bluuebunny/crossref_metadata_2025 huggingface dataset:
Dispersal timescale of protoplanetary disks in the low-metallicity young cluster Dolidze 25
Authors: Guarcello M. G. , Biazzo K. , Drake J. J. , Micela G. , Prisinzano L. , Sciortino S. , Damiani F. , Flaccomio E. , Neiner C. , Wright N. J.
Published: April 2021

Context. The dispersal of protoplanetary disks sets the timescale that is available for planets to assemble, and thus it is one of the fundamental parameters in theories of planetary formation. Disk dispersal is determined by several properties of the central star, the disk itself, and the surrounding environment. In particular, the metallicity of disks may affect their evolution, but controversial results have been published so far: disks in low-metallicity clusters appear to disperse rapidly, while some evidence supports the existence of accreting disks that are several million years old in the Magellanic Clouds.

Aims. We study the dispersal timescale of disks in Dolidze 25, the young cluster in the proximity of the Sun with the lowest metallicity, to understand whether disk evolution is affected by the low metallicity of the cluster.

Methods. We analyzed Chandra ACIS-I observations of the cluster and combined the resulting source catalog with existing optical and infrared catalogs of the region. We selected the disk-bearing population in a circular region with a diameter of 1° centered on Dolidze 25 from criteria based on infrared colors, and we selected the disk-less population within a smaller central region from the X-ray sources with O infrared counterparts. In both cases, criteria were applied to discard contaminating sources in the foreground or background. We derived stellar parameters from isochrones that were fit to color-magnitude diagrams.

Results. We derived a disk fraction of ∼34% and a median age of the cluster of 1.2 Myr. To minimize the effect of incompleteness and spatial inhomogeneity in the list of members, we restricted this calculation to stars in a magnitude range within which our selection of cluster members is fairly complete. We also adopted different cuts in stellar masses. When we compare this estimate with existing estimates of the disk fraction of clusters younger than 10 Myr, the disk fraction of Dolidze 25 appears to be lower than what is expected based on its age alone.

Conclusions. Even though our results are not conclusive given the intrinsic uncertainty on stellar ages estimated from isochrone fitting to color-magnitude diagrams, we suggest that disk evolution in Dolidze 25 may be affected by the environment. Given the poor O-star population and low stellar density of the cluster, it is more likely that the disk dispersal timescale is dictated more by the low metallicity of the cluster than by external photoevaporation or dynamical encounters.
Multi-band observations of Swift J0840.7−3516: A new transient ultra-compact X-ray binary candidate
Authors: Coti Zelati F. , de Ugarte Postigo A. , Russell T. D. , Borghese A. , Rea N. , Esposito P. , Israel G. L. , Campana S.
Published: April 2021

We report on multi-band observations of the transient source Swift J0840.7−3516, which was detected in outburst in 2020 February by the Neil Gehrels Swift Observatory. The outburst episode lasted just ∼5 days, during which the X-ray luminosity quickly decreased from LX ≈ 3 × 1037 d102 erg s−1 at peak down to LX ≈ 5 × 1033 d102 erg s−1 in quiescence (0.3−10 keV; d10 is the distance to the source in units of 10 kpc). Such a marked and rapid decrease in the flux was also registered at UV and optical wavelengths. In outburst, the source showed considerable aperiodic variability in the X-rays on timescales as short as a few seconds. The spectrum of the source in the energy range 0.3−20 keV was well described by a thermal, blackbody-like, component plus a non-thermal, power law-like, component and it softened considerably as the source returned to quiescence. The spectrum of the optical counterpart in quiescence showed broad emission features mainly associated with ionised carbon and oxygen, superposed on a blue continuum. No evidence for bright continuum radio emission was found in quiescence. We discuss possible scenarios for the nature of this source and show that the observed phenomenology points to a transient ultra-compact X-ray binary system.
Research on roll profile electromagnetic control ability in optimal electromagnetic stick parameter
Authors: Yang Tingsong , Liu Jiayang , Ren Xinyi , Wang Yingwei , Du Fengshan
Published: April 2021

Roll profile electromagnetic control technology (RPECT) is a new strip flatness control technology. As the control element, electromagnetic sticks have a great effect on the control ability of RPECT. To improve control ability and extend service life, effective control ratio of electromagnetic stick is presented in this paper. The ratio is designed based on the structure character of electromagnetic stick, and can be used to evaluate the key parameter of electromagnetic stick. Based on the coupled FEM, the heat flux density of the roll inner hole and the temperature distribution of electromagnetic stick are analyzed for different effective control ratios; the average contact pressure between electromagnetic stick and electromagnetic control roll is studied to evaluate the change of force roll profile; the state of roll profile and the stress state of the roll are researched to analyze the comprehensive control ability. Through the verification on the roll profile electromagnetic control experimental platform, the reasonable selection range of effective control ratio, which can be used to expand the roll profile axial affected area, is from 0.5 to 0.583. In order to increase the roll crown, the selection of ηd needs to consider the current density and the optimal selection range of effective control ratio.
Antivirale Eigenschaften des Extrakts aus Cistus × incanus L. Pandalis auch bei SARS-CoV-2 in vitro nachgewiesen
Authors: Träder Jens-Martin
Published: April 2021

Da es noch keine zuverlässige Therapie und nicht in ausreichender Menge zugelassene Impfstoffe gegen SARS-CoV-2 gibt, sucht die Forschung nach vielversprechenden, wirksamen Substanzen, die bereits verfügbar sind. In dieser Studie soll untersucht werden, ob das pflanzliche Präparat Cystus Pandalis® in vitro antivirale Eigenschaften gegen SARS-CoV-2 aufweist, da es sich bereits gegen mehrere andere Viren als wirksam erwiesen hat. Am Fraunhofer Institut für Zelltherapie und Immunologie (IZI) wurden Zellkulturen unter Anwendung von Cystus Pandalis®-Extrakt (CPE) mit SARS-CoV-2 infiziert, und die Reduktion der Infektionsrate wurde durch den Vergleich von fokusbildenden Einheiten bewertet. Eine fast vollständige Reduktion der Infektionsrate durch CPE wurde bei Konzentrationen von mehr als 15,6 µg/ml mit einer berechneten EC50 von 1,94 µg/ml beobachtet. Der Wirkmechanismus dieses Extraktes beruht möglicherweise auf den hochpolymeren Polyphenolen, die bestimmte virale Epitope umhüllen, wodurch CPE als Eintrittsinhibitor wirkt. Aufgrund der hohen In-vitro-Aktivität erscheint es sinnvoll, CPE als Prophylaxe gegen Infektionen mit SARS-CoV-2 einzusetzen.
Nicht fernmetastasiertes kastrationsresistentes Prostatakarzinom (M0CRPC)
Authors: Spiegelhalder Philipp , Bögemann Martin
Published: April 2021

Das Auftreten von Fernmetastasen stellt beim nicht fernmetastasierten kastrationsresistenten Prostatakarzinom (M0CRPC) einen prognostisch ungünstigen Wendepunkt dar. Dabei haben M0CRPC-Patienten mit kurzer PSA-Verdopplungszeit ein besonders hohes Progressionsrisiko. Für diese Patienten gab es lange Zeit, bis auf das abwartende Beobachten unter Beibehaltung der klassischen Androgendeprivationstherapie (ADT), keine weiteren Therapieoptionen. Das seit Januar 2019 verfügbare Next-Generation Antiandrogen Apalutamid verlängerte in der Zulassungsstudie SPARTAN beim Hochrisiko-M0CRPC das metastasenfreie Überleben signifikant gegenüber Placebo. Die vorliegenden Patientenfälle aus der SPARTAN-Studie und dem Apalutamid Härtefallprogramm sind Beispiele für die positiven Effekte, die Apalutamid im M0CRPC-Stadium erzielen kann.
Mariendistel bei Lebererkrankungen
Authors: Koch Anna K. , Langhorst Jost
Published: April 2021

Mariendistel ist das am häufigsten angewandte Phytotherapeutikum bei Patienten mit Lebererkrankungen. Von der Europäischen Zulassungsbehörde EMA wird der Einsatz dieser Heilpflanze als „traditional use“ klassifiziert. Studien belegen die Wirksamkeit einer unterstützenden Behandlung mit Mariendistelextrakt insbesondere bei toxischen Leberschäden zum Beispiel durch Alkohol und Knollenblätterpilzvergiftung. Erste Hinweise deuten auf eine ergänzende Wirksamkeit von Mariendistel in Kombination mit einer Veränderung des Lebensstils auch bei Hepatitis B hin. Nähere Untersuchungen müssen diesen Effekt in Zukunft jedoch noch bestätigen.
40 Jahre Interdisziplinäres Transplantationszentrum am Universitätsklinikum Schleswig-Holstein, Campus Lübeck – Team Spirit at its Best
Authors: Nitschke Martin , Lapshyn Hryhoriy , Keck Tobias
Published: April 2021

In der Transplantationsmedizin bilden sich in den letzten Jahrzehnten vermehrt fächerübergreifende Organzentren, die im Rahmen einer interdisziplinären Kooperation eine optimale Versorgung vor, während und nach der Transplantation solider Organe gewährleisten können. Am Standort Lübeck wurde seit der Gründung des Zentrums vor 40 Jahren die Interdisziplinarität zwischen der Transplantationschirurgie und der Nephrologie gelebt, sodass sich ein auf die Nierentransplantation spezialisiertes Zentrum entwickeln konnte. Neben der medizinisch-fachlichen konnte eine organisatorische und baulich-infrastrukturelle Zentrumsbildung realisiert werden, die Vorbildcharakter für interdisziplinäre Transplantationszentren erreichte. Eine hohe Expertise minimalinvasiver Operationstechniken gemeinsam mit einer spezialisierten Transplantationsnephrologie bilden dabei die Basis für eine höchstmögliche Patientenzufriedenheit.
Pyridine-Mediated B–B Bond Activation of (RO)2B–B(OR)2 for Generating Borylpyridine Anions and Pyridine-Stabilized Boryl Radicals as Useful Boryl Reagents in Organic Synthesis
Authors: Tsurugi Hayato , Mashima Kazushi , Misal Castro Luis C. , Sultan Ibrahim
Published: April 2021

Significant developments have been achieved in recent years toward the utilization of (RO)2B–B(OR)2 for exploring transition-metal-free organic transformations in organic synthesis. Among the various combinations of Lewis bases with diborons developed so far, pyridine derivatives are simple, commercially available, and cheap compounds to expand the synthetic utility of diborons by generating borylpyridine anions and pyridine-stabilized boryl radicals via B–B bond cleavage. These borylpyridine species mediate a series of transformations in both a catalytic and stoichiometric manner for C–X activation (X = halogen, CO2H, NR2) and concomitant C-borylation, hydroboryl­ation, C–C bond formation, and reduction reactions.

1 Introduction

2 Reaction Pathway for B–B Bond Cleavage of Diborons with Electron-Deficient Pyridines

3 Pyridine-Mediated B–B Bond Activation of (RO)2B–B(OR)2 for Application in Organic Synthesis

3.1 Dehalogenative C-Borylation

3.2 Desulfonative C-Borylation

3.3 Decarboxylative C-Borylation

3.4 Deaminative C-Borylation

3.5 Hydroborylation

3.6 C–C Bond Formation

3.7 Pyridine Functionalization

3.8 Deoxygenation and N-Borylation Reactions

4 Conclusions
Fibrinolysis in Acute and Chronic Cardiovascular Disease
Authors: Kietsiriroje Noppadol , Ariëns Robert A.S. , Ajjan Ramzi A.
Published: April 2021

The formation of an obstructive thrombus within an artery remains a major cause of mortality and morbidity worldwide. Despite effective inhibition of platelet function by modern antiplatelet therapies, these agents fail to fully eliminate atherothrombotic risk. This may well be related to extensive vascular disease, beyond the protective abilities of the treatment agents used. However, recent evidence suggests that residual vascular risk in those treated with modern antiplatelet therapies is related, at least in part, to impaired fibrin clot lysis. In this review, we attempt to shed more light on the role of hypofibrinolysis in predisposition to arterial vascular events. We provide a brief overview of the coagulation system followed by addressing the role of impaired fibrin clot lysis in acute and chronic vascular conditions, including coronary artery, cerebrovascular, and peripheral vascular disease. We also discuss the role of combined anticoagulant and antiplatelet therapies to reduce the risk of arterial thrombotic events, addressing both efficacy and safety of such an approach. We conclude that impaired fibrin clot lysis appears to contribute to residual thrombosis risk in individuals with arterial disease on antiplatelet therapy, and targeting proteins in the fibrinolytic system represents a viable strategy to improve outcome in this population. Future work is required to refine the antithrombotic approach by modulating pathological abnormalities in the fibrinolytic system and tailoring therapy according to the need of each individual.
Fibrinolysis in Venous Thromboembolism
Authors: Undas Anetta
Published: April 2021

Fibrinolysis is of paramount importance in maintaining or regaining the patency of veins and pulmonary arteries obstructed by thrombi. Growing experimental and clinical evidence indicates that impaired fibrinolysis mediated by multiple complex mechanisms is involved in venous thromboembolism (VTE). Global plasma fibrin clot lysis markers, especially clot lysis time, have been reported to predict recurrent deep-vein thrombosis and pulmonary embolism. The current overview summarizes available data linking fibrinolysis to VTE and its long-term sequelae.
Managing Pandemics with Health Informatics: Successes and Challenges
Authors: Basit Mujeeb A. , Lehmann Christoph U. , Medford Richard J.
Published: April 2021

Introduction: The novel COVID-19 pandemic struck the world unprepared. This keynote outlines challenges and successes using data to inform providers, government officials, hospitals, and patients in a pandemic.

Methods: The authors outline the data required to manage a novel pandemic including their potential uses by governments, public health organizations, and individuals.

Results: An extensive discussion on data quality and on obstacles to collecting data is followed by examples of successes in clinical care, contact tracing, and forecasting. Generic local forecast model development is reviewed followed by ethical consideration around pandemic data. We leave the reader with thoughts on the next inevitable outbreak and lessons learned from the COVID-19 pandemic.

Conclusion: COVID-19 must be a lesson for the future to direct us to better planning and preparing to manage the next pandemic with health informatics.
Synergien nutzen: Sicherheitsdienste im Klinikbereich
Authors: Hartmann Axel
Published: April 2021

Sicherheitsdienstleistungen im Krankenhausbereich bieten eine differenzierte Situation und können polarisieren. Die Gefühlslage kann von Wohlbehaglichkeit bis zur Unsicherheit von Patienten, Besuchern und Mitarbeitern führen. Die Übernahme von zusätzlichen Dienstleistungen kann diesen Eindruck ausgleichen, so die Mitarbeiter des Sicherheitsdienstes im Alltagsbild der Klinik erscheinen.
Resolving ECRH deposition broadening due to edge turbulence in DIII-D
Authors: Brookman M. W. , Austin M. E. , Petty C. C. , La Haye R. J. , Barada K. , Rhodes T. L. , Yan Z. , Köhn A. , Thomas M. B. , Leddy J. , Vann R. G. L.
Published: April 2021

Microwave heat pulse propagation experiments have demonstrated a correlation between millimeter-scale turbulence and deposition profile broadening of electron cyclotron (EC) waves on the DIII-D tokamak. In a set of discharges in DIII-D, a variation in edge density fluctuations on the mm-scale is associated with 40%–150% broader deposition profiles, expressed in terms of normalized minor radius, as compared with equilibrium ray tracing. The 1D power profile is determined from transport analysis of the electron temperature response to EC power modulation using perturbative analysis with a square wave power modulation at 20–70 Hz, producing a series of Fourier harmonics that are fit collectively to resolve transport. Fitting an integrated heat flux expressed in the Fourier basis of the modulation to diffusive, convective, and coupled transport terms in a linear model can resolve the broadened EC deposition width from the power perturbation to resolve a broadening in each case. The best fit degree of beam broadening observed scales approximately linearly with the Doppler backscattering measured fluctuation level in the steep gradient region. Quantifying the effect of edge fluctuation broadening on EC current drive power needs of future devices will require 3D full-wave codes that can be validated on the current generation of machines. These DIII-D experiments provide a quantitative measure of fluctuation effects and a dataset to benchmark full-wave simulations that can model and eventually predict nonlinear effects neglected by 1D equilibrium beam and ray tracing.
A micromechanics model to predict effective thermal conductivity of rGO/MMT/polymer composites
Authors: Cong Chaonan , Chen Yongqiang , Huang Zhuping , Bai Shulin
Published: April 2021

In recent years, enhanced thermal conductive properties of polymer composites filled with reduced graphene oxide (rGO) have been studied for diverse applications. However, rGO fillers tend to form aggregates, making it difficult to reach the maximum enhancement through the use of rGO. Experiments have shown that the hydrogen bond between rGO and montmorillonite (MMT) can lead to a stable dispersion of rGO with the result of improving the effective thermal conductivity (ETC) of the composite. However, the mechanisms of this phenomenon are not yet well known. In this work, a micromechanics-based method is proposed to provide an analytical expression of the ETC of rGO/MMT/polymer composites. The predictions are in good agreement with the experimental data, demonstrating the effectiveness of the proposed framework. Also, the effect of the orientation of the fillers is investigated, which useful to determine the optimal orientation and filling ratio to meet various requirements in the material performance design and preparation of rGO/MMT/polymer composites.
Time series simulation for multiple wind farms based on HMMs and regular vine copulas
Authors: Qu Kai , Si Gangquan , Sun Xiang , Lian Wenli , Huang Yuehui , Li Pai
Published: April 2021

The randomness and fluctuation of wind power cause difficulties in electric utilities operation and dispatch. Although the methods for simulating wind power time series have been studied by researchers for decades, methods designed for the single wind farm output or the aggregated output of multiple wind farms are inefficient in capturing the spatial dependence among regional multiple wind farms. Also, abnormal or missing data are quite common in the wind power field, which is often ignored by traditional multi-dimensional correlation modeling methods, resulting in being imprecise and unstable encountering the situation of missing data. In this paper, the discrete hidden Markov model (HMM) and regular vine copulas are applied to accurately reproduce the joint distribution of regional wind farms. The regular vine copulas can take various bivariate copulas as blocks to precisely and flexibly describe the dependence structures of multiple wind farm outputs, and using HMM, we were able to model transition probability for different dependence structures. Enough synthetic time series of multiple wind farms can be generated by the proposed method, and it is of great significance for the long-term scheduling of power systems. The effectiveness of the proposed method is tested using the datasets of five wind farms in Northwest China as a case. The simulation results prove that the proposed method can accurately model the dependence structures among multiple wind farms and statistical characteristics of power outputs, and are more robust when there are missing data in wind power records especially.
Density reduction on plasma sheath using pulsed magnetic field
Authors: Xu Jiahao , Li Xiaoping , Liu Donglin , Xu Cong , Qin Yongqiang
Published: April 2021

When a space vehicle travels through the atmosphere at a hypersonic speed, it is enveloped by a plasma sheath. The density of plasma sheath is high enough such that communication and telemetry signals are prevented from passing to and from the vehicle, which is called communication blackout. A method to reduce plasma density for communication blackout mitigation by using pulsed magnetic field is proposed in this paper. In order to study the effect of pulsed magnetic field on plasma density, a two-dimensional axisymmetric model was established. The simulation results suggested that the pulsed magnetic field can reduce the plasma sheath density of 5 cm thickness by more than 90%, and was of sufficient size (about 5 cm) and time duration (about 330 μs) to permit transmission of data. On the basis of the simulation results, the interaction mechanism between pulsed magnetic field and plasma is explained by theoretical analysis. Furthermore, experiments of the plasma density reduction by pulsed magnetic field are performed. The experimental results suggested that a 0.55T pulsed magnetic field can reduce the plasma sheath density of 14 cm thickness by 43%–78%, which verifies the effectiveness of the pulsed magnetic field method. A comparison of results from simulation and experiment provided strong evidence for the correctness of the simulation model. The simulation results also show that low pressure and high initial electron density are beneficial to the reduction of plasma density, which also explains the phenomenon in the experiment. In addition, it is found in the experiment that two continuous reverse pulses can play the same role in reducing the plasma density, which provides the possibility for the continuous reduction of plasma density. These investigations could have a significant benefit on the design and optimization of pulsed magnetic field mitigation scheme for the blackout problem.
Photon–electron coincidence experiments at synchrotron radiation facilities with arbitrary bunch modes
Authors: Ozga C. , Honisch C. , Schmidt Ph. , Holzapfel X. , Zindel C. , Küstner-Wetekam C. , Richter C. , Hergenhahn U. , Ehresmann A. , Knie A. , Hans A.
Published: April 2021

We report the adaptation of an electron–photon coincidence detection scheme to the multibunch hybrid mode of the synchrotron radiation source BESSY II (Helmholtz-Zentrum Berlin). Single-event-based data acquisition and evaluation, combined with the use of relative detection times between the coincident particles, enable the acquisition of proper coincidence signals from a quasi-continuous excitation pattern. The background signal produced by accidental coincidences in the time difference representation is modeled using the non-coincident electron and photon spectra. We validate the method by reproducing previously published results, which were obtained in the single bunch mode, and illustrate its usability for the multibunch hybrid mode by investigating the photoionization of CO2 into CO2+ B satellite states, followed by subsequent photon emission. The radiative lifetime obtained and the electron binding energy are in good agreement with earlier publications. We expect this method to be a useful tool to extend the versatility of coincident particle detection to arbitrary operation modes of synchrotron radiation facilities and other excitation sources without the need for additional experimental adjustments.
Chalcogenide phase-change devices for neuromorphic photonic computing
Authors: Brückerhoff-Plückelmann Frank , Feldmann Johannes , Wright C. David , Bhaskaran Harish , Pernice Wolfram H. P.
Published: April 2021

The integration of artificial intelligence systems into daily applications like speech recognition and autonomous driving rapidly increases the amount of data generated and processed. However, satisfying the hardware requirements with the conventional von Neumann architecture remains challenging due to the von Neumann bottleneck. Therefore, new architectures inspired by the working principles of the human brain are developed, and they are called neuromorphic computing. The key principles of neuromorphic computing are in-memory computing to reduce data shuffling and parallelization to decrease computation time. One promising framework for neuromorphic computing is phase-change photonics. By switching to the optical domain, parallelization is inherently possible by wavelength division multiplexing, and high modulation speeds can be deployed. Non-volatile phase-change materials are used to perform multiplications and non-linear operations in an energetically efficient manner. Here, we present two prototypes of neuromorphic photonic computation units based on chalcogenide phase-change materials. First is a neuromorphic hardware accelerator designed to carry out matrix vector multiplication in convolutional neural networks. Due to the neuromorphic architecture, this prototype can already operate at tera-multiply-accumulate per second speeds. Second is an all-optical spiking neuron, which can serve as a building block for large-scale artificial neural networks. Here, the whole computation is carried out in the optical domain, and the device only needs an electrical interface for data input and readout.
Reduced coercive field in epitaxial thin film of ferroelectric wurtzite Al0.7Sc0.3N
Authors: Yazawa Keisuke , Drury Daniel , Zakutayev Andriy , Brennecka Geoff L.
Published: April 2021

Epitaxial ferroelectric wurtzite films exhibiting clear polarization-electric field hysteresis behavior are presented. The coercive field of this epitaxial Al0.7Sc0.3N film on the W/c-sapphire substrate is 0.4 ± 0.3 MV cm−1 (8%) smaller than that of a conventional fiber textured film on a Pt/TiOx/SiO2/Si substrate, attributed to the 0.01 ± 0.007 Å smaller c-axis lattice parameter in the epitaxial film. The strain and decrease in the coercive field most likely originate from epitaxial strain rather than the mismatch in the thermal coefficient of expansion. These results provide insight for further coercive field reduction of wurtzite ferroelectrics using epitaxial mismatch strain.
Majorana zero mode in the vortex of artificial topological superconductor
Authors: Zhu Zhen , Zheng Hao , Jia Jin-feng
Published: April 2021

Majorana zero mode, the bound state of Majorana fermion in a condensed matter system, plays a critical role in fault-tolerant topological quantum computation. It can be realized in the vortex of a two-dimensional topological superconductor as a zero-energy excitation. A topological superconductor can be constructed by coupling superconductivity to the topological surface states by the proximity effect. In this review article, we discuss the fabrication of such artificially engineered topological superconductors by molecular beam epitaxy. The topological phase and superconductivity are exhibited in Bi2Se3/NbSe2 and Bi2Te3/NbSe2 heterostructures simultaneously. Several characteristic features of Majorana zero mode have been revealed in the vortex by a low-temperature scanning tunneling microscope and corroborated by theoretical results. The discovery of Majorana zero mode may pave the way for further applications in topological quantum computing.
A drift kinetic model for the expander region of a magnetic mirror
Authors: Wetherton B. A. , Le A. , Egedal J. , Forest C. , Daughton W. , Stanier A. , Boldyrev S.
Published: April 2021

We present a drift kinetic model for the free expansion of a thermal plasma out of a magnetic nozzle. This problem relates to plasma space propulsion systems, natural environments such as the solar wind, and end losses from the expander region of mirror magnetically confined fusion concepts such as the gas dynamic trap. The model incorporates trapped and passing orbit types encountered in the mirror expander geometry and maps to an upstream thermal distribution. This boundary condition and quasineutrality require the generation of an ambipolar potential drop of ∼5Te/e, forming a thermal barrier for the electrons. The model for the electron and ion velocity distributions and fluid moments is confirmed with data from a fully kinetic simulation. Finally, the model is extended to account for a population of fast sloshing ions arising from neutral beam heating within a magnetic mirror, again resulting in good agreement with a corresponding kinetic simulation.
A large fixed bed reactor for MRI operando experiments at elevated temperature and pressure
Authors: Ridder Harm , Sinn Christoph , Pesch Georg R. , Ilsemann Jan , Dreher Wolfgang , Thöming Jorg
Published: April 2021

Recently, in situ studies using nuclear magnetic resonance (NMR) have shown the possibility to monitor local transport phenomena of gas-phase reactions inside opaque structures. Their application to heterogeneously catalyzed reactions remains challenging due to inherent temperature and pressure constraints. In this work, an NMR-compatible reactor was designed, manufactured, and tested, which can endure high temperatures and increased pressure. In temperature and pressure tests, the reactor withstood pressures up to 28 bars at room temperature and temperatures over 400 °C and exhibited only little magnetic shielding. Its applicability was demonstrated by performing the CO2 methanation reaction, which was measured operando for the first time by using a 3D magnetic resonance spectroscopic imaging sequence. The reactor design is described in detail, allowing its easy adaptation for different chemical reactions and other NMR measurements under challenging conditions.
Combinatorial synthesis of non-stoichiometric SiOx thin films via high-throughput reactive sputtering
Authors: Park Jihun , Shin Sang Ho , Bae Jong-Seong , Zhang Xiaohang , Takeuchi Ichiro , Lee Seunghun
Published: April 2021

Oxygen vacancy defects have been widely studied for fundamental research and industrial applications, because they significantly influence the physical properties of oxides. Precise and systematic control over oxygen deficiency is a prerequisite for qualitative and quantitative studies on the effect of oxygen defects. In this paper, we report a novel approach to accurately control the oxygen deficiency of oxide thin films using high-throughput reactive sputtering (HTRS). SiOx combinatorial libraries consisting of 110 × 130 cells (cell area of 1 cm2) were fabricated on a large-scale glass substrate (110 × 130 cm2). These libraries allow for macroscopic analysis tools that are not amenable to the existing combinatorial methods, such as optical and x-ray spectroscopies. The cells exhibit spatial gradients in optical constants and optical transmission depending on the oxygen deficiency, indicating a gradual transition from Si to SiO2. X-ray photoelectron spectroscopy analysis reveals that the libraries consisting of silicon oxides with diverse oxidation states are in good accordance with the continuous compositional variation. The HTRS method demonstrates the controllability of oxygen deficiency by 0.5% (Δδ ≈ 0.01) and provides potential controllability of 0.05% (Δδ ≈ 0.001). Our approach provides the systematic control of oxygen deficiency and makes a step toward discovering the emerging properties of non-stoichiometric oxides.
Analysis of parameters of coaxial dielectric barrier discharges in argon flow at atmospheric pressure
Authors: Li Hui , Yuan Chengxun , Kudryavtsev Anatoly , Astafiev Aleksandr , Bogdanov Evgeny , Katircioglu T. Yasar , Rafatov Ismail
Published: April 2021

This work deals with the numerical and experimental investigation of atmospheric pressure dielectric barrier discharges (DBDs). In the experiment, the current and voltage of DBD sustained in an argon flow in coaxial discharge cell are measured. Numerical models are based on the drift-diffusion theory of gas discharges. Different modelling approaches, where the electron kinetics is determined on the basis of the Maxwellian electron energy distribution function (EEDF), vs models with more realistic EEDF obtained from the solution of the electron Boltzmann equation are implemented. The effect of energy loss due to heating of the gas is considered.
Interfacial waves modulated by linear shear flow of the upper layer in a two-layer fluid with arbitrary layer depths
Authors: Li Shaofeng , Yu Chengcheng , Qian Suhui , Song Jinbao , Cao Anzhou
Published: April 2021

Both surface and internal freak waves can be regarded as special interfacial waves. Using a two-layer model, we investigated the influence of linear shear flow (LSF) in the upper layer on interfacial waves. Specially, the model was designed to study the effects of wind shear on surface freak waves and LSF on internal freak waves. Based on the model, a nonlinear Schrödinger equation was derived to describe interfacial-wave evolution. The unstable regions where interfacial freak waves occur were identified via analysis of modulational instability. According to these unstable regions, the elevation of interfacial freak waves was studied using the Peregrine Breather solution. It is found that the steepnesses and heights of surface freak waves decrease under positive vorticity and increase under negative vorticity during supercritical up-flow. In contrast, they increase under positive vorticity and decrease under negative vorticity during supercritical down-flow. The reason is that negative vorticity which has a convergent effect on the waves is easy to excite surface freak waves under supercritical up-flow, whereas positive vorticity has a convergent effect under supercritical down-flow. In addition, the steepnesses and heights of internal freak waves decrease under positive vorticity and uniform down-flow, whereas increase under negative vorticity and uniform up-flow. The convergent effect of negative vorticity and uniform up-flow promote the generation of internal freak waves.
Development of a novel approach to detect damage in concrete structures with millimeter wave radar assessment system
Authors: Singh Sanjeev K. , Narang Naina , Singh Dharmendra
Published: April 2021

Nonintrusive damage assessment of concrete structures is evolving using newer technological interventions. Researchers are using different assessment techniques having their intrinsic limitations. A few are partially destructive, whereas others only provide qualitative information about the damages. Therefore, there is a need for a method using high-resolution imaging techniques for the assessment of exact damages and their depth along with intensity. Millimeter wave may be one of the good options for damage assessment. It is an efficient technique used in imaging applications due to its high resolution and effective penetration. Therefore, a novel millimeter wave assessment method is used in this study as a nondestructive post-fire damage test of concrete based civil engineering structures. An active millimeter wave radar system of 55–65 GHz has been used to measure the complex relative permittivity of concrete cube specimens for evaluation of damages caused by fire. In this study, fire damaged and control concrete cube specimens of 150 mm size were used for the measurement. The results were compared with the existing technique of ultrasonic pulse velocity, and it was found to be in good agreement.
A new linear forcing method for isotropic turbulence with controlled integral length scale
Authors: Janin Jérémie , Duval Fabien , Friess Christophe , Sagaut Pierre
Published: April 2021

Turbulence is a common feature to all flows that surround us. Despite its ubiquity, particularly in industrial flows, it is very difficult to provide a mathematical framework for the generation of turbulent eddies. Several methods have been proposed which are able to reproduce realistic features for velocity fluctuations, exhibiting proper space- and time-correlations. Focusing on physical space forcing, these methods are usually first evaluated upon sustained homogeneous isotropic turbulence by introducing a body force to the Navier–Stokes equations. Since the pioneering work of Lundgren, these techniques usually experience difficulties in predicting the integral length scale. The present study provides a forcing through a reconstruction approach which consists in building velocity fluctuations with a prescribed energy spectrum model. The proposed approach is assessed by performing large-eddy simulations of a sustained homogeneous isotropic turbulence in a triply periodic box. Properties of this forcing technique are discussed, drawing on both spatial and time correlations and also on the shape of energy spectrum together with the level of resolved turbulent kinetic energy. A special attention is put on the control of resolved turbulent energy. In this framework, an efficient selective forcing technique is derived, making use of spectral space features. The results show that the proposed approach allows to drive efficiently the resolved kinetic energy toward its target value while preserving the integral length scale independent of the domain size. It is observed that the resulting longitudinal length scale is overestimated by 13%, while the two-time correlations are recovered when using stochastic frequencies.
Physics-informed neural networks for rarefied-gas dynamics: Thermal creep flow in the Bhatnagar–Gross–Krook approximation
Authors: De Florio Mario , Schiassi Enrico , Ganapol Barry D. , Furfaro Roberto
Published: April 2021

This work aims at accurately solve a thermal creep flow in a plane channel problem, as a class of rarefied-gas dynamics problems, using Physics-Informed Neural Networks (PINNs). We develop a particular PINN framework where the solution of the problem is represented by the Constrained Expressions (CE) prescribed by the recently introduced Theory of Functional Connections (TFC). CEs are represented by a sum of a free-function and a functional (e.g., function of functions) that analytically satisfies the problem constraints regardless to the choice of the free-function. The latter is represented by a shallow Neural Network (NN). Here, the resulting PINN-TFC approach is employed to solve the Boltzmann equation in the Bhatnagar–Gross–Krook approximation modeling the Thermal Creep Flow in a plane channel. We test three different types of shallow NNs, i.e., standard shallow NN, Chebyshev NN (ChNN), and Legendre NN (LeNN). For all the three cases the unknown solutions are computed via the extreme learning machine algorithm. We show that with all these networks we can achieve accurate solutions with a fast training time. In particular, with ChNN and LeNN we are able to match all the available benchmarks.
Harmonics as an alternative method for measuring I during x-ray absorption spectroscopy experiments at laboratory scale
Authors: Bes René , Takala Saara , Huotari Simo
Published: April 2021

In the recent years, the advent of an efficient and compact laboratory-scale spectrometer for x-ray absorption spectroscopy experiments has been extensively reported in the literature. Such modern instruments offer the advantage to routinely use x-ray absorption spectroscopy on systematic studies, which is usually unconceivable at synchrotron radiation source facilities due to often limited time access. However, one limiting factor is the fact that due to laboratory x-ray source brightness compared to a synchrotron, two separate measures of the incoming and transmitted x-ray intensities, i.e., the so-called I0 and I1, respectively, are usually required. Herein, we introduce and discuss an alternative approach for measuring I0 and I1 simultaneously. Based on the usage of harmonics arising naturally from the use of monochromator crystals, the reliability and robustness of our proposed approach is demonstrated through experiments at the Co K-edge measured using Co metal foil and at the Nd L3-edge measured in Nd2O3.
On the lattice Boltzmann method and its application to turbulent, multiphase flows of various fluids including cryogens: A review
Authors: Petersen K. J. , Brinkerhoff J. R.
Published: April 2021

Cryogenic fluids are used in a myriad of different applications not limited to green fuels, medical devices, spacecraft, and cryoelectronics. In this review, we elaborate on these applications and synthesize recent lattice Boltzmann methods (LBMs) including collision operators, boundary conditions, grid-refinement techniques, and multiphase models that have enabled the simulation of turbulence, thermodynamic phase change, and non-isothermal effects in a wide array of fluids, including cryogens. The LBM has reached a mature state over the last three decades and become a strong alternative to the conventional Navier–Stokes equations for simulating complex, rarefied, thermal, multiphase fluid systems. Moreover, the method's scalability boosts the efficiency of large-scale fluid flow computations on parallel clusters, including heterogeneous clusters with graphics card-based accelerators. Despite this maturity, the LBM has only recently experienced limited use in the study of cryogenic fluid systems. Therefore, it is fitting to emphasize the usefulness of the LBM for simulating computationally prohibitive, complex cryogenic flows. We expect that the method will be employed more extensively in the future owing to its simple representation of molecular interaction and consequently thermodynamic changes of state, surface tension effects, non-ideal effects, and boundary treatments, among others.
Inspection of structures interaction in laminar separation bubbles with extended proper orthogonal decomposition applied to multi-plane particle image velocimetry data
Authors: Verdoya J. , Dellacasagrande M. , Lengani D. , Simoni D. , Ubaldi M.
Published: April 2021

This work reports the application of an extended proper orthogonal decomposition (E-POD) procedure to multi-plane particle image velocimetry (PIV) measurements describing the evolution of laminar separation bubbles (LSBs). Measurements were performed over a flat plate installed between adjustable end-walls providing a prescribed adverse pressure gradient for two Reynolds numbers (Re = 70 000, 150 000) and free-stream turbulence intensity levels (Tu = 1.5%, 2.5%). A wall-normal and two wall-parallel measuring planes located at different distance from the wall were considered. POD was applied to the entire PIV planes as well as on their sub-domains, showing the main flow features occurring in the different regions of the LSB. Then, the application of E-POD on different plane partitions revealed the existing correlation between the main dynamics observed in the forward part of the bubble and the breakup events occurring in the reattachment region. The E-POD modes computed in the breakup region resemble streaky structures when PIV snapshots are projected onto the POD eigenvectors of the near wall plane. Otherwise, Kelvin–Helmholtz rolls dominate the E-POD modes obtained by projection of the snapshot matrices on the basis computed in the plane located far from the wall. The main scales of the coherent structures highlighted by the E-POD modes were also characterized by means of the streamwise and spanwise autocorrelation functions of E-POD filtered fields. Data in this work clearly highlight the similarity properties of the main flow features observed in LSBs once scaled with the momentum thickness of the boundary layer at the separation position.
Host–guest exchange contribution to transition temperature downshift in nanocrystalline Fe(pyrazine)[Pt(CN)4] thin films prepared by matrix-assisted pulsed laser evaporation
Authors: Sawczak Mirosław , Jendrzejewski Rafał , Maskowicz Dominik , Garcia Yann , Dîrtu Marinela , Kumar Varun , Śliwiński Gerard
Published: April 2021

The influence of guest molecules affecting the spin transition characteristics of iron(II) complexes represents a widely discussed topic because it opens the possibility of using this type of materials in many fields of science, especially if the material properties could be tuned in a controlled way. We report an experimental observation of the spin transition in thin films of a 3D Hoffman framework nanocrystalline material Fe(pyrazine)[Pt(CN)4] deposited by nanosecond laser ablation at λ = 1064 nm of its cryo-cooled colloidal suspension in water and water-free organic solvents. For vacuum deposited films (thickness 120 nm), the substantial downshift in temperature, gradual spin transition, and shrinkage of the temperature hysteresis compared to the starting material are ascribed to incomplete removal of water molecules from the porous network and partial destruction of the crystalline site caused by laser heating. The destructive effect of laser irradiation occurring in vacuum conditions was not observed for deposition conducted in N2 at atmospheric pressure. In this case, thin films reproducing properties of the reference material with transition temperature near 276 K and 12 K wide hysteresis were obtained. In addition, the changes in the spin switching characteristics associated with the exchange of guest molecules in the SCO crystal lattice were observed using a water-free solvent as a matrix for the laser based thin film deposition. The observed laser induced host–guest exchange indicates on the possibility of selective modification of thin layers of SCO materials to obtain their desired characteristics.
Mapping the evolution of Bi/Ge(111) empty states: From the wetting layer to pseudo-cubic islands
Authors: Goto F. , Calloni A. , Albani G. , Picone A. , Brambilla A. , Zucchetti C. , Bottegoni F. , Finazzi M. , Duò L. , Ciccacci F. , Bussetti G.
Published: April 2021

Semiconductors interfaced with heavy elements possessing a strong atomic spin–orbit coupling are important building blocks for the development of new spintronic devices. Here, we present a microscopic and spin-resolved spectroscopic investigation of ultrathin Bi films grown onto a Ge(111) substrate. At monolayer coverage, a Bi wetting layer is formed, characterized by a semiconducting behavior and a (3×3)R30° superstructure. The wetting layer supports the subsequent growth of Bi islands with a pseudo-cubic structure similar to that of Bi(110), showing a well-defined orientation with respect to the substrate high-symmetry directions. We performed photoemission and spin-resolved inverse photoemission experiments at off-normal electron emission and incidence, respectively, along the substrate Γ¯K¯ direction. Inverse photoemission, in particular, highlights the presence of a spin-polarized empty Bi state, not reported so far, due to the strong spin–orbit effects characteristic of the Bi surface and thin layers. Finally, scanning tunneling spectroscopy is employed to link the observed spectroscopic features to either the wetting layer or the Bi islands.
Increase of Gilbert damping in Permalloy thin films due to heat-induced structural changes
Authors: Schulz Frank , Lawitzki Robert , Głowiński Hubert , Lisiecki Filip , Träger Nick , Kuświk Piotr , Goering Eberhard , Schütz Gisela , Gräfe Joachim
Published: April 2021

Spin-wave based computing requires materials with low Gilbert damping, such as Ni80Fe20 (Permalloy) or yttrium iron garnet, in order to allow for spin-wave propagation on a length scale comparable to the device size. Many devices, especially those that rely on spin–orbit effects for operation, are subject to intense Joule heating, which can exacerbate electromigration and induce local phase changes. Here, the effect of annealing on the Gilbert damping coefficient α of 36 nm Py thin films grown on a Si substrate is examined. Ferromagnetic resonance measurements, high resolution transmission electron microscopy, as well as energy dispersive x-ray spectroscopy have been employed to determine α while also studying structural changes in the thin films. The Gilbert damping parameter was found to increase sixfold when annealed at 350 °C, which was linked to the diffusion of Ni atoms into the Si substrate on a length scale of up to 50 nm. The results demonstrate that magnonic devices have to be treated with caution when Joule heating occurs due to its detrimental effects on the magnonic properties, but the effect can potentially be exploited in the fabrication of magnonic devices by selectively modifying the magnonic damping locally.