bluuebunny/crossref_metadata_2025 huggingface dataset:
Observation of nonlinear sheath oscillations in symmetric capacitive discharges at low pressures
Authors: Sun Jing-Yu , Zhang Quan-Zhi , Wang You-Nian
Published: January 2021

The mechanism of nonlinear oscillations in symmetric capacitively coupled plasmas is studied by the particle-in-cell/Monte Carlo collisions approach. A physical origin of this nonlinear phenomenon is identified by spatiotemporal kinetic analysis of electron dynamics. It is found that multi-beams of high-energy electrons are stimulated at the sheath expansion phase, following with reversed electric field filaments. The instantaneous absence of the quasi-neutrality in the vicinity of the sheaths is responsible for the observed phenomenon. In addition, a simple theoretical model is introduced to qualitatively illustrate the numerical findings. Our simulations demonstrate that the frequency and intensity of this nonlinearity are very sensitive to the plasma density, sheath velocity, and sheath thickness. More nonlinear oscillations could be stimulated at the condition of high density and high sheath velocity, while a large sheath thickness normally induces large-amplitude oscillations. A simple relation of pressure and gap distance for nonlinear sheath oscillations has been built.
Observation of rotating magnetohydrodynamic modes in the plume of a high-current hollow cathode
Authors: Becatti Giulia , Goebel Dan M. , Zuin Matteo
Published: January 2021

High-current hollow cathodes are widely used in electric propulsion as well as for laboratory plasma generation applications. The plasma region just outside of high-current cathodes is characterized by the presence of many fluctuations, which can develop coherent plasma structures affecting the operation and life of the cathode. The properties of plasma oscillations have been investigated in the exterior region of a high-current hollow cathode operating at 25–150 A of discharge current with an applied axial magnetic field. Electrostatic and magnetic probes were used to measure the electromagnetic fluctuations, and correlation analysis between each of the probes signals provides the spatiotemporal characterization of the generated waves. The results of this investigation reveal the presence of a coherent magnetohydrodynamic (MHD) azimuthal mode with a fundamental frequency of 58 kHz. This mode has features of a helical kink instability with azimuthal wave number m=1 and axial wavenumber kz=50m−1 that is readily observed in high-speed Fast-Cam images. The occurrence of this mode, the frequency, and the wavenumber at onset are found to be predicted well by the ideal MHD theory, considering the boundary condition of a non-line-tying cylindrical anode. Investigation of the MHD mode properties at different discharge currents and mass flow rate shows additional features that could qualitatively agree with resistive MHD modes. In particular, when the plasma has a finite conductivity associated with anomalous resistivity in the cathode plume, a gradual emergence of modes at relatively low discharge currents are observed.
Development of 10 MHz–1000 MHz small leadless electric field probe
Authors: Sheng Mingjie , Zhou Zhongyuan , Gu Yixing , Hu Peng , Xiao Yang , Zhou Qi
Published: January 2021

In order to realize the miniaturization and leadless function of the electric field probe working from 10 MHz to 1000 MHz, a small stand-alone probe based on the dipole and Schottky detector diode is developed in this paper. First, a 20 mm dipole printed on the circuit board is adopted as the receiving antenna, and the Schottky detector diode is connected across the two arms of the dipole. Then, the signal output by the detector diode is amplified by a chopper amplifier circuit, which also isolates the alternating component. Finally, a microprogrammed control unit is set inside the metal shield to realize data acquisition and storage. The size of the probe developed is not exceeding 20 × 20 × 30 mm3, and the characteristics of the probe are temperature dependent. The field strength from 1.4 V/m to 1627 V/m can be measured within 10 MHz–1000 MHz, achieving a dynamic range over 61 dB at 21 °C. It has the advantages of small size, large dynamic range, and integrated data collection and storage.
Maximizing spin–orbit torque efficiency of Ta(O)/Py via modulating oxygen-induced interface orbital hybridization
Authors: Yang Liupeng , Fei Yining , Zhou Kaiyuan , Chen Lina , Fu Qingwei , Li Liyuan , Yan Chunjie , Li Haotian , Du Youwei , Liu Ronghua
Published: January 2021

Spin–orbit torques due to interfacial Rashba and spin Hall effects have been widely considered as a potentially more efficient approach than the conventional spin-transfer torque to control the magnetization of ferromagnets. We report a comprehensive study of spin–orbit torque efficiency in Ta(O)/Ni81Fe19 bilayers by tuning low-oxidation of β-phase tantalum and find that the spin Hall angle θDL increases from ∼−0.18 of the pure Ta/Py to the maximum value ∼−0.30 of Ta(O)/Py at 7.8% oxidation. Furthermore, we distinguish the spin–orbit torque efficiency generated by the bulk spin Hall effect and interfacial Rashba effect, respectively, via a series of Ta(O)/Cu(0–2 nm)/Py control experiments. The latter has more than twofold enhancement and is even more significant than the former at the optimum oxidation level. Our results indicate that 65% enhancement of the efficiency should be related to the modulation of the interfacial Rashba-like spin–orbit torque due to oxygen-induced orbital hybridization across the interface. Our results suggest that the modulation of interfacial coupling via oxygen-induced orbital hybridization can be an alternative method to boost the change-spin conversion efficiency.
Collective spin dynamics under dissipative spin Hall torque
Authors: Tserkovnyak Yaroslav , Maniv Eran , Analytis James G.
Published: January 2021

Current-induced spin torques in layered magnetic heterostructures have many commonalities across broad classes of magnetic materials. These include not only collinear ferromagnets, ferrimagnets, and antiferromagnets but also more complex noncollinear spin systems. We develop a general Lagrangian–Rayleigh approach for studying the role of dissipative torques, which can pump energy into long-wavelength magnetic dynamics, causing dynamic instabilities. While the Rayleigh structure of such torques is similar for different magnetic materials, their consequences depend sensitively on the nature of the order and, in particular, on whether there is a net magnetic moment. The latter endows the system with a unipolar switching capability, while magnetically compensated materials tend to evolve toward limit cycles, at large torques, with chirality dependent on the torque sign. Apart from the ferromagnetic and antiferromagnetic cases, we discuss ferrimagnets, which display an intricate competition between switching and limit cycles. As a simple case for compensated noncollinear order, we consider isotropic spin glasses and a scenario of their coexistence with a collinear magnetic order.
ITER cold VDEs in the limit of perfectly conducting walls
Authors: Clauser C. F. , Jardin S. C.
Published: January 2021

Recently, it has been shown that a vertical displacement event (VDE) can occur in ITER even when the walls are perfect conductors, as a consequence of the current quench (CQ) [A. H. Boozer, Phys. Plasmas 26, 114501 (2019)]. We used the extended-MHD code M3D-C1 with an ITER-like equilibrium and induced a CQ to explore cold VDEs in the limit of perfectly conducting walls, using different wall geometries. In the case of a rectangular first wall with the side walls far away from the plasma, we obtained very good agreement with the analytical model developed by Boozer that considers a top/bottom flat-plates wall. We show that the solution in which the plasma remains at the initial equilibrium position is improved when bringing the side walls closer to the plasma. When approximating the ITER first wall as a perfect conductor, the plasma remains stable at the initial equilibrium position far beyond the value predicted by the flat-plates wall limit. When considering an opposite limit in which only the inner shell of the ITER vacuum vessel acts as a perfect conductor, the plasma is displaced during the CQ, but the edge safety factor remains above 2 longer in the current decay compared to the flat-plates wall limit. In all the simulated cases, the VDE is found to be strongly dependent on the plasma current, in agreement with a similar finding in the flat-plates wall limit, showing an important difference with hot VDEs in which the CQ is not a necessary condition.
Mixed convection between rotating sphere and concentric cubical enclosure
Authors: Chen Z. , Yang L. M. , Shu C. , Zhao X. , Liu N. Y. , Liu Y. Y.
Published: January 2021

This paper presents numerical investigations of the mix convection between a rotating inner sphere and a concentric cubical enclosure, using the recently developed immersed boundary-simplified lattice Boltzmann method. The validity of the method has been established through benchmark tests, and a grid independence study is also carried out to ensure the accuracy of the conveyed results. Various factors that may influence the mixed convection system, such as the rotational direction, Rayleigh number, and rotational Reynolds number, are considered in the present study. Three representative rotational axes, namely, the vertical, the horizontal, and the diagonal axes, are selected. The Rayleigh number spans from 104 to 106, which covers the transition range from a conduction-dominated system to a convection-dominated one. Moreover, the rotational Reynolds number varies from 0 to 300. Distinct flow patterns, global heat transfer behavior, and the heat transfer rates on cubic walls are studied to reveal the characteristics of this problem. It is found that the rotationality of the inner sphere would increase the global heat transfer rate of the system and the rotating motion would stimulate heat transfer in the radial direction of the rotational axis while suppressing the thermal expansion in the axial direction.
Emergent rhythms in coupled nonlinear oscillators due to dynamic interactions
Authors: Dixit Shiva , Nag Chowdhury Sayantan , Prasad Awadhesh , Ghosh Dibakar , Shrimali Manish Dev
Published: January 2021

The role of a new form of dynamic interaction is explored in a network of generic identical oscillators. The proposed design of dynamic coupling facilitates the onset of a plethora of asymptotic states including synchronous states, amplitude death states, oscillation death states, a mixed state (complete synchronized cluster and small amplitude desynchronized domain), and bistable states (coexistence of two attractors). The dynamical transitions from the oscillatory to the death state are characterized using an average temporal interaction approximation, which agrees with the numerical results in temporal interaction. A first-order phase transition behavior may change into a second-order transition in spatial dynamic interaction solely depending on the choice of initial conditions in the bistable regime. However, this possible abrupt first-order like transition is completely non-existent in the case of temporal dynamic interaction. Besides the study on periodic Stuart–Landau systems, we present results for the paradigmatic chaotic model of Rössler oscillators and the MacArthur ecological model.
Comparative study of the dynamics of laser breakdown in water and hexane using interference microscopy
Authors: Kononenko V.V. , Gololobov V.M. , Kononenko T.V. , Goncharov E.A. , Konov V.I.
Published: January 2021

The changes in the optical properties of water and hexane under femtosecond irradiation (Ti : Al2O3 laser, wavelength 800 nm, intensity ∼1013 W cm−2) are investigated in the cavitation (bubble-formation) regime using interference microscopy in a time interval of ∼1.5 ns since the impact onset. A comparison of the dynamics of radiation-induced processes (solvation of excess electrons, pair recombination, and development of precavitation processes) is performed. The excited-carrier concentration is estimated, and these estimates are found to be inconsistent with the amount of energy that must be transferred to the liquid during a pulse to implement its heating and subsequent cavitation. This inconsistency is especially pronounced for hexane, where ionisation processes can barely be detected by interferometry. The experimental results put new questions about the mechanisms of energy transfer in both polar and nonpolar liquids subjected to intense laser irradiation.
Pulse energy limitation of high-power nanosecond lasers due to plasma production in spatial filters
Authors: Kuzmin A.A. , Khazanov E.A. , Shaykin A.A.
Published: January 2021

For a neodymium glass laser, which is used to pump the parametric amplifier of the PEARL facility, we investigate the problem of filling the pinholes of vacuum spatial filters with plasma resulting from the ablation of the pinhole surface by laser radiation. The time of plasma expansion is measured and the causes of its appearance are determined, among which the main ones are the spherical aberrations of the lenses of spatial filters, which increase the intensity at the pinhole edges. With the total spherical aberration of the spatial filters, which lowers the Strehl number to 0.15, two nanosecond pulses with energies of 130 – 140 J, delayed relative to each other by 1.8 ns and freely passing through the final spatial filter, are generated on the PEARL facility.
Light – current characteristics of high-power pulsed semiconductor lasers (1060 nm) operating at increased (up to 90 °C) temperatures
Authors: Gavrina P.S. , Podoskin A.A. , Fomin E.V. , Veselov D.A. , Shamakhov V.V. , Slipchenko S.O. , Pikhtin N.A. , Kop’ev P.S.
Published: January 2021

Pulsed radiative characteristics of high-power semiconductor lasers based on an asymmetric InGaAs/AlGaAs/GaAs heterostructure with an active region including two quantum wells and a gradient waveguide on the side of the p-emitter are studied. It is shown that the use of the proposed design allows efficient laser operation under pumping by 100-ns current pulses in the temperature range 25 – 90 °C. The lasers with a Fabry – Perot cavity 2900 μm long demonstrated peak powers of 62 W (injection current 123 A) and 43 W (122 A) at temperatures of 25 and 90 °C, respectively. It is found that at room temperature and currents of ∼50A, a decrease in the cavity length to 600 μm does not cause a decrease in the output power with respect to the power of lasers with a long (2900 μm) cavity. An increase in temperature to 90 °C at high injection currents leads to a sharp decrease in the radiative efficiency of lasers with a short (600 μm) cavity and to the change of their operation regime to the two-band lasing.
Simultaneous denitrification and hexavalent chromium removal by a newly isolated Stenotrophomonas maltophilia strain W26 under aerobic conditions
Authors: An Qiang , Deng Shu-man , Zhao Bin , Li Zheng , Xu Jia , Song Jia-Li
Published: January 2021

Environmental contextIndustrial development has caused the release of hexavalent chromium and nitrates into the environment. Interactions of hexavalent chromium and nitrates with microorganisms are important both for understanding environmental behaviour and for treatment options. Bacterial removal of both chromium and nitrate was optimised in waters relevant to waste streams and the environment.
Abstract An isolated strain of the bacterium Stenotrophomonas maltophilia strain W26, is shown to be capable of the simultaneous removal of nitrate and CrVI under aerobic conditions. Notably, 10mg L−1 of CrVI and 500mg L−1 of nitrate were reduced by 92.6% and 85.2%, respectively, by strain W26. Results showed that an excellent denitrification efficiency of 96.0% could be reached at the optimal conditions of a C/N ratio of 10, using a carbon source of trisodium citrate, at pH 7.5, and a nitrate concentration of 500mg L−1. Strain W26 could also effectively remove high concentrations of CrVI (50mg L−1, 93.2%) and nitrate (700mg L−1, 97.4%). By using the N balance analysis, energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS), the denitrification and CrVI transformation processes were verified. CrVI, immobilised on the cell surface by W26, was reduced to CrIII, through interaction with of O=C and N-H groups. This study indicates that the isolated strain W26 has the potential to treat wastewater containing combined nitrate and CrVI contamination.
Researcher disillusionment and ungoverned damage to Becher Point Wetlands, Western Australia
Authors: Fulton Graham R.
Published: January 2021

Researcher disillusionment, angry mobs and four-wheel-drives damage the sandy headland at Becher Point, in Western Australia.
A genome-scale CRISPR screen reveals factors regulating Wnt-dependent renewal of mouse gastric epithelial cells
Authors: Murakami Kazuhiro , Terakado Yumi , Saito Kikue , Jomen Yoshie , Takeda Haruna , Oshima Masanobu , Barker Nick
Published: January 2021

Significance

Wnt activation is critically important during both early development and throughout adulthood for the maintenance and regeneration of tissue-resident stem cells. However, the underlying mechanism regulating Wnt-dependent epithelial renewal and differentiation in the stomach remains poorly understood. Here we apply genome-scale CRISPR-Cas9 knockout screening to three-dimensional ex vivo stomach organoids to reveal important mechanistic insight into Wnt-dependent epithelial renewal in mouse gastric epithelia. Our organoid-based screening strategy can be readily applied to a wide variety of organoids derived from different sources, potentially providing important insights on multiple biological phenomena.
Human subjects exploit a cognitive map for credit assignment
Authors: Moran Rani , Dayan Peter , Dolan Raymond J.
Published: January 2021

Significance

Credit assignment (CA) to relevant actions poses a challenge because one is often flooded with reward feedback that is not easily causally attributed. We addressed this issue in a reinforcement learning framework wherein choice is mutually controlled by value-caching model-free (MF) and prospective, planning model-based (MB) systems. We find knowledge, stored in a cognitive map, filters exuberant reward feedback to guide CA in both systems but based on different attribute dimensions. In MF, CA is boosted for outcomes that are relevant (causally related) to one’s choice, whereas in MB, CA is enhanced for outcomes that attract greater attention during the deliberation process that preceded a choice. We consider normative and mechanistic accounts, including how these processes are instrumental to adaptation.
Evolutionarily stable strategies in stable and periodically fluctuating populations: The Rosenzweig–MacArthur predator–prey model
Authors: Grunert Katrin , Holden Helge , Jakobsen Espen R. , Stenseth Nils Chr.
Published: January 2021

Significance

Many evolutionary studies of ecological systems assume, explicitly or implicitly, ecologically stable population dynamics. Ecological analyses typically assume, on the other hand, no evolution. We study a model (using predator–prey dynamics as an example) combining ecology and evolution within the same framework. For this purpose, we use the evolutionarily stable strategies (ESSs) framework, emphasizing that evolutionary change, in general, will occur as a result of mutant strategies being able to invade a population. The significance of our contribution is to derive mathematical conditions for the existence of an ESS in a periodically limit-cycle ecological system.
Major alterations in the mononuclear phagocyte landscape associated with COVID-19 severity
Authors: Kvedaraite Egle , Hertwig Laura , Sinha Indranil , Ponzetta Andrea , Hed Myrberg Ida , Lourda Magda , Dzidic Majda , Akber Mira , Klingström Jonas , Folkesson Elin , Muvva Jagadeeswara Rao , Chen Puran , Gredmark-Russ Sara , Brighenti Susanna , Norrby-Teglund Anna , Eriksson Lars I. , Rooyackers Olav , Aleman Soo , Strålin Kristoffer , Ljunggren Hans-Gustaf , Ginhoux Florent , Björkström Niklas K. , Henter Jan-Inge , Svensson Mattias ,   Karolinska KI/K COVID-19 Study Group, Sandberg John Tyler , Bergsten Helena , Björkström Niklas K , Brighenti Susanna , Buggert Marcus , Butrym Marta , Chambers Benedict J , Chen Puran , Cornillet Martin , Cuapio Angelica , Lozano Isabel Diaz , Dzidic Majda , Emgård Johanna , Flodström-Tullberg Malin , Gorin Jean-Baptiste , Gredmark-Russ Sara , Haroun-Izquierdo Alvaro , Hertwig Laura , Kalsum Sadaf , Klingström Jonas , Kokkinou Efthymia , Kvedaraite Egle , Ljunggren Hans-Gustaf , Marquardt Nicole , Lourda Magdalini , Maleki Kimia T , Malmberg Karl-Johan , Michaëlsson Jakob , Mjösberg Jenny , Moll Kirsten , Muvva Jagadeeswara Rao , Norrby-Teglund Anna , Medina Laura M Palma , Parrot Tiphaine , Radler Lena , Ringqvist Emma , Sandberg Johan K , Sekine Takuya , Soini Tea , Svensson Mattias , Tynell Janne , von Kries Andreas , Wullimann David , Perez-Potti André , Rivera-Ballesteros Olga , Maucourant Christopher , Varnaite Renata , Akber Mira , Berglin Lena , Brownlie Demi , Loreti Marco Giulio , Sohlberg Ebba , Kammann Tobias , Henriksson Elisabeth , Strålin Kristoffer , Aleman Soo , Sönnerborg Anders , Dillner Lena , Färnert Anna , Glans Hedvig , Nauclér Pontus , Rooyackers Olav , Mårtensson Johan , Eriksson Lars I , Persson Björn P , Grip Jonathan , Unge Christian
Published: January 2021

Significance

While broad efforts toward getting an overview of immune cell and soluble factor alterations in COVID-19 are under way, a deep and comprehensive understanding of the mononuclear phagocyte system, including circulating progenitors, is still largely lacking. This study provides a reference for the mononuclear phagocyte response to SARS-CoV-2 infection and unravels mononuclear phagocyte dysregulations associated with severe COVID-19.
Tocopherol controls D1 amino acid oxidation by oxygen radicals in Photosystem II
Authors: Kumar Aditya , Prasad Ankush , Sedlářová Michaela , Kale Ravindra , Frankel Laurie K. , Sallans Larry , Bricker Terry M. , Pospíšil Pavel
Published: January 2021

Significance

During oxygenic photosynthesis Photosystem II is damaged by reactive oxygen species (ROS). It is known that α-tocopherol protects the photosystem from a subset of this oxidative damage. The sites that were protected and the mechanisms leading to protein damage had not been determined. Herein, we identify the ROS responsible for damage on the reducing side of Photosystem II, the protein residues that are damaged by these ROS, and we propose a model localizing α-tocopherol within the photosystem yielding the observed protection.
Microbes in biogeochemical cycles: a perspective on climate resilient agriculture
Authors: Gurung Aditi , Mattoo Rohini
Published: January 2021

Microorganisms, which are ubiquitous players in all major agro-ecosystems, play important roles in biogeochemical cycles. Due to anthropogenic activities and current practices of agriculture, there has been interference in the natural cycling of essential elements and nutrients. A harmony in the functioning of natural biogeochemical cycles in the soil is essential for maintaining all life on Earth. Therefore, usage of beneficial soil microorganisms is important for sustaining agriculture due to poor soil health conditions that prevail because of excessive chemical inputs both in the past and present to increase crop yields. In this review, we focus on how the terrestrial soil microbes are involved in the interplay between biogeochemical cycles, sustainable agricultural practices, and climate change. We have highlighted the mechanisms by which microbes, through aiding the mineralization processes, support plant growth in cycling of carbon, nitrogen, phosphorus, and sulfur. Microorganisms further support plant growth to adapt to climate change although few specific mechanisms are known, but many others by which they aid plants remain enigmatic. Despite the various gaps that remain, we advocate that coupling biogeochemical cycles research with sustainable agricultural practices using plant-microbe interchange is highly warranted. Therefore, to feed a growing global population and to preserve ecosystem functions, we propose that the agricultural practices should be conducted in a manner to regulate greenhouse gases release and safeguard our environmental resources due to climate change.
A mouse model of human TLR4 D299G/T399I SNPs reveals mechanisms of altered LPS and pathogen responses
Authors: Richard Katharina , Piepenbrink Kurt H. , Shirey Kari Ann , Gopalakrishnan Archana , Nallar Shreeram , Prantner Daniel J. , Perkins Darren J. , Lai Wendy , Vlk Alexandra , Toshchakov Vladimir Y. , Feng Chiguang , Fanaroff Rachel , Medvedev Andrei E. , Blanco Jorge C.G. , Vogel Stefanie N.
Published: January 2021

Two cosegregating single-nucleotide polymorphisms (SNPs) in human TLR4, an A896G transition at SNP rs4986790 (D299G) and a C1196T transition at SNP rs4986791 (T399I), have been associated with LPS hyporesponsiveness and differential susceptibility to many infectious or inflammatory diseases. However, many studies failed to confirm these associations, and transfection experiments resulted in conflicting conclusions about the impact of these SNPs on TLR4 signaling. Using advanced protein modeling from crystallographic data of human and murine TLR4, we identified homologous substitutions of these SNPs in murine Tlr4, engineered a knock-in strain expressing the D298G and N397I TLR4 SNPs homozygously, and characterized in vivo and in vitro responses to TLR4 ligands and infections in which TLR4 is implicated. Our data provide new insights into cellular and molecular mechanisms by which these SNPs decrease the TLR4 signaling efficiency and offer an experimental approach to confirm or refute human data possibly confounded by variables unrelated to the direct effects of the SNPs on TLR4 functionality.
Double-objective optimization of electro-thermal (E-T) micro-actuator for fiber switch
Authors: Chen Hao , Wang Xin-jie , Cao Yun , Wang Jiong , Xi Zhan-wen , Nie Wei-rong
Published: January 2021

In this paper, a novel optimization method, in which composed of the genetic algorithm, particle swarm optimization (GA–PSO) and improved gradient descent algorithm, are used to conduct a double-objective optimization for the U-shaped actuator. In the procedure of optimization, two objectives, i.e. force and displacement, and four main sizes are utilized. Before, the deep reactive-ion etch (DRIE) technology is applied to the fabrication of the U-shaped actuator. When different voltages are applied on the actuator, the displacement obtained from numerical calculation always shows a good agreement with that from experiment by edge detection algorithm. Similar phenomenon can be also seen when an external force supplied by the nanoindentation system FemtoTools in the experiment is loaded on the actuator. Based on the validated simulation model of the U-shaped actuator, the improved gradient descent method ensures its displacement very close to 50 µm (target displacement) while the GA–PSO algorithm is used to maximize the output force. In this procedure, the hybrid optimization method implemented by Matlab is incorporated into ANSYS simulation. Preliminary analysis shows that the displacement and force of the particles in each iteration concentrate together with the iteration growing. Fine convergence, whose velocity only depends on the number of particle in the algorithm, is also found in each optimization. Furthermore, the optimized actuators have homologous value of the size variables. At 15 V voltage, the displacement and largest output force of the U-shaped actuator are 2 mN and 50.1 µm, respectively. Finally, an actuator with 30% improvement of the output force is obtained when the displacement condition is meet. According to the optimization result and further parametric scanning simulation analysis, the design range and fabrication error of the sizes of the U-shaped actuator are obtained.
Rotational speed measurements of small spherical particles driven by acoustic viscous torques utilizing an optical trap
Authors: Lamprecht Andreas , Goering Christoph , Schaap Iwan A T , Dual Jurg
Published: January 2021

Two orthogonal standing acoustic waves, generated by piezoelectric excitation, can form a two-dimensional pressure field in microfluidic devices. A phase difference of the excitation waves can be employed to rotate spherical µm-sized silica particles by a torque mediated through the viscous boundary δ around the particle. The measurement of the rotational rate is, so far, limited to high-speed cameras and their frame rate, and gets increasingly difficult when the sphere gets smaller. We report here a new method for measuring the rotational rate of µm sized spherical particles. We utilize an optical trap with high-speed position detection to overcome the frame rate limitation of wide field image recording. The power spectrum of an optically trapped, rotating particle reveals additional peaks corresponding to the rotational frequencies—compared to a non-rotating particle. We validate our method at low rotational rates against high-speed video observation. To demonstrate the potential of this method we addressed a recent controversy about the rotation of particles with a relatively large viscous boundary layer δ. We measured steady-state rotational rates up to 229 Hz (13.8 × 103 rpm) for a particle with a radius R ≈ δ. Recent numerical research suggests that in this regime the existing theoretical approach (valid for

R
≫
δ

) overpredicts the steady-state rotational rate by a factor of 10. With our new method we also confirm the numerical results experimentally.
A combined laboratory and synchrotron in-situ photoemission study of the rutile TiO2 (110)/water interface
Authors: Byrne Conor , Zahra Khadisha M , Dhaliwal Simran , Grinter David C , Roy Kanak , Garzon Wilson Q , Held Georg , Thornton Geoff , Walton Alex S
Published: January 2021

In-situ analysis of the TiO2/water interface via near ambient pressure–x-ray photoelectron spectroscopy (NAP–XPS) is demonstrated in both a lab based system (NAP-cell configuration) and synchrotron endstation (backfill configuration). Ultra-thin wetting layers of liquid water (∼10 nm) are formed on a rutile TiO2 surface with minimal contamination present in addition to unique insight during the growth of the liquid films as indicated via NAP–XPS, in-situ sample temperature and background vapour pressure monitoring. Chemical changes at the solid/liquid interface are also demonstrated via healing of Ti3+ surface defect states. Photon depth profiling of the as grown liquid layers indicate that the formed films are ultra-thin (∼10 nm) and likely to be continuous in nature. This work demonstrates a novel and flexible approach for studying the solid/liquid interface via NAP–XPS which is readily integrated with any form of NAP–XPS system, thereby making a critical interface of study available to a wide audience of researchers for use in operando electrochemical and photocatalytic research.
Corrigendum: Role of the electron–phonon coupling in tuning the thermal boundary conductance at metal-dielectric interfaces by inserting ultrathin metal interlayers (2021 J. Phys.: Condens. Matter
33 085702)
Authors: Oommen Shany Mary , Pisana Simone
Published: January 2021

Some typographical errors were made in the original version of the manuscript associated with the value of the electron–phonon coupling constant for Ta, which are corrected here.
Feature extraction method of rolling bearing based on adaptive divergence matrix linear discriminant analysis
Authors: Shi Mingfeng , Cao Zheng , Liu Yongbin , Liu Fang , Lu Siliang , Li Guoli
Published: January 2021

Status feature extraction is crucial to bearing fault diagnosis and the maintenance of rotating machinery. There are many challenges in extracting the effective status features from vibration signals for bearing fault diagnosis. A linear discriminant analysis (LDA) based on an adaptive divergence matrix (ALDA) is proposed to extract the status features of rolling bearings in this paper. The main idea of the method is that the sample clustering evaluation index (SI) is used to adjust the weight of the within-class divergence matrix of the LDA algorithm to reduce the cross or overlap among different types of samples, especially for the marginal samples. In the method, vibration signals of the rolling bearing under different running conditions are acquired, and the original features, such as time domain and frequency domain, are extracted from the vibration signals. Then, the optimal exponential weight of the within-class divergence matrix of the LDA is selected with the maximum SI. The optimal fusion status features of the bearing under different conditions were extracted by the ALDA algorithm from the original features. Finally, the fusion features were identified by the support vector machine classifier to verify the effectiveness of the proposed method. The experimental results show that the bearing status features extracted by ALDA can be used to identify the bearing status effectively.
Low-threshold upconverted single-mode lasing from CdS hexagonal microcavities
Authors: Mi Yang , Kong Lei , Wu Yaoyao , Shi Jinchun , Luo Sheng-Nian
Published: January 2021

Upconversion micro/nanolasers are promising in fundamental physics research and practical applications. However, due to the limitation of gain medium and cavity quality, such lasers still suffer from a high lasing threshold (P
th). Herein, upconverted whispering-gallery-mode lasing by two-photon absorption is achieved from CdS microplatelets with single-mode emission and low threshold (∼1.2 mJ cm−2). The threshold is three times lower than the best reported value in previous CdS upconversion lasers. Moreover, wavelength-tunable upconverted single-mode lasing is demonstrated from 510.4 to 518.9 nm with narrow linewidths around 0.85 nm, which is further verified through numerical simulations. In addition, the size-dependent lasing behavior is realized from single-mode to multimode oscillation; the corresponding lasing threshold decreases with increasing cavity edge length (L), following a P
th ∝ 1/L
2 relationship. These results underscore the promise of CdS microplatelets for developing chip-level frequency upconversion lasers.
Tailored negative/positive photoresponse of BP via doping
Authors: Liu Yue , Tan Yang , Liu Yanran , Jiang Xiantao , Zhang Han , Chen Feng
Published: January 2021

Black phosphorus (BP) is a promising material for photodetectors due to its excellent and broadband photoresponse. To realize a wide application of BP in photodetection, there is a continuous eagerness for new approaches to tailor photoresponse of BP for a specific purpose, such as high sensitivity and switching of negative/positive responses. Here, we demonstrate that the ion irradiation with controllable conditions can enhance the photoresponsivity of BP for two orders compared to the pristine one, and can select the positive/negative photoresponse of the BP. The range of the tailored photoresponse covers the whole optical spectrum, ranging from the visible (532 nm) to the mid-infrared (10 μm). This work shows a pathway to modulate the photoresponse of BP, which opens new possibilities for potential photonic applications.
Ultralow dark current infrared photodetector based on SnTe quantum dots beyond 2 μm at room temperature
Authors: Feng Yajun , Chang Huicong , Liu Yingbo , Guo Nan , Liu Junku , Xiao Lin , Li Lishuo
Published: January 2021

Quantum dots (QDs) are promising materials used for room temperature mid-infrared (MIR) photodetector due to their solution processing, compatibility with silicon and tunability of band structure. Up to now, HgTe QDs is the most widely studied material for MIR detection. However, photodetectors assembled with HgTe QDs usually work under cryogenic cooling to improve photoelectric performance, greatly limiting their application at room temperature. Here, less-toxic SnTe QDs were controllably synthesized with high crystallinity and uniformity. Through proper ligand exchange and annealing treatment, the photoconductive device assembled with SnTe QDs demonstrated ultralow dark current and broadband photo-electric response from visible light to 2 μm at room temperature. In addition, the visible and near infrared photo-electric performance of the SnTe QDs device were well maintained even standing 15 d in air. This excellent performance was due to the effective protection of the ligand on surface of the QDs and the effective transport of photo-carriers between the SnTe interparticles. It would provide a new idea for environmentally friendly mid-IR photodetectors working at room temperature.
Boosting an anapole mode response through electromagnetic interactions beyond near-field limit in individual all-dielectric disk-ring nanostructures
Authors: Deng Yan-Hui , Yang Zhong-Jian , Hu Ma-Long , Du Xiao-Jing , He Jun
Published: January 2021

Anapole modes of all-dielectric nanostructures hold great promise for many nanophotonic applications. However, anapole modes can hardly couple to other modes through far-field interactions, and their near-field enhancements are dispersed widely inside the nanostructures. These facts bring challenges to the further increasing of the response of an anapole mode. Here, we theoretically show that an anapole mode response in a dielectric nanostructure can be boosted through electromagnetic interactions with the coupling distance of a wavelength scale, which is beyond both the near-field and far-field limits. The all-dielectric nanostructure consists of a disk holding an anapole mode and a ring. Both analytical calculations and numerical simulations are carried out to investigate the electromagnetic interactions in the system. It is found that the electric dipoles associated with the fields of the anapole mode on the disk undergo retardation-related interactions with the electric dipoles associated with the ring, leading to the efficiently enhanced response of the anapole mode. The corresponding near field enhancement on the disk can reaches more than 90 times for a slotted silicon disk-ring nanostructure, where the width of the slot is 10 nm. This enhancement is about 5 times larger than that of an individual slotted disk. Our results reveal the greatly enhanced anapole mode through electromagnetic couplings in all-dielectric nanostructures, and the corresponding large field enhancement could find important applications for enhanced nonlinear photonics, near-field enhanced spectroscopies, and strong photon–exciton couplings.
A spectrally bright wavelength-switchable vacuum ultraviolet source driven by quantum coherence in strong-field-ionized molecules
Authors: Wan Yuexin , Liu Zhaoxiang , Yao Jinping , Xu Bo , Chen Jinming , Zhang Fangbo , Zhang Zhihao , Qiao Lingling , Cheng Ya
Published: January 2021

We report generation of spectrally bright vacuum ultraviolet (VUV) and deep UV (DUV) coherent radiations at the wavelengths of 192 nm, 198 nm and 204 nm. These DUV/VUV radiations originate from resonant four-wave mixing assisted by quantum coherence in tunnel-ionized CO molecules. The electronic coherence is created when the pump pulses resonantly excite electronic transitions of CO+. The technique allows for the selective switch of DUV/VUV wavelengths provided by the abundant energy levels of molecular ions. The developed source can have arbitrary polarization states by manipulating the polarization of the pump pulse. It also exhibits a spectral bandwidth of 5∼7 cm−1, a divergence angle of 3∼5 mrad, a pulse duration of ∼10 ps, and a photon flux of ∼1010 photons/s. The superior temporal and spectral properties give rise to a broadband Raman comb in the DUV/VUV region.
Abundant wave solutions to two novel KP-like equations using an effective integration method
Authors: Ghanbari Behzad , Kuo Chun-Ku
Published: January 2021

In this work, two new nonlinear evolution equations arising from the B-type Kadomtsev-Petviashvili equation, called BKP-like equations, are investigated. The integration technique that used in this paper to determine the exact solutions of the equation is the generalized exponential rational function method. The examined models may be extended to diversify problems in natural phenomena, such as ocean waves. After applying the aforesaid method, abundant wave solutions are formally generated with some free parameters to exhibit various versions of propagations of traveling solitary waves. Notably, upon choosing appropriate values to free parameters, some kink and periodic waves are demonstrated in 3D figures and 2D contour plots. Most of all, the results show that free parameters drastically influence the existence of all kinds of traveling waves, including nature, profile, and stability. The method used in this paper can be easily adopted in other similar equations in mathematical physics.
Roadmap on biology in time varying environments
Authors: Murugan Arvind , Husain Kabir , Rust Michael J , Hepler Chelsea , Bass Joseph , Pietsch Julian M J , Swain Peter S , Jena Siddhartha G , Toettcher Jared E , Chakraborty Arup K , Sprenger Kayla G , Mora T , Walczak A M , Rivoire O , Wang Shenshen , Wood Kevin B , Skanata Antun , Kussell Edo , Ranganathan Rama , Shih Hong-Yan , Goldenfeld Nigel
Published: January 2021

Biological organisms experience constantly changing environments, from sudden changes in physiology brought about by feeding, to the regular rising and setting of the Sun, to ecological changes over evolutionary timescales. Living organisms have evolved to thrive in this changing world but the general principles by which organisms shape and are shaped by time varying environments remain elusive. Our understanding is particularly poor in the intermediate regime with no separation of timescales, where the environment changes on the same timescale as the physiological or evolutionary response. Experiments to systematically characterize the response to dynamic environments are challenging since such environments are inherently high dimensional. This roadmap deals with the unique role played by time varying environments in biological phenomena across scales, from physiology to evolution, seeking to emphasize the commonalities and the challenges faced in this emerging area of research.
A simplified Parisi ansatz
Authors: Franchini Simone
Published: January 2021

Based on simple combinatorial arguments, we formulate a generalized cavity method where the Random Overlap Structure (ROSt) probability space of Aizenmann, Sims and Starr is obtained in a constructive way, and we use it to give a simplified derivation of the Parisi formula for the free energy of the Sherrington–Kirkpatrick model.
Analytic continuation and reciprocity relation for collinear splitting in QCD *
Authors: Chen Hao , Yang Tong-Zhi , Zhu Hua-Xing , Zhu Yu-Jiao
Published: January 2021

It is well-known that direct analytic continuation of the DGLAP evolution kernel (splitting functions) from space-like to time-like kinematics breaks down at three loops. We identify the origin of this breakdown as due to splitting functions not being analytic functions of external momenta. However, splitting functions can be constructed from the squares of (generalized) splitting amplitudes. We establish the rules of analytic continuation for splitting amplitudes, and use them to determine the analytic continuation of certain holomorphic and anti-holomorphic part of splitting functions and transverse-momentum dependent distributions. In this way we derive the time-like splitting functions at three loops without ambiguity. We also propose a reciprocity relation for singlet splitting functions, and provide non-trivial evidence that it holds in QCD at least through three loops.
Confinement and the global SU(3) color symmetry *
Authors: Chen Ying
Published: January 2021

The global

color symmetry and its physical consequences are discussed. The Nöther current is actually governed by the conserved matter current of color charges if the color field generated by this charge is properly polarized. The color field strength of a charge can have a uniform part due to the nontrivial QCD vacuum field and the nonzero gluon condensate, which implies that the self-energy of a system with a net color charge is infinite and, therefore, cannot exist as a free state. This is precisely what color confinement means. Accordingly, the Cornell type potential with the feature of Casimir scaling is derived for a color singlet system composed of a static color charge and an anti-charge. The uniform color field also implies that a hadron has a minimal size and minimal energy. Furthermore, the global

color symmetry requires that the minimal irreducible color singlet systems can only be

,

,

,

,

,

,

, etc., therefore a multi-quark system can only exist as a molecular configuration if there are no other binding mechanisms.
Double-heavy tetraquark states with heavy diquark-antiquark symmetry *
Authors: Cheng Jian-Bo , Li Shi-Yuan , Liu Yan-Rui , Si Zong-Guo , Yao Tao
Published: January 2021

We calculate the masses of the

(

;

) tetraquark states with the aid of heavy diquark-antiquark symmetry (HDAS) and the chromomagnetic interaction (CMI) model. The masses of the highest-spin (

) tetraquarks that have only the

color structure are related with those of conventional hadrons using HDAS. Thereafter, the masses of their partner states are determined with the mass splittings in the CMI model. Our numerical results reveal that (i) the lightest

(

) is an

state around 3929 MeV (53 MeV above the

threshold), and none of the double-charm tetraquarks are stable; (ii) the stable double-bottom tetraquarks are the lowest

around 10488 MeV (

MeV below the

threshold) and the lowest

around 10671 MeV (

MeV below the

threshold); and (iii) the two lowest

tetraquarks, namely the lowest

around 7167 MeV and the lowest

around 7223 MeV, are in the near-threshold states. Moreover, we discuss the constraints on the masses of double-heavy hadrons. Specifically, for the lowest nonstrange tetraquarks, we obtain

MeV,

MeV, and

MeV.
Nucleon stripping in deuteron-induced spallation reactions at hundreds MeV/nucleon *
Authors: Song Qu-Fei , Xu Su-Yang , Su Jun
Published: January 2021

A nucleon-nucleus dynamics model was developed to investigate the proton-, neutron-, and deuteron-induced reactions at hundreds of MeV/nucleon. In this model, the trajectory of incident nucleon is described by classical mechanics, and the probability of reaction between the nucleon and nucleus is calculated by exponential damping. It is shown that the total reaction cross sections calculated by the model agree in general with the predictions by the CDCC and the experimental data. The model was applied to investigate the nucleon stripping in deuteron-induced reactions and its symmetry energy dependence.