bluuebunny/crossref_metadata_2025 huggingface dataset:
Catalytic C2H2 synthesis via low temperature CO hydrogenation on defect-rich 2D-MoS2 and 2D-MoS2 decorated with Mo clusters
Authors: Young Brett T. , Pathan Md Afjal Khan , Jiang Tao , Le Duy , Marrow Nikki , Nguyen Trong , Jordan Cody E. , Rahman Talat S. , Popolan-Vaida Denisia M. , Vaida Mihai E.
Published: February 2020

Rational design of novel catalytic materials used to synthesize storable fuels via the CO hydrogenation reaction has recently received considerable attention. In this work, defect poor and defect rich 2D-MoS2 as well as 2D-MoS2 decorated with Mo clusters are employed as catalysts for the generation of acetylene (C2H2) via the CO hydrogenation reaction. Temperature programmed desorption is used to study the interaction of CO and H2 molecules with the MoS2 surface as well as the formation of reaction products. The experiments indicate the presence of four CO adsorption sites below room temperature and a competitive adsorption between the CO and H2 molecules. The investigations show that CO hydrogenation is not possible on defect poor MoS2 at low temperatures. However, on defect rich 2D-MoS2, small amounts of C2H2 are produced, which desorb from the surface at temperatures between 170 K and 250 K. A similar C2H2 signal is detected from defect poor 2D-MoS2 decorated with Mo clusters, which indicates that low coordinated Mo atoms on 2D-MoS2 are responsible for the formation of C2H2. Density functional theory investigations are performed to explore possible adsorption sites of CO and understand the formation mechanism of C2H2 on MoS2 and Mo7/MoS2. The theoretical investigation indicates a strong binding of C2H2 on the Mo sites of MoS2 preventing the direct desorption of C2H2 at low temperatures as observed experimentally. Instead, the theoretical results suggest that the experimental data are consistent with a mechanism in which CHO radical dimers lead to the formation of C2H2 that presents an exothermic desorption.
Photochemical dynamics under incoherent illumination: Light harvesting in self-assembled molecular J-aggregates
Authors: Morales-Curiel Luis Felipe , León-Montiel Roberto de J.
Published: February 2020

Transport phenomena in organic, self-assembled molecular J-aggregates have long attracted a great deal of attention due to their potential role in designing novel organic photovoltaic devices. A large number of theoretical and experimental studies have been carried out describing excitonic energy transfer in J-aggregates under the assumption that excitons are induced by a coherent laser-light source or initialized by a localized excitation on a particular chromophore. However, these assumptions may not provide an accurate description to assess the efficiency of J-aggregates, particularly as building blocks of organic solar cells. Under natural conditions, J-aggregates would be subjected to an incoherent source of light (as is sunlight), which would illuminate the whole photosynthetic complex rather than a single molecule. In this work, we present the first study of the efficiency of photosynthetic energy transport in self-assembled molecular aggregates under incoherent sunlight illumination. By making use of a minimalistic model of a cyanine dye J-aggregate, we demonstrate that long-range transport efficiency is enhanced when exciting the aggregate with incoherent light. Our results thus support the conclusion that J-aggregates are, indeed, excellent candidates for devices where efficient long-range incoherently induced exciton transport is desired, such as in highly efficient organic solar cells.
Wide-range line shape control of Fano-like resonances in all-dielectric multilayer structures based on enhanced light absorption in photochromic waveguide layers
Authors: Motokura Kengo , Kang Byungjun , Fujii Minoru , Nesterenko Dmitry V. , Sekkat Zouheir , Hayashi Shinji
Published: February 2020

We have succeeded in controlling the line shape of Fano-like resonances in all-dielectric multilayer structures in a wide range by UV light irradiation. Multilayer structures consisting of a waveguide layer supporting a half-leaky guided mode, a spacer layer, and another waveguide layer supporting a planar waveguide mode are known to exhibit Fano-like line shapes in attenuated total reflection spectra due to coupling between the half-leaky guided mode and the planar waveguide mode. Using a photochromic layer, i.e., a layer doped with spiropyran molecules, as one of the waveguide layers, we controlled the amount of light absorption in the waveguide layer by varying the UV irradiation dose. We demonstrated that the line shape changes dramatically depending on the UV dose, from the electromagnetically induced transparency-like to electromagnetically induced absorption-like line shape (or vice versa) passing through the Fano-like line shape. We also demonstrated that the photochromic response induced by UV irradiation in the Fano-resonant multilayer structure is enhanced by a factor of ∼100 relative to that in a single photochromic layer. Our analyses based on electromagnetic calculations suggest that the dramatic line shape change and the enhanced photochromic response are the consequences of enhanced local electric fields inside the photochromic waveguide layer combined with the photoinduced increase in the imaginary part of the dielectric constant.
Field localization of hexagonal and short-range ordered plasmonic nanoholes investigated by cathodoluminescence
Authors: Vu Thi Dung , Ohno Takazumi , Yamamoto Naoki , Sannomiya Takumi
Published: February 2020

Plasmonic nanoholes have attracted significant attention among nanoplasmonic devices, especially as biosensing platforms, where nanohole arrays can efficiently enhance and confine the electromagnetic field through surface plasmon polaritons, providing a sensitive detection. In nanohole arrays, the optical resonances are typically determined by the inter-hole distance or periodicity with respect to the surface plasmon wavelength. However, for short-range ordered (SRO) arrays, the inter-hole distance varies locally, so the plasmon resonance changes. In this study, we investigate the local resonance of SRO nanoholes using a cathodoluminescence technique and compare it with hexagonally ordered nanoholes. The cathodoluminescence photon maps and resonance peak analysis reveal that the electric fields are confined at the edges of holes and that their resonances are determined by inter-hole distances as well as by their distributions. This demonstrates the Anderson localization of the electromagnetic waves showing locally enhanced electromagnetic local density of states in SRO nanoholes.
Assessment of the mechanical errors of a prototype of an optical multilateration system
Authors: Guillory J. , Truong D. , Wallerand J.-P.
Published: February 2020

We are developing a multilateration system at a reasonable cost that aims at an accuracy better than 50 µm determined with a consistent metrological approach. In this context, an absolute distance meter, developed in-house, is used as a unique telemetric system to feed the different measurement heads of the multilateration system through a network of optical fibers. The uncertainty contribution for a distance measurement of the telemetric system itself, in a controlled environment, is from 2 µm up to 100 m (k = 1). In this paper, the uncertainty contribution due to mechanical designs of the measurement heads and the target is estimated: the gimbal mechanisms we have designed are presented and their sources of error are identified, experimentally quantified, and minimized. At the end, we demonstrate that the current design of the measurement head does not induce errors higher than 2 µm on the measured distances and the design of the target does not induce errors higher than 9 µm.
Experimental investigation of unstart dynamics driven by subsonic spillage in a hypersonic scramjet intake at Mach 6
Authors: Devaraj Manoj Kumar K. , Jutur Prahallada , Rao Srisha M. V. , Jagadeesh Gopalan , Anavardham Ganesh T. K.
Published: February 2020

Understanding start–unstart behavior of intakes in hypersonic Mach numbers is essential for seamless operation of scramjet engines. We consider a high compression ratio intake (CR = 40) at a Mach number of M = 6 in this work. Start–unstart characteristics are studied in a hypersonic wind tunnel at a flight realistic Reynolds number (Re = 8.7 × 106/m, M = 6). A flap provided at the rear end of the isolator simulates the effect of backpressure for throttling ratios in the range of 0–0.69. Experiments are conducted in two modes: (a) with the flap fixed at a particular throttling ratio and (b) the flap moved to a particular throttling ratio after the started flow has been established. Unsteady pressure measurements and time-resolved Schlieren visualization are undertaken. Modal analysis of pressure (using fast Fourier transform) and Schlieren images (using dynamic mode decomposition) are carried out. The intake shows started behavior for throttling ratios up to 0.31 and a dual behavior, where it remains started in dynamic flap runs but unstarted in fixed flap runs for throttling ratios of 0.35 and 0.42. The intake exhibits a staged evolution to a large amplitude oscillatory unstart for throttling ratios of 0.55 and 0.69, with frequencies of 950 Hz and 1100 Hz, respectively. For the first time, a staged evolution (5 stages) to a subsonic spillage oscillatory unstart of a hypersonic intake is detailed using corroborative evidence from both time-resolved Schlieren and pressure measurements. A precursor to the final large amplitude oscillatory unstart is identified, and the flow mechanism for sustained oscillations is explained.
Ab initio study of the miscibility for solid hydrogen–helium mixtures at high pressure
Authors: Jiang Xingxing , Zheng Yueshao , Xue Xiong-Xiong , Dai Jiayu , Feng Yexin
Published: February 2020

Understanding the behavior of H2–He binary mixtures at high pressure is of great importance. Two more recent experiments [J. Lim and C. S. Yoo, Phys. Rev. Lett. 120, 165301 (2018) and R. Turnbull et al., ibid. 121, 195702 (2018)] are in conflict, regarding the miscibility between H2 and He in solids at high pressure. On the basis of first-principles calculations combined with the structure prediction method, we investigate the miscibility for solid H2–He mixtures at pressures from 0 GPa to 200 GPa. It is found that there is no sign of miscibility and chemical reactivity in H2–He mixtures with any H:He ratio. Moreover, instead of H2–He mixtures, the calculated Raman modes of the N–H mixtures can better explain the characteristic peaks observed experimentally, which were claimed to be the H–He vibrational modes. These calculation results are more in line with the experimental findings by Turnbull et al. [Phys. Rev. Lett. 121, 195702 (2018)].
2D-IR studies of cyanamides (NCN) as spectroscopic reporters of dynamics in biomolecules: Uncovering the origin of mysterious peaks
Authors: Chalyavi Farzaneh , Adeyiga Olajumoke , Weiner Julia M. , Monzy Judith N. , Schmitz Andrew J. , Nguyen Justin K. , Fenlon Edward E. , Brewer Scott H. , Odoh Samuel O. , Tucker Matthew J.
Published: February 2020

Cyanamides (NCN) have been shown to have a larger transition dipole strength than cyano-probes. In addition, they have similar structural characteristics and vibrational lifetimes to the azido-group, suggesting their utility as infrared (IR) spectroscopic reporters for structural dynamics in biomolecules. To access the efficacy of NCN as an IR probe to capture the changes in the local environment, several model systems were evaluated via 2D IR spectroscopy. Previous work by Cho [G. Lee, D. Kossowska, J. Lim, S. Kim, H. Han, K. Kwak, and M. Cho, J. Phys. Chem. B 122(14), 4035–4044 (2018)] showed that phenylalanine analogues containing NCN show strong anharmonic coupling that can complicate the interpretation of structural dynamics. However, when NCN is embedded in 5-membered ring scaffolds, as in N-cyanomaleimide and N-cyanosuccinimide, a unique band structure is observed in the 2D IR spectrum that is not predicted by simple anharmonic frequency calculations. Further investigation indicated that electron delocalization plays a role in the origins of the band structure. In particular, the origin of the lower frequency transitions is likely a result of direct interaction with the solvent.
Atomic scale step structure and orientation of a curved surface ZnO single crystal
Authors: Grånäs Elin , Arndt Björn , Seitz Christoph , Wagstaffe Michael , Stierle Andreas
Published: February 2020

We have investigated the surface structure of a curved ZnO-crystal, going from the (0001)-facet at 0° miscut to the (101¯4)-facet at a miscut of 24.8° using scanning tunneling microscopy and low energy electron diffraction. We find that the surface separates locally into (0001)-terraces and (101¯4)-facets, where the ratio between the facets depends on the miscut angle. In X-ray photoemission spectroscopy (XPS) the intensity of an O 1s component scaling with the step density of the surface is observed. No other facets were observed and the surface maintains a high degree of order over all angles. Such a curved ZnO crystal can be used for systematic studies relating the step density to the chemical reactivity using XPS to probe the curved surface at different positions.
Electrostatic solitary structures in warm multi-ion dusty plasmas: The effect of an external magnetic field and nonthermal electrons
Authors: Elkamash I. S.
Published: February 2020

Adopting a multi-fluid dynamical approach, the propagation of weakly nonlinear electrostatic solitary waves in a warm multi-ion dust plasma is investigated. In particular, a plasma is composed of positively and negatively charged ions and positively or negatively charged dust in the presence of superthermal electrons immersed in an external magnetic field. In the linear regime, two modes exist, namely, the slow and fast ion-acoustic modes. Employing the reductive perturbation technique, the governing equation of the nonlinear propagation for the electrostatic solitary pulse is derived. The polarity and structural characteristics (amplitude and width) of the localized electrostatic pulse in the plasma are thus analyzed for various values of relevant plasma configurations, namely, the degree of the superthermality (κ), the magnetic field strength Ωj, and the adiabatic ion thermal pressure coefficient σj. Our investigations should be useful to better understand the characteristics of the low-frequency electrostatic solitary wave that are ubiquitous in the laboratory and space plasmas, where a warm dusty multi-ion plasma with the energetic (suprathermal) electrons exists and an external magnetic field is included.
Stoichiometry, band alignment, and electronic structure of Eu2O3 thin films studied by direct and inverse photoemission: A reevaluation of the electronic band structure
Authors: Hadamek Tobias , Rangan Sylvie , Viereck Jonathan , Shin Donghan , Posadas Agham B. , Bartynski Robert A. , Demkov Alexander A.
Published: February 2020

The electronic structure of Eu sesquioxide (Eu2O3) presents a significant challenge to the electronic structure theory due to the presence of correlated Eu semicore 4f electrons. The bandgap values do not agree between computational methods, and even experimentally, there are discrepancies between reports. Eu2O3 was grown epitaxially in a thin film form on n-type GaN (0001) by molecular beam epitaxy. The film was analyzed using UV and x-ray photoemission spectroscopies as well as inverse photoelectron spectroscopy in order to characterize both occupied and unoccupied states. Signatures of Eu2+ are detected after annealing in UHV or after exposure to air, which can be removed by subsequent O2 annealing. The sample reduction is shown to strongly affect the electronic structure. The bandgap of 4.3 eV, electron affinity of 2.2 eV, and band alignment to the substrate with a valence band offset of 0.2 eV for a stoichiometric Eu2O3 film were extracted from the measurements of the occupied and unoccupied electronic states. The electronic structure is interpreted in view of recent theoretical models, and the energy band alignment across the Eu2O3/GaN interface is discussed.
Ti- and Fe-related charge transition levels in β−Ga2O3
Authors: Zimmermann Christian , Frodason Ymir Kalmann , Barnard Abraham Willem , Varley Joel Basile , Irmscher Klaus , Galazka Zbigniew , Karjalainen Antti , Meyer Walter Ernst , Auret Francois Danie , Vines Lasse
Published: February 2020

Deep-level transient spectroscopy measurements on β-Ga2O3 crystals reveal the presence of three defect signatures labeled E2a, E2b, and E3 with activation energies at around 0.66 eV, 0.73 eV, and 0.95 eV below the conduction band edge. Using secondary ion mass spectrometry, a correlation between the defect concentration associated with E3 and the Ti concentration present in the samples was found. Particularly, it is found that E3 is the dominant Ti-related defect in β-Ga2O3 and is associated with a single Ti atom. This finding is further corroborated by hybrid functional calculations that predict Ti substituting on an octahedral Ga site, denoted as TiGaII, to be a good candidate for E3. Moreover, the deep level transient spectroscopy results show that the level previously labeled E2 and attributed to Fe substituting on a gallium site (FeGa) consists of two overlapping signatures labeled E2a and E2b. We tentatively assign E2a and E2b to Fe substituting for Ga on a tetrahedral or an octahedral site, respectively.
Structural properties and magnetoresistance of La1.952Sr0.048CuO4 thin films
Authors: Zaytseva I. , Minikayev R. , Dobročka E. , Špankova M. , Bruyant N. , Cieplak Marta Z.
Published: February 2020

The evolution of the structural and transport properties of underdoped La1.952Sr0.048CuO4 thin films under a compressive epitaxial strain has been studied. The films of different thicknesses d (from 26 nm to 120 nm) were deposited using an insulating target. The onset of superconductivity in the films is observed at temperatures as high as 26 K, while small residual resistance persists at low temperatures, indicating that superconductivity is inhomogeneous. The resistance measured under a perpendicular magnetic field saturates below about 0.65 K, suggesting a possible existence of nonconventional metallic state. The magnetic-field-tuned quasi-superconductor to insulator transition is observed at a magnetic field of about 32 T.
Non-standing spin-waves in confined micrometer-sized ferromagnetic structures under uniform excitation
Authors: Pile S. , Feggeler T. , Schaffers T. , Meckenstock R. , Buchner M. , Spoddig D. , Zingsem B. , Ney V. , Farle M. , Wende H. , Ohldag H. , Ney A. , Ollefs K.
Published: February 2020

A non-standing characteristic of directly imaged spin-waves in confined micrometer-sized ultrathin Permalloy (Ni80Fe20) structures is reported along with evidence of the possibility to alter the observed state by modifications to the sample geometry. Using micromagnetic simulations, the presence of the spin-wave modes excited in the Permalloy stripes along with the quasi-uniform modes was observed. The predicted spin-waves were imaged in direct space using time resolved scanning transmission x-ray microscopy, combined with a ferromagnetic resonance excitation scheme (STXM-FMR). STXM-FMR measurements revealed a non-standing characteristic of the spin-waves. Also, it was shown by micromagnetic simulations and confirmed using STXM-FMR results that the observed characteristic of the spin-waves can be influenced by the local magnetic fields in different sample geometries.
Harnessing polymer grafting to control the shape of plasmonic nanoparticles
Authors: Zhou Ying , Yan Liting , Maji Tanmoy , Lévêque Gaëtan , Gkikas Manos , Fytas George
Published: February 2020

Matrix-free polymer grafted nanoparticles (NPs) are single component polymer nanocomposites (PNCs) for which the often reported severe aggregation of the conventional PNCs can be suppressed. For a given particle core, the size and shape of the polymer grafted nanoparticles can be controlled by the molecular weight of the polymer and its grafting density. However, the degree of homogeneity of one-component PNCs depends on the grafted chain molecular weight and grafting density, as well as on the shape of grafted NPs. Surface plasmon resonance enhanced dynamic light scattering from very dilute solutions, yielding both translational and rotational transport coefficients, complemented by UV–Vis extinction spectra, can detect deviations from spheres. Here, we report that poly(isobutylene)-grafted Ag NPs strongly deviate from the spherical shape and are modeled as prolate spheroids. This NP asphericity, due to inhomogeneous grafting, can impact the structure and properties of plasmonic PNCs in the solid state. Thus, characterizing this behavior is a crucial step prior to the formation of one-component PNCs.
Confinement-induced ordering of grafted nanoparticles aided by diblock copolymers
Authors: Gupta Supriya , Chokshi Paresh
Published: February 2020

Self-assembly behavior of polymer grafted nanoparticles in ordered phases of geometrically confined diblock copolymers is studied using self-consistent field theory. Entropy loss and structural frustration introduced by physical confinement significantly alter the morphology of ordered phases from the bulk behavior. In particular, a rich variety of three-dimensional microstructures, for example, helical structures, are obtained under confinement. In the present study, we demonstrate that ordered microstructures of diblock copolymers can be employed as promising structural scaffolds to host and self-assemble nanoparticles within the selective domain. Templated self-assembly of nanoparticles offers a potential route to fabricate advanced nanomaterials with superior properties. Analysis reveals various stable equilibrium phases of block copolymers embedded with nanoparticles with a high degree of nanoscale ordering. The arrangement of nanoparticles is controlled by tuning various parameters such as block fraction in diblock copolymers, particle loading, size and number of grafted chains, and degree of confinement. At a low volume fraction, nanoparticles self-organize into chiral microstructures, such as single and double helices, even though the system contains only achiral species. Upon enhancing particle loading, the helical structure becomes less favorable and various other three-dimensional phases such as ring and disk morphologies are obtained. The regions of helical, ring, disk, and concentric lamellar phases are identified in terms of parameters related to grafted particles. Understanding the factors affecting localization of nanoparticles enables us to control the particulate self-assembly behavior of nanoparticles to design novel and advanced nanocomposites with desirable properties.
Self-trapped hole and impurity-related broad luminescence in β-Ga2O3
Authors: Frodason Y. K. , Johansen K. M. , Vines L. , Varley J. B.
Published: February 2020

This work explores the luminescence properties of self-trapped holes and impurity-related acceptors using one-dimensional configuration coordinate diagrams derived from hybrid functional calculations. The photoluminescence spectrum of as-grown β-Ga2O3 typically consists of a broad band in the wavelength region from ultraviolet to green and is often dominated by an impurity independent ultraviolet band that is commonly attributed to self-trapped holes. Here, we use the self-trapped hole as a benchmark to evaluate the accuracy of the theoretical defect luminescence spectra and estimate the optical properties of MgGa, BeGa, CaGa, CdGa, ZnGa, LiGa, and NO acceptor impurities, as well as their complexes with hydrogen donors. We also explore VGa acceptors complexed with hydrogen and SiGa donor impurities. The results show that these defects can give rise to broad luminescence bands peaking in the infrared to visible part of the spectrum, making them potential candidates for the defect origin of broad luminescence bands in β-Ga2O3.
A real-time XAS PEEM study of the growth of cobalt iron oxide on Ru(0001)
Authors: Ruiz-Gómez S. , Mandziak A. , Prieto J. E. , Aristu M. , Trapero E. M. , Soria G. D. , Quesada A. , Foerster M. , Aballe L. , de la Figuera J.
Published: February 2020

The growth of mixed cobalt-iron oxides on Ru(0001) by high-temperature oxygen-assisted molecular beam epitaxy has been monitored in real time and real space by x-ray absorption photoemission microscopy. The initial composition is a mixed Fe–Co(II) oxide wetting layer, reflecting the ratio of the deposited materials. However, as subsequent growth of three dimensional spinel islands nucleating on this wetting layer takes place, the composition of the oxide in the wetting layer changes as iron is transferred into the spinel islands. The composition of the islands themselves also changes during growth.
Non-radiative decay and fragmentation in water molecules after 1a1−14a1 excitation and core ionization studied by electron-energy-resolved electron–ion coincidence spectroscopy
Authors: Sankari Anna , Stråhlman Christian , Sankari Rami , Partanen Leena , Laksman Joakim , Kettunen J. Antti , Galván Ignacio Fdez. , Lindh Roland , Malmqvist Per-Åke , Sorensen Stacey L.
Published: February 2020

In this paper, we examine decay and fragmentation of core-excited and core-ionized water molecules combining quantum chemical calculations and electron-energy-resolved electron–ion coincidence spectroscopy. The experimental technique allows us to connect electronic decay from core-excited states, electronic transitions between ionic states, and dissociation of the molecular ion. To this end, we calculate the minimum energy dissociation path of the core-excited molecule and the potential energy surfaces of the molecular ion. Our measurements highlight the role of ultra-fast nuclear motion in the 1a1−14a1 core-excited molecule in the production of fragment ions. OH+ fragments dominate for spectator Auger decay. Complete atomization after sequential fragmentation is also evident through detection of slow H+ fragments. Additional measurements of the non-resonant Auger decay of the core-ionized molecule (1a1−1) to the lower-energy dication states show that the formation of the OH+ + H+ ion pair dominates, whereas sequential fragmentation OH+ + H+ → O + H+ + H+ is observed for transitions to higher dication states, supporting previous theoretical investigations.
Numerical study of the Richtmyer–Meshkov instability of a three-dimensional minimum-surface featured SF6/air interface
Authors: Guan Ben , Wang Dayi , Wang Ge , Fan E. , Wen Chih-Yung
Published: February 2020

The Richtmyer–Meshkov instability of a three-dimensional (3D) minimum-surface featured SF6/air interface subjected to a planar weak incident shock is numerically studied. The focus is placed on presenting more intuitive details of the complex shock-interface interactions. In the present work, 3D Euler equations are solved. The fifth-order weighted essentially non-oscillatory scheme and the level-set method combined with the real ghost fluid method are adopted. The gas interface morphologies are precisely reproduced according to the previous experimental images, the wave systems in 3D space are illustrated, and the velocity distribution in a characteristic plane is depicted. Based on which, the unknown lagging structure in the previous experiment can be reasonably explained. It is actually the soap fog driven by the flow field. The baroclinic vorticity generation and the perturbation amplitude growth histories are measured. The present numerical study well confirms the 3D curvature effect and supports the extended 3D theoretical model for the heavy/light interface scenario.
A kinetic Fokker–Planck approach to model hard-sphere gas mixtures
Authors: Hepp C. , Grabe M. , Hannemann K.
Published: February 2020

Since its first introduction, it has always been a subject of research to find models for a meaningful approximation of the highly accurate but complex Boltzmann equation. In the kinetic Fokker–Planck (FP) approach, a FP operator in velocity space is employed to approximate the collision integral of the Boltzmann equation. Instead of directly solving the resulting FP equation, a Monte Carlo technique is used to model an associated random process. This approach leads to an efficient stochastic solution algorithm. In recent years, the FP ansatz has become increasingly popular. Nevertheless, the modeling of gas mixtures in the context of kinetic FP has so far only been addressed in a very few papers. This article introduces a kinetic FP model that is capable of describing gas mixtures with particles interacting according to the hard-sphere collision model. The model is constructed to reproduce Grad’s 13 moment equations on a Navier–Stokes level of accuracy for gas mixtures with an arbitrary number of constituents. A stochastic simulation algorithm is derived that ensures a correct evolution of the species diffusion velocities and the species temperatures for a homogeneous gas, regardless of the applied time step size. It is shown that the proposed model is capable of correctly predicting shear stresses, heat fluxes, and diffusion velocities for different test cases, employing a He–Ar mixture.
Transverse localization of light in laser written designed disorder
Authors: Gianfrate A. , Dominici L. , Ballarini D. , Sanvitto D. , Leonetti M.
Published: February 2020

Transverse Anderson localization provides the lateral confinement of electromagnetic waves in disordered systems that are invariant along the propagation direction. Here, we demonstrate a disorder induced confinement in glass microstructures where disorder is fabricated ad hoc by the femtosecond direct laser writing technique. By employing a high numerical aperture objective, we are able to write parallel arrays of tiny tubes with a refractive index higher than the surrounding glass and to arrange them in a disordered fashion in the transversal plane. We demonstrate that these paraxial scatterers are supporting transverse localization and that the confinement strength depends on the disorder properties. The proposed approach, which relies on a user-controlled positioning of individual scatterers, allows us to finely tune the structural design, maximizing the transversal confinement.
Collisional energy transfer in the HeH+–H reactive system
Authors: Desrousseaux Benjamin , Lique François
Published: February 2020

The HeH+ molecule is the first to be formed in the Universe. Its recent detection, in the interstellar medium, has increased the interest in the study of the physical and chemical properties of this ion. Here, we report exact quantum time-independent calculations of the collisional cross sections and rate coefficients for the rotational excitation of HeH+ by H. Reactive and exchange channels are taken into account in the scattering calculations. Cross sections are computed for energies of up to 10 000 cm−1, enabling the computation of rate coefficients for temperatures of up to 500 K. The strongest collision-induced rotational HeH+ transitions are those with Δj = 1. Previous results obtained using approximate treatment are compared to the new ones, and significant differences are found. The new rate coefficients are also compared to those for electron-impact rotational excitation, and we found that collisions with H dominate the excitation of HeH+ in media where the electron fraction is less than 10−4. In the light of those results, we recommend the use of the new HeH+–H collisional data in order to accurately model HeH+ excitation in both the interstellar media and early Universe.
Hydrogenation and hydrogen diffusion at the anatase TiO2(101) surface
Authors: Nagatsuka Naoki , Wilde Markus , Fukutani Katsuyuki
Published: February 2020

Hydrogenation of TiO2 enhances its visible photoabsorption, leading to efficient photocatalytic activity. However, the role of hydrogen has not been fully understood. The anatase TiO2(101) surface treated by hydrogen ion irradiation at 500 eV was investigated by photoemission spectroscopy and nuclear reaction analysis. Hydrogen irradiation induces an in-gap state 1–1.6 eV below the Fermi level and a downward band bending of 0.27 eV. The H depth profile at 300 K shows a surface peak with an H amount of (2.9 ± 0.3) × 1015 cm−2 with little concentration in a deeper region. At 200 K, on the other hand, the H depth profile shows a maximum at about 1 nm below the surface corresponding to an H amount of (6.1 ± 0.3) × 1015 cm−2 along with a broad distribution extending to 50 nm at an average concentration of 0.8 at. %. These results show that H diffusion in anatase TiO2 is much faster than in rutile TiO2 [Y. Ohashi, J. Phys. Chem. C 123, 10319–10324 (2019)]. The H diffusion coefficient at 200 K is determined to be 2.7 ± 0.1 × 10−13 m2 s−1.
Intramolecular hydrogen bonding protects the hydroxyl group from attack by fluctuating solvent forces
Authors: Akiva Amit , Chuntonov Lev
Published: February 2020

Ultrafast spectroscopy of molecular systems involving hydrogen- (H−) bonding has been at the forefront of fundamental chemical and physical research for several decades. Among the spectroscopic observables of the ultrafast dynamics is the pure dephasing of vibrationally excited molecules. Using third-order nonlinear vibrational spectroscopy, including polarization-selective transient grating measurements of vibrational lifetime and orientational diffusion as well as two-dimensional infrared spectroscopy, we determined different individual line shape components of hydroxyl stretching (νOH) excitations in a homologous series of chlorophenols and obtained the corresponding pure dephasing rates. The pure dephasing rates are correlated with vibrational anharmonicity of the νOH mode, which is tuned remotely from the hydroxyl site by changing the position of the chlorine substituents on the phenol ring. We found that in molecules where the hydroxyl group is in its free form, the pure dephasing rates scale linearly with the mode’s anharmonicity such that assuming it is dominated by the third-order diagonal term, the ultrafast dynamics follow the prediction of the Kubo–Oxtoby theory. However, in the intramolecularly H-bonded ortho-chlorophenols, this trend is reversed, and the pure dephasing slows down by ∼50% for an increase in anharmonicity of only a few wavenumbers. Because the νOH mode’s anharmonicity is known to reflect the H-bonding strength, our results suggest that intramolecular H-bonding can serve as a mechanism of protection from fluctuating forces exerted by the solvent. Such an effect can be relevant for ultrafast dynamics in biomolecules, where H-bonding plays a central role.
Capillary flow of sodium and zinc ionomers
Authors: Zuliki Muaad , Zhang Shiling , Tomkovic Tanja , Hatzikiriakos Savvas G.
Published: February 2020

The capillary flow properties of several commercial ionomers (sodium and zinc) were studied to assess their processability in terms of instabilities such as wall slip and melt fracture. Using capillary dies of various diameters and lengths to control capillary extrusion pressure, it was found that the viscosity of these polymers exhibits a relatively small dependence on pressure, more importantly at relatively smaller pressures. Using capillaries of various diameters at fixed length-to-diameter ratios, it was also found that the no-slip boundary condition is a valid assumption for these polymers due to the strong ionic associations and strong interactions with the capillary wall. All ionomers were found to exhibit gross melt fracture (no sharkskin), a phenomenon more dominantly observed at lower temperatures. The occurrence of gross melt fracture and the absence of surface (sharkskin) melt fracture is a characteristic of extensional strain-hardening polymers, noting that all ionomers examined exhibit this phenomenon. The critical shear stress for the onset of gross melt fracture was found to depend on the lifetime of associations, τS (τS∝ZE/ZS21/5, where ZE is the number of entanglements and ZS is the number of associations), independent of temperature, molecular weight, and type of ion (zinc or sodium).
Ferromagnetic behaviors in monolayer MoS2 introduced by nitrogen-doping
Authors: Chen Mingyue , Hu Ce , Luo Xingfang , Hong Aijun , Yu Ting , Yuan Cailei
Published: February 2020

Effective functionalization of magnetic properties through substitutional doping may extend the spintronic applications of two-dimensional (2D) semiconductor MoS2. Here, the magnetoelectric properties of nitrogen-doped monolayer MoS2 are investigated by first-principles calculations, revealing that the N-p and S-p states are strongly hybridized with the Mo-d states, thus leading to the appearance of magnetism as verified experimentally. We demonstrate in situ doping of monolayer MoS2 with nitrogen via a convenient chemical vapor deposition method. Incorporation of nitrogen into MoS2, leading to the evolution of magnetism, is evidenced by combining x-ray photoelectron spectroscopy and vibrating sample magnetometer measurements. By comparison with pristine monolayer MoS2, the distinct ferromagnetism behaviors of nitrogen-doped monolayer MoS2 are observed up to room temperature, while the semiconducting nature persists. Our work introduces an efficient and feasible approach to realize magnetism in the 2D limit and explores potential applications in semiconductor spintronics.
On ergodic flows with simple Lebesgue spectrum
Authors: Prikhod’ko A. A.
Published: February 2020

We prove the existence of ergodic flows with invariant probability measure having a Lebesgue spectrum of multiplicity

.

Bibliography: 15 titles.
The Cauchy problem for an abstract second order ordinary differential equation
Authors: Gavrilov V. S.
Published: February 2020

We prove the existence and uniqueness of a solution for the Cauchy problem for a linear abstract second order differential equation, obtain its representation, and prove that it is continuously dependent on the time at which the initial conditions are specified. Based on these results, we prove the existence and uniqueness of a solution of the Cauchy problem for a nonlinear abstract second order differential equation. This result is applied to show that the initial-boundary value problem for a nonlinear hyperbolic divergence structure equation has a unique solution.

Bibliography: 49 titles.
Kripke semantics for the logic of problems and propositions
Authors: Onoprienko A. A.
Published: February 2020

In this paper we study the propositional fragment

of the joint logic of problems and propositions introduced by Melikhov. We provide Kripke semantics for this logic and show that

is complete with respect to those models and has the finite model property. We consider examples of the use of

-models usage. In particular, we prove that

is a conservative extension of the logic

. We also show that the logic

is complete with respect to Kripke frames with sets of audit worlds introduced by Artemov and Protopopescu (who called them audit set models).

Bibliography: 31 titles.
Sustainable goat production: modelling optimal performance in extensive systems
Authors: Godber O. F. , Chentouf M. , Wall R.
Published: February 2020

Context
Strategies for achieving greater ruminant livestock productivity are essential to meet the food demands of growing populations, but sustainable changes are difficult to identify given the inherent complexity of such systems. Systems models can address this issue by allowing the impact of potential changes to be explored.

Aims
To develop a holistic systems model for goat production in an extensive Mediterranean environment which could allow changes in key management factors influencing the system to be investigated.

Methods
Initially, a conceptual comprehensive stock-and-flow model of a representative Mediterranean goat production system was constructed. This was used to identify informative indicators that would represent the overall technical and economic performance of the system. Sub-models were then assembled to build the full systems model. The model was parameterised with data collected over 3 years for goat holdings in northern Morocco. Scenario analysis techniques are used to explore the strategies that optimise performance under climate and feed price challenges.

Key results
Meat production is particularly important during periods of drought when increased meat yields can counteract the expected reduction in milk yields, to protect human food security, prevent excessive rangeland degradation and preserve natural nutritional resources. Feed price shocks during drought can have significant negative impacts on the system and zero feed input is shown to be a more sustainable strategy than reliance on high price feed during drought. Any alternative feed sources need to have a high forage component to reduce grazing periods significantly and promote rangeland preservation.

Implications
A diverse management strategy with a mixed meat and dairy semi-intensive production is more stable than specialised dairy systems and allows goat production and financial viability of intensification to be maintained under climatic stress; maintaining meat production was necessary to optimise performance.

Conclusions
The model allows improved insight into management strategies which could optimise animal husbandry performance in goat subsistence systems. However, the work also demonstrates the difficulty of constructing a truly holistic model since, to be practical, such constructs must necessarily be bounded; parameter selection and the limits to the boundaries imposed are inevitably critical.
The size of the immune repertoire of bacteria
Authors: Bradde Serena , Nourmohammad Armita , Goyal Sidhartha , Balasubramanian Vijay
Published: February 2020

Significance

Some bacteria possess an adaptive immune system that maintains a memory of past viral infections in the CRISPR loci of their genomes. This memory is used to mount targeted responses against later threats but is remarkably shallow: it remembers only a few dozen to a few hundred viruses. We present a statistical theory of CRISPR-based immunity that quantitatively predicts the depth of bacterial immune memory in terms of a tradeoff with fundamental constraints of the cellular biochemical machinery.
Older mothers produce more successful daughters
Authors: Kroeger Svenja B. , Blumstein Daniel T. , Armitage Kenneth B. , Reid Jane M. , Martin Julien G. A.
Published: February 2020

Annual reproductive success and senescence patterns vary substantially among individuals in the wild. However, it is still seldom considered that senescence may not only affect an individual but also affect age-specific reproductive success in its offspring, generating transgenerational reproductive senescence. We used long-term data from wild yellow-bellied marmots (Marmota flaviventer) living in two different elevational environments to quantify age-specific reproductive success of daughters born to mothers differing in age. Contrary to prediction, daughters born to older mothers had greater annual reproductive success on average than daughters born to younger mothers, and this translated into greater lifetime reproductive success. However, in the favorable lower elevation environment, daughters born to older mothers also had greater age-specific decreases in annual reproductive success. In the harsher higher elevation environment on the other hand, daughters born to older mothers tended to die before reaching ages at which such senescent decreases could be observed. Our study highlights the importance of incorporating environment-specific transgenerational parent age effects on adult offspring age-specific life-history traits to fully understand the substantial variation observed in senescence patterns in wild populations.
Integrated functional genomic analyses of Klinefelter and Turner syndromes reveal global network effects of altered X chromosome dosage
Authors: Zhang Xianglong , Hong David , Ma Shining , Ward Thomas , Ho Marcus , Pattni Reenal , Duren Zhana , Stankov Atanas , Bade Shrestha Sharon , Hallmayer Joachim , Wong Wing Hung , Reiss Allan L. , Urban Alexander E.
Published: February 2020

In both Turner syndrome (TS) and Klinefelter syndrome (KS) copy number aberrations of the X chromosome lead to various developmental symptoms. We report a comparative analysis of TS vs. KS regarding differences at the genomic network level measured in primary samples by analyzing gene expression, DNA methylation, and chromatin conformation. X-chromosome inactivation (XCI) silences transcription from one X chromosome in female mammals, on which most genes are inactive, and some genes escape from XCI. In TS, almost all differentially expressed escape genes are down-regulated but most differentially expressed inactive genes are up-regulated. In KS, differentially expressed escape genes are up-regulated while the majority of inactive genes appear unchanged. Interestingly, 94 differentially expressed genes (DEGs) overlapped between TS and female and KS and male comparisons; and these almost uniformly display expression changes into opposite directions. DEGs on the X chromosome and the autosomes are coexpressed in both syndromes, indicating that there are molecular ripple effects of the changes in X chromosome dosage. Six potential candidate genes (
RPS4X
,
SEPT6
,
NKRF
,
CX0rf57
,
NAA10
, and
FLNA
) for KS are identified on Xq, as well as candidate central genes on Xp for TS. Only promoters of inactive genes are differentially methylated in both syndromes while escape gene promoters remain unchanged. The intrachromosomal contact map of the X chromosome in TS exhibits the structure of an active X chromosome. The discovery of shared DEGs indicates the existence of common molecular mechanisms for gene regulation in TS and KS that transmit the gene dosage changes to the transcriptome.
Analytical distributions for detailed models of stochastic gene expression in eukaryotic cells
Authors: Cao Zhixing , Grima Ramon
Published: February 2020

Significance

The random nature of gene expression is well established experimentally. Mathematical modeling provides a means of understanding the factors leading to the observed stochasticity. In this article, we extend the classical two-state model of stochastic mRNA dynamics to include a considerable number of salient features of single-cell biology, such as cell division, replication, mRNA maturation, dosage compensation, and growth-dependent transcription. By means of biologically relevant approximations, we obtain expressions for the time-dependent distributions of mRNA and protein numbers. These provide insight into how fluctuations are modified and controlled by complex intracellular processes.
An experimental test of the area–heterogeneity tradeoff
Authors: Ben-Hur Eyal , Kadmon Ronen
Published: February 2020

A fundamental property of ecosystems is a tradeoff between the number and size of habitats: as the number of habitats within a fixed area increases, the average area per habitat must decrease. This tradeoff is termed the “area–heterogeneity tradeoff.” Theoretical models suggest that the reduction in habitat sizes under high levels of heterogeneity may cause a decline in species richness because it reduces the amount of effective area available for individual species under high levels of heterogeneity, thereby increasing the likelihood of stochastic extinctions. Here, we test this prediction using an experiment that allows us to separate the effect of the area–heterogeneity tradeoff from the total effect of habitat heterogeneity. Surprisingly, despite considerable extinctions, reduction in the amount of effective area available per species facilitated rather than reduced richness in the study communities. Our data suggest that the mechanism behind this positive effect was a decrease in the probability of deterministic competitive exclusion. We conclude that the area–heterogeneity tradeoff may have both negative and positive implications for biodiversity and that its net effect depends on the relative importance of stochastic vs. deterministic drivers of extinction in the relevant system. Our finding that the area–heterogeneity tradeoff may contribute to biodiversity adds a dimension to existing ecological theory and is highly relevant for understanding and predicting biodiversity responses to natural and anthropogenic variations in the environment.