bluuebunny/crossref_metadata_2025 huggingface dataset:
Performance analysis of single‐walled carbon nanotube bundle interconnects for three‐dimensional integration applications
Authors: Qian Libo , Zhu Zhangming , Ding Ruixue , Yang Yintang
Published: March 2013

Compact equivalent circuit models for single‐walled carbon nanotube (SWCNT) bundles are described, and the performance of SWCNT bundle interconnects is evaluated and compared with traditional Cu interconnects at different interconnect levels for through‐silicon‐via‐based three‐dimensional integration. It is shown that at local level, carbon nanotube bundle interconnects exhibit lower signal delay and smaller optimal wire size. At intermediate and global levels, delay improvement becomes more significant with technology scaling and increasing wire lengths. For 1 mm intermediate and 10 mm global level interconnects, the delay of SWCNT bundles can reach 45.49 and 51.84% of that of Cu wires, respectively.
Thermodynamics of iodide adsorption at the instantaneous air-water interface
Authors: Stern Abraham C. , Baer Marcel D. , Mundy Christopher J. , Tobias Douglas J.
Published: March 2013

We performed molecular dynamics simulations using both polarizable and non-polarizable force fields to study the adsorption of iodide to the air-water interface. A novel aspect of our analysis is that the progress of ion adsorption is measured as the distance from the instantaneous interface, which is defined by a coarse-graining scheme proposed recently by Willard and Chandler [“Instantaneous liquid interfaces,” J. Phys. Chem. B 114, 1954–1958 (2010)10.1021/jp909219k]. Referring structural and thermodynamic quantities to the instantaneous interface unmasks molecular-scale details that are obscured by thermal fluctuations when the same quantities are referred to an average measure of the position of the interface, such as the Gibbs dividing surface. Our results suggest that an ion adsorbed at the interface resides primarily in the topmost water layer, and the interfacial location of the ion is favored by enthalpy and opposed by entropy.
Ionization of Rydberg H2 molecules at doped silicon surfaces
Authors: Sashikesh G. , Ford M. S. , Softley T. P.
Published: March 2013

The present study focuses on the interaction of H2 Rydberg molecules with doped silicon semiconductor surfaces. Para-H2 Rydberg states with principal quantum numbers n = 17–21 and core rotational quantum number N+ = 2 are populated via resonant two-colour two-photon (vacuum ultraviolet-ultraviolet) excitation and collide at grazing incidence with a surface. For small Rydberg-surface separation, the Rydberg states are ionized due to the attractive surface potential experienced by the Rydberg electron and the remaining ion-core is detectable by applying a sufficiently strong external electric field. It is found that the surface ionization profiles (ion signal vs applied field) of H2 on p-type doped Si surfaces show a higher detected ion signal than for n-type Si surfaces, while an Au surface shows lower detected ion signal than either type of Si surface. It is shown that ion detectability decreases with increasing dopant density for both types of Si surfaces. Higher-n Rydberg states show higher ion detectability than lower-n Rydberg states but this variation becomes smaller when increasing the dopant density for both p- and n-type surfaces. Theoretical trajectory simulations were developed with a 2D surface potential model and using the over-the-barrier model for the ionization distance; the results help to explain the observed variations of the experimental surface ionization profiles with dopant density and type.
A comprehensive model for the electrical nanocontact on germanium for scanning spreading resistance microscopy applications
Authors: Schulze Andreas , Verhulst Anne S. , Nazir Aftab , Hantschel Thomas , Eyben Pierre , Vandervorst Wilfried
Published: March 2013

Quantitative carrier profiling represents a key element in the process development of future nanoelectronic devices. During the last decade, scanning spreading resistance microscopy (SSRM) has evolved as the method of choice for two-dimensional carrier mapping due to its unique spatial resolution and high sensitivity when applied to silicon (Si)-based devices. While the electrical nanocontact between a SSRM probe and Si is well documented, the insight is insufficient to understand or make predictions about the properties of the SSRM contact in case of high-mobility germanium (Ge) samples. Therefore, we present in this paper a model describing this contact in more detail, taking into account the effects of the applied pressure as this leads to the formation of a β-Sn pocket right underneath the probe and a spatially non-homogeneous bandgap reduction in the underlying Ge. The resistance probed through the resulting Schottky contact is further influenced by the dimensions of the nanocontact and in particular by the spatial extent of the surface states which are present at the cross-sectional surface. To account for the low-bias IV-characteristics of n-Ge, the model also includes trap-assisted tunneling. Using this model, we are able to describe the role of probe properties such as probe radius and resistivity on the shape (steepness, saturation, non-linearity) of the Ge calibration curve. We demonstrate experimentally and by simulation that low-resistivity probes are indispensable for a high sensitivity when applying SSRM to highly doped samples.
Sedimentation equilibrium and the generalized Archimedes' principle
Authors: Parola Alberto , Buzzaccaro Stefano , Secchi Eleonora , Piazza Roberto
Published: March 2013

The buoyancy concept is critically re-examined for applications to dispersions of nano-particles, such as colloids, proteins, or macromolecules. It is shown that when the size of the buoyant particle is not too different (say, at most a factor of ten) from the size of the dispersed particles, new intriguing phenomena emerge, leading to the violation of the Archimedes' principle. The resulting buoyancy force depends not only on the volume of the particle and on the mass density of the dispersion, but also on the relative size of the particles, on their geometry, and on the interactions between the buoyant particle and the fluid. Explicit expressions for such a generalized Archimedes' principle are obtained and the results are tested against targeted experiments in colloidal dispersions.
Simulation studies of the Cl− + CH3I SN2 nucleophilic substitution reaction: Comparison with ion imaging experiments
Authors: Zhang Jiaxu , Lourderaj Upakarasamy , Sun Rui , Mikosch Jochen , Wester Roland , Hase William L.
Published: March 2013

In the previous work of Mikosch et al. [Science 319, 183 (2008)]10.1126/science.1150238, ion imaging experiments were used to study the Cl− + CH3I → ClCH3 + I− reaction at collision energies Erel of 0.39, 0.76, 1.07, and 1.9 eV. For the work reported here MP2(fc)/ECP/d direct dynamics simulations were performed to obtain an atomistic understanding of the experiments. There is good agreement with the experimental product energy and scattering angle distributions for the highest three Erel, and at these energies 80% or more of the reaction is direct, primarily occurring by a rebound mechanism with backward scattering. At 0.76 eV there is a small indirect component, with isotropic scattering, involving formation of the pre- and post-reaction complexes. All of the reaction is direct at 1.07 eV. Increasing Erel to 1.9 eV opens up a new indirect pathway, the roundabout mechanism. The product energy is primarily partitioned into relative translation for the direct reactions, but to CH3Cl internal energy for the indirect reactions. The roundabout mechanism transfers substantial energy to CH3Cl rotation. At Erel = 0.39 eV both the experimental product energy partitioning and scattering are statistical, suggesting the reaction is primarily indirect with formation of the pre- and post-reaction complexes. However, neither MP2 nor BhandH/ECP/d simulations agree with experiment and, instead, give reaction dominated by direct processes as found for the higher collision energies. Decreasing the simulation Erel to 0.20 eV results in product energy partitioning and scattering which agree with the 0.39 eV experiment. The sharp transition from a dominant direct to indirect reaction as Erel is lowered from 0.39 to 0.20 eV is striking. The lack of agreement between the simulations and experiment for Erel = 0.39 eV may result from a distribution of collision energies in the experiment and/or a shortcoming in both the MP2 and BhandH simulations. Increasing the reactant rotational temperature from 75 to 300 K for the 1.9 eV collisions, results in more rotational energy in the CH3Cl product and a larger fraction of roundabout trajectories. Even though a ClCH3–I− post-reaction complex is not formed and the mechanistic dynamics are not statistical, the roundabout mechanism gives product energy partitioning in approximate agreement with phase space theory.
Influence of exciton lifetime on charge carrier dynamics in an organic heterostructure
Authors: Agrawal Kanika L. , Sykes Matthew E. , Hyup An Kwang , Frieberg Bradley , Green P. F. , Shtein Max
Published: March 2013

Interactions between charge carriers and excitons, as well as between excitons and optical cavity modes in organic optoelectronic devices are fundamental to their operational limits and chief in preventing the realization of certain phenomena, such as electrically pumped organic lasing. We uncovered a previously unreported phenomenon, wherein optical cavity-modulated exciton decay rate leads to a concomitant modulation in the electrical current of an archetypal NPD/Alq3 organic light emitting device operated in forward bias. The magnitude of this variation is sensitive to the local dielectric environment of the device and is found to be as large as 15%.
Experimental and theoretical studies of scaling of sizes and intrinsic viscosity of hyperbranched chains in good solvents
Authors: Li Lianwei , Lu Yuyuan , An Lijia , Wu Chi
Published: March 2013

Using a set of hyperbranched polystyrenes with different overall molar masses but a uniform subchain length or a similar overall molar mass but different subchain lengths, we studied their sizes and hydrodynamic behaviors in toluene (a good solvent) at T = 25 °C by combining experimental (laser light scattering (LLS) and viscometry) and theoretical methods based on a partially permeable sphere model. Our results show that both the average radii of gyration (⟨Rg⟩) and hydrodynamic radius (⟨Rh⟩) are scaled to the weight-average molar mass (Mw) as ⟨Rg⟩ ∼ ⟨Rh⟩ ∼ MwγMw,sφ, with γ = 0.47 ± 0.01 and φ = 0.10 ± 0.01; and their intrinsic viscosity ([η]) quantitatively follow the Mark-Houwink-Sakurada (MHS) equation as [η] = KηMwνMw,sμ with Kη = 2.26 × 10−5, ν = 0.39 ± 0.01, and μ = 0.31 ± 0.01, revealing that these model chains with long subchains are indeed fractal objects. Further, our theoretical and experimental results broadly agree with each other besides a slight deviation from the MHS equation for short subchains, similar to dendrimers, presumably due to the multi-body hydrodynamic interaction. Moreover, we also find that the average viscometric radius (⟨Rη⟩) determined from intrinsic viscosity is slightly smaller than ⟨Rh⟩ measured in dynamic LLS and their ratio (⟨Rη⟩/⟨Rh⟩) roughly remains 0.95 ± 0.05, reflecting that linear polymer chains are more draining with a smaller ⟨Rh⟩ than their hyperbranched counterparts for a given intrinsic viscosity. Our current study of the “defect-free” hyperbranched polymer chains offers a standard model for further theoretical investigation of hydrodynamic behaviors of hyperbranched polymers and other complicated architectures, in a remaining unexploited research field of polymer science.
Prediction of rock salt structure of (InN)32 nanoparticles from first principles calculations
Authors: Kaur Prabhsharan , Sekhon S. S. , Kumar Vijay
Published: March 2013

From first principles calculations, we show that (InN)32 nanoparticles favor rock salt structure compared with wurtzite structure in bulk. A phase transition from wurtzite to rock salt structure is known to occur in bulk InN at 12.1 GPa and higher values of pressure for AlN and GaN. However, at the nanoscale we show that this structural transition takes place in (InN)32 without applying pressure. The charge asymmetry value “g” and cation/anion size ratio in InN describe very well this behavior. Similar studies on nanoparticles of AlN and GaN as well as a few other binary compounds such as MgS, AgI, ZnO, and CdSe, however, do not show such a transition. Our results suggest (InN)32 to be a unique candidate as further calculations on a few larger size (InN)n nanoparticles show that a filled cage (two shells) (InN)12@(InN)48 structure of (InN)60 has higher binding energy compared with a rock salt structure of (InN)64 leading to the conclusion that other 3D structures are likely to become favorable over rock salt structure for larger sizes.
Ionic arrest of segmental motion and emergence of spatio-temporal heterogeneity: A fluorescence investigation of (polyethylene glycol + electrolyte) composites
Authors: Guchhait Biswajit , Biswas Ranjit
Published: March 2013

Temperature dependent steady state and time resolved fluorescence measurements have been performed to explore the interaction and dynamics in polymer-electrolyte composite of the following general formula: [0.85 PEG + 0.15{f KNO3+ (1−f) LiNO3}], with f denoting fraction of potassium ion in the 0.15 mol electrolyte present in the medium. Poly(ethylene glycol) with number-averaged molecular weight of 300 (PEG300) has been employed as polymer and C153 as the fluorescent probe. Substantial excitation wavelength dependence of probe fluorescence emission in presence of electrolyte suggests presence of spatial heterogeneity which vanishes either upon raising temperature or removing the electrolyte. This has been interpreted as arising from the cation-induced arrest of polymer segmental motion. Temporal heterogeneity in these composites is manifested via fractional viscosity dependence of average solvation and rotation rates of the dissolved probe. Viscosity decoupling of these rates in composites is found to depend on cation identity and is also reflected via the corresponding activation energies. The degree of decoupling differs between solvation and rotation, inducing an analogy to the observations made in deeply supercooled liquids. In addition, conformity to hydrodynamic predictions is recovered by measuring f dependent solute rotation at higher temperatures. Several complimentary but different experiments are suggested to re-examine the mechanism proposed here, based on the fluorescence results, for the emergence of spatio-temporal heterogeneity in these composites and its disappearance either in the absence of any electrolyte or at higher temperatures.
Onset of size effect in lattice thermal conductivity of thin films
Authors: Maznev A. A.
Published: March 2013

The onset of size effect in phonon-mediated thermal conductivity along a thin film at temperatures comparable to or greater than the Debye temperature is analyzed theoretically. Assuming a quadratic frequency dependence of phonon relaxation rates in the low-frequency limit, a simple closed-form expression for the reduction of the in-plane thermal conductivity of thin films is derived. The effect scales as the square root of the film thickness, which leads to the prediction of a measurable thermal conductivity reduction in Si at room temperature for “macroscopic” thicknesses ∼100 μm. However, this prediction needs to be corrected to account for the deviation from the ω−2 dependence of phonon lifetimes at sub-THz frequencies due to the transition from Landau-Rumer to Akhiezer mechanism of phonon dissipation.
Terahertz quantum cascade lasers with thin resonant-phonon depopulation active regions and surface-plasmon waveguides
Authors: Salih M. , Dean P. , Valavanis A. , Khanna S. P. , Li L. H. , Cunningham J. E. , Davies A. G. , Linfield E. H.
Published: March 2013

We report three-well, resonant-phonon depopulation terahertz quantum cascade lasers with semi-insulating surface-plasmon waveguides and reduced active region (AR) thicknesses. Devices with thicknesses of 10, 7.5, 6, and 5 μm are compared in terms of threshold current density, maximum operating temperature, output power, and AR temperature. Thinner ARs are technologically less demanding for epitaxial growth and result in reduced electrical heating of devices. However, it is found that 7.5-μm-thick devices give the lowest electrical power densities at threshold, as they represent the optimal trade-off between low electrical resistance and low threshold gain.
Integrated computation of finite-time Lyapunov exponent fields during direct numerical simulation of unsteady flows
Authors: Finn Justin , Apte Sourabh V.
Published: March 2013

The computation of Lagrangian coherent structures typically involves post-processing of experimentally or numerically obtained fluid velocity fields to obtain the largest finite-time Lyapunov exponent (FTLE) field. However, this procedure can be tedious for large-scale complex flows of general interest. In this work, an alternative approach involving computation of the FTLE on-the-fly during direct numerical simulation of the full three dimensional Navier-Stokes equations is developed. The implementation relies on Lagrangian particle tracking to compose forward time flow maps, and an Eulerian treatment of the backward time flow map [S. Leung, J. Comput. Phys. 230, 3500–3524 (2011)] coupled with a semi-Lagrangian advection scheme. The flow maps are accurately constructed from a sequence of smaller sub-steps stored on disk [S. Brunton and C. Rowley, Chaos 20, 017503 (2010)], resulting in low CPU and memory requirements to compute evolving FTLE fields. Several examples are presented to demonstrate the capability and parallel scalability of the approach for a variety of two and three dimensional flows.
Spatiotemporal analysis of propagation mechanism of positive primary streamer in water
Authors: Fujita Hidemasa , Kanazawa Seiji , Ohtani Kiyonobu , Komiya Atsuki , Sato Takehiko
Published: March 2013

Currently, further clarification of pre-breakdown phenomena in water such as propagation mechanisms of primary and secondary streamers are needed because applications of aqueous plasma to environmental and medical treatments are increasing. In this study, a series of primary streamer propagations in ultrapure water was visualized at 100-Mega frames per second (100 Mfps) in the range of 400 μm square using an ultra high-speed camera with a microscope lens when a single-shot pulsed positive voltage was applied to a needle electrode placed in a quartz cell. Every observation was synchronized with the waveforms of the applied voltage and the discharge current. The primary streamer, having many filamentary channels, started to propagate semi-spherically with a velocity of about 2 km/s when the pulsed currents occurred. Although most filamentary channels disappeared 400 ns after the beginning of the primary streamer, a few of them continued propagating with almost the same velocity (about 2 km/s) as long as the repetitive pulsed currents flowed. Shock waves were iteratively generated and streamer channels were formed while the repetitive pulsed currents were flowing. Thus, we concluded that the positive primary streamer in water propagates progressively with each repetitive pulsed current.
Note: A simple thermal gradient annealing unit for the treatment of thin films
Authors: Metting C. J. , Bunn J. K. , Fadimba J. , Underwood E. , Zhu Y. , Koley G. , Crawford T. , Hattrick-Simpers J.
Published: March 2013

A gradient annealing cell has been developed for the high-throughput study of thermal annealing effects on thin-film libraries in different environments. The inexpensive gradient annealing unit permits temperature gradients as large as 28 °C/mm and can accommodate samples ranging in length from 13 mm to 51 mm. The system was validated by investigating the effects of annealing temperature on the crystallinity, resistivity, and transparency of tin-doped indium oxide deposited on a glass substrate by magnetron sputtering. The unit developed in this work will permit the rapid optimization of materials properties such as crystallinity, homogeneity, and conductivity across a variety of applications.
Annealing effects on superconductivity in Rb0.81Fe1.72Se2 single crystal
Authors: Zhang Z. T. , Yang Z. R. , Li L. , Sun Y. P. , Du H. F. , Yang J. Y. , Pi L. , Zhang C. J. , Tian M. L. , Zhang Y. H.
Published: March 2013

The annealing effects on superconductivity in Rb0.81Fe1.72Se2 are investigated. For as-grown single crystal and the one annealed with furnace cooling, magnetic susceptibility exhibits a weak diamagnetic transition at 30 K. Consistently, the resistivity curve only displays a small drop at 30 K and an insulating behavior at lower temperatures. These features together with scanning electron microscope (SEM) data indicate that the superconducting phase exists as clusters in insulating matrix. As for the crystal annealed with fast quenching, resistivity results reveal a Tconset≈30 K and a Tczero≈10 K but the susceptibility does not show diamagnetic transition until the temperature is cooled down to 10 K. SEM results show that the surface of quenched sample is more homogeneous than the one annealed with furnace cooling. We argue that the annealing at high temperature makes the coexistence of superconducting and insulating phases becomes homogeneous. Then, the fast quenching preserves this state in which percolative superconducting paths could be easily formed. In comparison, during the furnace cooling, the temperature drops slowly and results in the segregation of the superconducting phase from the insulating phase into isolated clusters.
“Bloch wave” modification of stimulated Raman by stimulated Brillouin scattering
Authors: Dodd E. S. , Vu H. X. , DuBois D. F. , Bezzerides B.
Published: March 2013

Using the reduced-description particle-in-cell (RPIC) method, we study the coupling of backward stimulated Raman scattering (BSRS) and backward stimulated Brillouin scattering (BSBS) in regimes where the reflectivity involves the nonlinear behavior of particles trapped in the daughter plasma waves. The temporal envelope of a Langmuir wave (LW) obeys a Schrödinger equation where the potential is the periodic electron density fluctuation resulting from an ion-acoustic wave (IAW). The BSRS-driven LWs in this case have a Bloch wave structure and a modified dispersion due to the BSBS-driven spatially periodic IAW, which includes frequency band gaps at kLW∼kIAW/2∼k0 (kLW, kIAW, and k0 are the wave number of the LW, IAW, and incident pump electromagnetic wave, respectively). This band structure and the associated Bloch wave harmonic components are distinctly observed in RPIC calculations of the electron density fluctuation spectra and this structure may be observable in Thomson scatter. Bloch wave components grow up in the LW spectrum, and are not the result of isolated BSRS. Self-Thomson scattered light from these Bloch wave components can have forward scattering components. The distortion of the LW dispersion curve implies that the usual relationship connecting the frequency shift of the BSRS-scattered light and the density of origin of this light may become inaccurate. The modified LW frequency results in a time-dependent frequency shift that increases as the IAW grows, detunes the BSRS frequency matching condition, and reduces BSRS growth. A dependence of the BSRS reflectivity on the IAW Landau damping results because this damping determines the levels of IAWs. The time-dependent reflectivity in our simulations is characterized by bursts of sub-picosecond pulses of BSRS alternating with multi-ps pulses of BSBS, and BSRS is observed to decline precipitously as soon as SBS begins to grow from low levels. In strong BSBS regimes, the Bloch wave effects in BSRS are strong and temporal anti-correlation with BSRS is due to pump depletion in addition to frequency detuning. In most cases studied, BSBS suppressed the time-averaged reflectivity of BSRS compared to the levels obtained with fixed ions (and therefore no BSBS). The strong spatial modulation of the Bloch Langmuir waves appears to weaken electron trapping and thereby lowers the inflated reflectivity levels of BSRS.
Nonlinear interaction and parametric instability of kinetic Alfvén waves in multicomponent plasmas
Authors: Zhao J. S. , Wu D. J. , Yang L. , Lu J. Y.
Published: March 2013

Nonlinear couplings among kinetic Alfvén waves are investigated for a three-component plasma consisting of electrons, protons, and heavy ions. The parametric instability is investigated, and the growth rate is obtained. In the kinetic regime, the growth rate for the parallel decay instability increases with the heavy ion content, but the growth rate for the reverse decay is independent of the latter since the perpendicular wavelength is much larger than the ion gyroradius. It decreases with the heavy ion content when the perpendicular wavelength is of the order of the ion gyroradius. It is also found that in the short perpendicular wavelength limit, the growth rate is only weakly affected by the heavy ions. On the other hand, in the inertial regime, for both parallel and reverse decay cases, the growth rate decreases as the number of heavy ions becomes large.
Re-entrant relaxor behavior of Ba5RTi3Nb7O30 (R = La, Nd, Sm) tungsten bronze ceramics
Authors: Li Kun , Li Zhu Xiao , Qiang Liu Xiao , Ming Chen Xiang
Published: March 2013

Ba5RTi3Nb7O30 (R = La, Nd, Sm) tungsten bronze ceramics were prepared, and the dielectric and ferroelectric properties were investigated over a broad temperature range. The relaxor nature was determined for all compositions in their permittivity curves, and a second anomaly of the dielectric loss (tan δ) was observed around 250 K in Ba5NdTi3Nb7O30 and around 275 K in Ba5SmTi3Nb7O30. Both the maximum and remanent polarization tended to decrease and vanish at low temperatures in the ferroelectric phase for all compositions, which was referred to as the low temperature re-entrant relaxor behavior. The remanent polarization increased with decreasing temperature first and then reached the maximum value at the re-entrant temperature (Tr). For Ba5RTi3Nb7O30 (R = La, Nd, Sm), Tr decreased with the radius of R3+ cations and the applied field amplitude.
Optical guided modes coupled with Čerenkov radiation excited in Si slab using angular-resolved electron energy-loss spectrum
Authors: Saito H. , Chen C. H. , Kurata H.
Published: March 2013

Retardation effects in the valence electron energy-loss spectrum (EELS) of a Si slab are analyzed by angular-resolved EELS. The dispersion curves of the valence spectra excited in a slab are directly observed from a specimen area with several different thicknesses and are interpreted by performing a calculation of the dispersion relation using Kröger's formula. The dispersion curves observed below about 3 eV are attributed to guided modes coupled with Čerenkov radiation (ČR). The coupling between guided modes and ČR is found to be dependent on the sample thickness (t). For the sample with t > 150 nm, the intensity of the guided modes increased linearly with thickness, revealing the coupling with ČR. For t < 150 nm, however, the intensity of the guided modes rapidly decreased due to a diminished coupling with ČR, resulting from the thickness-dependent dispersion curves of the guided modes.
Study of 0.9 BaTiO3-0.1 NixZn1−xFe2O4 magneto-electric composite ceramics
Authors: Upadhyay Sanjay Kumar , Reddy V. Raghavnedra
Published: March 2013

Magnetic, ferroelectric, and magneto-electric studies are reported on 0.9 BaTiO3-0.1 NixZn1−xFe2O4 (x = 0 to 1.0 at 0.2). The bi-phase nature of the prepared composites is confirmed by the x-ray diffraction measurements. The simultaneous presence of room temperature ferroelectric and magnetic orderings is confirmed by measuring the room temperature P-E and M-H loops of the prepared composites. The magneto-electric behavior is found maximum for the composite consisting of Ni0.8Zn0.2Fe2O4 as magnetic phase, which is explained on the basis of the magnetostrictive behavior of NixZn1−xFe2O4 phase.
Carrier tuned rectifying-like behavior in superconducting La1.8Sr0.2CuO4/La1.9Sr0.1CuO4 bilayers
Authors: Zhang Y. , Li P. G. , Wang G. F. , Xing Y. , Wu D. S. , Shen J. Q. , Lei M. , Tang W. H.
Published: March 2013

A bilayer structure of superconducting overdoped La1.8Sr0.2CuO4 and underdoped La1.9Sr0.1CuO4 films was fabricated using pulsed laser deposition and wet chemical etching techniques. The difference in carrier concentrations in the two layers causes rectifying-like behavior when the films are cooled below a critical temperature Tc. This behavior can be interpreted within the framework of quenched superconducting films, with carrier migration occurring between the two layers at very low positive current. These results suggest that electric field-controlled carrier migration between two layers in a bilayer structure can yield new interfacial properties, which would be of interest for device applications.
The material dependence of temperature measurement resolution in thermal scanning electron microscopy
Authors: Wu Xiaowei , Hull Robert
Published: March 2013

Thermal scanning electron microscopy is a recently developed temperature mapping technique based on thermal diffuse scattering in electron backscatter diffraction in a scanning electron microscope. It provides nano-scale and non-contact temperature mapping capabilities. Due to the specific temperature sensitive mechanism inherent to this technique, the temperature resolution is highly material dependent. A thorough investigation of what material properties affect the temperature resolution is important for realizing the inherent temperature resolution limit for each material. In this paper, three material dependent parameters—the Debye-Waller B-factor temperature sensitivity, backscatter yield, and lattice constant—are shown to control the temperature resolution.
Influence of internal absorption and interference on the optical efficiency of thin-film GaN-InGaN light-emitting diodes
Authors: Heikkilä Oskari , Oksanen Jani , Tulkki Jukka
Published: March 2013

We present a first-principle method for quantitative modeling of optical energy flow and dissipation in thin-film (TF) light-emitting diodes (LEDs) based on highly general Green's function method. Unlike conventional models, the presented model simultaneously accounts for interference, near-field effects, and internal absorption in determining the radiance generated by a LED. We show that these effects have a profound influence on the efficiency of LEDs and strongly affect the light extraction efficiency (LEE) and the internal quantum efficiency. According to our results, the LEE of an InGaN-GaN TF-LED with untextured surfaces and typical active region (AR) thickness on the order of 10 nm is 67% while a LED with a thin AR exhibits only a LEE of 29%. Based on the numerical results, we discuss the factors that affect the overall efficiency and design considerations to optimize the structure of thin-film LEDs.
Asymmetry tuning of Fano resonances in GaAs photonic crystal cavities
Authors: Valentim P. T. , Vasco J. P. , Luxmoore I. J. , Szymanski D. , Vinck-Posada H. , Fox A. M. , Whittaker D. M. , Skolnick M. S. , Guimarães P. S. S.
Published: March 2013

We investigate the reflectivity spectra of photonic crystal cavities using the polarization of the incoming exciting light to tune the Fano interference between the radiation reflected by the polarized cavity mode and the light scattered by the photonic crystal pattern. The reflectivity is controlled by the polarization of the incident radiation, with the change from symmetrical to asymmetrical lineshapes well described by the Fano resonance formula. We use the scattering matrix formalism to obtain the reflectivity lineshapes by relating the electromagnetic field incident on the cavity to the radiation that is reflected in qualitative good agreement with the experimental results.
Chemisorption of hydrogen on Fe clusters through hybrid bonding mechanisms
Authors: Takahashi Keisuke , Isobe Shigehito , Ohnuki Somei
Published: March 2013

The interaction of H and Fe clusters of up to nine atoms were investigated within a density functional theory. Calculations indicate that one gas-phase Fe atom can absorb ten H atoms, an amount 2.5 times more than methane (CH4). The magnetic state of Fe atoms non-uniformly decrease by increasing the number of H. The bonding of Fe-H in FeH clusters consists of charge transfer and electron pairing. Thus, two types of bondings are involved. The bond mechanism is general in nature within transition metal clusters, bringing insight for the development of heterogeneous catalyst and hydrogen storage materials.
Proterozoic ocean redox and biogeochemical stasis
Authors: Reinhard Christopher T. , Planavsky Noah J. , Robbins Leslie J. , Partin Camille A. , Gill Benjamin C. , Lalonde Stefan V. , Bekker Andrey , Konhauser Kurt O. , Lyons Timothy W.
Published: March 2013

The partial pressure of oxygen in Earth’s atmosphere has increased dramatically through time, and this increase is thought to have occurred in two rapid steps at both ends of the Proterozoic Eon (∼2.5–0.543 Ga). However, the trajectory and mechanisms of Earth’s oxygenation are still poorly constrained, and little is known regarding attendant changes in ocean ventilation and seafloor redox. We have a particularly poor understanding of ocean chemistry during the mid-Proterozoic (∼1.8–0.8 Ga). Given the coupling between redox-sensitive trace element cycles and planktonic productivity, various models for mid-Proterozoic ocean chemistry imply different effects on the biogeochemical cycling of major and trace nutrients, with potential ecological constraints on emerging eukaryotic life. Here, we exploit the differing redox behavior of molybdenum and chromium to provide constraints on seafloor redox evolution by coupling a large database of sedimentary metal enrichments to a mass balance model that includes spatially variant metal burial rates. We find that the metal enrichment record implies a Proterozoic deep ocean characterized by pervasive anoxia relative to the Phanerozoic (at least ∼30–40% of modern seafloor area) but a relatively small extent of euxinic (anoxic and sulfidic) seafloor (less than ∼1–10% of modern seafloor area). Our model suggests that the oceanic Mo reservoir is extremely sensitive to perturbations in the extent of sulfidic seafloor and that the record of Mo and chromium enrichments through time is consistent with the possibility of a Mo–N colimited marine biosphere during many periods of Earth’s history.
Xenopuscytoplasmic linker–associated protein 1 (XCLASP1) promotes axon elongation and advance of pioneer microtubules
Authors: Marx Astrid , Godinez William J. , Tsimashchuk Vasil , Bankhead Peter , Rohr Karl , Engel Ulrike
Published: March 2013

Dynamic microtubules (MTs) are required for neuronal guidance, in which axons extend directionally toward their target tissues. We found that depletion of the MT-binding protein Xenopus cytoplasmic linker–associated protein 1 (XCLASP1) or treatment with the MT drug Taxol reduced axon outgrowth in spinal cord neurons. To quantify the dynamic distribution of MTs in axons, we developed an automated algorithm to detect and track MT plus ends that have been fluorescently labeled by end-binding protein 3 (EB3). XCLASP1 depletion reduced MT advance rates in neuronal growth cones, very much like treatment with Taxol, demonstrating a potential link between MT dynamics in the growth cone and axon extension. Automatic tracking of EB3 comets in different compartments revealed that MTs increasingly slowed as they passed from the axon shaft into the growth cone and filopodia. We used speckle microscopy to demonstrate that MTs experience retrograde flow at the leading edge. Microtubule advance in growth cone and filopodia was strongly reduced in XCLASP1-depleted axons as compared with control axons, but actin retrograde flow remained unchanged. Instead, we found that XCLASP1-depleted growth cones lacked lamellipodial actin organization characteristic of protrusion. Lamellipodial architecture depended on XCLASP1 and its capacity to associate with MTs, highlighting the importance of XCLASP1 in actin–microtubule interactions.
SNARE complexes of different composition jointly mediate membrane fusion inArabidopsiscytokinesis
Authors: El Kasmi Farid , Krause Cornelia , Hiller Ulrike , Stierhof York-Dieter , Mayer Ulrike , Conner Laura , Kong Lingtian , Reichardt Ilka , Sanderfoot Anton A. , Jürgens Gerd
Published: March 2013

Membrane fusion is mediated by soluble N-ethylmaleimide–sensitive factor attachment protein receptor (SNARE) complexes. Although membrane fusion is required for separating daughter cells in eukaryotic cytokinesis, the SNARE complexes involved are not known. In plants, membrane vesicles targeted to the cell division plane fuse with one another to form the partitioning membrane, progressing from the center to the periphery of the cell. In Arabidopsis, the cytokinesis-specific Qa-SNARE KNOLLE interacts with two other Q-SNAREs, SNAP33 and novel plant-specific SNARE 11 (NPSN11), whose roles in cytokinesis are not clear. Here we show by coimmunoprecipitation that KNOLLE forms two SNARE complexes that differ in composition. One complex is modeled on the trimeric plasma membrane type of SNARE complex and includes, in addition to KNOLLE, the promiscuous Qb,c-SNARE SNAP33 and the R-SNARE vesicle-associated membrane protein (VAMP) 721,722, also involved in innate immunity. In contrast, the other KNOLLE-containing complex is tetrameric and includes Qb-SNARE NPSN11, Qc-SNARE SYP71, and VAMP721,722. Elimination of only one or the other type of KNOLLE complex by mutation, including the double mutant npsn11 syp71, causes a mild or no cytokinesis defect. In contrast, the two double mutants snap33 npsn11 and snap33 syp71 eliminate both types of KNOLLE complexes and display knolle-like cytokinesis defects. Thus the two distinct types of KNOLLE complexes appear to jointly mediate membrane fusion in Arabidopsis cytokinesis.
Aurora at the pole and equator: overlapping functions of Aurora kinases in the mitotic spindle
Authors: Hochegger Helfrid , Hégarat Nadia , Pereira-Leal Jose B.
Published: March 2013

The correct assembly and timely disassembly of the mitotic spindle is crucial for the propagation of the genome during cell division. Aurora kinases play a central role in orchestrating bipolar spindle establishment, chromosome alignment and segregation. In most eukaryotes, ranging from amoebas to humans, Aurora activity appears to be required both at the spindle pole and the kinetochore, and these activities are often split between two different Aurora paralogues, termed Aurora A and B. Polar and equatorial functions of Aurora kinases have generally been considered separately, with Aurora A being mostly involved in centrosome dynamics, whereas Aurora B coordinates kinetochore attachment and cytokinesis. However, double inactivation of both Aurora A and B results in a dramatic synergy that abolishes chromosome segregation. This suggests that these two activities jointly coordinate mitotic progression. Accordingly, recent evidence suggests that Aurora A and B work together in both spindle assembly in metaphase and disassembly in anaphase. Here, we provide an outlook on these shared functions of the Auroras, discuss the evolution of this family of mitotic kinases and speculate why Aurora kinase activity may be required at both ends of the spindle microtubules.
Influence of the Leader protein coding region of foot-and-mouth disease virus on virus replication
Authors: Belsham Graham J.
Published: March 2013

The foot-and-mouth disease virus (FMDV) Leader (L) protein is produced in two forms, Lab and Lb, differing only at their amino-termini, due to the use of separate initiation codons, usually 84 nt apart. It has been shown previously, and confirmed here, that precise deletion of the Lab coding sequence is lethal for the virus, whereas loss of the Lb coding sequence results in a virus that is viable in BHK cells. In addition, it is now shown that deletion of the ‘spacer’ region between these two initiation codons can be tolerated. Growth of the virus precisely lacking just the Lb coding sequence resulted in a previously undetected accumulation of frameshift mutations within the ‘spacer’ region. These mutations block the inappropriate fusion of amino acid sequences to the amino-terminus of the capsid protein precursor. Modification, by site-directed mutagenesis, of the Lab initiation codon, in the context of the virus lacking the Lb coding region, was also tolerated by the virus within BHK cells. However, precise loss of the Lb coding sequence alone blocked FMDV replication in primary bovine thyroid cells. Thus, the requirement for the Leader protein coding sequences is highly dependent on the nature and extent of the residual Leader protein sequences and on the host cell system used. FMDVs precisely lacking Lb and with the Lab initiation codon modified may represent safer seed viruses for vaccine production.
The role of SENCos as leaders
Authors: Tissot Catherine
Published: March 2013

The year 2014 marks an important milestone for the SENCo role. It is the 20‐year anniversary of the requirement for schools to have a named person as lead for special educational needs. This article, by Catherine Tissot from the University of Reading, explores the vision of the role as seen in Government guidance and documents and compares this with the views of those in post who are undertaking a required training programme to become a qualified SENCo. An optional questionnaire was distributed to all SENCos at Induction (Time 1) and repeated upon completion of the course (Time 2), and ten semi‐structured follow‐up interviews were conducted with volunteers to explore emerging themes. Differences were seen in the sample between those that were part of the senior leadership team in terms of their views on their ability to lead and direct practice, resource management and the strategic goals of the role.
Characterising Vulnerability to Poverty in Rural Haiti: A Multilevel Decomposition Approach
Authors: Échevin Damien
Published: March 2013

This article characterises vulnerability to poverty in Haiti using a unique survey conducted in 2007 in rural areas. In a first step, using two‐level linear random coefficient models of both per capita consumption and per capita income, the article assesses the impact of self‐reported shocks on households' economic well‐being. In a second step, the prediction model is used to calculate various measures of vulnerability to poverty, considering various types of shocks. Empirical findings show that self‐reported (or observable) idiosyncratic shocks, in particular health‐related shocks, have larger impact on vulnerability to poverty than observable covariate shocks. These results are in line with the fact that many households reported idiosyncratic health shocks as being the worst shocks they experienced. On the other hand, unobservable idiosyncratic shocks appear to have generally more influence on households' vulnerability to poverty than unobservable covariate ones. We also show that omitting self‐reported shocks in the analysis leads to an underestimate of households' vulnerability to poverty.
Sub‐dissociative dose intranasal ketamine for limb injury pain in children in the emergency department: A pilot study
Authors: Yeaman Fiona , Oakley Ed , Meek Robert , Graudins Andis
Published: March 2013

Objective

The present study aims to conduct a pilot study examining the effectiveness of intranasal (IN) ketamine as an analgesic for children in the ED.

Methods

The present study used an observational study on a convenience sample of paediatric ED patients aged 3–13 years, with moderate to severe (≥6/10) pain from isolated limb injury. IN ketamine was administered at enrolment, with a supplementary dose after 15 min, if required. Primary outcome was change in median pain rating at 30 min. Secondary outcomes included change in median pain rating at 60 min, patient/parent satisfaction, need for additional analgesia and adverse events being reported.

Results

For the 28 children included in the primary analysis, median age was 9 years (interquartile range [IQR] 6–10). Twenty‐three (82.1%) were male. Eighteen (64%) received only one dose of IN ketamine (mean dose 0.84 mg/kg), whereas 10 (36%) required a second dose at 15 min (mean for second dose 0.54 mg/kg). The total mean dose for all patients was 1.0 mg/kg (95% CI: 0.92–1.14). The median pain rating decreased from 74.5 mm (IQR 60–85) to 30 mm (IQR 12–51.5) at 30 min (P < 0.001, Mann–Whitney). For the 24 children who contributed data at 60 min, the median pain rating was 25 mm (IQR 4–44). Twenty (83%) subjects were satisfied with their analgesia. Eight (33%) were given additional opioid analgesia and the 28 reported adverse events were all transient and mild.

Conclusions

In this population, an average dose of 1.0 mg/kg IN ketamine provided adequate analgesia by 30 min for most patients.
Expression analysis of chlorophyllid α binding protein, a secretory, red fluorescence protein in the midgut of silkworm, Bombyx mori
Authors: Chen Lin , Yang Rui , Hu Xiao‐Long , Xiang Xing‐Wei , Wu Xiao‐Feng
Published: March 2013

Chlorophyllid α binding protein (chbp) was recently characterized by its ability to bind the prosthetic group of chlorophylls and little information is known regarding its expression. In the present study, we found that chpb was expressed highly and exclusively in the midgut of silkworm, Bombyx mori. The expression level of chbp was very high in the newly molted fifth instar larvae followed by gradual decline in the same instar. Our results demonstrated that CHBP was a secretory protein and located mainly in the apical of midgut epithelial cells. Real‐time polymerase chain reaction analysis results showed that chpb highly expressed in the anterior midgut, threefold and sixfold higher compared with that of the middle midgut and posterior midgut, respectively, and chpb expression declined in darkness. In addition, the expression of chbp was affected by high‐dose virus or bacterium infection.
Prevalence and significance of autoantibodies in patients with alcoholic liver disease
Authors: Lian Min , Hua Jing , Sheng Li , Qiu De Kai
Published: March 2013

Objective

This study aimed to evaluate the prevalence and significance of serum autoantibodies in alcoholic liver disease (ALD) patients.

Methods

In total, 90 male patients diagnosed with ALD or ALD overlapping with chronic hepatitis B (CHB) were included and their medical records were retrospectively reviewed. Clinical data and laboratory findings were collected. Anti‐nuclear antibody (ANA), anti‐mitochondrial antibody (AMA) and anti‐smooth muscle antibody (SMA) were detected by indirect immunofluorescent assay.

Results

Autoantibodies were found in 69.6% (48/69) of patients with ALD and 66.7% (14/21) of those with ALD overlapping with CHB. The prevalence of total ANA in ALD patients was 63.8% (44/69). High titers of autoantibodies and multi‐autoantibodies were found to be more often associated with cirrhosis than non‐cirrhosis. There was a significant difference in the levels of globulin, white blood cell and platelet count (P < 0.05) between patients with positive and negative autoantibodies. However, the values of the other parameters were similar in the two groups. Patients with ALD more frequently had positive autoantibodies than those with CHB alone (69.6% vs 37.5%, P < 0.01). And 10.4% of ALD patients with positive autoantibodies had systemic autoimmune or vascular diseases, which was not found in the CHB patients.

Conclusions

Autoantibodies are frequently present in patients with ALD and correlate to advanced liver disease. A high prevalence of autoantibodies in ALD may indicate that alcoholic‐associated immune disturbance occurs during the development of the disease.