bluuebunny/crossref_metadata_2025 huggingface dataset:
The various accretion modes of AM Herculis: Clues from multi-wavelength observations in high accretion states
Authors: Schwope A. D. , Worpel H. , Traulsen I. , Sablowski D.
Published: August 2020

We report onXMM-NewtonandNuSTARX-ray observations of the prototypical polar, AM Herculis, supported by ground-based photometry and spectroscopy, all obtained in high accretion states. In 2005, AM Herculis was in its regular mode of accretion, showing a self-eclipse of the main accreting pole. X-ray emission during the self-eclipse was assigned to a second pole through its soft X-ray emission and not to scattering. In 2015, AM Herculis was in its reversed mode with strong soft blobby accretion at the far accretion region. The blobby acretion region was more luminous than the other, persistently accreting, therefore called main region. Hard X-rays from the main region did not show a self-eclipse indicating a pronounced migration of the accretion footpoint. Extended phases of soft X-ray extinction through absorption in interbinary matter were observed for the first time in AM Herculis. The spectral parameters of a large number of individual soft flares could be derived. SimultaneousNuSTARobservations in the reversed mode of accretion revealed clear evidence for Compton reflection of radiation from the main pole at the white dwarf surface. This picture is supported by the trace of the Fe resonance line at 6.4 keV through the whole orbit. Highly ionized oxygen lines observed with the Reflection Grating Spectrometer (RGS) were tentatively located at the bottom of the accretion column, although the implied densities are quite different from expectations. In the regular mode of accretion, the phase-dependent modulations in the ultraviolet (UV) are explained with projection effects of an accretion-heated spot at the prime pole. In the reversed mode projection effects cannot be recognized. The light curves reveal an extra source of UV radiation and extended UV absorbing dips. An HαDoppler map obtained contemporaneously with theNuSTARandXMM-Newtonobservations in 2015 lacks the typical narrow emission line from the donor star but reveals emission from an accretion curtain in all velocity quadrants, indicating widely dispersed matter in the magnetosphere.
A hierarchical field-level inference approach to reconstruction from sparse Lyman-α forest data
Authors: Porqueres Natalia , Hahn Oliver , Jasche Jens , Lavaux Guilhem
Published: August 2020

We address the problem of inferring the three-dimensional matter distribution from a sparse set of one-dimensional quasar absorption spectra of the Lyman-α forest. Using a Bayesian forward modelling approach, we focus on extending the dynamical model to a fully self-consistent hierarchical field-level prediction of redshift-space quasar absorption sightlines. Our field-level approach rests on a recently developed semiclassical analogue to Lagrangian perturbation theory (LPT), which improves over noise problems and interpolation requirements of LPT. It furthermore allows for a manifestly conservative mapping of the optical depth to redshift space. In addition, this new dynamical model naturally introduces a coarse-graining scale, which we exploited to accelerate the Markov chain Monte-Carlo (MCMC) sampler using simulated annealing. By gradually reducing the effective temperature of the forward model, we were able to allow it to first converge on large spatial scales before the sampler became sensitive to the increasingly larger space of smaller scales. We demonstrate the advantages, in terms of speed and noise properties, of this field-level approach over using LPT as a forward model, and, using mock data, we validated its performance to reconstruct three-dimensional primordial perturbations and matter distribution from sparse quasar sightlines.
Shear measurement bias
Authors: Pujol Arnau , Sureau Florent , Bobin Jerome , Courbin Frederic , Gentile Marc , Kilbinger Martin
Published: August 2020

We present a study of the dependencies of shear bias on simulation (input) and measured (output) parameters, noise, point-spread function anisotropy, pixel size, and the model bias coming from two different and independent galaxy shape estimators. We used simulated images from GALSIM based on the GREAT3 control-space-constant branch, and we measured shear bias from a model-fitting method (GFIT) and a moment-based method (Kaiser-Squires-Broadhurst). We show the bias dependencies found on input and output parameters for both methods, and we identify the main dependencies and causes. Most of the results are consistent between the two estimators, an interesting result given the differences of the methods. We also find important dependences on orientation and morphology properties such as flux, size, and ellipticity. We show that noise and pixelization play an important role in the bias dependencies on the output properties and galaxy orientation. We show some examples of model bias that produce a bias dependence on the Sérsic index n as well as a different shear bias between galaxies consisting of a single Sérsic profile and galaxies with a disc and a bulge. We also see an important coupling between several properties on the bias dependences. Because of this, we need to study several measured properties simultaneously in order to properly understand the nature of shear bias. This paper serves as a first step towards a companion paper that describes a machine learning approach to modelling shear bias as a complex function of many observed properties.
Regolith behavior under asteroid-level gravity conditions: low-velocity impacts into mm- and cm-sized grain targets
Authors: Brisset J. , Cox C. , Anderson S. , Hatchitt J. , Madison A. , Mendonca M. , Partida A. , Remie D.
Published: August 2020

Context.In situ observations of small asteroids, such as Itokawa, Ryugu, and Bennu, show that surfaces covered by boulders and coarse terrain are frequent on such bodies. Regolith grain sizes have distributions on approximately mm and cm scales, and the behavior of such large grains in the very low-gravity environments of small body surfaces dictates their morphology and evolution.

Aims.In order to support the understanding of natural processes (e.g., the recapturing of impact ejecta) or spacecraft-induced interactions (e.g., the fate of a small lander), we aim to experimentally investigate the response of coarse-grained target surfaces to very-low-speed impacts (below 2 m s−1).

Methods.We present the outcome of 86 low-speed impacts of a cm-sized spherical projectile into a bed of simulated regolith, composed of irregular mm- and cm-sized grains. These impacts were performed under vacuum and microgravity conditions. Our results include measurements for the projectile coefficient of restitution and penetration depth, as well as ejecta production, speed, and mass estimation. As part of our data analysis, we compared our data set with impacts performed in similar conditions with fine grain regolith targets to determine the dependence of our measurements on the target grain size.

Results.We find that impact outcomes include the frequent occurrence of projectile bouncing and tangential rolling on the target surface upon impact. Ejecta is produced for impact speeds higher than about 12 cm s−1, and ejecta speeds scale with the projectile to target the grain size ratio and the impact speed. Ejected mass estimations indicate that ejecta is increasingly difficult to produce for increasing grain sizes. Coefficients of restitution of rebounding projectiles do not display a dependency on the target grain size, unlike their maximum penetration depth, which can be scaled with the projectile to target grain size ratio. Finally, we compare our experimental measurements to spacecraft data and numerical work on Hayabusa 2’s MASCOT landing on the surface of the asteroid Ryugu.
NiAl thin film growth on Ni(001) substrate using molecular dynamics simulations
Authors: El Azrak Hicham , Hassani Abdessamad , Sbiaai Khalid , Hasnaoui Abdellatif
Published: August 2020

We have studied thin film growth of NiAl on Nickel (001) substrate using molecular dynamics simulations (MD) based on the Embedded Atom Method (EAM) potential. An incidence energy of 0.06 eV at 800 K, 900 K and 1000 K was considered. After the deposition process, we have obtained a B2-NiAl structure film with different percentages; 32.6% for the temperature 1000 K, 30% for 900 K and 25% for 800 K. Our investigation has prompt us to analyze the crystalline structure. During the evolution of deposited film, we observe the formation of grains with different orientation, as well as the appearance of vacancies in Ni and Al sublattices and antisites.
Analysis of torsional vibration effect on the diesel engine block vibration
Authors: Ni Shiwei , Guo Yibin , Lv Binglin , Wang Donghua , Li Wanyou , Shuai Zhijun
Published: August 2020

In this paper, the coupling effect between the crankshaft torsional vibration and the low speed diesel engine block vibration is investigated. Using finite element method (FEM), a model of low speed diesel engine is established to study the vibration response. The mode results of FEM agree very well with the test. The additional torques acting on the low-speed diesel engine caused by torsional vibration are discussed in detail. The vibration response of the low-speed diesel engine considering the effect of torsional vibration is studied using FEM simulation. By analyzing the effect of torsional vibration, the results demonstrate that the crankshaft torsional vibrations have important effects on the engine block vibration. The results from this study can provide useful theoretical guidance to predict vibration of low-speed diesel engine.
Progress on Iridium-Catalyzed Hydrosilylation of Alkenes and Alkynes
Authors: Ding Shengtao , Gao Weiwei
Published: August 2020

Hydrosilylation of multiple carbon–carbon bonds is a well-known process for the construction of organosilicon compounds. Nowadays, precious metal catalysts, especially platinum complexes, still occupy dominant positions in such processes. However, one important member of the precious metal family, iridium, is less used in this field. As early research mainly focused on developing stable and effective iridium catalysts, recent advances have disclosed the specific efficiency of simple iridium catalytic systems in the synthesis of functional organo­silicon compounds. This short review summarizes the utilization of iridium complexes for the hydrosilylation of alkenes and alkynes, with an emphasis on the recent advances published in the last decade.

1 Introduction

2 Iridium-Catalyzed Hydrosilylation of Alkenes

3 Iridium-Catalyzed Hydrosilylation of Alkynes

4 Conclusions and Perspectives
Flocking transition within the framework of Kuramoto paradigm for synchronization: Clustering and the role of the range of interaction
Authors: Escaff Daniel , Delpiano Rafael
Published: August 2020

A Kuramoto-type approach to address flocking phenomena is presented. First, we analyze a simple generalization of the Kuramoto model for interacting active particles, which is able to show the flocking transition (the emergence of coordinated movements in a group of interacting self-propelled agents). In the case of all-to-all interaction, the proposed model reduces to the Kuramoto model for phase synchronization of identical motionless noisy oscillators. In general, the nature of this non-equilibrium phase transition depends on the range of interaction between the particles. Namely, for a small range of interaction, the transition is first order, while for a larger range of interaction, it is a second order transition. Moreover, for larger interaction ranges, the system exhibits the same features as in the case of all-to-all interaction, showing a spatially homogeneous flux when flocking phenomenon has emerged, while for lower interaction ranges, the flocking transition is characterized by cluster formation. We compute the phase diagram of the model, where we distinguish three phases as a function of the range of interaction and the effective coupling strength: a disordered phase, a spatially homogeneous flocking phase, and a cluster-flocking phase. Then, we present a general discussion about the applicability of this way of modeling to more realistic and general situations, ending with a brief presentation of a second example (a second model with a conservative interaction) where the flocking transition may be studied within the framework that we are proposing.
Ultrahigh photovoltage responsivity of PEDOT:PSS–silicon hybrid heterojunction photodiodes
Authors: Mosaddegh Amirhossein , Noroozi Aliakbar , Javadi Mohammad , Abdi Yaser
Published: August 2020

Strong inversion at the poly(3,4-ethylenedioxythiophene): polystyrene sulfonate PEDOT:PSS/silicon interface facilitates the separation of excess carriers and obstructs surface recombination, both are of utmost importance for optoelectronic detectors. In this view, low-temperature solution-processed PEDOT:PSS/silicon hybrid heterojunctions possess great potential for light detection applications. We investigate the performance of hybrid PEDOT:PSS/silicon photodetectors following long-period exposure to ambience. In addition, the effect of PEDOT:PSS conductivity on the performance of hybrid heterojunction photodiodes is also explored. In the self-powered photovoltage mode, the hybrid photodiode displays an ultrahigh responsivity of 106 V/W, a noise equivalent power of 10 pW/Hz, and a detectivity up to 1010 Jones. Thermal noise is identified as the main limiting factor in the device performance. The hybrid photodetector demonstrates a desirable stability over long-time storage in air.
Intrinsic self-healing polymers for advanced lithium-based batteries: Advances and strategies
Authors: Xu JianHua , Ding ChenDi , Chen Peng , Tan LingHua , Chen ChunBo , Fu JiaJun
Published: August 2020

Advanced rechargeable lithium-based batteries have a profound effect on our global society and polymer materials are one of the key components of these batteries. The key roles of polymers applied in battery technology are presented in terms of binders, package coatings, separators, and electrolytes. However, the loathsomely structural changes during repeated charge/discharge processes result in the mechanical fracture problems of polymers inside batteries, which significantly reduce the cycling lifetimes. The use of intrinsic self-healing polymers as substitutes is one of the most favored strategies for reviving lithium-based batteries since self-healing polymers spontaneously eliminate the mechanical cracks or damages and result in greatly enhanced electrochemical performances. In this review, we first introduce the advances and working mechanism of intrinsic self-healing polymers. Then, we discuss the opportunities and challenges in the development of advanced lithium-based batteries with Si, Li-metal, S electrodes, and polymer electrolytes, respectively, and summarize the up-to-date key progress in intrinsic self-healing polymers for solving the above-mentioned challenges. Finally, we propose some designing principles of desired intrinsic self-healing polymers from the perspectives of basic structures, ionic conductivities, mechanical properties, chemical interactions, and the self-healing capabilities.
Neutral particle drag on parallel flow shear driven instability
Authors: Sasaki M. , Kobayashi T. , Inagaki S. , Kasuya N. , Kosuga Y.
Published: August 2020

The neutral drag effect on the parallel velocity gradient driven instability (PVG) in the presence of density inhomogeneity is theoretically investigated. The dispersion relation of PVG mode with the effect of the density gradient and neutral particle drag is derived, and its solution is analytically obtained. The neutral particle drag gives rise to the phase shift between parallel flow and electrostatic potential fluctuations and modifies the parallel compression. As a result, the stability of the PVG mode changes. It is found that the neutral particle drag does not only reduce but also enhances the instability. Specifically, near the marginal condition, the neutral particle effect suppresses the density gradient effect, and the parameter region where the PVG mode is linearly unstable significantly expands.
Conformational transition of SARS-CoV-2 spike glycoprotein between its closed and open states
Authors: Gur Mert , Taka Elhan , Yilmaz Sema Zeynep , Kilinc Ceren , Aktas Umut , Golcuk Mert
Published: August 2020

In 2020, the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has infected millions of people worldwide and caused the coronavirus disease 2019 (COVID-19). Spike (S) glycoproteins on the viral membrane bind to ACE2 receptors on the host cell membrane and initiate fusion, and S protein is currently among the primary drug target to inhibit viral entry. The S protein can be in a receptor inaccessible (closed) or accessible (open) state based on down and up positions of its receptor-binding domain (RBD), respectively. However, conformational dynamics and the transition pathway between closed to open states remain unexplored. Here, we performed all-atom molecular dynamics (MD) simulations starting from closed and open states of the S protein trimer in the presence of explicit water and ions. MD simulations showed that RBD forms a higher number of interdomain interactions and exhibits lower mobility in its down position than its up position. MD simulations starting from intermediate conformations between the open and closed states indicated that RBD switches to the up position through a semi-open intermediate that potentially reduces the free energy barrier between the closed and open states. Free energy landscapes were constructed, and a minimum energy pathway connecting the closed and open states was proposed. Because RBD-ACE2 binding is compatible with the semi-open state, but not with the closed state of the S protein, we propose that the formation of the intermediate state is a prerequisite for the host cell recognition.
Experimental demonstration of externally driven millimeter-wave particle accelerator structure
Authors: Othman Mohamed A. K. , Picard Julian , Schaub Samuel , Dolgashev Valery A. , Lewis Samantha M. , Neilson Jeffery , Haase Andrew , Jawla Sudheer , Spataro Bruno , Temkin Richard J. , Tantawi Sami , Nanni Emilio A.
Published: August 2020

We report the experimental demonstration of a mm-wave electron accelerating structure powered by a high-power rf source. We demonstrate reliable coupling of an unprecedented rf power—up to 575 kW into the mm-wave accelerator structure using a quasi-optical setup. This standing wave accelerating structure consists of a single-cell copper cavity and a Gaussian to TM01 mode converter. The accelerator structure is powered by 110 GHz, 10-ns long rf pulses. These pulses are chopped from 3 ms pulses from a gyrotron oscillator using a laser-driven silicon switch. We show an unprecedented high gradient up to 230 MV/m that corresponds to a peak surface electric field of more than 520 MV/m. We have achieved these results after conditioning the cavity with more than 105 pulses. We also report preliminary measurements of rf breakdown rates, which are important for understanding rf breakdown physics in the millimeter-wave regime. These results open up many frontiers for applications not only limited to the next generation particle accelerators but also x-ray generation, probing material dynamics, and nonlinear light-matter interactions at mm-wave frequency.
In-plane ferroelectricity and enhanced Curie temperature in perovskite BaTiO3 epitaxial thin films
Authors: Komatsu Katsuyoshi , Suzuki Ippei , Aoki Takumi , Hamasaki Yosuke , Yasui Shintaro , Itoh Mitsuru , Taniyama Tomoyasu
Published: August 2020

In-plane ferroelectric polarization in BaTiO3 (BTO) epitaxial thin films on MgAl2O4(001) (MAO) is reported. The directional dependence of both in-plane polarization curves and Raman spectroscopy shows that the films have an orthorhombic structure at room temperature, in contrast to the tetragonal structure of the corresponding bulk. The largest in-plane polarization value among BTO-based tensile-strained films is obtained. The temperature dependence of the lattice constants shows that the Curie temperature of the thin films is as high as 220 °C, which is higher than that of the bulk by 100 °C. The significant enhancement of the Curie temperature is attributed to high-quality coherent epitaxial growth due to perfect matching between the lattice parameter of the c-axis of BTO and that of MAO.
Sustainable atmospheric-pressure plasma treatment of cellulose triacetate (CTA) films for electronics
Authors: Sun Xiaohang , Bourham Mohamed , Barrett Devin G. , Pal Lokendra , McCord Marian
Published: August 2020

Surface treatments of cellulose triacetate (CTA) films via atmospheric pressure plasmas containing helium and either O2 or C3F6 as plasma reactive gas were performed to study their effects on moisture barrier, transmittance, thermal, surface chemistry, and morphological properties. Plasma treated CTA films were characterized using X-ray photoelectron spectroscopy (XPS), attenuated total reflectance-Fourier transform infrared spectroscopy, time-of-flight secondary ion mass spectrometry (ToF-SIMS), differential scanning calorimetry, thermogravimetric analysis, and scanning electron microscopy analytical techniques. Both surface chemical and morphological changes were correlated with water vapor transmission rates (WVTRs) and contact angle measurements. XPS spectra showed that the relative chemical composition of the C 1s spectra after O2 plasma treatments exhibits an increase in the relative amount of C—C bonds, which may be due to a change in surface cross-linking. ToF-SIMS spectra showed the depth of treatment of atmospheric plasma treatment of CTA films at about 100 nm. The WVTR of the CTA film was reduced up to 20% after sustainable atmospheric O2/helium plasma, while no significant changes were observed in light transmittance. Thus, the use of sustainable atmospheric plasmas to enhance moisture barrier while maintaining other critical properties such as light transmittance, thermal stability, and morphology of a CTA film could provide significant benefits to the electronics industry.
Order-indeterminant event-based maps for learning a beat
Authors: Byrne Áine , Rinzel John , Bose Amitabha
Published: August 2020

The process by which humans synchronize to a musical beat is believed to occur through error-correction where an individual’s estimates of the period and phase of the beat time are iteratively adjusted to align with an external stimuli. Mathematically, error-correction can be described using a two-dimensional map where convergence to a fixed point corresponds to synchronizing to the beat. In this paper, we show how a neural system, called a beat generator, learns to adapt its oscillatory behavior through error-correction to synchronize to an external periodic signal. We construct a two-dimensional event-based map, which iteratively adjusts an internal parameter of the beat generator to speed up or slow down its oscillatory behavior to bring it into synchrony with the periodic stimulus. The map is novel in that the order of events defining the map are not a priori known. Instead, the type of error-correction adjustment made at each iterate of the map is determined by a sequence of expected events. The map possesses a rich repertoire of dynamics, including periodic solutions and chaotic orbits.
Effects of strain on thermal conductivity of silicon dioxide thin films using test method based on 3-ω technique and uniaxial strain setup
Authors: Li Zhibin , Wang Hairong , Zhao Huiying , Gu Hanqing , Wang Jiuhong , Wei Xueyong
Published: August 2020

We propose a test method to study the effects of strain on the thermal conductivity of thin films. First, a strain setup was designed to apply stress to a thin film, and a test system was built to measure its thermal conductivity by combining the strain setup with the 3-ω method. The strain setup can apply stress to the specimen by adjusting load weights, while the strain of a thin film was obtained by measuring the applied stress with a force sensor. Second, the effects of strain on the resistance and temperature coefficients of a metal thin film were studied using the strain setup and the four-wire resistance measurement method; the results show that the resistance and temperature coefficients of metal thin films decrease with strain. Finally, the effects of strain on the thermal conductivity of a silicon dioxide thin film and silicon substrate were studied using the proposed method and test system. As the strain increased from 0% to 0.072%, the thermal conductivity of the 300-nm thick silicon dioxide thin film decreased from 0.907 W/(m K) to 0.817 W/(m K). The thermal conductivity of the 0.5-mm thick silicon substrate fluctuated in the range of 130.6 W/(m K) to 118.8 W/(m K) and then tended to stabilize around 126.4 W/(m K).
Effect of gas type on insulation recovery performance and repetitive breakdown stability of a corona-stabilized plasma closing switch
Authors: Li Longjie , Huang Zongze , Li Jiangtao
Published: August 2020

The corona-stabilized plasma closing switch, which utilizes the stabilization effect resulted from the movement and accumulation of corona-generated space charge to improve the repetitive performance, has a great potential in repetitive pulsed power systems. In this paper, the influence of gas type on the recovery performance and repetitive breakdown stability of a corona-stabilized plasma closing switch is investigated. The results are analyzed from the memory effect of residual plasma, the development and propagation characteristics of streamer corona, and the thermo-hydrodynamic process of discharge channel. The enhancement effect of residual plasma on corona stabilization of the subsequent breakdown in the repetitive operation of the gas gap with highly inhomogeneous electric field and strong electronegative gas is proposed. The development and propagation characteristics of streamer corona in different gases that can lead to significant differences in the corona stabilization effect of breakdown are clarified. It is also found that the gas with small molecular mass and higher gas velocity exhibits excellent insulation recovery in the gas switch with uniform fields, but displays poor repetitive performance in the corona-stabilized switch with a rod-plate electrode.
Dimensional effects of electrically exploding aluminum wires in argon gas: Experimental investigation
Authors: Liu Haoyu , Zhao Junping , Zhang Rui , Guo Chong , Zhang Qiaogen
Published: August 2020

The strong dependence of electrical explosion of wires (EEW) on wire dimensions is demonstrated experimentally from three perspectives: electrical characteristics, spatial structures, and nanopowder properties. Electrical characteristics of EEW were explored by measuring current and voltage waveforms of exploding 20–100 μm-diameter and 2–10 cm-long wires in argon gas. The discharge mode, energy deposition, and breakdown characteristics of EEW were analyzed based on the calculation of several electrical parameters. Laser-based diagnostics and multi-frame photographs were used to obtain the EEW spatial structures and their evolutionary characteristics. The radial distribution of exploding wires in the early and diffusion stages was obtained according to the analysis of shadowgraphs and interference images. The optical observations suggested that nonuniformity of EEW spatial structures becomes appreciable with the increase of wire dimensions. Inhomogeneities in exploding wires (e.g., residual cores, gaps, local hot spots, and stratification phenomena) and the causes of their formation were also discussed. The morphology and particle size distribution of nanopowders produced by EEW were also observed via transmission electron microscopy as well. The statistical results show that increasing wire dimensions (diameter and length) increase the average diameter and broaden the size distribution of nanopowders.
Dyson-orbital concepts for description of electrons in molecules
Authors: Ortiz J. V.
Published: August 2020

Dyson orbitals, their electron-binding energies, and probability factors provide descriptions of electrons in molecules that are experimentally verifiable and that generalize qualitatively useful concepts of uncorrelated, molecular-orbital theory to the exact limit of Schrödinger’s time-independent equation. Dyson orbitals are defined as overlaps between initial, N-electron states and final states with N ± 1 electrons and therefore are useful in the prediction and interpretation of many kinds of spectroscopic and scattering experiments. They also are characteristic of N-electron initial states and may be used to construct electron densities, one-electron properties, and total energies with correlated Aufbau procedures that include probability factors between zero and unity. Relationships with natural orbitals, Kohn–Sham orbitals, and Hartree–Fock orbitals facilitate insights into the descriptive capabilities of Dyson orbitals. Electron-propagator approximations that employ the Dyson quasiparticle equation or super-operator secular equations enable direct determination of Dyson orbitals and obviate the need for many-electron wavefunctions of initial or final states. Numerical comparisons of the amplitudes and probability factors of Dyson orbitals calculated with several self-energy approximations reveal the effects of electron correlation on these uniquely defined, one-electron wavefunctions.
Cascaded wavelength multiplexed refractive index sensors in optical fibers based on surface plasmon resonances
Authors: Tabassum Rana , Kant Ravi
Published: August 2020

Surface plasmon resonance (SPR) based cascaded wavelength multiplexed fiber-optic sensors provide immense scope for multi-channel and multi-analyte detection benefiting from all the advantages prerogative to single-channel fiber-optic sensors. This work describes the numerical simulations carried out for performance analysis of SPR based refractive index (RI) sensor implemented in cascaded dual- and triple-channel fiber-optic configurations using thin films of Ag, Cu, and Au as plasmonic metals and ZnO and Si as high RI overlayers. A dual-channel sensor is simulated using Ag and Cu/ZnO layers in two well-separated sensing channels on a multimode optical fiber, while a triple-channel sensor is studied using Ag, Cu/ZnO, and Au/Si in the three sensing channels. Due to different SPR resonance wavelengths of Ag, Cu, and Au, distinct sets of SPR spectra are obtained when the sensor response is analyzed by varying analyte RIs circumscribing different sensing regions of the cascaded fiber-optic probe. This feature furnishes an efficient option for easy tailoring of operating range of the sensor desired for different applications. The reported results provide promising perspectives for in-line sensing applications to analyze different constituents of the mixtures of biomolecules, clinical samples, petroleum products, and others.
Phase behavior of the quantum Lennard-Jones solid
Authors: Wiebe H. , Underwood T. L. , Ackland G. J.
Published: August 2020

The Lennard-Jones (LJ) potential is perhaps one of the most widely used models for the interaction of uncharged particles, such as noble gas solids. The phase diagram of the classical LJ solid is known to exhibit transitions between hcp and fcc phases. However, the phase behavior of the quantum LJ solid remains unknown. Thermodynamic integration based on path integral molecular dynamics (PIMD) and lattice dynamics calculations are used to study the phase stability of the hcp and fcc LJ solids. The hcp phase is shown to be stabilized by quantum effects in PIMD, while fcc is shown to be favored by lattice dynamics, which suggests a possible re-entrant low pressure fcc phase for highly quantum systems. Implications for the phase stability of noble gas solids are discussed. For parameters equating to helium, the expansion due to zero-point vibrations is associated with quantum melting: neither crystal structure is stable at zero pressure.
Competition between the shake-off and knockout mechanisms in the double and triple photoionization of the halothane molecule (C2HBrClF3)
Authors: Santos A. C. F. , Lago A. F. , Lucas C. A. , de Souza G. G. B.
Published: August 2020

The ratios of single, double, and triple ionizations to the total photoionization of the halothane (C2HBrClF3) molecule have been investigated by a single-photon ionization in the energy range from 21.21 eV to 320 eV. In the valence region, the multiple ionization results can be described by a sum of contributions generated from the shake-off and the two-step one models. At low photon energies (from the threshold of triple ionization up to 100 eV), the triple photoionization dynamics of halothane can be reasonably well described by a model involving a classical electron impact double ionization of the singly ionized parent ion.
Atomistic defects as single-photon emitters in atomically thin MoS2
Authors: Barthelmi K. , Klein J. , Hötger A. , Sigl L. , Sigger F. , Mitterreiter E. , Rey S. , Gyger S. , Lorke M. , Florian M. , Jahnke F. , Taniguchi T. , Watanabe K. , Zwiller V. , Jöns K. D. , Wurstbauer U. , Kastl C. , Weber-Bargioni A. , Finley J. J. , Müller K. , Holleitner A. W.
Published: August 2020

Precisely positioned and scalable single-photon emitters (SPEs) are highly desirable for applications in quantum technology. This Perspective discusses single-photon-emitting atomistic defects in monolayers of MoS2 that can be generated by focused He-ion irradiation with few nanometers positioning accuracy. We present the optical properties of the emitters and the possibilities to implement them into photonic and optoelectronic devices. We showcase the advantages of the presented emitters with respect to atomistic positioning, scalability, long (microsecond) lifetime, and a homogeneous emission energy within ensembles of the emitters. Moreover, we demonstrate that the emitters are stable in energy on a timescale exceeding several weeks and that temperature cycling narrows the ensembles' emission energy distribution.
Symmetric Airy electron plasma wave
Authors: Chen Yaohui , Wu Lixun , Liu Yujun , Wu You , Lin Zejia , Deng Dongmei
Published: August 2020

A symmetric Airy electron plasma (SAiEP) wave, which is caused by launching four Airy beams symmetrically in the initial plane in an unmagnetized collisionless plasma, is analytically investigated in this paper. In addition to intensity distributions, evolutions, and the potential of the SAiEP wave with different parameters, the difference between the SAiEP wave and the Airy-like electron plasma wave is studied as well. The results show that the SAiEP wave with different distances between the main lobes in the initial plane behaves differently as the decay factor changes. When the decay factor increases, the frequency and the amplitude of the potential become smaller. Besides, the SAiEP wave has the autofocusing property, while the Airy-like electron plasma wave has the weak diffraction property.
Room temperature infrared detectors made of PbTe/CdTe multilayer composite
Authors: Chusnutdinow S. , Schreyeck S. , Kret S. , Kazakov A. , Karczewski G.
Published: August 2020

We report on fabrication and characterization of infrared detectors made of a composite material—PbTe/CdTe multilayer (ML). The multilayer consists of 10 repetitions of 35 nm thick PbTe layers and 75 nm thick CdTe layers grown by molecular beam epitaxy on GaAs (100) semi-insulating substrates. Simple technological methods were used to manufacture photoresistors from the structure containing the PbTe/CdTe composite. The front-side illuminated photodetectors show a cut-off wavelength of 3.57 μm and a peak current responsivity of 127 mA/W at a bias voltage of 10 V, a frequency of 730 Hz, and a temperature of 300 K. The specific detectivity of photoresistors at the peak wavelength of 2.9 μm equals 2.7 × 1010 cm·Hz1/2/W and 6.1 × 109 cm·Hz1/2/W for 77 and 300 K, respectively. Although the ML photoresistors were not optimized, neither antireflection coated nor lithographically defined, their detectivity, especially at room temperature, is highly comparable to that of photoconducting infrared detectors available in the market. Possible mechanisms causing the relatively high performance of PbTe/CdTe ML detectors have been discussed in detail. These are a decrease in the electron concentration in the conducting PbTe layers caused by capturing some mobile electrons by dangling bonds present at the PbTe/CdTe interfaces and the effective suppression of the Auger recombination in nanostructures made of narrow and wide bandgap semiconductors.
Non-volatile, small-signal capacitance in ferroelectric capacitors
Authors: Luo Yuan-Chun , Hur Jae , Wang Panni , Khan Asif Islam , Yu Shimeng
Published: August 2020

Tunable, non-volatile, small-signal capacitance is observed and characterized in a TiN/ferroelectric Hf0.5Zr0.5O2 (HZO)/TiN stack. The non-volatility of the small-signal capacitance originates from the non-uniform distribution of oxygen vacancies near/at the bottom electrode, resulting in polarity-dependent responses of the domain-wall vibration. Our hypothesis also agrees with the observed frequency dispersion, which could be explained with the Maxwell Wagner effect. Furthermore, we have shown more than 104 endurance and 10-year retention at 85 °C for this non-volatile capacitance. With tunable capacitance at a fixed bias, HZO capacitors can potentially be applied to reconfigurable analog or mixed-signal circuits.
Effects of exciton deconfinement on the transient photoluminescence from thermally activated delayed fluorescence host–guest systems
Authors: Hauenstein C. , Gottardi S. , Bobbert P. A. , Coehoorn R. , van Eersel H.
Published: August 2020

For thermally activated delayed fluorescence (TADF) host–guest systems used in organic light-emitting diodes, understanding of the transient photoluminescence (PL) measurements is crucial for accurate determination of the photophysical rates of the emitter. Here, we study how the PL is affected by triplet-exciton deconfinement from the guest to the host molecules. This deconfinement can complicate the analysis of the PL decay and potentially lead to a loss of efficiency. From an analytical model, we find that the transient PL intensity remains bi-exponential in the presence of exciton deconfinement for the case of fast triplet diffusion, albeit with a longer decay time of the delayed component. Deconfinement might, therefore, not always be recognizable from a single transient PL measurement. The role of deconfinement depends on the energetic disorder, the guest concentration, and the energy difference ΔET between triplet-exciton energies on the host and guest molecules and is effectively suppressed for ΔET>0.2eV. We find from analytical modeling and kinetic Monte Carlo simulations that the decay can become non-bi-exponential and even show a distinct third decay step. The shape of the decay curves depends on the characteristic times for guest–host transfer and host diffusion, relative to the prompt and delayed decay times of the TADF emitter. A comparison with available experimental data is included, finding qualitative agreement with dedicated deconfinement studies and indicating the influence of other processes for the often observed power-law decay at long time scales.
Solitary ion acoustic waves in a plasma with regularized κ-distributed electrons
Authors: Liu Y.
Published: August 2020

This work has been focused on the investigation of the existence conditions and the characteristics of ion acoustic soliton (IAS) in a plasma, which is composed of cold ions and regularized κ-distributed electrons. It is found that the propagation speed of the IAS should be larger than the actual ion acoustic velocity in the model. When the superthermal spectral index κ > 1.5, there exists IAS with only positive potential. In that case, the impact of the cutoff parameter α on the IAS is rather small. When κ < 1.5, however, the properties of IAS will exhibit a completely different behavior. The most significant change is that there will be IAS with negative potential if κ is small enough. The value of κ for the presence of the negative potential IAS decreases with the increase in α. The width of the IAS is determined by the Mach number, the superthermal index κ, and the cutoff parameter α. In addition, there is no singularity for the existence conditions of the IAS in the whole range κ > 0. It indicates that the regularized κ-distribution introduced by Scherer et al. (2017) can be relevant to the fluid description of the nonthermal plasma. The results obtained in the present study might be useful for the understanding of the nonlinear electrostatic phenomena in space plasmas.
Ion-mediated hopping electrode polarization model for impedance spectra of CH3NH3PbI3
Authors: Almora Osbel , González-Lezcano Alfredo , Guerrero Antonio , Brabec Christoph J. , Garcia-Belmonte Germà
Published: August 2020

Methylammonium lead iodide (CH3NH3PbI3) is one of the most attractive materials for optoelectronic applications, and it is the most typical absorber in perovskite solar cells, which are unprecedentedly successful devices in terms of power conversion efficiency. In this work, the conductivity and capacitance spectra of symmetrically contacted Au/CH3NH3PbI3/Au thick pellets are measured via impedance spectroscopy at different temperatures in dark equilibrium. The experimental conductivity spectra are parameterized and showed to follow the formalism of hopping DC conductivity in the CH3NH3PbI3 bulk. The presence of several regimes for the general Jonscher's “universal” conductivity–frequency response is highlighted and associated with the ionic–electronic overlapping conductivities. For the capacitance spectra, the general features of electrode polarization capacitance at the CH3NH3PbI3/Au interfaces are identified but yet are found to be in disagreement with some trends of classical ionic conductivity models, unable to separate different contributions. Accordingly, an analytical model is proposed accounting for hopping processes where the low frequency activation energy is split into ionic and electronic components. Our parameterizations and analytical model discern between the bulk/interface and ionic/electronic phenomena and estimate the multiple activation energies in this hybrid halide perovskite.
Trap state mediated triplet energy transfer from CdSe quantum dots to molecular acceptors
Authors: Jin Tao , Lian Tianquan
Published: August 2020

Triplet energy transfer (TET) from quantum dots (QDs) to molecular acceptors has received intense research interest because of its promising application as triplet sensitizers in photon up-conversion. Compared to QD band edge excitons, the role and mechanism of trap state mediated TET in QD-acceptor complexes have not been well understood despite the prevalence of trap states in many QDs. Herein, TET from trap states in CdSe QDs to adsorbed 9-anthracene carboxylic acid (ACA) is studied with steady state photoluminescence, transient absorption spectroscopy, and time-resolved photoluminescence. We show that both band edge and trap excitons undergo direct Dexter energy transfer to form the triplet excited state of ACA. The rate of TET decreases from (0.340 ± 0.002) ns−1 to (0.124 ± 0.004) ns−1 for trap excitons with decreasing energy from 2.25 eV to 1.57 eV, while the TET rate from band edge excitons is 13–37 times faster than trapped excitons. Despite slightly higher TET quantum efficiency from band edge excitons (∼100%) than trapped excitons (∼95%), the overall TET process from CdSe to ACA is dominated by trapped excitons because of their larger relative populations. This result demonstrates the important role of trap state mediated TET in nanocrystal sensitized triplet generation.
Fast reinforcement learning with generalized policy updates
Authors: Barreto André , Hou Shaobo , Borsa Diana , Silver David , Precup Doina
Published: August 2020

The combination of reinforcement learning with deep learning is a promising approach to tackle important sequential decision-making problems that are currently intractable. One obstacle to overcome is the amount of data needed by learning systems of this type. In this article, we propose to address this issue through a divide-and-conquer approach. We argue that complex decision problems can be naturally decomposed into multiple tasks that unfold in sequence or in parallel. By associating each task with a reward function, this problem decomposition can be seamlessly accommodated within the standard reinforcement-learning formalism. The specific way we do so is through a generalization of two fundamental operations in reinforcement learning: policy improvement and policy evaluation. The generalized version of these operations allow one to leverage the solution of some tasks to speed up the solution of others. If the reward function of a task can be well approximated as a linear combination of the reward functions of tasks previously solved, we can reduce a reinforcement-learning problem to a simpler linear regression. When this is not the case, the agent can still exploit the task solutions by using them to interact with and learn about the environment. Both strategies considerably reduce the amount of data needed to solve a reinforcement-learning problem.
Physician–patient racial concordance and disparities in birthing mortality for newborns
Authors: Greenwood Brad N. , Hardeman Rachel R. , Huang Laura , Sojourner Aaron
Published: August 2020

Significance

A large body of work highlights disparities in survival rates across Black and White newborns during childbirth. We posit that these differences may be ameliorated by racial concordance between the physician and newborn patient. Findings suggest that when Black newborns are cared for by Black physicians, the mortality penalty they suffer, as compared with White infants, is halved. Strikingly, these effects appear to manifest more strongly in more complicated cases, and when hospitals deliver more Black newborns. No such concordance effect is found among birthing mothers.
Siberian and temperate ecosystems shape Northern Hemisphere atmospheric CO
2
seasonal amplification
Authors: Lin Xin , Rogers Brendan M. , Sweeney Colm , Chevallier Frédéric , Arshinov Mikhail , Dlugokencky Edward , Machida Toshinobu , Sasakawa Motoki , Tans Pieter , Keppel-Aleks Gretchen
Published: August 2020

Significance

The increasing atmospheric CO
2
seasonal cycle amplitude in the Northern Hemisphere suggests northern ecosystems are responding strongly to global change. Considerable uncertainties remain regarding drivers of these changes and their locations. We find that seasonal flux changes in Siberian and temperate ecosystems together shape the increasing CO
2
amplitude. Particularly, enhanced seasonal carbon exchange in Siberia drives most of observed amplitude increases at the surface of northern high latitudes. Arctic-boreal North America shows much smaller changes in flux seasonality and has only localized impacts, consistent with more browning in this region from field and satellite observations. Our findings highlight divergent ecosystem responses among regions, countering the simple narrative that CO
2
fertilization and climate warming are the dominant drivers.