bluuebunny/crossref_metadata_2025 huggingface dataset:
A case for low atmospheric oxygen levels during Earth's middle history
Authors: Planavsky Noah J. , Cole Devon B. , Isson Terry T. , Reinhard Christopher T. , Crockford Peter W. , Sheldon Nathan D. , Lyons Timothy W.
Published: August 2018

The oxygenation of the atmosphere — one of the most fundamental transformations in Earth's history — dramatically altered the chemical composition of the oceans and provides a compelling example of how life can reshape planetary surface environments. Furthermore, it is commonly proposed that surface oxygen levels played a key role in controlling the timing and tempo of the origin and early diversification of animals. Although oxygen levels were likely more dynamic than previously imagined, we make a case here that emerging records provide evidence for low atmospheric oxygen levels for the majority of Earth's history. Specifically, we review records and present a conceptual framework that suggest that background oxygen levels were below 1% of the present atmospheric level during the billon years leading up to the diversification of early animals. Evidence for low background oxygen levels through much of the Proterozoic bolsters the case that environmental conditions were a critical factor in controlling the structure of ecosystems through Earth's history.
Mitigation of magnetic noise originating from ionosphere using TEC data retrieved by GNSS for detection of magnetic anomaly signals
Authors: Xia Tai‐Ran , Du Chang‐Ping
Published: August 2018

Magnetic noise originating from the ionosphere may be estimated by using the total electron concentration data retrieved by the global navigation satellite systems. This provides a useful scheme for mitigation of magnetic noise coming from the fluctuating ionosphere, which is a major interference source in the magnetic anomaly detection applications.
Far‐field boundary estimation for the high‐power UWB pulsed antennas
Authors: Wang Shao‐fei , Xie Yan‐zhao
Published: August 2018

In this study, a method to estimate the far‐field boundary of the high‐power ultra‐wideband (UWB) pulsed antennas is presented. By analysing the properties of the UWB pulsed antennas, it shows that the radiation space should be separated based on the behaviours of time or phase differences caused by the distribution of radiation elements of the antenna. In the time domain, characteristic parameters of the radiated pulse can be different due to various waveforms, which means that the far‐field condition is waveform dependent. So, for all the various waveforms, it is difficult to formulate a universal far‐field condition with a certain time‐domain parameter. Therefore, the far‐field boundary is better to be estimated in the frequency domain, which is obtained by substituting the cut‐off frequencies of the UWB system into the classical far‐field conditions. The cut‐off frequencies are determined by the 90% energy edge frequencies of the radiating field. Finally, a reflector Impulse Radiating Antenna (IRA) system is developed to verify the proposed method. The electric fields of the IRA from the near‐ to far‐field regions are measured, which indicates that the far‐field boundary calculated by the proposed method agrees with the experimental result well.
A star-forming dwarf galaxy candidate in the halo of NGC 4634
Authors: Stein Y. , Bomans D. J. , Kamphuis P. , Jütte E. , Langener M. , Dettmar R.-J.
Published: August 2018

Context. The halos of disk galaxies form a crucial connection between the galaxy disk and the intergalactic medium. Massive stars, H II regions, or dwarf galaxies located in the halos of galaxies are potential tracers of recent accretion and/or outflows of gas, and are additional contributors to the photon field and the gas phase metallicity.

Aims. We investigate the nature and origin of a star-forming dwarf galaxy candidate located in the halo of the edge-on Virgo galaxy NGC 4634 with a projected distance of 1.4 kpc and a Hα star formation rate of ∼4.7 × 10−3 M⊙ yr−1 in order to increase our understanding of these disk-halo processes.

Methods. With optical long-slit spectra we measured fluxes of optical nebula emission lines to derive the oxygen abundance 12 + log(O/H) of an H II region in the disk of NGC 4634 and in the star-forming dwarf galaxy candidate. Abundances derived from optical long-slit data and from Hubble Space Telescope (HST) r-band data, Hα data, Giant Metrewave Radio Telescope (GMRT) H I data, and photometry of SDSS and GALEX data were used for further analysis. With additional probes of the luminosity–metallicity relation in the B-band from the Hα-luminosity, the H I map, and the relative velocities, we are able to constrain a possible origin of the dwarf galaxy candidate.

Results. The high oxygen abundance (12 + log(O/H) ≈ 8.72) of the dwarf galaxy candidate leads to the conclusion that it was formed from pre-enriched material. Analysis of auxiliary data shows that the dwarf galaxy candidate is composed of material originating from NGC 4634. We cannot determine whether this material has been ejected tidally or through other processes, which makes the system highly interesting for follow up observations.
The ALMA-PILS survey: Stringent limits on small amines and nitrogen-oxides towards IRAS 16293–2422B
Authors: Ligterink N. F. W. , Calcutt H. , Coutens A. , Kristensen L. E. , Bourke T. L. , Drozdovskaya M. N. , Müller H. S. P. , Wampfler S. F. , van der Wiel M. H. D. , van Dishoeck E. F. , Jørgensen J. K.
Published: August 2018

Context. Hydroxylamine (NH2OH) and methylamine (CH3NH2) have both been suggested as precursors to the formation of amino acids and are therefore, of interest to prebiotic chemistry. Their presence in interstellar space and formation mechanisms, however, are not well established.

Aims. We aim to detect both amines and their potential precursor molecules NO, N2O, and CH2NH towards the low-mass protostellar binary IRAS 16293–2422, in order to investigate their presence and constrain their interstellar formation mechanisms around a young Sun-like protostar.

Methods. ALMA observations from the unbiased, high-angular resolution and sensitivity Protostellar Interferometric Line Survey (PILS) are used. Spectral transitions of the molecules under investigation are searched for with the CASSIS line analysis software.

Results. CH2NH and N2O are detected for the first time, towards a low-mass source, the latter molecule through confirmation with the single-dish TIMASSS survey. NO is also detected. CH3NH2 and NH2OH are not detected and stringent upper limit column densities are determined.

Conclusions. The non-detection of CH3NH2 and NH2OH limits the importance of formation routes to amino acids involving these species. The detection of CH2NH makes amino acid formation routes starting from this molecule plausible. The low abundances of CH2NH and CH3NH2 compared to Sgr B2 indicate that different physical conditions influence their formation in low- and high-mass sources.
Core fragmentation and Toomre stability analysis of W3(H2O)
Authors: Ahmadi A. , Beuther H. , Mottram J. C. , Bosco F. , Linz H. , Henning Th. , Winters J. M. , Kuiper R. , Pudritz R. , Sánchez-Monge Á. , Keto E. , Beltran M. , Bontemps S. , Cesaroni R. , Csengeri T. , Feng S. , Galvan-Madrid R. , Johnston K. G. , Klaassen P. , Leurini S. , Longmore S. N. , Lumsden S. , Maud L. T. , Menten K. M. , Moscadelli L. , Motte F. , Palau A. , Peters T. , Ragan S. E. , Schilke P. , Urquhart J. S. , Wyrowski F. , Zinnecker H.
Published: August 2018

Context. The fragmentation mode of high-mass molecular clumps and the properties of the central rotating structures surrounding the most luminous objects have yet to be comprehensively characterised.

Aims. We study the fragmentation and kinematics of the high-mass star-forming region W3(H2O), as part of the IRAM NOrthern Extended Millimeter Array (NOEMA) large programme CORE.

Methods. Using the IRAM NOEMA and the IRAM 30 m telescope, the CORE survey has obtained high-resolution observations of 20 well-known highly luminous star-forming regions in the 1.37 mm wavelength regime in both line and dust continuum emission.

Results. We present the spectral line setup of the CORE survey and a case study for W3(H2O). At ~0.′′35 (700 AU at 2.0 kpc) resolution, the W3(H2O) clump fragments into two cores (west and east), separated by ~2300 AU. Velocity shifts of a few km s−1 are observed in the dense-gas tracer, CH3CN, across both cores, consistent with rotation and perpendicular to the directions of two bipolar outflows, one emanating from each core. The kinematics of the rotating structure about W3(H2O) W shows signs of differential rotation of material, possibly in a disk-like object. The observed rotational signature around W3(H2O) E may be due to a disk-like object, an unresolved binary (or multiple) system, or a combination of both. We fit the emission of CH3CN (12K−11K), K = 4−6 and derive a gas temperature map with a median temperature of ~165 K across W3(H2O). We create a Toomre Q map to study thestability of the rotating structures against gravitational instability. The rotating structures appear to be Toomre unstable close to their outer boundaries, with a possibility of further fragmentation in the differentially rotating core, W3(H2O) W. Rapid cooling in the Toomre unstable regions supports the fragmentation scenario.

Conclusions. Combining millimetre dust continuum and spectral line data toward the famous high-mass star-forming region W3(H2O), we identify core fragmentation on large scales, and indications for possible disk fragmentation on smaller spatial scales.
Segregation effect and N2 binding energy reduction in CO-N2 systems adsorbed on water ice substrates
Authors: Nguyen T. , Baouche S. , Congiu E. , Diana S. , Pagani L. , Dulieu F.
Published: August 2018

Context. CO and N2 are two abundant species in molecular clouds. CO molecules are heavily depleted from the gas phase towards the centre of pre-stellar cores, whereas N2 maintains a high gas phase abundance. For example, in the molecular cloud L183, CO is depleted by a factor of ≈400 in its centre with respect to the outer regions of the cloud, whereas N2 is only depleted by a factor of ≈20. The reason for this difference is not yet clear, since CO and N2 have identical masses, similar sticking properties, and a relatively close energy of adsorption.

Aims. We present a study of the CO-N2 system in sub-monolayer regimes, with the aim to measure, analyse and elucidate how the adsorption energy of the two species varies with coverage, with much attention to the case where CO is more abundant than N2.

Methods. Experiments were carried out using the ultra-high vacuum (UHV) set-up called VENUS. Sub-monolayers of either pure 13CO or pure 15N2 and 13CO:15N2 mixtures were deposited on compact amorphous solid water ice, and crystalline water ice. Temperature-programmed desorption experiments, monitored by mass spectrometry, are used to analyse the distributions of binding energies of 13CO and 15N2 when adsorbed together in different proportions.

Results. The distribution of binding energies of pure species varies from 990 K to 1630 K for 13CO, and from 890 K to 1430 K for 15N2. When a CO:N2 mixture is deposited, the 15N2 binding energy distribution is strongly affected by the presence of 13CO, whereas the adsorption energy of CO is unaltered.

Conclusions. Whatever types of water ice substrate we used, the N2 effective binding energy was significantly lowered by the presence of CO molecules. We discuss the possible impact of this finding in the context of pre-stellar cores.
Deutsche Gesellschaft für Physikalische Medizin und Rehabilitation e.V.
Authors: Krischak Gert
Published: August 2018

Der Jahreskongress der Deutschen Gesellschaft für Physikalische Medizin und Rehabilitation e.V. (DGPMR) erneuert sich
Base-Promoted Tandem Cyclization for the Synthesis of Polyfunctional 2-Hydroxy-2,3-dihydrofurans from Arylglyoxal Monohydrates and 3-(1H-Indol-3-yl)-3-oxopropanenitrile
Authors: Liu Yi , Wu An-Xin , Cai Qun , Sheng Hui-Yang , Li Deng-Kui
Published: August 2018

An efficient base-promoted tandem cyclization for the synthesis of polyfunctional 2-hydroxy-2,3-dihydrofurans from arylglyoxal monohydrates and 3-(1H-indol-3-yl)-3-oxopropanenitrile has been established. The investigation of the mechanism suggested that this reaction proceeds through a Knoevenagel condensation–Michael addition–oxidation–cyclization sequence. This method demonstrates the compatibility with a wide range of functional groups to produce the 2-hydroxy-2,3-dihydrofuran scaffolds in good to excellent yields in one pot.
One-Pot Synthesis of Tetraazamacrocyclic Complexes from the Arnold Salt
Authors: Woźny Mateusz
Published: August 2018

We present an improved synthesis of bis(hexafluorophosphate) Arnold salt, which is a synthon of triformylmethane. The salt is shown to be a substrate for the one-pot, aqueous synthesis of macro­cyclic tetraiminato complexes of copper(II) and nickel(II). The synthesis of complexes is a major improvement over the original stepwise procedure, and is characterized by short reaction time, ease of product separation, scalability, and high yields.
Directed Zincation or Magnesiation of 2- and 4-Pyrones and Their Derivatives
Authors: Knochel Paul , Ziegler Dorothée , Klier Lydia , Müller Nicolas , Karaghiosoff Konstantin
Published: August 2018

A regioselective magnesiation of the 2-pyrone scaffold was developed. Magnesiation of this heterocycle by using TMPMgCl·LiCl (TMP = 2,2,6,6-tetramethylpiperidyl) followed by trapping reactions with electrophiles such as aldehydes, allylic bromides, acid chlorides, and aryl iodides provided functionalized 2-pyrones. Furthermore, methyl coumalate and 3,5-dibromo-2H-pyran-2-one were zincated by using TMPZnCl·LiCl to afford zincated heterocycles, which reacted with typical electrophiles. A second magnesiation at position C3 of the 2-pyrone scaffold was achieved by using TMPMgCl·LiCl. Also, the zincation of the 4-pyrone scaffold at position C2 is reported, leading to functionalized 4-pyrones.
Emergent Properties of Natural Products
Authors: Herzon Seth
Published: August 2018

Emergence is the phenomenon by which novel properties arise from the combination of simpler fragments that lack those properties at their given levels of hierarchal complexity. Emergence is a centuries-old concept that is commonly invoked in biological systems. However, the penetration of this idea into chemistry, and studies of natural products in particular, has been more limited. In this article I will describe how the perspective of emergence provided a framework to elucidate the complex properties of two classes of natural products – the diazofluorene antitumor agent lomaiviticin A and the genotoxic bacterial metabolites known as colibactins, and sets the stage for a third class of molecules – antibiotics derived from the fungal metabolite pleuromutilin. Embracing the idea of emergence helped us to connect the aggregate reactivities of the colibactins and lomaiviticin A with their biological phenotypes. Emergence is a top-down approach to natural products and complements the classical bottom-up analysis of functional group structure and reactivity. It is a useful intellectual framework to study the complex evolved properties of natural products.

1 Introduction

2 Diazofluorenes

3 Precolibactins and Colibactins

4 Pleuromutilins

5 Discussion and Conclusion
Variant of the Technique for Laryngeal Microsurgery in Cases of Difficult Laryngoscopy
Authors: Setton Antonio , D'avila Jeferson , Gurgel Ricardo , Tsuji Domingos , D'avila Daniel , Góis Carlos , Meurer Ana , Gurgel Helaina
Published: August 2018

Introduction Low exposure of the larynx can make laryngeal microsurgery difficult or even impossible. The application of rigid and contact endoscopy enabled oblique and retrograde angled visualization, allowing transoperative staging with greater reach of the anatomical areas. However, there is difficulty or even impossibility of performing the surgical act, due to the incompatibility of the angled path with the straight surgical tools.

Objective To demonstrate the efficiency of the variant of the technique for laryngeal microsurgery in cases of difficult laryngoscopy and to analyze the new surgical instruments specific to the endoscopic procedure.

Methods This is a cross-sectional retrospective study, based on the analysis of 30 medical records of patients treated surgically at a philanthropic hospital in the state of Sergipe, Brazil, between the years of 2014 and 2015.

Results The technical variant used 30- and 70-degree endoscopes that provided complete oblique view of the endolarynx. The association of angled instruments (forceps, suction pumps, retractors and scissors) enabled the execution of the surgical procedures.

Conclusion The association of rigid endoscopy with angled instruments promoted full visualization of the surgical lesion and operative resolution.
Predicting search time when hunting for multiple moving targets: A recursive harmonic law
Authors: Weng Tongfeng , Zhang Jie , Small Michael , Yang Huijie , Hui Pan
Published: August 2018

We investigate searching for multiple mobile objects on networks and introduce the concept of mean random search time (MRST) to quantify the expected time a searcher takes to capture moving targets specified in advance. We consider this quantity averaged over all initial conditions for a searcher and multiple targets called the global MRST. We find that the growth of global MRST follows a recursive harmonic law with respect to that of stalking the individuals. In particular, when the diffusive laws of moving targets are identical, the global MRST shows a logarithmic increase with the number of moving targets. Moreover, utilizing the recursive harmonic law, we can accurately predict the expected successive time interval for capturing a new moving target. The recursive harmonic law unveils the underlying mechanism governing the search time when hunting for multiple moving targets on networks.
A cryogenically cooled high voltage DC photoemission electron source
Authors: Lee Hyeri , Liu Xianghong , Cultrera Luca , Dunham Bruce , Kostroun Vaclav O. , Bazarov Ivan V.
Published: August 2018

Linear electron accelerators and their applications such as ultrafast electron diffraction require compact high-brightness electron sources with high voltage and electric field at the photocathode to maximize the electron density and minimize space-charge induced emittance growth. Achieving high brightness from a compact source is a challenging task because it involves an often-conflicting interplay between various requirements imposed by photoemission, acceleration, and beam dynamics. Here we present a new design for a compact high voltage DC electron gun with a novel cryogenic photocathode system and report on its construction and commissioning process. This photoemission gun can operate at ∼200 kV at both room temperature and cryogenic temperature with a corresponding electric field of 10 MV/m, necessary for achieving high quality electron beams without requiring the complexity of guns, e.g., based on RF superconductivity. It hosts a compact photocathode plug compatible with that used in several other laboratories opening the possibility of generating and characterizing electron beam from photocathodes developed at other institutions.
Variational integrators for inertial magnetohydrodynamics
Authors: Kraus Michael
Published: August 2018

Recently, an extended version of magnetohydrodynamics that incorporates electron inertia, dubbed inertial magnetohydrodynamics, has been proposed [Lingam et al., Phys. Lett. A, 379, 570–576 (2015)]. This model features a noncanonical Hamiltonian formulation with a number of conserved quantities, including the total energy and modified versions of magnetic and cross helicity. In this work, a variational integrator is presented which preserves these conservation laws to machine accuracy. As long as effects due to finite electron mass are neglected, the scheme preserves the magnetic field line topology so that unphysical reconnection is absent. Only when the effects of finite electron mass are added, magnetic reconnection takes place. The excellent conservation properties of the method are illustrated by numerical examples in 2D.
Self-assembled single-digit nanometer memory cells
Authors: Hong J. , Dong K. , Bokor J. , You L.
Published: August 2018

The current spintronic research focuses on lowering switching energy and maintaining good thermal stability of nanomagnets, which could ensure further development of memory technology. Here, we investigate a single-digit nanometer magnetic tunnel junction composed of self-assembled FePt nanopillars isolated by crystallized ZrO2. We find that the lateral size range of the operational device could be sub-7-nm by maintaining outstanding thermal stability.
Exact solutions to a class of time fractional evolution systems with variable coefficients
Authors: Dorjgotov Khongorzul , Ochiai Hiroyuki , Zunderiya Uuganbayar
Published: August 2018

We explicitly give new group invariant solutions to a class of Riemann-Liouville time fractional evolution systems with variable coefficients. These solutions are derived from every element in an optimal system of Lie algebras generated by infinitesimal symmetries of evolution systems in the class. We express the solutions in terms of Mittag-Leffler functions, generalized Wright functions, and Fox H-functions and show that these solutions solve diffusion-wave equations with variable coefficients. These solutions contain previously known solutions as particular cases. Some plots of solutions subject to the order of the fractional derivative are illustrated.
Dielectric virial expansion of polarizable dipolar spheres
Authors: Lian Huada , Qin Jian , Freed Karl F.
Published: August 2018

The dielectric virial expansion is developed for composite systems with embedded interacting dielectric dipolar spheres. Introducing a multiple-scattering expansion for the polarization energy in the presence of an external field enables the derivation of a virial expansion for the polarizability. Substituting the polarizability into the Clausius-Mossotti relation yields the virial series for the effective medium permittivity. When the dipole moment of the particles or inclusions vanishes, the leading-order term in the series reduces to the Maxwell-Garnett mixing rule, whereas the higher-order terms provide corrections that become important at higher densities. The dielectric virial coefficients are readily evaluated by replacing the surface charge contributions with image lines. Numerical data are presented for the second virial coefficients to illustrate the effects of polarization.
Biosensor response from target molecules with inhomogeneous charge localization
Authors: Kase Hiroto , Negishi Ryota , Arifuku Michiharu , Kiyoyanagi Noriko , Kobayashi Yoshihiro
Published: August 2018

We analyzed the sensor response from aptamer-modified carbon nanotube thin film transistors that adsorb immunoglobulin E (IgE) with an inhomogeneous charge distribution. The net charge of the target molecules within the Debye length reflects the polarity of the electrical sensor signal. The complicated sensor response, which depends on the Debye length, can be interpreted by two kinds of adsorption states considering the influence of steric hindrance by previously adsorbed IgE molecules. These results explain the anomalous behavior of the sensor response in previous reports and pave the way to control the dynamic range.
Diffusion processes in a poly-crystalline zeolitic material: A molecular dynamics study
Authors: Thomas Angela Mary , Subramanian Yashonath
Published: August 2018

Extensive molecular dynamics simulations of xenon in two classes of zeolite crystal systems, one consisting of purely intra-crystalline space and the other with both intra- and inter-crystalline space are reported. The latter mimics a typical poly-crystalline sample of zeolite. Comparison of results from these two systems provides insights into the structure and dynamics in the presence of inter-crystalline space. The temperature, as well as the distance between the crystallites, has been varied. The density distribution and diffusivities calculated inside the poly-crystalline system show that the interfacial region between the crystal and the inter-crystalline region acts as a bottleneck for diffusion through the system. At lower temperatures, the particles are trapped at the interface due to the pronounced energy minima present in that region. With the increase in temperature, the particles are able to overcome this barrier frequently, and the transport across the inter-crystalline region is increased. A ballistic or superdiffusive motion is seen in the inter-crystalline region along all the axes except along the axis which has the inter-crystalline space. The transition time for ballistic to diffusive motion increases with the increase in the length of the inter-crystalline space. Velocity auto- and cross correlation functions exhibit strong oscillations and exchange of kinetic energy along directions perpendicular to the direction of the inter-crystalline space. These results explain why uptake and PFG-NMR measurements exhibit lower values for diffusivity for the same system when compared to Quasi-Elastic Neutron Scattering. Thus, using molecular dynamics simulations, we were able to correlate the difference of diffusivity values measured using various experimental methods where these inter-crystalline regions are common.
Large-eddy simulation of airfoil flow near stall condition at Reynolds number 2.1 × 106
Authors: Asada Kengo , Kawai Soshi
Published: August 2018

This paper investigates an airfoil flow involving a turbulent transition and separations near the stall condition at a high Reynolds number Rec = 2.1 × 106 (based on the freestream velocity and the airfoil chord) and provides the wall-resolved large-eddy simulation (LES) database for near-wall models in LES. The present results are compared with the existing experimental and computational data. The wall-resolved LES with the finest mesh (Δξ+,Δη+,Δζ+: chordwise, wall normal, spanwise ≲25, 0.8, 13) and the widest spanwise extent (approximately 5% of the chord length) resolves the key phenomena of the flow (i.e., laminar separation, transition to turbulence, turbulent reattachment, turbulent boundary layer development, and turbulent separation) and well predicts turbulence statistics. The present LES also clarifies unsteady flow features associated with shear-layer instability: the high frequency unsteadiness of St ≃ 130 (based on the freestream velocity and the airfoil chord) at the laminar separation bubble near the leading edge and low frequency unsteadiness of St ≃ 2 at the turbulent separation near the trailing edge. The characteristic frequencies can be scaled to 0.035 and 0.033 by the local momentum thickness and the shear layer velocity which are similar to the natural frequency of the laminar and turbulent shear layer, respectively. With regard to the near-wall modeling in LES, the obtained database indicates that the pressure-gradient term in the mean streamwise-momentum equation is not negligible at the laminar and turbulent separated regions. This fact suggests that the widely used equilibrium wall model is not sufficient, and the inclusion of the pressure-gradient term is necessary for wall modeling in LES of such an airfoil flow. Additionally, influences of computational mesh resolution and spanwise extent on the computational results in wall-resolved LES are investigated.
Modeling and experimental characterization of the plasma produced by a velvet cathode in a linear induction accelerator
Authors: Plewa J. M. , Eichwald O. , Yousfi M. , Wattieaux G. , Cartier S. , Cartier F. , Poulet F. , Bernigaud V. , Ribière M. , Delaunay R. , d'Almeida T. , Maisonny R.
Published: August 2018

A high power electron diode is used to generate an intense high quality pulsed electron beam (2.6 kA, 4 MeV) in order to produce a bremsstrahlung radiation pulse for the first axis of the flash radiography facility named Epure. The plasma created by surface flashover of the velvet cathode provides a zero work function emitter used to produce the space-charge-limited electron beam. In order to optimize the design of diodes and to better understand the plasma dynamics, we have developed a 0D Collisional-Radiative Model (CRM) which describes the time-dependent evolution of the density of the plasma species in three plasma compositions: 100% H, 95% H + 5% C, and 64% H + 31% O + 5% C. The non-equilibrium electron energy distribution functions (EEDFs) are pre-calculated for a large range of electron mean energies for each mixture. EEDFs and cross sections of electron impact processes are then used to tabulate the electron rate coefficients needed to simulate the time-dependent plasma species densities. The evolution of the electron mean energy is estimated through the electron beam current density itself inferred from particle-in-cell calculations experimentally validated. Visible emission spectroscopy measurements were performed in order to investigate the plasma composition, to measure the Hα/Hβ intensity ratio, and to estimate the electron density. It was shown that the electron density in our setup is between 1014 and 1016 cm−3. Experimental results were compared to the 0D CRM. Results from the time-dependent CRM show that for the three studied plasma compositions, maximum electron densities range from 0.9 × 1014 cm−3 to 1.7 × 1014 cm−3 and that the electron energy averaged over the time interval of the electronic beam pulse is about 3.5 eV. An estimate of the electron energy inside the plasma during the relaxation provides values ranging from 0.10 eV to 0.12 eV based on comparison between the calculated and measured Hα/Hβ intensity ratio averaged over 5 μs. Moreover, main reactions involved in the evolution of the electron density were pointed out.
Low-voltage dielectric elastomer actuators with stretchable electrodes fabricated by supersonic cluster beam implantation
Authors: Taccola Silvia , Bellacicca Andrea , Milani Paolo , Beccai Lucia , Greco Francesco
Published: August 2018

Supersonic cluster beam implantation of Ag nanoparticles is proposed for the fabrication of stretchable and compliant electrodes for dielectric elastomer actuators (DEAs) with reduced thickness. Thanks to the low-energy and finely tunable implantation process, a nanocomposite Ag/polydimethylsiloxane electrode layer is produced with a moderate stiffening effect for the DEA in contrast with a common deposition strategy for electrodes. Thin DEAs with an overall thickness of 17 μm were fabricated and tested under different preloading conditions, demonstrating a max uniaxial actuation strain of 2.5% at an actuation voltage of 765 V, lower than the typical voltage values of DEAs. The electrodes remained conductive up to 40% strain, and they fully recovered the original resistance after 70% stretching. Our results represent a significant step towards the development of DEAs operating at reduced actuation voltages, by stacking of micrometer-thick elastomer films, paving the way to novel applications in soft robotics.
Using an iterative eigensolver and intertwined rank reduction to compute vibrational spectra of molecules with more than a dozen atoms: Uracil and naphthalene
Authors: Thomas Phillip S. , Carrington Tucker , Agarwal Jay , Schaefer Henry F.
Published: August 2018

We use a direct product basis, basis vectors computed by evaluating matrix-vector products, and rank reduction to calculate vibrational energy levels of uracil and naphthalene, with 12 and 18 atoms, respectively. A matrix representing the Hamiltonian in the direct product basis and vectors with as many components as there are direct product basis functions are neither calculated nor stored. We also introduce an improvement of the Hierarchical Intertwined Reduced-Rank Block Power Method (HI-RRBPM), proposed previously in Thomas and Carrington, Jr. [J. Chem. Phys. 146, 204110 (2017)]. It decreases the memory cost of the HI-RRBPM and enables one to compute vibrational spectra of molecules with over a dozen atoms with a typical desktop computer.
Glassy dynamics of two poly(ethylene glycol) derivatives in the bulk and in nanometric confinement as reflected in its inter- and intra-molecular interactions
Authors: Jasiurkowska-Delaporte Małgorzata , Kossack Wilhelm , Kipnusu Wycliffe K. , Sangoro Joshua R. , Iacob Ciprian , Kremer Friedrich
Published: August 2018

The inter- and intra-molecular interactions as they evolve in the course of glassy solidification are studied by broadband dielectric—and Fourier-transform infrared—spectroscopy for oligomeric derivatives of poly(ethylene glycol) derivatives, namely, poly(ethylene glycol) phenyl ether acrylate and poly(ethylene glycol) dibenzoate in the bulk and under confinement in nanoporous silica having mean pore diameters 4, 6, and 8 nm, with native and silanized inner surfaces. Analyzing the spectral positions and the oscillator strengths of specific IR absorption bands and their temperature dependencies enables one to trace the changes in the intra-molecular potentials and to compare it with the dielectrically determined primarily inter-molecular dynamics. Special emphasis is given to the calorimetric glass transition temperature Tg and Tαβ ≈ 1.25Tg, where characteristic changes in conformation appear, and the secondary β-relaxation merges with the dynamic glass transition (α-relaxation). Furthermore, the impact of main chain conformations, inter- and intra-molecular hydrogen bonding, and nanometric confinement on the dynamic glass transition is unraveled.
Time base evaluation for atom gravimeters
Authors: Cui Jiafeng , Xu Yaoyao , Chen Lele , Qi Kun , Zhou Minkang , Duan Xiaochun , Hu Zhongkun
Published: August 2018

Time is an inevitable quantity involved in absolute gravity measurements, and 10 MHz frequency standards are usually utilized as time base. Here we investigate the influence of time base bias on atom-interferometry-based gravity measurements and present an onsite calibration of the time base bias relying on an atom gravimeter itself. With a microwave source referenced to the time base, the time base bias leads to a magnified frequency shift of the microwave source output. The shift is then detected by Ramsey spectroscopy with the clock transition of 87Rb atoms as a frequency discriminator. Taking advantage of available free-fall cold atoms and developed techniques of measuring the atom energy level shift in atom gravimeters, the calibration achieves an accuracy of 0.6 mHz for the time base. And the corresponding error for gravity measurements is constrained to 0.1 μGal, meeting the requirement of state-of-the-art gravimeters. The presented evaluation is important for the applications of atom gravimeters.
Mechanistic study of the photoexcitation, photoconversion, and photodissociation of CS2
Authors: Trabelsi Tarek , Al-Mogren Muneerah Mogren , Hochlaf Majdi , Francisco Joseph S.
Published: August 2018

Carbon disulfide is a prototype molecular system for studies of photophysical processes in molecules at different time scales and is also relevant to astrophysics. Here, reliable molecular properties are computed for linear SCS, bent cyc-CS2, and linear CSS forms using highly correlated post Hartree-Fock methods in conjunction with large basis sets. Structures are identified using explicitly correlated and standard coupled cluster techniques. Evolution of the lowest-lying singlet and triplet electronic states of the three isomers along the SS and CS stretching coordinates and along the bending angle are mapped at the multireference configuration interaction (MRCI)/aug-cc-pV(5+d)Z level of theory. The computations suggest that the 1B2(1Σ+) electronic state of the SCS isomer plays an important role in the photoconversion of CS2 to cyc-CS2 and CSS. Photoconversion competes with photodissociation. Plausible mechanisms for the production of S2 and CS diatomics after the photoexcitation of SCS are proposed. To aid in the identification of CSS in the laboratory and in astrophysical media, a set of spectroscopic constants and rovibrational levels for CSS are reported.
General theory of photoexcitation induced photoelectron circular dichroism
Authors: Harvey Alex G. , Mašín Zdeněk , Smirnova Olga
Published: August 2018

The photoionization of chiral molecules prepared in a coherent superposition of excited states can give access to the underlying chiral coherent dynamics in a procedure known as photoexcitation induced photoelectron circular dichroism (PXECD). As in photoelectron circular dichroism (PECD), chirality manifests as asymmetric photoelectron emission in the forward/backward direction (relative to the laser propagation direction). However, in PXECD, the asymmetric photoemission is additionally contingent on coherence. This exclusive dependence on coherence can also be seen in a different part of the photoelectron angular distribution (PAD), where it is not contingent on the chirality of the molecule, thus allowing extension of PXECD’s sensitivity to tracking coherence to non-chiral molecules. Here we present a general theory of PXECD based on angular momentum algebra and derive explicit expressions for all pertinent asymmetry parameters which arise for the arbitrary polarization of pump (which prepares the superposition of excited states) and ionizing probe pulses. The theory is developed in a way that clearly and simply separates chiral and non-chiral contributions to the PAD and also demonstrates how PXECD and PECD-type contributions, which may be distinguished by whether the pump or ionizing probe pulse enables chiral response, are mixed when arbitrary polarization is used.
Enhanced surface optical phonon in CdTe thin film observed by Raman scattering
Authors: Liu Dexiong , Chen Junhua , Wang Dongming , Wu Lingling , Wang Deliang
Published: August 2018

Surface optical (SO) phonon modes are characteristic atomic vibrations confined within the first several atom layers of the free surface of a polar solid material. Raman scattering of SO modes is hardly to be observed due to extremely weak scattering from few surface atom layers. In principle, the SO modes are associated with a long-range Fröhlich interaction with the optical modes in a polar material and would lead to strong or weak anharmonic coupling with these modes depending on mode polarization. In this report, both the SO and the bulk Raman scattering efficiency were dramatically enhanced in CdTe thin films by employing silver nano-plasmonic enhanced Raman scattering and maximized free surface atomic vibration. Raman scattering phonon overtones of the longitudinal optical (LO) mode up to the fifth order were observed. Strong and rich information on the multi-phonon anharmonic couplings of the SO mode with the LO mode and the overtones was well resolved and clarified.
Interface carbon defects at 4H-SiC(0001)/SiO2 interfaces studied by electron-spin-resonance spectroscopy
Authors: Umeda T. , Kim G.-W. , Okuda T. , Sometani M. , Kimoto T. , Harada S.
Published: August 2018

We study an electron-spin-resonance (ESR) signal of carbon dangling-bond defects at 4H-SiC(0001)/SiO2 interfaces, which we call an “interface carbon defect.” The ESR signal is close to a c-axial type of the PbC centers (interfacial carbon dangling bonds) that have originally been found in porous-SiC/SiO2 interfaces. The interface carbon defects were always formed with an areal density of 3–4 × 1012 cm−2 after the standard dry oxidation of 4H-SiC(0001) surfaces. They act as electron traps and decrease the amount of free electrons in the channel region, consequently reducing the field-effect mobility of Si-face 4H-SiC MOSFETs. They were eliminated by optimum post-oxidation anneals (POAs) in either NO or POCl3 environment. Furthermore, POCl3 POAs at 1000 °C introduced a high density (1.7 × 1012 cm−2) of phosphorus donors into the channel region, increasing the free-carrier density as compared with the case of NO POAs.
Enhancement of thermal conductivity across the metal-insulator transition in vanadium dioxide
Authors: Chen Lu , Xiang Ziji , Tinsman Colin , Asaba Tomoya , Huang Qing , Zhou Haidong , Li Lu
Published: August 2018

Metal-to-insulator transition (MIT) in vanadium dioxide (VO2) was investigated by electrical and thermal transport measurements. We report an order-of-magnitude enhancement of thermal conductivity across the MIT region in the VO2 single crystal. The magnetic field dependent measurement reveals that the thermal conductivity peak does not show an obvious dependence on the magnetic field, which indicates that the enhancement of thermal conductivity could come from neutral heat carriers such as phonons. Our experiment provides a direction of achieving thermal management in phase-change materials.
L-box—A tool for measuring the “yield stress”: A theoretical study
Authors: Chaparian Emad , Nasouri Babak
Published: August 2018

Yield-stress fluids can form non-flat arrested profiles when they disembogue under the effect of gravity. Relying on this behavior, L-box tests have been used to retrieve fluid properties, specifically yield stress of Self-Consolidating Concrete (SCC) and cement paste. In this study, we aim to find a correlation between the final shape of the sample and the value of yield stress, using theoretical approaches. First, the Cauchy equation for yield-stress fluids is solved asymptotically, and an analytical expression for yield stress is presented. Then, to validate our assumptions in the first approach, the method of characteristics of perfect plasticity is investigated. We show that if the flow is inertialess, the viscosity of the sample does not affect the final shape considerably. We also investigate, in detail, the cases where the sample is not exactly a “simple” yield-stress fluid, i.e., exhibits slightly thixotropic behavior such as SCC and cement paste.
Study on formation mechanism of atmospheric pressure glow discharge air plasma jet
Authors: Liu Wenzheng , Li Zhiyi , Zhao Luxiang , Zheng Qingtian , Ma Chuanlong
Published: August 2018

Based on the results of needle electrode discharge experiments and electric field simulations, this study proposes a tip extensional ionization theory for explaining the formation mechanism of atmospheric pressure glow discharge (APGD) plasma jets. Under the condition of DC power supply, atmospheric pressure glow discharge (APGD) air plasma jets are realized without airflow. It is found that the necessary initial electrons for discharge are derived from free electrons in space, residual electrons, or runaway electrons, and the difference of the electric field intensity between the needle electrode tip and the lateral side of the needle electrode is an essential condition for the formation of the plasma jet. It is further discovered that a space electric field with transitive change is generated in the formation process of the plasma jet, and therefore a phenomenon occurs: the plasma jet generated from the high voltage electrode exceeds the lateral ground potential electrode. This study provides a theoretical basis for the analysis of the formation mechanism of plasma jet under various discharge conditions and promotes further research such as on the formation process of the lightning leader and lightning protection.
Well converged quantum rate constants for the H2 + OH → H2O + H reaction via transition state wave packet
Authors: Sun Peng , Zhang Zhaojun , Chen Jun , Liu Shu , Zhang Dong H.
Published: August 2018

Transition state wave packet calculations have been carried out to compute cumulative reaction probabilities for the H2 + OH reaction on the NN1 potential energy surface, as given in the work of Chen et al., from which well converged thermal rate constants for the reaction up to a temperature of 1000 K were obtained. It was found that both the centrifugal sudden approximation and the “J-K-shifting” approximation slightly underestimated the thermal rate constants, while the ring-polymer molecular dynamics overestimated the rates in the low temperature region. After considering the correction of the barrier height by spin-orbit coupling effect and the more accurate level of theory, the calculated rate constants were in good consistency with experimental measurements in the entire temperature region for this benchmark reaction.
Liquid-infused surface tuned to resist E. coli adhesion
Authors: Leahy Rhys
Published: August 2018

By testing different degrees of hardness in materials and viscosity in infusion oils, the authors successfully patterned a liquid-infused surface to control biological interactions.
Standing on giant shoulders: a personal recollection of the lives and achievements of eminent animal scientists 1965–2015
Authors: Bell Alan
Published: August 2018

This article is a compilation of pieces that are part biographical sketches and part personal recollections of 18 scientists with whom the author was acquainted in three continents over almost 50 years. The subjects, from Australia, the United States and the United Kingdom, will be recognisable to many in the field, especially more experienced scientists. For younger scientists, the article also is intended to put a human face on a generation of famous researchers who otherwise would be familiar only as somewhat anonymous authors of classic papers and reviews.
Susceptibility of forage legumes to infestation by the pea aphid Acyrthosiphon pisum (Harris) (Hemiptera: Aphididae)
Authors: Kordan Bożena , Stec Katarzyna , Słomiński Paweł , Giertych Marian J. , Wróblewska-Kurdyk Anna , Gabrys Beata
Published: August 2018

The small-seeded legumes are important forage crops for grazing animals and contribute nitrogen to succeeding crops in crop rotation systems. However, the susceptibility of several of the forage legumes to the specialist pea aphid Acyrthosiphon pisum (Harris) has never been investigated. The present study on aphid probing behaviour using the Electrical Penetration Graph technique revealed that the forage legumes studied were (i) highly acceptable (common vetch Vicia sativa L.), (ii) acceptable (wooly vetch Vicia villosa Roth), (iii) moderately acceptable (fodder galega Galega orientalis Lam., crimson clover Trifolium incarnatum L., Persian clover Trifolium resupinatum L., white clover Trifolium repens L.), (iv) barely acceptable (common bird’s-foot-trefoil Lotus corniculatus L., yellow lucerne Medicago falcata L., alfalfa Medicago sativa L., sand lucerne Medicago × varia Martyn, common bird’s-foot Ornithopus sativus Brot., alsike clover Trifolium hybridum L., red clover Trifolium pratense L., common sainfoin Onobrychis viciifolia Scop.), and (v) unacceptable (white melilot Melilotus albus Medik.) to the pea aphid. On (i) plants, probing occupied 85% of experimental time, all aphids (100%) succeeded in feeding on phloem sap, phloem phase occupied 50% of probing time, sap ingestion periods were long (mean duration: 100.8 ± 28.2 min.) and engaged 97% of the phloem phase. On (ii) plants, probing occupied 73% of exp. time, feeding activity occurred in 66.7% of aphids, phloem phase occupied 30% of probing time, sap ingestion periods were long (mean duration: 115.5 ± 46.7 min) and engaged 80% of the phloem phase. On (iii) plants, probing ranged from 53% of exp. time on T. repens to 70% on T. incarnatum and T. resuspinatum, feeding occurred in 35.3% of aphids on T. resuspinatum up to 54.5% on T. incarnatum, phloem phase occupied 10% of exp. time on G. orientalis, T. incarnatum, and T. resuspinatum and 20% on T. repens, sap ingestion periods were from 9.8 ± 1.8 min. on G. orientalis to 51.9 ± 20.7 min. long on T. resuspinatum and engaged from 30% of phloem phase on G. orientalis to 80% on T. incarnatum. On (iv) plants, probing occupied 25% of exp. time on O. viciifolia up to 38% on O. sativus and T. hybridum, feeding occurred in 6.7% of aphids on T. hybridum to 28% on O. sativus, phloem phase occupied less than 1% of probing time on all plants except O. viciifolia (4%) and O. sativus (5%) and it consisted mainly of salivation. On M. albus (v), probing occupied 22% of experimental time, the probes were short (1.8 ± 0.3 min), and no aphid on M. albus showed feeding on phloem sap. M. albus can be recommended for intercropping, ‘push-pull’ strategies, or as a barrier crop against A. pisum in sustainable agricultural practices.