bluuebunny/crossref_metadata_2025 huggingface dataset:
The application of infrared spectroscopy to probe the surface morphology of alumina-supported palladium catalysts
Authors: Lear Timothy , Marshall Robert , Antonio Lopez-Sanchez J. , Jackson S. David , Klapötke Thomas M. , Bäumer Marcus , Rupprechter Günther , Freund Hans-Joachim , Lennon David
Published: October 2005

Five alumina-supported palladium catalysts have been prepared from a range of precursor compounds [palladium(II) nitrate, palladium(II) chloride, palladium(II) acetylacetonate, and tetraamminepalladium(II) tetraazidopalladate(II)] and at different metal loadings (1–7.3wt%). Collectively, this series of catalysts provides a range of metal particle sizes (1.2–8.5nm) that emphasize different morphological aspects of the palladium crystallites. The infrared spectra of chemisorbed CO applied under pulse-flow conditions reveal distinct groupings between metal crystallites dominated by low index planes and those that feature predominantly corner/edge atoms. Temperature-programmed infrared spectroscopy establishes that the linear CO band can be resolved into contributions from corner atoms and a combination of (111)∕(111) and (111)∕(100) particle edges. Propene hydrogenation has been used as a preliminary assessment of catalytic performance for the 1wt% loaded catalysts, with the relative inactivity of the catalyst prepared from palladium(II) chloride attributed to a diminished hydrogen supply due to decoration of edge sites by chlorine originating from the preparative process. It is anticipated that refinements linking the vibrational spectrum of a probe molecule with surface structure and accessible adsorption sites for such a versatile catalytic substrate provide a platform against which structure/reactivity relationships can be usefully developed.
Ab initio density-functional study of the bridging addition of acrylonitrile on the Si(100) surface
Authors: Cobian M. , Boureau G. , Hafner J. , Kresse G.
Published: October 2005

Acrylonitrile may react with the Si(100) surface in a number of ways. Fifteen different configurations have been identified. This study which complements an earlier study devoted to cycloadditions and bonds involving a single atom deals essentially with configurations involving cumulative double bonds. Factors affecting the relative stability of various mesomeric forms are shown to be the proximity to tetrahedral geometry and the compatibility of the dipole form with buckled structures. Tripods are shown to be a way to accommodate a priori unfavorable structures.
Surface acoustic wave investigations of the metal-to-insulator transition of V2O3 thin films on lithium niobate
Authors: Müller C. , Nateprov A. A. , Obermeier G. , Klemm M. , Tidecks R. , Wixforth A. , Horn S.
Published: October 2005

Thin V2O3 films were deposited on a piezoelectric substrate by electron-beam evaporation. Surface acoustic waves were generated by interdigital transducers. The attenuation and sound velocity were investigated from 260 to 10 K, providing an insight into the temperature-dependent electrical, dielectrical, and elastic properties of V2O3 at the metal-to-insulator transition.
Microstructural, ferroelectric, and dielectric properties of Bi3.15Nd0.85Ti3O12 ceramics
Authors: Qi Y. J. , Xiao X. , Lu C. J. , Mao X. Y. , Chen X. B.
Published: October 2005

Dense Bi3.15Nd0.85Ti3O12 (BNdT) ceramics of a layered perovskite structure were sintered at 1100 °C by solid state reaction. Ferroelectric domains were probably observed in plate-shaped grains. The BNdT ceramics exhibit saturated ferroelectric hysteresis loops with a remanent polarization (2Pr) of 45μC∕cm2 and a coercive field of 67.6kV∕cm. The dielectric constant and dissipation factor of the ceramics at 100 kHz are 221 and 0.0064, respectively. A broad dielectric peak was observed around 408 °C, and it might come from the oxygen-vacancy-related dielectric relaxation. The leakage current density of the ceramics is less than 7.5×10−7A∕cm2 under an applied field below 239kV∕cm. The BNdT ceramics show Schottky emission behavior under low electric field below 75kV∕cm.
A diffusion quantum Monte Carlo study on the lowest singlet and triplet electronic states of BN molecule
Authors: Lu Shih-I
Published: October 2005

Ab initio calculation of both the lowest singlet and triplet electronic states of BN has been performed by the fixed-node Ornstein-Uhlenbeck diffusion quantum Monte Carlo method with the floating spherical Gaussian orbitals and spherical Gaussian geminals. The Monte Carlo calculation gives equilibrium bond lengths and equilibrium harmonic frequencies of 1.3317(7)Å and 1529(7)cm−1, respectively, for the lowest triplet state and 1.2751(7)Å and 1709(8)cm−1, respectively, for the lowest singlet state. Also, the Monte Carlo calculation reports an energy separation of 178(83)cm−1 between the two electronic states and recommends the ground state is the lowest triplet state.
Electronic transport in nanostructured films of La0.67Sr0.33MnO3
Authors: Ghosh Barnali , Kar Sohini , Brar Loveleen K. , Raychaudhuri A. K.
Published: October 2005

In this paper we report electronic transport in nanostructured films of the rare-earth manganite La0.67Sr0.33MnO3. The films were grown by chemical solution deposition. The films show a resistivity peak in the temperature range of 250–265 K and have average grain size (∼50–60nm). The grain size can be controlled by postdeposition annealing. The films also show a rise in resistivity at low temperature (T<40K), reasonable low-field magnetoresistance up to 200 K, and nonlinear conductivity that shows up below 30 K. We ascribe these behaviors to the large number of natural grain boundaries that are present in these nanostructured films. We were also able to map the inhomogeneous local electronic properties arising from these grain boundaries using a variable-temperature scanning-tunneling microscope. We found that as the temperature is lowered, due to differences between the electronic properties of the grains and grain boundaries, the transport becomes more inhomogeneous. The nonlinear conduction as well as the low-field magnetoresistance in these nanostructured films closely resemble those in films with artificial grain boundaries.
Dispersion in microchannels with temporal temperature variations
Authors: Tripathi Anubhav , Bozkurt Ozgur , Chauhan Anuj
Published: October 2005

While amplifying DNA strands in a microfluidic device, the sample is subjected to cyclic changes in temperature. We investigate the dispersion of molecules in a microchannel, as these undergo a contraction–expansion flow that is driven by temporally changing temperatures. In this paper, the method of multiple time scales with regular expansions is used to obtain the effective dispersivity and the analytical results are compared with computational fluid dynamics simulations. Due to the thermal expansion of the carrier fluid, the cyclic temperature variations lead to both axial and lateral velocities. These periodic velocity profiles lead to an increase in axial dispersion. The dispersion coefficient increases as the square of the channel position from the center of the microchannel. Due to the quadratic variation of the dispersion coefficient in the axial direction, the concentration profile is non-Gaussian and a complex function of frequency and magnitude of the temporal oscillations and the dimensions of the microchannel. Analytical expressions for dispersion coefficient are derived for cyclic profiles of any shape; and results are computed and discussed for particular cases of cosine and step-function temperature cycles. The value for effective dispersion is also evaluated for a sample temperature profile that occurs in the microfluidic DNA amplification processes. The dispersion coefficient for step changes in temperature is found to be substantially larger than that for the case of sinusoidal temperature changes at low frequencies. We believe that the results of this study will enhance our understanding of transport in microscale systems that are subjected to temporally changing temperatures, and likely lead to technological advances in diverse areas relevant to microreactor design and DNA amplification.
Deep-level defects introduced by 1 MeV electron radiation in AlInGaP for multijunction space solar cells
Authors: Lee H. S. , Yamaguchi M. , Ekins-Daukes N. J. , Khan A. , Takamoto T. , Agui T. , Kamimura K. , Kaneiwa M. , Imaizumi M. , Ohshima T. , Itoh H.
Published: October 2005

Presented in this paper are 1 MeV electron irradiation effects on wide-band-gap (1.97 eV) (Al0.08Ga0.92)0.52In0.48P diodes and solar cells. The carrier removal rate estimated in p-AlInGaP with electron fluence is about 1cm−1, which is lower than that in InP and GaAs. From high-temperature deep-level transient spectroscopy measurements, a deep-level defect center such as majority-carrier (hole) trap H2 (Eν+0.90±0.05eV) was observed. The changes in carrier concentrations (Δp) and trap densities as a function of electron fluence were compared, and as a result the total introduction rate, 0.39cm−1, of majority-carrier trap centers (H1 and H2) is different from the carrier removal rate, 1cm−1, in p-AlInGaP. From the minority-carrier injection annealing (100mA∕cm2), the annealing activation energy of H2 defect is ΔE=0.60eV, which is likely to be associated with a vacancy-phosphorus Frenkel pair (Vp-Pi). The recovery of defect concentration and carrier concentration in the irradiated p-AlInGaP by injection relates that a deep-level defect H2 acts as a recombination center as well as compensator center.
Optical-geometrical effects on the photoluminescence spectra of Si nanocrystals embedded in SiO2
Authors: Ferre R. , Garrido B. , Pellegrino P. , Perálvarez M. , García C. , Moreno J. A. , Carreras J. , Morante J. R.
Published: October 2005

We demonstrate that thickness, optical constants, and details of the multilayer stack, together with the detection setting, strongly influence the photoluminescence spectra of Si nanocrystals embedded in SiO2. Due to multiple reflections of the visible light against the opaque silicon substrate, an interference pattern is built inside the oxide layer, which is responsible for the modifications in the measured spectra. This interference effect is complicated by the depth dependence of (i) the intensity of the excitation laser and (ii) the concentration of the emitting nanocrystals. These variations can give rise to apparent features in the recorded spectra, such as peak shifts, satellite shoulders, and even splittings, which can be mistaken as intrinsic material features. Thus, they can give rise to an erroneous attribution of optical bands or estimate of the average particle size, while they are only optical-geometrical artifacts. We have analyzed these effects as a function of material composition (Si excess fraction) and thickness, and also evaluated how the geometry of the detection setup affects the measurements. To correct the experimental photoluminescence spectra and extract the true spectral shape of the emission from Si nanocrystals, we have developed an algorithm based on a modulation function, which depends on both the multilayer sequence and the experimental configuration. This procedure can be easily extended to other heterogeneous systems.
Axial Young’s modulus prediction of single-walled carbon nanotube arrays with diameters from nanometer to meter scales
Authors: Sun C. H. , Li F. , Cheng H. M. , Lu G. Q.
Published: October 2005

Based on a self-similar array model, we systematically investigated the axial Young’s modulus (Yaxis) of single-walled carbon nanotube (SWNT) arrays with diameters from nanometer to meter scales by an analytical approach. The results show that the Yaxis of SWNT arrays decreases dramatically with the increases of their hierarchy number (s) and is not sensitive to the specific size and constitution when s is the same, and the specific Young’s modulus Yaxiss is independent of the packing configuration of SWNTs. Our calculations also show that the Yaxis of SWNT arrays with diameters of several micrometers is close to that of commercial high performance carbon fibers (CFs), but the Yaxiss of SWNT arrays is much better than that of high performance CFs.
Fast multielement phase-controlled photoacoustic imaging based on limited-field-filtered back-projection algorithm
Authors: Yang Diwu , Xing Da , Gu Huaimin , Tan Yi , Zeng Lvming
Published: October 2005

In this paper, the multielement phase-controlled technique and the limited-field -filtered back-projection algorithm are used to investigate the two-dimensional fast noninvasive photoacoustic imaging. By the use of the former to collect photoacoustic signals, which are of high signal-to-noise ratio, one needs not to average the data and can acquire them in less than 5s. The later can greatly improve the lateral resolution of the multielement linear transducer array imaging system from 1.5mmto0.24mm. This method and system can provide a fast and reliable approach to photoacoustic imaging that could be applied to noninvasive imaging and clinic diagnosis.
Photonic crystal templates for organic solid-state lasers
Authors: Yokoyama Shiyoshi , Nakahama Tatsuo , Mashiko Shinro , Nakao Masashi , Yamada Motohiro , Nishio Kazuyuki , Masuda Hideki
Published: October 2005

We report a solid-state laser composed of an Al2O3 photonic crystal and an organic gain medium. The photonic crystal was fabricated through the nanoimprinting technique and an electrochemical process, which enables transfer of a periodic pattern to the photonic crystal and control of its stop band. When the photonic crystal was infiltrated with the polymer medium containing laser dye, we obtained laser emission under optical excitation. The minimum laser threshold was about 2.4nJ∕pulse, where the linewidth of the laser emission was as narrow as 0.09 nm. We explain the laser action based on the band edge effect, while the precise control of the laser mode and oscillation wavelength depends on control of the stop band and small changes in the refractive index of the gain medium.
Local-strain effects in Si∕SiGe∕Si islands on oxide
Authors: Chiang K. N. , Chang C. H. , Peng C. T.
Published: October 2005

The tensile-strained Si, based on the misfit between Si and SiGe gives high speed and high drive current to the metal-oxide-silicon field effect transistors. In order to achieve the total system minimum energy, the island edge, within some characteristic length, bends upwards giving rise to a distorted lattice, as simulated by the finite element method. The finding indicates that the conventional strain partition rule of Si∕SiGe∕Si layers used for a large island size (>10μm) is not adequate for a small island size (<200nm) due to the significant local-strain effect of the edge lattice distortion. For a small island size, the bending from the edge can significantly affect the strain on the surface of the top Si layer, and a compressive strain or reduced tensile strain occurs at the center of the top Si layer, while the conventional strain partition rule predicts a uniform tensile strain on the top Si layer for any size of Si∕SiGe∕Si islands.
Stokes and anti-Stokes photoluminescence towards five different Inx(Al0.17Ga0.83)1−xAs∕Al0.17Ga0.83As quantum wells
Authors: Machida S. , Tadakuma T. , Satake A. , Fujiwara K. , Folkenberg J. R. , Hvam J. M.
Published: October 2005

Stokes and anti-Stokes photoluminescence (AS-PL) has been investigated in a step-graded Inx(Al0.17Ga0.83)1−xAs∕Al0.17Ga0.83As quantum-well (QW) heterostructure consisting of five QWs with different x values. Stokes PL spectra of this sample show a significant difference in PL intensity between the wells under indirect excitation conditions due to the existence of competitive resonant and nonresonant capture processes, while they exhibit a rather uniform PL intensity distribution under direct excitation. When the excitation wavelength is tuned to 810 nm for AS-PL detection, it is transparent to the five QWs and thus the photoabsorption can only occur in the GaAs (rear buffer and front cap) layers. It is found that the AS-PL spectra show a similar intensity distribution to the one observed under the indirect excitation. This result means that the AS-PL intensity distribution of the QWs is basically determined by the competitive capture of photoexcited carriers through the thick barriers, generated far from the five wells due to the nonlinear excitation processes in GaAs.
Pb
Ti
O
3
content dependence of crystal structure and electrical properties of (100)-/(001)-oriented epitaxial Pb(Mg1∕3Nb2∕3)O3-PbTiO3 films grown by metalorganic chemical vapor deposition
Authors: Yokoyama Shintaro , Okamoto Satoshi , Okamoto Shoji , Funakubo Hiroshi , Matsuda Hirofumi , Iijima Takashi , Saito Keisuke , Okino Hirotake , Yamamoto Takashi
Published: October 2005

Pb Ti O 3 content (x) dependencies of the crystal structure, and dielectric and piezoelectric properties were investigated for epitaxial (1−x)Pb(Mg1∕3Nb2∕3)O3-xPbTiO3[PMN-PT] films, 2–3μm in thickness, grown on (100)cSrRuO3∕∕(100)SrTiO3 substrates. (100)-/(001)-oriented epitaxial films with the x ranging from 0 to 1 were successfully grown at 650 °C by metalorganic chemical vapor deposition irrespective of x. The constituent phase changed from a rhombohedral (pseudocubic) single phase, a mixture phase of rhombohedral (pseudocubic) and tetragonal phases, and a tetragonal single phase with increasing x. The film with the mixture phase was formed when x=0.40–0.55, which was different from that reported for single crystals. The dependence of relative dielectric constant on x was maximum at the mixed phase region, which was similar to the case of a PMN-PT sintered body, but the magnitude of these dependencies was relatively lower than the reported one for the single crystals and sintered bodies. The longitudinal piezoelectric coefficient (d33,f) and the transverse coefficient (e31,f) of 100-120pm∕V and ∼−11.0C∕m2 were calculated, respectively, for the film with x=0.39, which corresponds to a larger x edge of the rhombohedral (pseudocubic) region.
Observation of propagation properties in polymeric optical waveguides by polarized near-field scanning optical microscopy
Authors: Mitsui Tadashi
Published: October 2005

A polarized guide-collection-mode near-field scanning optical microscopy (NSOM) technique was used to characterize clearly the periodic intensity modulation and multimode propagation within a polymeric optical waveguide by selecting the polarization component. The polarized NSOM technique revealed that the periodic intensity modulation along the waveguide axis has a polarization property whose electric vector is perpendicular to the waveguide axis, and that the period of intensity modulation nearly equals the wavelength inside the waveguide. The intensity modulation originates from a standing wave caused by a resonator formed between the entrance and exit facets.
Elasticity of planar fiber networks
Authors: Wu X.-F. , Dzenis Y. A.
Published: October 2005

A micromechanics model is proposed for the elasticity of planar fiber networks (FNs). The FN is created by random deposition of linearly elastic straight rods within a region. The rods are bonded rigidly at contacts. Under external in-plane loading, the FN deformation consists of fiber bending, elongation, and contraction. An effective constitutive relation for fiber network is developed by averaging the strain energy dissipated by all possible fiber deformations in all directions. Numerical calculations are performed to analyze the effects of fiber aspect ratio and fiber concentration on the effective stiffness of the planar random FN. Finite element analysis (FEA) is performed and compared with the theoretical predictions of the effective FN moduli at several fiber concentrations. FEA results are in good agreement with theoretical predictions. The present model can be used for the prediction of mechanical properties, scaling analysis, and optimization of fiber assemblies.
Density and production of NH and NH2 in an Ar–NH3 expanding plasma jet
Authors: van den Oever P. J. , van Helden J. H. , Lamers C. C. H. , Engeln R. , Schram D. C. , van de Sanden M. C. M. , Kessels W. M. M.
Published: October 2005

The densities of NH and NH2 radicals in an Ar–NH3 plasma jet created by the expanding thermal plasma source were investigated for various source-operating conditions such as plasma current and NH3 flow. The radicals were measured by cavity ringdown absorption spectroscopy using the (0,0) band of the AΠ3←XΣ−3 transition for NH and the (0,9,0)-(0,0,0) band of the ÃA12←X̃B12 transition for NH2. For NH, a kinetic gas temperature and rotational temperature of 1750±100 and 1920±100K were found, respectively. The measurements revealed typical densities of 2.5×1012cm−3 for the NH radical and 3.5×1012cm−3 for the NH2 radical. From the combination of the data with ion density and NH3 consumption measurements in the plasma as well as from a simple one-dimensional plug down model, the key production reactions for NH and NH2 are discussed.
Effect of electric/magnetic field on pinned/biased moments at the interfaces of magnetic superlattices
Authors: Padhan P. , Prellier W.
Published: October 2005

We have observed the pinned/biased moments in the superlattices consisting of a ferromagnetic (FM) SrRuO3 (SRO) and an antiferromagnetic (AFM) SrMnO3 (SMO) bilayer. The alternate stacking of SRO and SMO leading to a low-field positive magnetoresistance with enhanced hysteretic field-dependent magnetoresistance under the application of the out-of-plane magnetic field. We attribute these effects to the observed biased/pinned magnetic moments in the SRO layer in the vicinity of the interfaces. In addition, the biased/pinned moments can be oriented under the application of either the out-of-plane magnetic field or a combination of out-of-plane magnetic field and in-plane electric field. These results will bring new insights in the understanding of the coupling at the AFM/FM interface that can be useful for creating new exotic phenomena at the interfaces of the multilayer.
Temperature dependence of magnetization in arrays of submicrometer Fe disks
Authors: Takagaki Y. , Herfort J. , Ploog K. H.
Published: October 2005

We investigate the magnetization in the arrays of submicrometer-size disks fabricated from an epitaxial Fe layer grown on GaAs(001). The Fe disks having a layer thickness of 20nm undergo a transition between multiple and single magnetic domains when their diameter is about 100nm. Remarkable temperature dependence is found in the characteristics of the magnetization. (1) The saturation magnetization increases with decreasing temperature. While the low-temperature increase is more pronounced for smaller disk diameters, it is independent of the magnetic-domain state in the disks. (2) Magnetic hysteresis exhibits two-component-like behavior at low temperatures for ultrasmall disks. The additional component that emerges with lowering temperature gives rise to slow saturation of the magnetization, and is possibly responsible for the low-temperature increase of the saturation magnetization.
Dielectric properties and Maxwell-Wagner relaxation of compounds ACu3Ti4O12 (A=Ca,Bi2∕3,Y2∕3,La2∕3)
Authors: Liu Jianjun , Duan Chun-gang , Mei W. N. , Smith R. W. , Hardy J. R.
Published: October 2005

We have studied the frequency and temperature dependences of permittivity and impedance of the compounds ACu3Ti4O12 (A=Ca,Bi2∕3,Y2∕3,La2∕3) in the ranges of 10−1–106Hz and −150–200°C. All compounds investigated display similar dielectric properties. Specifically, they all have a Debye-like relaxation and their dielectric constants are independent of frequency and temperature over a wide range. They all have two electrical responses in impedance formalism, indicating that there are two distinct contributions. We attribute them to grains and grain boundaries in the ceramic samples and explain the dielectric behaviors by Maxwell-Wagner relaxation arising at the interfaces between grains and their boundaries.
Intersubband photoconductivity at 1.6μm using a strain-compensated AlN∕GaN superlattice
Authors: Baumann E. , Giorgetta F. R. , Hofstetter D. , Lu H. , Chen X. , Schaff W. J. , Eastman L. F. , Golka S. , Schrenk W. , Strasser G.
Published: October 2005

We report on intersubband absorption, photovoltaic, and photoconductive detection of near-infrared radiation in regular AlN∕GaN superlattice structures. Photoconductive detection was achieved up to temperatures of 120 K. Simulation of the transition energies using a self-consistent Schrödinger-Poisson equation solver for our specific well width is in good agreement with the measurements. For a well width of 17 Å, the transition energy between ground state and first excited state in the GaN well is around 6300cm−1 which corresponds to 1.6μm.
Detection of deuterium and hydrogen using laser-induced helium gas plasma at atmospheric pressure
Authors: Kurniawan Koo Hendrik , Lie Tjung Jie , Suliyanti Maria Margaretha , Hedwig Rinda , Abdulmadjid Syahrun Nur , Pardede Marincan , Idris Nasrullah , Kobayashi Takao , Kusumoto Yoshihumi , Kagawa Kiichiro , Tjia May On
Published: October 2005

An experimental study on gas analysis by means of laser-induced breakdown spectroscopy was conducted using a Nd-yttrium aluminum garnet laser (1,064 nm, 120 mJ, 8 ns) and helium host gas at atmospheric pressure on a sample of mixed water (H2O) and heavy water (D2O) in vapor form. It was shown that completely resolved hydrogen (Hα) and deuterium (Dα) emission lines that are separated by only 0.179 nm could be obtained at a properly delayed detection time when the charged particles responsible for the strong Stark broadening effect in the plasma have mostly disappeared. It is argued that the helium metastable excited state plays an important role in the hydrogen excitation process.
Readout of single spins via Fano resonances in quantum point contacts
Authors: Mourokh L. G. , Puller V. I. , Smirnov A. Yu. , Bird J. P.
Published: October 2005

We examine the feasibility of performing single-spin readout in a small quantum dot (SQD), using a quantum point contact (QPC) that is coupled to it by a larger dot with a quasicontinuous spectrum. When the Fermi energy in the QPC is approximately equal to one of the discrete levels of the SQD, a Fano resonance is observed in its conductance. We propose a procedure that uses such Fano peaks to determine the spin projection of a single electron in the SQD, in the presence of an external magnetic field that causes Zeeman splitting of its levels. We also show that this structure can exhibit Rabi oscillations when subject to microwave irradiation.
Terahertz radiation from nonstoichiometric CuInSe2 films excited by femtosecond laser pulses
Authors: Adomavičius R. , Krotkus A. , Kois J. , Bereznev S. , Mellikov E.
Published: October 2005

We report on the observation of efficient terahertz radiation from the surface of CuInSe2 excited by femtosecond laser pulses. Terahertz radiation emitted by polycrystalline CuInSe2 layers manufactured by using electrodeposition technology was as powerful as the signals radiated by single-crystalline semiconductor surfaces. It has been found that terahertz radiation efficiency is critically dependent on the stoichiometry of the CuInSe2 layers. The results of a double-pulse excitation experiment have indicated that terahertz radiation from the photoexcited surfaces of CuInSe2 samples was caused by the presence of a built-in electrical field at those surfaces.
Experimental observation of attractive and repulsive thermal forces on microcantilevers
Authors: Gotsmann B. , Dürig U.
Published: October 2005

We report measurements of thermal forces acting on a microcantilever near a substrate surface in air. In magnitude and direction, the observed force depends on the temperatures of substrate and cantilever, which were varied independently. The data are explained by considering interface scattering at the substrate surface as expressed by an accommodation coefficient of less than unity. The observed forces effectively act in the direction of the thermal gradient—opposite to thermophoresis of free particles suspended in a gas. The observation thus exhibits similarities with the so-called negative thermophoresis.
p
type doping of zinc oxide by arsenic ion implantation
Authors: Braunstein G. , Muraviev A. , Saxena H. , Dhere N. , Richter V. , Kalish R.
Published: October 2005

p type doping of polycrystalline ZnO thin films, by implantation of arsenic ions, is demonstrated. The approach consisted of carrying out the implantations at liquid-nitrogen temperature (∼−196°C), followed by a rapid in situ heating of the sample, at 560°C for 10min, and ex situ annealing at 900°C for 45min in flowing oxygen. p type conductivity with a hole concentration of 2.5×1013cm−2 was obtained using this approach, following implantation of 150keV 5×1014As∕cm2. A conventional room-temperature implantation of 1×1015As∕cm2, followed by the same ex situ annealing, resulted in n type conductivity with a carrier concentration of 1.7×1012cm−2.
Enhanced deep ultraviolet luminescence from AlGaN quantum wells grown in the three-dimensional mode
Authors: Borisov B. , Nikishin S. , Kuryatkov V. , Temkin H.
Published: October 2005

We report a significant improvement in the room temperature cathodoluminescence efficiency of AlGaN quantum wells when the three-dimensional growth mode is induced by reduced flux of ammonia. We interpret this observation in terms of formation of quantum dots of AlGaN in Al0.45Ga0.55N wells. Reflection high electron diffraction images and detailed measurements of the cathodoluminescence intensity, linewidth, and wavelength as a function of growth conditions are consistent with the presence of quantum dots.
Topological defects and the Staebler-Wronski effect in hydrogenated amorphous silicon
Authors: Du Mao-Hua , Zhang S. B.
Published: October 2005

We propose that the light-induced formation of topological defects may be the origin of the Staebler-Wronski effect in hydrogenated amorphous silicon. Such defect is characterized by a five- and seven-membered ring pair and two dangling bonds, which can trap mobile H to form a 2H metastable complex. This model shows that the photogeneration of the dangling bonds is the result of the topological transformations, whereas the role of the H is to move the photogenerated dangling bonds away from where they were generated.
Phloem hydrostatic pressure relates to solute loading rate: a direct test of the Münch hypothesis
Authors: Gould Nick , Thorpe Michael R. , Koroleva Olga , Minchin Peter E. H.
Published: October 2005

According to the Münch hypothesis, a flow of solution through the sieve tubes is driven by a hydrostatic pressure difference between the source (or collection) phloem and the sink (or release) phloem. A high hydrostatic pressure is maintained in the collection phloem by the active uptake of sugar and other solutes, with a concomitant inflow of water. A lower pressure is maintained in the release phloem through solute unloading. In this work we directly test the role of solute uptake in creating the hydrostatic pressure associated with phloem flow. Solute loading into the phloem of mature leaves of barley and sow thistle was reduced by replacing the air supply with nitrogen gas. Hydrostatic pressure in adjacent sieve elements was measured with a sieve-element pressure probe, a cell pressure probe glued to the exuding stylet of aphids that had been feeding from the phloem. Sieve element sap was sampled by aphid stylectomy; sap osmotic pressure was determined by picolitre osmometry and its sugar concentration by enzyme-linked fluorescence assays. Samples were taken with a time resolution of ~2–3 min. In accordance with Münch’s proposal a drop in osmotic and hydrostatic pressure in the source phloem following treatment of the source leaf with N2 was observed. A decrease in sugar concentration was the major contributor to the change in osmotic pressure. By observing these variables at a time resolution of minutes we have direct observation of the predictions of Münch.
The importance of nitrate in ameliorating the effects of ammonium and urea nutrition on plant development: the relationships with free polyamines and plant proline contents
Authors: Houdusse Fabrice , Zamarreño Angel M. , Garnica Maria , García-Mina Josemaria
Published: October 2005

In order to investigate the possible involvement of free polyamines and proline in the mechanism underlying the action of nitrate in correcting the negative effects associated with ammonium and urea nutrition in certain plant species, we studied plant contents of free polyamines and proline associated with nitrogen nutrition involving different nitrogen forms (nitrate, ammonium, urea) in two plant species, wheat and pepper. The results showed that ammonium nutrition and, to a lesser extent, urea nutrition were associated with significant increases in plant putrescine content that were well correlated with reductions in plant growth. These negative effects of ammonium and urea nutrition were corrected by the presence of nitrate in the nutrient solution; the presence of nitrate was also related to a significant decrease in the plant putrescine content. These results are compatible with a specific effect of nitrate reducing ammonium accumulation through the improvement of ammonium assimilation. As for the plant proline content, in pepper a slight increase in this parameter was associated with ammonium and urea nutrition, but it was also decreased by the presence of nitrate in the nutrient solution. These changes, however, were not so clearly related to the variations in plant growth as in the case of putrescine content. These results are compatible with the hypothesis that putrescine biosynthesis might be related to proline degradation by a specific pathway related to ammonium detoxification.
Salinity and the growth of non-halophytic grass leaves: the role of mineral nutrient distribution
Authors: Hu Yuncai , Fricke Wieland , Schmidhalter Urs
Published: October 2005

Salinity is increasingly limiting the production of graminaceous crops constituting the main sources of staple food (rice, wheat, barley, maize and sorghum), primarily through reductions in the expansion and photosynthetic yield of the leaves. In the present review, we summarise current knowledge of the characteristics of the spatial distribution patterns of the mineral elements along the growing grass leaf and of the impact of salinity on these patterns. Although mineral nutrients have a wide range of functions in plant tissues, their functions may differ between growing and non-growing parts of the grass leaf. To identify the physiological processes by which salinity affects leaf elongation in non-halophytic grasses, patterns of mineral nutrient deposition related to developmental and anatomical gradients along the growing grass leaf are discussed. The hypothesis that a causal link exists between ion deficiency and / or toxicity and the inhibition of leaf growth of grasses in a saline environment is tested.
Short-term storage of carbohydrate in stem tissue of apple (Malus domestica), a woody perennial: evidence for involvement of the apoplast
Authors: McQueen Joanna C. , Minchin Peter E. H. , Thorpe Michael R. , Silvester Warwick B.
Published: October 2005

This work investigates the pathway and mechanism for lateral retrieval of carbohydrate into the transport phloem of apple stems (Malus domestica Borkh.). A heat exchanger was set up on the stem, allowing rapid chilling and subsequent re-warming of stem segments while the time course of axial transport of 11C-labelled photoassimilate was measured at a position ∼65 mm downstream of the heat exchanger. Whenever axial transport was blocked by a sudden chill at the heat exchanger, transport 65 mm downstream from the blockage immediately slowed but did not stop, showing that there was retrieval of solutes into the pathway (buffering), within that 65 mm of stem, to help maintain the axial flow. Use of PCMBS, an inhibitor of sugar transporters, showed that the buffering included retrieval of sugar from the apoplast. We concluded that in apple, apoplastic sugar in stem tissue can buffer phloem transport during short-term changes in supply and demand for carbohydrates. Buffering was stronger when mobile reserves in the stem were higher, for example late in the photoperiod, or if carbohydrate demand in the terminal sink was increased. We also suggest that the concentration of sugars in the apoplast is a regulator of carbohydrate storage and re-mobilisation.
Osmotic stress changes carbohydrate partitioning and fructose-2,6-bisphosphate metabolism in barley leaves
Authors: Villadsen Dorthe , Rung Jesper Henrik , Nielsen Tom Hamborg
Published: October 2005

Carbohydrate metabolism was investigated in barley leaves subjected to drought or osmotic stress induced by sorbitol incubation. Both drought and osmotic stress resulted in accumulation of hexoses, depletion of sucrose and starch, and 5–10-fold increase in the level of the regulatory metabolite fructose-2,6-bisphosphate (Fru-2,6-P2). These changes were paralleled by an increased activity ratio of fructose-6-phosphate,2-kinase / fructose-2,6-bisphosphatase (F2KP). The drought-induced changes in carbohydrate content and Fru-2,6-P2 metabolism were reversed upon re-watering. This reveals a reversible mechanism for modification of the F2KP enzyme activity. This suggests that F2KP might be involved in altering carbohydrate metabolism during osmotic stress. However, labelling with [14C]-CO2 showed that sucrose synthesis was not inhibited, despite the increased Fru-2,6-P2 levels, and demonstrated that increased flux into the hexose pools probably derived from sucrose hydrolysis. Similar effects of osmotic stress were observed in leaf sections incubated in the dark, showing that the changes did not result from altered rates of photosynthesis. Metabolism of [14C]-sucrose in the dark also revealed increased flux into hexoses and reduced flux into starch in response to osmotic stress. The activities of a range of enzymes catalysing reactions of carbohydrate metabolism in general showed only a marginal decrease during osmotic stress. Therefore, the observed changes in metabolic flux do not rely on a change in the activity of the analysed enzymes. Fructose-2,6-bisphosphate metabolism responds strongly to drought stress and this response involves modification of the F2KP activity. However, the data also suggests that the sugar accumulation observed during osmotic stress is mainly regulated by another, as yet unidentified mechanism.
How does temperature affect C and N allocation to the seeds during the seed-filling period in pea? Effect on seed nitrogen concentration
Authors: Larmure Annabelle , Salon Christophe , Munier-Jolain Nathalie G.
Published: October 2005

The effect of moderate temperature on seed N concentration during the seed-filling period was evaluated in pea (Pisum sativum L.) kept in growth cabinets and the relation between plant assimilate availability and the variation of seed N concentration with temperature was investigated. Seed N concentration of pea was significantly lowered when temperature during the seed-filling period decreased from a day / night temperature of 25 / 20°C to 15 / 10°C. Our results demonstrate that during the seed-filling period mechanisms linked with assimilate availability can modify seed N accumulation rate and / or seed-filling duration between 25 / 20°C and 15 / 10°C. At the lower temperature (15 / 10°C), an increased C availability resulting from an enhanced carbon fixation per degree-day allowed new competing vegetative sinks to grow as pea is an indeterminate plant. Consequently N availability to filling seeds was reduced. Because the rate of seed N accumulation per degree-day mainly depends on N availability to filling seeds, the rate of seed N accumulation was lower at the low temperature of our study (15 / 10°C) than at 25 / 20°C while seed growth rate per degree-day remains unaffected, consequently seed N concentration was reduced. Concomitantly, the increased C availability at the lower temperature prolonged the duration of the seed-filling period.
Induced conformational changes upon Cd
2+
binding at photosynthetic reaction centers
Authors: Ishikita Hiroshi , Knapp Ernst-Walter
Published: October 2005

Cd
2+
binding at the bacterial photosynthetic reaction center (bRC) from
Rhodobacter sphaeroides
is known to inhibit proton transfer (PT) from bulk solvent to the secondary quinone Q
B
. To elucidate this mechanism, we calculated the pK
a
for residues along the water channels connecting Q
B
with the stromal side based on the crystal structures of WT-bRC and Cd
2+
-bound bRC. Upon Cd
2+
binding, we observed the release of two protons from His-H126/128 at the Cd
2+
binding site and significant pK
a
shifts for residues along the PT pathways. Remarkably, Asp-L213 near Q
B
, which is proposed to play a significant role in PT, resulted in a decrease in pK
a
upon Cd
2+
binding. The direct electrostatic influence of the Cd
2+
-positive charge on these pK
a
shifts was small. Instead, conformational changes of amino acid side chains induced electrostatically by Cd
2+
binding were the main mechanism for these pK
a
shifts. The long-range electrostatic influence over ≈12 Å between Cd
2+
and Asp-L213 is likely to originate from a set of Cd
2+
-induced successive reorientations of side chains (Asp-H124, His-H126, His-H128, Asp-H170, Glu-H173, Asp-M17, and Asp-L210), which propagate along the PT pathways as a “domino” effect.
Degradation of the membrane-localized virulence activator TcpP by the YaeL protease in
Vibrio cholerae
Authors: Matson Jyl S. , DiRita Victor J.
Published: October 2005

A common mechanism inhibiting the activity of transcription factors is their sequestration to the membrane until they are needed, at which point they are released from the membrane by proteolysis. Acting in contrast to this inhibition mechanism are virulence regulators of
Vibrio cholerae
, the ToxR and TcpP proteins, which are localized to the inner membrane of the cell, where they bind promoter DNA and activate gene expression. TcpP is rapidly degraded in the absence of another protein, TcpH. We used a genetic screen to identify regulators of TcpP stability and identified the YaeL membrane-localized zinc metalloprotease as responsible for degrading TcpP in the absence of TcpH. In
Escherichia coli
, DegS and YaeL cooperate to degrade RseA, an antisigma factor that sequesters σ
E
to the inner membrane, thereby inhibiting the activity of σ
E
. When
yaeL
was disrupted in a
V. cholerae tcpH
mutant, we observed accumulation of a lower molecular weight species of TcpP. This observation is consistent with TcpP being partially degraded in the absence of YaeL. A mutant lacking both DegS and YaeL continued to accumulate the TcpP degradation product, indicating that protease other than DegS is acting before YaeL in degrading TcpP. The YaeL-dependent degradation pathway is active in TcpH
+
cells under conditions that are not favorable for virulence gene activation. This work expands the knowledge of YaeL-dependent processing in the bacterial cell and reveals an unexpected layer of virulence gene regulation in
V. cholerae
.
Receptor-mediated glutamate release from volume sensitive channels in astrocytes
Authors: Takano Takahiro , Kang Jian , Jaiswal Jyoti K. , Simon Sanford M. , Lin Jane H.-C. , Yu Yufei , Li Yuxing , Yang Jay , Dienel Gerald , Zielke H. Ronald , Nedergaard Maiken
Published: October 2005

Several lines of work have shown that astrocytes release glutamate in response to receptor activation, which results in a modulation of local synaptic activity. Astrocytic glutamate release is Ca
2+
-dependent and occurs in conjunction with exocytosis of glutamate containing vesicles. However, astrocytes contain a millimolar concentration of cytosolic glutamate and express channels permeable to small anions, such as glutamate. Here, we tested the idea that astrocytes respond to receptor stimulation by dynamic changes in cell volume, resulting in volume-sensitive channel activation, and efflux of cytosolic glutamate. Confocal imaging and whole-cell recordings demonstrated that astrocytes exhibited a transient Ca
2+
-dependent cell volume increase, which activated glutamate permeable channels. HPLC analysis revealed that glutamate was released in conjunction with other amino acid osmolytes. Our observations indicate that volume-sensitive channel may constitute a previously uncharacterized target for modulation of astrocyte-neuronal interactions.
Arp2/3 complex-deficient mouse fibroblasts are viable and have normal leading-edge actin structure and function
Authors: Di Nardo Alessia , Cicchetti Gregor , Falet Hervé , Hartwig John H. , Stossel Thomas P. , Kwiatkowski David J.
Published: October 2005

RNA interference silencing of up to 90% of Arp3 protein expression, a major subunit of the Arp2/3 complex, proportionately decreases the intracellular motility of
Listeria monocytogenes
and actin nucleation activity ascribable to the Arp2/3 complex in mouse embryonic fibroblasts. However, the Arp2/3-deficient cells exhibit unimpaired lamellipodial actin network structure, translational locomotion, spreading, actin assembly, and ruffling responses. In addition, Arp3-silenced cells expressing neural Wiskott-Aldrich syndrome protein-derived peptides that inhibit Arp2/3 complex function in wild-type cells retained normal PDGF-induced ruffling. The Arp2/3 complex can be dispensable for leading-edge actin remodeling.
Self-administration of a food security scale by adolescents: item functioning, socio-economic position and food intakes
Authors: Gulliford Martin C , Mahabir Deepak , Nunes Cheryl , Rocke Brian
Published: October 2005

Objective

To evaluate the reliability and validity of a six-item food security scale when self-administered by adolescents.

Design

Cross-sectional questionnaire survey including the six-item food security measure, socio-economic variables and a food-frequency questionnaire.

Setting

Representative sample of 29 schools in Trinidad.

Subjects

In total 1903 students aged approximately 16 years.

Results

Item affirmatives ranged from 514 (27%) for the ‘balanced meal’ item to 128 (7%) for the ‘skipped or cut meals often’ item and 141 (7%) for the ‘hungry’ item. Item-score correlations ranged from 0.444 to 0.580. Cronbach'sαwas 0.77. Relative item severities from the Rasch model ranged from −1.622 (standard error 0.043) for the ‘balanced meal’ item to 1.103 (0.068) for the ‘skipped or cut meals often’ item and 0.944 (0.062) for the ‘hungry’ item. The ‘hungry’ item gave a slightly lower relative severity in boys than girls. Food insecurity was associated with household overcrowding (adjusted odds ratio comparing highest and lowest quartiles 2.61, 95% confidence interval 1.75 to 3.91), lack of pipe-borne water in the home, low paternal education or paternal unemployment. After adjusting for socio-economic variables, food insecurity was associated with less frequent consumption of fruit (0.75, 0.60 to 0.94) or fish (0.72, 0.58 to 0.88) but more frequent consumption of biscuits or cakes (1.47, 1.02 to 2.11).

Conclusions

The food security scale provides a valid, reliable measure in adolescents, although young people report being hungry but not eating relatively more frequently than adults. Food-insecure adolescents have low socio-economic position and may eat less healthy diets.