bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation of magnetic structure and magnetization process of yttrium iron garnet film by Lorentz microscopy and electron holography
Authors: Xia W. X. , Chun Y. S. , Aizawa S. , Yanagisawa K. , Krishnan Kannan. M. , Shindo D. , Tonomura A.
Published: December 2010

The micromagnetic structure and magnetization process of perpendicular Y3Fe5O12 (YIG) films were studied by Lorentz microscopy and electron holography. The closure domain structure inside the thin transmission electron microscopy specimen exhibits the same period as the magnetization pattern observed by magnetic force microscopy indicating the perpendicular anisotropy of the YIG film. Through observation of stray fields, it is concluded that the shapes of domain and domain walls are sensitive to the specimen thickness; moreover, a closure domain configuration observed in thin specimen is the stable energy state as determined by the balance between the crystalline anisotropy and shape anisotropy. Domain wall movement is observed by applying a magnetic field, in situ, inside the microscope in both horizontal and perpendicular directions; the saturation fields observed are qualitatively in agreement with the results of the hysteresis loop.
Madelung representation of damped parametric quantum oscillator and exactly solvable Schrödinger–Burgers equations
Authors: Büyükaşık Şirin A. , Pashaev Oktay K.
Published: December 2010

We construct a Madelung fluid model with time variable parameters as a dissipative quantum fluid and linearize it in terms of Schrödinger equation with time-dependent parameters. It allows us to find exact solutions of the nonlinear Madelung system in terms of solutions of the Schrödinger equation and the corresponding classical linear ordinary differential equation with variable frequency and damping. For the complex velocity field, the Madelung system takes the form of a nonlinear complex Schrödinger–Burgers equation, for which we obtain exact solutions using complex Cole–Hopf transformation. In particular, we give exact results for nonlinear Madelung systems related with Caldirola–Kanai-type dissipative harmonic oscillator. Collapse of the wave function in dissipative models and possible implications for the quantum cosmology are discussed.
Enhanced piezoelectric property of porous lead zirconate titanate ceramics with one dimensional ordered pore structure
Authors: Guo Rui , Wang Chang-An , Yang AnKun , Fu JunTao
Published: December 2010

Lead zirconate titanate (PZT) ceramics with one dimensional ordered pore structure (1–3 type porous PZT ceramics) were fabricated in this study. The special structure not only enhanced the piezoelectric and dielectric properties effectively but also further decreased the acoustic impedance. All samples exhibited excellent piezoelectric properties despite high porosities. The d33 value was 608 pC /N (remained 88% that of dense PZT) when the porosity was up to 68.7%. The d33 value was 690 pC /N (same as dense PZT) when the porosity was 41.7%. The lowest acoustic impedance (Z) reached 1.3 MRayls. These results are promising for improving performance in hydrophones applications.
Kinetics of illuminated complex plasmas considering Mie scattering by spherical dust particles with a size distribution
Authors: Sodha M. S. , Mishra S. K. , Misra Shikha
Published: January 2011

In this paper Mie scattering of light by dust particles having Mathis, Rumpl, and Nordsieek power law distribution of size has been incorporated in the formulation of the kinetics of an illuminated complex plasma which takes into account the ionization of neutral atoms by an external agency, ion-electron recombination, photoemission of electrons by the dust particles, and accretion of electrons and ions on the surface of the particles; the number and energy balance of the constituent species has also been taken into account. An interesting conclusion is that unlike the usual case (when Mie scattering is neglected) the charge on a particle is not proportional to the radius and that for certain sets of parameters the smaller particles are negatively charged while the larger particles, carry positive charge.
Microwave atomic force microscopy imaging for nanometer-scale electrical property characterization
Authors: Zhang Lan , Ju Yang , Hosoi Atsushi , Fujimoto Akifumi
Published: December 2010

We introduce a new type of microscopy which is capable of investigating surface topography and electrical property of conductive and dielectric materials simultaneously on a nanometer scale. The microwave atomic force microscopy is a combination of the principles of the scanning probe microscope and the microwave-measurement technique. As a result, under the noncontact AFM working conditions, we successfully generated a microwave image of a 200-nm Au film coating on a glass wafer substrate with a spatial resolution of 120 nm and a measured voltage difference of 19.2 mV between the two materials.
Modeling of tumor’s tissue heating by nanoparticles
Authors: Fasla Badia , Benmouna Réda , Benmouna Mustapha
Published: December 2010

The knowledge of temperature profiles in space and time throughout tumored tissues is a crucial step in designing efficient hyper thermal therapies for cancer. The present work is a contribution in modeling these profiles based on distributions of nanospheres and pointlike particles. Heat diffusion equations are solved under different conditions to rationalize the effects of boundary conditions and size of heating particles. The case of pointlike heating sources is found to be much simpler and more convenient to trace back the effects of metabolism and blood perfusion.
Energy conversion in a glass-laser-induced blast wave in air
Authors: Wang Bin , Komurasaki Kimiya , Yamaguchi Toshikazu , Shimamura Kohei , Arakawa Yoshihiro
Published: December 2010

Near-infrared solid laser-induced blast waves were investigated using a Q-switched Nd:glass laser oscillating at 1053 nm wavelength, up to 2.0 J/pulse laser energy Ei, and 33 ns pulse duration (full width at half maximum). Half-shadowgraph half-self-emission visualization elucidated laser detonation waves and blast waves. Laser output and transmission through the waves were measured using pairs of a photodetectors and energy meters. Results show volumetric absorption in this near-infrared region, which is mainly attributable to low inverse-Bremsstrahlung absorption coefficients at short wavelengths. Some input laser energy was converted into blast wave energy: 59% at Ei=1.0 J/pulse, which approximates that of CO2 laser-induced blast waves.
Thermomechanical mechanism of orientational optical nonlinearity in twisted nematic liquid crystals
Authors: Poursamad J. B. , Aleksanyan A. K. , Hakobyan R. S.
Published: December 2010

In a nonuniform nematic liquid crystal director reorientation may take place as a result of a temperature gradient. We formulated a two-dimensional model of the temperature gradient caused by the light absorption of a Gaussian laser beam impinging normally on the liquid crystal cell. Within this model, we calculated the director reorientation and the subsequent optical nonlinearity of the liquid crystal.
Temperature-dependent local structure of LaFeAsO1−xFx: Probing the atomic correlations
Authors: Tyson T. A. , Wu T. , Woicik J. C. , Ravel B. , Ignatov A. , Zhang C. L. , Qin Z. , Zhou T. , Cheong S.-W.
Published: December 2010

The local structure of the parent and doped LaFeAsO1−xFx (pnictide) compounds were studied by x-ray absorption spectroscopy and density functional methods. In the doped system, the Fe–As and Fe–Fe correlations are both well modeled by an Einstein model. For the Fe–As bonds, the Einstein temperatures are identical for the doped (11%) and undoped samples but the doped sample is found to have a lower level of static disorder. Doping is found to increases the effective Einstein temperature of Fe–Fe atomic correlation. The results suggest that the onset of superconductivity in the F doped system may be related to enhanced magnetic interactions. Density functional calculations of the total charge density reveal strong bonding between neighboring As ions but metal-like behavior in the Fe layers. It is also seen directly that the replacement of oxygen by fluorine modifies the electron charge density mainly on the Fe sites.
Influence of krypton atoms on the structure of hydrogenated amorphous carbon deposited by plasma enhanced chemical vapor deposition
Authors: Oliveira M. H. , Viana G. A. , de Lima M. M. , Cros A. , Cantarero A. , Marques F. C.
Published: December 2010

Hydrogenated amorphous carbon (a-C:H) films were prepared by plasma enhanced chemical vapor deposition using methane (CH4) plus krypton (Kr) mixed atmosphere. The depositions were performed as function of the bias voltage and krypton partial pressure. The goal of this work was to study the influence of krypton gas on the physical properties of a-C:H films deposited on the cathode electrode. Krypton concentration up to 1.6 at. %, determined by Rutherford Back-Scattering, was obtained at high Kr partial pressure and bias of −120 V. The structure of the films was analyzed by means of optical transmission spectroscopy, multi-wavelength Raman scattering and Fourier Transform Infrared spectroscopy. It was verified that the structure of the films remains unchanged up to a concentration of Kr of about 1.0 at. %. A slight graphitization of the films occurs for higher concentration. The observed variation in the film structure, optical band gap, stress, and hydrogen concentration were associated mainly with the subplantation process of hydrocarbons radicals, rather than the krypton ion energy.
The weakly coupled fractional one-dimensional Schrödinger operator with index 1 < α ≤ 2
Authors: Hatzinikitas Agapitos N.
Published: December 2010

Considering the space fractional Weyl operator \documentclass[12pt]{minimal}\begin{document}$\hat{\mathcal {P}}^{\alpha }$\end{document}P̂α on the separable Hilbert space \documentclass[12pt]{minimal}\begin{document}$\mathcal {H}=L^2({\mathbb R},dx)$\end{document}H=L2(R,dx) we determine the asymptotic behavior of both the free Green's function and its variation with respect to energy in one dimension for bound states. Later, we specify the Birman–Schwinger representation for the Schrödinger operator \documentclass[12pt]{minimal}\begin{document}$\hat{H}_g=K_{\alpha }\hat{\mathcal {P}}^{\alpha }+g\hat{V}$\end{document}Ĥg=KαP̂α+gV̂ and extract the finite-rank portion which is essential for the asymptotic expansion of the ground state. Finally, we determine necessary and sufficient conditions for there to be a bound state for small coupling constant g.
On the absence of absolutely continuous spectra for Schrödinger operators on radial tree graphs
Authors: Exner Pavel , Lipovský Jiří
Published: December 2010

The subject of the paper is Schrödinger operators on tree graphs which are radial, having the branching number \documentclass[12pt]{minimal}\begin{document}$b_n$\end{document}bn at all the vertices at the distance \documentclass[12pt]{minimal}\begin{document}$t_n$\end{document}tn from the root. We consider a family of coupling conditions at the vertices characterized by \documentclass[12pt]{minimal}\begin{document}$(b_n-1)^2+4$\end{document}(bn−1)2+4 real parameters. We prove that if the graph is sparse so that there is a subsequence of \documentclass[12pt]{minimal}\begin{document}$\lbrace t_{n+1}-t_n\rbrace$\end{document}{tn+1−tn} growing to infinity, in the absence of the potential the absolutely continuous spectrum is empty for a large subset of these vertex couplings, but on the the other hand, there are cases when the spectrum of such a Schrödinger operator can be purely absolutely continuous.
Basins of coexistence and extinction in spatially extended ecosystems of cyclically competing species
Authors: Ni Xuan , Yang Rui , Wang Wen-Xu , Lai Ying-Cheng , Grebogi Celso
Published: December 2010

Microscopic models based on evolutionary games on spatially extended scales have recently been developed to address the fundamental issue of species coexistence. In this pursuit almost all existing works focus on the relevant dynamical behaviors originated from a single but physically reasonable initial condition. To gain comprehensive and global insights into the dynamics of coexistence, here we explore the basins of coexistence and extinction and investigate how they evolve as a basic parameter of the system is varied. Our model is cyclic competitions among three species as described by the classical rock-paper-scissors game, and we consider both discrete lattice and continuous space, incorporating species mobility and intraspecific competitions. Our results reveal that, for all cases considered, a basin of coexistence always emerges and persists in a substantial part of the parameter space, indicating that coexistence is a robust phenomenon. Factors such as intraspecific competition can, in fact, promote coexistence by facilitating the emergence of the coexistence basin. In addition, we find that the extinction basins can exhibit quite complex structures in terms of the convergence time toward the final state for different initial conditions. We have also developed models based on partial differential equations, which yield basin structures that are in good agreement with those from microscopic stochastic simulations. To understand the origin and emergence of the observed complicated basin structures is challenging at the present due to the extremely high dimensional nature of the underlying dynamical system.
Abundance of stable periodic behavior in a Red Grouse population model with delay: A consequence of homoclinicity
Authors: Slipantschuk Julia , Ullner Ekkehard , Baptista Murilo da Silva , Zeineddine Mohammed , Thiel Marco
Published: December 2010

Shrimp-shaped periodic regions embedded in chaotic regions in two-dimensional parameter spaces are of specific interest for physical and biological systems. We provide the first observation of these shrimp-shaped stability regions in a parameter space of a continuous time-delayed population model, obtained by taking the delays as bifurcation parameters. The parameter space organization is governed by the presence of infinitely many periodicity hubs, which trigger the spiraling organization of these shrimp-shaped periodic regions around them. We provide evidence that this spiraling organization in the parameter space is a consequence of the existence of homoclinic orbits in the phase space.
A mechanism for damage formation in GaN during rare earth ion implantation at medium range energy and room temperature
Authors: Ruterana P. , Lacroix B. , Lorenz K.
Published: January 2011

A detailed investigation of the crystallographic damage has been carried out in GaN following 300 keV rare earth ion implantation at room temperature by varying the fluence from 7×1013 to 5×1016 at/cm2. It is shown that above a threshold fluence around 2×1015 at/cm2, nanocrystallization takes place from the surface, subsequent to the formation of a planar defects network consisting of basal and prismatic stacking faults. This network starts to form at the lowest analyzed fluence mostly around the mean projected range. When the fluence increases, it propagates toward the surface, reaching it just before the on-set of the nanocrystallization. A model based on the mechanical breakdown of the GaN wurtzite structure mediated by prismatic stacking faults is proposed.
From simple to complex patterns of oscillatory behavior in a model for the mammalian cell cycle containing multiple oscillatory circuits
Authors: Gérard Claude , Goldbeter Albert
Published: December 2010

We previously proposed an integrated computational model for the network of cyclin-dependent kinases (Cdks) that controls the dynamics of the mammalian cell cycle [C. Gérard and A. Goldbeter, “Temporal self-organization of the cyclin/Cdk network driving the mammalian cell cycle,” Proc. Natl. Acad. Sci. U.S.A. 106, 21643 (2009)]. The model contains four Cdk modules regulated by reversible phosphorylation, Cdk inhibitors, protein synthesis or degradation, and the balance between antagonistic effects of the tumor suppressor pRB and the transcription factor E2F. Increasing the level of a growth factor above a critical threshold triggers the transition from a quiescent, stable steady state to self-sustained oscillations in the Cdk network. These oscillations correspond to the repetitive, transient activation of cyclin D/Cdk4–6 in G1, cyclin E/Cdk2 at the G1/S transition, cyclin A/Cdk2 in S and at the S/G2 transition, and cyclin B/Cdk1 at the G2/M transition. This periodic, ordered activation of the various cyclin/Cdk complexes can be associated with cell proliferation. The multiplicity of feedback loops within the Cdk network is such that it contains at least four distinct circuits capable of producing oscillations. The tight coupling of these oscillatory circuits generally results in simple periodic behavior associated with repetitive cycles of mitosis or with endoreplication. The latter corresponds to multiple passages through the phase of DNA replication without mitosis. We show here that, as a result of the interaction between the multiple oscillatory circuits, particularly when attenuating the strength of the oscillatory module involving cyclin B/Cdk1, the model for the Cdk network can also produce complex periodic oscillations, quasiperiodic oscillations, and chaos. Numerical simulations based on limited explorations in parameter space nevertheless suggest that these complex modes of oscillatory behavior remain less common than the evolution to simple periodic oscillations of the limit cycle type, holding with the view that simple periodic oscillations in the Cdk network correspond to its physiological mode of dynamic behavior.
Hierarchical genetic networks and noncoding RNAs
Authors: Zhdanov Vladimir P.
Published: December 2010

In eukaryotic cells, many genes are transcribed into noncoding RNAs. Such RNAs may associate with mRNAs and inhibit their translation and facilitate degradation. To clarify what may happen in this case, we propose a kinetic model describing the effect of noncoding RNAs on a mRNA-protein network with the hierarchical three-layer architecture. For positive regulation of the layers, our model predicts either bistability with a fairly narrow hysteresis loop or a unique steady state. For negative or mixed regulation, the steady state is found to be unique.
Identifiability and observability analysis for experimental design in nonlinear dynamical models
Authors: Raue A. , Becker V. , Klingmüller U. , Timmer J.
Published: December 2010

Dynamical models of cellular processes promise to yield new insights into the underlying systems and their biological interpretation. The processes are usually nonlinear, high dimensional, and time-resolved experimental data of the processes are sparse. Therefore, parameter estimation faces the challenges of structural and practical nonidentifiability. Nonidentifiability of parameters induces nonobservability of trajectories, reducing the predictive power of the model. We will discuss a generic approach for nonlinear models that allows for identifiability and observability analysis by means of a realistic example from systems biology. The results will be utilized to design new experiments that enhance model predictiveness, illustrating the iterative cycle between modeling and experimentation in systems biology.
Delay-enhanced spatiotemporal order in coupled neuronal systems
Authors: Wu Hao , Hou Zhonghuai , Xin Houwen
Published: December 2010

In a network of noisy neuron oscillators with time-delayed coupling, we uncover a phenomenon of delay-enhanced spatiotemporal order. We find that time delay in the coupling can dramatically enhance the temporal coherence and spatial synchrony of the noise-induced spike trains. In addition, if the delay time is tuned to nearly match the intrinsic spiking period of the neuronal network, both the coherence and the synchrony reach maximum levels, demonstrating an interesting type of resonance phenomenon with delay. Such findings are shown to be robust to the change of the noise intensity and the rewiring probability of small-world network.
Glass transitions in nanoscale heated volumes of thin polystyrene films
Authors: Li Alex G. , Burggraf Larry W.
Published: December 2010

Glass transitions in confined polystyrene films on a silicon substrate were studied using atomic force microscopy incorporating a thermal tip. Three-dimensional spatial nanoconfinements were achieved by controlling size and boundary conditions of small heated volumes of polymer nanostrands drawn from the polymer surface with the thermal tip, using appropriate loads and temperatures at the tip–polymer contact. Finite element analysis was performed to model mechanical contact and thermal transport, including the effects of contact radius, film thickness, and load on temperature and pressure distributions in the confined volume at the contact. The glass transition temperature (Tg) was measured by observing the softening of polymers with increasing temperature. The measured surface Tg exhibited a strong size dependence, while the subsurface Tg increased with decreasing the distance to the substrate. A large increase in the surface Tg was observed when the radius of contact was reduced below about 10 nm. The increase in the glass transition temperature at the surface was attributed to the presence of surface and line tension at the nanometer contact, while the enhanced Tg near the substrate was attributed to the pinning effects that reduces the mobility of the polymer molecules in the film over several hundreds of nanometers away from the polymer–substrate interface.
DNA-RNA transcription as an impact of viscosity
Authors: Zdravković Slobodan , Satarić Miljko V. , Hadžievski Ljupčo
Published: December 2010

The impact of viscosity on DNA dynamics is studied both analytically and numerically. It is assumed that the viscosity exists at the segments where DNA molecule is surrounded by RNA polymerase. We demonstrate that the frictional forces destroy the modulation of the incoming solitonic wave. We show that viscosity, crucial for demodulation, is essential for DNA-RNA transcription.
A robust two-gene oscillator at the core of Ostreococcus tauri circadian clock
Authors: Morant Pierre-Emmanuel , Thommen Quentin , Pfeuty Benjamin , Vandermoere Constant , Corellou Florence , Bouget François-Yves , Lefranc Marc
Published: December 2010

The microscopic green alga Ostreococcus tauri is rapidly emerging as a promising model organism in the green lineage. In particular, recent results by Corellou et al. [Plant Cell 21, 3436 (2009)] and Thommen et al. [PLOS Comput. Biol. 6, e1000990 (2010)] strongly suggest that its circadian clock is a simplified version of Arabidopsis thaliana clock, and that it is architectured so as to be robust to natural daylight fluctuations. In this work, we analyze the time series data from luminescent reporters for the two central clock genes TOC1 and CCA1 and correlate them with microarray data previously analyzed. Our mathematical analysis strongly supports both the existence of a simple two-gene oscillator at the core of Ostreococcus tauri clock and the fact that its dynamics is not affected by light in normal entrainment conditions, a signature of its robustness.
Blood flow in microvascular networks: A study in nonlinear biology
Authors: Geddes John B. , Carr Russell T. , Wu Fan , Lao Yingyi , Maher Meaghan
Published: December 2010

Plasma skimming and the Fahraeus–Lindqvist effect are well-known phenomena in blood rheology. By combining these peculiarities of blood flow in the microcirculation with simple topological models of microvascular networks, we have uncovered interesting nonlinear behavior regarding blood flow in networks. Nonlinearity manifests itself in the existence of multiple steady states. This is due to the nonlinear dependence of viscosity on blood cell concentration. Nonlinearity also appears in the form of spontaneous oscillations in limit cycles. These limit cycles arise from the fact that the physics of blood flow can be modeled in terms of state dependent delay equations with multiple interacting delay times. In this paper we extend our previous work on blood flow in a simple two node network and begin to explore how topological complexity influences the dynamics of network blood flow. In addition we present initial evidence that the nonlinear phenomena predicted by our model are observed experimentally.
Introduction to Focus Issue: Dynamics in Systems Biology
Authors: Brackley Chris A. , Ebenhöh Oliver , Grebogi Celso , Kurths Jürgen , de Moura Alessandro , Romano M. Carmen , Thiel Marco
Published: December 2010

The methods of nonlinear systems form an extensive toolbox for the study of biology, and systems biology provides a rich source of motivation for the development of new mathematical techniques and the furthering of understanding of dynamical systems. This Focus Issue collects together a large variety of work which highlights the complementary nature of these two fields, showing what each has to offer the other. While a wide range of subjects is covered, the papers often have common themes such as “rhythms and oscillations,” “networks and graph theory,” and “switches and decision making.” There is a particular emphasis on the links between experimental data and modeling and mathematical analysis.
Modeling the complex dynamics of enzyme-pathway coevolution
Authors: Schütte Moritz , Skupin Alexander , Segrè Daniel , Ebenhöh Oliver
Published: December 2010

Metabolic pathways must have coevolved with the corresponding enzyme gene sequences. However, the evolutionary dynamics ensuing from the interplay between metabolic networks and genomes is still poorly understood. Here, we present a computational model that generates putative evolutionary walks on the metabolic network using a parallel evolution of metabolic reactions and their catalyzing enzymes. Starting from an initial set of compounds and enzymes, we expand the metabolic network iteratively by adding new enzymes with a probability that depends on their sequence-based similarity to already present enzymes. Thus, we obtain simulated time courses of chemical evolution in which we can monitor the appearance of new metabolites, enzyme sequences, or even entire organisms. We observe that new enzymes do not appear gradually but rather in clusters which correspond to enzyme classes. A comparison with Brownian motion dynamics indicates that our system displays biased random walks similar to diffusion on the metabolic network with long-range correlations. This suggests that a quantitative molecular principle may underlie the appearance of punctuated equilibrium dynamics, whereby enzymes occur in bursts rather than by phyletic gradualism. Moreover, the simulated time courses lead to a putative time-order of enzyme and organism appearance. Among the patterns we detect in these evolutionary trends is a significant correlation between the time of appearance and their enzyme repertoire size. Hence, our approach to metabolic evolution may help understand the rise in complexity at the biochemical and genomic levels.
Principles of the radiative ablation modeling
Authors: Saillard Yves , Arnault Philippe , Silvert Virginie
Published: December 2010

Indirectly driven inertial confinement fusion (ICF) rests on the setting up of a radiation temperature within a laser cavity and on the optimization of the capsule implosion ablated by this radiation. In both circumstances, the ablation of an optically thick medium is at work. The nonlinear radiation conduction equations that describe this phenomenon admit different kinds of solutions called generically Marshak waves. In this paper, a completely analytic model is proposed to describe the ablation in the subsonic regime relevant to ICF experiments. This model approximates the flow by a deflagrationlike structure where Hugoniot relations are used in the stationary part from the ablation front up to the isothermal sonic Chapman–Jouguet point and where the unstationary expansion from the sonic point up to the external boundary is assumed quasi-isothermal. It uses power law matter properties. It can also accommodate arbitrary boundary conditions provided the ablation wave stays very subsonic and the surface temperature does not vary too quickly. These requirements are often met in realistic situations. Interestingly, the ablated mass rate, the ablation pressure, and the absorbed radiative energy depend on the time history of the surface temperature, not only on the instantaneous temperature values. The results compare very well with self-similar solutions and with numerical simulations obtained by hydrodynamic code. This analytic model gives insight into the physical processes involved in the ablation and is helpful for optimization and sensitivity studies in many situations of interest: radiation temperature within a laser cavity, acceleration of finite size medium, and ICF capsule implosion, for instance.
Slip length for longitudinal shear flow over a dilute periodic mattress of protruding bubbles
Authors: Crowdy Darren
Published: December 2010

An analytical formula for the frictional slip length associated with transverse shear flow over a bubble mattress comprising a dilute periodic array of parallel circular-arc grooves protruding into the fluid has recently been presented by Davis and Lauga [Phys. Fluids 21, 011701 (2009)]. This letter derives an analytical formula for the slip length associated with longitudinal shear flow over the same surface. The formula is in excellent agreement with a phenomenological result based on finite element simulations given by Teo and Khoo [Microfluid. Nanofluid. 9, 499 (2010)].
Comment on “On the ionization equilibrium of hot hydrogen plasma and thermodynamic consistency of formulating finite partition functions” [Phys. Plasmas 17, 062701 (2010)]
Authors: Potekhin A. Y.
Published: December 2010

Zaghloul [Phys. Plasmas 17, 062701 (2010)] reconsiders the occupation probability formalism in plasma thermodynamics and claims inconsistencies in previous models. I show that the origin of this incorrect claim is an omission of the configurational factor from the partition function.
Response to “Comment on ‘On the ionization equilibrium of hot hydrogen plasma and thermodynamic consistency of formulating finite partition functions’ ” [Phys. Plasmas 17, 124705 (2010)]
Authors: Zaghloul Mofreh R.
Published: December 2010

Potekhin [Phys. Plasmas 17, 124705 (2010)] claims that the inconsistencies in previous models of the well-known occupation probability formalism, which we have pointed out in Zaghloul [Phys. Plasmas 17, 062701 (2010)], are due to omission of the configurational factor from the partition function in our work. We show that this claim is not justified, and thus explain the existence of these inconsistencies in the previous models we referred to in Zaghloul [Phys. Plasmas 17, 062701 (2010)], and reconfirm the correctness of our work and conclusions.
Settling-induced heat transport
Authors: Blanchette François , Douandju William , Montroy Sydney M.
Published: December 2010

We investigate the influence of settling particles on heat transport within suspensions. We focus on particles that equilibrate their temperature with the surrounding fluid much faster than their typical settling time. Such particles act as heat carriers and heat transport therefore occur through both diffusion and particle settling. We quantify this effect by deriving the relevant governing equations. We show the effect of particle settling on heat transport as the governing parameter, ϕ(κs/κf)(L/R)Pes, increases, where ϕ is the particle concentration, L is the vertical extent of the domain, R is the particle radius, κs and κf are the thermal conductivity of the solid and fluid phases, respectively, and Pes is the particle Péclet number. We investigate the stabilizing effect this enhanced transport has on unstable density gradients via a linear stability analysis. We conclude by discussing systems where this effect is important, such as rivers coming into the ocean, magma chambers, and when large concentrations of volcanic and forest fire ashes are present in the atmosphere.
Crossed-beam energy transfer in implosion experiments on OMEGA
Authors: Igumenshchev I. V. , Edgell D. H. , Goncharov V. N. , Delettrez J. A. , Maximov A. V. , Myatt J. F. , Seka W. , Shvydky A. , Skupsky S. , Stoeckl C.
Published: December 2010

Radiative hydrodynamic simulations of implosion experiments on the OMEGA laser system [Boehly et al., Opt. Commun. 133, 495 (1997)] show that energy transfer between crossing laser beams can reduce laser absorption by 10%–20%. A new quantitative model for the crossed-beam energy transfer has been developed, allowing one to simulate the coupling of multiple beams in the expanding corona of implosion targets. Scattered-light and bang-time measurements show good agreement with predictions of this model when nonlocal heat transport is employed. The laser absorption can be increased by narrowing laser beams and/or employing two-color light, which both reduce the crossed-beam energy transfer.
Correlation between the nanoscale electrical and morphological properties of crystallized hafnium oxide-based metal oxide semiconductor structures
Authors: Iglesias V. , Porti M. , Nafría M. , Aymerich X. , Dudek P. , Schroeder T. , Bersuker G.
Published: December 2010

The relationship between electrical and structural characteristics of polycrystalline HfO2 films has been investigated by conductive atomic force microscopy under ultrahigh vacuum conditions. The results demonstrate that highly conductive and breakdown (BD) sites are concentrated mainly at the grain boundaries (GBs). Higher conductivity at the GBs is found to be related to their intrinsic electrical properties, while the positions of the electrical stress-induced BD sites correlate to the local thinning of the dielectric. The results indicate that variations in the local characteristics of the high-k film caused by its crystallization may have a strong impact on the electrical characteristics of high-k dielectric stacks.
Electrical study of trapped charges in nanoscale Ge islands by Kelvin probe force microscopy for nonvolatile memory applications
Authors: Lin Z. , Brunkov P. , Bassani F. , Bremond G.
Published: December 2010

Isolated Germanium nanoisland on top of silicon dioxide (SiO2) layer has been studied by Kelvin probe force microscopy (KPFM) at room temperature. Different surface potentials between Ge island and SiO2 dielectric layer were directly visualized from the KPFM image. The image contrast greatly increased after electron injection by applying a negative bias of −7 V. The dissipation of injected electrons was evaluated by measuring the surface potential variation due to the leakage of these injected charges. The long retention time of local charges in Ge dot is promising for applications in nonvolatile memories.
Surface-plasmon-induced enhancement of magneto-optical Kerr effect in all-nickel subwavelength nanogratings
Authors: Grunin A. A. , Zhdanov A. G. , Ezhov A. A. , Ganshina E. A. , Fedyanin A. A.
Published: December 2010

Enhancement of transversal magneto-optical Kerr effect (TKE) is controlled experimentally in magnetoplasmonic subwavelength nanogratings made of nickel films by resonant excitation of surface plasmon-polaritons (SPPs). Almost one order of magnitude increase of the TKE value is observed in the spectral range of Wood’s anomaly corresponding to the fulfillment of the phase-matching conditions for SPP excitation.
Performance enhancement of terahertz metamaterials on ultrathin substrates for sensing applications
Authors: Tao Hu , Strikwerda Andrew C. , Liu Mengkun , Mondia Jessica P. , Ekmekci Evren , Fan Kebin , Kaplan David L. , Padilla Willie J. , Zhang Xin , Averitt Richard D. , Omenetto Fiorenzo G.
Published: December 2010

We design, fabricate, and characterize split-ring resonator (SRR) based planar terahertz metamaterials (MMs) on ultrathin silicon nitride substrates for biosensing applications. Proof-of-principle demonstration of increased sensitivity in thin substrate SRR-MMs is shown by detection of doped and undoped protein thin films (silk fibroin) of various thicknesses and by monitoring transmission changes using terahertz time-domain spectroscopy. SRR-MMs fabricated on thin film substrates show significantly better performance than identical SRR-MMs fabricated on bulk silicon substrates paving the way for improved biological and chemical sensing applications.
Ion-beam induced domain structure in piezoelectric PMN-PT single crystal
Authors: Kim Kyou-Hyun , Payne David A. , Zuo Jian-Min
Published: December 2010

We report an investigation of the domain structure in Pb(Mg1/3Nb2/3)O3-30%PbTiO3 single crystals after ion milling. We show that ion milling induces microdomains, typically 0.1–1 μm in size. The induced microdomains disappear after temperature annealing or electric poling, leaving behind nanodomains of a few nanometers in size. We attribute the microdomains to surface stress induced by ion milling. The results demonstrate the general importance of separating sample preparation artifacts from the true domain structure in the study of ferroic materials.
Electrical signatures of ferromagnetism in epitaxial FeSi2 nanowires
Authors: Kim T. , Bird J. P.
Published: December 2010

We perform electrical characterization of epitaxial FeSi2 nanowires (NWs) realized by reactive epitaxy. Typical resistance values exceed 100 kΩ, a high value that is attributed to the combined influence of interfacial scattering and process-related damage. Negative magnetoresistance due to weak localization, as well as hysteresis and anisotropic magnetoresistance, are also observed at low temperatures, confirming the ferromagnetic nature of these NWs.
Ambipolar diffusion of photoexcited carriers in bulk GaAs
Authors: Ruzicka Brian A. , Werake Lalani K. , Samassekou Hassana , Zhao Hui
Published: December 2010

The ambipolar diffusion of carriers in bulk GaAs is studied by using an ultrafast pump-probe technique with a high spatial resolution. Carriers with a pointlike spatial profile are excited by a tightly focused pump laser pulse. The spatiotemporal dynamics of the carriers are monitored by a time-delayed and spatially scanned probe pulse. Ambipolar diffusion coefficients are deduced from linear fits to the expansion of the area of the profiles, and are found to decrease from about 170 cm2 s−1 at 10 K to about 20 cm2 s−1 at room temperature. Our results are consistent with those deduced from previously measured mobilities.
Spontaneous formation of vertically anticorrelated epitaxial islands on ultrathin substrates
Authors: Ni Y. , He L. H.
Published: December 2010

Exploration of self-assembled epitaxial islands on ultrathin substrates opens a way for fabricating mechanoelectric heterostructures, while the effect of substrate thickness remains unclear. By using phase field simulations, we demonstrate spontaneous formation of a vertically anticorrelated quantum dot growth on the top and bottom surfaces of an ultrathin substrate. The mechanism of this vertical anticorrelation is due to the overlapping effect of the fringe elastic field modulated by the substrate thickness. Good agreements with the pattern of epitaxial islands on nanowire and nanomembrane are observed. The obtained result provides a guideline for tailoring the ordering of heteroepitaxial island growth.
Embedded clusters and magnetism in Cr-doped AlAs: A first-principles study
Authors: Qiu Yao , Zhao Yong-Hong , Liu Yong , Zhao Guo-Ping , Wu Shao-Quan
Published: December 2010

Extensive density functional theory investigations have been made on the spatial distribution of Cr atoms and associated magnetism of zinc-blende Cr:AlAs. The calculated results show that embedded Cr clusters, formed on the substitutional Al and interstitial sites, can lead to great changes in the local structure and magnetism of Cr:AlAs, which is very different from that assumed by the usual homogeneous model.
Graphene quantum dots embedded in hexagonal boron nitride sheets
Authors: Li Junwen , Shenoy Vivek B.
Published: January 2011

We have carried out first-principles calculations on electronic properties of graphene quantum dots embedded in hexagonal boron nitride monolayer sheets. The calculations with density functional theory show that the band gaps of quantum dots are determined by the quantum confinement effects and the hybridization of π orbitals from B, N, and C atoms. The energy states near the Fermi level are found to be strongly localized within and in the vicinity of the quantum dots.
Influence of Ti on the formation and stability of gas-phase Mg nanoparticles
Authors: Krishnan Gopi , Palasantzas G. , Kooi B. J.
Published: December 2010

The effect of titanium on magnesium nanoparticle formation is investigated in relation to the importance of Mg in hydrogen storage. Addition of Ti reduces the Mg-nanoparticle sizes in the range of 5–20 nm and leads to less protective Mg-oxide shells. This in return accelerates the evaporation of Mg that leads to hollow Mg cores. The presence of oxygen plays a dual role in forming MgO protected stable Mg nanoparticles above a critical size (∼15 nm) and hollow ones below this size both due to evaporation and oxidation associated Kirkendall effects.
Lyotropic chromonic liquid crystal semiconductors for water-solution processable organic electronics
Authors: Nazarenko V. G. , Boiko O. P. , Anisimov M. I. , Kadashchuk A. K. , Nastishin Yu. A. , Golovin A. B. , Lavrentovich O. D.
Published: December 2010

We propose lyotropic chromonic liquid crystals (LCLCs) as a distinct class of materials for organic electronics. In water, the chromonic molecules stack on top of each other into elongated aggregates that form orientationally ordered phases. The aligned aggregated structure is preserved when the material is deposited onto a substrate and dried. The dried LCLC films show a strongly anisotropic electric conductivity of semiconductor type. The field-effect carrier mobility measured along the molecular aggregates in unoptimized films of LCLC V20 is 0.03 cm2 V−1 s−1. Easy processibility, low cost, and high mobility demonstrate the potential of LCLCs for microelectronic applications.
Photoinduced evolution of surface-potential undulation observed on vacuum-deposited thin films of tris(8-hydroxyquinolinato) aluminum
Authors: Ozasa Kazunari , Ito Hiromi , Maeda Mizuo , Hara Masahiko
Published: January 2011

We investigated surface-potential (SP) undulation on thin films of tris(8-hydroxyquinolinato) aluminum (Alq3) using Kelvin probe force microscopy with intermittent photoexposure. SP undulation with a cloudlike morphology of 200–300 nm in lateral size was observed for Alq3 films of 10–200 nm in thickness. A short photoexposure increased the SP undulation approximately twice as that of the unexposed values, while the SP average decreased monotonically. We analyzed the origin of the SP undulation and the mechanism of its photoenhancement based on its morphology, film thickness dependence, and photoexposure dependence. We suggested nonuniform distributions of mobility and charged traps.
Multiplexed biomarker detection using x-ray fluorescence of composition-encoded nanoparticles
Authors: Hossain Mainul , Wang Chaoming , Su Ming
Published: December 2010

Multiple DNA and protein biomarkers have been detected based on characteristic x-ray fluorescence of a panel of metal and alloy nanoparticles, which are modified with ligands of biomarkers to create a one-to-one correspondence and immobilized on ligand-modified substrates after forming complexes with target biomarkers in three-strand or sandwich configuration. By determining the presence and concentration of nanoparticles using x-ray fluorescence, the nature and amount of biomarkers can be detected with limits of 1 nM for DNA and 1 ng/ml for protein. By combining high penetrating ability of x-rays, this method allows quantitative imaging of multiple biomarkers.
Cavity-involved plasmonic metamaterial for optical polarization conversion
Authors: Li T. , Wang S. M. , Cao J. X. , Liu H. , Zhu S. N.
Published: December 2010

We experimentally demonstrate a plasmonic assisted Fabry–Perot cavity in a metal/insulator/metal trilayer structure with L-shaped hole arrays inside, which significantly contribute to the mechanism to realize a nearly complete polarization conversion (=0.93) in optical transmissions at near-infrared wavelength. This interesting property is found arising from an overlap of the cavity and plasmonic modes in two orthogonal polarization states. This discovered physics remarkably endows this plasmonic metamaterial with good optical performance and looser fabrication requirement, not only indicating practical applications but also providing fruitful inspirations in future nanophotonic designs.
Effects of point defects on thermal and thermoelectric properties of InN
Authors: Levander A. X. , Tong T. , Yu K. M. , Suh J. , Fu D. , Zhang R. , Lu H. , Schaff W. J. , Dubon O. , Walukiewicz W. , Cahill D. G. , Wu J.
Published: January 2011

In contrast to most semiconductors, electrical conductivity of InN is known to increase upon high-energy particle irradiation. The effects of irradiation on its thermal and thermoelectric properties have yet to be investigated. Here we report the thermal conductivity of high-quality InN to be 120 W/m K and examine the effects of point defects generated by irradiation on the thermal conductivity and Seebeck coefficient. We show that irradiation can be used to modulate the thermal and thermoelectric properties of InN by controlling point defect concentrations. The thermoelectric figure of merit of InN was found to be insensitive to irradiation.
Raising the scientific level and networking in Africa
Authors: Feder Toni
Published: December 2010

Bringing top scientists to Africa has a greater impact than sending individual African scientists abroad.
Infrared radiation and planetary temperature
Authors: Pierrehumbert Raymond T.
Published: December 2010

Infrared radiative transfer theory, one of the most productive physical theories of the past century, has unlocked myriad secrets of the universe including that of planetary temperature and the connection between global warming and greenhouse gases.
Spin-polarized supercurrents for spintronics
Authors: Eschrig Matthias
Published: December 2010

A marriage between superconductivity and ferromagnetism is opening the door for new spin-based applications.
Tasmanian and Victorian populations of the fern Asplenium hookerianum result from independent dispersals from New Zealand
Authors: Perrie Leon R. , Ohlsen Daniel J. , Shepherd Lara D. , Garrett Michael , Brownsey Patrick J. , Bayly Michael J.
Published: January 2011

The fern Asplenium hookerianum Colenso (Aspleniaceae) is indigenous to New Zealand and Australia. In New Zealand, it is widespread and genetically diverse, with 26 haplotypes previously identified for the chloroplast trnL–trnF locus. In Australia, A. hookerianum is currently known only from two small populations in Victoria and two in Tasmania. The present study assessed the diversity, relationships and biogeographic history of the Australian populations. A single trnL–trnF haplotype was identified in Tasmanian populations, and it was shared with populations in south-western New Zealand. The single haplotype found in Victorian populations was unique and most similar to a haplotype found in populations from central and eastern North Island, New Zealand. Relationships among haplotypes suggest that the two Australian haplotypes are derived within the group (not close to the root of the haplotype network) and only distantly related. This pattern is consistent with two independent dispersals of A. hookerianum from New Zealand to Australia. These findings are unique in providing evidence for more than one trans-Tasman dispersal event in a species of vascular plant.