bluuebunny/crossref_metadata_2025 huggingface dataset:
Afterglow processes responsible for memory effect in nitrogen
Authors: Pejović M. M. , Nešić N. T. , Pejović M. M. , Živanović E. N.
Published: July 2012

The mechanisms responsible for memory effect in nitrogen at 6.6 mbars have been analysed based on experimental data of electrical breakdown time delay as a function of afterglow period. The analysis has shown that positive ions remaining from previous discharge, as well as metastable and highly vibrationally excited molecules, are responsible for memory effect in the early afterglow. These molecules lead to the formation of positive ions in mutual collisions in the afterglow. Positive ions initiate secondary electron emission from the cathode of a nitrogen-filled tube when voltage higher than static breakdown voltage is applied on the electrodes. On the other hand, N(S4) atoms have a large influence on memory effect in late afterglow. They recombine on the cathode surface forming N2(AΣ3u+) metastable molecules, which release secondary electrons in collision with the cathode. The higher values of electrical breakdown time delay in the case of the tube with borosilicate glass walls than in the case of the tube with copper walls are a consequence of faster de-excitation of neutral active particles on the glass. Indirect confirmation of this assumption has been obtained when the tubes were irradiated with gamma radiation.
Hole transport in pure and doped hematite
Authors: Liao Peilin , Carter Emily A.
Published: July 2012

Hematite (α-Fe2O3) is a promising candidate for use in photovoltaic (PV) and photoelectrochemical devices. Its poor conductivity is one major drawback. Doping hematite either p-type or n-type greatly enhances its measured conductivity and is required for potential p-n junctions in PVs. Here, we study hole transport in pure and doped hematite using an electrostatically embedded cluster model with ab initio quantum mechanics (unrestricted Hartree-Fock theory). Consistent with previous work, the model suggests that hole hopping is via oxygen anions for pure hematite. The activation energy for hole mobility is predicted to be at least 0.1 eV higher than the activation energy for electron mobility, consistent with the trend observed in experiments. We examine four dopants—magnesium(II), nickel(II), copper(II), and manganese(II/III) in direct cation substitution sites—to gain insight into the mechanism by which conductivity is improved. The activation energies are used to assess qualitative effects of different dopants. The hole carriers are predicted to be attracted to O anions near the dopants. The magnitude of the trapping effect is similar among the four dopants in their +2 oxidation states. The multivalent character of Mn doping facilitates local hole transport around Mn centers via a low-barrier O-Mn-O pathway, which suggests that higher hole mobility can be achieved with increasing Mn doping concentration, especially when a network of these low-barrier pathways is produced. Our results suggest that the experimentally observed conductivity increase in Mg-, Ni-, and Cu-doped p-type hematite is mostly due to an increase in hole carriers rather than improved mobility, and that Mg-, Ni-, and Cu-doping perform similarly, while the conductivity of Mn-doped hematite might be significantly improved in the high doping concentration limit.
Controlled formation of charge depletion zones by molecular doping in organic pin-diodes and its description by the Mott-Schottky relation
Authors: Kleemann H. , Lüssem B. , Leo K.
Published: July 2012

Molecular doping of organic semiconductors is a key technology for highly efficient organic light-emitting diodes. Nevertheless, the underlying fundamental mechanisms are under discussion. This is because of the complex situation of structural disorder and strong polaronic coupling in such systems. We provide for the first time a systematic study of the formation of charge depletion zones in organic pin-diodes comprising molecular doped hole and electron transport layers. Impedance spectroscopy is employed to study the capacitance of these depletion zones. In particular, we show that the voltage dependent capacitance function obeys the Mott-Schottky relation concerning the influence of doping and the effect of an additional depletion zone given by the intrinsic interlayer. From temperature dependent measurements of the depletion capacitance, we can deduce the amount of active dopant states, their activation energy, and the spatial field distribution within the junction. The measured activation energy of the dopant states and the overall value of active dopant molecules suggest a highly efficient doping process, where dopant molecules act as shallow acceptor states.
Study of multiferroic properties in Bi5Fe0.5Co0.5Ti3O15 thin films
Authors: Sun Hui , Lu Xiaomei , Xu Tingting , Su Jie , Jin Yaming , Ju Changcheng , Huang Fengzhen , Zhu Jinsong
Published: July 2012

To explore the novel thin film with multiferroicity at room temperature, the bismuth-layer-structured Bi5Fe0.5Co0.5Ti3O15 (BFCT) thin films were prepared using chemical solution deposition technique. The microstructure, electric, and magnetic properties were investigated in BFCT film. A defined hysteresis loop of the BFCT film was obtained with the remnant polarization (2Pr) ∼ 31.7 μC/cm2 at 1 kHz under the electric field 300 kV/cm. To exclude contribution of the leakage current to polarization, we studied the dependence of hysteresis loops on the measuring frequency in the range from 100 Hz to 2 kHz and made the positive-up-negative-down (PUND) measurements in BFCT thin film. Both the results indicate the intrinsic ferroelectric property, and the leakage current does not play a big role in BFCT film. Meanwhile, the ɛ-V curve can also support the natural ferroelectricity in the BFCT film. We also found that the BFCT film shows weak ferromagnetism with the saturated magnetization (Ms) ∼2.6 emu/cm3. Furthermore, the magneto-dielectric effect was observed with MDC ∼ 0.39% at the frequency 100 kHz. The origin of weak ferromagnetism and the magneto-dielectric effect was discussed.
Dielectric studies and band gap tuning of ferroelectric Cr-doped ZnO nanorods
Authors: Gupta Manoj K. , Sinha Nidhi , Kumar Binay
Published: July 2012

Effect of Cr-doping on the optical behavior of ZnO nanorods (NRs) (size: diameter ∼ 40 nm and length ∼ 400 nm) is reported. Significant red shift of 18 nm was observed in UV-Vis studies, i.e., a band gap tuning is achieved by Cr doping. In photoluminescence studies, a very remarkable blue shift of 16 nm in green emission was observed. Significant shifts in various modes of Raman spectra of Cr-doped ZnO nanorods are observed in low and high wavenumber region, along with appearance and disappearance of other peaks. The results suggest that Cr-doping can affect the defects and oxygen vacancies in ZnO nanomaterials giving the possibility of fine band gap tuning for tailor made applications of nano-optoelectronics devices. A very high dielectric constant (950) at low frequency side and ferroelectric phase transition (69 °C) were found for Cr-doped ZnO NR, which make it suitable for charge storage and nanoscale memory devices.
Coherent phonon dynamics at the martensitic phase transition of Ni2MnGa
Authors: Mariager S. O. , Caviezel A. , Beaud P. , Quitmann C. , Ingold G.
Published: July 2012

We use time-resolved optical reflectivity to study the laser stimulated dynamics in the magnetic shape memory alloy Ni2MnGa. We observe two coherent optical phonons, at 1.2 THz in the martensite phase and at 0.7 THz in the pre-martensite phase, which we interpret as a zone-folded acoustic phonon and a heavily damped amplitudon, respectively. In the martensite phase the martensitic phase transition can be induced by a fs laser pulse on a timescale of a few ps.
Thermal conductivity modeling of periodic porous silicon with aligned cylindrical pores
Authors: Hsieh Tse-Yang , Lin Herng , Hsieh Tsang-Jen , Huang Juan-Chen
Published: July 2012

We present a frequency-dependent phonon Boltzmann transport equation (BTE) solver to study phonon transport in arbitrary geometries. For composite and porous structures, most simulations adopted either gray-medium approximation or geometric simplification in phonon BTE model. To show the importance of considering the frequency-dependent phonon transport, transverse thermal transport in periodic porous silicon (PS) with aligned square-cylindrical pores is investigated by the present frequency-dependent phonon BTE solver and gray-medium phonon BTE solver. It is found that phonon size effect is underestimated by adopting the gray-medium approximation in sub-micron scale. To demonstrate geometry effect, the frequency-dependent phonon BTE solver is applied to study transverse thermal transport in the PS with square-cylindrical and circular-cylindrical pores for various characteristic sizes and porosities. The pore shape is found to make great difference to the thermal conductivity of the PS when the characteristic size is decreased or the porosity is increased. Our results indicate the importance of considering the frequency dependence of phonon transport as well as the exact geometry of material structure in the analysis of micro- and nanostructured materials.
High pressure melting curve of tin measured using an internal resistive heating technique to 45 GPa
Authors: Weir S. T. , Lipp M. J. , Falabella S. , Samudrala G. , Vohra Y. K.
Published: July 2012

The high pressure melting curve of tin was measured to 45 GPa using a designer diamond anvil cell with an integrated internal resistive heating element. Melting of the tin sample was detected by an abrupt increase in the electrical resistance of the sample and also by a change in the slope of the electrical heating power versus temperature curve. The melting temperatures determined by these two methods are in good agreement with each other. We find that the melting temperature of tin tends to monotonically increase with increasing pressure and reaches a temperature of about 2000 K at 45 GPa.
Structural properties and energetics of diffuse 87Rb clusters in three-dimension
Authors: Debnath Pankaj Kumar , Chakrabarti Barnali , Das Tapan Kumar , Canuto Sylvio
Published: July 2012

A correlated two-body basis function is used to describe the three-dimensional bosonic clusters interacting via two-body van der Waals potential. We calculate the ground state and the zero orbital angular momentum excited states for RbN clusters with up to N = 40. We solve the many-particle Schrödinger equation by potential harmonics expansion method, which keeps all possible two-body correlations in the calculation and determines the lowest effective many-body potential. We study energetics and structural properties for such diffuse clusters both at dimer and tuned scattering length. The motivation of the present study is to investigate the possibility of formation of N-body clusters interacting through the van der Waals interaction. We also compare the system with the well studied He, Ne, and Ar clusters. We also calculate correlation properties and observe the generalised Tjon line for large cluster. We test the validity of the shape-independent potential in the calculation of the ground state energy of such diffuse cluster. These are the first such calculations reported for Rb clusters.
Piezoresponse properties of orderly assemblies of BaTiO3 and SrTiO3 nanocube single crystals
Authors: Mimura K. , Kato K. , Imai H. , Wada S. , Haneda H. , Kuwabara M.
Published: July 2012

Orderly assemblies of BaTiO3 (BT) nanocubes, SrTiO3 (ST) nanocubes and BT-ST mixture nanocubes were fabricated on Pt-coated Si substrate directly by solution self-assembly and heated at 850 °C. The dielectric nanocubes aligned face to face in a quite wide region of several tens of square-micrometers with a height of one micrometer, and even inside of the structures was ordered. The piezoresponse of BT-ST mixture assembly showed non-linear curve and stepwise behavior at high poling field, which differed from ferroelectric BT and paraelectric ST nanocube assemblies.
Light controlled magnetoresistance and magnetic field controlled photoresistance in CoFe film deposited on BiFeO3
Authors: Kundys B. , Meny C. , Gibbs M. R. J. , Da Costa V. , Viret M. , Acosta M. , Colson D. , Doudin B.
Published: July 2012

We present a magnetoresistive—photoresistive device based on the interaction of a piezomagnetic CoFe thin film with a photostrictive BiFeO3 (BFO) substrate that undergoes light-induced strain. The magnitude of the resistance and magnetoresistance in the CoFe film can be controlled by the wavelength of the incident light on the BiFeO3. Moreover, a light-induced decrease in anisotropic magnetoresistance is detected due to an additional magnetoelastic contribution to magnetic anisotropy of the CoFe film. This effect may find applications in photo-sensing systems, wavelength detectors and can possibly open a research development in light-controlled magnetic switching properties for next generation magnetoresistive memory devices.
Shift of morphotropic phase boundary in high-performance [111]-oriented epitaxial Pb (Zr, Ti) O3 thin films
Authors: Yu Qi , Li Jing-Feng , Zhu Zhi-Xiang , Xu Ying , Wang Qing-Ming
Published: July 2012

High-performance epitaxial niobium-doped lead zirconate titanate thin films [Pb(ZrxTi1−x)0.98Nb0.02O3] with a fixed thickness were deposited on [111]-cut single-crystalline SrTiO3 substrates by a sol-gel process as a function of Zr/Ti ratio ranging from 20/80 to 80/20. An obvious shift of morphotropic phase boundary (MPB) was observed in the [111]-oriented epitaxial films. Deviating from the Zr/Ti ratio of 52/48 in bulk materials, the MPB composition in the as-deposited films was found to move to a lower Zr/Ti ratio between 30/70 and 40/60, which agrees with the theoretical analysis on the basis of lattice mismatch between films and substrates and is further confirmed by the XRD patterns and Raman spectrum as well as ferroelectric test. Furthermore, a superior remnant polarization (Pr) value among all the compositions was obtained at a Zr/Ti ratio of 30/70, indicating that the extrinsic ferroelectric polarization near the new morphotropic phase boundary will lead to outstanding dielectric and piezoelectric performance in the epitaxial PZT thin film system.
Asymmetries in vertical vorticity and vertical velocity arising during nonlinear homogeneous spindown
Authors: Benthuysen J. A. , Thomas L. N.
Published: July 2012

During the spindown of a unidirectional, geostrophic current in a homogeneous fluid, asymmetry arises in the vertical velocity and vertical relative vorticity fields. A closed-form, time-dependent solution valid to order Rossby number is derived to explore these asymmetries. Momentum advection in the interior and the Ekman layer leads to competing tendencies in the vertical vorticity's evolution. In the interior, momentum advection hastens spindown in cyclonic regions. In the Ekman layer, momentum advection weakens Ekman pumping over Ekman suction and thus tends to slow the spindown of cyclonic vorticity. It is shown that the former effect dominates, and hence cyclonic vorticity decays faster than anticyclonic vorticity.
Control of unsteadiness of a shock wave/turbulent boundary layer interaction by using a pulsed-plasma-jet actuator
Authors: Narayanaswamy Venkateswaran , Raja Laxminarayan L. , Clemens Noel T.
Published: July 2012

A pulsed-plasma jet actuator is used to control the unsteady motion of the separation shock of a shock wave/boundary layer interaction formed by a compression ramp in a Mach 3 flow. The actuator is based on a plasma-generated synthetic jet and is configured as an array of three jets that can be injected normal to the cross-flow, pitched, or pitched and skewed. The typical peak jet exit velocity of the actuators is about 300 m/s and the pulsing frequencies are a few kilohertz. A study of the interaction between the pulsed-plasma jets and the shock/boundary layer interaction was performed in a time-resolved manner using 10 kHz schlieren imaging. When the actuator, pulsed at StL ≈ 0.04 (f = 2 kHz), was injected into the upstream boundary layer, the separation shock responded to the plasma jet by executing a rapid upstream motion followed by a gradual downstream recovery motion. Schlieren movies of the interaction showed that the separation shock unsteadiness was locked to the pulsing frequency of the actuator, with amplitude of about one boundary layer thickness. Wall-pressure measurements made under the intermittent region showed about a 30% decrease in the overall magnitude of the pressure fluctuations in the low-frequency band associated with unsteady large-scale motion of the separated flow. Furthermore, by increasing the pulsing frequency to 3.3 kHz, the amplitude of the separation shock oscillation was reduced to less than half the boundary layer thickness. Investigation into the effect of the actuator location on the shock wave/boundary layer interaction (SWBLI) showed qualitatively and quantitatively that the actuator placed upstream of the separation shock caused significant modification to the SWBLI unsteadiness, whereas injection from inside the separation bubble did not cause a noticeable effect.
Secondary energy growth and turbulence suppression in conducting channel flow with streamwise magnetic field
Authors: Dong Shuai , Krasnov Dmitry , Boeck Thomas
Published: July 2012

The effects of a streamwise magnetic field on conducting channel flow are studied by analyzing secondary linear perturbations evolving on streamwise streaks and by direct numerical simulations of relaminarization. By means of an optimal perturbation approach, magnetic damping is found to increase the streamwise wavelength of the most amplified secondary perturbations and to reduce their amplification level. Complete suppression of secondary instability is observed at a critical magnetic interaction parameter that depends on the streak amplitude and on the Reynolds number when the transient evolution of the streaky basic flow is taken into account. Relaminarization in the direct numerical simulation occurs at lower values of the interaction parameter than the critical values from the stability computations for the streak amplitudes considered. The dependence of these threshold values of the interaction parameters on the Reynolds number is fairly similar between simulations and stability analysis. Relaminarization thresholds from the simulations are also in good agreement with experiments on pipe flow with streamwise magnetic field.
Large eddy simulation of smooth-wall, transitional and fully rough-wall channel flow
Authors: Saito Namiko , Pullin Dale I. , Inoue Michio
Published: July 2012

Large eddy simulation (LES) is reported for both smooth and rough-wall channel flows at resolutions for which the roughness is subgrid. The stretched vortex, subgrid-scale model is combined with an existing wall-model that calculates the local friction velocity dynamically while providing a Dirichlet-like slip velocity at a slightly raised wall. This wall model is presently extended to include the effects of subgrid wall roughness by the incorporation of the Hama's roughness function \documentclass[12pt]{minimal}\begin{document}$\Delta U^+(k_{s\infty }^+)$\end{document}ΔU+(ks∞+) that depends on some geometric roughness height ks∞ scaled in inner variables. Presently Colebrook's empirical roughness function is used but the model can utilize any given function of an arbitrary number of inner-scaled, roughness length parameters. This approach requires no change to the interior LES and can handle both smooth and rough walls. The LES is applied to fully turbulent, smooth, and rough-wall channel flow in both the transitional and fully rough regimes. Both roughness and Reynolds number effects are captured for Reynolds numbers Reb based on the bulk flow speed in the range 104–1010 with the equivalent Reτ, based on the wall-drag velocity uτ varying from 650 to 108. Results include a Moody-like diagram for the friction factor f = f(Reb, ε), ε = ks∞/δ, mean velocity profiles, and turbulence statistics. In the fully rough regime, at sufficiently large Reb, the mean velocity profiles show collapse in outer variables onto a roughness modified, universal, velocity-deficit profile. Outer-flow stream-wise turbulence intensities scale well with uτ for both smooth and rough-wall flow, showing a log-like profile. The infinite Reynolds number limits of both smooth and rough-wall flows are explored. An assumption that, for smooth-wall flow, the turbulence intensities scaled on uτ are bounded above by the sum of a logarithmic profile plus a finite function across the whole channel suggests that the infinite Reb limit is inviscid slip flow without turbulence. The asymptote, however, is extremely slow. Turbulent rough-wall flow that conforms to the Hama model shows a finite limit containing turbulence intensities that scale on the friction factor for any small but finite roughness.
Reduction of mean-square advection in turbulent passive scalar mixing
Authors: Bos Wouter J. T. , Rubinstein Robert , Fang Le
Published: July 2012

Direct numerical simulation data show that the variance of the coupling term in passive scalar advection by a random velocity field is smaller than it would be if the velocity and scalar fields were statistically independent. This effect is analogous to the “depression of nonlinearity” in hydrodynamic turbulence. We show that the trends observed in the numerical data are qualitatively consistent with the predictions of closure theories related to Kraichnan's direct interaction approximation. The phenomenon is demonstrated over a range of Prandtl numbers. In the inertial-convective range the depletion is approximately constant with respect to wavenumber. The effect is weaker in the Batchelor range.
Equivalence of the Wei potential model and Tietz potential model for diatomic molecules
Authors: Jia Chun-Sheng , Diao Yong-Feng , Liu Xiang-Jun , Wang Ping-Quan , Liu Jian-Yi , Zhang Guang-Dong
Published: July 2012

By employing the dissociation energy and the equilibrium bond length for a diatomic molecule as explicit parameters, we generate improved expressions for the well-known Rosen-Morse, Manning-Rosen, Tietz, and Frost-Musulin potential energy functions. It is found that the well-known Tietz potential function that is conventionally defined in terms of five parameters [T. Tietz, J. Chem. Phys. 38, 3036 (1963)10.1063/1.1733648] actually only has four independent parameters. It is shown exactly that the Wei [Phys. Rev. A 42, 2524 (1990)]10.1103/PhysRevA.42.2524 and the well-known Tietz potential functions are the same solvable empirical function. When the parameter h in the Tietz potential function has the values 0, +1, and −1, the Tietz potential becomes the standard Morse, Rosen-Morse, and Manning-Rosen potentials, respectively.
A lateral double-diffused magnetic sensitive metal-oxide-semiconductor field-effect transistor with integrated n-type Hall plate
Authors: Janković N. , Pantić D. , Batcup S. , Igić P.
Published: July 2012

A magnetic sensitive device, lateral double-diffused magnetic sensitive metal-oxide-semiconductor field-effect transistor (LD MagFET), combining the sensory operation of conventional magnetic sensitive metal-oxide-semiconductor field-effect transistors (MagFETs) and Hall plates is proposed. The sensor device is fully compatible with a high-voltage complementary metal-oxide-semiconductor (CMOS) technology. It is found that the LD MagFET with integrated Hall plate exhibits an order of magnitude higher relative magnetic sensitivity in comparison with the split-drain silicon MagFETs in standard CMOS.
Effective light trapping in thin film silicon solar cells from textured Al doped ZnO substrates with broad surface feature distributions
Authors: Wang Yanfeng , Zhang Xiaodan , Bai Lisha , Huang Qian , Wei Changchun , Zhao Ying
Published: July 2012

We used a multi-step process to make aluminum-doped ZnO (AZO) films with a wide range distribution of textures for light trapping in thin film silicon solar cells, which includes AZO deposition, HCl etching, AZO re-deposition, and HCl re-etching. The large features created by the first etching provide an effective light trapping for long wavelength light; the small features from the second etching enhances the short wavelength light trapping. Microcrystalline silicon solar cells deposited on the above-mentioned AZO show an improved photocurrent density without loss in the open-circuit voltage and fill factor, resulting in an overall increase in efficiency by 14.64%.
Mechanism of formation of the misfit dislocations at the cubic materials interfaces
Authors: Wang Yi , Ruterana P. , Kret S. , Chen J. , El Kazzi S. , Desplanque L. , Wallart X.
Published: July 2012

High-angle annular dark-field scanning transmission electron microscopy and molecular dynamic simulation are applied to study the misfit dislocations at the GaSb/GaAs interface. In the investigated samples, three types of misfit dislocations have been observed: shuffle and glide set Lomer dislocations and 60° dislocation pairs. The dislocation density tensor analysis is next used to quantify the Burgers vector of misfit dislocations and investigate the misfit dislocation formation mechanism. This work demonstrates that, in these hetero-structures, the dominant mechanism underlying the formation of misfit dislocations is the glide and reaction of 60° dislocations. It is shown that the final structure of each misfit dislocation depends on the Burgers vectors of the initial 60° dislocations. Finally, this analysis points out an approach to determine the local rotation at interface due to mixed type dislocations.
Stress dependence of thermally driven pyroelectric charge release during FER-FEO phase transformations in [011] cut relaxor ferroelectric crystals
Authors: Dong Wen D. , Finkel Peter , Amin Ahmed , Lynch Christopher S.
Published: July 2012

The stress dependence of thermally driven polarization change is reported for a ferroelectric rhombohedral to ferroelectric orthorhombic phase transformation in [011] cut and poled Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT). A jump in polarization and strain is associated with a phase transformation of the ferroelectric material. The phase transformation temperature can be tuned, over a broad temperature range, through the application of bias stress. This phenomenon has applications in the field of energy harvesting and thermal sensing.
Real time quasiparticle tunneling measurements on an illuminated quantum capacitance detector
Authors: Stone K. J. , Megerian K. G. , Day P. K. , Echternach P. M. , Bueno J. , Llombart N.
Published: July 2012

Quasiparticle tunneling events are measured in real time using a quantum capacitance detector (QCD), allowing for the extraction of tunneling rates as a function of temperature and optical loading of radiation coming from a black body source filtered to 200 m. The measurements are used to corroborate the basic operating principles of the QCD. An estimate of the residual quasiparticle density is made, and the noise equivalent power (NEP) is assessed to be 7.2×10−20W/Hz1/2 at the lowest signal power of 9.2×10−20W. This NEP was higher than the photon noise by only a factor of 7 over a wide signal power range.
Nusselt number and friction factor correlations for solar air heater duct with broken V-down ribs combined with staggered rib roughness
Authors: Patil Anil K. , Saini J. S. , Kumar K.
Published: July 2012

Artificial roughening of a broad wall of solar air heater leads to significant enhancement in heat transfer besides comparable rise in friction losses. This paper presents the outcome of experimental study on heat transfer and fluid friction characteristics of solar air heater duct roughened with broken V-down rib combined with staggered rib piece. Experimental data were collected on a high aspect ratio rectangular duct by varying the Reynolds number from 3000 to 17 000, relative gap position (s′/s) 0.2–0.8, relative staggered rib position (p′/p) 0.2–0.8, relative staggered rib size (r/e) 1–2.5, for the fixed values of relative roughness pitch (p/e) of 10, relative roughness height (e/Dh) of 0.043, relative gap size (g/e) of 1, and angle of attack (α) of 60°. The effect of flow Reynolds number and roughness parameters on Nusselt number and friction factor has been explored and the results are compared with continuous V-down rib roughened duct and smooth duct under similar flow conditions. Correlations for the Nusselt number and friction factor as a function of Reynolds number and roughness parameters have been developed.
Surface-bound-exciton emission associated with domain interfaces in m-plane ZnO films
Authors: Kuo C. C. , Lin B. H. , Yang Song , Liu W. R. , Hsieh W. F. , Hsu C.-H.
Published: July 2012

Small amount of (101¯3)ZnO domains were found in the m-plane ZnO films grown on m-sapphire by pulsed laser deposition, which provide strain relaxation of the m-ZnO matrix behaving as a low strain layer. Through carefully correlating low-temperature polarized photoluminescence spectra with the x-ray diffraction peak intensity ratio of (101¯3)ZnO/(101¯0)ZnO of the samples grown at different temperature and after thermal treatment, we found that the broad-band emission around 3.17 eV may result from the interface defects trapped excitons at the boundaries between the (101¯3)ZnO domains and the m-ZnO matrix. The more (101¯3)ZnO domains in the m-ZnO layer cause the more surface boundary that makes the stronger surface-bound-exciton emission. And the a-axes of both the (101¯3)ZnO domains and the m-ZnO matrix are aligned with the c-axis of the sapphire (α-Al2O3) substrate. The c-axis of the (101¯3)ZnO domains rotates by about ±59° against the common a-axis of the m-ZnO.
Edge effect on thermal transport in graphene nanoribbons: A phonon localization mechanism beyond edge roughness scattering
Authors: Wang Yan , Qiu Bo , Ruan Xiulin
Published: July 2012

Equilibrium molecular dynamics simulations show that graphene nanoribbons (GNRs) with zigzag edges have higher thermal conductivity (κ) than armchair-edged ones, and the difference diminishes with increasing temperature or ribbon width. The dominant phonon wavelength for thermal transport can be much longer (by orders of magnitude) than the difference between the “roughness” of smooth zigzag and armchair edges. Therefore, the roughness scattering theory is not sufficient to explain the largely different κ of GNRs with different edge chiralities. Cross-sectional decomposition of the steady-state heat flux shows significant suppression of thermal transport at edges, especially in armchair ones. This behavior is explored by phonon spectra analysis. Considerable phonon localization at edges is concluded to underlie the edge-chirality dependent κ of GNRs.
Magnetoresistance and magnetocaloric properties involving strong metamagnetic behavior in Fe-doped Ni45(Co1−xFex)5Mn36.6In13.4 alloys
Authors: Chen L. , Hu F. X. , Wang J. , Bao L. F. , Sun J. R. , Shen B. G. , Yin J. H. , Pan L. Q.
Published: July 2012

Here, we report the co-substitution of Fe and Co for Ni atoms on metamagnetic behavior, martensitic transformation, and transport and magnetocaloric properties in Ni45(Co1−xFex)5Mn36.6In13.4 (x = 0∼0.05) alloys. It is found that the introduction of Fe atoms stabilizes martensitic phase and shifts martensitic temperature (TM) to higher temperature. Meanwhile, the Curie temperature TC of parent phase notably decreases. Upon Fe doping, the low magnetization of martensitic phase keeps nearly unchanged while the magnetization of parent phase slightly decreases. As a result, the Fe-doped samples maintain strong metamagnetic behavior and show great MR and MCE in an extended temperature range around room temperature. The hysteresis loss is reduced upon Fe-doping, which leads to an enhancement of effective RC by 15%.
Interface roughness scattering in ultra-thin N-polar GaN quantum well channels
Authors: Singisetti Uttam , Hoi Wong Man , Mishra Umesh K.
Published: July 2012

In this Letter, we report experimental and theoretical investigations on the effect of the channel thickness on the low-field electron mobility in N-polar GaN quantum well channels. From temperature dependent Hall mobility data and numerical modeling of the mobility, the interface roughness is identified as a strong factor in determining the low field mobility as the channel thickness is scaled down. In the graded AlGaN back-barrier N-polar GaN field effect transistor structures studied here, the roughness leads to localization of electrons at a channel thickness of 3.5 nm leading to extremely low mobility.
Enhanced high thermal conductivity and low permittivity of polyimide based composites by core-shell Ag@SiO2 nanoparticle fillers
Authors: Zhou Yongcun , Wang Lu , Zhang Hu , Bai Yuanyuan , Niu Yujuan , Wang Hong
Published: July 2012

A kind of polymer based composites was prepared by embedding the fillers of core-shell Ag@SiO2 nanoparticles into the polyimide (PI) matrix. The obtained Ag@SiO2/PI (50% vf of fillers) composites show remarkably improved high thermal conductivity and low relative permittivity. The maximum value of the thermal conductivity of composites is 7.88 W/(mK) and the relative permittivity and dielectric loss are about 11.7 and 0.015 at 1 MHz, respectively. Compared with self-passivated nanometer Al* particles composites, core-shell Ag@SiO2 nano-composite is beneficial to increase the thermal conductivity and reduce the permittivity of the composites. The relative mechanism was studied and discussed.
Material with high dielectric constant, low dielectric loss, and good mechanical and thermal properties produced using multi-wall carbon nanotubes wrapped with poly(ether sulphone) in a poly(ether ether ketone) matrix
Authors: Zhang Shuling , Wang Hongsong , Wang Guibin , Jiang Zhenhua
Published: July 2012

A material with high dielectric constant, low dielectric loss, and good mechanical and thermal properties was produced using multi-wall carbon nanotubes (MWCNTs) wrapped with poly(ether sulphone) (PES) dispersed in a poly(ether ether ketone) (PEEK) matrix. The material was fabricated using melt-blending, and MWCNT/PEEK composites show different degrees of improvement in the measured dielectric, mechanical, and thermal properties as compared to pure PEEK. This is attributed to the high conductivity of MWCNTs, the effect of wrapping MWCNTs with PES, the good dispersion of the wrapped MWCNTs in PEEK, and the strong interfacial adhesion between the wrapped MWCNTs and the PEEK.
Graphene photodetectors get gain
Authors: Wilson R. Mark
Published: July 2012

By spraying quantum dots onto a graphene flake in a circuit, researchers have produced a phototransistor a billion times more sensitive than any prior graphene-based device.
Canada’s researchers fret over shifts in funding landscape
Authors: Feder Toni
Published: July 2012

Moves to increase global competitiveness could hurt the country’s research enterprise.
New international scientific organization is launched
Authors: Kramer David
Published: July 2012

Goal is to harmonize peer review criteria and other research policy issues among developed and developing nations.
Topological phases and quasiparticle braiding
Authors: Read Nicholas
Published: July 2012

Phases of matter distinguished by topological properties sometimes possess quasiparticles with bizarre statistics. Those that do may see applications in quantum information processing.
Discovery or fluke: statistics in particle physics
Authors: Lyons Louis
Published: July 2012

When you’re searching for elusive manifestations of new physics, it’s easy to be fooled by statistical fluctuations or instrumental quirks.
Musical rhythms: The science of being slightly off
Authors: Hennig Holger , Fleischmann Ragnar , Geisel Theo
Published: July 2012

With a statistical understanding of our natural rhythmic imperfections, one can make computer-generated music sound more human.
Erratum to: Estimating mineralisation of organic nitrogen from biosolids and other organic wastes applied to soils in subtropical Australia
Authors: Pu Guixin , Bell Mike , Barry Glenn , Want Peter
Published: July 2012

One major benefit of land application of biosolids is to supply nitrogen (N) for agricultural crops, and understanding mineralisation processes is the key for better N-management strategies. Field studies were conducted to investigate the process of mineralisation of three biosolids products (aerobic, anaerobic, and thermally dried biosolids) incorporated into four different soils at rates of 7?90 wet t/ha in subtropical Queensland. Two of these studies also examined mineralisation rates of commonly used organic amendments (composts, manures, and sugarcane mill muds).
Organic N in all biosolids products mineralised very rapidly under ambient conditions in subtropical Queensland, with rates much faster than from other common amendments. Biosolids mineralisation rates ranged from 30 to 80% of applied N during periods ranging from 3.5 to 18 months after biosolids application; these rates were much higher than those suggested in the biosolids land application guidelines established by the NSW EPA (15% for anaerobic and 25% for aerobic biosolids). There was no consistently significant difference in mineralisation rate between aerobic and anaerobic biosolids in our studies. When applied at similar rates of N addition, other organic amendments supplied much less N to the soil mineral N and plant N pools during the crop season.
A significant proportion of the applied biosolids total N (up to 60%) was unaccounted for at the end of the observation period. High rates of N addition in calculated Nitrogen Limited Biosolids Application Rates (850?1250 kg N/ha) resulted in excessive accumulation of mineral N in the soil profile, which increases the environmental risks due to leaching, runoff, or gaseous N losses. Moreover, the rapid mineralisation of the biosolids organic N in these subtropical environments suggests that biosolids should be applied at lower rates than in temperate areas, and that care must be taken with the timing to maximise plant uptake and minimise possible leaching, runoff, or denitrification losses of mineralised N.
Formal mismatches and functional advantage in syntactic change
Authors: Madariaga Nerea
Published: July 2012

This paper relies on the idea that syntactic change stems from linguistic factors that are different in nature and, consequently, trigger different results. Specifically, I distinguish the causes, processes and results related to two different kinds of syntactic change, a ‘formal’ type of change vs. a ‘functional’ one. The hypotheses pursued here are the following: (i) Mismatches between the formal features a learner has acquired and certain data she receives during the language acquisition period lead to a syntactic change type, which restructures completely the syntactic derivation involved; (ii) The advantage of parsing one variant over parsing another triggers a different kind of change, namely one that affects specific instances or uses / registers of the crucial syntactic structure. To illustrate this, I analyze the role of functional advantage and formal changes in the historical development of the case system of Russian non-verbal predication.
The cohesiveness of English and German compounds
Authors: Berg Thomas
Published: July 2012

This paper compares the cohesiveness of English and German compounds. Cohesiveness is understood as the extent to which two given elements are integrated into a larger structural unit. The null hypothesis according to which the compounds in the two languages are equicohesive is rejected on the strength of an extended quantitative analysis. The results of ten empirical tests are consistent with the hypothesis that English compounds are less cohesive than their German counterparts. As the degree of cohesion is inversely related to the position of a given unit in the linguistic hierarchy, English compounds are argued to be more phrase-like, whereas German compounds are more word-like. German imposes more rigorous constraints on compounding than English. Thus, the prototypical categories of English and German compounds differ in terms of their formal content. Since compounds are essentially words, two somewhat disparate definitions of word prevail in the two languages. Following up on an idea put forward by Klinge (2009), the cross-linguistic difference emanates from the varying importance of inflectional morphology in the two languages. Cohesiveness is supposedly a level-specific rather than a language-wide factor.
Complement Coercion
Authors: Katsika Argyro , Braze David , Deo Ashwini , Piñango Maria Mercedes
Published: July 2012

Although Complement Coercion has been systematically associated with computational cost, there remains a serious confound in the experimental evidence built up in previous studies. The confound arises from the fact that lexico-semantic differences within the set of verbs assumed to involve coercion have not been taken into consideration. From among the set of verbs that have been reported to exhibit complement coercion effects we identified two clear semantic classes — aspectual verbs and psychological verbs. We hypothesize that the semantic difference between the two should result in differing processing profiles. Aspectual predicates (begin) trigger coercion and processing cost while psychological predicates (enjoy) do not. Evidence from an eye-tracking experiment supports our hypothesis. Coercion costs are restricted to aspectual predicates while no such effects are found with psychological predicates. These findings have implications for how these two kinds of predicates might be lexically encoded as well as for whether the observed interpolation of eventive meaning can be attributed to type-shifting (e.g., McElree, Traxler, Pickering, Seely, & Jackendoff, 2001) or to pragmatic-inferential processes (e.g., De Almeida, 2004).
Processing morphologically conditioned word accents
Authors: Söderström Pelle , Roll Mikael , Horne Merle
Published: July 2012

The present response time study investigated the influence Central Swedish word accents have on the interpretation of inflectional morphology. Effects of stem tone match/mismatch on the interpretation of Swedish present and past tense suffixes were tested. Both Accent 1 and Accent 2 were found to influence listeners’ response times related to decisions on verb tense. It thus seems that both word accents can facilitate online interpretation of words. Previous studies where tasks have not required suffix interpretation have only found an effect of Accent 1 patterns on Accent 2-associated suffixes. Accent 2 suffixes further yielded generally greater response times than Accent 1-associated suffixes. Different possible explanations for this are discussed.
Bioenergetic Response by Steelhead to Variation in Diet, Thermal Habitat, and Climate in the North Pacific Ocean
Authors: Atcheson Margaret E. , Myers Katherine W. , Beauchamp David A. , Mantua Nathan J.
Published: July 2012

Energetic responses of steelhead Oncorhynchus mykiss to climate‐driven changes in marine conditions are expected to affect the species’ ocean distribution, feeding, growth, and survival. With a unique 18‐year data series (1991–2008) for steelhead sampled in the open ocean, we simulated interannual variation in prey consumption and growth efficiency of steelhead using a bioenergetics model to evaluate the temperature‐dependent growth response of steelhead to past climate events and to estimate growth potential of steelhead under future climate scenarios. Our results showed that annual ocean growth of steelhead is highly variable depending on prey quality, consumption rates, total consumption, and thermal experience. At optimal growing temperatures, steelhead can compensate for a low‐energy diet by increasing consumption rates and consuming more prey, if available. Our findings suggest that steelhead have a narrow temperature window in which to achieve optimal growth, which is strongly influenced by climate‐driven changes in ocean temperature.
Feeding Strategies and Diets of Young-of-the-Year Muskellunge from Two Large River Ecosystems
Authors: Kapuscinski Kevin L. , Farrell John M. , Murry Brent A.
Published: July 2012

We analyzed stomach contents from 674 young-of-the-year (age-0) muskellunge Esox masquinongy sampled in New York waters of the St. Lawrence and upper Niagara rivers to (1) describe diets and document use of nonnative prey, (2) examine the feeding strategy (generalized versus specialized) and the importance of different prey types, (3) evaluate temporal patterns in feeding strategy and prey importance, and (4) determine how prey length related to muskellunge length and whether this relationship differed among prey types. Banded killifish Fundulus diaphanus, native cyprinids, and tessellated darters Etheostoma olmstedi were the most important prey numerically and by weight in the St. Lawrence River. Native cyprinids, banded killifish, and darters (Etheostoma spp. and Percina spp.) were the most important prey in the Niagara River, but nonnative cyprinids were more important by weight than darters. Muskellunge from both rivers exhibited a specialized feeding strategy, with individuals specializing on different prey types. The muskellunge feeding strategy and the prey types of greatest importance were consistent among years and among months within years. The relationship between prey length and muskellunge length differed among prey types: as muskellunge length increased, lengths of laterally compressed, spiny prey increased at a slower rate than did the lengths of fusiform prey. Mean prey length as a proportion of predator length declined with increasing muskellunge length in the St. Lawrence River but was constant in the Niagara River. In the St. Lawrence River, prey length as a proportion of predator length decreased for all prey types except cyprinids, for which length was a constant proportion of predator length. Our results can be used to guide evaluations of prey fish assemblages at muskellunge nursery sites and to prioritize sites as candidates for protection, restoration, or use as stocking locations.

Received November 10, 2011; accepted February 13, 2012
The political economy of oil and ‘rebellion’ in Nigeria's Niger Delta
Authors: Nwajiaku-Dahou Kathryn
Published: July 2012

The escalation in armed attacks on Nigeria's oil industry and the massive expansion in oil theft generated a veritable industry in the study of the political economy of war dominated by public-choice strands. Critical scholarship on the Niger Delta challenges this work for its neglect of history in explaining the shift from peaceful protest in the 1990s to armed struggle. Yet taking history seriously need not blind us to the ‘critical breaks’. Nigeria's transition to civilian rule in 1999 brought state and non-state actors into a complicit union as rebellion and oil bunkering consolidated a pre-existing parallel economy.

[L'économie politique du pétrole et la « rébellion » dans le Delta du Niger, fief du Nigéria]. L'escalade dans les attaques armées sur l'industrie pétrolière du Nigéria et l'expansion massive dans le vol de pétrole ont généré une véritable industrie dans l'étude de l'économie politique de la guerre, dominée par quelques choix publics. L'étude critique sur le Delta du Niger conteste ce travail pour sa négligence de l'histoire pour expliquer ce passage de la manifestation pacifique dans les années 1990 à la lutte armée. Pourtant prendre l'histoire au sérieux ne doit pas nous aveugler sur « les ruptures critiques ». La transition du Nigéria vers un régime civil en 1999, a amené les acteurs de l'Etat et ceux qui ne relèvent pas de l'État à se fondre dans une union de complicité dès lors que la rébellion et le vol de pétrole avaient consolidé une économie parallèle préexistante.

Mots-clés :le pétrole ; la sécurité ; le Delta du Niger ; l'économie politique ; le militantisme ; l'identité