bluuebunny/crossref_metadata_2025 huggingface dataset:
Direct measurement of transversely isotropic DNA nanotube by force–distance curve‐based atomic force microscopy
Authors: Ma Zhipeng , Kim Young‐Joo , Park Seongsu , Hirai Yoshikazu , Tsuchiya Toshiyuki , Kim Do‐Nyun , Tabata Osamu
Published: October 2015

DNA origami is one of the most promising ways to create novel two‐dimensional (2D) and 3D structures, assemble inorganic and organic materials, and synthesise functional micro/nano systems. In particular, DNA origami structures consisting of nanotube configurations can function as mechanical components for encapsulating materials such as gold particles or drug proteins, due to their tubular structure, relatively high rigidity, high aspect ratio and other desirable characteristics, but certain mechanical properties such as radial rigidity have yet to be fully determined experimentally. A report is presented on the direct measurement of the radial modulus of a DNA nanotube structure by force–distance curve‐based atomic force microscopy, in a magnesium ion solution. A Hertz model, corrected using the finite‐element method to achieve greater realism, was employed to determine the DNA nanotube's actual radial modulus in two states, corresponding to the rigidity of a porous and electrostatically repulsive nanotube lattice, and the rigidity of a packed and elastic honeycomb lattice. Furthermore, the biphasic radial modulus was verified by estimation of the inter‐helix electrostatic force and torsional rigidity of a six‐helix DNA nanotube, with results comparable to those reported elsewhere. The anisotropy of the DNA nanotube honeycomb lattice revealed by the authors’ radial measurements should be useful when developing new DNA structures and may enable further applications that utilise DNA origami structures as a mechanical component.
Peeling condition analysis of biomimetic adhesive structure – a finite element study
Authors: Hung Chih Yi , Sung Cheng Kuo
Published: October 2015

Gecko and many insects have nanoscale fibrillary structures on their feet serving as adhesive devices. In recent years, van der Waals interaction has been proven to be the primary molecular origin for this kind of phenomena. However, the peeling zone and the cohesive zone both play significant roles in the peeling process while the peeling zone can be described by van der Waals force and the cohesive zone is dependent of molecular interaction. In this reported work, the case of peeling of two elastic bodies, in which the pull‐off force depends linearly on the cohesive stress and is independent of the work of adhesion is considered. The adhesion interaction and peeling condition between a single biomimetic adhesive structure and a substrate is simulated as an axisymmetric geometries model, by encoding van der Waals force and molecular interaction in COMSOL software. The simulation takes theoretical fundamental equations as inputs, and by varying relative peel angles, functional variables are built to estimate peeling processes of the biomimetic adhesive structure in various conditions. The results show that the maximum pull‐off force of the structure with different materials and pull‐off force is decreasing in the peeling process but the cohesive force immediately raises while the contact area becomes smaller. Stress concentration occurs both on the top and at the base of the structure during the peeling process. The simulation results demonstrate that an optimal shape of the adhesive structure can be achieved by examining the simulated pull‐off forces. To avoid failure occurring during the peeling process, the structure with a large base can decrease the stress concentrate at the bottom. Based on the analysis, the adhesive structure with an optimised half‐hourglass shape is proposed.
Biological particle manipulation: an example of Jurkat enrichment
Authors: Altinagac Emre , Kizil Huseyin , Trabzon Levent
Published: October 2015

Dielectrophoresis‐based separation of microparticles and living cells are studied with computational and experimental methods. The flow behaviours of particles are modelled and simulated using COMSOL Multiphysics 4.3a software (COMSOL Ltd). Lab‐on‐a‐chip devices having a titanium (Ti) interdigitated electrode layer on a glass substrate and a PDMS microchannel are fabricated to investigate the most effective design for separating particles based on their sizes. Polystyrene particles in different diameters (3.2 and 9.8 µm) are used in the experiments. Green polystyrene particles from red ones are fully separated in a current design. Enrichment of Jurkat cells having 10.1 average diameter in phosphate buffer solution (PBS) medium is achieved.
Micro‐electro‐mechanical systems capacitive ultrasonic transducer with a higher electromechanical coupling coefficient
Authors: Miao Jing , Shen Wenjiang , He Changde , Xue Chenyang , Xiong Jijun
Published: October 2015

Since the proposing of capacitive micromachined ultrasonic transducer by Khuri Yakub group in 1994 that this kind of transducer occupying the advantages of wide bandwidth, impedance matching well with the propagation medium especially in fluid and air and high sensitivity, has shown a great potential for wide ranges of applications. This Letter reports kind of micro‐electro‐mechanical systems (MEMS) capacitive ultrasonic transducer with the novel cavities embedded in the device layer of silicon on insulator wafer bonded with a glass substrate. The optimum geometric dimensions are confirmed by both mechanical vibrating of the membrane and the electrical characteristics analysis. Finite‐element analysis is adopted to determine the operation mode. The safety and reliability of the proposed device is ensured by the obtained deflections and equivalent stress under operation/collapse voltage. The bottom electrodes of the proposed transducer are fabricated on the top surface of the glass substrate. The parallel parasitic capacitance is reduced, thus improving the electromechanical coupling coefficient. The test results show that the electromechanical coupling coefficient is 69.65%, which demonstrates that this proposed MEMS capacitive ultrasonic transducer structure can enhance the performance significantly.
Microfluidic chip using foil‐assisted CO2 laser ablation for suspended particle separation
Authors: Chung Chen‐Kuei , Long H.P. , Lai C.C.
Published: October 2015

Separation is one of the important pretreatment processes during detection in lab‐on‐a‐chip. In this reported work, polydimethylsiloxane (PDMS) on a glass microchip with a combination of the spiral channel and backward facing step structure was designed to optimise the separation of suspended particles without any extra active powers of the electric or magnetic field. The spiral microfluidic chip was fabricated first by the foil‐assisted CO2 laser ablated polymethylmethacrylate (PMMA) master mould, followed by repetitive PDMS moulding and then bonded to a glass substrate. The CO2 laser ablation of PMMA in air normally generated poor surface quality comprising bulges and scorches. The metal‐foil‐assisted laser ablation can effectively improve the above defects with conducting cover protection. The average height of the bulges was reduced from 5.0 to 1.5 μm and the channel width was reduced from 230 to 120 μm. The finished separation chips were operated at various syringe‐controlled flow rates of 5–20 µL/min to test the performance. A high separation efficiency of about 99% could be achieved within a certain flow range of less than 15 µL/min under the simple structure with low‐cost and time‐saving.
Gate dielectric material dependence of current‐voltage characteristics of ballistic Schottky barrier graphene nanoribbon field‐effect transistor and carbon nanotube field‐effect transistor for different channel lengths
Authors: Ahmed Sheikh , Shawkat Mashiyat , Chowdhury Md. Iramul , Mominuzzaman Sharif
Published: October 2015

Currently, the advancement of silicon transistor technology is being hindered by different issues such as scaling limits. It has become imperative to replace existing silicon technology with new technology to continue the scaling of MOSFETs. Thus, new materials and new production techniques are being studied laboriously to continue the trend set by Moore's Law. The graphene nanoribbon (GNR) and the carbon nanotube (CNT) are two such promising materials that can replace silicon in future MOSFETs. A study has been conducted of the effect of the relative dielectric constant on the device performances of a ballistic Schottky barrier GNR field‐effect transistor (GNRFET) and a CNT field‐effect transistor (CNTFET) for two different channel lengths and a comparative analysis between the two transistors is provided. When a gate material with a high relative dielectric constant is used in FETs, it has been observed that both the transistors show higher on‐state drain currents for the different channel lengths. Moreover, the on and off‐state current ratios and transconductance for the GNRFET and the CNTFET are calculated and plotted for further differentiation between the performances of the GNRFET and the CNTFET.
Jagged discharge electrodes powered by triboelectric generator
Authors: Yu Bocheng , Han Mengdi , Chen Haotian , Su Zongming , Zhang Jinxin , Zhang Haixia
Published: October 2015

This Letter proposes jagged discharge electrode with low discharge voltage, which is fabricated by the MEMS fabrication technique. The voltage multiplier, as energy accumulation module, was analysed and modified. Finite‐element analysis has been done for simulating the arc generation. The discharge form of this device was investigated through the damage on the two electrodes by microscopic images. An encapsulated liquid‐based triboelectric generator was utilised to charge high voltage for self‐powering the system. This novel discharge system is promising for applications in sterilisation, ozone production and arc lightening.
Size‐tunable synthesis of mono‐disperse wastewater‐derived carbon spheres with polyacrylamide as a directing agent
Authors: Tang Chuanqiu , Zhang Pingping , Sun Yong , Bai Li
Published: October 2015

Highly mono‐disperse carbon spheres (CSs) with a tunable diameter of 300–4000 nm are shown to be successfully synthesised using sugar‐rich wastewater as carbon sources and polyacrylamide (PAM) as a size‐controlling agent. The effects of PAM and pH on the morphology and size were also investigated. Experimental results showed that PAM acted as a size‐directing agent which directs the self‐assembly of sugar from wastewater to form the spheroidal particles. The size of CSs could be increased from 300 to 600 nm without any alteration in the morphologies by altering the solution pH from 7 to 12. Furthermore, the size of spheroidal carbon particles can be easily controlled by increasing the concentration of PAM from 0.05 to 0.1% (w/v) at pH 12. The largest sizes of CSs grew nearly 4000 nm without damage to their morphology or broadening of their size distribution with the addition of 0.1% PAM. On the basis of the experimental results, a mechanism is proposed to elucidate the formation of CSs with a wide diameter range. It is believed that this work not only provides a novel potential way to utilise wastewater, but also puts forward a facile sustainable approach to synthesise size‐controllable CSs.
Investigation of thermal effects in a resonance condition of microfibre double‐knot resonators as high‐order filter
Authors: Nodehi Somayeh , Mohammed Waleed Soliman , Ahmad Harith , Harun Sulaiman Wadi
Published: October 2015

Theoretical and experimental investigations are conducted into the thermal effect on resonance conditions of microfibre double‐knot resonators. A double‐knot microfibre resonator which utilises heat for optical path correction is introduced to increase the finesse. The proposed resonator consists of two knots with radii of 357.66 and 357.73 µm which are placed in series. Each individual knot has a finesse of 5 and an extinction ratio of 6 dB. When placed in series, the extinction ratio of the comb spectrum varies from 3.5 to 15 dB by controlling the resonance wavelength of both knots through optical correction. Optical path correction is implemented by placing a hot metal bar with a temperature of 30°C close to the smallest knot. This path resulted in a flat comb spectrum with a high extinction ration of 15 dB. The produced resonance has an unchanged free spectral range of 715 pm, a quality factor of 20 000, FWHD of 85 pm and a finesse of 9.5.
Determining the pivotal plane of fluid lipid membranes in simulations
Authors: Wang Xin , Deserno Markus
Published: October 2015

Each leaflet of a curved lipid membrane contains a surface at which the area strain vanishes, the so-called pivotal plane. Its distance z0 from the bilayer’s midplane arises in numerous contexts, for instance the connection between monolayer and bilayer moduli, stress-profile moments, or area-difference elasticity theories. Here, we propose two precise methods for determining the location of the pivotal plane in computer simulations, both of which rely on monitoring the lipid imbalance across a curved bilayer. The first method considers the ratio of lipid number between the two leaflets of cylindrical or spherical vesicles; it hence requires lipid flip-flop for equilibration. The second method looks at the leaflet difference across local sections cut out from a buckled membrane; this observable equilibrates even in the absence of flip-flop. We apply our methods to two different coarse-grained lipid models, the generic three-bead solvent-free Cooke model and a ten-bead representation of dimyristoylphosphocholine with the explicit solvent MARTINI model. The Cooke model is amenable to both methods and gives results that agree at the percent level. Using it, we also show that the pivotal plane moves outward as lipid curvature becomes more positive. The MARTINI model can only be analyzed with the buckling method; the obtained value z0 = 0.850(11) nm lies about 0.4 nm inwards of the glycerol backbone and is hence unexpectedly small. We attribute this to limitations of the coarse-grained description, suggesting that the location of the pivotal plane might be a good indicator for how well lipid models capture the microscopic origins of curvature elasticity. Finally, we also show that the pivotal plane position itself moves as the membrane is bent. The leading correction is linear in curvature, dependent on the Poisson ratio, and can matter when analyzing experimental results obtained from highly curved inverse hexagonal phases.
Simulation of space charge compensation in a multibeamlet negative ion beam
Authors: Sartori E. , Maceina T. J. , Veltri P. , Cavenago M. , Serianni G.
Published: October 2015

Ion beam space charge compensation occurs by cumulating in the beam potential well charges having opposite polarity, usually generated by collisional processes. In this paper we investigate the case of a H− ion beam drift, in a bi-dimensional approximation of the NIO1 (Negative Ion Optimization phase 1) negative ion source. H− beam ion transport and plasma formation are studied via particle-in-cell simulations. Differential cross sections are sampled to determine the velocity distribution of secondary particles generated by ionization of the residual gas (electrons and slow H2+ ions) or by stripping of the beam ions (electrons, H, and H+). The simulations include three beamlets of a horizontal section, so that multibeamlet space charge and secondary particle diffusion between separate generation regions are considered, and include a repeller grid biased at various potentials. Results show that after the beam space charge is effectively screened by the secondary plasma in about 3 μs (in agreement with theoretical expectations), a plasma grows across the beamlets with a characteristic time three times longer, and a slight overcompensation of the electric potential is verified as expected in the case of negative ions.
Spherical quartz crystals investigated with synchrotron radiation
Authors: Pereira N. R. , Macrander A. T. , Hill K. W. , Baronova E. O. , George K. M. , Kotick J.
Published: October 2015

The quality of x-ray spectra and images obtained from plasmas with spherically bent crystals depends in part on the crystal’s x-ray diffraction across the entire crystal surface. We employ the energy selectivity and high intensity of synchrotron radiation to examine typical spherical crystals from alpha-quartz for their diffraction quality, in a perpendicular geometry that is particularly convenient to examine sagittal focusing. The crystal’s local diffraction is not ideal: the most noticeable problems come from isolated regions that so far have failed to correlate with visible imperfections. Excluding diffraction from such problem spots has little effect on the focus beyond a decrease in background.
Determination of the effective diffusivity of water in a poly (methyl methacrylate) membrane containing carbon nanotubes using kinetic Monte Carlo simulations
Authors: Mermigkis Panagiotis G. , Tsalikis Dimitrios G. , Mavrantzas Vlasis G.
Published: October 2015

A kinetic Monte Carlo (kMC) simulation algorithm is developed for computing the effective diffusivity of water molecules in a poly(methyl methacrylate) (PMMA) matrix containing carbon nanotubes (CNTs) at several loadings. The simulations are conducted on a cubic lattice to the bonds of which rate constants are assigned governing the elementary jump events of water molecules from one lattice site to another. Lattice sites belonging to PMMA domains of the membrane are assigned different rates than lattice sites belonging to CNT domains. Values of these two rate constants are extracted from available numerical data for water diffusivity within a PMMA matrix and a CNT pre-computed on the basis of independent atomistic molecular dynamics simulations, which show that water diffusivity in CNTs is 3 orders of magnitude faster than in PMMA. Our discrete-space, continuum-time kMC simulation results for several PMMA-CNT nanocomposite membranes (characterized by different values of CNT length L and diameter D and by different loadings of the matrix in CNTs) demonstrate that the overall or effective diffusivity, Deff, of water in the entire polymeric membrane is of the same order of magnitude as its diffusivity in PMMA domains and increases only linearly with the concentration C (vol. %) in nanotubes. For a constant value of the concentration C, Deff is found to vary practically linearly also with the CNT aspect ratio L/D. The kMC data allow us to propose a simple bilinear expression for Deff as a function of C and L/D that can describe the numerical data for water mobility in the membrane extremely accurately. Additional simulations with two different CNT configurations (completely random versus aligned) show that CNT orientation in the polymeric matrix has only a minor effect on Deff (as long as CNTs do not fully penetrate the membrane). We have also extensively analyzed and quantified sublinear (anomalous) diffusive phenomena over small to moderate times and correlated them with the time needed for penetrant water molecules to explore the available large, fast-diffusing CNT pores before Fickian diffusion is reached.
Oscillatory solitons of U(1)-invariant mKdV equations. I. Envelope speed and temporal frequency
Authors: Anco Stephen C. , Sattar Mia Abdus , Willoughby Mark R.
Published: October 2015

Harmonically modulated complex solitary waves which are a generalized type of envelope soliton (herein called oscillatory solitons) are studied for the two U(1)-invariant integrable generalizations of the modified Korteweg-de Vries equation, given by the Hirota equation and the Sasa-Satsuma equation. A bilinear formulation of these two equations is used to derive the oscillatory 1-soliton and 2-soliton solutions, which are then written out in a physical form parameterized in terms of their speed, modulation frequency, and phase. Depending on the modulation frequency, the speeds of oscillatory waves (1-solitons) can be positive, negative, or zero, in contrast to the strictly positive speed of ordinary solitons. When the speed is zero, an oscillatory wave is a time-periodic standing wave. Properties of the amplitude and phase of oscillatory 1-solitons are derived. Oscillatory 2-solitons are graphically illustrated to describe collisions between two oscillatory 1-solitons in the case when the speeds are distinct. In the special case of equal speeds, oscillatory 2-solitons are shown to reduce to harmonically modulated breather waves.
Optical diagnostic and electrical analysis in dusty RF discharges containing plasmoids
Authors: Lagrange J. F. , Géraud-Grenier I. , Faubert F. , Massereau-Guilbaud V.
Published: October 2015

The presence of hydrogenated carbon nitride a-CNx:H particles confined in an argon dusty discharge induces the appearance of instabilities. Those instabilities, also called plasmoids, are luminous regions which move through the plasma and rotate around the biased electrode circumference. Electrical characteristics of the plasma have been used to evidence the presence of dust particles and to demonstrate that plasmoid appearance is triggered by particles. The light emitted by the plasma is analysed by optical emission spectroscopy. This paper presents the spatial distribution of excited species, such as CN, Ar I… between electrodes both inside plasmoids and in the surrounding dusty plasma. Obtained results allow to get information for the electron energy distribution function. Moreover, the interplay between plasmoid behaviour and particle presence in the plasma is shown.
First-principles equation of state and electronic properties of warm dense oxygen
Authors: Driver K. P. , Soubiran F. , Zhang Shuai , Militzer B.
Published: October 2015

We perform all-electron path integral Monte Carlo (PIMC) and density functional theory molecular dynamics (DFT-MD) calculations to explore warm dense matter states of oxygen. Our simulations cover a wide density-temperature range of 1–100 g cm−3 and 104–109 K. By combining results from PIMC and DFT-MD, we are able to compute pressures and internal energies from first-principles at all temperatures and provide a coherent equation of state. We compare our first-principles calculations with analytic equations of state, which tend to agree for temperatures above 8 × 106 K. Pair-correlation functions and the electronic density of states reveal an evolving plasma structure and ionization process that is driven by temperature and density. As we increase the density at constant temperature, we find that the ionization fraction of the 1s state decreases while the other electronic states move towards the continuum. Finally, the computed shock Hugoniot curves show an increase in compression as the first and second shells are ionized.
Adsorption and diffusion of Ru adatoms on Ru(0001)-supported graphene: Large-scale first-principles calculations
Authors: Han Yong , Evans James W.
Published: October 2015

Large-scale first-principles density functional theory calculations are performed to investigate the adsorption and diffusion of Ru adatoms on monolayer graphene (G) supported on Ru(0001). The G sheet exhibits a periodic moiré-cell superstructure due to lattice mismatch. Within a moiré cell, there are three distinct regions: fcc, hcp, and mound, in which the C6-ring center is above a fcc site, a hcp site, and a surface Ru atom of Ru(0001), respectively. The adsorption energy of a Ru adatom is evaluated at specific sites in these distinct regions. We find the strongest binding at an adsorption site above a C atom in the fcc region, next strongest in the hcp region, then the fcc-hcp boundary (ridge) between these regions, and the weakest binding in the mound region. Behavior is similar to that observed from small-unit-cell calculations of Habenicht et al. [Top. Catal. 57, 69 (2014)], which differ from previous large-scale calculations. We determine the minimum-energy path for local diffusion near the center of the fcc region and obtain a local diffusion barrier of ∼0.48 eV. We also estimate a significantly lower local diffusion barrier in the ridge region. These barriers and information on the adsorption energy variation facilitate development of a realistic model for the global potential energy surface for Ru adatoms. This in turn enables simulation studies elucidating diffusion-mediated directed-assembly of Ru nanoclusters during deposition of Ru on G/Ru(0001).
Kinematic analysis of in situ measurement during chemical mechanical planarization process
Authors: Li Hongkai , Wang Tongqing , Zhao Qian , Meng Yonggang , Lu Xinchun
Published: October 2015

Chemical mechanical planarization (CMP) is the most widely used planarization technique in semiconductor manufacturing presently. With the aid of in situ measurement technology, CMP tools can achieve good performance and stable productivity. However, the in situ measurement has remained unexplored from a kinematic standpoint. The available related resources for the kinematic analysis are very limited due to the complexity and technical secret. In this paper, a comprehensive kinematic analysis of in situ measurement is provided, including the analysis model, the measurement trajectory, and the measurement time of each zone of wafer surface during the practical CMP process. In addition, a lot of numerical calculations are performed to study the influences of main parameters on the measurement trajectory and the measurement velocity variation of the probe during the measurement process. All the efforts are expected to improve the in situ measurement system and promote the advancement in CMP control system.
Strain induced room temperature ferromagnetism in epitaxial magnesium oxide thin films
Authors: Jin Zhenghe , Nori Sudhakar , Lee Yi-Fang , Kumar D. , Wu Fan , Prater J. T. , Kim Ki Wook , Narayan Jagdish
Published: October 2015

We report on the epitaxial growth and room-temperature ferromagnetic properties of MgO thin films deposited on hexagonal c-sapphire substrates by pulsed laser deposition. The epitaxial nature of the films has been confirmed by both θ-2θ and φ-scans of X-ray diffraction pattern. Even though bulk MgO is a nonmagnetic insulator, we have found that the MgO films exhibit ferromagnetism and hysteresis loops yielding a maximum saturation magnetization up to 17 emu/cc and large coercivity, Hc = 1200 Oe. We have also found that the saturation magnetization gets enhanced and that the crystallization degraded with decreased growth temperature, suggesting that the origin of our magnetic coupling could be point defects manifested by the strain in the films. X-ray (θ-2θ) diffraction peak shift and strain analysis clearly support the presence of strain in films resulting from the presence of point defects. Based on careful investigations using secondary ion mass spectrometer and X-ray photoelectron spectroscopy studies, we have ruled out the possibility of the presence of any external magnetic impurities. We discuss the critical role of microstructural characteristics and associated strain on the physical properties of the MgO films and establish a correlation between defects and magnetic properties.
Time dependent semiclassical tunneling through one dimensional barriers using only real valued trajectories
Authors: Herman Michael F.
Published: October 2015

The time independent semiclassical treatment of barrier tunneling has been understood for a very long time. Several semiclassical approaches to time dependent tunneling through barriers have also been presented. These typically involve trajectories for which the position variable is a complex function of time. In this paper, a method is presented that uses only real valued trajectories, thus avoiding the complications that can arise when complex trajectories are employed. This is accomplished by expressing the time dependent wave packet as an integration over momentum. The action function in the exponent in this expression is expanded to second order in the momentum. The expansion is around the momentum, p0*, at which the derivative of the real part of the action is zero. The resulting Gaussian integral is then taken. The stationary phase approximation requires that the derivative of the full action is zero at the expansion point, and this leads to a complex initial momentum and complex tunneling trajectories. The “pseudo-stationary phase” approximation employed in this work results in real values for the initial momentum and real valued trajectories. The transmission probabilities obtained are found to be in good agreement with exact quantum results.
Size and shape of grain boundary network components and their atomic structures in polycrystalline nanoscale materials
Authors: Xu Tao , Li Mo
Published: October 2015

Microstructure in polycrystalline materials is composed of grain boundary plane, triple junction line, and vertex point. They are the integral parts of the grain boundary network structure and the foundation for the structure-property relations. In polycrystalline, especially nanocrystalline, materials, it becomes increasingly difficult to probe the atomistic structure of the microstructure components directly in experiment due to the size limitation. Here, we present a numerical approach using pair correlation function from atomistic simulation to obtain the detailed information for atomic order and disorder in the grain boundary network in nanocrystalline materials. We show that the atomic structures in the different microstructural components are related closely to their geometric size and shape, leading to unique signatures for atomic structure in microstructural characterization at nanoscales. The dependence varies systematically with the characteristic dimension of the microstructural component: liquid-like disorder is found in vertex points, but a certain order persists in triple junctions and grain boundaries along the extended dimensions of these microstructure components.
Elimination of a spiral wave pinned at an obstacle by a train of plane waves: Effect of diffusion between obstacles and surrounding media
Authors: Tanaka Masanobu , Hörning Marcel , Kitahata Hiroyuki , Yoshikawa Kenichi
Published: October 2015

In excitable media such as cardiac tissue and Belousov-Zhabotinsky reaction medium, spiral waves tend to anchor (pin) to local heterogeneities. In general, such pinned waves are difficult to eliminate and may progress to spatio-temporal chaos. Heterogeneities can be classified as either the absence or presence of diffusive interaction with the surrounding medium. In this study, we investigated the difference in the unpinning of spiral waves from obstacles with and without diffusive interaction, and found a profound difference. The pacing period required for unpinning at fixed obstacle size is larger in case of diffusive obstacles. Further, we deduced a generic theoretical framework that can predict the minimal unpinning period. Our results explain the difference in pacing periods between for the obstacles with and without diffusive interaction, and the difference is interpreted in terms of the local decrease of spiral wave velocity close to the obstacle boundary caused in the case of diffusive interaction.
Pulsed electron beam propagation in argon and nitrogen gas mixture
Authors: Kholodnaya G. E. , Sazonov R. V. , Ponomarev D. V. , Remnev G. E. , Zhirkov I. S.
Published: October 2015

The paper presents the results of current measurements for the electron beam, propagating inside a drift tube filled in with a gas mixture (Ar and N2). The experiments were performed using the TEA-500 pulsed electron accelerator. The main characteristics of electron beam were as follows: 60 ns pulse duration, up to 200 J energy, and 5 cm diameter. The electron beam propagated inside the drift tube assembled of three sections. Gas pressures inside the drift tube were 760 ± 3, 300 ± 3, and 50 ± 1 Torr. The studies were performed in argon, nitrogen, and their mixtures of 33%, 50%, and 66% volume concentrations, respectively.
Influence of the lattice strain decay on the diameter of self assembled secondary phase nanorod array in epitaxial films
Authors: Shi Jack J. , Wu Judy Z.
Published: October 2015

A theoretical model based on an analytical solution of the elastic energy of strained lattices is developed to study the diameter of self-assembled vertically-aligned secondary phase nanorods in epitaxial films. In this model, the nanorod diameter is calculated by minimizing the energy due to the formation of the nanorods, the elastic energy of the film and nanorod lattices, and the interfacial energy on the nanorod surface. The calculated nanorod diameter is consistent with experimental measurements of BaZrO3 and BaSnO3 nanorods in YBa2Cu3O7−δ films with different nanorod densities. The primary mechanism that determines the nanorod diameter is found, for the first time, to be the lattice strain decay inside the nanorods, which depends only on the ratios of elastic constants of nanorod material and is independent of film/nanorod lattice mismatch. The discovered correlation between the nanorod diameter and the elastic properties of the secondary phase oxides can be used as a guidance in the quest of the self-assembled nanorods with different diameters in epitaxial nanocomposite films.
Terahertz dielectric response of photoexcited carriers in Si revealed via single-shot optical-pump and terahertz-probe spectroscopy
Authors: Minami Yasuo , Horiuchi Kohei , Masuda Kaisei , Takeda Jun , Katayama Ikufumi
Published: October 2015

We have demonstrated accurate observations of terahertz (THz) dielectric response due to photoexcited carriers in a Si plate via single-shot optical-pump and THz-probe spectroscopy. In contrast to conventional THz time-domain spectroscopy, this spectroscopic technique allows single-shot detection of the THz response of materials at a given delay time between the pump and THz pulses, thereby sufficiently extending the time interval between the pump pulses. As a result, we can accurately measure the dielectric properties of materials, while avoiding artifacts in the response caused by the accumulation of long-lived photoexcited carriers. Using our single-shot scheme, the transmittance of a Si plate was measured in the range of 0.5–2.5 THz with different pump fluences. Based on a Drude model analysis, the optically induced complex dielectric constant, plasma frequency, and damping rate in the THz region were quantitatively evaluated.
Tailoring superelasticity of soft magnetic materials
Authors: Cremer Peet , Löwen Hartmut , Menzel Andreas M.
Published: October 2015

Embedding magnetic colloidal particles in an elastic polymer matrix leads to smart soft materials that can reversibly be addressed from outside by external magnetic fields. We discover a pronounced nonlinear superelastic stress-strain behavior of such materials using numerical simulations. This behavior results from a combination of two stress-induced mechanisms: a detachment mechanism of embedded particle aggregates and a reorientation mechanism of magnetic moments. The superelastic regime can be reversibly tuned or even be switched on and off by external magnetic fields and thus be tailored during operation. Similarities to the superelastic behavior of shape-memory alloys suggest analogous applications, with the additional benefit of reversible switchability and a higher biocompatibility of soft materials.
Giant piezoelectricity of monolayer group IV monochalcogenides: SnSe, SnS, GeSe, and GeS
Authors: Fei Ruixiang , Li Wenbin , Li Ju , Yang Li
Published: October 2015

We predict enormous, anisotropic piezoelectric effects in intrinsic monolayer group IV monochalcogenides (MX, M=Sn or Ge, X=Se or S), including SnSe, SnS, GeSe, and GeS. Using first-principle simulations based on the modern theory of polarization, we find that their piezoelectric coefficients are about one to two orders of magnitude larger than those of other 2D materials, such as MoS2 and GaSe, and bulk quartz and AlN which are widely used in industry. This enhancement is a result of the unique “puckered” C2v symmetry and electronic structure of monolayer group IV monochalcogenides. Given the achieved experimental advances in the fabrication of monolayers, their flexible character, and ability to withstand enormous strain, these 2D structures with giant piezoelectric effects may be promising for a broad range of applications such as nano-sized sensors, piezotronics, and energy harvesting in portable electronic devices.
Oxygen related recombination defects in Ta3N5 water splitting photoanode
Authors: Fu Gao , Yan Shicheng , Yu Tao , Zou Zhigang
Published: October 2015

A key route to improving the performance of Ta3N5 photoelectrochemical film devices in solar driving water splitting to hydrogen is to understand the nature of the serious recombination of photo-generated carriers. Here, by using the temperature-dependent photoluminescence (PL) spectrum, we confirmed that for the Ta3N5 films prepared by nitriding Ta2O5 precursor, one PL peak at 561 nm originates from deep-level defects recombination of the oxygen-enriched Ta3N5 phases, and another one at 580 nm can be assigned to band recombination of Ta3N5 itself. Both of the two bulk recombination processes may decrease the photoelectrochemical performance of Ta3N5. It was difficult to remove the oxygen-enriched impurities in Ta3N5 films by increasing the nitriding temperatures due to their high thermodynamically stability. In addition, a broadening PL peak between 600 and 850 nm resulting from oxygen related surface defects was observed by the low-temperature PL measurement, which may induce the surface recombination of photo-generated carriers and can be removed by increasing the nitridation temperature. Our results provided direct experimental evidence to understand the effect of oxygen-related crystal defects in Ta3N5 films on its photoelectric performance.
Marangoni boundary layer flow and heat transfer of copper-water nanofluid over a porous medium disk
Authors: Lin Yanhai , Zheng Liancun
Published: October 2015

In this paper we present a study of the Marangoni boundary layer flow and heat transfer of copper-water nanofluid over a porous medium disk. It is assumed that the base fluid water and the nanoparticles copper are in thermal equilibrium and that no slippage occurs between them. The governing partial differential equations are transformed into a set of ordinary differential equations by generalized Kármán transformation. The corresponding nonlinear two-point boundary value problem is solved by the Homotopy analysis method and the shooting method. The effects of the solid volume fraction, the permeability parameter and the Marangoni parameter on the velocity and temperature fields are presented graphically and analyzed in detail.
Transition in hypersonic boundary layers
Authors: Zhang Chuanhong , Zhu Yiding , Chen Xi , Yuan Huijing , Wu Jiezhi , Chen Shiyi , Lee Cunbiao , Gad-el-Hak Mohamed
Published: October 2015

Transition and turbulence production in a hypersonic boundary layer is investigated in a Mach 6 wind tunnel using Rayleigh-scattering visualization, fast-response pressure measurements, and particle image velocimetry. It is found that the second-mode instability is a key modulator of the transition process. Although the second-mode is primarily an acoustic wave, it causes the formation of high-frequency vortical waves, which triggers a fast transition to turbulence.
Measuring soil organic carbon: which technique and where to from here?
Authors: Johns Timothy J. , Angove Michael J. , Wilkens Sabine
Published: October 2015

This review compares and contrasts analytical techniques for the measurement of total soil organic carbon (TOC). Soil TOC is seen to be a highly important health and quality indicator for soils, as well as having the potential to sequester atmospheric carbon. Definition of the form of organic carbon measured by a given method is vital to the selection of appropriate methodology, as well as the understanding of what exactly is being measured. Historically, studies of TOC have ranged from basic measures, such as colour and gravimetric analyses, to dry and wet oxidation techniques. In more recent times, various spectroscopic techniques and the application of remote or mobile approaches have gained prominence. The different techniques, even the oldest ones, may have their place in current research depending on research needs, the available time, budget and access to wider resources. This review provides an overview of the various methods, highlights advantages, limitations and research opportunities and provides an indication of what the method actually measures so that meaningful comparisons can be made.
Soil residuals and plant uptake of Cu and Zn from biosolids applied to a clay loam soil under field conditions in Victoria, Australia
Authors: Beshah Firew H. , Porter Nichola A. , Wrigley Roger , Meehan Barry , Adams Mike
Published: October 2015

A field experiment was conducted to investigate the effects of incorporating anaerobically digested dewatered biosolids (DWB) and composted biosolids (CB) on the availability of the heavy metals Cu and Zn to canola (Brassica napus cv. Beacon) and oats (Avena sativa cv. Echidna) grown in a clay loam soil. DWB at rates of 0, 5, 25, 45 and 65 t dry solids (ds) ha–1 and CB at rates of 0, 10 30, 50 and 70 t ds ha–1 were incorporated into the soil to a depth of approximately 15 cm. The plots were arranged in triplicate, in a randomised complete block design. Canola and oat seeds were sown at a seeding rate of 5 and 100 kg ha–1, respectively. After the crop harvest, total and diethylenetriamine penta-acetic acid (DTPA)-extractable heavy metals in biosolids-amended soil were determined using X-ray fluorescence (XRF) and inductively coupled plasma mass spectrometry (ICP-MS), respectively. Total metals in plant leaves were analysed using ICP-MS. In these biosolids, only Cu and Zn were high enough to significantly increase their concentration in the soil and plant tissue. The results showed that application of biosolids significantly (P < 0.001) increased DTPA-extractable and total concentrations of Cu and Zn in the amended soil. The ratio of DTPA-extractable to total (XRF) Cu and Zn also changed with increasing application rates of DWB and CB. The change in the ratio was more pronounced in soils receiving DWB, probably associated with the significant (P < 0.001) decrease in soil pHw with their loading rate. Positive correlations were also noted between the application rate of biosolids and the Cu and Zn levels in the canola and oat leaves.
Global nutrient transport in a world of giants
Authors: Doughty Christopher E. , Roman Joe , Faurby Søren , Wolf Adam , Haque Alifa , Bakker Elisabeth S. , Malhi Yadvinder , Dunning John B. , Svenning Jens-Christian
Published: October 2015

Significance

Animals play an important role in the transport of nutrients, but this role has diminished because many of the largest animals have gone extinct or experienced massive population declines. Here, we quantify the movement of nutrients by animals in the land, sea, rivers, and air both now and prior to their widespread reductions. The capacity to move nutrients away from hotspots decreased to 6% of past values across land and ocean. The vertical movement of phosphorus (P) by marine mammals was reduced by 77% and movement of P from sea to land by seabirds and anadromous fish was reduced by 96%, effectively disrupting an efficient nutrient distribution pump that once existed from the deep sea to the continental interiors.
College football, elections, and false-positive results in observational research
Authors: Fowler Anthony , Montagnes B. Pablo
Published: October 2015

Significance

We reassess the surprising finding that college football games influence incumbent support in subsequent elections. Because independent replication is impossible for such nonexperimental findings, we proceed by testing multiple independent hypotheses that should hold if college football games indeed influence elections. In each case, the evidence suggests that the original finding was a false positive. For example, if college football games indeed influence elections, this effect should be greatest in places where the public is most interested in college football. However, we find the opposite. We conclude with general recommendations for evaluating surprising research findings and avoiding similar false-positive results—particularly for nonexperimental work in the social sciences where independent replication is impossible.
Test of Martin’s overkill hypothesis using radiocarbon dates on extinct megafauna
Authors: Surovell Todd A. , Pelton Spencer R. , Anderson-Sprecher Richard , Myers Adam D.
Published: October 2015

Significance

Coincident with the human colonization of the Western Hemisphere, dozens of genera of Pleistocene megafauna were lost to extinction. Following Martin, we argue that declines in the record of radiocarbon dates of extinct genera may be used as an independent means of detecting the first presence of humans in the New World. Our results, based on analyses of radiocarbon dates from Eastern Beringia, the contiguous United States, and South America, suggest north to south, time, and space transgressive declines in megafaunal populations as predicted by the overkill hypothesis. This finding is difficult to reconcile with other extinction hypotheses. However, it remains to be determined whether these findings will hold with larger samples of radiocarbon dates from all regions.
Impacts of high-latitude volcanic eruptions on ENSO and AMOC
Authors: Pausata Francesco S. R. , Chafik Leon , Caballero Rodrigo , Battisti David S.
Published: October 2015

Significance

In the model simulations analyzed here, large high-latitude volcanic eruptions have global and long-lasting effects on climate, altering the spatiotemporal characteristic of the El Niño–Southern Oscillation (ENSO) on both short (<1 y) and long timescales and affecting the strength of the Atlantic Meridional Overturning Circulation (AMOC). In the first 8–9 mo following the start of the eruption, El Niño-like anomalies develop over the equatorial Pacific. The large high-latitude eruptions also trigger a strengthening of the AMOC in the first 25 y after the eruption, which is associated with an increase in ENSO variability. This is then followed by a weakening of the AMOC lasting another 30–35 y, associated with decreased ENSO variability.
Two contemporaneous mitogenomes from terminal Pleistocene burials in eastern Beringia
Authors: Tackney Justin C. , Potter Ben A. , Raff Jennifer , Powers Michael , Watkins W. Scott , Warner Derek , Reuther Joshua D. , Irish Joel D. , O’Rourke Dennis H.
Published: October 2015

Significance

Beringia gave rise to the first Western Hemisphere colonists, although the genetic characterization of that source population has remained obscure. We report two mitogenomes from human remains within Beringia, with an age (∼11,500 cal B.P.) that postdates the end of the initial colonization by only a few millennia. The mitochondrial lineages identified (B2, C1b) are rare to absent in modern northern populations, indicating greater genetic diversity in early Beringia than in modern populations of the region. The antiquity and geographic location of these two burials, and the combined genomic and archaeological analyses, provide new perspectives on the link between Asia and the Americas, and the genetic makeup of the first Americans.
Purkinje cell activity during classical conditioning with different conditional stimuli explains central tenet of Rescorla–Wagner model
Authors: Rasmussen Anders , Zucca Riccardo , Johansson Fredrik , Jirenhed Dan-Anders , Hesslow Germund
Published: October 2015

Significance

The Rescorla–Wagner model of associative learning has guided research in behavioral and neural sciences for several decades. Although phenomena associated with the model have previously been linked to nucleo-olivary inhibition, many questions regarding the neural mechanisms underlying the model still remain. In this paper, we present evidence from our eyeblink conditioning setup, indicating that the variables used in Rescorla and Wagner's model have physiological correlates.