverse problem methodology. This leads to the pipeline called FAMOUS, whose performance are highlighted for the optimization of the axial information of myosin structure, whose dimensions are close to the axial resolution limit. For the first time, the 3D organization of the myosin in skeletal muscle is visually shown from an unsliced whole muscle, starting with a solution of optical microscopy. The axial visualization of this organization presently disclosed were never shown until now without a preliminary procedure of sample slicing and labelling. Our original solution FAMOUS delivers a new point of view of this biological structure in the 3D and especially in the optical axis. Image information theoretically expected are now revealed visually in the optical axis for the first time in a whole organ unsliced and label free.
Out-of-time-ordered correlators and the Loschmidt echo in the quantum kicked top: how low can we go?
Authors: PG Sreeram , Madhok Vaibhav , Lakshminarayan Arul
Published: April 2021

The out-of-time-ordered correlators (OTOCs) and the Loschmidt echo are two measures that are now widely being explored to characterize sensitivity to perturbations and information scrambling in complex quantum systems. Studying few qubits systems collectively modeled as a kicked top, we solve exactly the three- and four-qubit cases, giving analytical results for the OTOC and the Loschmidt echo. While we may not expect such few-body systems to display semiclassical features, we find that there are clear signatures of the exponential growth of OTOC even in systems with as low as four qubits in appropriate regimes, paving way for possible experimental measurements. We explain qualitatively how classical phase space structures like fixed points and periodic orbits have an influence on these quantities and how our results compare to the large-spin kicked top model. Finally we point to a peculiar case at the border of quantum–classical correspondence which is solvable for any number of qubits and yet has signatures of exponential sensitivity in a rudimentary form.
Quantum phases and thermodynamics of a frustrated spin-1/2 ladder with alternate Ising–Heisenberg rung interactions
Authors: Saniur Rahaman Sk , Sahoo Shaon , Kumar Manoranjan
Published: April 2021

We study a frustrated two-leg spin ladder with alternate isotropic Heisenberg and Ising rung exchange interactions, whereas, interactions along legs and diagonals are Ising-type. All the interactions in the ladder are anti-ferromagnetic in nature and induce frustration in the system. This model shows four interesting quantum phases: (i) stripe rung ferromagnetic (SRFM), (ii) stripe rung ferromagnetic with edge singlet (SRFM-E), (iii) anisotropic antiferromagnetic (AAFM), and (iv) stripe leg ferromagnetic (SLFM) phase. We construct a quantum phase diagram for this model and show that in stripe rung ferromagnet (SRFM), the same type of sublattice spins (either isotropic S-type or discrete anisotropic σ-type spins) are aligned in the same direction. Whereas, in anisotropic antiferromagnetic phase, both S and σ-type of spins are anti-ferromagnetically aligned with each other, two nearest S spins along the rung form an anisotropic singlet bond whereas two nearest σ spins form an Ising bond. In large Heisenberg rung exchange interaction limit, spins on each leg are ferromagnetically aligned, but spins on different legs are anti-ferromagnetically aligned. The thermodynamic quantities like specific heat C

v
(T), magnetic susceptibility χ(T) and thermal entropy S(T) are also calculated using the transfer matrix method for various phases. The magnetic gap in the SRFM and the SLFM can be noticed from χ(T) and C

v
(T) curves.
Field induced hysteretic structural phase switching and possible CDW in Re-doped MoTe2
Authors: Vasdev Aastha , Kamboj Suman , Sirohi Anshu , Mandal Manasi , Marik Sourav , Singh Ravi Prakash , Sheet Goutam
Published: April 2021

Novel electronic systems displaying exotic physical properties can be derived from complex topological materials through chemical doping. MoTe2, the candidate type-II Weyl semimetal shows dramatically enhanced superconductivity up to 4.1 K upon Re doping in Mo sites. Based on bulk transport and local scanning tunnelling microscopy here we show that Re doping also leads to the emergence of a possible charge density wave phase in Re0.2Mo0.8Te2. In addition, the tunnelling I–V characteristics display non-linearity and hysteresis which is commensurate with a hysteresis observed in the change in tip-height (z) as a function of applied voltage V. The observations indicate an electric field induced hysteretic switching consistent with piezoelectricity and possible ferroelectricity.
High-order simulation scheme for active particles driven by stress boundary conditions
Authors: Deußen B , Jayaram A , Kummer F , Wang Y , Speck T , Oberlack M
Published: April 2021

We study the dynamics and interactions of elliptic active particles in a two dimensional solvent. The particles are self-propelled through prescribing a fluid stress at one half of the fluid-particle boundary. The fluid is treated explicitly solving the Stokes equation through a discontinuous Galerkin scheme, which allows to simulate strictly incompressible fluids. We present numerical results for a single particle and give an outlook on how to treat suspensions of interacting active particles.
Quantum magnetotransport oscillations in graphene nanoribbons coupled to superconductors
Authors: Takagaki Y
Published: April 2021

Magnetotransport properties of zigzag and armchair graphene nanoribbons that are in contact with superconductors are investigated using a tight-binding model. The cyclotron orbital motion together with the quantum interference under the coexistence of Andreev and normal reflections gives rise to a number of oscillations in characteristic magnetic-field regimes when the superconducting coupling is weak. The oscillations become irregular and/or suppressed as the coupling is made strong. The period of the oscillations differs from that when a nonrelativistic two-dimensional electron gas is employed rather than the graphene sheet. The modifications of the oscillations are attributed to the phase shift associated with the reflection from the graphene–superconductor interface. The presence of a magnetic field suppresses the quantum blocking of Andreev transmission, which occurs for the edge mode of zigzag nanoribbons, in the same way regardless of it being induced by the Andreev retro- or specular reflection.
The optimisation of paediatric CT examinations in Scotland: phase one; benchmarking current performance
Authors: Worrall Mark , MacDonald Nicola , Gillen Rebecca , Hince Andrew , Hampson Lee , Duguid Rebecca , McCallum Stephen , Gentle David
Published: April 2021

To benchmark the dose from paediatric head and chest examinations on computed tomography (CT) scanners throughout Scotland, to identify scanners that may require optimisation and to provide optimisation advice based on the protocols from better performing scanners. Anthropomorphic phantoms corresponding to 1, 5 and 10 year olds were sent to 50 CT scanners around Scotland. Head and chest examinations were undertaken by local staff using local techniques on each scanner with each phantom, and details of the protocols used were recorded. Computed tomography dose index (CTDI)vol and dose length product (DLP) were recorded post-scan. There is a significant variation in performance throughout Scotland. For head examinations, the highest DLP is 13 times the lowest for an equivalent sized phantom. For chest examinations, the highest is 128 times the lowest for an equivalent sized phantom. The wide range of CT dose measurements indicates the potential for variation in image quality across Scotland. Feedback has been provided to all participating sites on their individual results compared to the national data set. Specific feedback was provided where relevant on potential considerations for optimisation. Scanners that may be undertaking paediatric CT head and chest examinations in a sub-optimal manner throughout Scotland have been identified along with those aspects of a scan protocol that are most likely to lead to sub-optimal performance.
Virtual-sample-based defect detection algorithm for aluminum tube surface
Authors: Lang Ning , Wang Decheng , Cheng Peng , Zuo Shanchao , Zhang Pengfei
Published: April 2021

A surface defect is an important factor that affects product quality. However, due to the large differences in area of different surface defects, and noise on various surfaces, defect detection is challenging. The convolutional neural network (CNN)-based methods recently developed for defect detection produced higher recognition rates than traditional methods. However, they are typically trained using a supervised learning strategy and large defect sample sets which limits the practical use of these algorithms. This study proposes a novel virtual sample generation algorithm to solve the problem of insufficient defective samples and time-consuming manual annotation in current CNN-based defect detection algorithms. Next, an improved domain-adversarial neural network is proposed, which is trained on virtual and actual datasets to achieve unsupervised learning. Considering the imbalance in actual dataset, algorithm accuracy is improved by changing the proportions of defective and non-defective samples in the virtual sample set, and this strategy is experimentally verified. The performance of the proposed algorithm is compared with several top-performing defect inspection algorithms. The experimental results show that the proposed algorithm exhibits superior performance when compared to other algorithms.
Chiro-optical response of a wafer scale metamaterial with ellipsoidal metal nanoparticles
Authors: Suchitta Aakansha , Suri Priyanka , Xie Zhuolin , Xu Xianfan , Ghosh Ambarish
Published: April 2021

We report a large chiro-optical response from a nanostructured film of aperiodic dielectric helices decorated with ellipsoidal metal nanoparticles. The influence of the inherent fabrication variation on the chiro-optical response of the wafer-scalable nanostructured film is investigated using a computational model which closely mimics the material system. From the computational approach, we found that the chiro-optical signal is strongly dependent on the ellipticities of the metal nanoparticles and the developed computational model can account for all the variations caused by the fabrication process. We report the experimentally realized dissymmetry factor ∼1.6, which is the largest reported for wafer scalable chiro-plasmonic samples till now. The calculations incorporate strong multipolar contributions of the plasmonic interactions to the chiro-optical response from the tightly confined ellipsoidal nanoparticles, improving upon the previous studies carried in the coupled dipole approximation regime. Our analyzes confirm the large chiro-optical response in these films developed by a scalable and simple fabrication technique, indicating their applicability pertaining to manipulation of optical polarization, enantiomer selective identification and enhanced sensing and detection of chiral molecules.
Development of a multifunctional system based on CoFe2O4@polyacrylic acid NPs conjugated to folic acid and loaded with doxorubicin for cancer theranostics
Authors: Arkaban Hassan , Khajeh Ebrahimi Ahmad , Yarahmadi Ali , Zarrintaj Payam , Barani Mahmood
Published: April 2021

In this work, a multifunctional theranostic nanocomposite based on CoFe2O4@polyacrylic acid (PAA)-Folic Acid (FA) Doxorubicin (Dox)load NPs was designed for the multifunctional cancer treatment. Several techniques such as TEM, DLS, ζ-potential, vibrating sample magnetometer, XRD, and UV−Vis spectrophotometer were applied for investigating physicochemical properties of the nanosystem. The percentage of the loaded drug, loading efficiency, in vitro release (pH 5.4 and 7.4), in
vitro MRI measurements, and MTT assay (4T1 and 9A9 cell lines) were evaluated. Results showed that the percentage of loaded drug and loading efficiency was 53.33 ± 3.5 and 80.00 ± 5.3%, respectively, showing the system’s high ability for Dox encapsulation. Release study showed that Dox loaded in the CoFe2O4@PAA-FA(Dox)load NPs released faster at pH 5.4 than pH 7.4. In vitro, MRI measurements confirmed that CoFe2O4@PAA NPs could be used as a contrast agent in MRI measurements with r
2 = 18.2 mM−1 s−1. MTT assay demonstrated the biocompatibility of NPs, also showed a more efficient therapeutic effect for CoFe2O4@PAA-FA(Dox)load NPs than free Dox and CoFe2O4@PAA(Dox)load NPs.
Fabrication of graphene: CdSe quantum dots/CdS nanorod heterojunction photodetector and role of graphene to enhance the photoresponsive characteristics
Authors: Perumal Veeramalai Chandrasekar , Kollu Pratap , Lin Guochen , Zhang Xiaoming , Li Chuanbo
Published: April 2021

Integration of graphene with semiconducting quantum dots (QDs) provides an elegant way to access the intrinsic properties of graphene and optical properties of QDs concurrently to realize the high-performance optoelectronic devices. In the current article, we have demonstrated the high-performance photodetector based on graphene: CdSe QDs/CdS nanorod heterostructures. The resulting heterojunction photodetector with device configuration ITO/graphene: CdSe/CdS nanorods/Ag show excellent operating characteristics including a maximum photoresponsivity of 15.95 AW−1 and specific detectivity of 6.85 × 1012 Jones under 530 nm light illumination. The device exhibits a photoresponse rise time of 545 ms and a decay time of 539 ms. Furthermore, the study of the effect of graphene nanosheets on the performance enhancement of heterojunction photodetector is carried out. The results indicate that, due to the enhanced energy transfer from photoexcited QDs to graphene layer, light absorption is increased and excitons are generated led to the enhancement of photocurrent density. In addition to that, the graphene: CdSe QDs/CdS nanorod interface can facilitate charge carrier transport effectively. This work provides a promising approach to develop high-performance visible-light photodetectors and utilizing advantageous features of graphene in optoelectronic devices.
Photo generated charge transport studies of defects-induced shuttlecock-shaped ZnO/Ag hybrid nanostructures
Authors: Choudhary Siddharth , Vashisht Garima , Malik Rakesh , Dong Chung-Li , Chen Chi-Liang , Kandasami Asokan , Annapoorni S
Published: April 2021

We report the stimulating effects of interfacial charge transfer process between spherical Ag nanoparticles and shuttlecock-shaped ZnO nanostructures observed by UV−visible spectroscopy and x-ray absorption spectroscopy. In specific, ZnO nanorods and shuttlecock-shaped ZnO/Ag nanostructures were developed using a simple chemical colloidal method and characterized for structural variations using XRD. The observed red shift in plasmonic peak and the increase in Urbach energy signify interfacial interactions and increased randomness in the hybrid ZnO/Ag nanostructures. Simultaneously, the enhanced intensity of deep-level emission in the ZnO/Ag hybrid suggests the increased recombination rate of electron-hole pairs. The red and blue emissions evolving with temperature subsequently suggests the presence of oxygen vacancies or zinc interstitials in the system. The decrease in intensities and emerging features in O K-edge and Zn L-edge indicates the charge transfer from Ag to ZnO at the interface of ZnO/Ag hybrids. Moreover, the differences in absorption edges with alternating light on/off conditions were analyzed for the exploitation of this ZnO-based system in various applications.
Controllable morphology of electrospun nanofiber membranes with tunable groove structure and the enhanced filtration performance for ultrafine particulates
Authors: Lou Yaoyuan , Ding Shanshan , Wang Bin , Wang Jie , Sun Qing , Jin Xu , Li Xiuyan
Published: April 2021

As researchers are striving to develop high-performance filtration membranes with hierarchical micro/nano structures, the challenges and costs of processing often limit creative innovation. Here, we propose a polyethersulfone/polyacrylonitrile (PES/PAN) nanofiber membrane with groove structure by electrospinning and facile post-processing. The resulted membrane can form a groove structure on the surface of the fiber after being soaked in chloroform, thereby increasing the collision probability and extending the residence time for ultrafine particulates and improving the filtration efficiency. The groove structure can be attributed to the solubility of PES constituent in chloroform, while PAN constituent will not be dissolved, thus forming a high-performance nanofiber membrane with high filtration efficiency (ca. 99.54%) and withstand pressure drop (ca. 133.9 Pa) for dioctyl phthalate aerosol particles with diameter of 0.3 μm. The results show that this convenient and low-cost fabrication technology can be used to prepare high-performance nanofiber membrane based air filters that have broad application prospects in respiratory protective equipment.
Oxygen-rich PdSnCu nanocrystals with particle connection features as enhanced catalysts for ethanol oxidation reaction
Authors: Xie Jian , Yang Hui , Dong Qizhi , Qin Qian , Hu Chao , Yu Gang
Published: April 2021

Most electrocatalysts show a high mass and special activity during the ethanol oxidation reaction, but those still suffer from limited stability, finite renewable capability and poor anti-poisoning durability. Furthermore, the reliable structure and appropriate composition of catalysts are fairly associated with the electrocatalysis performance. Herein, we report the development of trimetallic Pd61Sn34Cu5 nanocrystals (NCs) whose rough surfaces are rich in step atoms and coupled with abundant of SnOx and CuO, which may effectively boost reaction activity and rapidly remove carbonaceous intermediate, respectively. Under the tuning on the composition, the defect rich Pd61Sn34Cu5 NCs exhibit elevated electrocatalysis activity and durability for ethanol oxidation reaction with an optimized mass activity (1.26 A

mg

Pd

−
1

) and specific activity (10.6 mA cm−2), which is about 2.21 and 2.58 times greater than that of the commercial Pd/C catalyst (0.57 A

mg

Pd

−
1

and 4.1 mA cm−2).
Nanoscale refractory doped titanium nitride field emitters
Authors: Nardi A , Turchetti M , Britton W A , Chen Y , Yang Y , Dal Negro L , Berggren K K , Keathley P D
Published: April 2021

Refractory materials exhibit high damage tolerance, which is attractive for the creation of nanoscale field-emission electronics and optoelectronics applications that require operation at high peak current densities and optical intensities. Recent results have demonstrated that the optical properties of titanium nitride, a refractory and CMOS-compatible plasmonic material, can be tuned by adding silicon and oxygen dopants. However, to fully leverage the potential of titanium (silicon oxy)nitride, a reliable and scalable fabrication process with few-nm precision is needed. In this work, we developed a fabrication process for producing engineered nanostructures with gaps between 10 and 15 nm, aspect ratios larger than 5 with almost 90° steep sidewalls. Using this process, we fabricated large-scale arrays of electrically-connected bow-tie nanoantennas with few-nm free-space gaps. We measured a typical variation of 4 nm in the average gap size. Using applied DC voltages and optical illumination, we tested the electronic and optoelectronic response of the devices, demonstrating sub-10 V tunneling operation across the free-space gaps, and quantum efficiency of up to 1 × 10−3 at 1.2 μm, which is comparable to a bulk silicon photodiode at the same wavelength and three orders of magnitude higher than with nearly identical gold devices. Tests demonstrated that the titanium silicon oxynitride nanostructures did not significantly degrade, exhibiting less than 5 nm of shrinking of the average gap dimensions over few-μm2 areas after 10 h of operation. Our results will be useful for developing the next generation of robust and CMOS-compatible nanoscale devices for high-speed and low-power field-emission electronics and optoelectronics applications.
Highly conductive and transparent electrospun indium tin oxide nanofibers calcined by microwave plasma
Authors: Cheng Jun , Zhang Xi , Yang Zhuanqing , Xiang Gang
Published: April 2021

In this work, indium tin oxide (ITO) nanofibers have been prepared by electrospinning of polymers and post-growth microwave plasma calcination (MPC). Interestingly, compared to traditional calcination in furnace, MPC can accelerate the degradation of high polar polymers and improve adhesion of ITO nanofibers to the sapphire substrate. Further characterizations reveal that the ITO nanofibers with diameters of 100–150 nm prepared by MPC at 600 °C can reach a low sheet resistance of 269 Ω/sq and a high transmittance of 90.7% at 550 nm simultaneously, which has not been previously reported by others. Our results show that the efficient MPC method has great potential in preparation of metal-oxide nanofibers for electrical and optical applications.
An approach for estimating dosimetric uncertainties in deformable dose accumulation in pencil beam scanning proton therapy for lung cancer
Authors: Amstutz Florian , Nenoff Lena , Albertini Francesca , Ribeiro Cássia O , Knopf Antje C , Unkelbach Jan , Weber Damien C , Lomax Antony J , Zhang Ye
Published: April 2021

Deformable image registration (DIR) is an important component for dose accumulation and associated clinical outcome evaluation in radiotherapy. However, the resulting deformation vector field (DVF) is subject to unavoidable discrepancies when different algorithms are applied, leading to dosimetric uncertainties of the accumulated dose. We propose here an approach for proton therapy to estimate dosimetric uncertainties as a consequence of modeled or estimated DVF uncertainties. A patient-specific DVF uncertainty model was built on the first treatment fraction, by correlating the magnitude differences of five DIR results at each voxel to the magnitude of any single reference DIR. In the following fractions, only the reference DIR needs to be applied, and DVF geometric uncertainties were estimated by this model. The associated dosimetric uncertainties were then derived by considering the estimated geometric DVF uncertainty, the dose gradient of fractional recalculated dose distribution and the direction factor from the applied reference DIR of this fraction. This estimated dose uncertainty was respectively compared to the reference dose uncertainty when different DIRs were applied individually for each dose warping. This approach was validated on seven NSCLC patients, each with nine repeated CTs. The proposed model-based method is able to achieve dose uncertainty distribution on a conservative voxel-to-voxel comparison within ±5% of the prescribed dose to the ‘reference’ dosimetric uncertainty, for 77% of the voxels in the body and 66%–98% of voxels in investigated structures. We propose a method to estimate DIR induced uncertainties in dose accumulation for proton therapy of lung tumor treatments.
A novel calibration for L-shell x-ray fluorescence measurements of bone lead concentration using the strontium Kβ/Kα ratio
Authors: Gherase Mihai R , Serna Blaz , Kroeker Sarah
Published: April 2021

Objective. Lead (Pb) is a well-known toxic element. In vivo bone Pb concentration measurement is a long-term exposure metric complementary to blood Pb concentration measurement which is a metric of recent exposure. In vivo human tibia bone Pb measurements using Pb K-shell or L-shell x-ray fluorescence (KXRF or LXRF) emissions were developed in the 1980s. KXRF bone Pb measurements using Cd-109 gamma rays and coherent-to-fluorescence ratio to account for differences between phantom and in vivo measurements, was employed in human studies. Bone Pb LXRF method employed x-ray tubes. However, calibration procedures using ultrasound measurements of the soft tissue thickness (STT) proved inaccurate. Approach. In this study, bone and soft tissue (ST) phantoms simulated in vivo bone Pb measurements. Seven plaster-of-Paris cylindrical bone phantoms containing 1.01 mg g−1 of strontium (Sr) were doped with Pb in 0, 8, 16, 29, 44, 59, and 74 μg g−1 concentrations. Polyoxymethylene (POM), resin, and wax were each used to fabricate four ST phantoms in the approximate 1–4 mm thickness range. Pb LXRF measurements were performed using a previously developed optimal grazing incidence position method. Main results. Linear attenuation coefficients measurements of ST materials indicated that POM and resin mimicked well attenuation of Pb x-rays in skin and adipose tissue, respectively. POM and resin data indicated a bone Pb detection limit of 20 μg g−1 for a 2 mm STT. Derived relationships between the Pb concentration, Pb LXRF and Sr K
β
/K
α
ratio data did not require STT knowledge. Applied to POM and resin data, the new calibration method yielded unbiased results. Significance. In vivo bone Pb measurements in children were suggested following considerations of radiation dose, STT, detectability and distribution of Pb and Sr in bone. This research meets with the concerns regarding the negative effects of low levels of Pb exposure on neurodevelopment of children.
Trapped upper hybrid waves as eigenmodes of non-monotonic background density profiles
Authors: Senstius M G , Nielsen S K , Vann R G L
Published: April 2021

Non-monotonic plasma density structures such as blobs and magnetic islands give rise to trapped upper hybrid (UH) waves. Trapped UH waves which satisfy Bohr–Sommerfeld quantization can be thought of as eigenmodes of a cavity. Using fully kinetic particle-in-cell simulations, we verify the existence of these UH eigenmodes and demonstrate their significance as only eigenfrequencies become unstable to three-wave interactions. The eigenmodes can be excited through parametric decay instabilities (PDIs) of an X-mode pump wave at approximately twice the UH frequency, as could be the case for a gyrotron beam traversing a blob in a magnetically confined fusion plasma. We derive a closed expression for the wavenumber of UH waves, which is accurate both close to the UH layer and to the electron cyclotron resonance. This allows for fast analysis of eigenmodes in a non-monotonic structure. An expression for the amplification of PDI daughter waves in an inhomogeneous plasma is extended to a decay region where the first several derivatives vanish. From the amplification in a convective PDI, we estimate the growth rate of the absolute PDI involving the trapped waves. We show that the excitation of eigenmodes through PDIs in our simulations are indeed absolute rather than convective due to the trapping of the daughter waves. Additionally, we show that only eigenmodes get excited through the PDIs, and that we are able to predict the growth rates of the daughter waves and how they scale with the pump wave intensity. This is evidence supporting a fundamental assumption of analytical theory describing low threshold strong scattering observed in magnetically confined fusion experiments during second harmonic electron cyclotron resonance heating (ECRH). Such low threshold instabilities can degrade ECRH performance but also offer novel uses for ion heating or as diagnostics.
Observation of quasi-coherent density fluctuation in scrape-off layer enhancing boundary transport in high-

βN

hybrid plasmas on DIII-D
Authors: Hong R , Rhodes T L , Li Z-Y , Wang H , Zeng L , Barada K , Wang G , Watkins J G , Peebles W A
Published: April 2021

We report the observation of a quasi-coherent fluctuation (QCF) by the Doppler backscattering system in the scrape-off layer (SOL) region of the DIII-D tokamak. This QCF is observed in high power, high performance hybrid plasmas with near double-null divertor shape during the electron cyclotron heating period. This mode is correlated with a steepened SOL density profile, and leads to significantly elevated particle and heat fluxes between edge localized modes. The SOL QCF is a long-wavelength ion-scale fluctuation (

k

θ

ρ

s

≈
0.2

–0.4 and

k

r

ρ

s

≈
0.03

), and propagates in the ion diamagnetic direction in the plasma frame. Its radial expanse is about 1.5–2 cm, well beyond the typical width of heat flux λ

q
on DIII-D. Also, the SOL QCF does not show any clear dependence on the effective SOL collisionality, and thus may raise issues on the control of plasma-material interactions in low collisionality plasmas in which the blob-induced transport is reduced. A linear simulation using BOUT++ with a five-field reduced model is performed and compared with experimental observations. In simulation results, an interchange-like density perturbation can be driven by the SOL density gradient, and its peak location and the radial width of the density perturbation are in agreement with the experimental observations.
Formation and evolution of post-solitons following a high intensity laser-plasma interaction with a low-density foam target
Authors: Blackman David R , Adak Amitava , Singh Prashant K , Lad Amit D , Chatterjee Gourab , Ridgers Christopher P , Del Sorbo Dario , Trines Raoul M G M , Robinson A P L , Nazarov Wigen , Ravindra Kumar G , Pasley John
Published: April 2021

The formation and evolution of post-solitons has been discussed for quite some time both analytically and through the use of particle-in-cell (PIC) codes. It is however only recently that they have been directly observed in laser-plasma experiments. Relativistic electromagnetic (EM) solitons are localised structures that can occur in collisionless plasmas. They consist of a low-frequency EM wave trapped in a low electron number-density cavity surrounded by a shell with a higher electron number-density. Here we describe the results of an experiment in which a 100 TW Ti:sapphire laser (30 fs, 800 nm) irradiates a

0.03
 

g
c

m

−
3

TMPTA foam target with a focused intensity

I

l

=
9.5
×

10

17

 

W
c

m

−
2

. A third harmonic (

λ

p
r
o
b
e

≃
266

nm) probe is employed to diagnose plasma motion for 25 ps after the main pulse interaction via Doppler-Spectroscopy. Both radiation-hydrodynamics and 2D PIC simulations are performed to aid in the interpretation of the experimental results. We show that the rapid motion of the probe critical-surface observed in the experiment might be a signature of post-soliton wall motion.
Effect of the toroidal flow and flow shear on the m/n

=

2/1 tearing mode in J-TEXT tokamak
Authors: Shao Junren , Liu Hai , Xu Yuhong , Chen Zhipeng , Wang Tong , Cheng Jun , Wang Xianqu , Huang Jie , Liu Haifeng , Zhang Xin , Xu Kangzhong , Tang Changjian
Published: April 2021

The effect of the toroidal flow and flow shear on the m/n

=

2/1 tearing mode (TM) has been investigated in J-TEXT tokamak, where m and n are the poloidal and toroidal mode numbers. It is found that the toroidal flow increment is linearly modulated by the bias current/return current. The frequency of the 2/1 TM is also found to be proportional to the toroidal flow during the bias phase, which is consistent with the theoretical expectation. The electron diamagnetic drift frequency is almost constant before and during the bias phase. Moreover, the statistical analysis shows that the saturated island width of the TM is more correlated to the toroidal flow amplitude than the flow shear, which reveals that the effect of the TM depends on the magnitude of the toroidal flow rather than the flow shear. This result may illustrate the process of the 2/1 TM controlled by the electrode biasing, and suggests that changing the magnitude of toroidal flow is a possible method for stabilizing the TM.
Effects of energetic particles on the density-gradient-driven collisionless trapped electron mode instability in tokamak plasmas
Authors: Hussain M S , Guo Weixin , Wang Lu
Published: April 2021

We investigate analytically the effects of energetic particles (EPs) on the instability of the density-gradient-driven collisionless trapped electron mode (CTEM) through linear gyrokinetic theory and bounce kinetic theory in tokamak plasmas. The effects of EPs, including fusion-born alpha particles and neutral-beam-injection-driven beam ions, on the CTEM instability are compared for the dynamic model with slowing-down (SD) and equivalent Maxwellian (EM) equilibrium EP distribution functions and dilution model. It is found that the density-gradient-driven CTEM instability in the long wavelength regime can be further destabilized by EPs mainly due to the downshift in the real frequency of the mode by dilution effects. This is attributed to more resonant electrons around the smaller phase velocity of the drift wave and the consequent stronger excitation of CTEM instability. The growth rate is slightly higher for the dilution model as compared to that for the dynamic model since the Landau damping effects of EPs are neglected in the dilution model. Moreover, there is no significant difference in the growth rate between the cases of SD and EM equilibrium EP distribution functions, except for the case of alpha particles and with relatively higher electron temperature.
A non-twisting flux tube for local gyrokinetic simulations
Authors: Ball Justin , Brunner Stephan
Published: April 2021

Local gyrokinetic simulations use a field-aligned domain that twists due to the magnetic shear of the background magnetic equilibrium. However, if the magnetic shear is strong and/or the domain is long, the twist can become so extreme that it fails to properly resolve the turbulence. In this work, we derive and implement the ‘non-twisting flux tube,’ a local simulation domain that remains rectangular at all parallel locations. Convergence and runtime tests indicate that it can calculate the heat flux more efficiently than the conventional flux tube. For one test case, it was 30 times less computationally expensive and we found no case for which it was more expensive. It is most advantageous when the magnetic shear is high and the domain includes at least two regions of turbulent drive (e.g. stellarator simulations, pedestal simulations, tokamak simulations with several poloidal turns). Additionally, it more accurately models the inboard midplane when the magnetic shear is large. Lastly, we show how the non-twisting flux tube can be generalized to allow further optimization and control of the simulation domain.
On the quasi-stationary approach to solve the electron Boltzmann equation in pulsed plasmas
Authors: Tejero-del-Caz A , Guerra V , Pinhão N , Pintassilgo C D , Alves L L
Published: April 2021

This work analyzes the temporal evolution of the electron kinetics in dry-air plasmas (80% N2: 20% O2), excited by electric-field pulses with typical rise-times of 10−9 and 10−6 s, applied to a stationary neutral gaseous background at pressures of 105, 133 Pa and temperature of 300 K. The study is based on the solution of the electron Boltzmann equation (EBE), adopting either (i) a time-dependent formulation that considers an intrinsic time evolution for the electron energy distribution function (EEDF), assuming the classical two-term expansion and a space-independent exponential temporal growth of the electron density; or (ii) a quasi-stationary approach, where the time-independent form of the EBE is solved for different values of the reduced electric-field over the duration of the pulse. The EBE was solved using the LisbOn KInetics Boltzmann solver (LoKI-B), whose original capabilities were extended to accept time-dependent non-oscillatory electric fields as input data. The role of electron–electron collisions, under specific conditions, is also reported and discussed. The simulations show that the quasi-stationary approach gives solutions similar to the time-dependent formulation for rise-times longer than the characteristic evolution time of the EEDF, i.e. 20 ns at 105 Pa and 20 μs at 133 Pa, meaning that a quasi-stationary description is possible in a high-collisionality situation and long rise-times (e.g. microsecond pulses at atmospheric pressure), failing for faster rise-times (e.g. nanosecond pulses for both pressures considered here).