bluuebunny/crossref_metadata_2025 huggingface dataset:
Global optimisation scheme based on triple‐objective ABC algorithm for designing fully optimised multi‐layer radar absorbing material
Authors: Toktas Abdurrahim , Ustun Deniz , Tekbas Mustafa
Published: April 2020

Multilayer radar absorbing material (MRAM) is composed by superimposing different dielectric material layers with various thicknesses for reducing the reflection of electromagnetic (EM) wave. In this study, a novel triple‐objective optimisation scheme based on Pareto‐integrated artificial bee colony (P‐ABC) algorithm is presented for the fully‐optimised design of four broad‐band and broad‐angle MRAMs (BB‐MRAMs) at the most interested radar bands 2–8, 8–12, 12–18 and 2–18 GHz between the angle range of 0°–60°. Two objective functions depending on total reflections (TRs) with TE and TM polarisations are constituted by taking the weighted mean of the TR in the incident wave angle and frequency. The BB‐MRAMs are optimally designed by determining simultaneously the design variables of the thickness and material of each layer for minimising synchronously the three objective functions TE‐TR, TM‐TR and total thickness through the P‐ABC, as well as by assuring the trade‐off among the objectives. The BB‐MRAMs are also verified under various cases through a comparison with simulated results by a full‐wave simulator. The designed BB‐MRAMs are even compared with the near‐optimal MRAMs reported elsewhere. Therefore, the fully‐optimised BB‐MRAMs by the proposed triple‐objective scheme are the global optimal designs thanks to the robust P‐ABC algorithm.
Dynamics of DiskMass Survey galaxies in refracted gravity
Authors: Cesare V. , Diaferio A. , Matsakos T. , Angus G.
Published: April 2020

We aim to verify whether refracted gravity (RG) is capable of describing the dynamics of disk galaxies without resorting to the presence of dark matter. RG is a classical theory of gravity in which the standard Poisson equation is modified with the introduction of the gravitational permittivity, which is a universal monotonic function of the local mass density. We used the rotation curves and the radial profiles of the stellar velocity dispersion perpendicular to the galactic disks of 30 disk galaxies from the DiskMass Survey (DMS) to determine the gravitational permittivity. RG describes the rotation curves and the vertical velocity dispersions by requiring galaxy mass-to-light ratios that are in agreement with stellar population synthesis models, and disk thicknesses that are in agreement with observations, once observational biases are taken into account. Our results rely on setting the three free parameters of the gravitational permittivity for each individual galaxy. However, we show that the differences of these parameters from galaxy to galaxy can, in principle, be ascribed to statistical fluctuations. We adopted an approximate procedure to estimate a single set of parameters that may properly describe the kinematics of the entire sample and suggest that the gravitational permittivity is indeed a universal function. Finally, we showed that the RG models of the individual rotation curves can only partly describe the radial acceleration relation (RAR) between the observed centripetal acceleration derived from the rotation curve and the Newtonian gravitational acceleration originating from the baryonic mass distribution. Evidently, the RG models underestimate the observed accelerations by 0.1 to 0.3 dex at low Newtonian accelerations. An additional problem that ought to be considered is the strong correlation, at much more than 5σ, between the residuals of the RAR models and three radially-dependent properties of the galaxies, whereas the DMS data show a considerably less significant correlation, at more than 4σ, for only two of these quantities. These correlations might be the source of the non-null intrinsic scatter of the RG models: this non-null scatter is at odds with the observed intrinsic scatter of other galaxy samples different from DMS, which is consistent with zero. Further investigations are required to assess whether these discrepancies in the RAR originate from the DMS sample, which might not be ideal for deriving the RAR, or whether they are genuine failures of RG.
Inductive temperature measurement: A new sensor improvement for industrial applications
Authors: Gonçalves Ricardo Spyrides Boabaid Pimentel , Haueisen Jens , Marques Jefferson Luiz Brum
Published: April 2020

A remote temperature sensing technique was developed by measuring exponential decay current pulses in a Helmholtz coil. After an initial calibration to extract a mathematical function relating the time constant (τ) to the temperature of the object sensed, the temperature of other similar objects can be estimated with less power, less strict positioning of the object, and more sensitivity than previous techniques, even inside a water-based fluid.
Atomistic simulations of α-Fe/Nd2Fe14B magnetic core/shell nanocomposites with enhanced energy product for high temperature permanent magnet applications
Authors: Westmoreland Sam C. , Skelland Connor , Shoji Tetsuya , Yano Masao , Kato Akira , Ito Masaaki , Hrkac Gino , Schrefl Thomas , Evans Richard F. L. , Chantrell Roy W.
Published: April 2020

Nd 2 Fe 14 B has generated significant interest since its discovery in the 1980s due to its impressive energy density, which makes it a prime candidate for use in permanent magnet applications. Its performance is known to suffer greatly at the high temperatures required for motor applications around 450K. Core/shell nanocomposites provide a potential route to improve material performance by combining the highly anisotropic permanent magnet with a material with high moment and high Curie temperature. We have used an atomistic spin model to investigate the magnetic properties of Nd2Fe14B with α-Fe in a core/shell nanostructure. We find that at typical motor operating temperatures, increasing α-Fe content reduces the coercivity of the system while enhancing the saturation magnetization. The overall effect is that an improvement in BHmax is seen with increasing α-Fe up to an optimal value of 70vol.%. This property of core/shell nanostructures would make them a suitable substitute for pure Nd2Fe14B while simultaneously lowering the raw material cost of the permanent magnet component of high-performance motors.
Bias induced spin state transition mediated by electron excitations
Authors: Hao Hua , Jia Ting , Zheng Xiaohong , Liu Peng , Zeng Zhi
Published: April 2020

Recent experiments reported that spin state transitions were realized by applying bias voltages. However, these bias-induced transitions are not fully understood, especially the mechanism. It is well established in experiments that the metal-to-ligand charge transfer (MLCT) excitation activated by light radiation can lead to the transition from low spin (LS) to high spin (HS), and the transition from HS to LS can be achieved by light due to the metal-centered (MC) excitation. Moreover, electronic excitations are accessible by inelastic cotunneling in molecular junctions under bias voltages. Based on these two facts, we propose that the MLCT excitation is responsible for the bias-induced transition from LS to HS, and the bias-induced transition from HS to LS is attributed to the MC excitation. The rationality of our proposed mechanism is demonstrated by comparing first-principles results and experimental observations. Threshold voltages of MLCT and MC excitations predicted in theory are consistent with bias voltages used to reach the transition from LS to HS and that from HS to LS in the experiment [Miyamachi et al., Nat. Commun. 3, 938 (2012)]. Activation of MLCT or MC excitation depends on the bias polarity, which can explain the bias-polarity dependence of the transition in the experiment. Our study is important for further design of molecular spintronic devices working on the bias-controlled transition.
Machine learning surrogate models for Landau fluid closure
Authors: Ma Chenhao , Zhu Ben , Xu Xue-Qiao , Wang Weixing
Published: April 2020

The first result of applying the machine/deep learning technique to the fluid closure problem is presented in this paper. As a start, three different types of neural networks [multilayer perceptron (MLP), convolutional neural network (CNN), and two-layer discrete Fourier transform (DFT) network] were constructed and trained to learn the well-known Hammett–Perkins Landau fluid closure in configuration space. We find that in order to train a well-preformed network, a minimum size of the training data set is needed; MLP also requires a minimum number of neurons in the hidden layers that equals the degrees of freedom in Fourier space, despite the fact that training data are being fed into the configuration space. Out of the three models, DFT performs the best for the clean data, most likely due to the existence of the simple Fourier expression for the Hammett–Perkins closure, but it is the least robust with respect to input noise. Overall, with appropriate tuning and optimization, all three neural networks are able to accurately predict the Hammett–Perkins closure and reproduce the intrinsic nonlocal feature, suggesting a promising path to calculating more sophisticated closures with the machine/deep learning technique.
A study of SCL sheath in presence of two dust species in a photoemissive environment
Authors: Deka Rinku , Bora Madhurjya P.
Published: April 2020

We have presented a basic model for a one dimensional collisionless space charge limited (SCL) plasma sheath consisting of electrons, ions, and two kinds of dust populations—a nano-dust population and a micrometer sized dust population. We have assumed that the nano-dust particles, plasma electrons, photoelectrons, and ions are the constituents of the plasma fluid and the micrometer sized dust particles behave as suspended impurities in the plasma without affecting the plasma dynamics. We have assumed that the charges of the micrometer-dusts are determined from the current balance on them and the charges on the nano-dusts are fixed. Due to photoemission, like the lunar surface charges to a positive potential, so the nano-dust and micrometer-dust particles charge to a positive potential. The electron densities have been derived by assuming both the electrons and photoelectrons to be Maxwellian, whereas the ion and nano-dust densities are derived from energy conservation of the ions and nano-dust particles and the continuity equations. Being a constituent of plasma, the nano-dusts do affect the sheath dynamics through the Poisson equation, which determines the plasma potential in the sheath region. The typical conditions for the levitation of dust particles in an SCL sheath including the maximum height and maximum size of the particles are calculated.
Achieving 280 Gbar hot spot pressure in DT-layered CH capsule implosions at the National Ignition Facility
Authors: Döppner T. , Hinkel D. E. , Jarrott L. C. , Masse L. , Ralph J. E. , Benedetti L. R. , Bachmann B. , Celliers P. M. , Casey D. T. , Divol L. , Field J. E. , Goyon C. , Hatarik R. , Hohenberger M. , Izumi N. , Khan S. F. , Kritcher A. L. , Ma T. , MacGowan B. J. , Millot M. , Milovich J. , Nagel S. , Pak A. , Park J. , Patel P. , Tommasini R. , Volegov P. , Weber C. , Landen O. L. , Callahan D. A. , Hurricane O. A. , Edwards M. J.
Published: April 2020

We are reporting on a series of indirect-drive 0.9-scale CH capsule implosions (inner radius = 840 μm) fielded in low gas-fill (0.6 mg/cm3) hohlraums of 6.72 mm diameter at the National Ignition Facility. Thanks to the 11%-reduction of the capsule size at a given hohlraum diameter compared to previously tested full-scale capsules, we achieved good hot spot symmetry control near 33% cone-fraction and without the need to invoke cross beam energy transfer. As a result, we achieved a hot spot pressure of 280 ± 40 Gbar, which is the highest pressure demonstrated in layered DT implosions with CH capsules to date. Pushing this design to higher velocity resulted in a reduction of neutron yield. Highly resolved capsule simulations suggest that higher Au M-shell preheat resulted in an increase in Atwood number at the ablator–ice interface, which leads to increased fuel-ablator instability and mixing. The results reported here provide important scaling information for next-generation CH designs.
Global geodesic acoustic mode in an ideal magnetohydrodynamic tokamak plasma
Authors: Ren Haijun , Wei Lai , Zhang Debing , Xu X. Q.
Published: April 2020

A concise and transparent second order ordinary differential equation (ODE) describing the radial structure of the global geodesic acoustic mode (GAM) is analytically presented in a low-β tokamak plasma. The large-aspect-ratio and circular cross section are assumed to linearize the ideal magnetohydrodynamic equations. We show clearly how finite β-dependent terms affect the global GAM frequency and radial mode structure. A typical Wentzel–Kramers–Brillouin form of solution is found for some reversed shear equilibria. For some other equilibria with lower β, even also in a reversed shear tokamak, the GAM continuum is upraised by the high order β-dependent terms so that its maximum is beyond ωG, where ωG is the classical local frequency of GAM. As a result, no self-consistent solution to the ODE can be found.
Experimental observations of topologically guided water waves within non-hexagonal structures
Authors: Makwana Mehul P. , Laforge Nicolas , Craster Richard V. , Dupont Guillaume , Guenneau Sébastien , Laude Vincent , Kadic Muamer
Published: April 2020

We investigate symmetry-protected topological water waves within a strategically engineered square lattice system. Thus far, symmetry-protected topological modes in hexagonal systems have primarily been studied in electromagnetism and acoustics, i.e., dispersionless media. Herein, we show experimentally how crucial geometrical properties of square structures allow for topological transport that is ordinarily forbidden within conventional hexagonal structures. We perform numerical simulations that take into account the inherent dispersion within water waves and devise a topological insulator that supports symmetry-protected transport along the domain walls. Our measurements, viewed using a high-speed camera under stroboscopic illumination, unambiguously demonstrate the valley-locked transport of water waves within a non-hexagonal structure. Due to the tunability of the energy's directionality by geometry, our results could be used for developing highly efficient energy harvesters, filters, and beam-splitters within dispersive media.
Multipactor discharge in circular waveguide window
Authors: Zhang Xue , Tang Haobei , Chen Xuyuan , Ma Minglin , Yang Wanchun , Cai Chenglin
Published: April 2020

To study the multipactor effect on the surface of a circular waveguide window excited by the TE11 mode, the effects of the radius of the window, frequency, and style of polarization of the electromagnetic field and the reflection coefficient of the incident wave are examined in this paper using a Monte Carlo algorithm and theoretical analysis. The results show that the character of the multipactor is dominated by the longitudinal velocity of the secondary electrons, which is directly proportional to the square of their oscillatory velocity and inversely proportional to the phase velocity of the RF field. Either increasing the radius of the window disk or decreasing the field frequency leads to the aggravation of multipactor discharge. Moreover, applying the circularly polarized TE11 mode in a circular waveguide window generates electrons at a higher velocity normal to the window disk than that with linearly polarized TE11 mode transmission. In addition, the increase in the reflection coefficient of the incident wave imposes a longitudinal gradient force in the vicinity of the window disk, which also boosts the longitudinal velocity of the secondary electrons and degrades multipactor discharge upstream of the window box.
Tungsten-doped Ge2Sb2Te5 phase change material for high-speed optical switching devices
Authors: Guo Pengfei , Burrow Joshua A. , Sevison Gary A. , Kwon Heungdong , Perez Christopher , Hendrickson Joshua R. , Smith Evan M. , Asheghi Mehdi , Goodson Kenneth E. , Agha Imad , Sarangan Andrew M.
Published: April 2020

The large impedance mismatch between the highly resistive amorphous state and the highly conductive crystalline state of Ge2Sb2Te5 is an impediment for the realization of high-speed electrically switched optical devices. In this paper, we demonstrate that tungsten doping can reduce this resistivity contrast and also results in a lower amorphous state resistivity. Additionally, it lowers the contact resistance, improves the optical contrast, and extends the face-centered-cubic state up to 350 °C, with a minimal impact on thermal conductivity.
Strong current response to slow modulation: A metabolic case-study
Authors: Forastiere Danilo , Falasco Gianmaria , Esposito Massimiliano
Published: April 2020

We study the current response to periodic driving of a crucial biochemical reaction network, namely, substrate inhibition. We focus on the conversion rate of substrate into product under time-varying metabolic conditions, modeled by a periodic modulation of the product concentration. We find that the system exhibits a strong nonlinear response to small driving frequencies both for the mean time-averaged current and for the fluctuations. For the first, we obtain an analytic formula by coarse-graining the original model to a solvable one. The result is nonperturbative in the modulation amplitude and frequency. We then refine the picture by studying the stochastic dynamics of the full system using a large deviation approach that allows us to show the resonant effect at the level of the time-averaged variance and signal-to-noise ratio. Finally, we discuss how this nonequilibrium effect may play a role in metabolic and synthetic networks.
Two-dimensional Ruddlesden–Popper layered perovskite for light-emitting diodes
Authors: Sun Bo , Xu Ying , Chen Yonghua , Huang Wei
Published: April 2020

Solution-processed metal halide perovskite light-emitting diodes (PeLEDs) have attracted extensive attention due to the great potential application in energy-efficient lighting and displays. Two-dimensional Ruddlesden–Popper (2DRP) layered perovskites exhibit high photoluminescence quantum efficiency, improved film morphology, and enhanced operational stability over their three-dimensional counterparts, making them attractive for high-performance PeLEDs. In addition, 2DRP perovskite materials with a tunable exciton binding energy are suitable for preparing PeLEDs with color-tunability. In this perspective, we first introduce the merits of the 2DRP layered perovskites in terms of their structural characteristics. The progress in 2DRP PeLEDs is then reviewed. The challenges and new opportunities of the PeLEDs are finally discussed. We hope to open up new perspectives for rational designs of the 2DRP perovskite materials for PeLEDs with unprecedented efficiency and stability.
Dissipative couplings in cavity magnonics
Authors: Wang Yi-Pu , Hu Can-Ming
Published: April 2020

Cavity magnonics is an emerging field that studies the strong coupling between cavity photons and collective spin excitations such as magnons. This rapidly developing field connects some of the most exciting branches of modern physics, such as quantum information and quantum optics, with one of the oldest sciences on Earth, the magnetism. The past few years have seen a steady stream of exciting experiments that demonstrate novel magnon-based transducers and memories. Most of such cavity magnonic devices rely on coherent coupling that stems from the direct dipole–dipole interaction. Recently, a distinct dissipative magnon–photon coupling was discovered. In contrast to coherent coupling that leads to level repulsion between hybridized modes, dissipative coupling results in level attraction. It opens an avenue for engineering and harnessing losses in hybrid systems. This article gives a brief review of this new frontier. Experimental observations of level attraction are reviewed. Different microscopic mechanisms are compared. Based on such experimental and theoretical reviews, we present an outlook for developing open cavity systems by engineering and harnessing dissipative couplings.
Measurement of sub-nanonewton forces inside a scanning electron microscope
Authors: Klauser Waldemar , Bartenwerfer Malte , Fatikow Sergej
Published: April 2020

van der Waals forces, electrostatic interactions, and capillary forces are the dominant force interactions at the micro- and nanoscale. This complex ensemble of surface forces is oftentimes summarized as adhesion and is important for various applications and research fields. So far, numerous measurement techniques have evolved in this field. However, there is still a lack of experimental insight into the complex interplay of van der Waals, electrostatic, and capillary forces for small force ranges below 10 nN, as this is the order of magnitude of the latter, which can shadow other interactions in ambient and even inert gas environments. To exclude capillary forces and thus to turn the van der Waals and electrostatic forces into the most significant interactions, we develop an interferometric force spectroscopy setup based on a scanning probe technique, featuring a sub-nanonewton resolution, and integrate it into the vacuum chamber of a scanning electron microscope. In this work, we describe the setup integration, show the long-term drift behavior and resolution capabilities, and conduct first measurements of adhesion energies between a silica colloidal probe and a silicon substrate. The presented setup shows its capability to reliably measure adhesive interactions in vacuum and an ambient environment with a sub-nanonewton resolution proving its potential to allow for the investigation of the separate contribution of capillary, van der Waals, and electrostatic interactions to adhesion and for a systematic experimental validation of the established adhesion theories and approximations on the micro- and nanoscale.
Pressure induced phase transitions in BaZr(PO4)2 studied using x-ray diffraction, Raman spectroscopy, and first principles calculations
Authors: Varma Meera , Poswal H. K. , Velaga Srihari
Published: April 2020

Structural stability and polymorphic phase transitions in barium zirconium diorthophosphate, a technologically important compound consisting of the polyhedral framework structure, has been studied under high pressure (HP). With the combined study of x-ray diffraction (up to ∼12 GPa) and Raman spectroscopy at high pressure (up to ∼16 GPa), we observed three reversible pressure induced polymorphic phase transitions. The ambient phase transforms at a very low pressure (0.4 GPa) to a triclinic structure (HP-1 phase). Ambient and HP-1 phases coexist up to ∼2 GPa before transforming to the monoclinic HP-2 phase. Further, another transition is observed around ∼8 GPa (HP-3). On complete release of pressure, the sample reverts to the ambient phase with traces of the HP-1 phase. First principles based phonon and structural relaxation calculations are used to compare experimental findings. This study establishes a polymorphic structural sequence in yavapaiite type compounds.
Nitrogen-rich silicon nitride proves viable for future use as a quantum photonics platform
Authors: Liebendorfer Adam
Published: April 2020

Demonstration shows how to integrate single atom-like systems with coherent memories into a chip-scale photonic material.
Epitaxial growth of the cubic L21-Mn2.6Ga Heusler alloy on MgO(001)
Authors: Gutiérrez-Pérez Rocío M. , Holguín-Momaca José T. , Tian Guo , Ojha Shuchi Sunil , López Antón Ricardo , Ross Caroline A. , Olive-Méndez Sion F.
Published: April 2020

The Mn3Ga Heusler alloy possesses different crystalline structures representing a range of properties of interest for spintronic applications. We report on the structural and magnetic characterization of the disordered cubic-fcc L21-Mn2.6Ga thin films grown on MgO(001) substrates. The first two nanometers of thickness of the Mn2.6Ga thin films are highly strained to the substrate with a lattice mismatch of 9.54%, playing the role of a template layer for the subsequent growth of relaxed L21-Mn2.6Ga. Once the films reach a critical thickness of 15 nm, the cubic phase reorients its epitaxial relationship from a (001) to a (111) in-plane orientation. Magnetic measurements show that the samples exhibit perpendicular magnetic anisotropy and also that the usually antiferromagnetic L21-Mn3Ga films are ferromagnetic with a Curie temperature >400 K due to partially compensated Mn moments.
Photochemistry from low-lying states of HOSO+
Authors: Trabelsi Tarek , Rohacs Natasa , Francisco Joseph S.
Published: April 2020

Using configuration interaction ab initio methods, the evolution of the lowest electronic states of singlet and triplet spin multiplicities of HOSO+ along the stretching and bending coordinates of is investigated. Equilibrium geometries, rotational constants, and harmonic vibrational frequencies of the lowest electronic states are calculated, i.e., X1A′, 11A″, 13A′, and 13A″. The global minimum of the 11A″ state is located below the first dissociation limit and its calculated lifetime is predicted to be 0.40 µs, making it suitable for detection by laser-induced fluorescence. According to the potential energy surfaces, HOSO+ should produce SO2+ and H after ultraviolet photon absorption to the 21A′ state. This work opens the door to investigate the branching ratio and the production rates of SO2+, SO+, and OH from HOSO+. These insights can help understand the SO2 cycle in the earth’s atmosphere and its effect on cooling our planet.
Single photon emission and single spin coherence of a nitrogen vacancy center encapsulated in silicon nitride
Authors: Smith Joe , Monroy-Ruz Jorge , Rarity John G. , C. Balram Krishna
Published: April 2020

Finding the right material platform for engineering efficient photonic interfaces to solid state emitters has been a long-standing bottleneck for scaling up solid state quantum systems. In this work, we demonstrate that nitrogen rich silicon nitride, with its low auto-fluorescence at visible wavelengths, is a viable quantum photonics platform by showing that nitrogen vacancy centers embedded in nanodiamonds preserve both their quantum optical and spin properties post-encapsulation. Given the variety of high-performance photonic components already demonstrated in silicon nitride, our work opens up a promising avenue for building integrated photonic platforms using solid state emitters.
Thermionic microwave gun for terahertz and synchrotron light sources
Authors: Kutsaev S. V. , Agustsson R. , Berry R. , Borland M. , Chao D. , Chimalpopoca O. , Gavryushkin D. , Gusarova M. , Hartzell J. , Meyer D. , Nassiri A. , Smirnov A. Yu. , Smith T. , Sun Y. , Verma A. , Waldschmidt G. , Zholents A.
Published: April 2020

Conventional thermionic microwave and radio frequency (RF) guns can offer high average beam current, which is important for synchrotron light and terahertz (THz) radiation source facilities, as well as for industrial applications. For example, the Advanced Photon Source at Argonne National Laboratory is a national synchrotron-radiation light source research facility that utilizes thermionic RF guns. However, these existing thermionic guns are bulky, difficult to handle and install, easily detuned, very sensitive to thermal expansion, and due for a major upgrade and replacement. In this paper, we present the design of a new, more stable, and reliable gun with optimized electromagnetic performance, improved thermal engineering, and a more robust cathode mounting technique, which is a critical step to improve the performance of existing and future light sources, industrial accelerators, and electron beam-driven THz sources. We will also present a fabricated gun prototype and show results of high-power and beam tests.
The role of plasmonic excitations in the optical activity of periodic structures with configurational chirality
Authors: Epstein Eliav David , Singh Leeju , Sternklar Shmuel , Gorodetski Yuri
Published: April 2020

Broken mirror symmetry of chiral structures imposes a lack of mirror symmetry in the scattering profile. When an energy dissipation channel is introduced in the system, an overall optical activity arises. Plasmonic nanostructures, therefore, are an ideal platform to induce optical activity by means of constitutional or configurational chirality. We experimentally investigate the mechanism of plasmonically induced configurational chirality in a periodic monoclinic hole array with a broken mirror symmetry. The resulting optical activity of the structure is studied by using k-space leakage radiation measurements.
High-temperature hypersonic Laval nozzle for non-LTE cavity ringdown spectroscopy
Authors: Dudás Eszter , Suas-David Nicolas , Brahmachary Shuvayan , Kulkarni Vinayak , Benidar Abdessamad , Kassi Samir , Charles Christine , Georges Robert
Published: April 2020

A small dimension Laval nozzle connected to a compact high enthalpy source equipped with cavity ringdown spectroscopy (CRDS) is used to produce vibrationally hot and rotationally cold high-resolution infrared spectra of polyatomic molecules in the 1.67 µm region. The Laval nozzle was machined in isostatic graphite, which is capable of withstanding high stagnation temperatures. It is characterized by a throat diameter of 2 mm and an exit diameter of 24 mm. It was designed to operate with argon heated up to 2000 K and to produce a quasi-unidirectional flow to reduce the Doppler effect responsible for line broadening. The hypersonic flow was characterized using computational fluid dynamics simulations, Pitot measurements, and CRDS. A Mach number evolving from 10 at the nozzle exit up to 18.3 before the occurrence of a first oblique shock wave was measured. Two different gases, carbon monoxide (CO) and methane (CH4), were used as test molecules. Vibrational (Tvib) and rotational (Trot) temperatures were extracted from the recorded infrared spectrum, leading to Tvib = 1346 ± 52 K and Trot = 12 ± 1 K for CO. A rotational temperature of 30 ± 3 K was measured for CH4, while two vibrational temperatures were necessary to reproduce the observed intensities. The population distribution between vibrational polyads was correctly described with TvibI=894±47 K, while the population distribution within a given polyad (namely, the dyad or the pentad) was modeled correctly by TvibII=54±4 K, testifying to a more rapid vibrational relaxation between the vibrational energy levels constituting a polyad.
An optical trap nudges a nanoparticle into its motional ground state
Authors: Hill Heather M.
Published: April 2020

Cooling techniques borrowed from atomic physics bring a room-temperature speck of glass into the quantum regime.
Opening a new university offers opportunities to try new approaches and reach new populations
Authors: Feder Toni
Published: April 2020

Brand recognition, funding, and language barriers are common challenges.
Take your pick: A new warhead or a “new program of record”
Authors: Kramer David
Published: April 2020

Administration officials say a proposed new weapon for the US Navy won’t require nuclear testing.
Influence of protodioscin content on digestibility and in vitro degradation kinetics in Urochloa brizantha cultivars
Authors: Leal Eduardo Souza , Ítavo Luís Carlos Vinhas , do Valle Cacilda Borges , Ítavo Camila Celeste Brandão Ferreira , Dias Alexandre Menezes , dos Santos Difante Gelson , Barbosa-Ferreira Marcos , Nonato Lucimara Modesto , de Melo Gleice Kelli Ayardes , Gurgel Antonio Leandro Chaves
Published: April 2020

Five cultivars of Urochloa brizantha (Hochst. ex A.Rich.) R.D. Webster (syn. of Brachiaria brizantha) were evaluated for nutritional value and an anti-nutritional factor (protodioscin), in order to determine whether protodioscin content was correlated with reduced feed quality. We evaluated cvv. Arapoty, Paiaguas, Xaraes, Marandu and Piata and grouped the results into summer, autumn, winter and spring seasons. Protodioscin content and chemical composition of leaves, in vitro digestibility and cumulative gas production were analysed. Data were evaluated by analysis of variance as a completely randomised experimental design in a factorial arrangement (five cultivars × four seasons). There was no significant interaction between cultivar and season. All grasses showed highest protodioscin contents during autumn. Protodioscin contents ranged from 5.6 g kg–1 (spring) to 19.2 g kg–1 (autumn). Crude protein content varied significantly across seasons. No significant effect was detected for neutral detergent fibre (NDF) content among seasons. Cultivar Arapoty showed the highest NDF content in summer (669.3 g kg–1) and the lowest in spring (601.9 g kg–1). The best in vitro digestibility coefficients were observed in spring. The protodioscin content of U. brizantha cultivars can negatively affect their digestibility and some parameters of cumulative in vitro gas production.
Variation in the aggressiveness of Xanthomonas citri subsp. citri pathotypes A and A* on three Citrus species, and epiphytic growth on some citrus weeds
Authors: Ebrahimi Zohreh , Rezaei Rasool , Masoumi-Asl Asad , Charehgani Habiballah
Published: April 2020

Citrus bacterial canker, caused by Xanthomonas citri subsp. citri (Xcc), is a widespread disease in citrus-producing areas of the tropics and subtropics. It is a serious threat to most commercial citrus cultivars and species. In this study, aggressiveness of different isolates of Xcc was determined on leaves of Citrus aurantiifolia, Citrus limon ‘Eureka’ and Citrus sinensis, and the population dynamics of isolates of two Xcc pathotypes (A and A*) was evaluated on eight plant species considered weeds of citrus, including Amaranthus caudatus, Medicago sativa, Sorghum halepense, Xanthium strumarium, Portulaca oleracea, Avena ludoviciana, Plantago lanceolata and Chenopodium album under greenhouse conditions. Isolates varied from aggressive to weakly aggressive on the basis of the intensity and persistence of water soaking and the development of necrosis 12 days post-inoculation. Both Xcc pathotypes multiplied on all plant species tested except Portulaca oleracea up to 20 days post-inoculation under greenhouse conditions. A high bacterial growth rate was observed on Medicago sativa and Plantago lanceolata. Strains of the A* pathotype successfully proliferated on all weeds except Portulaca oleracea, attaining a population density even higher than that of the A pathotype. The results clearly suggest that weed management is an important strategy in controlling canker disease in citrus-growing areas.
The surface tension of surfactant-containing, finite volume droplets
Authors: Bzdek Bryan R. , Reid Jonathan P. , Malila Jussi , Prisle Nønne L.
Published: April 2020

Surface tension influences the fraction of atmospheric particles that become cloud droplets. Although surfactants are an important component of aerosol mass, the surface tension of activating aerosol particles is still unresolved, with most climate models assuming activating particles have a surface tension equal to that of water. By studying picoliter droplet coalescence, we demonstrate that surfactants can significantly reduce the surface tension of finite-sized droplets below the value for water, consistent with recent field measurements. Significantly, this surface tension reduction is droplet size-dependent and does not correspond exactly to the macroscopic solution value. A fully independent monolayer partitioning model confirms the observed finite-size-dependent surface tension arises from the high surface-to-volume ratio in finite-sized droplets and enables predictions of aerosol hygroscopic growth. This model, constrained by the laboratory measurements, is consistent with a reduction in critical supersaturation for activation, potentially substantially increasing cloud droplet number concentration and modifying radiative cooling relative to current estimates assuming a water surface tension. The results highlight the need for improved constraints on the identities, properties, and concentrations of atmospheric aerosol surfactants in multiple environments and are broadly applicable to any discipline where finite volume effects are operative, such as studies of the competition between reaction rates within the bulk and at the surface of confined volumes and explorations of the influence of surfactants on dried particle morphology from spray driers.
The spatiotemporal spread of human migrations during the European Holocene
Authors: Racimo Fernando , Woodbridge Jessie , Fyfe Ralph M. , Sikora Martin , Sjögren Karl-Göran , Kristiansen Kristian , Vander Linden Marc
Published: April 2020

The European continent was subject to two major migrations of peoples during the Holocene: the northwestward movement of Anatolian farmer populations during the Neolithic and the westward movement of Yamnaya steppe peoples during the Bronze Age. These movements changed the genetic composition of the continent’s inhabitants. The Holocene was also characterized by major changes in vegetation composition, which altered the environment occupied by the original hunter-gatherer populations. We aim to test to what extent vegetation change through time is associated with changes in population composition as a consequence of these migrations, or with changes in climate. Using ancient DNA in combination with geostatistical techniques, we produce detailed maps of ancient population movements, which allow us to visualize how these migrations unfolded through time and space. We find that the spread of Neolithic farmer ancestry had a two-pronged wavefront, in agreement with similar findings on the cultural spread of farming from radiocarbon-dated archaeological sites. This movement, however, did not have a strong association with changes in the vegetational landscape. In contrast, the Yamnaya migration speed was at least twice as fast and coincided with a reduction in the amount of broad-leaf forest and an increase in the amount of pasture and natural grasslands in the continent. We demonstrate the utility of integrating ancient genomes with archaeometric datasets in a spatiotemporal statistical framework, which we foresee will enable future studies of ancient populations’ movements, and their putative effects on local fauna and flora.
A corpus analysis of the structural elaboration of Spanish
heritage language learners
Authors: Collentine Karina , Collentine Joseph
Published: April 2020

Research on heritage language learner (HLL)
grammar provides insights into bilingual developmental trajectories
(Bolger & Zapata,
2011). More research is needed on the effects of
cognitive processes on HLL grammar under real-time communicative
pressures (Jegerski,
2017). The present corpus-based study analyzes the role of
cognitive factors on HLLs’ (N = 65) production of
structural elaboration (i.e., syntactic modifiers and embedding),
which is cognitively challenging to monolinguals (Ferreira, 1991). The
analysis of the participants’ production in an instant-messaging
task indicates that, even though advanced HLLs may be fairly
homogeneous in their general grammatical and lexical abilities, they
vary significantly in the production of structural elaboration in
syntactic frames (e.g., verb phrases with clitics, relative clauses)
that interact strongly with working memory and attentional
resources.
Realizations of /b/ in the Spanish of Lima, Peru
Authors: Yarrington Kara
Published: April 2020

In canonical Spanish, the letters  and
 represent the same phoneme: /b/. The phoneme has two main
allophones, essentially in complementary distribution: [b] and [β]
(Harris, 1969).
Previous research has found allophonic deviations, such as [v], [Ø],
and [w], in both monolinguals (Sadowsky, 2010) and bilinguals (Phillips, 1982; Stevens, 2000). Previous research has not
extensively explored the production of /b/ in Peruvian Spanish.
Fifty-one participants were recorded at a university in Lima, Peru
reading isolated words and paragraphs. Half of the 60 target words
were spelled with  and the other half with . This
study supports previous literature, demonstrating that Peruvian
Spanish produces two complementary allophones of .
‘Debemos aprender y manejar un poco mejor el español’
Authors: Jiménez Lizama Pamela
Published: April 2020

This is a preliminary research about the
linguistic attitudes of Afro-Peruvian participants living in El
Carmen, a district located in Chincha (Peru), at the South-Central
coast of Peru. Data were collected from in-depth interviews
conducted to Afro-Peruvian participants born in El Carmen.
Linguistic attitudes are addressed from a Mentalist approach (González, 2009; Zamora, 2015). Results
reveal that Afro-Peruvian participants experience linguistic
uncertainty about their own way of speaking as they consider it
incorrect compared to the Lima inhabitants’ way of speaking, which
they perceive as more prestigious. On the other hand, they tend to
assess negatively the way of speaking of the Peruvian Highlands
inhabitants, as they consider these regions are plenty of indigenous
languages from the Andes.
Language choice and use by bilingual preschoolers
Authors: Barrera Tobón Carolina , Park-Johnson Sung , Brito Jazmin
Published: April 2020

In a Spanish-immersion preschool with a dual
population of heritage speakers (HS) and second-language learners
(L2) of Spanish, we explore the language choices students make when
their school language differs from the dominant language (English)
and factors that contribute to their language choice. Observational
data suggest students exhibit a type of interlocutor-dependent
diglossia, typically reserving English for peer interactions and
Spanish for interactions with teachers. Data from a language
elicitation task revealed that a students’ language background (L2
vs HS) is not a significant predictor of their Spanish production;
Spanish exposure proved to be the most significant factor. Case
studies confirmed these findings and further revealed the multiple
factors that make up Spanish exposure and predict students’ language
use.
Calculative and relational trust in the management of coastal floods and earthquakes: a comparative study (Confianza calculativa y relacional en la gestión de inundaciones costeras y terremotos: un estudio comparativo)
Authors: Bertoldo Raquel , Tanga Rocco , Dias Pierre , Guignard Séverin , Schleyer-Lindenmann Alexandra
Published: April 2020

Local communities have perfected their knowledge about their environments for generations. Considering modern management dynamics and the changing characteristics of their immediate environments, local communities must trust the authorities’ management of these risks. However, different types of risks expose these communities. This article proposes a comparative analysis of local trust dynamics between a locality in the French coast exposed to flood risks, and a town in inner Italy exposed to earthquake risks. The study focuses on how participants express calculative or relational trust through interviews. Results show that French participants consider the local risks of coastal floods to be minimal. In this sense they trust local authorities with the ability to manage these situations, even if generalized concerns over relational trust are also expressed. In Italy local inhabitants express a high awareness of earthquake risks. But the lack of preventive action from local authorities is associated with the expression of low calculative and relational trust.
Structural modal identification and health monitoring of building structures using self-sensing cementitious composites
Authors: Ding Siqi , Wang You-Wu , Ni Yi-Qing , Han Baoguo
Published: April 2020

Recently self-sensing cementitious composite has demonstrated its strong potentiality for structural health monitoring of civil infrastructures because of its low-cost, long-term stability and compatibility with concrete structures. In this paper, we propose novel hybrid nanocarbon materials engineered cement-based sensors (HNCSs) with high-sensitivity, which are fabricated with self-sensing cementitious composites containing electrostatic self-assembled CNT/NCB composite fillers. The mechanical property and sensing performance of the HNCSs are pre-characterized under static and dynamic compressive loadings. The HNCSs are then integrated into a five-story building model via custom-made clamps to verify the feasibility for dynamic response measurements. Results show that the developed sensors have satisfactory mechanical property and excellent pressure-sensitive reproducibility and stability. With clamps holding on the building model, the HNCSs perform satisfactorily under sinusoidal excitations in the frequency range from 2 to 40 Hz. In addition, the modal frequencies and their changes of the building model caused by ‘damage’ simulated through adding additional masses identified by the HNCSs are favorably consistent with the counterparts acquired by accelerometers and strain gauges, indicating that the developed HNCSs have great potential for structural modal identification and damage detection applications.
Hydroxamic acid-functionalized graphene thin films as nanocatalysts towards organophosphate degradation
Authors: Hostert Leandro , Zarbin Aldo J G , Orth Elisa S
Published: April 2020

Herein we describe the covalent functionalization of graphene oxide with hydroxamic acid groups (GOHD) anchored directly on the carboxylate groups. The functionalization was confirmed by several characterization techniques, such as infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy and Raman spectroscopy. The anchored groups have many potential applications, but we focused on its catalytic activity towards organophosphate (OPs) degradation, a serious environmental and health worldwide issue. The material was applied as nanocatalysts towards the degradation of the organophosphate of diethyl 2,4-dinitrophenyl phosphate and the real-life pesticide dimethyl 4-nitrophenyl phosphate (Paraoxon). High catalytic increments were obtained up to 108 fold (Paraoxon). Thus, reactions that would take over millions of years are reduced to a couple of days. Overall, the nanocatalyst shows potential as efficient detoxifying agents to eliminate chemical warfare stocks and pesticides by employing a practical material that can be deposited on any substrate and even over large areas.
The test function conjecture for parahoric local models
Authors: Haines Thomas , Richarz Timo
Published: April 2020

We prove the test function conjecture of Kottwitz and the first-named author for local models of Shimura varieties with parahoric level structure, and their analogues in equal characteristic.
Bounded and divergent trajectories and expanding curves on homogeneous spaces
Authors: Khalil Osama
Published: April 2020

Suppose

g
t

g_t

is a

1
1

-parameter

A
d

\mathrm {Ad}

-diagonalizable subgroup of a Lie group

G
G

and

Γ
>
G

\Gamma > G

is a lattice. We study the dimension of bounded and divergent orbits of

g
t

g_t

emanating from a class of curves lying on leaves of the unstable foliation of

g
t

g_t

on the homogeneous space

G

/

Γ

G/\Gamma

. We obtain sharp upper bounds on the Hausdorff dimension of divergent on average orbits and show that the set of bounded orbits is winning in the sense of Schmidt (and, hence, has full dimension). The class of curves we study is roughly characterized by being tangent to copies of

S
L

(
2
,

R

)

\mathrm {SL}(2,\mathbb {R})

inside

G
G

, which are not contained in a proper parabolic subgroup of

G
G

.

We describe applications of our results to problems in Diophantine approximation by number fields and intrinsic Diophantine approximation on spheres. Our methods also yield the following result for lines in the space of square systems of linear forms: suppose

φ
(
s
)
=
s
Y
+
Z

\varphi (s) = sY + Z

where

Y
∈

G
L

(
n
,

R

)

Y\in \mathrm {GL}(n,\mathbb {R})

and

Z
∈

M

n
,
n

(

R

)

Z\in M_{n,n}(\mathbb {R})

. Then, the dimension of the set of points

s
s

such that

φ
(
s
)

\varphi (s)

is singular is at most

1

/

2

1/2

while badly approximable points have Hausdorff dimension equal to

1
1

.