bluuebunny/crossref_metadata_2025 huggingface dataset:
Simulation of supersonic molecular beam injection fueling into H-mode plasmas on EAST using BOUT++
Authors: Qian Y. Z. , Xia T. Y. , Huang Y. Q. , Sun Z. , Zuo G. Z. , Xu W. , Meng X. C. , Huang M. , Li C. L. , Cao B. , Wang Y. M. , Zhang T. , Ye K. X. , Wang Y. F. , Zang Q. , Li Y. Y. , Hu J. S.
Published: January 2020

Transport dynamic 2D simulations for supersonic molecular beam injection (SMBI) fueling into H-mode deuterium plasmas on the Experimental Advanced Superconducting Tokamak (EAST) is first simulated using a seven-field two-fluid model in the BOUT++ framework. The SMB is assumed to be injected into plasma from the midplane at the low field side with a fixed width and constant molecular flux. The different densities and injection velocities of SMBI are investigated within the upper single-null geometry of EAST. The simulations indicate that the SMBI has a self-shielding effect on molecules' inward transport into the plasma, and the deposition of SMBI leads to a large increase in plasma density and decrease in plasma temperature. There is a velocity threshold for SMB penetrating the pedestal and depositing at the top of density pedestal. However, the deposition point would be back toward the plasma boundary after SMB arriving at the deepest penetration position. Comparing the different molecular injection velocities and densities, the outcomes demonstrate that the depth of deposition is closely related to the injection velocity rather than the molecular density. The simulated results show good agreement with the EAST experiments by comparing the electron density profiles obtained by simulation and experiment, respectively. These results will be helpful for guiding future experiments, as well as the design of the SMBI system.
Experimental study of inertia-based passive flexibility of a heaving and pitching airfoil operating in the energy harvesting regime
Authors: Siala Firas F. , Kamrani Fard Kiana , Liburdy James A.
Published: January 2020

The effects of passive, inertia-induced surface flexibility at the leading and trailing edges of an oscillating airfoil energy harvester are investigated experimentally at reduced frequencies of k = fc/U∞ = 0.10, 0.14, and 0.18. Wind tunnel experiments are conducted using phase-resolved, two-component particle image velocimetry to understand the underlying flow physics, as well as to obtain force and pitching moment estimates using the vortex-impulse theory. Results are obtained for leading and trailing edge flexibility separately. It is shown that both forms of flexibility may alter the leading edge vortex inception and detachment time scales, as well as the growth rate of the circulation. In addition, surface flexibility may also trigger the generation of secondary vortical structures and suppress the formation of trailing edge vortices. The total energy harvesting efficiency is decomposed into contributions of heaving and pitching motions. Relative to the rigid airfoil, the flexible leading and trailing edge segments are shown to increase the energy harvesting efficiency by approximately 17% and 25%, respectively. However, both the flexible leading and trailing edge airfoils operate most efficiently at k = 0.18, whereas the peak efficiency of the rigid airfoil occurs at k = 0.14. It is shown that the flexible leading and trailing edge airfoils enhance the heaving contribution to the total efficiency at k = 0.18 and the negative contribution of the pitching motion at high reduced frequencies can be alleviated by using a flexible trailing edge.
Direct laser writing of graphene electrodes
Authors: Li Guijun
Published: January 2020

Direct laser writing of graphene electrodes is an emerging research field for the rapid fabrication of two-dimensional carbon electronic materials with wide applications, ranging from supercapacitors and batteries to sensors, electrocatalysts, actuators, etc. Many types of carbon-containing raw materials can be converted to graphene by one-step laser scribing, without complicated chemical synthesis routines, using a variety of lasers. This perspective categorizes the principles of direct laser writing of graphene, according to the different types of raw materials, different types of lasers, and different applications. The future directions of laser synthesized graphene are also discussed.
Evolution of crystallographic structure and ferroelectricity of Hf0.5Zr0.5O2 films with different deposition rate
Authors: Kim Taeho , An Minho , Jeon Sanghun
Published: January 2020

Hf0.5Zr0.5O2 films are one of the most attractive HfO2-based ferroelectric films because of good ferroelectricity, extreme thinness, and excellent compatibility with silicon devices. The origin of the ferroelectricity of Hf0.5Zr0.5O2 films is the noncentrosymmetric orthorhombic phase (space group Pca21). The effects of process temperature, annealing temperature, thickness, and doping to increase the portion of the orthorhombic phase, which contributes to ferroelectricity, have been studied extensively. However, although most studies have used atomic layer deposition, no study has been reported on the effect of the deposition rate on the ferroelectricity of Hf0.5Zr0.5O2 films. In this work, the influences of the deposition rate on the ferroelectricity and crystal structure of Hf0.5Zr0.5O2 films were examined. In order to conduct systematic and quantitative analysis, measurements of switching transient current, ferroelectric P-E curve, dielectric constant, deconvolution of grazing angle incidence X-ray diffraction, and piezoresponse force microscopy were performed. Hf0.5Zr0.5O2 films with a deposition rate of 1.1 Å/cycle have a more ideal hysteresis curve shape, higher remanent polarization (initial state: 16 μC/cm2, wake up state: 22 μC/cm2), and a higher orthorhombic phase portion than other deposition rates.
The MAPHEUS module CellFix for studying the influence of altered gravity on the physiology of single cells
Authors: Liemersdorf Christian , Lichterfeld Yannick , Hemmersbach Ruth , Hauslage Jens
Published: January 2020

Gravity is the only constant stimulus during the evolution of life. To investigate the impact of the absence of gravity on living systems, their molecular and morphological status has to be studied under microgravity conditions. The experiment unit CellFix was developed in order to provide the possibility of exposure and chemical fixation of small biological systems, such as neurons, stem cells, small animals, yeast cultures, plants, etc., at dedicated time points during a sounding rocket flight. The current version of CellFix consists of two culture bags containing cell cultures in a temperature-controlled pressure vessel. The biosystems in the culture bags can be fixed by pumping the fixative [e.g., paraformaldehyde (PFA), methanol, RNAlater, or others] from a connected bag into the cell suspension. The mechatronic basis of the experiment unit is constructed from compartments of the shelf parts. Open source microcontroller systems (Arduino) or gear pumps, accumulators, etc., from the model making sector are affordable and reliable components to build up an experiment on an unmanned space mission such as a sounding rocket flight. Also, new technologies such as fused deposition modeling were used to construct structures and brackets, which were tested successfully in environmental tests and real space flights (MAPHEUS 7 and 8 sounding rocket missions). In combination with the possibility to handle the experiment as a late access insert in a standardized rocket compartment, CellFix provides a multiusable experiment unit for performing life science experiments in space.
Two-dimensional kinetic simulation of plasma dynamics in the post-arc stage of vacuum circuit breakers
Authors: Wang Dan , Wang Lijun , Liu Jie , Yan Chao , Lin Xin , Jia Shenli
Published: January 2020

In this paper, the plasma decay process is simulated with a two-dimensional kinetic model. The charged particles including electrons and singly charged copper ions are processed with the particle-in-cell method, and the electric field is solved in cylindrically symmetric coordinates. When the residual magnetic field is not taken into consideration, electrons react to the transient recovery voltage instantaneously, leaving an ion sheath in the vicinity of the postarc cathode where the electric field is significantly enhanced. The sheath expanding velocity increases as the overall plasma density decreases. Charged particles move not only along the axial direction but also toward the shield of the arc chamber. When the shield is at postarc cathode potential, the radial expansion of electrons is reduced, while that of ions is facilitated. In addition, postarc current is higher than that in simulation with the shield at postarc anode potential. These results are consistent with those in previously published works. When the axial magnetic field is applied, electrons rotate around the magnetic lines and instabilities develop, resulting in density fluctuations. Besides that, the postarc current is higher than those in the case without the magnetic field.
Tuning ferroelectricity by charge doping in two-dimensional SnSe
Authors: Zhu Liying , Lu Yan , Wang Li
Published: January 2020

Tuning ferroelectricity in two-dimensional (2D) ferroelectric materials is important for future applications. Using first-principles calculations, we show that charge doping is an effective way of tuning the ferroelectricity of group IV monochalcogenides MX (M = Ge, Sn; X = S, Se). Our calculations show that hole doping can decrease and even turn off ferroelectricity in SnSe. This can be explained by the change in strengths of in-plane bonds and out-of-plane bonds in this material. In addition, we find that charge doping can effectively change the lattice constants of MX. This indicates that these materials may be good substrates for constructing van der Waals heterojunctions with other 2D materials, in which the moiré pattern can be effectively tuned by doping electrons and holes.
Shaping effects on scrape-off layer plasma turbulence: A rigorous validation of three-dimensional simulations against TCV measurements
Authors: Riva F. , Tsui C. K. , Boedo J. A. , Ricci P. ,   TCV Team
Published: January 2020

The effect of plasma shaping on scrape-off layer (SOL) plasma turbulence is investigated through a rigorous validation exercise. Two- and three-dimensional simulations of the SOL plasma dynamics in three TCV limited discharges are carried out with the GBS code. These discharges realize an almost circular magnetic equilibrium, an elongated equilibrium, and an elongated equilibrium with negative triangularity. For the three plasma discharges, three simulations are performed, considering (i) a three-dimensional model with an explicit dependence on elongation, triangularity, and the inverse aspect ratio; (ii) a circular three-dimensional model in the infinite aspect ratio limit; and (iii) a two-dimensional model, which assumes a circular magnetic equilibrium in the infinite aspect ratio limit, cold ions, and interchange driven turbulence in the sheath limited regime. Ten validation observables common to simulations and experimental measurements from a reciprocating probe located at the TCV outer midplane are identified, and the agreement between experimental and numerical results relative to each observable is evaluated. The composite metric introduced by Ricci et al. [Phys. Plasmas 18, 032109 (2011)] is then used to assess the overall agreement between simulations and experimental measurements. It is found that the shaping model implemented in GBS improves the description of SOL plasma turbulence, taking into account the impact of elongation and triangularity.
Coherent remote control of quantum emitters embedded in polymer waveguides
Authors: Landowski Alexander , Gutsche Jonas , Guckenbiehl Stefan , Schönberg Marius , von Freymann Georg , Widera Artur
Published: January 2020

We report on the coherent internal-state control of single-crystalline nanodiamonds, containing on average 1200 nitrogen-vacancy (NV) centers, embedded in three-dimensional direct-laser-written waveguides. We excite the NV centers by light propagating through the waveguide, and we show that emitted fluorescence can be efficiently coupled to the waveguide modes. We find an average coupling efficiency of 21.6% into all guided modes. Moreover, we investigate optically detected magnetic-resonance spectra as well as Rabi oscillations recorded through the waveguide-coupled signal. Our work shows that the system is well suited for magnetometry and remote readout of spin coherence in a freely configurable waveguide network, overcoming the need for direct optical access of NV centers in nanodiamonds. These waveguide-integrated sensors might open up new applications, such as determining magnetic field distributions inside opaque or scattering media, or photosensitive samples, such as biological tissue.
Energy-Casimir, dynamically accessible, and Lagrangian stability of extended magnetohydrodynamic equilibria
Authors: Kaltsas D. A. , Throumoulopoulos G. N. , Morrison P. J.
Published: January 2020

The formal stability analysis of Eulerian extended magnetohydrodynamics (XMHD) equilibria is considered within the noncanonical Hamiltonian framework by means of the energy-Casimir variational principle and the dynamically accessible stability method. Specifically, we find explicit sufficient stability conditions for axisymmetric XMHD and Hall MHD (HMHD) equilibria with toroidal flow and for equilibria with arbitrary flow under constrained perturbations. The dynamically accessible, second-order variation of the Hamiltonian, which can potentially provide explicit stability criteria for generic equilibria, is also obtained. Moreover, we examine the Lagrangian stability of the general quasineutral two-fluid model written in terms of MHD-like variables, by finding the action and the Hamiltonian functionals of the linearized dynamics, working within a mixed Lagrangian-Eulerian framework. Upon neglecting electron mass, we derive a HMHD energy principle, and in addition, the perturbed induction equation arises from Hamilton's equations of motion in view of a consistency condition for the relation between the perturbed magnetic potential and the canonical variables.
Hyaluronic acid-based hydrogels with independently tunable mechanical and bioactive signaling features
Authors: Godesky Madison D. , Shreiber David I.
Published: January 2020

Extracellular matrix provides critical signaling context to resident cells through mechanical and bioactive properties. To realize the potential of tissue engineering and regenerative medicine, biomaterials should allow for the independent control of these features. This study investigates a hydrogel system based on thiol-modified hyaluronic acid (HA-S) and polyethylene glycol diacrylate (PEGDA). The mechanical properties of HAS-PEGDA are dictated by two cytocompatible crosslinking reactions that occur at distinct time points: a rapid, Michael-type nucleophilic addition reaction between HA-thiols and PEG-acrylates and a prolonged maturation of disulfide crosslinks from remaining thiols. It is hypothesized that these reactions would enable the independent tuning of the mechanical and bioactive features of HAS-PEGDA. Rheological studies confirmed that initial gelation reached completion by 1 day, at which point the shear modulus was proportional to the concentration of PEGDA. Over time, the shear modulus evolved dramatically, and final stiffness depended on the availability of HA-thiols. The addition of PEG-monoacrylate (PEGMA) after the initial gelation occupied a percentage of remaining thiols to prevent disulfide crosslinking, decreasing the steady-state stiffness in a dose-dependent manner. A fraction of the PEGMA was then replaced with acrylated peptide ligands to introduce specific bioactivity to the otherwise non-cell-adhesive network. The degree of latent stiffening was controlled by the total amount of peptide-PEGMA, while adhesivity was tuned with the balance of bioactive and inactive peptides. The functional effects of the tunable mechanical and bioadhesive ligand properties were confirmed with assays of cell adhesion and morphology.
Surface engineering within a microchannel for hydrodynamic and self-assembled cell patterning
Authors: Rima Xilal Y. , Walters Nicole , Nguyen Luong T. H. , Reátegui Eduardo
Published: January 2020

The applications of cell patterning are widespread due to the high-throughput testing and different resolutions offered by these platforms. Cell patterning has aided in deconvoluting in vivo experiments to better characterize cellular mechanisms and increase therapeutic output. Here, we present a technique for engineering an artificial surface via surface chemistry to form large-scale arrays of cells within a microchannel by employing microstamping. By changing the approach in surface chemistry, H1568 cells were patterned hydrodynamically using immunoaffinity, and neutrophils were patterned through self-assembly via chemotaxis. The high patterning efficiencies (93% for hydrodynamic patterning and 68% for self-assembled patterning) and the lack of secondary adhesion demonstrate the reproducibility of the platform. The interaction between H1568 and neutrophils was visualized and quantified to determine the capability of the platform to encourage cell-cell interaction. With the introduction of H1568 cells into the self-assembled patterning platform, a significant hindrance in the neutrophils' ability to swarm was observed, indicating the important roles of inflammatory mediators within the nonsmall cell lung cancer tumor microenvironment.
Quantifying and optimizing photocurrent via optical modeling of gold nanostar-, nanorod-, and dimer-decorated MoS2 and MoTe2
Authors: Cristiano Michele N. , Tsoulos Ted V. , Fabris Laura
Published: January 2020

Finite element simulations through COMSOL Multiphysics were used to optically model systems composed of Mo dichalcogenide layers (MoTe2 and MoS2) and Au nanoparticles (spherical dimers, nanorods, and nanostars) to understand how their fundamental material properties as well as their interactions affect the photocurrent response. The absorption cross sections of the various Au nanoparticles linearly increase with respect to their increasing dimensions, hence being ideal tunable systems for the enhancement of the electric field in the dichalcogenide layers under visible and near infrared. The photocurrent through the MoTe2 and MoS2 substrates was enhanced by the addition of Au nanoparticles when the plasmonic response was localized in the area of the particle in contact with the substrate. Based on these findings, the use of Au nanoparticles can greatly improve the unique photocurrent properties of Mo dichalcogenides; however, nanoparticle orientation and size must be considered to tune the enhancement at the specific wavelengths. This computational work provides useful design rules for the use of plasmonic nanomaterials in photocatalytic and photocurrent enhancement of transition metal dichalcogenides.
Buckling of blue phosphorus nanotubes under axial compression: Insights from molecular dynamics simulations
Authors: Jiang Shiping , Wu Huiling , Kou Liangzhi , Tang Chun , Wang Chengyuan , Chen Changfeng
Published: January 2020

We report on mechanical properties of blue phosphorus nanotubes (BluePNTs) from systematic molecular dynamics simulations, adopting a Stillinger-Weber potential with parameters determined by fitting to energetic and structural data from first-principles calculations. Our results corroborate the previously reported bending poison effect and size-dependent buckling behaviors. Under axial compression, current simulations predict a shell-to-column buckling mode transition for BluePNTs with increasing aspect ratios; further compression of BluePNTs with large aspect ratios results in a column-to-shell buckling mode transition. Associated critical buckling strains can be described by the continuum mechanics theory. We also simulated buckling behavior of black phosphorus nanotubes (BlackPNTs) and found that the buckling modes of BluePNTs exhibit much less chirality dependence compared to BlackPNTs, stemming from subtle structural differences between these two closely related yet distinct systems. The present results offer insights into key structural and mechanical properties of BluePNTs for fundamental understanding and potential applications of this relatively new member of the large and diverse nanotube family of materials.
Measurements of the energy distribution of electrons lost from the minimum B-field—The effect of instabilities and two-frequency heating
Authors: Izotov I. , Tarvainen O. , Skalyga V. , Mansfeld D. , Koivisto H. , Kronholm R. , Toivanen V. , Mironov V.
Published: January 2020

Further progress in the development of electron cyclotron resonance (ECR) ion sources (ECRISs) requires deeper understanding of the underlying physics. One of the topics that remains obscure, though being crucial for the performance of the ECRIS, is the electron energy distribution (EED). A well-developed technique of measuring the EED of electrons escaping axially from the magnetically confined plasma of an ECRIS was used for the study of the EED in an unstable mode of plasma confinement, i.e., in the presence of kinetic instabilities. The experimental data were recorded for pulsed and CW discharges with a room-temperature 14 GHz ECRIS at the JYFL accelerator laboratory. The measurements were focused on observing differences between the EED escaping from stable and unstable plasmas. It was found that nonlinear phenomena alter the EED noticeably. The electron losses are enhanced in both unstable regimes, with two-frequency heating suppressing the instabilities. It has been shown earlier that two-frequency heating boosts the ECRIS performance presumably owing to the suppression of instabilities. We report the observed changes in EED introduced by the secondary frequency in different regimes, including an off-resonance condition, where the secondary frequency is lower than the minimum frequency satisfying the resonance condition for cold electrons at the magnetic field minimum. Finally, we suggest an experimental method of qualitative evaluation of the energy distribution of electrons confined in the magnetic trap using a method of measuring energy distribution of lost electrons during the plasma decay in pulsed operation of the ion source.
Study on the breakdown characteristics of the trigatron spark gap triggered by plasma jet
Authors: Chen Li , Fan Hao , Cao Ruifeng , Yang Weihong , Li Ying
Published: January 2020

The breakdown characteristics of a trigatron spark gap triggered by a plasma jet are studied in this paper; the development of a plasma jet and the influence of the gap distance, working coefficient, and plasma jet ejection properties on breakdown characteristics are compared. The results show that the plasma jet ejecting process can be divided into expanding, steady, and dissipating phases. The electric field distortion induced by the plasma jet is different during the expanding and dissipating phase, in which the plasma jet length increases and the radius of the curvature of the plasma jet front decreases, respectively. As the two processes have different variation rates, a faster increasing rate of the breakdown delay can be obtained during the dissipating phase. A detailed physical mode that explains the effects on the triggered breakdown process is presented. The shape of a plasma jet induced by polyethylene and ceramic surface discharge changes to a great extent during the dissipating phase; a more stable plasma jet can be obtained when induced only by polyethylene, resulting in a smaller breakdown delay under a low working coefficient. The ultraviolet radiation (UV) generated by the plasma jet is effective in reducing the critical breakdown electric field, while the electric field distortion induced by the plasma jet is the main reason behind the triggered breakdown under different working coefficients; the UV could play a limited role in the triggered breakdown process.
MTJ based magnetic sensor for current measurement in grid
Authors: Gao Kai-Zhong , Yin Xiaolu , Yang Yi , Ewing Dan , De Rego Paul J. , Liou Sy-Hwang
Published: January 2020

In this paper, the status and the challenges of utilizing MTJ based magnetic sensor for Grid sensing are reviewed. And it is shown with both modeling and experiment that an optimized MTJ based magnetic sensor can be utilized to monitor Grid current, particularly for each individual transmission line. Unlike the traditional approach, where the sensing element needs to be either integrated with, in contact with or near the transmission line, this measurement technique can be based on a contactless or a “remote” sensing setup, where the sensor is placed away from the Grid line. From the perspective of sensor, the sensitivity, the signal-to-noise ratio and the linearity of MTJ based magnetic sensor can all meet the requirement of application. It is demonstrated that an optimized DC measurement, in addition to AC measurement, can also be utilized for applications in the Grid system, such as solar energy generation.
Magnetic and transport behaviors of non-centrosymmetric Nd7Ni2Pd
Authors: Pathak Arjun K. , Mudryk Y. , Provino A. , Manfrinetti P. , Pecharsky V. K.
Published: January 2020

Crystallographic, magnetic, electrical transport and thermodynamic properties of pseudo-binary Nd7Ni2Pd compound have been studied using temperature-dependent x-ray powder diffraction and physical property measurements. Compared to the ferromagnetic parent Nd7Pd3, the ground state of Nd7Ni2Pd is antiferromagnetic, and it exhibits strong metamagnetism. The measurements indicate two antiferromagnetic transitions in fields less than 8 kOe: a second-order paramagnetic to antiferromagnetic at TN2 = 29 K and a weak first-order antiferromagnetic to antiferromagnetic transition at TN1 = 24.5 K. The compound becomes ferromagnetic in fields of 8 kOe and higher with TC = 30 K. Temperature dependence of lattice parameters is anomalous, most prominently in the basal plane at ∼30 K; however, there is no detectable structural distortion or clear volume discontinuity around 25 K, suggesting a significant weakening of the first-order transition when compared to the binary Nd7Pd3.
Interaction of two magnetic micro-chains in a rotating field
Authors: Cheng Jia-Hong , Lin Chih-Ru , Chen Ching-Yao
Published: January 2020

Interactions between two chains consisted of micro-sized magnetic beads are experimentally investigated. Driven by a rotating field, three distinct modes of magnetic interactions are identified, referred to as chaining, locking and transit. The two chains gradually approach to form a longer chain in the chaining mode. The locking mode refers the chains undergo an interesting orbital-like circular motion, which mimics a binary star system. The chains could also evolve from locking to chaining in the transit mode. A necessary criterion for a locking mode is derived, which agrees excellently with the correspondent experiments.
Current driven domain wall dynamics in ferrimagnetic strips explained by means of a two interacting sublattices model
Authors: Martínez Eduardo , Raposo Víctor , Alejos Óscar
Published: January 2020

The current-driven domain wall dynamics along ferrimagnetic elements are here theoretically analyzed as a function of temperature by means of micromagnetic simulations and a one dimensional model. Contrarily to conventional effective approaches, our model takes into account the two coupled ferromagnetic sublattices forming the ferrimagnetic element. Although the model is suitable for elements with asymmetric exchange interaction and spin-orbit coupling effects due to adjacent heavy metal layers, we here focus our attention on the case of single-layer ferrimagnetic strips where domain walls adopt achiral Bloch configurations at rest. Such domain walls can be driven by either out-of-plane fields or spin transfer torques upon bulk current injection. Our results indicate that the domain wall velocity is optimized at the angular compensation temperature for both field-driven and current-driven cases. Our advanced models allow us to infer that the precession of the internal domain wall moments is suppressed at such compensation temperature, and they will be useful to interpret state-of-the art experiments on these elements.
Crystallographic inversion-mediated superparamagnetic relaxation in Zn-ferrite nanocrystals
Authors: Sai Ranajit , Arackal Sarath , Kahmei R. D. Ralandinliu , Bhat Navakanta , Yamaguchi Masahiro , Shivashankar S. A.
Published: January 2020

Crystallographic inversion induced shift of resonance frequency in zinc ferrite nanoparticle (ZF-NP) samples is studied here. ZF-NP samples were synthesized by a solution-based, low-temperature (<200 °C), microwave-assisted solvothermal (MAS) process. Owing to the far-from-equilibrium processing condition, the MAS process produces a very high degree of crystallographic inversion, δ=0.61, in the as-synthesized nanocrystallites. A rapid thermal annealing (RTA) technique was adopted to tune-down crystallographic inversion without altering the crystallite sizes in annealed samples. The crystal structures, particle shapes, and compositions of the nanocrystalline samples were characterized by XRD, SEM and Raman spectroscopy. The samples are phase-pure, with particle size in the range 8-16 nm and their compositions are stoichiometrically accurate. The resonance phenomena in 1 to 10 GHz frequency range was measured by analyzing the impedance mismatch of a microstrip line with the magnetic material loaded on to it. The RTA protocol enables tuning of the resonance phenomena in the ZF-NC samples above 6 GHz with tunable range of ∼500 MHz
Lattice constant prediction of A2XY6 cubic crystals (A = K, Cs, Rb, TI; X = tetravalent cation; Y = F, Cl, Br, I) using computational intelligence approach
Authors: Alade Ibrahim Olanrewaju , Olumegbon Ismail Adewale , Bagudu Aliyu
Published: January 2020

Lattice constant mismatch between materials affects the quality of thin film fabrication. For this reason, lattice constants information is vital in the design of materials for technological applications. The determination of lattice constants via experimental analysis is relatively expensive and laborious. As a result, several linear empirical models have been proposed to predict the lattice constant of crystal structures. However, the accuracies of these models are limited partly due to their failure to account for nonlinearity in the atomic parameters-lattice constant relationship. Machine learning techniques have shown excellent ability to deal with nonlinear problems in many areas of materials science; hence, they are considered suitable computation tools to study the crystal structure of materials. In this contribution, we developed a support vector regression (SVR) model to predict the lattice constant of cubic crystals of the form A2XY6 (A = K, Cs, Rb, TI; X = tetravalent cation; and Y = F, Cl, Br, I). The SVR algorithm uses the ionic radii and electronegativities data of the constituent elements of A2XY6 cubic crystals as model inputs. The robustness of the proposed model was demonstrated by comparing our result with an existing linear model based on 26 cubic crystal samples. The result revealed a total relative deviation of 1.757 and 2.704 for the SVR model and the existing linear equation, respectively. This result proves that the SVR model has a huge potential in the search for new materials for different applications.
A new sliding discrete Fourier transform phase difference measurement method for extreme frequency signals
Authors: Shen Ting’ao , Chen Liwei , Guan Jinfa , Duan Jimiao
Published: January 2020

While there are many ultralow frequency signals and ultrahigh frequency signals in the vibration engineering field, the existing discrete Fourier transform (DFT) spectrum analysis methods bring about significant phase difference errors when measuring these extreme frequency signals. In order to improve the performance of these methods, a new sliding DFT phase difference measurement method for extreme frequency signals is proposed. First, the spectrum of extreme frequency signals is analyzed, which is used to illuminate the contribution of negative frequency. Then, the spectrum leakage is restrained by adopting rectangular self-convolution windows (RSCWs). Finally, the sliding recursive algorithm is introduced to reduce the computational load. The whole processes of formula derivation for phase difference measurement by adopting different RSCWs are described in detail. Simulations show that the proposed method obtains a better real time characteristic and a higher phase difference measurement precision than conventional DFT methods, which is suitable especially for extreme frequency vibration signals.
Rare-earth and precious-metal free Cu-based metallic glasses with superior glass-forming ability and processability
Authors: Saini Jaskaran Singh , Palian Collin , Lei Fuqiong , Dyall Alexander , AuYeung Nicholas , McQuade Ryan , Gupta Sanu K. , Cann David P. , Xu Donghua
Published: January 2020

Metallic glasses have many fascinating properties such as theoretical-limit approaching strength, high wear and corrosion resistance, and extremely smooth surfaces enabling high-performance thin film diodes. Copper-based metallic glasses are of particular interest due to the low cost and attractive characteristics of the base element, but the copper-based metallic glasses known to date rely on rare-earth or precious metals that have limited supplies and relatively high cost, in order to achieve good glass-forming ability. Here, we report our discovery of a series of rare-earth and precious-metal free copper-based metallic glasses formulated as Cu46Zr47−xHfxAl7 (8 ≤ x ≤ 20, at. %), which possess superior glass-forming ability and processability. Fully amorphous ingots with a large cross section of 15 (all x) to 28.5 mm (x = 13.5) diameter can be readily produced by a simple water quenching method. The Cu46Zr33.5Hf13.5Al7 alloy, in particular, presents the highest glass-forming ability and processability of all known copper-based metallic glasses. The adjustable Hf content in the composition offers a range of physical properties (e.g., density) that can be chosen based on applications. We also discuss the physical origin of the superior glass-forming ability and processability in these copper-based metallic glasses.
A simple and cost-efficient technique to generate hyperpolarized long-lived 15N-15N nuclear spin order in a diazine by signal amplification by reversible exchange
Authors: Roy Soumya S. , Rayner Peter J. , Burns Michael J. , Duckett Simon B.
Published: January 2020

Signal Amplification by Reversible Exchange (SABRE) is an inexpensive and simple hyperpolarization technique that is capable of boosting nuclear magnetic resonance sensitivity by several orders of magnitude. It utilizes the reversible binding of para-hydrogen, as hydride ligands, and a substrate of interest to a metal catalyst to allow for polarization transfer from para-hydrogen into substrate nuclear spins. While the resulting nuclear spin populations can be dramatically larger than those normally created, their lifetime sets a strict upper limit on the experimental timeframe. Consequently, short nuclear spin lifetimes are a challenge for hyperpolarized metabolic imaging. In this report, we demonstrate how both hyperpolarization and long nuclear spin lifetime can be simultaneously achieved in nitrogen-15 containing derivatives of pyridazine and phthalazine by SABRE. These substrates were chosen to reflect two distinct classes of 15N2-coupled species that differ according to their chemical symmetry and thereby achieve different nuclear spin lifetimes. The pyridazine derivative proves to exhibit a signal lifetime of ∼2.5 min and can be produced with a signal enhancement of ∼2700. In contrast, while the phthalazine derivative yields a superior 15 000-fold 15N signal enhancement at 11.7 T, it has a much shorter signal lifetime.
Vortex breakdown in the lower fluid of two-fluid swirling flow
Authors: Naumov Igor V. , Sharifullin Bulat R. , Shtern Vladimir N.
Published: January 2020

This paper describes the first experimental evidence of the vortex breakdown development in the lower fluid in a sealed vertical cylindrical container in which two immiscible fluids circulate, driven by a rotating lid. The lower fluid is water, and the upper fluid is sunflower oil. In both fluids, the rotation generates centrifugal meridional circulations separated by a thin anticentrifugal circulation layer attached to the interface from below. An advanced technique of particle image velocimetry and proper laser illumination allows for the measurement of velocity and recognition of the patterns of flow in oil and water. As the rotation speeds up, a tornadolike swirling ascending jet forms near the axis-bottom intersection. A circulation cell (vortex-breakdown bubble, VBB) then emerges near the center of the water domain, approaches the bottom, and disappears. This scenario of the appearance and disappearance of the VBB is similar to that occurring in a single-fluid flow and in the upper fluid of a two-fluid flow.
Two-dimensional manipulation of a magnetic robot using a triad of electromagnetic coils
Authors: Lee H. J. , Jeon S. M.
Published: January 2020

Different magnetic navigation systems (MNSs) have been investigated for the wireless manipulation of biomedical magnetic robots. Here we propose a novel MNS simply composed of a triad of electromagnetic coils (TEC) that can effectively manipulate a magnetic robot in two-dimensional (2D) environments. We derived a constraint equation of the TEC’s input currents in order to manipulate the magnetic robot’s 2D aligning and propelling motions in a controlled manner. We also examined the TEC’s ability to manipulate those motions by simulating the TEC’s magnetic field and the corresponding magnetic force in terms of several newly defined dimensionless variables. We then constructed the proposed TEC and demonstrated several controlled 2D motions of a magnetic robot to show the validity of the proposed system and the robot manipulation method.
Enhanced sample pre-concentration by ion concentration polarization on a paraffin coated converging microfluidic paper based analytical platform
Authors: Perera A. T. K. , Phan Dinh-Tuan , Pudasaini Sanam , Liu Yu , Yang Chun
Published: January 2020

Microfluidic paper-based analytical devices (μPADs) represent a modest and feasible alternative for conventional analytical methods. However, the inadequate sensitivity of these devices limits the possible applications of μPADs. In this scenario, inducing ion concentration polarization (ICP) on μPADs has shown promise to overcome this limitation by preconcentrating the analytes of interest. Here, we report a μPAD implementing ICP using an off-shelf Nafion® membrane as the perm selective membrane. Two types of devices with a geometrical configuration of a straight channel converging at the middle connecting to circular reservoirs at the end of channels were fabricated. The devices are comprised of a single input channel and an absorption channel. The Nafion membrane is attached to the absorption channel of the device, which is encased by heating with paraffin films at both sides to lower the electro-osmotic flow generated by an applied DC electric field that is needed for ICP. The field induced ICP enables obtaining a maximum concentration factor of more than 2000 folds for fluorescein sodium salt solution on the μPAD. Also, since evaporation of the sample solution was reported to be of great influence on the concentration factor, we analyze the effect of sample solution evaporation on sample preconcentration. Furthermore, our reported fabrication method for μPAD can lower the fabrication cost down to 0.3 USD. This device shows the potential to be developed for serving as a diagnostic and environmental monitoring platform.
Analytical model for light modulating impedance spectroscopy (LIMIS) in all-solid-state p-n junction solar cells at open-circuit
Authors: Almora Osbel , Miravet Daniel , Matt Gebhard J. , Garcia-Belmonte Germà , Brabec Christoph J.
Published: January 2020

Potentiostatic impedance spectroscopy (IS) is a well-known tool for characterization of materials and electronic devices. It can be complemented by numerical simulation strategies relying on drift-diffusion equations without any equivalent circuit-based assumptions. This implies the time-dependent solutions of the transport equations under small perturbation of the external bias applied as a boundary condition at the electrodes. However, in the case of photosensitive devices, a small light perturbation modulates the generation rate along the absorber bulk. This work then approaches a set of analytical solutions for the signals of IS and intensity modulated photocurrent and photovoltage spectroscopies, intensity modulated photocurrent spectroscopy (IMPS) and intensity modulated photovoltage spectroscopy (IMVS), respectively, from one-sided p-n junction solar cells at the open-circuit. Subsequently, a photoimpedance signal named “light intensity modulated impedance spectroscopy” (LIMIS = IMVS/IMPS) is analytically simulated, and its difference with respect to IS suggests a correlation with the surface charge carrier recombination velocity. This is an illustrative result and the starting point for future more realistic numerical simulations.
Entanglement-based 3D magnetic gradiometry with an ultracold atomic scattering halo
Authors: Shin D K , Ross J A , Henson B M , Hodgman S S , Truscott A G
Published: January 2020

Ultracold collisions of Bose–Einstein condensates can be used to generate a large number of counter-propagating pairs of entangled atoms, which collectively form a thin spherical shell in momentum space, called a scattering halo. Here we generate a scattering halo initially composed of pairs in a symmetric entangled state in spin, and observe a coherent oscillation with an anti-symmetric state during their separation, due to the presence of an inhomogeneous magnetic field. We demonstrate a novel method of magnetic gradiometry based on the evolution of pairwise correlation, which is insensitive to common-mode fluctuations of the magnetic field. Furthermore, the highly multimode nature and narrow radial width of scattering halos enable a 3D reconstruction of the interrogated field. Based on this, we apply Ramsey interferometry to realise a 3D spatial reconstruction of the magnetic field without the need for a scanning probe.
Study of temperature dependent viscosity of different types of engine used oils
Authors: Raţiu S , Alexa V , Josan A , Cioată V G , Kiss I
Published: January 2020

The article presents a study on the change in kinematic viscosity with the temperature for three samples of synthetic used oil (SAE 5W-30). Samples were taken after a 10,000 km run on the occasion of periodically changing oil from three engines with close cylindrical capacities (one diesel engine – VW 1.9 TDI, one gasoline engine – Audi 1.8 Turbo and one spark engine – Audi 1.8 Turbo, working with GPL). Comparatively, viscosity measurements were made for the same oils before being introduced into the engines. The kinematic viscosity was measured experimentally using the Brookfield viscometer from 5 to 5 degrees Celsius. To eliminate the errors, the measurements were made under the same conditions for all samples, being repeated three times, the values taken into consideration for a given temperature being made up of averages of the three measurements.
Evaluation of deterioration of engine oil properties in the function of mileage
Authors: Wierzbicka N , Szadkowska D , Patalas A , Talar R , Łabudzki R , Zawadzki P
Published: January 2020

The paper involve testing of various engine oils – synthetic and semi – synthetic – in terms of viscosity change at different temperatures and the degree of wear. New and used oils were compared. This is an important issue for determining the reliability of motor vehicles, anticipated repairs and maintenance. As a result of the process of exploitation, engine oils are subjected to physicochemical changes. The impact on the deterioration in the condition of the lubricating liquid have, among others high pressure, temperature, pollution or oil oxidation. Therefore, it is necessary to change the engine oil after the mileage recommended by the producer . However, these recommendations may not be adequate for the actual consumption of liquids, which is determined by the technical condition of the engine and the course of the operation process. Determining the optimal replacement time is an important issue due to the reduction of operating costs and reduction of emissions of environmentally harmful exhaust. For this purpose, the viscosity depending on the temperature of different oils with various degrees of wear, tear, and obsolescence were measured. Characteristic points were determined and a mathematical model describing these changes was created. It was noticed that the greatest changes in viscosity occur at a temperature of 0 °C to 40 °C, whereas from 40 °C the viscosity changes appear in a smaller range for all oils and the viscosity was below 100 mPa·s. Results of comparing the new and used oil was evaluation of the change of their lubricating properties. The aim of this paper was to conduct viscosity tests of selected engine oils using a rotational viscometer in order to check the degree of engine oil consumption due to the degree of exploitation.
Control system of multi-disc mill with a new structural solution
Authors: Kruszelnicka W , Tomporowski A , Flizikowski J , Kasner R
Published: January 2020

The study presents the issues involved in control and monitoring of functional characteristics of the process of grinding, on the example of a multi-disc mill, designed according to a new solution. The authors’ original system for control and monitoring of the mill operational parameters has been presented. The aim of this work is to develop a methodology for integration of the control, process and logistic modules of a multi-disc mill designed for industrial purposes. The structure of the control and monitoring systems has been analyzed. The structure was used for tests of the mill operational parameters whose results were used for evaluation of the mill operation.
The improvement of steel properties using Al2O3 coatings deposited by plasma spraying
Authors: Benea M L , Benea L P
Published: January 2020

It is well-know that the numerous functions of use of materials can be realized at a high level of performance by using plasma jet coatings, with the reduction of the consumption of important strategic metals. These are determined by the excellent resilience to extreme temperatures, corrosion and wear of the coatings.

This paper aims to characterize coating layers based on Al2O3 realized by plasma jet spray by examining its hardness, thermal shock resistance, traction resistance.
Indetermination versus incompatibility in dynamic systems with dry friction
Authors: Alaci S , Ciornei F C , Pentiuc R D , Ciornei M C , Românu I C
Published: January 2020

The study of the dynamical behavior of a system becomes really complex when friction forces are introduced in calculus since they directly depend on the values of the normal reactions and on the motion of the system, but the motion, at its turn, depends upon the forces from the system. The analysis is more difficult when dry friction, characterized by inequalities, is present between the parts of the system. When inequalities are involved in dynamical equilibrium equations, theoretically simultaneous equilibrium states may occur. In scientific literature there are famous examples supporting this statement. The present paper presents the dynamical study of a simple system, namely a ball obliged to roll in a groove with flat walls.

It is proved experimentally that the motion of the ball is a planar one. The dynamical analysis of the system with planar motion leads to an undeterminate system of equations and therefore the spatial approach of the system is required. After writing the equations of the spatial motion of the ball, an incompatible system of equations is obtained.