bluuebunny/crossref_metadata_2025 huggingface dataset:
Objektivierung der chirurgischen Operations-Qualität durch standardisierte Komplikationserfassung
Authors: Schmidt Jörg , Schmidt Ina
Published: January 2021

Die Erfassung der Ergebnisqualität medizinischer Leistungen ist sowohl vom Gesetzgeber gewünscht als auch aus Sicht der Versorgungsforschung sinnvoll. Diese Messung erfolgt jedoch hauptsächlich durch Patientenbefragungen bzw. durch Messung der patientenorientierten Parameter über den Gesamtverlauf der Behandlung. Gerade in operativen Fächern kann eine solche, mit subjektiven Parametern im Vordergrund stehende Messung das Ergebnis der rein operativen Leistung nicht darstellen. Gerade in der Unfallchirurgie, einem Fach, in dem die Nach- und Weiterbehandlung nach operativer Versorgung einer Verletzung eine entscheidende Rolle spielt, sollten die rein operativen Leistungen auch separat bewertet werden. Es wird ein Vorschlag unterbreitet, wie die operativen Leistungen in Addition zur Ergebnismessung qualitativ bewertet und gleichzeitig die interne Qualitätssicherung strukturiert werden kann.
Biaryl Construction Based on Nickel-Catalyzed C–O Bond Activation
Authors: Liu Feng , Diao Haiyan , Shi Zhangjie
Published: January 2021

Nickel-catalyzed carbon–oxygen bond activation is one of the most powerful strategies for the direct construction of various biaryl compounds. Under nickel catalysis, efficiently produced and naturally abundant arenol-based electrophiles can be activated and coupled with different aryl nucleophiles, including nucleophiles containing magnesium, zinc, boron, etc., to produce biaryl structural units. This Account summarizes recent progress on biaryl synthesis via nickel-catalyzed C–O bond activation.

1 Introduction

2 Coupling of Arenols and Arenol Derivatives with Aryl Magnesium Reagents

3 Coupling of Arenols and Arenol Derivatives with Aryl Zinc Reagents

4 Coupling of Arenols and Arenol Derivatives with Aryl Boron Reagents

5 Others

6 Conclusion
A Facile Total Synthesis of Mubritinib
Authors: Kuang Chunxiang , Wang Rong , Cui Menghan , Yang Qing
Published: January 2021

A five-step, practical, and concise total synthesis of mubritinib is described. The synthesis utilized Friedel–Crafts acylation, click reaction, reduction, and demethylation for the construction of the triazole ring system as key steps. Another important feature of this synthesis is the Bredereck oxazole synthesis. The main advantages of this process are the improved yield and decreased number of reaction steps, which paves the way for the industrial-scale synthesis of mubritinib.
Stereoretentive Olefin Metathesis: A New Avenue for the Synthesis of All-cis Poly(p-phenylene vinylene)s and Stereo­defined Polyalkenamers
Authors: Michaudel Quentin , Kempel Samuel J. , Hsu Ting-Wei
Published: January 2021

Olefin metathesis has tremendously impacted all fields of synthetic chemistry. However, the control of the olefin stereochemistry during this process remains a grand challenge. Recent innovations in catalyst design have permitted control of the stereochemistry of the olefin product. Here, we discuss the development of stereoretentive olefin metathesis, with an emphasis on the synthesis of stereodefined polyalkenamers through ring-opening metathesis polymerization (ROMP). We then present our application of this unique reaction manifold to the preparation of all-cis poly(p-phenylene vinylene)s (PPVs). A dithiolate Ru catalyst was found to deliver perfect cis selectivity for the polymerization of a paracyclophane diene monomer. By using optimized conditions, all-cis PPVs with narrow dispersities and predictable molar masses were obtained by varying the ratio of monomer to catalyst. The high chain fidelity of the stereoretentive ROMP with a paracyclophane diene monomer enabled the preparation of well-defined diblock copolymers with a norbornene co-monomer. Photochemical isomerization of all-cis to all-trans PPVs was effected with both homopolymers and diblock copolymers. This process was shown to be selective for the PPV block, and resulted in changes in optical properties, polymer size, and solubility. Stereoretentive ROMP provides a promising platform for synthesizing polymers with unique properties, including photoresponsive all-cis PPVs with living characteristics.

1 Introduction

2 Synthetic Applications of Stereoretentive Olefin Metathesis

3 Stereocontrol of Polyalkenamers through Stereoretentive ROMP

4 Stereoretentive ROMP To Access All-cis Poly(p-phenylene vinylene)s

5 Conclusion
The Synthesis of Conjugated Bis-Aryl Vinyl Substrates and Their Photoelectrocyclization Reactions towards Phenanthrene Derivatives
Authors: Rainier Jon D. , Zhao Xuchen
Published: January 2021

The photoelectrocyclization of conjugated vinyl biaryls has proven to be a valuable and efficient strategy for generating phenanthrene derivatives. Contained in this review is an overview of the mechanism for the transformation and a discussion of the reaction scope with a focus on the electrocyclization itself, rearomatization, and the application of the reaction in natural product synthesis.

1 Introduction

2 The Synthesis of Conjugated Vinyl Biaryls

3 Mechanistic Studies

4 Substrate Scope

5 Applications

6 Conclusions
Forskolin Editing via Radical Iodo- and Hydroalkylation
Authors: Pruteanu Elena , Tappin Nicholas D. C. , Kulciţki Veaceslav , Renaud Philippe , Gîrbu Vladilena , Morarescu Olga , Dénès Fabrice
Published: January 2021

The modification of highly oxygenated forskolin as well as manoyl and epi-manoyl oxide, two less functionalized model substrates sharing the same polycyclic skeleton, via intermolecular carbon-centered radical addition to the vinyl moiety has been investigated. Highly regio- and reasonably stereoselective iodine atom transfer radical addition (ATRA) reactions were developed. Unprotected forskolin afforded an unexpected cyclic ether derivative. Protection of the 1,3-diol as an acetonide led the formation of the iodine ATRA product. Interestingly, by changing the mode of initiation of the radical process, in situ protection of the forskolin 1,3-diol moiety as a cyclic boronic ester took place during the iodine ATRA process without disruption of the radical chain process. This very mild radical-mediated in situ protection of 1,3-diol is expected to be of interest for a broad range of radical and non-radical transformations. Finally, by using our recently developed tert-butyl­catechol-mediated hydroalkylation procedure, highly efficient preparation of forskolin derivatives bearing an extra ester or sulfone group was achieved.
Synthesis of New Dialkyl 2,2′-[Carbonylbis(azanediyl)]dibenzoates via Curtius Rearrangement
Authors: Khouili Mostafa , Pujol Maria Dolors , Yassine Hasna , Bouali Jamila , Oumessaoud Asmaa , Ourhzif El Mahdi , Hamri Salha , Hafid Abderrafia
Published: January 2021

The 2-(alkylcarbonyl)benzoic acids obtained by esterification of phthalic anhydride are converted into azide derivatives: alkyl 2-[(azidocarbonyl)amino]benzoates and to ureas: dialkyl 2,2′-[carbonylbis(azanediyl)]dibenzoates. These transformations were carried out using classical Curtius rearrangement conditions in the presence of diphenylphosphoryl azide (DPPA) in a basic medium, followed by hydrolysis. Subsequently, a final condensation reaction of these urea derivatives enabled us to obtain, for the first time, the new alkyl derivatives, alkyl 2-[2,4-dioxo-1,2-dihydroquinazolin-3(4H)-yl]benzoates. All the new compounds obtained in satisfactory yields were characterized by 1H and 13C NMR, and by X-ray crystallographic analysis.
Ventricular Septal Rupture Complicating an Acute ST-Segment Elevation Myocardial Infarction during the COVID-19 Pandemic
Authors: Tanto Ines V. , Dharma Surya , Juzar Dafsah A. , Bono Arinto A.H.
Published: January 2021

Ventricular septal rupture (VSR) is rare but a lethal complication of acute myocardial infarction (MI). Definite treatment requires the surgical closure of the VSR and coronary artery bypass grafting (CABG). However, the optimal timing for surgery is still controversial, particularly during the novel coronavirus disease 2019 (COVID-19) pandemic where medical procedures should be performed within the safest environment. Before surgery, a proper management in the intensive cardiovascular care unit is essential to maintain the stability of the hemodynamic profile related with VSR and determines the prognosis of the patient. We described a case of VSR complicating an anterior wall MI in a patient who admitted to our hospital during the COVID-19 pandemic that was treated successfully by surgical closure of the VSR and CABG.
Prevalence of Acute Traumatic Coagulopathy in Acutely Traumatized Dogs and Association with Clinical and Laboratory Parameters at Presentation
Authors: Herrero Yaiza , Jud Schefer Rahel , Muri Benjamin M. , Sigrist Nadja E.
Published: January 2021

Objective The aim of this study was to determine the prevalence of acute traumatic coagulopathy (ATC) and identify associated clinical and laboratory parameters including rotational thromboelastometry.

Study Design Dogs presenting within 6 hours after trauma were allocated to the ATC or non-ATC group based on thromboelastometry analysis (ex-tem S, in-tem S, fib-tem S). ATC was defined as ≥2 hypocoagulable parameters in 1 profile and ≥ 1 hypocoagulable parameter in an additional profile. Parameters used were ex-tem and in-tem clotting time (CT), clot formation time (CFT), maximum clot firmness (MCF), maximum lysis and fib-tem MCF. Clinical and laboratory parameters at presentation, animal trauma triage (ATT) score, transfusion requirement and outcome were compared. Logistic regression was used to identify independent factors associated with ATC.

Results Eleven of 33 dogs presented with ATC and showed ex-tem CT and CFT prolongation and reduced MCF amplitude in all profiles (all p < 0.001). pH (p = 0.043) and potassium concentration (p = 0.022) were significantly lower and bleeding (p = 0.027) and plasma transfusions (p = 0.001) more common in dogs with ATC. Time after trauma (p = 0.040) and Animal Trauma Triage score (p = 0.038, including haematocrit as confounding factor) were associated with the presence of ATC.

Conclusion Acute traumatic coagulopathy is more common in traumatized dogs than previously reported. Acute traumatic coagulopathy was associated with acidosis, Animal trauma triage score, time after trauma and higher transfusion needs. Coagulation abnormalities include ex-tem CT and CFT prolongations and decreased clot strength.
Multiple Cartilaginous Exostoses Causing Severe Cervical Myelopathy in a Puppy Dog
Authors: Menezes Mareliza Possa de , Facin Andréia Coutinho , Máximo Larissa Godoi , Luzzi Mayara de Cássia , Dias Luis Gustavo Gosuen Gonçalves , Minto Bruno Watanabe
Published: January 2021

This study aimed to report a case of multiple cartilaginous exostoses (MCE) causing severe cervical myelopathy in a puppy dog. An 80-day-old Dachshund cross weighing 2.2 kg presented with progressive development of non-ambulatory tetraparesis, proprioceptive ataxia in all four limbs, and cervical hyperesthesia. Multiple calcified masses in the cervical spine at the levels of C1–C2 and C4–C7, with several points of spinal cord compression, were identified. Ventral atlantoaxial fusion was performed. Four days later, four masses were surgically removed by dorsal laminectomy of C1–C2 and C4–C7, and a right facetectomy between C4 and C5 was performed. Multiple cartilaginous exostoses were confirmed by histopathological examination. Thirty-six months after surgery, the patient showed no recurrence of neurological signs. Ventral atlantoaxial fusion, and surgical removal of MCE masses followed by decompression was effective on alleviating clinical sings in the short and medium term.
Improving Laparoscopic Techniques Using Speckle Imaging
Authors: Larter Raima
Published: January 2021

Investigators reduce inaccuracies due to noise in laser speckle contrast imaging by using multiple camera exposures and demonstrate the method in study of a live animal.
Signatures of electronic and nuclear coherences in ultrafast molecular x-ray and electron diffraction
Authors: Rouxel Jérémy R. , Keefer Daniel , Mukamel Shaul
Published: January 2021

Femtosecond x-ray and electron diffraction hold promise to image the evolving structures of single molecules. We present a unified quantum-electrodynamical formulation of diffraction signals, based on the exact many-body nuclear + electronic wavefunction that can be extracted from quantum chemistry simulations. This gives a framework for analyzing various approximate molecular dynamics simulations. We show that the complete description of ultrafast diffraction signals contains interesting contributions involving mixed elastic and inelastic scattered photons that are usually masked by other larger contributions and are neglected. These terms include overlaps of nuclear wavepackets between different electronic states that provide an electronic decoherence mechanism and are important for the time-resolved imaging of conical intersections.
Stainless microfluidic probe with 2D-array microapertures
Authors: Takahashi Koki , Kamiya Shogo , Takao Hidekuni , Shimokawa Fusao , Terao Kyohei
Published: January 2021

A microfluidic probe (MFP) does not require physical walls for flow channels, enabling application of a chemical solution in an open space by injecting and aspirating the solution. However, in conventional MFP fabrication methods, the use of a 2D aperture array at narrow intervals to enhance the function of treatment remains limited. In this study, we developed a stainless MFP (stMFP) to produce a 2D aperture array at narrow intervals. The stMFP was developed using a stacking technique in which stainless steel substrates fabricated by photolithography and a wet etching process were stacked and bonded through thermal diffusion. This process resulted in a 6-row and 8-column aperture array with an aperture size of 100 × 150 µm and a narrow interval of 50 µm. The surface treatment area was evaluated by biopatterning of a fluorescent antibody. The results showed that the stMFP biopatterned a minimum treatment area of 3.3 × 103 µm2, which could be controlled between 5.1 × 104 µm2 and 3.0 × 105 µm2 by changing the aperture arrangement. In addition, when two types of fluorescent antibodies were alternately injected in the row direction, six independent treatment areas of 6.1 × 104 µm2 were formed over a wide area of 3.8 × 105 µm2. Furthermore, biopatterning using a 4 × 4 aperture array showed that a 2D treatment area with 4-rows and 2-columns can be produced with an area of 4.5 × 105 µm2. A single stMFP can form various 2D treatment patterns, which is expected to realize high-performance bioprocessing in the field of biology.
Evaporation of droplets capable of bearing viruses airborne and on hydrophobic surfaces
Authors: Hasan Md Syam , Sobolev Konstantin , Nosonovsky Michael
Published: January 2021

Airborne and deposited water microdroplets can carry viruses including coronaviruses. The evaporation of microdroplets containing virus particles often leads to virus inactivation. Microdroplet evaporation involves various mechanisms such as diffusion, the Kelvin effect, infrared irradiation, and the role of solutes. For the evaporation of airborne water microdroplets, temperature and relative humidity of ambient air are important factors. However, for sessile droplets deposited on solid surfaces, wetting and porosity become important factors that control evaporation on regular, superhydrophobic, and photocatalytic surfaces. An experimental study of the effect of wetting properties and porosity on the evaporation rates on the polypropylene non-woven medical fabric was consistent with the theoretical models. Highly porous tile surfaces exhibited 2.2–4 times faster evaporation rates than nonporous surfaces.
Impact of current-induced degradation process on the electro-optical characteristics of InGaN/GaN multiple-quantum-well photodetectors fabricated on sapphire substrate
Authors: Dalapati Pradip , Yamamoto Kosuke , Egawa Takashi , Miyoshi Makoto
Published: January 2021

The impact of defects on the degradation behaviors of InGaN/GaN multiple-quantum-well photodetectors submitted to dc current stress has been intensively studied. The root mechanism for degradation has been studied employing combined electro-optical measurements. The collected results indicate that (i) stress can induce an increase in parasitic current leakage paths and trap-assisted tunneling in reverse and subturn-on forward bias ranges, respectively; (ii) during stress, the overall capacitance increases and localization improves in the apparent carrier concentration within the active region; (iii) stress causes a significant decrease in quantum well intensity and an increase in yellow luminescence; (iv) stress induces an increase in the external quantum efficiency due to broadening of the space-charge region; and (v) the detectivity of the device decreases after the stress treatment. These results suggest that degradation is largely attributed to the activation of initially inactive defects, mainly Mg–H, C-related, and VGa defects in the investigated devices, with consequent worsening of their performances.
Carrier dynamics of silicon vacancies of SiC under simultaneous optically and electrically excitations
Authors: Yamazaki Yuichi , Chiba Yoji , Sato Shin-ichiro , Makino Takahiro , Yamada Naoto , Satoh Takahiro , Kojima Kazutoshi , Hijikata Yasuto , Tsuchida Hidekazu , Hoshino Norihiro , Lee Sang-Yun , Ohshima Takeshi
Published: January 2021

Silicon carbide (SiC) is an important wide bandgap semiconductor used for diverse applications from heat spreading to high-power electronics. It is readily doped, has high thermal conductivity, and is used for application in mature device fabrication techniques. To improve the performance of SiC electronic devices, built-in sensors, which should ideally be inexpensive integrated with the device, and not perturb device operations, are quite useful. Here, we studied the optical properties of the negatively silicon vacancy under simultaneous optical and electrical excitation to uncover the carrier dynamics, as the luminescence intensity is determined by competition between the two excitation pathways. We also observe optically detected magnetic resonance (ODMR) and observe that the ODMR contrast is decreased by injected current, which is consistent with the decrease in the pumping rate of optical excitation in the competitive process. Our studies show that an embedded quantum sensor is possible in practical SiC devices, opening new opportunities for device control and optimization.
Near-field models and simulations of pellet ablation in tokamaks
Authors: Bosviel Nicolas , Parks Paul , Samulyak Roman
Published: January 2021

Detailed numerical studies of the ablation of a single neon pellet in the plasma disruption mitigation parameter space have been performed. Simulations were carried out using FronTier, a hydrodynamic/low magnetic Reynolds number MHD code with explicit tracking of material interfaces. FronTier's physics models resolve the pellet surface ablation and the formation of a dense, cold cloud of ablated material, the deposition of energy from hot plasma electrons, the expansion of the ablation cloud along magnetic field lines, and the radiation losses. A local thermodynamic equilibrium model based on Saha equations has been used to resolve atomic processes in the cloud and Redlich–Kwong corrections to the ideal gas equation of state for cold and dense gases, which have been used near the pellet surface. The FronTier pellet code is a next generation of the code described in [R. Samulyak et al., Nucl. Fusion 47, 103 (2007)]. It has been validated against the semi-analytic improved neutral gas shielding model in the 1D spherically symmetric approximation. Main results include quantification of the influence of atomic processes and Redlich–Kwong corrections on the pellet ablation in spherically symmetric approximation and verification of analytic scaling laws in a broad range of pellet and plasma parameters. Using axially symmetric MHD simulations, the properties of ablation channels and the reduction of pellet ablation rates in magnetic fields of increasing strength have been studied. While the main emphasis has been given to neon pellets for the plasma disruption mitigation, selected results on deuterium fueling pellets have also been presented.
Carrier lifetime control by intentional boron doping in aluminum doped p-type 4H-SiC epilayers
Authors: Murata K. , Tawara T. , Yang A. , Takanashi R. , Miyazawa T. , Tsuchida H.
Published: January 2021

The carrier lifetime control in p-type 4H-SiC epilayers with intentional aluminum (Al) and boron (B) doping is demonstrated as part of work to develop a p-type “recombination-enhancing layer” for n-channel insulated gate bipolar devices fabricated on p-type substrates. The (Al + B)-doped epilayers (Al: 5 × 1017, B: 4 × 1016 cm−3) showed a very short minority carrier lifetime of less than 20 ns at 293 K, resembling that of highly Al-doped epilayers (Al: 1 × 1019 cm−3). Besides, the minority carrier lifetimes in (Al + B)-doped epilayers are stable against post-annealing in Ar and H2 ambient, while that of Al-doped epilayers varied considerably. PiN diodes with a 10 μm-thick (Al + B)-doped buffer layer inserted on p-type substrates showed no evident degradation after a stress test under a pulse current density of 2000 A/cm2.
Metal organic framework/layer double hydroxide/graphene oxide nanocomposite supercapacitor electrode
Authors: Elsonbaty Ahmed , Harb Mohamed , Soliman Moataz , Ebrahim Shaker , Eltahan Ayman
Published: January 2021

Layered Double Hydroxide (LDH) based on Metal Organic Framework (MOF) structures has attracted a great deal of attention due to their high surface area, tailoring structure of the MOF, and high pseudocapacitance of LDH. Herein, an Ni-ZIF-67/Mn-LDH supercapacitor electrode was prepared via the solvothermal method at room temperature. A supercapacitor electrode based on Ni-ZIF-67/GO-LDH by replacing active metal Mn with graphene oxide (GO) was also synthesized to enhance the capacitance retention and stability from 78% to 97% after 1000 cycles. The morphology of these electrodes was characterized by scanning electron microscopy (SEM). It was found that the specific surface areas of Ni-ZIF-67/GO-LDH and Ni-ZIF-67/Mn-LDH are 82 and 20 m2 g−1. The electrochemical performance of the two nanocomposite supercapacitor electrodes was observed by cyclic voltammetry, charge–discharge, and electrochemical impedance spectroscopy measurements. The Ni-ZIF-67/GO-LDH electrode produced a specific capacitance (Cs) of 1036 F/g at 1 A/g, while the Ni-ZIF-67/Mn-LDH electrode results in a superior Cs value of 1420 F/g at 1 A g−1 with an energy density of 44 Wh/kg and a power density of 3.5 kW/kg.
Enhanced oil-in-water droplet generation in a T-junction microchannel using water-based nanofluids with shear-thinning behavior: A numerical study
Authors: Besanjideh Mohsen , Shamloo Amir , Kazemzadeh Hannani Siamak
Published: January 2021

Nanofluids are widely used as the continuous phase during droplet formation in microsystems due to their impressive features such as excellent thermal, magnetic, and interfacial properties. Although it is well-known that nanofluids are susceptible to exhibit non-Newtonian behavior even at a low concentration of nanoparticles, effects of non-Newtonian behavior of nanofluids have not been studied on droplet formation thus far. In this study, oil-in-water droplet formation with a relatively high viscosity ratio of the immiscible phases was studied numerically in a T-junction microchannel. To inspect the non-Newtonian effects of aqueous nanofluids on droplet formation, empirical data on the rheological behavior of various types of nanofluids were explored. Finally, two water-based nanofluids with shear-thinning behavior were chosen as the continuous phase for numerical simulations. The numerical procedure was validated against some experimental models. Afterward, droplet length was determined for different capillary numbers, flow rate ratios, and nanoparticle concentrations, and some scaling laws were proposed to predict droplet length in different droplet formation regimes. The results showed that using nanofluids with shear-thinning behavior as the continuous phase results in a decrease in droplet size, and this reduction is more intensified as the concentration of nanoparticles increases. Furthermore, it was observed that the change in the droplet formation regime through manipulating the flow rates does not occur easily when pure water is used as the continuous fluid due to the high viscosity ratio of the immiscible phases. However, when nanofluids are employed as the continuous fluid, the droplet formation regime can be changed more easily due to the enhancement of viscous shear force in the continuous phase. Hence, in addition to the well-known advantages of nanofluids in droplet formation processes, nanofluids can be raised as a new alternative for the continuous phases to administer the droplet size and formation regimes rather than using chemical additives for tuning the rheological properties.
Transition from noise-induced to self-sustained current spiking generated by a NbOx thin film threshold switch
Authors: Johnson B. A. , Brahim K. , Balanov A. G. , Savel'ev S. , Borisov P.
Published: January 2021

A transition to self-sustained current oscillations was investigated in a circuit with a NbOx thin film device, acting as an artificial neuron. Above a threshold of the applied voltage, the circuit begins to demonstrate persistent but rather random current spiking, which becomes more regular with increasing applied voltage. Experimental measurements reveal two scaling regions of the interspike interval dependence on source voltage: an initial logarithmic dependence, which transitions to a power law with an exponent of -1/2. Using a numerical model of the artificial neuron circuit, we observe good agreement with our experimental data. We show that the logarithmic scaling behavior is associated with noise-induced spiking, while the power law is attributed to noisy self-sustained oscillations, which would exist in the system even with the absence of noise. These findings stress the importance of noise in the dynamics of NbOx threshold switches and shed light on their spiking response to variation of the input signals. The reported approach to spiking control in NbOx artificial oscillation neurons can help to develop an optimal design for neuromorphic neural networks and oscillator-based computing systems.
Quantitative evaluation of laser-induced fluorescence in magnetized low-pressure argon plasma
Authors: Bergert Roman , Isberner Leonard W. , Mitic Slobodan , Thoma Markus H.
Published: January 2021

A new quantitative evaluation of tunable diode laser induced fluorescence (TDLIF) measurements in magnetized plasma is presented in this article, taking into account Zeeman splitting of energetic levels as well as inter- and intra-multiplet mixing, defining the density distribution (alignment) of the excited 2p8 multiplet of argon. TDLIF measurements were used to evaluate light-transport properties in a strongly magnetized optically thick argon plasma under different pressure conditions. Therefore, a coupled system of rate balance equations was constructed to describe laser pumping of individual magnetic sub-levels of the 2p8 state through frequency-separated sub-transitions originating from 1s4 magnetic sub-levels. The density distribution of the 2p8 multiplet was described by balancing laser pumping with losses, including radiative decay, transfer of excitation between the neighboring levels within the 2p8 multiplet driven by neutral collisions, and quenching due to electron and neutral collisions. Resulting 2p8 magnetic sub-level densities were then used to model polarization dependent fluorescence, considering self-absorption, which could be directly compared with measured polarization-resolved TDLIF measurements. The achieved results enable to obtain unique solutions for the 1s4 and 1s5 magnetic sub-level densities which were found to be in good agreement with the densities obtained by laser absorption measurements. It is shown that polarization resolved TDLIF measurements in magnetized plasma conditions have strong pressure dependence. The effective disalignment rate constant which redistributes the 2p8 sub-levels among each other has to be considered for a correct description of the TDLIF. This rate is dependent on the neutral gas density and a specific rate coefficient. With the presented method, 1s state densities involved in the TDLIF can be determined without any absolute intensity calibration in an optically thick plasma. Additionally, the presented measurement method and model can help to further understand and improve the description of optical emission of argon based on individual sub-transition descriptions under magnetized conditions.
Determination of single and double helical structures in a swirling jet by spectral proper orthogonal decomposition
Authors: Zhang Yang , Vanierschot Maarten
Published: January 2021

This paper studies the coherent structures found in an annular swirling jet flow undergoing vortex breakdown with control parameters, the Reynolds number Re = 8500 and the swirl number Sw = 0.38. The flow field is simulated using the large eddy simulation method with a dynamic k model. The first- and second-order statistics of the velocity fields are compared to tomographic particle image velocimetry measurements of the same flow configuration to validate the numerical simulation. The fast Fourier transform of the sampled velocity and pressure signals indicates a precessing vortex core with a frequency of 22 Hz. This frequency is in line with the one detected by spectral proper orthogonal decomposition, which is utilized to identify the coherent structures in the near-field region of the swirling flow in the present work. In detail, apart from the single helical structure usually found in swirling flows, a double helix, rarely observed in turbulent swirling jets, is also identified. This structure is not a second-order harmonic mode of the single one, as shown by statistical analysis of the mode temporal coefficients. Moreover, the calculation of energy production shows that this coherent precessing motion extracts energy from the mean flow field in the wake behind the bluff-body and in the breakup region of the vortex.
Effect of conductivity on the electromigration-induced morphological evolution of islands with high symmetries of surface diffusional anisotropy
Authors: Santoki Jay , Mukherjee Arnab , Schneider Daniel , Nestler Britta
Published: January 2021

We report on the electromigration-induced morphological evolution of islands (vacancies, precipitates, and homoepitaxial adatom clusters) using a phase-field method with high symmetries of surface diffusional anisotropy. The analysis emphasizes on islands migrating in the {100} and {111} planes of the face-centered-cubic crystal, which resembles fourfold and sixfold symmetries, respectively. The numerical results intend to elaborate on the role of conductivity contrast between the island and the matrix and the misorientation of the fast diffusion direction with respect to the applied electric field on the morphological evolution. Based on numerical results, a morphological diagram is constructed in the plane of misorientation angle and conductivity contrast delineating a rich variety of morphologies, which includes steady-state, time-periodic, zigzag oscillations, and island breakup. While the shape of the island is primarily dictated by the conductivity contrast, the migration modes depend on the misorientation. The various migration modes are further distinguished based on the shape of the island such as a faceted wedge or seahorse morphology, an oscillatory characteristic such as standing wave or traveling wave time-periodic oscillations, and different breakup features. The steady-state kinetics obtained from the fourfold and sixfold symmetries are critically compared with the twofold symmetry, isotropic analytical, and numerical findings. Our result suggests that the steady-state velocity decreases with the symmetry fold of the island. Furthermore, the influence of variation in conductivity contrast and misorientation on kinetics in the time-periodic oscillations are discussed. Finally, the numerically obtained stable facets are compared with the analytically derived orientations. The observed results have direct repercussions in terms of the fabrication of nanopatterns and the performance of thin-film interconnects.
Unidirectional current-driven toron motion in a cylindrical nanowire
Authors: Hu Qiyang , Lyu Boyao , Tang Jin , Kong Lingyao , Du Haifeng , Wang Weiwei
Published: January 2021

A magnetic toron is a spatially localized three-dimensional spin texture composed of skyrmionic layers with two Bloch points at its two ends. The magnetic toron can, thus, be stabilized in chiral magnets using external fields. In this work, we studied the toron dynamics induced by electric currents in a cylindrical nanowire using micromagnetic simulations. We show that the toron performs a unidirectional motion in a nanowire where the current is applied along the wire direction. The current-induced toron motion can be divided into three regions: static region for a small current due to the pinning effect, toron moving region for a large current, and toron annihilation region for a large reversal current. Moreover, the moving direction can be tuned by the sign of Dzyaloshinskii–Moriya interaction. Such peculiar dynamics indicates that the magnetic toron is a possible candidate as an information carrier.
Volume compression of period 4 elements: Zn, Ge, As, and Se above 200 GPa: Ordering of atomic volume by atomic number
Authors: Akahama Y. , Kamiue K. , Okawa N. , Kawaguchi S. , Hirao N. , Ohishi Y.
Published: January 2021

X-ray diffraction measurements of period 4 elements, including Zn, Ge, As, and Se, were extended up to pressures of 251, 249, 250, and 317 GPa, respectively, and the structural phase transitions were investigated. The hcp phase of Zn was stable up to 251 GPa, while a decrease in the optical reflectance of the sample above 50 GPa suggests a change in the electronic structure, such as a semimetallic transition. Ge transformed from the Cmca phase to the hcp phase with a volume reduction (−ΔV) of approximately 1% at 180 GPa. In the stable region of the Cmca phase, the hcp phase, which has a larger atomic volume than the Cmca phase, coexisted with the Cmca phase, and both atomic volumes reversed at approximately 180 GPa. For As, the monoclinic host–guest phase transformed to the bcc phase with −ΔV = 2.6% at 126 GPa. The β-Po-type phase of Se transformed to the bcc phase with −ΔV = 1.9% at 140 GPa, and the bcc phase was stable up to 317 GPa although a bcc–fcc phase transition was theoretically predicted. The equations of state of the monatomic metallic high-pressure phases were determined. The atomic volume of the monatomic metallic phases for period 4 elements increased with increasing atomic number, and the systematicity reported for period 5 elements was observed. Moreover, in the monatomic metallic phases of typical group 12–17 elements for periods 4 and 5, the atomic volume is ordered with increasing atomic number above 200 GPa.
Topology of the warm plasma dispersion relation at the second harmonic electron cyclotron resonance layer
Authors: Joostens P. L. , Westerhof E.
Published: January 2021

The warm plasma dispersion relation, for waves in the electron cyclotron resonance range of frequencies, can be cast into the form of a bi-quadratic equation for N⊥, where the coefficients are a function of N⊥2 and an iterative procedure is required to obtain a solution. However, this iterative procedure is not well understood and fails to converge toward a solution at the second harmonic resonance layer, in particular at higher densities where the wave can couple to an electron Bernstein wave. This paper focuses on a solution to the poor convergence of the iterative method, enabling determination of the topology of the dispersion relation around the second harmonic using a fully relativistic code for oblique waves. A feed-forward controller is proposed with the ability to adjust the rotation of a step of N⊥2 within the complex plane, while also limiting the step-size. It is shown that implementation of the controller stabilizes unstable solutions, while improving overall robustness of the iteration. This allows the evaluation of the coupling between the fast extraordinary mode and electron Bernstein waves at the second harmonic electron cyclotron resonance layer, for non-perpendicularly propagating waves.
Strain-induced cooling-heating switching of anisotropic magneto-Peltier effect
Authors: Hirai Takamasa , Sepehri-Amin Hossein , Hasegawa Kento , Koyama Tomohiro , Iguchi Ryo , Ohkubo Tadakatsu , Chiba Daichi , Uchida Ken-ichi
Published: January 2021

Uniaxial-strain-induced switching between cooling and heating generated by the anisotropic magneto-Peltier effect (AMPE) is demonstrated using a Ni thin film deposited on an organic flexible substrate, where 1%-order strain can be introduced by stretching the substrate. By means of the lock-in thermography technique, we observed the reversible sign reversal of the AMPE-induced temperature modulation when the inverse magnetostrictive effect in the Ni layer changes its magnetization direction. Our demonstration would pave the way for realizing the active and versatile thermal management based on spin caloritronics.
Broadening of the optical absorption spectra in ZnO nanowires induced by mixed-phase MgxZn1−xO shells
Authors: Xue Z. X. , Qu Y. , Zan Y. H. , Ban S. L.
Published: January 2021

When MgZnO serves as the shell to passivate a ZnO nanowire, the proportion of Mg is usually small to avoid the unexpected spectrum from the wurtzite to rock salt transformation. Using the effective mass approximation, we investigate the impact of a mixed-phase MgxZn1−xO shell on the optical absorption spectra in ZnO nanowires. The results show that the dual absorption peaks from the coexisting two sets of band offset tend to appear as an intrinsic line broadening. This is because the spacing of dual peaks is small and even less than the full width at half maximum to be distinguished. The dual peaks get closer by increasing x or core size since the energy levels become less insensitive to the difference of the potentials. Enhanced confinement of an electron from higher x and smaller core size induces not only a blueshift and a slower saturation but also a sharper peak. The above two aspects make the dual peaks appear always as a broadening in inter-band V1–C1 transitions, while only appear as a broadening in inter-subband C1–C2 transitions when the core radius gets larger than the critical value for a certain x. The broadening from the mixed-phase MgZnO-coated ZnO nanowire could be restricted by increasing the core size or the proportion of Mg in the shell.
Nonexistence of invariant tori transverse to foliations: An application of converse KAM theory
Authors: Duignan Nathan , Meiss James D.
Published: January 2021

Invariant manifolds are of fundamental importance to the qualitative understanding of dynamical systems. In this work, we explore and extend MacKay’s converse Kolmogorov–Arnol’d–Moser condition to obtain a sufficient condition for the nonexistence of invariant surfaces that are transverse to a chosen 1D foliation. We show how useful foliations can be constructed from approximate integrals of the system. This theory is implemented numerically for two models: a particle in a two-wave potential and a Beltrami flow studied by Zaslavsky (Q-flows). These are both 3D volume-preserving flows, and they exemplify the dynamics seen in time-dependent Hamiltonian systems and incompressible fluids, respectively. Through both numerical and theoretical considerations, it is revealed how to choose foliations that capture the nonexistence of invariant tori with varying homologies.
A key bidirectional switching issue in optogenetics emulated with laser dyes to illustrate its mitigation using nonlinear optical tools
Authors: Wang Yisen , Goun Alexei , Laforge Francois , Quine Zachary , Rabitz Herschel
Published: January 2021

Conventionally, bidirectional optogenetic switches are controlled with linear excitation (e.g., monochromatic CW light), which has serious limitations when there is a spectral overlap between the “on” and “off” states of the switch. The spectral crosstalk lowers the selectivity of the photoactivation step, resulting in a moderate photoequilibrium value and a poor dynamic range for the switch. Using stimulated depletion quenching (SDQ), which is a nonlinear optical strategy similar to STED, we demonstrate enhanced photoactivation selectivity on one side of the switch, thus shifting the photoequilibrium beyond what is achievable with CW light. The discussion is built around Cph8 as a prototypical bidirectional optogenetic switch lacking complete photoreversibility upon CW excitation because of the spectral crosstalk. We use two fluorescent dyes as analogues to emulate the key spectral feature of the on and off states of Cph8; in this way, we focus on the initial photoactivation step and abstract from the complicated subsequent dynamics. By applying SDQ to a mixture of the dyes, we enhance the selectivity of the photoactivation beyond the linear regime. Increased selectivity of the photoactivation step via nonlinear optical techniques should translate into an improved dynamic range for a broad variety of bidirectional switches. These experiments provide a basis to further expand the foundations for non-conventional optical control methods of biological switching.
Transmission electron microscopy analysis of reduction reactions and phase transformations in Nb2O5 films deposited by atomic layer deposition
Authors: Twigg M. E. , Kozen A. C. , Ruppalt L. B. , Prokes S. M. , Cho H. S.
Published: January 2021

Amorphous films of Nb2O5 composition were deposited by thermal atomic layer deposition on (001) Si substrates and subsequently crystallized by annealing in forming gas at temperatures ranging from 550 °C to 1000 °C. After subjecting these films to an 850 °C anneal, cross-sectional transmission electron microscopy revealed the presence of B-Nb2O5 and T-Nb2O5 phases in the matrix, as well as reduced R-NbO2 in floret-shaped regions. Annealing at 1000 °C completed the reduction process, resulting in the insulator-to-metal transition (IMT) capable T-NbO2 phase throughout the film. ALD films of composition Nb2O5 were also deposited on electron-transparent SiN membranes and then subjected to 550 °C and 1000 °C anneals. Here, the 550 °C anneal induced the B-Nb2O5 and T-Nb2O5 phases without inducing the R-NbO2 phase. The 1000 °C anneal of the films deposited on SiN membranes retained B-Nb2O5 while inducing the R-NbO2 phase, but without bringing the process to completion and inducing the T-NbO2 phase. The effectiveness of the 1000 °C reducing annealing treatment to induce the T-NbO2 phase for Nb2O5 films deposited on (001) Si substrates, while stopping short of this transition for films deposited on SiN membranes, suggests the importance of the SiO2 layer on the Si substrate in contributing to the reduction reaction that results in the technologically important insulator-to-metal transition (IMT)-capable T-NbO2 phase.
Defect-mediated domain-wall motion and enhanced electric-field-induced strain in hot-pressed K0.5Na0.5NbO3 lead-free piezoelectric ceramics
Authors: Liu Yi-Xuan , Thong Hao-Cheng , Cheng Yue-Yu-Shan , Li Jia-Wang , Wang Ke
Published: January 2021

Since the extrinsic contribution is the key to electric-field-induced strain in ferroelectrics, engineering the interaction between defect and domain-wall motion has been an effective approach for enhancing the strain performance. While acceptor doping has been frequently employed in the lead-free (K, Na)NbO3 (KNN) system, the individual influence of intrinsic defects is still ill-understood. In this work, pure KNN ceramics with various concentrations of intrinsic defects were prepared by hot-pressing at different temperatures. Meanwhile, the microstructure, electrical properties, and defect chemistry were systematically investigated. An enhanced normalized strain d33* of 320 pm/V with good temperature stability was obtained in the KNN sample hot-pressed at 1000 °C, which is two times larger than that of reported normally sintered KNN. Besides, an asymmetric bipolar strain was found accompanied by the presence of offset polarization. The phenomena can be explained by a qualitative model involving unswitchable domains and intrinsic defects. The present study could enable further understanding of defect engineering and demonstrate a possible manipulation of intrinsic defects to enhance the strain performance of KNN-based piezoceramics.
Site control of quantum emitters in gallium nitride by polarity
Authors: Nguyen Minh Anh Phan , Hite Jennifer , Mastro Michael A. , Kianinia Mehran , Toth Milos , Aharonovich Igor
Published: January 2021

Gallium nitride (GaN) is a promising platform for integrated nanophotonic circuitry due to highly versatile growth protocols for the material. With the discovery of quantum emitters hosted by its lattice, potential applications of GaN have expanded to quantum-based technologies, despite the fact that the atomic structures of the emitters are unknown. Thus, we investigate the nature of quantum emitters grown in various samples of differing growth orientations—namely, Ga-polar, N-polar, and a combination of the two in an alternating periodic pattern. We showcase the unique growth technique used to fabricate these samples and characterize the emitters that form as a result. Through measurements of photoluminescence, cathodoluminescence, and Raman spectroscopy, we observe consistent formation of quantum emitters within Ga-polar regions of the grown GaN, attributed to overall defectivity caused by the specific growth procedure used to synthesize Ga-polar GaN. Our findings shed light onto the origins of the quantum emitters and are used to demonstrate site-selective formation of the emitters in GaN.
Polyamorphism in a solute-lean Al–Ce metallic glass
Authors: Yin Ziliang , Lou Hongbo , Sheng Hongwei , Zeng Zhidan , Mao Wendy L. , Zeng Qiaoshi
Published: January 2021

Polyamorphism discovered in lanthanide-rich metallic glasses (MGs) has been attributed to the electronic transition of the lanthanide element as a solvent element. In this work, we report that pressure-induced polyamorphism still exists in a Ce-poor Al93Ce7 binary MG where the 4f electron element serves as a solute and solute–solute avoidance is expected. The polyamorphic transition, observed by in situ high-pressure synchrotron x-ray diffraction, is accompanied by a volume collapse of ∼0.78% and occurs over a narrow pressure range from ∼0.8 to ∼1.8 GPa. Further synchrotron Ce L3-edge x-ray absorption spectroscopy measurements reveal that pressure-induced 4f electron delocalization underlies the polyamorphic transition. Molecular dynamics simulations confirm that the Ce atoms in the MG are completely isolated by the solvent Al atoms. This result demonstrates that 4f element-bearing alloys with extremely dilute concentrations can also exhibit polyamorphic states originating from electronic transitions, extending the compositional space of polyamorphism of MGs into very dilute regions. Our work suggests that tunable properties under compressive stress could be achieved in MGs by even minor doping of elements prone to electronic transitions.