bluuebunny/crossref_metadata_2025 huggingface dataset:
LIStEN: L′ band Imaging Survey for Exoplanets in the North
Authors: Musso Barcucci Arianna , Launhardt Ralf , Müller André , Kennedy Grant M. , van Boekel Roy , Henning Thomas , Ruh Henrik L. , Marino Sebastian , Pearce Tim D. , Brems Stefan S. , Ertel Steve , Spalding Eckhart A.
Published: January 2021

Context. Planetary systems and debris discs are natural by-products of the star formation process, and they affect each other. The direct imaging technique allows simultaneous imaging of both a companion and the circumstellar disc it resides in, and is thus a valuable tool to study companion-disc interactions. However, the number of systems in which a companion and a disc have been detected at the same time remains low.

Aims. Our aim is to increase this sample, and to continue detecting and studying the population of giant planets in wide orbits.

Methods. We carry out the L′ band Imaging Survey for Exoplanets in the North (LIStEN), which targeted 28 nearby stars: 24 are known to harbour a debris disc (DD) and the remaining 4 are protoplanetary disc-hosting stars. We aim to detect possible new companions, and study the interactions between the companion and their discs. Angular differential imaging observations were carried out in the L′ band at 3.8 μm using the LMIRCam instrument at the LBT, between October 2017 and April 2019.

Results. No new companions were detected. We combined the derived mass detection limits with information on the disc, and on the proper motion of the host star, to constrain the presence of unseen planetary and low-mass stellar companion around the 24 disc-hosting stars in our survey. We find that 2 have an uncertain DD status and the remaining 22 have disc sizes compatible with self-stirring. Three targets show a proper motion anomaly (PMa) compatible with the presence of an unseen companion.

Conclusions. Our achieved mass limits combined with the PMa analysis for HD 113337 support the presence of a second companion around the star, as suggested in previous RV studies. Our mass limits also help to tighten the constraints on the mass and semi-major axis of the unseen companions around HD 161868 and HD 8907.
Dynamically inflated wind models of classical Wolf-Rayet stars
Authors: Poniatowski L. G. , Sundqvist J. O. , Kee N. D. , Owocki S. P. , Marchant P. , Decin L. , de Koter A. , Mahy L. , Sana H.
Published: January 2021

Context. Vigorous mass loss in the classical Wolf-Rayet (WR) phase is important for the late evolution and final fate of massive stars.

Aims. We develop spherically symmetric time-dependent and steady-state hydrodynamical models of the radiation-driven wind outflows and associated mass loss from classical WR stars.

Methods. The simulations are based on combining the opacities typically used in static stellar structure and evolution models with a simple parametrised form for the enhanced line opacity expected within a supersonic outflow.

Results. Our simulations reveal high mass-loss rates initiated in deep and hot, optically thick layers around T ≈ 200 kK. The resulting velocity structure is non-monotonic and can be separated into three phases: (i) an initial acceleration to supersonic speeds (caused by the static opacity), (ii) stagnation and even deceleration, and (iii) an outer region of rapid re-acceleration (by line opacity). The characteristic structures seen in converged steady-state simulations agree well with the outflow properties of our time-dependent models.

Conclusions. By directly comparing our dynamic simulations to corresponding hydrostatic models, we explicitly demonstrate that the need to invoke extra energy transport in convectively inefficient regions of stellar structure and evolution models, in order to prevent drastic inflation of static WR envelopes, is merely an artefact of enforcing a hydrostatic outer boundary. Moreover, the dynamically inflated inner regions of our simulations provide a natural explanation for the often-found mismatch between predicted hydrostatic WR radii and those inferred from spectroscopy; by extrapolating a monotonic β-type velocity law from the observable supersonic regions to the invisible hydrostatic core, spectroscopic models likely overestimate the core radius by a factor of a few. Finally, we contrast our simulations with alternative recent WR wind models based on co-moving frame (CMF) radiative transfer to compute the radiation force. Since CMF transfer currently cannot handle non-monotonic velocity fields, the characteristic deceleration regions found here are avoided in such simulations by invoking an ad hoc very high degree of clumping.
Low thermal conductivity of the superfast rotator (499998) 2011 PT
Authors: Fenucci Marco , Novaković Bojan , Vokrouhlický David , Weryk Robert J.
Published: January 2021

Context.Asteroids with a diameter of up to a few dozen meters may spin very fast and complete an entire rotation within a few minutes. These small and fast-rotating bodies are thought to be monolithic objects because the gravitational force due to their small size is not strong enough to counteract the strong centripetal force caused by the fast rotation. This argument means that the rubble-pile structure is not feasible for these objects. Additionally, it is not clear whether the fast spin prevents dust and small particles (regolith) from being kept on their surface.

Aims.We develop a model for constraining the thermal conductivity of the surface of the small, fast-rotating near-Earth asteroids. This model may suggest whether regolith is likely present on these objects.

Methods.Our approach is based on the comparison of the measured Yarkovsky drift and a predicted value using a theoretical model that depends on the orbital, physical and thermal parameters of the object. The necessary parameters are either deduced from statistical distribution derived for near-Earth asteroids population or determined from observations with associated uncertainty. With this information, we performed Monte Carlo simulations and produced a probability density distribution for the thermal conductivity.

Results.Applying our model to the superfast rotator asteroid (499998) 2011 PT, we find that the measured Yarkovsky drift can only be achieved when the thermal conductivityKof the surface is low. The resulting probability density function for the conductivity is bimodal, with two most likely values being around 0.0001 and 0.005 W m−1K−1. Based on this, we find that the probability thatKis lower than 0.1 W m−1K−1is at least 95%. This low thermal conductivity might indicate that the surface of 2011 PT is covered with a thermal insulating layer, composed of a regolith-like material similar to lunar dust.
AT 2019avd: a novel addition to the diverse population of nuclear transients
Authors: Malyali A. , Rau A. , Merloni A. , Nandra K. , Buchner J. , Liu Z. , Gezari S. , Sollerman J. , Shappee B. , Trakhtenbrot B. , Arcavi I. , Ricci C. , van Velzen S. , Goobar A. , Frederick S. , Kawka A. , Tartaglia L. , Burke J. , Hiramatsu D. , Schramm M. , van der Boom D. , Anderson G. , Miller-Jones J. C. A. , Bellm E. , Drake A. , Duev D. , Fremling C. , Graham M. , Masci F. , Rusholme B. , Soumagnac M. , Walters R.
Published: January 2021

We report on SRG/eROSITA, ZTF, ASAS-SN, Las Cumbres, NEOWISE-R, and Swift XRT/UVOT observations of the unique ongoing event AT 2019avd, located in the nucleus of a previously inactive galaxy at z = 0.029. eROSITA first observed AT 2019avd on 2020-04-28 during its first all sky survey, when it was detected as an ultra-soft X-ray source (kT ~ 85 eV) that was ≳90 times brighter in the 0.2−2 keV band than a previous 3σ upper flux detection limit (with no archival X-ray detection at this position). The ZTF optical light curve in the ~450 days preceding the eROSITA detection is double peaked, and the eROSITA detection coincides with the rise of the second peak. Follow-up optical spectroscopy shows the emergence of a Bowen fluorescence feature and high-ionisation coronal lines ([Fe X] 6375 Å, [Fe XIV] 5303 Å), along with persistent broad Balmer emission lines (FWHM ~ 1400 km s−1). Whilst the X-ray properties make AT 2019avd a promising tidal disruption event (TDE) candidate, the optical properties are atypical for optically selected TDEs. We discuss potential alternative origins that could explain the observed properties of AT 2019avd, such as a stellar binary TDE candidate, or a TDE involving a super massive black hole binary.
Contribution of archaeobotany to understand taphonomic phenomena. The case of a Preboreal palaeochannel of Autrecourt-et-Pourron (Ardennes, France)
Authors: Schaal Caroline , Naton Henri-Georges
Published: January 2021

Palaeoecology, through the analysis of the interactions between environmental factors and ecosystems, refines the knowledge of the structuring process of plant communities and helps to understand the complexity of past environments. However, it is necessary to analyse the taphonomic phenomena (deposition, conservation, degradation) affecting plant macrofossil assemblages in order to perform relevant palaeoecological analyses. Indeed, plant macrofossils may be under or over-represented in carpological assemblages, depending on the resistance of their cell membranes and the sedimentary condition deposits. For this reason, it is necessary to estimate the representative quality of the conserved part as a source of information. Like all archaeological documents, the plant archives are distorted by the processes of formation of the sedimentary levels and, ignore the diagenetic history of the sedimentary layers could lead to wrong palaeoecological interpretations. To this aim, we analysed plant macrofossils contained in the wet sediments of a Meuse palaeochannel (Autrecourt-et-Pourron, Ardennes, France). This archaeobotanical study of an oxbow lake dated to the Preboreal (11.7–10.7 ka cal. BP), provides a reference of a taphonomic referential according to a hierarchy of organic remain preservations. This framework successfully helped the palaeoecological interpretations of the Autrecourt-et-Pourron off-site, and it has brought robustness to environmental history reconstruction of the early Holocene in the Ardennes Meuse.
Semiglobal optimal feedback stabilization of autonomous systems via deep neural network approximation
Authors: Kunisch Karl , Walter Daniel
Published: January 2021

A learning approach for optimal feedback gains for nonlinear continuous time control systems is proposed and analysed. The goal is to establish a rigorous framework for computing approximating optimal feedback gains using neural networks. The approach rests on two main ingredients. First, an optimal control formulation involving an ensemble of trajectories with ‘control’ variables given by the feedback gain functions. Second, an approximation to the feedback functions via realizations of neural networks. Based on universal approximation properties we prove the existence and convergence of optimal stabilizing neural network feedback controllers.
Actively modulated propagation of electromagnetic wave in hybrid metasurfaces containing graphene
Authors: Nan Jiameng , Yang Ruisheng , Xu Jing , Fu Quanhong , Zhang Fuli , Fan Yuancheng
Published: January 2021

Here we present the actively modulated transportation of electromagnetic wave through hybrid metasurfaces containing graphene. The hybrid metasurfaces are composed of patterned metallic layers of extraordinary transmission and backed with graphene-sandwich layers. With the designed metallic layer with perforated structure, we demonstrated effective modulation on the on-resonance transmission amplitude by increasing the bias voltage from 0 to 4 V to electrically tune the Fermi level as well as the sheet resistance of the graphene-sandwich structure. We also found that the modulation depth can be further improved by properly designing the perforated metallic structure. By change the geometry from cut-wire structure to the “butterfly”-like pattern we preliminarily achieved 19.2% improvement on the on-resonance transmission modulation. The measured transmittances of the active metasurfaces show good agreement with the numerical simulations with fitted graphene sheet resistances. The hybrid metasurfaces presented in this work may be deployed in a wide range of applications based on active electromagnetic or optical modulations.
Quel soutien des médecins hospitaliers à la pratique d’activité physique des patients atteints du cancer ? Le cas du CHRU de Nancy
Authors: Houtmann Bastien , Rotonda Christine , Omorou Abdou Yacoubou , Gendarme Sophie , Martin-Krumm Charles , Van Hoye Aurélie
Published: January 2021

De nombreux effets bénéfiques de l’activité physique (AP) sont identifiés pour les patients atteints de cancer. La prescription d’AP adaptée pour les patients atteints d’une affection de longue durée est inscrite dans la loi depuis 2016, et les premières études montrent qu’elle serait efficace pour augmenter le niveau d’AP dans d’autres pays. L’OMS caractérise la prescription de manière générale à travers six étapes. L’objectif de cette étude est d’observer et comparer à travers les critères définis par l’OMS comment, au sein du CHRU Nancy Brabois et l’Institut de Cancérologie de Lorraine (ICL), l’activité physique adaptée est prescrite aux patients atteints de cancer et quel est le parcours des patients suite à cette prescription. Huit professionnels de santé ont été interrogés. Une approche déductive a été mobilisée pour coder les unités de sens au sein des différentes étapes de la prescription. Les résultats montrent que les étapes 1, 2, 6 sont effectués lors des consultations par les professionnels. Néanmoins, le décret de loi n°2016-1990 n’a pas modifié les habitudes d’information et de prescription des professionnels de santé, et sans la légitimité de la prescription, l’AP reste un supplément au parcours de soins plutôt que l’une de ses composantes.
COVID-19 Treatment: Drug Safety Prior to Conception and During Pregnancy and Breastfeeding
Authors: Cavalcante Marcelo Borges , Cavalcante Candice Torres de Melo Bezerra , Braga Ana Catherine Sampaio , Andrade Dennyse Araújo , Montenegro Mariana Albuquerque , Santos Paula Andrade Neiva , Motoyama Paula Vitória Pereira , Rocha Marcelo Gondim , Dib Luciana Azôr , Araujo Júnior Edward
Published: January 2021

In December 2019, a new viral respiratory infection known as coronavirus disease 2019 (COVID-19) was first diagnosed in the city of Wuhan, China. COVID-19 quickly spread across the world, leading the World Health Organization to declare it a pandemic on March 11, 2020. The disease is caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a similar virus to those involved in other epidemics such as severe acute respiratory syndrome coronavirus (SARS-CoV) and Middle East respiratory syndrome coronavirus (MERS-CoV). Epidemiological studies have shown that COVID-19 frequently affects young adults of reproductive age and that the elderly and patients with chronic disease have high mortality rates. Little is known about the impact of COVID-19 on pregnancy and breastfeeding. Most COVID-19 cases present with mild flu-like symptoms and only require treatment with symptomatic relief medications, whereas other cases with COVID-19 require treatment in an
intensive care unit. There is currently no specific effective treatment for COVID-19. A large number of drugs are being used to fight infection by SARS-CoV-2. Experience with this therapeutic arsenal has been gained over the years in the treatment of other viral, autoimmune, parasitic, and bacterial diseases. Importantly, the search for an effective treatment for COVID-19 cannot expose pregnant women infected with SARS-CoV-2 to the potential teratogenic risks of these drugs. Therefore, it is necessary to determine and understand the safety of anti-COVID-19 therapies prior to conception and during pregnancy and breastfeeding.
Retrorektales Teratom (Dermoidzyste) des Erwachsenen – Diagnostik und Therapie am Beispiel einer Kasuistik
Authors: Bebobru Mathias , Nasri Farid-Ahmed , Niculescu-Valaenu Maximilian , Friedhoff Klaus
Published: January 2021

Anamnese Eine 29-jährige Patientin mit seit 2 Jahren bestehenden Schmerzen der unteren Lendenwirbelsäule wurde chirurgisch vorgestellt.

Diagnostik und Befunde Ursache der Schmerzen war ein retrorektaler präsakraler zystischer Tumor. Zur Diagnosestellung erfolgten eine transvaginale Endosonografie, eine CT-Untersuchung mit Kontrastmittel und eine MRT-Untersuchung des kleinen Beckens.

Therapie und Verlauf Es erfolgte die operative Entfernung des Tumors. Histologisch zeigte sich ein monodermales zystisches Teratom. Der postoperative Verlauf war unauffällig.

Diskussion Retrorektale Tumoren, die nicht mit dem Rektum in Beziehung stehen, sind insgesamt selten. Je nach Lage des Tumors sollten diese durch einen ventralen transabdominalen oder dorsalen Zugang operativ entfernt werden.
Trainingsmodell zum Verständnis der Handmuskulatur
Authors: Andreou Andreas , Ganser Joachim
Published: January 2021

Welcher Muskel ist in welchem Umfang an einer bestimmten Alltagsaktivität beteiligt? Die Autoren entwickelten Übungen, mit denen Therapeuten ihr Verständnis bezüglich des Zusammenwirkens von extrinsischer Unterarm- und intrinsischer Handmuskulatur spielerisch verbessern können.
Mobilisierende Schiene bei Rhizarthrose zeigt positive Effekte
Authors: Weyand Daniela , Steinbacher Barbara
Published: January 2021

Immobilisierende Schienen sind der Goldstandard in der konservativen Behandlung von Rhizarthrose. Neuere Entwicklungen hingegen erhalten die Mobilität des Daumens in der Orthese. In ihrer Bachelorarbeit befragten zwei Ergotherapeutinnen Patienten, die mit einer solch neuartigen Schiene behandelt wurden, nach ihrer Zufriedenheit.
17-Hydroxyprogesterone Caproate for the Prevention of Recurrent Preterm Birth – A Systematic Review and Meta-analysis Taking into Account the PROLONG Trial
Authors: Kuon Ruben-J. , Berger Richard , Rath Werner
Published: January 2021

Background Prior spontaneous preterm birth is a strong risk factor for the recurrence of spontaneous preterm birth in a subsequent pregnancy and has been evaluated in prevention studies using progesterone (natural progesterone administered orally or vaginally, and 17-hydroxyprogesterone caproate [17-OHPC]) as a selection criterion. Based on the findings of a randomized, placebo-controlled study, 17-OHPC was approved for use in 2011 by the Food and Drug Administration in the USA for the prevention of recurrent preterm birth. The approval was granted with qualification that a subsequent confirmatory study would need to be carried out, the results of which have just been published (PROLONG trial).

Method A systematic literature search for the period from 1970 to April 2020 using the search terms “preterm birth” and “17-OHPC” or “progesterone” was carried out. Only randomized, placebo-controlled studies of women with singleton pregnancies who received 17-OHPC to prevent recurrent preterm birth were included in the subsequent meta-analysis. The relative risk and associated 95% confidence intervals were calculated. The heterogeneity between studies was evaluated with I2 statistics.

Results In addition to the original study used for the approval and the PROLONG trial, only one other study was found which met the inclusion criteria (total number of patients: 2221). With considerable heterogeneity between the studies, particularly with respect to the risk factors for preterm birth, the comparison between 17-OHPC and placebo showed no significant reduction in preterm birth rates before 37, 35 and 32 weeks of gestation and no significant differences with regard to the prevalence of miscarriage before 20 weeks of gestation or fetal deaths (antepartum or intrapartum) after 20 weeks of gestation and neonatal morbidity.

Conclusion Based on the currently available data, 17-OHPC cannot be recommended for the prevention of recurrent preterm birth. Further randomized, placebo-controlled studies with clearly defined, comparable risk factors are required to identify the group of pregnant women which could benefit from the use of 17-OHPC to prevent preterm birth.
HyperEmesis Level Prediction (HELP Score) Identifies Patients with Indicators of Severe Disease: a Validation Study
Authors: MacGibbon Kimber W. , Kim Sarah , Mullin Patrick M. , Fejzo Marlena S.
Published: January 2021

Objective Hyperemesis gravidarum (HG) severity can be underestimated resulting in undertreatment and adverse outcomes. This study was conducted to validate a tool (HELP Score) designed to score HG severity.

Materials and Methods A survey link which included PUQE and HELP Score (HELP) tool questions was posted on websites related to HG. HELP scores were compared to PUQE scores for indicators of severe disease.

Results HELP classified 92% of women reporting “nothing goes or stays down” as severe, compared to 58% using PUQE. Women self-categorizing symptoms as severe were more likely categorized as severe using HELP. Women hospitalized for HG were more likely classified as severe using HELP. HELP performs better than PUQE in identifying patients with severe symptoms requiring intervention.

Conclusion This study provides a novel tool that should be implemented to determine the need for intervention for NVP that may be overlooked using PUQE or empirical assessment.
Results with Posterior Scleral Reinforcement for Progressive Highly Myopic Children in Hungary
Authors: Széll Noémi , Boross Adrienn , Facskó Andrea , Sohajda Zoltán
Published: January 2021

Purpose We have been performing posterior scleral reinforcement in our ophthalmological department since 1992 on progressive highly myopic eyes. Here, we report on our results with this technique in the foregoing 7 years in a retrospective comparative design.

Methods Thirty-eight eyes of 32 patients, operated according to Snyder-Thompsonʼs method, were enrolled in this study, and a control group of 9 age- and myopia-matched childrenʼs 14 eyes was built for comparison. Pre- and postoperative best-corrected visual acuity, subjective refractive error (spherical equivalent of spectacle dioptres), and axial length were recorded. Changes within groups were calculated, as well as baseline parameters and their changes during follow-up, and compared between the groups. Correlation analysis was performed to identify factors that could influence myopia progression.

Results Myopic progression was significantly lower in the operated than in the nonoperated group, both in terms of mean annual axial length as well as refractive error changes (0.21 ± 0.08 mm versus 0.49 ± 0.19 mm and 0.18 ± 0.29 D versus 0.6 ± 0.33 D, respectively). Mean overall visual improvement was more explicit in operated eyes as compared to those left untreated (0.15 ± 0.09 versus 0.01 ± 0.1). No association of any factor with myopia progression could be identified. We encountered no serious or lasting complications.

Conclusion In our clinical practice, posterior scleral reinforcement according to Snyder-Thompson proved to be a safely applicable and effective surgical method to stop or significantly retard pathological increases in axial length and dioptres, and thus can help prevent the onset of myopic degenerative lesions, and irreversible visual impairment in the long run.
A Cascade Process of Hydroxamates Renders 1,6-Dioxa-3,9-diazaspiro[4.4]nonane-2,8-diones
Authors: Nazarian Zohreh , Forsyth Craig M.
Published: January 2021

A cascade route to 1,6-dioxa-3,9-diazaspiro[4.4]nonane-2,8-diones from N,O-diacyl hydroxylamines consisting of a two-step procedure is described. The key transformation is a [3,3]-sigmatropic rearrangement of N,O-diacyl hydroxylamines promoted by formation of a silylketenaminal followed by an intramolecular cyclization and a final spirocyclization. The optimum reaction conditions employ a one-fold excess of each reagent and are utilized to prepare a range of structurally diverse examples of this class of compound.
Allegra Transcatheter Heart Valve inside a Degenerated Sutureless Aortic Bioprosthesis
Authors: Vondran Maximilian , Abt Bernd , Nef Holger , Rastan Ardawan J.
Published: January 2021

Transcatheter aortic valve-in-valve implantation (VIV) is increasingly being used to successfully treat degenerated surgical aortic valve bioprostheses (SAVs). The new self-expanding transcatheter heart valve Allegra, from New Valve Technology with its special implantation mechanism, has proven its safety and feasibility for patients with degenerated SAVs, but it has never been used in the latest-generation sutureless SAV. To the best of our knowledge, this is the first description of the successful VIV of the Allegra prosthesis into a degenerated sutureless SAV, and the procedure yielded an excellent postinterventional hemodynamic results.
Automatic Feynman diagram generation for nonlinear optical spectroscopies and application to fifth-order spectroscopy with pulse overlaps
Authors: Rose Peter A. , Krich Jacob J.
Published: January 2021

Perturbative nonlinear optical spectroscopies are powerful methods to understand the dynamics of excitonic and other condensed phase systems. Feynman diagrams have long provided the essential tool to understand and interpret experimental spectra and to organize the calculation of spectra for model systems. When optical pulses are strictly time ordered, only a small number of diagrams contribute, but in many experiments, pulse-overlap effects are important for interpreting results. When pulses overlap, the number of contributing diagrams can increase rapidly, especially with higher order spectroscopies, and human error is especially likely when attempting to write down all the diagrams. We present an automated Diagram Generator (DG) that generates all the Feynman diagrams needed to calculate any nth-order spectroscopic signal. We characterize all perturbative nonlinear spectroscopies by their associated phase-discrimination condition as well as the time intervals where pulse amplitudes are nonzero. Although the DG can be used to automate impulsive calculations, its greatest strength lies in automating finite pulse calculations where pulse overlaps are important. We consider third-order transient absorption spectroscopy and fifth-order exciton–exciton interaction 2D (EEI2D) spectroscopy, which are described by six or seven diagrams in the impulsive limit, respectively, but 16 or 240 diagrams, respectively, when pulses overlap. The DG allows users to automatically include all relevant diagrams at a relatively low computational cost, since the extra diagrams are only generated for the inter-pulse delays where they are relevant. For EEI2D spectroscopy, we show the important effects of including the overlap diagrams.
Solving the problem of overdetermination of quasisymmetric equilibrium solutions by near-axis expansions. I. Generalized force balance
Authors: Rodríguez E. , Bhattacharjee A.
Published: January 2021

It is well known that the process of construction of quasisymmetric magnetic fields in magnetostatic equilibrium with isotropic pressure suffers from the problem of overdetermination. This has led to the widespread belief that global quasisymmetric solutions are likely not to exist. We develop a general near-axis expansion procedure that does not rely on the assumption of magnetostatic equilibria with isotropic pressure. We then demonstrate that in equilibria with anisotropic pressure, it is possible to circumvent the problem of overdetermination and carry out the power-series solutions to higher order. This suggests, contrary to current belief, that the existence of globally quasisymmetric fields is likely if one relaxes the assumption of magnetostatic equilibria with isotropic pressure.
A new instrument for kinetics and branching ratio studies of gas phase collisional processes at very low temperatures
Authors: Durif O. , Capron M. , Messinger J. P. , Benidar A. , Biennier L. , Bourgalais J. , Canosa A. , Courbe J. , Garcia G. A. , Gil J. F. , Nahon L. , Okumura M. , Rutkowski L. , Sims I. R. , Thiévin J. , Le Picard S. D.
Published: January 2021

A new instrument dedicated to the kinetic study of low-temperature gas phase neutral–neutral reactions, including clustering processes, is presented. It combines a supersonic flow reactor with vacuum ultra-violet synchrotron photoionization time-of-flight mass spectrometry. A photoion–photoelectron coincidence detection scheme has been adopted to optimize the particle counting efficiency. The characteristics of the instrument are detailed along with its capabilities illustrated through a few results obtained at low temperatures (<100 K) including a photoionization spectrum of n-butane, the detection of formic acid dimer formation, and the observation of diacetylene molecules formed by the reaction between the C2H radical and C2H2.
Single copper sites dispersed on defective TiO2−x as a synergistic oxygen reduction reaction catalyst
Authors: Li Minchan , Qin Ning , Ji Zongwei , Gan Qingmeng , Wang Zhenyu , Li Yingzhi , Cao Lujie , Yuan Huimin , He Dongsheng , Chen Zhenhua , Luo Guangfu , Zhang Kaili , Lu Zhouguang
Published: January 2021

Catalysts containing isolated single atoms have attracted much interest due to their good catalytic behavior, bridging the gap between homogeneous and heterogeneous catalysts. Here, we report an efficient oxygen reduction reaction (ORR) catalyst that consists of atomically dispersed single copper sites confined by defective mixed-phased TiO2−x. This synergistic catalyst was produced by introducing Cu2+ to a metal organic framework (MOF) using the Mannich reaction, occurring between the carbonyl group in Cu(acac)2 and the amino group on the skeleton of the MOF. The embedding of single copper atoms was confirmed by atomic-resolution high-angle annular dark-field scanning transmission electron microscopy and x-ray absorption fine structure spectroscopy. Electronic structure modulation of the single copper sites coupling with oxygen vacancies was further established by electron paramagnetic resonance spectroscopy and first-principles calculations. Significantly enhanced ORR activity and stability were achieved on this special Cu single site. The promising application of this novel electrocatalyst was demonstrated in a prototype Zn–air battery. This strategy of the stabilization of single-atom active sites by optimization of the atomic and electronic structure on a mixed matrix support sheds light on the development of highly efficient electrocatalysts.
Solving the population balance equation for non-inertial particles dynamics using probability density function and neural networks: Application to a sooting flame
Authors: Seltz Andrea , Domingo Pascale , Vervisch Luc
Published: January 2021

Numerical modeling of non-inertial particles dynamics is usually addressed by solving a population balance equation (PBE). In addition to space and time, a discretization is required also in the particle-size space, covering a large range of variation controlled by strongly nonlinear phenomena. A novel approach is presented in which a hybrid stochastic/fixed-sectional method solving the PBE is used to train a combination of an artificial neural network (ANN) with a convolutional neural network (CNN) and recurrent long short-term memory artificial neural layers. The hybrid stochastic/fixed-sectional method decomposes the problem into the total number density and the probability density function of sizes, allowing for an accurate treatment of surface growth/loss. After solving for the transport of species and temperature, the input of the ANN is composed of the thermochemical parameters controlling the particle physics and of the increment in time. The input of the CNN is the shape of the particle size distribution (PSD) discretized in sections of size. From these inputs, in a flow simulation, the ANN–CNN returns the PSD shape for the subsequent time step or a source term for the Eulerian transport of the particle size density. The method is evaluated in a canonical laminar premixed sooting flame of the literature, and for a given level of accuracy (i.e., a given discretization of the size space), a significant computing cost reduction is achieved (six times faster compared to a sectional method with ten sections and 30 times faster for 100 sections).
Collisional ferrohydrodynamics of magnetic fluid droplets on superhydrophobic surfaces
Authors: Sahoo Nilamani , Khurana Gargi , Samanta Devranjan , Dhar Purbarun
Published: January 2021

The study reports the aspects of post-impact hydrodynamics of ferrofluid droplets on superhydrophobic (SH) surfaces in the presence of a horizontal magnetic field. A wide gamut of dynamics was observed by varying the impact Weber number (We), the magnetic field strength (manifested through the magnetic Bond number (Bom), which is defined as the ratio of magnetic force to surface tension force), and the Hartmann number (Ha), defined as the ratio of magnetic force to the viscous force. For a fixed We ∼ 60, we observed that at moderately low Bom ∼300, droplet rebound off the SH surface is suppressed. The noted We is chosen to observe various impact outcomes and to reveal the consequent ferrohydrodynamic mechanisms. We also show that ferrohydrodynamic interactions lead to asymmetric spreading due to variation in magnitude of the Lorentz force, and the droplet spreads preferentially in a direction orthogonal to the magnetic field lines. We show analytically that during the retraction regime, the kinetic energy of the droplet is distributed unequally in the transverse (orthogonal to the external horizontal magnetic field) and longitudinal (along the direction of the magnetic field) directions. This ultimately leads to the suppression of droplet rebound. We studied the role of Bom at fixed We ∼ 60 and observed that the liquid lamella becomes unstable at the onset of retraction phase, through nucleation of holes, their proliferation and rupture after reaching a critical thickness only on SH surfaces, but is absent on hydrophilic surfaces. We propose an analytical model to predict the onset of instability at a critical Bom. The model shows that the critical Bom is a function of the impact We, and the critical Bom decreases with increasing We. We illustrate a phase map encompassing all the post-impact ferrohydrodynamic phenomena on SH surfaces for a wide range of We and Bom.
Classification of the major nonlinear regimes of oscillations, oscillation properties, and mechanisms of wave energy dissipation in the nonlinear oscillations of coated and uncoated bubbles
Authors: Sojahrood A. J. , Haghi H. , Karshafian Raffi , Kolios Michael C.
Published: January 2021

Acoustic waves are dissipated when they pass through bubbly media. Dissipation by bubbles takes place through thermal damping (Td), radiation damping (Rd), and damping due to the friction of the liquid (Ld) and friction of the coating (Cd). Knowledge of the contributions of Td, Rd, Ld, and Cd during nonlinear bubble oscillations will help in optimizing bubble and ultrasound exposure parameters for the relevant applications by maximizing a desirable outcome or oscillation pattern. In this work, we investigate the mechanisms of dissipation in bubble oscillations and their contribution to the total damping (Wtotal) in various nonlinear regimes. By using a bifurcation analysis, we have classified nonlinear dynamics of bubbles that are sonicated with their third superharmonic (SuH) and second SuH resonance frequency (fr), pressure dependent resonance frequency (PDfr), fr, subharmonic (SH) resonance (fsh = 2fr), pressure dependent SH resonance (PDfsh), and 1/3 order SH resonance, which are important exposure ranges for various applications. The corresponding Td, Rd, Ld, Cd, Wtotal, scattering to dissipation ratio, maximum wall velocity, and maximum backscattered pressure from non-destructive oscillations of bubbles were calculated and analyzed using the bifurcation diagrams. Universal ultrasound exposure parameter ranges are revealed in which a particular non-destructive bubble related phenomenon (e.g., wall velocity) is enhanced. The enhanced bubble activity is then linked to relevant ultrasound applications. This paper represents the first comprehensive analysis of the nonlinear oscillations regimes, the corresponding damping mechanisms, and the bubble related phenomena.
Performance of a flexoelectric actuator for lamb wave excitation
Authors: Wei Chao , Wang Zhiguo , Huang Wenbin
Published: January 2021

A flexoelectric actuator represents a new approach for exciting Lamb waves in plate structures and, thus, can be potentially used for active structural health monitoring systems and microsensors. This paper analytically investigated the performance of a flexoelectric actuator for Lamb wave excitation. The constitutive equation for a thin plate flexoelectric structure was derived using the thermodynamics theory. A significant size effect could be demonstrated by the constitutive equation, which suggests a greatly enhanced curvature excitation performance at a small dimension. The interaction between the ideally bonded flexoelectric actuator with the plate could be simplified into two pairs of pin force and pin moment under the assumption of a weak coupling condition. The strain and the displacement responses to the pin-force and pin-moment pairs were obtained using the integral transform techniques and residue calculus. The pin-moment component mainly yielded an antisymmetric Lamb wave mode, while the pin force was reminiscent of its piezoelectric counterpart. The tuning of either a symmetric or an antisymmetric mode could be achieved by choosing an appropriate excitation frequency. The response under a five-cycle Hanning-window toneburst excitation signal was compared with the finite element analysis results and good agreement between them was found.
Imaging of surface acoustic waves on GaAs using 2D confocal Raman microscopy and atomic force microscopy
Authors: Rummel Brian Douglas , Miroshnik Leonid , Patriotis Marios , Li Andrew , Sinno Talid R. , Henry Michael David , Balakrishnan Ganesh , Han Sang M.
Published: January 2021

Surface acoustic wave devices have been fabricated on a GaAs 100 substrate to demonstrate the capability of 2D Raman microscopy as an imaging technique for acoustic waves on the surface of a piezoelectric substrate. Surface acoustic waves are generated using a two-port interdigitated transducer platform, which is modified to produce surface standing waves. We have derived an analytical model to relate Raman peak broadening to the near-surface strain field of the GaAs surface produced by the surface acoustic waves. Atomic force microscopy is used to confirm the presence of a standing acoustic wave, resolving a total vertical displacement of 3 nm at the antinode of the standing wave. Stress calculations are performed for both imaging techniques and are in good agreement, demonstrating the potential of this Raman analysis.
Kinetic model for molecular beam epitaxy growth of InAsSbBi alloys
Authors: Schaefer Stephen T. , Milosavljevic Marko S. , Kosireddy Rajeev R. , Johnson Shane R.
Published: January 2021

The growth of Bi-containing III-V alloys requires careful control over temperature and group-V fluxes due to the low equilibrium solubility of Bi and its tendency to surface segregate into Bi-rich droplet features. A model for molecular beam epitaxy growth based on the kinetics of atomic desorption, incorporation, surface accumulation, and droplet formation is applied to the bismide alloy InAsSbBi grown on GaSb substrates. A steady-state solution is derived for the Bi, Sb, and As mole fractions and surface layer coverages based on the Bi, Sb, and As fluxes. A nonlinear least-squares algorithm is used to fit the growth model parameters to experimentally measured Bi mole fractions in bulk and quantum well InAsSbBi samples grown at 400 °C and 420 °C. The Bi mole fraction ranges from 0.12% to 1.86% among 17 samples examined. The results indicate that as the growth temperature increases, the rate of Bi incorporation decreases and the rate of Bi self-desorption increases. A strong interaction is observed between Bi and As that plays a role in the desorption of excess Bi from the growth surface, thus reducing the likelihood of Bi-rich droplet formation when an excess As flux is present. Significantly, the model predicts that the incorporation of Bi is limited to mole fractions of 1.43% at 400 °C and 0.30% at 420 °C in lattice-matched bulk InAsSbBi grown on GaSb substrates.
High-performance polymer semiconductor-based ferroelectric transistor nonvolatile memory with a self-organized ferroelectric/dielectric gate insulator
Authors: Xu Meili , Zhang Xindong , Qi Weihao , Li Shizhang , Wang Wei
Published: January 2021

Ferroelectric organic field-effect transistor nonvolatile memories (Fe-OFET-NVMs) offer attractive features for future memory applications, such as flexible and wearable electronics. Polymer semiconductor-based top-gate Fe-OFET-NVMs possess natural advantages in the device structure and processing manufacturing, compared to small-molecule semiconductor-based bottom-gate Fe-OFET-NVMs. However, their performances, such as mobility and operating voltages, should be further improved to be comparable to those of the latter. In this Letter, we develop a route to achieve high-performance top-gate Fe-OFET-NVMs, by employing a polymer semiconductor channel and self-organized ferroelectric/dielectric gate insulators, which were processed by a solution spin-coating technique. The optimal Fe-OFET-NVM exhibits a high mobility of 1.96 cm2/V s on average, a reliable endurance over 400 cycles, a stable retention capability over 6 × 104 s, and a life more than one year. Furthermore, the operating voltage of the Fe-OFET-NVM is reduced to ±20 V by scaling down the thickness of the ferroelectric/dielectric gate insulator. The whole performances of our memories are comparable to or better than those of the previous Fe-OFET-NVMs.
Application of the Gram–Schmidt factorization of the deformation gradient to a cone and plate rheometer
Authors: Paul A. Sandipan , Freed B. Alan D. , Benjamin C. Chandler C.
Published: January 2021

In this paper, we study the cone and plate rheometer using the Gram–Schmidt factorization of the deformation gradient. This new solution has several advantages over the traditional approach. It is shown that with the use of these kinematics, one can avoid the need for using a convected, curvilinear, coordinate system, which often leads to cumbersome calculations. Here, the use of a convected coordinate system has been replaced with a certain orthonormal coordinate system that arises from the Gram–Schmidt factorization of the deformation gradient. Moreover, by using this solution procedure, it is possible to obtain the normal stress differences and shear stress explicitly. Therefore, this solution procedure opens up a possibility for characterizing material properties by using only a cone and plate rheometer.
On the optimization of knot allocation for B-spline parameterization of the dielectric function in spectroscopic ellipsometry data analysis
Authors: Likhachev D. V.
Published: January 2021

Dielectric function representation by B-splines became quite popular and widely used in the context of spectroscopic ellipsometry data interpretation. B-splines are defined by a polynomial degree and a sequence of knots (i.e., the number and positions of knots). Defining the knot sequence is non-trivial, and this task has a significant effect on the actual effectiveness of the B-spline parameterization in spectroscopic ellipsometry data analysis. In this paper, we propose a simple, practical, and systematic knot placement scheme that improves ordinary trial-and-error technique in establishing the knot spacing. The approach suggested here is based on an integral span, a measure introduced in this work. The proposed procedure provides a possibility to determine the knot locations automatically (or, at least, semi-automatically) and excludes widespread modeling ambiguities associated with uncertain knot vector. Moreover, our approach guarantees the absence of non-monotonic behavior of the mean-squared-error function and thereby improves the accuracy of our analysis. The performance of the proposed method has been tested for several real cases of the study.
Localization of water surface waves in a heterostructure channel with corrugated sidewalls
Authors: Zhang Jia-Yi , Liu Ting , Tao Jia , Fan Ya-Xian , Tao Zhi-Yong
Published: January 2021

This paper describes the fabrication of a water channel heterostructure by combining two types of periodic sidewalls with different duty ratios. This enables the manipulation and localization of water surface waves in bands that are traditionally inaccessible. It is well known that such forbidden bands can be created by the introduction of periodicity, in which the wave propagation is efficiently attenuated when the Bragg condition is satisfied. Through experiments and simulations, we show that an extraordinary transmission arises in the bandgap after two types of periodic channels are combined, even though they have similar forbidden bands. Waves that cannot travel along each channel then begin to propagate along the heterostructure channel. The measured surface amplitude of the water waves indicates that the localization around the interface of two periodic structures is responsible for the extraordinary transmission. The localized energy of water waves shifts according to the distance between the two periodic structures, and the localization and transmission disappear at certain distances. The measurement and analysis of this intriguing phenomenon of water wave manipulation will benefit applications in the collection and utilization of water wave energy.
Inertial focusing of elliptical particles and formation of self-organizing trains in a channel flow
Authors: Hu Xiao , Lin Jianzhong , Guo Yu , Ku Xiaoke
Published: January 2021

The inertial focusing of elliptical particles and the formation of self-organizing trains in a channel flow are studied by using the lattice Boltzmann method. The effects of particle aspect ratio (α), particle concentration (Φ), Reynolds number (Re), and blockage ratio (k) on self-organizing single-line and staggered particle trains are explored. The results show that a single-line particle train is dynamically formed mainly due to the inclination of height (IH) for the particles in the train. The elliptical particle with large α, Φ, Re, and small k facilitates self-organizing of the particle train with relatively stable spacing for a long travel distance. With increasing α, Φ, Re, and k, the value of IH increases and the interparticle spacing decreases. Four kinds of stability conditions for a self-organizing staggered particle train exist depending on Re, k, and α. The threshold Re to form the stable staggered particle train increases with increasing k and is insensitive to α. As Re increases, the spacing of the staggered particle train for the particles with low k and large α is more likely to fluctuate within a certain range. The staggered particle train can be dynamically formed when Re is larger than a critical value. This critical value of Re increases with increasing k and decreasing α. The interparticle spacing of the formed staggered particle train, which is insensitive to Φ, increases with increasing Re and α and decreasing k.