bluuebunny/crossref_metadata_2025 huggingface dataset:
Riemann problems and wave interactions for a non-symmetric Keyfitz–Kranzer system with a source term
Authors: He Fen , Chen Tingting , Zhang Qingling , Wang Zhen
Published: January 2022

In this paper, we study the Riemann problems and wave interactions for a non-symmetric Keyfitz–Kranzer system with the source term βρ with initial data. We show the existence of an intricate δ-shock wave solution satisfying the generalized Rankine–Hugoniot conditions and δ-shock wave entropy condition. In particular, a remarkable behavior for the solution may occur. For the time 0<t<t̂, we show the existence of a δ-shock wave. In addition, for t⩾t̂, the δ-shock wave disappears and the solution is constructed by contact discontinuities. The double Riemann problem for this system with three piecewise constant states is also considered, and its global solutions are constructed by analyzing the interactions between two different waves, including δ-shock wave and contact discontinuity.
Organic abrasive machining system for optical fabrication with 0.1-mm spatial resolution
Authors: Matsuzawa Yusuke , Hiraguri Kentaro , Hashizume Hirokazu , Mimura Hidekazu
Published: January 2022

High-precision optics for short-wavelength regions, such as x rays and extreme ultraviolet light, generally require nanometer-level figure accuracy on their surfaces. Such optics are finished via a numerically controlled figure correction process in which the dwelling time of the machining tool on the workpiece is controlled. Due to the limitation of the machined spot size, it is difficult to remove mid-spatial-frequency (1 to 10 mm−1) errors on an optical surface. To realize a high-spatial-resolution figure correction process for high-precision optics, we have been developing the organic abrasive machining (OAM) technique, which can generate a 100 µm machined spot using a small elastic rotation tool in a slurry that includes acrylic particles. In this study, an OAM apparatus that can measure the machining load was constructed. The effects of the machining and slurry conditions were investigated and high-spatial-resolution machining on a flat glass substrate was demonstrated. The root-mean-square roughness of the surface after OAM processing was below 0.2 nm. Patterns with a minimum line and space size of 100 µm were successfully fabricated.
A broadband optical fiber transmission-based time domain measurement system for nanosecond-level transient electric field
Authors: Kong Xu , Xing Wen-qi , Xie Yan-zhao , Zheng Zhou , Sun Zhen-dong
Published: January 2022

A novel nanosecond transient electric field (E-field) measurement system is developed in this paper to measure the E-field pulse caused by the operation of the high-voltage switch (switching E-field pulse) in the substation. An electrically small rod antenna is used as the receiving antenna and is matched by the operational amplifier with high input impedance to achieve broadband frequency response and stable working performance. A broadband analog optical fiber transmission system is further designed based on the high-frequency circuit model of the electronic components. Unlike the traditional frequency domain E-field measurement methods, the developed measurement system can directly output the time domain waveform of the switching E-field pulse. It also has the advantages of adjustable sensitivity, portability, and anti-electromagnetic interference. The calibrated measurement bandwidth ranges from 200 Hz to 680 MHz. Furthermore, the switching E-field pulse in an ultra-high voltage substation is measured and analyzed to verify the effectiveness of the fabricated measurement system.
Impact of operation parameters on the degradation of 233 nm AlGaN-based far-UVC LEDs
Authors: Glaab J. , Ruschel J. , Lobo Ploch N. , Cho H. K. , Mehnke F. , Sulmoni L. , Guttmann M. , Wernicke T. , Weyers M. , Einfeldt S. , Kneissl M.
Published: January 2022

The impact of the operation parameters current and temperature on the degradation of AlGaN-based 233 nm far-ultraviolet-C LEDs is investigated. The observed effects can be divided into two groups: First, a rapid reduction in the optical power to about 50%–30% of the initial value during the first ∼100 h of operation, which is accompanied by an increase in the current below the diffusion voltage from 0.3 to about 1 μA, and a reduction in the hydrogen concentration in the p-side close to the active region. The second group is represented by a gradual reduction of the optical power, which runs in parallel to the effects in the first group and dominates for operation times ≥100 h. The reduction of the optical power is due to a decrease in the slope of the optical power–current characteristic. All effects are accelerated at increased stress currents and current densities—the reduction in the optical power at low (∼20 mA) and high measuring current (∼80 mA) scales with the current to the power of three. For example, after 250 h of operation, the relative optical power at a measuring current of 20 mA has decreased to about 40% when the LED was operated at a stress current of 20 mA and to <10% for a stress current of 100 mA. Furthermore, temperature has no significant impact on the reduction of the optical power during operation, i.e., the relative optical power reduced to about 25% after 250 h both when the LEDs were operated at 20 °C and when they were operated at 75 °C.
The effect of the cavity formation on the energy consumption characteristics of the agitated gas–liquid bioreactor
Authors: Wang Peng , Wang Shiji , Gu Yandong , Si Qiaorui , Yuan Shouqi
Published: January 2022

Detailed power consumption characteristics from experiments and simulations of gas–liquid stirred tanks with shear-thinning power-law liquids are presented. The motion of bubbles was investigated based on the Euler–Euler approach with a bubble cluster concept. The drag coefficient of bubbles with a constant bubble diameter was modeled as the Schiller and Naumann function. The predicted power consumption of a gas–liquid mixture shows reasonable agreement with experimental data with a maximum deviation of 8.9%. For the studied aerated systems, a qualitatively new power reduction correction equation was derived and demonstrated a reasonable agreement with experimental results compared with the literature-reported equations. The effect of the concentrations and gas flow rates on power consumption was presented. It was found that the power consumption of different mixtures is related to the change in the critical generalized Reynolds number, which was Reg = 440, 230, 100, 30, and 25 for 0.2%, 0.4%, 0.62%, 0.85%, and 1.25%, respectively.
Quantum Monte Carlo formulation of the second order algebraic diagrammatic construction: Toward a massively parallel correlated excited state method
Authors: Kulahlioglu Adem Halil , Rehn Dirk , Dreuw Andreas
Published: January 2022

The quantum Monte Carlo (QMC) algebraic diagrammatic construction (ADC) method is introduced, which solves the eigenvalue problem of the second-order ADC scheme for the polarization propagator stochastically within the framework of QMC methodology allowing for massively parallel computations. As common virtue of the Monte Carlo integration techniques, quantum Monte Carlo algebraic diagrammatic construction (QMCADC) enables exploitation of the sparsity of the effective ADC matrix, and it reduces the memory requirements by storing only a portion of configurations at each iteration. Furthermore, distributing memory and processing loads to different computing nodes enables the use of fast developing parallel computing resources. Here, the theory and implementation of QMCADC is reported and its viability is demonstrated by the first proof-of-principle calculations. The focus lies on the first excited state and the reproduction of the corresponding lowest vertical excitation energy of various molecular systems. QMCADC is shown to be a genuine stochastic solution of the ADC eigenvalue problem, and exact ADC values can be obtained with a marginal controllable error.
QED effects on high-order harmonic generation from ultraintense laser-irradiated solid-plasmas
Authors: Hu Siyun , Chen Zi-Yu
Published: January 2022

High-order harmonic generation (HHG) from relativistically intense laser irradiation of solid-density plasmas provides novel coherent light sources in the extreme-ultraviolet (XUV) to x-ray spectral region with attosecond duration and high intensity even toward the Schwinger limit. However, whether the HHG process and mechanism are effective at extremely high laser intensities in the QED-plasma regime remains unclear, since QED processes, such as discrete synchrotron radiation, quantum radiation reaction, and pair creation, would change the energy partition and particle dynamics. In this work, through particle-in-cell simulations, we numerically demonstrate that the HHG process with the relativistically oscillating mirror mechanism can be scaled to an ultrahigh intensity level of 1024 W/cm2. The high harmonic spectrum, attosecond pulses, and conversion efficiency are not significantly affected by the QED processes. This result is of great benefit to the generation of coherent XUV and x-ray light sources with higher intensity, higher cutoff frequency, and shorter duration.
Diffusive instability in hyperbolic reaction–diffusion equation with different inertia
Authors: Ghorai Santu , Poria Swarup , Bairagi Nandadulal
Published: January 2022

This work considers a two-dimensional hyperbolic reaction–diffusion system with different inertia and explores criteria for various instabilities, like a wave, Turing, and Hopf, both theoretically and numerically. It is proven that wave instability may occur in a two-species hyperbolic reaction–diffusion system with identical inertia if the diffusion coefficients of the species are nonidentical but cannot occur if diffusion coefficients are identical. Wave instability may also arise in a two-dimensional hyperbolic reaction–diffusion system if the diffusivities of the species are equal, which is never possible in a parabolic reaction–diffusion system, provided the inertias are different. Interestingly, Turing instability is independent of inertia, but the stability of the corresponding local system depends on the inertia. Theoretical results are demonstrated with an example where the local interaction is represented by the Schnakenberg system.
Global solutions of a doubly tactic resource consumption model with logistic source
Authors: Wang Jianping
Published: January 2022

We study a doubly tactic resource consumption model (ut = Δu − ∇ · (u∇w), vt = Δv − ∇ · (v∇u) + v(1 − vβ−1), wt = Δw − (u + v)w − w + r) in a smooth bounded domain Ω∈R2 with homogeneous Neumann boundary conditions, where r∈C1(Ω̄×[0,∞))∩L∞(Ω×(0,∞)) is a given non-negative function fulfilling ∫tt+1∫Ω|∇r|2<∞ for all t ≥ 0. It is shown that, first, if β > 2, then the corresponding Neumann initial-boundary problem admits a global bounded classical solution. Second, when β = 2, the Neumann initial-boundary problem admits a global generalized solution.
Quantitative scanning microwave microscopy of 2D electron and hole gases in AlN/GaN heterostructures
Authors: Wang Xiaopeng , Fabi Gianluca , Chaudhuri Reet , Hickman Austin , Asadi Mohammad Javad , Nomoto Kazuki , Xing Huili Grace , Jena Debdeep , Farina Marco , Hwang James C. M.
Published: January 2022

Although the scanning microwave microscope (SMM) is based on the atomic force microscope (AFM), the SMM differs from the AFM by being able to sense subsurface electromagnetic properties of a sample. This makes the SMM promising for in-depth nondestructive characterization of nanoelectronic structures. However, the SMM raw data are convoluted with the sample topography, making it especially challenging for quantitative characterization of nonplanar structures. In this paper, using the topography information simultaneously obtained by the AFM and the in situ extracted probe geometry, we de-embed from the topography-corrupted SMM data the sheet resistance of 2D electron or hole gas (2DEG or 2DHG) buried at the interface of an AlN/GaN heterostructure, including the lateral depletion of the 2DEG from an etched step. The SMM results are validated by Hall-effect measurements. The limitation and possible improvement in the present technique are discussed. With improved setup, the SMM can be used to nondestructively monitor the local sheet resistance of 2DEG or 2DHG during device manufacture. These studies help to pave the way to 3D microwave tomography on the nanometer scale.
Quantum-chemistry study of the ground and excited state absorption of distyrylbenzene: Multi vs single reference methods
Authors: Roldao Juan Carlos , Oliveira Eliezer Fernando , Milián-Medina Begoña , Gierschner Johannes , Roca-Sanjuán Daniel
Published: January 2022

State-of-the-art complete active space self-consistent field/complete active space second order perturbation theory (CASPT2) calculations are used to investigate the role of double excitations on the ground state absorption (GSA) and excited state absorption (ESA) spectra of distyrylbenzene, an important prototype medium-sized π-conjugated organic compound for optoelectronics. The multi-reference results are compared with linear and quadratic response time-dependent density functional theory (DFT) results, revealing an incomplete description of the electronic transitions in the latter. Careful selection of the active space and basis set in the CASPT2 approach allows for a reliable description of the GSA and ESA features; cost-effective DFT-based geometries can be utilized without a significant loss of accuracy. Double excitations are shown to play a pivotal role already for higher excited states in the GSA spectrum, however, without a relevant impact on the discernible spectral features. In the ESA, which shows a much more complex electronic situation, the crucial importance of double (and higher) excitations in all relevant electronic transitions, indeed, mandates a multiconfigurational treatment as done in the present benchmark study.
Revealing the tempering embrittlement in a medium entropy alloy containing carbon atoms
Authors: Pan S. , Shang X. K. , He B. B. , Huang M. X.
Published: January 2022

In general, annealing treatment is frequently used to recover the ductility of high/medium entropy alloys after deformation. However, the present work demonstrates that the ductility of a CoCrNiVC medium entropy alloy could be substantially reduced after the tempering process, which is similar to the tempering embrittlement in some steels. Numerous carbides with chromium enrichment are formed at the shear bands and grain boundaries during tempering at 700 °C for 30 min. The carbides embedded at grain boundaries result in a localized strain concentration during plastic deformation, facilitating the nucleation of the micro-cracks. The segregation of carbon at the grain boundary decreases its cohesion energy, accelerating the propagation of cracks and the development of intergranular fracture.
Tip-enhanced Raman spectroscopy of confined carbon chains
Authors: Tschannen Cla Duri , Vasconcelos Thiago L. , Novotny Lukas
Published: January 2022

Long linear chains of carbon encapsulated in carbon nanotubes represent the finite realization of carbyne, the truly one-dimensional carbon allotrope. Driven by advances in the synthesis of such structures, carbyne has attracted significant interest in recent years, with numerous experimental studies exploring its remarkable properties. As for other carbon nanomaterials, Raman spectroscopy has played an important role in the characterization of carbyne. In particular, tip-enhanced Raman scattering (TERS) has enabled imaging and spectroscopy down to the single-chain level. In this article, we provide a general introduction to carbyne and discuss the principles and experimental implementation of TERS as a key technology for the investigation of this material system. Within this context, the development of optical nanoantennas as TERS probes is addressed. We then summarize the latest progress in the Raman spectroscopic characterization of confined carbyne, with a focus on the findings assisted by TERS. Finally, we discuss open questions in the field and outline how TERS can contribute to solving them in future studies.
Galvanically replaced artificial interfacial layer for highly reversible zinc metal anodes
Authors: Xiong Peixun , Kang Yingbo , Yuan Haocheng , Liu Qing , Baek Sang Ha , Park Jae Min , Dou Qingyun , Han Xiaotong , Jang Woo-Sung , Kwon Seok Joon , Kim Young-Min , Li Wenwu , Park Ho Seok
Published: January 2022

Interface modification is considered as a straightforward strategy to regulate the electrochemical environment of metal anodes and to provide a physically protective interphase. Herein, we develop galvanically replaced artificial interfacial layers, where Sn, Sb, and Bi layers are uniformly grown on Zn anodes, for use in high-performance aqueous rechargeable zinc batteries. The corrosion and dendrite formation of Zn metal are inhibited by manipulating the uniform Zn deposition behavior and facile plating/stripping, as verified by electrochemical characterizations and postmortem, in situ optical, and computational analyses. Considering that the thickness, morphology, and crystallinity of the interfacial layers vary depending on their chemical identity, the Sn modified Zn anode (Zn|Sn) exhibits the optimum electrochemical performance owing to its highest Zn affinity and hierarchical structure. Consequently, symmetric cells with Zn|Sn anodes demonstrate stable plating/stripping over 2200 h at 1 mA cm−2 and a long cycle life of 2000 h at a high current density of 4 mA cm−2. In particular, the full cells by pairing Zn|Sn with β-MnO2 deliver a high capacity of 92.8 mA h g−1 even at a high current rate of 5000 mA g−1, 73% capacity retention after 1000 cycles at 1000 mA g−1, and improved cycle stability under low N/P ratio (<50) and high cathode mass loading (∼15.8 mg cm−2).
Full-frequency dynamical Bethe–Salpeter equation without frequency and a study of double excitations
Authors: Bintrim Sylvia J. , Berkelbach Timothy C.
Published: January 2022

The Bethe–Salpeter equation (BSE) that results from the GW approximation to the self-energy is a frequency-dependent (nonlinear) eigenvalue problem due to the dynamically screened Coulomb interaction between electrons and holes. The computational time required for a numerically exact treatment of this frequency dependence is O(N6), where N is the system size. To avoid the common static screening approximation, we show that the full-frequency dynamical BSE can be exactly reformulated as a frequency-independent eigenvalue problem in an expanded space of single and double excitations. When combined with an iterative eigensolver and the density fitting approximation to the electron repulsion integrals, this reformulation yields a dynamical BSE algorithm whose computational time is O(N5), which we verify numerically. Furthermore, the reformulation provides direct access to excited states with dominant double excitation character, which are completely absent in the spectrum of the statically screened BSE. We study the 21Ag state of butadiene, hexatriene, and octatetraene and find that GW/BSE overestimates the excitation energy by about 1.5–2 eV and significantly underestimates the double excitation character.
Clarifying duplicated electromagnetic characteristics for 220-GHz two-beam extended interaction oscillator
Authors: Bi Liangjie , Xu Che , Qin Yu , Jiang Xinyu , Liu Ran , Wang Bin , Li Hailong , Meng Lin , Yin Yong
Published: January 2022

In this paper, we clarify the duplicated electromagnetic characteristics between the proposed two-beam overmoded multi-gap structure published in the paper titled “Tractable resonant structure with two nonuniform beams for a high-power 0.22-THz extended interaction oscillator” [Bi et al., IEEE Electron Device Lett. 42(6), 931–934 (2021)] and conventional multi-gap structures from the physical concept point of view. The replacement of the TE10 mode by the TE30 mode used in the interaction gaps provides the basis for the duplicated electromagnetic field distributions and frequencies between the two structures. The concept of magnetic coupling is proposed to support the resonant condition that supports duplication of the TE30 field and the frequency of the single-gap structure into the periodic standing-wave field of the multi-gap structure. With this concept, the perturbation of different axial phase shifts across one period to the standing-wave field of the TE30-0 mode is analyzed to clarify the profiles of the dispersion curves of the TE30 mode in the overmoded structure and the TE10 mode in the conventional structure. To demonstrate the profiles, a 220-GHz overmoded and conventional structure with nine gaps is designed, and their dispersion curves are obtained by using eigenmode simulations. In addition, the effect of the difference in the boundary conditions of the geometries of these two structures on the magnetic field distribution is analyzed to demonstrate the duplication of the ohmic losses between the two structures. The physical analysis in the duplicated electromagnetic characteristics lays a foundation for the promising design of the overmoded structure with two beams for high frequency extended interaction oscillators.
Cavity-enhanced saturated absorption spectroscopy of the (30012) − (00001) band of 12C16O2
Authors: Tan Y. , Xu Y.-R. , Hua T.-P. , Liu A.-W. , Wang J. , Sun Y. R. , Hu S.-M.
Published: January 2022

The (30012) ← (00001) band of 12C16O2 in the 1.6 μm region is used for satellite observation of carbon dioxide in the Earth’s atmosphere. Here, we report a Doppler-free spectroscopy study of this band with comb-locked wavelength-modulated cavity-enhanced absorption spectroscopy. Frequencies of 18 transitions with the rotational quantum numbers up to 42 were determined with sub-kHz accuracy, corresponding to a fractional uncertainty at the 10−12 level. With this precision, we revealed an anomalous decrease of the line shift and an increase of the line broadening for the Lamb dips of CO2 in the low-pressure regime compared to values obtained from Doppler-limited spectra at higher pressures.
Reciprocating and flapping motions of unstart shock in a scramjet isolator
Authors: Li Nan
Published: January 2022

Unstable movement of the unstart shock may pose a threat to the safety of a scramjet. The perturbation induced by the unstable movement can also influence the shock structure and the downstream flow, possibly causing a dynamic load on the wall or affecting downstream combustion. Without a thorough analysis of the isolator flow or by ignoring its properties, it is not possible to understand some of the phenomena prevalent in downstream combustion. In this study, two types of instabilities were observed in the unstart shock system. It is shown that if the flow distortion is not severe, the instability in the streamwise direction plays a dominant role. Sequential displacement of the downstream shock was observed in this mode. The time delay between sequential shock motions indicates their response to the movement of the first separation shock. With a highly distorted flow, a flapping mode that resulted in instability in the vertical direction with an asymmetrical effect on the pressures at the walls was observed. In this situation, the shock structure is successively attached to the wall from the head to the tail. By conducting a dynamic mode decomposition analysis, several oscillatory modes, characterized by low-frequency periodicity in the streamwise and vertical directions, were revealed in the shock system. Subsequently, the feasibility of considering the periodical deflection of the incoming flow induced by the significantly unequal amplitudes of shock movements at the two walls as the underlying mechanism for the flapping mode is explored.
Nonaxisymmetry and flow transition in evaporating water drops
Authors: Josyula Tejaswi , Esther Blesso Vidhya Y. , Vasa Nilesh J. , Mahapatra Pallab Sinha , Pattamatta Arvind
Published: January 2022

Understanding the internal flow in evaporating sessile drops is of paramount importance in a myriad of applications such as ink-jet printing, surface patterning, and medical diagnostics. Marangoni flow driven by a gradient in surface tension is an essential internal flow mechanism, whose characteristics in evaporating water drops remain elusive in the literature. Here, by employing infrared thermography and particle image velocimetry, we show that the manifestation of Marangoni flow as a convective cell at the liquid–vapor interface results in a nonaxisymmetric internal flow field. Eventually, during evaporation, the flow transitions to a buoyancy-dominated regime, where an axisymmetric toroidal flow is observed. This transition marks a reversal in the flow along with an order of magnitude decrease in velocity. We corroborate this experimentally observed transition using previously reported analytical and scaling frameworks. Finally, we present hitherto unreported features correlating the three aspects of evaporating water drops, viz., contact line dynamics, thermal field, and internal flow field, which are generally investigated independently.
Heterogeneous thermal conductance of nanoparticle–fluid interfaces: An atomistic nodal approach
Authors: Jiang Mingxuan , Olarte-Plata Juan D. , Bresme Fernando
Published: January 2022

The Interfacial Thermal Conductance (ITC) is a fundamental property of materials and has particular relevance at the nanoscale. The ITC quantifies the thermal resistance between materials of different compositions or between fluids in contact with materials. Furthermore, the ITC determines the rate of cooling/heating of the materials and the temperature drop across the interface. Here, we propose a method to compute local ITCs and temperature drops of nanoparticle–fluid interfaces. Our approach resolves the ITC at the atomic level using the atomic coordinates of the nanomaterial as nodes to compute local thermal transport properties. We obtain high-resolution descriptions of the interfacial thermal transport by combining the atomistic nodal approach, computational geometry techniques, and “computational farming” using non-equilibrium molecular dynamics simulations. We use our method to investigate the ITC of nanoparticle–fluid interfaces as a function of the nanoparticle size and geometry, targeting experimentally relevant structures of gold nanoparticles: capped octagonal rods, cuboctahedrons, decahedrons, rhombic dodecahedrons, cubes, icosahedrons, truncated octahedrons, octahedrons, and spheres. We show that the ITC of these very different geometries varies significantly in different regions of the nanoparticle, increasing generally in the order face < edge < vertex. We show that the ITC of these complex geometries can be accurately described in terms of the local coordination number of the atoms in the nanoparticle surface. Nanoparticle geometries with lower surface coordination numbers feature higher ITCs, and the ITC generally increases with the decreasing particle size.
Ionization state calculation of materials in high energy density system based on an improved calculation method of individual electron accounting model
Authors: Ok Chang-Son , Hong Kwon-Ryong , Jang Paeksan
Published: January 2022

In this paper, an improved calculation method of the individual electron accounting model (IEM) is proposed, and based on it, the ionization state of materials in the high energy density system is calculated. The Newton–Raphson method is introduced to the IEM to establish a method for calculating the ionization state that can ensure high accuracy with a small number of iterations. The method for determining the Zimmerman–More parameters used in this method is established. The reliability of the proposed method is verified through comparison with the calculation results of the Thomas–Fermi model and the BADGER code.
Theoretical and experimental analysis of pulse compression capability in non-linear magnetic transmission line
Authors: Rahman MuhibUr , Wu Ke
Published: January 2022

This paper presents a theoretical and experimental analysis of nonlinear magnetic transmission lines and demonstrates the phenomenon and capability of a simultaneous rise and fall time compression. A theoretical approach is formulated in which a new version of the modified Korteweg–de Vries equation is developed utilizing the Gardner–Morikawa transformation, continuum limit approximation, Toda-lattice approximation, and Mei theory of Maxwellian circuits. The proposed theoretical foundation work is validated through experimental demonstration. The pulse generation in a nonlinear magnetic transmission line is then studied in detail, and the output pulse characteristics are explored under different magnetic field strengths and arbitrary magnetization directions. In particular, output waveforms are analyzed in terms of pulse amplitude, full width half maximum, detailed ringing level, and figure of merit. Magnetic losses that arise in the ferrite material are modeled. It is shown that these losses are responsible for originating dissipative effects, which in turn deteriorate pulse shaping and increase ringing level. The localized disturbance within ferrimagnetic materials is also studied, and its impact on the output waveforms is also discussed. This study can potentially open up a new and fruitful entry to explore magnetic materials and their impacts in the field of ultrafast electronics in parallel with nonlinear electrical transmission lines.
Stronger orientation of state-selected OCS molecules with relative-delay-adjusted nanosecond two-color laser pulses
Authors: Hossain Md. Maruf , Zhang Xiang , Minemoto Shinichirou , Sakai Hirofumi
Published: January 2022

Using the all-optical molecular orientation technique with intense nonresonant two-color laser pulses, stronger molecular orientation |⟨cos θ2D⟩| ∼ 0.34 is achieved by employing the following two strategies: (1) carbonyl sulfide molecules lying in the lower rotational states are selected using a home-built molecular deflector and (2) the rising parts of the two wavelengths of the pump pulse are adjusted by introducing a Michelson-type delay line in the optical path. The achieved degree of molecular orientation is higher than that observed in the proof-of-principle experiment [Oda et al., Phys. Rev. Lett. 104, 213901 (2010)] by about an order of magnitude and the highest ever characterized directly by Coulomb explosion imaging with appropriate probe polarization.
Solitonic natural orbitals in Coulombic systems
Authors: Cioslowski Jerzy , Prątnicki Filip , Strasburger Krzysztof
Published: January 2022

High-accuracy electronic structure calculations on the members of the helium isoelectronic series and the H2 molecule with a stretched bond reveal that the ground-state wavefunctions of these Coulombic systems give rise to natural orbitals (NO) with unusual properties. These solitonic NOs (SoNOs) possess fewer nodes than expected from their small occupation numbers, exhibit substantial spatial localization, and respond (with approximate retention of their shapes) in a paradoxical manner (e.g., by moving away from nuclei upon an increase in the nuclear charge or decrease in the internuclear distance) to changes in the underlying Hamiltonian. An efficient tool for the identification of the SoNOs is provided by an index constructed from two expectation values pertaining to a given NO and the corresponding occupation number. In the case of the helium-like species, the rapid decay of the occupation numbers of the SoNOs with increasing nuclear charge Z is governed by an asymptotic expression that involves the radial positions and spreads of the orbitals. Three s-type SoNOs (with the occupation numbers amounting to only ∼7.9·10−67, 6.8·10−92, and 9.0·10−113 in the case of the helium atom) are predicted to turn into unoccupied NOs at Z equal to ∼2.673, 2.587, and 2.536, respectively. The persistence of the analogous p-type orbital beyond Z = 2 is consistent with the computed properties of the σu-type SoNO of the H2 molecule with a stretched bond. In particular, the profiles of this SoNO along two perpendicular lines bear great resemblance to the radial profiles of its p-type counterpart.
Imaging and measuring the electronic properties of epitaxial graphene with a photoemission electron microscope
Authors: Niefind F. , Bell H. G. , Mai T. , Hight Walker A. R. , Elmquist R. E. , Pookpanratana S.
Published: January 2022

A photoemission electron microscope (PEEM) was recently commissioned at the NIST. To benchmark its capabilities, epitaxial graphene on 4H-SiC (0001) was imaged and analyzed in the PEEM and compared to other complementary imaging techniques. We determine our routine spatial resolution to be about 50 nm. Using the well-known electronic structure of graphene as a reference, we outline a procedure to calibrate our instrument in energy and momenta in the micrometer-angle-resolved photoemission spectroscopy (μ-ARPES). We also determine the energy and momenta resolution to be about 300 meV, 0.08 Å−1 (ky), and 0.2 Å−1 (kx), respectively. We identify distinct regions of the graphene surface based on intensity contrast rising from topographic and electronic contrasts as well as μ-ARPES. These regions are one layer graphene, one SiC buffer layer, and ≥2 layers of graphene (or graphite). These assignments are confirmed using confocal laser scanning microscopy and Raman spectroscopy. Finally, the PEEM instrument had enough sensitivity to observe the flatband in monolayer epitaxial graphene, which we attribute to the presence of compressive strain, −1.2%, in the graphene sample.
The prediction of energy conversion during the self-propelled jumping of multidroplets based on convolutional neural networks
Authors: Dai Liyu , Ding Siyu , Gao Sihang , Hu Zhifeng , Yuan Zhiping , Wu Xiaomin
Published: January 2022

The energy conversion efficiency (the ratio of the maximum jumping kinetic energy to the maximum surface energy released from droplet coalescence) is an essential indicator of the self-propelled jumping of droplets, which determines its value for applications in various fields. In the practical condensation process, the initial states of the multidroplets with different sizes and distributions have a significant effect on the energy conversion efficiency, but the mechanism behind this effect remains unclear. This paper reveals the effect of the initial states of droplets on the energy conversion efficiency of multidroplet jumping (mainly three droplets) from the perspective of energy conversion and the internal flow of the merged droplets. Different initial states will lead to different flow directions of the liquid microclusters inside the merged droplets. The consistency between the flow direction and the jumping direction will affect the energy conversion efficiency. To characterize this effect quantitatively, we construct a machine learning model based on a convolutional neural network to predict the energy conversion efficiency of multidroplet jumping with different initial distribution angles and radius ratios. The input of the neural network is the images of the initial state of the droplets, and the output is the energy conversion efficiency. After training, the neural network can predict the energy conversion efficiency of multidroplet jumping with an arbitrary initial state.
Role of oxygen migration on the thermal stability of the perpendicular magnetic anisotropy in bottom and top structures
Authors: Du Wei , Liu Mengli , Han Fengxuan , Su Hua , Zhang Huaiwu , Liu Bo , Meng Hao , Tang Xiaoli
Published: January 2022

The effect of interfacial oxygen migration on the thermal stability of the perpendicular magnetic anisotropy (PMA) in bottom and top structures was investigated in detail. By controlling the diffusion of thermally activated oxygen atoms, PMA with high thermal stability was achieved in the top structure. Compared with the bottom structure, the range of annealing temperature for which PMA was observed was extended to higher temperature (60 °C higher) via the strong Fe–O bonding in the top structure. Through detailed x-ray photoelectron spectroscopy analyses, the chemical states of different elements in CoFeB/MgO layers and the oxygen atom diffusion were investigated to understand the mechanisms behind the obtained high thermal stability of the PMA. It was found that the absence of thermally activated oxygen atom migration in the top structure is the main reason for the high thermal stability of the PMA. This study provides a promising way to obtain PMA with high thermal stability in CoFeB–MgO-based spintronic devices, which is significant to improve the compatibility of magnetic memories with the semiconductor integrated technology.
All-optical differentiator in frequency domain
Authors: Zhang Wenshuai , Wang Yongsheng , Xu Dingyu , Luo Hailu , Wen Shuangchun
Published: January 2022

Signal processing is a focused topic with communication technologies developing rapidly nowadays. However, optical signal processing methods are not so mature compared to the digital signal processors. Here, we propose an all-optical differentiator in frequency domain designed with fundamental optical elements, which is able to give the first order differentiation of the input signal. A fully theoretical description of the differentiator and its transfer function are demonstrated and discussed. According to experiments, the differentiator is proved reliable and the results match well with simulations. Moreover, an application of the frequency domain differentiator for measuring small time delay changes is also demonstrated and discussed. We believe that this work can give different perspectives of optical signal processing in frequency domain.
Study on the flow-induced vibration of a two-tandem cylinder system in rigid body motion
Authors: Wu Wenbo , Wang Jiasong , Hu Zhongming
Published: January 2022

The flow-induced vibration (FIV) of a cylinder cluster is often observed in subsea pipelines and marine risers. The motion of the cylinder clusters was often modeled as the equation of motion of a particle, which has ignored the torsion freedom. Hence, the answers to the following questions are still unavailable—what are the impacts of torsion on the FIV of a cylinder cluster? Does torsional freedom facilitate the development of new features in FIV? In the present work, the FIV of a two-tandem cylinder system was numerically studied under the consideration of torsional freedom. It was found that six well-defined regimes were formed in the FIV of the cylinder system with the increase in the reduced velocity. The formation of different regimes mainly occurred by the accouplement of two frequencies—the vortex shedding frequency and the natural frequency of the cylinder system. A quirky low frequency dominated the cross-flow vibration at some reduced velocities, significantly magnifying the cross-flow vibration and the torsional vibration. The two cylinders acted as two feet treading water alternatively, enabling the cylinder system to move further on one side at such low frequencies. The characteristics of the amplitudes and frequency responses vs Ur* were qualitatively similar when the stiffness ratio k* was in the range of 10 ≤ k* ≤ 50, where Ur* was the torsional reduced velocity which was defined by the uniform velocity U divided torsional natural frequency frn and diameter of the cylinder D.
Dewetting regimes of condensation droplets in a microgroove
Authors: Wang He , Wu Suchen , Deng Zilong , Liu Xiangdong , Zhang Chengbin
Published: January 2022

This paper describes a numerical investigation of the groove-embedded droplet dewetting process, namely the spontaneous transition from the Wenzel state to the Cassie state, using the multiphase lattice Boltzmann method. Numerical simulations are employed to reproduce the dynamic behaviors of extension, squeezing, rupture, and ejection of condensation droplets in a groove, allowing us to examine how the groove geometry and wettability affect the dewetting process. Our results identify three dewetting regimes, namely retention, partial dewetting, and complete dewetting. As the groove aspect ratio and hydrophilicity decrease, the dewetting regime changes from retention to partial dewetting, and then to complete dewetting. The partial dewetting and complete dewetting are two effective ways for droplet removing. In particular, a groove sidewall with enhanced hydrophobicity is desirable to stimulate the dewetting process.
Impact of interlayer insulator formation methods on HfOx ferroelectricity in the metal–ferroelectric–insulator–semiconductor stack
Authors: Min Kyung Kyu , Kwon Seok Jin , Kim Yeonwoo , Yu Junsu , Lee Jong-Ho , Park Byung-Gook , Kwon Daewoong
Published: January 2022

It has been reported that the HfOx-based metal–ferroelectric–insulator–semiconductor (MFIS) stack is one of the most feasible structures for memory applications in ferroelectric devices. In addition, in MFIS stacks, the formation of a high-quality thin insulator is considered to be a crucial process, because it determines the device performance and reliability. In this study, the effects of different SiO2 thin interfacial layers (ILs) formed by chemical oxidation and atomic layer deposition (ALD) on the ferroelectricity of HfOx were investigated in MFIS stacks. Notably, the IL formation method affected the crystallization temperature of HfOx ferroelectricity. In particular, the chemical oxide IL sample was sufficiently crystallized only at an RTA temperature greater than 800 °C, whereas the ALD oxide IL sample began to undergo a complete ferroelectric phase transition from a low temperature (600 °C). The x-ray analysis verified that the IL formation method affected the initial film state of the HfOx layer by modulating the Hf-O bonding states, resulting in a different temperature dependence for ferroelectricity formation during the subsequent crystallization annealing stage. Consequently, it was confirmed that stable polarization (2Pr > 30 μC/cm2) could be obtained over a wide temperature range (600–800 °C) through IL material engineering; this could facilitate the integration of HfOx-based ferroelectric devices in terms of the heat budget and the application of ferroelectric devices as commercial devices.
The symmetry-preserving mean field condition for electrostatic correlations in bulk
Authors: Hu Zhonghan
Published: January 2022

Accurate simulations of a condensed system of ions or polar molecules are concerned with proper handling of the involved electrostatics. For such a Coulomb system at a charged planar interface, the Coulomb interaction averaged over the lateral directions with preserved symmetry serves as a necessary constraint in building any accurate handling that reconciles a simulated singlet charge density with the corresponding macroscopic charge/dielectric response. At present, this symmetry-preserving mean field (SPMF) condition represented in the reciprocal space is conjectured to be necessary for a simulated bulk system to reproduce correctly the charge structure factor of the macroscopic bulk as well. In this work, we further examine analytically the asymptotic behavior of the charge structure factor at small wavenumbers for an arbitrary charge–charge interaction. In light of our theoretical predictions, simulations with lengths of nearly 0.1 μm are carried out to demonstrate that typical efficient methods violating the SPMF condition, indeed, fail to capture the exact charge correlations at small wavenumbers for both ionic and polar systems. However, for both types of systems, these existing methods can be simply amended to match the SPMF condition and subsequently to precisely probe the electrostatic correlations at all length scales.
Comparative analysis of polaritons in bulk, dielectric slabs, and planar cavities with implications for cavity-modified reactivity
Authors: Vurgaftman Igor , Simpkins Blake S. , Dunkelberger Adam D. , Owrutsky Jeffrey C.
Published: January 2022

We examine closely the differences between the densities of vibrational states of bulk, slab, and cavity polariton modes under weak and moderate inhomogeneous broadening. While existing theoretical treatments are often based on a comparative analysis of “bare” vibrations and cavity polaritons, in the strong-coupling regime, only differences between slab/bulk polaritons on the one hand and cavity polaritons on the other hand are meaningful since “bare” vibrations are not observed experimentally. We find that polaritons in cavities significantly detuned from resonance with molecular transitions at zero in-plane wavevector do not differ appreciably from bulk polaritons in their density of vibrational states. Only cavity polaritons with sufficiently weak inhomogeneous broadening and tuned to resonance near normal incidence display a pronounced density-of-state enhancement. These results shed light on the heretofore puzzling observations of modified chemical reactivity only at zero detuning and supply a new baseline for assessing the explanatory power of proposed theories of cavity-modified chemistry.
Numerical investigation of high-frequency pulsating electrohydrodynamic jet at low electric Bond numbers
Authors: Guan Yin , Wu Shuang , Wang Mengduo , Tian Yu , Yu Chuanpeng , Lai Wuxing , Huang YongAn
Published: January 2022

Electrohydrodynamic jet printing is a highly promising technology for the fabrication of three-dimensional micro/nanoscopic structures, but the advancement of this technology is hindered by the insufficient understanding of many aspects of its mechanisms. Here we conduct a numerical investigation on high-frequency (∼1 kHz) pulsating electrohydrodynamic jet at low electric Bond numbers (Boe = 0.15–0.7). By analyzing the entire jetting process using the voltage distribution, electric charge density, and flow field obtained from the numerical results, we overcome the limitations of experimental approach and demonstrate the influences of electric voltage (Φ), nozzle-to-substrate distance (H), and liquid surface tension coefficient (γ) on the dynamic behaviors and durations of the three jetting stages: (1) cone formation, (2) jetting, and (3) meniscus oscillation. Furthermore, as a measure of the relative significance of the electric force to the surface tension force, the impacts of Boe on the jetting process are also examined. Results show that some critical aspects of the pulsating jetting process are closely related to Boe: (1) the transitional values of Boe between the four observed jetting regimes on the variations of Φ, H, and γ apply to all three parameters; (2) the nondimensionalized Taylor cone length scales with Boe according to a power law; (3) the jetting processes that have similar Boe collapse onto a universal profile. These new findings of pulsating electrohydrodynamic jet provide a useful supplement to the currently inadequate comprehension of the complicated electrohydrodynamic jet printing process.
‘We will have to remember this as teachers’
Authors: Dooly Melinda
Published: January 2022

Applying interaction analysis to transcriptions of online
meetings held weekly over a ten-week period between two groups of
student-teachers, this chapter considers how telecollaboration (also known
as Virtual Exchange) in teacher education can support the development of
teachers’ digital competences and teacher identity through peer-supported
online collaboration. The analysis shows how sustained use of online
collaborative learning allows for moments of alignment and misalignment
(dissonance) that afford learning opportunities for the participants as they
become increasingly participative and cohesive in their online professional
community.