bluuebunny/crossref_metadata_2025 huggingface dataset:
The concept of collision strength and a unified kinetic calculation for hard-sphere interactions and inverse square force law interactions
Authors: Chang Yongbin
Published: November 2003

With a concept of collision strength and other associated definitions, a unified kinetic theory for both hard-sphere interactions and inverse square force law interactions is developed. Collision frequencies that associate with many kinds of physical terms are calculated and expressed by a series special function Υj(α,x). Among them are arbitrary higher order linear Fokker–Planck coefficients, collision frequency, and energy exchange frequency. In case of a two-temperature system, the total collision rate, energy exchange rate, and collision strength rate are calculated and expressed in a uniform expression. A primitive form of Coulomb logarithm 12Γ(0,hmin) is found by comparing the exact form of equilibration time with Spitzer’s result. Many unifications are found from the unified expression. The threshold value of collision strength has unified activation energy in chemical reaction rate theory and ionization energy in Thomson’s classical ionization theory. An incomplete gamma function has unified Arrhenius exponential coefficient in chemical reaction rate theory and Coulomb logarithm in plasma physics.
Existence of the self-graviting Chern–Simons vortices
Authors: Chae Dongho , Choe Kwangseok
Published: November 2003

We prove existence of multivortex solutions of the self-dual Einstein–Chern–Simons–Higgs system, proposed by Clément [Phys. Rev. D 54, 1844–1847 (1996)]. We consider both the topological and the nontopological boundary conditions for open, conformally flat manifolds. For nontopological boundary conditions we use perturbation argument from a solution of the Liouville equation combined with the implicit function theorem. Using this argument we have existence for arbitrary positive number for the gravitational constant. For topological boundary condition we construct solutions for small gravitational constant by using the super/subsolution method. For sufficiently large gravitational constant we have a nonexistence result for the radially symmetric topological solutions. We also obtain the decay estimates near infinity for both of the topological and the nontopological solutions.
Simulations of Raman laser amplification in ionizing plasmas
Authors: Clark Daniel S. , Fisch Nathaniel J.
Published: November 2003

By using the amplifying laser pulse in a plasma-based backward Raman laser amplifier to generate the plasma by photoionization of a gas simultaneous with the amplification process, possible instabilities of the pumping laser pulse can be avoided. Particle-in-cell simulations are used to study this amplification mechanism, and earlier results using more elementary models of the Raman interaction are verified [D. S. Clark and N. J. Fisch, Phys. Plasmas 9, 2772 (2002)]. The effects (unique to amplification in ionizing plasmas and not included in previous simulations) of blueshifting of the pump and seed laser pulses as well as the generation of a wake are observed not significantly to impact the amplification process. As expected theoretically, the peak output intensity is found to be limited to I∼1017 W/cm2 by forward Raman scattering of the amplifying seed. The integrity of the ionization front of the seed pulse against the development of a possible transverse modulation instability is also demonstrated.
Particle-in-cell simulations of Raman laser amplification in preformed plasmas
Authors: Clark Daniel S. , Fisch Nathaniel J.
Published: November 2003

Two critical issues in the amplification of laser pulses by backward Raman scattering in plasma slabs are the saturation mechanism of the amplification effect (which determines the maximum attainable output intensity of a Raman amplifier) and the optimal plasma density for amplification. Previous investigations [V. M. Malkin et al., Phys. Rev. Lett. 82, 4448 (1999)] identified forward Raman scattering and modulational instabilities of the amplifying seed as the likely saturation mechanisms and lead to an estimated unfocused output intensity of 1017 W/cm2. The optimal density for amplification is determined by the competing constraints of minimizing the plasma density so as to minimize the growth rate of the instabilities leading to saturation but also maintaining the plasma sufficiently dense that the driven Langmuir wave responsible for backscattering does not break prematurely. Here, particle-in-cell code simulations are presented which verify that saturation of backward Raman amplification does occur at intensities of ∼1017 W/cm2 by forward Raman scattering and modulational instabilities. The optimal density for amplification in a plasma with the representative temperature of Te=200 eV is also shown in these simulations to be intermediate between the cold plasma wave-breaking density and the density limit found by assuming a water bag electron distribution function.
Pyroelectric infrared sensor-based thermometer for monitoring indoor objects
Authors: Tsai C. F. , Young M. S.
Published: November 2003

This article describes a system for measuring temperature by monitoring an object’s radiation in the infrared spectrum. Using a measuring device by passing through a data acquisition interface, a long-term observation of the temperature variance of objects on a personal computer by the LabVIEW software is conducted. A special mechanism joined with a pyroelectric infrared (PIR) sensor, optical chopper, and Fresnel lens is presented in this system. This separable architecture makes the lens easily replaceable and portable. In this study, the PIR sensor into a quantitative measurement for long-term and long-distance applications with calibration equipment based on a blackbody and some electrometers was successfully applied. Experimental results show that the measuring device only has an average error rate of 1.21% in the overall range from 40 to 200 °C, and field of view is 4.58°. The results confirm that noncontacted temperature measurement using a PIR sensor is feasible.
Novel voltage compressor circuit by transmission lines
Authors: Nassisi V. , Belloni F. , Doria D. , Lorusso A.
Published: November 2003

In this article we describe the design and the experimental results of a circuit able to compress a rectangular pulse causing its amplitude to increase. Utilizing a pulse forming line of 12 m long and a storage line of 6 m, both connected on a load resistor by means of fast transistor switch, a time compression factor of 2 was achieved. Charging the pulse forming line at V0, the output matched pulse was V0/2, 120 ns. Instead, the compressor output pulse was V0, 60 ns against a V0, 120 ns pulse delivered by a 12 m Blumlein line charged at V0. High voltage short pulse circuits open horizons in the field of accelerator construction.
Permeation rate measurements by electrical analysis of calcium corrosion
Authors: Paetzold R. , Winnacker A. , Henseler D. , Cesari V. , Heuser K.
Published: November 2003

Highly sensitive permeation measurements are crucial for the characterization and development of polymeric substrates for flexible display applications. In particular, organic light-emitting devices require substrates with extremely low permeation rates for water and oxygen. Here we demonstrate a concept for measuring ultralow permeation rates. The amount of oxidative degradation in a thin Ca sensor is monitored by in situ resistance measurements. The benefits of this technique are demonstrated for polyester foils with single- and double-sided barrier coatings. A sensitivity limit is imposed by the quality of the encapsulation. The resulting base line contribution to the water vapor transmission rate of a glass reference is below 10−6 g/m2 day at accelerated test conditions.
Low-frequency electromagnetic solitary and shock waves in an inhomogeneous dusty magnetoplasma
Authors: Shukla P. K.
Published: November 2003

It is shown that the nonlinear dynamics of one-dimensional Shukla mode [Phys. Lett. A 316, 238 (2003)] is governed by a modified Kortweg–de Vries–Burgers equation. The latter admits stationary solutions in the form of either a solitary wave or a monotonic/oscillatory shock. The present nonlinear waves may help to understand the salient features of localized density and magnetic field structures in molecular dusty clouds as well as in low-temperature laboratory dusty plasma discharges.
Unified form for parallel ion viscous stress in magnetized plasmas
Authors: Held E. D.
Published: November 2003

In this work a unified form for the parallel ion viscous stress in a magnetized plasma is presented. Approximately valid for arbitrary collisionality, the integral nature of this generalized closure results from assuming the maximal ordering between collisional pitch-angle scattering and free streaming effects and from taking a Chapman–Enskog-type approach which includes the parallel ion viscous stress itself as a drive. The ion drift kinetic equation is solved in a sheared slab using an expansion in eigenfunctions of the Lorentz scattering operator. Integrating the coefficient equations in space and taking the proper velocity space moments couples the parallel viscous stress closure to an integral momentum restoring term, thus generalizing the concept of momentum conservation for simplified Coulomb collision operators. The integral closure involves following ions along magnetic field lines which are the ideal, time-independent characteristics of the perturbed distribution function. The fact that the viscous stress and momentum restoring term appear in the kernels of these field line integrals means that in general the closure has the form of coupled Volterra equations with an inhomogeneous term supplied by the traditional flow gradient drive. It is shown that the unified closure agrees both qualitatively and quantitatively with previous results and hence represents a generalized physical form for the parallel ion viscous stress in magnetized plasmas.
Behavior of a zonal flow near the threshold
Authors: Marchenko V. S. , Goloborod’ko V. Ya. , Reznik S. N.
Published: November 2003

Numerical solutions of the model equation describing nonlinear dynamics of a zonal flow near marginal stability [Phys. Rev. Lett. 89, 185002 (2002)] are presented for different parameter regimes. The present simulations confirm the conclusion that below certain critical values of the drift wave to zonal flow growth rates ratio the system bifurcates from the stationary state to limit cycle behavior. Well below the bifurcation point, oscillations of the zonal flow amplitude become chaotic.
Three-dimensional isotropic magnetohydrodynamic turbulence and thermal velocity of the solar wind ions
Authors: Bershadskii A.
Published: November 2003

It is shown that fluctuations of the solar wind ions velocity (as measured on the kinetic level by the SWICS-detector on board the Advanced Composition Explorer) exhibit statistical properties which are in very good agreement with predictions of the three-dimensional (3D) isotropic magnetohydrodynamics (MHD) turbulence theory [Biskamp and Müller, Phys. Plasmas 7, 4889 (2000)]. The question is: How can 3D isotropic MHD be used to describe the interaction of the solar wind magnetic field with the kinetic (collisionless) ions?
A thermodynamic limitation on the maximum speed of wetting of a solid surface by a liquid
Authors: Gao Y. X.
Published: November 2003

A thermodynamic formulation is applied to examine the wetting process of a solid surface by a liquid. Attention is focused on the change of the Gibbs free energy of a given gas/liquid/solid system and the moving speed of the contact line on the solid surface. The present study demonstrates that there is a thermodynamic limitation on the wetting speed in a given system. This thermodynamic limitation leads to the verification of the postulate suggested by Blake and Ruschak [Nature (London) 282, 489 (1979)] that there is a maximum speed at which wetting can proceed for the given system.
Curvature wave-front sensors for electron density characterization in plasmas
Authors: Baker K. L.
Published: November 2003

In this article we examine the use of a curvature wave-front sensor to accurately measure the Laplacian of the line-integrated electron density formed in laser-produced and Z-pinch plasma experiments. Specifically, we propose designs for single shot curvature wave-front sensors capable of quantitatively determining the electron density present in a high density plasma. Wave optics simulations of the proposed designs are presented and are shown to quantitatively reconstruct the phase of a light beam passing through the simulated plasma. A laboratory demonstration of the single shot curvature wave-front sensor is also presented. For this demonstration, a liquid-crystal spatial light modulator is used to introduce a spatially varying phase, thus simulating a phase profile that could occur when a probe passes through a plasma. The phase change measured by the curvature sensor is then computed and shown to accurately reproduce the phase written to the spatial light modulator. Merits associated with the use of a curvature sensor are also discussed.
High resolution hard x-ray spectroscopy of femtosecond laser-produced plasmas with a CZT detector
Authors: Chen L. M. , Forget P. , Toth R. , Kieffer J. C. , Krol A. , Chamberlain C. C. , Hou B. X. , Nees J. , Mourou G.
Published: November 2003

We present measurement of characteristic Kα emission from Mo, Ag, and La targets irradiated by a 60 fs, 600 mJ, 10 Hz Ti:sapphire laser pulse at 1017–1019 W/cm2. These x-ray emissions can potentially be used in applications from laser-based hard x-ray sources to x-ray mammography so detailed knowledge of the spectra is required to assess imaging of the figure of merit. We show here that high resolving hard x-ray spectroscopy can be achieved, with resolving powers (E/ΔE) of 60 at 18 keV, with cadmium–zinc–telluride detection system. The Kα conversion efficiency from the laser light to the Kα photon was optimized thanks to this diagnostic and values as high as 2×10−5 were obtained.
Homodyne detection technique using spontaneously generated reference signal in picosecond thermoreflectance measurements
Authors: Taketoshi Naoyuki , Baba Tetsuya , Schaub Emmanuel , Ono Akira
Published: November 2003

A new detection technique for picosecond thermoreflectance measurements has been developed. Conventional picosecond thermoreflectance measurements detect the signal amplitude of a reflected probe laser beam synchronized with the modulation frequency of the pump laser beam using a lock-in amplifier. Our new detection technique uses the signal phase of the lock-in output instead of the signal amplitude. Thermoreflectance signals for molybdenum thin films deposited on glass substrates were observed at room temperature. The signal-to-noise ratio of the phase detection was about four times better than that of the amplitude detection. The signal phase detected by this model is insensitive to fluctuation of both pump and probe beams. According to this technique, picosecond thermoreflectance measurements can apply not only to single layer metal thin films of around 100 nm thickness, but also to thicker metal films, metal–nonmetal multilayer thin films, and many other thin films.
Particle-beam experiment to study heterogeneous surface reactions relevant to plasma-assisted thin film growth and etching
Authors: Jacob Wolfgang , Hopf Christian , von Keudell Achim , Meier Matthias , Schwarz-Selinger Thomas
Published: November 2003

An ultrahigh-vacuum-based particle-beam experiment to study heterogeneous surface reactions relevant to plasma–surface interaction processes is presented. The experiment comprises two radical beam sources and a source for low energy ions. As diagnostic tools real-time in situ ellipsometry and infrared spectroscopy are implemented. The infrared sensitivity for thin films is enhanced through application of an optical cavity substrate. The fluxes of the radical beam sources are quantified absolutely for the production of hydrogen atoms and methyl radicals. The ion source is also quantified for a wide variety of ionic species, e.g., He+, Ar+, H+, H2+, H3+, and CH3+. Ion energies from above 1 keV down to 1 eV are achievable. The setup allows one to investigate heterogeneous surface processes of one single species or simultaneous interaction of up to three different, individually controllable species with a surface of interest. By running the radical sources to produce hydrogen and methyl radicals and the ion source with the ions mentioned, microscopic surface processes relevant to deposition and erosion of hydrocarbon layers in low-pressure gas discharges were studied in great detail. Sample results for the hydrogen CH3 growth synergism, ion-assisted film growth, and chemical sputtering are presented to demonstrate the capability of the setup.
Field-effect transistors on tetracene single crystals
Authors: de Boer R. W. I. , Klapwijk T. M. , Morpurgo A. F.
Published: November 2003

We report on the fabrication and electrical characterization of field-effect transistors at the surface of tetracene single crystals. We find that the mobility of these transistors reaches the room-temperature value of 0.4 cm2/V s. The nonmonotonous temperature dependence of the mobility, its weak gate voltage dependence, as well as the sharpness of the subthreshold slope, confirm the high quality of single-crystal devices. This is due to the fabrication process that does not substantially affect the crystal quality.
Characteristics of SiO2/n-GaN interfaces with β-Ga2O3 interlayers
Authors: Nakano Yoshitaka , Kachi Tetsu , Jimbo Takashi
Published: November 2003

We report on the characteristics of SiO2/n-GaN metal-oxide-semiconductor (MOS) structures with β-Ga2O3 interlayers. β-Ga2O3 15 nm thick was grown by dry oxidation at 800 °C for 6 h, and 100-nm-thick SiO2 was then deposited by sputtering. Capacitance–voltage measurements show a low interface trap density of ∼3.9×1010 eV−1 cm−2, probably indicating an unpinning of the surface Fermi level. Additionally, current–voltage measurements display a low leakage current of ∼1.2 μA/cm2 at a gate voltage of +20 V, regardless of rough oxide surface, as confirmed by atomic force microscopy observations. Thus, the stacked SiO2/β-Ga2O3 insulator is found to improve both the electrical interface properties and the gate dielectric characteristics of the GaN MOS structures.
Leakage mechanisms and dielectric properties of Al2O3/TiN-based metal-insulator-metal capacitors
Authors: Meng Shuang , Basceri C. , Busch B. W. , Derderian G. , Sandhu G.
Published: November 2003

We characterized thin Al2O3 dielectrics with TiN electrodes in a three-dimensional, high-aspect-ratio, metal–insulator–metal capacitor structure. Transmission electron microscopy images did not reveal any interfacial layer(s) or intermixing of the films. This was confirmed by series capacitance analysis. Extensive electrical characterization indicated a well-behaved dielectric response. Time and frequency domain measurements did not show any significant dielectric relaxation. Charge transport was controlled by a direct tunneling mechanism in the field range of 1.5 to 6 MV/cm for a 50 Å film. The Fowler–Nordheim tunneling mechanism dominated the high field range (>6 MV/cm for a 50 Å film), and the leakage currents became independent of dielectric thickness. The electron tunneling effective mass was found to be 0.2 me.
Electrically switchable and thermally erasable biphotonic holographic gratings in dye-doped liquid crystal films
Authors: Lee C.-R. , Mo T.-S. , Cheng K.-T. , Fu T.-L. , Fuh A. Y.-G.
Published: November 2003

This study investigates high-resolution photoinduced biphotonic holographic gratings in azo-dye-doped liquid crystal films. A biphotonic grating (BG) is formed under the illumination of one linearly polarized green light with the simultaneous irradiation of an interference pattern created by two linearly polarized red lights. This study ascribes the formation of this grating to two mechanisms. One mechanism is the green-light-inducing strong dye absorption followed by adsorption through the trans–cis isomerization; the other mechanism is the inhibition effect of adsorption induced by the red light through the cis–trans inverse isomerization. These produce a twisted nematic structure-modulated pattern, which, in turn, causes the BG. Additional experiments demonstrate that the formed BGs are electrically switchable and thermally erasable.
Effects of transition curvature on perpendicular magnetic recording performance
Authors: van der Heijden P. A. A. , Clinton T. W. , Erden M. F.
Published: November 2003

The effect of magnetic transition curvature has been studied for a perpendicular recording system. The curvature of the medium transitions is varied in a controlled manner by altering the write poles using a focused ion beam. Tracks are written using these write heads and are characterized with a magnetic force microscope, which demonstrates the ability to manipulate transition shape and even correct the curvature. The effect of transition curvature on the perpendicular recording performance is characterized by spinstand measurements and bit error rate simulations. These results show a significant performance loss, demonstrating that transition curvature degrades perpendicular recording performance.
Evidence of short-range antiferroelectric local states in lanthanum- and titanium-modified Sr0.3Ba0.7Nb2O6 ferroelectric ceramics
Authors: Amorı́n H. , Pérez J. , Fundora A. , Portelles J. , Guerrero F. , Soares M. R. , Martı́nez E. , Siqueiros J. M.
Published: November 2003

Structural and electrical measurements were performed on lanthanum- and titanium-modified Sr0.3Ba0.7Nb2O6 ferroelectric (FE) ceramics. Dielectric properties show a well-defined relaxor anomaly around −50 °C with double-loop hysteresis curves from this point to the transition temperature. The thesis of short-range antiferroelectric (AFE) local states having incommensurate (INC) structure embedded in the FE polar matrix is proposed to explain the observed behavior. Structural lattice parameters show negative expansion coefficients and INC superlattice diffraction spots were observed through the selected-area diffraction patterns in the [110] zone for this minority local states. The titanium modification of this system seems to be the key fact in the coupling of the INC structure to the AFE local states in the FE–AFE coexistence region.
Thickness and temperature dependence of stress relaxation in nanoscale aluminum films
Authors: Hyun S. , Brown W. L. , Vinci R. P.
Published: November 2003

We have found that stress relaxation of nanoscale Al thin films is strongly dependent on both film thickness and temperature. Films 33, 107, and 205 nm thick prepared by evaporation onto a silicon nitride membrane substrate were studied using membrane resonance. A single thermal cycle to 300 °C was used to establish a stress, after which the time dependence of the stress was measured for the three film thicknesses at 50, 75, and 100 °C. The relaxation rate is highest for the highest temperature and the thinnest film. A dislocation locking mechanism is suggested as a possible explanation for the observed thickness dependence.
Phase transition in relaxor ferroelectrics studied by mechanical measurements
Authors: Yan Feng , Bao Peng , Wang Yening
Published: November 2003

We report the mechanical properties of [(1−x)%]Pb(Mg1/3Nb2/3)O3−x%PbTiO3 ceramics with PbTiO3 content changed from 23% to 0% measured at the vibration frequency of about 1 kHz. Two modulus kinks can be observed in any of the samples. The kink appears at higher temperature can be attributed to the stress-induced relaxation of nanodomains. Another modulus kink at a lower temperature appears near the Vogel–Fulcher freezing temperature. An associated internal friction peak can also be observed at this temperature. This kink and the internal friction peak can be explained to be due to a ferroelectric phase transition, which becomes weaker with the decrease of PbTiO3 content.
Coordination and interface analysis of atomic-layer-deposition Al2O3 on Si(001) using energy-loss near-edge structures
Authors: Kimoto K. , Matsui Y. , Nabatame T. , Yasuda T. , Mizoguchi T. , Tanaka I. , Toriumi A.
Published: November 2003

The coordination and interface of Al2O3 formed on Si(001) by atomic layer deposition (ALD) were studied using electron energy-loss spectroscopy in a transmission electron microscope. Al energy-loss near-edge structures (ELNESs) were interpreted using first-principles calculations. The Al L23 ELNESs show two peaks at 78.2 and 79.7 eV, which originate from tetrahedrally and octahedrally coordinated aluminum, respectively. The depth profile of coordination in ALD Al2O3/Si was investigated. While both tetrahedrally and octahedrally coordinated Al atoms exist in the ALD Al2O3, the former is dominant near the interface. Aluminum silicate was detected near the interface, and it may cause the difference in aluminum coordination.
Native hole traps of ferromagnetic Ga1−xMnxAs layers on (100) GaAs substrates
Authors: Yoon I. T. , Park C. J. , Cho H. Y. , Kang T. W. , Kim K. H. , Kim D. J.
Published: November 2003

Dominant hole traps of ferromagnetic Ga1−xMnxAs and epilayers with an Mn mole fraction of x≈2.2% and 4.4% were identified employing deep-level transient spectroscopy. Three hole traps with binding energies of EA=0.38±0.01 eV at 140 K, EB=0.43±0.01 eV at 220 K, and EC=0.65±0.01 eV at 300 K above the top of the valence band were observed. Comparing with theoretical data of GaAs, it appears most likely that the trap with EA is associated with a gallium vacancy (VGa) or the arsenic antisite complex (GaAs+VAs), whereas the traps with EB and EC are associated with two charge states of arsenic antisite (AsGa) defect. The hole capture cross sections were determined as σp(A)=3.7×10−11, σp(B)=1.5×10−14, and σp(C)=1.1×10−14 cm2, respectively. The samples with x≈2.2% and x≈4.4% show typical behavior for metallic Ga1−xMnxAs and insulator Ga1−xMnxAs, respectively, through Hall measurements.
Temperature dependence of the electrical and electromechanical properties of lead zirconate titanate thin films
Authors: Maiwa Hiroshi , Kim Seung-Hyun , Ichinose Noboru
Published: November 2003

The temperature dependence of the electrical and electromechanical properties of Pb(Zr,Ti)O3 (PZT) (Zr/Ti=30/70, 52/48, and 70/30) thin films are investigated. The 1-μm-thick PZT thin films were prepared on (111)Pt/Ti/SiO2/Si substrates by chemical solution deposition. The temperature dependence of the dielectric and ferroelectric properties of the films were measured in the temperature range from −250 to 150 °C. The temperature-dependent strain loops from PZT films were measured using scanning probe microscopy in the temperature range from −100 to 150 °C. The field-induced displacement increased with increase of the temperature; however, their temperature dependence was relatively small, compared with that reported for bulk PZT ceramics. The results indicate that a thermally activated extrinsic ferroelastic contribution is not predominant in thin PZT films.
Amplitude-modulated electrostatic nanolithography in polymers based on atomic force microscopy
Authors: Lyuksyutov Sergei F. , Paramonov Pavel B. , Juhl Shane , Vaia Richard A.
Published: November 2003

Amplitude modulated electrostatic lithography using atomic force microscopy (AFM) on 20–50 nm thin polymer films is discussed. Electric bias of AFM tip increases the distance over which the surface influences the oscillation amplitude of an AFM cantilever, providing a process window to control tip-film separation. Arrays of nanodots, as small as 10–50 nm wide by 1–10 nm high are created via a localized Joule heating of a small fraction of polymer above the glass transition temperature, followed by electrostatic attraction of the polarized viscoelastic polymer melt toward the AFM tip in the strong (108–109 V/m) nonuniform electric field.
Two-dimensional micrometer-sized single-crystalline ZnO thin nanosheets
Authors: Hu J. Q. , Bando Y. , Zhan J. H. , Li Y. B. , Sekiguchi T.
Published: November 2003

Two-dimensional micrometer-sized single-crystalline ZnO thin nanosheets were achieved on a large scale, in which Zn thin nanosheets (precursor) were first grown via a thermal decomposition and reduction of the starting ZnS powder, and then converted to the ZnO nanosheets via a simple oxidation process. The ZnO nanosheets, growing along [100] or [010] direction and enclosed by ± (001) facets, have lateral dimensions up to several hundreds of microns, and thicknesses of 30–70 nm. Both room-temperature cathodoluminescence and photoluminescence measurements reveal that the present ZnO nanosheets have visible emission bands ranging from the green to red.
Optical trap setup for measuring microtubule pushing forces
Authors: Kerssemakers J. W. J. , Janson M. E. , van der Horst A. , Dogterom M.
Published: November 2003

We present an optical trap design for force measurements of polymerizing microtubules. These stiff, filamentous cell components contribute to dynamic processes by generating pushing forces, for example during cell division. Although single traps are widely used for molecular pulling processes, studying pushing by flexible filaments requires extra measures. We introduce multiple, asymmetric traps for directional stabilization and bracing of the microtubules for enhanced rigidity. Our method performs in a force range which was inaccessible so far, namely near the stall force of a polymerizing microtubule. The described methods open the way to the study of other polymerizing biomolecular systems as well.
Nanoscale surface and subsurface defects induced in lithium niobate by a femtosecond laser
Authors: Stach Eric A. , Radmilovic Velimir , Deshpande Devesh , Malshe Ajay , Alexander Dennis , Doerr David
Published: November 2003

In this letter, electron and ion microscopy techniques have been used to characterize the changes that result when single crystals of lithium niobate are processed using a focused femtosecond laser. The prevailing observation is that of competing processes—ablation and partial redeposition, thermal shock, and extreme quenching, as well as effects associated with shock wave propagation, resulting in both amorphization and heavily defective regions at the focal point of the laser pulse. The observed microstructural defects have a direct implication in optical memory or waveguide writing, where the goal is to realize consistent structural features with uniform optical properties.
Low-density polymer thin film formation in supercritical carbon dioxide
Authors: Koga Tadanori , Seo Y.-S. , Jerome J. L. , Ge S. , Rafailovich M. H. , Sokolov J. C. , Chu B. , Seeck O. H. , Tolan M. , Kolb R.
Published: November 2003

We report a method for producing stable low-density polymer films by using supercritical carbon dioxide (scCO2). Two different molecular weight polystyrene films with various thicknesses were exposed to scCO2 along the density fluctuation ridge in P–T phase diagram. The swollen structures could be then frozen by flash evaporation of CO2 without forming additional voids. X-ray reflectivity data clearly showed that exposure to scCO2 could be used to produce uniform low-density films of about 2Rg thick or less, where Rg is radius of polymer gyration.
Observation of a pseudogap at terahertz frequencies in the ferromagnetic metallic phase of La2−2xSr1+2xMn2O7 (x=0.3)
Authors: Takahashi Kouhei , Kida Noriaki , Tonouchi Masayoshi
Published: November 2003

We have directly measured the low-energy (0.5–3 meV) complex optical spectra of magnetoresistive La2−2xSr1+2xMn2O7 (x=0.3) thin films by using THz time-domain spectroscopy. a-axis oriented thin films of La2−2xSr1+2xMn2O7 (x=0.3) were epitaxially grown on MgO(100) substrates by pulsed laser deposition technique. The films showed paramagnetic insulator to ferromagnetic metal transition at 240 K. In the ferromagnetic metallic phase, we found that the real part of the optical conductivity spectrum exhibits a clear gap signature around 2 meV, which infringes the Drude-like behavior as expected from the electronic and magnetic properties. This provides an optical identification of a pseudogap in La2−2xSr1+2xMn2O7 (x=0.3).
Electronic structure of pentacene adsorbates on Au(111) surfaces
Authors: Suzuki Taku , Kurahashi Mitsunori , Ju Xin , Yamauchi Yasushi
Published: November 2003

The electronic structure of pentacene deposited on a Au(111) substrate in the initial stage of growth was investigated using metastable deexcitation spectroscopy. The occupation of the pentacene π* 4b1u orbital, which corresponds to the lowest unoccupied molecular orbital of the gas phase species, was found at the Fermi level. The donation and backdonation-type interactions between the pentacene adsorbate and the Au surface are discussed.
Patterned growth of coiled carbon nanotubes by a template-assisted technique
Authors: Zhong D. Y. , Liu S. , Wang E. G.
Published: November 2003

A method for controlled synthesis of coiled carbon nanotubes (CNTs) is demonstrated, in which three-dimensional columns of aligned CNTs are used as a template. The coiled CNTs with pitches and coil diameters from 100 to 300 nm are regrown on the straight CNT arrays and the mesoporous structure between the CNT arrays produces an asymmetric growth condition for the coil formation. As observed using transmission electron microscopy, the graphitic layers on the tube wall are stacking-disordered due to the coil geometry. The growth mechanism of the coiled CNTs is also proposed.
Patterning-based investigation of the length-scale dependence of the surface evolution during multilayer epitaxial growth
Authors: Shah S. , Garrett T. J. , Limpaphayom K. , Tadayyon-Eslami T. , Kan H. C. , Phaneuf R. J.
Published: November 2003

We describe an investigation of the lateral length scale dependence of the evolution of topographical corrugations during multilayer molecular beam epitaxial growth in the GaAs/AlAs multilayer system. By patterning the substrate at series of well-defined spatial periods, we are able to study selectively the changes which occur as a function of lateral period over a wide range of corrugation amplitudes. A critical pattern period, which increases monotonically with thickness, separates an initial long spatial period regime where roughness is amplified, from a later, short spatial period regime in which the topography of the growing surface smoothes out.
Using antiferromagnetic/ferromagnetic bilayers as detection layers in magnetic tunnel junctions
Authors: Malinowski G. , Hehn M. , Sajieddine M. , Montaigne F. , Jouguelet E. , Canet F. , Alnot M. , Lacour D. , Schuhl A.
Published: November 2003

It is shown that the association of an antiferromagnetic material with a ferromagnetic material in an exchange-coupled bilayer, often used in spintronic devices as a magnetic reference or pinned system, can be used as a detection layer in magnetoresistive sensors. The magnetic response is shown to be reversible and linear in an adjustable field window. The sensitivity is studied as a function of temperature.
The Synthesis of Some Chiral 2-Aminoalkyloxazole-4-carboxylates from Isoxazol-5(2H)-ones
Authors: Cox Matthew , Prager Rolf H. , Svensson Carina E.
Published: November 2003

Ethyl 4-methyl-5-oxo-2,5-dihydroisoxazole-3-carboxylate can be N-acylated by a number of natural and synthetic phthalimidylamino acids in the presence of carbodiimides. The N-acylated products form the corresponding oxazoles smoothly when irradiated at 300 nm in acetone. Removal of the phthalimido protecting group then gives 2-aminoalkyloxazole-4-carboxylate esters in good overall yields, and without significant racemization at any step.
Competitive Intramolecular Diels - Alder Reactions of bis-α,β-Unsaturated Ester Derivatives of Enzymatically Derived and Enantiopure cis-1,2-Dihydrocatechols. Enantiodivergent Synthesis of Monochiral Bicyclo[2.2.2]oct-2-enes
Authors: Banwell Martin G. , Chun Cai , Edwards Alison J. , Vögtle Markus M.
Published: November 2003

bis-Crotonate and related α,β-unsaturated ester derivatives of readily available and enantiomerically pure cis-1,2-dihydrocatechols engage, upon heating in refluxing toluene, in two competitive intramolecular Diels–Alder reactions to give varying mixtures of chromatographically separable and pseudo-enantiomeric bicyclo[2.2.2]oct-2-enes. Such adducts, many of which have been characterized by single-crystal X-ray analysis, are likely to serve as useful building blocks in natural products synthesis.
Phenology of carpophilus beetle populations (Coleoptera: Nitidulidae, Carpophilus spp.) in a fruit dump in northern Victoria
Authors: Hossain M. S. , Williams D. G.
Published: November 2003

Carpophilus spp. are important pests of stone fruit in Australia. Maintenance of good orchard hygiene has been promoted as a way of reducing pressure from Carpophilus spp. In northern Victoria, Australia, it is common practice for fruit processors to dispose of waste fruit in dumps, many of which are near orchards. The importance of such dumps to Carpophilus spp. was not previously known. Seasonal variation of Carpophilus spp. in a fruit dump in Cobram, northern Victoria, was studied from September 1998 to September 2000. Three locations within the dump were randomly selected and inspected for presence of adults, larvae and pupae of Carpophilus spp. at regular intervals. Adults were used to determine species composition. Three species, C. hemipterus, C. humeralis and C. davidsoni were observed, with the former almost always dominant throughout monitoring. Carpophilus davidsoni was recorded only twice and in small numbers. The greatest number of C. hemipterus adults occurred during autumn and spring. Larval populations were high in late spring and early autumn and overwintering occurred as adults, larvae and pupae. The potential of populations of Carpophilus spp. in the fruit dump to cause damage in nearby ripening stone fruit is discussed.
Comparing different sources of sulfur for high-rainfall pastures insouth-western Australia
Authors: Bolland M. D. A. , Yeates J. S. , Clarke M. F.
Published: November 2003

The dry herbage yield increase (response) of subterranean clover (Trifolium subterraneum L.)-based pasture (>85% clover) to applications of different sources of sulfur (S) was compared in 7 field experiments on very sandy soils in the > 650 mm annual average rainfall areas of south-western Australia where S deficiency of clover is common when pastures grow rapidly during spring (August–November). The sources compared were single superphosphate, finely grained and coarsely grained gypsum from deposits in south-western Australia, and elemental S. All sources were broadcast (topdressed) once only onto each plot, 3 weeks after pasture emerged at the start of the first growing season. In each subsequent year, fresh fertiliser-S as single superphosphate was applied 3 weeks after pasture emerged to nil-S plots previously not treated with S since the start of the experiment. This was to determine the residual value of sources applied at the start of the experiment in each subsequent year relative to superphosphate freshly-applied in each subsequent year. In addition, superphosphate was also applied 6, 12 and 16 weeks after emergence of pasture in each year, using nil-S plots not previously treated with S since the start of the experiment. Pasture responses to applied S are usually larger after mid-August, so applying S later may match plant demand increasing the effectiveness of S for pasture production and may also reduce leaching losses of the applied S.At the same site, yield increases to applied S varied greatly, from 0 to 300%, at different harvests in the same or different years. These variations in yield responses to applied S are attributed to the net effect of mineralisation of different amounts of S from soil organic matter, dissolution of S from fertilisers, and different amounts of leaching losses of S from soil by rainfall. Within each year at each site, yield increases were mostly larger in spring (September–November) than in autumn (June–August). In the year of application, single superphosphate was equally or more effective than the other sources. In years when large responses to S occurred, applying single superphosphate later in the year was more effective than applying single superphosphate 3 weeks after pasture emerged (standard practice), so within each year the most recently applied single superphosphate treatment was the most effective S source. All sources generally had negligible residual value, so S needed to be applied each year to ensure S deficiency did not reduce pasture production.
Induction of chill-induced ripening in Fuji apples is a function of both temperature and time
Authors: Jobling J. , Pradhan R. , Morris S. C. , Wade N. L.
Published: November 2003

Ethylene production is stimulated by chilling in some cultivars of apples, citrus, cucumbers and pears. The apple varieties Granny Smith, Lady Williams and Fuji can be induced to ripen by a period of chilling at 0°C in air, which hastens the onset of the rise in ethylene production.Fuji apples were susceptible to rapid ripening if stored in air at low temperatures (<10°C). The induction of rapid ripening occurred in both early and late harvested fruit and was correlated with increased activity of 1-aminocyclopropane-1-carboxylic acid oxidase during low temperature storage. The induction of rapid ripening caused the fruit to soften more quickly after cold storage than after continuous exposure to 20°C. Rapid ripening could be prevented by storing fruit in controlled atmosphere (CA) storage (2%�O2 and <1% CO2). Fruit had lower internal ethylene levels following CA storage than following low temperature air storage. The practical solution for growers would therefore be to store Fuji apples in CA, even for short periods, to optimise fruit quality for the consumer.
The mature activating natural killer cell immunologic synapse is formed in distinct stages
Authors: Orange Jordan S. , Harris K. Eliza , Andzelm Milena M. , Valter Markus M. , Geha Raif S. , Strominger Jack L.
Published: November 2003

Natural killer (NK) cells form a structure at their interface with a susceptible target cell called the activating NK cell immunologic synapse (NKIS). The mature activating NKIS contains a central and peripheral supramolecular activation cluster (SMAC), and includes polarized surface receptors, filamentous actin (F-actin) and perforin. Evaluation of the NKIS in human NK cells revealed CD2, CD11a, CD11b and F-actin in the peripheral SMAC (pSMAC) with perforin in the central SMAC. The accumulation of F-actin and surface receptors was rapid and depended on Wiskott–Aldrich syndrome protein-driven actin polymerization. The accumulation at and arrangement of these molecules in the pSMAC was not affected by microtubule depolymerization. The polarization of perforin, however was slower and required intact actin, Wiskott–Aldrich syndrome protein, and microtubule function. Thus the process of CD2, CD11a, CD11b, and F-actin accumulation in the pSMAC and perforin accumulation in the central SMAC of the NKIS are sequential processes with distinct cytoskeletal requirements.
Allosteric determinants in guanine nucleotide-binding proteins
Authors: Hatley Mark E. , Lockless Steve W. , Gibson Scott K. , Gilman Alfred G. , Ranganathan Rama
Published: November 2003

Members of the G protein superfamily contain nucleotide-dependent switches that dictate the specificity of their interactions with binding partners. Using a sequence-based method termed statistical coupling analysis (SCA), we have attempted to identify the allosteric core of these proteins, the network of amino acid residues that couples the domains responsible for nucleotide binding and protein–protein interactions. One-third of the 38 residues identified by SCA were mutated in the G protein G
sα
, and the interactions of guanosine 5′-3-
O
-(thio)triphosphate- and GDP-bound mutant proteins were tested with both adenylyl cyclase (preferential binding to GTP-G
sα
) and the G protein βγ subunit complex (preferential binding to GDP-G
sα
). A two-state allosteric model predicts that mutation of residues that control the equilibrium between GDP- and GTP-bound conformations of the protein will cause the ratio of affinities of these species for adenylyl cyclase and Gβγ to vary in a reciprocal fashion. Observed results were consistent with this prediction. The network of residues identified by the SCA appears to comprise a core allosteric mechanism conferring nucleotide-dependent switching; the specific features of different G protein family members are built on this core.
Diversification of furanocoumarin-metabolizing cytochrome P450 monooxygenases in two papilionids: Specificity and substrate encounter rate
Authors: Li Weimin , Schuler Mary A. , Berenbaum May R.
Published: November 2003

Diversification of cytochrome P450 monooxygenases (P450s) is thought to result from antagonistic interactions between plants and their herbivorous enemies. However, little direct evidence demonstrates the relationship between selection by plant toxins and adaptive changes in herbivore P450s. Here we show that the furanocoumarin-metabolic activity of CYP6B proteins in two species of swallowtail caterpillars is associated with the probability of encountering host plant furanocoumarins. Catalytic activity was compared in two closely related CYP6B4 and CYP6B17 groups in the polyphagous congeners
Papilio glaucus
and
Papilio canadensis
. Generally, P450s from
P. glaucus
, which feeds occasionally on furanocoumarin-containing host plants, display higher activities against furanocoumarins than those from
P. canadensis
, which normally does not encounter furanocoumarins. These P450s in turn catalyze a larger range of furanocoumarins at lower efficiency than CYP6B1, a P450 from
Papilio polyxenes
, which feeds exclusively on furanocoumarin-containing host plants. Reconstruction of the ancestral CYP6B sequences using maximum likelihood predictions and comparisons of the sequence and geometry of their active sites to those of contemporary CYP6B proteins indicate that host plant diversity is directly related to P450 activity and inversely related to substrate specificity. These predictions suggest that, along the lineage leading to
Papilio
P450s, the ancestral, highly versatile CYP6B protein presumed to exist in a polyphagous species evolved through time into a more efficient and specialized CYP6B1-like protein in
Papilio
species with continual exposure to furanocoumarins. Further diversification of
Papilio
CYP6Bs has likely involved interspersed events of positive selection in oligophagous species and relaxation of functional constraints in polyphagous species.
Endothelial lineage-mediated loss of the GATA cofactor Friend of GATA 1 impairs cardiac development
Authors: Katz Samuel G. , Williams Aimee , Yang Jifu , Fujiwara Yuko , Tsang Alice P. , Epstein Jonathan A. , Orkin Stuart H.
Published: November 2003

GATA transcription factors, together with Friend of GATA (FOG) cofactors, are required for the differentiation of diverse cell types. Multiple aspects of hematopoiesis are controlled by the interaction of FOG-1 with the GATA-1/2/3 subfamily. Likewise, FOG-2 is coexpressed with the GATA-4/5/6 subfamily at other sites, including the heart and gonads. FOG-2 and GATA-4 are required for cardiac development. Through transgenic rescue of hematopoietic defects of FOG-1
–/–
embryos we define an unsuspected role for FOG-1 in heart development. In particular, rescued FOG-1
–/–
mice die at embryonic day (E) 14.5 with cardiac defects that include double outlet right ventricle and a common atrioventricular valve. Using conditional inactivation of
Fog
-
1
we assign the cell of origin in which FOG-1 function is required. Neural crest cells migrate properly into FOG-1
–/–
hearts and mice with FOG-1 conditionally excised from neural crest derivatives fail to develop cardiac abnormalities. In contrast, conditional inactivation of FOG-1 in endothelial-derived tissues by means of Tie-2-expressed Cre recapitulates the rescue-knockout defects. These findings establish a nonredundant requirement for FOG-1 in the outlet tract and atrioventricular valves of the heart that depend on expression in endothelial-derived tissue and presumably reflect cooperation with the GATA-4/5/6 subfamily.