bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of the externally driven velocity shear on the turbulence radial wavenumber spectral shift and its amplitude
Authors: Xiao G. L. , Zou X. L. , Zhong W. L. , Song S. D. , Liang A. S. , Liu A. D. , Xu M. , Duan X. R.
Published: July 2019

It has been observed that the plasma velocity shear can be strongly affected by external source input, such as neutral beam injection, lower hybrid current drive, supersonic molecule beam injection, and impurity injection. Such a change in velocity shear can lead to turbulence suppression or enhancement by inducing a spectral shift in the turbulence radial wavenumber spectrum. A theoretical model, based on the nonlinear evolution of the turbulence amplitude with an externally driven velocity shear, combined with the thermal transport equation, has been used to describe the turbulence evolution. A critical growth rate γ0 for the turbulence regulation has been identified in this theoretical model, and the parametric dependency of γ0 is investigated. A threshold Uc of the reduction value of the velocity shear rate U, intimately related to γ0, has been found for the triggering radial wavenumber shift. This indicates that the turbulence could be regulated by external source input, when U > Uc.
Enhanced mobility of Sn-doped Ge thin-films (≤50 nm) on insulator for fully depleted transistors by nucleation-controlled solid-phase crystallization
Authors: Xu Chang , Gong Xiangsheng , Miyao Masanobu , Sadoh Taizoh
Published: July 2019

High-speed fully depleted thin-film transistors (TFTs) for low-power consumption are required for next-generation electronics, such as three-dimensional large-scale integrated circuits and advanced system-in-displays. For this purpose, high-carrier-mobility semiconductor thin-films (thickness: ≤∼50 nm) on insulator structures should be fabricated under low-temperature processing conditions (≤500 °C). To achieve this, solid-phase crystallization of amorphous GeSn (a-GeSn) with low Sn concentration (2%) is investigated for a wide range of film thicknesses (30 − 200 nm), where thin a-Si underlayers (thickness: 0 − 20 nm) are introduced between a-GeSn films and substrates. GeSn is polycrystallized by annealing at 450 °C, keeping Si underlayers amorphous. Crystal grains of almost identical sizes are obtained for GeSn thicknesses of 30 − 50 nm, though grain sizes significantly decrease for thicknesses exceeding 50 nm owing to enhanced bulk nucleation. A detailed analysis of GeSn films (thickness: 50 nm) reveals that grain sizes are decreased by introducing a-Si underlayers (thickness: 3 − 20 nm), e.g., from ∼10 μm to 2 − 3 μm. This phenomenon is attributed to the change in dominant nucleation sites from the interface to the bulk, which significantly decreases grain-boundary scattering of carriers through a decrease in the barrier heights at grain boundaries. As a result, a high carrier mobility of 200 − 300 cm2/V s is realized for GeSn thin-films (thickness: 30 − 50 nm) grown with a-Si underlayers. The mobility (200 − 300 cm2/V s) is the largest ever reported data for Ge and GeSn thin-films (thickness: 30 − 50 nm) grown at low temperatures (≤500 °C). This technique will facilitate the realization of high-speed fully depleted TFTs for next-generation electronics.
Bandwidth extension of seismometer by using a novel topology leaf spring
Authors: Yao Zhenjing , Duan Yanli , Li Lixin , Hong Li
Published: July 2019

A novel topology leaf spring as a substitute for the traditional spring was designed to expand the effective bandwidth of a seismometer. The finite element analysis showed that the seismometer with the new topology spring has better performance than that with the traditional spring. Compared with the traditional pendulum, the proposed topology structure was featured with lower natural frequency and higher spurious frequency. The bandwidth of the proposed seismometer was enhanced to [2 s, 72 Hz] with an increase of 43% over the traditional seismometer bandwidth of [1 s, 51 Hz] as well as the signal distortion of the seismometer was also reduced with the proposed topology spring.
Light scattering by correlated disordered assemblies of nanoantennas
Authors: El Shamy Eslam , Jaeck Julien , Haïdar Riad , Bouchon Patrick
Published: July 2019

Optical nanoantennas are widely used to build absorbing metasurfaces with applications in photodetection, solar cells, and sensing. Most of the time, the nanoantennas are assembled as a periodic distribution, but there have been various works where disordered arrays are used, either to get rid of diffraction orders or due to a fabrication process that prevents any determined distribution. Here, we investigate both theoretically and experimentally the unavoidable scattering introduced by such disorders. By introducing a perturbation on the positions of 1D arrays of metal-insulator-metal (MIM) nanoantennas, the light is scattered rather than increasingly absorbed. The scattering occurs only in the plane of incidence and on a given spectral range. We show how this scattering can be manipulated from 0% to 55% of the incoming light.
Numerical investigation of plasma properties for the microwave discharge ion thruster μ10 using PIC-MCC simulation
Authors: Yamashita Y. , Tani Y. , Tsukizaki R. , Koda D. , Nishiyama K.
Published: July 2019

This paper reports the numerical investigation of plasma properties for the microwave discharge ion thruster μ10. The model consists of a particle in cell simulation and a Monte Carlo collision simulation. The results indicate that the plasma density and the electron temperature in the confined region are larger than those in other regions and are qualitatively consistent with probe measurements. Moreover, we traced the trajectories of charged particles to investigate the plasma generation and transport. The electron trajectories indicate that electrons are strongly confined by the mirror magnetic field and the sheath, which indicates that the confinement depends on the electron energy. As a result, the electron energy distribution function is a combination of two Maxwellian distributions. Although the hot electrons account for 3.4% of all electrons, they account for 50.1% of the ionization and can generate plasma with an excitation loss of 1/3 of that of cold electrons. The ion trajectories indicate that they are affected by the magnetic field. To investigate the effect of the magnetic field on the transport, we evaluate the ion and electron current percentage toward the wall and compare with the wall surface percentage. The ion and electron current ratios differ because of diffusion with respect to the magnetic field. The ion current percentage is larger than the surface area percentage in the grid, which indicates that ions are transported to the grid more efficiently due to the magnetic field. Therefore, the effect on ions by the magnetic field is one of the most important criteria for microwave discharge ion thrusters.
Confinement effects on the orientation of graphene in multilayer polymer nanocomposites during lamination: A molecular dynamics simulation
Authors: Shi Meinong , Yang Weimin , Cheng Lisheng , Zhen Xiangshi , Jiao Zhiwei
Published: July 2019

As a stacking form of ultrathin polymer films, multilayer nanostructures are of great interest in various applications. Coarse-grained molecular dynamics simulations were carried out to understand the confinement effects on the orientation of graphene sheets in multilayer polymer films during lamination. The influences of position, strain rate, expansion type, and arrangement pattern on the orientation of graphene sheets in the near-boundary and internal layers were considered. It was found that the confinement effects induce the graphene sheets to gradually orient parallel to the plane of the layer during lamination. Such effects are more obvious in the near-boundary layer than in the internal layer. With the same strain, a smaller strain rate gives rise to more obvious effects on the in-plane orientation of graphene sheets in both the near-boundary and internal layers. Biaxial expansion also makes the graphene sheets orient more parallel to the plane of the layer. This work is helpful for better understanding the lamination process and the designing of multilayer nanocomposites.
Diagnosis of fast ions produced by negative-ion neutral-beam injection with fast-ion deuterium-alpha spectroscopy
Authors: Muscatello C. M. , Heidbrink W. W. , Boivin R. L. , Chrystal C. , Collins C. S. , Fujiwara Y. , Yamaguchi H.
Published: July 2019

Negative-ion neutral-beam injection (NNBI) is an important source of heating and current drive for next-step fusion devices where the injected energy can range from hundreds of keV to 1 MeV. Few diagnostics are suitable for phase-space resolved measurements of fast ions with energy in excess of 100 keV. A study to assess the feasibility of fast-ion deuterium-alpha (FIDA) spectroscopy to diagnose high-energy ions produced by NNBI is presented. Case studies with the Large Helical Device (LHD) and JT-60SA illustrate possible solutions for the measurement. The distribution function of fast ions produced by NNBI is calculated for both devices, and the FIDA spectrum is predicted by synthetic diagnostic simulation. Results with 180 keV NNBI in LHD show that, with a judicious choice of viewing geometry, the FIDA intensity is comparable to that obtained with the existing FIDA system. The measurement is more challenging with the 500 keV NNBI in JT-60SA. Simulations predict the FIDA intensity to be about 1% of the background bremsstrahlung, which is small compared to existing FIDA implementations with positive neutral-beam injection where signal levels are an order of magnitude larger. The sampling time required to extract the small FIDA signal is determined using a probabilistic approach. Results indicate that long averaging periods, from ones to tens of seconds, are needed to resolve the FIDA signal in JT-60SA. These long averaging times are suitable in long-pulse (∼100 s), steady-state devices like JT-60SA where an important measurement objective is the spatial profile of the slowing-down distribution of fast ions.
Enhancement in hyperthermia efficiency under in situ orientation of superparamagnetic iron oxide nanoparticles in dispersions
Authors: Ranoo Surojit , Lahiri B. B. , Muthukumaran T. , Philip John
Published: July 2019

To minimize the exposure time in magnetic fluid hyperthermia based cancer therapy, it is important to improve the heating efficiency. We demonstrate a 62% enhancement in heating efficiency through in situ orientation of magnetic nanoparticles (MNP) along the direction of the radio frequency alternating magnetic field using a static external magnetic field of 80 G in phosphate coated superparamagnetic Fe3O4 MNP dispersions. The heating efficiency increase in oriented samples is due to the enhanced effective anisotropy energy density along the linear chainlike structures of the MNPs, as confirmed from atomic force microscopy and the larger dynamic hysteresis loop area.
Micro instabilities and rotating spokes in the near-anode region of partially magnetized plasmas
Authors: Boeuf J. P.
Published: July 2019

Electron and ion transport in the near-anode region of a partially magnetized plasma under conditions typical of Hall thrusters or magnetron discharges is studied with fully kinetic, Particle-In-Cell Monte Carlo Collision (PIC-MCC) simulations assuming a uniform magnetic field and no ionization. We derive a simple relation that defines the magnetic field at the transition point between negative and positive sheaths. For magnetic fields around or above this transition point, PIC-MCC simulations show the development of short wavelength azimuthal instabilities that cascade to longer wavelengths (“rotating spokes”) as the magnetic field is increased. Both short-wavelength and large-wavelength fluctuations can coexist under some conditions. A detailed study of the fluid dispersion relation is used to analyze the PIC-MCC results. Small coherent structures can be associated with the destabilization of ion sound waves by density gradient and collisions. Longer wavelengths or rotating spokes are characteristic of the collisionless Simon-Hoh instability. The small structures are dominant for larger plasma density gradients, while the larger structures correspond to smaller density gradients and larger magnetic fields. Anomalous transport associated with these instabilities can be significant, with effective collision frequencies larger than 2×107 s−1 in xenon for magnetic fields above the transition point.
Evidence of nanostructuring and reduced thermal conductivity in n-type Sb-alloyed SnSe thermoelectric polycrystals
Authors: Gainza J. , Serrano-Sánchez F. , Gharsallah M. , Carrascoso F. , Bermúdez J. , Dura O. J. , Mompean F. J. , Biskup N. , Meléndez J. J. , Martínez J. L. , Alonso J. A. , Nemes N. M.
Published: July 2019

SnSe has been recently reported as an attractive thermoelectric material, with an extraordinarily high, positive, Seebeck coefficient. Here, we describe the synthesis, structural, microscopic, and thermoelectric characterization of Sn1–xSbxSe intermetallic alloys prepared by a straightforward arc-melting technique. Sb-doped tin selenide was synthesized as strongly nanostructured polycrystalline pellets. Neutron diffraction studies reveal that Sb is placed at the Sn sublattice in the crystal structure, showing concentrations as high as 30%, and generates a significant number of Sn vacancies, while the increase of the interlayer distances favors the nanostructuration. The material is nanostructured both out-of-plane in nanometer-scale layers and in-plane by ∼5 nm undulations of these layers. This nanostructuring, along with an increased amount of Sn vacancies, accounts for a reduction of the thermal conductivity, which is highly desirable for thermoelectric materials. The phonon mean free path is estimated to be on the order of 2 nm from low temperature, thermal conductivity, and specific heat, in accordance with the nanostructuration observed by high-resolution transmission electron microscopy. The thermal conductivity of SnSe is characterized by three independent techniques to assure a room temperature value of Sn0.8Sb0.2Se of κ ∼ 0.6 W/m K. The freshly prepared Sb-doped compounds exhibit an abrupt change in the type of charge carriers, leading to large, negative Seebeck coefficients, although the arc-melt synthesized pellets remain too resistive for thermoelectric applications. Cold-pressed pellets evolve to be p-type at room temperature, but reproducibly turn n-type around 500 K, with increased electrical conductivity and maximum observed figure of merit, ZT ∼ 0.3 at 908 K.
New formulation of local-equilibrium thermodynamics
Authors: Yoshida Nobuo
Published: July 2019

This study points out that the conventional separation of balance equations for energy in fluids into a flow and a source term is not thermodynamically valid. It corrects this inadequacy and thereby identifies an expression for the nonnegative rate of entropy production that is a sum of products of kinetic and thermodynamic quantities. Here, the kinetic and corresponding thermodynamic quantities are the flow of internal energy and the gradient of the reciprocal temperature; the flow of each component and the negative gradient of its chemical potential divided by the temperature; the rate of each chemical reaction and its affinity divided by the temperature; and the conversion of mechanical energy into internal energy and the reciprocal temperature. One of the deductions from this expression is that the internal energy of a fluid never turns into its mechanical energy on its own, a fact which had heretofore not been actually proved in general. On the other hand, the stability condition of local equilibrium leads to a nonpositive integral over the volume of a system under suitable boundary conditions. The integrand is found to be the same form as the entropy production expression, with each thermodynamic quantity replaced by its time derivative. It thus turns out that the thermodynamic quantities always vary temporally so as to lower the entropy production of the system. It can also be seen that if a particular kinetic and thermodynamic quantity pair alone is considered only locally, then the absolute value of the latter invariably lessens with time.
Bi2Ne: Weakly bound cluster of diatomic bismuth with neon
Authors: Endo Asuka , Hatanaka Miho , Ueno Nami , Morisawa Yusuke , Wakabayashi Tomonari
Published: July 2019

The A–X transition of diatomic bismuth, Bi2, was revisited by laser induced fluorescence in solid Ne at 3 K. Molecular constants, i.e., vibrational frequencies of 137 cm–1 and 174 cm–1, were reproduced for the upper and lower electronic states as reported by Bondybey et al. [Chem. Phys. Lett. 76, 30 (1980)]. Two-dimensional mapping of emission spectra confirmed satellite bands in higher and lower excitation/emission energies for each of the major bands in the vibrational progression of v′–v″ (v′ = 0–5, v″ = 5–12). Based on the molecular orbital calculations, presence of clusters, Bi2Nen (n = 1–6), is proposed for possible carriers of the observed satellites. For the relatively large matrix shift of ∼67 cm−1 in solid Ne for the term energy of the A state, the diatomic bismuth is supposed to exist as a linearly coordinated cluster of Bi2Ne in the matrix.
Triplet emission of atomic ytterbium isolated in a xenon matrix
Authors: Kleshchina N. N. , Kalinina I. S. , Lambo R. , Buchachenko A. A. , Bezrukov D. S. , Hu S.-M.
Published: July 2019

The electronic transitions of ytterbium atoms in a solid Xe matrix grown at 4.8 K are investigated. Absorption bands are detected in the regions of the gas-phase 6s2 1S0 → 4f135d6s2 and 6s2 1S0 → 6s6p 1P1 transitions. Both bands indicate that Yb atoms occupy multiple trapping sites, of which three are identified. Emission induced by the 6s2 1S0 → 6s6p 1P1 excitation is found to be concentrated entirely in the region of the 6s6p 3PJ → 6s2 1S0 decay, whereas the singlet emission is completely quenched. Multiple emission peaks are observed and the effects of annealing and prolonged irradiation on their amplitudes are found to be significant and are interpreted as a consequence of Yb population transfer from one type of site to another. Modeling of the ground-state site structure and stability predicts three Yb/Xe occupation types, substitutional (ss), tetravacancy (tv) and hexavacancy (hv), in order of decreasing stability. Their tentative associations with observed absorption and emission features are discussed. Time correlated single photon spectroscopy is used to determine the lifetimes of the individual emission bands. They are found to be different from each other with indications of a mixture of short- and long- lived 6s6p 3PJ fine-structure components and demonstrate distinct temperature dependencies. A dramatic decrease in the lifetime of the emission peak tentatively assigned to the most stable site with temperature is explained by a competition between the radiative and non-radiative decay paths of the 6s6p 3P1 state. The mechanism of the latter can be attributed to electron–phonon coupling as confirmed by a model of the temperature-dependence of the lifetime.
The role of spin-orbit coupling in the optical spectroscopy of atomic sodium isolated in solid xenon
Authors: de Pujo P. , Ryan M. , Crépin C. , Mestdagh J.-M. , McCaffrey J. G.
Published: July 2019

Molecular dynamics calculations, based on the diatomics-in-molecules method, have been used to probe the manifestations of spin-orbit (SO) coupling in the experimental absorption bands of atomic sodium isolated in solid xenon. Inclusion of SO coupling of –320 cm−1 in spectral simulations of the 3p2P←3s2S transition leads to unequal band spacings which very closely match the asymmetrical bandshape observed for blue single vacancy (SV) site occupancy. This SO value, extracted in a previous MCD study, reveals the dramatic change in the effective SO coupling constant of the Na atom (from the gas phase value of +17 cm−1) in solid Xe when it is close to the 12 xenon atoms in the first surrounding sphere. In contrast, the symmetrical three-fold split band of the red tetra vacancy (TV) site in Na/Xe is not affected nearly as much by SO coupling. This reflects a greatly reduced “external heavy atom” effect when the 24 Xe atoms surrounding the Na atom in TV are located at greater distances. The contrasting behavior of sodium in the SV and TV sites suggests a strong dependence of the SO coupling strength on the Na–Xe distance.
Electron-induced delayed desorption of solid argon doped with methane
Authors: Khyzhniy I. V. , Uyutnov S. A. , Bludov M. A. , Savchenko E. V. , Bondybey V. E.
Published: July 2019

The total yield of particles desorption from solid Ar doped with CH4 under irradiation with an electron beam was studied at 5 K. The measurements were carried out at a CH4 concentration of 1 and 5%. The effect of explosive delayed desorption from the surface of argon matrix was discovered in both mixtures. With a higher concentration of CH4, it appeared at lower doses and was more pronounced. Two types of self-oscillations were observed: long-period bursts (on a time scale of about 25 min) and short-period oscillations (of about 10 s). In pure solid Ar delayed desorption was not observed despite the accumulation of a significant number of excess electrons, exceeding their number in mixtures of Ar and CH4 as it was found by measurements of thermally stimulated exoelectron emission. This finding discards the model of Coulomb explosion for the phenomenon detected. In this paper we focused on the role of hydrogen (one of the radiolysis products) in delayed desorption. The formation of atomic hydrogen in the matrix was traced via cathodoluminescence by the emission band of the excimer Ar2H* at 166 nm. Desorption of excited hydrogen atoms in the excited state was detected by the Ly-α emission line. A decrease of the Ar2H* band intensity at higher concentration of CH4 was found evidencing bleaching these centers likely due to recombination of H atoms with energy release and formation of molecular hydrogen. The data obtained give additional evidence in favor of the hypothesis that the exothermic reactions of radiolysis products serve as a stimulating factor for delayed desorption.
Luminescence of molecular nitrogen in cryogenic plasmas
Authors: Boltnev R. E. , Bykhalo I. B. , Khmelenko V. V. , Krushinskaya I. N. , Lee D. M. , McColgan P. T. , Sheludiakov S. , Pelmenev A. A.
Published: July 2019

Great enhancement of molecular nitrogen luminescence in the afterglow of nitrogen-helium gas mixtures was observed at temperatures ≤ 10 K. The effect is explained by the increased efficiency of the recombination of nitrogen atoms and energy transfer from metastable nitrogen molecules and helium atoms to nitrogen molecules in the cold dense helium vapor.
Thermoluminescence of nitrogen–neon and nitrogen–argon nanoclusters immersed in superfluid helium
Authors: Meraki Adil , McColgan Patrick T. , Sheludiakov S. , Lee David M. , Khmelenko Vladimir V.
Published: July 2019

Ensembles of nanoclusters created by injection of nitrogen atoms and molecules as well as rare gas (RG) atoms (Ne and Ar) into superfluid 4He have been studied via optical and electron spin resonance (ESR) spectroscopies. We studied the dynamics of thermoluminescence spectra emitted during the warming of porous structures formed by nitrogen–neon and nitrogen–argon nanoclusters inside superfluid helium. We show experimental evidence that quantum vortices initiate chemical reactions in porous ensembles of nanoclusters. Using this experimental approach, it is possible to study chemical reactions of heavy atoms and molecules at very low temperatures where normally their diffusion and quantum tunneling in solid matrices are completely suppressed.
Effect of the polymer ordering on the optical spectra and thermoluminescence of polygermane and polysilane films and nanocomposites
Authors: Ostapenko N. I. , Kerita O. A. , Ostapenko Yu. V. , Chursanova М. V.
Published: July 2019

Comparative study of optical spectra and thermoluminescence of poly(di-n-hexylgermane) (PDHGe) and poly(di-n-hexylsilane) (PDHS) films and nanocomposites with different degrees of ordering have been carried out in the temperature range 5–200 K. The disordering processes, which are essential for PDHGe, lead to the appearance of additional bands in its optical spectra associated with different set of trans- and gauche-conformations of the polymer chain as well as to the broadening of vibrational bands in Raman spectrum. It is shown that polymer chains of confined PDHGe introduced into the nanopores of SBA-15 silica, in contrast to those of PDHS have the gauche-conformation instead of the trans-conformation, as a result of decrease of intermolecular interaction between the polymer chain segments and increase of their mobility. Besides, appearance of discrete levels of the carriers’ activation energy in thermoluminescence of both polymers were observed, energies of which coincide with the optical vibration quanta. Disordering processes cause reduction of the number of observed discrete levels of the activation energy for PDHGe.
Composite films of single-walled carbon nanotubes with strong oxidized graphene: Characterization with spectroscopy, microscopy, conductivity measurements (5–291 K) and computer modeling
Authors: Karachevtsev V. A. , Plokhotnichenko A. M. , Karachevtsev M. V. , Linnik A. S. , Kurnosov N. V.
Published: July 2019

The hybridization of 1D carbon nanotubes and 2D graphene family is able to form 3D nanostructures with significantly improved electrical, mechanical and thermal properties, which make them very useful for huge potential applications. In this work the graphene oxide-single walled carbon nanotube (GO-SWNT) hybrids prepared in aqueous suspension and films obtained by vacuum filtration are studied with UV–IR absorption spectroscopy, scanning electron microscopy (SEM) and computer simulation. Low-temperature measurements of conductivity of these films in the temperature range 5–291 K were also performed. For hybrid preparation SWNTs with prevailing content of semiconducting nanotubes (up to 95%) and graphene oxide with small C:O ratio (about 1.3) were selected. SEM analysis of a cutoff of the composite GO-SWNT film showed that the film is formed by composition of thin layers which are preferably located along the surface of the film with laminar, rather dense package. We have found spectroscopic manifestation of the interaction between GO and SWNT in the hybrid, estimated the interaction energy between components, revealed the conductivity in the composite film although in the GO film we have not observed a noticeable conductivity. It was also demonstrated that the behavior of the temperature dependence of the conductivity in the film of pure SWNTs and in the composite one is different. The decrease in the conductivity with lowering of temperature indicates that this dependence is similar with the conductivity observed in semiconducting systems.
The impact of a low-frequency magnetic field on the properties of the main and additional echo signals in manganese ferrite
Authors: Mamniashvili G. I. , Gegechkori T. O. , Gavasheli T. A.
Published: July 2019

An experimental study of the features of additional echo signal formation is described, the mechanism of which is different from the classical Hahn mechanism, in the MnxFe2-xO4 system at helium temperatures. It was found that in the MnxFe2-xO4 system, the maximum intensity of the additional echo corresponds to a ferrite having a minimum magnetocrystalline anisotropy. Exposure to a low-frequency magnetic field led to the detection of the correlation effect between the changes of the main and additional signals in manganese ferrite, at helium temperatures. This indicates that they have an intra-boundary origin, which contradicts the known interpretations of manganese ferrite NMR spectrum. The possible physical nature of the observed effect is discussed.
Low-Temperature feature of grain-boundary hardening of nanocrystalline titanium
Authors: Smolianets R. V. , Moskalenko V. A.
Published: July 2019

The yield strength σ0.2 of titanium polycrystals in tension and in the temperature range of 4.2–395 K is studied as a function of grain size (d) ranging from micro- to nanometer dimensions. It was found that at temperatures below ∼180 K, the σ0.2 (d) dependences are not described by the classical Hall–Petch relation, shifting instead to higher stresses at nanometer size (d). The characteristics of grain-boundary hardening observed at low temperatures are explained using theoretical models, according to which in nanometer-size grains, the diameter of a dislocation loop originating at a grain boundary is proportional to d, with the nucleation stress being σ ∼ 1/d. The critical value dnc is estimated, below which the ratio σ0.2 ∼ 1/d holds at a fixed temperature. It is established that the dnc value decreases with an increase in the temperature of the experiment.
Switch mechanism paves way for flexible, stretchable, transistor-free organic image sensors
Authors: Bandari Anashe
Published: July 2019

Researchers demonstrate a proof-of-concept pixel for transistor-free organic image sensors.
Mechanical defects in solar cells can be found using advanced image processing
Authors: Bandari Anashe
Published: July 2019

A new method improves current solar cell defect detection techniques by using image subtraction to increase contrast and enhance the photoluminescence signature of cracks.
Seed structure and physiology in relation to recruitment ecology in Leucospermum (Proteaceae) in fynbos
Authors: Brits G. J. , Manning J. C.
Published: July 2019

Development of embryo envelopes in Leucospermum cordifolium (Salisb. ex Knight) Fourcade is presented in a detailed anatomical study, and their structure interpreted ecologically. To support interpretation results for at least six other species of Leucospermum are reviewed, confirming that L. cordifolium is representative of this shrubby group occurring in fynbos, a fire-prone Mediterranean-type vegetation subject to summer drought. The fate of the water-permeable seed coverings subsequent to dispersal is followed in seeds stored experimentally underground. The testa at maturity effectively excludes oxygen in intact soil-stored seeds, thus creating a less common type of physical dormancy which we term ‘anoxia PY’ (oxygen-impermeable physical dormancy). We postulate ‘fire-mediated desiccation-scarification’ testa breakage on a large scale in freshly dispersed (by ants) soil-stored young-seeds, dynamically regulated by drying of different testa layers through fire heat shock (but also by post-fire ambient climate heat), thus alleviating anoxia PY in, and causing undelayed germination of, a major part of the young-seed bank within the ensuing winter germination season. Concurrently a patchy disturbance pattern within a lesser portion of the young-seed cohort causes uneven underground desiccation-scarification by fire, resulting in variable degrees of oxygenation and thus temporally extended (erratic) germination of young-seeds. Both of these strategies are primary long term fitness traits in Leucospermum. By contrast the persistent older-seed cohort, stored underground during the inter-fire period, may become weathered by soil and climate factors (‘soil-mediated abrasion’), which alleviates anoxia PY in old seeds. Thermodormancy of these embryos (physiological dormancy, PD) is enforced in unburnt vegetation by two narrow habitat-dependent daily temperature requirements (~10°C × 20°C), and these have specific ecological functions. The complex Leucospermum system includes balanced adaptive responses to multiple selective pressures. We propose a coherent mechanistic profile for this fynbos genus, synthesising data partly from the literature of other fire-prone ecosystems.
A Scalable, Combined-Batch, and Continuous-Flow Synthesis of a Bio-Inspired UV-B Absorber
Authors: York Mark , Jarvis Karen E. , Freemont Jamie A. , Ryan John H. , Savage G. Paul , Logan Stephanie A. , Bright Larissa
Published: July 2019

A new, chromatography-free synthesis for the preparation of an experimental UV-B absorber is reported. A key step of the process is a one-pot partial reduction of a symmetrical imide with a sequential dehydration step. The synthesis uses several continuous-flow steps to increase sample throughput and was used to prepare sufficient material to support further testing activities in >99% purity.
Fire regime and ecosystem responses: adaptive forest management in a changing world (Part 2)
Authors: Moya Daniel , Certini Giacomo , Fulé Peter Z.
Published: July 2019

Fire is an ecological factor in ecosystems around the world, made increasingly more critical by unprecedented shifts in climate and human population pressure. The knowledge gradually acquired on the subject is needed to improve fire behaviour understanding and to enhance fire management decision-making. This issue (Volume 28, issue 7, International Journal of Wildland Fire) is Part 2 of a special issue aimed at synthesising ongoing research on preventive management and post-fire restoration, including characterisation of the wildland–urban interface (WUI) and assessing the post-fire restoration of wilderness and WUI areas. Landscape management was also investigated using remote sensing techniques and simulation modelling to improve ecosystem resilience. As in Part 1 (Volume 28, issue 5, International Journal of Wildland Fire), the current issue covers diverse forest settings under scenarios of changing climate and land use. The broad geographical range of these studies highlights key similarities of wildfire issues around the world, but detailed data show unique local circumstances that must be considered. The new information from these six papers helps advance fire ecology and management during a period of rapid change.
Prestimulus feedback connectivity biases the content of visual experiences
Authors: Rassi Elie , Wutz Andreas , Müller-Voggel Nadia , Weisz Nathan
Published: July 2019

Ongoing fluctuations in neural excitability and in networkwide activity patterns before stimulus onset have been proposed to underlie variability in near-threshold stimulus detection paradigms—that is, whether or not an object is perceived. Here, we investigated the impact of prestimulus neural fluctuations on the content of perception—that is, whether one or another object is perceived. We recorded neural activity with magnetoencephalography (MEG) before and while participants briefly viewed an ambiguous image, the Rubin face/vase illusion, and required them to report their perceived interpretation in each trial. Using multivariate pattern analysis, we showed robust decoding of the perceptual report during the poststimulus period. Applying source localization to the classifier weights suggested early recruitment of primary visual cortex (V1) and ∼160-ms recruitment of the category-sensitive fusiform face area (FFA). These poststimulus effects were accompanied by stronger oscillatory power in the gamma frequency band for face vs. vase reports. In prestimulus intervals, we found no differences in oscillatory power between face vs. vase reports in V1 or in FFA, indicating similar levels of neural excitability. Despite this, we found stronger connectivity between V1 and FFA before face reports for low-frequency oscillations. Specifically, the strength of prestimulus feedback connectivity (i.e., Granger causality) from FFA to V1 predicted not only the category of the upcoming percept but also the strength of poststimulus neural activity associated with the percept. Our work shows that prestimulus network states can help shape future processing in category-sensitive brain regions and in this way bias the content of visual experiences.
Perturbation of the interactions of calmodulin with GRK5 using a natural product chemical probe
Authors: Beyett Tyler S. , Fraley Amy E. , Labudde Emily , Patra Dhabaleswar , Coleman Ryan C. , Eguchi Akito , Glukhova Alisa , Chen Qiuyan , Williams Robert M. , Koch Walter J. , Sherman David H. , Tesmer John J. G.
Published: July 2019

G protein-coupled receptor (GPCR) kinases (GRKs) are responsible for initiating desensitization of activated GPCRs. GRK5 is potently inhibited by the calcium-sensing protein calmodulin (CaM), which leads to nuclear translocation of GRK5 and promotion of cardiac hypertrophy. Herein, we report the architecture of the Ca
2+
·CaM–GRK5 complex determined by small-angle X-ray scattering and negative-stain electron microscopy. Ca
2+
·CaM binds primarily to the small lobe of the kinase domain of GRK5 near elements critical for receptor interaction and membrane association, thereby inhibiting receptor phosphorylation while activating the kinase for phosphorylation of soluble substrates. To define the role of each lobe of Ca
2+
·CaM, we utilized the natural product malbrancheamide as a chemical probe to show that the C-terminal lobe of Ca
2+
·CaM regulates membrane binding while the N-terminal lobe regulates receptor phosphorylation and kinase domain activation. In cells, malbrancheamide attenuated GRK5 nuclear translocation and effectively blocked the hypertrophic response, demonstrating the utility of this natural product and its derivatives in probing Ca
2+
·CaM-dependent hypertrophy.
Increased ER–mitochondria tethering promotes axon regeneration
Authors: Lee Soyeon , Wang Wei , Hwang Jinyeon , Namgung Uk , Min Kyung-Tai
Published: July 2019

Significance

Small organelles such as endoplasmic reticulum (ER) and mitochondria play key roles in cellular functions and survival. Furthermore, physical tethering between ER–mitochondria allows communication between these 2 organelles, and proteins involved in the contact sites have been identified in various cells. However, physiological significances of ER–mitochondria contacts in axons are unknown. Here, we discover that Grp75 mRNA is locally translated in injured axonal tips. Up-regulation of Grp75 promotes ER–mitochondria tethering and enhances axon regeneration in vitro. Increased levels ofGrp75 in dorsal root ganglion neurons facilitates axon regeneration and functional recovery of animals with nerve injury. These results imply that overexpression of Grp75 may provide a therapeutic strategy to treat and enhance axonal regeneration following nerve injury.
Acute social isolation alters neurogenomic state in songbird forebrain
Authors: George Julia M. , Bell Zachary W. , Condliffe Daniel , Dohrer Kirstin , Abaurrea Teresa , Spencer Karen , Leitão Albertine , Gahr Manfred , Hurd Paul J. , Clayton David F.
Published: July 2019

Significance

Our results show that the experience of being alone has immediate consequences on brain gene activity. Clearly this is important for the human context, where loneliness (i.e., perceived social isolation) is a risk factor for psychological and neurodegenerative disorders. As the response occurs in brain areas involved in higher-order cognition and perception, these changes in gene activity may influence the ongoing processing of experience. Prior studies in humans have measured effects of social isolation in circulating leukocytes, but not in brain, and studies in mammalian models have typically focused on effects of much longer isolation periods (weeks or more). The results also bear on interpretation of animal experiments where short-term isolation is used to establish the baseline reference condition.
Deep learning of spontaneous arousal fluctuations detects early cholinergic defects across neurodevelopmental mouse models and patients
Authors: Artoni Pietro , Piffer Arianna , Vinci Viviana , LeBlanc Jocelyn , Nelson Charles A. , Hensch Takao K. , Fagiolini Michela
Published: July 2019

Significance

Neurodevelopmental spectrum disorders such as autism (ASD) are typically diagnosed at an age beyond the heightened plasticity of the infant brain, when behavioral intervention would be most effective. Here, we show that mouse models of idiopathic or monogenic ASD share common alterations in arousal modulation that can be detected by machine learning early in life. In this transfer study across species and measures, we show that a neural network trained on mice can be refined by transfer learning to be useful for ASD patients, even when different proxies of arousal fluctuations are used (e.g., pupillometry or heart rate variation). This now offers a quantitative, noninvasive, and highly translational biomarker for the early detection of developmental disorders.
The neural circuit linking mushroom body parallel circuits induces memory consolidation in
Drosophila
Authors: Awata Hiroko , Takakura Mai , Kimura Yoko , Iwata Ikuko , Masuda Tomoko , Hirano Yukinori
Published: July 2019

Significance

The augmentation of memory through spaced learning has been shown across the animal kingdom. The animals’ brain would be equipped with the neural circuit that perceives spaced repetition and launches the molecular mechanism of memory consolidation, although those neural circuit-based mechanisms are unknown. In the
Drosophila
aversive spaced training paradigm, we proposed the neurons which could be differentially activated during spaced learning. Manipulation of the neural activity during spaced learning suggested that the identified neural circuit is significant in gene expression for long-term memory (LTM) formation. Thus, our study suggested the neural computation model which detects spaced learning and launches gene expression for memory augmentation.
Gain control of saccadic eye movements is probabilistic
Authors: Lisi Matteo , Solomon Joshua A. , Morgan Michael J.
Published: July 2019

Saccades are rapid eye movements that orient the visual axis toward objects of interest to allow their processing by the central, high-acuity retina. Our ability to collect visual information efficiently relies on saccadic accuracy, which is limited by a combination of uncertainty in the location of the target and motor noise. It has been observed that saccades have a systematic tendency to fall short of their intended targets, and it has been suggested that this bias originates from a cost function that overly penalizes hypermetric errors. Here, we tested this hypothesis by systematically manipulating the positional uncertainty of saccadic targets. We found that increasing uncertainty produced not only a larger spread of the saccadic endpoints but also more hypometric errors and a systematic bias toward the average of target locations in a given block, revealing that prior knowledge was integrated into saccadic planning. Moreover, by examining how variability and bias covaried across conditions, we estimated the asymmetry of the cost function and found that it was related to individual differences in the additional time needed to program secondary saccades for correcting hypermetric errors, relative to hypometric ones. Taken together, these findings reveal that the saccadic system uses a probabilistic-Bayesian control strategy to compensate for uncertainty in a statistically principled way and to minimize the expected cost of saccadic errors.
Human species-specific loss of CMP-
N
-acetylneuraminic acid hydroxylase enhances atherosclerosis via intrinsic and extrinsic mechanisms
Authors: Kawanishi Kunio , Dhar Chirag , Do Raymond , Varki Nissi , Gordts Philip L. S. M. , Varki Ajit
Published: July 2019

Significance

Cardiovascular disease (CVD) events like heart attacks and strokes due to atherosclerotic narrowing of arteries are the commonest cause of worldwide deaths, but many first-time events occur in individuals without known risk factors. In contrast, such events are extremely rare in other animals despite some of the same risk factors. While environmental and behavioral factors likely contribute to the difference, we show here that a human-specific genetic mutation affecting cell-surface molecules called sialic acids may be one other factor. We also show that the same mutation can help explain the apparently human-specific increased risk of CVD events associated with red meat consumption. The humanized mouse systems we present could be explored as models for future studies of atherosclerosis.
Observation of methane filled hexagonal ice stable up to 150 GPa
Authors: Schaack Sofiane , Ranieri Umbertoluca , Depondt Philippe , Gaal Richard , Kuhs Werner F. , Gillet Philippe , Finocchi Fabio , Bove Livia E.
Published: July 2019

Significance

Gas clathrates in which water cages enclose the guest gas molecules naturally form on our planet, for instance on ocean floors. Related methane hydrates are also expected to be present under very high pressures (10 to 200 GPa) in giant planetary interiors such as Uranus or Neptune. However, the stability of such structures at these pressures is currently debated. Joint Raman spectroscopy and ab initio simulations show the stability of a high-pressure methane hydrate phase up to at least 150 GPa, the highest pressure explored to date for such compounds. The structure of this phase and the complex transition mechanism from the known MH-III phase are detailed and shown to be in accordance with all known experimental observations.
A photostable fluorescent marker for the superresolution live imaging of the dynamic structure of the mitochondrial cristae
Authors: Wang Chenguang , Taki Masayasu , Sato Yoshikatsu , Tamura Yasushi , Yaginuma Hideyuki , Okada Yasushi , Yamaguchi Shigehiro
Published: July 2019

Significance

Stimulated emission depletion (STED) microscopy is one of the most appealing tools to visualize nanoscale cellular structures and dynamics in living cells. However, its practical utility is significantly limited by the rapid photobleaching of fluorescent dyes under the ultrastrong depletion laser. In this context, superphotostable fluorescent probes, which enable repeated recording of the STED images, are crucial chemical tools to extend the application of STED microscopy in live-cell imaging. Herein, we report a developed fluorescent probe, MitoPB Yellow, which has the characters of outstanding photostability, long fluorescence lifetime, and mitochondrial inner membrane selectivity for staining. In combination with a time-gated-STED microscopy, the mitochondrial inner-membrane structures and dynamics can be impressively visualized in living cells.
Trading amino acids at the aphid–
Buchnera
symbiotic interface
Authors: Feng Honglin , Edwards Noel , Anderson Catriona M. H. , Althaus Mike , Duncan Rebecca P. , Hsu Yu-Ching , Luetje Charles W. , Price Daniel R. G. , Wilson Alex C. C. , Thwaites David T.
Published: July 2019

Significance

Plant sap-feeding insects thrive despite feeding exclusively on a diet lacking in essential amino acids. This nutritional deficit is countered through endosymbiotic relationships with microbial symbionts. Nonessential amino acids, vital for microbial symbionts, are utilized by symbiont metabolic pathways and yield essential amino acids required by their eukaryotic hosts. Symbionts are completely dependent on their host to meet nutritional requirements. The endosymbionts are surrounded individually by host-derived symbiosomal membranes and are housed within specialized host bacteriocyte cells. The transport capabilities of the symbiosomal membrane remain unknown. Here, we identify a transport system that mediates a crucial step in this metabolic complementarity: a transporter capable of transporting nonessential amino acids across the symbiosomal membrane of the pea aphid
Acyrthosiphon pisum
.