bluuebunny/crossref_metadata_2025 huggingface dataset:
Constraint on ion–neutral drift velocity in the Class 0 protostar B335 from ALMA observations
Authors: Yen Hsi-Wei , Zhao Bo , Koch Patrick M. , Krasnopolsky Ruben , Li Zhi-Yun , Ohashi Nagayoshi , Takakuwa Shigehisa
Published: March 2018

Aims. Ambipolar diffusion can cause a velocity drift between ions and neutrals. This is one of the non-ideal magnetohydrodynamics (MHD) effects proposed to enable the formation of large-scale Keplerian disks with sizes of tens of au. To observationally study ambipolar diffusion in collapsing protostellar envelopes, we compare here gas kinematics traced by ionized and neutral molecular lines and discuss the implication on ambipolar diffusion.

Methods. We analyzed the data of the H13CO+ (3–2) and C18O (2–1) emission in the Class 0 protostar B335 obtained with our ALMA observations. We constructed kinematical models to fit the velocity structures observed in the H13CO+ and C18O emission and to measure the infalling velocities of the ionized and neutral gas on a 100 au scale in B335.

Results. A central compact (~1′′–2′′) component that is elongated perpendicular to the outflow direction and exhibits a clear velocity gradient along the outflow direction is observed in both lines and most likely traces the infalling flattened envelope. With our kinematical models, the infalling velocities in the H13CO+ and C18O emission are both measured to be 0.85 ± 0.2 km s−1 at a radius of 100 au, suggesting that the velocity drift between the ionized and neutral gas is at most 0.3 km s−1 at a radius of 100 au in B335.

Conclusions. The Hall parameter for H13CO+ is estimated to be ≫1 on a 100 au scale in B335, so that H13CO+ is expected to be attached to the magnetic field. Our non-detection or upper limit of the velocity drift between the ionized and neutral gas could suggest that the magnetic field remains rather well coupled to the bulk neutral material on a 100 au scale in this source, and that any significant field-matter decoupling, if present, likely occurs only on a smaller scale, leading to an accumulation of magnetic flux and thus efficient magnetic braking in the inner envelope. This result is consistent with the expectation from the MHD simulations with a typical ambipolar diffusivity and those without ambipolar diffusion. On the other hand, the high ambipolar drift velocity of 0.5–1.0 km s−1 on a 100 au scale predicted in the MHD simulations with an enhanced ambipolar diffusivity by removing small dust grains, where the minimum grain size is 0.1 μm, is not detected in our observations. However, because of our limited angular resolution, we cannot rule out a significant ambipolar drift only in the midplane of the infalling envelope. Future observations with higher angular resolutions (~0. ′′1) are needed to examine this possibility and ambipolar diffusion on a smaller scale.
Reactive collision of electrons with CO+ in cometary coma
Authors: Moulane Y. , Mezei J. Zs. , Laporta V. , Jehin E. , Benkhaldoun Z. , Schneider I. F.
Published: March 2018

Context. In order to improve our understanding of the kinetics of the cometary coma, theoretical studies of the major reactive collisions in these environments are needed. Deep in the collisional coma, inelastic collisions between thermal electrons and molecular ions result in recombination and vibrational excitation, the rates of these processes being particularly elevated due to the high charged particle densities in the inner region.

Aims. This work addresses the dissociative recombination, vibrational excitation, and vibrational de-excitation of electrons with CO+ molecular cations. The aim of this study is to understand the importance of these reactive collisions in producing carbon and oxygen atoms in cometary activity.

Methods. The cross-section calculations were based on multichannel quantum defect theory. The molecular data sets, used here to take into account the nuclear dynamics, were based on ab initio R-matrix approach.

Results. The cross-sections for the dissociative recombination, vibrational excitation, and vibrational de-excitation processes, for the six lowest vibrational levels of CO+ – relevant for the electronic temperatures observed in comets – are computed, as well as their corresponding Maxwell rate coefficients. Moreover, final state distributions for different dissociation pathways are presented.

Conclusions. Among all reactive collisions taking place between low-energy electrons and CO+, the dissociative recombination is the most important process at electronic temperatures characterizing the comets. We have shown that this process can be a major source of O(3P), O(1D), O(1S), C(3P) and C(1D) produced in the cometary coma at small cometocentric distances.
Faire étalonner son audiomètre. Quand, pourquoi et comment ?
Authors: Meyer-Bisch Christian
Published: March 2018

L’étalonnage d’un audiomètre doit être contrôlé régulièrement ainsi que cela se fait pour la plupart des instruments de mesure. Le
vieillissement de certains composants de l’appareil lui-même ou de ses transducteurs, son transport éventuel ou, tout simplement,
l’infl uence de son environnement sont à tout moment susceptibles de modifi er les caractéristiques de la chaîne de mesure. Pour
harmoniser ces contrôles, on se réfère à des normes internationales, qui peuvent être matérielles (CEI) ou méthodologiques (ISO). Ces
normes sont adoptées dans la quasi-totalité des pays du monde et sont réexaminées au plus tard tous les cinq ans. Certains contrôles
de routine sont à effectuer avant chaque utilisation, mais les contrôles d’étalonnage qui demandent l’intervention de techniciens
spécialisés devraient être réalisés chaque année. Dans une première partie, nous abordons les aspects techniques, et dans la seconde,
les procédures mises en oeuvre.
Environmental drivers of fish spatial distribution and activity in a reservoir with water level fluctuations
Authors: Roy R. , Tissot L. , Argillier C.
Published: March 2018

The aquatic ecosystem structuration in human influenced environment, is closely dependent of the associated uses, which are generally fluctuant. We conducted an extended field monitoring on a reservoir under water level fluctuations (WLF), in order to study the responses of fish fauna to changes in environmental conditions. The study design was based on a monitoring of fish behaviour by telemetry in a reservoir with a particular attention to the littoral zone because of its front line position during WLF. The results of this study, which was conducted on the Bariousses reservoir, located on the Vézère river (Corrèze, France), are summarized in this article. The study revealed that WLF induced a temporal variability in the littoral zone surface. In addition, we observed a gradual decline in structural complexity of littoral habitats with a tendency towards homogenisation (dominance of fine substrates and absence of vegetation) in relation with the drop in water level. Behavioural individual responses of pikeperch, perch and pike were highly variable in relation to environmental fluctuations. Temperature and photoperiod were the two main parameters controlling fish activity and spatial distribution. Water level affected part of fish assemblage: some individuals were more mobile and left the littoral zone when inshore habitats were less complex (low water level).
Microhabitat selection and distribution of functional feeding groups of mayfly larvae (Ephemeroptera) in lotic karst habitats
Authors: Vilenica Marina , Brigić Andreja , Sartori Michel , Mihaljević Zlatko
Published: March 2018

Research examining mayfly ecology in karst streams and rivers has increased in recent years, though microhabitat preferences remain poorly characterized. We examined mayfly assemblage taxonomy, functional feeding groups and microhabitat preferences in two contrasting lotic Dinaric karst catchments, one pristine and one anthropogenically impacted. At monthly intervals over a one-year period, all major microhabitats (i.e.dominated by boulders, cobbles, sand, silt, mosses, or angiosperms) were sampled at sites spanning springs, upper, middle and lower river reaches, and tufa barriers. In both catchments, mayfly species richness was comparable among microhabitats, while mayfly abundance was highest on mosses and lowest on silt. NMDS ordination did not group assemblages according to microhabitat type, which may reflect the greater influence of physical and chemical water properties. In both catchments and all microhabitats, mayfly assemblages were dominated by grazers/scrapers at upstream sites and by detritivores at downstream sites. Active filter feeders were more abundant in microhabitats with silt substrates and lower current velocities. This study demonstrated that certain mayfly species strongly preferred a specific microhabitat type, reflecting their water current preferences and feeding strategies, while other species shifted between microhabitats, likely in search of food resources and shelter. The results emphasize the importance of habitat heterogeneity in supporting diverse communities in karst rivers.
Construct Validity for Measuring Entrepreneurial Readiness Among Malaysian Higher Education Students: A Stochastic Measurement Model Approach
Authors: Jusoh M.S. , Hj Din M.S. , Hazliza  , Suriani T.
Published: March 2018

Instrument construct is one of the most important issues in conducting research. Without proper consideration in tackling the issue, it is difficult for the instrument to be considered as valid and reliable. If construct validity is accurate, then it will provide a clearer and more precise descriptive analysis on the concepts being investigated. The most important criteria that need to be considered in answering the construct validity are reliability and validity. In traditional measurement model, the understanding of reliability and validity is totally different from the one offered by Rasch model. Regardless of the difference, an internal consistency is still widely being used as the primary method to measure the item sampling. Using this model, local dependence and item fit are most considered in getting valid, reliable, and consistent, hence its significance. Finally the study applies goodness of measure purposely to answer issues related to validity and reliability tests. Principal components analysis was carried out to test the construct of questionnaires used in the study.
Factors Influencing the Use of ICT in Rural School Libraries
Authors: Ismail Adila , Affandy Habee Bullah , Hamzah Mohammad Rezal
Published: March 2018

The basis of the study is to discover the use of ICT among students in rural school libraries in a district located in Northern Malaysia. The study is conducted with the aim to identify the factors influencing the utilization of the technology in the students’ day-to-day activities. The study used the use of ICT model, with 4 independent variables. This study has used the quantitative method, with 400 students from the total of 4 existing rural secondary schools in Malaysia as the respondents. The result shows only two independent variables as the significant factors responsible for the said intention. The results are enclosed, and the recommendations for future planning are also discussed.
An ionospheric index suitable for estimating the degree of ionospheric perturbations
Authors: Wilken Volker , Kriegel Martin , Jakowski Norbert , Berdermann Jens
Published: March 2018

Space weather can strongly affect trans-ionospheric radio signals depending on the used frequency. In order to assess the strength of a space weather event from its origin at the sun towards its impact on the ionosphere a number of physical quantities need to be derived from scientific measurements. These are for example the Wolf number sunspot index, the solar flux density F10.7, measurements of the interplanetary magnetic field, the proton density, the solar wind speed, the dynamical pressure, the geomagnetic indices Auroral Electrojet, Kp, Ap and Dst as well as the Total Electron Content (TEC), the Rate of TEC, the scintillation indices S4 and σ(ϕ) and the Along-Arc TEC Rate index index. All these quantities provide in combination with an additional classification an orientation in a physical complex environment. Hence, they are used for brief communication of a simplified but appropriate space situation awareness. However, space weather driven ionospheric phenomena can affect many customers in the communication and navigation domain, which are still served inadequately by the existing indices. We present a new robust index, that is able to properly characterize temporal and spatial ionospheric variations of small to medium scales. The proposed ionospheric disturbance index can overcome several drawbacks of other ionospheric measures and might be suitable as potential driver for an ionospheric space weather scale.
Positioning performance of the NTCM model driven by GPS Klobuchar model parameters
Authors: Hoque Mohammed Mainul , Jakowski Norbert , Berdermann Jens
Published: March 2018

Users of the Global Positioning System (GPS) utilize the Ionospheric Correction Algorithm (ICA) also known as Klobuchar model for correcting ionospheric signal delay or range error. Recently, we developed an ionosphere correction algorithm called NTCM-Klobpar model for single frequency GNSS applications. The model is driven by a parameter computed from GPS Klobuchar model and consecutively can be used instead of the GPS Klobuchar model for ionospheric corrections. In the presented work we compare the positioning solutions obtained using NTCM-Klobpar with those using the Klobuchar model. Our investigation using worldwide ground GPS data from a quiet and a perturbed ionospheric and geomagnetic activity period of 17 days each shows that the 24-hour prediction performance of the NTCM-Klobpar is better than the GPS Klobuchar model in global average. The root mean squared deviation of the 3D position errors are found to be about 0.24 and 0.45 m less for the NTCM-Klobpar compared to the GPS Klobuchar model during quiet and perturbed condition, respectively. The presented algorithm has the potential to continuously improve the accuracy of GPS single frequency mass market devices with only little software modification.
Die Rolle von Biomarkern in Diagnose, Prognose und Therapie von Patienten unter immunonkologischer Therapie mit urologischen Malignomen
Authors: Compérat Eva , Eymerit Caroline , Moroch Julien , Varinot Justin
Published: March 2018

In den letzten Jahren haben Fortschritte in der Grundlagenforschung neue Einsichten in die Tumorbiologie gestattet, dadurch konnten neue Therapien entwickelt werden. Diese Übersichtsarbeit beleuchtet die Rolle des Pathologen und wie er anhand von Gewebemarkern helfen kann, eine Therapieentscheidung zu treffen. Wir erklären die Problematik der molekularen Blasentumoruntergruppen, die Rolle der neoadjuvanten Chemotherapie und die der Immune Checkpoint Inhibitoren, des Weiteren gehen wir auf das Nierenkarzinom und dessen Therapiemöglichkeiten ein, mit besonderem Augenmerk auf das klarzellige Nierenkarzinom als häufigsten Nierenkarzinomtyp. Wir streifen kurz das Prostatakarzinom, das als hormonabhängiger Tumor wahrscheinlich einen anderen Therapieansatz braucht. Wir versuchen, die Machbarkeit und Grenzen vom pathologischen Standpunkt her zu beleuchten.
Immuntherapie mit Checkpoint-Inhibitoren beim lokal fortgeschrittenen und metastasierten Urothelzellkarzinom
Authors: Miller Kurt , Gschwend Jürgen , Merseburger Axel , Retz Margitta , Stenzl Arnulf
Published: March 2018

Checkpoint-Inhibitoren haben in der bislang limitierten Therapie des Urothelzellkarzinoms eine neue Ära eingeleitet. Dies spiegelt sich in der aktuellen S3-Leitlinie zum Harnblasenkarzinom derzeit noch nicht wider. Da es sich bei der Krebsimmuntherapie um ein neues Therapieprinzip handelt, stellen sich gegenwärtig Fragen für den Praxisalltag: Auf welchen Daten beruhen die Zulassungen der einzelnen Wirkstoffe? Wie verändern sich die Therapiealgorithmen? Worauf muss beim Therapiemanagement geachtet werden? Welche Nebenwirkungen können auftreten, wie lassen sie sich erkennen und behandeln? Die vorliegende Publikation verfolgt das Ziel, diese Fragen zu beantworten.
Pressure induced electronic phase transitions and superconductivity in n-type Bi2Te3
Authors: Zhang Junliang , Zhang Sijia , Kong Panpan , Yang Liuxiang , Jin Changqing , Liu Qingqing , Wang Xiancheng , Yu Jiancheng
Published: March 2018

Temperature dependent-electrical resistance of n-type Bi2Te3 was investigated under high pressure. Superconductivity was detected at 4.9 GPa with Tconset = 2.8 K. Resistance and Tc suggest that there are two electronic phase transitions below 10 GPa. We conjecture that the bulk insulating phase first changes to semimetal and then to metal. The evolution of the Hall coefficient is qualitatively consistent with the proposed electronic phase transition. The origin of superconductivity and topological properties are also discussed.
Rotor-angle versus voltage instability in the third-order model for synchronous generators
Authors: Sharafutdinov Konstantin , Rydin Gorjão Leonardo , Matthiae Moritz , Faulwasser Timm , Witthaut Dirk
Published: March 2018

We investigate the interplay of rotor-angle and voltage stability in electric power systems. To this end, we carry out a local stability analysis of the third-order model which entails the classical power-swing equations and the voltage dynamics. We provide necessary and sufficient stability conditions and investigate different routes to instability. For the special case of a two-bus system, we analytically derive a global stability map.
Behavior of collisional sheath in electronegative plasma with q-nonextensive electron distribution
Authors: Borgohain Dima Rani , Saharia K.
Published: March 2018

Electronegative plasma sheath is addressed in a collisional unmagnetized plasma consisting of q-nonextensive electrons, Boltzmann distributed negative ions and cold fluid positive ions. Considering the positive ion-neutral collisions and ignoring the effects of ionization and collisions between negative species and positive ions (neutrals), a modified Bohm sheath criterion and hence floating potential are derived by using multifluid model. Using the modified Bohm sheath criterion, the sheath characteristics such as spatial profiles of density, potential and net space charge density have been numerically investigated. It is found that increasing values of q-nonextensivity, electronegativity and collisionality lead to a decrease of the sheath thickness and an increase of the sheath potential and the net space charge density. With increasing values of the electron temperature to negative ion temperature ratio, the sheath thickness increases and the sheath potential as well as the net space charge density in the sheath region decreases.
Understanding the shock and detonation response of high explosives at the continuum and meso scales
Authors: Handley C. A. , Lambourn B. D. , Whitworth N. J. , James H. R. , Belfield W. J.
Published: March 2018

The shock and detonation response of high explosives has been an active research topic for more than a century. In recent years, high quality data from experiments using embedded gauges and other diagnostic techniques have inspired the development of a range of new high-fidelity computer models for explosives. The experiments and models have led to new insights, both at the continuum scale applicable to most shock and detonation experiments, and at the mesoscale relevant to hotspots and burning within explosive microstructures. This article reviews the continuum and mesoscale models, and their application to explosive phenomena, gaining insights to aid future model development and improved understanding of the physics of shock initiation and detonation propagation. In particular, it is argued that “desensitization” and the effect of porosity on high explosives can both be explained by the combined effect of thermodynamics and hydrodynamics, rather than the traditional hotspot-based explanations linked to pressure-dependent reaction rates.
Thermal conductivity of ternary III-V semiconductor alloys: The role of mass difference and long-range order
Authors: Mei S. , Knezevic I.
Published: March 2018

Thermal transport in bulk ternary III-V arsenide (III-As) semiconductor alloys was investigated using equilibrium molecular dynamics with optimized Albe-Tersoff empirical interatomic potentials. Existing potentials for binary AlAs, GaAs, and InAs were optimized to match experimentally obtained acoustic-phonon dispersions and temperature-dependent thermal conductivity. Calculations of thermal transport in ternary III-Vs commonly employ the virtual-crystal approximation (VCA), where the structure is assumed to be a random alloy and all group-III atoms (cations) are treated as if they have an effective weighted-average mass. Here, we showed that it is critical to treat atomic masses explicitly and that the thermal conductivity obtained with explicit atomic masses differs considerably from the value obtained with the average VCA cation mass. The larger the difference between the cation masses, the poorer the VCA prediction for thermal conductivity. The random-alloy assumption in the VCA is also challenged because X-ray diffraction and transmission electron microscopy show order in InGaAs, InAlAs, and GaAlAs epilayers. We calculated thermal conductivity for three common types of order (CuPt-B, CuAu-I, and triple-period-A) and showed that the experimental results for In0.53Ga0.47As and In0.52Al0.48As, which are lattice matched to the InP substrate, can be reproduced in molecular dynamics simulation with 2% and 8% of random disorder, respectively. Based on our results, thermal transport in ternary III-As alloys appears to be governed by the competition between mass-difference scattering, which is much more pronounced than the VCA suggests, and the long-range order that these alloys support.
Distributed feedback interband cascade lasers with top grating and corrugated sidewalls
Authors: Xie Feng , Stocker Michael , Pham John , Towner Frederick , Shen Kun , Wang Jie , Lascola Kevin
Published: March 2018

Distributed feedback (DFB) interband cascade lasers (ICLs) with a 1st order top surface grating were designed and fabricated. Partially corrugated sidewalls were implemented to suppress high order lateral modes. The DFB ICLs have 4 mm long and 4.5 μm wide ridge waveguides and are mounted epi-up on AlN submounts. We demonstrated a continuous-wave (CW) DFB ICL, from a first wafer which has a large detuning of the gain peak from the DFB wavelength, with a side mode suppression ratio of 30 dB. With proper matching of grating feedback and the gain peak wavelength for the second wafer, a DFB ICL was demonstrated with a maximum CW output power and a maximum wall plug efficiency reaching 42 mW and 2%, respectively, at 25 °C. The lasing wavelengths of both lasers are around 3.3 μm at 25 °C.
Detection of generalized synchronization using echo state networks
Authors: Ibáñez-Soria D. , Garcia-Ojalvo J. , Soria-Frisch A. , Ruffini G.
Published: March 2018

Generalized synchronization between coupled dynamical systems is a phenomenon of relevance in applications that range from secure communications to physiological modelling. Here, we test the capabilities of reservoir computing and, in particular, echo state networks for the detection of generalized synchronization. A nonlinear dynamical system consisting of two coupled Rössler chaotic attractors is used to generate temporal series consisting of time-locked generalized synchronized sequences interleaved with unsynchronized ones. Correctly tuned, echo state networks are able to efficiently discriminate between unsynchronized and synchronized sequences even in the presence of relatively high levels of noise. Compared to other state-of-the-art techniques of synchronization detection, the online capabilities of the proposed Echo State Network based methodology make it a promising choice for real-time applications aiming to monitor dynamical synchronization changes in continuous signals.
A postprocessing method in the HMC framework for predicting gene function based on biological instrumental data
Authors: Feng Shou , Fu Ping , Zheng Wenbin
Published: March 2018

Predicting gene function based on biological instrumental data is a complicated and challenging hierarchical multi-label classification (HMC) problem. When using local approach methods to solve this problem, a preliminary results processing method is usually needed. This paper proposed a novel preliminary results processing method called the nodes interaction method. The nodes interaction method revises the preliminary results and guarantees that the predictions are consistent with the hierarchy constraint. This method exploits the label dependency and considers the hierarchical interaction between nodes when making decisions based on the Bayesian network in its first phase. In the second phase, this method further adjusts the results according to the hierarchy constraint. Implementing the nodes interaction method in the HMC framework also enhances the HMC performance for solving the gene function prediction problem based on the Gene Ontology (GO), the hierarchy of which is a directed acyclic graph that is more difficult to tackle. The experimental results validate the promising performance of the proposed method compared to state-of-the-art methods on eight benchmark yeast data sets annotated by the GO.
New insights onto dissociation of state-selected O2+ ions investigated by double imaging photoelectron photoion coincidence: The superimposed 32Πu and c4Σu− inner-valence states
Authors: Tang Xiaofeng , Garcia Gustavo A. , Nahon Laurent
Published: March 2018

The double imaging photoelectron photoion coincidence technique has been applied to investigate the dissociation of state-selected O2+(32Πu, c4Σu−) ions at hv = 25.4 eV. It is shown that the O2+ ions prepared in the 32Πu inner-valence state can dissociate toward two channels where a distinct changeover from the third dissociation limit O(3P) + O+(2D) to the fifth limit O(3P) + O+(2P) is observed at a binding energy of ∼23.8 eV. Up to four dissociation limits have been identified in the dissociation of the v = 0 vibrational level of the c4Σu− electronic state, and in particular, the products toward the third limit with a very weak intensity are definitely identified and assigned. In addition, the individual contributions of the two superimposed 32Πu and c4Σu− states to the fifth dissociation limit are clearly separated and determined for the first time. The anisotropy parameters of the O+ fragment ion toward different dissociation limits have also been measured and exhibit specific state-selected characteristics. The dissociation mechanisms of the 32Πu and c4Σu− states including predissociation and tunneling motion are proposed based on the present experimental results and the existing theoretical potential energy curves.
Simplified calculation approaches designed to reproduce the geometry of hydrogen bonds in molecular complexes in aprotic solvents
Authors: Shenderovich Ilya G.
Published: March 2018

The impact of the environment onto the geometry of hydrogen bonds can be critically important for the properties of the questioned molecular system. The paper reports on the design of calculation approaches capable to simulate the effect of aprotic polar solvents on the geometric and NMR parameters of intermolecular hydrogen bonds. A hydrogen fluoride and pyridine complex has been used as the main model system because the experimental estimates of these parameters are available for it. Specifically, F–H, F⋯N, and H–N distances, the values of 15N NMR shift, and spin–spin coupling constants 1J(19F1H), 1hJ(1H15N), and 2hJ(19F15N) have been analyzed. Calculation approaches based on the gas-phase and the Polarizable Continuum Model (PCM) approximations and their combinations with geometric constraints and additional noncovalent interactions have been probed. The main result of this work is that the effect of an aprotic polar solvent on the geometry of a proton–donor⋯H⋯proton–acceptor complex cannot be reproduced under the PCM approximation if no correction for solvent–solute interactions is made. These interactions can be implicitly accounted for using a simple computational protocol.
An orbital instability of minimal plane Couette turbulence
Authors: Ishikawa Toshio , Takehiro Shin-ichi , Yamada Michio
Published: March 2018

While oblique stripes have been observed in both laboratory and numerical experiments, their mechanism has not yet been theoretically understood. We investigate an orbital instability of plane Couette flow to infinitesimal disturbances using Lyapunov analysis, assuming the main flow to be a tessellation by identical copies of a minimal turbulence which reduces the numerical cost. Because of the periodicity of the linearized equations in the streamwise and spanwise directions, Bloch’s theorem is applicable and an orbital instability of disturbances with scales larger than the minimal flow unit can be investigated by a calculation within the minimal flow unit. By comparing Lyapunov exponents, we find that the most unstable mode has the Bloch wavenumber parallel to the streamwise direction, which however does not correspond to oblique patterns observed in laboratory experiments and numerical simulations. Therefore the infinitesimal orbital instability of minimal plane Couette turbulence does not explain the obliqueness of the stripe pattern.
An investigation of the sites occupied by atomic barium in solid xenon—A 2D-EE luminescence spectroscopy and molecular dynamics study
Authors: Davis Barry M. , Gervais Benoit , McCaffrey John G.
Published: March 2018

A detailed characterisation of the luminescence recorded for the 6p 1P1–6s 1S0 transition of atomic barium isolated in annealed solid xenon has been undertaken using two-dimensional excitation–emission (2D-EE) spectroscopy. In the excitation spectra extracted from the 2D-EE scans, two dominant thermally stable sites were identified, consisting of a classic, three-fold split Jahn-Teller band, labeled the blue site, and an unusual asymmetric 2 + 1 split band, the violet site. A much weaker band has also been identified, whose emission is strongly overlapped by the violet site. The temperature dependence of the luminescence for these sites was monitored revealing that the blue site has a non-radiative channel competing effectively with the fluorescence even at 9.8 K. By contrast, the fluorescence decay time of the violet site was recorded to be 4.3 ns and independent of temperature up to 24 K. The nature of the dominant thermally stable trapping sites was investigated theoretically with Diatomics-in-Molecule (DIM) molecular dynamics simulations. The DIM model was parameterized with ab initio multi-reference configuration interaction calculations for the lowest energy excited states of the Ba⋅Xe pair. The simulated absorption spectra are compared with the experimental results obtained from site-resolved excitation spectroscopy. The simulations allow us to assign the experimental blue feature spectrum to a tetra-vacancy trapping site in the bulk xenon fcc crystal—a site often observed when trapping other metal atoms in rare gas matrices. By contrast, the violet site is assigned to a specific 5-atom vacancy trapping site located at a grain boundary.
Perspective: The future of quantum dot photonic integrated circuits
Authors: Norman Justin C. , Jung Daehwan , Wan Yating , Bowers John E.
Published: March 2018

Direct epitaxial integration of III-V materials on Si offers substantial manufacturing cost and scalability advantages over heterogeneous integration. The challenge is that epitaxial growth introduces high densities of crystalline defects that limit device performance and lifetime. Quantum dot lasers, amplifiers, modulators, and photodetectors epitaxially grown on Si are showing promise for achieving low-cost, scalable integration with silicon photonics. The unique electrical confinement properties of quantum dots provide reduced sensitivity to the crystalline defects that result from III-V/Si growth, while their unique gain dynamics show promise for improved performance and new functionalities relative to their quantum well counterparts in many devices. Clear advantages for using quantum dot active layers for lasers and amplifiers on and off Si have already been demonstrated, and results for quantum dot based photodetectors and modulators look promising. Laser performance on Si is improving rapidly with continuous-wave threshold currents below 1 mA, injection efficiencies of 87%, and output powers of 175 mW at 20 °C. 1500-h reliability tests at 35 °C showed an extrapolated mean-time-to-failure of more than ten million hours. This represents a significant stride toward efficient, scalable, and reliable III-V lasers on on-axis Si substrates for photonic integrate circuits that are fully compatible with complementary metal-oxide-semiconductor (CMOS) foundries.
Enhanced shock wave generation via pre-breakdown acceleration using water electrolysis in negative streamer pulsed spark discharges
Authors: Lee Kern , Chung Kyoung-Jae , Hwang Y. S.
Published: March 2018

This paper presents a method for enhancement of shock waves generated from underwater pulsed spark discharges with negative (anode-directed) subsonic streamers, for which the pre-breakdown process is accelerated by preconditioning a gap with water electrolysis. Hydrogen microbubbles are produced at the cathode by the electrolysis and move towards the anode during the preconditioning phase. The numbers and spatial distributions of the microbubbles vary with the amplitude and duration of each preconditioning pulse. Under our experimental conditions, the optimum pulse duration is determined to be ∼250 ms at a pulse voltage of 400 V, where the buoyancy force overwhelms the electric force and causes the microbubbles to be swept out from the water gap. When a high-voltage pulse is applied to the gap just after the preconditioning pulse, the pre-breakdown process is significantly accelerated in the presence of the microbubbles. At the optimum preconditioning pulse duration, the average breakdown delay is reduced by 87% and, more importantly, the energy consumed during the pre-breakdown period decreases by 83%. This reduced energy consumption during the pre-breakdown period, when combined with the morphological advantages of negative streamers, such as thicker and longer stalks, leads to a significant improvement in the measured peak pressure (∼40%) generated by the underwater pulsed spark discharge. This acceleration of pre-breakdown using electrolysis overcomes the biggest drawback of negative subsonic discharges, which is slow vapor bubble formation due to screening effects, and thus enhances the efficiency of the shock wave generation process using pulsed spark discharges in water.
Experimental and theoretical investigation of the temperature dependent electronic quenching of O(1D) atoms in collisions with Kr
Authors: Nuñez-Reyes Dianailys , Kłos Jacek , Alexander Millard H. , Dagdigian Paul J. , Hickson Kevin M.
Published: March 2018

The kinetics and dynamics of the collisional electronic quenching of O(1D) atoms by Kr have been investigated in a joint experimental and theoretical study. The kinetics of quenching were measured over the temperature range 50–296 K using the Laval nozzle method. O(1D) atoms were prepared by 266 nm photolysis of ozone, and the decay of the O(1D) concentration was monitored through vacuum ultraviolet fluorescence at 115.215 nm, from which the rate constant was determined. To interpret the experiments, a quantum close-coupling treatment of the quenching transition from the 1D state to the 3Pj fine-structure levels in collisions with Kr, and also Ar and Xe, was carried out. The relevant potential energy curves and spin-orbit coupling matrix elements were obtained in electronic structure calculations. We find reasonable agreement between computed temperature-dependent O(1D)–Rg (Rg = Ar, Kr, Xe) quenching rate constants and the present measurements for Kr and earlier measurements. In particular, the temperature dependence is well described.
Analytical description of the current-voltage relationship in organic-semiconductor diodes
Authors: Wetzelaer G. A. H.
Published: March 2018

The description of the current-voltage relationship in disordered organic-semiconductor diodes is complicated by the effects of diffusion and a charge-carrier mobility that depends on charge concentration, electric field and temperature. Here, an analytical model is presented that accurately describes the drift-diffusion current through disordered organic semiconductors over the full voltage range. The model applies to single-carrier devices in which the organic-semiconductor layer is situated between an Ohmic injecting contact and an extracting contact of which the barrier can be varied. The analytical description can be used to extract charge-transport parameters, such as mobility and energetic disorder, from experimental current-voltage characteristics of devices of virtually any layer thickness.
Structure and optical properties of 2D layered MoS2 crystals implemented with novel friction induced crystal growth
Authors: Tanabe Tadao , Ito Takafumi , Oyama Yutaka
Published: March 2018

We used X-ray diffraction, and Raman and photoluminescence (PL) spectroscopies to examine the structure and optical properties of molybdenum disulfide (MoS2) crystals grown by friction at the interface between two materials. MoS2 is produced chemically from molybdenum dithiocarbamates (MoDTC) in synthetic oil under sliding friction conditions. The X-ray diffraction (XRD) patterns indicate that the structure of the MoS2 is layered with the c-axis perpendicular to the surface. The MoS2 layer was formed on stainless steel and germanium by friction at the interface between these materials and high carbon chromium bearing steel. The number of layers is estimated to be N (N > 6) from the distance between the Raman frequencies of the E12g and A1g modes. For MoS2 grown on stainless steel, exciton peak is observed in the PL spectrum at room temperature. These results show that this friction induced crystal growth method is viable for synthesizing atomic layers of MoS2 at solid surfaces.
Detailed characterisation of focused ion beam induced lateral damage on silicon carbide samples by electrical scanning probe microscopy and transmission electron microscopy
Authors: Stumpf F. , Abu Quba A. A. , Singer P. , Rumler M. , Cherkashin N. , Schamm-Chardon S. , Cours R. , Rommel M.
Published: March 2018

The lateral damage induced by focused ion beam on silicon carbide was characterized using electrical scanning probe microscopy (SPM), namely, scanning spreading resistance microscopy and conductive atomic force microscopy (c-AFM). It is shown that the damage exceeds the purposely irradiated circles with a radius of 0.5 μm by several micrometres, up to 8 μm for the maximum applied ion dose of 1018 cm−2. Obtained SPM results are critically compared with earlier findings on silicon. For doses above the amorphization threshold, in both cases, three different areas can be distinguished. The purposely irradiated area exhibits resistances smaller than the non-affected substrate. A second region with strongly increasing resistance and a maximum saturation value surrounds it. The third region shows the transition from maximum resistance to the base resistance of the unaffected substrate. It correlates to the transition from amorphized to defect-rich to pristine crystalline substrate. Additionally, conventional transmission electron microscopy (TEM) and annular dark-field STEM were used to complement and explain the SPM results and get a further understanding of the defect spreading underneath the surface. Those measurements also show three different regions that correlate well with the regions observed from electrical SPM. TEM results further allow to explain observed differences in the electrical results for silicon and silicon carbide which are most prominent for ion doses above 3 × 1016 cm−2. Furthermore, the conventional approach to perform current-voltage measurements by c-AFM was critically reviewed and several improvements for measurement and analysis process were suggested that result in more reliable and impactful c-AFM data.
Diagnostic study of multiple double layer formation in expanding RF plasma
Authors: Chakraborty Shamik , Paul Manash Kumar , Roy Jitendra Nath , Nath Aparna
Published: March 2018

Intensely luminous double layers develop and then expand in size in a visibly glowing RF discharge produced using a plasma source consisting of a semi-transparent cylindrical mesh with a central electrode, in a linear plasma chamber. Although RF discharge is known to be independent of device geometry in the absence of magnetic field, the initiation of RF discharge using such a plasma source results in electron drift and further expansion of the plasma in the vessel. The dynamics of complex plasma structures are studied through electric probe diagnostics in the expanding RF plasma. The measurements made to study the parametric dependence of evolution of double layer structures are analyzed and presented here. The plasma parameter measurements suggest that the complex potential structures initially form with low potential difference between the layers and then gradually expand producing burst oscillations. The present study provides interesting information about the stability of plasma sheath and charge particle dynamics in it that are important to understand the underlying basic sheath physics along with applications in plasma acceleration and propulsion.
Observation of large exchange bias and topological Hall effect in manganese nitride films
Authors: Meng Meng , Li Shuwei , Saghayezhian Mohammad , Plummer E. W. , Jin Rongying
Published: March 2018

The magnetic and magneto-transport properties of manganese nitride films grown by molecular beam epitaxy have been investigated. Due to the mixed ferrimagnetic (FI) phase (ε-phase with TFI ∼ 738 K) and the antiferromagnetic phase (ζ-phase with TN ∼ 273 K), we observe magnetization hysteresis loops with non-zero exchange bias below TN, reaching ∼0.22 T at 5 K. This indicates that noncollinear spins exist at the interfaces of two phases, creating competition between interfacial Dzyaloshinskii-Moriya and exchange interactions. Strikingly, in addition to the normal Hall effect by the Lorentz force and the anomalous Hall effect by magnetizatism, we observe another contribution, namely, topological Hall effect below 75 K. This verifies the existence of topological spin texture, which is the consequence of competing interactions controlled by both applied field and temperature. Our work demonstrates that spintronic devices may be fabricated, exploiting rich magnetic properties of different phases.
AI characterizes the interface between zinc oxide and water
Authors: Johnson Sally Cole
Published: March 2018

Machine learning technique interprets and resolves the vibrational fingerprints of molecules to characterize the interface of metal oxides and water.
Quantum materials science meets spintronics
Authors: Johnson Sally Cole
Published: March 2018

Combining quantum-spin system science and spintronics, developed separately, reveals a potential route to atomic wiring for spin currents.
Chemsex among men who have sex with men in Germany: motives, consequences and the response of the support system
Authors: Graf Niels , Dichtl Anna , Deimel Daniel , Sander Dirk , Stöver Heino
Published: March 2018

Background
In Germany, drug use in sexual settings (i.e. chemsex) among men who have sex with men (MSM) has increasingly been the subject of discussion for considerable time. At the same time, however, little is known about this practice. It is against this background that what is currently known about chemsex among MSM in Germany is discussed. Methods: The present study observations are essentially based on the results of two research projects of a qualitative–explorative nature. In-depth interviews with drug-using MSM (n = 14), as well as qualitative, problem-centred interviews with drug-using MSM (n = 75) and expert interviews (n = 27) were conducted within these research projects. Results: Chemsex is a minority behaviour among MSM in Germany. The reasons for using drugs in sexual settings are manifold. For the most part, the effects of the drugs are used to intensify sexual feelings and to achieve greater intimacy. Men who consider their consumption to be problematic, in particular, report a range of negative consequences, such as sexually transmissible infections. Even though chemsex is a minority behaviour, suitable offers of support are, hence, necessary, especially for these men. However, such offers are not yet available in most German cities. Conclusions: In order to close this gap in provision of support services, tangible practical steps, such as further training of people who work at drug and gay advisory services, are necessary, along with further research into the backgrounds and contexts of chemsex.
What are the drivers of dangerous fires in Mediterranean France?
Authors: Lahaye S. , Curt T. , Fréjaville T. , Sharples J. , Paradis L. , Hély C.
Published: March 2018

Wildfire containment is often very challenging for firefighters, especially for large and rapidly spreading fires where the risk of firefighter entrapment is high. However, the conditions leading to these ‘dangerous’ fires are poorly understood in Mediterranean Europe. Here, we analyse reports and interviews of firefighters over the last 40 years in four regions of south-eastern France and investigate the weather conditions that induce large fires, fast-growing fires and fires that are conducive to entrapment. We adopt a quantile regression model to test the effect of weather conditions across different fire sizes and growth rates. The results show that strong winds drive the largest fires everywhere except in Corsica, the southernmost region, where high temperature is the main driver. Strong winds also drive entrapments whereas high temperatures induce rapidly spreading fires. This emphasises that wind-driven fire is the dominant pattern of dangerous fires in France, but it reveals that large ‘convective’ fires can also present considerable danger. Beyond that, the Fire Weather Index appears to be a good predictor of large fires and fires conducive to entrapments. Identifying weather conditions that drive ‘dangerous’ wildfires will provide useful information for fire agencies to better prepare for adverse fire behaviours.