bluuebunny/crossref_metadata_2025 huggingface dataset:
Converting lower temperature heat into energy
Authors: Lim Alane
Published: June 2021

Thermally regenerative electrochemical cycle systems may sustainably salvage much of the world’s wasted heat.
Linear embedding of nonlinear dynamical systems and prospects for efficient quantum algorithms
Authors: Engel Alexander , Smith Graeme , Parker Scott E.
Published: June 2021

The simulation of large nonlinear dynamical systems, including systems generated by discretization of hyperbolic partial differential equations, can be computationally demanding. Such systems are important in both fluid and kinetic computational plasma physics. This motivates exploring whether a future error-corrected quantum computer could perform these simulations more efficiently than any classical computer. We describe a method for mapping any finite nonlinear dynamical system to an infinite linear dynamical system (embedding) and detail three specific cases of this method that correspond to previously studied mappings. Then we explore an approach for approximating the resulting infinite linear system with finite linear systems (truncation). Using a number of qubits only logarithmic in the number of variables of the nonlinear system, a quantum computer could simulate truncated systems to approximate output quantities if the nonlinearity is sufficiently weak. Other aspects of the computational efficiency of the three detailed embedding strategies are also discussed.
Unidirectional transport of superparamagnetic beads and biological cells along oval magnetic elements
Authors: Block Findan , Klingbeil Finn , Deshpande Sughosh , Sajjad Umer , Seidler Dennis , Arndt Christine , Sindt Sandra , Selhuber-Unkel Christine , McCord Jeffrey
Published: June 2021

Precise movement control is a key feature for the use of superparamagnetic microbeads in medical and biological lab-on-chip applications. We demonstrate the unidirectional transport of magnetic and biological carriers along a chain of oval shaped magnetic thin film elements by in-plane rotating magnetic fields, enabling controllable manipulation and separation schemes. The same fundamental unidirectional movement is realized independent of the sense of magnetic field rotation and orientation of the magnetic pathway. The flowless directional transport of magnetically labeled rat embryonic fibroblasts is presented, validating the applicability of the structures for biological purposes. The lined up ferromagnetic structures are a critical building block for the construction of flexible pathways for biological lab-on-a-chip applications.
Phase resolved observation of spin wave modes in antidot lattices
Authors: Groß Felix , Zelent Mateusz , Gangwar Ajay , Mamica Sławomir , Gruszecki Paweł , Werner Matthias , Schütz Gisela , Weigand Markus , Goering Eberhard J. , Back Christian H. , Krawczyk Maciej , Gräfe Joachim
Published: June 2021

Antidot lattices have proven to be a powerful tool for spin wave band structure manipulation. Utilizing time-resolved scanning transmission x-ray microscopy, we are able to experimentally image edge-localized spin wave modes in an antidot lattice with a lateral confinement down to <80 nm×130 nm. At higher frequencies, spin wave dragonfly patterns formed by the demagnetizing structures of the antidot lattice are excited. Evaluating their relative phase with respect to the propagating mode within the antidot channel reveals that the dragonfly modes are not directly excited by the antenna but need the propagating mode as an energy mediator. Furthermore, micromagnetic simulations reveal that additional dispersion branches exist for a tilted external field geometry. These branches correspond to asymmetric spin wave modes that cannot be excited in a non-tilted field geometry due to the symmetry restriction. In addition to the band having a negative slope, these asymmetric modes also cause an unexpected transformation of the band structure, slightly reaching into the otherwise empty bandgap between the low frequency edge modes and the fundamental mode. The presented phase resolved investigation of spin waves is a crucial step for spin wave manipulation in magnonic crystals.
Effects of evaporation on chemical reactions in counterflow spray flames
Authors: Xie Wenwen , Wu Wantong , Ren Zhuyin , Liu Hong , Ihme Matthias
Published: June 2021

The role of evaporation on chemical reactions in counterflow spray flames remains a key issue due to the non-linear inter-phase interactions through mass, momentum, and energy conservation. An extended chemical explosive mode analysis to illustrate the role of evaporation (ECEMA) was previously developed by separating the evaporation source term from non-chemical terms and projecting them onto the chemical explosive mode (CEM). Evaporation was found to promote chemical reactions when the fuel supply effect dominated the evaporative cooling and to inhibit reactions otherwise. In this work, ECEMA is applied to one-dimensional laminar and three-dimensional turbulent counterflow spray flames. For laminar cases, ECEMA is applied to multi-modal spray flame solutions including the distributed, collocated, and cool flame. The analysis for the collocated and cool flame shows similar behavior, namely, that evaporation inhibits chemical reactions due to heat absorption near the fuel injection region and enhances chemistry around the zero-crossing CEM. For the distributed flame, the promotion effect is observed for most of the domain. For the turbulent counterflow flame, three CEM regions are identified, namely, a hybrid region, an inhibition region, and a promotion region. In particular, for the hybrid region near the spray injection side, the contribution of evaporation to chemical reactions changes from inhibition to promotion. For the inhibition region in the middle, significant suppressing of chemical reactions by evaporation is observed. In the promotion region near the oxidizer side, evaporation remains promoting chemical reactions. For the case investigated, the dominant combustion modes are the assisted ignition and local extinction.
Particle flux and particle density source due to gyro-center heat source
Authors: Miyato N.
Published: June 2021

A particle flux induced by a source in the gyro-center phase space is investigated through push-forward representations of the particle flux. The difference between the particle and gyro-center density sources is represented by the divergence of the particle flux due to the source in the gyro-center space. A gradient of a gyro-center perpendicular heat source causes a particle flux that may modify the particle density profile even when the source does not change positions of gyro-centers. The whole particle flux including the flux by the source is explicitly represented in terms of gyro-center fluid moments (gyrofluid moments) in the long wavelength limit of the standard electrostatic gyrokinetic model. Continuity equations for particle density with finite Larmor radius terms and the term related to the perpendicular heat source in the gyro-center space are derived from these representations by transforming gyrofluid moments to particle fluid moments. Finally, a vorticity equation with a source term stemming from a perpendicular heat source is derived from one of the continuity equations.
Specific cation stoichiometry control of SrMnO3-δ thin films via RHEED oscillations
Authors: Liu Qingqing , Zhong Qilan , Bai Jiawei , Yang Jing , Huang Rong , Bai Wei , Zhang Yuanyuan , Duan Chun-Gang , Tang Xiaodong
Published: June 2021

Cubic heteroepitaxial (001) SrMnO3-δ (SMO) films were grown on SrTiO3 substrates by atomic alternating layer molecular beam epitaxy. Precise control of cation stoichiometry was achieved by in situ reflection high-energy electron diffraction (RHEED) oscillation. During SMO film growth, a correlation between RHEED oscillation features and the cation stoichiometry/monolayer dose was established. In non-stoichiometric films, there were out-of-plane lattice expansions due to off-stoichiometry-dependent defects, including Ruddlesden–Popper SrO planar faults in Sr-rich films and Sr vacancy defect clusters in Mn-rich films.
Room temperature emission from single defects in WO3 enhanced by plasmonic nanocrystals
Authors: Ozceri Elif , Polat Nahit , Balci Sinan , Tarhan Enver
Published: June 2021

Room temperature light emission from optically active defect centers in two-dimensional layered materials has attracted great interest in recent years owing to the critical applications in the field of quantum information technologies. Therefore, efficient generation, detection, characterization, and manipulation of spatially localized emission from the defect centers are of crucial importance. Here, we report localized, stable, and bright room temperature photoluminescence (PL) emission from defects in WO3. In particular, the experimentally observed polarized and power dependent PL emission shows single photon characteristics. In addition, density functional theory calculations indicate that the source of the emission is most probably oxygen vacancy defects in WO3. The PL emission obtained from the localized defect centers in WO3 at room temperature has been, further, enhanced more than 20 times by using plasmonic gold nanoparticles.
Generation of straight and curved hollow plasma channels by laser-generated nonlinear wakefields and studies of ultra-intense laser pulse guiding
Authors: Ma Y. , Seipt D. , Krushelnick K. , Thomas A. G. R.
Published: June 2021

We report on a study of highly controllable, quasi-static hollow plasma channels generated by ion motion following a laser–plasma interaction via numerical simulations. These channels are generated by ion motion in a nonlinear wakefield, which has an asymmetry between focusing and defocusing periods. Such plasma channels, driven by a fs duration, 100 TW level laser pulse, have the capability to guide more powerful laser pulses. Moreover, we show that curved plasma channels can be generated in a transverse density gradient plasma and all-optical guiding of a second, significantly more powerful laser pulse in such a curved plasma channel. This mechanism may be useful for creating plasma optics for multi-stage TeV laser plasma accelerators and compact synchrotron radiation sources.
Demonstration of enhanced four-wave mixing by harnessing stimulated Brillouin scattering within a suspended cascaded microring resonator
Authors: Cheng Ming , Wang Kang , Sun Junqiang
Published: June 2021

We experimentally demonstrate the enhanced four-wave mixing (FWM) by harnessing the forward stimulated Brillouin scattering (FSBS) within a silicon-based cascaded racetrack microring resonator (MRR). The frequency spacing of the split resonant peaks is precisely designed to match the Brillouin frequency shift (BFS). The cooperative interaction of the FSBS resonance and cascaded MRR resonance achieves an FWM enhancement of 2.97 and 2.43 dB for anti-Stokes and Stokes sidebands under the launched pump power of 35.48 mW and probe power of 17.78 mW. The BFS from 3.34 to 7.13 GHz is demonstrated by changing the waveguide width. Moreover, we show that this same system behaves as a single-sideband modulator, providing more than the 17 dB single-sideband rejection ratio under the condition that the probe light and Stokes are resonant in the cascaded MRR. Building on these results, this device opens the door to new types of all-silicon Brillouin laser, amplifier, isolator, and single-sideband modulator.
Restructuring of rotating spokes in response to changes in the radial electric field and the neutral pressure of a cylindrical magnetron plasma
Authors: Sengupta M. , Smolyakov A. , Raitses Y.
Published: June 2021

Nonlinear plasma structures in the partially magnetized E×B plasma of a cylindrical magnetron are investigated using 2D3V particle-in-cell Monte Carlo collision simulations. In the early phase of the discharge, plasma gradients and radial electric fields excite a lower hybrid type instability that forms long wavelength rotating density spokes. As the discharge grows in density by ionization and the cathode gets shielded by the formation of an ion sheath, radial electric fields diminish in the quasineutral region of the discharge. This induces a transition of the spokes into short-scale spoke-on-spoke modes. The short wavelength structures can be reversed back into a long spiral spoke by lowering the neutral pressure, which revives the radial electric fields via a turbulent plasma expansion. Plasma phenomena connected to the rotating spoke include the anomalous radial transport and loss of electrons through the spoke, azimuthal dragging of ions by the spoke’s field, plasma temperature modulations by the spoke structure, and formation of electron vortices around equipotential islands, in some cases with opposing rotations to the underlying E×B drift. Electron scattering from non-ionizing collisions with neutrals also has a minor influence on the instability.
Superconducting qubits in a flip-chip architecture
Authors: Conner C. R. , Bienfait A. , Chang H.-S. , Chou M.-H. , Dumur É. , Grebel J. , Peairs G. A. , Povey R. G. , Yan H. , Zhong Y. P. , Cleland A. N.
Published: June 2021

Flip-chip architectures have recently enabled significant scaling-up of multi-qubit circuits and have been used to assemble hybrid quantum systems that combine different substrates, for example, for quantum acoustics experiments. The standard flip-chip method uses superconducting galvanic connections between two substrates, typically implemented using sophisticated indium wafer-bonding systems, which give highly reliable and temperature-cyclable assemblies, but are expensive, somewhat inflexible in design, and require robust substrates that can sustain the large compressive forces required to cold-weld the indium bonds. A much simpler method is to assemble dies using very low-force contacts and air-dried adhesives, although this does not provide a galvanic contact between the dies. Here, we demonstrate that the latter technique can be used to reliably couple superconducting qubit circuits, in which the qubits are on separate dies, without the need for a galvanic connection. We demonstrate full vector qubit control of each qubit on each of the two dies, with high-fidelity single-shot readout, and further demonstrate entanglement-generating excitation swaps as well as benchmark a controlled-Z entangling gate between the two qubits on the two dies. This exemplifies a simple and inexpensive assembly method for two-plus-one-dimensional quantum circuit integration that supports the use of delicate or unusually shaped substrates.
Generation of supersonic jets from underwater electrical explosions of wire arrays
Authors: Maler D. , Efimov S. , Rososhek A. , Bland S. N. , Krasik Ya. E.
Published: June 2021

Underwater electrical explosion experiments of cylindrical or conical wire arrays accompanied by the generation of fast (up to ∼4500 m/s) water jets are presented. In these experiments, a pulse generator with a stored energy of up to ∼5.7 kJ, current amplitude of up to ∼340 kA, and rise time of ∼0.85 μs was used to electrically explode copper and aluminum wire arrays underwater. Streak and fast framing shadow imaging was used to extract the space–time resolved velocity of the ejected jet from the array while it propagates in air. The jet generation occurs due to high pressure and density of water formed in the vicinity of the array axis by the imploding shockwave. It was shown that the velocity of the jet ejected from the array depends on the array geometry and the thickness of the water layer above the array. The results suggest that ≥50% of the energy deposited into the array is transferred to the kinetic energy of this jet and the axial waterflow.
Electronic, vibrational, and torsional couplings in N-methylpyrrole: Ground, first excited, and cation states
Authors: Davies Alexander R. , Kemp David J. , Wright Timothy G.
Published: June 2021

The electronic spectrum associated with the S1 ← S0 (Ã1A2←X̃1A1) one-photon transition of jet-cooled N-methylpyrrole is investigated using laser-induced fluorescence (LIF) and (1 + 1) resonance-enhanced multiphoton ionization (REMPI) spectroscopy; in addition, the (2 + 2) REMPI spectrum is considered. Assignment of the observed bands is achieved using a combination of dispersed fluorescence (DF), two-dimensional LIF (2D-LIF), zero-electron-kinetic energy (ZEKE) spectroscopy, and quantum chemical calculations. The spectroscopic studies project the levels of the S1 state onto those of either the S0 state, in DF and 2D-LIF spectroscopy, or the ground state cation (D0+) state, in ZEKE spectroscopy. The assignments of the spectra provide information on the vibrational, vibration-torsion (vibtor), and torsional levels in those states and those of the S1 levels. The spectra are indicative of vibronic (including torsional) interactions between the S1 state and other excited electronic states, deduced both in terms of the vibrational activity observed and shifts from expected vibrational wavenumbers in the S1 state, attributed to the resulting altered shape of the S1 surface. Many of the ZEKE spectra are consistent with the largely Rydberg nature of the S1 state near the Franck–Condon region; however, there is also some activity that is less straightforward to explain. Comments are made regarding the photodynamics of the S1 state.
Experimental investigation on the effect of particles on large scale vortices of an isolated hemispherical roughness element
Authors: Gao Tian-da , Sun Jiao , Chen Wen-yi , Fan Ying , Zhang Yan-tao
Published: June 2021

Particle image velocimetry (PIV) was used to investigate the effect of 155 μm polystyrene particles on the wake structure of an isolated hemispherical roughness element placed in a laminar boundary layer of a flat plate. The main purpose of this study was to investigate the influence of particles on the large-scale vortices induced by the hemisphere. The turbulence statistics and the main modes of proper orthogonal decomposition (POD) in whole field of view (FOV) were comparatively analyzed. The shedding frequency was analyzed by the power spectral density (PSD) function, and the hairpin vortex head structure was conditionally detected by the spatial multi-scale local average function. The results showed that by introducing particles, the statistics in the near-wall region downstream of the hemisphere were significantly changed. PSD results showed that the existence of particles led to the shedding of structures with multiple frequencies and inhibited the shedding of primary structures. Further conclusions could be drawn through POD and hairpin vortex head extraction: the existence of particles changed the type of vortex shedding behind the hemisphere, thereby reducing the number and the vorticity intensity of hairpin vortex heads in the range near the peak, and promoting the scale of the prograde vortex structure.
An application of a Si/CdTe Compton camera for the polarization measurement of hard x rays from highly charged heavy ions
Authors: Tsuzuki Yutaka , Watanabe Shin , Oishi Shimpei , Nakamura Nobuyuki , Numadate Naoki , Odaka Hirokazu , Uchida Yuusuke , Yoneda Hiroki , Takahashi Tadayuki
Published: June 2021

Methods to measure the polarization of x rays from highly charged heavy ions with a significantly higher accuracy than that of the existing technology are needed to explore relativistic and quantum electrodynamics effects, including the Breit interaction. We developed an Electron Beam Ion Trap Compton Camera (EBIT-CC), a new Compton polarimeter with pixelated multi-layer silicon, and cadmium telluride counters. The EBIT-CC detects the three-dimensional position of Compton scattering and photoelectric absorption, and thus, the degree of polarization of incoming x rays can be evaluated. We attached the EBIT-CC on the Tokyo Electron Beam Ion Trap (Tokyo-EBIT) in the University of Electro-Communications. An experiment was performed to evaluate its polarimetric capability through an observation of radiative recombination x rays emitted from highly charged krypton ions, which were generated by the Tokyo-EBIT. The CC of the EBIT-CC was calibrated for the ∼75 keV x rays. We developed event reconstruction and selection procedures and applied them to every registered event. As a result, we successfully obtained the polarization degree with an absolute uncertainty of 0.02. This uncertainty is small enough to probe the difference between the zero-frequency approximation and full-frequency-dependent calculation for the Breit interaction, which is expected for dielectronic recombination x rays of highly charged heavy ions.
Site-specific generation of excited state wavepackets with high-intensity attosecond x rays
Authors: Fouda Adam E. A. , Ho Phay J.
Published: June 2021

High-intensity attosecond x rays can produce coherent superpositions of valence-excited states through two-photon Raman transitions. The broad-bandwidth, high-field nature of the pulses results in a multitude of accessible excited states. Multiconfigurational quantum chemistry with the time-dependent Schrödinger equation is used to examine population transfer dynamics in stimulated x-ray Raman scattering of the nitric oxide oxygen and nitrogen K-edges. Two pulse schemes initiate wavepackets of different characters and demonstrate how chemical differences between core-excitation pathways affect the dynamics. The population transfer to valence-excited states is found to be sensitive to the electronic structure and pulse conditions, highlighting complexities attributed to the Rabi frequency. The orthogonally polarized two-color-pulse setup has increased selectivity while facilitating longer, less intense pulses than the one-pulse setup. Population transfer in the 1s → Rydberg region is more effective but less selective at the nitrogen K-edge; the selectivity is reduced by double core-excited states. Result interpretation is aided by resonant inelastic x-ray scattering maps.
Ultrathin 2D-oxides: A perspective on fabrication, structure, defect, transport, electron, and phonon properties
Authors: Radha Santosh Kumar , Crowley Kyle , Holler Brian A. , Gao Xuan P. A. , Lambrecht Walter R. L. , Volkova Halyna , Berger Marie-Hélène , Pentzer Emily , Pachuta Kevin G. , Sehirlioglu Alp
Published: June 2021

In the field of atomically thin 2D materials, oxides are relatively unexplored in spite of the large number of layered oxide structures amenable to exfoliation. There is an increasing interest in ultrathin film oxide nanostructures from applied points of view. In this Perspective paper, recent progress in understanding the fundamental properties of 2D oxides is discussed. Two families of 2D oxides are considered: (1) van der Waals bonded layered materials in which the transition metal is in its highest valence state (represented by V2O5 and MoO3) and (2) layered materials with ionic bonding between positive alkali cation layers and negatively charged transition metal oxide layers (LiCoO2). The chemical exfoliation process and its combination with mechanical exfoliation are presented for the latter. Structural phase stability of the resulting nanoflakes, the role of cation size, and the importance of defects in oxides are discussed. Effects of two-dimensionality on phonons, electronic band structures, and electronic screening are placed in the context of what is known on other 2D materials, such as transition metal dichalcogenides. The electronic structure is discussed at the level of many-body-perturbation theory using the quasiparticle self-consistent GW method, the accuracy of which is critically evaluated including effects of electron–hole interactions on screening and electron–phonon coupling. The predicted occurrence of a two-dimensional electron gas on Li-covered surfaces of LiCoO2 and its relation to topological aspects of the band structure and bonding is presented as an example of the essential role of the surface in ultrathin materials. Finally, some case studies of the electronic transport and the use of these oxides in nanoscale field-effect transistors are presented.
Three-dimensional core–shell CoFe Prussian blue analog at NiCoFe layered ternary hydroxide electrocatalyst for efficient oxygen evolution reaction
Authors: Wang Ting , Pang Qi , Li Bolin , Chen Yibo , Zhang Jin Zhong
Published: June 2021

Layered double hydroxides are one of the most effective electrocatalysts owing to their compositional and structural flexibility. However, their self-stacking leads to limited active sites and low conductivity. In this work, a three-dimensional (3D) core–shell architecture with spatially separated active sites has been fabricated based on layered ternary nickel cobalt iron hydroxide (NiCoFe-LTH) nanosheets and cobalt iron Prussian blue analog (CoFe-PBA) on nickel foam (NF) (i.e., CoFe-PBA@NiCoFe-LTH/NF) with CoFe-PBA as self-sacrificial templates that are partially in situ transformed into NiCoFe-LTH nanosheets. The CoFe-PBA@NiCoFe-LTH/NF has a well-defined core–shell 3D flower-like nanostructure in which NiCoFe-LTH nanosheets create the larger shell while CoFe-PBA nanocubes form the small core. This hybrid structure is evaluated as an electrocatalyst for oxygen evolution reaction (OER) and found to exhibit a low overpotential of 228 mV at 10 mA cm−2, a low Tafel slope of 36 mV dec−1, and good catalytic stability for 72 h in 1.0 M alkaline solution. The strong performance is attributed to the unique 3D core–shell flower-like nanosheet architecture that avoids the stacking of the 2D LTH, provides abundant spatially separated active sites, and enhances electron transport and stability. Furthermore, the OER mechanism and growth process of the electrocatalysts were systematically studied. These results suggest that such electrocatalysts with unique architecture are promising for efficient and durable OER.
Maximum-entropy revisited: Optimal filtering of spectra
Authors: Le L. V. , Kim T. J. , Kim Y. D. , Aspnes D. E.
Published: June 2021

In spectroscopy, the objective is to obtain information by analyzing spectra that ideally are undistorted and noise-free. In standard Fourier-space filtering, this goal cannot be achieved because of apodization, which forces a trade-off among errors arising from distortion, noise leakage, and Gibbs oscillations. We show that low-order coefficients can be preserved and apodization, and its associated errors eliminated with the corrected maximum-entropy (M-E) filter obtained here. Although the Burg derivation begins as M-E, by making certain assumptions the Burg approach yields a procedure that deconvolves (sharpens) structure in spectra, thereby violating the basic M-E principle of leaving the low-order coefficients intact. The corrected solution preserves these data and projects the trends established by them into the white-noise region in a model-independent way, thereby eliminating apodization and its associated errors. For a single Lorentzian line, the corrected M-E approach has an exact analytic solution, which reveals not only how M-E performs its extension but also why it works particularly well for line shapes resulting from first-order decay processes. The corrected M-E filter is quantitatively superior to any previous filtering method, including recently proposed high-performance linear filters, yet requires only minimal computational effort. Examples, including multiple differentiation, are provided.
Quantifying particle-scale 3D granular dynamics during rapid compaction from time-resolved in situ 2D x-ray images
Authors: Gupta A. , Crum R. S. , Zhai C. , Ramesh K. T. , Hurley R. C.
Published: June 2021

Understanding the particle-scale dynamics of granular materials during rapid compaction and flow is of fundamental importance for manufacturing, planetary science, geology, and defense applications. Time-resolved 2D radiography and static 3D x-ray tomography are powerful in situ tools for studying particle-scale dynamics but provide detail only in 2D or with significant time-scale limitations, respectively. Here, we introduce a new method that uses 2D in situ x-ray imaging for determining time-resolved 3D particle-scale dynamics in rapidly compressed granular materials. The method employs initial particle packing structures obtained from x-ray tomography, a 2D x-ray image generation algorithm, and an optimization algorithm. We first describe and validate the method using finite element simulations. We then apply the technique to x-ray phase-contrast images obtained during rapid compaction of granular materials with varying particle morphology and sample thickness. The depth-resolved particle-scale dynamics reveal complex velocity and porosity fields evolving heterogeneously along and perpendicular to the compaction direction. We characterize these features, their fluctuations near the compaction front, and the compaction front thickness. Our technique can be applied to understanding granular dynamics during rapid compaction events, and rearrangements during slower, but non-quasi-static, flows.
Computational investigation of half-Heusler/MgO magnetic tunnel junctions with (001) orientation
Authors: Ma Jianhua , Xie Yunkun , Munira Kamaram , Ghosh Avik W. , Butler William H.
Published: June 2021

A series of half-metallic XYZ half-Heusler alloys is combined with MgO to create Heusler–MgO junctions. The electronic and magnetic properties of these junctions are investigated. The strong oxidation between metal and oxygen atoms causes the systems with pure YY interfaces to be the most stable cases. We conclude that uniaxial anisotropy can be induced in Heusler layers adjacent to MgO. The type of interface layers determines the half-metallicity and anisotropy (in-plane or perpendicular) in the Heusler–MgO junctions. The capacity to retain both half-metallicity and perpendicular magnetic anisotropy in NiMnSb/MgO and CoTiSn/MgO junctions with a MnMn interface layer makes these structures potential candidates as electrode layers in spin transfer torque random access memory devices.
Quantum hydrodynamics of the spinor Bose–Einstein condensate at non-zero temperatures
Authors: Andreev Pavel A. , Mosaki I. N. , Trukhanova Mariya Iv.
Published: June 2021

A finite temperature hydrodynamic model is derived for the spin-1 ultracold bosons by the many-particle quantum hydrodynamic method. It is presented as the two fluid model of the Bose–Einstein condensate (BEC) and normal fluid. The continuity, Euler, spin evolution, and nematic tensor evolution equations are derived for each fluid. The linear and quadratic Zeeman effects are included. Scalar and spin–spin like short-range interactions are considered in the first order by the interaction radius. Obtained hydrodynamic equations are also represented as the set of two nonlinear Pauli equations. The spectrum of the bulk collective excitations is considered for the ferromagnetic phase in the small temperature limit. The spin wave is not affected by the presence of the small temperature in the described minimal coupling model, where the thermal part of the spin-current of the normal fluid is neglected. The two sound waves are affected by the spin evolution in the same way as the change of spectrum of the single sound wave in BEC, where speed of sound is proportional to g1+g2 with gi as the interaction constants.
Propagation of threading dislocations and effects of Burgers vectors in HVPE-grown GaN bulk crystals on Na-flux-grown GaN substrates
Authors: Hamachi T. , Tohei T. , Hayashi Y. , Imanishi M. , Usami S. , Mori Y. , Ikarashi N. , Sakai A.
Published: June 2021

The propagation behavior of threading dislocations (TDs) and the effects of Burgers vectors in hydride vapor phase epitaxy (HVPE) GaN bulk crystals generated on Na-flux-grown GaN and in a commercially available HVPE-grown GaN bulk crystal were investigated. Analyses based on chemical etching and transmission electron microscopy (TEM) revealed a close correlation between the etch pit sizes and the Burgers vector of these TDs. The existence of TDs with the unique Burgers vector b = 1m + 1c was observed for the first time ever using a large-angle convergent-beam electron diffraction technique and plan-view bright-field scanning TEM. Multi-photon excitation photoluminescence microscopy observations showed that TDs with b = 1c had a meandering morphology in contrast to the linear morphology of TDs with b = 1a, 1a + 1c, or 1m + 1c in both types of HVPE-grown GaN crystals. The inclinations of TDs with b = 1a and 1a + 1c in HVPE-grown GaN on Na-flux-grown GaN were greatly affected by large symmetrical hexagonal hillocks. The TDs with b = 1a were inclined in the slope directions of the hillock planes, while those with b = 1a + 1c were inclined in the a directions parallel or antiparallel to the a component in their Burgers vector. These inclinations were readily explained by the isotropic elastic theory of an individual TD. The hillocks were produced around pairs of parallel mixed TDs for which the a components were opposite to one another. This phenomenon was attributed to inclusions at the interface between the Na-flux-grown GaN substrate and the HVPE-grown layer. The origins of other TDs including unusual ones having b = 1m + 1c are also discussed herein.
Study of coherent structures and heat flux transportation under different stratification stability conditions in the atmospheric surface layer
Authors: Li Xuebo , Wang Guohua , Zheng Xiaojing
Published: June 2021

A field experiment was carried out on a dry flat bed of Qingtu Lake in Minqin, China to measure the velocity and temperature in the atmospheric surface layer at high Reynolds number. The facility, the Qingtu Lake Observation Array, permits synchronous multi-point measurements of three-dimensional wind velocity and temperature at different wall-normal and spanwise positions. Data were selected to analyze the characteristics of the large-scale coherent structures under different stratification stability conditions. The results confirm the previous findings that the positive buoyancy can be considered as a wall-normal force to have a “lifting” effect increasing the size of large-scale structures and further illustrate that negative buoyancy in the stable condition has an opposite effect leading to small structures with less wall-normal coherence. The stability dependence of structure inclination angles for all three velocity components is built by a parametric model indicating a log-linear trend under near-neutral and unstable conditions. In addition, the unique measurement array at this facility also permits us to study the three-dimensional form of these features and the associated temperature fluctuations. By computing the space average for momentum and heat flux, we found that the threshold stability parameter z/L=−0.1, where z = 2.5 m and L is the Obukhov length scale, can act as a role to determine the dominant flow by shear-driven and buoyancy-driven, respectively. Last, the streamwise length scales for temperature component are investigated where a smaller length scale corresponds to a stronger buoyancy condition, but with larger values at higher heights.
Optical and electronic properties of SiTex (x = 1, 2) from first-principles
Authors: Bhattarai Romakanta , Shen Xiao
Published: June 2021

The optical and electronic properties of α-SiTe, β-SiTe, and RX-SiTe2 are investigated. A detailed analysis of electronic properties is done using standard density functional theory (DFT) and hybrid functional methods. The static dielectric properties are investigated using the density functional perturbation theory method. The optical properties are studied under three different methods: standard DFT, many-body Green's functions, and the Bethe–Salpeter equation. Our calculations show that the SiTe compounds possess extremely high static dielectric constants in their bulk forms [ε0(⊥) = 68.58 and ε0(‖) = 127.29 for α-SiTe, and ε0(⊥) = 76.23 and ε0(‖) = 74.61 for β-SiTe]. The frequency-dependent dielectric functions Im(ε) have very large values (>100) in the optical regime, which are among the highest of layered materials, suggesting them as excellent light absorbents in the corresponding frequencies. α-SiTe exhibits a high degree of optical anisotropy as compared to the other two compounds, consistent with their structural configurations. A strong interlayer excitonic effect is observed in bulk RX-SiTe2. In addition, an analysis of Raman intensity is also performed.
Octahedral tilting dominated phase transition in compressed double perovskite Ba2SmBiO6
Authors: Wang Yanju , Zhang Lingkong , Ma Shuailing , Zhao Yongsheng , Tan Dayong , Chen Bin
Published: June 2021

The comprehension of structural behaviors in double perovskites is crucial for their functional optimization, especially when applying external regulations. Here, to inquire about potential structures with better magnetic performance, high-pressure phase transformation in double perovskite Ba2SmBiO6 was first investigated up to 50 GPa via in situ high-pressure x-ray diffraction and Raman spectroscopy. A pressure-induced phase transition from cubic Fm-3m to orthorhombic Pnma is discovered at 4.8 GPa, accompanied by the splitting of the diffraction peaks. Above 19.8 GPa, the new phase becomes distorted as shown by the peak recombination and broadening. The variation of Raman spectra also confirms the formation and distortion of the high-pressure phase during compression, through the evolution of Bi–O stretching, Bi–O bending, octahedral rotation, and Ba-sites translation modes. The analysis of tilt angles and distortion factor evinced that the octahedral BiO6 tilting is the key factor for the phase transition occurrence. Based on the Mulliken populations analyses, the Bi–O bonds undergo a covalent-ionic-antibonding transition across the phase transition under compression. Our exploration of the phase transition mechanism guides the modulation of the magnetic and electronic properties under extreme conditions.
Real time THz imaging—opportunities and challenges for skin cancer detection
Authors: Lindley-Hatcher H. , Stantchev R. I. , Chen X. , Hernandez-Serrano A. I. , Hardwicke J. , Pickwell-MacPherson E.
Published: June 2021

It was first suggested that terahertz imaging has the potential to detect skin cancer twenty years ago. Since then, THz instrumentation has improved significantly: real time broadband THz imaging is now possible and robust protocols for measuring living subjects have been developed. Here, we discuss the progress that has been made as well as highlight the remaining challenges for applying THz imaging to skin cancer detection.
General expression of aerodynamic force under different boundary conditions (slip, partial slip, no-slip)
Authors: Dynnikova Galina Ya.
Published: June 2021

Integral expression is derived for aerodynamic forces in unsteady separated flows of an incompressible Newtonian fluid via the characteristics of the flow on the body surface including the vortex flux generated by it. The expression obtained is valid for unsteady and steady flows under the no-slip or the partial slip boundary conditions in a viscous fluid as well as for complete slip in the case of an ideal fluid including the flows with tangential discontinuity of the velocity field. Unlike the number of existing formulas, the expression does not contain the volume integrals and is applicable for the case of multiple bodies. The expression greatly simplifies a calculation of the hydrodynamic force when using vortex meshless methods. The formula obtained satisfies the fundamental law of hydrodynamic momentum conservation. It is derived mathematically rigorously without any assumptions.
HIF-1α is a negative regulator of interferon regulatory factors: Implications for interferon production by hypoxic monocytes
Authors: Peng Travis , Du Shin-Yi , Son Myoungsun , Diamond Betty
Published: June 2021

Significance

Clinical studies have shown that defects in type I interferon (IFN) production or antibodies to IFN appear to correlate with severe COVID-19 infection. Here, we demonstrate that proinflammatory cytokines but not type I IFN are produced by hypoxic human monocytes. We show that hypoxia suppresses production of type I IFN but not nuclear factor-κB–dependent proinflammatory cytokines. We demonstrate that hypoxia-inducible factor-1α is a direct transcriptional suppressor of interferon regulatory factors, the transcriptional activators of type I IFN. These findings may aid in understanding and control of impaired IFN production by severe acute respiratory syndrome coronavirus 2 infection.
Ecotourism in Crete at the Milia Mountain Retreat
Authors: Jeannon Marine , Labbé Emilie , Louis Orianne , Sanjivy Agnès
Published: June 2021

The story of Milia Mountain Retreat reflects changes in tourism demand worldwide which have been accelerated by the Covid-19 pandemic. Located in Western Crete, it has seen a significant increase in domestic tourists and a strong growth of demand from travellers seeking authentic experiences in the Mediterranean.

Information

Written on the basis of material provided by Tassos Gourgouras of Milia Mountain Retreat, in the context of Skema’s Strategic Marketing Projects programme.

© CAB International 2021
In Quebec, A Historic Convent is Reborn as a Wellness and Therapy Centre
Authors: Vindolet Camille , Labbé Emilie , Bressy Sophie de , Couttet Alizée
Published: June 2021

The Hôtel-Dieu de Québec was founded in the 17th century to house the Augustinian Sisters, whose role included providing care and healing for the sick and the poor in the New France colonies.

Information

For SKEMA: Written on the basis of material provided by Isabelle Houde (Assistant Executive Director) and Isabelle Duchesneau (Executive Director) of Le Monastère des Augustines.

© CAB International 2021
Exploring the Case In Quebec, A Historic Convent is Reborn as a Wellness and Therapy Centre
Authors: Vindolet Camille , Labbé Emilie , Bressy Sophie de , Couttet Alizée , Ward-Perkins David
Published: June 2021

Introduction

The project of Le Monastère des Augustines is situated on the permeable frontiers connecting heritage tourism, wellness tourism and religious tourism. The notes and exercises below will help researchers and students explore the relations between the three.
IPC recovery length of 45 minutes improves muscle oxygen saturation during active sprint recovery
Authors: Seeley Afton D. , Jacobs Kevin A.
Published: June 2021

Ischemic preconditioning (IPC) involves brief, repeated bouts of limb occlusion and reperfusion capable of improving exercise performance at least partially by enhancing local skeletal muscle oxygenation. This study sought to investigate the effect of a lower limb IPC protocol, with either a 5‐min or 45‐min post‐application delay, on vastus lateralis tissue saturation index (TSI) and systemic cardiac hemodynamics at rest and during short‐duration intense cycling. Twelve young adults randomly completed four interventions: IPC (at 220 mmHg) with 5‐min delay (IPC5), IPC with 45‐min delay (IPC45), SHAM (at 20 mmHg) with 5‐min delay (SHAM5), and SHAM with 45‐min delay (SHAM45). Following IPC intervention and recovery delay, participants completed 5, 60‐s high‐intensity (100% W peak) cycle sprints separated by 120‐sec of active recovery (30% W peak). Compared to baseline, TSI immediately following IPC5, but pre‐exercise, remained lower than the equivalent for IPC45 (−5.9 ± 1.5%, p = .002). IPC, imposed at least 45‐min before the completion of five 60‐s sprint cycling efforts, significantly enhanced TSI during active recovery between sprint intervals compared to a 5‐min delay (6.6 ± 2.4%, p = .021), and identical SHAM conditions (SHAM5: 5.8 ± 2.2%, p = .024; SHAM45: 6.2 ± 2.5%, p = .029). A 45‐min delay following IPC appears to provide heightened skeletal muscle metabolic rebound prior to intense sprint cycling as compared to a 5‐min delay. Furthermore, IPC followed by a 45‐min delay enhanced recovery of skeletal muscle oxygenation during low intensity active sprint recovery, despite an unchanged decline in skeletal muscle oxygenation during near‐maximal sprinting efforts.
MICAL2 enhances branched actin network disassembly by oxidizing Arp3B-containing Arp2/3 complexes
Authors: Galloni Chiara , Carra Davide , Abella Jasmine V.G. , Kjær Svend , Singaravelu Pavithra , Barry David J. , Kogata Naoko , Guérin Christophe , Blanchoin Laurent , Way Michael
Published: June 2021

The mechanisms regulating the disassembly of branched actin networks formed by the Arp2/3 complex still remain to be fully elucidated. In addition, the impact of Arp3 isoforms on the properties of Arp2/3 are also unexplored. We now demonstrate that Arp3 and Arp3B isocomplexes promote actin assembly equally efficiently but generate branched actin networks with different disassembly rates. Arp3B dissociates significantly faster than Arp3 from the network, and its depletion increases actin stability. This difference is due to the oxidation of Arp3B, but not Arp3, by the methionine monooxygenase MICAL2, which is recruited to the actin network by coronin 1C. Substitution of Arp3B Met293 by threonine, the corresponding residue in Arp3, increases actin network stability. Conversely, replacing Arp3 Thr293 with glutamine to mimic Met oxidation promotes disassembly. The ability of MICAL2 to enhance network disassembly also depends on cortactin. Our observations demonstrate that coronin 1C, cortactin, and MICAL2 act together to promote disassembly of branched actin networks by oxidizing Arp3B-containing Arp2/3 complexes.
Germinal center–dependent and –independent memory B cells produced throughout the immune response
Authors: Viant Charlotte , Wirthmiller Tobias , ElTanbouly Mohamed A. , Chen Spencer T. , Kara Ervin E. , Cipolla Melissa , Ramos Victor , Oliveira Thiago Y. , Stamatatos Leonidas , Nussenzweig Michel C.
Published: June 2021

Memory B cells comprise a heterogenous group of cells that differ in origin and phenotype. During the early phases of the immune response, activated B cells can differentiate into IgM-expressing memory cells, short-lived plasma cells, or seed germinal centers (GCs). The memory compartment is subsequently enriched by B cells that have been through several rounds of division and selection in the GC. Here, we report on the use of an unbiased lineage-tracking approach to explore the origins and properties of memory B cell subsets in mice with an intact immune system. We find that activated B cells continue to differentiate into memory B cells throughout the immune response. When defined on the basis of their origins, the memory B cells originating from activated B cells or GCs differ in isotype and overall gene expression, somatic hypermutation, and their affinity for antigen.
A study of the formation of isotopically pure 28Si layers for quantum computers using conventional ion implantation
Authors: Schneider Ella B , England Jonathan , Antwis Luke , Royle Alex , Webb Roger , Gwilliam Russell
Published: June 2021

We have investigated the use of conventional ion implantation to fabricate enriched 28Si layers for use in quantum computers. The final compositions of samples enriched using ultra-low energy (ULE) (800 eV and 2 keV) and low energy (20 keV) 28Si implants of varying fluences (1 × 1016–3.8 × 1017 cm−2) using two different implanters were measured using channelled Rutherford Backscattering Spectroscopy (RBS). The dynamic, binary collision approximation program TRIDYN was used to model the implantation profiles to guide the analysis of the RBS spectra. It was found that ULE implants achieved high 28Si enrichment levels but were heavily contaminated with oxygen due to poor vacuum in the implanter wafer end station. It was shown that oxidation could be reduced by using an accelerator with an end station with better vacuum and increasing the implant energy to 20 keV. However, TRIDYN simulations predict that the best 28Si enrichment levels that could be achieved under these conditions would saturate at ∼99.2% due to self-sputtering. We modelled a range of conditions with TRIDYN and so recommend low energies (<3 keV), ultra-high vacuum implantation for high 28Si enrichment (>99.9%) with the lowest possible fluences (∼5–10 × 1017 cm−2).