bluuebunny/crossref_metadata_2025 huggingface dataset:
New BRITE-Constellation observations of the roAp star α Cir
Authors: Weiss W. W. , Fröhlich H.-E. , Kallinger T. , Kuschnig R. , Popowicz A. , Baade D. , Buzasi D. , Handler G. , Kochukhov O. , Koudelka O. , Moffat A. F. J. , Pablo B. , Wade G. , Zwintz K.
Published: August 2020

Context. Chemically peculiar (CP) stars with a measurable magnetic field comprise the group of mCP stars. The pulsating members define the subgroup of rapidly oscillating Ap (roAp) stars, of which α Cir is the brightest member. Hence, α Cir allows the application of challenging techniques, such as interferometry, very high temporal and spectral resolution photometry, and spectroscopy in a wide wavelength range, that have the potential to provide unique information about the structure and evolution of a star.

Aims. Based on new photometry from BRITE-Constellation, obtained with blue and red filters, and on photometry from WIRE, SMEI, and TESS we attempt to determine the surface spot structure of α Cir and investigate pulsation frequencies.

Methods. We used photometric surface imaging and frequency analyses and Bayesian techniques in order to quantitatively compare the probability of different models.

Results. BRITE-Constellation photometry obtained from 2014 to 2016 is put in the context of space photometry obtained by WIRE, SMEI, and TESS. This provides improvements in the determination of the rotation period and surface features (three spots detected and a fourth one indicated). The main pulsation frequencies indicate two consecutive radial modes and one intermediate dipolar mode. Advantages and problems of the applied Bayesian technique are discussed.
Extreme intra-hour variability of the radio source J1402+5347 discovered with Apertif
Authors: Oosterloo T. A. , Vedantham H. K. , Kutkin A. M. , Adams E. A. K. , Adebahr B. , Coolen A. H. W. M. , Damstra S. , de Blok W. J. G. , Dénes H. , Hess K. M. , Hut B. , Loose G. M. , Lucero D. M. , Maan Y. , Morganti R. , Moss V. A. , Mulder H. , Norden M. J. , Offringa A. R. , Oostrum L. C. , Orrù E. , Ruiter M. , Schulz R. , van den Brink R. H. , van der Hulst J. M. , van Leeuwen J. , Vermaas N. J. , Vohl D. , Wijnholds S. J. , Ziemke J.
Published: August 2020

The propagation of radio waves from distant compact radio sources through turbulent interstellar plasma in our Galaxy causes these sources to twinkle, a phenomenon called interstellar scintillation. Such scintillations are a unique probe of the micro-arcsecond structure of radio sources as well as of the sub-AU-scale structure of the Galactic interstellar medium. Weak scintillations (i.e. an intensity modulation of a few percent) on timescales of a few days or longer are commonly seen at centimetre wavelengths and are thought to result from the line-of-sight integrated turbulence in the interstellar plasma of the Milky Way. So far, only three sources were known that show more extreme variations, with modulations at the level of some dozen percent on timescales shorter than an hour. This requires propagation through nearby (d ≲ 10 pc) anomalously dense (ne ∼ 102 cm−3) plasma clouds. Here we report the discovery with Apertif of a source (J1402+5347) showing extreme (∼50%) and rapid variations on a timescale of just 6.5 min in the decimetre band (1.4 GHz). The spatial scintillation pattern is highly anisotropic, with a semi-minor axis of about 20 000 km. The canonical theory of refractive scintillation constrains the scattering plasma to be within the Oort cloud. The sightline to J1402+5347, however, passes unusually close to the B3 star Alkaid (η UMa) at a distance of 32 pc. If the scintillations are associated with Alkaid, then the angular size of J1402+5347 along the minor axis of the scintels must be smaller than ≈10 μas, yielding an apparent brightness temperature for an isotropic source of ≳1014 K.
Alone but not lonely: Observational evidence that binary interaction is always required to form hot subdwarf stars
Authors: Pelisoli Ingrid , Vos Joris , Geier Stephan , Schaffenroth Veronika , Baran Andrzej S.
Published: August 2020

Context.Hot subdwarfs are core-helium burning stars that show lower masses and higher temperatures than canonical horizontal branch stars. They are believed to be formed when a red giant suffers an extreme mass-loss episode. Binary interaction is suggested to be the main formation channel, but the high fraction of apparently single hot subdwarfs (up to 30%) has prompted single star formation scenarios to be proposed.

Aims.We investigate the possibility that hot subdwarfs could form without interaction by studying wide binary systems. If single formation scenarios were possible, there should be hot subdwarfs in wide binaries that have undergone no interaction.

Methods.Angular momentum accretion during interaction is predicted to cause the hot subdwarf companion to spin up to the critical velocity. The effect of this should still be observable given the timescales of the hot subdwarf phase. To study the rotation rates of companions, we have analysed light curves from the Transiting Exoplanet Survey Satellite for all known hot subdwarfs showing composite spectral energy distributions indicating the presence of a main sequence wide binary companion. If formation without interaction were possible, that would also imply the existence of hot subdwarfs in very wide binaries that are not predicted to interact. To identify such systems, we have searched for common proper motion companions with projected orbital distances of up to 0.1 pc to all known spectroscopically confirmed hot subdwarfs usingGaiaDR2 astrometry.

Results.We find that the companions in composite hot subdwarfs show short rotation periods when compared to field main sequence stars. They display a triangular-shaped distribution with a peak around 2.5 days, similar to what is observed for young open clusters. We also report a shortage of hot subdwarfs with candidate common proper motion companions. We identify only 16 candidates after probing 2938 hot subdwarfs with good astrometry. Out of those, at least six seem to be hierarchical triple systems, in which the hot subdwarf is part of an inner binary.

Conclusions.The observed distribution of rotation rates for the companions in known wide hot subdwarf binaries provides evidence of previous interaction causing spin-up. Additionally, there is a shortage of hot subdwarfs in common proper motion pairs, considering the frequency of such systems among progenitors. These results suggest that binary interaction is always required for the formation of hot subdwarfs.
The path to instability in compact multi-planetary systems
Authors: Petit Antoine C. , Pichierri Gabriele , Davies Melvyn B. , Johansen Anders
Published: August 2020

The dynamical stability of tightly packed exoplanetary systems remains poorly understood. While a sharp stability boundary exists for a two-planet system, numerical simulations of three-planet systems and higher show that they can experience instability on timescales up to billions of years. Moreover, an exponential trend between the planet orbital separation measured in units of Hill radii and the survival time has been reported. While these findings have been observed in numerous numerical simulations, little is known of the actual mechanism leading to instability. Contrary to a constant diffusion process, planetary systems seem to remain dynamically quiescent for most of their lifetime before a very short unstable phase. In this work, we show how the slow chaotic diffusion due to the overlap of three-body resonances dominates the timescale leading to the instability for initially coplanar and circular orbits. While the last instability phase is related to scattering due to two-planet mean motion resonances (MMRs), for circular orbits the two-planets MMRs are too far separated to destabilise systems initially away from them. The studied mechanism reproduces the qualitative behaviour found in numerical simulations very well. We develop an analytical model to generalise the empirical trend obtained for equal-mass and equally spaced planets to general systems on initially circular orbits. We obtain an analytical estimate of the survival time consistent with numerical simulations over four orders of magnitude for the planet-to-star-mass ratio ε, and 6 to 8 orders of magnitude for the instability time. We also confirm that measuring the orbital spacing in terms of Hill radii is not adapted and that the right spacing unit scales as ε1∕4. We predict that beyond a certain spacing, the three-planet resonances are not overlapped, which results in an increase of the survival time. We confirm these findings with the aid of numerical simulations of three-planet systems with different masses. We finally discuss the extension of our result to more general systems, containing more planets on initially non-circular orbits.
Mechanical, electrochemical and structural characteristics of friction stir spot welds of aluminium alloy 6063
Authors: Mulaba-Kapinga Delphine , Nyembwe Kasongo Didier , Ikumapayi Omolayo Michael , Akinlabi Esther Titilayo
Published: August 2020

The work presents the friction stir spot welding (FSSW) of AA6063. The evolving properties due to the influence of process parameters and the efficacy of metallurgical, structural, mechanical, and electrochemical integrities were studied. FSSW was conducted on 2mm thickness by varying the rotational speed of 600, 900 and 1200 rpm and the dwell time at 10 and 15 s. The evolving microstructures, hardness, corrosion, shear tensile behaviours and X-ray diffraction characteristics of the as-received material and the welds were studied. As the tool rotational speed increased at a constant dwell time, a smooth and debris free spot welds were noticed, more HAZ formations became visible and more intermetallic phases of aluminium magnesium (AlMg) were formed although with very low peaks during structural assessment. Furthermore, the hardness values increased up to a certain limit and then decreased, the corrosion properties in artificial seawater (ASW) shown significant improvement on the spot-welded samples and the tensile shear strength was also improved. It would be recommended that spot welds at 900 rpm and 10 and/or 15 s for applications where the hardness is significant imperative and at 1200 rpm with 10 and/or 15 s dwell time where higher tensile shear strength is required and lastly, 1200 rpm at 15 s where corrosion application is significant.
Study on screening of canola varieties with high light use efficiency and evaluation of selecting indices
Authors: Wang Rui , Peng Wenli , Hu Liyong , Wu Weixian
Published: August 2020

High light use efficiency is an important factor for yield improvement during the growing season for winter canola. This study explored the evaluation method of high light use efficiency during the whole growth period in order to screen high light use coefficient of crop genotypes in canola producing areas of Southwest China. The pot experiment was conducted with sixty canola cultivars which had already been planted in the crops planting areas of the middle and upper reaches of Yangtze River. The plant height, root neck diameter, number of pods per main inflorescence, pods per plant, dry weight of shoots, seed weight per plant, pericarp weight per plant, ratio of pericarps to seeds weight per plant, seeds number per pod and 1000-grain weight were investigated under the shading treatment of reducing the incoming solar light by 20%. The high light use coefficient of canola cultivars was evaluated comprehensively by principal component analysis, membership function, cluster analysis and stepwise regression analysis. With these analyses, the original twelve indices related to light use efficiency could be synthesized into the four independent indices which represented 86.4% of all the investigated information of canola with high photosynthetic efficiency. Sixty varieties were classified into three groups by cluster analysis, and ZS12, GYZ6, FY792, RHY6, CZY3 and ZYZ19 displayed higher light use efficiency; such 18 varieties as XDZY9, XY1, YY50 and so on, were medium light efficient ones; and the rest 36 varieties such as LY9, ZYZ781, SG127 and so on, fell to the relatively lower light use efficiency categories. The comprehensive evaluation in this study had screened such four indicators as the stem dry weight per plant, the pod number per plant, the seed number per pod and the 1000-seed weight, which could be regarded as identification indicators for high light use efficiency of canola.
No vagina, one vagina, or multiple vaginae? An integrative study ofPseudaxine trachuri(Monogenea, Gastrocotylidae) leads to a better understanding of the systematics ofPseudaxineand related genera
Authors: Bouguerche Chahinez , Tazerouti Fadila , Gey Delphine , Justine Jean-Lou
Published: August 2020

The presence/absence and number of vaginae is a major characteristic for the systematics of the Monogenea. Three gastrocotylid genera share similar morphology and anatomy but are distinguished by this character:PseudaxineParona & Perugia, 1890 has no vagina,AllogastrocotyleNasir & Fuentes Zambrano, 1983 has two vaginae, andPseudaxinoidesLebedev, 1968 has multiple vaginae. In the course of a study ofPseudaxine trachuriParona & Perugia 1890, we found specimens with structures resembling “multiple vaginae”; we compared them with specimens without vaginae in terms of both morphology and molecular characterisitics (COI barcode), and found that they belonged to the same species. We also investigated the male copulatory organ (MCO) of this species, the accuracy of the original description of which is known to be a matter of debate. We found that the genital atrium is armed with 12 hooks arranged as a single circle and a central hollow stylet which is probably involved in traumatic insemination. We redescribedPseudaxine trachuribased on newly collected specimens from off the coast of Algeria and Museum specimens from off France. Specimens from the type-host,Trachurus trachurus,were found to be similar, for both molecular sequences and morphology, to those found onBoops boops. We can therefore confirm, for the first time with molecular evidence, thatB. boopsis a host of this parasite. We consider thatPseudaxinoideswas erected on the basis of an erroneous interpretation of structures which are not vaginae and, consequently, propose the transfer of most of its species toPseudaxine,asP. australis(Lebedev, 1968) n. comb.,P. bychowskyi(Lebedev, 1977) n. comb.,P. caballeroi(Lebedev, 1977) n. comb.,P. cariacoensis(Nasir & Fuentes-Zambrano, 1983) n. comb., andP. vietnamensis(Lebedev, Parukhin & Roitman, 1970) n. comb. We also proposeAllogastrocotyle dillonhargisorumnom. nov. forPseudaxine bivaginalisDillon & Hargis, 1965 to avoid a secondary homonymy.
Ernährungsmedizinische Aspekte beim Reizdarmsyndrom – ein Update
Authors: Hetterich Larissa , Stengel Andreas
Published: August 2020

Ernährungsmedizinische Aspekte spielen beim Reizdarmsyndrom eine große Rolle. So berichtet die Mehrzahl der Patienten von Nahrungsmittelunverträglichkeiten als verursachenden oder verschlimmernden Faktor der Beschwerden. Obwohl sich diese nicht immer objektivieren lassen, haben diätetische Interventionen in der Therapie des Reizdarmsyndroms einen relevanten Stellenwert. Ebenso wächst die Studienlage zum Einsatz von Probiotika beim Reizdarmsyndrom an. Die vorliegende Arbeit gibt ein Update zu ernährungsmedizinischen Interventionsmöglichkeiten beim Reizdarmsyndrom.
Tausendsassa vergangener Zeiten
Authors: Lorenz Daniel
Published: August 2020

Die Bibernelle verwendet man heutzutage zur Behandlung von Katarrhen in den oberen Luftwegen – im Mittelalter war sie als Rundum-Heilmittel beliebt.
Gegensätze in Balance
Authors: Hünefeld Chloe
Published: August 2020

Im Yoga findet sich das Äquivalent zu Parasympathikus und Sympathikus in den Hauptenergiekanälen Ida Nadi und Pingala Nadi. Ein Schwerpunkt der Yogatherapie sind gesunderhaltende Techniken, die eine gleichmütige innere Haltung fördern sollen. Im Beitrag sind mehrere Übungen vorgestellt, die auch auf den Parasympathikus wirken und bei verschiedenen Indikationen eingesetzt werden können.
Die Sympathikus-Therapie
Authors: Heesch Dieter , Oberhofer Andrea
Published: August 2020

Die Sympathikus-Therapie geht davon aus, dass Gelenkblockierungen an der Wirbelsäule zu einer lokal begrenzten Sympathikotonie führen können. Je nach Lokalisation der Sympathikusirritation können verschiedenste chronische Beschwerden ohne eine sonst erkennbare Ursache auftreten. Die Sympathikus-Therapie bedient sich bei der Behandlung manueller Techniken und der Mikropressur, bei der ein Reflex- oder Akupunkturpunkt touchiert wird.
Polyvagal-Therapie: Verändern durch Verstehen
Authors: Schneider Jacqueline
Published: August 2020

Die Polyvagal-Theorie von Stephen W. Porges sieht drei Akteure im Mittelpunkt des autonomen Geschehens – Sympathikus sowie ventraler und dorsaler Vagusast – und lässt sich sehr gut in therapeutische Konzepte integrieren. Für den Therapeuten gilt es, den Zustand des Patienten zwischen Entspannung, Aktion und Erstarrung zu erkennen und diesen unter anderem durch Wissensvermittlung, eigene Balance und körperliche Berührung zu regulieren. Im vorgestellten Fall lernte die Klientin, ihre übermächtigen Symptome wie Ängste, Panikattacken, Schmerzen und Ohrgeräusche mithilfe autonom wirksamer Techniken zu kontrollieren.
Wir werden gebraucht
Authors: Dollbaum-Paulsen Conny
Published: August 2020

Wie ergeht es den Heilpraktikern zu Zeiten von Corona? Was sind die momentanen Herausforderungen, aber auch Chancen? Und weshalb ist der Heilpraktikerberuf so systemrelevant wie nie zuvor? Ein Gespräch mit HP Conny Dollbaum-Paulsen vom Heilnetz.
New Dimensions of Brønsted Base Catalyzed Carbon–Carbon Bond-Forming Reactions
Authors: Yamashita Yasuhiro , Kobayashi Shū
Published: August 2020

Catalytic carbon–carbon bond-forming reactions of weakly acidic carbon pronucleophiles (pK
a in DMSO ≥30) were developed using strong alkaline metal Brønsted bases as catalysts. Not only weakly acidic amides, esters, nitriles, sulfonamides without any activating group, and alkyl azaarenes, but also alkyl arenes such as toluene, were applicable for the reactions, which are difficult to be applied in typical Brønsted base catalyzed reactions. Expansion to enantioselective reactions was also revealed to be possible. The reactions are atom economical and require only inexpensive alkaline metals rather than precious transition metals.

1 Introduction

2 Catalytic Direct-Type Addition Reactions of Weakly Acidic Carbonyl and Related Pronucleophiles

3 Catalytic Direct-Type Addition Reactions of Alkyl Azaarenes

4 Catalytic Direct-Type Addition Reactions of Alkyl Arenes

5 Conclusion
Prolapso de cúpula vaginal, prevalencia en mujeres en climaterio, en el Quindío, Colombia, 2007-2017
Authors: De La Hoz Franklin José Espitia
Published: August 2020

Objetivo establecer la prevalencia de prolapso de cúpula vaginal en mujeres del Quindío en climaterio, así como los factores asociados a su aparición.

Métodos Se realizó un estudio de corte transversal. Se evaluaron retrospectivamente las historias clínicas de 3,576 pacientes ambulatorias, en una clínica de alta complejidad de la ciudad de Armenia (Quindío), Colombia; entre enero de 2007 y junio de 2017. Se determinó la prevalencia de prolapso de cúpula vaginal y se analizaron los datos socio-demográficos, clínicos y quirúrgicos.

Resultados La edad media en las mujeres fue de 59,7 ± 14,7 años, con predominancia de las hispánicas (58,5%). La prevalencia de prolapso de cúpula vaginal fue del 14,17%. En el subgrupo de mujeres histerectomizadas, la prevalencia fue del 21,64% en las realizadas por prolapso y del 6,34% en las hechas vía abdominal. En el análisis multivariado, los factores asociados a prolapso de cúpula vaginal fueron: 65 o más años (OR: 4,76; 1,57–20,82), IMC3 25 (OR: 8,42; 2,68–31,04), multíparas (OR: 9,03; 2,75–32.27), antecedente de cirugía vaginal (OR: 7.04; 1.96–28.49) y presencia de enfermedades pulmonares crónicas (OR: 5,31; 1,64–23,57).

Conclusión la prevalencia global de prolapso de cúpula vaginal, en las mujeres del Quindío, fue del 14,17%. En Colombia existen pocos datos registrados al respecto, pero con la información presente, se manifiesta la necesidad de elaborar efectivas estrategias de prevención, detección y manejo.
Identifying materials with charge–spin physics using charge–spin susceptibility computed from first principles
Authors: Rodrigues J. N. B. , Wagner Lucas K.
Published: August 2020

The authors present a quantity termed charge–spin susceptibility, which measures the charge response to spin degrees of freedom in strongly correlated materials. This quantity is simple to evaluate using both standard density functional theory and many-body electronic structure techniques, enabling comparison between different levels of theory. A benchmark on 28 layered magnetic materials shows that large values of charge–spin susceptibility correlate with unconventional ground states such as disordered magnets and unconventional superconductivity.
Conformal welding problem, flow line problem, and multiple Schramm–Loewner evolution
Authors: Katori Makoto , Koshida Shinji
Published: August 2020

A quantum surface (QS) is an equivalence class of pairs (D, H) of simply connected domains D⊊C and random distributions H on D induced by the conformal equivalence for random metric spaces. This distribution-valued random field is extended to a QS with N + 1 marked boundary points (MBPs) with N∈Z≥0. We propose the conformal welding problem for it in the case of N∈Z≥1. If N = 1, it is reduced to the problem introduced by Sheffield, who solved it by coupling the QS with the Schramm–Loewner evolution (SLE). When N ≥ 3, there naturally appears room for making the configuration of MBPs random, and hence, a new problem arises how to determine the probability law of the configuration. We report that the multiple SLE in H driven by the Dyson model on R helps us to fix the problems and makes them solvable for any N ≥ 3. We also propose the flow line problem for an imaginary surface with boundary condition changing points (BCCPs). In the case when the number of BCCPs is two, this problem was solved by Miller and Sheffield. We address the general case with an arbitrary number of BCCPs in a similar manner to the conformal welding problem. We again find that the multiple SLE driven by the Dyson model plays a key role to solve the flow line problem.
Dynamic evolution of thermally induced element distribution in nitrogen modified phase change materials
Authors: Shen Jiabin , Li Tao , Chen Xin , Jia Shujing , Lv Shilong , Li Lin , Song Zhitang , Zhu Min
Published: August 2020

In the semiconductor industry, doping modification is a common and effective method to regulate the properties of materials. For Ge2Sb2Te5 (GST) phase change materials, incorporation with nitrogen has been widely reported due to improvement in its thermal stability and reduction in its power consumption. However, whether in amorphous or crystalline structures, the distribution of N is still unclear since it is low in content and insensitive in the electron microscopy detection. Here, by employing advanced atom probe tomography technology, we directly reveal the three-dimensional element distribution in different N-doped GST (NGST) structures and systematically analyze the evolution of element distribution during phase change. Nitrogen is found to be homogenously distributed in the as-deposit amorphous NGST as nanoscale N-rich clusters most together with germanium. The N-rich clusters remains nearly the same during the phase transition from amorphous to rocksalt phase, but change in the cluster become increasingly significant as the heating temperature continues rising, where GeN begins to precipitate at the grain boundaries. Furthermore, it is found that precipitated GeN clusters are turning into more Ge-rich in the two step phase transitions of NGST, e.g., Ge/N ratio equals 1.2 in rocksalt structure and subsequently becomes 21 in the hexagonal phase.
Viscous flow properties and hydrodynamic diameter of phenothiazine-based redox-active molecules in different supporting salt environments
Authors: Wang Yilin , Kaur Aman Preet , Attanayake N. Harsha , Yu Zhou , Suduwella Thilini M. , Cheng Lei , Odom Susan A. , Ewoldt Randy H.
Published: August 2020

We report viscous flow properties of a redox-active organic molecule, N-(2-(2-methoxyethoxy)ethyl)phenothiazine (MEEPT), a candidate for non-aqueous redox flow batteries, and two of its radical cation salts. A microfluidic viscometer enabled the use of small sample volumes in determining viscosity as a function of shear rate and concentration in the non-aqueous solvent, acetonitrile, both with and without supporting salts. All solutions tested show Newtonian behavior over shear rates of up to 30 000 s−1, which was rationalized by scaling arguments for the diffusion-based relaxation time of a single MEEPT molecule without aggregation. Neat MEEPT is flowable but with a large viscosity (412 mPa⋅s at room temperature), which is ∼1000 times larger than that of acetonitrile. MEEPT solutions in acetonitrile have low viscosities; at concentrations up to 0.5 M, the viscosity increases by less than a factor of two. From concentration-dependent viscosity measurements, molecular information was inferred from intrinsic viscosity (hydrodynamic diameter) and the Huggins coefficient (interactions). Model fit credibility was assessed using the Bayesian Information Criterion. It is found that the MEEPT and its charged cations are “flowable” and do not flocculate at concentrations up to 0.5 M. MEEPT has a hydrodynamic diameter of around 8.5 Å, which is almost insensitive to supporting salt and state of charge. This size is comparable to molecular dimensions of single molecules obtained from optimized structures using density functional theory calculations. The results suggest that MEEPT is a promising candidate for redox flow batteries in terms of its viscous flow properties.
Role of the ferroelastic strain in the optical absorption of BiVO4
Authors: Hill Christina , Weber Mads C. , Lehmann Jannis , Leinen Tariq , Fiebig Manfred , Kreisel Jens , Guennou Mael
Published: August 2020

Bismuth vanadate (BiVO4) has recently been under focus for its potential use in photocatalysis thanks to its well-suited absorption edge in the visible light range. Here, we characterize the optical absorption of a BiVO4 single crystal as a function of temperature and polarization direction by reflectance and transmittance spectroscopy. The optical bandgap is found to be very sensitive to the temperature, and to the tetragonal-to-monoclinic ferroelastic transition at 523 K. The anisotropy, as measured by the difference in the absorption edge for the light polarized parallel and perpendicular to the principal axis, is reduced from 0.2 eV in the high-temperature tetragonal phase to 0.1 eV at ambient temperature. We show that this evolution is dominantly controlled by the ferroelastic shear strain. These findings provide a route for further optimization of bismuth vanadate-based light absorbers in photocatalytic devices.
Enhancing the photoelectrical performance of graphene/4H-SiC/graphene detector by tuning a Schottky barrier by bias
Authors: Sun Cunzhi , Chen Xiufang , Hong Rongdun , Li Xiaomeng , Xu Xiangang , Chen Xiaping , Cai Jiafa , Zhang Xue-Ao , Cai Weiwei , Wu Zhengyun , Zhang Feng
Published: August 2020

Graphene/4H-SiC/graphene photodetectors, as well as graphene/4H-SiC heterojunctions, have been fabricated and characterized by utilizing a heating decomposition method. High-quality graphene has been grown on an n− doped 4H-SiC substrate along with a 900 °C hydrogenation process. Temperature-dependent current–voltage characteristics of the graphene/4H-SiC heterojunction have been measured to obtain the Schottky barrier height. The bias-dependent Schottky barrier height (varying from 0.43 eV to 0.41 eV) was found and could result mainly from the electrical doping and Fermi level shifting in graphene. With the increase in the bias, the unsaturated dark current of graphene/4H-SiC/graphene photodetectors indicated the electron diffusion at the graphene/4H-SiC heterojunction. The increased responsivity peaks come from the absorption of the graphene layer in the UV range and the long lifetime of photo-induced thermal electronic carriers being contributed to the bandgap shrinking of graphene and reduction of the Schottky barrier height. The photodetectors biased at 6 V showed a responsivity of 40 A/W, an external quantum efficiency of 1.38 × 104%, and a detectivity of 9 × 1011 Jones, which are larger than those of previously reported similar devices based on graphene/SiO2 or graphene/SiC.
Below bandgap photoluminescence of an AlN crystal: Co-existence of two different charging states of a defect center
Authors: Zhou Qin , Zhang Zhaofu , Li Hui , Golovynskyi Sergii , Tang Xi , Wu Honglei , Wang Jiannong , Li Baikui
Published: August 2020

The below bandgap optical transitions of an aluminum nitride (AlN) crystal grown on a tungsten (W) substrate by physical vapor transport (PVT) are investigated by below-bandgap-excited photoluminescence (PL) spectroscopy and first-principles calculations. Oxygen (O) is the only impurity in the AlN-on-W crystal grown by PVT. By analyzing the excitation-power-, excitation-photon-energy-, and temperature-dependence of the PL spectra, the emission peaks of defect complexes involving aluminum vacancy (VAl) and substitutional oxygen (ON) with different spatial and atomic configurations, i.e., VAl–ON and VAl–2ON with ON featuring axial or basal configurations, are identified. It is revealed that two different charging states coexist in thermal equilibrium for each configuration of VAl–ON complexes. The optical transitions between the conduction band and (VAl–ON)2− and/or (VAl–2ON)1− contribute the UV emissions and those between the valence band and (VAl–ON)1− or (VAl–2ON)0 contribute the red emissions.
A superlattice-based resonant cavity-enhanced photodetector operating in the long-wavelength infrared
Authors: Letka V. , Craig A. P. , Bainbridge A. , Marshall A. R. J.
Published: August 2020

The design, fabrication, and characterization of a resonant cavity-enhanced photodetector (RCE PD) operating in the long-wavelength infrared regime are demonstrated. The incorporation of the low bandgap InAs/InAs0.70Sb0.30 type-II strained-layer superlattice into the absorber layer of the detector cavity, along with the high-reflectivity (Rm > 0.9) AlAs0.08Sb0.92/GaSb distributed Bragg reflector pairs, results in resonant enhancement at 7.7–7.8 μm, which is a spectral region relevant in applications in sensing of chemical warfare agents and in medical biomarker diagnostics. These resonant wavelength peaks also display a high quality factor in the range of 76–86 and a small temperature coefficient of 0.52 nm K−1. An nBn architecture, where an Al0.71Ga0.29As0.08Sb0.92 layer acts as a barrier for majority electrons while minimizing the valence band offset with the absorber, is also incorporated into the cavity in order to improve the electrical properties of the detector. Spectral response measurements yield a peak external quantum efficiency of 14.6% and a peak responsivity of 0.91 A W−1 at 77 K and −0.8 V; meanwhile, a dark current density of 2.0 × 10−4 A cm−2 at 77 K results in a specific detectivity of 3.7 × 1010 cm Hz1/2 W−1, coming close to the theoretical background-limited D* of an ideal broadband photovoltaic detector with the superlattice composition as that of the RCE PD.
Scattering below the ground state for the 2D non-linear Schrödinger and Klein–Gordon equations revisited
Authors: Guo Zihua , Shen Jia
Published: August 2020

We revisit the scattering problems for the 2D mass super-critical Schrödinger and Klein–Gordon equations with radial data below the ground state in the energy space. We give an alternative proof of energy scattering for both the defocusing and focusing cases using the ideas in the work of Dodson and Murphy [Proc. Am. Math. Soc. 145, 4859 (2017)]. Our results also include the exponential type nonlinearities, which seem to be new for the focusing exponential non-linear Schrödinger equation.
Entrainment flow of a jet emerging into a half-space with the no-slip boundary condition
Authors: Gusarov A. V.
Published: August 2020

The current development of micro-scale technologies increases the interest in viscous flows with low and moderate Reynolds numbers. This work theoretically studies the entrainment flow of a viscous jet emerging from a plane wall into a half-space with the objective to understand the conditions where a similarity model can approximate a realistic flow. Two similarity models having analytic solutions are considered: the flow dominated by the momentum flux and the flow dominated by the mass flux. Algorithms are proposed to evaluate the parameters of the similarity models from the mass and momentum balances. Distributions of flow parameters and stresses on the wall are calculated for the similarity models. They are compared with the corresponding distributions obtained by computational fluid dynamics for a more realistic model with a finite size of the jet source and competitive influence of the mass and momentum fluxes. This comparison validates the mass-dominated similarity model at the jet Reynolds number Re ≤ 10 and the momentum-dominated similarity model at Re ≥ 30. The obtained results are applied to the problem of laser evaporation in selective laser melting. It is shown that the theoretically estimated flow velocity corresponds to the experimentally observed one. The theory explains the formation of the experimentally observed denuded zone and its widening by decreasing the ambient gas pressure.
Thermal rate constants for electron attachment to N2O: An example of endothermic attachment
Authors: Sawyer Jordan C. , Miller Thomas M. , Ard Shaun G. , Sweeny Brendan C. , Viggiano Albert A. , Shuman Nicholas S.
Published: August 2020

Rate constants for dissociative electron attachment to N2O yielding O− have been measured as a function of temperature from 400 K to 1000 K. Detailed modeling of kinetics was needed to derive the rate constants at temperatures of 700 K and higher. In the 400 K–600 K range, upper limits are given. The data from 700 K to 1000 K follow the Arrhenius equation behavior described by 2.4 × 10−8 e−0.288 eV/kT cm3 s−1. The activation energy derived from the Arrhenius plot is equal to the endothermicity of the reaction. However, calculations at the CCSD(T)/complete basis set level suggest that the lowest energy crossing between the neutral and anion surfaces lies 0.6 eV above the N2O equilibrium geometry and 0.3 eV above the endothermicity of the dissociative attachment. Kinetic modeling under this assumption is in modest agreement with the experimental data. The data are best explained by attachment occurring below the lowest energy crossing of the neutral and valence anion surfaces via vibrational Feshbach resonances.
Difference projection-after-variation double-hybrid density functional theory applied to the calculation of vertical excitation energies
Authors: Kempfer-Robertson Emily M. , Pike Thomas Dane , Thompson Lee M.
Published: August 2020

The use of projection-after-variation double-hybrid density functional theory is proposed and examined as a difference method for the calculation of excited states. The strengths and weaknesses of the proposed method are discussed with particular reference to connections with linear response coupled-cluster theory. Vertical excitation energies are computed for the 28 molecule benchmark of Schreiber and co-workers in order to compare how the model performs with linear response coupled-cluster theories and multireference perturbation theory. The findings of this study show that the proposed method can achieve standard deviations in the error of computed vertical excitation energies compared to complete active space second-order perturbation theory of similar size to linear response coupled-cluster theories.
Core annular flow theory as applied to the adiabatic section of heat pipes
Authors: Rath Aishwarya , Flynn M. R.
Published: August 2020

Core annular flow theory is used to model the parallel flow of fluids of different phases and has been used to describe drag reduction in the context of internal flows bounded by superhydrophobic surfaces. The work presented here is an extension of core annular flow theory to the study of the adiabatic section of heat pipes. Our aim is to develop a first-principles estimate of the conditions necessary to maximize the (counter) flow of liquid and vapor and, by extension, the axial flow of heat. The planar and axisymmetric geometries are examined as are heat pipes containing vs being devoid of a wick. In the wick vs no-wick cases, the peripheral return flow of liquid is, respectively, driven by capillarity and by gravity. Our model is used to predict velocity profiles and the flux-maximizing pressure gradient ratio (vapor-to-liquid). We further obtain estimates for the optimum thickness of the liquid layer. Note finally that when the liquid flow occurs via capillary pumping, there is a minimum surface tension below which the wick cannot supply a sufficient flow of liquid. We characterize this critical point in terms of the properties of the working fluid and of the wick.
Spin dynamics and relaxation in 7.6 nm thin film of La0.7Sr0.3MnO3/SrTiO3: ac magnetic susceptibility and magnetic viscosity investigations
Authors: Mottaghi Navid , Seehra Mohindar S. , Shi Jianhang , Jain Menka , Holcomb Mikel B.
Published: August 2020

Analysis of the results from our investigations of the temperature dependence of ac susceptibilities (χ′ and χ′′) and magnetic viscosity in a 7.6 nm thin film of La0.7Sr0.3MnO3 grown on SrTiO3 (001) substrate is presented. The Curie temperature (TC) of this film is magnetic field (H) dependent, varying as [TC(H)−TC(0)]∼Hn with TC(0) = 270 K and n = 0.15. Temperature dependence of χ′ and χ′′ measured at ac frequencies fm in the range of 0.1–10 kHz shows a broad peak near 230 K associated with the blocking temperature (TB) of spin clusters present in the 1.4 nm surface layer and a frequency dependent peak near 270 K associated with TC. The mean relaxation time τ determined from the Cole–Cole analysis of the temperature dependent χ′ and χ′′ is shown to fit the Vogel–Fulcher law: τ=τ0exp[ΔE/kB(T−T0)] with T0 = 245 K, ΔE/kB = 270 K = TC, and τ0 = 1.2 × 10−9 s. Magnetic viscosity S (measured in H = 0 for a sample cooled in H = 50 Oe) determined from the fit to the magnetization: M (t) = M (0) – S ln t, with time t up to 2 h, shows a peak at 230 K above which M (2 h) switches to negative values for temperatures up to TC(0). It is argued that this negative magnetization results from an interaction between the superparamagnetic spin clusters and the ferromagnetic phase, both being present in the temperature range of TB < T < TC.
Looking at the bigger picture: Identifying the photoproducts of pyruvic acid at 193 nm
Authors: Samanta B. R. , Fernando R. , Rösch D. , Reisler H. , Osborn D. L.
Published: August 2020

Photodissociation of pyruvic acid (PA) was studied in the gas-phase at 193 nm using two complementary techniques. The time-sliced velocity map imaging arrangement was used to determine kinetic energy release distributions of fragments and estimate dissociation timescales. The multiplexed photoionization mass spectrometer setup was used to identify and quantify photoproducts, including isomers and free radicals, by their mass-to-charge ratios, photoionization spectra, and kinetic time profiles. Using these two techniques, it is possible to observe the major dissociation products of PA photodissociation: CO2, CO, H, OH, HCO, CH2CO, CH3CO, and CH3. Acetaldehyde and vinyl alcohol are minor primary photoproducts at 193 nm, but products that are known to arise from their unimolecular dissociation, such as HCO, H2CO, and CH4, are identified and quantified. A multivariate analysis that takes into account the yields of the observed products and assumes a set of feasible primary dissociation reactions provides a reasonable description of the photoinitiated chemistry of PA despite the necessary simplifications caused by the complexity of the dissociation. These experiments offer the first comprehensive description of the dissociation pathways of PA initiated on the S3 excited state. Most of the observed products and yields are rationalized on the basis of three reaction mechanisms: (i) decarboxylation terminating in CO2 + other primary products (∼50%); (ii) Norrish type I dissociation typical of carbonyls (∼30%); and (iii) O—H and C—H bond fission reactions generating the H atom (∼10%). The analysis shows that most of the dissociation reactions create more than two products. This observation is not surprising considering the high excitation energy (∼51 800 cm−1) and fairly low energy required for dissociation of PA. We find that two-body fragmentation processes yielding CO2 are minor, and the expected, unstable primary co-fragment, methylhydroxycarbene, is not observed because it probably undergoes fast secondary dissociation and/or isomerization. Norrish type I dissociation pathways generate OH and only small yields of CH3CO and HOCO, which have low dissociation energies and further decompose via three-body fragmentation processes. Experiments with d1-PA (CH3COCOOD) support the interpretations. The dissociation on S3 is fast, as indicated by the products’ recoil angular anisotropy, but the roles of internal conversion and intersystem crossing to lower states are yet to be determined.
Quasi-stationary modeling of the DBD plasma flow control around airfoil
Authors: Adamiak Kazimierz
Published: August 2020

This paper presents the results of numerical simulation of a dielectric barrier discharge (DBD) plasma actuator and shows its effectiveness to control air flow around the NACA(National Advisory Committee for Aeronautics)0015 airfoil. The actuator consists of two tape electrodes separated by a dielectric layer, and it is mounted on the suction side of the airfoil at 18% of the chord length. An alternating voltage with 20 kV magnitude and 10 kHz frequency is applied between both electrodes. The physical model of the DBD includes the drift of two ionic species, positive and negative, and the Poisson equation for the electric potential distribution. The spatio-temporal distribution of the electric field, the space charge density in the ambient air, and the surface charge density on the dielectric layer have been determined. The time average electric body force was entered into the air flow model, which was solved using the Spalart–Allmaras turbulence technique. The simulation of the air flow was performed for the free-stream velocities between 5 m/s and 20 m/s (Reynolds numbers 1.65 × 105–6.61 × 105 based on the chord length). The results of computations show the effect of the electrohydrodynamic actuation on the flow pattern, the lift and drag coefficients, the pressure coefficient, and the flow fluctuation near the airfoil. The ability of the DBD actuation to effectively control the aerodynamic airfoil characteristics has been confirmed, and its limitations for the discussed case have been determined.
Anisotropic band structure of TiS3 nanoribbon revealed by polarized photocurrent spectroscopy
Authors: Lian Zhen , Jiang Zeyu , Wang Tianmeng , Blei Mark , Qin Ying , Washington Morris , Lu Toh-Ming , Tongay Sefaattin , Zhang Shengbai , Shi Su-Fei
Published: August 2020

A re-discovered member of the layered material family, Titanium Trisulfide (TiS3), has attracted intense research interest recently for the possibility of realizing an exciton insulator in the monolayer limit. However, due to their quasi-one-dimensional nature, thin TiS3 flakes are typically in the form of nanoribbons that are challenging to characterize by optical absorption spectra, due to their small cross section. Here, we employ a sensitive photocurrent spectroscopy technique to probe the absorption of a thin TiS3 nanoribbon in a field-effect transistor configuration. We have found a significant modification of the band structure of the thin TiS3 nanoribbon, compared to its bulk counterpart. In addition, the polarization-dependent photocurrent spectra of thin TiS3 nanoribbons exhibit greatly enhanced anisotropy compared to that of a thick TiS3 device. The atomically thin TiS3 flake, thus, not only provides an exciting platform for investigating many-body physics but also enables anisotropic quantum optoelectronics.
H2O–CO and D2O–CO complexes: Intra- and intermolecular rovibrational states from full-dimensional and fully coupled quantum calculations
Authors: Felker Peter M. , Bačić Zlatko
Published: August 2020

We present efficient yet rigorous, full-dimensional quantum bound-state calculations of the fully coupled J = 0 and one intra- and intermolecular rovibrational levels of H2O–CO and D2O–CO complexes. The new ab initio nine-dimensional (9D) potential energy surface (PES) [Y. Liu and J. Li, Phys. Chem. Chem. Phys. 21, 24101 (2019)] is employed. In the spirit of the recently introduced general procedure [P. M. Felker and Z. Bačić, J. Chem. Phys. 151, 024305 (2019)], the 9D rovibrational Hamiltonian is partitioned into a 5D (rigid-monomer) intermolecular Hamiltonian, two intramolecular vibrational Hamiltonians—one for the water monomer (3D) and another for the CO monomer (1D), and a 9D remainder term. The low-energy eigenstates of the three reduced-dimension Hamiltonians are used to build up the 9D product contracted basis, in which the matrix of the full rovibrational Hamiltonian is diagonalized. In line with the findings of our earlier study referenced above, the 5D intermolecular eigenstates included in the 9D bases extend up to at most 230 cm−1 above the lowest-energy state of the given parity, much less than the intramolecular fundamentals of the two complexes that span the range of energies from about 1200 cm−1 to 3800 cm−1. The resulting Hamiltonian matrices are small for the 9D quantum problem considered, ≈ 10 000 for J = 0 and 13 500 for J = 1 calculations, allowing for direct diagonalization. The 9D calculations permit exploring a number of features of the rovibrational level structure of H2O–CO and D2O–CO that are beyond the quantum 5D rigid-monomer treatments reported to date. These include the differences in the magnitudes of the hydrogen-exchange tunneling splittings computed in 9D and 5D, the sensitivity of the tunneling splittings to the intramolecular vibrational excitation, the frequency shifts of the intramolecular vibrational modes, which, depending on the mode, can be either blue- or redshifts, and the effects of the excitation of the intramolecular fundamentals on the low-lying intermolecular eigenstates. Also examined is the extent of the eigenstate delocalization over the two minima on the PES. Whenever possible, a comparison is made with the experimental data in the literature.
Reconfigurable spin orbit logic device using asymmetric Dzyaloshinskii–Moriya interaction
Authors: Shi Yinuo , Chi Kequn , Li Zhou , Zhang Wenbiao , Xing Yun , Meng Hao , Liu Bo
Published: August 2020

A spin–orbit torque-based logic device that combines the Dzyaloshinskii–Moriya interaction and asymmetric shape anisotropy is proposed in this paper. Through magnetization switching of the magnetic tunnel junction (MTJ), four distinct input cases are determined to perform all of the 16 basic Boolean functions by a single magnetic tunnel junction (MTJ). With various combinations of the tilted angle of the MTJ and the value of current density, a single MTJ can serve as a reconfigurable logic gate.