bluuebunny/crossref_metadata_2025 huggingface dataset:
Does Early Phonetic Differentiation Predict Later Phonetic Development? Evidence From a Longitudinal Study of /ɹ/ Development in Preschool Children
Authors: Munson Benjamin , Logerquist Mara K. , Kim Hyuna , Martell Alisha , Edwards Jan
Published: June 2021

Purpose

We evaluated whether children whose inaccurate /ɹ/ productions showed evidence phonetic differentiation with /w/ at 3.5–4.5 years of age improved in /ɹ/ production over the next year more than children whose inaccurate productions did not show evidence of such differentiation. We also examined whether speech perception, inhibitory control, and vocabulary size predicted growth in /ɹ/.

Method

A set of typically developing, monolingual English-speaking preschool children (n= 136) produced tokens of /ɹ/− and /w/−initial words at two time points (TPs), at which they were 39–52 and 51–65 months old. Children's productions of /ɹ/ and /w/ were narrowly phonetically transcribed. Children's productions at the earlier time point were rated by naïve listeners using a visual analog scale measure of phoneme goodness; these ratings were used to assess the degree of phonetic differentiation between /ɹ/ and /w/.

Results

Accuracy for both phonemes varied considerably at both TPs. The growth in accuracy of /ɹ/ between the two TPs was not predicted by any individual-differences measures, nor by the degree of differentiation between /ɹ/ and /w/at the earlier time point.

Conclusion

Low vocabulary size, low inhibitory control, poor speech perception, and the absence of early phonetic differentiation are not necessarily limiting factors in predicting /ɹ/ growth in individual children in the age range we studied.
Upgrading wave energy test sites by including overplanting: a techno‐economic analysis
Authors: Blavette Anne , Bonnard Charles‐Henri , Daminov Ildar , Bourguet Salvy , Soulard Thomas
Published: June 2021

Dynamic rating is an approach which implies to operate an electrical network closer to its thermal limits. This approach may be very beneficial for wave farms, as they are expected to present a highly fluctuating electrical current profile while benefiting from the large thermal inertia of the soil where their export cable will be buried. However, as the implementation of this approach is still in its infancy for offshore wind farms, it may be expected that the first wave farms, under the form of small‐scale test sites, will be sized with respect to electrical current limits at a first stage. This sizing may be upgraded at a second stage when design methods will have included dynamic rating. However, this raises the question of the economic feasibility of this two‐step approach, which is studied in this paper. Also, performing such a techno‐economic analysis requires developing an electrothermal model of the export cable able to represent its transient response in a sufficiently precise manner while requiring also a reasonable computing time. In this perspective, a comparative analysis between several electrothermal modelling methods is also described in this paper.
Ammonia snow lines and ammonium salts desorption
Authors: Kruczkiewicz F. , Vitorino J. , Congiu E. , Theulé P. , Dulieu F.
Published: June 2021

Context. The nitrogen reservoir in planetary systems is a long-standing problem. Some of the N-bearing molecules are probably incorporated into the ice bulk during the cold phases of the stellar evolution, and may be gradually released into the gas phase when the ice is heated, for example in active comets. The chemical nature of the N-reservoir should greatly influence how, when, and in what form N returns to the gas phase, or is incorporated into the refractory material forming planetary bodies.

Aims. We present the study of the thermal desorption of two ammonium salts, ammonium formate and ammonium acetate, from a gold surface and from a water ice substrate.

Methods. Temperature-programmed desorption experiments and Fourier transform infrared reflection spectroscopy were conducted to investigate the desorption behavior of ammonium salts.

Results. Ammonium salts are semi-volatile species releasing neutral species as major components upon desorption, namely ammonia and the corresponding organic acid (HCOOH and CH3COOH), at temperatures higher than the temperature of thermal desorption of water ice. Their desorption follows a first-order Wigner-Polanyi law. We find the first-order kinetic parameters A = 7.7 ± 0.6 × 1015 s−1 and Ebind = 68.9 ± 0.1 kJ mol−1 for ammonium formate and A = 3.0 ± 0.4 × 1020 s−1 and Ebind = 83.0 ± 0.2 kJ mol−1 for ammonium acetate. The presence of a water ice substrate does not influence the desorption kinetics. Ammonia molecules locked in salts desorb as neutral molecules at temperatures much higher than previously expected, and that are usually attributed to refractory materials.

Conclusions. The ammonia snow line has a smaller radius than the water snow line. As a result, the NH3/H2O ratio content in Solar System bodies can be a hint to where they formed and subsequently migrated.
Rotation periods for cool stars in the open cluster NGC 3532
Authors: Fritzewski D. J. , Barnes S. A. , James D. J. , Strassmeier K. G.
Published: June 2021

Context. A very rich cluster intermediate in age between the Pleiades (150 Myr) and the Hyades (600 Myr) is needed to probe the rotational evolution, especially the transition between fast and slow rotation that occurs between the two ages.

Aims. We study the rich 300 Myr-old open cluster NGC 3532 to probe this important transition and to provide constraints on angular momentum loss. Measuring the rotation periods builds on our prior work of providing spectroscopic membership information for the cluster, and it supports the chromospheric activity measurements of cluster stars that we provide in a companion paper.

Methods. Using 42 d-long photometric time series observations obtained with the Yale 1 m telescope at CTIO, we measured rotation periods for members of NGC 3532 and compared them with the predictions of angular momentum evolution models.

Results. We directly measured 176 photometric rotation periods for the cluster members. An additional 113 photometric rotation periods were identified using activity information, described fully in the companion paper, resulting in a total sample containing 279 rotation periods for FGKM stars in NGC 3532. The colour-period diagram constructed from this rich data set shows a well-populated and structured slow rotator sequence, and a fast rotator sequence evolved beyond zero-age main sequence age whose stars are in transition from fast to slow rotation. The slow rotator sequence itself is split into slightly slower and faster rotators, a feature we trace to photometric binary status. We also identify an extended slow rotator sequence extending to P ∼ 32 d, apparently the analogue of the one we previously identified in NGC 2516. We compare our period distribution to rotational isochrones in colour-period space and find that all considered models have certain shortcomings. Using more detailed spin-down models, we evolve the rotation periods of the younger NGC 2516 forward in time and find that the spindown of the models is too aggressive with respect to the slow rotators. In contrast, stars on the evolved fast rotator sequence are not spun down strongly enough by these models. Our observations suggest a shorter crossing time for the rotational gap, one we estimate to be ∼80 Myr for early-K dwarfs.
Existe-t-il un mode de mastication spécifique aux malocclusions de classe II subdivision ?
Authors: Raymond Jean-Louis , Saive-Noll Marie
Published: June 2021

Notre étude a consisté à enregistrer le mode de mastication de 26 sujets composant notre échantillon et présentant une malocclusion de classe II subdivision afin de déterminer s’il existait pour ces malocclusions une mastication singulière.

Les résultats montrent que sur les 26 sujets étudiés, 25 sujets exercent une mastication préférentielle du côté de la distoclusion molaire. Il semblerait donc que l’asymétrie morphologique s’accompagne d’une « asymétrie fonctionnelle masticatrice » laquelle pourrait expliquer l’étiopathogénie de ces malocclusions singulières.
Éléments de prise de décision thérapeutique, en cas d’asymétrie. 1re partie : les asymétries sans symptômes de DTM
Authors: Saulue Paul , Laluque Jean-François , d’Incau Emmanuel , Boileau Marie-José , Orthlieb Jean-Daniel
Published: June 2021

Un projet de correction d’une asymétrie doit-il être fondé seulement sur la référence à une normalité ? L’asymétrie faciale est globalement la règle, tant sur le plan anatomique que fonctionnel. Les caractéristiques des asymétries doivent être abordées et traitées avec discernement. Lorsqu’il s’agit de pratiquer des interventions esthétiques, il est nécessaire de bien appréhender les désirs et les besoins du patient. Sur le plan fonctionnel, le seuil de prise en charge dépend des capacités d’adaptation de l’appareil manducateur. Pour cela, l’orthodontiste doit prévoir dans son examen clinique une étape de dépistage des signes et symptômes des dysfonctionnements temporo-mandibulaires (DTM), pour apprécier les limites de ce potentiel d’adaptation neurophysiologique. Le praticien prendra soin d’associer le patient dans une « décision partagée », ce qui favorisera l’observance du patient durant le traitement, pour obtenir un bon niveau d’alliance thérapeutique, gage de satisfaction du résultat obtenu. La prise de décision thérapeutique se basera donc sur la demande du patient, l’évaluation diagnostique et l’estimation pronostique, et tiendra compte de la notion de médecine fondée sur les valeurs.
Adaptive wavelet schemes and finite volumes
Authors: Del Sarto Daniele , Deriaz Erwan , Lhebrard Xavier , Rigal Mathieu
Published: June 2021

We consider a procedure for combining high order finite volumes and tree-based nonuniform grids. Especially, we focus on efficient algorithms for third order multidimensional volume interpolation and communication between levels of refinement. In the end, numerical results are reviewed to validate our approach.
Neue Entwicklungen bei Diabetes mellitus Typ 1
Authors: Haberbosch Linus , Spranger Joachim
Published: June 2021

Was ist neu?

Monitoring Mit der zunehmenden Prävalenz von Continuous-Glucose-Monitoring (CGM) -Systemen gewinnt die Time in Range (TIR) als Parameter zur Optimierung der Blutzuckereinstellung bei Patienten mit Diabetes mellitus Typ 1 an Bedeutung. Zuletzt erfolgte der Nachweis einer verbesserten Prävention von kardiovaskulären Ereignissen und Schwangerschaftskomplikationen bei Patienten mit optimierter TIR. Zusätzlich zur TIR wird empfohlen, die Time below Range (TBR) zu erheben, um Hypoglykämien als klinisch relevante Ereignisse ebenfalls zu erfassen.

Hypoglykämien Hypoglykämien bleiben eine klinisch relevante Komplikation der Therapie des Diabetes mellitus Typ 1. Mit der Zulassung von nasalem Glukagon besteht nun gegenüber der klassischen Injektion eine Option als einfach anzuwendende Notfalltherapie. Mit der Entwicklung des im flüssigen Zustand stabilen Glukagon-Analogons Dasiglukagon steht potenziell in naher Zukunft darüber hinaus ein klassischer Notfall-Pen mit Fertiglösung zur Verfügung.

Insulintherapie Das neue schnellwirksame Insulin aspart (fast-acting Insulin aspart, FIASP) bietet neue Chancen für die Blutzuckeroptimierung von Typ-1-Diabetespatienten. 2019 wurde darüber hinaus das erste Hybrid-Closed-Loop-System zur Behandlung des Diabetes mellitus Typ 1 in Deutschland zugelassen. Bei diesem System erfolgt eine automatische Anpassung der Basalrate anhand des per CGM gemessenen Blutzuckers. Aufgrund der weiterhin notwendigen Bolusgaben und der Komplexität der Technologie bleibt eine sorgfältige Auswahl und adäquate Schulung der mit einem solchen System therapierten Patienten essenziell. Bei adäquater Anwendung ermöglicht ein Hybrid-Closed-Loop-System eine verbesserte Einstellung insbesondere des nächtlichen Blutzuckers.

Ergänzende Therapien Seit 2019 sind der SGLT-2-Inhibitor Dapagliflozin und der kombinierte SGLT-1/2-Inhibitor Sotagliflozin für die Therapie von unzureichend eingestellten Typ-1-Diabetikern mit einem BMI über 27 kg/m² und ohne Risikokonstellation für diabetische Ketoazidosen zugelassen. Die relevanteste Nebenwirkung ist die atypische normoglykäme Ketoazidose, weshalb eine initiale Risikoeinschätzung sowie eine angemessene Schulung des Patienten zur Durchführung und Interpretation von Ketonkörper- und pH-Messungen unter der Therapie von zentraler Bedeutung sind.
Rheuma und Lunge
Authors: Bastian Hans , Krause Andreas
Published: June 2021

Was ist neu?

Diagnostik Goldstandard in der Diagnostik einer ILD bei rheumatischen Erkrankungen bleibt weiterhin die hochauflösende, nicht kontrastmittelverstärkte HRCT. Verlässliche Biomarker für CTD-ILDs stehen für den klinischen Alltag noch nicht zur Verfügung. Die klinisch und apparativ erhobenen Befunde lassen fast immer eine belastbare Diagnose stellen. Eine histologische Sicherung ist nur bei unklaren Fällen nötig. Eine interessante diagnostische Option könnte in Zukunft die molekulare Diagnostik von Lungenparenchym sein.

Therapie MTX gilt nicht länger als Risikofaktor für die Entwicklung einer chronischen ILD bzw. einer Lungenfibrose bei RA. Neuere Daten weisen darauf hin, dass MTX die Ausbildung einer ILD bei RA sogar verhindern oder zumindest verzögern kann. In Studien bei Patienten mit SSc zeigten sich Hinweise für einen positiven Einfluss von Tocilizumab auf den Verlauf einer ILD mit Stabilisierung der forcierten Vitalkapazität in der Lungenfunktionsprüfung. Allerdings wurde der primäre Endpunkt der Studien – Verbesserung im modifizierten Rodnan-Skin-Score – nicht erreicht. Nintedanib wurde jüngst zur Behandlung Erwachsener mit SSc-ILD sowie bei Patienten mit chronisch PF-ILD bei unterschiedlichen Grunderkrankungen (u. a. RA) zugelassen.
Rural Aspirations: Reflections for Development Planning, Design and Localized Effects
Authors: Mausch Kai , Harris Dave , Revilla Diez Javier
Published: June 2021

In this editorial introduction to the Special Issue “Rural aspirations—Livelihood decisions and rural development trajectories”, we outline current views on aspirations and their relevance for development research, projects and approaches. Using several examples from Africa, we outline how the combination of the different theoretical perspectives, case studies and regional backgrounds provides deeper insights about the role of aspirations in shaping rural areas. The distinct entry points of the ‘bottom up’ local aspirations for future lives, the ‘top down’ aspirations as visions for change, and the process of negotiating between these provide novel insights into directions for development action as well as for future research in the field of aspirations in the development arena.
On the convergence of WKB approximations of the damped Mathieu equation
Authors: Nwaigwe Dwight
Published: June 2021

The form of the fundamental set of solutions of the damped Mathieu equation is determined by Floquet theory. In the limit as m → 0, we can apply WKB theory to get first order approximations of the fundamental set. WKB theory states that this approximation gets better as m → 0 and T is fixed. However, convergence of the periodic part and characteristic exponent is not addressed. We show that they converge to those predicted by WKB theory. We also provide a rate of convergence that is not dependent on T.
Wong–Zakai approximations and random attractors of non-autonomous stochastic discrete complex Ginzburg–Landau equations
Authors: Yang Yuan , Shu Ji , Wang Xiaohu
Published: June 2021

In this paper, we consider the Wong–Zakai approximations and random attractors for stochastic discrete complex Ginzburg–Landau equations driven by nonlinear multiplicative noise. We establish the existence of the random attractor for the approximate system. For linear multiplicative noise or additive noise, we study the convergence of the solutions and the upper semicontinuity of random attractors for the approximate equation when the perturbation parameters tend to zero.
Convergence of moments of twisted COE matrices
Authors: Berkolaiko Gregory , Booton Laura
Published: June 2021

We investigate eigenvalue moments of matrices from the circular orthogonal ensemble multiplicatively perturbed by a permutation matrix. More precisely, we investigate the variance of the sum of the eigenvalues raised to power k for arbitrary but fixed k and in the limit of a large matrix size. We find that when the permutation defining the perturbed ensemble has only long cycles, the answer is universal and approaches the corresponding moment of the circular unitary ensemble with a particularly fast rate: the error is of order 1/N3 and the terms of orders 1/N and 1/N2 disappear due to cancellations. We prove this rate of convergence using Weingarten calculus and classifying the contributing Weingarten functions first in terms of a graph model and then algebraically.
Affine Yangian and Schur functions on plane partitions of 4
Authors: Wang Na , Shi Linjie
Published: June 2021

In this paper, we first calculate the orthogonal basis of the vector space spanned by eiejeke0|0⟩, where ej are the generators of the affine Yangian of gl(1). The elements of this orthogonal basis correspond to three dimensional bosons. Then, we calculate the Schur functions of plane partitions of 4, we find that the plane partitions become Young diagrams, and the Schur functions on plane partitions become Schur functions on Young diagrams when h1 = 1, h2 = −1, and h3 = 0.
Comment on “Deep water gravity wave triad resonances on uniform flow” [Phys. Fluids 32, 076603 (2020)]
Authors: Kirby James T. , Smit Pieter B.
Published: June 2021

We consider the recent conclusion of Kouskoulas and Toledo [Phys. Fluids 32, 076603 (2020)] on the existence of resonant triads for surface waves propagating in a uniform current and show that their conclusion is based on a misinterpretation of the geometry of the wave components. We provide a proof of nonexistence for the more general case of waves traveling at arbitrary directions in the horizontal plane.
Explaining an unusual electromigration behavior—A comprehensive experimental and theoretical analysis using finite element method
Authors: Wang Z. , Alajlouni S. , Bermel P. , Shakouri A.
Published: June 2021

In metallic interconnects, it is generally assumed that electromigration (EM) failure location is independent of the applied electrical current and always occurs at the highest-current-density area. Our experiments show otherwise. We designed an Al interconnect that alters its failure location by only varying the applied current density. The failure occurs near the high for a current above 2 × 107 A/cm2, but at a location with 59% of the maximum for lower current densities. Thermoreflectance thermal imaging is employed to gather time-dependent high-resolution spatial temperature distributions of the Al interconnect during EM. More importantly, we propose a computationally inexpensive 2D finite element method that tracks EM evolution in time and matches well with the observations from different experimental conditions. A detailed analysis covering the major driving forces of EM is carried out to understand the complex physics behind EM. The atomic depletion rate contributed by each force is quantitatively studied. By examining the results from every tested experimental condition, the model reveals that the temperature gradient is the key reason causing atomic depletion near the failure location. Graphical illustrations and qualitative analysis are provided to intuitively show the key findings of our work.
Improved Ohmic contacts to plasma etched high Al fraction n-AlGaN by active surface pretreatment
Authors: Zhang N. , Xu F. J. , Lang J. , Wang L. B. , Wang J. M. , Liu B. Y. , Fang X. Z. , Yang X. L. , Kang X. N. , Wang X. Q. , Qin Z. X. , Ge W. K. , Shen B.
Published: June 2021

Improving the contact characteristics of Ti/Al/Ni/Au on plasma etched n-AlGaN has been attempted by an active pretreatment, which can provide Si and N atoms to occupy the possible metal and N vacancies. It is found that the contacts on both the as-grown and plasma-etched + pretreatment n-Al0.5Ga0.5N present truly Ohmic in nature, whereas the contacts on plasma-etched samples without pretreatment still remain rectifying. Surface atomic concentration analysis indicates that the plasma etching induced N or metal vacancies mostly act as acceptor-like states, leading to a severe compensation. Fortunately, these states can be effectively removed by the presently proposed pretreatment, and thus the Fermi level is raised up toward the conduction band edge, ensuring the formation of Ohmic contacts.
Development of a fast response neutron detector for the supersonic FRC collision process
Authors: Sahara N. , Asai T. , Kobayashi D. , Takahashi Ts. , Ogawa H. , Magee R.
Published: June 2021

The collisional merging experiments of the field-reversing configuration (FRC) at supersonic/Alfvénic velocities have been performed in the FRC Amplification via Translation-Collisional Merging device only in Japan. This experiment may excite shockwaves and cause particle acceleration. To obtain supporting evidence of particle acceleration by shockwaves, we have proposed to observe neutrons originating from the D–D fusion reaction of accelerated non-thermal particles. A plastic scintillation detector has been developed for the supersonic/Alfvénic collision/merging FRC experiment. The developed neutron detector has sufficient performance of neutron sensitivity and nanosecond response time. In the collisional merging process, we obtained a signal that could be considered a neutron, which is not predicted by the adiabatic compression process in the two-dimensional magnetohydrodynamics simulation.
Structural and dynamical heterogeneity of water trapped inside Na+-pumping KR2 rhodopsin in the dark state
Authors: Santra Mantu , Seal Aniruddha , Bhattacharjee Kankana , Chakrabarty Suman
Published: June 2021

Photoisomerization in the retinal leads to a channel opening in rhodopsins that triggers translocation or pumping of ions/protons. Crystal structures of rhodopsins contain several structurally conserved water molecules. It has been suggested that water plays an active role in facilitating the ion pumping/translocation process by acting as a lubricant in these systems. In this paper, we systematically investigate the localization, structure, dynamics, and energetics of the water molecules along the channel for the resting/dark state of KR2 rhodopsin. By employing several microseconds long atomistic molecular dynamics simulation of this trans-membrane protein system, we demonstrate the presence of five distinct water containing pockets/cavities separated by gateways controlled by protein side-chains. There exists a strong hydrogen bonded network involving these buried water molecules and functionally important key residues. We present evidence of significant structural and dynamical heterogeneity in the water molecules present in these cavities, with very rare exchange between them. The exchange time scale of such buried water with the bulk has an extremely wide range, from tens of nanoseconds to >1.5 µs. The translational and rotational dynamics of buried water are found to be strongly dependent on the protein cavity size and local interactions with a classic signature of trapped diffusion and rotational anisotropy.
Two-dimensional hybrid model of gradient drift instability and enhanced electron transport in a Hall thruster
Authors: Kawashima R. , Komurasaki K.
Published: June 2021

An axial–azimuthal two-dimensional Hall thruster discharge model was developed for analyzing gradient drift instability (GDI) and cross field electron transport enhancement induced solely by the GDI. A hybrid particle-fluid model was used for the partially ionized plasma, where the inertialess electron fluid in the quasineutral plasma was assumed. A nonoscillatory numerical method was proposed for the potential solver in the electron fluid model to avoid numerical instability and analyze the physics of GDI accurately. A simulation is performed for a 1 kW-class anode-layer-type Hall thruster, and the flow field with plasma instability is presented. Plasma instability with vortex-like structures is observed in the acceleration and plume regions. The generated plasma instability enhances the cross field electron transport in the axial direction around the channel exit and in the plume region. Grid convergence is confirmed regarding the effect of electron transport enhancement, which indicates that cross field electron transport enhancement is based on the plasma instability. Furthermore, the comparison between the simulation results and linear perturbation analyses demonstrates that the simulated plasma instability reflects the theory of GDI. Thus, it is concluded that the hybrid model is useful for the analyses of GDI, and the GDI can enhance the cross field electron transport in Hall thrusters.
Spatially resolved Fourier transform impedance spectroscopy: A technique to rapidly characterize interfaces, applied to a QD/SiC heterojunction
Authors: Kelley Mathew L. , Simin Grigory , Hussain Kamal , Khan Asif , Greytak Andrew B. , Chandrashekhar M. V. S.
Published: June 2021

We demonstrate a technique to quickly build and spatially map the frequency response of optoelectronic devices. The transfer function of a linear system is the Fourier transform of its impulse response. Such an impulse response is obtained from transient photocurrent measurements of devices such as photodetectors and solar cells. We introduce and apply Fourier transform impedance spectroscopy (FTIS) to a PbS colloidal quantum dot SiC heterojunction photodiode and validate the results using intensity-modulated photocurrent spectroscopy. Cutoff frequencies in the devices were as high as ∼10 kHz, showing their utility in advanced thin film and flexible electronics. The practical frequencies for FTIS lie in the mHz–kHz range, ideal for composite materials such as quantum dot films that are dominated by interfacial trap states. These can lead to characteristic lengths for charge collection ∼20–500 μm dominated by transmission line effects, rather than intrinsic diffusion and drift length scales, enabling extraction of interfacial capacitances and series/parallel resistances.
Large amplitude capillary-gravity solitary waves in a stratified fluid sandwiched between two deep homogeneous layers
Authors: Derzho Oleg G.
Published: June 2021

The study addresses the propagation of plane capillary gravity solitary waves of permanent form in a three layer formulation. The intermediate fluid is assumed to be stratified, while the upper and lower ones are homogeneous and infinitely deep. One or both interfaces separating these layers are subject to capillarity. The research can be applied to the case of two deep fluids when one of these fluids is stratified near the interface. The latter formulation is relevant to studies of capillary gravity waves in the transitional area between sea water and liquid carbon dioxide in the deep ocean. This has become an issue of importance for the secure storage of carbon dioxide, which is an environmental/technological problem in modern days. Therefore, we address a capillary-gravity wave motion beyond the well-examined cases of a free surface or two fluid flows. It is shown that in the considered formulation, capillary-gravity solitary waves of finite amplitude obey an integro-differential equation. This equation contains both Korteweg–de Vries (KdV) and Benjamin–Ono (BO) dispersion laws and a specific nonlinearity, which depends on the properties of the stratified layer. Capillary (KdV-type) dispersion dominates if the thickness of the stratified layer is d≪d∗. When d≫d∗, the gravitational (BO-type) dispersion determines the flow. The value d∗ depends on the mode number, gravitational acceleration, and capillarity effects. Analytical solutions for the amplitude function and the streamline patterns are presented.
57Fe Mössbauer isomer shift of pure iron and iron oxides at high pressure—An experimental and theoretical study
Authors: Desmarais Jacques K. , Bi Wenli , Zhao Jiyong , Hu Michael Y. , Alp Esen , Tse John S.
Published: June 2021

The 57Fe isomer shift (IS) of pure iron has been measured up to 100 GPa using synchrotron Mössbauer spectroscopy in the time domain. Apart from the expected discontinuity due to the α → ε structural and spin transitions, the IS decreases monotonically with increasing pressure. The absolute shifts were reproduced without semi-empirical calibrations by periodic density functional calculations employing extensive localized basis sets with several common density functionals. However, the best numerical agreement is obtained with the B1WC hybrid functional. Extension of the calculations to 350 GPa, a pressure corresponding to the Earth’s inner core, predicted the IS range of 0.00 to −0.85 mm/s, covering the span from Fe(0) to Fe(VI) compounds measured at ambient pressure. The calculations also reproduced the pressure trend from polymorphs of prototypical iron oxide minerals, FeO and Fe2O3. Analysis of the electronic structure shows a strong donation of electrons from oxygen to iron at high pressure. The assignment of formal oxidation to the Fe atom becomes ambiguous under this condition.
Low-threshold strain-compensated InGaAs/(In,Al)GaAs multi-quantum well nanowire lasers emitting near 1.3 μm at room temperature
Authors: Schmiedeke P. , Thurn A. , Matich S. , Döblinger M. , Finley J. J. , Koblmüller G.
Published: June 2021

Realizing telecom-band lasing in GaAs-based nanowires (NW) with low bandgap gain media has proven to be notoriously difficult due to the high compressive strain built up in the active regions. Here, we demonstrate an advanced coaxial GaAs-InGaAs multi-quantum well (MQW) nanowire laser that solves previous limitations by the introduction of a strain compensating InAlGaAs buffer layer between the GaAs core and the MQW active region. Using a buffer layer thickness comparable to the core diameter applies a significant tensile strain to the GaAs core which efficiently minimizes the compressive strain in the InGaAs MQW and enables large In-content without plastic relaxation. Experimental verification is shown for NW-lasers with an In-content of up to 40% in the MQW, evidencing a clear strain-relieved redshift of the lasing emission and a strong reduction of the lasing threshold compared to highly strained MQWs in state-of-the-art GaAs NW-lasers. This way we achieve optically pumped room temperature lasing operation with a threshold below 50 μJ cm−2 in the telecom O-band close to 1.3 μm.
Plasma fluorination on epoxy resin surface and its effect on flashover properties
Authors: Zhan Zhenyu , Wang Dong , Xin Weifeng , Liu Yang , Wang Leilei , Chen Taiyu , Teng Chenyuan
Published: June 2021

Epoxy resin is the main material of spacer in a gas insulated transmission line and other gas-insulated equipment. During long-term operation, the charge accumulates on the surface of the epoxy resin, which will distort the electric field and thus accelerate the failure of the insulation. In this paper, the surface of the epoxy resin was fluorinated by dielectric barrier discharge at different times. The surface physical, chemical, and flashover properties of the samples before and after modification were measured. The results show that the method used in this paper can graft fluorine on the surface of the sample, change the surface roughness, and make the electron trap shallower and the hole trap deeper. The appropriate modification time can reduce the charge accumulation on the surface, hinder the formation of flashover channels, and improve the surface flashover voltage, showing potential for use in the improvement of the insulating performance of insulating materials.
THz wave propagation in the stagnation region of reentry plasma sheath
Authors: Liu Jian-xun , Zhao Yuan , Lv Jin-jian , Qu Shi , Liu Tai-yang , Yu Tong-pu , Zhao Jun
Published: June 2021

By using two-dimensional particle-in-cell simulations, we demonstrate a terahertz (THz) wave propagating in the stagnation region of a reentry plasma sheath. When a THz wave propagates in the plasma sheath, the frequency blue shift is initiated as the wavelength is compressed. Attenuation is observed due to energy transfer from the THz wave to the plasma internal energy. Electrons are first accelerated mostly via oscillating in the electric field and partially via the wake field and then deliver their energies to the other particles via collisions. Detailed discussions show that increasing the intensity and frequency of the THz wave results in a higher transmission coefficient, which indicates that high power and high frequency methods are useful for communication blackout mitigation. This investigation of THz wave transmission in plasma will facilitate the mitigation of radio frequency blackout in spacecraft reentry in earth’s atmosphere communication.
MOVPE of GaN-based mixed dimensional heterostructures on wafer-scale layered 2D hexagonal boron nitride—A key enabler of III-nitride flexible optoelectronics
Authors: Sundaram Suresh , Vuong Phuong , Mballo Adama , Ayari Taha , Karrakchou Soufiane , Patriarche Gilles , Voss Paul L. , Salvestrini Jean Paul , Ougazzaden Abdallah
Published: June 2021

We summarize our recent progress in Metal organic vapor phase epitaxy (MOVPE) van der Waals epitaxy of wafer-scale 2D layered hexagonal boron nitride (h-BN) on sapphire and subsequently grown III-N materials. This one step growth process allows for mechanical transfer of GaN-based devices from h-BN on sapphire to various supports. We first review the growth of h-BN on unpatterned and patterned sapphire templates. Second, we describe h-BN growth on dielectric pre-patterned sapphire templates, which enables dicing-free GaN-based device structures’ pick-and-place heterogenous integration of III-N devices. Third, we review the growth of self-assembled 1D GaN-based nanowire light emitting diode (LED) structures on layered 2D h-BN for mechanical transfer of nanowire LEDs. Together, these results illustrate the potential of wafer-scale van der Waals h-BN MOVPE to enhance the III-N device functionality and to improve III-N processing technology.
The shift of breakdown voltage for silicon membrane strip detectors resulting from surface avalanche
Authors: Peng W. , Sabri Alirezaei I. , André N. , Zeng X. , Bouterfa M. , Wang B. , Zeng Y. , Flandre D.
Published: June 2021

Silicon membrane strip photodetectors are fabricated based on thin silicon-on-insulator (SOI) wafers. The thin SOI wafer is realized by exploiting a thinning process on backside. Such detectors can be implemented in proton-beam position detection because its ultra-thin membrane substrate can reduce beam scattering and offer the considerable advantages of higher radiation hardness. A p-spray implantation process is typically performed at the silicon surface between the n+-strips in order to insulate them, without requiring an extra photolithographic mask. In this paper, the sources of leakage current in the detector are first studied by considering both activation energy and simulation analysis in Silvaco TCAD. While the device is operating below avalanche breakdown voltage, the Shockley–Read–Hall process and trap-assisted-tunneling process are dominantly contributing to leakage current. The dominant breakdown voltage is attributed to the premature breakdown in the junction of p−spray/n+ region. The shift of this breakdown voltage under repeated avalanche processes is analyzed in-depth by both experiments and simulations, as a function of temperature and electrical stress conditions, which are introducing an important reliability problem. The electrical stress can be attributed to an increase in fixed charge density at the Si/SiO2 interface. The breakdown voltage finally increases by 4 V after successive avalanche breakdowns as a function of the applied excess bias voltage beyond breakdown voltage.
Generation of half-integer harmonics and efficient THz-to-visible frequency conversion in strained graphene
Authors: Ornigotti Marco , Ornigotti Luca , Biancalana Fabio
Published: June 2021

We study the generation of harmonics from graphene under the influence of an artificial magnetic field, generated via bending of a graphene flake. We show how the Landau level structure induced by the pseudomagnetic field breaks the centrosymmetry of graphene, thus allowing the generation of even harmonics. We also show that depending on the impinging pulse duration, the nonlinear signal does not only contain the integer harmonics of the impinging pulse but also its half-integer ones due to the peculiar square-root-like nature of Landau levels in graphene.
Aerodynamic characteristics and mechanisms for bionic airfoils with different spacings
Authors: Li Deyou , Chang Hong , Zuo Zhigang , Wang Hongjie , Liu Shuhong
Published: June 2021

In this study, the aerodynamic characteristics of multi-protuberance airfoils modeled on the fin of a humpback whale were investigated by numerically simulating the National Advisory Committee for Aeronautics 634-021 airfoils. For a Reynolds number of 1.8 × 105, the numerical simulation results obtained with no spacing between protuberances were compared with experimental values to verify the accuracy of the numerical method. The effects of different spacings on the aerodynamic performance of the airfoil at various angles of attack were investigated by setting the spacing between the two protuberances as 0.25, 0.5, and 0.75c. The results show that the lift coefficient was increased by 5%–15%, and the drag coefficient remained constant under different conditions when the spacing between the protuberances was 0.25c. The twin-protuberance airfoils with different spacings exhibited similar two-step stall characteristics. However, only the unspaced twin-protuberance airfoil had a one-sided stall. Simulations of the multi-protuberance airfoil showed that airfoils featuring spacings between protuberances exhibited good lift characteristics at large angles of attack. With an increase in the angle of attack, the lift coefficient steadily changed. Compared with the full-protuberance airfoil, the drag coefficient of the airfoil with spacing was significantly reduced.
Ultrasensitive detection of SARS-CoV-2 RNA and antigen using single-molecule optofluidic chip
Authors: Meena G. G. , Stambaugh A. M. , Ganjalizadeh V. , Stott M. A. , Hawkins A. R. , Schmidt H.
Published: June 2021

Nucleic acids and proteins are the two most important target types used in molecular diagnostics. In many instances, simultaneous sensitive and accurate detection of both biomarkers from the same sample would be desirable, but standard detection methods are highly optimized for one type and not cross-compatible. Here, we report the simultaneous multiplexed detection of SARS-CoV-2 RNAs and antigens with single molecule sensitivity. Both analytes are isolated and labeled using a single bead-based solid-phase extraction protocol, followed by fluorescence detection on a multi-channel optofluidic waveguide chip. Direct amplification-free detection of both biomarkers from nasopharyngeal swab samples is demonstrated with single molecule detection sensitivity, opening the door for ultrasensitive dual-target analysis in infectious disease diagnosis, oncology, and other applications.
Surface-copper-doped WO3 photoanode for photoelectrochemical water splitting
Authors: Ma Yuli , Hu Yun Hang
Published: June 2021

Surface Cu2+ dopants on WO3 photoanodes were created with a facile hydrothermal method for photoelectrochemical water splitting. The introduction of Cu2+ ions was demonstrated to significantly improve the interface charge transfer efficiency of WO3. Furthermore, the surface Cu2+ ions also acted as adsorption and activation sites for intermediate species, decreasing Gibbs free energy and thus enhancing the oxygen evolution reaction activity. Consequently, incident-photon-to-current-conversion efficiency was increased by 600% under the irradiation of 340 nm monochromatic light and 1.23 V (vs reversible hydrogen electrode) bias.
Effects of viscosity and elasticity on Rayleigh–Taylor instability in a cylindrical geometry
Authors: Sun Y. B. , Zeng R. H. , Tao J. J.
Published: June 2021

In this paper, we present a linear analysis of the Rayleigh–Taylor instability (RTI) in cylindrical geometry to investigate the effects of viscosity and elasticity on growth rates using a decomposition method. This method decomposes the fourth-order differential equations into two coupled second-order differential equations to easily obtain the dispersion relations. The motions of the interfaces are analyzed for the instability at liquid/liquid, solid/liquid, and solid/solid interfaces, and the results retrieve those previously obtained for inviscid fluids. Generally, the planar growth rates recover those in the cylindrical geometry when the dimensionless radius Br or mode number n is large enough. The RTI for different cylindrical geometries is particularly investigated to study the effects of viscosity, elasticity, and curvature. It is found that the n = 1 mode will always survive and dominate the motion of the interfaces when the dimensionless radius is significantly small. We believe that this method will provide the possibility of investigating the behaviors of different types of interfaces based on their driven conditions. Furthermore, this will help to find a way to study the evolution of low-mode asymmetries that is essential for controlling the integrity of a fusion target under study during implosion processes in high energy-density physical experiments. This method provides basic guidance for exploration of Bell–Plesset effects and of the transition from elasticity to plasticity in cylindrical geometry.
Oblique stationary solitary waves in turbulent free-surface flow
Authors: Schneider Wilhelm
Published: June 2021

It is shown that an oblique solitary wave may be caused by an oblique strip of enlarged bottom roughness. The analysis is valid for very large Reynolds numbers and very small slopes. Considered are strips with a constant width in the longitudinal direction and with constant roughness. For a strip whose length is much larger than its width, the equations of motion can be simplified by assuming a three-dimensional flow that is independent of the coordinate in the longitudinal direction of the strip. Furthermore, it is assumed that the Froude number in terms of the velocity component normal to the strip is slightly larger than the critical value 1. This facilitates application of an asymptotic expansion method developed previously for plane flow. The analysis does not require modeling of the Reynolds stresses. It turns out that the velocity profile of the three-dimensional flow is not skewed in the first order. The shape, amplitude, and position of the oblique stationary wave are obtained from solutions of the steady-state version of an extended Korteweg-de-Vries equation. In general, the oblique wave is a classical solitary wave with a long, but shallow tail. However, tails are missing for certain combinations of Froude number and parameters characterizing the strip. Measurements and numerical solutions of the full Reynolds equations are already available for orthogonal solitary waves, lending support to the results of the asymptotic analysis. In addition, a novel boundary condition at the free surface is given, and the velocity distribution in fully developed flow is determined.
Three-dimensional calculation physical model for corona onset characteristics of AC grading rings
Authors: Huang Shilong , Yan Xiaoliang , Liu Yunpeng , Ye Zijian , Zhang Guangzhou , Tang Jian , Liu Chen , Li Yongshuang , He Wangling , Quan Shanshan , Zhang Yuqing
Published: June 2021

Corona discharge on the surface of power transmission and transformation fittings becomes increasingly serious with increasing voltage levels, especially for many grading rings in transformer substations. With the enhancement of people’s environmental awareness, the environmental protection administration requires noise and electromagnetic environment at transformer substations shall meet relevant standards. In order to suppress corona discharge on the surface of a grading ring, it is necessary to study its corona onset characteristics. Considering the basic physical process of the corona discharge, in this study, the electric field intensity is first calculated at any point in the space around the grading ring through ring charge simulation. Then, based on the theory of secondary electron emission, criteria for calculating the onset voltage of negative corona of the grading ring are derived, leading to an area factor of a photon absorption function suitable for the grading ring. In this way, a three-dimensional (3D) calculation physical model of the corona onset suitable for the grading ring is developed. This study calculates the corona onset voltage and field intensity of the grading ring under the typical working conditions by using the proposed 3D calculation physical model of the corona onset. The calculation results are compared with test results of the corona onset voltage and field intensity of grading rings in an outdoor 750 kV transformer substation in an ultrahigh voltage (UHV) alternating current (AC) test base. Furthermore, the simulation results of the area factor of the photon absorption function, electron collision coefficient, electron adsorption coefficient, and effective ionization coefficient in the 3D calculation physical model are obtained. In this way, the accuracy of the 3D calculation physical model of the corona onset proposed in this paper is verified. The research results can provide a theoretical basis for the corona prevention design of grading rings in extra high voltage/UHV AC power transmission and transformation projects.
Gravity currents propagating at the base of a linearly stratified ambient
Authors: Dai Albert , Huang Yu-Lin , Hsieh Yu-Min
Published: June 2021

Gravity currents produced from a full-depth lock release propagating at the base of a linearly stratified ambient are investigated by means of newly conducted three-dimensional high-resolution simulations in conjunction with corresponding two-dimensional simulations and laboratory experiments. A passive tracer is implemented in the simulations to quantitatively measure the energies associated with the current and the ambient. The density of heavy fluid within the lock is ρ̃C, the density in the ambient of depth H̃ varies linearly from ρ̃b at the bottom to ρ̃0 at the top, and the ambient has an intrinsic frequency Ñ. Attention is focused on the initial slumping stage, during which the gravity currents propagate at a constant velocity Ṽ and the internal Froude number is defined as Fr=Ṽ/ÑH̃. The dynamics of the subcritical gravity currents, i.e., Fr<1/π, and the supercritical gravity currents, i.e., Fr>1/π, are qualitatively different and are examined with the help of three-dimensional and two-dimensional high-resolution simulations. For the subcritical gravity currents, the flow is dominated by the internal wave, the Kelvin–Helmholtz vortices are inhibited, and the two-dimensional simulation agrees well with and serves as a good surrogate model for the three-dimensional simulation in the slumping stage. For the supercritical gravity currents, the Kelvin–Helmholtz vortices are pronounced and prone to breakup into three-dimensional structures in the slumping stage. On the one hand, for the supercritical gravity currents, the kinetic energy associated with the current and the potential energy associated with the ambient are accurately captured by the two-dimensional simulation. On the other hand, the transition distance for the slumping stage and dissipation rate in the system are underpredicted while the kinetic energy associated with the ambient and the potential energy associated with the current are overpredicted by the two-dimensional simulation for the supercritical gravity currents. Therefore, information derived from the two-dimensional simulation for the supercritical gravity currents must be treated with care. The high-resolution simulations in this study also complement the existing shallow-water formulation, which has been reported to agree well with the two-dimensional simulations with good physical assumptions and simple mathematical models.