bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation of the electromagnetic interference shielding of titanium carbide coated nanoreinforced liquid crystalline polymer
Authors: Lozano K. , Espinoza L. , Hernandez K. , Adhikari A. R. , Radhakrishnan G. , Adams P. M.
Published: May 2009

The development and analysis of electrical and electromagnetic interference shielding effectiveness of titanium carbide (TiC)-coated carbon nanofiber (CNF) reinforced liquid crystalline polymer composites are presented. The studied samples consisted of different weight percentages (5, 10, and 15 wt %) of CNFs distributed and dispersed homogeneously within the polymeric matrix. A titanium carbide layer was deposited using pulsed laser deposition, and was conducted at room temperature, which eliminated possible thermal degradation of the polymer matrix. The effect of the thickness of the TiC layer on the electrical properties of the polymeric composites was analyzed. A synergistic behavior between the TiC coating and the polymer composite was observed for samples containing 10 wt % of NFs (within the percolation range), and the ability of the composite to shield electromagnetic interference was increased by 20–30 db.
Measurement of spontaneous polarization charge in C-face 3C-SiC/6H-SiC heterostructure with two-dimensional electron gas by capacitance-voltage method
Authors: Lu Jie , Thomas Chris I. , Chandrashekhar M. V. S. , Spencer Michael G.
Published: May 2009

A two-dimensional electron gas (2DEG) is observed in C-face 3C-SiC/6H-SiC polytype heterostructures by capacitance-voltage method. The carrier density of the 2DEG is found to be 2.5×1012 cm−2. By semiclassical analysis of the electrostatics, we extract the spontaneous polarization charge in 6H-SiC to be 3×1012 cm−2. This value quantitatively agrees well with previous measurements of the polarization charge in SiC.
Ionic conductivity and thermal stability of magnetron-sputtered nanocrystalline yttria-stabilized zirconia
Authors: Sillassen M. , Eklund P. , Sridharan M. , Pryds N. , Bonanos N. , Bøttiger J.
Published: May 2009

Thermally stable, stoichiometric, cubic yttria-stabilized zirconia (YSZ) thin-film electrolytes have been synthesized by reactive pulsed dc magnetron sputtering from a Zr–Y (80/20 at. %) alloy target. Films deposited at floating potential had a ⟨111⟩ texture. Single-line profile analysis of the 111 x-ray diffraction peak yielded a grain size of ∼20 nm and a microstrain of ∼2% regardless of deposition temperature. Films deposited at 400 °C and selected bias voltages in the range from −70 to −200 V showed a reduced grain size for higher bias voltages, yielding a grain size of ∼6 nm and a microstrain of ∼2.5% at bias voltages of −175 and −200 V with additional incorporation of argon. The films were thermally stable; very limited grain coarsening was observed up to an annealing temperature of 800 °C. Temperature-dependent impedance spectroscopy analysis of the YSZ films with Ag electrodes showed that the in-plane ionic conductivity was within one order of magnitude higher in films deposited with substrate bias corresponding to a decrease in grain size compared to films deposited at floating potential. This suggests that there is a significant contribution to the ionic conductivity from grain boundaries. The activation energy for oxygen ion migration was determined to be between 1.14 and 1.30 eV.
Classical theory for the in-plane scattering of atoms from corrugated surfaces: Application to the Ar–Ag(111) system
Authors: Pollak Eli , Miret-Artés Salvador
Published: May 2009

A classical Wigner in-plane atom surface scattering perturbation theory within the generalized Langevin equation formalism is proposed and discussed with applications to the Ar–Ag(111) system. The theory generalizes the well-known formula of Brako as well as the “washboard model.” Explicit expressions are derived for the joint angular and final momentum distributions, joint final energy, and angular distributions as well as average energy losses to the surface. The theory provides insight into the intertwining between the energy loss and angular dependence of the scattering. At low energies the energy loss in the horizontal direction is expected to be large, leading to a shift of the maximum of the angular distribution to subspecular angles, while at high energies the energy loss in the vertical direction dominates, leading to a superspecular maximum in the angular distribution. The same effect underlies the negative slope of the average final (relative) energy versus scattering angle at low energies which becomes positive at high energies. The theory also predicts that the full width at half maximum of the angular distribution varies as the square root of the temperature. We show how the theory provides insight into the experimental results for scattering of Ar from the Ag(111) surface.
Compact microwave re-entrant cavity applicator for plasma-assisted combustion
Authors: Hemawan Kadek W. , Wichman Indrek S. , Lee Tonghun , Grotjohn Timothy A. , Asmussen Jes
Published: May 2009

The design and experimental operation of a compact microwave/rf applicator is described. This applicator operates at atmospheric pressure and couples electromagnetic energy into a premixed CH4/O2 flame. The addition of only 2–15 W of microwave power to a premixed combustion flame with a flame power of 10–40 W serves to extend the flammability limits for fuel lean conditions, increases the flame length and intensity, and increases the number density and mixture of excited radical species in the flame vicinity. The downstream gas temperature also increases. Optical emission spectroscopy measurements show gas rotational temperatures in the range of 2500–3600 K. At the higher input power of ≥10 W microplasma discharges can be produced in the high electric field region of the applicator.
Well-width dependence of in-plane optical anisotropy in (001) GaAs/AlGaAs quantum wells induced by in-plane uniaxial strain and interface asymmetry
Authors: Tang C. G. , Chen Y. H. , Xu B. , Ye X. L. , Wang Z. G.
Published: May 2009

The well-width dependence of in-plane optical anisotropy (IPOA) in (001) GaAs/AlxGa1−xAs quantum wells induced by in-plane uniaxial strain and interface asymmetry has been studied comprehensively. Theoretical calculations show that the IPOA induced by in-plane uniaxial strain and interface asymmetry exhibits much different well-width dependence. The strain-induced IPOA is inversely proportional to the energy spacing between heavy- and light-hole subbands, so it increases with the well width. However, the interface-related IPOA is mainly determined by the probability that the heavy- and light-holes appear at the interfaces, so it decreases with the well width. Reflectance difference spectroscopy has been carried out to measure the IPOA of (001) GaAs/AlxGa1−xAs quantum wells with different well widths. Strain- and interface-induced IPOA have been distinguished by using a stress apparatus, and good agreement with the theoretical prediction is obtained. The anisotropic interface potential parameters are also determined. In addition, the energy shift between the interface- and strain-induced 1H1E reflectance difference (RD) structures, and the deviation of the 1L1E RD signal away from the prediction of the calculation model have been discussed.
Irreversible event-based model for thermal emission of electrons from isolated traps
Authors: Dimitrijev Sima
Published: May 2009

In spite of the irreversible nature of macroscopic processes, our understanding of the fundamental physical phenomena remains limited to reversible models (the Loschmidt’s paradox). We propose a direct irreversible model for the probability per unit time that an electron will be emitted from an isolated trap. This resolves a number of problems, including (1) the dubious link between emission measurements and the parameters of the independent capture process and (2) the elusive meaning of the degeneracy factor in the equilibrium Fermi–Dirac distribution.
Vibrational energy transfer in O2(v=2–8)–O2(v=) collisions
Authors: Sharma Ramesh D. , Welsh Judith A.
Published: May 2009

Starting with multipolar-multipolar interaction for intermolecular potential we have carried out a calculation of rate coefficients for transfer of one quantum of vibrational energy upon impact of O2(2≤v≤8) with O2(v=0) as a function of temperature (150 K≤T≤450 K). The equations for energy transfer, in the second order of perturbation theory, mediated by isotropic and anisotropic dispersion interactions, are derived. None of the parameters appearing in the calculation were adjusted to obtain agreement with the experimentally measured rate coefficients. The results of the calculation are compared with experimentally measured room temperature rate coefficients of the disappearance of O2(v) upon collision with O2(v=0). The agreement is found to be good for the disappearance of O2(v=3) and O2(v=5). For O2(v=2) the calculation gives a larger rate coefficient than the measured value, while for O2(v=4) it gives a smaller value than obtained by measurement. For O2(v=8) it agrees with one measurement and gives a value smaller than another measurement and a calculation.
Salt induced asymmetry in membrane simulations by partial restriction of ionic motion
Authors: Herrera Fernando E. , Pantano Sergio
Published: May 2009

The specific ionic composition differs considerably at both sides of biological membranes and specific lipid/electrolyte interactions may be essential for their structure, stability and function. Hence, explicit consideration of the ionic asymmetry is important to achieve an accurate description of lipid bilayers. Molecular dynamics simulations have proven to be a reliable tool to study biomembranes at atomic detail. Nevertheless, the use of periodic boundary conditions allows ions to diffuse rapidly and reach both sides of the bilayer. Therefore, ad hoc simulation schemes have to be applied to take into account ionic asymmetry. In this work we present a simple implementation to overcome this problem. A more realistic description of the biomembranes can be achieved by partially restricting the ionic motion in the direction normal to the membrane within a region of the space near to only one of the leaflets. This creates two different situations: one leaflet is highly exposed to ions while the second one can be completely or partially depleted of them. Comparison between this new method and control simulations performed using a previously proposed approach consisting of a double-membrane setup yielded an excellent agreement with a speed-up of nearly 60%. The performance of the method with different ionic species is explored and remaining limitations are examined.
Optical properties of bimetallic nanospheres: Effect of diffuse electron density profiles at the boundary surfaces
Authors: Nayak Malaya K. , Ghosh Swapan K.
Published: May 2009

The effect of diffuse electron density at the boundary surfaces of Au-core Ag-shell bimetallic nanospheres on their optical properties such as extinction spectra is investigated by considering a multiple shell model for both the interfaces consisting of exponentially decreasing electron density profiles corresponding to a minimized energy density functional. The dielectric constants for the shells of varying electron density have been obtained by proposing a new simple approach. The diffuseness of the electron density at the boundary surfaces is found to give rise to peak broadening to some extent and also seems to favor the experimental spectra.
Molecular beam sampling system with very high beam-to-background ratio: The rotating skimmer concept
Authors: Benedikt J. , Ellerweg D. , von Keudell A.
Published: May 2009

A novel method of reducing the background pressure in a vacuum system used for sampling a molecular beam from a high pressure region is presented. A triple differential pumping stage is constructed with a chopper with rotating skimmer within the first pumping stage, which serves effectively as a valve separating periodically the vacuum system from the ambient environment. The mass spectrometry measurement of the species in the molecular beam show an excellent beam-to-background ratio of 14 and a detection limit below 1 ppm. The potential of this method for detection of low density reactive species in atmospheric pressure plasmas is demonstrated for the detection of oxygen atoms generated in an atmospheric pressure microplasma source.
Resistive switching in nanostructured thin films
Authors: Silva H. , Gomes H. L. , Pogorelov Yu. G. , Stallinga P. , de Leeuw D. M. , Araujo J. P. , Sousa J. B. , Meskers S. C. J. , Kakazei G. , Cardoso S. , Freitas P. P.
Published: May 2009

Planar capacitor structures based on granular films composed of nanometric ferromagnetic grains embedded in an insulating Al2O3 matrix can switch between a high-conductance and a low-conductance state. The switching properties are induced by a forming process. The ON/OFF resistance ratio is as high as 104 under an electrical field of only 15 kV/m. This resistive switching is accompanied by a capacitive switching between two well-defined voltage-independent states, a behavior that is not readily explained by the filamentary type of conduction.
Fundamental mechanisms of oxygen plasma-induced damage of ultralow-k organosilicate materials: The role of thermal P3 atomic oxygen
Authors: Chaudhari Mrunalkumar , Du Jincheng , Behera Swayambhu , Manandhar Sudha , Gaddam Sneha , Kelber Jeffry
Published: May 2009

Fourier transform infrared (FTIR) spectroscopy, x-ray photoelectron spectroscopy (XPS), and ab initio density functional theory-based molecular dynamics simulations demonstrate fundamental mechanisms for CH3 abstraction from organosilicate films by thermal O(P3). Ex situ FTIR analysis demonstrates that film exposure to thermal O(P3) yields chemical changes similar to O2 plasma exposure. In situ XPS indicates that exposure to thermal O(P3) yields O/OH incorporation in the organosilicate film concurrent with carbon loss from the surface region. These results are consistent with simulations indicating specific low kinetic barrier (<0.1 eV) reactions resulting in concurrent Si–C bond scission and Si–O bond formation.
Self-assembly of nanocomponents into composite structures: Derivation and simulation of Langevin equations
Authors: Pankavich S. , Shreif Z. , Miao Y. , Ortoleva P.
Published: May 2009

The kinetics of the self-assembly of nanocomponents into a virus, nanocapsule, or other composite structure is analyzed via a multiscale approach. The objective is to achieve predictability and to preserve key atomic-scale features that underlie the formation and stability of the composite structures. We start with an all-atom description, the Liouville equation, and the order parameters characterizing nanoscale features of the system. An equation of Smoluchowski type for the stochastic dynamics of the order parameters is derived from the Liouville equation via a multiscale perturbation technique. The self-assembly of composite structures from nanocomponents with internal atomic structure is analyzed and growth rates are derived. Applications include the assembly of a viral capsid from capsomers, a ribosome from its major subunits, and composite materials from fibers and nanoparticles. Our approach overcomes errors in other coarse-graining methods, which neglect the influence of the nanoscale configuration on the atomistic fluctuations. We account for the effect of order parameters on the statistics of the atomistic fluctuations, which contribute to the entropic and average forces driving order parameter evolution. This approach enables an efficient algorithm for computer simulation of self-assembly, whereas other methods severely limit the timestep due to the separation of diffusional and complexing characteristic times. Given that our approach does not require recalibration with each new application, it provides a way to estimate assembly rates and thereby facilitate the discovery of self-assembly pathways and kinetic dead-end structures.
Magnetic field probes for use in radio frequency plasma
Authors: Reilly Michael P. , Lewis William , Miley George H.
Published: May 2009

An impedance analyzer has been used in the characterization of a magnetic induction probe (B-dot probe) for use in plasma. The role of the impedance analyzer was to determine the frequency response of a B-dot probe up to 100 MHz. The probe was specifically designed to take measurements in rf plasma driven at 13.56 MHz. Probe sensitivity and calibration are considered based on the impedance values obtained when a B-dot probe is swept over a wide frequency range. Effects such as unbalanced loads based on transmission line inductances and termination impedance are shown to be limiting factors on the probes useful frequency range. The use of an impedance analyzer allows these effects to readily be characterized.
A simple atomic force microscopy calibration method for direct measurement of surface energy on nanostructured surfaces covered with molecularly thin liquid films
Authors: Brunner Ralf , Etsion Izhak , Talke Frank E.
Published: May 2009

A simple calibration method is described for the determination of surface energy by atomic force microscopy (AFM) pull-off force measurements on nanostructured surfaces covered with molecularly thin liquid films. The method is based on correlating pull-off forces measured in arbitrary units on a nanostructured surface with pull-off forces measured on macroscopically smooth dip-coated gauge surfaces with known surface energy. The method avoids the need for complex calibration of the AFM cantilever stiffness and the determination of the radius of curvature of the AFM tip. Both of the latter measurements are associated with indirect and less accurate measurements of surface energy based on various contact mechanics adhesion models.
Statistical mechanical theory for non-equilibrium systems. IX. Stochastic molecular dynamics
Authors: Attard Phil
Published: May 2009

The general form for the probability density and for the transition probability of a nonequilibrium system is given. Maximization of the latter gives a generalized fluctuation-dissipation theorem by providing a molecular basis for Langevin’s friction force that avoids continuum hydrodynamics. The result shows that the friction coefficient must be proportional to the variance of the stochastic equations of motion. Setting the variance to zero but keeping the friction coefficient nonzero reduces the theory to a Hoover thermostat without explicit constraint, although such a limit violates the physical requirement of proportionality between the dissipation and the fluctuation. A stochastic molecular dynamics algorithm is developed for both equilibrium and nonequilibrium systems, which is tested for steady heat flow and for a time-varying, driven Brownian particle.
Quantification of unsteady heat transfer and phase changing process inside small icing water droplets
Authors: Jin Zheyan , Hu Hui
Published: May 2009

We report progress made in our recent effort to develop and implement a novel, lifetime-based molecular tagging thermometry (MTT) technique to quantify unsteady heat transfer and phase changing process inside small icing water droplets pertinent to wind turbine icing phenomena. The lifetime-based MTT technique was used to achieve temporally and spatially resolved temperature distribution measurements within small, convectively cooled water droplets to quantify unsteady heat transfer within the small water droplets in the course of convective cooling process. The transient behavior of phase changing process within small icing water droplets was also revealed clearly by using the MTT technique. Such measurements are highly desirable to elucidate underlying physics to improve our understanding about important microphysical phenomena pertinent to ice formation and accreting process as water droplets impinging onto wind turbine blades.
Residual stress analysis in chemical-vapor-deposition diamond films
Authors: Liu T. , Pinto H. , Brito P. , Sales L. A. , Raabe D.
Published: May 2009

Three groups of diamond films were deposited with variations in methane concentration, substrate material, and film thickness by a direct current chemical-vapor-deposition method. Stresses were measured by x-ray diffraction. The material reveals compressive stresses at the substrate interfaces due to thermal expansion mismatch. Increasing influence of defects leads to a drop in the compressive stresses and the formation of tensile stresses toward the growth front.
Filamentation of laser in a magnetized plasma under relativistic and ponderomotive nonlinearities
Authors: Singh Ranjeet , Tripathi V. K.
Published: May 2009

Filamentation of a circularly polarized short pulse laser propagating along the direction of ambient magnetic field in plasma is studied. The nonlinearity arises through the combined effect of relativistic mass variation and ponderomotive force induced electron cavitation. The growth rate is maximum Γmax for an optimum filament size, qopt−1. Γmax and qopt increases with plasma density and ambient magnetic field.
Analysis of the spectral relationships of cavity tones in subsonic resonant cavity flows
Authors: Malone J. , Debiasi M. , Little J. , Samimy M.
Published: May 2009

The understanding of the self-sustained flow-acoustic coupling mechanism in flows over shallow rectangular cavities is of great interest owing to its various practical applications. The ability to understand and predict the resonant frequencies in such flows has recently been advanced through contributions from signal processing theory and by viewing the Rossiter tones as the product of an amplitude modulation process between a fundamental aeroacoustic loop frequency (fa) and a modulating lower frequency. The results obtained using this approach applied to detailed and high-quality spectral data of shallow cavity flow over the Mach number range of 0.20–0.65 are presented and discussed. The new approach, while not a predictive technique, is used to clearly identify all the tones (Rossiter modes, their harmonics, and harmonics of fa) observed in the pressure spectra and to show relationships between the tones. The asymptotic growth with Mach number of fa and the small-step changes of the modulating lower frequency over the Mach number range studied provide insight into the variation of the Rossiter mode parameters. The results also indicate that the empirical parameters in the Rossiter equation vary with Mach number for fixed cavity geometry.
A nonmolecular derivation of Maxwell’s thermal-creep boundary condition in gases and liquids via application of the LeChatelier–Braun principle to Maxwell’s thermal stress
Authors: Brenner Howard
Published: May 2009

According to the LeChatelier–Braun principle, when a closed quiescent system initially in an equilibrium or unstressed steady state is subjected to an externally imposed “stress” it responds in a manner tending to alleviate that stress. Use of this entropically based qualitative rule, in combination with the notion of Maxwell thermal stresses existing in nonisothermal gases and liquids, enables one to (i) derive Maxwell’s thermal-creep boundary condition prevailing at the boundary between a solid and a fluid (either gas or liquid) and (ii) rationalize the phenomenon of thermophoresis in liquids, for which, in contrast with the case of gases, an elementary explanation is currently lacking. These two objectives are achieved by quantitatively interpreting the heretofore qualitative LeChatelier–Braun notion of stress in the present context as being the fluid’s stress tensor, the latter including Maxwell’s thermal stress. In effect, thermophoretic particle motion is interpreted as the manifestation of the fluid’s attempt to expel the particle from its interior so as to alleviate the thermal stress that would otherwise ensue were the particle to remain at rest (thus obeying the traditional no slip rather than thermal-creep boundary condition) following its introduction into the previously stress-free quiescent fluid. With Kn the Knudsen number in the case of rarefied gases, Maxwell’s thermal stress constitutes a noncontinuum phenomenon of O(Kn2), whereas his thermal-creep phenomenon constitutes a continuum phenomenon of O(Kn). That these two phenomena can, nevertheless, be proved to be synonymous (in the sense, so to speak, of being two sides of the same coin), as is done in the present paper, supports the “ghost effect” findings of Sone [Y. Sone, “Flows induced by temperature fields in a rarefied gas and their ghost effect on the behavior of a gas in the continuum limit,” Annu. Rev. Fluid Mech 32, 779 (2000)], which, philosophically, imply the artificiality of the distinction currently existing between continuum- and noncontinuum-level phenomena.
Turbulent boundary layers up to Reθ=2500 studied through simulation and experiment
Authors: Schlatter P. , Örlü R. , Li Q. , Brethouwer G. , Fransson J. H. M. , Johansson A. V. , Alfredsson P. H. , Henningson D. S.
Published: May 2009

Direct numerical simulations (DNSs) and experiments of a spatially developing zero-pressure-gradient turbulent boundary layer are presented up to Reynolds number Reθ=2500, based on momentum thickness θ and free-stream velocity. For the first time direct comparisons of DNS and experiments of turbulent boundary layers at the same (computationally high and experimentally low) Reθ are given, showing excellent agreement in skin friction, mean velocity, and turbulent fluctuations. These results allow for a substantial reduction of the uncertainty of boundary-layer data, and cross validate the numerical setup and experimental technique. The additional insight into the flow provided by DNS clearly shows large-scale turbulent structures, which scale in outer units growing with Reθ, spanning the whole boundary-layer height.
Can large-scale advanced-adiabatic compressed air energy storage be justified economically in an age of sustainable energy?
Authors: Pickard William F. , Hansing Nicholas J. , Shen Amy Q.
Published: May 2009

This article explores whether large-scale compressed air energy storage can be justified technically and economically in an era of sustainable energy. In particular, we present an integrated energy and exergy analysis of an idealized case of an advanced-adiabatic compressed air energy storage system and estimate its cycle efficiency. Based on our results, advanced-adiabatic compressed air energy storage (AA-CAES) seems to be technically feasible with a cycle efficiency of roughly 50% or better. However, our calculation shows that AA-CAES may not be as economically attractive as underground pumped hydro storage.
Tailoring exchange bias in half-metallic La2/3Sr1/3MnO3 thin films for spin valve applications
Authors: Muduli P. K. , Budhani R. C.
Published: May 2009

We have utilized the antiferromagnetic nature and structural/chemical compatibility of La0.45Sr0.55MnO3 with highly spin polarized La0.67Sr0.33MnO3 to prepare epitaxial exchange bias (EB) couples. A robust EB shift in magnetization hysteresis with associated interfacial exchange energy J≈0.13 erg/cm2 at 10 K along with enhanced coercivity is reported. The EB effect was engineered to bring coercivity contrast between La0.67Sr0.33MnO3 and cobalt films in La0.45Sr0.55MnO3/La0.67Sr0.33MnO3/SrTiO3/Co magnetic tunnel junctions.
GeTe
/
Sb
7
Te
3
superlatticelike structure for lateral phase change memory
Authors: Yang Hongxin , Chong Chong Tow , Zhao Rong , Lee Hock Koon , Li Jianming , Lim Kian Guan , Shi Luping
Published: May 2009

A series of superlatticelike (SLL) structure incorporated with two phase-change materials GeTe and Sb7Te3 was applied in lateral phase change memory. Power consumption and lifetime were used as two criteria to optimize the SLL structure. It was found that with the thickness ratio of GeTe to Sb7Te3 at 1.6, the RESET current could be as low as 1.5 mA and the endurance could reach as high as 5.3×106 cycles. By varying the thickness ratio of GeTe to Sb7Te3, the crystallization temperature of SLL structures and the performance of lateral phase change memory with these SLL structures can be controlled.
A simple model for the streamwise fluctuations in the log-law region of a boundary layer
Authors: Davidson P. A. , Krogstad P.-Å.
Published: May 2009

We build on the work of Davidson et al. [Phys. Fluids 18, 065112 (2006)] and propose an elementary model for the log-law region of a boundary layer. The model is remarkably simple, contains only one free parameter (which we set equal to unity) and, unlike Davidson et al., assumes very little about the shape of the boundary-layer eddies. The physical content of the model is simple: we assume that the two-point statistics of the streamwise velocity fluctuations know about the presence of the wall only to the extent that, over a range of eddy sizes, it imposes a kinetic energy scale proportional to the square of the shear velocity. Little else is assumed, other than classic Kolmogorov phenomenology for the small scales. Despite its naivety, and the minimal number of free parameters, the model is a good fit to experimental data for the k−1 law of the one-dimensional, longitudinal spectrum, Φuu(k), and also to Φuu(k) in the inertial range. It is also an excellent fit to experimental data for the real-space analog of the k−1 law; that is, the logarithmic law for the longitudinal structure function. In addition, the model predicts the cross-stream variation of the variance of the streamwise velocity fluctuations, ⟨ux2⟩, and, to within an additive constant, it too is a reasonable fit to the data. Our model differs from the classic analyses of Townsend [J. Fluid Mech. 165, 163 (1986)] and Perry et al. [J. Fluid Mech. 165, 163 (1986)] in three respects. First, we do not invoke the attached eddy hypothesis, which assumes that the vortical structures in the log-layer extend to the wall. Second, we predict the precise shape of Φuu(k) for all values of k and not just the k−1 region. Third, there are three adjustable parameters in the theory of Perry et al., whereas we have only one. It is instructive that a model which contains very little information about the morphology of the vorticity field, and has only one free parameter, is able to reproduce both the structural form for, and magnitude of, many features of the one-dimensional spectrum and the second-order structure function. This suggests that these two measures of the scale-by-scale energy distribution are insensitive to the detailed structure of the vorticity field. We argue that this is indeed the case.
Peculiar three-dimensional ordering in (In,Ga)As/GaAs(311)B quantum dot superlattices
Authors: Hanke M. , Schmidbauer M. , Wang Zh. M. , Mazur Yu. I. , Seydmohamadi Sh. , Salamo G. J. , Mishima T. D. , Johnson M. B.
Published: May 2009

The impact of the GaAs spacer layer thickness on the three-dimensional ordering in (In,Ga)As/GaAs(311)B quantum dot superlattices was investigated by high-resolution x-ray diffraction, cross-sectional transmission electron microscopy, and atomic force microscopy. Dramatic changes in both planar and vertical ordering could be observed. A distinct correlation was found in that the azimuthal angle of inclined vertical inheritance of the dot positions is perpendicular to the planar direction between the dot chains within individual quantum dot layers. These directions are close to [130] or [1¯03].
Nucleation thermodynamics of oxide during metal oxidation
Authors: Zhou Guangwen
Published: May 2009

The classical theory of nucleation has been extended to describe oxide nucleation during the oxidation of metals. It is found that the localized reaction of oxygen with an underlying metal substrate exerts a very strong influence on the free energy barrier of three-dimensional oxide nucleation, which can be characterized by an interfacial correlation function. Our results show that the nucleation barrier increases with the steepening of the contact angle between the nucleating phase and the substrate. This model is expected to find applicability in other reaction-induced heterogeneous nucleation systems.
Direct and wavelength modulation spectroscopy using a cw external cavity quantum cascade laser
Authors: Hancock G. , van Helden J. H. , Peverall R. , Ritchie G. A. D. , Walker R. J.
Published: May 2009

A continuous wave external cavity quantum cascade laser (EC-QCL) operating between 1872 and 1958 cm−1 has been used to make rotationally resolved measurements in the fundamental band of nitric oxide at 140 mTorr, and the ν2 band of water at atmospheric pressure. These measurements demonstrate the advantages of wide tunability and high resolution of the EC-QCL system. From direct absorption spectroscopy on nitric oxide a laser bandwidth of 20 MHz has been deduced and a sensitivity of 8.4×10−4 cm−1 Hz−1/2 was achieved. Wavelength modulation spectroscopy using current modulation enhances the sensitivity by a factor of 23 to 3.7×10−5 cm−1 Hz−1/2.
Low-temperature time-resolved cathodoluminescence study of exciton dynamics involving basal stacking faults in a-plane GaN
Authors: Corfdir P. , Ristić J. , Lefebvre P. , Zhu T. , Martin D. , Dussaigne A. , Ganière J. D. , Grandjean N. , Deveaud-Plédran B.
Published: May 2009

Time-resolved cathodoluminescence at 27 K has been performed on a-plane GaN grown by epitaxial lateral overgrowth. We detail the relaxation and recombination mechanisms of excitons [free or bound to neutral donors, or bound to I1-type basal stacking faults (BSFs)] in relation to the local density in BSFs. We describe the slow exciton capture rate on isolated BSFs by a diffusion model involving donors via a hopping process. Where BSFs are organized into bundles, we relate the shorter rise time to intra-BSF localization processes and the multiexponential decay to the type-II band alignment of BSFs in wurtzite GaN.
Depleting Rac1 in mouse rod photoreceptors protects them from photo-oxidative stress without affecting their structure or function
Authors: Haruta Masatoshi , Bush Ronald A. , Kjellstrom Sten , Vijayasarathy Camasamudram , Zeng Yong , Le Yun-Zheng , Sieving Paul A.
Published: May 2009

In nonphagocytic cells, Rac1 is a component of NADPH oxidase that produces reactive oxygen species [Ushio-Fukai M (2006)
Sci STKE
2006:re8]. Rac1 is expressed abundantly in mammalian retinal photoreceptors, where it is activated in response to light stimuli [Balasubramanian N, Slepak VZ (2003)
Curr Biol
13:1306–1310]. We used Cre-
LoxP
conditional gene targeting to knock down Rac1 expression in mouse rod photoreceptors and found protection against light-induced photoreceptor death compared with WT litter-mates. We also found a similar protective effect on rods using apocynin, which inhibits NADPH oxidase activity. These results implicate both neuronal Rac1 and NADPH oxidase in cell death in this model of CNS degeneration. Studies in which dominant-mutants of
Rac1
were expressed in transgenic
Drosophila
species demonstrated that Rac1 is a key regulator of photoreceptor morphogenesis and polarity [Chang HY, Ready DF (2000)
Science
290:1978–1980]. However, we found that diminished Rac1 expression in mouse rods had no effect on retinal structure or function examined by light microscopy, electron microscopy, rhodopsin measurement, electroretinogram activity, and visual acuity, indicating rod outer segment morphogenesis proceeded normally in
Rac1
conditional knockout mice. The lack of structural or functional effect of Rac1 depletion on photoreceptors, but protection under conditions of stress, indicate that the Rac1 pathway warrants exploration as a target for therapy in retinal neurodegenerative diseases.
Alteration of enzyme specificity by computational loop remodeling and design
Authors: Murphy Paul M. , Bolduc Jill M. , Gallaher Jasmine L. , Stoddard Barry L. , Baker David
Published: May 2009

Altering the specificity of an enzyme requires precise positioning of side-chain functional groups that interact with the modified groups of the new substrate. This requires not only sequence changes that introduce the new functional groups but also sequence changes that remodel the structure of the protein backbone so that the functional groups are properly positioned. We describe a computational design method for introducing specific enzyme–substrate interactions by directed remodeling of loops near the active site. Benchmark tests on 8 native protein–ligand complexes show that the method can recover native loop lengths and, often, native loop conformations. We then use the method to redesign a critical loop in human guanine deaminase such that a key side-chain interaction is made with the substrate ammelide. The redesigned enzyme is 100-fold more active on ammelide and 2.5e4-fold less active on guanine than wild-type enzyme: The net change in specificity is 2.5e6-fold. The structure of the designed protein was confirmed by X-ray crystallographic analysis: The remodeled loop adopts a conformation that is within 1-Å Cα RMSD of the computational model.
Quantitative analysis by in vivo imaging of the dynamics of vascular and axonal networks in injured mouse spinal cord
Authors: Dray Cyril , Rougon Geneviève , Debarbieux Franck
Published: May 2009

Understanding the endogenous repair capacity of spinal cord is pivotal to develop strategies to improve it. Here we design a paradigm of spinal cord lesion in the dorsal column using a 2-photon microscopy technique to dynamically and chronically monitor simultaneous changes of vascular and axonal networks in living mice up to 4 months postinjury. High-resolution images showed that early explorative sprouting of surviving injured axons resulted in extensive regrowth until and past the lesion site within 2 months. Blood vessel density was transiently up-regulated and most neurovascular interactions occurred within 2 weeks. Time-lapse analysis showed that neovessels exerted a potent growth stimulating action, but no guidance effect on neighboring sprouts, possibly because of their geometry and plasticity. Nevertheless, if reconnection depends on axon sprout density, stimulation of angiogenesis would probably be beneficial to repair. More generally, this imaging approach is showing promise to aid in monitoring brain diseases and the efficacy of potential treatments.
The discovery of 2,5-dialkylcyclohexan-1,3-diones as a new class of natural products
Authors: Franke S. , Ibarra F. , Schulz C. M. , Twele R. , Poldy J. , Barrow R. A. , Peakall R. , Schiestl F. P. , Francke W.
Published: May 2009

Orchids employing sexual deceit attract males of their pollinator species through specific volatile signals that mimic female-released sex pheromones. One of these signals proved to be 2-ethyl-5-propylcyclohexan-1,3-dione (chiloglottone1), a new natural product that was shown to be most important in the relations between orchids of the genus
Chiloglottis
, native to Australia, and corresponding pollinator species. Systematic investigations on the mass spectrometric fragmentation pattern of 2,5-dialkylcyclohexan-1,3-diones identified key ions providing information about the structures of the substituents at positions 2 and 5. Results enabled us to identify 2-ethyl-5-pentylcyclohexan-1,3-dione (chiloglottone2) and 2-butyl-5-methylcyclohexan-1,3-dione (chiloglottone3) as new natural products that play a decisive role in the pollination syndrome of some
Chiloglottis
species. During field bioassays, pure synthetic samples of chiloglottone1–3 or mixtures thereof proved to be attractive to the corresponding orchid pollinators. Because of their likely biogenesis from ubiquitous fatty acid precursors, 2,5-dialkylcyclohexan-1,3-diones may represent a hitherto overlooked, widespread class of natural products.
SPITZER QUASAR AND ULIRG EVOLUTION STUDY (QUEST).
IV. COMPARISON OF 1 Jy ULTRALUMINOUS INFRARED GALAXIES WITH PALOMAR-GREEN
QUASARS
Authors: Veilleux S. , Rupke D. S. N. , Kim D.-C. , Genzel R. , Sturm E. , Lutz D. , Contursi A. , Schweitzer M. , Tacconi L. J. , Netzer H. , Sternberg A. , Mihos J. C. , Baker A. J. , Mazzarella J. M. , Lord S. , Sanders D. B. , Stockton A. , Joseph R. D. , Barnes J. E.
Published: May 2009

We report the results from a comprehensive study of 74 ultraluminous infrared
galaxies (ULIRGs) and 34 Palomar-Green (PG) quasars within z ∼
0.3 observed with the Spitzer Infrared Spectrograph (IRS). The
contribution of nuclear activity to the bolometric luminosity in these systems
is quantified using six independent methods that span a range in wavelength and
give consistent results within ∼±10%–15% on average. This agreement suggests
that deeply buried active galactic nuclei (AGNs) invisible to
Spitzer IRS but bright in the far-infrared are not common
in this sample. The average derived AGN contribution in ULIRGs is ∼35%–40%,
ranging from ∼15%–35% among “cool”
(f
25/f
60 ⩽ 0.2)
optically classified H ii-like and LINER ULIRGs to ∼50 and ∼75% among
warm Seyfert 2 and Seyfert 1 ULIRGs, respectively. This number exceeds ∼80% in
PG QSOs. ULIRGs fall in one of three distinct AGN classes: (1) objects with
small extinctions and large polycyclic aromatic hydrocarbon (PAH) equivalent
widths are highly starburst-dominated; (2) systems with large extinctions and
modest PAH equivalent widths have larger AGN contributions, but still tend to be
starburst-dominated; and (3) ULIRGs with both small extinctions and small PAH
equivalent widths host AGN that are at least as powerful as the starbursts. The
AGN contributions in class 2 ULIRGs are more uncertain than in the other
objects, and we cannot formally rule out the possibility that these objects
represent a physically distinct type of ULIRGs. A morphological trend is seen
along the sequence (1)–(2)–(3), in general agreement with the standard ULIRG−QSO
evolution scenario and suggestive of a broad peak in extinction during the
intermediate stages of merger evolution. However, the scatter in this sequence,
including the presence of a significant number of AGN-dominated systems prior to
coalescence and starburst-dominated but fully merged systems, implies that black
hole accretion, in addition to depending on the merger phase, also has a strong
chaotic/random component, as in local AGNs.
Totally geodesic submanifolds of the complex and the quaternionic 2-Grassmannians
Authors: Klein Sebastian
Published: May 2009

In this article, the totally geodesic submanifolds in the complex

2
2

-Grassmannian

G
2

(

C

n
+
2

)

G_2(\mathbb {C}^{n+2})

and in the quaternionic

2
2

-Grassmannian

G
2

(

H

n
+
2

)

G_2(\mathbb {H}^{n+2})

are classified. It turns out that for both of these spaces, the earlier classification of maximal totally geodesic submanifolds in Riemannian symmetric spaces of rank

2
2

published by Chen and Nagano (1978) is incomplete. For example,

G
2

(

H

n
+
2

)

G_2(\mathbb {H}^{n+2})

with

n
≥
5

n \geq 5

contains totally geodesic submanifolds isometric to a

H

P
2

\mathbb {H}P^2

, its metric scaled such that the minimal sectional curvature is

1
5

\tfrac 15

; they are maximal in

G
2

(

H

7

)

G_2(\mathbb {H}^7)

.

G
2

(

C

n
+
2

)

G_2(\mathbb {C}^{n+2})

with

n
≥
4

n \geq 4

contains totally geodesic submanifolds which are isometric to a

C

P
2

\mathbb {C}P^2

contained in the

H

P
2

\mathbb {H}P^2

mentioned above; they are maximal in

G
2

(

C

6

)

G_2(\mathbb {C}^6)

. Neither submanifolds are mentioned by Chen and Nagano.
Regularity of dynamical Green’s functions
Authors: Diller Jeffrey , Guedj Vincent
Published: May 2009

For meromorphic maps of complex manifolds, ergodic theory and pluripotential theory are closely related. In nice enough situations, dynamically defined Green’s functions give rise to invariant currents which intersect to yield measures of maximal entropy. ‘Nice enough’ is often a condition on the regularity of the Green’s function. In this paper we look at a variety of regularity properties that have been considered for dynamical Green’s functions. We simplify and extend some known results and prove several others which are new. We also give some examples indicating the limits of what one can hope to achieve in complex dynamics by relying solely on the regularity of a dynamical Green’s function.
Asymptotic stability of the wave equation on compact surfaces and locally distributed damping-A sharp result
Authors: Cavalcanti M. , Domingos Cavalcanti V. , Fukuoka R. , Soriano J.
Published: May 2009

This paper is concerned with the study of the wave equation on compact surfaces and locally distributed damping, described by<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="StartLayout 1st Row u Subscript t t Baseline minus normal upper Delta Subscript script upper M Baseline u plus a left-parenthesis x right-parenthesis g left-parenthesis u Subscript t Baseline right-parenthesis equals 0 on reverse-solidus thinspace script upper M times right-bracket 0 comma normal infinity left-bracket comma EndLayout">utt−ΔMu+a(x)g(ut)=0on \thinspace M×]0,∞[,\begin{equation} \left . \begin {array}{l} u_{tt} - \Delta _{\mathcal {M}}u+ a(x) g(u_{t})=0 \; \text {on \thinspace }\mathcal {M}\times \left ] 0,\infty \right [ , \end{array} \right . \nonumber \end{equation}whereM⊂R3\mathcal {M}\subset \mathbb {R}^3is a smooth oriented embedded compact surface without boundary. Denoting byg\mathbf {g}the Riemannian metric induced onM\mathcal {M}byR3\mathbb {R}^3, we prove that for eachϵ>0\epsilon > 0, there exist an open subsetV⊂MV \subset \mathcal Mand a smooth functionf:M→Rf:\mathcal M \rightarrow \mathbb Rsuch thatmeas(V)≥meas(M)−ϵmeas(V)\geq meas(\mathcal M)-\epsilon,Hessf≈gHess f \approx \mathbf {g}onVVandinfx∈V|∇f(x)|>0\underset {x\in V}\inf |\nabla f(x)|>0.

In addition, we prove that ifa(x)≥a0>0a(x) \geq a_0> 0on an open subsetM∗⊂M\mathcal {M}{\ast } \subset \mathcal Mwhich containsM∖V\mathcal {M}\backslash Vand ifggis a monotonic increasing function such thatk|s|≤|g(s)|≤K|s|k |s| \leq |g(s)| \leq K |s|for all|s|≥1|s| \geq 1, then uniform and optimal decay rates of the energy hold.
Multidimensional operator multipliers
Authors: Juschenko K. , Todorov I. , Turowska L.
Published: May 2009

We introduce multidimensional Schur multipliers and characterise them, generalising well-known results by Grothendieck and Peller. We define a multidimensional version of the two-dimensional operator multipliers studied recently by Kissin and Shulman. The multidimensional operator multipliers are defined as elements of the minimal tensor product of several

C
∗

C^*

-algebras satisfying certain boundedness conditions. In the case of commutative

C
∗

C^*

-algebras, the multidimensional operator multipliers reduce to continuous multidimensional Schur multipliers. We show that the multipliers with respect to some given representations of the corresponding

C
∗

C^*

-algebras do not change if the representations are replaced by approximately equivalent ones. We establish a non-commutative and multidimensional version of the characterisations by Grothendieck and Peller which shows that universal operator multipliers can be obtained as certain weak limits of elements of the algebraic tensor product of the corresponding

C
∗

C^*

-algebras.
Distributional chaos revisited
Authors: Oprocha Piotr
Published: May 2009

In their famous paper, Schweizer and Smítal introduced the definition of a distributionally chaotic pair and proved that the existence of such a pair implies positive topological entropy for continuous mappings of a compact interval. Further, their approach was extended to the general compact metric space case.

In this article we provide an example which shows that the definition of distributional chaos (and as a result Li-Yorke chaos) may be fulfilled by a dynamical system with (intuitively) regular dynamics embedded in

R

3

\mathbb {R}^3

. Next, we state strengthened versions of distributional chaos which, as we show, are present in systems commonly considered to have complex dynamics.

We also prove that any interval map with positive topological entropy contains two invariant subsets

X
,
Y
⊂
I

X,Y \subset I

such that

f

|

X

f|_X

has positive topological entropy and

f

|

Y

f|_Y

displays distributional chaos of type

1
1

, but not conversely.