bluuebunny/crossref_metadata_2025 huggingface dataset:
Routes to complex dynamics in a ring of unidirectionally coupled systems
Authors: Perlikowski P. , Yanchuk S. , Wolfrum M. , Stefanski A. , Mosiolek P. , Kapitaniak T.
Published: March 2010

We study the dynamics of a ring of unidirectionally coupled autonomous Duffing oscillators. Starting from a situation where the individual oscillator without coupling has only trivial equilibrium dynamics, the coupling induces complicated transitions to periodic, quasiperiodic, chaotic, and hyperchaotic behavior. We study these transitions in detail for small and large numbers of oscillators. Particular attention is paid to the role of unstable periodic solutions for the appearance of chaotic rotating waves, spatiotemporal structures, and the Eckhaus effect for a large number of oscillators. Our analytical and numerical results are confirmed by a simple experiment based on the electronic implementation of coupled Duffing oscillators.
The existence of generalized synchronization of chaotic systems in complex networks
Authors: Hu Aihua , Xu Zhenyuan , Guo Liuxiao
Published: March 2010

The paper studies the existence of generalized synchronization in complex networks, which consist of chaotic systems. When a part of modified nodes are chaotic, and the others have asymptotically stable equilibriums or orbital asymptotically stable periodic solutions, under certain conditions, the existence of generalized synchronization can be turned to the problem of contractive fixed point in the family of Lipschitz functions. In addition, theoretical proofs are proposed to the exponential attractive property of generalized synchronization manifold. Numerical simulations validate the theory.
Ab initio study of point defect structures and energetics in ZrC
Authors: Kim Sungtae , Szlufarska Izabela , Morgan Dane
Published: March 2010

The potential use of ZrC for nuclear applications in irradiated environments makes it important to determine the structure and energetics of its point defects. In this paper the structures and energies of potential vacancy and interstitial point defects are examined by means of ab initio calculations. It is shown that C vacancies are easily formed and that their ab initio energetics are consistent with thermodynamic models of phase stability of the off-stoichiometric ZrCx (x<1) material. C interstitials are shown to be the most stable interstitial defect and form a C–C–C trimer along the ⟨101⟩ direction. C vacancies and interstitials are found to be dramatically more stable than antisite defects or Zr vacancies or interstitials.
Relaxation phenomena in tellurite glasses
Authors: El-Mallawany R. , Sidky M. , Afifi H.
Published: March 2010

The new semiconducting noncrystalline solid “tellurite glasses” of the form 0.7 TeO2–(0.3−x)V2O5–xAnOm have been prepared in bulk form with different compositions where AnOm is CeO2 or ZnO and x=0.03,0.05,0.07,0.10 mol %. Longitudinal ultrasonic attenuation in these glasses has been measured at frequencies of 2, 4, 6, and 8 MHz and in the temperature range of 100–300 K. The results showed the presence of a very well defined peak which shifts to higher temperature with increasing frequency, suggesting a kind of relaxation process. The acoustic activation energy, as well as the relaxation frequency, has been calculated and correlated with the relaxation strength for each composition. Correlations between the present low temperature of ultrasonic attenuation and the previous room temperature elastic moduli have been achieved for both glass series.
Light-induced stress relief to improve flaw tolerance in network polymers
Authors: Long Kevin N. , Dunn Martin L. , Scott Timothy F. , Turpin Lucas P. , Qi H. Jerry
Published: March 2010

We demonstrate the ability to use photoactivated stress relaxation to improve flaw tolerance in network polymers. Unlike most self-healing polymers, which effectively close flaws by locally introducing healing agents (such as uncured resins), here light is used to relax elevated stresses around a flaw before it reaches a critical state, which reduces the threat that the flaw poses to the structural integrity of the material. In this study, we fabricate specimens with well-defined flaws and uniaxially stretch them to failure. By irradiating the specimens with UV light (365 nm) before failure, the nominal strain at failure is increased by 70% and the corresponding nominal stress is increased by 30% compared with nonirradiated specimens. To better understand the phenomena that occur at the multiaxial stress state at the flaw, we model the photomechanics using a recently developed finite element approach that accurately describes the light propagation, photochemistry, radical-induced network evolution, and the mechanical behavior of the material. Model predictions agree well with the experimental results and elucidate the role that photoinduced stress relaxation has on improving flaw tolerance.
Effect of carbon addition on the single crystalline magnetostriction of Fe-X (X=Al and Ga) alloys
Authors: Huang Mianliang , Du Yingzhou , McQueeney Robert J. , Lograsso Thomas A.
Published: March 2010

The effect of carbon addition on the magnetostriction of Fe–Ga and Fe–Al alloys was investigated and is summarized in this study. It was found that the addition of carbon generally increased the magnetostriction over binary alloys of Fe–Ga and Fe–Al systems. The formation of carbide in the Fe–Ga–C alloys with a composition near D03 phase region decreased the magnetostriction drastically. Fe–Al–C and Fe–Ga–C alloys responded differently to thermal treatments; the magnetostriction in the quenched Fe–Al–C alloys is equal to or slightly lower than that of the slow cooled as is observed in binary Fe–Al alloy; in contrast, the magnetostriction is generally higher in quenched Fe–Ga–C alloys than slow cooled condition, consistent with the behavior of binary alloys of Fe–Ga. A significant increase in magnetostriction between 25% and 165% depending on the phase region in Fe–Ga–C alloys by quenching was observed in the A2+D03 two-phase region and D03 single phase region.
Multiscroll attractors by switching systems
Authors: Campos-Cantón E. , Barajas-Ramírez J. G. , Solís-Perales G. , Femat R.
Published: March 2010

In this paper, we present a class of three-dimensional dynamical systems having multiscrolls which we call unstable dissipative systems (UDSs). The UDSs are dissipative in one of its components but unstable in the other two. This class of systems is constructed with a switching law to display various multiscroll strange attractors. The multiscroll strange attractors result from the combination of several unstable “one-spiral” trajectories by means of switching. Each of these trajectories lies around a saddle hyperbolic stationary point. Thus, we describe how a piecewise-linear switching system yields multiscroll attractors, symmetric or asymmetric, with chaotic behavior.
Electronic and optical properties of Cu2ZnSnS4 and Cu2ZnSnSe4
Authors: Persson Clas
Published: March 2010

The electronic structure as well as the optical response of kesterite and stannite structures of Cu2ZnSnS4 and Cu2ZnSnSe4 are analyzed by a relativistic full-potential linearized augmented plane wave method. The energy dispersion of the conduction-band edge reveals larger effective electron mass of the two Cu2ZnSnS4 compounds (mc1≈0.18m0) compared with Cu2ZnSnSe4 (mc1≈0.07m0). Whereas the effective electron mass tensor is fairly isotropic, the effective hole masses show strong anisotropy. The fundamental band-gap energy is estimated to be Eg≈1.5 eV for Cu2ZnSnS4 and Eg≈1.0 eV for Cu2ZnSnSe4. The larger band gap results in a smaller high-frequency dielectric constant: ε∞≈6.7 for Cu2ZnSnS4 whereas ε∞≈8.6 for Cu2ZnSnSe4. The characteristic anisotropy of the dielectric function ε(ω) in the stannite compounds allows for a complementary identification of the crystalline structure type. Overall, however, all four compounds show similar atomic-resolved density-of-states, dielectric function, and optical absorption coefficient α(ω).
Morphological evolution of pulsed laser deposited ZrO2 thin films
Authors: Álvarez R. , Palmero A. , Prieto-López L. O. , Yubero F. , Cotrino J. , de la Cruz W. , Rudolph H. , Habraken F. H. P. M. , Gonzalez-Elipe A. R.
Published: March 2010

Morphological evolution of ZrO2 thin films deposited during pulsed laser deposition of Zr in O2 atmosphere has been experimentally studied at two different film deposition temperatures, 300 and 873 K. The roughness exponent, α, the growth exponent, β, the coarsening exponent, 1/z, and the exponent defining the evolution of the characteristic wavelength of the surface, p, for depositions at 300 K amounted to β=1.0±0.1, α=0.4±0.1, 1/z=0.34±0.03, and p=0.49±0.03, whereas for depositions carried out at 873 K amounted to β=0.3±0.3, α=0.4±0.2, and 1/z=0.0±0.2. Experimental error becomes important due to the flat morphology of the films inherent to the deposition technique. The change in the surface topography with the film temperature has been studied with the help of a simple Monte Carlo model which indicates the existence of two different growth regimes: a shadowing dominated growth, occurring at low temperatures, characterized by calculated values β=1.00±0.04, α=0.50±0.04, p=0.46±0.01, and 1/z=0.35±0.02 and a diffusion dominated growth that takes place at high temperatures as well as at low deposition rates, characterized by calculated values β=0.15±0.08, α=0.33±0.04, and 1/z=0.33±0.07. The good agreement obtained between the experimental and simulated parameters is discussed within the frame of the general characteristics of the deposition method.
Single-electron pumping from a quantum dot into an electrode
Authors: Sasaoka Kenji , Yamamoto Takahiro , Watanabe Satoshi
Published: March 2010

The transient current dynamics of a quantum capacitor consisting of a quantum dot connected to a single electrode has been theoretically investigated by the nonequilibrium Green’s function method. We have clarified the influence of dot-electrode coupling strength on the transient current behavior of the quantum capacitor. Our simulation reproduces very well the behaviors seen in recent experimental results by Fève et al., [Science 316, 1169 (2007)], such as the increase in maximum value of instantaneous current and the decrease in total amount of electrons pumped from the dot when the dot-electrode coupling increases.
Si/SiGe quantum cascade superlattice designs for terahertz emission
Authors: Matmon G. , Paul D. J. , Lever L. , Califano M. , Ikonić Z. , Kelsall R. W. , Zhang J. , Chrastina D. , Isella G. , von Känel H. , Müller E. , Neels A.
Published: March 2010

Quantum cascade lasers (QCLs) are compact sources that have demonstrated high output powers at terahertz (THz) frequencies. To date, all THz QCLs have been realized in III-V materials. Results are presented from Si1−xGex quantum cascade superlattice designs emitting at around 3 THz which have been grown in two different chemical vapor deposition systems. The key to achieving successful electroluminescence at THz frequencies in a p-type system has been to strain the light-hole states to energies well above the radiative subband states. To accurately model the emission wavelengths, a 6-band k⋅p tool which includes the effects of nonabrupt heterointerfaces has been used to predict the characteristics of the emitters. X-ray diffraction and transmission electron microscopy have been used along with Fourier transform infrared spectroscopy to fully characterize the samples. A number of methods to improve the gain from the designs are suggested.
Macromolecular dynamics in crowded environments
Authors: Echeverria Carlos , Kapral Raymond
Published: March 2010

The structural and dynamical properties of macromolecules in confining or crowded environments are different from those in simple bulk liquids. In this paper, both the conformational and diffusional dynamics of globular polymers are studied in solutions containing fixed spherical obstacles. These properties are studied as a function of obstacle volume fraction and size, as well as polymer chain length. The results are obtained using a hybrid scheme that combines multiparticle collision dynamics of the solvent with molecular dynamics that includes the interactions among the polymer monomers and between the polymer beads and obstacles and solvent molecules. The dynamics accounts for hydrodynamic interactions among the polymer beads and intermolecular forces with the solvent molecules. We consider polymers in poor solvents where the polymer chain adopts a compact globular structure in solution. Our results show that the collapse of the polymer chain to a compact globular state is strongly influenced by the obstacle array. A nonmonotonic variation in the radius of gyration with time is observed and the collapse time scale is much longer than that in simple solutions without obstacles. Hydrodynamic interactions are important at low obstacle volume fractions but are screened at high volume fractions. The diffusion of the globular polymer chain among the obstacles is subdiffusive in character on intermediate time scales where the dynamics explores the local structure of the heterogeneous environment. For large polymer chains in systems with high obstacle volume fractions, the chain adopts bloblike conformations that arise from trapping of portions of the chain in voids among the obstacles.
Vibrational resonance in neuron populations
Authors: Deng Bin , Wang Jiang , Wei Xile , Tsang K. M. , Chan W. L.
Published: March 2010

In this paper different topologies of populations of FitzHugh–Nagumo neurons have been introduce to investigate the effect of high-frequency driving on the response of neuron populations to a subthreshold low-frequency signal. We show that optimal amplitude of high-frequency driving enhances the response of neuron populations to a subthreshold low-frequency input and the optimal amplitude dependences on the connection among the neurons. By analyzing several kinds of topology (i.e., random and small world) different behaviors have been observed. Several topologies behave in an optimal way with respect to the range of low-frequency amplitude leading to an improvement in the stimulus response coherence, while others with respect to the maximum values of the performance index. However, the best results in terms of both the suitable amplitude of high-frequency driving and high stimulus response coherence have been obtained when the neurons have been connected in a small-world topology.
Computational approaches to charge transfer excitations in a zinc tetraphenylporphyrin and C70 complex
Authors: Ghosh Prasenjit , Gebauer Ralph
Published: March 2010

Electronic charge transfer plays an important role in novel nanostructured photovoltaic materials. Standard density functional theory (DFT) as well as time-dependent DFT severely underestimate the excitation energies related to such transitions. For the paradigmatic case of a donor-acceptor dyad formed by a zinc-porphyrin donor and a C70 fullerene acceptor these shortcomings are illustrated. A better quantitative estimate of the charge transfer energy is obtained from constrained DFT which is applied to this system in a novel implementation based on a penalty functional.
Modified formulation of a rate-dependent damage model for ductile materials
Authors: Zuo Q. H.
Published: March 2010

A modification to the rate-dependent damage and failure model developed by Addessio and Johnson [J. Appl. Phys. 74, 1640 (1993)] for ductile materials under high-rate loading is presented. In the current formulation the equilibrium stress, which is used to calculate the plastic strain rate and damage in the material, is defined as the orthogonal projection of the final stress onto an equilibrium yield surface, instead of being a projection of the trial stress onto the yield surface as is done in the original formulation. The modification makes the current formulation fully consistent with the viscoplasticity theory. An implicit algorithm is also presented for the modified model and numerical results of copper under uniaxial strain loading are given to show the features of the model and the algorithm. Comparisons with the results of the original formulation are also presented.
The effect of vacancies on dynamic response of single crystal Cu to shock waves
Authors: Luo Sheng-Nian , Germann Timothy C. , Tonks Davis L.
Published: March 2010

Using molecular dynamics (MD) simulations, we investigate the effect of vacancies on the dynamic response of single crystal Cu to [100] shock loading, including plasticity and spallation, for an initial vacancy concentration (cv) ranging from 0% to 2%. A fixed impact velocity is adopted, for which plasticity and spall do not occur in the defect-free Cu during compression or tension. We show that shear flow strength (compressional or tensile) and spall strength decrease with increasing cv. At the MD scales, the vacancy effect becomes pronounced for cv>0.25%, where heterogeneous nucleation of plasticity prevails. Tensile plasticity may play a key role in inducing local heating and the power-law reduction in spall strength. Void nucleation occurs preferentially at highly sheared (plastically deformed) sites.
An analytic model of thermal drift in piezoresistive microcantilever sensors
Authors: Loui A. , Elhadj S. , Sirbuly D. J. , McCall S. K. , Hart B. R. , Ratto T. V.
Published: March 2010

A closed-form semiempirical model has been developed to understand the physical origins of thermal drift in piezoresistive microcantilever sensors. The two-component model describes both the effects of temperature-related bending and heat dissipation on the piezoresistance. The temperature-related bending component is based on the Euler–Bernoulli theory of elastic deformation applied to a multilayer cantilever. The heat dissipation component is based on energy conservation per unit time for a piezoresistive cantilever in a Wheatstone bridge circuit, representing a balance between electrical power input and heat dissipation into the environment. Conduction and convection are found to be the primary mechanisms of heat transfer, and the dependence of these effects on the thermal conductivity, temperature, and flow rate of the gaseous environment is described. The thermal boundary layer value that defines the length scale of the heat dissipation phenomenon is treated as an empirical fitting parameter. Using the model, it is found that the cantilever heat dissipation is unaffected by the presence of a thin polymer coating; therefore, the residual thermal drift in the differential response of a coated and uncoated cantilever is the result of nonidentical temperature-related bending. Differential response data show that residual drift is eliminated under isothermal laboratory conditions but not the unregulated and variable conditions that exist in the outdoor environment (i.e., the field). The two-component model is then validated by simulating the thermal drifts of an uncoated and a coated piezoresistive cantilever under field conditions over a 24 h period using only meteorological data as input variables.
Semiconductor-metal transition characteristics of VO2 thin films grown on c- and r-sapphire substrates
Authors: Yang Tsung-Han , Aggarwal Ravi , Gupta Alok , Zhou Honghui , Narayan Roger J. , Narayan J.
Published: March 2010

We have made a comparative study of epitaxial growth of VO2 thin films on c-cut (0001) and r-cut (11¯02) sapphire substrates, and the semiconductor to metal transition (SMT) characteristics of these films have been correlated with their structural details. On c-sapphire, VO2 grows epitaxially in (002) orientation. These (002) oriented VO2 films have 60° twin boundaries due to three equivalent in-plane orientations. The epitaxial VO2 films on r-sapphire consisted of two orientations, namely (200) and (2¯11). The coexistence of these two orientations of VO2 has been explained on the basis of similarity of atomic arrangements in (200) and (2¯11) planes. The thermal hysteresis (ΔH), sharpness of the transition (ΔT), and the transition temperature for VO2 films on c-sapphire were found to be 4.8, 8.5, and 72.6 °C, respectively, which were higher than the corresponding values of 3.3, 5.4, and 60.3 °C for films on r-sapphire. The SMT temperature for VO2 films on c-sapphire was close to the bulk value of 68.0 °C. The significant decrease in transition temperature to 60.3 °C for VO2 films on r-sapphire has been attributed to the compressive strain along [002] direction of VO2.
Ferrimagnetism in zigzag graphene nanoribbons induced by main-group adatoms
Authors: Kan Erjun , Xiang Hongjun , Wu Fang , Lee Changhoon , Yang Jinlong , Whangbo Myung-Hwan
Published: March 2010

Density functional calculations for zigzag graphene nanoribbons (ZGNRs) with adsorbed adatom AD (=B,C,N) show that these adatoms prefer the sites near the edge, and convert the antiferromagnetism of pristine ZGNRs into ferrimagnetism with high magnetic moment (i.e., 1, 2, and 1 μB per adatom for AD=B, C, and N, respectively). Further, the migration of the adatoms from one edge to the other across the ribbon is difficult. Thus, the ZGNRs with adsorbed adatom are promising for the future development of nanoscale functional spintronics and electric devices.
Broadband transparency by graded metamaterials
Authors: Wei En-Bo , Sun L. , Yu K. W.
Published: March 2010

In the quasistatic limit, Rayleigh scattering is investigated for a graded spherical metamaterial when the wavelength of light is larger than the particle diameter. As a theoretical model, we have exactly derived the dipole factor of the Rayleigh scattering electric field induced by the graded sphere metamaterial, whose permittivity is given by the graded Drude model. Our results show that the amplitude of scattering field can be controlled and remains very small over a broad frequency band by tuning the gradation profiles of particle permittivity. This implies that a broadband transparency of electric field is achieved by using graded metamaterials. Here, we offer a solvable example of very small Rayleigh scattering in a broad frequency band.
Experimental study of foam jets
Authors: Lespiat Rémi , Höhler Reinhard , Biance Anne-Laure , Cohen-Addad Sylvie
Published: March 2010

We investigate the flow of a foam injected through a cylindrical inlet into a quiescent liquid which is miscible with the foaming solution. Depending on a Reynolds number, combining inlet diameter, liquid viscosity, and flow rate, the jet disperses into a conical plume, takes a stable cylindrical straight shape whose radius swells with flow rate or disintegrates into blobs. We compare this behavior to that reported for other complex fluid jets and present a simple physical model for the straight jet regime.
Reactivity of neutral and charged B13 clusters with O2: A theoretical study
Authors: Slough William J. , Kandalam Anil K. , Pandey Ravindra
Published: March 2010

The chemical reactivity of neutral, cationic, and anionic species of the gas phase B13 cluster with molecular oxygen, O2, was investigated using density functional theory. All three species of B13 interact with an oxygen molecule to generate a variety of stable isomers, with those representing a dissociative chemisorption process forming the most stable configurations. Our results also show site-specific bonding of oxygen to the B13(+/0/−) cluster. The effect of sequential ionization on the formation of products is pronounced. In ionic B13 clusters, in addition to energetics, the spin of the reactants and products plays a vital role in determining the most favorable product channel. In addition, this study reveals a richness of phenomena requiring a unified consideration of energy, geometry, spin conversion, and details of the electronic structure not previously illustrated for the reactivity of boron clusters.
Ab initio study on noncompensated CrO codoping of GaN for enhanced solar energy conversion
Authors: Pan Hui , Gu Baohua , Eres Gyula , Zhang Zhenyu
Published: March 2010

We describe a novel photocatalyst obtained by codoping GaN with CrO, according to a new “noncompensated” codoping concept based on first-principles calculations. The approach enables controllable narrowing of the GaN band gap with significantly enhanced carrier mobility and photocatalytic activity in the visible light region and thus offers immense potential for application in solar energy conversion, water splitting, and a variety of solar-assisted photocatalysis. Our calculations indicate that the formation energy for the cation doping is greatly reduced by noncompensated codoping with an anion. Although Cr doping alone can split the band gap with the formation of an intermediate band, the mobility is low due to carrier trapping by the localized states. The first-principles calculations also demonstrate that CrO codoping of GaN shifts the Fermi level into the conduction band resulting in high carrier density and mobility.
Electrical characterization of devices based on carbon nanotube films
Authors: Koechlin Charlie , Maine Sylvain , Haidar Riad , Trétout Brigitte , Loiseau Annick , Pelouard Jean-Luc
Published: March 2010

Statistical study of electrical conduction on a large array of devices based on carbon nanotube films shows a weakly dispersive film conductivity, and a specific contact resistance of 1.1 10−6 Ω cm2, which is four orders of magnitude lower than previously reported values. This allows identifying the conductivity of the carbon nanotube films as driven by a fluctuation induced tunneling mechanism. Such results pave the way to the realization of optoelectronic devices, such as highly sensitive light or gas sensor arrays.
Analysis of the continuous-configuration time-dependent self-consistent field method applied to system-bath dynamics
Authors: López-López Sergio , Nest Mathias
Published: March 2010

We have implemented and studied the continuous-configuration time-dependent self-consistent field scheme, a variation of the multiconfiguration time-dependent Hartree method, which aims to get around the latter’s exponential scaling problem, especially with regard to system-bath dynamics. We present applications to quantum dissipative dynamics and an analysis of the computational effort. Namely, propagation times within this scheme scale linearly with the number of bath modes.
Size-dependent thermal conductivity of individual single-crystalline PbTe nanowires
Authors: Roh Jong Wook , Jang So Young , Kang Joohoon , Lee Seunghyun , Noh Jin-Seo , Kim Woochul , Park Jeunghee , Lee Wooyoung
Published: March 2010

We investigated the thermal conductivity of individual single-crystalline PbTe nanowires grown by a chemical vapor transport method. Thermal conductivities of PbTe nanowires 182–436 nm in diameter were measured using suspended microdevices. The thermal conductivity of a PbTe nanowire appeared to decrease with decreasing nanowire diameter and was measured to be 1.29 W/mK for a 182 nm nanowire at 300 K, which is about half of that of bulk PbTe. Our results indicate that phonon transport through a PbTe nanowire is effectively suppressed by the enhanced phonon boundary scattering due to size effects.
Anisotropic heat propagation velocity in quantum cascade lasers
Authors: Vitiello Miriam S. , Scamarcio Gaetano
Published: March 2010

We report on the time-resolved measurement of the in-plane (v∥) and cross-plane (v┴) components of the heat transfer velocity in GaAs/Al0.15Ga0.85As quantum-cascade heterostructures. We compared the heating and cooling stages both in the active region and in the substrate with models of heat transfer in nanostructures. We found that v⊥ is reduced by a factor of ∼6.5 with respect to that of the corresponding bulk material due to the additional thermal resistance of each interface and to the phonon interference effects in the multilayered structure. The v∥ component is reduced by ∼30% due to interface roughness.
Nonequilibrium rovibrational energy distributions of hydrogen isotopologues in an expanding plasma jet
Authors: Gabriel O. , van den Dungen J. J. A. , Schram D. C. , Engeln R.
Published: March 2010

State resolved densities of high rovibrationally excited hydrogen isotopologues H2, HD, and D2 in the electronic ground state have been measured in a supersonically expanding plasma jet. The obtained state distributions differ substantially from thermal equilibrium. Moreover, the distributions are not the same for H2, HD, and D2 indicating different formation and relaxation rates for each isotopologue. Mechanisms for this deviation from a Boltzmann distribution are given and compared to hydrogen reactions in other environments. The difference between the measured highest occupied rovibrational states in H2, HD, and D2 is ascribed to an isotope effect in the dissociation process.
Multiband quantum transport simulations of ultimate p-type double-gate transistors: Influence of the channel orientation
Authors: Cavassilas Nicolas , Pons Nicolas , Michelini Fabienne , Bescond Marc
Published: March 2010

We present a ballistic real-space six-band k.p transport model to study the influence of the channel orientation in double-gate p-type metal-oxide-semiconductor (pMOS) transistors. The six-band k.p Hamiltonian is integrated into a self-consistent two-dimensional ballistic transport simulator based on the nonequilibrium Green’s function formalism. The impact of the transport direction is analyzed as a function of the Si transistor channel length. We show that direct source-drain tunneling strongly degrades the subthreshold behavior in short [110]-oriented transistors. This result contradicts the commonly accepted idea that [110] channel orientation provides the best performances for pMOS devices.
Three stage-volume phase transitions of a side-chain liquid crystalline elastomer immersed in nematic solvents
Authors: Matsuyama Akihiko , Kushibe Yoshinari
Published: March 2010

We theoretically study volume phase transitions of a side-chain liquid crystalline elastomer (LCE) immersed in nematic solvents. Six different uniaxial nematic phases (N1∥, N1⊥, N2∥, N2⊥, N3∥, and N3⊥) are defined by using orientational order parameter Sm of a side-chain mesogen, Sb of a backbone chain, and S0 of a nematic solvent inside the gel. We derive the free energy of a side-chain LCE dissolved in nematic solvents and calculate the swelling behavior of the LCE, the order parameters, and the deformations of the LCE as a function of temperature. We find various phase transitions of the LCE, such as the isotropic (I)-N1∥-N3⊥ and the I-N2∥-N3∥, etc., accompanied by volume phase transitions. These results present new concepts in the structure of a side-chain LCE dispersed in nematic solvent molecules.
A method for the calculation of rate constants from stochastic transition paths
Authors: Klenin Konstantin V. , Wenzel Wolfgang
Published: March 2010

We present a novel and efficient method for computation of rate constants in the systems where two metastable states are separated by a high free energy barrier. Our approach is based on the thermodynamic integration applied to the grand canonical ensemble of the stochastic transition paths. As illustrated on a multidimensional model system, the required computational costs depend only weakly on the barrier height, which provides a speedup of orders of magnitude in comparison to direct simulations.
Intrinsic electrocaloric effects in ferroelectric poly(vinylidene fluoride-trifluoroethylene) copolymers: Roles of order of phase transition and stresses
Authors: Li B. , Ren W. J. , Wang X. W. , Meng H. , Liu X. G. , Wang Z. J. , Zhang Z. D.
Published: March 2010

The electrocaloric effects accompanied with the ferroelectric to paraelectric phase transitions in poly(vinylidene fluoride-trifluoroethylene) are investigated within the Landau–Devonshire theory. Just changing the nature of the phase transition from the first-order to the second-order reduces the isothermal entropy change, adiabatic temperature change and refrigerant capacity. The isothermal entropy change in the second-order transition is about one half of that in the first-order one, which is confirmed by experiments and is also consistent with the magnetocaloric counterpart. Converting to be film also leads to the reduction in electrocaloric effects, generally ascribed to the decrease of pyroelectric coefficients.
Strong drive compression of a gas-cooled positron plasma
Authors: Cassidy D. B. , Greaves R. G. , Meligne V. E. , Mills A. P.
Published: March 2010

The use of rotating electric fields to control plasmas has found numerous applications in the manipulation and storage of antimatter. When used in strong magnetic fields plasma heating caused by the applied field is mitigated by cyclotron cooling, leading to an efficient broadband mode of compression known as the strong drive regime. We have found that it is possible to access the strong drive regime in a low field trap where cyclotron cooling is negligible and a gas is used for cooling, and we have been able to compress positron plasmas to more than 10% of the Brillouin density limit.
Effects of atomic-scale surface morphology on carbon nanotube alignment on thermally oxidized silicon surface
Authors: Yamada Kazuki , Chiashi Shohei , Takahashi Katsuhiro , Homma Yoshikazu
Published: March 2010

We have investigated the effects of atomic-scale surface morphology on the single-walled carbon nanotube (SWNT) growth by using atomic step-structure-controlled SiO2/Si substrates. SWNTs initially extended randomly on the surface, and when they became longer than 3 μm, they followed the atomic step morphology with a height of 0.6 nm. This indicates that SWNT extension along the surface is greatly affected by the surface morphology of the substrate. The present results also explain why the SWNT orientation on a normal SiO2/Si surface is random. SWNTs extend along the surface morphology based on the roughness of the SiO2 surface.
A high-k Tb2TiO5 nanocrystal memory
Authors: Pan Tung-Ming , Chen Fa-Hsyang , Jung Ji-Shing
Published: March 2010

In this letter, a metal-oxide-high-k-oxide-silicon (MOHOS) memory structure incorporating a high-k Tb2TiO5 nanocrystal film as the charge trapping layer is reported for nonvolatile memory application. The structural and morphological features of these films were explored by x-ray diffraction, transmission electron microscopic, atomic force microscopy, and x-ray photoelectron spectroscopic. The Tb2TiO5 MOHOS-type memory annealed 800 °C exhibited large threshold voltage shifting (memory window of 2.9 V) and long data retention (charge loss of ∼15 % after ten years for programmed state at room temperature). These results are attributed to the higher probability for trapping the charge carrier due to the formation of a well-crystallized Tb2TiO5 nanocrystal structure with a higher dielectric constant.
Correlating structural and resistive changes in Ti:NiO resistive memory elements
Authors: Heinonen O. , Siegert M. , Roelofs A. , Petford-Long A. K. , Holt M. , d’Aquila K. , Li W.
Published: March 2010

Structural and resistive changes in Ti-doped NiO resistive random access memory structures that occur upon electroforming have been investigated using hard x-ray microscopy. Electroforming leads to structural changes in regions of size up to about one micrometer, much larger than the grain size of the structure. Such changes are consistent with a migration of ionic species or defects during electroforming over regions containing many crystalline grains.
Effect of trace moisture on friction
Authors: Liu Y. , Szlufarska I.
Published: March 2010

We report that even in nominally dry conditions trace moisture present on hydrophilic surfaces of SiC leads to a considerable increase in friction via formation of hydrogen bonds across the sliding interface. We perform quantum mechanical calculations to demonstrate that frictional instabilities on such surfaces are related to formation and breaking of hydrogen bonds between surface hydroxyl groups and to the elastic rotation of these groups. We perform a theoretical analysis based on the modified Prandtl–Tomlinson model and we predict that in the presence of trace moisture friction force will have logarithmic dependence on the sliding velocity.
Investigating the origin of Fermi level pinning in Ge Schottky junctions using epitaxially grown ultrathin MgO films
Authors: Zhou Yi , Han Wei , Wang Yong , Xiu Faxian , Zou Jin , Kawakami R. K. , Wang Kang. L.
Published: March 2010

Fermi level (FL) pinning at the Ge valence band results in a high Schottky barrier height for all metal/n-Ge contacts. The origin of this pinning effect has been ascribed to either metal induced gap states or surface states arise from the native defects at the Ge surface, such as dangling bonds. The discrepancy in the reported results/explanations is mainly due to the lack of an explicit characterization of a high quality metal/Ge or metal/ultrathin oxide/Ge junction, which should be ideally single crystalline, atomically smooth and free of process-induced defects or intermixing. We report the Schottky characteristics of high quality metal/MgO/n-Ge junctions with the ultrathin MgO epitaxially grown on Ge. We find the depinning effect displays a weak dependence on the MgO thickness, indicating the interface states due to the native defects on Ge surface are likely to play the dominant role in FL pinning.
Critical oxygen concentration in hydrogenated amorphous silicon solar cells dependent on the contamination source
Authors: Woerdenweber Jan , Merdzhanova Tsvetelina , Stiebig Helmut , Beyer Wolfhard , Gordijn Aad
Published: March 2010

For hydrogenated amorphous silicon (a-Si:H) solar cells, the critical concentration of a given impurity defines the lowest concentration which causes a decay of solar cell efficiency. Values of 2–5×1019 cm−3 are commonly found for the critical oxygen concentration (COcrit) of a-Si:H. Here we report a dependence of COcrit on the contamination source. For state-of-the-art a-Si:H solar cells prepared at the same plasma deposition conditions, we obtain with a (controllable) chamber wall leak COcrit ∼2×1019 cm−3 while for a leak in the gas supply line a higher COcrit of ∼2×1020 cm−3 is measured. No such dependence is observed for nitrogen.
Simultaneous generation of intersubband absorption and quantum well intermixing through silicon ion implantation in undoped InGaAs/AlAsSb coupled double quantum wells
Authors: Cong G. W. , Akimoto R. , Gozu S. , Mozume T. , Hasama T. , Ishikawa H.
Published: March 2010

We demonstrated the intersubband absorption in undoped InGaAs/AlAsSb coupled double quantum wells through silicon ion implantation and rapid thermal annealing. For an implantation dose of 1×1014 cm−2, the actual carrier density of a sample annealed at 600 °C for 1 min was ∼7.5×1013 cm−2 (∼75% activation efficiency); the activation energy was ∼1.41 eV. The simultaneously generated quantum well intermixing (QWI) was nonuniform due to the silicon ion distribution. The effects of QWI nonuniformity on both intersubband and interband transitions were explained by eight-band k⋅p calculation. This study will open a route for monolithic integration of intersubband-transition-based high-speed all-optical switches.
Fluorinated HfO2 gate dielectric engineering on In0.53Ga0.47As metal-oxide-semiconductor field-effect-transistors
Authors: Chen Yen-Ting , Zhao Han , Wang Yanzhen , Xue Fei , Zhou Fei , Lee Jack C.
Published: March 2010

In this work, we demonstrate that the electrical performance of HfO2/In0.53Ga0.47As gate stack can be greatly improved by incorporating fluorine (F) and engineering its concentration depth profile with respect to HfO2 bulk and the HfO2/In0.53Ga0.47As interface. We introduce F into gate stacks in two ways: CF4 plasma treatment has been performed after 8 nm HfO2 deposition or after partial deposition of HfO2 4 nm and followed by 4 nm HfO2 deposition to make the overall thickness 8 nm. The latter one incorporates more F into the HfO2 and shows great improvements. Fluorine is believed to reduce fixed charge by forming Hf–F bonds in the HfO2 bulk and also passivate the interface traps in the HfO2/In0.53Ga0.47As interface.
Thermally mediated multiferroic composites for the magnetoelectric materials
Authors: Lu S. G. , Fang Z. , Furman E. , Wang Y. , Zhang Q. M. , Mudryk Y. , Gschneidner K. A. , Pecharsky V. K. , Nan C. W.
Published: March 2010

A magnetoelectric (ME) composite through thermal mediation is presented, which is different from the traditional strain/stress mediated ME composites. The ME laminate uses the large magnetocaloric effect, that is, a temperature change induced in the ferromagnetic Gd crystal by a magnetic field, and a large pyroelectric response in the relaxor ferroelectric polymer. Consequently, a simple laminate composite can produce a ME response ∼0.5 V/(cm Oe). The ME coefficient was further enhanced to ∼0.9 V/(cm Oe) by exploiting the magnetic flux concentration effect. The approach opens up an avenue in developing ME materials for broad range of applications.
The distribution of the greater broad-nose bat Scoteanax rueppellii (Microchiroptera: Vespertilionidae) in relation to climate and topography.
Authors: Wilson P. D.
Published: March 2010

Concepts of the distribution of the greater broad-nose bat (Scoteanax rueppellii) have changed significantly as occurrence records have accumulated over the years. Early accounts of the species' distribution suggested that it was restricted to the heavily timbered areas of eastern Australia, and occurred over a wide range of altitudes. However, recent summaries of the distribution of the species differ significantly from these early accounts. To reconcile these discrepancies, I collated records from museum collections and wildlife databases. These data clearly indicate that stated altitudinal limits for the species are not correct. The currently known southern limit of the species is near Eden, New South Wales (NSW). The distribution of the species was modelled using the DOMAIN climate matching algorithm. The model indicates that S. rueppellii may occur in East Gippsland, Victoria, suggests its likely occurrence in inland Queensland and northern NSW, but a low likelihood of occurrence in inland southern NSW. However, the data show strong spatial and temporal biases that restrict the confidence that may be placed in the model. It is argued that species distributions must be regarded as open and evolving hypotheses.
Evidence for an extended reproductive season in the spotted-tailed quoll Dasyurus maculatus.
Authors: Körtner G.
Published: March 2010

Spotted-tailed quoll (Dasyurus maculatus) raise only one litter per year. They have a maximum of six young per litter, usually born in July or August and weaned after 120 to 150 days when they have a body mass of 300-600 g. A trapping survey indicated that occasionally reproduction is substantially later with weaning occuring in late February.
Spermophagy by follicular cumulus cells in the common brushtail possum Trichosurus vulpecula following co-culture of sperm and immature ovarian oocytes.
Authors: Chapman J. A. , Breed W. G.
Published: March 2010

This is a pilot study to investigate the effects of incubating cumulus oophorus-encased ovarian oocytes of the common brushtail possum (Trichosurus vulpecuila) with cauda epididymal sperm to determine if sperm could penetrate the cumulus oophous and thereby remove the need to mechanically denude in vitro matured ovarian oocyctes, and if sperm-zona binding would occur under these conditions. No fertilisation or sperm-zona pellucida binding took place. Some spermatozoa within the cumulus oophorus layer were phagocytosed.
The impact of urease inhibitor on the bioavailability of nitrogen in urea and in comparison with other nitrogen sources in ryegrass (Lolium perenne L.)
Authors: Dawar K. , Zaman M. , Rowarth J. S. , Blennerhassett J. , Turnbull M. H.
Published: March 2010

Improving nitrogen (N)-use efficiency of applied urea is critical to maximise its uptake and decrease environmental impact. Two glasshouse-based studies were conducted to investigate the potential of incorporating urea fertiliser with urease inhibitor (N-(n-butyl) thiophosphoric triamide (NBPT) or ‘Agrotain’) to enhance fertiliser N uptake efficiency. Topsoil (0–0.075 m, Typic Haplustepts silt loam) from a pasture site near Lincoln, Canterbury, New Zealand, was collected and ryegrass (Lolium perenne L.) was grown from seed in standard plant trays maintained at soil moisture contents of 75–80% field capacity. Urea, Agrotain-treated urea, ammonium nitrate, ammonium sulfate, or sodium nitrate, were applied in granular form at rates equivalent to 25 or 50 kg N/ha with 4 replicates. Herbage was harvested 21 and 42 days after application of treatments to assess dry matter (DM) production, N uptake, leaf amino acid, ammonium (NH4+) and nitrate (NO3–) concentrations, and nitrate reductase activity (NRA). In a separate pot experiment, granular 15N urea (10 atom%) with or without Agrotain was applied to ryegrass at 25 kg N/ha. At 0.5, 1, 2, 3, 5, 10, and 21 days after treatment application, 3 pots per treatment were destructively sampled to determine urea hydrolysis, herbage DM, and 15N uptake. In both experiments, Agrotain-treated urea improved bio-availability of added N and resulted in significantly higher herbage DM yield and N uptake than urea alone or other forms of N fertilisers. Agrotain-treated urea applied at 25 kg N/ha increased N response by 66% compared with urea alone (and by greater proportions compared with the other fertiliser forms). Agrotain-treated urea applied at 25 kg N/ha produced significantly higher uptake efficiency (13 g DM/g of applied N) than at 50 kg N/ha (5 g DM/g of applied N). Tissue amino acids, NH4+ and NO3– contents, and NRA were not significantly influenced by any type of fertiliser. Results from the 15N experiment support the suggestion that a delay in urea hydrolysis by Agrotain provided an opportunity for direct plant uptake of an increased proportion of the applied urea-N than in the case of urea alone. Treating urea with Agrotain thus has the potential to increase N-use efficiency and herbage production.
Incidence of root and hypocotyl diseases in lupin crops in Western Australia between 1986 and 2005
Authors: Thomas G. J. , MacLeod W. J. , Sweetingham M. W.
Published: March 2010

Three separate surveys were carried out in commercial lupin crops in the major lupin growing region of Western Australia in 1986, 1990, and 2004–05. In total, 333 sites were sampled and plants assessed for the incidence and cause of root and hypocotyl rots. Measurements were made of plant density and sowing depth at all sites.
In all surveys, root rot was more common than hypocotyl rot. Root rot occurred in more than 95% of sites in each survey; however, a greater proportion of sites had high levels of root rot in early surveys. The incidence of root rot within sites decreased from an average of 34.9% in 1986 to 10.2% in 2004–05. Hypocotyl rot incidence varied among surveys, incidence of infected paddocks, and within-paddock incidence was greatest in the 1990 survey. Hypocotyl rot incidence was lowest in the 2004–05 survey.
Rhizoctonia solani and Pleiochaeta setosa were commonly isolated from root lesions and R. solani was the predominant pathogen isolated from hypocotyl lesions. Analysis of the R. solani isolates by pectic zymogram showed that the ZG3 strain was most regularly isolated from roots and hypocotyls.
This series of surveys indicates that the incidence of root rots in commercial lupin paddocks in Western Australia has decreased dramatically over the past 20 years; however, root rot still occurs in most paddocks regardless of soil type, location, crop rotation, and management systems.