bluuebunny/crossref_metadata_2025 huggingface dataset:
Taming the excited states of butadiene, hexatriene, and octatetraene using state specific multireference perturbation theory with density functional theory orbitals
Authors: Manna Shovan , Chaudhuri Rajat K. , Chattopadhyay Sudip
Published: June 2020

To compute the electronic excitation energies, a state-specific multireference Møller–Plesset perturbation theory (SSMRPT) with a complete active space configuration interaction reference function constructed using the orbitals obtained by the density functional theory (DFT) is presented as an accurate, as well as computationally affordable, and efficient protocol at the level of second order. The global hybrid B3LYP (Becke, 3-parameter, Lee–Yang–Parr) functional has been used to generate orbitals. The present method, called DFT-SSMRPT, uses perturbers that are individual Slater determinants and accounts for the coupling between the nondynamical and dynamical correlation effects. We have applied the new method to compute excitation energies in conjugated systems of π-electrons such as trans-1,3-butadiene, trans,trans-1,3,5-hexatriene, and all-trans-1,3,5,7-octatetraene. The ordering of the excited states is correctly reproduced by the DFT-SSMRPT calculations. The relative ordering of low-lying excited 1Bu and 1Ag states alters when the length of the polyene changes. The results match reasonably well with the literature including experimental and best theoretical findings. The accuracy of the method is sufficient to discern the energy gap between the close low-lying singlet and triplet states. The DFT-SSMRPT appears as an affordable computational ab initio avenue for a qualitatively correct description of excitation energies.
Polarity balance for attractor self-reproducing
Authors: Li Chunbiao , Sun Jiayu , Lu Tianai , Sprott Julien Clinton , Liu Zuohua
Published: June 2020

There are complex chaotic manifolds in practical nonlinear dynamical systems, especially in nonlinear circuits and chemical engineering. Any system attractor has its own geometric and physical properties, such as granularity, orientation, and spatiotemporal distribution. Polarity balance plays an important role in the solution of a dynamical system including symmetrization, attractor merging, and attractor self-reproducing. The absolute value function and the signum function manage and control the polarity balance, strictly regulating the attractor distribution by switching the polarity balances. Attractor self-reproducing is an attractive regime for constructing the desired multistability, where the coexisting attractors at different positions can be extracted by a selected initial value. Polarity balance is the key factor for attractor self-reproducing, where the offset boosting of an attractor needs an available polarity controller to restore the imbalanced polarity.
Electronic excitation of ethanol by low-energy electron impact
Authors: Falkowski Alan Guilherme , Lima Marco A. P. , Kossoski Fábris
Published: June 2020

We report computed differential cross sections (DCSs) for electron impact excitation of the lower-lying states of both trans and gauche tautomers of ethanol, as well as total cross sections for the 15 eV–50 eV energy range. The Schwinger multichannel (SMC) method with pseudopotentials has been employed, and in our most sophisticated calculation in terms of multichannel coupling, 431 open target states have been considered. We found an overall good agreement with the available experimental data at intermediate scattering angles and at higher impact energies. Although we have used a Born-closure scheme for the higher partial waves, we have found discrepancies in the forward direction that were assigned to a poor description of the long-range component of the lower partial waves. Meanwhile, the lack of more Rydberg states could be related to the overestimated DCSs at lower energies. Missing open channels are usually evoked to explain the remaining discrepancies to experiment, but here, we argue that other factors should also be involved. Aiming at an improved description of the target states, we have proposed a simple procedure for selecting the pairs of hole and particle orbitals while keeping the single excitation prescription of the current SMC implementation. A quantitative assessment of the collision process should further consider the individual contribution of each tautomer, which presented quite distinct DCSs in some cases. Our computed excitation energies also support that the second absorption band of ethanol is comprised of three singlet states of each tautomer, rather than the previously suggested two or four states.
Synchrotron x-ray computed microtomography for high pressure science
Authors: Guignot N. , King A. , Boulard E.
Published: June 2020

X-ray computed microtomography (XCT) has been a very promising and exciting technique for high pressure (HP) science since the introduction of the first HP setups optimized for tomography in the mid-2000s. Different experimental stations are now available using diamond anvil cells (DACs) or large volume presses, with their own benefits and limitations: access to very high pressures but at room temperature on one hand, high temperature (HT) at moderate pressures on the other, and slow acquisitions being an undesired common point between all techniques. We believe that we are at a turning point where current and future developments boost the interest of the technique for the HP community. Time-resolved experiments, with less than 1 s per tomogram, will become routinely available. Fast tomography will greatly reduce the problem of motion artifacts at HT, allowing new topics to be explored. Computing and data treatment issues must be taken into account to effectively exploit the large volumes of data produced. Foreseeable developments will allow higher pressures to be reached in larger volume presses and higher T in DACs. Furthermore, improved XCT resolution in large samples (several hundreds of μm in diameter) recorded in situ will offer to be an effective alternative to ex situ microscopy.
Switching between spectral broadening and narrowing of the exciton absorption band of a CH3NH3PbI3 film on altering the polarity of an applied electric field
Authors: Awasthi Kamlesh , Kala Kannankutty , Rana Shailesh , Diau Eric Wei-Guang , Ohta Nobuhiro
Published: June 2020

Electric field-induced broadening and narrowing of an exciton absorption band have been observed to depend on the polarity of the applied electric field for methylammonium lead triiodide perovskite (MAPbI3) as a thin film sandwiched between a conducting film of fluorine-doped tin oxide (FTO) and an insulating film of poly(methyl methacrylate) (PMMA). The width of the absorption band increased or decreased when the direction of the applied field was toward FTO or PMMA, respectively, indicating that the spectral broadening and narrowing become switchable on altering the direction of the applied electric field. When titanium oxide (TiO2) in a compact layer was introduced between the MAPbI3 and FTO layers, the linear electric field effect that depended on the polarity was either not observed or decreased significantly although the quadratic field effects on the exciton absorption band were similarly observed with or without the TiO2 layer.
Investigations of tip vortex mitigation by using roughness
Authors: Asnaghi Abolfazl , Svennberg Urban , Gustafsson Robert , Bensow Rickard E.
Published: June 2020

The application of artificial roughness to mitigate tip vortex cavitation inception is analyzed through numerical and experimental investigations carried out on an elliptical foil. Different roughness configurations and sizes are tested, and effects on cavitation inception, drag, and lift are studied. Implicit Large Eddy Simulation is employed to conduct the simulation on a proper grid resolution having the tip vortex spatial resolution as fine as 0.062 mm. Two different approaches including using a rough wall function and resolving the flow around roughness elements are evaluated. New experiments, performed in the cavitation tunnel at Kongsberg Hydrodynamic Research Center, for the rough foil are presented. The vortical structures and vorticity magnitude distributions are employed to demonstrate how different roughness patterns and configurations contribute to the vortex roll-up and consequently on the tip vortex strength. It is found that the application of roughness on the leading edge, tip region, and trailing edge of the suction side is acceptable to mitigate the tip vortex and also to limit the performance degradation. This is regarded to be in close relation with the way that the tip vortex forms in the studied operating condition. The boundary layer characteristics show that roughness separation line is the reason for a more even distribution of vorticity over the tip compared to the smooth foil condition, leading to a reduction in vortex strength. For the optimum roughness pattern, both the numerical results and experimental measurements show a decrease in the tip vortex cavitation inception as large as 33% compared to the smooth foil condition with a drag force increase observed to be less than 2%.
Large valley degeneracy and high thermoelectric performance in p-type Ba8Cu6Ge40-based clathrates
Authors: Sato H. K. , Tamaki H. , Kanno T.
Published: June 2020

We demonstrate both theoretically and experimentally the high thermoelectric performance of p-type Ba8Cu6Ge40. Density functional theory calculations for Ba8Cu6Ge40 find that the valence band maximum consists of 12-fold degenerated valleys with light band effective masses, indicative of excellent electronic properties. It is also indicated that changing the Cu/Ge ratio is effective in controlling the carrier type. Motivated by these calculation results, a series of Ba8Cu6−xGe40+x samples with different Ge substitution amounts x are fabricated and the transport properties are characterized. The carrier type is effectively controlled with x, and the p-type Ba8Cu5.7Ge40.3 sample shows a high power factor of ∼1 mW/mK2, much higher than the previously reported values of n-type samples. These results emphasize the importance of the descriptor-based investigation into the electronic structures of clathrate thermoelectric materials.
Chlorine termination of selenium dangling bonds decreases tellurium-diffusion-induced acceptor states in hexagonal selenium
Authors: Imura S. , Mineo K. , Miyakawa K. , Kubota M. , Nanba M.
Published: June 2020

In this study, we examined the effects of doping chlorine (Cl) into crystalline selenium (c-Se) on diminishing the tellurium-diffusion-induced shallow acceptor states associated with the dangling bonds that appear at the ends of Se chains by theoretical analysis with the first-principles calculations. In this model, the negatively charged dangling bonds can be neutralized by inserting monovalent Cl atoms. Furthermore, the defect termination by doping Cl into fabricated Se thin films was experimentally demonstrated. Low-temperature cathodoluminescence measurements were implemented to show that acceptor-related emissions from the c-Se films were significantly decreased by Cl termination of the dangling bonds, experimentally confirming the results of the simulations.
Toward monitoring the dissipative vibrational energy flows in open quantum systems by mixed quantum–classical simulations
Authors: Kim Chang Woo , Rhee Young Min
Published: June 2020

In open quantum system dynamics, rich information about the major energy relaxation channels and corresponding relaxation rates can be elucidated by monitoring the vibrational energy flow among individual bath modes. However, such calculations often become tremendously difficult as the complexity of the subsystem–bath coupling increases. In this paper, we attempt to make this task feasible by using a mixed quantum–classical method, the Poisson-bracket mapping equation with non-Hamiltonian modification (PBME-nH) [H. W. Kim and Y. M. Rhee, J. Chem. Phys. 140, 184106 (2014)]. For a quantum subsystem bilinearly coupled to harmonic bath modes, we derive an expression for the mode energy in terms of the classical positions and momenta of the nuclei, while keeping consistency with the energy of the quantum subsystem. The accuracy of the resulting expression is then benchmarked against a numerically exact method by using relatively simple models. Although our expression predicts a qualitatively correct dissipation rate for a range of situations, cases involving a strong vibronic resonance are quite challenging. This is attributed to the inherent lack of quantum back reaction in PBME-nH, which becomes significant when the subsystem strongly interacts with a small number of bath modes. A rigorous treatment of such an effect will be crucial for developing quantitative simulation methods that can handle generic subsystem–bath coupling.
Enhancement of photoelectrochemical activity of TiO2 electrode by particulate/dense double-layer formation
Authors: Hayashi Naruki , Kato Kosaku , Yamakata Akira
Published: June 2020

Photoelectrochemical water splitting has attracted significant attention as an environment-friendly method to generate H2 and O2. Electrodes composed of powders exhibit a large surface area and are favorable for surface reactions; however, their high resistance prevents charge transportation. In contrast, photoelectrodes composed of a dense film exhibit high conductivity; however, they constitute a small surface area. Therefore, a combination of these two films can lead to higher photoelectrochemical activities. Herein, a particulate/dense TiO2 hybrid electrode exhibited eightfold and twofold higher activities for water oxidation at sufficiently positive potentials as compared to those of the single particulate and dense film electrodes, respectively. Electrochemical impedance measurements and the light intensity dependence of the photocurrent suggest that the activity enhancement is responsible for the synergistic effects of effective charge separation in the highly conductive dense TiO2 film and effective hole-consuming reaction at the particulate TiO2 layer. However, the activity rather decreased near the onset potential of water oxidation (<0.3 V) under the illumination of light near the bandgap energy (375 nm). Such an activity decrease was not observed for the 340 nm illumination; hence, the recombination of charge carriers generated in dense and particulate layers is responsible: the charge transfer resistance at the particulate/dense interface prevents the effective charge separation. These results demonstrate that the combination of particulate matter and dense films can produce a synergistic effect; however, the resistance at the junction remains a significant bottleneck, rendering resistance reduction necessary to maximize the advantages of hybrid electrodes, especially under the illumination of longer wavelength light.
TiSr antisite: An abundant point defect in SrTiO3
Authors: Karjalainen Antti , Prozheeva Vera , Makkonen Ilja , Guguschev Christo , Markurt Toni , Bickermann Matthias , Tuomisto Filip
Published: June 2020

We present a systematic study of the positron lifetime as a function of measurement temperature in strontium titanate (SrTiO3) single crystals grown in different conditions and by different synthesis methods. We combine our experimental results with state-of-the-art theoretical calculations of positron annihilation parameters. We find that the essentially omnipresent 180–190 ps lifetime component is most likely the TiSr antisite defect, possibly coupled with one or more oxygen vacancies, supporting the importance of the TiSr antisite related defects in SrTiO3.
Reversible transition between bipolar resistive switching and threshold switching in 2D layered III–VI semiconductor GaSe
Authors: Du Huiying , Tu Meilin , Luo Songwen , Liu Yuhuan , Qiu Xinyue , Lu Haipeng , Li Shangdong , Yuan Shuoguo , Huang Wen , Jie Wenjing , Hao Jianhua
Published: June 2020

Recently, two-dimensional (2D) layered materials have emerged as promising candidates for resistive switching (RS) devices. However, challenges in controllable conversion of RS types in such 2D materials still remain. Here, we report the experimental realization of reversible transition between non-volatile bipolar resistive switching (BRS) and volatile threshold switching (TS) in 2D layered III–VI semiconductor gallium selenide (GaSe) nanosheets through appropriately setting the compliance current (Icc). Under a relatively high Icc value of 1 mA, the device shows non-volatile BRS performance with a high ON/OFF ratio of nearly 104, a long retention time of 12 000 s, and a high endurance of 1200 switching cycles. Furthermore, under a relatively low Icc (lower than 10 μA), the volatile TS behaviors can be observed. For the former, the large Icc can generate stable conductive filaments (CFs) of Ga vacancy. Thus, the breakage of the stable CFs needs a high reverse voltage to re-align the Ga vacancy. For the latter, the low Icc generated unstable CFs can be broken by the current induced Joule heat. This study establishes the feasibility of integrating different RS types in 2D layered semiconductor nanosheets and understanding the underlying physical mechanism of different RS types in the 2D platform.
Dust vortex flow analysis in weakly magnetized plasma
Authors: Kumar Prince , Sharma Devendra
Published: June 2020

Analysis of driven dust vortex flow is presented in a weakly magnetized plasma. The 2D hydrodynamic model is applied to the confined dust cloud in a non-uniform magnetic field in order to recover the dust vortex flow driven in a conservative force field setup, in the absence of any non-conservative fields or dust charge variation. Although the time independent electric and magnetic fields included in the analysis provide conservative forcing mechanisms, when a drift based mechanism, recently observed in a dusty plasma experiment by M. Puttscher and A. Melzer [Phys. Plasmas 21, 123704 (2014)] is considered, the dust vortex flow solutions are shown to be recovered. We have examined the case where a purely ambipolar electric field, generated by polarization produced by the electron E×B drift, drives the dust flow. A sheared E×B drift flow is facilitated by the magnetic field gradient, driving the vortex flow in the absence of ion drag. The analytical stream-function solutions have been analyzed with varying magnetic field strengths, gradients, and kinematic viscosities of the dust fluid. The effect of the B field gradient is analyzed which contrasts that of the E field gradient present in the plasma sheath.
Three-dimensional wake dynamics behind a tapered cylinder with large taper ratio
Authors: De Arnab Kumar , Sarkar Sandip
Published: June 2020

We have performed direct numerical simulations of flow past a tapered circular cylinder during the early transition to three dimensions for two successive taper ratios (TR) of 20 and 12.5. Our results indicate the random occurrence of vortex splits and dislocations as the topology of the shedding signature. In particular, we observe oblique cellular shedding with multiple spanwise patterns and oppositely oriented oblique cells in the shed structure. Unlike flow imposed shear, the vortex formation length becomes sensitive to the taper ratio, which removes oblique frequency waves noticed for lower shear rate. The local Strouhal frequency (Stz) at the higher TR case exhibits a decreasing trend with remarkably smaller finite jumps at the cell boundaries and is found close to uniform cylinder flow. The wavelet analysis reveals the narrowing of the spectrum at a lower TR. A higher TR case shows a distinctly regular and evenly spaced spectrum which does not reach the maximum Stz, making it a rare event. The present results show that tapering causes the appearance of a secondary motion, which completely reverses at the downstream cylinder wake. Our numerical calculations show that pressure has an indirect role in the growth of the secondary instabilities, where isobars align along with the taper profile. The geometrically induced shear promotes greater mixing in the near wake, and we found that the maximum cross-stream velocity never exceeds 10% of the mean flow even with the steepest TR. The streamwise growth of the defect layer is slower for increasing TR and reaches an early saturation. Although the velocity deficit is higher at the steepest TR, it causes a delay in the momentum recovery along the streamwise direction. The shape factor for the lower TR case shows a delay in the laminar–turbulent transition. Finally, our global stability analysis results employing dynamic mode decomposition revealed a nonlinear dynamical system with spanwise dissipation of the dynamic modes.
Temperature dependent elastic constants and thermodynamic properties of BAs: An ab initio investigation
Authors: Malica Cristiano , Dal Corso Andrea
Published: June 2020

We present an ab initio study of the temperature dependent elastic constants of boron arsenide, a semiconductor that exhibits ultra-high thermal conductivity and is under investigation for thermal management in electronics. We test the consistency of our predictions by computing the temperature dependent sound velocity of the longitudinal acoustic mode along the [111] direction and comparing with experiments. Furthermore, as a by-product, we present the room temperature phonon dispersions and the temperature dependent thermal expansion, isobaric heat capacity, and average Grüneisen parameter compared with the most updated experiments and previous calculations when available. Finally, we present the theoretical estimate of the temperature dependent mean square atomic displacements.
Shock recompaction of spall damage
Authors: Jones D. R. , Fensin S. J. , Morrow B. M. , Martinez D. T. , Hixson R. S.
Published: June 2020

Spall fracture is a high strain-rate damage phenomenon associated with shock or impulsive loading events. When a material that has been subjected to shock compression is allowed to release, rarefaction waves propagate into the sample and reduce the internal stress to zero. If multiple rarefaction waves intersect, they generate tension which, if sufficient, can nucleate voids in the material. It has been observed in several works investigating spall fracture that although the shock-wave profiles suggested spall occurred, imaging of the recovered sample revealed no voids or cracks. In this study, we aim to determine whether a second shock event could recompact existing spall damage, and if so, what form does the microstructure at the recompaction interface have? Through a series of gas-gun flyer-plate impact experiments, we demonstrate that modest shock stresses of 2 GPa–3 GPa are enough to both fully compact a damaged copper target back to a state of zero porosity and, furthermore, drive recrystallization of the interface such that there is a new bond formed where the free surfaces were brought together.
Size-extensive seniority-zero energy functionals derived from configuration interaction with double excitations
Authors: Vu Nam , DePrince A. Eugene
Published: June 2020

The doubly occupied configuration interaction (DOCI) approach can provide an accurate black-box description of nondynamic electron correlation at a computational cost that increases combinatorially with the system size. Remarkably, a pair coupled-cluster doubles (pCCD) approach (also known as the antisymmetrized product of one-reference orbital geminals) can reproduce DOCI energies with only a quadratic number of wave function parameters, and, when neglecting the cost associated with any two-electron integral transformations, these parameters can be determined at a cubic computational cost. Other simpler seniority-zero approaches derived from size-extensive modified configuration interaction doubles functionals can also provide approximations to DOCI energies at similar computational costs. We develop seniority-zero formulations of the coupled-electron pair approximation, the averaged coupled-pair functional, averaged quadratic coupled-cluster, and the parametric two-electron reduced density matrix (p2RDM) approach. These methods are Hermitian and thus offer several potential advantages over pCCD theory, including a reduction in the number of variable parameters and simplified definitions of reduced density matrices. Of the methods investigated, only the pair p2RDM (pp2RDM) approach yields energies that are comparable in quality to pCCD and DOCI. For the molecular systems investigated, pp2RDM-derived RDMs are found to be better approximations to DOCI ones than those obtained from pCCD.
Kinetics of permeation and absorption of hydrogen in palladium during bending and unbending of a palladium cantilever
Authors: Feldman E. P. , Lyubimenko E. N. , Gumennyk K. V.
Published: June 2020

The paper gives an analytical solution for the practically important problem of finding the magnitude of the mechanical deflection of a thin palladium plate (cantilever) during its one-sided saturation with hydrogen. A reasonably simple model is proposed, which permits us to derive and analyze a system of kinetic equations defining the concentration gradient of atomic hydrogen across the plate. We perform numerical integration and asymptotic analysis of the obtained governing equations (subject to acceptable initial and boundary conditions) and thus describe the temporal evolution of the deflection. The latter is found to be in good agreement with time dependence of a palladium cantilever bending obtained in the experimental part of the work. These results permit us to determine an important kinetic coefficient, namely, the permeation rate of hydrogen through the palladium surface.
Toward a fully automated calculation of rovibrational infrared intensities for semi-rigid polyatomic molecules
Authors: Erfort Sebastian , Tschöpe Martin , Rauhut Guntram
Published: June 2020

The implementation of a new program for the variational calculation of rovibrational state energies and infrared intensities is presented. The program relies on vibrational self-consistent field and vibrational configuration interaction theory and is based on the Watson Hamiltonian. All needed prerequisites, i.e., multidimensional potential energy and dipole moment surfaces, comprehensive symmetry information, the determination of vibrational wave functions, and an efficient calculation of partition functions, are computed in a fully automated manner, which allows us to calculate rovibrational spectra in a black-box type fashion. Moreover, the use of a molecule specific rotational basis leads to reliable rovibrational line lists. Benchmark calculations are provided for thioformaldehyde (H2CS), which shows strong Coriolis coupling effects and a complex rovibrational spectrum. The underlying multidimensional potential energy surface has been calculated at the level of explicitly correlated coupled-cluster theory.
Bimolecular photoinduced electron transfer in non-polar solvents beyond the diffusion limit
Authors: Nançoz Christoph , Rumble Christopher , Rosspeintner Arnulf , Vauthey Eric
Published: June 2020

Electron transfer (ET) quenching dynamics in non-polar solvents are investigated using ultrafast spectroscopy with a series of six fluorophore/quencher pairs, covering a driving force range of more than 1.3 eV. The intrinsic ET rate constants, k0, deduced from the quenching dynamics in the static regime, are of the order of 1012–1013 M−1 s−1, i.e., at least as large as in acetonitrile, and do not exhibit any marked dependence on the driving force. A combination of transient electronic and vibrational absorption spectroscopy measurements reveals that the primary product of static quenching is a strongly coupled exciplex that decays within a few picoseconds. More weakly coupled exciplexes with a longer lifetime are generated subsequently, during the dynamic, diffusion-controlled, stage of the quenching. The results suggest that static ET quenching in non-polar solvents should be viewed as an internal conversion from a locally excited state to a charge-transfer state of a supermolecule rather than as a non-adiabatic ET process.
Molecular and thermodynamics descriptions of flow-induced
crystallization in semi-crystalline polymers
Authors: Chen Wei , Zhang Qianlei , Zhao Jingyun , Li Liangbin
Published: June 2020

The flow-induced crystallization (FIC) is commonly encountered in the polymer industry as more than 70% of commercial polymers are crystalline, which needs to be processed before the final application. The complicated external flow field, i.e., shear or extensional flow, results in a great challenge in understanding the FIC phenomenon from both general thermodynamics and detailed molecular level aspects. The current tutorial first describes the general phenomenon of FIC from the aspect of different morphologies and enhanced kinetics induced by the flow. Second, characterization methods for monitoring FIC are introduced. Here, the in situ synchrotron x-ray scattering and non-equilibrium molecular dynamics simulation are selected as typical examples. Then, the theoretical descriptions of FIC are summarized from the aspects of molecular origin and thermodynamics. The coil–stretch transition theory and later developed stretched network theory are highlighted, where the former mainly accounts for polymer dilute solution and the latter for highly entangled cases. Also, multi-step features for the formation of various intermediate states during flow-induced nucleation are depicted. Despite non-equilibrium nature, the FIC can still be treated by thermodynamics, especially under weak flow conditions. The classic entropy reduction model is introduced together with later modifications. In all, understanding the fundamental mechanism of FIC is crucial for optimizing external processing parameters and internal molecular characteristics, and useful to guide current or further applied techniques.
Acoustic levitation in mid-air: Recent advances, challenges, and future perspectives
Authors: Andrade Marco A. B. , Marzo Asier , Adamowski Julio C.
Published: June 2020

Mid-air acoustic levitation is becoming a powerful tool to suspend and manipulate millimetric objects. Because of its unique characteristics, acoustic levitation is suitable to trap a wide variety of materials such as liquids, solids, soap bubbles, and even living creatures. Acoustic levitation can also be combined with noncontact measurement systems, allowing contactless analysis and characterization of levitating samples. In this article, we review some of the advances that have been made over the last decade. We also present the technical challenges that must be overcome in order to extend the capability of current acoustic levitation devices and, finally, we point out future directions for acoustic levitation.
High-resolution photoelectron imaging of MnB3−: Probing the bonding between the aromatic B3 cluster and 3d transition metals
Authors: Cheung Ling Fung , Czekner Joseph , Kocheril G. Stephen , Wang Lai-Sheng
Published: June 2020

The B3 triangular unit is a fundamental bonding motif in all boron compounds and nanostructures. The isolated B3− cluster has a D3h structure with double σ and π aromaticity. Here, we report an investigation of the bonding between a B3 cluster and a 3d transition metal using high-resolution photoelectron imaging and computational chemistry. Photoelectron spectra of MnB3− are obtained at six different photon energies, revealing rich vibrational information for the ground state detachment transition. The electron affinity of MnB3 is determined to be 1.6756(8) eV, and the most Franck–Condon-active mode observed has a measured frequency of 415(6) cm−1 due to the Mn—B3 stretch. Theoretical calculations show that MnB3− has a C2v planar structure, with Mn coordinated to one side of the triangular B3 unit. The ground states of MnB3− (6B2) and MnB3 (5B2) are found to have high spin multiplicity with a significant decrease in the Mn—B bond distances in the neutral due to the detachment of an Mn—B3 anti-bonding electron. The Mn atom is shown to have weak interactions with the B3 unit, which maintains its double aromaticity with relatively small structural changes from the bare B3 cluster. The bonding in MnB3 is compared with that in 5d MB3 clusters, where the strong metal–B3 interactions strongly change the structures and bonding in the B3 moiety.
Electrical and optical properties of degenerate and semi-insulating ZnGa2O4: Electron/phonon scattering elucidated by quantum magnetoconductivity
Authors: Look David C. , Leedy Kevin D. , Horng Ray-Hua , Santia Marco D. , Badescu Stefan C.
Published: June 2020

We study the electrical and optical properties of degenerate ZnGa2O4 films grown by metalorganic chemical vapor deposition (MOCVD) on sapphire and semi-insulating films grown by pulsed laser deposition (PLD) on fused silica. After a forming-gas anneal at 700 °C, the MOCVD film is highly conducting, with a room-temperature carrier concentration of 2 × 1020 cm−3, a mobility of 20 cm2/V s, and direct bandgap absorptions at 3.65 eV and 4.60 eV. Under the same annealing conditions, the PLD film is semi-insulating, with a direct bandgap absorption at 5.25 eV. The phonon structure, important for electrical and thermal conduction as well as superconductivity and other quantum phenomena, is very complicated due to the large number of atoms (and, thus, phonon branches) in the unit cell. However, we show that the phonon contributions to electron mobility (μph) can be directly measured by quantum-based magnetoconductivity over the temperature span T = 10–200 K. From an approximate analytical formula, μph = function (Tph, T), we calculate an effective phonon energy kTph(T) that takes account of all phonon contributions at temperature T. For T = 10–200 K, the value of kTph ranges from about 10 to 90 meV, consistent with the energy range of the ZnGa2O4 phonon density of states (at 0 K) calculated by density functional theory. The total measured mobility can then be modeled by μtot−1 = μii−1 + μph−1, where μii is the mobility due to ionized-impurity scattering. With a high bandgap, controllable conductivity, high breakdown voltage, and bulk-growth capability, ZnGa2O4 offers opportunities for high-power electronics and UV detectors.
Electrical stimulation extends the time limits for very fast chilling of lamb loins
Authors: Jacob Robin H. , Rosenvold Katja , North Michael , Kemp Robert , Warner Robyn D.
Published: June 2020

Context
Very fast chilling (VFC) involves cooling meat to approximately –1°C before the onset of rigor, and offers potential benefits compared with conventional chilling that include accelerated tenderisation, improved shelf life and reduced inventory costs. However, the practical difficulties of achieving the required temperature profile prevents adoption of VFC commercially.

Aims
The objective of this study was to determine if electrical stimulation could be a way of making VFC easier to achieve for lamb meat. The hypothesis tested was that electrical stimulation would reduce the rate of chilling required with very fast chilling by accelerating the rate of pH decline post-mortem.

Methods
The experiment was a 2 × 3 factorial design whereby 54 loins from 27 lambs were allocated to one of six different treatments: no electrical stimulation and electrical stimulation, and chilling rates to reach −1°C at 1 h (Fast), 1.5 h (Moderate) and 2.5 h (Slow) post-mortem respectively.

Key results
Without electrical stimulation, shear forces were lowest for the Moderate chilling rate; but with electrical stimulation, consistently low shear force values were obtained with all chilling rates. Muscle pH depended on treatment, although this effect also depended on the time post-mortem. Shear force depended on chilling rate only when there was no electrical stimulation. Without electrical stimulation, the optimal chilling rate was the Moderate treatment. Effects on sarcomere length accounted for some, but not all, of the effects of treatment on shear force.

Conclusions
Electrical stimulation therefore reduced the chilling rate required to optimise tenderness with VFC, and could be a component of a practical VFC regime for lamb meat.

Implications
VFC could become a practical chilling method, but only when sensory evaluation supports the favourable shear force findings established in this study. This would require evaluation of VFC at a commercial scale.
Regulation of the size of photosystem II light harvesting antenna represents a universal mechanism of higher plant acclimation to stress conditions
Authors: Borisova-Mubarakshina Maria M. , Vetoshkina Daria V. , Naydov Ilya A. , Rudenko Natalia N. , Zhurikova Elena M. , Balashov Nikolai V. , Ignatova Lyudmila K. , Fedorchuk Tatyana P. , Ivanov Boris N.
Published: June 2020

We investigated acclimatory responses of Arabidopsis plants to drought and salinity conditions before the appearance of obvious signs of damage caused by these factors. We detected changes indicating an increase in the reduction level of the chloroplast plastoquinone pool (PQ pool) 5–7 days after introduction of the stress factors. After 10–14 days, a decrease in the size of PSII light harvesting antenna was observed in plants under conditions of drought and salinity. This was confirmed by a decrease in content of PSII antenna proteins and by downregulation of gene expression levels of these proteins under the stress conditions. No changes in values of performance index and maximum quantum yield of PSII were detected. Under drought and salinity, the content of hydrogen peroxide in leaves was higher than in control leaves. Thus, we propose that reduction of the size of PSII antenna represents one of the universal mechanisms of acclimation of higher plants to stress factors and the downsizing already begins to manifest under mild stress conditions. Both the PQ pool reduction state and the hydrogen peroxide content are important factors needed for the observed rearrangement.
Diurnal changes of the ascorbate-glutathione cycle components in wheat genotypes exposed to drought
Authors: Aliyeva Durna R. , Aydinli Lala M. , Zulfugarov Ismayil S. , Huseynova Irada M.
Published: June 2020

The ascorbate-glutathione (AsA-GSH) cycle is a major pathway of H2O2 scavenging in plants. The effect of diurnal variations in hydrogen peroxide (H2O2) content, the intensity of lipid peroxidation (malondialdehyde, MDA), photosynthesis, antioxidants and antioxidative enzyme activities involved in AsA-GSH metabolism has been studied comparatively in leaves of durum (Triticum durum Desf.) and bread (Triticum aestivum L.) wheat genotypes exposed to soil drought. Drought stress caused an increase in the content of H2O2, MDA, alterations in the activities of AsA-GSH cycle enzymes and quantitative changes in AsA and GSH content during the day. PSII efficiency was significantly lower in the control and drought exposed leaves at the highest temperature in the afternoon. The ascorbate peroxidase activity was found to increase and ascorbic acid amount decreased with increasing temperature during the day. Further, the glutathione amount and glutathione reductase activity increased at the expense of the regeneration of the oxidised form of glutathione. Our results revealed that wheat can tolerate drought stress by enhancing the antioxidant enzyme activities and alteration of the concentration of ascorbate and glutathione.
Policy changes in dam construction and biodiversity conservation in the Yangtze River Basin, China
Authors: Xu Hongzhang , Pittock Jamie
Published: June 2020

Damming rivers addresses a range of society’s needs, but at the cost of fragmentation and other negative effects on freshwater ecosystems. This article examines hydropower development and fish conservation in the Upper Yangtze River Basin to explore strategies for managing dams more sustainably at the basin scale. We highlight the need to limit the effects of hydropower dams on freshwater biodiversity, and that protecting fish in reserves could be one of the most effective approaches to limiting the ecological effects of dams on fish. However, in the Yangtze River basin there are dams on the rivers in all but 1 of the 14 fish reserves mapped in this study, thus compromising the effectiveness of the reserves. In addition, the removal of some dams may not be as effective as suggested. Thus, we propose that limiting dam construction in protected tributaries is a ready-to-adopt conservation strategy. However, the adoption of this policy by the Chinese government will be determined by which of two competing policy changes (i.e. gradual or sudden) in the policy subsystem of dam construction will prevail. In this paper we illustrate how greater triage in the Upper Yangtze River Basin can deliver services to people and conserve freshwater biodiversity.
Retrograde migration supplies resident memory T cells to lung-draining LN after influenza infection
Authors: Stolley J. Michael , Johnston Timothy S. , Soerens Andrew G. , Beura Lalit K. , Rosato Pamela C. , Joag Vineet , Wijeyesinghe Sathi P. , Langlois Ryan A. , Osum Kevin C. , Mitchell Jason S. , Masopust David
Published: June 2020

Numerous observations indicate that resident memory T cells (TRM) undergo unusually rapid attrition within the lung. Here we demonstrate that contraction of lung CD8+ T cell responses after influenza infection is contemporized with egress of CD69+/CD103+ CD8+ T cells to the draining mediastinal LN via the lymphatic vessels, which we term retrograde migration. Cells within the draining LN retained canonical markers of lung TRM, including CD103 and CD69, lacked Ly6C expression (also a feature of lung TRM), maintained granzyme B expression, and did not equilibrate among immunized parabiotic mice. Investigations of bystander infection or removal of the TCR from established memory cells revealed that the induction of the TRM phenotype was dependent on antigen recognition; however, maintenance was independent. Thus, local lung infection induces CD8+ T cells with a TRM phenotype that nevertheless undergo retrograde migration, yet remain durably committed to the residency program within the draining LN, where they provide longer-lived regional memory while chronicling previous upstream antigen experiences.
APMP supplementary comparison of air kerma in ISO 4037 wide and narrow series x-ray beams: APMP.RI(I)-S3
Authors: Butler D J , Saito N , Büeermann L , Lee J -H , Laban J , Srimanoroth S , Kulkarni M S , Tebekana N
Published: June 2020

The results of a regional supplementary comparison of air kerma standards from eight standards laboratories are presented. The three transfer ionisation chambers (two model Exradin A4 chambers and one Exradin A5 chamber manufactured by Standard Imaging, Inc, Middleton, MI, USA) were measured at each laboratory over the period 2013 to 2016. Air kerma calibration coefficients for the transfer instruments were compared for the ISO 4037 narrow- and wide-spectrum series of x-ray beams, in the range from 30 kV to 300 kV. Results from the five primary standard and three secondary standard laboratories were obtained. For each radiation quality, the results were expressed as the ratio of the laboratory to the comparison reference value, which was the average of three laboratories selected for this purpose before the comparison began. The A5 transfer standard was also compared for air kerma at protection-level 137Cs gamma rays. Laboratories reported their conversion coefficients for ambient dose equivalent, H*(10), and so the comparison also served as an indirect test of this quantity. Overall, the laboratories were in general agreement within the expanded uncertainties claimed by the laboratories. The comparison is designated APMP.RI(I)-S3 under the international arrangements for comparisons conducted to support the CIPM MRA.

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To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.

The final report has been peer-reviewed and approved for publication by the CCRI, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).
Facile synthesis of graphitic carbon nitride via copolymerization of melamine and TCNQ for photocatalytic hydrogen evolution
Authors: Wang Fengzhi , Lei Weisheng , Pan Xinhua , Ye Zhizhen
Published: June 2020

Graphitic carbon nitride (g-C3N4) has been regarded as an intriguing photocatalyst applying to hydrogen generation but suffering rapid recombination of photoinduced electron-hole pairs and insufficient absorption under visible light. We developed a novel one-pot thermal copolymerization method of melamine as a precursor and 7,7,8,8-tetracyanoquinodimethane (TCNQ) as a comonomer to synthesize modified g-C3N4 (abbreviated as X% TCNQ) for the first time, aiming to directly incorporate TCNQ molecular into carbon nitride skeleton for the substitution of low-electronegative carbon for high-electronegative nitride atom. Results revealed that the as-prepared photocatalysts by copolymerization of melamine with TCNQ retained the original framework of g-C3N4, and dramatically altered the electronic and optical properties of carbon nitride. Various measurements confirmed that as-synthesized samples exhibited larger specific surface areas, faster photogenerated charge transfer and broader optical absorption by decreasing the π-deficiency and extending the π-conjugated system, thus facilitating the photocatalytic activity. Specifically, the 0.3% TCNQ exhibited as high as seven times than the pristine g-C3N4 on photocatalytic H2 generation and kept its photoactivity for five circles. This work highlights a feasible approach of chemical protocols for the molecular design to synthesize functional carbon nitride photocatalysts by copolymerizing appropriate g-C3N4 precursor and comonomers.
Effects of bending strain and crack direction on crack-based strain sensors
Authors: Kwon Yongmin , Park Chan , Kim Jungmin , Kim Hyonguk , Park Cheoljeong , Lee Byeongjun , Jeong Yeondo , Cho Seong J
Published: June 2020

Inspired by the sensory organs of spiders, crack-based strain sensors are flexible sensors fabricated by depositing a thin layer of metal onto a stretchable polymer. However, to date, most studies on crack-based sensors have considered only linear strain, even when bending is considered, which do not analyze how sensor resistance depends on complex strains (linear, convex, and concave). For each given type of strain, this study examined how the distance between cracks depends on the crack direction. This study also analyzed how the crack-generation mechanism depends on the relation between film-bending axis and crack direction. Thus, a device was proposed herein to test the crack-based sensors and demonstrate how this device can be used to measure the bending direction.
Non-Markovian effects on charging and self-discharging process of quantum batteries
Authors: Kamin F H , Tabesh F T , Salimi S , Kheirandish F , Santos Alan C
Published: June 2020

The performance of quantum technologies that use entanglement and coherence as a resource is highly limited by the effects of decoherence due to their interaction with some environment. In particular, it is important to take into account situations where such devices unavoidably interact with surrounding. Here, we study memory effects on energy and ergotropy of quantum batteries in the framework of open system dynamics, where the battery and charger are individually allowed to access a bosonic environment. Our investigation shows that the battery can be fully charged as well as its energy can be preserved for long times in non-Markovian dynamics compared with Markovian dynamics. Moreover, the non-Markovianity increase makes it possible to extract the total stored energy as work and the discharge time becomes longer. Our results indicate that memory effects can play a significant role in improving the performance of quantum batteries.