bluuebunny/crossref_metadata_2025 huggingface dataset:
Photoredox-Enabled Decarboxylative Synthesis of Unnatural α-Amino Acids
Authors: Kärkäs Markus D. , Shatskiy Andrey
Published: May 2021

Recently, development of general synthetic routes to unnatural α-amino acids has gained significant momentum, driven by the high demand for such building blocks in fundamental research within molecular and structural biology, as well as for development of new pharmaceuticals. Herein, we highlight the recent progress in employing photoredox-mediated synthetic methods for accessing unnatural α-amino acids with a focus on various decarboxylative radical-based strategies.
Cyanide Anions as Nucleophilic Catalysts in Organic Synthesis
Authors: Christoffers Jens , Kieslich David
Published: May 2021

The nucleophilic addition of a cyanide anion to a carbonyl group is the basis for several cyanide-catalyzed organic reactions, which are summarized in this review. Since cyanide is also a good leaving group, it is an excellent catalyst for transacylation reactions. As an electron-withdrawing group, it also stabilizes a negative charge in its α-position, thus allowing the umpolung of aldehydes to formyl anion equivalents. The two leading examples are the benzoin condensation and the Michael–Stetter reaction furnishing α-hydroxy ketones and 1,4-dicarbonyl compounds, which are both catalyzed by cyanides. The review also covers variants like the silyl-benzoin coupling, the aldimine coupling and the imino-Stetter reaction. Moreover, some cyanide-catalyzed heterocyclic syntheses are reviewed.

1 Introduction

2 Nucleophilic Additions

2.1 Cyanohydrin Formation

2.2 Corey–Gilman–Ganem and Related Oxidation Reactions

2.3 Conjugate Addition

2.4 Intramolecular Carbocyanation

3 Transacylation Reactions

3.1 Ester Hydrolysis and Transesterification

3.2 Formation of Amides

3.3 Ketones from Esters

3.4 Esters from Ketones

4 Transformations Involving an Umpolung

4.1 Benzoin Condensation

4.2 Aldimine Coupling

4.3 Michael–Stetter Reaction

4.4 Imino-Stetter Reaction

5 Formation of Heterocycles

5.1 Oxazolines from Isocyanoacetates

5.2 Imidazoles from TosMIC via Oxazolines

5.3 Bargellini Reaction

6 Conclusion
Endoscopistsʼ diagnostic accuracy in detecting upper gastrointestinal neoplasia in the framework of artificial intelligence studies
Authors: Frazzoni Leonardo , Antonelli Giulio , Arribas Julia , Libanio Diogo , Ebigbo Alanna , van der Sommen Fons , de Groof Albert Jeroen , Fukuda Hiromu , Ohmori Masayasu , Ishihara Ryu , Wu Lianlian , Yu Honggang , Mori Yuichi , Repici Alessandro , Bergman Jacques J. G. H. M. , Sharma Prateek , Messmann Helmut , Hassan Cesare , Fuccio Lorenzo , Dinis-Ribeiro Mário
Published: May 2021

Background Estimates on miss rates for upper gastrointestinal neoplasia (UGIN) rely on registry data or old studies. Quality assurance programs for upper GI endoscopy are not fully established owing to the lack of infrastructure to measure endoscopists’ competence. We aimed to assess endoscopists’ accuracy for the recognition of UGIN exploiting the framework of artificial intelligence (AI) validation studies.

Methods Literature searches of databases (PubMed/MEDLINE, EMBASE, Scopus) up to August 2020 were performed to identify articles evaluating the accuracy of individual endoscopists for the recognition of UGIN within studies validating AI against a histologically verified expert-annotated ground-truth. The main outcomes were endoscopists’ pooled sensitivity, specificity, positive and negative predictive value (PPV/NPV), and area under the curve (AUC) for all UGIN, for esophageal squamous cell neoplasia (ESCN), Barrett esophagus-related neoplasia (BERN), and gastric adenocarcinoma (GAC).

Results Seven studies (2 ESCN, 3 BERN, 1 GAC, 1 UGIN overall) with 122 endoscopists were included. The pooled endoscopists’ sensitivity and specificity for UGIN were 82 % (95 % confidence interval [CI] 80 %–84 %) and 79 % (95 %CI 76 %–81 %), respectively. Endoscopists’ accuracy was higher for GAC detection (AUC 0.95 [95 %CI 0.93–0.98]) than for ESCN (AUC 0.90 [95 %CI 0.88–0.92]) and BERN detection (AUC 0.86 [95 %CI 0.84–0.88]). Sensitivity was higher for Eastern vs. Western endoscopists (87 % [95 %CI 84 %–89 %] vs. 75 % [95 %CI 72 %–78 %]), and for expert vs. non-expert endoscopists (85 % [95 %CI 83 %–87 %] vs. 71 % [95 %CI 67 %–75 %]).

Conclusion We show suboptimal accuracy of endoscopists for the recognition of UGIN even within a framework that included a higher prevalence and disease awareness. Future AI validation studies represent a framework to assess endoscopist competence.
Quadratic relations of the deformed W-superalgebra Wq,t(sl(2|1))
Authors: Kojima Takeo
Published: May 2021

We revisit the free field construction of the deformed W-superalgebras Wq,t(sl(2|1)) by Ding and Feigin, Contemp. Math. 248, 83–108 (1998), where the basic W-current and screening currents have been found. In this paper, we introduce higher W-currents and obtain a closed set of quadratic relations among them. These relations are independent of the choice of Dynkin diagrams for the superalgebra sl(2|1), although the screening currents are not. This allows us to define Wq,t(sl(2|1)) by generators and relations.
Laser absorption measurements of electron density in nanosecond-scale atmospheric pressure pulsed plasmas
Authors: Yong T. , Abdalla A. I. , Cappelli M. A.
Published: May 2021

We report on time-resolved measurements of electron number density by continuous-wave laser absorption in a low-energy nanosecond-scale laser-produced spark in atmospheric pressure air. Laser absorption is a result of free-free and bound-free electron excitation, with the absorption coefficient modeled and evaluated using estimates of the time-variation in electron temperature and probe laser absorption path length. Plasma electron number densities are determined to be as high as ne=7×1019 cm−3 and decay to 1/e of their peak values over a period of about 50 ns following plasma formation using a 20 mJ, 10 ns pulse width frequency-doubled Nd:YAG laser. The measured plasma densities at later times are shown to be in reasonable agreement with Stark broadening measurements of the 3s[5So]-3p[5P] electronic transition in atomic oxygen at 777 nm. This study provides support for the use of such continuous wave laser absorption for time resolved electron density measurements in low energy spark discharges in air, provided that an estimate of the electron temperature and laser path length can be made by accompanying diagnostics.
A semiconductor physics based model for thermal characteristics in electronic electrolytic energy storage devices
Authors: Yamada Hidenori , Yamada Toshishige
Published: May 2021

A model for ultracapacitor capacitance and ion screening length based on semiconductor physics is presented in this paper. Screening length is related to capacitance as the plate-plate separation in a double-layer, and thus both are related to dissolved ion density in the electrolyte. Furthermore, this dissolved ion density can be expressed in terms of an effective bandgap assigned to the electrolyte/solvent pair. Therefore, by knowing the effective bandgap, we can explain the published experimental measurements of the dependence of capacitance and screening length on temperature. For electrolytes commonly used in ultracapacitor applications, the effective bandgap is estimated to be on the order of a few 100 meV.
Decay and subluminality of modes of all wave numbers in the relativistic dynamics of viscous and heat conductive fluids
Authors: Freistühler Heinrich , Reintjes Moritz , Temple Blake
Published: May 2021

To further confirm the causality and stability of a second-order hyperbolic system of partial differential equations that models the relativistic dynamics of barotropic fluids with viscosity and heat conduction [H. Freistühler and B. Temple, J. Math. Phys. 59, 063101 (2018)], this paper studies the Fourier–Laplace modes of this system and shows that all such modes, relative to arbitrary Lorentz frames, (a) decay with increasing time and (b) travel at subluminal speeds. Stability is also shown for the related model of non-barotropic fluids [H. Freistühler and B. Temple, Proc. R. Soc. A 470, 20140055 (2014) and H. Freistühler and B. Temple, Proc. R. Soc. A 473, 20160729 (2017)]. Even though these properties had been known for a while in the sense of numerical evidence, the fully analytical proofs for the subluminality of modes of arbitrary wave numbers in arbitrary frames given here appear to be the first regarding any four-field formulation of dissipative relativistic fluid dynamics.
Modulation theory for pattern forming systems with a spatial 1:2-resonance
Authors: Gauß Nicole , Schneider Guido , Ali Sunny Danish , Zimmermann Dominik
Published: May 2021

It is the purpose of this paper to justify the use of modulation equations for pattern forming systems in the case of multiple Turing instabilities with critical wave numbers having a ratio 1:2 by proving approximation results, presenting attractivity results, and discussing the existence of modulating fronts.
Two-brightness-amplifier imaging system for energetic-materials-combustion study
Authors: Gubarev F. A. , Moldabekov A. S. , Mostovshchikov A. V. , Li L.
Published: May 2021

This paper discusses a laser monitor with two channels for acquiring images synchronized in time and its use for visualizing the surface of metal nanopowders during combustion. Each channel is an independent optical system based on a copper bromide vapor brightness amplifier and a high-speed camera that allows visualizing a specified area of the sample. Thus, the laser monitor allows real-time imaging of the same sample area with different spatial resolutions and simultaneously two areas of the sample. In comparison with the “master oscillator–power amplifier” system and a bistatic laser monitor in the proposed system, the radiation pulses of the brightness amplifiers are synchronized in such a way that the inversion in the active media is formed at different time intervals. Such a system makes it possible to register processes in one area of the sample in the mode of double frames with a time shift of 35 ns. As an additional option in the proposed system, it is possible to implement a laser illumination mode in which an additional camera is used with a narrow-band filter installed on it for the emission wavelength of brightness amplifiers, and the same radiation from the brightness amplifier is used as an illuminating light source. The proposed technique was used to visualize the combustion of aluminum nanopowders without additives in real time in the area of laser initiation with different spatial resolutions and nanoAl + microAl + microFe powder mixtures in the laser ignition area and the adjacent area of the sample simultaneously as the combustion wave propagates.
Edge turbulent transport toward the L–H transition in ASDEX Upgrade and JET-ILW
Authors: Bonanomi N. , Angioni C. , Plank U. , Schneider P. A. , Maggi C. F. ,   ASDEX Upgrade Team,   EUROFusion MST1 Team,,   JET Contributors
Published: May 2021

This work combines experimental observations from the ASDEX Upgrade and the JET-ILW tokamaks and related gyrokinetic simulations on the L-mode edge turbulence with different isotopes. The evolution of the edge logarithmic gradients and the edge radial electric field with increasing input power and the correlation between the two are studied. It is found that the edge ion temperature profile plays the dominant role in the evolution of the edge radial electric field in the considered cases. More input power and ion heat flux are needed in hydrogen to obtain values of Ti and R/LTi similar to the ones observed in deuterium. As a consequence, more power is needed in hydrogen to develop values of the edge radial electric field similar to those in deuterium plasmas. These observations point to a key role of the dependence of the edge turbulence on the main ion mass in determining the different L–H power thresholds with different isotopes. This dependence is found in gyrokinetic simulations to be connected to the parallel electron dynamics, i.e., to a different kinetic response of passing electrons with different main ion mass. The gyrokinetic simulations indicate different roles of R/LTe, R/LTi, and R/Ln in driving or stabilizing the edge turbulence at different wavelengths and indicate a strong role of the external flow shear in stabilizing the edge turbulence. The simulations indicate also that instabilities at finite values of kx play an important role in edge conditions.
Predicting operational windows of ELMs suppression by resonant magnetic perturbations in the DIII-D and KSTAR tokamaks
Authors: Hu Q. M. , Nazikian R. , Logan N. C. , Park J.-K. , Paz-Soldan C. , Yang S. M. , Grierson B. A. , In Y. , Jeon Y. M. , Kim M. , Kim S. K. , Orlov D. M. , Park G. Y. , Yu Q.
Published: May 2021

A newly developed plasma response model, combining the nonlinear two-fluid MHD code TM1 and toroidal MHD code GPEC run in ideal mode, quantitatively predicts the narrow isolated q95 windows (Δq95 ∼ 0.1) of edge-localized mode (ELM) suppression by n = 1, 2, and 3 resonant magnetic perturbations (RMPs) in both DIII-D and KSTAR tokamaks across a wide range of plasma parameters. The key physics that unites both experimental observations and our simulations is the close alignment of essential resonant q-surfaces and the location of the top of the pedestal prior to an ELM. This alignment permits an applied RMP to produce field penetration due to the lower E × B rotation at the pedestal top rather than being screened. The model successfully predicts that narrow magnetic islands form when resonant field penetration occurs at the top of pedestal, and these islands are easily screened when q95 moves off resonance, leading to very narrow windows of ELM suppression (typically Δq95 ∼ 0.1). Furthermore, the observed reduction in the pedestal height is also well captured by the calculated classical collisional transport across the island. We recover observed q95, βN and plasma shape dependence of ELM suppression due to the effect of magnetic islands on pedestal transport and peeling-ballooning-mode stability. Importantly, experiments do occasionally observe wide windows of ELM suppression (Δq95 > 0.5). Our model reveals that at low pedestal-top density multiple islands open, leading to wide operational windows of ELM suppression consistent with experiment. The model indicates that wide q95 windows of ELM suppression can be achieved at substantially higher pedestal pressure with less confinement degradation in DIII-D by operating at higher toroidal mode number (n = 4) RMPs. This can have significant implications for the operation of the ITER ELM control coils for maintaining high confinement together with ELM suppression.
Effect of multibanded magnetic field on convective heat transport in linearly heated porous systems filled with hybrid nanofluid
Authors: Manna Nirmal K. , Mondal Chitrak , Biswas Nirmalendu , Sarkar U. K. , Öztop Hakan F. , Abu-Hamdeh Nidal H.
Published: May 2021

The paper attempts to enhance the control of convective transport phenomena in magnetothermal devices applying a technique of multibanded magnetic field. For this demonstration, a typical cavity-like thermal system is considered involving linear heating, porous substance, hybrid nanofluid, and magnetic field. Four identical bands of magnetic fields are applied horizontally with uniform inactive zones between the bands. The transport equations of the coupled multiphysics evolving from the thermal buoyancy (due to linear heating at one sidewall and isothermal cooling at the opposite sidewall), filled porous medium, spatially intermittently active magnetic fields, and the engineered working fluid of Cu–Al2O3/water hybrid nanofluid are solved by an indigenously developed computing code. The study is conducted using the pertinent dimensionless parameters for the following ranges: Darcy–Rayleigh number (Ram = 1–104), Darcy number (Da = 10−5 − 10−1), Hartmann number (Ha = 0–70), and concentration of hybrid nanoparticles ϕ (= 0–2%). The convective phenomena are analyzed using the heatlines (for heat transport), streamlines (flow pattern), isotherms (static temperature), and the average Nusselt number (for heat transfer). The outcomes of this technique of multibanded magnetic field are rigorously compared with other established application methods of magnetic fields. It establishes different local behaviors along with an improved heat transfer. Heatline visualization reveals the definite portraits of heat flow paths depending upon parametric values. Furthermore, the presence of linear heating is in particular treated to explore the insight of linear heating (that featuring multiple heating and cooling zones along with the linear heater), utilizing the local Nusselt number and heatlines. One of the important advantages of this new technique is it is more energy-efficient particularly for the square or shallow cavity. The multibanded magnetic field shows a promising technique for the control of convective transport phenomena involving coupled multiphysics used during sophisticated applications (such as materials processing, biomedical applications, etc.).
Numerical computation of the transport matrix in a tokamak plasma with electrostatic turbulence
Authors: Sun Shiqiao , Zhu Siqiang , Dai Zongliang , Wang Shaojie
Published: May 2021

Based on the phase-space nonlinear turbulent transport equation, a numerical code NDTM (Numerical Diagnosis of Transport Matrix) is developed to compute the transport matrix in a tokamak plasma with nonlinear electrostatic turbulence. The NDTM code can be used as a diagnostic tool for a nonlinear gyrokinetic turbulence simulation code, it obtains the transport matrix from the gyrocenter orbits in the fluctuating field found by the latter. As an application, we use the code to compute the ion transport matrix in a nonlinear ion-temperature-gradient-driven turbulence field found by the NLT code. The computed transport matrix indicates an inward thermal pinch driven by the density gradient and an inward particle pinch driven by the temperature gradient. The ion effective heat diffusivity and effective particle diffusivity are computed by the transport matrix; the numerical results agree well with NLT results.
Influence of thermalization protocol on Poiseuille flow of confined soft glass
Authors: Vaibhav Vinay , Chaudhuri Pinaki
Published: May 2021

Using extensive molecular dynamics simulations, we study how the Poiseuille flow of a model confined soft glass is determined by thermalization protocols. We contrast the steady-state behavior as well as the onset of flow, using two different thermostats, one where the confined glass is directly thermalized, whereas in the other case the glass is thermalized via the confining walls. The latter setup leads to a spatially non-uniform temperature profile within the channel, during flow, which allows for probing the rheological response of the confined glass under this additional perturbation and thereby investigate the deviations from bulk rheology. Finally, we also examine how this response depends upon varying the channel widths. Our study illustrates the competing effects due to the stress gradients, the intrinsic non-local correlations of glassy systems, and the presence or absence of thermal gradients.
Multi-replica biased sampling for photoswitchable π-conjugated polymers
Authors: Fortino Mariagrazia , Cozza Concetta , Bonomi Massimiliano , Pietropaolo Adriana
Published: May 2021

In recent years, π-conjugated polymers are attracting considerable interest in view of their light-dependent torsional reorganization around the π-conjugated backbone, which determines peculiar light-emitting properties. Motivated by the interest in designing conjugated polymers with tunable photoswitchable pathways, we devised a computational framework to enhance the sampling of the torsional conformational space and, at the same time, estimate ground- to excited-state free-energy differences. This scheme is based on a combination of Hamiltonian Replica Exchange Method (REM), parallel bias metadynamics, and free-energy perturbation theory. In our scheme, each REM samples an intermediate unphysical state between the ground and the first two excited states, which are characterized by time-dependent density functional theory simulations at the B3LYP/6-31G* level of theory. We applied the method to a 5-mer of 9,9-dioctylfluorene and found that upon irradiation, this system can undergo a dihedral inversion from −155° to 155°, crossing a barrier that decreases from 0.1 eV in the ground state (S0) to 0.05 eV and 0.04 eV in the first (S1) and second (S2) excited states. Furthermore, S1 and even more S2 were predicted to stabilize coplanar dihedrals, with a local free-energy minimum located at ±44°. The presence of a free-energy barrier of 0.08 eV for the S1 state and 0.12 eV for the S2 state can trap this conformation in a basin far from the global free-energy minimum located at 155°. The simulation results were compared with the experimental emission spectrum, showing a quantitative agreement with the predictions provided by our framework.
The role of tension–compression asymmetrical microcrack evolution in the ignition of polymer-bonded explosives under low-velocity impact
Authors: Liu Rui , Wang Xin-Jie , Chen Peng-Wan , Kang Ge , Zhu Shun-Peng , Guo Yan-Song
Published: May 2021

The influence of microcrack on the ignition of polymer-bonded explosives is missing a comprehensive description of the cracking microstructure characteristics. In this article, the mechanical–thermal–chemical response of octahydro-1,3,5,7-tetranitro-tetrazocine (HMX)-based polymer-bonded explosives (PBXs) under low-velocity impact is investigated by a dynamic damage viscoelastic model with tension–compression asymmetrical microcrack evolution and a friction-based hotspot formation mechanism. The microcrack evolution fully considers cracking nucleation and growth, where the nucleation depends on tension or compression condition and the growth follows the law of the energy-release rate. The simulation concerns the mechanical and ignition response of HMX-based PBX in the Steven test. The cracking formation from tension or compression is captured, and the damage morphology is well simulated. The simulation on the ignition response reveals the effect of the cracking microstructure characteristics, including the initial microcrack density number and the tension–compression asymmetrical nucleation rate. In addition, heterogeneous microcrack density number is constructed by unimodal normal distribution and bimodal normal distribution, corresponding to pristine and damaged scenarios, respectively. The uncertainties in the microcrack density number are propagated and quantities in the mechanical–thermal–chemical-coupled model and further, the effect on the ignition, are obtained.
Effect of crystallinity on the performance of AlN-based resistive random access memory using rapid thermal annealing
Authors: Shen Xuping , Gao Haixia , Duan Yiwei , Sun Yuxin , Guo Jingshu , Yu Zhenxi , Wu Shuliang , Ma Xiaohua , Yang Yintang
Published: May 2021

This Letter studies the effect of crystallinity on the performance of AlN-based resistive random access memory using rapid thermal annealing. We compared I–V characters of devices fabricated at different annealing temperatures. By increasing the crystallinity of an AlN film, switching voltages and the memory window increase. Meanwhile, the reliability of the device improves. It is found that the electron conduction mechanism fits in with the space-charge-limited conduction model. Based on the above phenomena, we purpose that the crystallization leads to a decrease in vacancies within the AlN film, while it enhances local effects of grain boundaries on the electron transport. Both of these conclusions can result in an increase in switching voltages and the memory window. This paper can provide a platform for further studies on improving the performance of AlN-based devices.
First-principles study of benzo[a]pyrene-7,8-dione and DNA adducts
Authors: Liu Yue , Ren Xinguo , He Lixin
Published: May 2021

Polycyclic aromatic hydrocarbons (PAHs) are widely distributed in environments, and some of them are causative agents of human cancer. Previous studies concluded that benzo[a]pyrene-7,8-dione (BPQ), which is one kind of carcinogenic PAH metabolites, forms covalently bonded adducts with DNA, and the major adduct formed is a deoxyguanosine adduct. In this work, we investigate the interactions between BPQ and DNA molecules via first-principles calculations. We identify six possible DNA adducts with BPQ. In addition to the four adducts forming covalent bonds, there are two adducts bound purely by van der Waals (vdW) interactions. Remarkably, the two vdW-bound adducts have comparable, if not larger, binding energies as the covalent adducts. The results may help us gain more understanding of the interactions between PAH metabolites and DNA.
Acoustic metamaterials
Authors: Li Jensen , Wen Xinhua , Sheng Ping
Published: May 2021

Waves are generally characterized by angular frequency ω and wavevector k. Accordingly, this tutorial is structured into two parts, one on resonance-based acoustic metamaterials, in the frequency domain, and one on topological acoustics, based on the wavevector domain as topological structures inherently involve spatial configurations that are a step beyond the simple periodic lattices. Each part will begin with a brief introduction of the basic principles, followed by two examples described in detail. In the first part, we present decorated membrane resonators and the broadband optimal acoustic absorption structures, the latter being crucial for the potential applications of acoustic metamaterials. In the second part, we discuss how to construct the Dirac cone, a special type of dispersion from either accidental degeneracy or symmetry protection, which can be shown to lead to negative, zero, or positive refractive indices. The shifting and gapping of these Dirac cones in the reciprocal space can result in effects on acoustic waves similar to that of a magnetic field on an electron. More generally, they lead to edge states resulting from a real-space gauge field as well as topological bandgaps.
Origin of high hardness and optoelectronic and thermo-physical properties of boron-rich compounds B6X (X = S, Se): A comprehensive study via DFT approach
Authors: Hossain M. M. , Ali M. A. , Uddin M. M. , Islam A. K. M. A. , Naqib S. H.
Published: May 2021

In the present study, the structural and hitherto uninvestigated mechanical (elastic stiffness constants, machinability index, Cauchy pressure, anisotropy indices, brittleness/ductility, Poisson's ratio), electronic, optical, and thermodynamic properties of novel boron-rich compounds B6X (X = S, Se) have been explored using density functional theory. The estimated structural lattice parameters were consistent with the prior report. The mechanical and dynamical stability of these compounds have been established theoretically. The materials are brittle in nature and elastically anisotropic. The value of fracture toughness, KIC for the B6S and B6Se, are ∼ 2.07 MPam0.5, evaluating the resistance to limit the crack propagation inside the materials. Both B6S and B6Se compounds possess high hardness values in the range of 31–35 GPa and have the potential to be prominent members of the class of hard compounds. Strong covalent bonding and sharp peak at low energy below the Fermi level confirmed by partial density of states (PDOS) resulted in the high hardness. The profile of band structure as well as density of states assesses the indirect semiconducting nature of the titled compounds. The comparatively high value of Debye temperature (ΘD), minimum thermal conductivity (Kmin), lattice thermal conductivity (kph), low thermal expansion coefficient, and low density suggest that both boron-rich chalcogenides might be used as thermal management materials. Large absorption capacities in the mid-ultraviolet region (3.2–15 eV) of the studied materials and low reflectivity (∼16%) are significantly noted. Such favorable features give promise to the compounds under investigation to be used in UV surface-disinfection devices as well as medical sterilizer equipment applications. Excellent correlations are found among all the studied physical properties of these compounds.
Reduction of MOS interfacial states between
β
-Ga2O3 and Al2O3 insulator by self-reaction etching with Ga flux
Authors: Feng Boyuan , He Tao , He Gaohang , Zhang Xiaodong , Wu Ying , Chen Xiao , Li Zhengcheng , Zhang Xinping , Jia Zhitai , Niu Gang , Guo Qixin , Zeng Zhongming , Ding Sunan
Published: May 2021

In this Letter, self-reaction etching (SRE) with Ga flux demonstrates the capability of eliminating surface contaminations and damage, as well as improving the electrical characteristics of the interface between monoclinic gallium oxide (β-Ga2O3) and the insulator. Compared to post-tetramethyl ammonium hydroxide wet chemical treatment, SRE is a low damage repair method that effectively removes surface contaminants introduced during previous inductively coupled plasma etching of β-Ga2O3 without surface damage. As a consequence, the surface band bending on the β-Ga2O3 surface decreased as demonstrated by the core-level peak shifts of x-ray photoemission spectroscopy, which indicated fewer negative charges remained on the surface. Furthermore, the interface state density (Dit) between β-Ga2O3 and an Al2O3 insulator was determined by using high-temperature conductance and photoassisted C–V measurements. The Dit dropped significantly for samples treated by SRE as compared with other treatments. These results suggested that SRE is an attractive etching candidate for future Ga2O3 power device fabrication.
Dissipation scaling and structural order in turbulent channel flows
Authors: Lee T.-W.
Published: May 2021

Scaling and structural evolutions are contemplated in a new perspective for turbulent channel flows. The total integrated turbulence kinetic energy and the total dissipation can be viewed as global constraints on the turbulence structure, leading to predictable, ordered scaling for u′2 and v′2 through its first and second gradients, respectively. This self-similarity allows for profile reconstructions at any Reynolds numbers based on a common template through simple multiplicative operations. Using these scaled variables in the Lagrangian transport equation derives the Reynolds shear stress, which in turn computes the mean velocity profile through the Reynolds-averaged Navier–Stokes equation. The dissipation scaling along with the transport equations renders succinct views of the turbulence dynamics and its structural characteristics. In this way, variable profiles can be analytically reconstructed, which bears potential implications toward solvability and computability of turbulent flows in canonical and other geometries.
Two-fluid model of rf current condensation in magnetic islands
Authors: Jin S. , Reiman A. H. , Fisch N. J.
Published: May 2021

The stabilization of tearing modes with rf waves is subject to a nonlinear effect, termed rf current condensation, that has the potential to greatly enhance and localize current driven within magnetic islands. Here we extend previous investigations of this effect with a two fluid model that captures the balance of diffusive and thermal equilibration processes within the island. We show that the effective power and resulting strength of the condensation effect can be greatly enhanced by avoiding collisional heat loss to the ions. The relative impact of collisions on the overall power balance within the island depends on the ratio of the characteristic diffusion timescale and the electron–ion equilibration time, rather than the latter alone. Although relative heat loss to ions increases with island size, the heating efficiency does as well. In particular, we show that the latter safely dominates for large deposition profiles, as is typically the case for lower hybrid current drive. This supports the possibility of passive stabilization of neoclassical tearing modes without the precise aiming of the rf waves required for electron cyclotron current drive stabilization.
Radiation-induced conductivity in polystyrene, a common insulating polymer with a hopping conduction
Authors: Tyutnev Andrey , Saenko Vladimir , Mullakhmetov Ilshat , Agapov Ilya
Published: May 2021

Radiation-induced conductivity (RIC) of polystyrene has been studied experimentally and numerically mostly in a small-signal regime in a broad time range from some nanoseconds to seconds. It has been established that hole transport is dispersive with a low value of the dispersion parameter α = 0.35. We have suggested a direct method of determination of the frequency factor of the Rose–Fowler–Vaisberg model, which has been parameterized using computer simulations by the trial and error method. The main outstanding concern is the application of the Onsager theory of geminate recombination concerning the field dependence of the free carrier yield and the possible frequency factor increase at high electric fields. The effect of hopping transport on the RIC in this common insulating polymer is still to be understood.
Overlapped and sequential metasurface modulations for Bi-Chromatic beams generation
Authors: Faenzi Marco , González-Ovejero David , Maci Stefano
Published: May 2021

This paper describes the generation of directive beams at two different frequencies with the same circular metasurface (MTS) antenna based on a surface wave (SW) excitation. Two methods are presented to achieve the desired bi-chromatic beam operation. The first one consists in mathematically superimposing two MTS modulations, each one matched to the SW wavelength at a different frequency. In the second method, the period of the MTS modulation matches the SW wavelengths at two different frequencies in two different regions of the antenna, i.e., close to the center for the high frequency band and close to the periphery for the low frequency band. The first method allows one to have different feed points for each beam in a self-diplexed structure, although it is also possible to use a single feed configuration and a diplexer. The second approach only holds for a single physical feed-point. Numerical and experimental results are shown.
Crystal Engineering of Sterically Shielded Hexa-
Authors: Reger David , Hampel Frank , Jux Norbert
Published: May 2021

The crystal structures of four pentakis-tert-butyl hexa-peri-hexabenzocoronenes (HBCs), each with an additional sixth substituent namely iodide, methoxy, formyl, and nitro, are presented. We show that the additional substituent has a significant impact on the packing in the solid state and the data obtained can be utilised for crystal engineering. By introducing an electron accepting substituent it was possible to achieve columnar arrangements that were previously unknown for such highly tert-butylated HBCs. In this way we provide insight into the aggregation behaviour of nanographenes with sterically highly shielded edges.
Impaired inhibitory GABAergic synaptic transmission and transcription studied in single neurons by Patch-seq in Huntington’s disease
Authors: Paraskevopoulou Foteini , Parvizi Poorya , Senger Gökçe , Tuncbag Nurcan , Rosenmund Christian , Yildirim Ferah
Published: May 2021

Significance

Although the genetic basis of HD is known, the molecular mechanisms underlying neuronal dysfunction remain unclear. Combining electrophysiological and transcriptional analyses of single neurons (Patch-sequencing [Patch-seq]), this study connects transcriptional dysregulation and synaptic transmission deficits, two key disease features, in HD. We identify a number of genes whose expression changes are correlated with physiological deficiencies in mutant Htt neurons. We validate the use of the Patch-seq system for screening and identifying potential therapeutic interventions. We show that pharmacological inhibition of an epigenetic regulator rectifies several functional, morphological, and transcriptional deficits in mutant neurons. This work suggests previously unknown gene–neuronal function relationships as potential targets in HD and also highlights advances in single-cell transcriptomics and their use in understanding human disease.
Immune evasion in HPV−head and neck precancer–cancer transition is driven by an aneuploid switch involving chromosome 9p loss
Authors: William William N. , Zhao Xin , Bianchi Joy J. , Lin Heather Y. , Cheng Pan , Lee J. Jack , Carter Hannah , Alexandrov Ludmil B. , Abraham Jim P. , Spetzler David B. , Dubinett Steven M. , Cleveland Don W. , Cavenee Webster , Davoli Teresa , Lippman Scott M.
Published: May 2021

Significance

We report somatic copy-number alterations (SCNAs) that contribute to an immune microenvironment switch during human papillomavirus-negative head and neck cancer (HNSC) development. Specific and nonspecific SCNA levels were examined in a large prospective oral precancer (188 patients) cohort, 2 HNSC (343, 196 patients) cohorts, and 32 cell lines. Chromosome 9p21.3 loss in precursor lesions, the genomic driver of malignant transition, was enhanced by cumulative 9p-arm gene-dosage decreases, cell-intrinsic senescence suppression, and extrinsic decreases in chemokine, cytokine, and NF-κB pathways. Furthermore, 9p-arm loss andJAK2-PD-L1codeletion were associated with PD-1 inhibitor resistance. These data reveal an oncogenic immune paradox, aneuploid checkpoint to neoplastic transformation, and immune interception and therapeutic strategies for HPV−HNSC and possibly other CN-driven tumors or diseases.
Density-independent plasmons for terahertz-stable topological metamaterials
Authors: Wang Jianfeng , Sui Xuelei , Duan Wenhui , Liu Feng , Huang Bing
Published: May 2021

Significance

Plasmons, collective electron density oscillations in metals or doped semiconductors, provide an efficient way to couple light and matter at subwavelength scales. Usually, plasmons are carrier density (
n
) dependent, which may cause unstable functionalities of plasmons, especially for cutting-edge terahertz technology. Here, we reveal a unified mechanism for generating unusual
n
-independent plasmons (DIPs), where terahertz DIPs can be excited in some low-dimensional topological semimetals. Stable terahertz spectroscopy from narrowband to broadband and even a quantization can be achieved in topological metamaterials. Our study not only broadens the concept of plasmons by combining with exotic topological states but also paves a way to designing a compact device for stable terahertz applications.
One-trial perceptual learning in the absence of conscious remembering and independent of the medial temporal lobe
Authors: Squire Larry R. , Frascino Jennifer C. , Rivera Charlotte S. , Heyworth Nadine C. , He Biyu J.
Published: May 2021

Significance

Studies of memory have established a distinction between ordinary recollection of the past (declarative memory), which depends on medial temporal lobe (MTL) structures and other (nondeclarative) forms of memory that are expressed through performance and depend on other brain systems. One phenomenon that has eluded classification is one-trial perceptual learning, whereby a degraded image of an object, which is difficult to identify, becomes recognizable after a single exposure to the original image. This effect was fully intact in memory-impaired patients with hippocampal or larger MTL lesions and persisted undiminished for more than 5 mo, despite impaired memory for the test format and the images themselves. Perceptual learning is MTL-independent (nondeclarative) and occurs without a requirement to consciously remember.
Distinct pacing profiles result in similar perceptual responses and neuromuscular fatigue development: Why different “roads” finish at the same line?
Authors: Azevedo Rafael de Almeida , Silva‐Cavalcante Marcos David , Cruz Ramon , Couto Patrícia , Lima‐Silva Adriano E. , Bertuzzi Romulo
Published: May 2021

The current study analysed the effect of distinct pacing profiles (i.e. U, J, and inverted J) in the perceptual responses and neuromuscular fatigue (NMF) development following a 4‐km cycling time trial (TT). Twenty‐one cyclists with similar training status were allocated into three different groups based on their pacing profile spontaneously adopted during TT. Rating of perceived exertion (RPE), oxygen uptake (⩒O2) and heart rate (HR) were continuously recorded. NMF was assessed by using isometric maximal voluntary contractions (IMVC), while the central [i.e. voluntary activation (VA)] and peripheral fatigue of knee extensors [i.e. peak torque of potentiated twitches (TwPt)] were evaluated using electrically evoked contractions performed pre and 2 min after the TT. TT performance was not different amongst pacing profiles (U = 377 ± 20 s; J = 392 ± 23 s; J‐i = 381 ± 20 s) (all P > 0.05). RPE, ⩒O2 and HR increased similarly throughout the TT regardless the pacing strategy (all P > 0.05). Similarly, IMVC (U = −9.9 ± 8.8; J = −9.6 ± 4.5%; J‐i = −13.8 ± 11.3%), VA (U = −2.3 ± 1.7%; J = −5.4 ± 2.2%; J‐i = −6.4 ± 4.5%) and TwPt (U = −32.5 ± 12.0%; J = −29.5 ± 8.0%; J‐i = −33.6 ± 13.6%) were similar amongst pacing profiles (all P > 0.05). Therefore, endurance athletes with similar training status showed the same perceived responses and NMF development regardless the pacing profile spontaneously adopted. It was suggested that these responses occurred in order to preserve a similar rate of change in systemic responses (i.e. RPE, ⩒O2 and HR) and NMF development, ultimately resulting in same TT performance.

Highlights

Different pacing profiles resulted in the same performance in a 4‐km cycling time trial.

The similar performance might be due to achievement of the same sensory tolerance limit.

There was no difference for perceptual, metabolic and neuromuscular fatigue responses.
Highly efficient second harmonic generation of thin film lithium niobate nanograting near bound states in the continuum
Authors: Huang Zhijin , Wang Mengjia , Li Yang , Shang Jumei , Li Ke , Qiu Wentao , Dong Jiangli , Guan Heyuan , Chen Zhe , Lu Huihui
Published: May 2021

Bound states in the continuum (BICs) are ubiquitous physical phenomena where such states occur due to strong coupling between leaky modes in side lossy systems. BICs in meta-optics and nanophotonics enable optical mode confinement to strengthen local field enhancement in nonlinear optics. In this study, we numerically investigate second-harmonic generation (SHG) in the vicinity of BICs with a photonic structure comprising one-dimensional nanogratings and a slab waveguide made of lithium niobate (LiNbO3, LN). By breaking the symmetry of LN nanogratings, BICs transition to quasi-BICs, which enable strong local field confinement inside LN slab waveguide to be supported, thereby resulting in improving SHG conversion with lower pump power of fundamental frequency (FW). With a peak intensity of 1.33 GW cm−2 at the FW, our structure features a second-harmonic conversion efficiency up to 8.13 × 10−5 at quasi-BICs. We believe that our results will facilitate the application of LN in integrated nonlinear nanophotonic.
Strong boundary and trap potential effects on emergent physics in ultra-cold fermionic gases
Authors: Hauck J B , Honerkamp C , Kennes D M
Published: May 2021

The field of quantum simulations in ultra-cold atomic gases has been remarkably successful. In principle it allows for an exact treatment of a variety of highly relevant lattice models and their emergent phases of matter. But so far there is a lack in the theoretical literature concerning the systematic study of the effects of the trap potential as well as the finite size of the systems, as numerical studies of such non periodic, correlated fermionic lattices models are numerically demanding beyond one dimension. We use the recently introduced real-space truncated unity functional renormalization group to study these boundary and trap effects with a focus on their impact on the superconducting phase of the 2D Hubbard model. We find that in the experiments not only lower temperatures need to be reached compared to current capabilities, but also system size and trap potential shape play a crucial role to simulate emergent phases of matter.
A Bayesian interpretation of inconsistency measures in cosmology
Authors: Lin Weikang , Ishak Mustapha
Published: May 2021

Measures of inconsistency and tension between datasets have become an essential part of cosmological analyses. It is important to accurately evaluate the significance of such tensions when present. We propose here a Bayesian interpretation of inconsistency measures that can extract information about physical inconsistencies in the presence of data scatter. This new framework is based on the conditional probability distribution of the level of physical inconsistency given the obtained value of the measure. We use the index of inconsistency as a case study to illustrate the new interpretation framework, but this can be generalized to other metrics. Importantly, there are two aspects in the quantification of inconsistency that behave differently as the number of model parameters increases. The first is the probability for the level of physical inconsistency to reach a threshold which drops with the increase of the number of parameters under consideration. The second is the actual level of physical inconsistency which remains rather insensitive to such an increase in parameters. The difference between these two aspects is often overlooked, which leads to a long-standing ambiguity: when a given inconsistency is found between two constraints, its “significance” seems to be lower when considered in a higher-dimensional parameter space. This ambiguity is resolved by the Bayesian interpretation we introduce in this work because the conditional probability distribution includes all the statistical information of the level of physical inconsistency. Finally, we apply the Bayesian interpretation to examine the (in)consistency between Planck versus the Cepheid-based local measurement, the Dark Energy Survey (DES), the Atacama Cosmology Telescope (ACT) and WMAP. We confirm and revisit the degrees of previous physical inconsistencies and show the stability of the new interpretation with respect to the number of cosmological parameters compared to the commonly used n-σ interpretation when applied to cosmological tensions in multi-parameter spaces.