bluuebunny/crossref_metadata_2025 huggingface dataset:
Approach for allocation of transmission loss based on contribution of generators and loads in injected complex power into network lines
Authors: Khosravi Masoud , Monsef Hassan , Aliabadi Mahmoud H.
Published: October 2017

During recent years, the shift from monopoly integrated power systems to restructured power systems caused an increased competition among the electricity market. In restructured power systems, providing a fair and impartially service pricing is still in discussion on ‘who should be reprimand’ for the losses contribution. The loss allocation (LA) causes appropriate economic penalties or rewards to generators and consumers. This study presents a reasonable method for LA in power systems. This method is based on the injected active and reactive power into network lines. At first, the contribution of the loads in the loss of each line is obtained regardless of the generators. Then, the loss of lines is allocated to source buses and the contribution of each generator in the loss of each line is calculated. At the final step, a normalisation factor is introduced and the final contribution of each load and each generator in the loss of each line is calculated separately. The proposed algorithm is simple and easy to implement on the large‐scale power systems.‏ This proposed method has been applied to the IEEE 14‐bus and IEEE 30‐bus test systems, and the obtained results are compared with other existing LA methods.
Comparison of digital PWM control strategies for high‐power interleaved DC–DC converters
Authors: Calderon‐Lopez Gerardo , Villarruel‐Parra Alejandro , Kakosimos Panagiotis , Ki Shu‐Kong , Todd Rebecca , Forsyth Andrew J
Published: October 2017

Three pulse‐width‐modulation (PWM) digital control approaches are evaluated to provide the current sharing between phases in high‐power dual‐interleaved DC–DC converters. The implementation of a digital peak current, multi‐sample averaged current and an enhanced single‐sample averaged current control in a TMS320F28377D is described. A summary of stability requirements is provided for designing the controllers and experimental results from a 60 kW, 75 kHz silicon carbide DC–DC converter are used to evaluate the steady‐state and dynamic performance of the three control methods. Overall the best performance in terms of tracking and speed of response was achieved by the enhanced single‐sample method. The multi‐sampled technique provided the highest tracking accuracy, but at the expense of the slowest dynamic response. The fastest dynamic response was achieved by the digital peak current control, but this method is limited by poor noise immunity and instability for duty ratios in the region of 0.5.
Active‐clamped ZVS current‐fed push–pull isolated dc/dc converter for renewable energy conversion applications
Authors: Wu Qunfang , Wang Qin , Xu Jialin , Xu Zilong
Published: October 2017

This study introduces a new active‐clamped current‐fed push–pull dc–dc converter for renewable energy conversion applications. The proposed converter conserves small input current pulsation, high‐voltage conversion ratio, zero‐voltage switching (ZVS) and zero‐current‐switching operation for primary switches and rectifier diodes, respectively, over a large load range. Also, the additional active clamping circuit serves to suppress the voltage spike across all primary switches, as well as assists in achieving ZVS operation. So, the low‐voltage switches with low on‐state resistance can be adopted. These features can reduce switching loss, voltage stress, transformer turns ratio and diode reverse‐recovery effect. More importantly, similar characteristics can be obtained with minimised switches compared with the reported converters that enable to reduce the cost and improve the reliability. Detailed steady‐state operation, analysis, performance comparison, experimental results and loss breakdown of the proposed converter are fully discussed in this study. Finally, a 520 W prototype verifies the theoretical analysis.
Stator flux estimation with vector transforming and signal filtering method for electrical machines
Authors: Liu Ying , Cheng Shanmei , Ning Bowen , Li Yesong
Published: October 2017

Stator flux estimation for electrical machine using voltage model (VM) with a simple structure and the least parameters has been widely researched in high‐performance drive systems. Existing low‐pass filter (LPF)‐based estimators either respond slowly or cannot adequately suppress DC drifts, thus, a vector transforming and signal filtering method using VM is proposed for flux estimation. An original flux vector is directly produced through a transformation for motor back electromotive force, and then, the desired flux is obtained through an optimised filter which is designed by combing LPF and band‐pass filter with an optimal function. The proposed estimator can both eliminate DC drifts and obtain a fast response and high accuracy, and additionally, its structure is simplified by the decomposing process, which significantly reduces the computation and occupied resources. The effects of cut‐off frequencies on dynamical responses and flux harmonics are investigated and the limitations are obtained. This estimator is applicable to extensive strategies, for instance, the implementation of a direct torque control‐based electrical drive system is carried out. Theoretical analysis, simulation, and experiment are conducted to validate the feasibility and effectiveness of the proposed scheme.
Review of dynamic effects and reliability of depletion and enhancement GaN HEMTs for power switching applications
Authors: De Santi Carlo , Meneghini Matteo , Meneghesso Gaudenzio , Zanoni Enrico
Published: October 2017

GaN‐based transistors are promising devices for power switching applications, but their unique properties require careful design of the circuit in order to achieve the best performance and reliability. The first part will focus on the characterisation of deep‐level effects in enhancement‐ and depletion‐mode HEMTs, which limit the performance of the transistor. Threshold voltage instabilities in MIS‐HEMT structures, caused by charge trapping under the gate, and their dependence on SiN acting as the gate dielectric will be reviewed. ON‐resistance increase, caused by charge trapping in the gate–drain access region, will then be discussed in normally off gate injection transistors, as well as the effect of the switching frequency on the trapping–de‐trapping equilibrium condition. The second part of the paper will discuss possible failure modes related to operating conditions, starting with the oxidation of the surface and the inverse piezoelectric effect at high gate–drain voltage. To have a complete picture of high‐field effects, the gate dielectric and passivation robustness will be investigated. Time‐dependent degradation will then be analysed in both gate reverse and forward‐bias conditions. Finally, failures related to off‐state stress and to power dissipation and electric field during an ESD event in AlGaN/GaN‐HEMTs will be discussed.
Miniaturised ultra‐wideband band‐pass filter using quasi‐lumped symmetrical EBG
Authors: Ramakrishnan G. , Sivakumar R.
Published: October 2017

This study presents a novel design of a miniaturised ultra wideband (UWB) band‐pass filter (BPF) by integrating quasi‐lumped structure with electro‐magnetic band gap (EBG) cells. The proposed filter is designed to cover the UWB bandwidth of 3.1–10.6 GHz. The UWB BPF filter design is validated using both circuit simulation and electromagnetic full wave simulation. The compact UWB BPF is simulated, fabricated and the performance metrics are measured. A good agreement between simulated and measured results is obtained. Good performances such as return loss better than 14 dB, upper stop‐band attenuation better than 20 dB and good selectivity are achieved.
Super-Gau Hygieneskandal: Kommunikation im Krisenfall: Wie Krankenhäuser sich rüsten sollten
Authors: Ellerhoff Steffen
Published: October 2017

Verunreinigte Babynahrung, wiederkehrende Infektionen auf Intensivstationen, nicht steriles Operationsmaterial – die Schlagzeilen, die sich aus solchen Vorkommnissen in den Medien widerspiegeln, lauten dann: „Todeskeime im Krankenhaus“, „Staatsanwaltschaft ermittelt nach Säuglingstod“, „Hat sich die Klinik krank gespart?“ Solche Überschriften können ein Krankenhaus in eine tiefe Krise stürzen.
Branche in Zahlen
Authors: Mewis Dirk
Published: October 2017

Dieser Artikel ist nur als PDFDokument verfügbar.
Legal Compliance: Eine weiße Weste haben
Authors: Thalmayr Maria
Published: October 2017

Die ständig wachsende Zahl immer neuer Gesetze, Normen und Verordnungen stellt die Verantwortlichen in den Krankenhäusern vor eine große Herausforderung. Wie kann eine Gesundheitseinrichtung sicherstellen, dass sie alle relevanten Normen, Vorschriften und Gesetze kennt und die daraus resultierenden Verpflichtungen einhält?
CT, MRT & CO: Wieviel Strom verbrauchen Großgeräte?
Authors: Witt Daniel , Brüning Cord
Published: October 2017

Berechnungen zu den Stromkosten radiologischer Großgeräte wurden schon mehrfach publiziert, allerdings überwiegend basierend auf Nennwert-Hochrechnungen und somit angreifbaren Empfehlungen. Daher wurde von der Hochschule Hamm-Lippstadt im Detail geforscht und gemessen.
Pharmacology of Mycobacterial Drugs in Children
Authors: Goldman Jennifer , Abdel-Rahman Susan
Published: October 2017

To effectively treat tuberculosis (TB), optimization of therapy guided by an understanding of pharmacokinetic-pharmacodynamic principles represents the strategy most likely to influence favorable patient outcomes. However, challenges are often encountered during TB treatment given the concomitant administration of multiple drugs, some with poorly defined therapeutic targets, for prolonged durations. Treatment is further complicated in children as many antitubercular drugs have not been extensively studied in the pediatric population where the impact of human development on drug disposition is relevant, but poorly understood. In this review, the pharmacokinetics (PK) of antitubercular drugs will be reviewed in the context of the pediatric population. Observed differences between adults and children with respect to TB therapy will be highlighted, and future considerations to enhance our understanding of TB drugs used in children will be explored.
Die arthroskopische Synovialektomie der Metacarpophalangealgelenke bei rheumatoider Arthritis
Authors: Kittel Margarethe , Borisch Nicola
Published: October 2017

Zur arthroskopischen Synovialektomie der Metacarpophalangealgelenke (MCP-Gelenke) sind bisher kaum Arbeiten erschienen. Sie berichten jedoch über vielversprechende Ergebnisse. Ziel der vorliegenden Arbeit ist die Auswertung der subjektiven Ergebnisse nach arthroskopischer Synovialektomie bei Patienten mit rheumatoider Arthritis. Von 2009 bis 2013 wurden 137 arthroskopische Synovialektomien der MCP- und der proximalen Interphalangealgelenke (PIP) bei 77 Patienten mit rheumatoider Arthritis durchgeführt. Nach Berücksichtigung der Ausschlusskriterien verblieben 41 Patienten, bei denen ein oder mehrere MCP-Gelenke oder zusätzlich ein PIP-Gelenk behandelt wurden. Telefonisch konnten 39 Patienten mit 76 MCP-Gelenken nach durchschnittlich 22,7 (9–42) Monaten retrospektiv zu Schmerzreduktion, Funktionsverbesserung und Zufriedenheit mit dem Eingriff befragt werden. 37 Patienten mit 74 operierten Gelenken waren mit dem Eingriff zufrieden und würden ihn erneut durchführen lassen. Die Verringerung des Ruhe- und Bewegungsschmerzes war signifikant, ohne dass hierbei ein Zusammenhang mit dem präoperativen Röntgenstadium festzustellen war. Intraoperativ konnte in allen Fällen eine Synovialitis bestätigt werden. Die Ergebnisse der vorgelegten Arbeit zeigen, dass mit der arthroskopischen Synovialektomie der MCP-Gelenke bei rheumatoider Arthritis eine hohe Patientenzufriedenheit erreicht werden kann. Voraussetzung für die Indikation ist ein intakter Bandapparat der MCP-Gelenke ohne biomechanische Veränderungen.
15.1.4 Pyridines (Update 2016)
Authors: Spitzner D.
Published: October 2017

This chapter is an update to the 2004 Science of Synthesis contribution on pyridines. It covers the literature up until early 2016. This update covers the synthesis of pyridines, pyridine 1-oxides, pyridinium salts, and some di- and tetrahydropyridines. Pyridines and their derivatives are substructures in many natural products, drugs, pesticides, and other molecules of interest, and numerous methods are available for their synthesis.
1.5 Cyclization Reactions of Alkenes and Alkynes
Authors: Zhang L.
Published: October 2017

Discussed in this chapter are two classes of metal-catalyzed cyclization reactions of alkenes and alkynes, namely one where unactivated carbon–carbon double or triple bonds act as nucleophiles to attack tethered electrophiles, and the other where the π-system is activated by a metal-based π-acid and is subsequently attacked by carbonucleophiles. In the former scenario, the in situ generation of electrophiles is typically promoted by hard Lewis acid catalysts, which initiate Prins, aza-Prins, or carbonyl-ene reactions. In the latter scenario, the coordination of a carbon–carbon double or triple bond to a soft Lewis acidic metal catalyst lowers the energy of the π* orbital and thereby enables attack by nucleophiles. A large array of cyclic structural motifs are accessible, many in a stereoselective manner, via such metal catalysis. These motifs, including tetrahydrofurans, tetrahydropyrans, cycloalkenes, dihydronaphthalenes, carbazoles, coumarins, quinolinones, benzopyrans, dihydroquinolines, and phenanthrenes, are essential components of various bioactive compounds and natural products. Exemplary applications of these methods in the syntheses of natural products and relevant structures are also discussed.
1.6 Metal-Catalyzed Cyclization Reactions of Allenes
Authors: Phelps A. , Alderson J. , Schomaker J. M.
Published: October 2017

Allenes represent a unique scaffold for powerful cyclization reactions due to the ability to incorporate additional functionality into the newly formed ring. Metal-catalyzed cyclization reactions of allenes represent a powerful strategy for the synthesis of highly functionalized heterocycles and carbocycles. A variety of metals can be used to facilitate cyclization; the nature of the metal influences which allene carbon is attacked by an internal nucleophile, leading to convenient access to multiple ring systems from a simple precursor. The unique axial chirality of allenes can dictate the stereochemistry featured in the ring through axial-to-point chirality transfer.
1.8 Metal-Catalyzed Intramolecular C—N and C—O Bond Formation
Authors: Beccalli E. M. , Bonetti A. , Mazza A.
Published: October 2017

Transition-metal-catalyzed intramolecular C—N and C—O bond formation using unsaturated alkene and alkyne systems containing tethered nitrogen nucleophiles (such as amines, amides, sulfonamides, amidines, azides, carbamates, guanidines, hydrazones, imines, and ureas) or oxygen nucleophiles (such as alcohols, ketones, phenols, hydroxylamines, and carboxylic acids) represents an efficient method for the preparation of heterocycles. Various reaction types may be involved, including amination, hydroamination, oxidative amination, carbamoylation, carboamination, alkoxylation, hydroalkoxylation, oxidative alkoxylation, hydroacyloxylation, carboalkoxylation, and alkoxycarbonylation. Depending on the type of reaction, the choice of transition-metal complex to be used plays a fundamental role in obtaining a successful reaction.
Study on coupled dynamics of ship and flooding water based on experimental and SPH methods
Authors: Cheng H. , Zhang A. M. , Ming F. R.
Published: October 2017

The present paper studies the fluid dynamics during the flooding of a damaged ship numerically and experimentally. Attention is focused on the fluid flow characteristics and the fluid-structure interactions. The Smoothed Particle Hydrodynamics (SPH) method with an improved boundary treatment is established, which is able to capture the flow behaviors effectively. Fairly good agreement is obtained between the computational and experimental results. Based on the SPH method, the simulations are carried out for the flooding of a damaged ship with different opening sizes, opening positions, and numbers of the flooding cabins. Besides, the effects of the wave are also taken into account. The fluid behaviors are described and analyzed in detail. It is found that, during the first phase of flooding, an inflow jet with a large velocity is formed, significantly influencing the inner flows and the ship responses. During the progressive flooding phase, sloshing, crushing of the free surface, wave breaking, and vortex shedding are observed which are coupled with the ship motions. In addition, some relevant conclusions are enclosed for the motion laws of the damaged ship. This work provides physical insight into the flooding of the damaged ship, which is helpful to understand the coupled dynamics of the ship and flooding water.
Particle trapping and ponderomotive processes during breaking of ion acoustic waves in plasmas
Authors: Kakad Bharati , Kakad Amar , Omura Yoshiharu
Published: October 2017

Recent fluid simulations show that the ponderomotive potentials and ponderomotive frequencies of electrons and ions can be used as proxies to identify steepening and breaking of the ion acoustic solitary waves (IASWs) in plasmas. However, the behavior of these proxies may deviate in the presence of kinetic effects such as particle trapping. We performed one-dimensional particle-in-cell (PIC) simulations to examine the effects of kinetic processes on the behavior of these proxies at the breaking of IASWs in plasmas. The electron and ion equilibrium densities were superimposed by a long-wavelength Gaussian type perturbation, which initially evolves into two IASWs observed as two phase space vortices due to the trapping of electrons in the ion acoustic (IA) potentials. These IASW structures grow due to the steepening of their trailing edges, and later they break into a chain of IA phase space vortices. Each of these vortices is associated with a bipolar electric field resulting in a positive potential structure. We examined the amplitude, width, and phase velocity of the IASWs at their breaking process to clarify their link with the trapping velocity. In addition, we estimated electron and ion ponderomotive potentials and frequencies from the PIC simulations to verify their applicability in identifying wave breaking limit under the kinetic regime. The present study shows that the behavior of the ponderomotive potential during the IA wave breaking process is similar to the one, which is proposed through fluid simulations. We find that IA wave breaking occurs when the maximum trapping velocity of the electron (Vtrap + Vs) exceeds its thermal velocity. The present simulation study shows that both maximum electron trapping velocity and ponderomotive potential can be used to identify the IA wave breaking processes in plasmas.
Force probe simulations using a hybrid scheme with virtual sites
Authors: Schäfer Ken , Oestereich Marco , Gauss Jürgen , Diezemann Gregor
Published: October 2017

Hybrid simulations, in which a part of the system is treated with atomistic resolution and the remainder is represented on a coarse-grained level, allow for fast sampling while using the accuracy of atomistic force fields. We apply a hybrid scheme to study the mechanical unfolding and refolding of a molecular complex using force probe molecular dynamics (FPMD) simulations. The degrees of freedom of the solvent molecules are treated in a coarse-grained manner while atomistic resolution is retained for the solute. The coupling between the solvent and the solute is provided using virtual sites. We test two different common coarse-graining procedures, the iterative Boltzmann inversion method and the force matching procedure, and find that both methodologies give similar results. The results of the FPMD simulations are compared to all-atom simulations of the same system and we find that differences between these simulations and the ones using the hybrid scheme are in a similar range as the differences obtained when using different atomistic force fields. Thus, a hybrid scheme yields qualitatively correct results in the strong non-equilibrium situation the system is experiencing in FPMD simulations.
Low-Reynolds-number flow around a wall-mounted square cylinder: Flow structures and onset of vortex shedding
Authors: Rastan M. R. , Sohankar A. , Alam Md. Mahbub
Published: October 2017

A direct numerical simulation is applied to investigate three-dimensional unsteady flow characteristics around a finite wall-mounted square cylinder with an aspect ratio of 7 at a Reynolds number (Re) of 40-250. Determination of Re for the onset of vortex shedding and Re influence on the wake structure and integral parameters are the major objectives of the current research. The results show that the vortex shedding inception occurs within the range of 75 < Re < 85. Re has a considerable effect on the mean wake topology and integral parameters. As such, the wake flow changes from a dipole to a quadrupole type, when the flow changes from steady to unsteady. A transition flow commences at Re = 150-200, where the wake instabilities are intensified with increasing Re, and the force signal oscillation alters from a sinusoidal to a chaotic type. Finally, the wake flow becomes turbulent at Re > 200.
Mobility in excess of 106 cm2/V s in InAs quantum wells grown on lattice mismatched InP substrates
Authors: Hatke A. T. , Wang T. , Thomas C. , Gardner G. C. , Manfra M. J.
Published: October 2017

We investigate the transport properties of a two-dimensional electron gas residing in strained composite quantum wells of In0.75Ga0.25As/InAs/In0.75Ga0.25As cladded with In0.75Al0.25As barriers grown metamorphically on insulating InP substrates. By optimizing the widths of the In0.75Ga0.25As layers, the In0.75Al0.25As barrier, and the InAs quantum well, we demonstrate mobility in excess of 1×106 cm2/V s. Mobility vs. density data indicate that scattering is dominated by a residual three dimensional distribution of charged impurities. We extract the effective Rashba parameter and spin-orbit length for these composite quantum wells.
A nanoscale pn junction in series with tunable Schottky barriers
Authors: Aspitarte Lee , McCulley Daniel R. , Minot Ethan D.
Published: October 2017

PN junctions in nanoscale materials are of interest for a range of technologies including photodetectors, solar cells, and light-emitting diodes. However, Schottky barriers at the interface between metal contacts and the nanomaterial are often unavoidable. The effect of metal-semiconductor interfaces on the behavior of nanoscale diodes must be understood, both to extract the characteristics of the pn junction, and to understand the overall characteristics of the final device. Here, we study the current-voltage characteristics of diodes that are formed in fully suspended carbon nanotubes (CNTs). We utilize tunable Schottky barrier heights at the CNT-metal interface to elucidate the role of the Schottky barriers on the device characteristics. We develop a quantitative model to show how a variety of device characteristics can arise from apparently similar devices. Using our model we extract key parameters of the Schottky barriers and the pn junction, and predict the overall I-V characteristics of the device. Our equivalent circuit model is relevant to a variety of nanomaterial-based diode devices that are currently under investigation.
Highly stable flexible thermistor properties of spinel Mn-Co-Ni oxide films on silver/carbon micro-pinecone array composite electrodes
Authors: Nakajima Tomohiko , Hanawa Satomi , Tsuchiya Tetsuo
Published: October 2017

We fabricated flexible Mn1.56Co0.96Ni0.48O4 (MCN) thermistors with stable electrical properties by precisely optimizing precursors and electrodes. The composite Ag and carbon micro-pinecone (CMP) arrays were fabricated with a KrF laser directly from polyimide sheets containing silica nanoparticles and functioned well as electrodes with high bending resistance. The electrical resistance was stable even after 10 000 bending test cycles. The well-crystallized MCN film thermistors were fabricated on the Ag/CMP composite electrodes by KrF laser irradiation at 55 mJ·cm−2 for 600 pulses to optimize the precursor films consisting of MCN nanoparticles and amorphous Mn-Co-Ni oxides. The MCN film thermistors showed high thermistor constants at 3633 K, low electrical resistivity at 10.7 kΩ·cm at 37 °C, and remarkably good stability during 10 000 bending cycles (the change in resistance was only 0.6%). The MCN film thermistors also had excellent temperature cycle resistance at 20–150 °C (3000 cycles). Thus, we improved the reliability of flexible thermistors for application in various kinds of wearable devices.
Protonated ions as systemic trapping agents for noble gases: From electronic structure to radiative association
Authors: Ozgurel O. , Pauzat F. , Pilmé J. , Ellinger Y. , Bacchus-Montabonel M.-C. , Mousis O.
Published: October 2017

The deficiencies of argon, krypton, and xenon observed in the atmosphere of Titan as well as anticipated in some comets might be related to a scenario of sequestration by H3+ in the gas phase at the early evolution of the solar nebula. The chemical process implied is a radiative association, evaluated as rather efficient in the case of H3+, especially for krypton and xenon. This mechanism of chemical trapping might not be limited to H3+ only, considering that the protonated ions produced in the destruction of H3+ by its main competitors present in the primitive nebula, i.e., H2O, CO, and N2, might also give stable complexes with the noble gases. However the effective efficiency of such processes is still to be proven. Here, the reactivity of the noble gases Ar, Kr, and Xe, with all protonated ions issued from H2O, CO, and N2, expected to be present in the nebula with reasonably high abundances, has been studied with quantum simulation method dynamics included. All of them give stable complexes and the rate coefficients of their radiative associations range from 10−16 to 10−19 cm3 s−1, which is reasonable for such reactions and has to be compared to the rates of 10−16 to 10−18 cm3 s−1, obtained with H3+. We can consider this process as universal for all protonated ions which, if present in the primitive nebula as astrophysical models predict, should act as sequestration agents for all three noble gases with increasing efficiency from Ar to Xe.
Investigation of the two- and three-fragment photodissociation of the tert-butyl peroxy radical at 248 nm
Authors: Nichols Bethan , Sullivan Erin N. , Ryazanov Mikhail , Hong Cynthia M. , Neumark Daniel M.
Published: October 2017

The photodissociation dynamics of the tert-butyl peroxy (t-BuOO) radical are studied by fast-radical-beam coincidence translational spectroscopy. The neutral t-BuOO radical is formed by photodetachment of the corresponding t-BuOO− anion at 700 nm (1.77 eV), followed by dissociation at 248 nm (5.00 eV). Photofragment mass and translational energy distributions are obtained. The major channel is found to be three-body fragmentation to form O, CH3, and acetone (83%), with minor two-body fragmentation channels leading to the formation of O2 + tert-butyl radical (10%) and HO2 + isobutene (7%). Experimental results show that the translational energy distribution for two-body dissociation peaks is close to zero translational energy, with an isotropic angular distribution of fragments. These results indicate that two-body fragmentation proceeds via internal conversion to the ground electronic state followed by statistical dissociation. For three-body dissociation, the translational energy distribution peaks closer to the maximal allowed translational energy and shows an anisotropic distribution of the plane of the dissociating fragments, implying rapid dissociation on an excited-state surface. A small shoulder in the three-body translational energy distribution suggests that some three-fragment dissociation events proceed by a different mechanism, involving internal conversion to the ground electronic state followed by sequential dissociation.
Comparative simulations of microjetting using atomistic and continuous approaches in the presence of viscosity and surface tension
Authors: Durand O. , Jaouen S. , Soulard L. , Heuzé O. , Colombet L.
Published: October 2017

We compare, at similar scales, the processes of microjetting and ejecta production from shocked roughened metal surfaces by using atomistic and continuous approaches. The atomistic approach is based on very large scale molecular dynamics (MD) simulations with systems containing up to 700 × 106 atoms. The continuous approach is based on Eulerian hydrodynamics simulations with adaptive mesh refinement; the simulations take into account the effects of viscosity and surface tension, and the equation of state is calculated from the MD simulations. The microjetting is generated by shock-loading above its fusion point a three-dimensional tin crystal with an initial sinusoidal free surface perturbation, the crystal being set in contact with a vacuum. Several samples with homothetic wavelengths and amplitudes of defect are simulated in order to investigate the influence of viscosity and surface tension of the metal. The simulations show that the hydrodynamic code reproduces with very good agreement the profiles, calculated from the MD simulations, of the ejected mass and velocity along the jet. Both codes also exhibit a similar fragmentation phenomenology of the metallic liquid sheets ejected, although the fragmentation seed is different. We show in particular, that it depends on the mesh size in the continuous approach.
Origin of the onset of Rayleigh-Bénard convection in a concentrated suspension of microgels with a yield stress behavior
Authors: Métivier C. , Li C. , Magnin A.
Published: October 2017

In this paper, we propose to explore experimentally the origin of the onset of motion in a well-known Carbopol gel, a concentrated suspension of microgels, when submitted to a vertical temperature gradient, namely, the Rayleigh-Bénard Convection (RBC). We consider three possible scenarios: (i) the gel behaves as an elasto-viscoplastic material, (ii) the gel presents a low-stress viscosity μ+ below the yield stress τy, and (iii) the gel can be considered as a two phase system, say the microgels and the solvent, i.e., a porous medium. We propose a complete rheological characterization of Carbopol 940. Creep measurements lead to obtain an instantaneous viscosity plateau μ+∼tm with m≈1. For the first time, we measure and provide permeability values k in the Carbopol gels. We show that k = O(10−14) m2 and k∝τy0.2. Our study focuses on the reference case of the RBC with no-slip conditions at walls, and new results are provided. The results lead to the conclusion that the control parameter is the (inverse) of the yield number Y, ratio between the yield stress and the buoyancy stress, and they show that the critical value is 1/Yc≈80 for no-slip conditions. One shows that both scenarios (i) and (ii) lead to recover 1/Y as the control parameter. By considering the Carbopol gels as porous media [scenario (iii)], one finds that the critical porous Rayleigh-Darcy number is Rap = O(10−4).
Formation and decomposition of CO2-filled ice
Authors: Massani B. , Mitterdorfer C. , Loerting T.
Published: October 2017

Recently it was shown that CO2-filled ice is formed upon compression of CO2-clathrate hydrate. Here we show two alternative routes of its formation, namely, by decompression of CO2/ice VI mixtures at 250 K and by isobaric heating of CO2/high-density amorphous ice mixtures at 0.5–1.0 GPa above 200 K. Furthermore, we show that filled ice may either transform into the clathrate at an elevated pressure or decompose to “empty” hexagonal ice at ambient pressure and low temperature. This complements the literature studies in which decomposition to ice VI was favoured at high pressures and low temperatures.
Experimental and numerical investigation on bubble dynamics near a free surface and a circular opening of plate
Authors: Liu N. N. , Wu W. B. , Zhang A. M. , Liu Y. L.
Published: October 2017

Dynamics behavior for a submerged oscillating bubble is closely related to the physical properties of boundaries adjacent to the bubble. For an incomplete boundary, such as a ship structure broken by the shock wave from underwater explosion attack, the bubble load formed after the shock wave may cause secondary damage to it, and the jet characteristics generated during the bubble collapse are worth exploring. Based on the incompressible potential flow method, a boundary integral method with axisymmetric code is employed to investigate the jet features of the bubble under the combined action of a free surface above and a fixed plate with a centric circular opening below. For the numerical divergence caused by the expanding bubble infinitely approaching the rim of the circular opening, the bubble walls above and below the opening are, respectively, fused with the rigid wall, and the initial infinite flow field surrounding the bubble is then divided into two independent basins that are both required to be solved. Several experiments of a spark-generated bubble oscillating near a free surface and a rigid plate with a circular opening are conducted and the numerical results are validated. Following that, two typical cases with a dominant jet, respectively, directing upward and downward are analysed in detail, and some new phenomena are discovered. Additionally, another particular case that the upward and downward jet collides in the vicinity of the opening centroid is also presented. Finally, the initial bubble-free surface distance effects upon the bubble movement and the jet developments are analysed and discussed.
Communication: A hydrogen-bonded difluorocarbene complex: Ab initio and matrix isolation study
Authors: Sosulin Ilya S. , Shiryaeva Ekaterina S. , Tyurin Daniil A. , Feldman Vladimir I.
Published: October 2017

Structure and spectroscopic features of the CF2⋯HF complexes were studied by ab initio calculations at the CCSD(T) level and matrix isolation FTIR spectroscopy. The calculations predict three stable structures. The most energetically favorable structure corresponds to hydrogen bonding of HF to the lone pair of the C atom (the interaction energy of 3.58 kcal/mol), whereas two less stable structures are the H⋯F bonded complexes (the interaction energies of 0.30 and 0.24 kcal/mol). The former species was unambiguously characterized by the absorptions in the FTIR spectra observed after X-ray irradiation of fluoroform in a xenon matrix at 5 K. The corresponding features appear at 3471 (H–F stretching), 1270 (C–F symmetric stretching, shoulder), 1175 (antisymmetric C–F stretching), and 630 (libration) cm−1, in agreement with the computational predictions. To our knowledge, it is the first hydrogen-bonded complex of dihalocarbene. Possible weaker manifestations of the H⋯F bonded complexes were also found in the C–F stretching region; however, their assignment is tentative. The H⋯C bonded complex is protected from reaction yielding a fluoroform molecule by a remarkably high energy barrier (23.85 kcal/mol), so it may be involved in various chemical reactions.
The resonant multi-pulse ionization injection
Authors: Tomassini Paolo , De Nicola Sergio , Labate Luca , Londrillo Pasquale , Fedele Renato , Terzani Davide , Gizzi Leonida A.
Published: October 2017

The production of high-quality electron bunches in Laser Wake Field Acceleration relies on the possibility to inject ultra-low emittance bunches in the plasma wave. In this paper, we present a new bunch injection scheme in which electrons extracted by ionization are trapped by a large-amplitude plasma wave driven by a train of resonant ultrashort pulses. In the Resonant Multi-Pulse Ionization injection scheme, the main portion of a single ultrashort (e.g., Ti:Sa) laser system pulse is temporally shaped as a sequence of resonant sub-pulses, while a minor portion acts as an ionizing pulse. Simulations show that high-quality electron bunches with normalized emittance as low as 0.08 mm × mrad and 0.65% energy spread can be obtained with a single present-day 100TW-class Ti:Sa laser system.
Classical and exotic magnetism: Recent advances and perspectives
Authors: Kivshar Yuri , Roberts Andrew P.
Published: October 2017

Motivated by the pioneering studies of Eremenko of magneto-optical effects in antiferromagnetic crystals, we describe an expansion of the horizons of classical magnetism to include study of Earth's magnetic field and natural environments. We also review briefly examples of exotic magnetism not directly associated with alignment of quantum spins in traditional ferromagnetic and antiferromagnetic crystalline structures. While many such cases have long been known, recent breakthroughs are associated with so-called optical magnetism that became a reality due to development of the field of metamaterials.
Observation of new magnetic ground state in frustrated quantum antiferromagnet spin-liquid system Cs2CuCl4
Authors: Kim Hyeong-Jin , Haines C. R. S. , Liu C. , Chun Sae Hwan , Kim Kee Hoon , Yi H. T. , Cheong Sang-Wook , Saxena Siddharth S.
Published: October 2017

Cs2CuCl4 is known to possess a quantum spin-liquid phase with antiferromagnetic interaction below 2.8 K. We report the observation of a new metastable magnetic phase of the triangular frustrated quantum spin system Cs2CuCl4 induced by the application of hydrostatic pressure. We measured the magnetic properties of Cs2CuCl4 following the application and release of pressure after 3 days. We observed a previously unknown ordered magnetic phase with a transition temperature of 9 K. Furthermore, the recovered sample with new magnetic ground state possesses an equivalent crystal structure to the uncompressed one with antiferromagnetic quantum spinliquid phase.
Photo-spintronics of spin-orbit active electric weak links
Authors: Shekhter R. I. , Entin-Wohlman O. , Jonson M. , Aharony A.
Published: October 2017

We show that a carbon nanotube can serve as a functional electric weak link performing photo-spintronic transduction. A spin current, facilitated by strong spin-orbit interactions in the nanotube and not accompanied by a charge current, is induced in a device containing the nanotube weak link by circularly polarized microwaves. Nanomechanical tuning of the photo-spintronic transduction can be achieved due to the sensitivity of the spinorbit interaction to geometrical deformations of the weak link.
Suppression of the superconductivity in ultrathin amorphous Mo78Ge22 films observed by STM
Authors: Lotnyk D. , Onufriienko O. , Samuely T. , Shylenko O. , Komanický V. , Szabó P. , Feher A. , Samuely P.
Published: October 2017

In contact with a superconductor a normal metal modifies its properties due to Andreev reflection. In the current work the local density of states (LDOS) of superconductor–normal metal Mo78Ge22–Au bilayers are studied by means of STM applied from the Au side. Three bilayers have been prepared on silicate glass substrate consisting of 100, 10 and 5 nm MoGe thin films covered always by 5 nm Au layer. The tunneling spectra were measured at temperatures from 0.5 to 7 K. The two-dimensional cross-correlation between topography and normalized zero-bias conductance indicates a proximity effect between 100 and 10 nm MoGe thin films and Au layer where a superconducting gap slightly smaller than that of bulk MoGe is observed. The effect of the thinnest 5 nm MoGe layer on Au leads to much smaller gap moreover the LDOS reveals almost completely suppressed coherence peaks. This is attributed to a strong pair-breaking effect of spin-flip processes at the interface between MoGe films and the substrate.
The magnon BEC observation by switch off method
Authors: Bunkov Yury
Published: October 2017

The Bose–Einstein condensation (BEC) corresponds to the formation of a collective quantum state in which macroscopic number of particles is governed by a single wave function. The magnon BEC forms by excited non-equilibrium magnons and manifests itself by coherent precession of magnetization even in an inhomogeneous magnetic field. The magnon BEC is very similar to an atomic BEC, but the potential of the interaction between magnons may variate very significantly. The superfluid phases of 3He are the best antiferromagnetic system for investigations of magnon BEC and spin superfluidity. The 6 different states of magon BEC were observed in 3He. Recently magnon BEC was observed in antiferromagnets with Suhl–Nakamura interaction and ferrites. Here we review for the first time the switch off NMR method, when magnon BEC forms during a long radiofrequency pulse. The new experimental results are discussed.
Generic features of the primary relaxation in glass-forming materials (Review Article)
Authors: Kokshenev Valery B.
Published: October 2017

We discuss structural relaxation in molecular and polymeric supercooled liquids, metallic alloys and orientational glass crystals. The study stresses especially the relationships between observables raised from underlying constraints imposed on degrees of freedom of vitrification systems. A self-consistent parametrization of the α-timescale on macroscopic level results in the material-and-model independent universal equation, relating three fundamental temperatures, characteristic of the primary relaxation, that is numerically proven in all studied glass formers. During the primary relaxation, the corresponding small and large mesoscopic clusters modify their size and structure in a self-similar way, regardless of underlying microscopic realizations. We show that cluster-shape similarity, instead of cluster-size fictive divergence, gives rise to universal features observed in primary relaxation. In all glass formers with structural disorder, including orientational-glass materials (with the exception of plastic crystals), structural relaxation is shown to be driven by local random fields. Within the dynamic stochastic approach, the universal subdiffusive dynamics corresponds to random walks on small and large fractals.
Magnetic phenomena in Co-containing layered double hydroxides
Authors: Vieira Daniel E. L. , Salak Andrei N. , Fedorchenko Alexey V. , Pashkevich Yurii G. , Fertman Elena L. , Desnenko Vladimir A. , Babkin Roman Yu. , Čižmár Erik , Feher Alexander , Lopes Augusto B. , Ferreira Mário G. S.
Published: October 2017

Magnetic behavior of CoII(n)AlIII layered double hydroxides (LDHs) (n = Co/Al = 2 and 3) intercalated with nitrate was studied as a function of temperature. Both LDH compounds are paramagnetic above about 8 K. A rapid increase of their magnetic moments occurs below this temperature until the moments reach the maximum values at Tmax of 4.0 K and 3.2 K for Co(2)Al–NO3 and Co(3)Al–NO3, respectively. Below Tmax, the zero-field-cooled and the field-cooled static magnetization curves are strongly different. Along with this low-temperature phenomena, Co(2)Al–NO3 and Co(3)Al–NO3 demonstrate anomalous behavior of their temperature dependence magnetic susceptibility in a higher-temperature range: between 75 and 175 K, both the paramagnetic Curie temperature and the effective magnetic moment change in a non-monotonous way. Possible structural reasons of the observed magnetic behavior of the CoII(n)AlIII LDHs are discussed.
Synthesis, crystal structure, electric and magnetic properties of new UNiSi2 splat
Authors: Molčanová Z. , Mihalik M. , Mihalik M. , Rajňák M. , Zentková M. , Huráková M. , Kavečanský V. , Paukov M. , Havela L. , Cieslar M. , Milianchuk K.
Published: October 2017

We explored the crystal structure, magnetic and transport properties of UNiSi2 material, which was prepared by rapid solidification—splat cooling. The UNiSi2 splat is mostly single phase, the refinement of crystal structure indicated orthorhombic CeNiSi2-type structure (space group Cmcm) with lattice parameters a = 4.0082 Å, b = 16.0813 Å and c = 4.0064 Å. Also SEM analysis revealed the morphology exhibiting dendritic grains in the matrix. TEM images indicate mixed structure formed by crystalline particles embedded into amorphous or nanocrystalline matrix. Magnetic and electrical properties of the splat resemble properties of samples, which were prepared by conventional methods, exhibiting a ferromagnetic transition at about 91 K and similar temperature dependence of resistivity. The coercive field of μ0Hc = 2.25 T is much enhanced due to the magnetic anisotropy introduced by the sample preparation technique. Barkhausen jumps were observed on the hysteresis loop. Magnetization of the sample does not saturate in magnetic fields up to μ0H = 18 T.
Effect of the exchange interaction anisotropy on the magnetic quantum phase transitions in dimerized antiferromagnets
Authors: Lyashenko T. I. , Kalita V. M. , Loktev V. M.
Published: October 2017

We present a theoretical description of a quantum phase transition in a dimerized antiferromagnet, induced by an external magnetic field. The description of such transitions is constructed by determining the minimum of the Lagrange function which depends on the parameters of the ground-state crystal wavefunction. We determine that during a crystal transition from the singlet state of the dimer to the state with a noncollinear spin orientation, an order-order type phase transition occurs. We show that in the case of a single-axis character of the exchange anisotropy, the location of the quantum phase transition critical point is affected by the spin-spin interactions inside the dimer. Additionally, analogous to the classical Néele antiferromagnets, single-axis type anisotropic spin-spin interactions between dimers, shift the point of the spin-flip transition from the noncollinear antiferromagnetic phase to the ferromagnetic phase.
Processes of excitation energy transport in EuPO4 and EuP3O9 nanocrystals
Authors: Kononets N. V. , Seminko V. V. , Maksimchuk P. O. , Aslanov A. V. , Bespalova I. I. , Masalov A. A. , Malyukin Yu. V.
Published: October 2017

Processes of excitation energy transport were investigated for EuPO4 and EuP3O9 nanocrystals, in which Eu3+ ions form three- and one-dimensional subsystems, respectively. It was determined that for EuPO4 nanocrystals 5D0 luminescence quenching manifested itself even at low temperatures due to effective phonon-assisted energy migration. At the same time, for EuP3O9 nanocrystals no influence of energy migration on the luminescence quenching was observed in the whole temperature range from 10 to 293 K that can be ascribed to modification of phonon spectra for EuP3O9 nanocrystals as compared to their bulk counterparts.
Numerical study on the axial segregation dynamics of a binary-size granular mixture in a three-dimensional rotating drum
Authors: Yang Shiliang , Sun Yuhao , Zhang Liangqi , Chew Jia Wei
Published: October 2017

Granular materials are ubiquitous in our daily life and inherent in multitudinous industrial processes. Differences in the granular properties such as size and density inevitably induce segregation. By means of the discrete element method, a binary-size mixture in a three-dimensional rotating drum is numerically simulated to explore the segregation dynamics of the granular material along the axial direction. Snapshots of the distribution of the two particle types in the rotating drum are presented with respect to time to illustrate the spatial evolution of the size-induced segregation structure. The space-time plots of various axial characteristics indicate that (i) radial segregation does not affect the axial distribution of total mass and mass fraction, but axial segregation leads to the formation of axial bands; (ii) greater non-dimensionalized collision forces for both the large and small particles develop where the large particles dominate; and (iii) axial segregation gives rise to the variation of the gyration radii of both particle types along the drum length. In addition, axial flow of both particle types in both directions indicates the dynamic axial exchanges, and the effect of the end walls on the axial flow direction is limited to less than 25% of the drum length from the end walls.