bluuebunny/crossref_metadata_2025 huggingface dataset:
Diffusion creep of dry, melt‐free olivine
Authors: Faul Ulrich H. , Jackson Ian
Published: April 2007

Deformation experiments were conducted on fine‐grained (3–6 μm), fully synthetic Fo90 olivine aggregates in a gas‐medium apparatus at 300 MPa confining pressure and temperatures of 1150–1360°C. The strain rates of the solution‐gelation‐derived and therefore genuinely melt‐free, dry samples are about two orders of magnitude lower than the strain rates for nominally melt‐free aggregates at the same pressure and temperature conditions and grain size. Benchmark deformation tests with Anita Bay dunite and mild steel reproduce published data. The creep strength of melt‐added sol‐gel olivine is similar to the published creep strength of dry, melt‐bearing olivine derived from natural rocks. Nonlinear least‐squares fits to the melt‐free deformation data give an activation energy of 484 kJ/mol, a stress exponent of 1.4, and a grain‐size exponent of 3 over a range of stresses from 15 to 210 MPa. These results suggest that small amounts of melt may be similarly effective in reducing the creep strength of upper mantle rocks as small amounts of water. However, a possible contribution of grain boundary composition to the observed differences in rheology in the absence of melt cannot be conclusively ruled out by the current experiments.
Influence of continental air mass transport on atmospheric CO2 in the western North Pacific
Authors: Wada Akira , Sawa Yousuke , Matsueda Hidekazu , Taguchi Shoichi , Murayama Shohei , Okubo Saki , Tsutsumi Yukitomo
Published: April 2007

Since 1993, atmospheric carbon dioxide (CO2) has been continuously observed by the Japan Meteorological Agency at Minamitorishima station (24°18′N, 153°58′E), located about 2000 km off the Asian continent in the western North Pacific. The long‐term record shows high‐frequency measurements with interesting episodic events with extremely low CO2 mixing ratios 5–10 ppm below the background seasonal cycle. These extremely low CO2 (ELC) events occur several times each year, primarily in July, August, and September, although the number of events varies from year to year. The origins of air masses associated with the ELC events were defined by backward trajectory analyses as well as chemical characterizations using simultaneous observations of other trace gases (CO, CH4, and O3). The results indicate that the air masses with extremely low CO2 were influenced by active biospheric uptake in summer over different continental sink regions in Siberia, northern Asia, and Southeast Asia due to rapid long‐range transport driven by strong northerly or southerly winds. The spatial scale of the widespread low‐CO2 distribution for the ELC events in 2001 was captured by a simulation experiment using a three‐dimensional chemical transport model. It clearly revealed that the Intertropical Convergence Zone around 20°N in the western North Pacific during summer blocked further southward intrusion of ELC events through the lower troposphere.
Validation of Odin/OSIRIS stratospheric NO2 profiles
Authors: Brohede Samuel M. , Haley Craig S. , McLinden Chris A. , Sioris Christopher E. , Murtagh Donal P. , Petelina Svetlana V. , Llewellyn Edward J. , Bazureau Ariane , Goutail Florence , Randall Cora E. , Lumpe Jerry D. , Taha Ghassan , Thomasson Larry W. , Gordley Larry L.
Published: April 2007

This paper presents the validation study of stratospheric NO2 profiles retrieved from Odin/OSIRIS measurements of limb‐scattered sunlight (version 2.4). The Optical Spectrograph and Infrared Imager System (OSIRIS) NO2 data set is compared to coincident solar occultation measurements by the Halogen Occultation Experiment (HALOE), Stratospheric Aerosol and Gas Experiment (SAGE) II, SAGE III, and Polar Ozone and Aerosol Measurement (POAM) III during the 2002–2004 period. Comparisons with seven Systeme d'Analyse par Observation Zenithal (SAOZ) balloon measurements are also presented. All comparisons show good agreement, with differences, both random and systematic, of less than 20% between 25 km and 35 km. Inconsistencies with SAGE III below 25 km are found to be caused primarily by diurnal effects from varying NO2 concentrations along the SAGE III line‐of‐sight. On the basis of the differences, the OSIRIS random uncertainty is estimated to be 16% between 15 km and 25 km, 6% between 25 km and 35 km, and 9% between 35 km and 40 km. The estimated systematic uncertainty is about 22% between 15 and 25 km, 11–21% between 25 km and 35 km, and 11–31% between 35 km and 40 km. The uncertainties for AM (sunrise) profiles are generally largest and systematic deviations are found to be larger at equatorial latitudes. The results of this validation study show that the OSIRIS NO2 profiles are well behaved, with reasonable uncertainty estimates between 15 km and 40 km. This unique NO2 data set, with more than hemispheric coverage and high vertical resolution will be of particular interest for studies of nitrogen chemistry in the middle atmosphere, which is closely linked to ozone depletion.
Mechanisms for cessation of magmatic resurfacing on Venus
Authors: Reese C. C. , Solomatov V. S. , Orth C. P.
Published: April 2007

Proposed mechanisms of resurfacing on Venus about 0.3–1 Gyr ago usually involve either some form of tectonic resurfacing in which Venusian lithosphere is recycled mechanically or magmatic resurfacing where essentially immobile lithosphere is covered by lava. The focus of this study is mechanisms of magmatic resurfacing in the stagnant lid regime of mantle convection. Parameterized convection models suggest that cessation of magmatic resurfacing can occur in several ways. (1) The mantle temperature drops sufficiently such that mantle rising adiabatically does not cross the solidus. (2) The molten layer migrates below the solid/melt density inversion at 250–500 km so that no melt can escape. (3) Sublithospheric small‐scale convection stops and conductive thickening of the lid suppresses melting. In each case, inability of magma to penetrate thickened Venusian lithosphere may play a role. The timing of melt cessation and duration of late stage resurfacing depend on various factors such as mantle rheology, degree of mantle depletion, and depth of resurfacing. The models indicate that the waning stages of resurfacing which result in surface age variations can last ∼0.1–1 Gyr. A general trend of recent lithospheric thickening is also predicted. Some cases exhibit a rapid transition from relatively thin to thick lid as suggested by previous authors.
Hydrometeorological application of a microwave link: 2. Precipitation
Authors: Leijnse H. , Uijlenhoet R. , Stricker J. N. M.
Published: April 2007

The suitability of a 27‐GHz microwave link for measuring path‐averaged precipitation is investigated. Theoretical analyses show that the specific attenuation of an electromagnetic signal at this frequency varies nearly linearly with the rainfall intensity, which is ideal for line‐integrating instruments. The dependence of this relation on the drop size distribution and on the temperature is small, so that uncertainties in these variables do not play large roles in the estimation of rainfall intensity. Data from an experiment with a 4.89‐km microwave link and a line configuration of seven tipping bucket rain gauges are used to test whether this instrument is indeed suitable for the estimation of path‐averaged rainfall. Results from this experiment show that the attenuation due to wet antennas can have a significant effect on the retrieved rainfall intensity. However, when a two‐parameter wet antenna correction function is applied to the link data, comparisons with the rain gauge data show that the instrument is indeed well suited for the measurement of path‐averaged rainfall.
Laboratory‐scale investigation of saltwater intrusion dynamics
Authors: Goswami Rohit R. , Clement T. Prabhakar
Published: April 2007

Experiments were completed in a laboratory‐scale, porous media tank to study the transport patterns of a saltwater wedge in a freshwater aquifer. Three types of experiments were performed to develop: (1) steady state salt‐wedge data observed under different hydraulic gradient conditions; (2) transient salt‐wedge data observed under intruding‐wedge conditions; and (3) transient salt‐wedge data observed under receding‐wedge conditions. Furthermore, flux measurements were made to quantify the flow characteristics of three distinct steady state experiments. The saltwater intrusion model SEAWAT was used to simulate these data sets. The model results along with the experimental data are presented as benchmark problems for testing density‐coupled groundwater flow models. A worthiness analysis was completed to test the sensitivity of these experimental problems to density‐coupling effects. The results of our analysis show that the proposed benchmark is a more robust alternative to the traditional Henry problem. These new experimental data sets can be used to assess the performance of saltwater intrusion models under both steady state and transient conditions.
A closed‐form solution for a confined flow into a tunnel during progressive drilling in a multi‐layer groundwater flow system
Authors: Yang Shaw‐Yang , Yeh Hund‐Der
Published: April 2007

A mathematical model is developed to describe the groundwater inflow into a tunnel in a multi‐layer aquifer system. Based on the model, the closed‐form solution is derived to estimate the groundwater flow rate entering the multi‐layer tunnel during progressive drilling. The solution has an integrand not only consisting of the product and square of the Bessel functions but also having a singularity at the origin. A unified numerical approach is proposed to evaluate the solution with accuracy to five decimal places. This approach includes a singularity removal scheme, the Gaussian quadrature, and the Shanks method. For a multi‐layer formation, the results obtained from the solution based on the equivalent hydraulic conductivity and the newly derived solution differ significantly. This solution is capable of estimating the maximum flow rate inside the horizontal tunnel, and thus can be used as a tool for designing the drainage tunnel system in a multi‐layer formation.
Evaluation of the Stability of Blood Flow over Time in the Dominant Hemisphere: A Functional Transcranial Doppler Study
Authors: Vadikolias Konstantinos M , Artemis Nikolaos D , Mitsias Panayiotis D , Heliopoulos John N , Tripsianis Grigorios A , Vadikolia Chrisa M , Proios Hariklia S , Serdari Aspasia E , Piperidou Charitomeni N , Milonas Ioannis A
Published: April 2007

Functional transcranial Doppler (fTCD) has been used for the identification of cerebral hemispheric dominance in various cognitive tasks. In our study, we have used fTCD with the aim to compare blood flow patterns in the hemispheres not only during the task activation periods but also in the post-stimulus phase. Normal volunteers, 25 right and 25 left-handed, were included. Mean flow velocities (FVs) in the bilateral middle cerebral arteries were recorded during the performance of six cognitive tasks and during the intervals between tasks. The lateralization index (LI) was calculated separately for each test (LI1-6), on the basis of the percent change of blood FV from baseline. To estimate flow fluctuations, a novel index, the LI-variability, was also calculated using a formula constituted by the minimum and maximum mean values recorded at specific time intervals during the entire procedure. Laterization indices, LI-3 and LI-4, corresponding to word generation and reading aloud tasks, produced the highest degree of activation. A perfect agreement (Cohen's κ = 1.000, P < 0.001) was observed among LI-3, LI-4, and LI-V. The repetition of recordings gave excellent test—retest reliability in 10 randomly selected participants. Our results suggest that the hemisphere that is characterized as dominant by fTCD maintains a more stable flow pattern during the performance of successive cognitive tasks. Although it could not be considered as a clinically useful tool as yet, this observation introduces a novel parameter such as the stability of blood flow over time, which could potentially provide insight in the study of cerebral functions.
Domain growth kinetics and wall strain behavior in BaMgF4 ferroelectric crystal by piezoresponse force microscopy
Authors: Zeng Huarong , Shimamura Kiyoshi , Villora Encarnacion G. , Takekawa Shunji , Kitamura Kenji
Published: April 2007

The sidewise domain dynamic and wall strain behavior in the atomic force microscope (AFM) tip electric field has been investigated in ferroelectric BaMgF4 single crystal by piezoresponse force microscopy. Unusual 180° domain wall strain phenomenon and its dynamics in the domain decay process of BaMgF4 crystal were directly visualized by AFM. The dependence of the lateral domain size on the switching voltage pulse magnitude and duration was measured and discussed. It was shown that the defects in the crystal play an important role in such abnormal wall strain behavior, and the sidewise domain kinetics reveals an activation mechanism of the wall motion in the bulk BaMgF4 single crystal.
Effect of preannealing on final texture and magnetic induction in thin-gauged 3% Si–Fe strips containing 0.1% Mn and 0.011% S
Authors: Cho S. S. , Kim S. B. , Soh J. Y. , Oh J. M. , Han S. O. , Heo N. H.
Published: April 2007

In 0.1mm thick 3% Si–Fe strips containing 0.1% manganese and 0.011% sulfur, the preannealed strips were composed of {110} grains after final annealing at 1200°C, while the other strips without preannealing consisted of {100} or {111} grains. This is due to the difference in surface-energy-induced selective growth kinetics in which the main governing factor is probably by the primary grain size. In the preannealed strip with a higher final reduction, the relatively smaller grain size effect produced the decrease in total number of the {110} grains and thus the sharper {110}⟨001⟩ final texture favorable for the higher magnetic induction.
Magnetovolume effect and magnetic transition in Gd5Si4
Authors: Altounian Z. , Liu X. B.
Published: April 2007

Magnetocaloric compound Gd5Si4 has a higher Curie temperature TC=336K than that of Gd pure metal (TC=294K). High temperature synchrotron x-ray powder diffraction experiments have been performed for Gd5Si4 from 300to400K. Rietveld fitting of the results indicate that the compound retains the orthorhombic Gd5Si4-type structure with a space group of Pnma in the above temperature range, where the unit cell is composed of two well defined Gd–Si slabs connected to each other by Si–Si bonds along the b axis. The unit cell volume expands almost linearly with increasing temperature below and above TC. However, the lattice thermal expansion is anisotropic and discontinuous around TC. The lattice constants change from a=7.4834(1)Å, b=14.7476(3)Å, and c=7.7493(2)toa=7.4846(2)Å, b=14.7452(4)Å, and c=7.7560(1) as the temperature is increased from 325to345K. b contracts by about 0.02% while c expands by about 0.08%. Electronic structure calculations show that the anisotropic lattice expansion near TC changes the valence electron distribution between Gd and Si and thus to the Ruderman-Kittel-Kasuya-Yosida interaction, which affects the magnetic ordering and the magnetic transition in Gd5Si4.
Growth of ferroelectric bismuth lanthanum nickel titanate thin films by rf magnetron sputtering
Authors: Kobune Masafumi , Fukushima Koji , Yamaji Toru , Tada Hideto , Yazawa Tetsuo , Fujisawa Hironori , Shimizu Masaru , Nishihata Yasuo , Matsumura Daiju , Mizuki Jun’ichiro , Yamaguchi Hideshi , Kotaka Yasutoshi , Honda Koichiro
Published: April 2007

The epitaxial growth, structural properties, and ferroelectric properties of bismuth lanthanum nickel titanate (Bi1−xLax) (Ni0.5Ti0.5)O3 (BLNT) thin films deposited on Pt(100)∕MgO(100) substrates by rf magnetron sputtering have been investigated using x-ray diffraction, transmission electron microscope, and polarization–electric field hysteresis loop measurements. The ferroelectric BLNT(00ℓ) phase with c-axis orientation and a single-phase tetragonal perovskite structure appeared at x⩾0.3. The tetragonality (c∕a) increased significantly from 1.004 to 1.028 with increasing La content. The fabricated BLNT films of x⩾0.3 indicated the apparent fourfold rotational symmetry observed for a MgO(202) substrate, a bottom Pt(202) electrode, and a BLNT(101) ferroelectric film, based on ϕ scan measurements. These results imply that the present La-substituted BLNT films are grown heteroepitaxially at x⩾0.3. It was confirmed that Bi in the BLNT films is in a trivalent state at A sites in the perovskite crystal, based on x-ray anomalous diffraction measurements and x-ray absorption near edge structure spectra. The sputtering technique using compacted powder targets designed by taking the bond dissociation energy of metal oxides into account provided epitaxial perovskite-structured BLNT thin films on Pt(100)∕MgO(100) substrates. It is shown that the c-axis oriented epitaxial BLNT film exhibits a hysteresis loop shape with a Pr value of 12μC∕cm2 that is comparable to typical high-performance Bi3.25La0.75Ti3O12 (BLT) film.
Spectral imbalance and the normalized dissipation rate of turbulence
Authors: Bos W. J. T. , Shao L. , Bertoglio J.-P.
Published: April 2007

The normalized turbulent dissipation rate Cϵ is studied in decaying and forced turbulence by direct numerical simulations, large-eddy simulations, and closure calculations. A large difference in the values of Cϵ is observed for the two types of turbulence. This difference is found at moderate Reynolds number, and it is shown that it persists at high Reynolds number, where the value of Cϵ becomes independent of the Reynolds number, but is still not unique. This difference can be explained by the influence of the nonlinear cascade time that introduces a spectral disequilibrium for statistically nonstationary turbulence. Phenomenological analysis yields simple analytical models that satisfactorily reproduce the numerical results. These simple spectral models also reproduce and explain the increase of Cϵ at low Reynolds number that is observed in the simulations.
Structural and dynamical properties for confined polymers undergoing planar Poiseuille flow
Authors: Zhang Junfang , Hansen J. S. , Todd B. D. , Daivis Peter J.
Published: April 2007

The authors present the results from nonequilibrium molecular dynamics simulations for the structural and dynamical properties of highly confined linear polymer fluids undergoing planar Poiseuille flow. They study systems confined within pores of several atomic diameters in width and investigate the dependence of the density profiles, the mean squared radius of gyration, the mean squared end-to-end distance, streaming velocity, strain rate, shear stress, and streaming angular velocity as functions of average fluid density and chain length. Their simulation results show that, sufficiently far from the walls, the radius of gyration for molecules under shear in the middle of the pore follows the power law Rg=ANbν, where Nb is the number of bonds and the exponent has a value of 0.5 which resembles the value for a homogeneous equilibrium fluid. Under the conditions simulated, the authors find the onset of flat velocity profiles but with very little wall slippage. These flat profiles are most likely due to the restricted layering of the fluid into just one or two molecular layers for narrow pore widths compared to chain length, rather than typical plug-flow conditions. The angular velocity is shown to be proportional to half the strain rate in the pore interior when the chain length is sufficiently small compared to the pore width, consistent with the behavior for homogeneous fluids in the linear regime.
Liquid film dynamics in horizontal and tilted tubes: Dry spots and sliding drops
Authors: King A. A. , Cummings L. J. , Naire S. , Jensen O. E.
Published: April 2007

Using a model derived from lubrication theory, we consider the evolution of a thin viscous film coating the interior or exterior of a cylindrical tube. The flow is driven by surface tension and gravity and the liquid is assumed to wet the cylinder perfectly. When the tube is horizontal, we use large-time simulations to describe the bifurcation structure of the capillary equilibria appearing at low Bond number. We identify a new film configuration in which an isolated dry patch appears at the top of the tube and demonstrate hysteresis in the transition between rivulets and annular collars as the tube length is varied. For a tube tilted to the vertical, we show how a long initially uniform rivulet can break up first into isolated drops and then annular collars, which subsequently merge. We also show that the speed at which a localized drop moves down the base of a tilted tube is nonmonotonic in tilt angle.
Simple implementation of complex functionals: Scaled self-consistency
Authors: Lima Matheus P. , Pedroza Luana S. , da Silva Antonio J. R. , Fazzio A. , Vieira Daniel , Freire Henrique J. P. , Capelle K.
Published: April 2007

We explore and compare three approximate schemes allowing simple implementation of complex density functionals by making use of self-consistent implementation of simpler functionals: (i) post-local-density approximation (LDA) evaluation of complex functionals at the LDA densities (or those of other simple functionals) (ii) application of a global scaling factor to the potential of the simple functional, and (iii) application of a local scaling factor to that potential. Option (i) is a common choice in density-functional calculations. Option (ii) was recently proposed by Cafiero and Gonzalez [Phys. Rev. A 71, 042505 (2005)]. We here put their proposal on a more rigorous basis, by deriving it, and explaining why it works, directly from the theorems of density-functional theory. Option (iii) is proposed here for the first time. We provide detailed comparisons of the three approaches among each other and with fully self-consistent implementations for Hartree, local-density, generalized-gradient, self-interaction corrected, and meta-generalized-gradient approximations, for atoms, ions, quantum wells, and model Hamiltonians. Scaled approaches turn out to be, on average, better than post approaches, and unlike these also provide corrections to eigenvalues and orbitals. Scaled self-consistency thus opens the possibility of efficient and reliable implementation of density functionals of hitherto unprecedented complexity.
Assessment of the efficiency of long-range corrected functionals for some properties of large compounds
Authors: Jacquemin Denis , Perpète Eric A. , Scalmani Giovanni , Frisch Michael J. , Kobayashi Rika , Adamo Carlo
Published: April 2007

Using the long-range correction (LC) density functional theory (DFT) scheme introduced by Iikura et al. [J. Chem. Phys. 115, 3540 (2001)] and the Coulomb-attenuating model (CAM-B3LYP) of Yanai et al. [Chem. Phys. Lett. 393, 51 (2004)], we have calculated a series of properties that are known to be poorly reproduced by standard functionals: Bond length alternation of π-conjugated polymers, polarizabilities of delocalized chains, and electronic spectra of extended dyes. For each of these properties, we present cases in which traditional hybrid functionals do provide accurate results and cases in which they fail to reproduce the correct trends. The quality of the results is assessed with regard to experimental values and/or data arising from electron-correlated wave function approaches. It turns out that (i) both LC-DFT and CAM-B3LYP provide an accurate bond length alternation for polyacetylene and polymethineimine, although for the latter they decrease slightly too rapidly with chain length. (ii) The LC generalized gradient approximation and MP2 polarizabilities of long polyphosphazene and polymethineimine oligomers agree almost perfectly. In the same way, CAM-B3LYP corrects the major part of the B3LYP faults. (iii) LC and CAM techniques do not help in correcting the nonrealistic evolution with chain length of the absorption wavelengths of cyanine derivatives. In addition, though both schemes significantly overestimate the ground to excited state transition energy of substituted anthraquinone dyes, they provide a more consistent picture once a statistical treatment is performed than do traditional hybrid functionals.
Coupled cluster study of the energetic properties of S2x (x=,+1,1)
Authors: Grant Daniel J. , Dixon David A. , Francisco Joseph S.
Published: April 2007

Ab initio electronic structure calculations are reported for S2, and its ions S2+ and S2−. Geometric parameters are calculated using the singles and doubles coupled cluster method, including a perturbational correction for connected triple excitation, together with systematic sequences of correlation consistent basis sets extrapolated to the complete basis set (CBS) limit. Energetic and structural properties of S2 and the S2 cation and anion are reported. The heat of formation of S2 (Σg−3) at 0K in the gas phase is predicted to be 29.8kcal∕mol from the average of CBS two extrapolation procedures, less than the experimental heat of formation of S2 of 30.66±0.07kcal∕mol. The 0K adiabatic ionization potential and electron affinity are predicted to be 9.37 and 1.68eV, respectively.
Microcavity enhanced spontaneous emission from silicon nanocrystals
Authors: Belarouci A. , Gourbilleau F.
Published: April 2007

An approach fully based on the rf magnetron sputtering of a pure silica target has been developed to deposit a silicon nanocrystal based optical planar microcavity. Tunable narrow emission bands, directionality of the radiation pattern along the normal of the cavity surface, and resonant enhancement of the luminescence intensity have been demonstrated. Time resolved photoluminescence measurements also confirmed an increase of the spontaneous emission rate of silicon nanocrystals when they are embedded inside the optical resonator. These results are attributed to the anisotropic redistribution of the optical density of states induced by the resonator.
Mode transitions and hysteresis in inductively coupled plasmas
Authors: Daltrini A. M. , Moshkalev S. A. , Monteiro M. J. R. , Besseler E. , Kostryukov A. , Machida M.
Published: April 2007

Optical emission spectroscopy as a noninvasive plasma diagnostic was employed to study mode transitions and hysteresis in an inductively coupled plasma in Ar and Ar∕N2 mixtures. Using selected Ar lines, basic plasma parameters, relevant to the analysis of the mode transitions, were evaluated. Small changes of the electron energy distribution function in the vicinity of the mode transition were detected. The role of metastable Ar atoms in mode transitions and in a hysteresis was clarified. Enhanced production of metastables in the hysteresis region as well as faster transitions in plasmas with higher influence of metastables were observed.
Most stable structure of fullerene[20] and its novel activity toward addition of alkene: A theoretical study
Authors: Zhang Congjie , Sun Wenxiu , Cao Zexing
Published: April 2007

Structures and stabilities of fullerene C20 and C20− have been investigated by the density functional theory and CCSD(T) calculations. In consideration of the Jahn-Teller distortion of Ih-symmetric C20, possible subgroup symmetries have been used in the full geometry optimization. On the basis of relative energetics, vibrational analyses, and electron affinities, fullerenes C20 and C20− have most stable D2h and Ci structures, respectively. The controversy on the relative stability of fullerene[20] arises from the use of different subgroups in calculation and the basis set dependence in vibrational analysis. Predicted nucleus-independent chemical shift values show that the most stable fullerene C20 and its derivatives C20(C2H2)n and C20(C2H4)n (n=1–3) exhibit remarkable aromaticity, while C20(C2H2)4 and C20(C2H4)4 have no spherical aromaticity. The C20 (D2h) cage has remarkable activity toward the addition of olefin, and such feasibility of the addition reaction is ascribed to strong bonding interactions among frontier molecular orbitals from C20 and olefin. Calculations indicate that both C20(C2H2)n and C20(C2H4)n have similar features in electronic spectra.
Removal of resonances by rotation in linearly degenerate two-dimensional oscillator systems
Authors: Khasin Michael , Friedland Lazar
Published: April 2007

A system of two nonlinearly interacting, resonant harmonic oscillators is investigated, seeking transformation to approximate action-angle variables in the vicinity of the equilibrium via the canonical perturbation theory. A variety of polynomial perturbations dependent on parameters is considered. The freedom of choice of the zero-order approximation characteristic of a linearly degenerate (resonant) system is used to cancel lower-order resonant terms in the canonical perturbation series. It is found that the cancellation of the resonant terms is only possible for particular values of parameters of the interaction term. These special sets of parameters include all the cases with the Panlevé property.
Coil-globule transition of a single short polymer chain: An exact enumeration study
Authors: Ponmurugan M. , Narasimhan S. L. , Krishna P. S. R. , Murthy K. P. N.
Published: April 2007

The authors present an exact enumeration study of short self-avoiding walks in two as well as in three dimensions that addresses the question, “what is the shortest walk for which the existence of all the three scaling regimes—coil, globule, and the theta—could be demonstrated.” Even though they could easily demonstrate the coil and the globule phase from free energy considerations, they could demonstrate the existence of a theta temperature only by using a scaling form for the distribution of gyration radius. That even such short walks have a scaling behavior is an unexpected result of this work.
Biocatalytic growth of semiconductor nanowires
Authors: Rath S. , Sarangi S. N. , Sahu S. N.
Published: April 2007

A synthetic protocol using DNA as a biocatalyst has been described to electrodeposit HgTe-DNA nanowires (NWs). As evidenced from transmission electron microscopy, Fourier-transform infrared and optical absorption studies, the growth of HgTe NWs is ascribed to the electroactive aggregation of respective cations with DNA followed by cathodic deposition and surface diffusion. The choice of biocatalyst is shown to play an important role for NW growth, which is confirmed with the choice of two different DNA sequences. Additional confirmation of NW growth has been established for a different system, CdSe NW synthesized using the similar principle.
High dynamic range streak camera for subpicosecond time-resolved x-ray spectroscopy
Authors: Bonté C. , Harmand M. , Dorchies F. , Magnan S. , Pitre V. , Kieffer J.-C. , Audebert P. , Geindre J.-P.
Published: April 2007

The full characterization of a time resolved x-ray spectrometer is presented. It is based on the coupling of a conical crystal with a subpicosecond x-ray streak camera. The detector is designed to operate in accumulation mode at high repetition rate (up to 1 kHz) allowing signal to noise ratio as high as 104:1. Optical switches have been used to limit the jitter induced in the subpicosecond range, demonstrating the very long term stability (a few hours) of the entire device. The data analysis have been developed to get the spectral and temporal resolution of an ultrashort laser-plasma-based x-ray source.
Influence of silicon doping on vacancies and optical properties of AlxGa1−xN thin films
Authors: Slotte J. , Tuomisto F. , Saarinen K. , Moe C. G. , Keller S. , DenBaars S. P.
Published: April 2007

The authors have used positron annihilation spectroscopy and photoluminescence measurements to study the influence of silicon doping on vacancy formation in AlGaN:Si structures. The results show a correlation between the Doppler broadening measurements and the intensity from 510nm photoluminescence transition. The reduction in the W parameter when the [Si]∕[Al+Ga] fraction in the gas phase is above 3×10−4 indicates that the positrons annihilate in an environment where less Ga 3d electrons are present, i.e., they are trapped in group-III vacancies. The observation of vacancies at these silicon concentrations coincides with the onset of the photoluminescence transition at 510nm.
Large magnetic moment observed in Co-doped ZnO nanocluster-assembled thin films at room temperature
Authors: Zhao Z. W. , Tay B. K. , Chen J. S. , Hu J. F. , Lim B. C. , Li G. P.
Published: April 2007

Co-doped ZnO nanocluster-assembled films were deposited by nanocluster-beam deposition. Zn0.986Co0.014O nanoclusters remained wurtzite in structure with size of 5nm. Compared with bulk ZnO, a blueshift of 0.28eV was observed in the absorption edge of the film. Two photo-luminescence bands at 378 and 510nm were detected. Room-temperature ferromagnetism was observed in doped ZnO nanocluster-assembled film. Moreover, it exhibited a large saturated magnetization of 1.4μB∕Co and increased to 3.65μB∕Co after the film was annealed. The possible mechanisms on the observed ferromagnetism and enhanced magnetic moment were discussed.
Photon-assisted breakdown, negative resistance, and switching in a quantum-well transistor laser
Authors: James A. , Walter G. , Feng M. , Holonyak N.
Published: April 2007

Data are presented on the transistor laser with collector bias and photon-assisted tunneling causing, under the constraints IE+IB+IC=0 (α=ΔIC∕ΔIE) and α→1, breakdown and negative resistance effects in the IC-VCE characteristics. Collector bias, aided by photon-assisted tunneling (Franz—Keldysh absorption), supplies holes to the n-p-n transistor base by tunneling escape of electrons (ΔIB=0), “feeding” quantum-well recombination radiation (generation and regeneration, ΔIE=ΔIC=ΔIhv) and yielding the negative resistance/switching condition α→1 (α=ΔIC∕ΔIE, ΔIC=ΔIE, ΔIB=0, IE+IB+IC=0), and, as a consequence, corners, negative resistance, switching, vertical collector current (ΔVCE≈0), spectral change, and mode hopping effects in the IC-VCE characteristics.
Phase locking of nanosecond pulses in a passively Q-switched two-element fiber laser array
Authors: Kong Fanting , Liu Liping , Sanders Charlotte , Chen Y. C. , Lee Kotik K.
Published: April 2007

Phase locking of Brillouin backscattering Q-switched laser pulses that are much shorter than the round-trip time of the resonators has been demonstrated in a two-element fiber laser array. Despite the stochastic dynamics of nonlinear pulse generation, simultaneous generation and phase locking of short pulses have been achieved by using diffractive coupling and spatial filtering in an external resonator.
Analog integrator for the Korea superconducting tokamak advanced research magnetic diagnostics
Authors: Bak J. G. , Lee S. G. , Son D. , Ga E. M.
Published: April 2007

An analog integrator, which automatically compensates an integrating drift, has been developed for the magnetic diagnostics in the Korea superconducting tokamak advanced research (KSTAR). The compensation of the drift is done by the analog to digital converter-register-digital to analog converter in the integrator. The integrator will be used in the equilibrium magnetic field measurements by using inductive magnetic sensors during a plasma discharge in the KSTAR machine. Two differential amplifiers are added to the signal path between each magnetic sensor and the integrator in order to improve the performance of the integrator because a long signal cable of 100 m will be used for the measurement in the KSTAR machine. In this work, the characteristics of the integrator with two differential amplifiers are experimentally investigated.
Ab initio photoionization dynamics of β-alanine
Authors: Tian Shan Xi , Yang Jinlong
Published: April 2007

Photoionization dynamics of β-alanine is studied by the trajectory simulations using the ab initio potential energy surface. Vertical photoionization in the spirit of the Franck-Condon principle is assumed both for the adiabatic and thermostatic simulations. Both intramolecular proton transfer and fragmentation while only the proton transfer are found in the thermostatic and adiabatic simulations, respectively, for the conformer having the intramolecular hydrogen bond N⋯H–O. The theoretical predictions are in line with the experimental observations available in the literatures. It is reported for the first time that the thermostatic temperatures strongly affect the fragmentation processes induced by photoionization.
Metal-induced photoluminescence quenching in thin organic films originating from noncontact energy transfer between single molecule and atom
Authors: Wu Y. , Wu H. R. , Wang M. L. , Lu M. , Song Q. L. , Ding X. M. , Hou X. Y.
Published: April 2007

Severe quenching of photoluminescence in dye-doped organic thin films is observed after submonolayer metal (metal atoms) deposition. Insertion of a spacer layer between the organic film and metal atoms has minor effect on eliminating the quenching, indicating that it is a long-range noncontact interaction. The phenomenon is regarded as a result of Förster energy transfer between organic molecules and metal atoms. The origin of the transfer is the coupling between dipoles in excited organic molecules and electron transitions in isolated atoms. Atoms among most elements rather than metals are capable of being involved in such a noncontact energy transfer process.
Microstructure and recording mechanism of Ge∕Au bilayer media for write-once optical disc
Authors: Wu T. H. , Kuo P. C. , Fang Yen-Hsiang , Chen Jung-Po , Yen Po-Fu , Jeng Tzuan-Ren , Wu Chih-Yuan , Huang Der-Ray
Published: April 2007

The recording mechanism of Ge∕Au bilayer and its dynamic tests for write-once blue laser high density DVD (HD DVD) are investigated. It is found that Ge2Au3 phase is nucleated between amorphous Ge and crystalline Au layer after room temperature deposition. Crystallization of Ge∕Au interface layer at 170–190°C is induced by the nucleated Ge2Au3 sites at the interface, the bilayer structure is further heated to 200–450°C. After heating above 320°C, crystallized Ge are segregated at the grain boundary. The dynamic test results show that this Ge∕Au bilayer films can be applied to 1×–2× HD DVD-R.
Vertical stacks of shape-engineered InAs∕InAlGaAs quantum dot and its influences on the lasing characteristics
Authors: Kim Jin Soo , Lee Cheul-Ro , Choi Byung Seok , Kwack Ho-Sang , Lee Chul Wook , Sim Eun Deok , Oh Dae Kon
Published: April 2007

The formation characteristics on the vertical stacks of shape-engineered InAs∕InAlGaAs quantum dots (QDs), which were formed by the alternate growth method (AGQDs), were studied in terms of the modulation in strain field and phase separation. The threshold current of the broad-area laser diodes (LDs) with five stacks of the AGQDs (AGQD-LDs) was 4.5 times smaller than that of the LDs with seven stacks of the conventionally grown QDs (CQD-LDs). The slope efficiency for the AGQD-LDs was 0.16W∕A, which was higher than that of the CQD-LDs of 0.9W∕A. These results can be attributed to better confinement of the electron wave function in QDs.
Uniaxial-stress induced phase transitions in [001]C-poled 0.955Pb(Zn1∕3Nb2∕3)O3–0.045PbTiO3
Authors: Janolin Pierre-Eymeric , Dkhil Brahim , Davis Matthew , Damjanovic Dragan , Setter Nava
Published: April 2007

First order rhombohedral to orthorhombic stress-induced phase transitions have been evidenced by bulk charge-stress measurements and x-ray diffraction derived lattice strain measurements in [001]C-poled 0.955Pb(Zn1∕3Nb2∕3)O3–0.045PbTiO3 (PZN-4.5PT). The transitions are induced by uniaxial compressive loads applied either along or perpendicular to the poling direction. In each case, they occur via rotation of the polar vector in the Cm monoclinic plane and the induced lattice strain is hysteretic yet reversible. Although no depoling is observed in the transverse mode net depolarization is observed under longitudinal stress which is important for the use of [001]C-poled PZN-PT and (1−x)Pb(Mg1∕3Nb2∕3)O3–xPbTiO3 single crystals in Tonpilz-type underwater projectors.
Temperature-insensitive strain sensor with polarization-maintaining photonic crystal fiber based Sagnac interferometer
Authors: Dong Xinyong , Tam H. Y. , Shum P.
Published: April 2007

A fiber-optic strain sensor is demonstrated by using a short length of polarization-maintaining photonic crystal fiber (PM-PCF) as the sensing element inserted in a Sagnac loop interferometer. Spectrum shift in response of strain with a sensitivity of 0.23pm∕με is achieved, and the measurement range, by stretching the PM-PCF only, is up to 32mε. Due to the ultralow thermal sensitivity of the PM-PCF, the proposed strain sensor is inherently insensitive to temperature, eliminating the requirement for temperature compensation.
Chemical sensors for sensing gas adsorbed on the inner surface of carbon nanotube channels
Authors: Jung Hyun Young , Jung Sung Mi , Kim JuRae , Suh Jung Sang
Published: April 2007

The authors have developed gas sensors that operate when gas flowing through carbon nanotube (CNT) channels is adsorbed on the inner surface of the channels. CNTs fabricated on anodic alumina membranes were used. The CNTs are well ordered and connected in parallel, forming parallel channels. The sensors are highly responsive to NH3 and NO2 molecules and the response times are relatively short. They are completely recovered within 10min when a dc voltage of 10V is applied for 2min. The fabrication processes are relatively simple and do not require special techniques such as e-beam lithography.
Enhanced red phosphorescence in nanosized CaTiO3:Pr3+ phosphors
Authors: Zhang Xianmin , Zhang Jiahua , Nie Zhaogang , Wang Meiyuan , Ren Xinguang , Wang Xiao-jun
Published: April 2007

The red photoluminescence and phosphorescence originating from D21-H43 transition of Pr3+ in CaTiO3 nanoparticles are studied as a function of Pr3+ concentrations. The nanophosphors exhibit both longer persistence time of 30min and higher quenching concentration of 0.4mol% than the bulk (10min and 0.1mol%). The initial phosphorescence in the nanophosphor is an order of magnitude stronger than that in the bulk at the corresponding quenching concentrations. Phosphorescence decay patterns and diffused reflectance spectra before and after ultraviolet exposure indicate the existence of more traps contributing to phosphorescence in the nanoparticles.
Low-temperature interface engineering for high-quality ZnO epitaxy on Si(111) substrate
Authors: Wang X. N. , Wang Y. , Mei Z. X. , Dong J. , Zeng Z. Q. , Yuan H. T. , Zhang T. C. , Du X. L. , Jia J. F. , Xue Q. K. , Zhang X. N. , Zhang Z. , Li Z. F. , Lu W.
Published: April 2007

Zn O ( 0001 ) ∕ Si ( 111 ) interface is engineered by using a three-step technique, involving low-temperature Mg deposition, oxidation, and MgO homoepitaxy. The double heterostructure of MgO(111)∕Mg(0001)∕Si(111) formed at −10°C prevents the Si surface from oxidation and serves as an excellent template for single-domain ZnO epitaxy, which is confirmed with in situ reflection high-energy electron diffraction observation and ex situ characterization by transmission electron microscopy, x-ray diffraction, and photoluminescence. The low-temperature interface engineering method can also be applied to control other reactive metal/Si interfaces and obtain high-quality oxide templates accordingly.
Design of a physical vapor transport cell for time controlled deposition of nucleation phase organic thin films
Authors: Mea Jesse S. , Gauvin Serge , Ashrit P. V.
Published: April 2007

A portable high vacuum chamber has been designed to implement a solenoid operated shutter used as a substrate cache during short duration deposition of organic thin films via the physical vapor transport (PVT) method. This PVT cell was designed for the study of gravity effects on nucleation phase organic thin films obtained in laboratory unit g conditions and especially low g conditions found onboard parabolic flights. The design challenges met were, notably, the timely control of deposition on the substrate during parabolas and maintenance of the experimental cell pressure during operation of the shutter. Nucleation phase thin films of the organic hole transporting semiconductor N,N′-bis(3-methylphenyl)-N,N′-bis(phenyl)benzidine (TPD), obtained with the use of the PVT cells, show that the moving shutter has an effect on the convective PVT gas flow; however, as convection is reduced, this effect is observed to be equally reduced.
Transient diffusion and cluster formation of water molecules on Rh(111) at 20K
Authors: Beniya Atsushi , Mukai Kozo , Yamashita Yoshiyuki , Yoshinobu Jun
Published: April 2007

The authors investigated the initial stage of water adsorption on Rh(111) at 20K, using infrared reflection absorption spectroscopy. In this low coverage region, isolated water molecules and small water clusters are observed. Since thermal diffusion is suppressed at 20K, the formation of water clusters at low coverage is controlled by both coverage and transient diffusion on the surface. Within a simple random walk model of the transient diffusion and clustering process, the authors estimate the mean lateral displacement from the first impact point to the final adsorption site to be 7.6Å; an incoming water molecule on Rh(111) is trapped with eight postcollision hops on the average.
Aldolase provides an unusual binding site for thrombospondin-related anonymous protein in the invasion machinery of the malaria parasite
Authors: Bosch Jürgen , Buscaglia Carlos A. , Krumm Brian , Ingason Bjarni P. , Lucas Robert , Roach Claudia , Cardozo Timothy , Nussenzweig Victor , Hol Wim G. J.
Published: April 2007

An actomyosin motor located underneath the plasma membrane drives motility and host-cell invasion of apicomplexan parasites such as
Plasmodium falciparum
and
Plasmodium vivax
, the causative agents of malaria. Aldolase connects the motor actin filaments to transmembrane adhesive proteins of the thrombospondin-related anonymous protein (TRAP) family and transduces the motor force across the parasite surface. The TRAP–aldolase interaction is a distinctive and critical trait of host hepatocyte invasion by
Plasmodium
sporozoites, with a likely similar interaction crucial for erythrocyte invasion by merozoites. Here, we describe 2.4-Å and 2.7-Å structures of
P. falciparum
aldolase (PfAldo) obtained from crystals grown in the presence of the C-terminal hexapeptide of TRAP from
Plasmodium berghei
. The indole ring of the critical penultimate Trp-residue of TRAP fits snugly into a newly formed hydrophobic pocket, which is exclusively delimited by hydrophilic residues: two arginines, one glutamate, and one glutamine. Comparison with the unliganded PfAldo structure shows that the two arginines adopt new side-chain rotamers, whereas a 25-residue subdomain, forming a helix–loop–helix unit, shifts upon binding the TRAP-tail. The structural data are in agreement with decreased TRAP binding after mutagenesis of PfAldo residues in and near the induced TRAP-binding pocket. Remarkably, the TRAP- and actin-binding sites of PfAldo seem to overlap, suggesting that both the plasticity of the aldolase active-site region and the multimeric nature of the enzyme are crucial for its intriguing nonenzymatic function in the invasion machinery of the malaria parasite.
Seismological support for the metastable superplume model, sharp features, and phase changes within the lower mantle
Authors: Sun Daoyuan , Tan Eh , Helmberger Don , Gurnis Michael
Published: April 2007

Recently, a metastable thermal-chemical convection model was proposed to explain the African Superplume. Its bulk tabular shape remains relatively stable while its interior undergoes significant stirring with low-velocity conduits along its edges and down-welling near the middle. Here, we perform a mapping of chemistry and temperature into P and S velocity variations and replace a seismically derived structure with this hybrid model. Synthetic seismogram sections generated for this 2D model are then compared directly with corresponding seismic observations of P (P, P
C
P, and PKP) and S (S, S
C
S, and SKS) phases. These results explain the anticorrelation between the bulk velocity and shear velocity and the sharpness and level of SKS travel time delays. In addition, we present evidence for the existence of a D” triplication (a putative phase change) beneath the down-welling structure.