bluuebunny/crossref_metadata_2025 huggingface dataset:
Proteomics: A Shotgun Approach without Two‐dimensional Gels
Authors: Delahunty Claire , Yates John R
Published: September 2006

Proteome analysis has been most commonly accomplished by the combination of two‐dimensional electrophoresis and mass spectrometry, but this method suffers some drawbacks that limit its usefulness for large‐scale analysis. New ‘shotgun’ techniques allow for the detection of proteins from complex mixtures and are rapidly replacing gel‐based methods for certain applications.
Promotion of axonal maturation and prevention of memory loss in mice by extracts of Astragalus mongholicus
Authors: Tohda C , Tamura T , Matsuyama S , Komatsu K
Published: September 2006

Background and purpose:

Neurons with atrophic neurites may remain alive and therefore may have the potential to regenerate even when neuronal death has occurred in some parts of the brain. This study aimed to explore effects of drugs that can facilitate the regeneration of neurites and the reconstruction of synapses even in severely damaged neurons.

Experimental approach:

We investigated the effects of extracts of Astragalus mongholicus on the cognitive defect in mice caused by injection with the amyloid peptide Aβ(25‐35). We also examined the effect of the extract on the regeneration of neurites and the reconstruction of synapses in cultured neurons damaged by Aβ(25‐35).

Key results:

A. mongholicus extract (1 g kg−1 day−1 for 15 days, p.o.) reversed Aβ(25‐35)‐induced memory loss and prevented the loss of axons and synapses in the cerebral cortex and hippocampus in mice. Treatment with Aβ(25‐35) (10 μM) induced axonal atrophy and synaptic loss in cultured rat cortical neurons. Subsequent treatment with A. mongholicus extract (100 μg/ml) resulted in significant axonal regeneration, reconstruction of neuronal synapses, and prevention of Aβ(25‐35)‐induced neuronal death. Similar extracts of A. membranaceus had no effect on axonal atrophy, synaptic loss, or neuronal death. The major known components of the extracts (astragalosides I, II, and IV) reduced neurodegeneration, but the activity of the extracts did not correlate with their content of these three astragalosides.

Conclusion and implications:

A. mongholicus is an important candidate for the treatment of memory disorders and the main active constituents may not be the known astragalosides.

British Journal of Pharmacology (2006) 149, 532–541. doi:10.1038/sj.bjp.0706865
Vibrational dynamics of DNA. III. Molecular dynamics simulations of DNA in water and theoretical calculations of the two-dimensional vibrational spectra
Authors: Lee Chewook , Park Kwang-Hee , Kim Jin-A , Hahn Seungsoo , Cho Minhaeng
Published: September 2006

A theoretical description of the vibrational excitons in DNA is presented by using the vibrational basis mode theory developed in Papers I and II. The parameters obtained from the density functional theory calculations, such as vibrational coupling constants and basis mode frequencies, are used to numerically simulate two-dimensional (2D) IR spectra of dGn:dCn and dAn:dTn double helices with n varying from 1 to 10. From the molecular dynamics simulations of dG5C5 and dA5T5 double helices in D2O solution, it is found that the thermally driven internal motions of these systems in an aqueous solution do not induce strong fluctuations of basis mode frequencies nor vibrational couplings. In order to construct the two-exciton Hamiltonian, the vibrational anharmonicities of eight basis modes are obtained by carrying out B3LYP∕6-31G* calculations for the nine basis modes. The simulated 2D IR spectra of dGn:dCn double helix in D2O solution are directly compared with closely related experimental results. The 2D IR spectra of dGn:dCn and dAn:dTn are found to be weakly dependent on the number of base pairs. The present work demonstrates that the computational procedure combining quantum chemistry calculation and molecular dynamics simulation methods can be of use to predict 2D IR spectra of nucleic acids in solutions.
Progress on common aspects of the EU-supplied ITER diagnostics and prediction of diagnostic performance
Authors: Ingesson L. C. , Campbell D. J. , Cecconello M. , Ciattaglia E. , Dirken P. , Hawkes N. , Walsh M. , von Hellermann M. , Kálvin S. , McCarthy P. , Neubauer O. , Petrizzi L.
Published: September 2006

The European Union will supply a number of diagnostics for ITER. Significant progress has been made on the design and integration of these diagnostics. Specific topics, in common for several of the diagnostics, discussed are port-plug integration, simplification of labyrinths against neutron streaming, and design measures to protect and to be able to replace sensitive optical components. Performance analysis to predict the likely capability of the diagnostics to meet the ITER measurement requirements will be an important aspect of the design process. The interpretation of the measurement requirements, specifically of spatial resolution in the case of indirect measurements, is discussed on the basis of two examples, and methods of performance analysis are compared.
Multispectral x-ray imaging for core temperature and density maps retrieval in direct drive implosions
Authors: Tommasini Riccardo , Koch Jeffrey A. , Izumi Nobuhiko , Welser Leslie A. , Mancini Roberto C. , Delettrez Jacques , Regan Sean , Smalyuk Vladimir
Published: September 2006

We report on the experiments aimed at obtaining core temperature and density maps in direct drive implosions at the Omega laser facility using multimonochromatic x-ray imagers. These instruments use an array of pinholes and a flat multilayer mirror to provide unique multispectral images distributed over a wide spectral range. Using argon as a dopant in the direct-drive filled plastic shells produces emission images in the Ar He-β and Ly-β spectral regions. These images allow the retrieval of temperature and density maps of the plasma. We deployed three identical multimonochromatic x-ray imagers in a quasiorthogonal line-of-sight configuration to allow tomographic reconstruction of the structure of the imploding core.
Fast ion source and detector for investigating the interaction of turbulence with suprathermal ions in a low temperature toroidal plasma
Authors: Plyushchev G. , Diallo A. , Fasoli A. , Furno I. , Labit B. , Müller S. H. , Podestà M. , Poli F. M. , Boehmer H. , Heidbrink W. W. , Zhang Y.
Published: September 2006

A specific experimental apparatus consisting of an ion source and a detector for the investigation of the interaction between suprathermal ions and drift-wave turbulence is developed on the toroidal plasma experiment. Due to the low plasma temperature (∼5eV), a spatially localized, small-size ion source (∼4cm) mounted inside the vacuum vessel with relatively low ion energy (∼100eV–1keV) can be used. The source consists of an aluminosilicate Li-6 ion emitter (6mm diameter, 10–30μA current) installed on a two-dimensional (2D) poloidally moving system. The location, energy, and current density profile of the ion beam will be measured using a 2D movable gridded energy analyzer.
Surface plasmon resonance in conducting metal oxides
Authors: Rhodes Crissy , Franzen Stefan , Maria Jon-Paul , Losego Mark , Leonard Donovan N. , Laughlin Brian , Duscher Gerd , Weibel Stephen
Published: September 2006

We report the initial observation of surface plasmon resonance (SPR) in a conducting metal oxide thin film. The SPR phenomenon has been observed by attenuated total reflection of near-infrared radiation and is in agreement with electron energy loss spectroscopy measurements. To date, only metals are known to exhibit surface plasmon resonance and only noble metals have practical application. According to theory SPR should be observable in any conductor. This theoretical prediction is verified in the present study. The compositions of many conducting metal oxides are systematically variable, suggesting a significant advance in thin film characterization and innovative possibilities for versatile and sensitive chemical sensing applications.
Influence of annealing on the structural and optical properties of ZnO:Tb thin films
Authors: Teng X. M. , Fan H. T. , Pan S. S. , Ye C. , Li G. H.
Published: September 2006

The influence of annealing on the morphological, structural, and optical properties of ZnO:Tb thin films on Si substrate grown by magnetron cosputtering is investigated. It has been found that the ZnO:Tb thin films with structures of tetrapod and screwlike nanorod are formed after annealing at temperature of 950°C. X-ray photoelectron spectroscopy, energy dispersive spectroscopy, and Raman analyses prove that the tetrapod-aiguille zinc oxide (T-A-ZnO) and the screwlike nanorods are composed of Zn, Tb, and O elements. The photoluminescence spectra of the ZnO:Tb thin films with the T-A-ZnO structure and the screwlike nanorods are featured with two ultraviolet emission peaks and one strong green emission band, and the photoluminescence intensity increases with increasing annealing temperature. The surface defects in the T-A-ZnO structure and the screwlike nanorods are considered to be responsible for enhanced green emission in the annealed ZnO:Tb thin films.
A model for oxidation kinetics in air at room temperature of hydrogen-terminated (1  ) Si
Authors: Cerofolini G. F. , Mascolo D. , Vlad M. O.
Published: September 2006

A quantitative model is proposed for the description of the oxidation kinetics in air at room temperature of single crystalline, hydrogen-terminated, (1 0 0) silicon. The theory separates the growth kinetics of the interfacial suboxide from those of the outer stoichiometric oxide. The theory proceeds assuming that the suboxide grows along the surface at the border of oxidized-silicon clusters, while the formation of the stoichiometric oxide takes place on the top of the suboxide at a rate decaying exponentially with the oxide thickness. In these hypotheses the kinetics of suboxide formation are found to depend on the initial concentration of (defective) oxo groups, while the growth of the stoichiometric oxide is described by the Elovich equation both in the short- and long-time limits.
Loading dynamics of optical trap and parametric excitation resonances of trapped atoms
Authors: Wu Jinwei , Newell Raymond , Hausmann Marc , Vieira David J. , Zhao Xinxin
Published: September 2006

We study the loading dynamics of an optical dipole trap and an optical lattice both experimentally and theoretically. A simple power dependence for the number of trapped atoms (N∝P3∕2) is revealed in both cases. We then study the parametric excitation of the trapped atoms. High order parametric resonance is observed close to but lower than 4ν in a CO2 laser optical lattice. The existence of the high harmonic and its shift toward lower frequency are attributed to the anharmonicity of the optical trapping potential. We investigate the discrepancy between experimentally measured optical lattice frequencies and the theoretical calculation for several published experiments and present corrected formula for trap frequency calculations. Using this corrected formula and accounting for the off-center lattice sites, we present a modified formula for calculating the optical lattice frequency and obtain better agreement between experimental measurement and theoretical calculation.
Study on liquid-liquid transition of chlorinated butyl rubber by positron annihilation lifetime spectroscopy
Authors: Wu Jinrong , Huang Guangsu , Pan Qiying , Qu Liangliang , Zhu Yuchan , Wang Bo
Published: September 2006

The existence of liquid-liquid transition (Tll) above the glass transition (Tg) in amorphous polymers remains a controversial topic. In this letter, positron annihilation lifetime spectroscopy was used to detect Tll in cured and uncured chlorinated butyl rubber. It is found that the temperature spectra of orthopositronium lifetime and free-volume fraction of both samples clearly demonstrate two inflection points around −70 and −10°C, corresponding to Tg and Tll, respectively, while the orthopositronium intensity decreases at the transition regions, which may imply molecular cooperativity. Moreover, two equations should be adopted to describe the development of free-volume fraction after Tg.
Determination of interface state distribution in polysilicon thin film transistors from low-frequency noise measurements: Application to analysis of electrical properties
Authors: Pichon L. , Boukhenoufa A. , Cordier C. , Cretu B.
Published: September 2006

Low-frequency noise is studied in n-channel furnace solid phase crystallized and in laser solid phase crystallized (LSPC) polysilicon TFTs biased from weak to strong inversion. Noise analysis is supported by theoretical results of the additivity of generation-recombination spectra to explain trapping/detrapping processes following the tunneling theory of carriers into the gate oxide. In the weak inversion region the normalized drain current spectral density is inversely proportional to the number of trapped carriers. The corresponding distribution of the trap states [density of states (DOS)] in the polysilicon band gap at the interface is determined. In the strong inversion region the normalized drain current spectral density is proportional to the effective oxide trap number/(freecarriernumber)2 ratio. For LSPC devices the DOS is one decade lower and the corresponding effective oxide trap number is one decade higher. The results are attributed to the effects of the laser annealing on the active layer crystal quality. Quantitative dependence of DOS with static conduction parameters in relation with interface quality is then analyzed.
The impact of the operating field strength on the lasing properties of GaAs∕(Al,Ga)As quantum-cascade lasers
Authors: Schrottke L. , Giehler M. , Hey R. , Grahn H. T.
Published: September 2006

The gain coefficient of several GaAs∕AlxGa1−xAs quantum-cascade lasers (QCLs) with a nominal Al content of x=0.45 has been calculated as a function of transition energy and electric field strength. We solve the Schrödinger and Poisson equations self-consistently in the framework of a linear scattering-rate model with periodic boundary conditions. The actual layer thicknesses as well as the Al content of the barriers have been obtained from x-ray diffraction. The calculated gain characteristics exhibit a large range of transition energies and a corresponding range of possible operating field strengths. These results may provide an explanation for the observation of a rather large range of the lasing energies for QCLs with nominally identical cascade structures. The comparison with the experimental values of the lasing energy reveals that most of the lasers operate below the designed field strength. The analysis of the operating field strengths and the threshold current densities indicates larger losses for higher field strengths probably due to leakage currents.
High resolution quantitative two-dimensional dopant mapping using energy-filtered secondary electron imaging
Authors: Kazemian P. , Mentink S. A. M. , Rodenburg C. , Humphreys C. J.
Published: September 2006

We have quantified two-dimensional dopant profiles in Si with high accuracy using a commercial field emission gun scanning electron microscope with added secondary electron energy-filtering capabilities. Quantification was achieved for dopant concentrations of 2.8×1017–7.5×1019cm−3 with an accuracy of ±8.5%. Using energy filtering, we have measured the surface potential difference ΔΦs across a 3nm wide p-doped Si layer with respect to the n-doped substrate of a test structure to be 0.72±0.15V. Spatial resolution limits are discussed and are shown to be limited by the secondary electron escape depth. A technique for the rapid collection of calibrated energy-filtered images is also proposed.
Electrothermal simulation of the self-heating effects in GaN-based field-effect transistors
Authors: Turin Valentin O. , Balandin Alexander A.
Published: September 2006

We report results of the analytical and numerical investigation of self-heating effects in GaN-based high-power field-effect transistors. The problem of heat transfer in a transistor structure has been solved both analytically, using the method of images, and numerically. Two-dimensional electrothermal simulations of the GaN metal-semiconductor field-effect transistors on SiC and sapphire substrate have been performed in a framework of the drift-diffusion model. Using the physical-based simulations, we studied the dependence of the hot-spot temperature on the gate-to-gate pitch in the transistors with multiple gate fingers. Particular attention has been paid to comparison of self-heating effects in GaN transistors on SiC and sapphire substrates. The obtained results can be used for optimization of the thermal design of the GaN-based high-power field-effect transistors.
Capillarity and electromigration effects on asperity contact evolution in microelectromechanical systems switches
Authors: Kim Ji Hee , Srolovitz David J. , Cha Pil-Ryung , Yoon Jong-Kyu
Published: September 2006

Morphology evolution of asperity contacts in microelectromechanical systems switches is examined in the framework of the phase field method. Surface mass diffusion, driven by capillarity, rapidly increases the asperity contact radius at early times, decreases it slowly at later times, and, possibly, pinches off the contact due to a Rayleigh instability. Electromigration accelerates this process but retards or prevents the pinch off at late times. The evolution occurs faster when the asperity size and/or density are smaller. Approximate analytical results for the evolution kinetics are provided.
Toughening and reinforcing alumina matrix composite with single-wall carbon nanotubes
Authors: Fan Jin-Peng , Zhuang Da-Ming , Zhao Da-Qing , Zhang Gong , Wu Min-Sheng , Wei Fei , Fan Zhuang-Jun
Published: September 2006

The authors report an efficient way of incorporating single-wall carbon nanotubes (SWNTs) into alumina matrix with strong interfaces by heterocoagulation. The fracture toughness of SWNTs/Al2O3 composite reaches 6.40±0.3MPam1∕2, which is twice as high as that of unreinforced alumina. The flexure strength of the composite also increases by 20%. The main toughening mechanism is crack bridging of SWNTs, and SWNT pullout takes effect also.
Hysteretic resistance concepts in ferroelectric thin films
Authors: Meyer René , Waser Rainer
Published: September 2006

Hysteretic resistance effects based on a correlation between ferroelectric polarization and conductivity might become of particular interest for nonvolatile memory applications, because they are not subject to the scaling restrictions of charge based memories such as the ferroelectric random access memory. Two basic concepts, a metal-ferroelectric-metal structure and a metal-ferroelectric-semiconductor structure are discussed in the literature. This contribution discusses the principle of operation of those concepts in terms of the band model. A generalized model is proposed, which is based on a conductive metal-ferroelectric-semiconductor-metal structure. Here, the existence of a low and a high conductive state originates from a switch of the polarization in the ferroelectric layer and a resulting positive or negative polarization charge at the ferroelectric-semiconductor interface. Charge carriers in the film are attracted by or depleted at the interface giving rise to different local conductivities. By simulation, the effect of internal screening caused by mobile charge carriers on the hysteretic current-voltage behavior and the depolarizing field in the ferroelectric are estimated. The simulation discloses a switching ratio up to several orders of magnitude and a conductivity window, which scales with the donor concentration. It may also explain resistive switching in systems consisting only of one ferroelectric layer by assuming the presence of nonferroelectric interface layers.
Homogeneity of Pb(Zr,Ti)O3 thin films by chemical solution deposition: Extended x-ray absorption fine structure spectroscopy study of zirconium local environment
Authors: Malic Barbara , Arcon Iztok , Kodre Alojz , Kosec Marija
Published: September 2006

Sols for Pb(Zr0.53Ti0.47)O3 (PZT) thin films were prepared by 2-methoxyethanol route from lead acetate, titanium n-propoxide, and zirconium n-propoxide, the latter either unmodified or modified with acetylacetone or acetic acid in a 2∕1 molar ratio and deposited on sapphire (0001). By Zr K-edge extended x-ray absorption fine structure (EXAFS) spectroscopy, the structural changes in the Zr local environment, induced by the addition of the two modifiers, were followed from the synthesis of the PZT sol to the transition to the amorphous film. In the unmodified PZT sol segregation of Zr species occurs from the original dimers present in the Zr propoxide solution in 2-methoxyethanol. The immediate neighborhood of Zr atoms changes markedly at the transition from the sol to the amorphous film: the local structure around Zr atoms is similar to the one found in tetragonal zirconia particles. The modification of Zr propoxide with acetylacetone in 2-methoxyethanol results in Zr monomers. In PZT sol, clustering of Zr species is observed continuing into the amorphous film. By modification with acetic acid the original dimeric structure of the Zr precursor is retained in the PZT sol and further in the amorphous film. Selective modification of Zr propoxide with acetic acid therefore results in a more homogeneous distribution of Zr atoms in the PZT sol and amorphous film than in both as-received and acetylacetone-modified Zr propoxide.
Pulsed photothermal deflection with a top-hat beam excitation
Authors: Li Bincheng , Blaschke Holger , Ristau Detlev
Published: September 2006

A top-hat beam excitation is used in pulsed photothermal deflection (PTD) experiments. Based on the Fresnel diffraction model a theory is developed to describe accurately the PTD amplitude obtained with the top-hat beam excitation. The comparison between the theoretical PTD amplitudes achieved with a Gaussian and a top-hat beam excitation shows that the use of top-hat beam excitation improves the measurement sensitivity of the PTD technique. Good agreement between theoretical calculations and experimental results is obtained.
Microstructure and transport properties of Y-rich YBa2Cu3O7−δ thin films
Authors: Wang H. , Serquis A. , Maiorov B. , Civale L. , Jia Q. X. , Arendt P. N. , Foltyn S. R. , MacManus-Driscoll J. L. , Zhang X.
Published: September 2006

Epitaxial YXBa2Cu3O7−δ (YXBCO) thin films were deposited by pulsed laser deposition on both single crystal SrTiO3 (100) and buffered polycrystalline metal substrates, where X=0.9, 1.0, 1.1, 1.2, and 1.3. The self-field critical current density (Jc) of YXBCO exhibits the best performance at X=1.1 for the samples on both single crystal substrates and metal substrates. Epitaxial Y2O3 nanoparticles were observed in Y-rich samples (X>1.0) by X-ray diffraction and cross-sectional transmission electron microscopy. The field-dependence and angular-dependence measurements show that Y2O3 nanoparticles improve the in-field Jc performance, especially in the low field regime, without reducing self-field Jc of YBCO films.
Integration of SrBi2Ta2O9 thin films for high density ferroelectric random access memory
Authors: Wouters D. J. , Maes D. , Goux L. , Lisoni J. G. , Paraschiv V. , Johnson J. A. , Schwitters M. , Everaert J.-L. , Boullart W. , Schaekers M. , Willegems M. , Vander Meeren H. , Haspeslagh L. , Artoni C. , Caputa C. , Casella P. , Corallo G. , Russo G. , Zambrano R. , Monchoix H. , Vecchio G. , Van Autryve L.
Published: September 2006

Ferroelectric random access memory (FeRAM) is an attractive candidate technology for embedded nonvolatile memory, especially in applications where low power and high program speed are important. Market introduction of high-density FeRAM is, however, lagging behind standard complementary metal-oxide semiconductor (CMOS) because of the difficult integration technology. This paper discusses the major integration issues for high-density FeRAM, based on SrBi2Ta2O9 (strontium bismuth tantalate or SBT), in relation to the fabrication of our stacked cell structure. We have worked in the previous years on the development of SBT-FeRAM integration technology, based on a so-called pseudo-three-dimensional (3D) cell, with a capacitor that can be scaled from quasi two-dimensional towards a true three-dimensional capacitor where the sidewalls will importantly contribute to the signal. In the first phase of our integration development, we integrated our FeRAM cell in a 0.35μm CMOS technology. In a second phase, then, possibility of scaling of our cell is demonstrated in 0.18μm technology. The excellent electrical and reliability properties of the small integrated ferroelectric capacitors prove the feasibility of the technology, while the verification of the potential 3D effect confirms the basic scaling potential of our concept beyond that of the single-mask capacitor. The paper outlines the different material and technological challenges, and working solutions are demonstrated. While some issues are specific to our own cell, many are applicable to different stacked FeRAM cell concepts, or will become more general concerns when more developments are moving into 3D structures.
Texture control and seeded nucleation of nanosize structures of ferroelectric thin films
Authors: Muralt Paul
Published: September 2006

An overview is given on nucleation phenomena of Pb(Zr,Ti)O3 (PZT) thin films on Pt(111)-based substrates. Emphasis is given on in situ growth methods, particularly in situ reactive sputtering from three metallic targets. Growth of PZT thin films is discussed from the point of view of the PbOx–TiO2 phase diagram, PbO vapor pressure, and classical nucleation theory. The role of thin TiO2 affinity layers and spots is explained in the frame of this theory. Activation energies for desorption and chemisorption are adapted to comply with the fact that nucleation rates on TiO2 are much larger than the ones on bare Pt(111). The model reproduces well the PbO surface flux from bare Pt(111) to the affinity spots in the case of PbTiO3 nucleation and the reversed tendency in the case of PZT 40∕60 nucleation, explaining experimental observations. The critical size of nuclei was calculated to contain 8–10unit cells for PbTiO3∕Pt nucleation and 14–17 for PZT/Pt nucleation.
Nonlinearity and fatigue in ferroelectric lead zirconate titanate
Authors: Zhang Yong , Lupascu Doru C.
Published: September 2006

Different fatigue states of a soft composition of bulk ferroelectric lead zirconate titanate are characterized by measurement of the nonlinearity of domain wall motion. The dc field-dependent Rayleigh constants were measured for the dielectric as well as piezoelectric coefficients. The limits of the Rayleigh law near the coercive field and implications for the Preisach model are discussed. Due to fatigue, the nonlinearity of domain wall motion (Rayleigh coefficient) reduces stronger than the dielectric constant itself. 90° domain wall motion is more affected by fatigue than 180° switching which is displayed by an increasing disparity between the piezoelectric and dielectric Rayleigh constants. Like other material coefficients, fatigue as reflected in the Rayleigh coefficient is largely determined by the near electrode volume.
Quantitative measurement of domain inversion in RuO2:LiNbO3 crystal by digital holographic interferometry
Authors: Qu Weijuan , Liu De’an , Zhi Ya’nan , Luan Zhu , Liu Liren , Zhou Yu , Lu Wei , Wang Chunhua
Published: September 2006

We quantitatively study the domain inversion in a RuO2:LiNbO3 crystal wafer by the digital holographic interferometry. The crystal wafer is placed into one arm of a Mach-Zehnder-type interferometer to record a series of holograms. Making use of the angular spectrum backward propagation algorithm, we reconstruct the optical wave field in the crystal plane. The extracted phase difference from the reconstructed optical wave field is a well linear function of the applied external voltage. We deduce that the linear electro-optic coefficient of the detected RuO2:LiNbO3 crystal sample is 9.1×10−12m∕V. An unexpected phase contrast at the antiparallel domain wall is observed and the influence of the applied external voltage on it is studied in detail. Also the built-in internal field is quantitatively measured as 0.72kV∕mm.
Phase velocity fluctuations and gain in Cherenkov free-electron lasers
Authors: de la Fuente I. , van der Slot P. J. M. , Boller K.-J.
Published: September 2006

We report on the influence that waveguide-induced fluctuations in the phase velocity of the radiation wave have on the gain of Cherenkov-type free-electron lasers. We theoretically analyze low-gain Cherenkov free-electron lasers with a compact design that require resonator feedback for operation. We find that even small spatial variations of the waveguide parameters along the propagation direction can lead to significant degradation of the gain, and we present typical values for the required degree in waveguide precision that would eliminate such effects.
Laser ablation of optically thin absorbing liquid layer predeposited onto a transparent solid substrate
Authors: Kudryashov S. I. , Lyon K. , Shukla S. , Murry D. , Allen S. D.
Published: September 2006

Ablation of optically thin liquid 2-propanol layers of variable thickness on IR-transparent solid Si substrate by a nanosecond CO2 laser has been experimentally studied using time-resolved optical interferometric and microscopy techniques. Basic ablation parameters—threshold fluences for surface vaporization and explosive homogeneous boiling of the superheated liquid, ablation depths, vaporization (ablation) rates, and characteristic ablation times versus laser fluence—were measured as a function of alcohol layer thickness. The underlying ablation mechanisms, their thermodynamics, and microscopic details are discussed.
Rectifying characteristics and photovoltaic effect in heterojunctions of La0.9Sr0.1MnO3∕Nb-doped SrTiO3
Authors: Luo Z. , Gao J.
Published: September 2006

Heterojunctions were fabricated by depositing La0.9Sr0.1MnO3 (LSMO) films on 0.8wt% Nb-doped SrTiO3 substrates. Such heterojunctions showed good rectifying characteristics and clear photovoltaic effect. When the temperature increases from 50K to room temperature, the diffusion voltage (Vd) decreases from 0.77to0.22V and the photovoltage Voc monotonically dropped from 2to1mV. No sudden change of Vd or Voc was observed at the metal-insulator transition temperature, which differs from the previous works. This is probably caused by of the difference between the band structure of LSMO and the manganites used in previous works.
Porosity-induced blueshift of photoluminescence in CdSe
Authors: Monaico E. , Ursaki V. V. , Tiginyanu I. M. , Dashevsky Z. , Kasiyan V. , Boyd Robert W.
Published: September 2006

Porous CdSe layers have been fabricated by anodic etching of n-type single crystalline substrates with different values of conductivity. The morphology and porosity of the layers thus produced were found to be controlled by the conductivity of the material, anodization voltage, and conditions of in situ UV illumination. The porosity-induced changes in the photoluminescence spectra were studied. The decrease of the skeleton size down to 10–20nm was found to result in a blueshift of the excitonic emission lines by 10meV which was attributed to quantum-size effects in the nanocrystalline CdSe porous skeleton. An increase of the exciton–LO-phonon interaction by a factor of 1.5 in a weak-to-intermediate confinement regime was deduced from the analysis of temperature dependence of the free exciton luminescence line.
Analysis of key parameters affecting the thermal behavior and performance of quantum cascade lasers
Authors: Zhu Cheng , Zhang Yong-gang , Li Ai-zhen , Tian Zhao-bing
Published: September 2006

In this paper, we present an investigation of some key parameters affecting the thermal behavior and performance of quantum cascade lasers (QCLs). We take into account the temperature dependent heat conducting parameters of the layers, including their interface thermal resistance. Our study shows that for QCL structures with a rather thick active core comprised of many heterointerfaces, the thermal boundary resistances play a crucial role. We use a finite element method to simulate the heat dissipation in QCLs with different structures and different packaging methods. These are then quantitatively compared with existing experimental data. Results show that (1) epilayer-up mounting with buried and/or thick gold plated structures is a good substitute for epilayer-down mounting, and (2) using InP cladding and plasmon layer replacing InAlAs∕InGaAs further improves heat transfer characteristics. On the other hand, for reaching cw operation at room temperature, the driving current density must be optimized to a significantly lower level than what is conventionally believed. The simulations also reveal that the substantial nonuniformity of temperature distribution in the active core of QCLs should have a significant effect on the resulting laser spectra. In this paper, we also present investigations and discussions on the thermal performance of InGaAs∕AlGaAsSb QCLs and its correlations to various parameters.
Magnetophotoluminescence study of GaxIn1−xP quantum wells with CuPt-type long-range ordering
Authors: Shao Jun , Lü Xiang , Yue Fangyu , Huang Wei , Guo Shaoling , Chu Junhao
Published: September 2006

Magnetophotoluminescence (PL) measurements are performed on GaxIn1−xP∕AlGaInP quantum wells with CuPt-type long-range ordering. Curve-fitting and second-order derivative operations are conducted, respectively, on the PL spectra, and two different PL components are identified with an energetic separation of about 5∼25meV. Obvious diamagnetic shift can be observed only for the PL component with higher energy, indicating the excitonic feature of the related PL transition. The in-(001)-plane exciton reduced effective mass and binding energy are evaluated based solely on the excitonic PL component, by a quasi-two-dimensional exciton effective mass approximation. The results suggest that the ordering competes with compressive strain, and enlarges the exciton reduced effective mass and binding energy. The enlargement is discussed and a comparison with previous reports is given.
Magnetic monopoles in quantum adiabatic dynamics and the immersion property of the control manifold
Authors: Viennot David
Published: September 2006

It is well known that the Berry phase of a cyclic adiabatic dynamical system appears formally as the flux of a magnetic field in the control parameter manifold. In this electromagnetic picture a level crossing appears as a Dirac magnetic monopole in this manifold. We make an extensive study of the magnetic monopole model of eigenvalue crossings. We show that the properties of the monopole magnetic field in the control manifold are determined by the immersion of the control manifold in a space given by the universal classifying theorem of fiber bundles. We give a detailed illustrative study of the simple but instructive case of a two level crossing of a system controlled by a two-dimensional manifold.
Implications of ab initio energetics on the thermodynamics of Fe–Cr alloys
Authors: Caro A. , Caro M. , Lopasso E. M. , Crowson D. A.
Published: September 2006

The authors analyze the implications of the recently reported results of ab initio calculations of formation energies of the Fe–Cr alloy. The formation energies show a change in sign from negative to positive as Cr composition increases above ∼10%. By developing a classic potential to evaluate the thermodynamic properties, they determine the location of the solubility limit and compare it with earlier results. A significant difference appears in a region of temperature and composition that is relevant for the nuclear applications of this alloy. Experimental results seem to confirm the validity of the location of the new solvus line.
Coupling between octahedral tilting and ferroelectric order in tetragonal tungsten bronze-structured dielectrics
Authors: Levin Igor , Stennett Martin C. , Miles Gabrielle C. , Woodward David. I. , West Anthony R. , Reaney Ian M.
Published: September 2006

Strong coupling between local polar displacements and a commensurate octahedral tilting is proposed to explain the onset of classic ferroelectric behavior in tetragonal tungsten bronzelike dielectrics Ba2LaxNd1−xNb3Ti2O15. The ferroelectric phase transition is associated with a discontinuous non-lock-in transformation of an incommensurate tilted structure to a commensurate superstructure. In a manner reminiscent of perovskitelike oxides, the driving force for commensurate tilting increases as the average ionic radius of the rare-earth ion decreases; no classical ferroelectric transition is observed for compositions with x>0.75, which remain incommensurate and exhibit only relaxor behavior below room temperature.
Field-induced entropy change in the manganite with significant short-range magnetic order
Authors: Jia L. , Liu G. J. , Wang J. Z. , Sun J. R. , Zhang H. W. , Shen B. G.
Published: September 2006

Effects of short-range magnetic order on magnetic entropy change have been studied for the manganese oxide Eu0.55Sr0.45MnO3. Superparamagnetic clusters composed of seven to ten Mn ions, depending on applied field, have been derived in the paramagnetic state of the compound based on the analysis of dc susceptibility. The presence of short-range magnetic order greatly depresses the magnetic entropy of the paramagnetic phase; thus the entropy changes at the field-induced paramagnetic to ferromagnetic phase transition. The maximum entropy change detected is only ∼7J∕kgK for a field change of 0–5T, about one-fifth of the theoretical expectation. The experimental results can be well elucidated within the mean field theory. It is suggested that a way of destroying the short-range order would enhance the magnetic entropy change greatly.
Enzymatic glucose biosensor based on ZnO nanorod array grown by hydrothermal decomposition
Authors: Wei A. , Sun X. W. , Wang J. X. , Lei Y. , Cai X. P. , Li C. M. , Dong Z. L. , Huang W.
Published: September 2006

We report herein a glucose biosensor based on glucose oxidase (GOx) immobilized on ZnO nanorod array grown by hydrothermal decomposition. In a phosphate buffer solution with a pH value of 7.4, negatively charged GOx was immobilized on positively charged ZnO nanorods through electrostatic interaction. At an applied potential of +0.8V versus Ag∕AgCl reference electrode, ZnO nanorods based biosensor presented a high and reproducible sensitivity of 23.1μAcm−2mM−1 with a response time of less than 5s. The biosensor shows a linear range from 0.01to3.45mM and an experiment limit of detection of 0.01mM. An apparent Michaelis-Menten constant of 2.9mM shows a high affinity between glucose and GOx immobilized on ZnO nanorods.
Insight into the atomic-scale mechanism of liquid metal embrittlement
Authors: Sigle W. , Richter G. , Rühle M. , Schmidt S.
Published: September 2006

A method has been developed to investigate material embrittlement on the atomistic level. By ion implantation the embrittling agent is introduced into a small volume enclosing a segment of a grain boundary of a thin specimen prepared for transmission electron microscopy (TEM). After allowing the implanted ions to segregate at the grain boundary, the position of the ions is determined by atomic-resolution TEM. In the present study this was applied to the Al(Ga) system. Close correspondence with previous ab initio calculations is found and a model for the initial stages of embrittlement is proposed.
Increased Schottky barrier heights for Au on n- and p-type GaN using cryogenic metal deposition
Authors: Wang Hung-Ta , Jang S. , Anderson T. , Chen J. J. , Kang B. S. , Ren F. , Voss L. F. , Stafford L. , Khanna R. , Gila B. P. , Pearton S. J. , Shen H. , LaRoche Jeffrey R. , Smith Kurt V.
Published: September 2006

An enhancement of ∼0.18eV (an 18% increase) in Schottky barrier height was obtained for Au deposited at cryogenic temperatures on n-type GaN relative to conventional deposition at 300K (barrier height of 1.0eV). Enhancements of 0.04–0.11eV were achieved for Au deposition on p-GaN under the same conditions. The increase in barrier height on n-GaN persists for annealing temperatures up to ∼200°C. At higher annealing temperatures, both types of diodes show a deterioration in rectifying behavior. The reverse current of low temperature deposited diodes was approximately two orders of magnitude lower than conventional Au∕n-GaN diodes. The ideality factor of the cryogenically processed n-type devices (∼1.06) was similar to that for room temperature diodes (1.13). This simple process method has potential for improving output resistance and power gain and lowering gate leakage current and noise in GaN-based transistors.
Boundary Work: Knowledge, Policy, and the Urban Environment
Authors: Owens Susan , Petts Judith , Bulkeley Harriet
Published: September 2006

This paper explores the relations between different forms of knowledge and urban environmental policy arenas. It briefly considers the evolution of the urban environmental agenda and growing interest in questions of knowledge transfer. It then explores reasons for an apparent knowledge – policy ‘gap’, including familiar explanations, such as the problems of communicating research findings, as well as those based on more subtle and complex interpretations of both knowledge and policy processes. It concludes with some proposals for thinking about the boundary between knowledge and policy and constructive ways to enhance the sustainable urban environment agenda. The paper introduces the other contributions in this theme issue—concerned with diverse aspects of knowledge transfer in the context of urban environments—and draws upon insights from a seminar series at which these papers were first presented.
Designing Urban Knowledge: Competing Perspectives on Energy and Buildings
Authors: Guy Simon
Published: September 2006

The author engages with debates about buildings, energy efficiency, and the innovation process—issues that are of great significance for urban sustainability because buildings are such an important constituent of urban energy consumption. Within this context, the author explores what it might mean to develop an interdisciplinary understanding of technical change. Questioning conventional accounts, he develops a sociotechnical perspective on competing energy knowledges and contexts of design, development, and consumption. It is argued that energy research and policy-making for the built environment is underpinned by a common understanding of technical change, which fails to take account of the contextual nature of energy-related choice. Describing cultural, organisational, and commercial factors shaping technological innovation, the author explores how more-or-less energy-efficient choices influencing urban development are made in response to changing opportunities and practices which sometimes favor energy efficiency, sometimes not. The author draws upon sociological accounts of technical change and illustrates both a sociotechnical perspective on energy and buildings and a key role for sociologists in the field of architecture, energy, and environmental studies.
Retail Productivity and Land-Use Planning: Negotiating ‘Joined-up’ Retail Planning Policy
Authors: Guy Cliff
Published: September 2006

The author examines some recent changes in government policy in England relating to planning control over new retail development. In so doing, he investigates tensions between the government's overall economic policy and its land-use planning policy, particularly that involving development of large-format stores. The influence of interest groups, through processes of research and lobbying of government departments, is traced. The author then discusses the extent to which seemingly incompatible positions have been resolved in interdepartmental discussion, involving typical ‘British compromises’. One result of this process appears to be the formulation of ambiguous and unclear policies, which may have to be modified again in the near future.
Normal-repeat-length polyglutamine peptides accelerate aggregation nucleation and cytotoxicity of expanded polyglutamine proteins
Authors: Slepko Natalia , Bhattacharyya Anusri M. , Jackson George R. , Steffan Joan S. , Marsh J. Lawrence , Thompson Leslie Michels , Wetzel Ronald
Published: September 2006

The dependence of disease risk and age-of-onset on expanded CAG repeat length in diseases like Huntington's disease (HD) is well established and correlates with the repeat-length-dependent nucleation kinetics of polyglutamine (polyGln) aggregation. The wide variation in ages of onset among patients with the same repeat length, however, suggests a role for modifying factors. Here we describe the ability of normal-length polyGln repeat sequences to greatly accelerate the nucleation kinetics of an expanded polyGln peptide. We find that normal-length polyGln peptides enhance the
in vitro
nucleation kinetics of a Q
47
peptide in a concentration-dependent and repeat-length-dependent manner.
In vivo
, we show that coexpression of a Q
20
sequence in a
Drosophila
model of HD expressing Htt exon 1 protein with an Q
93
repeat accelerates both aggregate formation and neurotoxicity. The accelerating effect of short polyGln peptides is attributable to the promiscuity of polyGln aggregate elongation and reflects the intimate relationship between nucleus formation and early elongation events in establishing nucleation kinetics. The results suggest that the overall state of the polyGln protein network in a cellular environment may have a profound effect on the toxic consequences of polyGln expansion and thus may serve as a genetic modifier of age of onset in HD.
Endogenous retroviruses regulate periimplantation placental growth and differentiation
Authors: Dunlap Kathrin A. , Palmarini Massimo , Varela Mariana , Burghardt Robert C. , Hayashi Kanako , Farmer Jennifer L. , Spencer Thomas E.
Published: September 2006

Endogenous retroviruses (ERVs) are fixed and abundant in the genomes of vertebrates. Circumstantial evidence suggests that ERVs play a role in mammalian reproduction, particularly placental morphogenesis, because intact ERV envelope genes were found to be expressed in the syncytiotrophoblasts of human and mouse placenta and to elicit fusion of cells
in vitro
. We report here
in vivo
and
in vitro
experiments finding that the envelope of a particular class of ERVs of sheep, endogenous Jaagsiekte sheep retroviruses (enJSRVs), regulates trophectoderm growth and differentiation in the periimplantation conceptus (embryo/fetus and associated extraembryonic membranes). The enJSRV envelope gene is expressed in the trophectoderm of the elongating ovine conceptus after day 12 of pregnancy. Loss-of-function experiments were conducted
in utero
by injecting morpholino antisense oligonucleotides on day 8 of pregnancy that blocked enJSRV envelope protein production in the conceptus trophectoderm. This approach retarded trophectoderm outgrowth during conceptus elongation and inhibited trophoblast giant binucleate cell differentiation as observed on day 16. Pregnancy loss was observed by day 20 in sheep receiving morpholino antisense oligonucleotides.
In vitro
inhibition of the enJSRV envelope reduced the proliferation of mononuclear trophectoderm cells isolated from day 15 conceptuses. Consequently, these results demonstrate that the enJSRV envelope regulates trophectoderm growth and differentiation in the periimplantation ovine conceptus. This work supports the hypothesis that ERVs play fundamental roles in placental morphogenesis and mammalian reproduction.