bluuebunny/crossref_metadata_2025 huggingface dataset:
Pressure losses and oscillations in a compact valve of a steam turbine
Authors: Sláma Václav , Šimurda David , Mrózek Lukáš , Tajč Ladislav , Hála Jindřich , Radnic Tomáš
Published: October 2021

Characteristics of a new compact valve design for steam turbines are analysed by measuring pressure losses and oscillations on the valve model. It is the model of an intercept valve of the intermediate-pressure turbine part. This valve is relatively smaller hence cheaper than usual control and intercept valves. Besides, four different valve seat angles were tested in order to investigate the valve seat angle influence. In order to further clarify measured phenomena, the wide range of numerical simulations were also carried out. Measurements were performed in the Aerodynamic laboratory of the Institute of Thermomechanics of the Czech Academy of Sciences in an air test rig installed in a modular aerodynamic tunnel. Numerical simulations were performed in the Doosan Skoda Power Company using a package of ANSYS software tools. Measurement results are compared with numerical and generalized in the form of valve characteristics and pressure oscillation maps. As a result of the pressure loss analysis, pressure losses in similar valve assemblies can be predicted with required accuracy for each new turbine where modern compact valves are used. As a result of the pressure oscillation analysis, operating conditions at which dangerous flow instabilities can occur were identified. Thanks to this, the areas of safe and dangerous operating conditions can be predicted so that the operational reliability of the valve can be guaranteed.
A combination method for multi-criteria decision making problem in turning process
Authors: Duc Trung Do
Published: October 2021

This paper presents a multi-criteria decision making (MCDM) for a turning process. An experimental process was performed according to the sequence of a matrix using the Taguchi method with nine experiments. The parameters including workpiece speed, feed rate, depth of cut, and nose radius were selected as the input variables. At each experiment, three cutting force components that were measured in the three directions X, Y, and Z, were Fx, Fy, and Fz, respectively. The value of Material Removal Rate (MRR) was also calculated at each experiment. The main purpose of this study is determination of an experiment in total performed experiments simultaneously ensuring the minimum Fx, Fy, and Fz and the maximum MRR. The Entropy method was applied to determine the weights for parameters Fx, Fx, Fx, and MRR. Eight MCDM methods were applied for multi-criteria decision making, this has not been performed in any studies. The implementation steps of each method were also presented in this paper. Seven ones of these eight methods determined the best experiment in total nine performed experiments. A new multi-criteria decision-making method as well as orientation for the further works were also proposed in this study.
Lebendnierenspende und perioperative Therapie
Authors: Aßfalg Volker , Hüser Norbert , Hartmann Daniel
Published: October 2021

Die Lebendnierenspende stellt heute angesichts des Organspendermangels eine attraktive Möglichkeit zur Transplantation eines terminal nierenkranken Patienten dar. Dennoch darf das Risiko, das der Spender durch die Operation und die anschließende Einnierigkeit eingeht, nicht außer Acht gelassen werden. Während sich der vorangegangene Artikel mit der Vorbereitung und Abklärung der Eignung des potenziellen Spenders für die Nierenlebendspende beschäftigt, thematisiert der folgende Beitrag den chirurgischen Bereich der Transplantation, gibt Einblicke in moderne Operationstechniken, benennt technische und anatomische Herausforderungen und charakterisiert die verbundenen Risiken.
Integration of C-Acylation in the Solid-Phase Synthesis of Peptides and Peptidomimetics Employing Meldrum’s Acid, Phosphorus, and Sulfur Ylides
Authors: Rademann Jörg , Ahsanullah Ahsanullah , Hassan Abbas , Ansari Farzana L.
Published: October 2021

The modification of native peptides to peptidomimetics is an important goal in medicinal chemistry and requires, in many cases, the integration of C-acylation steps involving amino acids with classical peptide synthesis. Many classical C-acylation protocols involving Claisen condensations and the use of ylides are not compatible with peptide synthesis, mostly due to the requirements for strong bases leading to epimerization or deprotection of peptides. Meldrum’s acid as well as several specific phosphorus and sulfur ylides, however, are acidic enough to provide reactive C-nucleophiles under mildly basic conditions tolerated during peptide synthesis. This review provides an overview of peptide-compatible C-acylations using Meldrum’s acid and phosphorus and sulfur ylides, and their application in the medicinal chemistry of peptides.

1 Introduction

2 C-Acylation of Meldrum’s Acid

2.1 C-Acylation of Meldrum’s Acid on Solid Phase

3 Ylides as Substrates for C-Acylation

3.1 C-Acylation of Phosphorus Ylides in Solution Phase

3.2 C-Acylation of Solid-Supported Phosphorus Ylides

3.3 C-Acylation of Sulfur Ylides

3.4 C-Acylation of Solid-Supported Sulfur Ylides

4 Miscellaneous Ylides as Acyl Anion Equivalents

5 Summary
Cesarean Hysterectomy for Placenta Previa Accreta Using Retrograde Abdominal Hysterectomy Approaching from the Posterior Vaginal Wall
Authors: Hiramatsu Yuji
Published: October 2021

Hysterectomy for placenta percreta with bladder invasion is a difficult operation because of the high possibility of massive bleeding; therefore, surgery should be performed in a facility equipped with a sufficient number of trained staff. The degree of bladder invasion should be assessed correctly before the operation, and it is necessary to carefully consider how to address intraoperative complications and massive bleeding in the preoperative conference. The following should be prepared preoperatively: autologous blood and stored blood; ureteral catheter and insertion materials; materials to separate and tape the internal iliac artery and ureter; balloon for insertion into the common iliac artery or aorta and aortic clamps; and materials for compression suturing, such as B-Lynch suture. Sufficient informed patient consent is also required. During surgery, which may cause massive and sometimes life-threatening bleeding, the general rule is to begin at a safe site without adhesions and then treat the adhesion site. According to this rule, bladder dissection should be performed last in cases of placenta percreta with bladder invasion. As a surgical technique using this principle, we introduce retrograde hysterectomy approaching from the posterior vaginal wall.
Sequential dependency for affective appraisal of food images
Authors: Van der Burg Erik , Toet Alexander , Abbasi Zahra , Brouwer Anne-Marie , Van Erp Jan B. F. , Kallen Victor L. , Kaneko Daisuke , Kim Youjin , Kinnear Marise , de Kock Henriëtte L. , Kusbiantari Dyah , Lee Tzong-Ru , Liu Yingxuan , Luhovyy Bohdan L. , MacEachern Emily , Mezgebe Abadi Gebre , Nikolova Rouja , Olatunde Ganiyat , Srisayekti Wilis , Tahir Muhammad Rizwan , Ushiama Shota , Yürek Merve Aslıhan
Published: October 2021

How we perceive the world is not solely determined by our experiences at a given moment in time, but also by what we have experienced in our immediate past. Here, we investigated whether such sequential effects influence the affective appraisal of food images. Participants from 16 different countries (N = 1278) watched a randomly presented sequence of 60 different food images and reported their affective appraisal of each image in terms of valence and arousal. For both measures, we conducted an inter-trial analysis, based on whether the rating on the preceding trial(s) was low or high. The analyses showed that valence and arousal ratings for a given food image are both assimilated towards the ratings on the previous trial (i.e., a positive serial dependence). For a given trial, the arousal rating depends on the arousal ratings up to three trials back. For valence, we observed a positive dependence for the immediately preceding trial only, while a negative (repulsive) dependence was present up to four trials back. These inter-trial effects were larger for males than for females, but independent of the participants’ BMI, age, and cultural background. The results of this exploratory study may be relevant for the design of websites of food delivery services and restaurant menus.
Path-integral solution of MacArthur’s resource-competition model for large ecosystems with random species-resources couplings
Authors: Batista-Tomás A. R. , De Martino Andrea , Mulet Roberto
Published: October 2021

We solve MacArthur’s resource-competition model with random species-resource couplings in the “thermodynamic” limit of infinitely many species and resources using dynamical path integrals à la De Domincis. We analyze how the steady state picture changes upon modifying several parameters, including the degree of heterogeneity of metabolic strategies (encoding the preferences of species) and of maximal resource levels (carrying capacities), and discuss its stability. Ultimately, the scenario obtained by other approaches is recovered by analyzing an effective one-species-one-resource ecosystem that is fully equivalent to the original multi-species one. The technique used here can be applied for the analysis of other model ecosystems related to the version of MacArthur’s model considered here.
Spin–orbit torques of an in-plane magnetized system modulated by the spin transport in the ferromagnetic Co layer
Authors: Xue Fen , Lin Shy-Jay , Li Peng , Hwang William , Huang Yen-Lin , Tsai Wilman , Wang Shan X.
Published: October 2021

Spin–orbit torque (SOT) magnetoresistive random-access memory (MRAM) devices have been proposed for energy efficient memory and computing applications. New classes of materials such as antiferromagnets, topological insulators, and semimetals can generate spins with unconventional polarization and improve the efficiency of field-free SOT switching. In this work, we report significant changes in SOTs due to a Co thin film inserted in the Pt/Co/Mg/CoFeB heterostructures. Remarkably, the damping-like effective field has been enhanced by 7.4 times after inserting a thin Co layer with weak perpendicular magnetic anisotropy (PMA), while the field-like effective field is reduced to near zero value. Independent characterizations were performed to verify the presence of the changes in SOTs following spin modulation by the Co insertion layer. In addition, we found that the dynamic spin pumping coupling between Pt/Co with weak PMA and the in-plane CoFeB could significantly modulate the effective SOTs in the heterostructure, and this effect is dependent on the thickness of the spacer Mg through long-range spin-wave mediated coupling. Our work has experimentally demonstrated a new avenue to modulate SOTs with physically sputtered metal layers, and this finding is promising to enable flexible and efficient spin polarizations for MRAM devices.
Bound states in the continuum and Fano resonances in subwavelength resonator arrays
Authors: Ammari Habib , Davies Bryn , Hiltunen Erik Orvehed , Lee Hyundae , Yu Sanghyeon
Published: October 2021

When wave scattering systems are subject to certain symmetries, resonant states may decouple from the far-field continuum; they remain localized to the structure and cannot be excited by incident waves from the far field. In this work, we use layer-potential techniques to prove the existence of such states, known as bound states in the continuum, in systems of subwavelength resonators. When the symmetry is slightly broken, this resonant state can be excited from the far field. Remarkably, this may create asymmetric (Fano-type) scattering behavior where the transmission is fundamentally different for frequencies on either side of the resonant frequency. Using asymptotic analysis, we compute the scattering matrix of the system explicitly, thereby characterizing this Fano-type transmission anomaly.
Control of spin–charge conversion in van der Waals heterostructures
Authors: Galceran Regina , Tian Bo , Li Junzhu , Bonell Frédéric , Jamet Matthieu , Vergnaud Céline , Marty Alain , García Jose H. , Sierra Juan F. , Costache Marius V. , Roche Stephan , Valenzuela Sergio O. , Manchon Aurélien , Zhang Xixiang , Schwingenschlögl Udo
Published: October 2021

The interconversion between spin and charge degrees of freedom offers incredible potential for spintronic devices, opening routes for spin injection, detection, and manipulation alternative to the use of ferromagnets. The understanding and control of such interconversion mechanisms, which rely on spin–orbit coupling, is therefore an exciting prospect. The emergence of van der Waals materials possessing large spin–orbit coupling (such as transition metal dichalcogenides or topological insulators) and/or recently discovered van der Waals layered ferromagnets further extends the possibility of spin-to-charge interconversion to ultrathin spintronic devices. Additionally, they offer abundant room for progress in discovering and analyzing novel spin–charge interconversion phenomena. Modifying the properties of van der Waals materials through proximity effects is an added degree of tunability also under exploration. This Perspective discusses the recent advances toward spin-to-charge interconversion in van der Waals materials. It highlights scientific developments which include techniques for large-scale growth, device physics, and theoretical aspects.
Optimal flatness placement of sensors and actuators for controlling chaotic systems
Authors: Letellier Christophe , Barbot Jean-Pierre
Published: October 2021

Controlling chaotic systems is very often investigated by using empirical laws, without taking advantage of the structure of the governing equations. There are two concepts, observability and controllability, which are inherited from control theory, for selecting the best placement of sensors and actuators. These two concepts can be combined (extended) into flatness, which provides the conditions to fulfill for designing a feedback linearization or another classical control law for which the system is always fully observable and fully controllable. We here design feedback linearization control laws using flatness for the three popular chaotic systems, namely, the Rössler, the driven van der Pol, and the Hénon–Heiles systems. As developed during the last two decades for observability, symbolic controllability coefficients and symbolic flatness coefficients are introduced here and their meanings are tested with numerical simulations. We show that the control law works for every initial condition when the symbolic flatness coefficient is equal to 1.
Role of f-electrons in determining insulator to metal phase transitions of Ca(La1−xCex)2S4 (0 ≤ x ≤ 1) solid solution: A DFT + U study
Authors: Sarker Hori Pada , Huda Muhammad N.
Published: October 2021

For efficient usage of the rare earth-based materials in electronic or optoelectronic applications, their 4f electrons' behaviors must be understood properly. We have presented Hubbard U corrected density functional theory (DFT+U) study of structural, magnetic, electronic, and optical properties of a rare-earth chalcogenide system, Ca(La1−xCex)2S4 (0 ≤ x ≤ 1). A unique site selection technique based on local magnetic moment arrangements was applied to build the atomic arrangements for a Ce doped Ca(La1−xCex)2S4 solid solution. The incorporation of f-electrons by Ce doping modifies the properties of the parent compound, CaLa2S4. In conjunction with the DFT + U method, we applied spin–orbit coupling to determine the magnetic ground state. The inclusion of 25% Ce transforms the non-magnetic parent compound to an antiferromagnetic (AFM) compound, and AFM magnetic ordering remains unaltered throughout the whole solid solution series. In addition, these compounds also undergo insulator to semiconducting to metallic phase transitions as Ce concentration increases. While CaLa2S4 is an insulator, Ca(La1−xCex)2S4 with x = 0.25 and 0.50 are n-type semiconductors, and on the other hand, compounds with x = 0.75 and 1.0 are found to have metallic band structures. The Ce atoms in these materials were found to be in a mixed valence state, Ce3+/4+. We explained these phase transitions from the calculated electronic structures. In addition, we have presented an explanation for the experimentally observed red-orange colors of Ca(La0.25 Ce0.75)2S4 and CaCe2S4 compounds.
Reconstructing network structures from partial measurements
Authors: Tyloo Melvyn , Delabays Robin , Jacquod Philippe
Published: October 2021

The dynamics of systems of interacting agents is determined by the structure of their coupling network. The knowledge of the latter is, therefore, highly desirable, for instance, to develop efficient control schemes, to accurately predict the dynamics, or to better understand inter-agent processes. In many important and interesting situations, the network structure is not known, however, and previous investigations have shown how it may be inferred from complete measurement time series on each and every agent. These methods implicitly presuppose that, even though the network is not known, all its nodes are. Here, we investigate the different problem of inferring network structures within the observed/measured agents. For symmetrically coupled dynamical systems close to a stable equilibrium, we establish analytically and illustrate numerically that velocity signal correlators encode not only direct couplings, but also geodesic distances in the coupling network within the subset of measurable agents. When dynamical data are accessible for all agents, our method is furthermore algorithmically more efficient than the traditional ones because it does not rely on matrix inversion.
Temperature-dependent study on AlGaN-based deep ultraviolet light-emitting diode for the origin of high ideality factor
Authors: Liao Yanjun , Li Ding , Guo Qi , Liu Yufeng , Wang Haiming , Hu Weiguo , Wang Zhong Lin
Published: October 2021

Deep ultraviolet light-emitting diodes (DUV LEDs) are promising light sources for disinfection, especially during the pandemic of novel coronavirus (COVID-19). Despite much effort in the development of DUV LEDs, the device temperature and ideality factor are key parameters of devices, which are often neglected. Here, we developed a simple and convenient method to study the behavior of a 280 nm AlGaN-based DUV LED, obtaining the electrical, optical, and thermal properties within one measurement. From the experimental results, we find that the light output power and wall-plug efficiency of the AlGaN-based DUV LED are strongly affected by device temperature, ideality factor (β), and series resistance (Rs). β decreases from 9.3 to 8.1 at 40 mA when the temperature increases from 302 to 317 K. We compared these results with simulations and found that the high potential barriers inside the device and the carrier concentration in n-type or p-type layers, especially the hole concentration in p-type layers, are the two key factors for the high value of the ideality factor from the LED structure. As the device temperature increases, carriers with higher energy would overcome some potential barriers and Mg acceptor activation would be more efficient, which are beneficial for carrier transportation. However, these also lead to the carrier overflow and weaken the radiative recombination rate. The trade-off role of device temperature in carriers between transportation and overflow is needed to be considered in the future development of DUV LEDs with higher efficiency and higher brightness.
Chimera states for directed networks
Authors: Jaros Patrycja , Levchenko Roman , Kapitaniak Tomasz , Maistrenko Yuri
Published: October 2021

We demonstrate that chimera behavior can be observed in ensembles of phase oscillators with unidirectional coupling. For a small network consisting of only three identical oscillators (cyclic triple), tiny chimera islands arise in the parameter space. They are surrounded by developed chaotic switching behavior caused by a collision of rotating waves propagating in opposite directions. For larger networks, as we show for a hundred oscillators (cyclic century), the islands merge into a single chimera continent, which incorporates the world of chimeras of different configurations. The phenomenon inherits from networks with intermediate ranges of the unidirectional coupling and it diminishes as the coupling range decreases.
Vapor deposition of metal halide perovskite thin films: Process control strategies to shape layer properties
Authors: Guesnay Quentin , Sahli Florent , Ballif Christophe , Jeangros Quentin
Published: October 2021

Vapor-based processes are particularly promising to deposit the perovskite thin film absorber of solar cells. These deposition methods are up-scalable, involve a controlled solvent-free environment, have the ability to conformally coat rough substrates, involve soft, low-energy deposition conditions, are compatible with shadow masks for patterning, and are already widely deployed at the industrial level. Still, solar cells featuring layers processed with these methods have not yet reached the same performance as their solution-processed counterparts, in part, due the complexity of controlling the sublimation of the organic precursors. This Research Update will discuss the different vapor-based deposition processes that have been reported to deposit perovskite thin films and will discuss reaction chamber designs that provide an enhanced control over the deposition process. The second part of this Research Update will then link experimental observations regarding layer properties depending on process conditions to theoretical concepts describing the sublimation and condensation of precursors and the growth of the perovskite thin film.
Growth, optical, and wettability properties of iron modified titania and ferropseudobrookite thin films
Authors: Ferrara Maria Cristina , Mazzarelli Saverio , Schioppa Monica , Pilloni Luciano , Tapfer Leander
Published: October 2021

Iron (Fe)-modified titanium dioxide, Fe–TiO2, thin films with molar ratios Fe:Ti = 1:360, 1:60, and 1:30 and Fe-pseudobrookite, FeTi2O5 (molar ratio Fe:Ti = 1:2), were grown by the sol-gel process using acid-catalyzed solutions prepared with titanium isopropoxide and iron(III) chloride hexahydrate as Ti and Fe precursors, respectively. The layers were deposited by dip-coating onto soda–lime glasses and (100)-Si substrate wafers, and their chemical composition, crystal structure, and surface morphology were investigated in detail. For the low Fe-doped samples, the experimental results clearly indicate the formation of Fe–O–Ti heterolinkages. The films have an amorphous structure and high flatness surfaces if grown onto glass substrates. On the contrary, if grown onto (100)-Si substrates, they exhibit a granular structure (domain size ∼12 nm) made of a solid solution of Fe3+ ions within the anatase TiO2 lattice. For coatings with the molar ratio Fe:Ti = 1:2 (high Fe content), morphological investigations show the formation of wrinkled surfaces characterized by dendritic structures. X-ray diffraction measurements confirm the formation of nanocrystallites (domain size ∼15 nm) of pure, single-phase orthorhombic FeTi2O5. Wettability measurements conducted on amorphous low Fe-doped TiO2 samples revealed superhydrophilic properties with a surface–water contact angle <1°, whereas optical absorption and reflectance measurements yield bandgap widening and narrowing. A bandgap narrowing occurs with the formation of oxygen vacancies and of Ti3+ levels, but if the concentration of oxygen vacancies and Ti3+ levels increases, more electron donors are generated, which shift the Fermi level to the conduction band. This widening of the bandgap (blue shift) can be explained by the Burstein–Moss effect. The correlation of the large optical bandgap (3.61 < Eg < 3.74 eV) and the wettability results are interpreted and discussed with the presence of oxygen vacancies and Ti3+ and Fe3+ sites in the TiO2 matrix.
Homoepitaxial β-Ga2O3 transparent conducting oxide with conductivity σ = 2323 S cm−1
Authors: Jeon Hyung Min , Leedy Kevin D. , Look David C. , Chang Celesta S. , Muller David A. , Badescu Stefan C. , Vasilyev Vladimir , Brown Jeff L. , Green Andrew J. , Chabak Kelson D.
Published: October 2021

Conductive homoepitaxial Si-doped β-Ga2O3 films were fabricated by pulsed laser deposition with an as-deposited 2323 S cm−1 conductivity (resistivity = 4.3 × 10−4 Ω-cm, carrier concentration = 2.24 × 1020 cm−3, mobility = 64.5 cm2 V−1 s−1, and electrical activation efficiency = 77%). High quality homoepitaxial films deposited on commercial (010) Fe-compensated β-Ga2O substrates were determined by high-resolution transmission electron microscopy and x-ray diffraction. The β-Ga2O3 films have ∼70% transparency from 3.7 eV (335 nm) to 0.56 eV (2214 nm). The combination of high conductivity and transparency offers promise for numerous ultrawide bandgap electronics and optoelectronic applications.
Study of magnon–phonon non-equilibrium in a magnetic insulator—Thulium iron garnet
Authors: Lee Geun-Hee , Lee Taekhyeon , Cao Van Phuoc , Kim Dongha , Seo Min-Kyo , Jo Younghun , Jeong Jong-Ryul , Kim Kab-Jin
Published: October 2021

The non-equilibrium state between magnons and phonons is the key to understand the spin-caloric phenomena. We developed a unique optical reflectometry technique to spatially resolve Kerr angle (θK) and optical reflectance (R) in a magnetic insulator—thulium iron garnet (TmIG). The TmIG was subjected to a thermal gradient to estimate populations of thermally excited magnons and phonons through the variation of θK and R. The results showed that the spatial gradient of θK is different from that of R, indicating the non-equilibrium state between magnons and phonons. Particularly, the characteristic decay length of θK was significantly influenced by the heating power and the magnetic field, suggesting non-linear magnon scattering in a high magnon density regime. Our work not only provides a scheme to investigate the spatial profiles of magnons and phonons but also reveals the magnon–phonon non-equilibrium in TmIG. Hence, this report will stimulate further studies based on magnon–phonon non-equilibrium such as a transverse spin Seebeck effect and Bose–Einstein condensation.
On the relationships between different vortex identification methods based on local trace criterion
Authors: Liu Yangwei , Zhong Weibo , Tang Yumeng
Published: October 2021

Vortical flow is generally considered to be a flow with a rotational trend, but vortex regions vary depending on the vortex identification methods by which they are extracted. In this paper, theoretical relationships between commonly used Q series vortex criteria, eigenvalue-based vortex criteria, and the Rortex method are analytically derived and built based on the local trace (LT) criterion (LTcri). The projections of vortex regions extracted by different vortex criteria onto the LT-plane constructed by LTcri are presented to graphically discuss their physical meanings and interrelations. The LTcri-based method reflects the local swirling patterns of flow and provides new interpretations of various vortex criteria in terms of local flow patterns. The simple vortex models, including Rankin vortex and Burgers' vortex, forced isotropic turbulence flow, and a compressor corner separation flow case with a practical Mach number, are tested and analyzed. The potential of the LTcri-based method is shown both by analyzing vortex dynamic properties and by distinguishing the different swirling patterns of complex vortices in tangle. This contributes to the exploration of flow mechanisms and furthers investigations into vortex dynamics.
Ozone destruction due to the recombination of oxygen atoms
Authors: Pershin Andrey A. , Torbin Aleksei P. , Mikheyev Paul A. , Kaiser Ralf I. , Mebel Alexander M. , Azyazov Valeriy N.
Published: October 2021

Kinetics of ozone destruction due to the recombination of oxygen atoms produced by pulsed 266 nm laser photolysis of O3/M (M = CO2 and/or N2) mixtures was studied using the absorption and emission spectroscopy to follow time evolutions of O3 and electronically excited molecules O2* formed in the recombination process 2O(3P) + M → O2* + M. An unexpected high ozone destruction rate was observed when O2* was present in the system. The kinetic model developed for the oxygen nightglow on the terrestrial planets was adapted to interpret the detected temporal profiles of the ozone number density and the O2* emission intensities. It was deduced that the vibrationally excited singlet delta oxygen molecule O2(a1Δ, υ) formed in the secondary processes reacts efficiently with ozone in the process O2(a1Δ, υ ≥ 3) + O3 → 2O2 + O, and the rate constant of this process was estimated to be 3 × 10−11 cm3 s−1. Ab initio calculations at the CASPT2(14, 12)/cc-pVTZ/UωB97XD/cc-pVTZ level of theory were applied to find the reaction pathway from the reactants to products on the O5 potential energy surface. These calculations revealed that the O2(a1Δ) + O3 reaction is likely to proceed via singlet–triplet intersystem crossing exhibiting an energy barrier of 9.6 kcal/mol, which lies between two and three quanta of vibrational excitation of O2(a1Δ), and hence, O2(a1Δ, υ) with υ ≥ 3 could rapidly react with ozone.
Self-regulated growth of candidate topological superconducting parkerite by molecular beam epitaxy
Authors: Lapano Jason , Pai Yun-Yi , Mazza Alessandro R. , Zhang Jie , Isaacs-Smith Tamara , Gemperline Patrick , Zhang Lizhi , Li Haoxiang , Lee Ho Nyung , Eres Gyula , Yoon Mina , Comes Ryan , Ward T. Zac , Lawrie Benjamin J. , McGuire Michael A. , Moore Robert G. , Nelson Christopher T. , May Andrew F. , Brahlek Matthew
Published: October 2021

Ternary chalcogenides, such as parkerites and shandites, are a broad class of materials exhibiting a rich diversity of transport and magnetic behavior and an array of topological phases, including Weyl and Dirac nodes. However, they remain largely unexplored as high-quality epitaxial thin films. Here, we report the self-regulated growth of thin films of the strong spin–orbit coupled superconductor Pd3Bi2Se2 on SrTiO3 by molecular beam epitaxy. Films are found to grow in a self-regulated fashion, where, in excess Se, the temperature and relative flux ratio of Pd to Bi control the formation of Pd3Bi2Se2 due to the combined volatility of Bi, Se, and Bi–Se bonded phases. The resulting films are shown to be of high structural quality, and the stoichiometry is independent of the Pd:Bi and Se flux ratio and exhibits a superconducting transition temperature of 800 mK and a critical field of 17.7 ± 0.5 mT, as probed by transport and magnetometry. Understanding and navigating the growth of the chemically and structurally diverse classes of ternary chalcogenides open a vast space for discovering new phenomena and enabling new applications.
Interferometric measurement of co-operative evaporation in 2D droplet arrays
Authors: Edwards Andrew M. J. , Cater Jack , Kilbride Joseph J. , Le Minter Pierre , Brown Carl V. , Fairhurst David J. , Ouali Fouzia F.
Published: October 2021

The evaporation dynamics of multiple droplet arrays is important in inkjet printing and spray coating, where co-operative “shielding” effects increase the overall evaporation time. However, current measurement methods provide limited information on how individual droplets contribute to the overall dynamics. In this work, we present a simple interferometric technique for precise measurements of droplet evaporation rates, which is not possible via traditional approaches. We validate the technique on a single droplet. We then extend our analysis to ordered and random 2D arrays of droplets. We demonstrate that the evaporation rate is highly dependent on the position of the droplet within the array and its confinement. The more confined droplets exhibit lower evaporation rates. Our results of ten different configurations and well over 100 droplets are in good quantitative agreement with a recent analytical model of co-operative evaporation rates. Our approach opens up possibilities for studies of collective evaporation effects, including in areas of current importance such as sneezes and exhaled breath.
An experimental study on aquatic collapses of bidisperse granular deposits
Authors: He Kang , Shi Huabin , Yu Xiping
Published: October 2021

A laboratory experiment is conducted to study the mobility and the segregation of aquatic bidisperse granular columns. The effects of the ambient fluid, the particle composition, and the initial geometry on the dynamics of bidisperse granular columns are investigated. It is identified that the ambient fluid plays diverse roles in the phenomenon but is to retard the collapsing process in an overall sense. The instantaneous frontal positions of the granular mass in a bidisperse collapsing case could be shorter or longer than in a monodisperse case under the aquatic condition, but its final run-out is always longer. Compared to dry cases, particle segregations in aquatic cases are found to be more pronounced with columns composed of fine and coarse particles than with columns composed of fine and medium-sized particles. In general, the segregation phenomenon becomes less obvious at relatively large values of the finer-particle fraction and in cases with relatively small particle size difference. It is demonstrated that particle segregation contributes to an increased mobility of the bidisperse granular mass, probably due to the fact that smaller particles fall downward through the gaps between larger particles as the mixture deforms continuously, leading to an increased possibility for large particles to be separated by isolated small particles or an increased possibility for the rolling friction to take place of the sliding friction between large particles.
A new multiscale approach to rapidly determine the local emission current density of nanoscale metallic field emitters
Authors: Ludwick J. , Cahay M. , Hernandez N. , Hall H. , O’Mara J. , Jensen K. L. , Deane J. H. B. , Forbes R. G. , Back T. C.
Published: October 2021

We advocate the use of lookup tables in the development of extremely fast and accurate multiscale models based on the coupling of a quantum-mechanical wave impedance approach and finite-element simulations to determine the local emission current density (LECD) from a metallic emitter of arbitrary shape. The lookup tables are prepopulated with numerical solutions of LECD that can be adjusted to accommodate any form of higher order physics, which is critical for current state-of-the-art emitters. Results show that the use of lookup tables can speed up numerical simulations of the field emission current from metallic cathodes by a factor of about 1000× while retaining high precision, with a maximum error of less than 1% when compared to direct numerical solutions. Implementation of nanoscale emitter physics into lookup tables is discussed and used to assess the validity of the Kemble approximation for nanoscale metallic cathodes. The use of lookup tables is illustrated through a calculation of the LECDs of a metallic field emitter with a rugged surface and from an array of ellipsoid-on-a-post emitters. Section V contains our conclusions and suggestions for future work.
Entropy-based active learning of graph neural network surrogate models for materials properties
Authors: Allotey Johannes , Butler Keith T. , Thiyagalingam Jeyan
Published: October 2021

Graph neural networks trained on experimental or calculated data are becoming an increasingly important tool in computational materials science. Networks once trained are able to make highly accurate predictions at a fraction of the cost of experiments or first-principles calculations of comparable accuracy. However, these networks typically rely on large databases of labeled experiments to train the model. In scenarios where data are scarce or expensive to obtain, this can be prohibitive. By building a neural network that provides confidence on the predicted properties, we are able to develop an active learning scheme that can reduce the amount of labeled data required by identifying the areas of chemical space where the model is most uncertain. We present a scheme for coupling a graph neural network with a Gaussian process to featurize solid-state materials and predict properties including a measure of confidence in the prediction. We then demonstrate that this scheme can be used in an active learning context to speed up the training of the model by selecting the optimal next experiment for obtaining a data label. Our active learning scheme can double the rate at which the performance of the model on a test dataset improves with additional data compared to choosing the next sample at random. This type of uncertainty quantification and active learning has the potential to open up new areas of materials science, where data are scarce and expensive to obtain, to the transformative power of graph neural networks.
Preferential solvation and optical properties of eumelanin building blocks in binary mixture of methanol and water
Authors: Assis Oliveira Leonardo Bruno , Fonseca Tertius L. , Cabral Benedito J. C. , Coutinho Kaline , Canuto Sylvio
Published: October 2021

Employing a sequential quantum mechanical/molecular mechanical approach for polar protic solvents, we study the absorption spectrum of eumelanin building blocks including monomers, dimers, and tetramers in pure water and methanol and three water–methanol binary mixtures having water molar fractions (Xw = 0.25, 0.50, and 0.75). The binary mixture of solvents is a common situation in experiments, but theoretical studies are limited to the use of continuum models. Here, we use explicit solvent molecules, and specific solute–solvent interaction is analyzed and seen to play an important role. Effects of the electronic polarization of solute by the environment were included using a reliable iterative scheme. The results illustrate that the monomers, dimers, and tetramers are preferably solvated by methanol, but the composition of the mixture in the vicinity of the solute molecules is different from the bulk composition with a preferential microsolvation (hydrogen bonds) in water for most species considered. It is observed that the short-range electrostatic polarization effects of the hydrogen bonds lead to a slight blue shift of the excitation energies when the concentration of water in the mixture is enhanced. For the same species, there is an enhancement of the higher-energy absorption intensity caused by long-range electrostatic interactions with the environment and that the behavior of the experimental spectrum, which is characterized by a nearly monotonic decay from the ultraviolet to the infrared, is qualitatively reproduced by the superposition of the absorption spectra of monomers, dimers, and tetramers in the liquid phase.
Tutorial on elastic interaction models for multistep spin-crossover transitions
Authors: Nishino Masamichi , Singh Yogendra , Boukheddaden Kamel , Miyashita Seiji
Published: October 2021

Spin-crossover (SC) compounds are fascinating materials that exhibit colorful phase transitions induced by temperature, pressure, photoirradiation, etc. From the microscopic point of view, the electronic (spin) state of a molecule changes between the low-spin (LS) and high-spin (HS) states by such stimuli, and a variation of the molecular size follows through the vibronic coupling between the electronic state and structure in the molecule. This causes an elastic distortion and then an elastic interaction. The elastic interaction is essential in cooperative properties of SC phenomena. In this paper, we present a tutorial study on elastic interaction models for SC phenomena, which are the recent trend of modeling of SC compounds. We focus on multistep transitions, which are a topic of SC phenomena. We analyze the phase diagrams including the metastable phases for several SC systems, in which antiferromagnetic-like and ferrimagnetic-like phases are associated in addition to the LS and HS phases. Making use of the phase diagrams, we show various patterns of thermally induced SC transition with steps. We also investigate SC transitions with steps in a core-shell SC nanocomposite composed of two different SC compounds. We focus on two cases: the core has a lower transition temperature than the shell, and the core has a higher transition temperature. We show characteristic features of difference in the two systems.
Characterization of superconducting NbTiN films using a dispersive Fourier transform spectrometer
Authors: Lap B. N. R. , Khudchenko A. , Hesper R. , Rudakov K. I. , Dmitriev P. , Khan F. , Koshelets V. P. , Baryshev A. M.
Published: October 2021

We have built a terahertz dispersive Fourier transform spectrometer [Birch, Microchim. Acta 93, 105–122 (1987)] to study frequency properties of superconducting films used for fabrication of THz detectors. The signal reflected from the tested film is measured in time domain, which allows to separate it from the other reflections. The complex conductivity of the film depends on frequency and determines the reflection coefficient. By comparing the film reflection in the superconducting state (temperature is below Tc) with the reflection of the normal state, we characterize the film quality at terahertz frequencies. The method was applied to 70 and 200 nm thick Nb films on a silicon wafer and to 360 nm thick NbTiN films on silicon and quartz wafers. The strong-coupling coefficient, α, was found to be 3.52 for Nb and 3.71–4.02 for the NbTiN films. The experimental results were fitted using extended Mattis-Bardeen theory [Noguchi et al., Phys. Procedia 36, 318–323 (2012)] and show good agreement.
The role of Si vacancies in the segregation of O, C, and N at silicon grain boundaries: An ab initio study
Authors: Maji Rita , Contreras-García Julia , Capron Nathalie , Degoli Elena , Luppi Eleonora
Published: October 2021

Grain boundaries (GBs) are defects originating in multi-crystalline silicon during crystal growth for device Si solar cell fabrication. The presence of GBs changes the coordination of Si, making it advantageous for charge carriers to recombine, which brings a significant reduction of carrier lifetimes. Therefore, GBs can be highly detrimental for device performances. Furthermore, GBs easily form vacancies with deep defect electronic states and are also preferential segregation sites for various impurity species, such as C, N, and O. We studied from first principles the correlation between structural, energetics, and electronic properties of the Σ3{111} Si GB with and without vacancies, and the segregation of C, N, and O atoms. C and O atoms strongly increase their ability to segregate when vacancies are present. However, the electronic properties of the Σ3{111} Si GB are not affected by the presence of O, while they can strongly change in the case of C. For N atoms, it is not possible to find a clear trend in the energetics and electronic properties both with and without vacancies in the GB. In fact, as N is not isovalent with Si, as C and O, it is more flexible in finding new chemical arrangements in the GB structure. This implies a stronger difficulty in controlling the properties of the material in the presence of N impurity atoms compared to C and O impurities.
Anharmonicity of optical phonon modes in copper doped rutile TiO2 nanorod composed microflowers
Authors: Sahoo Subhashree , Ghorai Gurupada , Ghosh Kalyan , Das Bidyadhar , Sikdar Mrinal K. , Sahoo Pratap K.
Published: October 2021

Anharmonicity and impurities have a significant impact on the dynamic and optical properties of crystalline solids. In this report, we have performed temperature-dependent Raman spectroscopy in the range of 300–800 K for hydrothermally synthesized titanium dioxide (TiO2) nanorod composed microflowers doped with Cu. X-ray diffraction and high resolution transmission electron microscopy confirm the pure rutile phase of both pristine and Cu doped TiO2. The most intense Eg and A1g modes exhibit a frequency redshift, and the linewidth increases with temperature, which leads to Fano line shape type asymmetry. The anharmonicity induced phonon frequency shift as a function of temperature was well fitted using the Klemens model by combining three and four-phonon coupling processes. The Raman modes soften with the increasing concentration of Cu doping. The Cu dopant acts as an impurity, which manifests defect states to tune the bandgap and shorten the phonon lifetime and anharmonicity. Such an anharmonic effect can lead to applications in the sensing devices with suitable thermal and electrical conductivities.
A search for a DFT functional for actinide compounds
Authors: Mitrofanov Artem , Andreadi Nikolai , Korolev Vadim , Kalmykov Stepan
Published: October 2021

Actinide chemistry often lies beyond the applicability domain of the majority of modern theoretical tools due to high computational costs, relativistic effects, or just the absence of actinide data for semiempirical method fitting. On the other hand, radioactivity pushes the usage of computational methods instead of experimental ones. Here, we would like to present a novel relPBE functional as an actinide-fitted version of the PBE0 functional.
Multiphoton-excited dynamics of the trans or cis structural isomer of 1,2-dibromoethylene
Authors: Kim Junggil , Kim Sang Kyu
Published: October 2021

Photofragmentation dynamics of cis and trans isomers of 1,2-dibromoethylene (1,2-DBE) have been investigated by multiphoton excitation using a picosecond (ps) laser pulse. It has been found that the Br2+ product ion preferentially originates from the cis isomer rather than from trans. The Boltzmann-type isotropic low kinetic energy components of the Br+ and Br2+ product state distributions seem to be most likely from the unimolecular reactions of the vibrationally hot cationic ground state generated by the three-photon absorption at the photon energy below ∼38 000 cm−1. The highly anisotropic kinetic energy components of Br+ and Br2+ start to appear at the photon energy above ∼38 000 cm−1, where the Dn (n ≥ 1) − D0 transition is facilitated within the same ps laser pulse as the parent molecule is efficiently ionized by the two-photon absorption. The transition dipole moment of the D4 − D0 transition of the strongest oscillator strength has been theoretically predicted to be parallel to the C–Br bond or C=C bond axis for the trans or cis isomer, respectively. The fast anisotropic with the (β ∼ +2) component in the Br+ product distribution is thus likely from the trans isomer, whereas that of Br2+ (β ∼ −0.5) should be the consequence of the photodissociation of the cis isomer. The isomer-specific reactivity found here in the picosecond multiphoton excitation of 1,2-DBE provides a nice platform for the better understanding of the structure–reactivity relationship under the harsh condition of the strong or ultrashort optical field.