bluuebunny/crossref_metadata_2025 huggingface dataset:
Structure and lattice dynamics in PbTiO3–Bi(Zn1/2Ti1/2)O3 solid solutions
Authors: Chen Jun , Sun Xueyi , Deng Jinxia , Zu Yong , Liu Yuntao , Li Junhong , Xing Xianran
Published: February 2009

( 1 − x ) PbTiO 3 – x Bi ( Zn 1 / 2 Ti 1 / 2 ) O 3 solid solutions show a much enhanced tetragonality (c/a) and Curie temperature (TC). The detailed structure of (1−x)PbTiO3–xBi(Zn1/2Ti1/2)O3 is studied by means of neutron powder diffraction based on the Rietveld refinement. Zn exhibits a more polarizable property than Ti, resulting in a B-site cation splitting (0.27 Å) between Zn and Ti along c-axis direction. The spontaneous polarization displacements are enhanced by the substitution of Bi(Zn1/2Ti1/2)O3. The lattice dynamics study of (1−x)PbTiO3–xBi(Zn1/2Ti1/2)O3 by Raman scattering spectroscopy reveals that the optical modes [A1 (1TO), A1 (2TO), and E (2TO)] are abnormally hardened by the substitution of Bi(Zn1/2Ti1/2)O3 for PbTiO3, indicating the enhanced PS and the strong hybridization between Pb/Bi and O. The ceramic of (1−x)PbTiO3–xBi(Zn1/2Ti1/2)O3 (x=0.3) exhibits a low dielectric loss (tan δ) due to the d0 electronic structure.
Preparation of silicon nanowires by hydrothermal deposition on silicon substrates
Authors: Tang Y. H. , Pei L. Z. , Lin L. W. , Li X. X.
Published: February 2009

Smooth silicon nanowires (SiNWs) without metallic catalysts have been prepared using silicon monoxide as starting material by hydrothermal deposition on silicon substrates. Scanning electron microscopy and transmission electron microscopy demonstrate that SiNWs have smooth surfaces and around 170 nm in diameter as well as larger than 10 μm in length. High-resolution transmission electron microscopy shows that each nanowire consists a polycrystalline silicon core and an amorphous silica sheath. Si and silicon oxide, is proposed, are generated from silicon monoxide under high temperature and high pressure of hydrothermal conditions. The growth mechanism of silicon nanowires is proposed as the oxide-assisted growth mechanism.
The spectroscopic characterization of the methoxy radical. I. Rotationally resolved Ã A21–X̃ E2 electronic spectra of CH3O
Authors: Liu Jinjun , Chen Ming-Wei , Melnik Dmitry , Yi John T. , Miller Terry A.
Published: February 2009

New experimental data have been obtained for the methoxy radical by observing at high-resolution laser-induced fluorescence (LIF) and stimulated emission pumping (SEP) transitions between the X̃ E2 and lowest excited Ã A21 state. The SEP transitions were from the Ã state (pumped from the X̃ E23/2 spin-orbit component) to the X̃ E21/2 spin-orbit component. These data for the first time directly connect with high precision the spin-orbit components of the X̃ E2 ground state of CH3O. Surprisingly these new SEP observations are inconsistent with predictions of the X̃ state structure based on long-standing analyses primarily based on the microwave spectra of ground state CH3O. It is found that all the experimental data can be understood consistently when the previously accepted value of the spin-orbit coupling constant is adjusted and the reflection parity assignments in the X̃ state are reversed. The latter action changes the sign of a number of reflection-parity-dependent parameters in the X̃ state. The ramifications of the changes and the physical interpretation of the resulting parameters are discussed in some detail.
The spectroscopic characterization of the methoxy radical. II. Rotationally resolved Ã A21-X̃ E2 electronic and X̃ E2 microwave spectra of the perdeuteromethoxy radical CD3O
Authors: Liu Jinjun , Chen Ming-Wei , Melnik Dmitry , Miller Terry A. , Endo Yasuki , Hirota Eizi
Published: February 2009

Rotationally resolved laser-induced fluorescence (LIF) and stimulated emission pumping (SEP) Ã A21-X̃ E2 spectra of the perdeuteromethoxy radical (CD3O) have been observed. These data directly connect the two spin-orbit components (E1/2 and E3/2) of the ground electronic state with high precision. Molecular constants for both electronic states are determined in a global fitting that involves LIF, SEP, and pure rotational spectra in the microwave region. For the microwave transitions, the resolved hyperfine structure is analyzed providing molecular parameters characterizing it and hyperfine-free transitions for the global fitting. A complete “experimental” geometry for the methoxy radical at the C3v conical intersection is determined from the rotational constants of its isotopologs. The experimental isotopic dependence of other parameters in the effective Hamiltonians is compared to the theoretically expected variation. These comparisons allow considerable insight into the physical significance of a number of parameters in the effective Hamiltonian. In particular, experimental evidence is found for a previously predicted vibrational correction to the A rotational constant of a Jahn–Teller active molecule.
Nonlinear effective spin-mixing conductance in Pt/Ni80Fe20/Pt thin films
Authors: Cao R. , Fan X. , Moriyama T. , Xiao John Q.
Published: February 2009

In this study, the effective spin-mixing conductance in Ni80Fe20/Pt was investigated by measuring the interface-induced enhancement of the Gilbert damping constant. Ferromagnetic resonance spectra were measured in coplanar waveguide geometry with different incident microwave powers. The nonlinear behavior of normal Gilbert damping G0 and effective spin-mixing conductance g↑↓ have been observed when the incident microwave power is above a critical ac field hrf of 1.6 Oe. Both phenomena are explained by considering the coupling between spin coherent precession and spin wave modes. This work demonstrates the nonlinear behavior of the effective spin-mixing conductance g↑↓. It suggests that the nonlinear spin wave modes excited at high incident microwave power are detrimental to the spin pumping effect and should be avoided in future spin battery designs. The capability of tuning G0 and g↑↓ through the microwave power is also useful for the fundamental study on the damping mechanism.
Alternative ion-acoustic solitary waves in magnetized low beta plasma consisting of warm adiabatic ions, nonthermal electrons, and electrons having a vortexlike distribution
Authors: Islam Sk Anarul , Bandyopadhyay Anup , Das K. P.
Published: February 2009

The solitary wave structures of the ion-acoustic waves propagating obliquely to an external uniform magnetic field have been considered in a low beta plasma consisting of warm adiabatic ions, nonthermal electrons, due to Cairns et al. [Geophys. Res. Lett. 22, 2709 (1995)], which generates the fast energetic electrons and electrons having a vortexlike distribution, due to Schamel [Plasma Phys. 13, 491 (1971); 14, 905 (1972)], taking care of both free and trapped electrons, immersed in a uniform static magnetic field. The nonlinear dynamics of ion-acoustic waves in such a plasma is shown to be governed by Schamel’s modified Korteweg–de Vries–Zakharov–Kuznetsov equation. When the coefficient of the nonlinear term of this equation vanishes, the vortexlike velocity distribution function of electrons simply becomes the isothermal velocity distribution function of electrons and the nonlinear behavior of the same ion-acoustic wave is described by a Korteweg–de Vries–Zakharov–Kuznetsov (KdV-ZK) equation. A combined Schamel’s modified Korteweg–de Vries–Zakharov–Kuznetsov (S-KdV-ZK) equation is shown to describe the nonlinear behavior of ion-acoustic wave when the vortexlike velocity distribution function of electrons approaches the isothermal velocity distribution function of electrons, i.e., when the contribution of trapped electrons tends to zero. This combined S-KdV-ZK equation admits an alternative solitary wave solution having profile different from sech4 or sech2. The condition for the existence of this alternative solitary wave solution has been obtained. It is found that this alternative solitary wave solution approaches the solitary wave solution (sech2-profile) of the KdV-ZK equation when the contribution of trapped electrons tends to zero.
Quasielastic neutron scattering investigation of motion of water molecules in n-propyl alcohol-water mixture
Authors: Nakada Masaru , Maruyama Kenji , Yamamuro Osamu , Misawa Masakatsu
Published: February 2009

The dynamics of water molecules in the n-propyl alcohol-water mixtures is investigated by using quasielastic neutron scattering measurements. The dynamic structure factor S(Q,E) obtained from incoherent scattering of hydrogen atoms of water is fitted with jump diffusion and relaxing cage models. The diffusion constant obtained from the relaxing cage model, which gives better fitting with S(Q,E), shows better agreement to the experimental value than that of jump diffusion model. The dependence of translational relaxation time τT(Q) and stretched exponent βT(Q) on the fraction of hydrophobic hydrating water molecules in the solution is discussed.
Isothermal-isobaric molecular dynamics using stochastic velocity rescaling
Authors: Bussi Giovanni , Zykova-Timan Tatyana , Parrinello Michele
Published: February 2009

The authors present a new molecular dynamics algorithm for sampling the isothermal-isobaric ensemble. In this approach the velocities of all particles and volume degrees of freedom are rescaled by a properly chosen random factor. The technical aspects concerning the derivation of the integration scheme and the conservation laws are discussed in detail. The efficiency of the barostat is examined in Lennard-Jones solid and liquid near the triple point and compared to the deterministic Nosé–Hoover and the stochastic Langevin methods. In particular, the dependence of the sampling efficiency on the choice of the thermostat and barostat relaxation times is systematically analyzed.
Origin of ultralow permittivity in polyimide/mesoporous silicate nanohybrid films with high resistivity and high breakdown strength
Authors: Dang Zhi-Min , Ma Lan-Jie , Zha Jun-Wei , Yao Sheng-Hong , Xie Dan , Chen Qiang , Duan Xue
Published: February 2009

Ultralow dielectric permittivity (k=2.58) nanohybrid dielectric film was obtained by dispersing 3.0 wt % mesoporous silicate (MCM-41) particles with nanosize hollow channels into polyimide (PI) polymer. The ultralow k value of the hybrid film can be mainly attributed to the low k value of MCM-41 itself and the small air gaps in the hybrid films. High volume resistivity and high breakdown strength were also observed for those films. At high concentration of MCM-41 loading (>3.0 wt %), the k values of the films increased significantly due to the contribution of strong interfacial polarization and interaction among MCM-41 particles. The ultralow k feature of the PI/MCM-41 nanohybrid films was explained well by Maxwell–Garnett and Bruggeman equations. The PI/MCM-41 nanohybrid film with good thermal stability as well as excellent dielectric properties can be considered as good candidate for advanced dielectric materials.
Quinoid heteropentacenes as promising organic semiconductors for field-effect transistor applications
Authors: Kalb Wolfgang L. , Stassen Arno F. , Batlogg Bertram , Berens Ulrich , Schmidhalter Beat , Bienewald Frank , Hafner Andreas , Wagner Trixie
Published: February 2009

We report on a quinoid heteropentacene as p-type semiconductor in organic field-effect transistors. Both single crystal and thin-film transistors were fabricated with 7,14-diphenyl-chromeno[2,3-b]xanthene (DPCX). In this small molecule organic semiconductor the field-effect mobility is as high as 0.16 cm2/Vs in single-crystal devices and 0.01 cm2/Vs in thin-film devices. In addition, the devices show favorable properties such as near zero onset/threshold voltages and a small current hysteresis. X-ray diffraction experiments show the molecules to be arranged in slipped stacks and to have a flat backbone in the crystals. For thin films of DPCX the situation is complicated by the coexistence of a thin-film phase with the bulk phase. However, a comparison of DPCX thin films on octadecyltrichlorosilane (OTS)-treated and bare SiO2 gate dielectrics provides clear evidence that the OTS surface treatment leads to organic thin films with a better structural order. The low-cost synthesis and purification of DPCX along with the improved processability and the good electrical characteristics suggest that quinoid heteropentacenes are promising materials for organic field-effect transistors.
Third-order Douglas–Kroll self-consistent field energies for the neutral atoms H to Uuo
Authors: Saito Shiro L.
Published: February 2009

Third-order Douglas–Kroll self-consistent field (DK3-SCF) calculations with a finite-nucleus model were carried out for the neutral atoms H to Uuo, and DK3-SCF energies were obtained for them. The basis set used was the B-spline set. The parameters of the B-spline set were determined so as to reproduce the SQR-SCF limit energies given by Gaussian-type functions (GTFs). The SQR-SCF is a self-consistent field calculation with a simplified first-order Douglas–Kroll Hamiltonian (the “SQR” Hamiltonian) and can be carried out exactly with GTFs. The DK3-SCF energies given by this B-spline set should be highly accurate. A comparison is made with the DK3-SCF energies of Nakajima and Hirao [J. Chem. Phys. 116, 8270 (2002).
Fermions and noncommutative theories
Authors: Amorim Ricardo
Published: February 2009

By using a framework where the object of noncommutativity θμν represents independent degrees of freedom, we study the symmetry properties of an extended x+θ space-time, given by the group P′, which has the Poincaré group P as a subgroup. In this process we use the minimal canonical extension of the Doplicher–Fredenhagen–Roberts algebra. It is also proposed a generalized Dirac equation, where the fermionic field depends not only on the ordinary coordinates but on θμν as well. The dynamical symmetry content of such fermionic theory is discussed, and we show that its action is invariant under P′.
The characteristic crystallographic element norm: A descriptor of local structure in atomistic and particulate systems
Authors: Karayiannis Nikos Ch. , Foteinopoulou Katerina , Laso Manuel
Published: February 2009

We introduce the characteristic crystallographic element (CCE) norm as a powerful descriptor of local structure in atomistic and particulate systems. The CCE-norm is sensitive both to radial and orientational deviations from perfect local order. Unlike other measures of local order, the CCE-norm decreases monotonically with increasing order, is zero for a perfectly ordered environment, and is strictly discriminating among different, competing crystal structures in imperfectly ordered systems. The CCE-norm descriptor can be used as a sensitive, quantitative measure to detect and track changes in local order in atomistic and general particulate systems. In a specific example we show the ability of the CCE-norm to monitor the onset and evolution of order in an initially amorphous, densely packed assembly of hard-sphere chains generated through extensive Monte Carlo simulations [Phys. Rev. Lett. 100, 050602 (2008)].
Effects of ion beam heating on Raman spectra of single-walled carbon nanotubes
Authors: Hulman Martin , Skákalová Viera , Krasheninnikov A. V. , Roth S.
Published: February 2009

Free standing films of single-wall carbon nanotubes were irradiated with energetic N+ and C4+ ions. The observed changes in the Raman line shape of the radial breathing mode and the G band of the C4+ irradiated samples were similar to those found for a thermally annealed sample. We ascribe these changes to thermal desorption of volatile dopants from the initially doped nanotubes. A simple geometry of the experiment allows us to estimate the temperature rise by one-dimensional heat conductance equation. The calculation indicates that irradiation-mediated increase in temperature may account for the observed Raman spectra changes.
Thermodynamics of a conformational change using a random walk in energy-reaction coordinate space: Application to methane dimer hydrophobic interactions
Authors: Morozov A. N. , Lin S. H.
Published: February 2009

A random walk sampling algorithm allows the extraction of the density of states distribution in energy-reaction coordinate space. As a result, the temperature dependences of thermodynamic quantities such as relative energy, entropy, and heat capacity can be calculated using first-principles statistical mechanics. The strategies for optimal convergence of the algorithm and control of its accuracy are proposed. We show that the saturation of the error [Q. Yan and J. J. de Pablo, Phys. Rev. Lett. 90, 035701 (2003); E. Belardinelli and V. D. Pereyra, J. Chem. Phys. 127, 184105 (2007)] is due to the use of histogram flatness as a criterion of convergence. An application of the algorithm to methane dimer hydrophobic interactions is presented. We obtained a quantitatively accurate energy-entropy decomposition of the methane dimer cavity potential. The presented results confirm the previous results, and they provide new information regarding the thermodynamics of hydrophobic interactions. We show that the finite-difference approximation, which is widely used in molecular dynamic simulations for the energy-entropy decomposition of a free energy potential, can lead to a significant error.
Beam-loaded frequency shift in the high power microwave oscillator Bitron
Authors: Li Zheng-Hong
Published: February 2009

When a beam passes a cavity, a rf field will be excited, which can convert the beam’s electron energy into the rf field. The rf is determined by two factors: electron’s movement and the cavity’s resonant frequency. A self-consistent analysis is carried out to study this relation, and a beam-loaded frequency shift is found to be present in the high power microwave oscillator Bitron. Particle-in-cell simulation is also used to study the characteristics of the shift. The calculated beam-loaded frequency shift agrees with the simulated values.
Strong luminescence quantum-efficiency enhancement near prolate metal nanoparticles: Dipolar versus higher-order modes
Authors: Mertens H. , Polman A.
Published: February 2009

We present a theoretical study on the radiative and nonradiative decay rates of an optical emitter in close proximity to a prolate-shaped metal nanoparticle. We use the model developed by Gersten and Nitzan [J. Chem. Phys. 75, 1139 (1981)] that we correct for radiative reaction and dynamic depolarization. Based on this analytical model, we provide physical insight on the optimization of anisotropic metal nanoparticles for plasmon-enhanced luminescence. We demonstrate that for properly engineered emitter-nanoparticle geometries, quantum-efficiency enhancements from an initial value of 1% (in the absence of the nanoparticle) to 70% are feasible. In addition, we show that for large (>100 nm) nanoparticles, the influence of Ohmic losses on plasmon-enhanced luminescence is substantially reduced, which implies that, if prolate shaped, even lossy metals such as Al and Cu are suitable materials for optical nanoantennas.
Simple method for reducing shock-wave equation of state to zero Kelvin isotherm for metals
Authors: Jin Ke , Wu Qiang , Jing Fuqian , Li Xinzhu
Published: February 2009

A thermodynamic formulation is proposed for deducing 0 K isotherm from shock Hugoniot data. In comparison to previous published thermodynamic approaches, the characteristic of this one is not requiring heat capacity as input and the used values of Grüneisen parameter merely confined to around ambient condition. Therefore, it keeps away from the difficulties in determining reliable heat capacity and Grüneisen parameter at high temperatures by experiments and theories. The predicted 0 K isotherms for seven selected metals and their related parameters of initial densities, initial bulk moduli, and their first pressure derivatives are all in well agreement with available experiments and theoretical estimations.
Reducing the impact of inhomogeneous broadening on quantum dot based electromagnetically induced transparency
Authors: Lunnemann Per , Mørk Jesper
Published: February 2009

Slow light based on electromagnetically induced transparency in an inhomogeneously broadened quantum dot medium is investigated theoretically. Three schemes, Ξ, V, and Λ, are compared and it is shown that the V-scheme gives a group velocity that is more than three orders of magnitude smaller compared to the Ξ- and Λ-schemes. The physical mechanisms that make the V-scheme less vulnerable to inhomogeneous broadening are analyzed and discussed.
Mechanisms of microhole formation on glasses by an abrasive slurry jet
Authors: Wang J. , Nguyen T. , Pang K. L.
Published: February 2009

Abrasive jet micromachining is considered as a promising precision processing technology for brittle materials such as silicon substrates and glasses that are increasingly used in various applications. In this paper, the mechanisms of microhole formation on brittle glasses by an abrasive slurry jet are studied based on the viscous flow and erosion theories. It is shown that the hole cross section is characterized by a “W” shape and can be classified into three zones caused, respectively, by jet direct impact, viscous flow, and turbulent flow induced erosion. An analysis of the surface morphology shows that ductile-mode erosion is dominant. The effect of process parameters on material removal is studied which shows that increasing the pressure and erosion time increases the hole depth, but has little effect on the hole diameter.
In situ detection of porosity initiation during aluminum thin film anodizing
Authors: Van Overmeere Quentin , Nysten Bernard , Proost Joris
Published: February 2009

High-resolution curvature measurements have been performed in situ during aluminum thin film anodizing in sulfuric acid. A well-defined transition in the rate of internal stress-induced curvature change is shown to allow for the accurate, real-time detection of porosity initiation. The validity of this in situ diagnostic tool was confirmed by a quantitative analysis of the spectral density distributions of the anodized surfaces. These were obtained by analyzing ex situ atomic force microscopy images of surfaces anodized for different times, and allowed to correlate the in situ detected transition in the rate of curvature change with the appearance of porosity.
Effects of Eu substituting positions and concentrations on luminescent, dielectric, and magnetic properties of SrTiO3 ceramics
Authors: Jiang Chunge , Fang Liang , Shen Mingrong , Zheng Fengang , Wu Xinglong
Published: February 2009

The structural, luminescent, dielectric, and magnetic properties of multifunction Eu3+-doped SrTiO3 (STO) ceramics were investigated at room temperature. Three different charge compensation mechanisms were realized by substituting Eu ion at different sites. It was found that the multifunction properties of the samples strongly depended on the substituting positions of Eu ion. Compared with Eu substitution at Sr or Ti site samples, the photoluminescence intensities and dielectric constant of both Sr and Ti sites substituted samples were obviously enhanced, mainly ascribed to the small lattice distortion and unique charge compensation mechanism. A linear magnetization-magnetic field behavior revealed the paramagnetic nature of the Eu3+ doped STO and was sensitive to the Eu doping concentrations.
Inkjet printing of light emitting quantum dots
Authors: Haverinen Hanna M. , Myllylä Risto A. , Jabbour Ghassan E.
Published: February 2009

We demonstrate the fabrication of diodes having inkjet printed light emitting quantum dots layer. Close packing of printed layer is shown to be influenced by surface morphology of the underlying polymer layer and size variance of quantum dots used. We extend our approach to printing quantum dots onto a quarter video graphics array substrate (76 800 monochrome pixels). The purity of emitted electroluminescent spectra of resulting devices is related to coverage integrity of printed layer, which in turn is shown to be affected by the number of printed drops per pixel.
Self-organization of In nanostructures on Si surfaces
Authors: Xu Maojie , Okada Arifumi , Yoshida Shoji , Shigekawa Hidemi
Published: February 2009

Methods of forming various In nanostructures on Si surfaces are demonstrated. Using a high-index Si(311) surface, isolated nanotriangles and wires were grown by optimizing the deposition rate and substrate temperature. In contrast, nanodots were formed by the deposition of In on a Si(111)–In-31×31 surface at room temperature (RT) deposition. On a Si(111)–In-4×1/31×31 coexisting surface, nanowires were selectively grown in the Si(111)–In 4×1 area by RT deposition through the nucleation promoted by the boundary barrier produced by the surrounding 31×31 area. Details were studied using scanning tunneling microscopy.
Electronic structures of BC3 nanoribbons
Authors: Ding Yi , Wang Yanli , Ni Jun
Published: February 2009

Using first principles calculations, we investigate the electronic structures of BC3 nanoribbons. We find that BC3 nanoribbons show a rich variety of electronic properties. The BC3 nanoribbons with the armchair shaped edges are all semiconductors, while BC3 nanoribbons with the zigzag shaped edges are semiconductors or metals depending on the edge atoms. The metallicity of BC3 nanoribbons with the zigzag shaped edges is attributed to the π bonds formation between boron and carbon atoms and the lack of the carbon hexagons in the edge zigzag line.
Oxygen tracer diffusion in dense Ba0.5Sr0.5Co0.8Fe0.2O3−δ films
Authors: Wang L. , Merkle R. , Maier J. , Acartürk T. , Starke U.
Published: February 2009

Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3 - δ (BSCF) is an interesting material for high temperature oxygen permeation membranes and solid oxide fuel cell cathodes, applications for which oxygen transport properties are crucial. Here oxygen isotope exchange is performed on dense BSCF films prepared by pulsed laser deposition on MgO single crystal substrates. The oxygen isotope profile is analyzed by secondary ion mass spectrometry to extract tracer diffusion coefficients D∗ and effective surface exchange constants k∗. Tracer diffusion has a low activation energy of 0.5 eV. At moderate temperatures, the related oxygen vacancy diffusion coefficient DVÖ is significantly larger than that for (La,Sr)(Fe,Co)O3−δ perovskites.
Improved performance of polymer light-emitting diodes with nanocomposites
Authors: Hussain A. Mohammed , Neppolian B. , Kim Sun Hee , Kim Jin Young , Choi Hee-Chul , Lee Kwanghee , Park Seong-Ju , Heeger Alan J.
Published: February 2009

The characteristics of a hybrid polymer light-emitting diode (HPLED) with an active layer of poly [2-methoxy,5-(2-ethylhexoxy)-1,4-phenylenevinylene] blended with Au-capped TiO2 nanocomposites are reported. Both the increased current in the active layer and low turn-on voltage were attributed to incorporation of Au-capped TiO2 in the electroluminescent polymer. The maximal brightness of 11 630 cd/m2 was observed in HPLED with a 1:1 ratio of Au-capped TiO2. The enhanced performance was attributed to the roughness assisted charge transport induced by the Au-capped TiO2 nanocomposites in the active polymer.
Mechanically robust and electrically conductive carbon nanotube foams
Authors: Worsley Marcus A. , Kucheyev Sergei O. , Satcher Joe H. , Hamza Alex V. , Baumann Theodore F.
Published: February 2009

We describe the fabrication of ultralow-density carbon nanotube (CNT) foams that simultaneously exhibit high electrical conductivities and robust mechanical properties. Our approach utilizes carbon nanoparticles as a binder to crosslink randomly oriented bundles of single-walled CNTs. The resulting CNT foams are the stiffest low-density nanoporous solids reported and exhibit elastic behavior up to strains as large as ∼80%. The use of the carbon binder also allows bulk electrical conductivity to be maintained at low densities.
Para-sexiphenyl-CdSe/ZnS nanocrystal hybrid light emitting diodes
Authors: Simbrunner C. , Hernandez-Sosa G. , Baumgartner E. , Hesser G. , Roither J. , Heiss W. , Sitter H.
Published: February 2009

CdSe/ZnS core/shell nanocrystals (NCs) are integrated into para-sexiphenyl (p-6P) based hybrid light emitting diodes, to obtain green and red emission in addition to blue emission originated from p-6P. For the active region of the devices, ultrathin layers of p-6P and NCs are deposited by hot wall epitaxy and spin casting, respectively, resulting in current-voltage characteristics with small leakage currents and low onset voltages. The achieved electroluminescence exhibits narrow emission line widths and thus high color purity, as required for color display applications.
Annealing of self-assembled InAs/GaAs quantum dots: A stabilizing effect of beryllium doping
Authors: Pakarinen J. , Polojärvi V. , Aho A. , Laukkanen P. , Peng C. S. , Schramm A. , Tukiainen A. , Pessa M.
Published: February 2009

We investigated the effects of postgrowth thermal annealing on optical properties of beryllium-doped InAs quantum dot (QD) heterostructures grown by molecular beam epitaxy. Thermal annealing induced a blueshift of up to 200 meV in light emission from an undoped sample, while a sample having GaAs layer heavily doped with beryllium on top of the QD region exhibited a much smaller blueshift. This phenomenon is interpreted as due to suppression of annealing-induced In/Ga interdiffusion.
Correlation-length dependence of lifetime ratios: Individual estimation of interface profile parameters
Authors: Quang Doan Nhat , Tung Nguyen Huyen , Tuan Le , Hong Nguyen Trung , Hai Tran Thi
Published: February 2009

We show that the ratio between relaxation lifetimes dominated by roughness-related scatterings in heterostructures is a well-defined function of the correlation length. Thus, we propose an efficient method for individual estimation of the two size parameters of interface profiles from transport data. Instead of the normal simultaneous fitting of both parameters to lifetimes, we adopt a two-step procedure of (i) inferring the correlation length from some lifetime ratio and then (ii) fitting the roughness amplitude to some lifetime. Similarly, the ratio of roughness-induced linewidths in intersubband absorption may give such an estimation from optical data.
A Density Functional Theory Study on the Ring-Opening Polymerization of D-Lactide Catalyzed by a Bifunctional-Thiourea Catalyst
Authors: Zhu Rong-Xiu , Wang Ruo-Xi , Zhang Dong-Ju , Liu Cheng-Bu
Published: February 2009

The thiourea-catalyzed methanolysis of d-lactide, a model system for the initiation and propagation of the organocatalyzed ring-opening polymerization (ROP) of lactide, has been studied by performing density functional theory calculations. Both the catalyzed and uncatalyzed reactions are explored along two possible pathways: one involves the stepwise addition–elimination pathway and the other is related to the concerted pathway. It is found that the reaction without the presence of the catalyst is difficult because the barrier involved is as high as 176 kJ mol–1. With the aid of a thiourea catalyst, the barrier is reduced to 88 kJ mol–1 with a preference for the stepwise addition–elimination mechanism over the concerted one. The role of the catalyst has been rationalized by analyzing the frontier molecular orbital interactions between the catalyst and substrates and by performing natural population analysis. Finally, another mechanism involving acyl transfer is discussed for the thiourea-catalyzed ROP.
Spatio-temporal dynamics of fish feeding in the lower Mulgrave River, north-eastern Queensland: the influence of seasonal flooding, instream productivity and invertebrate abundance
Authors: Rayner Thomas S. , Pusey Bradley J. , Pearson Richard G.
Published: February 2009

Wet-season flooding causes dietary shifts in tropical freshwater fish by regulating instream productivity, habitat structure and food availability. These dynamics have been comprehensively documented worldwide, but data are limited for Australia’s Wet Tropics rivers. The aim of the present study was to extend our earlier fish–habitat model for these systems by examining the role of trophic dynamics in determining fish assemblage composition. Chlorophyll a and phaeophytin concentrations, benthic and littoral invertebrates and fish were collected at four sites in the lower Mulgrave River under a range of flow conditions. Wet-season flooding caused significant reductions in instream productivity, whereas habitat disturbance reduced densities and abundances of littoral and benthic invertebrates. However, volumetric gut contents of 1360 fish, from 36 species, revealed seasonal shifts in guild membership by only two species, with fish moving between sites to target their preferred prey items – largely irrespective of differences in habitat structure. As a result, the food consumed by the fish community present at each site closely reflected the seasonal availability of food resources. The present paper questions whether fish community composition in small tropical rivers can be accurately predicted from habitat surrogates alone and encourages consideration of constraints imposed by the trophic dynamics and reproductive ecology of fish.
α-Hemolysin fromEscherichia coliuses endogenous amplification through P2X receptor activation to induce hemolysis
Authors: Skals Marianne , Jorgensen Niklas R. , Leipziger Jens , Praetorius Helle A.
Published: February 2009

Escherichia coliis the dominant facultative bacterium in the normal intestinal flora.E. coliis, however, also responsible for the majority of serious extraintestinal infections. There are distinct serotypical differences between facultative and invasiveE. colistrains. Invasive strains frequently produce virulence factors such as α-hemolysin (HlyA), which causes hemolysis by forming pores in the erythrocyte membrane. The present study reveals that this pore formation triggers purinergic receptor activation to mediate the full hemolytic action. Non-selective ATP-receptor (P2) antagonists (PPADS, suramin) and ATP scavengers (apyrase, hexokinase) concentration dependently inhibited HlyA-induced lysis of equine, murine, and human erythrocytes. The pattern of responsiveness to more selective P2-antagonists implies that both P2X1and P2X7receptors are involved in HlyA-induced hemolysis in all three species. In addition, our results also propose a role for the pore protein pannexin1 in HlyA-induced hemolysis, as non-selective inhibitors of this channel significantly reduced hemolysis in the three species. In conclusion, activation of P2X receptors and possibly also pannexins augment hemolysis induced by the bacterial toxin, HlyA. These findings potentially have clinical perspectives as P2 antagonists may ameliorate symptoms during sepsis with hemolytic bacteria.
K
+
-dependent paradoxical membrane depolarization and Na
+
overload, major and reversible contributors to weakness by ion channel leaks
Authors: Jurkat-Rott Karin , Weber Marc-André , Fauler Michael , Guo Xiu-Hai , Holzherr Boris D. , Paczulla Agathe , Nordsborg Nikolai , Joechle Wolfgang , Lehmann-Horn Frank
Published: February 2009

Normal resting potential (P1) of myofibers follows the Nernst equation, exhibiting about −85 mV at a normal extracellular K
+
concentration ([K
+
]
o
) of 4 mM. Hyperpolarization occurs with decreased [K
+
]
o
, although at [K
+
]
o
< 1.0 mM, myofibers paradoxically depolarize to a second stable potential of −60 mV (P2). In rat myofiber bundles, P2 also was found at more physiological [K
+
]
o
and was associated with inexcitability. To increase the relative frequency of P2 to 50%, [K
+
]
o
needed to be lowered to 1.5 mM. In the presence of the ionophore gramicidin, [K
+
]
o
reduction to only 2.5 mM yielded the same effect. Acetazolamide normalized this increased frequency of P2 fibers. The findings mimic hypokalemic periodic paralysis (HypoPP), a channelopathy characterized by hypokalemia-induced weakness. Of myofibers from 7 HypoPP patients, up to 25% were in P2 at a [K
+
]
o
of 4 mM, in accordance with their permanent weakness, and up to 99% were in P2 at a [K
+
]
o
of 1.5 mM, in accordance with their paralytic attacks. Of 36 HypoPP patients, 25 had permanent weakness and myoplasmic intracellular Na
+
([Na
+
]
i
) overload (up to 24 mM) as shown by in vivo
23
Na-MRI. Acetazolamide normalized [Na
+
]
i
and increased muscle strength. HypoPP myofibers showed a nonselective cation leak of 12–19.5 μS/cm
2
, which may explain the Na
+
overload. The leak sensitizes myofibers to reduced serum K
+
, and the resulting membrane depolarization causes the weakness. We postulate that the principle of paradoxical depolarization and loss of function upon [K
+
]
o
reduction may apply to other tissues, such as heart or brain, when they become leaky (e.g., because of ischemia).
Phosphorylation of MeCP2 at Serine 80 regulates its chromatin association and neurological function
Authors: Tao Jifang , Hu Keping , Chang Qiang , Wu Hao , Sherman Nicholas E. , Martinowich Keri , Klose Robert J. , Schanen Carolyn , Jaenisch Rudolf , Wang Weidong , Sun Yi Eve
Published: February 2009

Mutations of
MECP2
(
Methyl-CpG Binding Protein 2
) cause Rett syndrome. As a chromatin-associated multifunctional protein, how MeCP2 integrates external signals and regulates neuronal function remain unclear. Although neuronal activity-induced phosphorylation of MeCP2 at serine 421 (S421) has been reported, the full spectrum of MeCP2 phosphorylation together with the in vivo function of such modifications are yet to be revealed. Here, we report the identification of several MeCP2 phosphorylation sites in normal and epileptic brains from multiple species. We demonstrate that serine 80 (S80) phosphorylation of MeCP2 is critical as its mutation into alanine (S80A) in transgenic knock-in mice leads to locomotor deficits. S80A mutation attenuates MeCP2 chromatin association at several gene promoters in resting neurons and leads to transcription changes of a small number of genes. Calcium influx in neurons causes dephosphorylation at S80, potentially contributing to its dissociation from the chromatin. We postulate that phosphorylation of MeCP2 modulates its dynamic function in neurons transiting between resting and active states within neural circuits that underlie behaviors.
Functional ENaC Channels Expressed in Endothelial Cells: a New Candidate for Mediating Shear Force
Authors: WANG SU , MENG FEI , MOHAN SINDU , CHAMPANERI BIPIN , GU YUCHUN
Published: February 2009

Endothelial cells (ECs) are regulated not only by circulating hormones, but also by mechanical stresses, such as shear force. Ion channels in ECs can signal rapid changes of shear forces and are involved in controling EC permeability, proliferation, and angiogenesis. In this study, we employed patch clamping and molecular biology approaches to clarify whether the epithelial sodium channel (ENaC) is functionally expressed in ECs. The α‐subunit of the ENaC was expressed in cultured human ECs and in intact ECs from a variety of rat arteries. In either inside‐ or outside‐out current recordings, inward currents with a conductance of 4.83 pS were detected in cultured human ECs, where these were sensitive to micromolar amiloride. The right shift of the I‐V curve in the condition of low cytoplasmic Na+implicated that these currents were carried by Na+. The currents were mediated by ENaC channels, as confirmed by ENaC knockdown experiments. However, the activity of ENaC was nearly absent in intact ECs, because its activity was greatly inhibited by cellular molecules, partly due to 11,12‐epoxyeicosatrienoic acid. In the outside‐out configuration, laminar flow directly enhanced ENaC opening probability, suggesting a potential role for ENaC in mediating shear force signaling events.
Modulation of Vascular O2Responses by Cytochrome 450‐4A ω‐Hydroxylase Metabolites In Dahl Salt‐Sensitive Rats
Authors: WANG JINGLI , SCHMIDT JAMES R. , ROMAN RICHARD J. , ANJAIAH SIDDAM , FALCK JOHN R. , LOMBARD JULIAN H.
Published: February 2009

Objective:This study evaluated the role of the 20‐HETE/cytochrome P450‐4A ω‐hydroxylase (CYP450‐4A) system in microvascular regulation in the skeletal muscle circulation following short‐term (three‐day) exposure to a high‐salt (HS) diet in Dahl salt‐sensitive (SS) rats.

Methods:The effects of inhibiting CYP450‐4A on resting diameter, O2‐induced constriction, and vasodilator responses to acetylcholine (ACh) and the nitric oxide (NO) donor, sodium nitroprusside (SNP), were evaluated in cremasteric arterioles of SS rats fed a low‐ (LS; 0.4% NaCl) or high‐salt (HS; 4% NaCl) diet for three days.

Results:The HS diet upregulated CYP450‐4A mRNA expression and led to an enhanced constriction of arterioles in response to elevated PO2in SS rats, which could be blocked by inhibiting CYP450‐4A enzymes with dibromododecenyl methylsulfimide (DDMS). DDMS also inhibited resting tone significantly in SS rats fed the HS, but not the LS, diet, despite similar resting diameters and active tone in the two groups. Arteriolar dilations in response to ACh and SNP were similar in SS rats fed the LS vs. the HS diet and were unaffected by DDMS.

Conclusions:These findings suggest that CYP450‐4A enzymes contribute to resting tone and to an enhanced response to elevated PO2in arterioles of Dahl‐SS rats fed the HS diet.
In situ tuning of a MEMS microphone using electrodeposited nanostructures
Authors: Je Sang-Soo , Harrison Jere C , Kozicki Michael N , Bakkaloglu Bertan , Kiaei Sayfe , Chae Junseok
Published: February 2009

This paper presents a new method for in situ tuning of acoustic sensitivity in micro-electro-mechanical-system (MEMS) microphones using silver metallic nano-electrodeposits. The nano-electrodeposits are electrochemically formed using an external dc bias under low power and at room temperature on an Ag-doped Ge30Se70 solid electrolyte film integrated with the microphone diaphragm. The growth/retraction mechanism generates mass/stress redistribution on the diaphragm and this effect is used to manipulate microphone sensitivity to incoming acoustic waves. Acoustic measurements with a reference microspeaker demonstrate that the microphone can achieve a tuning range of 0.6 dB (7.2%). This technique is useful for a variety of microdevice applications, including sensitivity matching for directional microphones (e.g., in hearing aids), post-package trimming and resonant frequency tuning.
Essential Role of Nuclear Localization for Yeast Ulp2 SUMO Protease Function
Authors: Kroetz Mary B. , Su Dan , Hochstrasser Mark
Published: February 2009

The SUMO protein is covalently attached to many different substrates throughout the cell. This modification is rapidly reversed by SUMO proteases. The Saccharomyces cerevisiae SUMO protease Ulp2 is a nuclear protein required for chromosome stability and cell cycle restart after checkpoint arrest. Ulp2 is related to the human SENP6 protease, also a nuclear protein. All members of the Ulp2/SENP6 family of SUMO proteases have large but poorly conserved N-terminal domains (NTDs) adjacent to the catalytic domain. Ulp2 also has a long C-terminal domain (CTD). We show that CTD deletion has modest effects on yeast growth, but poly-SUMO conjugates accumulate. In contrast, the NTD is essential for Ulp2 function and is required for nuclear targeting. Two short, widely separated sequences within the NTD confer nuclear localization. Efficient Ulp2 import into the nucleus requires the β-importin Kap95, which functions on classical nuclear-localization signal (NLS)-bearing substrates. Remarkably, replacement of the entire >400-residue NTD by a heterologous NLS results in near-normal Ulp2 function. These data demonstrate that nuclear localization of Ulp2 is crucial in vivo, yet only small segments of the NTD provide the key functional elements, explaining the minimal sequence conservation of the NTDs in the Ulp2/SENP6 family of enzymes.
Regulation of Distinct Septin Rings in a Single Cell by Elm1p and Gin4p Kinases
Authors: DeMay Bradley S. , Meseroll Rebecca A. , Occhipinti Patricia , Gladfelter Amy S.
Published: February 2009

Septins are conserved, GTP-binding proteins that assemble into higher order structures, including filaments and rings with varied cellular functions. Using four-dimensional quantitative fluorescence microscopy of Ashbya gossypii fungal cells, we show that septins can assemble into morphologically distinct classes of rings that vary in dimensions, intensities, and positions within a single cell. Notably, these different classes coexist and persist for extended times, similar in appearance and behavior to septins in mammalian neurons and cultured cells. We demonstrate that new septin proteins can add through time to assembled rings, indicating that septins may continue to polymerize during ring maturation. Different classes of rings do not arise from the presence or absence of specific septin subunits and ring maintenance does not require the actin and microtubule cytoskeletons. Instead, morphological and behavioral differences in the rings require the Elm1p and Gin4p kinases. This work demonstrates that distinct higher order septin structures form within one cell because of the action of specific kinases.
Enhanced myogenic constriction of mesenteric artery in heart failure relates to decreased smooth muscle cell caveolae numbers and altered AT1‐ and epidermal growth factor‐receptor function
Authors: Xu Ying , Henning Rob H. , Sandovici Maria , van der Want Johannes J. , van Gilst Wiek H. , Buikema Hendrik
Published: February 2009

Aims

We previously showed that enhanced myogenic constriction (MC) of peripheral resistance arteries involves active AT1 receptors in chronic heart failure (CHF). Recent data suggest both transactivation of EGF receptors and caveolae‐like microdomains to be implicated in the activity of AT1 receptors. Thus, we assessed their roles in increased MC in mesenteric arteries of CHF rats.

Methods and results

Male Wistar rats underwent myocardial infarction to induce CHF and were sacrificed after 12 weeks. The number of caveolae in smooth muscle cells (SMC) of mesenteric arteries of CHF rats was decreased by 43.6 ± 4.0%, this was accompanied by increased MC, which was fully normalized to the level of sham by antagonists of the AT1‐receptor (losartan) or EGF‐receptor (AG1478). Acute disruption of caveolae in sham rats affected caveolae numbers and MC to a similar extent as CHF, however MC was only reversed by the antagonist of the EGF‐receptor, but not by the AT1‐receptor antagonist. Further, in sham rats, MC was increased by a sub‐threshold concentration of angiotensin II and reversed by both AT1‐ as well as EGF‐receptor inhibition. In contrast, increased MC by a sub‐threshold concentration of EGF was only reversed by EGF receptor inhibition.

Conclusion

These findings provide the first evidence that decreased SMC caveolae numbers are involved in enhanced MC in small mesenteric arteries, by affecting AT1‐ and EGF‐receptor function. This suggests a novel mechanism involved in increased peripheral resistance in CHF.