bluuebunny/crossref_metadata_2025 huggingface dataset:
Immunolocalization of the PmSUC1 Sucrose Transporter in Plantago major Flowers and Reporter‐Gene Analyses of the PmSUC1 Promoter Suggest a Role in Sucrose Release from the Inner Integument
Authors: Lauterbach C. , Niedermeier M. , Besenbeck R. , Stadler R. , Sauer N.
Published: May 2007

Abstract: This paper presents a detailed analysis of the PmSUC1 gene from Plantago major, of its promoter activity in Arabidopsis, and of the tissue specific localization of the encoded protein in Plantago. PmSUC1 promoter activity was detected in the innermost layer of the inner integument (the endothel) of Arabidopsis plants expressing the gene of the green fluorescent protein (GFP) under the control of the PmSUC1 promoter. This promoter activity was confirmed with a PmSUC1‐specific antiserum that identified the PmSUC1 protein in the endothel of Plantago and of Arabidopsis plants expressing the PmSUC1 gene under the control of its own promoter. PmSUC1 promoter activity and PmSUC1 protein were also detected in pollen grains during maturation inside the anthers and in pollen tubes during and after germination. These results demonstrate that PmSUC1 is involved in sucrose partitioning to the young embryo and to the developing pollen and growing pollen tube. In the innermost cell layer of the inner integument, a tissue that delivers nutrients to the endosperm and the embryo, PmSUC1 may catalyze the release of sucrose into the apoplast.
Morphology and Biochemistry of Non‐Glandular Trichomes in Cistus salvifolius L. Leaves Growing in Extreme Habitats of the Mediterranean Basin
Authors: Tattini M. , Matteini P. , Saracini E. , Traversi M. L. , Giordano C. , Agati G.
Published: May 2007

Abstract: Here the functional roles of stellate and dendritic trichomes in Cistus salvifolius L leaves were studied by analysing i) both leaf surface and trichome morphology using scanning electron and light microscopy; and ii) the composition and localisation of polyphenols by coupling liquid chromatography with fluorescence spectroscopy and fluorescence microimaging. Red‐coloured compounds were detected in the stalk cells and the channel in the trichome arm, and appeared to be released at the tip end of the trichome branch. We identified such metabolites as ellagitannins, namely punicalagin and two galloyl derivatives of punicalagin. These ellagitannins accounted for 4.3 % of leaf dry weight and their concentration in the leaf leachate averaged 289.4 mg L‐1. The trichome arms exhibited an appreciable orange‐red autofluorescence (centred at 620 nm) when excited with UV light (at 365 nm) or emitted in the yellow waveband (peak centred at 566 nm) when stained with the Naturstoff reagent, and excited at 488 nm. The fluorescence signatures of the trichome arms were consistent with the presence of mono‐hydroxy B‐ring substituted flavonoids, which were identified as the mono‐ and di‐coumaroyl derivative of a kaempferol 3‐O‐glycoside. Our data may provide some insights on the functional roles of stellate and dendritic trichomes in the response mechanisms of C. salvifolius to Mediterranean‐type climate, based upon (i) the potential effect of released ellagitannins on the soil nitrogen dynamic and (ii) the ability of acylated kaempferol 3‐O‐glycosides to effectively absorb both the UV‐B and UV‐A wavelengths.
Virus‐Induced Changes in the Subcellular Distribution of Glutathione Precursors in Cucurbita pepo (L.)
Authors: Zechmann B. , Zellnig G. , Müller M.
Published: May 2007

Abstract: Changes in glutathione contents occur in plants during environmental stress situations, such as pathogen attack, as the formation of reactive oxygen species leads to the activation of the antioxidative defence system. As glutathione is synthesized out of its constituents cysteine, glycine, and glutamate the availability of these components will limit glutathione synthesis in plants especially during stress situations and therefore the ability of the plant to fight oxidative stress. To gain a deeper insight into possible limitations of glutathione synthesis during pathogen attack the present investigations were aimed to study how the subcellular distribution of glutathione precursors correlates with the subcellular distribution of glutathione during virus attack in plants. Selective antibodies against cysteine, glutamate, and glycine were used to study the impact of Zucchini yellow mosaic virus (ZYMV) infection on glutathione precursor contents within different cell compartments of cells from Cucurbita pepo (L.) plants with the transmission electron microscope (TEM). Generally, levels of cysteine and glutamate were found to be strongly decreased in most cell compartments of younger and older leaves including glutathione‐producing cell compartments such as plastids and the cytosol. The strongest decrease of cysteine was found in plastids (‐ 54 %) and mitochondria (‐ 51 %) of younger leaves and in vacuoles (‐ 37 %) and plastids (‐ 29 %) of older leaves. The strongest decrease of glutamate in younger leaves occurred in peroxisomes (‐ 67 %) and nuclei (‐ 58 %) and in peroxisomes (‐ 64 %) and plastids (‐ 52 %) of the older ones. Glycine levels were found to be strongly decreased (‐ 63 % in mitochondria and ‐ 53 % in plastids) in most cell compartments of older leaves and strongly increased (about 50 % in plastids and peroxisomes) in all cell compartments of the younger ones. These results indicate that low glycine contents in the older leaves were responsible for low levels of glutathione in these organs during ZYMV infection rather than limited amounts of cysteine or glutamate. Glutathione precursors were virtually absent in cell walls and intercellular spaces and play therefore no important role during ZYMV attack in the apoplast. While glutamate was absent in vacuoles, elevated levels of glycine (up to 30 %) and decreased cysteine contents (up to ‐ 37 %) were observed in vacuoles during ZYMV infection. The impact of the present results on the current knowledge about glutathione synthesis and degradation on the cellular level during ZYMV infection are discussed.
Electric-field-induced magnetization reduction in multiferroic Pb(Zr,Ti)O3–LaMnO3 composites
Authors: Gomi M. , Nishimura N. , Yokota T.
Published: May 2007

Magnetic and dielectric properties and the magnetoelectric effect of ceramics with a composition of 0.9 Pb(Zr,Ti)O3–0.1 LaMnO3 have been investigated. X-ray diffraction measurements showed that the sintered ceramics are composites containing a small amount of the (La,Pb)MnO3 phase in the Pb(Zr,Ti)O3 matrix. These composites were multiferroic, having ferromagnetic and ferroelectric Curie temperatures of 350 and 630K, respectively. The composite sintered at 1070°C exhibited a reduction of spontaneous magnetization as large as 30% at room temperature when an electric field of 0.4kV∕mm was applied. This reduction is ascribable to a change in hole concentration around the boundaries of the precipitated ferromagnetic (La,Pb)MnO3 grains and the resultant decrease of ferromagnetic Curie temperature.
A study on ferromagnetic resonance linewidth of single crystalline ultrathin Fe film grown on GaAs substrate
Authors: Zhai Y. , Ni C. , Xu Y. , Xu Y. B. , Wu J. , Lu H. X. , Zhai H. R.
Published: May 2007

We report ferromagnetic resonance studies on linewidth of single crystal ultrathin Fe films on GaAs(100). For different orientations of the magnetic field in the film plane, anisotropic linewidth has been observed. An expression for anisotropy of linewidth with isotropic damping was derived and also an expression for anisotropic damping constant was proposed. With these two expressions the data of the angular dependence of linewidth of a 5.2 ML (monolayer) film were fitted well. For the thicker film of 25 ML, the fitting of experimental angular dependence of linewidth could be improved if an inhomogeneous broadening is further considered.
Finite difference time domain simulation on near-field optics for granular recording media in hybrid recording
Authors: Nakagawa Katsuji , Kim Jooyoung , Itoh Akiyoshi
Published: May 2007

We demonstrate the near-field optics on granular recording media calculated by finite difference time domain (FDTD). Granular media and pattern media are necessary for hybrid recording to achieve a recording density of 1Tbit∕in.2. In FDTD simulation, the power of near-field optics from a plasmon antenna is affected by the presence of the medium. However, for further investigation, the model of this study included granular media. The grains are arrayed in a close-packed structure. From this analysis, the top of the grains shows strong power of near-field optics. The power intensity of the granular media under the apex of the plasmon antenna shows a narrow distribution with a sharp peak, about three times higher than that for film media. There are higher peaks in intensity at the surface of the grain than inside the grain. These results show that grains positioned at the apex of the antenna can be heated by a small, concentrated spot.
Preannealing effect on ordering transformation and magnetic properties of CoPt thin films
Authors: Yuan F. T. , Chang H. W. , Liao W. M. , Hsiao S. N. , Chen S. K. , Yao Y. D. , Lee H. Y.
Published: May 2007

Single layer CoPt thin films with thicknesses from 30to100nm were sputtered on glass substrates. A preannealing at 250°C for 80min was applied to the samples, before ordering treatment at 700°C for 10min. This preannealing process resulted in a 33%–65% decrease in coercivity and 23%–55% decrease in volume fraction of order phase f0. Results of morphology investigation showed that the preannealing increases the surface roughness, which mainly results from the elimination of defects. Structural results further suggest that the eliminated defects are mostly low dimensional, such as dislocations or vacancies. It can thus be concluded that those low dimensional imperfections in the CoPt films play an enhancing role in ordering transformation process.
Enhancement in coercivity of pulse-laser-deposition-made Nd–Fe–B thick film magnets by high-speed crystallization
Authors: Nakano M. , Takeda H. , Sato S. , Yanai T. , Yamashita F. , Fukunaga H.
Published: May 2007

In order to improve the magnetic properties of Nd–Fe–B thick film magnets prepared by pulsed laser deposition, high-speed crystallization method of a pulse annealing was adopted as a postannealing process. In the case of using a Nd2.4Fe14B target, the pulse annealing under an optimum condition for the period of 1.8s enabled us to enhance the coercivity by approximately 300kA∕m compared with the average value of samples annealed by a conventional method. The obtained sample whose composition was almost as same as the target’s one had the large coercivity of approximately 1300kA∕m, and values of remanence and (BH)max were 0.62T and 64kJ∕m3, respectively. It was also clarified that use of a Nd2.2Fe14B target together with the pulse annealing method is effective to increase remanence and (BH)max although the coercivity value decreased.
Microstructure of Co∕X (X=Cu,Ag,Au) epitaxial thin films grown on Al2O3(0001) substrates
Authors: Ohtake Mitsuru , Akita Yuta , Futamoto Masaaki , Kirino Fumiyoshi
Published: May 2007

Epitaxial thin films of Co∕X (X=Cu,Ag,Au) were prepared on Al2O3(0001) substrates at substrate temperatures of 100 and 300°C by UHV molecular beam epitaxy. A complicated microstructure was realized for the epitaxial thin films. In-situ reflection high-energy electron diffraction observation has shown that X atoms of the buffer layer segregated to the surface during Co layer deposition, and it yielded a unique epitaxial granular structure. The structure consists of small Co grains buried in the X buffer layer, where both the magnetic small Co grains and the nonmagnetic X layer are epitaxially grown on the single crystal substrate. The structure varied depending on the X element and the substrate temperature. The crystal structure of Co grains is influenced by the buffer layer material and determined to be hcp and fcc structures for the buffer layer materials of Au and Cu, respectively.
Enhancement of modulation rate of magneto-optical spatial light modulators with magnetophotonic crystals
Authors: Takahashi K. , Takagi H. , Shin K. H. , Uchida H. , Lim P. B. , Inoue M.
Published: May 2007

Thin-film-type magneto-optical spatial light modulator has been developed by combining one-dimensional magnetophotonic crystal (MPC) and micropatterned drive lines. The use of MPC is expected to be effective because the apparent Faraday effect, which is directly proportional to pixel contrast, is largely enhanced by the light localization of light in the vicinity of the magnetic defect in magnetophotonic crystal. The magnetophotonic crystal had a multilayer structure of (Ta2O5∕SiO2)k∕Bi: yttrium iron garnet∕(SiO2∕Ta2O5)k formed on a glass substrate, where k is the repetition number and one of optimization parameters in this study. The transmittance T decreased with an increase of k, while Faraday rotation θF increased, indicating that the enhancement of light modulation rate would be achieved by optimizing the figure of merit F defined by F≈Tsin2θF. At k=6, the maximum F=8.8 was obtained, which is about 20 times larger than that of single layer structure.
Room-temperature fabricated ZnCoO diluted magnetic semiconductors
Authors: Huang Hsin-Hung , Yang Chih-An , Huang Po-Hsiang , Lai Chih-Huang , Chin T. S. , Huang H. E. , Bor H. Y. , Huang R. T.
Published: May 2007

(0002) textured and epitaxial ZnCo0.07O films were fabricated at room temperature by ion beam deposition on Si substrates. Hall measurement revealed that ZnCo0.07O films were n-type semiconductors with carrier concentrations higher than 1019∕cm3. The carrier concentration of ZnCo0.07O can be manipulated by controlling the oxygen flow rate during deposition or by postannealing. The saturation magnetization and magnetoresistance ratios strongly depended on the carrier concentration. In addition, epitaxial (0002) ZnCo0.07O films, grown on Cu underlayers, showed room-temperature ferromagnetism, which may be potentially used for spintronic devices.
Control of the cation occupancies of MnZn ferrite synthesized via reverse micelles
Authors: Shultz M. D. , Allsbrook M. J. , Carpenter E. E.
Published: May 2007

Variations in cation occupancy in mixed metal ferrite systems can affect their electronic and magnetic properties. It is known that different synthesis parameters can lead to various cation distributions and the ability to tune these distributions is of great interest. This study uses the extended x-ray-absorption fine structure–IR relationship to investigate the effect of various Fe2+∕Fe3+ ratios in initial synthesis conditions on cation distribution for manganese zinc ferrite (MZFO). Differences in the precipitated material before firing could lead to differences in the final material if fired under similar conditions. This work uses several different ratios of Fe3+∕Fe2+, which will affect the initial cell potential for the reaction, to synthesize nano MZFO. All samples were fired for 5h at 500°C under flowing nitrogen. Transmission electron microscopy micrographs reveal highly crystalline uniform nanoparticles of 16±2nm. The x-ray diffraction revealed single phase crystalline MZFO with an average crystallite size of around 14nm. The saturation magnetization ranged from 43to68emu∕g as measured by vibrating-sample magnetometry. The Fourier transform infrared (FTIR) analysis was used to determine the cation occupancies while changing the initial Fe3+∕Fe2+ ratios from 10∕90 to 90∕10. The FTIR spectra revealed a shift in the first absorption region in the far IR from 566.98to549.62cm−1 corresponding to the octahedral occupancies. This shift corresponds to a change in the percentage of octahedral sites occupied by manganese from roughly 25% to 12%. This change in manganese occupancy is also observed in the iron occupancies, which in turn help to explain the variation in saturation magnetization.
Effect of application of a high magnetic field on the microstructure of Fe substituted layered double hydroxide clay for a magnetic application
Authors: Nakahira Atsushi , Murase Hideaki , Yasuda Hideyuki
Published: May 2007

In this study, the synthesis of Fe substituted layered double hydroxide (LDH) clays with unique layered structures, Mg∕Fe-LDH, was attempted by a coprecipitation method, and subsequent decomposition behaviors on in situ heat treatments under a high magnetic field were investigated for these LDH clays. Specifically, the evaluations of microstructure of Mg∕Fe-LDH were in detail carried out after in situ heat treatments with a high magnetic field of 10T. As a result, it was found that the thermal decomposition behaviors of Mg∕Fe-LDH on in situ heat treatments under the exposure of 10T were significantly different from the ones under 0T and the formation of magnesioferrite (MgFe2O4) with a spinel-type structure was enhanced by the application of a high magnetic field. Furthermore, there were some distinct differences between the morphologies of MgFe2O4 prepared between under 0 and 10T that were caused by the anisotropic magnetic susceptibility of MgFe2O4. Applying in situ heat treatment under 10T to the decomposition of Mg∕Fe-LDH led to the successful synthesis of nanosized MgFe2O4 at lower temperatures.
Structural studies of secondary crystallization products of the Fe23B6-type in a nanocrystalline FeCoB-based alloy
Authors: Long Jianguo , Ohodnicki P. R. , Laughlin D. E. , McHenry M. E. , Ohkubo T. , Hono K.
Published: May 2007

A stable Fe23B6-type phase formed in a nanocomposite soft magnetic alloy Fe40Co40Nb4B13Ge2Cu1 after thermal treatment was investigated. The primary crystallization temperature and second crystallization temperature for this alloy were determined to be 405 and 740°C, respectively. After annealing the sample at 820°C for 1h, a Fe23B6-type phase (FeCoNb)23B6 was observed. The structural information was investigated by x-ray diffraction, transmission electron microscopy, and three-dimensional atom probe. The Fe23B6-type phase contains about 33±5at.% Fe, 38±5at.% Co, 7±1at.% Nb, and 20±3at.% B. The Nb atoms tend to occupy the 8c sites and Co∕Fe atoms occupy the 4a, 32f, and 48h sites of the Fm3m space group for this structure.
Magnetic instabilities along the superconducting phase boundary of Nb∕Ni multilayers
Authors: Joshi Amish G. , Kryukov Sergiy A. , De Long Lance E. , Gonzalez Elvira M. , Navarro Elena , Villegas Javier E. , Vicent Jose L.
Published: May 2007

We report vibrating reed and superconducting quantum interference device magnetometer data that exhibit prominent dips or oscillations of the superconducting (SC) onset temperature, ΔTC(H)≈0.01–0.7K, for a [Nb(23nm)∕Ni(5nm)]5 multilayer (ML) in dc magnetic fields applied nearly parallel to the ML plane. The vibrating reed data exhibit reproducible structures below TC that may reflect multiple SC transitions, but they are sensitive to ac field amplitude and dc field orientation. This striking behavior poses challenges for theoretical and experimental investigations of interfaces between SC and ferromagnetic layers that involve magnetic pair breaking effects, “pi phase shifts” of the SC order parameter, and exotic (“LOFF”) pairing states. Alternatively, the anomalies may mark dynamical instabilities within a confined, strongly anisotropic Abrikosov vortex lattice.
Spontaneous and induced dynamic fluctuations in glass formers. I. General results and dependence on ensemble and dynamics
Authors: Berthier L. , Biroli G. , Bouchaud J.-P. , Kob W. , Miyazaki K. , Reichman D. R.
Published: May 2007

We study theoretically and numerically a family of multipoint dynamic susceptibilities that quantify the strength and characteristic length scales of dynamic heterogeneities in glass-forming materials. We use general theoretical arguments (fluctuation-dissipation relations and symmetries of relevant dynamical field theories) to relate the sensitivity of averaged two-time correlators to temperature and density to spontaneous fluctuations of the local dynamics. Our theoretical results are then compared to molecular dynamics simulations of the Newtonian, Brownian, and Monte Carlo dynamics of two representative glass-forming liquids, a fragile binary Lennard-Jones mixture, and a model for the strong glass-former silica. We justify in detail the claim made by Berthier et al. [Science 310, 1797 (2005)] that the temperature dependence of correlation functions allows one to extract useful information on dynamic length scales in glassy systems. We also discuss some subtle issues associated with the choice of microscopic dynamics and of statistical ensemble through conserved quantities, which are found to play an important role in determining dynamic correlations.
Null decomposition of conformal algebras
Authors: Mihai Dana , Sparling George A. J.
Published: May 2007

We analyze the decomposition of the enveloping algebra of the conformal algebra in arbitrary dimension with respect to the mass-squared operator. It emerges that the subalgebra that commutes with the mass-squared operator is generated by its Poincaré subalgebra together with a vector operator. The special cases of the conformal algebras of two and three dimensions are described in detail, including the construction of their Casimir operators.
Asymptotic analysis of the constant pressure turbulent boundary layer
Authors: Lundgren Thomas S.
Published: May 2007

The Navier-Stokes equations are expanded in asymptotic power series in a small parameter ϵ(=uτ∕Ue) which is determined as a function of Reynolds number by an asymptotic matching procedure. The present matched asymptotic expansion analysis differs from the more traditional approach by employing the unsteady Navier-Stokes equations instead of the unclosed Reynolds averaged equations. It is therefore not necessary to expand the Reynolds stress separately in the small parameter, and more importantly, the problem is mathematically well posed. The analysis is simpler, requires fewer assumptions, and gives information about all the velocity components. The main result of this analysis is an instantaneous log-law in the overlap region, of the form u+=κ−1ln(y+)+B, where the additive “constant” B is independent of y but depends on the outer scaled x,z,t variables. It is found that all the Reynolds stresses are constant in the overlap region. Estimates are made of the extent of the overlap region and the rate at which it is approached as Reynolds number tends to infinity.
Room temperature deposition of p-type arsenic doped ZnO polycrystalline films by laser-assist filtered cathodic vacuum arc technique
Authors: Yuen Clement , Yu S. F. , Leong E. S. P. , Lau S. P. , Pita K. , Yang H. Y. , Chen T. P.
Published: May 2007

The use of combined filtered cathodic vacuum arc (FCVA) technique and laser ablation to fabricate high-quality As doped ZnO (ZnO:As) films at room temperature is proposed. This is possible because FCVA technique is capable of realizing high-quality undoped ZnO films with extremely high resistivity (i.e., extremely low concentration of Zn interstitials) at low deposition temperature. In addition, laser ablation allows the generation of As plume to react with Zn ion species and O2 inside the FCVA chamber to form ZnO:As films. It was shown that high-quality p-type ZnO:As film with a resistivity of 0.05Ωcm, a mobility of 2cm2∕Vs, and a hole concentration of 4×1019cm−3 was obtained at room temperature by using the proposed deposited technique. X-ray photoemission spectroscopy analysis has indicated that complex of As substitutional Zn induces two Zn vacancies (i.e., AsZn–2VZn complex), which is likely to be the defect contributing to the formation of shallow acceptor lever inside the ZnO:As films. Furthermore, In∕Au Ohmic contacts deposited on p-type ZnO:As films and p-n ZnO based homojunction have been fabricated using plastic as the substrate.
Self-focusing instability in ionospheric plasma with thermal conduction
Authors: Sodha Mahendra Singh , Sharma Ashutosh , Verma M. P. , Faisal Mohammad
Published: May 2007

In this communication, an expression for the growth rate of self-focusing instability in the ionospheric plasma has been derived after taking finite thermal conduction into account. The instability arises on account of the depletion of electrons from regions where the irradiance of the perturbation is large. In contrast to earlier work, an appropriate energy balance equation for electrons and ions and the proper dependence of thermal conductivity on electron temperature have been used. The dependence of the growth rate of the filamentation instability on the background irradiation, thermal conductivity, and the wave number of transverse perturbation has been investigated. The mid-latitude daytime ionospheric model of Gurevich has been used for numerical computations, corresponding to a height of 200km. The gradient of irradiance perturbations is assumed to be along the magnetic field of the Earth. The numerical results have been illustrated graphically and discussed.
Solitary Alfvén waves in a dusty plasma
Authors: Choi Cheong Rim , Lee D.-Y.
Published: May 2007

The nonlinear solitary Alfvén wave in a magnetized dusty plasma with a low β assumption, obliquely propagating to an external magnetic field, is investigated based on the Sagdeev potential. It is found that there exists a double layer solution as well as the compressive solitary Alfvén waves. It is shown that the amplitude of the compressive and rarefactive solitary Alfvén waves decreases with a dust charge density, whereas that of the double layer behaves in the opposite way. In addition, it is found that the speed of the solitary Alfvén wave is independent of the dust charge density.
Electronic transport of the manganite-based heterojunction with high carrier concentrations
Authors: Xie Y. W. , Sun J. R. , Wang D. J. , Liang S. , Lü W. M. , Shen B. G.
Published: May 2007

The transport property of the manganite heterojunction La0.9Ca0.1MnO3+δ∕SrTiO3 (doped by 1wt%Nb) has been experimentally studied. The most important results of the present work are the discovery of the charge tunneling-dominated transport process, characterized by the appearance of the rectifying behaviors fairly described by the Newman equation I∝exp(αT)exp(βV) in a considerable temperature range (α and β are constants, and I and V are current and voltage, respectively). Significant modification of magnetic field to charge tunneling is also observed. It is believed that magnetic field depresses junction resistance by reducing depletion width of the junction.
Noncontact ballistic motion measurement using a fiber-optic confocal sensor
Authors: Shafir E. , Berkovic G. , Horovitz Y. , Appelbaum G. , Moshe E. , Horovitz E. , Skutelski A. , Werdiger M. , Perelmutter L. , Sudai M.
Published: May 2007

A fiber-optic confocal sensor for noncontact ballistic measurements is described. Determination of motion at velocities of 1.7 km/s with an uncertainty as small as ±0.3% is demonstrated for both a projectile and a free-surface target. The fibers detect the passage of the object at their conjugate image points created by low F/# optics. This results in an output signal comprising a train of sharp pulses each precisely identifying when the ballistic object traverses an image point. Since the ballistic object does not contact the sensor at the time of imaging, the measurements do not perturb the motion, enabling multi-fragment measurement, as well as repetitive measurements of the same object point.
Time scales for transition in Taylor-Couette flow
Authors: Czarny Olivier , Lueptow Richard M.
Published: May 2007

The time scale for onset and decay of vortices in a Taylor-Couette system cannot be predicted from linear stability analysis, yet it is important from a practical standpoint. A two-dimensional pseudospectral direct numerical simulation was used to examine the time scales for subcritical-to-supercritical transition and supercritical-to-subcritical transition for a variety of aspect ratios (Γ=H∕d=8,16,24,32,40,∞) and radius ratios (η=0.5, 0.7, and 0.9). A viscous time scale incorporating both the gap width, d, and the distance between the endwalls of the system, H, is most appropriate for the onset of Taylor vortices, although no time scale collapses the data for all aspect ratios and radius ratios. For decay, a viscous time scale using the gap width as the length scale collapses the data as the aspect ratio gets large. These results indicate that the onset of vortices is a consequence of the propagation of vortical structures related to the endwalls, while decay is related to viscous dissipation from the sidewalls.
Excited state calculations on fluorene-based polymer blends: Effect of stacking orientation and solvation
Authors: Ramon John Glenn S. , Bittner Eric R.
Published: May 2007

Polyfluorene-based polymer blends have been utilized in the development of optoelectronic devices. The constituent copolymers are chemically designed to facilitate more efficient electron/hole mobility, thereby enhancing control over exciton formation and dissociation. When appropriate pairs of these are blended together, intermolecular charged-particle localizations are induced, leading to significant intermolecular charge-transfer character and luminescence that exhibit some sensitivity to their interfacial orientation. The authors report on a time-dependent density functional theory quantum chemical investigation of the relevant excited states of the polymer blend poly[9,9-dioctylfluorene-co-N-(4-butylphenyl)diphenylamine]/poly(9,9-dioctylfluorene-co-benzothiadiazole. They show that the calculated excited states generally agree with experimental observations although there is a consistent underestimation of the charge-transfer states. Further, they show sensitivity to lateral shifts in interfacial stacking. Finally, solvation with a low dielectric solvent greatly stabilizes the charge-transfer states.
High power, low-noise, and multiply resonant photodetector for interferometric gravitational wave detectors
Authors: Grote H.
Published: May 2007

We have developed a new photodetector circuit for use in interferometric gravitational wave detectors. The circuit can detect high laser power with low noise and provide multiple outputs for different signal frequencies. The dynamic range of this circuit is increased in comparison with the photodetector design used until the end of 2005.
Ab initio simulation of a gadolinium-based magnetic resonance imaging contrast agent in aqueous solution
Authors: Pollet Rodolphe , Marx Dominik
Published: May 2007

The first ab initio molecular dynamics simulation of a Gd(III)-based contrast agent in explicit aqueous solution at ambient conditions as used in the actual magnetic resonance imaging of human bodies is presented. The description of the structure of this chelate complex is considerably improved with respect to typical force fields and ab initio calculations in continuum solvent models if the open 4f shell of Gd is included explicitly. The solvation-shell structure is revealed to be anionic and includes a rather short hydrogen bond donated by the hydroxypropyl arm.
Determination of diffusion lengths for intermixed quaternary quantum well with polarized edge-emitting photoluminescence
Authors: Xu C. D. , Mei T. , Dong J. R.
Published: May 2007

Diffusion lengths of the group III and V sublattices are quantitatively determined for intermixing of a quaternary InGaAs∕InP quantum well using polarized edge-emitting photoluminescence. Diffusion-length loci are plotted on a contour diagram of wavelength shifts of electron-heavy-hole and electron-light-hole transitions and illustrate the time progression of intermixing clearly. The plasma-enhanced intermixing effect is investigated using this technique, showing the difference of intermixing development in the early and the late stages. It is seen that the calculated diffusion-length ratio may change with the annealing duration.
Probing momentum distributions in magnetic tunnel junctions via hot-electron decay
Authors: Jansen R. , Banerjee T. , Park B. G. , Lodder J. C.
Published: May 2007

The tunnel momentum distribution in a (magnetic) tunnel junction is probed by analyzing the decay of the hot electrons in the Co metal anode after tunneling, using a three-terminal transistor structure in which the hot-electron attenuation is sensitive to the tunnel momentum distribution. Solid state amorphous Al2O3 barriers and the vacuum barrier of a scanning tunneling microscope are compared. For the former the attenuation length in nominally the same Co is strikingly larger (factor of 2), implying a more isotropic tunnel momentum distribution for Al2O3 barriers.
Cubic γ-Be3N2: A superhard semiconductor predicted from first principles
Authors: Gou Huiyang , Hou Li , Zhang Jingwu , Wang Zhibin , Gao Lihua , Gao Faming
Published: May 2007

The authors predict a superhard semiconductor phase of Be3N2 with cubic structure using first-principles calculations. The structural, mechanical, electronic, and optical properties of the Be3N2 have been investigated. Results indicate that the predicted Be3N2 phase is a wide gap semiconductor with a direct band gap of about 2.51eV. The calculated hardness of cubic γ-Be3N2 based on Mulliken overlap population analysis in first-principles technique approaches those of B4C and B6O. The higher mechanical property can be attributed to the existence of strong Be–N–Be covalent bond chains in the cubic structure. The obtained static dielectric constant of Be3N2 (4.6eV) is close to the spinel structure of Si3N4 (4.7eV).
Two dimensional diffraction enhanced imaging algorithm
Authors: Modregger Peter , Lübbert Daniel , Schäfer Peter , Köhler Rolf
Published: May 2007

Analyzer-based imaging provides refraction (phase) contrast due to angular filtering during reflection. By using two analyzer crystals with perpendicular diffraction planes (the so-called Bragg magnifier) the observable contrast is extended to two refraction directions. However, a nonlinear contribution of the two refraction directions to the images occurs and thus the standard diffraction-enhanced imaging algorithms are not suitable for image analysis in the case of the Bragg magnifier. Therefore, in this letter the authors introduce an algorithm (two dimensional diffraction enhanced imaging), which takes this nonlinear contribution into account and allows them to reconstruct the absorption, the horizontal, and the vertical refraction images.
High-speed thermal imaging of yttria-stabilized zirconia droplet impinging on substrate in plasma spraying
Authors: Shinoda Kentaro , Murakami Hideyuki , Kuroda Seiji , Oki Sachio , Takehara Kohsei , Etoh Takeharu Goji
Published: May 2007

The authors have developed an in situ monitoring system that captures the impacting phenomena of plasma-sprayed particles at 1×106frames∕s. The system clearly captured deformation and cooling processes of an yttria-stabilized zirconia droplet of 50μm in diameter impinging at 170m∕s on a smooth quartz glass substrate kept at room temperature. The images show that the liquid sheet jetting out sideways from the droplet detached from the substrate and kept on spreading without disintegration until its maximum extent. While the sheet was spreading, the center region of the flattened droplet cooled down much more rapidly.
Ballistic thermal conductance in a three-dimensional quantum wire modulated with stub structure
Authors: Peng Xiao-Fang , Chen Ke-Qiu , Zou B. S. , Zhang Yan
Published: May 2007

Ballistic thermal conductance in a three-dimensional quantum wire with a stub structure is presented under both stress-free and hard wall boundary conditions at low temperatures. A comparative analysis for two-dimensional and three-dimensional models is made. The results show that when stress-free boundary conditions are applied, the universal quantum thermal conductance can be observed regardless of the geometry details in the limit T→0, and the behavior of the thermal conductance is qualitatively similar to that calculated by two-dimensional model. However, when hard wall boundary conditions are applied, the thermal conductance displays different behaviors in both two-dimensional and three-dimensional models.
Enhanced tunability due to interfacial polarization in La0.7Sr0.3MnO3∕BaTiO3 multilayers
Authors: Wang C. C. , He M. , Yang F. , Wen J. , Liu G. Z. , Lu H. B.
Published: May 2007

Ba Ti O 3 single layer and La0.7Sr0.3MnO3∕BaTiO3 multilayer films were fabricated by laser molecular-beam epitaxy. The voltage tunability of these films was investigated systematically in the frequency ranging from 10kHzto1MHz. The results suggest that the sizable tunability arises from the interfacial polarization which can be strongly suppressed by applied dc biases. In multilayer films, remarkable enhancement in voltage tunability was observed, because the interfacial polarization was greatly enhanced by an interfacial polarization associated possibly with the Maxwell-Wagner relaxation. The authors’ results indicate that the voltage tunability in low frequency (⩽1MHz) has a dominating contribution from the interfacial polarization.
Electronic structures and bonding properties of chlorine-treated nitrogenated carbon nanotubes: X-ray absorption and scanning photoelectron microscopy studies
Authors: Ray S. C. , Pao C. W. , Tsai H. M. , Chiou J. W. , Pong W. F. , Chen C. W. , Tsai M.-H. , Papakonstantinou P. , Chen L. C. , Chen K. H. , Graham W. G.
Published: May 2007

The electronic and bonding properties of nitrogenated carbon nanotubes (N-CNTs) exposed to chlorine plasma were investigated using C and N K-edge x-ray absorption near-edge structure (XANES) and scanning photoelectron microscopy (SPEM). The C and N K-edge XANES spectra of chlorine-treated N-CNTs consistently reveal the formation of pyridinelike N-CNTs by the observation of 1s→π*(e2u) antibonding and 1s→π*(b2g) bonding states. The valence-band photoemission spectra obtained from SPEM images indicate that chlorination of the nanotubes enhances the C–N bonding. First-principles calculations of the partial densities of states in conjunction with C K-edge XANES data identify the presence of C–Cl bonding in chlorine treated N-CNTs.
Scanning Kelvin probe microscopy on organic field-effect transistors during gate bias stress
Authors: Mathijssen S. G. J. , Cölle M. , Mank A. J. G. , Kemerink M. , Bobbert P. A. , de Leeuw D. M.
Published: May 2007

The reliability of organic field-effect transistors is studied using both transport and scanning Kelvin probe microscopy measurements. A direct correlation between the current and potential of a p-type transistor is demonstrated. During gate bias stress, a decrease in current is observed, that is correlated with the increased curvature of the potential profile. After gate bias stress, the potential changes consistently in all operating regimes: the potential profile gets more convex, in accordance with the simultaneously observed shift in threshold voltage. The changes of the potential are attributed to positive immobile charges, which contribute to the potential, but not to the current.
Resonance acoustic-phonon spectroscopy for studying elasticity of ultrathin films
Authors: Ogi H. , Fujii M. , Nakamura N. , Shagawa T. , Hirao M.
Published: May 2007

Ultrahigh-frequency phonon resonances were excited in ultrathin films (∼5nm) by femtosecond light pulses, and their resonance frequencies were measured to determine the through-thickness elastic constants. The studied materials were Pt and Fe. The elastic stiffness increases with decreasing film thickness for both materials, whereas the normal strain showed opposite thickness behavior. Analysis of the wave propagation using the third-order elastic constants explained these trends.
Surface-induced anisotropy and multiple states in elongated magnetic nanoparticles
Authors: Leonov A. A. , Dragunov I. E. , Bogdanov A. N.
Published: May 2007

For ellipsoidal magnetic nanoparticles the values of surface-induced uniaxial anisotropy have been derived from an analytical model as functions of aspect ratios and particle sizes. The authors show that this specific anisotropy can stabilize multiple magnetic states in the system, suppress demagnetization effects, and prevent superparamagnetism. The calculated phase diagrams indicate the stability regions of different phases and the transition fields between them. By tuning sizes, geometry, and surface anisotropy of elongated particles a well-defined sequence of magnetic switching transitions can be realized in prescribed magnetic fields. This can be used in magnetic recording and spin electronic technologies.
Giant anisotropic magnetoresistance and magnetothermopower in cubic 3:4 uranium pnictides
Authors: Wiśniewski Piotr
Published: May 2007

Temperature dependence of the anisotropic magnetoresistance and magnetothermopower of cubic ferromagnets U3As4 and U3P4 was examined on bulk single-crystal samples, in the range from 4.2K to Curie points 198 and 138K, respectively. The anisotropic magnetoresistance exceeding 50% was observed, which is about twice as big as that of Permalloys. Moreover, it changes its magnitude and sign with temperature. Such an unusual magnetoresistance is accompanied by anisotropic magnetothermopower also strongly varying with temperature. Applicability of a two-current model to explain the observed phenomena is discussed, and a complementary mechanism of anisotropy induced by trigonal distortion of crystal lattice is proposed.
Giant dielectric response and relaxor behaviors induced by charge and defect ordering in Sr(Fe1∕2Nb1∕2)O3 ceramics
Authors: Liu Y. Y. , Chen X. M. , Liu X. Q. , Li L.
Published: May 2007

Dielectric spectra of Sr(Fe1∕2Nb1∕2)O3 ceramics were characterized in wide temperature (123–623K) and frequency (100Hz–1MHz) ranges. Two dielectric relaxations with strong frequency dispersion and following the Arrhenius law were detected in low and high temperature ranges, respectively, and between them there was a giant dielectric constant step. The high temperature relaxorlike dielectric peak could be almost completely removed by annealing in O2, and it should be assigned to be a defect ordering induced relaxor behavior, while the low temperature dielectric relaxation was proposed to stem from the electronic ferroelectricity. Moreover, it was speculated that the giant dielectric constant step resulted from the competing balance between the low and high temperature dielectric relaxations.
Cross-sectional observation of nanodomain dots formed in both congruent and stoichiometric LiTaO3 crystals
Authors: Daimon Yasuhiro , Cho Yasuo
Published: May 2007

Cross-sectional shapes of polarization reversal nanodomain dots, formed in both congruent and stoichiometric LiTaO3 single-crystal recording media, were studied using scanning nonlinear dielectric microscopy. It was confirmed that the thickness of the domain wall of the nanodomain formed in stoichiometric LiTaO3 is much smaller than that in congruent LiTaO3. The variation in the domain wall thickness was evaluated as a function of sample thickness and depth position. It was confirmed that the domain wall thickness at the bottom of the sample was thinner than that at the top surface of the sample.
Dispersive phase response in optical waveguide-resonator system
Authors: Choi Y.-S. , Davanço M. , Lee K. H. , Wang C.-F. , Mack J. , Blumenthal D. , Hu E. L.
Published: May 2007

The authors report on the dispersive phase response of light traversing a tapered optical fiber coupled to the whispering-gallery modes (WGMs) of GaAs microdisks with cavity Q factors of up to 3×105 at wavelengths of around 1.5μm. The group delay of the coupled light, that is, a derivative of the phase shift, becomes positive (+10ps) and then negative (−55ps) near the high-Q WGM resonances, as compared with a reference group delay without evanescent-wave coupling. The chromatic dispersion becomes as high as ±8ns∕nm near WGM wavelengths.
Investigation of twin boundary thickness and energy in CuAlNi shape memory alloy
Authors: Shilo D. , Mendelovich A. , Novák V.
Published: May 2007

The nanometer-scale thickness and energy of twin boundaries govern the martensitic twin structure and its dynamics, which are responsible for the actuation and superelasticity of shape memory alloys. In this letter the authors apply a method, which has been recently developed for investigating twin wall structures in ferroelectric crystals, on a shape memory alloy crystal. Fittings of simulated displacement fields to atomic force microscopy measurements allow them to extract the thickness of type-I twin boundaries in CuAlNi. Further, a relation between the twin boundary thickness and energy is developed and used for evaluating the twin boundary energy.
Absence of magnetic domain wall motion during magnetic field induced twin boundary motion in bulk magnetic shape memory alloys
Authors: Lai Y. W. , Scheerbaum N. , Hinz D. , Gutfleisch O. , Schäfer R. , Schultz L. , McCord J.
Published: May 2007

A detailed study of twin boundary motion in NiMnGa single crystals together with in situ magnetic domain observation is presented. Optical polarization microscopy in connection with a magneto-optical indicator film technique was used to investigate the reorganization of the magnetic domains during twin boundary motion over a wide magnetic field range. Images at different field strengths demonstrate that no magnetic domain wall motion within the twins takes place, even during the structural reorientation by twin boundary movement. This absence of interaction of magnetic and structural domains is different from currently proposed models, which assume domain wall movement under an external field.
High-intensity C-shaped nanoaperture vertical-cavity surface-emitting laser with controlled polarization
Authors: Rao Zhilong , Matteo Joseph A. , Hesselink Lambertus , Harris James S.
Published: May 2007

The authors designed and demonstrated a C-shaped nanoaperture (C aperture) vertical-cavity surface-emitting laser (VCSEL) with a maximum far-field power of 157μW coming from a 70nm C aperture. Simulation shows that the near-field full width at half maximum spot size at 30nm away from the C aperture is 94×108nm2 in X and Y directions. The authors estimate the peak near-field intensity from the C-aperture VCSEL to be as high as 19mW∕μm2. This high intensity and small spot size are promising for realizing near-field applications such as near-field imaging and ultradense near-field optical data storage.
Tunable thermal links
Authors: Chang C. W. , Okawa D. , Garcia H. , Yuzvinsky T. D. , Majumdar A. , Zettl A.
Published: May 2007

We demonstrate that the thermal conductance K of individual multiwall carbon nanotubes can be controllably and reversibly adjusted by sliding the outer shells of the tube with respect to the inner core in a telescopinglike manner. K shows an exponential dependence on the telescoping distance. Tunable nanoscale thermal links have immediate implications for nano- to macroscale thermal management, biosystems, and phononic information processing.