bluuebunny/crossref_metadata_2025 huggingface dataset:
Collective strong coupling in a plasmonic nanocavity
Authors: Varguet H. , Díaz-Valles A. A. , Guérin S. , Jauslin H. R. , Colas des Francs G.
Published: February 2021

Quantum plasmonics extends cavity quantum electrodynamics (cQED) concepts to the nanoscale, benefiting from the strongly subwavelength confinement of the plasmon modes supported by metal nanostructures. In this work, we describe in detail collective strong coupling to a plasmonic nanocavity. Similarities and differences to cQED are emphasized. We notably observe that the Rabi splitting can strongly deviate from the standard NeΔΩ1 law, where Ne is the number of emitters and ΔΩ1 is the Rabi splitting for a single emitter. In addition, we discuss the collective Lamb shift and the role of quantum corrections to the emission spectra.
Optimization of process parameters to generate plasma activated water and study of physicochemical properties of plasma activated solutions at optimum condition
Authors: Rathore Vikas , Nema Sudhir Kumar
Published: February 2021

Plasma-activated water (PAW) is gaining significant attention these days due to its potential use as a disinfectant, pesticide, food preservative, cancer cell treatment, fertilizer, etc. These applications of PAW depend on its reactivity (oxidizing-potential) and electrical conductivity (EC). In the present work, we have studied the effect of process parameters, viz., air flow rate, water stirrer speed, and the temperature of water during plasma–water interaction on the reactivity and EC of PAW using a three-way full factorial design of experiments. We have also attempted to optimize these process parameters. At optimum values of these parameters, we studied how the physicochemical properties of PAW vary by changing the volume of water and discharge power. Furthermore, we studied the physicochemical properties of the plasma-activated solution (PAS) and how the EC and pH of virgin solutions affect these properties. The obtained results of the present investigation showed that the flow rate of air, plasma treatment time with water, volume of water, and plasma discharge power play a significant role in controlling the reactivity and EC of PAW. Moreover, the pH and EC of virgin solution do not have a significant (p < 0.05) impact on the reactivity of PAS. This investigation also shows the study of aging time on reactive oxygen–nitrogen species and its effect on the physicochemical properties of PAW. Additionally, observed changes in physicochemical properties, NO3− ions, and H2O2 concentration in PAW were less than 10%. However, NO2− ions and dissolved O3 concentration in PAW decreased significantly over time.
Formation of vortex rings and hopfions in trapped Bose–Einstein condensates
Authors: Zou Shan , Bai Wen-Kai , Yang Tao , Liu Wu-Ming
Published: February 2021

The topological transition of vortex lines to vortex rings and hopfions is numerically investigated by the Gross–Pitaevskii equation in three-dimensional trapped Bose–Einstein condensates. The shape of the vortex rings formed by the two vortex lines of the vortex dipole depends strongly on the initial separation of the lines. An approximately perfect vortex ring can be obtained by choosing some suitable values of the separation. The deformation of the formed rings depends on the shape of the rings in turn. Furthermore, we show a feasible approach to generate vortex hopfions by imprinting a vortex line in the center of the generated vortex rings. Specifically, the movement of the vortex rings can excite helical waves along the central vortex line of the hopfion structure if the vortex ring is not perfect.
Explosively driven dynamic compaction of granular media
Authors: Han Panpan , Xue Kun , Bai Chunhua
Published: February 2021

This paper reports experimental investigations into the dynamic compaction of particle rings subjected to moderate explosions confined in a radial Hele-Shaw cell. The findings reveal marked transitions in the flow regimes corresponding to the evolution of the transient pressure fields inside the granular medium induced by unsteady gas infiltration. As the pressure fields evolve from being localized to diffusive with a substantial reduction in intensity, three sequent flow regimes with distinct rheologies are identified. Specifically, these flow regimes are found to be governed by the localized strong pressure field, then the competition between the diffusive pressure field and wall friction, and finally, solid stresses in the presence of rarefaction waves. A Bingham-type rheology can adequately describe the granular compaction when the pressure gradients remain the dominant driving forces, whereas the frictional nature of the granular flows becomes increasingly significant as the solid stresses set in. As the pressure gradients phase out, rarefaction decompaction commences. However, this only manages to relax the innermost layers of the compacted particles due to a distinctive compressive deformation pattern, giving rise to a discontinuous flow field. These findings shed light on the rheology of dense granular flows subjected to unsteady pressure loadings involving diverse flow–particle and particle–particle interactions.
Advanced hydrogenation process applied on Ge on Si quantum dots for enhanced light emission
Authors: Spindlberger Lukas , Kim Moonyong , Aberl Johannes , Fromherz Thomas , Schäffler Friedrich , Fournel Frank , Hartmann Jean-Michel , Hallam Brett , Brehm Moritz
Published: February 2021

For the development of photonic integrated circuits, it is mandatory to implement light sources on a Si-on-insulator (SOI) platform. However, point defects in the Si matrix and, e.g., at the Si/SiO2 interface act as nonradiative recombination channels, drastically limiting the performance of Si-based light emitters. In this Letter, we study how these defects can be healed by applying an advanced hydrogenation process, recently developed in photovoltaic research for the passivation of performance-limiting defects in Si solar cells. Upon hydrogenation, we observe an increase in the room temperature photoluminescence (PL) yield by a factor of more than three for defect-enhanced quantum dots (DEQDs) grown on float-zone Si substrates, revealing the potential of this technique to passivate detrimental defects. For DEQDs grown using SOI substrates, the PL yield enhancement even exceeds a factor of four, which we attribute to the additional passivation of defects originating from the substrate. The results for SOI substrates are of particular interest due to their relevance for future photonic integrated circuits.
A novel one-domain approach for modeling flow in a fluid-porous system including inertia and slip effects
Authors: Valdés-Parada F. J. , Lasseux D.
Published: February 2021

A new one-domain approach is developed in this work yielding an operational average description of one-phase flow in the classical Beavers and Joseph configuration including a porous medium topped by a fluid channel. The model is derived by considering three distinct regions: the homogeneous part of the porous domain, the inter-region, and the free fluid region. The development is carried out including inertial flow and slip effects at the solid–fluid interfaces. Applying an averaging procedure to the pore-scale equations, a unified macroscopic momentum equation, applicable everywhere in the system and having a Darcy form, is derived. The position-dependent apparent permeability tensor in this model is predicted from the solution of two coupled closure problems in the inter-region and in the homogeneous part of the porous medium. The performance of the model is assessed through in silico validations in different flow situations showing excellent agreement between the average flow fields obtained from direct numerical simulations of the pore-scale equations in the entire system and the prediction of the one-domain approach. Furthermore, validation with experimental data is also presented for creeping flow under no-slip conditions. In addition to the fact that the model is general from the point of view of the flow situations it encompasses, it is also simple and novel, hence providing a practical and interesting alternative to models proposed so far using one- or two-domain approaches.
Isotropic all-electric spin analyzer based on a quantum ring with spin–orbit couplings
Authors: Peng Shenglin , Ouyang Fangping , Sun Jian , Guo Ai-Min , Chakraborty Tapash , Luo Wenchen
Published: February 2021

Isotropic spin analysis is a key step in spintronics and could be useful in quantum information, which usually requires light as an essential component. It has not yet been realized in a solid-state device. Here, we propose an isotropic all electrical spin analyzer designed from a quantum ring with spin–orbit couplings by analytically and numerically modeling how the charge transmission rate depends on the polarization of the incident spin. The spin transport features are also demonstrated to be robust against ring structure defects, disorder, and a bias between the two leads at finite temperature in the nanoscale ring. Similar to the light polarizer/analyzer, this interesting two-dimensional electron system can be designed as a spin filter, spin polarizer, and a general spin analyzer with high resolution by simply tuning the spin–orbit couplings, which paves the way for realizing the tunable and integrable spintronics devices.
Shedding light on non-Ising polar domain walls: Insight from second harmonic generation microscopy and polarimetry analysis
Authors: Cherifi-Hertel Salia , Voulot Cédric , Acevedo-Salas Ulises , Zhang Yide , Crégut Olivier , Dorkenoo Kokou Dodzi , Hertel Riccardo
Published: February 2021

Polar domain walls are currently at the focus of intensive research owing to their unusual and highly localized functional properties, which bear great potential for technological applications. They can present unusual topological features, like swirling polar structures or defect lines. The prediction of possible non-Ising and chiral internal structures of polar domain walls has been a particularly important development in this topic over the past years. This Tutorial highlights the capabilities of non-linear optics to probe these newly discovered aspects in polar non-Ising type domain walls through the second-harmonic generation (SHG) process. Fundamental symmetry properties of domain walls are presented in the context of recent advances on chiral and abnormal polar structures. We introduce the basics of the SHG and its ability to probe the symmetry down to the nanoscale, and we explain how to obtain insight into the non-Ising character of polar domain walls by combining the SHG polarimetry analysis with modeling.
Second-harmonic generation in nonlinear plasmonic lattices enhanced by quantum emitter gain medium
Authors: Sukharev Maxim , Roslyak Oleksiy , Piryatinski Andrei
Published: February 2021

We report on a theoretical study of second-harmonic generation (SHG) in plasmonic nanostructures interacting with two-level quantum emitters (QEs) under incoherent energy pump. We generalize the driven-dissipative Tavis–Cummings model by introducing the anharmonic surface plasmon-polariton (SPP) mode coupled to QEs and examine physical properties of corresponding SPP-QE polariton states. Our calculations of the SHG efficiency for strong QE-SPP coupling demonstrate orders of magnitude enhancement facilitated by the polariton gain. We further discuss time-domain numerical simulations of SHG in a square lattice comprising Ag nanopillars coupled to QEs utilizing a fully vectorial nonperturbative nonlinear hydrodynamic model for conduction electrons coupled to Maxwell–Bloch equations for QEs. The simulations support the idea of gain enhanced SHG and show orders of magnitude increase in the SHG efficiency as the QEs are tuned in resonance with the lattice plasmon mode and brought above the population inversion threshold by incoherent pumping. By varying pump frequency and tuning QEs to a localized plasmon mode, we demonstrate further enhancement of the SHG efficiency facilitated by strong local electric fields. The incident light polarization dependence of the SHG is examined and related to the symmetries of participating plasmon modes.
Generalized equation of state for fluids: From molecular liquids to colloidal dispersions
Authors: Perdomo-Hurtado Luis , Valadez-Pérez Néstor Enrique , Millan-Malo Beatriz , Castañeda-Priego Ramón
Published: February 2021

In this work, a new parameterization for the Statistical Association Fluid Theory for potentials of Variable Range (SAFT-VR) is coupled to the discrete potential theory to represent the thermodynamic properties of several fluids, ranging from molecular liquids to colloidal-like dispersions. In this way, this version of the SAFT-VR approach can be straightforwardly applied to any kind of either simple or complex fluid. In particular, two interaction potentials, namely, the Lennard-Jones and the hard-core attractive Yukawa potentials, are discretized to study the vapor–liquid equilibrium properties of both molecular and complex liquids, respectively. Our results are assessed with Monte Carlo computer simulations and available and accurate theoretical results based on the self-consistent Ornstein–Zernike approximation.
Phonon transport in multiphase nanostructured silicon fabricated by high-pressure torsion
Authors: Shao Cheng , Matsuda Kensuke , Ju Shenghong , Ikoma Yoshifumi , Kohno Masamichi , Shiomi Junichiro
Published: February 2021

We present a combined experimental and numerical investigation of phonon transport in multiphase nanostructured silicon. The sample was synthesized by high-pressure torsion with a nominal pressure of 24 GPa. Based on the x-ray diffraction measurement, we have identified the existence of three phases of silicon in the sample: Si-I, Si-III, and Si-XII, with volume fractions of 66%, 25%, and 9% and average grain sizes of 25, 14, and 11 nm, respectively. The measured thermal conductivities of the sample in the temperature range of 150–330 K are on the order of 5 W/(m K) and exhibit weak temperature dependence. A multiscale modeling that incorporates first-principles lattice dynamics, the Monte Carlo ray-tracing method, and effective medium theory was used to understand the mechanism of phonon transport in multiphase nanostructured silicon as well as the weak temperature dependence. We found that the thermal conductivity of single-phase nanostructured silicon decreases with decreasing average grain size and is about an order of magnitude lower than the corresponding bulk counterpart when the average grain size is O(10nm). The weak temperature-dependent thermal conductivity in the nanostructured silicon is attributed to the strong elastic phonon–boundary scattering at the grain boundary. The thermal conductivity predicted from the multiscale modeling matches reasonably well with the measurement. This work provides insights into phonon transport in multiphase nanostructured materials and suggests that the effective thermal conductivity of nanostructured silicon from high-pressure torsion can be further reduced by increasing the volume fractions of the Si-III and Si-XII phases.
Nonequilibrium effects of cavity leakage and vibrational dissipation in thermally activated polariton chemistry
Authors: Du Matthew , Campos-Gonzalez-Angulo Jorge A. , Yuen-Zhou Joel
Published: February 2021

In vibrational strong coupling (VSC), molecular vibrations strongly interact with the modes of an optical cavity to form hybrid light–matter states known as vibrational polaritons. Experiments show that the kinetics of thermally activated chemical reactions can be modified by VSC. Transition-state theory, which assumes that internal thermalization is fast compared to reactive transitions, has been unable to explain the observed findings. Here, we carry out kinetic simulations to understand how dissipative processes, namely, those introduced by VSC to the chemical system, affect reactions where internal thermalization and reactive transitions occur on similar timescales. Using the Marcus–Levich–Jortner type of electron transfer as a model reaction, we show that such dissipation can change reactivity by accelerating internal thermalization, thereby suppressing nonequilibrium effects that occur in the reaction outside the cavity. This phenomenon is attributed mainly to cavity decay (i.e., photon leakage), but a supporting role is played by the relaxation between polaritons and dark states. When nonequilibrium effects are already suppressed in the bare reaction (the reactive species are essentially at internal thermal equilibrium throughout the reaction), we find that reactivity does not change significantly under VSC. Connections are made between our results and experimental observations.
Free-carrier-assisted mid-infrared microcavity soliton generation
Authors: Fan Weichen , Sun Qibing , Lu Zhizhou , Wang Leiran , Zhao Wei , Zhang Wenfu
Published: February 2021

Multi-photon absorption (MPA) and free-carrier (FC) effects, usually considered to be detrimental to microcomb generation by introducing strong nonlinear loss, also offer opportunities to overwhelm the thermal-optic effect by modifying the refractive index. Here, we derive the theoretical expression of solitons expanded with MPA and FC effects, accompanied by numerical simulations to reveal the dynamics and mechanism for capturing steady mid-infrared solitons in both Si and Ge microcavities. It is found that with increased FC lifetime, the intensity-dependent MPA underlies non-monotonous variation of nonlinear detuning which enables soliton generation. More interestingly, proper control on the FC lifetime admits bidirectional switching of soliton states (i.e., both decreasing and increasing the number of solitons) as well as self-starting solitons, yielding different technique routes toward microcavity solitons. This research could contribute to a better understanding of nonlinear behaviors influenced by FC effects and find practical applications by releasing the demand on precise control of laser sources, which is especially meaningful for the mid-infrared region.
Orbital entanglement and correlation from pCCD-tailored coupled cluster wave functions
Authors: Nowak Artur , Legeza Örs , Boguslawski Katharina
Published: February 2021

Wave functions based on electron-pair states provide inexpensive and reliable models to describe quantum many-body problems containing strongly correlated electrons, given that broken-pair states have been appropriately accounted for by, for instance, a posteriori corrections. In this article, we analyze the performance of electron-pair methods in predicting orbital-based correlation spectra. We focus on the (orbital-optimized) pair-coupled cluster doubles (pCCD) ansatz with a linearized coupled-cluster (LCC) correction. Specifically, we scrutinize how orbital-based entanglement and correlation measures can be determined from a pCCD-tailored CC wave function. Furthermore, we employ the single-orbital entropy, the orbital-pair mutual information, and the eigenvalue spectra of the two-orbital reduced density matrices to benchmark the performance of the LCC correction for the one-dimensional Hubbard model with the periodic boundary condition as well as the N2 and F2 molecules against density matrix renormalization group reference calculations. Our study indicates that pCCD-LCC accurately reproduces the orbital-pair correlation patterns in the weak correlation limit and for molecules close to their equilibrium structure. Hence, we can conclude that pCCD-LCC predicts reliable wave functions in this regime.
Flow past a transversely oscillating cylinder at lock-on region and three-dimensional Floquet stability analysis of its wake
Authors: Zhang H. , Xin D. , Zhan J. , Zhou L.
Published: February 2021

A numerical investigation is conducted on the flow past a transversely oscillating square cylinder at various amplitudes with a Reynolds number of 200 in the “lock-on” region. Floquet stability analysis was then applied to study the three-dimensional instability of its wake. The results show that mean recirculating region sizes decrease and force coefficients increase as the oscillating amplitude increases. The dynamic mode decomposition analysis reveals that although oscillating amplitude changes the topology of high order harmonic modes, the primary modes share similar features, which result in the classical “2S” mode at various amplitudes. The distinct high-order-harmonic modes lead to the difference of the flow pattern at various amplitudes. For the three-dimensional instability, the oscillating amplitudes can be divided into three stages, I (0 ≤ A/D < 0. 3), II (0.3 ≤ A/D < 0.4), and III (0.4 ≤ A/D < 0.7). In region I, the dominant Floquet mode is Mode-A corresponding to a long wavelength λz/D ≈ 3.49. As the oscillating amplitude increases to region III, the wavelength of the dominant mode abruptly changes to a much shorter wavelength λz/D ≈1.14 (a new mode called Mode-SA). Mode-SA shows similar features to Mode-A, except that this mode dissipates rapidly in the wake. Region II is the transitional region.
The effect of hydrogen bonds on the ultrafast relaxation dynamics of a BODIPY dimer
Authors: Fresch Elisa , Peruffo Nicola , Trapani Mariachiara , Cordaro Massimiliano , Bella Giovanni , Castriciano Maria Angela , Collini Elisabetta
Published: February 2021

The influence of hydrogen bonds (H-bonds) in the structure, dynamics, and functionality of biological and artificial complex systems is the subject of intense investigation. In this broad context, particular attention has recently been focused on the ultrafast H-bond dependent dynamical properties in the electronic excited state because of their potentially dramatic consequences on the mechanism, dynamics, and efficiency of photochemical reactions and photophysical processes of crucial importance for life and technology. Excited-state H-bond dynamics generally occur on ultrafast time scales of hundreds of femtoseconds or less, making the characterization of associated mechanisms particularly challenging with conventional time-resolved techniques. Here, 2D electronic spectroscopy is exploited to shed light on this still largely unexplored dynamic mechanism. An H-bonded molecular dimer prepared by self-assembly of two boron-dipyrromethene dyes has been specifically designed and synthesized for this aim. The obtained results confirm that upon formation of H-bonds and the dimer, a new ultrafast relaxation channel is activated in the ultrafast dynamics, mediated by the vibrational motions of the hydrogen donor and acceptor groups. This relaxation channel also involves, beyond intra-molecular relaxations, an inter-molecular transfer process. This is particularly significant considering the long distance between the centers of mass of the two molecules. These findings suggest that the design of H-bonded structures is a particularly powerful tool to drive the ultrafast dynamics in complex materials.
Multiphysics analysis of nsPEF induced electrodeformation in a dispersive cell model
Authors: Guo Fei , Qian Kun , Deng Hao , Li Xin
Published: February 2021

Exposed to the nanosecond pulsed electric field (nsPEF), biological cells can be stretched in the direction parallel to the electric field direction. A multiphysics model to investigate electrodeformation of a spherical cell with double-layered plasma membrane accounting for both electroporation and dielectric relaxation of the membrane is proposed. Transmembrane potential, Maxwell stress tensor, total elastic strain energy, and deformation degree, the typical influential factors and indicators for electroporation and electrodeformation, are probed via the above multiphysics model under the action of unipolar and bipolar nsPEFs. The results suggest that the double-layered model can reflect the experimental cellular deformation more accurately than the single-layered model in that the long axis of the ellipsoid is stretched several micrometers in the double-layered model, while it is stretched several nanometers in the single-layered model. And merging the effect of dielectric relaxation into the model leads to a relatively lighter but faster deformation extent, and applying bipolar nsPEF alleviates the stretch for electrodeformation quantified with the lower aspect ratio of two principal radii of the ellipsoidal cell and the lower elastic strain energy. Our model can reflect the temporal evolution of electroporation and electrodeformation procedure more accurately, which is instructive to exert the nsPEF in biochemical experiments and clinical applications.
Submonolayer quantum dot quantum cascade long-wave infrared photodetector grown on Ge substrate
Authors: Shen Zhijian , Deng Zhuo , Zhao Xuyi , Huang Jian , Cao Chunfang , Zou Xinbo , Liu Fengyu , Gong Qian , Chen Baile
Published: February 2021

A germanium (Ge) or germanium-on-silicon (Ge-on-Si) substrate is an attractive yet not well-studied platform for developing long-wave infrared photonics devices such as lasers and photodetectors. In this paper, we report a long-wave infrared quantum cascade photodetector grown on the Ge substrate with a submonolayer InAs/GaAs quantum dot as the infrared absorber. At 77 K under zero bias, the detector shows a differential-resistance area (R0A) product of 298.7 Ω·cm2. The normal-incident peak responsivity is 0.56 mA/W observed at 8.3 μm, corresponding to a Johnson noise limited detectivity of 1.5 × 108 cm·Hz1/2/W. In addition, the effect of the periodic stage number of active regions on device's performance is discussed in detail. The device characteristics presented in this work demonstrate the potential for monolithic integration of this quantum cascade detector with the Ge or Ge-on-Si substrate for large-scale, cost-effective sensing and imaging applications.
Topological transitions to Weyl states in bulk Bi2Se3: Effect of hydrostatic pressure and doping
Authors: Saha Sudip Kumar , Banerjee Hrishit , Kumar Manoranjan
Published: February 2021

Bi 2 Se 3 , a layered three-dimensional (3D) material, exhibits topological insulating properties due to the presence of surface states and a bandgap of 0.3 eV in the bulk. We study the effect of hydrostatic pressure P and doping with rare earth elements on the topological aspect of this material in bulk from a first principles perspective. Our study shows that under a moderate pressure of P>7.9GPa, the bulk electronic properties show a transition from an insulating to a Weyl semi-metal state due to band inversion. This electronic topological transition may be correlated to a structural change from a layered van der Waals material to a 3D system observed at P=7.9GPa. At large P, the density of states have a significant value at the Fermi energy. Intercalating Gd with a small doping fraction between Bi2Se3 layers drives the system to a metallic anti-ferromagnetic state, with Weyl nodes below the Fermi energy. At the Weyl nodes, time reversal symmetry is broken due to the finite local field induced by large magnetic moments on Gd atoms. However, substituting Bi with Gd induces anti-ferromagnetic order with an increased direct bandgap. Our study provides novel approaches to tune topological transitions, particularly in capturing the elusive Weyl semimetal states, in 3D topological materials.
Interlayer coupling effect on skyrmion dynamics in synthetic antiferromagnets
Authors: Qiu Lei , Shen Laichuan , Zhang Xichao , Zhou Yan , Zhao Guoping , Xia Weixing , Luo Hu-Bin , Liu J. Ping
Published: February 2021

Skyrmions in synthetic antiferromagnets (SAFs) could be immune to the skyrmion Hall effect and are, thus, promising in spintronics applications. We introduce breathing modes that can be realized by changing the magnetocrystalline anisotropy periodically in time to generate spin waves around a deformed SAF skyrmion. The net momentum transferred from the magnon spin currents results in a motion of the SAF skyrmion, which is two orders of magnitude faster than that of a ferromagnetic skyrmion. We also reveal that the velocity of the SAF skyrmion can be manipulated by the strength of antiferromagnetic coupling between layers, which is different from ferromagnetic and antiferromagnetic systems. This phenomenon originates from the damping-like character of the antiferromagnetic coupling and offers a dimension to optimize skyrmion dynamics in SAFs.
Effect of sample anisotropy on scanning near-field optical microscope images
Authors: Chui S. T. , Chen Xinzhong , Yao Ziheng , Bechtel Hans A. , Martin Michael C. , Carr G. L. , Liu Mengkun
Published: February 2021

Scattering-type scanning near-field optical microscopy (s-SNOM) has been widely used to characterize strongly correlated electronic, two dimensional, and plasmonic materials, and it has enormous potential for biological applications. Many of these materials exhibit anisotropic responses that complicate the extraction of dielectric constants from s-SNOM measurements. Here, we generalize our recently developed approach for retrieving the near-field scattering signal from isotropic systems and apply it to anisotropic dielectrics. Specifically, we compare our theoretical results with experimental measurements on modestly anisotropic sapphire that exhibit strong resonances at the infrared frequency range. Good agreement with the experimental result is found. Our result is important for understanding the near-field response of low damping, anisotropic polaritonic states in dielectric media.
Potential energy surfaces for high-energy N + O2 collisions
Authors: Varga Zoltan , Liu Yang , Li Jun , Paukku Yuliya , Guo Hua , Truhlar Donald G.
Published: February 2021

Potential energy surfaces for high-energy collisions between an oxygen molecule and a nitrogen atom are useful for modeling chemical dynamics in shock waves. In the present work, we present doublet, quartet, and sextet potential energy surfaces that are suitable for studying collisions of O2(3Σg−) with N(4S) in the electronically adiabatic approximation. Two sets of surfaces are developed, one using neural networks (NNs) with permutationally invariant polynomials (PIPs) and one with the least-squares many-body (MB) method, where a two-body part is an accurate diatomic potential and the three-body part is expressed with connected PIPs in mixed-exponential-Gaussian bond order variables (MEGs). We find, using the same dataset for both fits, that the fitting performance of the PIP-NN method is significantly better than that of the MB-PIP-MEG method, even though the MB-PIP-MEG fit uses a higher-order PIP than those used in previous MB-PIP-MEG fits of related systems (such as N4 and N2O2). However, the evaluation of the PIP-NN fit in trajectory calculations requires about 5 times more computer time than is required for the MB-PIP-MEG fit.
Vibrational quenching of CN− in collisions with He and Ar
Authors: Mant Barry , Yurtsever Ersin , González-Sánchez Lola , Wester Roland , Gianturco Franco A.
Published: February 2021

The vibrational quenching cross sections and corresponding low-temperature rate constants for the ν = 1 and ν = 2 states of CN−(1Σ+) colliding with He and Ar atoms have been computed ab initio using new three-dimensional potential energy surfaces. Little work has been carried out so far on low-energy vibrationally inelastic collisions for anions with neutral atoms. The cross sections and rates calculated at energies and temperatures relevant for both ion traps and astrochemical modeling are found by the present calculations to be even smaller than those of the similar C2−/He and C2−/Ar systems, which are in turn of the order of those existing for the collisions involving neutral diatom–atom systems. The implications of our finding in the present case mainly focus on the possible role of small computed rate constants in the dynamics of molecular cooling and the evolution of astrochemical modeling networks.
How Hall electric fields intrinsically chaotize and heat ions during collisionless magnetic reconnection
Authors: Yoon Young Dae , Bellan Paul M.
Published: February 2021

The origin of extreme and anomalous ion heating during magnetic reconnection has been a long-standing mystery. It is shown in this paper that, at the core of the process, the stochastic heating mechanism is responsible for this energization. The in-plane Hall electric fields that intrinsically develop during collisionless reconnection not only accelerate ions but also thermalize them by inducing chaotic motion. The mechanism explains various observed features of ion heating, e.g., its relation to the guide field strength and the ion mass-to-charge ratio.
Analysis of channel mobility in GaN-based metal-oxide-semiconductor field-effect transistors
Authors: Ito Kenji , Tomita Kazuyoshi , Kikuta Daigo , Horita Masahiro , Narita Tetsuo
Published: February 2021

The factors limiting channel mobility in AlSiO/p-type GaN-based metal-oxide-semiconductor field-effect transistors (MOSFETs) were systematically investigated. MOSFETs with various thin interfacial layers (ILs) between Al0.78Si0.22Oy films and Mg-doped GaN layers were prepared and found to exhibit different channel mobilities. The maximum effective mobility showed a significant correlation with the threshold voltage (Vt) and the hysteresis (ΔVt) in the transfer characteristics of these devices, such that the mobility decreased with increasing Vt and ΔVt. This effect can be explained by electron capture in and emission from border traps situated near the conduction band minimum for GaN. The insertion of a 3-nm-thick SiO2 IL drastically enhanced the effective mobility and simultaneously reduced the ΔVt value. Hall effect measurements with an applied gate voltage were used to determine the mobility of free electrons while excluding electrons captured in the border traps. The Hall effect mobility was much higher than the effective mobility, indicating that mobility was in fact reduced by the capture of electrons by the border traps. The ratio of electrons captured by border traps to the overall electrons induced by a gate bias was greatly lowered in a MOSFET incorporating a SiO2 IL. When a high vertical electric field of approximately 1 MV/cm was present in the device channel, the Hall effect mobility was slightly increased following the insertion of an IL. These results suggest that the IL reduced the interfacial roughness and/or affected the screening out of scattering due to potential fluctuations of the AlSiO.
Analysis of the kinetic energy functional in the generalized gradient approximation
Authors: Francisco Héctor I. , Carmona-Espíndola Javier , Gázquez José L.
Published: February 2021

A new density functional for the total kinetic energy in the generalized gradient approximation is developed through an enhancement factor that leads to the correct behavior in the limits when the reduced density gradient tends to 0 and to infinity and by making use of the conjoint conjecture for the interpolation between these two limits, through the incorporation, in the intermediate region of constraints that are associated with the exchange energy functional. The resulting functional leads to a reasonable description of the kinetic energies of atoms and molecules when it is used in combination with Hartree–Fock densities. Additionally, in order to improve the behavior of the kinetic energy density, a new enhancement factor for the Pauli kinetic energy is proposed by incorporating the correct behavior into the limits when the reduced density gradient tends to 0 and to infinity, together with the positivity condition, and imposing through the interpolation function that the sum of its integral over the whole space and the Weiszacker energy must be equal to the value obtained with the enhancement factor developed for the total kinetic energy.
Fe–Li complex emission in ZnO
Authors: Müller Raphael , Mangold Martin , Huber Florian , Schreck Matthias , Herr Ulrich , Thonke Klaus
Published: February 2021

In this work, we report on three new extremely sharp emission lines in zinc oxide (ZnO) related to iron–lithium complexes. The identification is based on a comparison of hydrothermally grown ZnO with high lithium concentration and a lithium-free sample grown by methane based chemical vapor deposition, which both were implanted with iron. After annealing in a mixed oxygen/argon atmosphere at 800°C, the lithium-free sample showed no additional lines besides the well-known emission at 693nm (1.78734eV), whereas the hydrothermally grown sample emitted three intense and sharp lines in photoluminescence (PL) spectroscopy. These emission lines at 705nm (1.75873eV), 712nm (1.74153eV), and 732nm (1.69283eV) were characterized by temperature dependent high resolution continuous wave (cw) and time-resolved PL spectroscopy, as well as by photoluminescence excitation spectroscopy, and are assigned to different Fe–Li complexes. We find a single thermally activated excited state for each of the complex emission lines, different from the 4T1→6A1 transition of Fe3+ with its at least three excited states. While time-resolved photoluminescence measurements of the Fe3+ transition show a lifetime of 24.9±0.5ms, we find a reduced lifetime of 8.5±1ms for the new zero phonon lines, pointing to stronger mixture of the Fe 3d states with surrounding p-orbitals.
Topological effects of phonons in GaN and AlGaN: A potential perspective for tuning phonon transport
Authors: Tang Dao-Sheng , Cao Bing-Yang
Published: February 2021

Tuning thermal transport in semiconductor nanostructures is of great significance for thermal management in information and power electronics. With excellent transport properties, such as ballistic transport, immunity to point defects and disorders, and forbidden backscattering, topological phonon surface states show remarkable potential in addressing this issue. Herein, topological phonon analyses are performed on hexagonal wurtzite gallium nitride (GaN) to check the topological characteristics of phonons. And other nitrides of the same family, i.e., AlN and AlGaN crystals, are also calculated from a topological phonon phase transition perspective. With the aid of first-principle calculations and topological phonon theory, Weyl phonon states, which host surfaces states without backscattering, are investigated for all these materials. The results show that there is no nontrivial topological phonon state in GaN. However, by introducing Al atoms, i.e., in wurtzite type AlN and AlGaN, more than one Weyl phonon point is found, confirmed by obvious topological characteristics, including non-zero integer topological charges, source/sink in Berry curvature distributions, surface local density of states, and surface arcs. As AlN and AlGaN are typical materials in AlGaN/GaN heterostructure based electronics, the existence of topological phonon states in them will benefit thermal management by facilitating the design of one-way interfacial phonon transport without backscattering.
Socio-ecological impacts of industrial aquaculture and ways forward to sustainability
Authors: Cánovas-Molina Almudena , García-Frapolli Eduardo
Published: February 2021

In recent decades, we have witnessed a rapid increase in world aquaculture production, the so-called ‘blue revolution’. So as to provide a holistic overview of the socio-ecological threats coupled with this increase, a literature review has been conducted. The following seven major socio-ecological impacts were identified: (i) the damage and destruction of natural environments, (ii) discharges; (iii) a risk to wild fish and shellfish populations, (iv) spatial conflicts, (v) threats to food security, (vi) unfairness in the access to commons; and (vii) the unequal distribution of benefits. So as to move forward from ‘blue revolution’ to a ‘blue evolution’ and attain sustainable aquaculture, the following tools have been identified as instrumental for the transition process: technical, management, governance and legal aspects.
Intracellular pathways for lignin catabolism in white-rot fungi
Authors: del Cerro Carlos , Erickson Erika , Dong Tao , Wong Allison R. , Eder Elizabeth K. , Purvine Samuel O. , Mitchell Hugh D. , Weitz Karl K. , Markillie Lye Meng , Burnet Meagan C. , Hoyt David W. , Chu Rosalie K. , Cheng Jan-Fang , Ramirez Kelsey J. , Katahira Rui , Xiong Wei , Himmel Michael E. , Subramanian Venkataramanan , Linger Jeffrey G. , Salvachúa Davinia
Published: February 2021

Significance

White-rot fungi play an essential role in global carbon cycling because of their extraordinary ability to extracellularly deconstruct lignin, a recalcitrant plant biopolymer. Despite this, the intracellular metabolism of lignin-deconstruction products by this fungal group has been largely overlooked, potentially due to a lack of genetic tools and challenging growth-tracking protocols, which complicate studies that are considered routine in other organisms. Here, we definitively demonstrate that white-rot fungi are also able to modify and utilize aromatic lignin-deconstruction products as a carbon source. Our study elucidates a critical process occurring in soil ecosystems, encouraging further study of lignin’s catabolic fate in diverse environmental conditions toward an improved understanding of the role of these fungi in facilitating carbon sequestration in nature.
A tandem activity-based sensing and labeling strategy enables imaging of transcellular hydrogen peroxide signaling
Authors: Iwashita Hidefumi , Castillo Erika , Messina Marco S. , Swanson Raymond A. , Chang Christopher J.
Published: February 2021

Significance

Hydrogen peroxide is a ubiquitous reactive oxygen species (ROS) with diverse signaling and stress contributions, but its transient and mobile nature makes it challenging to study in living systems. Here we report a tandem activity-based sensing and labeling strategy for capture and permanent recording of localized H
2
O
2
fluxes by fluorescence imaging. Application of this technology enables direct visualization of ROS transport in cell-to-cell communication using a microglia–neuron coculture model to monitor cell-specific elevations in H
2
O
2
levels. In addition to revealing a fundamental contribution of ROS to transcellular signaling, this work presages further opportunities to combine dual chemical sensing and labeling approaches to probe biology with improved spatial fidelity.
Unique dynamics and exocytosis properties of GABAergic synaptic vesicles revealed by three-dimensional single vesicle tracking
Authors: Park Chungwon , Chen Xingxiang , Tian Chong-Li , Park Gyu Nam , Chenouard Nicolas , Lee Hunki , Yeo Xin Yi , Jung Sangyong , Tsien Richard W. , Bi Guo-Qiang , Park Hyokeun
Published: February 2021

Significance

Despite playing an important role in maintaining brain function, the dynamics and exocytosis of inhibitory synaptic vesicles are poorly understood. Here, we tracked the three-dimensional position of single GABAergic vesicles up to the moment of exocytosis in real time by loading single GABAergic vesicles with quantum dots conjugated to antibodies against the luminal domain of the vesicular GABA transporter. We found that GABAergic synaptic vesicles have a smaller total travel length before fusion, a shorter fusion latency, and a higher prevalence of kiss-and-run fusion than synaptotagmin-1–labeled vesicles. Our findings provide evidence that inhibitory vesicles have a unique set of dynamics and exocytosis properties to support rapid inhibitory synaptic transmission.
The echo chamber effect on social media
Authors: Cinelli Matteo , De Francisci Morales Gianmarco , Galeazzi Alessandro , Quattrociocchi Walter , Starnini Michele
Published: February 2021

Significance

We explore the key differences between the main social media platforms and how they are likely to influence information spreading and the formation of echo chambers. To assess the different dynamics, we perform a comparative analysis on more than 100 million pieces of content concerning controversial topics (e.g., gun control, vaccination, abortion) from Gab, Facebook, Reddit, and Twitter. The analysis focuses on two main dimensions: 1) homophily in the interaction networks and 2) bias in the information diffusion toward like-minded peers. Our results show that the aggregation in homophilic clusters of users dominates online dynamics. However, a direct comparison of news consumption on Facebook and Reddit shows higher segregation on Facebook.
ELF3 activated by a superenhancer and an autoregulatory feedback loop is required for high-level HLA-C expression on extravillous trophoblasts
Authors: Li Qin , Meissner Torsten B. , Wang Fang , Du Ziming , Ma Sai , Kshirsagar Sarika , Tilburgs Tamara , Buenrostro Jason D. , Uesugi Motonari , Strominger Jack L.
Published: February 2021

Significance

Several techniques have identified ELF3 as particularly important in regulating trophoblast-specific HLA-C expression. This results from a single-nucleotide difference in the promotor of the HLA-C gene at the RFX5 binding site that creates an ELF3 binding site not found in the HLA-A or HLA-B promoters. We discovered a superenhancer and a positive autoregulatory feedback loop that promotes expression of the ELF3 gene in trophoblasts. Disruption of either the superenhancer by (+)-JQ1 or interference with the positive-feedback loop by wrenchnolol decreased ELF3 levels, and thus HLA-C expression. Aberrations of this complex regulatory system could be involved in control of infection, miscarriage, preterm birth, preeclampsia, as well as parturition in normal pregnancy and in development of choriocarcinoma.
The Syntax of Information-Structural Agreement
Authors: Mursell Johannes
Published: February 2021

In this research monograph, Johannes Mursell discusses the syntactic impact of information-structural features on agreement. So far, the syntactic contribution of this type of feature has mostly been reduced to movement of topics or foci clause-initial position. Here, the author looks at a different phenomenon, syntactic agreement, and how this process can be dependent on information-structural properties. Based partly on original fieldwork from a typologically diverse set of languages, including Tagalog, Swahili, and Lavukaleve, it is argued that for most areas for which information-structural features have been discussed, it is possible to find cases where these features influence phi-feature agreement. The analysis is then extended to cases of Association with Focus, which does not involve phi-features but can still be accounted for with agreement of information-structural features. The book achieves two main goals: first it provides a uniform analysis for different constructions in unrelated languages. Second, it also gives a new argument that information-structural features should be treated as genuine syntactic features.
CENP-A overexpression promotes aneuploidy with karyotypic heterogeneity
Authors: Shrestha Roshan L. , Rossi Austin , Wangsa Darawalee , Hogan Ann K. , Zaldana Kimberly S. , Suva Evelyn , Chung Yang Jo , Sanders Chelsea L. , Difilippantonio Simone , Karpova Tatiana S. , Karim Baktiar , Foltz Daniel R. , Fachinetti Daniele , Aplan Peter D. , Ried Thomas , Basrai Munira A.
Published: February 2021

Chromosomal instability (CIN) is a hallmark of many cancers. Restricting the localization of centromeric histone H3 variant CENP-A to centromeres prevents CIN. CENP-A overexpression (OE) and mislocalization have been observed in cancers and correlate with poor prognosis; however, the molecular consequences of CENP-A OE on CIN and aneuploidy have not been defined. Here, we show that CENP-A OE leads to its mislocalization and CIN with lagging chromosomes and micronuclei in pseudodiploid DLD1 cells and xenograft mouse model. CIN is due to reduced localization of proteins to the kinetochore, resulting in defects in kinetochore integrity and unstable kinetochore–microtubule attachments. CENP-A OE contributes to reduced expression of cell adhesion genes and higher invasion of DLD1 cells. We show that CENP-A OE contributes to aneuploidy with karyotypic heterogeneity in human cells and xenograft mouse model. In summary, our results provide a molecular link between CENP-A OE and aneuploidy, and suggest that karyotypic heterogeneity may contribute to the aggressive phenotype of CENP-A–overexpressing cancers.