bluuebunny/crossref_metadata_2025 huggingface dataset:
Axial proton probing of magnetic and electric fields inside laser-driven coils
Authors: Peebles J. L. , Davies J. R. , Barnak D. H. , Cracium T. , Bonino M. J. , Betti R.
Published: June 2020

In a laser-driven coil, a laser is used to eject electrons from a plate, which then draws a current through a loop. Diagnosing the field strength, geometry, and conditions within these loops has been one of the primary difficulties in fielding this type of target. In this paper, the diagnostic technique of axial proton probing with a mesh fiducial of a laser-driven coil is demonstrated. Multiple coil types were driven by a 1 ns, 1.25 kJ long pulse beam and probed several times. This technique provides significantly more information than transverse probing on electric- and magnetic-field strength in the region of interest and shows in our experiment complex, non-uniform current path structures and charge distribution.
Design and optimization of nanowire betavoltaic generators
Authors: Wagner D. L. , Novog D. R. , LaPierre R. R.
Published: June 2020

A model used to simulate and optimize the performance of nanowire-based betavoltaic generators is developed. The optimum nanowire array geometry is established for devices made of silicon, gallium arsenide, and gallium phosphide for both nickel-63 and tritium sources by computing the energy capture efficiency for each case. The captured power for nanowire devices is shown to be drastically greater compared to planar betavoltaic generators with maximum improvement factors of approximately 7, 3, 5, and 9 for devices utilizing radioisotope sources of nickel-63, nickel citrate, tritium, and tritiated butyl, respectively. In addition, nanowire devices do not suffer from self-shielding effects, a large limitation in conventional, planar betavoltaics. By coupling the spatial distribution of electron–hole pair generation rate calculated from Monte Carlo simulations and a semiconductor charge-transport model, the diode design is optimized for the maximum power output. The top performing devices, utilizing a tritium source, exhibited an output power of approximately 4, 6, and 2 μW cm−2 for silicon, gallium arsenide, and gallium phosphide, respectively. Overall device efficiencies were found to range from 4% to 10%, surpassing several betavoltaic devices reported in the literature. It was also found that, contrary to the traditional betavoltaic design, semiconductors with higher bandgaps do not necessarily result in the best device performance due to additional material parameters, such as surface recombination velocity. Potential improvements for nanowire-based betavoltaic generators are suggested for additional investigation.
Plasma formation and ablation dynamics of stainless steel cylindrical liner
Authors: Zhang Daoyuan , Wu Jian , Chen Ziwei , Lu Yihan , Shi Huantong , Wang Guanqiong , Xiao Delong , Ding Ning , Li Xingwen , Jia Shenli , Qiu Aici
Published: June 2020

Using laser shadowgraphy and interferometry on a Qin-1 facility, the initial plasma formation and dynamics of an exploding stainless steel liner were investigated. To obtain the absolute electron density distribution inside the liner, we established continuous wave laser interferometry using a streak camera to measure the shift in the fringes over time. Plasma is generated at the interior wall and flows toward the center with a velocity of ∼100 km/s, thus forming a column with higher density by accumulation. Simultaneously, a high-density plasma layer is formed near the interior surface and this layer flows toward the center at approximately 10 km/s. In addition, magnetohydrodynamics (MHD) instabilities were observed at the exterior surface using side-on laser shadow images at a much later time (∼400 ns). The growth in the amplitude and the wavelength of the perturbations were then analyzed. An MHD simulation of this process was then established to demonstrate that the high-density plasma layer carries part of the current and that it flows within the 10 km/s range after comparison with the experimental results. Finally, we measured the voltage and derived the change in the inductance. The results prove that part of the current flows through the center plasma column, which then influences the subsequent plasma flow.
Good Wannier bases in Hilbert modules associated to topological insulators
Authors: Ludewig Matthias , Thiang Guo Chuan
Published: June 2020

For a large class of physically relevant operators on a manifold with discrete group action, we prove general results on the (non-)existence of a basis of well-localized Wannier functions for their spectral subspaces. This turns out to be equivalent to the freeness of a certain Hilbert module over the group C*-algebra canonically associated with the spectral subspace. This brings into play K-theoretic methods and justifies their importance as invariants of topological insulators in physics.
Recurrence analysis of slow–fast systems
Authors: Kasthuri Praveen , Pavithran Induja , Krishnan Abin , Pawar Samadhan A. , Sujith R. I. , Gejji Rohan , Anderson William , Marwan Norbert , Kurths Jürgen
Published: June 2020

Many complex systems exhibit periodic oscillations comprising slow–fast timescales. In such slow–fast systems, the slow and fast timescales compete to determine the dynamics. In this study, we perform a recurrence analysis on simulated signals from paradigmatic model systems as well as signals obtained from experiments, each of which exhibit slow–fast oscillations. We find that slow–fast systems exhibit characteristic patterns along the diagonal lines in the corresponding recurrence plot (RP). We discern that the hairpin trajectories in the phase space lead to the formation of line segments perpendicular to the diagonal line in the RP for a periodic signal. Next, we compute the recurrence networks (RNs) of these slow–fast systems and uncover that they contain additional features such as clustering and protrusions on top of the closed-ring structure. We show that slow–fast systems and single timescale systems can be distinguished by computing the distance between consecutive state points on the phase space trajectory and the degree of the nodes in the RNs. Such a recurrence analysis substantially strengthens our understanding of slow–fast systems, which do not have any accepted functional forms.
Sunlight does not always speed up evaporation
Authors: Bandari Anashe
Published: June 2020

Counterintuitively, researchers find that in comparison to natural conditions, sunlight initially causes a reduction in droplet evaporation prior to accelerating it.
Influence of injection parameters on fueling efficiency of supersonic molecular beam injection into turbulent fusion plasmas
Authors: Avdeeva G. , Naulin V. , Nielsen A. H. , Juul Rasmussen J. , Thrysøe A. S.
Published: June 2020

The fueling efficiency of supersonic molecular beam injection (SMBI) depends on injection parameters. In this article, we report on simulations of SMBI into turbulent edge fusion plasmas. Density continuity equations, which describe the dynamics of molecules and Franck-Condon atoms, are coupled with the plasma equations in the hot-edge-sol-electrostatic (HESEL) drift-fluid model. Numerical simulations, with parameters relevant to experimental conditions, are performed in order to investigate the dependency of the fueling efficiency of SMBI on the molecular beam density, velocity, and beam width. In all conditions, the efficiency grows with the increase in the molecular beam velocity. The variation in efficiency with respect to the beam density depends on the plasma pressure and the ratio of the density source, produced by ionization of neutrals, to the plasma density source provided by core fueling. The effect of the molecular beam width is pronounced only if the beam density is high and the plasma, into which the beam is injected, is relatively dense and hot. The influence of plasma fluctuations on SMBI is weak; however, a strong neutral injection leads to suppression of a turbulence transport due to relaxation of pressure gradient profiles.
A first-principles prediction of an sp3 carbon allotrope comprising four-, five-, six-, and eight-member rings
Authors: Ma Jian-Li , Wu Yi-Long , Song Dan-Li , Fu Zhi-Fen , Zhou Jian-Ping , Liu Peng , Zhu Xuan-Min , Wei Qun
Published: June 2020

A superhard carbon phase with Pmmm (D2h1, 47) symmetry is predicted by using a recently developed particle swarm optimization method for searching for crystal structures. The carbon phase is an orthorhombic crystal system that contains 16 atoms per unit cell, named oC16, which has an all-sp3-hybridized bonding network and contains a large cavity. oC16 has a distinct topology, including zigzag four-, five-, six-, and eightfold carbon rings. The dynamic, elastic, and electronic properties of oC16 are investigated by first-principles calculations, and the results show that oC16 is more energetically stable than the experimentally synthesized T-carbon, BC8, and BC12. The phonon spectra and elastic constants confirm its dynamical and mechanical stability at zero pressure, respectively. The calculated bulk moduli and hardness indicate that oC16 is an ultra-incompressible and superhard material. Analyzing its electronic band structure reveals that oC16 has insulation characteristics with an indirect bandgap of 4.42 eV. Also investigated is how the elastic moduli of the oC16 phase depend on the crystal orientation. Because of its superhard and porous properties, the potential uses of oC16 include hydrogen storage, molecular sieves, coating, and tools for cutting, polishing, and grinding.
High thermoelectric power factor of p-type amorphous silicon thin films dispersed with ultrafine silicon nanocrystals
Authors: Pham Ngan Hoang , Vallin Örjan , Panda J. , Venkata Kamalakar M. , Guo Junji , Luo Jun , Wen Chenyu , Zhang Shi-Li , Zhang Zhi-Bin
Published: June 2020

Silicon, a candidate as an abundant-element thermoelectric material for low-temperature thermal energy scavenging applications, generally suffers from rather low thermoelectric efficiency. One viable solution to enhancing the efficiency is to boost the power factor (PF) of amorphous silicon (a-Si) while keeping the thermal conductivity sufficiently low. In this work, we report that PF >1 m Wm−1 K−2 is achievable for boron-implanted p-type a-Si films dispersed with ultrafine crystals realized by annealing with temperatures ≤600 °C. Annealing at 550 °C initiates crystallization with sub-5-nm nanocrystals embedded in the a-Si matrix. The resultant thin films remain highly resistive and thus yield a low PF. Annealing at 600 °C approximately doubles the density of the sub-5-nm nanocrystals with a bimodal size distribution characteristic and accordingly reduces the fraction of the amorphous phase in the films. Consequently, a dramatically enhanced electrical conductivity up to 104 S/m and hence PF > 1 m Wm−1 K−2 measured at room temperature are achieved. The results show the great potential of silicon in large-scale thermoelectric applications and establish a route toward high-performance energy harvesting and cooling based on silicon thermoelectrics.
Data-driven modeling of the wake behind a wind turbine array
Authors: Ali Naseem , Cal Raúl Bayoán
Published: June 2020

The wake flow in a wind turbine array boundary layer is described using the Koopman operator. Dynamics of the flow are decomposed into the linear and forcing terms, and the low-energy delay coordinates are revealed. The rare events show the non-Gaussian long tails that capture the switching and bursting phenomena. The near-wake region shows the incoherent phase space region, where the dynamics are strongly nonlinear. The far-wake region is marked with the small non-Gaussian forcing term, and the dynamics are largely governed by linear dynamics. The data-driven predictive model is built based on the Hankel-based dynamic mode decomposition and treats the nonlinear state of forcing term as external actuation. The model forecasts the evolution of the flow field for short-term timescales. The mean relative errors between the predictive and test fluctuating velocities are approximately 15%.
Identifying highly influential nodes in multilayer networks based on global propagation
Authors: Li Xin , Zhang Xue , Zhao Chengli , Yi Dongyun , Li Guochen
Published: June 2020

Based on percolation theory and the independent cascade model, this paper considers the selection of the optimal propagation source when the propagation probability is greater than the percolation threshold. First, based on the percolation characteristics of real networks, this paper presents an iterative algorithm of linear complexity to solve the probability of the propagation source transmitting information to the network's giant component, that is, the global propagation probability. Compared with the previous multiple local simulation algorithm, this algorithm eliminates random errors and significantly reduces the operation time. A sufficient and necessary condition is provided, and it is proved that the final propagation range of the propagation source obeys the bimodal distribution. Based on this sufficient and necessary condition, we extend the efficient iterative algorithm proposed in this article to multi-layer networks and find that for two-layer networks, the final propagation range of the propagation source follows a four-peak distribution. Through iterations and calculations, the probability of each peak and the number of nodes included can be directly obtained, and the propagation expectations of the nodes in the multi-layer network can then be calculated, which can result in a better ranking of the propagation influence of the nodes. In addition, to maximize the influence of multi-propagation sources, this paper also presents a de-overlapping method, which has evident advantages over traditional methods.
Charge transport properties in CdZnTeSe semiconductor room-temperature γ-ray detectors
Authors: Chaudhuri Sandeep K. , Sajjad Mohsin , Kleppinger Joshua W. , Mandal Krishna C.
Published: June 2020

CdxZn1−xTeySe1−y (CZTS) has emerged as a next-generation compound semiconductor for high energy gamma-ray detection. In the present study, we report for the first time the hole transport property measurements in CZTS based gamma-ray detectors in the planar configuration. Current–voltage measurements revealed a bulk resistivity of ∼5 × 108 Ω cm and the fabricated detectors produced well-resolved 5486 keV alpha particle peaks, for both electrons and holes drifting alike, when pulse-height spectra (PHS) were recorded using a 241Am radiation source. The PHS measurements were enabled to measure the charge transport properties for both the charge carriers. The mobility–lifetime product (μτ) for electrons and holes was calculated to be 6.4 × 10−4 cm2 V−1 and 8.5 × 10−5 cm2 V−1, respectively, using a single polarity Hecht plot regression method. The pre-amplifier pulses were also recorded and processed digitally to obtain electron and hole drift mobilities of 692 cm2 V−1 s−1 and 55 cm2 V−1 s−1, respectively, using a time-of-flight method. The measured transport properties indicated the hole lifetime to be greater than the electron lifetime by a factor of ∼1.5. Gamma-ray PHS were recorded using fabricated detectors that showed tailing of the 662 keV photopeak due to hole trapping effects. Depth dependent PHS were digitally generated from 2D biparametric plots to reveal the effects of hole trapping on the gamma PHS at different detector depths. Digital correction procedures were applied to generate well-resolved PHS with an energy resolution of ∼2% for 662 keV γ-rays.
Severe wave run-ups on fixed surface-piercing square column under focused waves
Authors: Fang Zhichao , Xiao Longfei , Wei Handi , Liu Mingyue , Guo Yinghao
Published: June 2020

Severe wave run-ups on a surface-piercing column leading to strong uprush water jets may cause unexpected impact loads on offshore structures. To reveal the underlying mechanism related to the complicated wave–column interaction, this paper investigates the occurrence and evolution of wave run-ups on a fixed surface-piercing square column under focused waves experimentally and numerically by comparing the wave run-up profiles, wave loads on the column, and velocity and pressure fields in the cases of different peak periods and steepnesses. The results manifested that the wave run-up under a very steep focused wave is significantly influenced by the localized nonlinear interaction between the wave crest and the uplifted water mound in front of the column and experiences a different regime from those primarily due to nonlinear wave diffraction. In the cases of breaking or nearly breaking focused waves, the sudden change in the fluid velocity on the wave crest when impacting on the uplifted water mound dramatically increases the peak value and gradient of dynamic pressure in the adjacent region and hence results in critical impact load on the column and strong accelerating effect of the uprush flow. Additionally, a larger peak period can further increase the thickness (or volume) of the uprush flow, potentially increasing the damage risk of offshore structures.
Adjustable super-resolution microscopy with diffractive spot array illumination
Authors: Xu Ning , Liu Guoxuan , Tan Qiaofeng
Published: June 2020

Diffractive super-resolution spot arrays offer the possibility of adjustable super-resolution microscopic imaging. By inserting a phase-only diffractive optical element (DOE) into the illumination system of a standard microscope, super-resolution information of the sample can be obtained by spots. Here, we report an adjustable super-resolution microscopy (ASM) that the imaging resolution and the number of spot arrays can be adjusted by DOEs. The results of 3 × 3 and 5 × 5 spot arrays with 50% and 70% of the Airy spot size are, respectively, realized to support the flexibility of the ASM. The resolution test target was used as a sample to show the ASM can achieve about double-resolution experimentally, illuminated by a uniform 3 × 3 spot array with 50% of the Airy spot size under a small numerical aperture objective. Moreover, imaging of cellular mitochondria was performed, substantially realized resolution beyond the diffraction limit. The ability to adjust the super-resolution of microscopy using DOEs is of great importance for further nanoscale imaging.
Electron plasma wave Thomson scattering on laboratory plasma jets
Authors: Banasek J. T. , Rocco S. V. R. , Potter W. M. , Lavine E. S. , Kusse B. R. , Hammer D. A.
Published: June 2020

Plasma jets created from a 15 μm thick Al foil on a 1 MA pulsed power machine were studied using a new electron plasma wave (EPW) Thomson scattering system in conjunction with previously developed ion acoustic wave (IAW) Thomson scattering and interferometry. These diagnostics give multiple ways of measuring the electron temperature and density of the jet. Analysis of the EPW feature found the on-axis density of the jet to be between 5×1018 and 1.4×1019 cm−3, which either matched or was higher than interferometry measurements. Outside of the jet, both of these diagnostics measured a density of 7×1017 cm−3. On one shot, the EPW spectral feature showed two pairs of peaks within a 250 μm scattering length on the edge of the jet, which shows that the boundary of the jet ∼1 mm radius jet is ≲ 0.1 mm. While electron temperature measurements of the plasma jet are complicated by the probe beam producing inverse bremsstrahlung heating of the jet, comparison of the electron temperature measured between IAW and EPW Thomson scattering showed the EPW feature to imply significantly higher electron temperatures than the IAW feature (e.g., 160 eV vs 70 eV in one case). Various sources of this discrepancy (for example, density gradients, collisions, and a lag in ionization) and their impact on the plasma are discussed.
Self-assembled epitaxial metal–semiconductor nanostructures with enhanced GeSi quantum dot luminescence
Authors: Zinovyev V. A. , Zinovieva A. F. , Nenashev A. V. , Dvurechenskii A. V. , Katsuba A. V. , Borodavchenko O. M. , Zhivulko V. D. , Mudryi A. V.
Published: June 2020

Hybrid structures containing Ag nanoparticles and GeSi quantum dots were developed using the self-organization of metal nanoislands on the surface of a strained semiconductor structure. The enhanced photoluminescence from GeSi quantum dots (QDs) coupled with Ag nanoislands was obtained. Ag nanoislands epitaxially grown on top of the multilayered structures with GeSi QDs support a surface plasmon resonance that can be tuned to the QD emission wavelength by changing Ag nanoparticle parameters. The numerical modeling of surface plasmon resonance allows attributing this effect to the increase of the recombination rate due to the coupling of QD emitters with Ag nanoislands.
Development of nuclear basis sets for multicomponent quantum chemistry methods
Authors: Yu Qi , Pavošević Fabijan , Hammes-Schiffer Sharon
Published: June 2020

The nuclear–electronic orbital (NEO) framework provides a practical approach for directly incorporating nuclear quantum effects and non-Born–Oppenheimer effects of specified nuclei, typically protons, into quantum chemistry calculations. Multicomponent wave function based methods, such as NEO coupled cluster singles and doubles, and multicomponent density functional theory (DFT), such as NEO-DFT, require the appropriate selection of electronic and nuclear basis sets. Although a wide array of electronic basis sets are available, systematically developed nuclear basis sets that balance accuracy and efficiency have been lacking. Herein, a series of nuclear basis sets are developed and shown to be accurate and efficient for describing both ground and excited state properties of multicomponent systems in which electrons and specified protons are treated quantum mechanically. Three series of Gaussian-type nuclear basis sets, denoted PB4, PB5, and PB6, are developed with varying levels of angular momentum. A machine-learning optimization procedure relying on the Gaussian process regression method is utilized to accelerate the optimization process. The basis sets are validated in terms of predictions of ground state energies, proton densities, proton affinities, and proton vibrational excitation energies, allowing the user to select the desired balance between accuracy and efficiency for the properties of interest. These nuclear basis sets will enhance the tractability of NEO methods for applications to a wide range of chemical systems.
Infinite switch simulated tempering in force (FISST)
Authors: Hartmann Michael J. , Singh Yuvraj , Vanden-Eijnden Eric , Hocky Glen M.
Published: June 2020

Many proteins in cells are capable of sensing and responding to piconewton-scale forces, a regime in which conformational changes are small but significant for biological processes. In order to efficiently and effectively sample the response of these proteins to small forces, enhanced sampling techniques will be required. In this work, we derive, implement, and evaluate an efficient method to simultaneously sample the result of applying any constant pulling force within a specified range to a molecular system of interest. We start from simulated tempering in force, whereby force is added as a linear bias on a collective variable to the system’s Hamiltonian, and the coefficient is taken as a continuous auxiliary degree of freedom. We derive a formula for an average collective-variable-dependent force, which depends on a set of weights learned on-the-fly throughout a simulation, that reflect the limit where force varies infinitely quickly. Simulation data can then be used to retroactively compute averages of any observable at any force within the specified range. This technique is based on recent work deriving similar equations for infinite switch simulated tempering in temperature, which showed that the infinite switch limit is the most efficient for sampling. Here, we demonstrate that our method accurately samples molecular systems at all forces within a user defined force range simultaneously and show how it can serve as an enhanced sampling tool for cases where the pulling direction destabilizes states that have low free-energy at zero-force. This method is implemented in and freely distributed with the PLUMED open-source sampling library, and hence can be readily applied to problems using a wide range of molecular dynamics software packages.
Experimental determination of the thermal, turbulent, and rotational ion motion and magnetic field profiles in imploding plasmas
Authors: Maron Yitzhak
Published: June 2020

A tutorial is presented on advances in spectroscopic diagnostic methods developed for measuring key plasma properties in pulsed-power systems such as Z-pinches, magnetized-plasma compression devices, ion and electron diodes, and plasma switches. The parameters measured include the true ion temperature in Z-pinch implosions, which led to a discovery that much of the ion kinetic energy at stagnation is stored in hydrodynamic rather than in thermal motion. This observation contributed a new important insight into the understanding of the ion thermalization at stagnation and stimulated further investigations of turbulence at stagnation, discussed here too. The second part of this tutorial is devoted to the development of measurements for magnetic-field distributions in Z-pinches and in other pulsed-power systems, as well as their use in studying the plasma dynamics, resistivity, and pressure and energy balance. The latter study raises intriguing questions on the implosion process. In particular, in Z-pinches, the current during stagnation was found to largely flow at relatively large radii, outside the stagnation region. The magnetic-field measurements also enable investigations into the compression of a pre-magnetized cylindrical plasma that uncover striking phenomena related to the current flow, where the current was found to redistribute toward the outer regions during the implosion. Observation of the rotation of the magnetized plasma is also discussed. Finally, experimental and theoretical investigations of a non-diffusive fast penetration of magnetic field into a low-density plasma, including its effect on the plasma dynamics, are described.
Available energy from diffusive and reversible phase space rearrangements
Authors: Kolmes E. J. , Helander P. , Fisch N. J.
Published: June 2020

Rearranging the six-dimensional phase space of particles in plasma can release energy. The rearrangement may happen through the application of electric and magnetic fields, subject to various constraints. The maximum energy that can be released through a rearrangement of a distribution of particles can be called its available or free energy. Rearrangement subject to phase space volume conservation leads to the classic Gardner free energy. Less free energy is available when constraints are applied, such as respecting conserved quantities. Also, less energy is available if particles can only be diffused in phase-space from regions of high phase-space density to regions of lower phase-space density. The least amount of free energy is available if particles can only be diffused in phase space, while conserved quantities still need to be respected.
Light-induced degradation and self-healing inside CH3NH3PbI3-based solar cells
Authors: Liu Xiaoliang , Han Qiang , Liu Yufei , Xie Chengyi , Yang Chenggang , Niu Dongmei , Li Youzhen , Wang Huanyou , Xia Lixin , Yuan Yongbo , Gao Yongli
Published: June 2020

CH3NH3PbI3 (MAPbI3)-based perovskite solar cells (PSCs) with special hole and electron transport layers (HTL and ETL) were prepared to study their light-induced degradation. Obvious degradation was observed under initial light exposure not only at the device level but also at the film morphology and electronic structure level. Device performance parameters, such as short-circuit current (JSC), power conversion efficiency, fill factor, and hysteresis effect, were aggravated with an initial light exposure of less than ∼8 h at 1 sun intensity. Meanwhile, the deteriorated crystallinity and electronic structure of the MAPbI3 film were also detected with x-ray diffraction, ultraviolet photoelectron spectroscopy, and UV-Visible absorption spectroscopy. The observed degradation is rationally related to the light-induced decomposition of MAPbI3. However, the degradation can be partly recovered with the following light exposure resulting in self-healing of the devices and MAPbI3 films. The self-healing behavior should be ascribed to the conversion of decomposition products back to MAPbI3, because the intermediates are wrapped tightly in the photoactive layer by the compact coverlayers of HTLs and ETLs and some reversible reactions occur consequently. The mechanism of self-healing is discussed by introducing the trapped states derived from ion migration. The PSCs prepared here imply a good optical stability and thus a good performance facilitated by tight wrapping of the active MAPbI3.
Nonlinear simulation of feedback instability using gyrofluid model of magnetosphere
Authors: Nishimura Seiya
Published: June 2020

The feedback instability occurs in a coupling system of the magnetosphere and the ionosphere and is a theoretical model explaining spontaneous structure formation of the quiet aurora. In this study, we perform a nonlinear simulation of the feedback instability using a gyrofluid model of the magnetosphere. Using the gyrofluid model makes it possible to properly discuss kinetic effects, such as the finite Larmor radius effect and the electron Landau damping, on nonlinear evolution of the feedback instability. In simulation results, it is observed that nonlinear saturation is reached when linearly unstable modes grow sufficiently. In a nonlinear saturation phase, vorticity in a plane perpendicular to a magnetic field has a complex structure, changing every moment. In addition, an energy flux from the ionosphere and energy dissipation due to the electron Landau damping are balanced in the nonlinear saturation phase. It is newly found that the process where generation of various modes by nonlinear coupling and dissipation of them by the electron Landau damping is indispensable for the nonlinear saturation of the feedback instability.
Dynamics of bubbles in cavitation cloud based on lattice model
Authors: Zhao Guoying , Chen Weizhong , Tao Feng , Zhang Lingling , Wu Yaorong
Published: June 2020

A lattice model is introduced to deal with the dynamics of bubbles in cavitation cloud driven by ultrasound, which makes it possible to extend the study of a finite number of bubbles to cloud with an infinite number of bubbles. In this model, the arrangement of bubbles in cloud is assumed to be a cubic lattice. The central bubble in one lattice cell is representative of all the bubbles in cloud. The numerical simulation shows that the bubble in cloud can be severely suppressed by other bubbles under a cubic lattice structure. An interesting phenomenon is found that the maximum radius of bubbles would be saturated when the driving amplitude exceeds a threshold in cavitation cloud, which makes it easy to understand that the sonoluminescence in a single bubble is always brighter than that in cloud.
Experimental study of the evolution of water-entry cavity bubbles behind a hydrophobic sphere
Authors: Zhang Q. , Zong Z. , Sun T. Z. , Chen Z. Y. , Li H. T.
Published: June 2020

This paper describes an experimental investigation of the cavity evolution and shedding wake behind a hydrophobic sphere during the water-entry process. Two distinct shedding phenomena are confirmed by varying the impact velocity and sphere size: regular air-bubble shedding and unstable air-cloud shedding. Both of these modes are highly dependent on the Weber and Bond numbers. Under the air-bubble shedding mode, approximately periodic big bubble shedding and low-frequency oscillation signals are observed. The relationship between big bubble shedding events and the corresponding acoustic signals is derived, and an empirical method for predicting the shedding period is proposed. The in-phase relationship between small bubble shedding and cavity rippling is confirmed, and we refer to the cavity shedding phenomenon as “acoustic” shedding. Unlike the observations of air-bubble shedding, the air-cloud shedding mode produces a group of disordered small bubbles from the rear of the cavity. Moreover, the cavity seal type has a significant effect on the cavity shedding mode. A deep seal always promotes the onset of air-cloud shedding, whereas surface seals with relatively low Bond numbers result in the air-bubble shedding mode. A surface seal suppresses resonance in the cavity volume. By observing the cavity motion, we find that air-cloud shedding is always accompanied by severe cavity resonance and a rapid decrease in cavity length. Under the air-bubble shedding mode, the cavity motion exhibits relatively weak oscillations.
Numerical simulation of droplet impact on vibrating low-adhesion surfaces
Authors: Moradi Mostafa , Rahimian Mohammad Hassan , Chini Seyed Farshid
Published: June 2020

The impact of droplets on low-adhesion solid surfaces vibrating in the vertical direction was numerically investigated. An axisymmetric multiphase lattice Boltzmann model capable of handling high density and viscosity ratios was implemented to simulate the impact. The effects of vibration parameters on the spreading, contact time, and droplet rebound velocity were addressed. According to the results, the phase angle of the surface vibration is the most dominant factor in determining the dynamics of the droplet upon impact. The contact time generally increases when the surface is vibrated. However, for a certain range of phase angles, the contact time can decrease, as compared to the stationary surface. The rebound velocity also shows a strong dependence on the vibration frequency and phase angle. For droplets with higher impact velocities, the surface vibration becomes a less important factor, whereas on surfaces with lower contact angles, the impact dynamics are much more heavily affected by the surface vibration. The rebound velocity is also heavily affected by surface vibration and varies depending on the frequency and phase angle. This study offers insights into the physics of droplet impact upon vibrating surfaces, which can be utilized to improve surface wettability control in applications where vibration is present.
Interface chemistry of pristine TiN/La:Hf0.5Zr0.5O2 capacitors
Authors: Hamouda W. , Lubin C. , Ueda S. , Yamashita Y. , Renault O. , Mehmood F. , Mikolajick T. , Schroeder U. , Negrea R. , Barrett N.
Published: June 2020

We present a hard and soft x-ray photoelectron spectroscopy study of the interface chemistry in pristine TiN/La-doped Hf0.5Zr0.5O2/TiN capacitors. An oxynitride phase (∼1.3 nm) is formed at the top interface, while a TiO2−δ phase was detected near the bottom interface. The oxygen vacancy (VO) concentration is higher at the top interface than in the film due to oxygen scavenging by the top electrode. The VO concentration was also found to increase from ∼1.5 to 1.9 × 1020 cm−3 when increasing La doping from 1.7 to 2.7 mol. %. Two La dopants are compensated by the formation of one positively charged VO.
Does sunlight always accelerate water droplet evaporation?
Authors: Yu Xiongjiang , Xu Jinliang
Published: June 2020

We investigate droplet evaporation, which is a natural phenomenon but the mechanism is not well understood. We are surprised to find that sunlight irradiation does not always enhance droplet evaporation, which is against the common sense that “Sun accelerates water evaporation.” This is true at least for short-time evaporation. A whole droplet lifetime consists of two regimes of evaporation: a light induced deterioration regime and an acceleration regime. The deterioration regime is explained by the decreased temperature difference from the droplet bottom to apex, weakening Marangoni flow to hinder conduction heat transfer from the substrate to the droplet. The enhanced regime is explained by the reduced light energy reflection via the droplet surface. The substrate conduction heat transfer and radiation heat transfer of light are coupled to dominate evaporation. The two mechanisms create opposite contributions, resulting in a constant evaporation rate for sunlight irradiation on a droplet. However, natural light decreases the evaporation rate vs time. Hence, evaporation rates with and without sunlight irradiation cross at a specific time. Our work enhances the fundamental understanding of droplet evaporation and provides a useful guideline for efficient solar energy utilization.
Study on the non-equilibrium temperature behavior of normal shock waves and the bulk viscosity
Authors: Ohr Young Gie
Published: June 2020

The abnormality of small overshoot in the temperature profile of strong normal shock waves has been resolved, and the bulk viscosity of dilute monatomic gases cannot be ignored. By introducing the total energy conservation equation rather than the internal energy equation, an equation for the non-equilibrium temperature has been suggested. The postulated temperature equation gives a monotonically increasing profile of Monte Carlo data. The Navier–Stokes approximation derives shock equations in one differential equation and one algebraic equation and gives that the ratio of the bulk viscosity to the shear viscosity is equal to 1/15 for dilute monatomic gases.
Polarization-resolved Er emission in Er doped GaN bulk crystals
Authors: Sun Z. Y. , Gong H. L. , Yan Y. Q. , Smith T. B. , Li J. , Lin J. Y. , Jiang H. X.
Published: June 2020

Erbium-doped GaN (Er:GaN) quasi-bulk crystals are emerging as a promising novel gain medium for high energy lasers emitting at the retina-safe wavelength window of 1.5 μm. We report the polarization-resolved photoluminescence (PL) emission spectroscopy studies, which revealed that the pumping efficiency with the excitation polarization parallel to the c-axis of GaN (E⇀||c⇀) is significantly higher than that with the excitation polarization perpendicular to the c-axis of GaN (E⇀⊥c⇀). This phenomenon is a direct consequence of the inherent polar wurtzite GaN lattice, giving rise to a net local field, surrounding each Er ion, along the c-axis of GaN. The temperature dependent behaviors of the PL emission spectra were explained in terms of the Boltzmann population distributions among sublevels within the 4I15/2 ground state and the 4I13/2 first excited state of Er3+ in GaN, thereby providing an improved understanding regarding the origin of the dominant emission lines observed near 1.5 μm. The results suggested that the polarization field in GaN can be exploited to enhance the effective Er excitation cross section by manipulating the polarization of the excitation light source.
Statistical quantum mechanical approach to diatom–diatom capture dynamics and application to ultracold KRb + KRb reaction
Authors: Yang Dongzheng , Huang Jing , Hu Xixi , Xie Daiqian , Guo Hua
Published: June 2020

A general and rigorous quantum method is proposed for studying capture dynamics between two diatomic molecules in full dimensionality. By solving the time-independent Schrödinger equation with proper boundary conditions, this method is ideally suited for studying quantum dynamics of cold and ultracold reactions. To illustrate its applicability, the capture dynamics between ultracold KRb molecules is characterized in full six dimensions for the first time using a first-principles based long-range interaction potential. The calculated capture rates for collisions involving distinguishable and indistinguishable 40K87Rb molecules are in good agreement with the experiment and exhibit clear Wigner threshold behaviors. Predictions for ultracold collisions between internally excited 40K87Rb suggest minor changes in the loss rate, consistent with experimental observations in similar systems.
Proteomic profiling uncovered the cytosolic superoxide dismutase BsSOD1 associated with plant defence in the herbal orchid Bletilla striata
Authors: Lu Bao-Wei , An Feng-Xia , Cao Liang-Jing , Yang Yong-Jian , Liu Peng-Ming , Wang Xuan , Yang Bao-Liang , Zhang Yu-Lei , Ding Yan-Feng , Liu Jun
Published: June 2020

The herbal orchid Bletilla striata (Thunb.) Rchb.f. has a long cultivation history and has been widely used in medicines and cosmetics. The fungal infection leaf blight (LB) seriously threatens B. striata cultivation. Here, we systemically collected wild B. striata accessions and isolated the accessions with strong resistance against LB. We carried out proteomic profiling analysis of LB-resistant and LB-susceptible accessions, and identified a large number of differentially expressed proteins with significant gene ontology enrichment for ‘oxidoreductase activity.’ Of the proteins identified in the reactive oxygen species signalling pathway, the protein abundance of the Cu–Zn superoxide dismutase BsSOD1 and its gene expression level were higher in LB-resistant accessions than in LB-susceptible lines. Transient expression of the dismutase fused with yellow fluorescent protein determined that its subcellular localisation is in the cytoplasm. Our study provides new insights into the molecular markers associated with fungal infection in B. striata.
Mycorrhiza induced resistance (MIR): a defence developed through synergistic engagement of phytohormones, metabolites and rhizosphere
Authors: Kadam Swapnil B. , Pable Anupama A. , Barvkar Vitthal T.
Published: June 2020

Plants get phosphorus, water and other soil nutrients at the cost of sugar through mycorrhizal symbiotic association. A common mycorrhizal network (CMN) – a dense network of mycorrhizal hyphae – provides a passage for exchange of chemicals and signals between the plants sharing CMN. Mycorrhisation impact plants at hormonal, physiological and metabolic level and successful symbiosis also regulates ecology of the plant rhizosphere. Apart from nutritional benefits, mycorrhisation provides an induced resistance to the plants known as mycorrhiza induced resistance (MIR). MIR is effective against soil as well as foliar pathogens and pest insects. In this review, molecular mechanisms underlying MIR such as role of phytohormones, their cross talk and priming effect are discussed. Evidence of MIR against economically important pathogens and pest insects in different plants is summarised. Mycorrhiza induces many plant secondary metabolites, many of which have a role in plant defence. Involvement of these secondary metabolites in mycorrhisation and their putative role in MIR are further reviewed. Controversies about MIR are also briefly discussed in order to provide insights on the scope for research about MIR. We have further extended our review with an open ended discussion about the possibilities for transgenerational MIR.
The interplay between chromophore and protein determines the extended excited state dynamics in a single-domain phytochrome
Authors: Slavov Chavdar , Fischer Tobias , Barnoy Avishai , Shin Heewhan , Rao Aditya G. , Wiebeler Christian , Zeng Xiaoli , Sun Yafang , Xu Qianzhao , Gutt Alexander , Zhao Kai-Hong , Gärtner Wolfgang , Yang Xiaojing , Schapiro Igor , Wachtveitl Josef
Published: June 2020

Significance

Bilin-binding photoreceptors are light-signaling proteins that mediate various processes from photomorphogenesis, phototaxis, chromatic acclimation, to photosynthesis. They are also promising tunable optical agents for use in optogenetics and superresolution microscopy. Using an integrated approach of crystallography, spectroscopy, and QM/MM calculations, this work examines the ultrafast dynamics of a photoactive single-domain phytochrome. Our work reveals in detail the critical role of the protein environment in defining the excited state lifetime and thereby the quantum efficiency of the bilin photoisomerization. This insight provides design principles for engineering of bilin-based photoreceptors for biotechnological and medical applications.
Functional analysis of the OsNPF4.5 nitrate transporter reveals a conserved mycorrhizal pathway of nitrogen acquisition in plants
Authors: Wang Shuangshuang , Chen Aiqun , Xie Kun , Yang Xiaofeng , Luo Zhenzhen , Chen Jiadong , Zeng Dechao , Ren Yuhan , Yang Congfan , Wang Lingxiao , Feng Huimin , López-Arredondo Damar Lizbeth , Herrera-Estrella Luis Rafael , Xu Guohua
Published: June 2020

Significance

Low availability of nitrogen (N), mainly nitrate in aerobic soils, is a primary limiting factor for crop production. Most terrestrial plants live in symbiosis with arbuscular mycorrhizal (AM) fungi to increase nutrient uptake, including N, from soil. Research on the AM symbiosis field has focused almost exclusively on ammonium as the form of N transferred to the plants, and there has been no direct evidence of N transfer as nitrate thus far. Here, we report that mycorrhizal rice could receive more than 40% of its N via the mycorrhizal pathway and that the AM-specific nitrate transporter OsNPF4.5 accounted for approximately 45% of the mycorrhizal nitrate uptake. Our work suggests the presence of a mycorrhizal route for nitrate uptake in plants.
Convergent evolution of conserved mitochondrial pathways underlies repeated adaptation to extreme environments
Authors: Greenway Ryan , Barts Nick , Henpita Chathurika , Brown Anthony P. , Arias Rodriguez Lenin , Rodríguez Peña Carlos M. , Arndt Sabine , Lau Gigi Y. , Murphy Michael P. , Wu Lei , Lin Dingbo , Shaw Jennifer H. , Kelley Joanna L. , Tobler Michael
Published: June 2020

Extreme environments test the limits of life; yet, some organisms thrive in harsh conditions. Extremophile lineages inspire questions about how organisms can tolerate physiochemical stressors and whether the repeated colonization of extreme environments is facilitated by predictable and repeatable evolutionary innovations. We identified the mechanistic basis underlying convergent evolution of tolerance to hydrogen sulfide (H
2
S)—a toxicant that impairs mitochondrial function—across evolutionarily independent lineages of a fish (
Poecilia mexicana
, Poeciliidae) from H
2
S-rich springs. Using comparative biochemical and physiological analyses, we found that mitochondrial function is maintained in the presence of H
2
S in sulfide spring
P. mexicana
but not ancestral lineages from nonsulfidic habitats due to convergent adaptations in the primary toxicity target and a major detoxification enzyme. Genome-wide local ancestry analyses indicated that convergent evolution of increased H
2
S tolerance in different populations is likely caused by a combination of selection on standing genetic variation and de novo mutations. On a macroevolutionary scale, H
2
S tolerance in 10 independent lineages of sulfide spring fishes across multiple genera of Poeciliidae is correlated with the convergent modification and expression changes in genes associated with H
2
S toxicity and detoxification. Our results demonstrate that the modification of highly conserved physiological pathways associated with essential mitochondrial processes mediates tolerance to physiochemical stress. In addition, the same pathways, genes, and—in some instances—codons are implicated in H
2
S adaptation in lineages that span 40 million years of evolution.
Understanding inclusion in collaborative governance: a mixed methods approach
Authors: Ansell Christopher , Doberstein Carey , Henderson Hayley , Siddiki Saba , ‘t Hart Paul
Published: June 2020

Who should be included in collaborative governance and how they should be included is an important topic, though the dynamics of inclusion are not yet well understood. We propose a conceptual model to shape the empirical analysis of what contributes to inclusion in collaborative processes. We propose that incentives, mutual interdependence and trust are important preconditions of inclusion, but that active inclusion management also matters a great deal. We also hypothesize that inclusion is strategic, with ‘selective activation’ of participants depending on functional and pragmatic choices. Drawing on cases from the Collaborative Governance Case Databank, we used a mixed method approach to analyse our model. We found support for the model, and particularly for the central importance of active inclusion management.