bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of adaptive traffic control benefits for recurring and non‐recurring traffic conditions
Authors: Stevanovic Aleksandar , Dakic Igor , Zlatkovic Milan
Published: August 2016

When adaptive traffic control systems are deployed in the field, agencies install them for one of two reasons: (i) to cope with day‐to‐day traffic fluctuations and/or (ii) to address frequent but sudden cases with special traffic (incidents, inclement weather etc.). There is an ongoing debate among researchers in which of these two cases adaptive systems are more effective. Yet, no previous studies have examined this issue with enough rigour and attention. This study compares InSync adaptive traffic control system to three conventional time‐of‐day (TOD) signal timing plans in a microsimulation environment to address aforementioned research question. A comprehensive set of scenarios and performance measures has been prepared to evaluate, in microsimulation, operations of an adaptive system InSync on a 12‐intersection corridor along SR‐421 in Volusia County, FL. The Vissim model of SR‐421 was carefully calibrated and validated to resemble the field conditions. The findings show that InSync outperformed the TOD signal timing plans on various spatial levels and its performance made bigger savings in the case of special non‐recurring traffic conditions.
Robust control of two parallel‐connected permanent magnet synchronous motors fed by a single inverter
Authors: Deng Zhenhua , Nian Xiaohong
Published: August 2016

Two parallel‐connected permanent magnet synchronous motors (PMSMs) fed by a single inverter is investigated in this study. A robust controller is designed for this system via interval matrix, and in terms of bilinear matrix inequalities, sufficient conditions for the existence of the robust controller are derived. The proposed controller not only can deal with the uncertainty of load, but also has robust to the parameter perturbation. The effectiveness of the proposed controller is proved by theory analyses and computer simulation. Besides, the simulation results show that the control performance of the proposed control strategy is better than that of the conventional master–slave strategy.
High step‐up/step‐down non‐isolated BDC with built‐in DC‐transformer for energy storage systems
Authors: Wu Hongfei , Lu Yangjun , Chen Liqun , Xu Peng , Xiao Xi , Xing Yan
Published: August 2016

A non‐isolated bidirectional DC–DC converter (BDC) is proposed for high step‐up/step‐down bidirectional power conversion applications. A DC‐transformer is integrated into a conventional non‐isolated buck–boost BDC to achieve high‐voltage conversion ratio and wide voltage/power range regulation simultaneously. The switches are shared by the buck–boost BDC and the DC‐transformer. Voltage stresses of switches are reduced by connecting the input and output of the DC‐transformer in‐series. The duty cycles of switches are used to make sure that the voltages on the two sides of the DC‐transformer are matched. As a result, the DC‐transformer always operates under the highest‐efficiency condition. The phase‐shift angle between the switching bridges is employed to achieve the power flow regulation. Soft‐switching of all the switches is achieved by adopting the pulse‐width modulation plus phase‐shift control strategy. Operation principles, characteristics and design considerations of the proposed BDC are analysed in detail. Experimental results from a 48 V/400 V–1 kW prototype verify the effectiveness of the proposed converter. The efficiency is demonstrated to peak at 96.6% for both the step‐up and step‐down modes.
Efficient global maximum power point tracking technique for a partially shaded photovoltaic string
Authors: Manickam Chakkarapani , Raman Guru Praanesh , Raman Guru Raghav , Ganesan Saravana Ilango , Chilakapati Nagamani
Published: August 2016

Maximum power point tracking (MPPT) is essential for a photovoltaic (PV) system in order to maximise the utilisation of solar energy. Under partially shaded conditions (PSC), PV strings with bypass diodes exhibit multiple peaks in the power–voltage (P–V) characteristics. Although various Global MPPT (GMPPT) algorithms have been proposed to address this issue, most of them cannot distinguish between PSC and uniform insolation, leading to the scan of the entire P–V curve under uniform insolation levels. This study introduces a general method to detect the occurrence of PSC in a PV string thereby dispensing the need to scan the entire PV curve under uniform insolation. Further, a simple technique is proposed to determine the GMPP with the minimum possible search space under PSC. The proposed algorithms for the detection of partial shading and GMPPT are validated experimentally.
An Alternative Route for Entrapped Inferior Orbital Nerve in Orbital Floor Fracture
Authors: Rao Anantheswar Y. N. , Jesudas Joyce
Published: August 2016

Orbital floor fractures pose a grave threat for injury to the infraorbital nerve, resulting in the patient suffering from a disturbing paraesthesia. It is challenging for the operating surgeon to release and secure the entrapped nerve with reconstruction of the orbital floor. We present an interesting case of orbital floor fracture with entrapped infraorbital nerve, wherein we have decompressed the nerve and provided it, a new course.
Molecular simulation of CO chemisorption on Co(0001) in presence of supercritical fluid solvent: A potential of mean force study
Authors: Asiaee Alireza , Benjamin Kenneth M.
Published: August 2016

For several decades, heterogeneous catalytic processes have been improved through utilizing supercritical fluids (SCFs) as solvents. While numerous experimental studies have been established across a range of chemistries, such as oxidation, pyrolysis, amination, and Fischer-Tropsch synthesis, still there is little fundamental, molecular-level information regarding the role of the SCF on elementary heterogeneous catalytic steps. In this study, the influence of hexane solvent on the adsorption of carbon monoxide on Co(0001), as the first step in the reaction mechanism of many processes involving syngas conversion, is probed. Simulations are performed at various bulk hexane densities, ranging from ideal gas conditions (no SCF hexane) to various near- and super-critical hexane densities. For this purpose, both density functional theory and molecular dynamics simulations are employed to determine the adsorption energy and free energy change during CO chemisorption. Potential of mean force calculations, utilizing umbrella sampling and the weighted histogram analysis method, provide the first commentary on SCF solvent effects on the energetic aspects of the chemisorption process. Simulation results indicate an enhanced stability of CO adsorption on the catalyst surface in the presence of supercritical hexane within the reduced pressure range of 1.0–1.5 at a constant temperature of 523 K. Furthermore, it is shown that the maximum stability of CO in the adsorbed state as a function of supercritical hexane density at 523 K nearly coincides with the maximum isothermal compressibility of bulk hexane at this temperature.
Understanding the mechanisms of interfacial reactions during TiO2 layer growth on RuO2 by atomic layer deposition with O2 plasma or H2O as oxygen source
Authors: Chaker A. , Szkutnik P. D. , Pointet J. , Gonon P. , Vallée C. , Bsiesy A.
Published: August 2016

In this paper, TiO2 layers grown on RuO2 by atomic layer deposition (ALD) using tetrakis (dimethyla-mino) titanium (TDMAT) and either oxygen plasma or H2O as oxygen source were analyzed using X-ray diffraction (XRD), Raman spectroscopy, and depth-resolved X-ray Photoelectron spectroscopy (XPS). The main objective is to investigate the surface chemical reactions mechanisms and their influence on the TiO2 film properties. The experimental results using XRD show that ALD deposition using H2O leads to anatase TiO2 whereas a rutile TiO2 is obtained when oxygen-plasma is used as oxygen source. Depth-resolved XPS analysis allows to determine the reaction mechanisms at the RuO2 substrate surface after growth of thin TiO2 layers. Indeed, the XPS analysis shows that when H2O assisted ALD process is used, intermediate Ti2O3 layer is obtained and RuO2 is reduced into Ru as evidenced by high resolution transmission electron microscopy. In this case, there is no possibility to re-oxidize the Ru surface into RuO2 due to the weak oxidation character of H2O and an anatase TiO2 layer is therefore grown on Ti2O3. In contrast, when oxygen plasma is used in the ALD process, its strong oxidation character leads to the re-oxidation of the partially reduced RuO2 following the first Ti deposition step. Consequently, the RuO2 surface is regenerated, allowing the growth of rutile TiO2. A surface chemical reaction scheme is proposed that well accounts for the observed experimental results.
Global structure search for molecules on surfaces: Efficient sampling with curvilinear coordinates
Authors: Krautgasser Konstantin , Panosetti Chiara , Palagin Dennis , Reuter Karsten , Maurer Reinhard J.
Published: August 2016

Efficient structure search is a major challenge in computational materials science. We present a modification of the basin hopping global geometry optimization approach that uses a curvilinear coordinate system to describe global trial moves. This approach has recently been shown to be efficient in structure determination of clusters [C. Panosetti et al., Nano Lett. 15, 8044–8048 (2015)] and is here extended for its application to covalent, complex molecules and large adsorbates on surfaces. The employed automatically constructed delocalized internal coordinates are similar to molecular vibrations, which enhances the generation of chemically meaningful trial structures. By introducing flexible constraints and local translation and rotation of independent geometrical subunits, we enable the use of this method for molecules adsorbed on surfaces and interfaces. For two test systems, trans-β-ionylideneacetic acid adsorbed on a Au(111) surface and methane adsorbed on a Ag(111) surface, we obtain superior performance of the method compared to standard optimization moves based on Cartesian coordinates.
Theoretical and experimental study on electron interactions with chlorobenzene: Shape resonances and differential cross sections
Authors: Barbosa Alessandra Souza , Varella Márcio T. do N. , Sanchez Sergio d’A. , Ameixa João , Blanco Francisco , García Gustavo , Limão-Vieira Paulo , Ferreira da Silva Filipe , Bettega Márcio H. F.
Published: August 2016

In this work, we report theoretical and experimental cross sections for elastic scattering of electrons by chlorobenzene (ClB). The theoretical integral and differential cross sections (DCSs) were obtained with the Schwinger multichannel method implemented with pseudopotentials (SMCPP) and the independent atom method with screening corrected additivity rule (IAM-SCAR). The calculations with the SMCPP method were done in the static-exchange (SE) approximation, for energies above 12 eV, and in the static-exchange plus polarization approximation, for energies up to 12 eV. The calculations with the IAM-SCAR method covered energies up to 500 eV. The experimental differential cross sections were obtained in the high resolution electron energy loss spectrometer VG-SEELS 400, in Lisbon, for electron energies from 8.0 eV to 50 eV and angular range from 7∘ to 110∘. From the present theoretical integral cross section (ICS) we discuss the low-energy shape-resonances present in chlorobenzene and compare our computed resonance spectra with available electron transmission spectroscopy data present in the literature. Since there is no other work in the literature reporting differential cross sections for this molecule, we compare our theoretical and experimental DCSs with experimental data available for the parent molecule benzene.
Pre-ordering of interfacial water in the pathway of heterogeneous ice nucleation does not lead to a two-step crystallization mechanism
Authors: Lupi Laura , Peters Baron , Molinero Valeria
Published: August 2016

According to Classical Nucleation Theory (CNT), the transition from liquid to crystal occurs in a single activated step with a transition state controlled by the size of the crystal embryo. This picture has been challenged in the last two decades by several reports of two-step crystallization processes in which the liquid first produces pre-ordered or dense domains, within which the crystal nucleates in a second step. Pre-ordering preceding crystal nucleation has been recently reported in simulations of ice crystallization, raising the question of whether the mechanism of ice nucleation involves two steps. In this paper, we investigate the heterogeneous nucleation of ice on carbon surfaces. We use molecular simulations with efficient coarse-grained models combined with rare event sampling methods and free energy calculations to elucidate the role of pre-ordering of liquid water at the carbon surface in the reaction coordinate for heterogeneous nucleation. We find that ice nucleation proceeds through a classical mechanism, with a single barrier between liquid and crystal. The reaction coordinate that determines the crossing of the nucleation barrier is the size of the crystal nucleus, as predicted by CNT. Wetting of the critical ice nuclei within pre-ordered domains decreases the nucleation barrier, increasing the nucleation rates. The preferential pathway for crystallization involves the early creation of pre-ordered domains that are the birthplace of the ice crystallites but do not represent a minimum in the free energy pathway from liquid to ice. We conclude that a preferential pathway through an intermediate-order precursor does not necessarily result in a two-step mechanism.
A novel double-focusing time-of-flight mass spectrometer for absolute recoil ion cross sections measurements
Authors: Sigaud L. , de Jesus V. L. B. , Ferreira Natalia , Montenegro E. C.
Published: August 2016

In this work, the inclusion of an Einzel-like lens inside the time-of-flight drift tube of a standard mass spectrometer coupled to a gas cell—to study ionization of atoms and molecules by electron impact—is described. Both this lens and a conical collimator are responsible for further focalization of the ions and charged molecular fragments inside the spectrometer, allowing a much better resolution at the time-of-flight spectra, leading to a separation of a single mass-to-charge unit up to 100 a.m.u. The procedure to obtain the overall absolute efficiency of the spectrometer and micro-channel plate detector is also discussed.
Magnetic cooling close to a quantum phase transition—The case of Er2Ti2O7
Authors: Wolf B. , Tutsch U. , Dörschug S. , Krellner C. , Ritter F. , Assmus W. , Lang M.
Published: August 2016

Magnetic cooling, first introduced in the late twenties of last century, has regained considerable interest recently as a cost-efficient and easy-to-handle alternative to 3He-based refrigeration techniques. Especially, adiabatic demagnetization of paramagnets—the standard materials for magnetic refrigeration—has become indispensable for the present space applications. To match the growing demand for increasing the efficiency in these applications, a new concept for magnetic cooling based on many-body effects around a quantum-critical-point has been introduced and successfully tested [B. Wolf et al., Proc. Natl. Acad. Sci. U.S.A. 108, 6862 (2011)]. By extending this concept to three-dimensional magnetic systems, we present here the magnetothermal response of the cubic pyrochlore material Er2Ti2O7 in the vicinity of its B-induced quantum-critical point which is located around 1.5 T. We discuss performance characteristics such as the range of operation, the efficiency, and the hold time. These figures are compared with those of state-of-the-art paramagnetic coolants and with other quantum-critical systems which differ by the dimensionality of the magnetic interactions and the degree of frustration.
Magneto-acoustic study near the quantum critical point of the frustrated quantum antiferromagnet Cs2CuCl4
Authors: Cong P. T. , Postulka L. , Wolf B. , van Well N. , Ritter F. , Assmus W. , Krellner C. , Lang M.
Published: August 2016

Magneto-acoustic investigations of the frustrated triangular-lattice antiferromagnet Cs2CuCl4 were performed for the longitudinal modes c11 and c33 in magnetic fields along the a-axis. The temperature dependence of the sound velocity at zero field shows a mild softening at low temperature and displays a small kink-like anomaly at TN. Isothermal measurements at T < TN of the sound attenuation α reveal two closely spaced features of different characters on approaching the material's quantum-critical point (QCP) at Bs ≈ 8.5 T for B || a. The peak at slightly lower fields remains sharp down to the lowest temperature and can be attributed to the ordering temperature TN(B). The second anomaly, which is rounded and which becomes reduced in size upon cooling, is assigned to the material's spin-liquid properties preceding the long-range antiferromagnetic ordering with decreasing temperature. These two features merge upon cooling suggesting a coincidence at the QCP. The elastic constant at lowest temperatures of our experiment at 32 mK can be well described by a Landau free energy model with a very small magnetoelastic coupling constant G/kB ≈ 2.8 K. The applicability of this classical model indicates the existence of a small gap in the magnetic excitation spectrum which drives the system away from quantum criticality.
Cation distribution in CuFe2O4 nanoparticles: Effects of Ni doping on magnetic properties
Authors: Thanh Nguyen Kim , Loan To Thanh , Anh Luong Ngoc , Duong Nguyen Phuc , Soontaranon Siriwat , Thammajak Nirawat , Hien Than Duc
Published: August 2016

The Cu1−xNixFe2O4 nanoparticles (with x = 0, 0.3, 0.5, 0.7, and 1) were synthesized by using spray co-precipitation method at annealing temperature Ta = 900 °C in air for 5 h. The crystal structure, microstructure, oxidation state, and magnetic properties of the samples were characterized by using X-ray diffraction, synchrotron X-ray diffraction, scanning electron microscopy, X-ray absorption spectroscopy, and vibrating sample magnetometer. It was shown that all the samples have cubic structure. Lattice constant and grain size decrease, while the Curie temperature TC increases with increasing of Ni2+ content. A small amount of Fe2+ was found in all the samples. Cation distribution was determined by using a combination of magnetization measurements, extended X-ray absorption fine structure analysis, and Rietveld refinement from synchrotron X-ray diffraction data. It was indicated that Ni2+ ions occupy in octahedral site only, while Cu2+ ions distribute in both tetrahedral and octahedral sites. The variation of magnetic parameters is discussed based on Ni2+ concentration, grain size, the cation distribution, surface effect, and the presence of Fe2+ ion in the samples.
An analysis of the growth of silver catalyzed InxGa1−xAs nanowires on Si (100) by metal organic chemical vapor deposition
Authors: Sarkar K. , Palit M. , Chattopadhyay S. , Banerji P.
Published: August 2016

A model is proposed here to understand the nucleation of III–V semiconductor nanowires (NW). Whereas the classical nucleation theory is not adequately sufficient in explaining the evolution of the shape of the NWs under different chemical environment such as flow rate or partial pressure of the precursors, the effect of adsorption and desorption mediated growth, and diffusion limited growth are taken into account to explain the morphology and the crystal structure of InxGa1−xAs nanowires (NW) on Silicon (100) substrates grown by a metalorganic chemical vapor deposition technique. It is found that the monolayer nucleus that originates at the triple phase line covers the entire nucleus-substrate (NS) region at a specific level of supersaturation and there are cases when the monolayer covers a certain fraction of the NS interface. When the monolayer covers the total NS interface, NWs grow with perfect cylindrical morphology and whenever a fraction of the interface is covered by the nucleus, the NWs become curved as observed from high resolution transmission electron microscopy images. The supersaturation, i.e., the chemical potential is found to be governed by the concentration of precursors into the molten silver which in the present case is taken as a catalyst. Our study provides new insights into the growth of ternary NWs which will be helpful in understanding the behavior of growth of different semiconducting NWs.
One-dimensional nonlinear theory for rectangular helix traveling-wave tube
Authors: Fu Chengfang , Wei Yanyu , Zhao Bo , Yang Yudong , Ju Yongfeng
Published: August 2016

A 1-D nonlinear theory of a rectangular helix traveling-wave tube (TWT) interacting with a ribbon beam is presented in this paper. The RF field is modeled by a transmission line equivalent circuit, the ribbon beam is divided into a sequence of thin rectangular electron discs with the same cross section as the beam, and the charges are assumed to be uniformly distributed over these discs. Then a method of computing the space-charge field by solving Green's Function in the Cartesian Coordinate-system is fully described. Nonlinear partial differential equations for field amplitudes and Lorentz force equations for particles are solved numerically using the fourth-order Runge-Kutta technique. The tube's gain, output power, and efficiency of the above TWT are computed. The results show that increasing the cross section of the ribbon beam will improve a rectangular helix TWT's efficiency and reduce the saturated length.
Pseudo-spark switch (PSS) characteristics under different operation conditions
Authors: Hamad B. H. , Lateef K. H. , Ahmad A. K.
Published: August 2016

The present paper concentrates on the characteristics of the pseudospark switch (PSS) designed in a previous work. The special characteristics of PSS make it a replacement for other high voltage switches such as thyratrons and ordinary high-pressure spark gaps. PSS is characterized by short rise time and small jitter time. The pseudo park chamber consists of two hollow cylindrical electrodes made of a stainless steel material (type 306L) separated by an insulator. The insulator used in our design is a glazed ceramic 70 mm in diameter and 3.5 mm in thickness. A PSS with an anode voltage of 29.2 kV, and a current of 3.6 kA and 11 ns rise time was achieved and used successfully at a repetition rate of about 2.2 kHz. A simple trigger circuit designed, built, and used effectively reaching more than 1.56 kV trigger pulse which is sufficient to ignite the argon gas inside the cathode to cause a breakdown. A non-inductive dummy load is designed to be a new technique to find the accurate value of the PSS inductance. A jitter time of ±10 ns pulses is observed to occur in a reliable manner for more than 6 h of continuous operation. In this research, the important parameters of this switch like rise time, peak current, and anode voltage were studied at various values of charging capacitance. The lifetime of this system is depending on the kind of the electrode material and on the type of insulation material in the main gap of the pseudospark switch.
Ideal magnetohydrodynamic theory for localized interchange modes in toroidal anisotropic plasmas
Authors: Shi Tonghui , Zheng L. J. , Wan B. N. , Sun Y. , Shen B. , Qian J. P.
Published: August 2016

Ideal magnetohydrodynamic theory for localized interchange modes is developed for toroidal plasmas with anisotropic pressure. The work extends the existing theories of Johnson and Hastie [Phys. Fluids 31, 1609 (1988)], etc., to the low n mode case, where n is the toroidal mode number. Also, the plasma compressibility is included, so that the coupling of the parallel motion to perpendicular one, i.e., the so-called apparent mass effect, is investigated in the anisotropic pressure case. The singular layer equation is obtained, and the generalized Mercier's criterion is derived.
Time-dependent, multimode interaction analysis of the gyroklystron amplifier
Authors: Swati M. V. , Chauhan M. S. , Jain P. K.
Published: August 2016

In this paper, a time-dependent multimode nonlinear analysis for the gyroklystron amplifier has been developed by extending the analysis of gyrotron oscillators by employing the self-consistent approach. The nonlinear analysis developed here has been validated by taking into account the reported experimental results for a 32.3 GHz, three cavity, second harmonic gyroklystron operating in the TE02 mode. The analysis has been used to estimate the temporal RF growth in the operating mode as well as the nearby competing modes. Device gain and bandwidth have been computed for different drive powers and frequencies. The effect of various beam parameters, such as beam voltage, beam current, and pitch factor, has also been studied. The computational results have estimated the gyroklystron saturated RF power ∼319 kW at 32.3 GHz with efficiency ∼23% and gain ∼26.3 dB with device bandwidth ∼0.027% (8 MHz) for a 70 kV, 20 A electron beam. The computed results are found to be in agreement with the experimental values within 10%.
Spectroscopic analysis of the NIR emission in Tm implanted AlxGa1-xN layers
Authors: Rodrigues J. , Fialho M. , Esteves T. C. , Santos N. F. , Ben Sedrine N. , Rino L. , Neves A. J. , Lorenz K. , Alves E. , Monteiro T.
Published: August 2016

AlxGa1-xN samples, with different AlN molar fractions, x = 0, 0.15, 0.77, and 1, grown by halide vapor phase epitaxy were implanted with Tm ions. Photoluminescence (PL) measurements revealed that after thermal annealing all the samples exhibit intraionic Tm3+ luminescence. In samples with x > 0, the low temperature emission is dominated by the lines that appear in the near infrared (NIR) spectral region, corresponding to the overlapped 1G4 → 3H5 and 3H4 → 3H6 multiplet transitions. A detailed spectroscopic analysis of NIR emission of the thulium implanted and annealed AlxGa1-xN layers is presented by using temperature dependent steady-state PL, room temperature PL excitation, and time resolved PL. The results indicate that the excitonic features sensitive to the alloy disorder are involved in the excitation population processes of the Tm3+ luminescence and the highest thermal stability for the NIR emission occurs for the AlN:Tm sample.
Characterizing the spin orbit torque field-like term in in-plane magnetic system using transverse field
Authors: Luo Feilong , Goolaup Sarjoosing , Li Sihua , Lim Gerard Joseph , Tan Funan , Engel Christian , Zhang Senfu , Ma Fusheng , Zhou Tiejun , Lew Wen Siang
Published: August 2016

In this work, we present an efficient method for characterizing the spin orbit torque field-like term in an in-plane magnetized system using the harmonic measurement technique. This method does not require a priori knowledge of the planar and anomalous hall resistances and is insensitive to non-uniformity in magnetization, as opposed to the conventional harmonic technique. We theoretically and experimentally demonstrate that the field-like term in the Ta/Co/Pt film stack with in-plane magnetic anisotropy can be obtained by an in-plane transverse field sweep as expected, and magnetization non-uniformity is prevented by the application of fixed magnetic field. The experimental results are in agreement with the analytical calculations.
Effects of trapped electrons on the oblique propagation of ion acoustic solitary waves in electron-positron-ion plasmas
Authors: Hafez M. G. , Roy N. C. , Talukder M. R. , Hossain Ali M.
Published: August 2016

The characteristics of the nonlinear oblique propagation of ion acoustic solitary waves in unmagnetized plasmas consisting of Boltzmann positrons, trapped electrons and ions are investigated. The modified Kadomtsev-Petviashivili (mKP) equation is derived employing the reductive perturbation technique. The parametric effects on phase velocity, Sagdeev potential, amplitude and width of solitons, and electrostatic ion acoustic solitary structures are graphically presented with the relevant physical explanations. This study may be useful for the better understanding of physical phenomena concerned in plasmas in which the effects of trapped electrons control the dynamics of wave.
THz elastic dynamics in finite-size CoFeB-MgO phononic superlattices
Authors: Ulrichs Henning , Meyer Dennis , Müller Markus , Wittrock Steffen , Mansurova Maria , Walowski Jakob , Münzenberg Markus
Published: August 2016

In this article, we present the observation of coherent elastic dynamics in a nano-scale phononic superlattice, which consists of only 4 bilayers. We demonstrate how ultra-short light pulses with a length of 40 fs can be utilized to excite a coherent elastic wave at 0.535 THz, which persist over about 20 ps. In later steps of the elastic dynamics, modes with frequency of 1.7 THz and above appear. All these modes are related to acoustic band gaps. Thus, the periodicity strongly manifests in the wave physics, although the system under investigation has only a small number of spatial periods. To further illustrate this, we show how by breaking the translational invariance of the superlattice, these features can be suppressed. Discussed in terms of phonon blocking and radiation, we elucidate in how far our structures can be considered as useful building blocks for phononic devices.
The effect of inter-granular constraints on the response of polycrystalline piezoelectric ceramics at the surface and in the bulk
Authors: Hossain Mohammad J. , Wang Zhiyang , Khansur Neamul H. , Kimpton Justin A. , Oddershede Jette , Daniels John E.
Published: August 2016

The electro-mechanical coupling mechanisms in polycrystalline ferroelectric materials, including a soft PbZrxTi1−xO3 (PZT) and lead-free 0.9375(Bi1/2Na1/2)TiO3-0.0625BaTiO3 (BNT-6.25BT), have been studied using a surface sensitive low-energy (12.4 keV) and bulk sensitive high-energy (73 keV) synchrotron X-ray diffraction with in situ electric fields. The results show that for tetragonal PZT at a maximum electric field of 2.8 kV/mm, the electric-field-induced lattice strain (ε111) is 20% higher at the surface than in the bulk, and non-180° ferroelectric domain texture (as indicated by the intensity ratio I002/I200) is 16% higher at the surface. In the case of BNT-6.25BT, which is pseudo-cubic up to fields of 2 kV/mm, lattice strains, ε111 and ε200, are 15% and 20% higher at the surface, while in the mixed tetragonal and rhombohedral phases at 5 kV/mm, the domain texture indicated by the intensity ratio, I111/I111¯ and I002/I200, are 12% and 10% higher at the surface than in the bulk, respectively. The observed difference in the strain contributions between the surface and bulk is suggested to result from the fact that surface grains are not constrained in three dimensions, and consequently, domain reorientation and lattice expansion in surface grains are promoted. It is suggested that the magnitude of property difference between the surface and bulk is higher for the PZT than for BNT-6.25BT due to the level of anisotropy in the strain mechanism. The comparison of the results from different methods demonstrates that the intergranular constraints have a significant influence on the electric-field-induced electro-mechanical responses in polycrystalline ferroelectrics. These results have implications for the design of higher performance polycrystalline piezoelectrics.
Properties of high-density, well-ordered, and high-energy metallic glass phase designed by pressurized quenching
Authors: Miyazaki Narumasa , Lo Yu-Chieh , Wakeda Masato , Ogata Shigenobu
Published: August 2016

We applied gigapascal-level compressive hydrostatic pressure to the melt-quenching process of metallic glass to obtain a unique high-pressure glass state with high density that is well-ordered yet has high energy. This state contradicts the common understanding that high-density, well-ordered metallic glass states have low energy. Through molecular dynamics simulations, we found that the high-pressure glass state of the metallic glass Zr50Cu40Al10 has a rich anti-free volume and that its relaxation is dominated by the annihilation of full icosahedra and the rich anti-free volume. The aging rate of the high-pressure metallic glass state (energy reduction rate) is almost the same as that of typical high-energy metallic glass, suggesting that it has a lifetime similar to that of a typical high-energy metallic glass that has been experimentally realized and reported previously [Wakeda et al., Sci. Rep. 5, 10545 (2015)]. Thus, the high-pressure phase can be realized even under the experimental cooling rate, suggesting its suitability for practical applications.
Thermodynamic analysis of conductive filaments
Authors: Karpov V. , Niraula D. , Karpov I.
Published: August 2016

We present a thermodynamic theory of the conductive filament growth and dissolution in random access memory describing the observed features of their current-voltage (IV) characteristics. Our theory is based on the self-consisted Fokker-Planck approach reducing the filament kinetics to its thermodynamics. Expressing the observed IV features through material parameters, our results pave a way to device improvements.
Bovine serum albumin detection and quantitation based on capacitance measurements of liquid crystals
Authors: Lin Chi-Hao , Lee Mon-Juan , Lee Wei
Published: August 2016

Liquid crystal (LC)-based biosensing is generally limited by the lack of accurate quantitative strategies. This study exploits the unique electric capacitance properties of LCs to establish quantitative assay methods for bovine serum albumin (BSA) biomolecules. By measuring the voltage-dependent electric capacitance of LCs under an alternating-current field with increasing amplitude, positive correlations were derived between the BSA concentration and the electric capacitance parameters of LCs. This study demonstrates that quantitative analysis can be achieved in LC-based biosensing through electric capacitance measurements extensively employed in LCD research and development.
Flexible, light trapping substrates for organic photovoltaics
Authors: Park Yoonseok , Berger Jana , Tang Zheng , Müller-Meskamp Lars , Lasagni Andrés Fabián , Vandewal Koen , Leo Karl
Published: August 2016

Micro-structured organic photovoltaic (OPV) devices on polyethylene terephthalate substrates are produced using direct laser interference patterning (DLIP). The performance of organic solar cells on these substrates is improved by a factor of 1.16, and a power conversion efficiency of 7.70% is achieved. We show that a shorter spatial period of the pattern allows for a stronger light trapping effect in solar cell, as it leads to a longer light path. Moreover, since the patterned structures are located on the outside of the fully encapsulated OPV devices, there are no problems with the roughness induced shunts.
Short-pulse excitation of microwave plasma for efficient diamond growth
Authors: Yamada Hideaki , Chayahara Akiyoshi , Mokuno Yoshiaki
Published: August 2016

To realize a variety of potential applications of diamonds, particularly in the area of power electronics, it is indispensable to improve their growth efficiency. Most conventional approaches have tried to achieve this simply by increasing the gas temperature; however, this makes it difficult to grow large diamond crystals. To improve the growth efficiency while lowering the gas temperature, we propose that using a pulse-modulated microwave plasma with a sub-millisecond pulse width can enhance the power efficiency of the growth rate of single-crystal diamonds. We found that using a sub-millisecond pulse-mode discharge could almost double the growth rate obtained using continuous mode discharge for a fixed average microwave power and gas pressure. A comparison between experimental observations of the optical emission spectra of the discharge and a numerical simulation of the gas temperature suggests that a decrease in the gas temperature was achieved, and highlights the importance of electron-dominated reactions for obtaining the enhancement of the growth rate. This result will have a large impact in the area of diamond growth because it enables diamond growth to be more power efficient at reduced temperatures.
Direct view at colossal permittivity in donor-acceptor (Nb, In) co-doped rutile TiO2
Authors: Mandal Suman , Pal Somnath , Kundu Asish K. , Menon Krishnakumar S. R. , Hazarika Abhijit , Rioult Maxime , Belkhou Rachid
Published: August 2016

Topical observations of colossal permittivity (CP) with low dielectric loss in donor-acceptor cations co-doped rutile TiO2 have opened up several possibilities in microelectronics and energy-storage devices. Yet, the precise origin of the CP behavior, knowledge of which is essential to empower the device integration suitably, is highly disputed in the literature. From spectromicroscopic approach besides dielectric measurements, we explore that microscopic electronic inhomogeneities along with the nano-scale phase boundaries and the low temperature polaronic relaxation are mostly responsible for such a dielectric behavior, rather than electron-pinned defect-dipoles/grain-boundary effects as usually proposed. Donor-acceptor co-doping results in a controlled carrier-hopping inevitably influencing the dielectric loss while invariably upholding the CP value.
Near-infrared radiation absorption properties of covellite (CuS) using first-principles calculations
Authors: Xiao Lihua , Wu Jianming , Ran Jingyu , Liu Yike , Qiu Wei , Lu Fanghai , Shao Fang , Tang Dongsheng , Peng Ping
Published: August 2016

First-principles density functional theory was used to investigate the electronic structure, optical properties and the origin of the near-infrared (NIR) absorption of covellite (CuS). The calculated lattice constant and optical properties are found to be in reasonable agreement with experimental and theoretical findings. The electronic structure reveals that the valence and conduction bands of covellite are determined by the Cu 3d and S 3p states. By analyzing its optical properties, we can fully understand the potential of covellite (CuS) as a NIR absorbing material. Our results show that covellite (CuS) exhibits NIR absorption due to its metal-like plasma oscillation in the NIR range.
Bait preference for remote camera trap studies of the endangered northern quoll (Dasyurus hallucatus)
Authors: Austin Caitlin , Tuft Katherine , Ramp Daniel , Cremona Teigan , Webb Jonathan K.
Published: August 2016

Estimating population size is crucial for managing populations of threatened species. In the Top End of northern Australia, populations of northern quolls (Dasyurus hallucatus), already affected by livestock grazing, inappropriate burning regimes and predation, have collapsed following the spread of the toxic cane toad (Rhinella marina). Cane toads are currently invading the Kimberley, where they pose a threat to quoll populations. To manage these populations, we need reliable methods for detecting and estimating quoll abundance. We deployed camera traps with lures containing tuna, peanut butter or no bait and found that baited cameras performed better than the unbaited control. Cameras with a tuna lure detected more individuals than cameras baited with peanut butter or no bait. Cameras with a tuna lure yielded more photographs per quoll than those baited with peanut butter or no bait. We identified individual quolls from unique spot patterns and found multiple photographs improved the accuracy of identification. We also found that population estimates for the sample area derived from camera trapping were consistent with those from live trapping using mark–recapture techniques.
Diversity, complementary distributions and taxonomy of Rhagada land snails (Gastropoda : Camaenidae) on the Burrup Peninsula, Western Australia
Authors: Johnson Michael S. , Stankowski Sean , Kendrick Peter G. , Hamilton Zoë R. , Teale Roy J.
Published: August 2016

Phylogenetic diversity of Rhagada land snails is high on the Burrup Peninsula, Western Australia, with four distinct clades, representing three of the four major clades of the Pilbara region. Detailed sampling indicated little geographic overlap of the four clades, conforming to the general rarity of congeneric sympatry in Australian camaenids. The diversity on the Burrup Peninsula includes three previously unclassified morphotypes. One of these lies within the broad endemic clade of the adjacent Dampier Archipelago, and is provisionally assigned to the island species R. perprima, based on phylogenetic evidence. The two other undescribed morphotypes constitute an endemic clade that is the sister group of the broader Dampier Archipelago clade. All COI p-distances within clades are less than 6%, whereas nearly all distances between clades exceed 10%, the gap corresponding to differences among species of Rhagada generally. One morphotype in the Burrup Peninsula endemic clade has a low spire and a distinctive keel, and is restricted to a single rockpile. Detailed local sampling revealed gradation between this form and the more widely distributed globose morphotype. On the basis of genetic similarity and morphological continuity, we describe the morphologically variable endemic Burrup Peninsula clade as Rhagada ngurrana, sp. nov., which has a distribution spanning only 9 km.
Archaeal flagellin combines a bacterial type IV pilin domain with an Ig-like domain
Authors: Braun Tatjana , Vos Matthijn R. , Kalisman Nir , Sherman Nicholas E. , Rachel Reinhard , Wirth Reinhard , Schröder Gunnar F. , Egelman Edward H.
Published: August 2016

Significance

Bacterial motility has been studied for many years, but much less is known about the flagellar system in archaea that provides motility. We have determined the structure of a flagellar-like filament from an archaeon using cryo-EM and can show how it has evolved combining domains from two different protein families. The mechanical properties of the filament are now explained from a computational analysis of the atomic model that we have been able to build. These results provide insights into how motile systems can arise by convergent evolution.
Against the new Cartesian Circle
Authors: Fulmer Everett , Ragland C.P.
Published: August 2016

In two recent papers, Michael Della Rocca accuses Descartes of reasoning circularly in the Fourth Meditation. This alleged new circle is distinct from, and more vicious than, the traditional Cartesian Circle arising in the Third Meditation. We explain Della Rocca’s reasons for this accusation, showing that his argument is invalid.
Microstructure and properties of lead-free brasses using post-processing heat treatment cycles
Authors: Toulfatzis A. I. , Pantazopoulos G. A. , Paipetis A. S.
Published: August 2016

We report the tailoring of the microstructure of lead-free brasses with a view to improving their machinability via the controlled augmentation of the β-phase. This should be performed while keeping the mechanical properties within the EN standard, as β-phase augmentation can lead to embrittlement. Twenty seven heat treatment protocols were performed in order to transform the microstructure and consequently modify the properties of three lead-free brasses. The most successful heat treatment was chosen for each studied alloy according to the above criteria. The selected protocols led to a combination of β-phase augmentation with mechanical properties conforming to standards providing a promising ground for improved machinability performance.

This paper is part of a Themed Issue on Brass Alloys.
Evaluation of a Sterile-Male Release Technique: A Case Study of Invasive Sea Lamprey Control in a Tributary of the Laurentian Great Lakes
Authors: Bravener Gale , Twohey Michael
Published: August 2016

Invasive species can have detrimental impacts on native species and ecosystem services for humans. A technique that involves sterilization and release of males into wild populations of the same species can be useful in the control of invasive or pest species. A sterile-male release technique (SMRT) was used on a novel vertebrate system, the invasive Sea Lamprey Petromyzon marinus in the Great Lakes, in an attempt to control population size. Sea Lamprey populations in the Great Lakes have been suppressed since the 1950s by (1) pesticide applications to kill larvae in streams and (2) barriers to block upstream spawning migrations. Here, we present a literature review and meta-analysis of the SMRT by using a case study from the St. Marys River, where the SMRT was applied as an experimental method of Sea Lamprey control from 1991 to 2011. Observations obtained from the St. Marys River during and after SMRT application were used to evaluate whether the SMRT was effective at suppressing reproduction. Males were successfully sterilized and exhibited normal mating behaviors. The survival of embryos in nests was lower during the years when the SMRT was applied (32%) than during the post-SMRT period (67%). The overall distribution of embryo viability in the river shifted after the SMRT was applied. During the SMRT application period, the observed ratios of sterile males to normal (fertile) males on nests were significantly different than expected, possibly due to an underestimation of adult Sea Lamprey abundance in the St. Marys River. Even at lower sterile male : normal male ratios, the number of viable embryos produced would have declined, but the level of reproductive suppression required to overcome recruitment variability was unclear. We discuss the effectiveness of the SMRT as it pertains to the Sea Lamprey, and we highlight difficulties in data interpretation and provide future direction for similar control programs.

Received December 1, 2015; accepted June 16, 2016 Published online August 31, 2016
Vitamin B1-deficient mice show impairment of hippocampus-dependent memory formation and loss of hippocampal neurons and dendritic spines: potential microendophenotypes of Wernicke–Korsakoff syndrome
Authors: Inaba Hiroyoshi , Kishimoto Takuya , Oishi Satoru , Nagata Kan , Hasegawa Shunsuke , Watanabe Tamae , Kida Satoshi
Published: August 2016

Patients with severe Wernicke–Korsakoff syndrome (WKS) associated with vitamin B1 (thiamine) deficiency (TD) show enduring impairment of memory formation. The mechanisms of memory impairment induced by TD remain unknown. Here, we show that hippocampal degeneration is a potential microendophenotype (an endophenotype of brain disease at the cellular and synaptic levels) of WKS in pyrithiamine-induced thiamine deficiency (PTD) mice, a rodent model of WKS. PTD mice show deficits in the hippocampus-dependent memory formation, although they show normal hippocampus-independent memory. Similarly with WKS, impairments in memory formation did not recover even at 6 months after treatment with PTD. Importantly, PTD mice exhibit a decrease in neurons in the CA1, CA3, and dentate gyrus (DG) regions of the hippocampus and reduced density of wide dendritic spines in the DG. Our findings suggest that TD induces hippocampal degeneration, including the loss of neurons and spines, thereby leading to enduring impairment of hippocampus-dependent memory formation.
Welding of unique and advanced alloys for space and high-temperature applications: welding and weldability of iridium and platinum alloys
Authors: David S. A. , Miller R. G. , Feng Z.
Published: August 2016

In the last five decades, significant advances have been made in developing alloys for space power systems for spacecraft that travel long distances to various planets. The spacecraft are powered by radioisotope thermoelectric generators (RTGs). The fuel element in RTGs is plutonia. For safety and containment of the radioactive fuel element, the heat source is encapsulated in iridium or platinum alloys. Ir and Pt alloys are the alloys of choice for encapsulating radioisotope fuel pellets. Ir and Pt alloys were chosen because of their high-temperature properties and compatibility with the oxide fuel element and the graphite impact shells. This review addresses the alloy design and welding and weldability of Ir and Pt alloys for use in RTGs.