bluuebunny/crossref_metadata_2025 huggingface dataset:
Pore fluid effects on shear modulus in a model of heterogeneous rocks, reservoirs, and granular media
Authors: Berryman James G.
Published: July 2005

To provide quantitative measures of the importance of fluid effects on shear waves in heterogeneous reservoirs, a model material called a “random polycrystal of porous laminates” is introduced. This model poroelastic material has constituent grains that are layered (or laminated), and each layer is an isotropic, microhomogeneous porous medium. All grains are composed of exactly the same porous constituents and have the same relative volume fractions. The order of lamination is not important because the up‐scaling method used to determine the transversely isotropic (hexagonal) properties of the grains is Backus averaging, which, for quasi‐static or long‐wavelength behavior, depends only on the volume fractions and layer properties. Grains are then jumbled together totally at random, filling all space, and producing an overall isotropic poroelastic medium. The poroelastic behavior of this medium is then analyzed using the Peselnick‐Meister‐Watt bounds (of Hashin‐Shtrikman type). We study the dependence of the shear modulus on pore fluid properties and determine the range of behavior to be expected. In particular, we compare and contrast these results to those anticipated from Gassmann's fluid substitution formulas and to the predictions of Mavko and Jizba for very low porosity rocks with flat cracks. This approach also permits the study of arbitrary numbers of constituents, but for simplicity, the numerical examples are restricted here to just two constituents. This restriction also permits the use of some special exact results available for computing the overall effective stress coefficient in any two‐component porous medium. The bounds making use of polycrystalline microstructure are very tight. Results for the shear modulus demonstrate that the ratio of compliance differences R (i.e., shear compliance changes over bulk compliance changes when going from drained to undrained behavior, or vice versa) is usually nonzero and can take a wide range of values, both above and below the value R = 4/15 valid for low porosity, very low aspect ratio flat cracks. Results show that the overall shear modulus in this model can depend relatively strongly on mechanical properties of the pore fluids, sometimes (but rarely) more strongly than the dependence of the overall bulk modulus on the fluids.
Three‐dimensional structure of P‐wave anisotropy beneath the Tohoku district, northeast Japan
Authors: Ishise Motoko , Oda Hitoshi
Published: July 2005

We retrieve three‐dimensional structures of isotropic and anisotropic velocities of P‐waves of the Tohoku district from first P‐arrival time data, assuming azimuthal anisotropy to be caused by hexagonal symmetry axes distributed horizontally in the Earth. The results show that the high‐velocity Pacific slab is clearly imaged in the isotropic velocity structure, even though the azimuthal anisotropy is taken into account. In addition, small‐scale low‐velocity regions and prominent low‐velocity anomalies are found just below the active volcanoes and in the mantle wedge above the high‐velocity Pacific slab, respectively. The fast propagation axis of P‐waves is in mostly E‐W direction in the upper crust, nearly N‐S and E‐W directions in the lower crust, E‐W direction in the mantle wedge, and N‐S direction in the descending Pacific slab. These features of the P‐wave anisotropy structure are consistent with those of lateral variations of the fast polarization directions measured previously by shear‐wave splitting observations. The plausible factor that causes the crust anisotropy is interpreted as being alignment or preferred orientation of microcracks and crust minerals. The mantle wedge anisotropy is attributed to lattice preferred orientation of the mantle minerals arising from present‐day mantle process such as the mantle wedge convection and the plate motion. However, the fast propagation axis of P‐waves in the slab is almost perpendicular to the magnetic lineation of the oceanic plate under the northwest Pacific, and thus the slab preserves the original anisotropic property that the Pacific plate gained when it formed.
Observations of upwelling and relaxation events in the northern Monterey Bay during August 2000
Authors: Ramp Steven R. , Paduan Jeffrey D. , Shulman Igor , Kindle John , Bahr Frederick L. , Chavez Francisco
Published: July 2005

The interplay between the Point Año Nuevo upwelling center, an offshore anticyclonic mesoscale eddy, and the waters of the Monterey Bay was studied during a series of up‐ and downwelling favorable wind events during August 2000. The upwelling events were characterized by the appearance of cold, salty water at Point Año Nuevo at the north end of the bay that subsequently spread southward across the mouth of the bay as the winds continued. During the downwelling/relaxation events, the surface current and temperature response was dominated by the onshore translation of the offshore eddy and by local surface heating in the bay itself. The circulation within the bay was cyclonic during both wind regimes but slightly more barotropic under poleward forcing. The ICON model, a nested, data assimilating, sigma coordinate model, was used to simulate the upwelling and relaxation events and calculate the subsurface current and density fields. The model reproduced the dominant current and temperature patterns outside the bay, including the southward flowing upwelling filament, the movement of the offshore eddy, the poleward flow off Point Sur, and the circulation within the bay. The model salinity fields at the surface and 100 m levels show that during upwelling, the bay was filled with higher‐salinity water stemming from the Point Año Nuevo upwelling center to the north. During downwelling, the source water for both the surface and 100 m levels was the colder, fresher California Current water offshore, which had advected southward well past Point Piños during the previous upwelling event.
Evaluating the effect of interannual variations of surface chlorophyll on upper ocean temperature
Authors: Gildor H. , Naik N. H.
Published: July 2005

An important issue in modeling and predicting upper ocean variability is the nature of the interactions between ocean biology, ocean dynamics, and irradiance penetration. Numerous studies using in situ observations and model simulations to investigate the effects of biota on light penetration have demonstrated that this biological‐physical feedback may be significant over a wide range of spatial and temporal scales. Using a general circulation model which takes into account interannual variations in surface chlorophyll for the period September 1997 to May 2003, we investigate the effect of varying chlorophyll concentration on surface temperature. We conclude that, by using climatological monthly mean chlorophyll values, we capture the first‐order effect of chlorophyll on light penetration.
Improved track forecasting of a typhoon reaching landfall from four‐dimensional variational data assimilation of AMSU‐A retrieved data
Authors: Zhao Ying , Wang Bin , Ji Zhongzhen , Liang Xudong , Deng Guo , Zhang Xin
Published: July 2005

In this study, an attempt to improve typhoon forecasts is made by incorporating three‐dimensional Advanced Microwave Sounding Unit‐A (AMSU‐A) retrieved wind and temperature and the central sea level pressure of cyclones from typhoon reports or bogus surface low data into initial conditions, on the basis of the Fifth‐Generation National Center for Atmospheric Research/Pennsylvania State University Mesoscale Model (MM5) four‐dimensional variational data assimilation (4DVar) system with a full‐physics adjoint model. All the above‐mentioned data are found to be useful for improvement of typhoon forecasts in this mesoscale data assimilation experiment. The comparison tests showed the following results: (1) The assimilation of the satellite‐retrieved data was found to have a positive impact on the typhoon track forecast, but the landing position error is ∼150 km. (2) The assimilation of both the satellite‐retrieved data and moving information of the typhoon center dramatically improved the track forecast and captured the recurvature and landfall. The mean track error during the 72‐hour forecast is 69 km. The predicted typhoon intensity, however, is much weaker than that from observations. (3) The assimilation of both the satellite‐retrieved data and the bogus surface low data improved the intensity and track forecasts more significantly than the assimilation of only bogus surface low data (bogus data assimilation) did. The mean errors during the 72‐hour forecast are 2.6 hPa for the minimum sea level pressure and 87 km for track position. However, the forecasted landing time is ∼6 hours earlier than the observed one.
Roll convection during a cold air outbreak: A large eddy simulation with stationary model domain
Authors: Gryschka M. , Raasch S.
Published: July 2005

A large eddy simulation (LES) of a cold air outbreak along with organized convection is presented. The computational grid was chosen to be fine enough to explicitly resolve small scale unorganized turbulence, while the size of the model domain was large enough to include the evolution of large scale organized convection. For the first time such an LES was performed with a stationary model domain, being one of the most extensive LES in meteorology so far. During the simulation, convective rolls were formed which showed typical characteristics as observed in nature, such as significantly increasing aspect ratios with increasing distance from the ice edge and orientation of the roll axes in direction of the mean wind shear vector.
Accurate imaging and prediction of Kanmon Strait tidal current structures by the coastal acoustic tomography data
Authors: Lin Ju , Kaneko Arata , Gohda Noriaki , Yamaguchi Keisuke
Published: July 2005

The Kanmon Strait acoustic tomography data acquired at a 5‐min interval are assimilated sequentially into a 2D ocean model on the basis of the ensemble Kalman filter scheme to image strong tidal current structures occurring in the strait. When the accurate range‐averaged currents obtained for the sound transmission lines connecting eight tomography stations are used as assimilation data, the complicated vortex‐imbedded currents are imaged with horizontal resolution and accuracy much better than the result of tomographic inversion. The assimilated currents are well compared to the shipboard ADCP data with a RMS difference of about 24 cm s−1 for both the horizontal velocity components. The assimilated volume transport across the strait also shows a good agreement with the transport estimated from the range‐averaged current on a pair of transmission lines crossing the strait, making a RMS difference of 3700 m3 s−1.
Changes in occurrence of cold surges over east Asia in association with Arctic Oscillation
Authors: Jeong Jee‐Hoon , Ho Chang‐Hoi
Published: July 2005

It has been newly found that the occurrence of cold surges in east Asia is significantly influenced by the Arctic Oscillation (AO). In the present study, the events of cold surge are objectively determined based on several synoptic criteria and the phase‐dependency of its occurrences in association with the AO has been revealed. During the negative AO phase, the frequency of cold surge occurrence is relatively increased than that of neutral and positive AO phases. The variation of upper level trough and jet stream over east Asia and the Siberian High in association of AO are suggested to explain the change of cold surge occurrences.
Two‐dimensional mapping of fine structures in the Kuroshio Current using seismic reflection data
Authors: Tsuji Takeshi , Noguchi Takashi , Niino Hiroshi , Matsuoka Toshifumi , Nakamura Yasuyuki , Tokuyama Hidekazu , Kuramoto Shin'ichi , Bangs Nathan
Published: July 2005

Multi‐channel seismic reflection data acquired in the Pacific Ocean off the Muroto peninsula of Shikoku Island, Japan reveal the two‐dimensional distribution of fine structures in the Kuroshio Current. Eighty‐one seismic sections, each extending 80 km perpendicular to the current and separated by 100 m, were acquired from 20 June to 15 August 1999 (57 days). The seismic data clearly show that fine structures extend over 40 km perpendicular to the current in almost all of the profiles. A simulation study using acoustic model from CTD data demonstrates that fine structure of temperature and salinity identified in CTD data acquired from the Kuroshio Current off the Ashizuri peninsula yield a synthetic seismic profile with characteristics similar to the Muroto transect profiles.
Influence of the skin effect and current risetime on the fragmentation of wires by pulsed currents
Authors: Wall D. P. , Allen J. E. , Molokov S.
Published: July 2005

This study considers the physical phenomenon whereby wires may fragment in the solid state when subject to a sufficiently high pulsed electric current. A mathematical model is constructed within continuum mechanics which considers both Lorentz force and thermal mechanisms for the creation of stress waves in a wire. Previous studies are extended by including the skin effect, that is allowing for the diffusion of current density across the wire, and also investigating the influence of current risetime. Axisymmetric solutions are sought for rigid-lubricated, clamped, and free wire ends. Analytical solutions are obtained for the case of rigid-lubricated wire ends, while for the other cases the governing equations are solved numerically using an application-specific explicit finite-difference scheme, which is staggered in time and space. The inclusion of the skin effect leads to significant qualitative and quantitative differences in results. For example, in some cases we find tension in the longitudinal (τzz) stress component, which experiments suggest to be responsible for the fragmentation process, while the uniform-current model predicts compression. In most cases, the inclusion of the skin effect leads to higher peak tensile τzz stresses. Some understanding of the present results is gained with reference to analytical quasistatic solutions. Stresses generated by the Lorentz force mechanism are found to be more sensitive than those generated by the thermal mechanism to the current risetime. In both cases axial stresses increase with decreasing current risetime. Despite the differences in the results obtained with the inclusion of the skin effect, our results support the broad conclusions of the uniform-current model results; the largest stresses are found at the clamps for a wire with clamped ends, while the largest stresses in a wire with free ends are generated by the thermal mechanism and are located at the center of the wire.
Theoretical study of guanine–Cu and uracil–Cu (neutral, anionic, and cationic). Is it possible to carry out a photoelectron spectroscopy experiment?
Authors: Martínez Ana
Published: July 2005

The structure and bonding of guanine–Cu and uracil–Cu (neutral, anionic, and cationic) are discussed on the basis of the calculated structures and energies. The interaction of the metal atom with guanine and uracil has been analyzed using the B3LYP density-functional approach. The removal of one electron from the neutral complexes produces the stabilization of one of the isomers, while the addition of one electron leads to a system where the metal atom is weakly bounded to guanine or uracil, according to the metal-bases bond distance that is long (2.29–2.90). For guanine–Cu and uracil–Cu, the vertical ionization energy of the anion is close to the dissociation energy of one hydrogen atom from guanine–Cu or uracil–Cu. In these cases, it could be possible to produce the detachment of one electron from the anion and also the removal of one hydrogen atom. This is important since the photoelectron spectroscopy of atomic or mixed-atomic cluster anions has proven to be a very effective tool in the study of small systems. For the analysis of copper atoms with DNA bases such as guanine and uracil, it is expected that the photoelectron spectra of the anion-bases complexes strongly resemble the spectrum of Cu−1, just shifted to higher electron binding energies due to the product stabilization. Hopefully, this information will be useful for the experimental groups.
Comment on “Curvy-steps approach to constraint-free extended-Lagrangian ab initio molecular dynamics, using atom-centered basis functions: Convergence toward Born–Oppenheimer trajectories” [J. Chem. Phys. 121, 11542 (2004)]
Authors: Iyengar Srinivasan S. , Schlegel H. Bernhard , Scuseria Gustavo E. , Millam John M. , Frisch Michael J.
Published: July 2005

The curvy-extended-Lagrangian molecular-dynamics (ELMD) approach [J. M. Herbert and M. Head-Gordon, J. Chem. Phys. 121, 11542 (2004)] is similar to atom-centered density-matrix propagation (ADMP) [H. B. Schlegel, J. M. Millam, S. S. Iyengar, G. A. Voth, A. D. Daniels, G. E. Scuseria, and M. J. Frisch, J. Chem. Phys. 114, 9758 (2001); S. S. Iyengar, H.B. Schlegel, J.M. Millam, G.A. Voth, G.E. Scuseria, and M.J. Frisch, ibid.115, 10291 (2001); H.B. Schlegel, S.S. Iyengar, X. Li, J.M. Millam, G.A. Voth, G.E. Scuseria, and M.J. Frisch, ibid. 117, 8694 (2002); S.S. Iyengar, H.B. Schlegel, G.A. Voth, J.M. Millam, G.E. Scuseria, and M.J. Frisch, Israel J. Chem. 42, 191 (2002)] and based on Car-Parrinello [Phys. Rev. Lett. 55, 2471 (1985)] extended-Lagrangian [H.C. Andersen, J. Chem. Phys. 72, 2384 (1980)] molecular dynamics. Similarities between curvy-ELMD and ADMP arise from using unconverged electronic single-particle density matrices within Gaussian basis functions as dynamical variables. Curvy-ELMD differs from ADMP in not requiring idempotency to be explicitly enforced. In this Comment, we address several misleading remarks in Refs. 1 [J.M. Herbert and M. Head-Gordon, J. Chem. Phys. 121, 11542 (2004)] and 8 [J.M. Herbert and M. Head-Gordon, J. Chem. Phys. (submitted)].
Response to “Comment on ‘Curvy-steps approach to constraint-free extended-Lagrangian ab initio molecular dynamics, using atom-centered basis functions: Convergence toward Born–Oppenheimer trajectories’ ” [J. Chem. Phys. 123, 027101 (2005)]
Authors: Herbert John M. , Head-Gordon Martin
Published: July 2005

In response to the Comment by Iyengar et al. [(unpublished)], we reiterate the differences between our “curvy-steps” implementation of extended-Lagrangian molecular dynamics and their “atom-centered density matrix propagation” technique. We further clarify our conclusions regarding adiabaticity indices and anomalous vibrational frequency shifts.
The macromolecular crystallography station at beamline BM16 at the ESRF
Authors: Juanhuix Jordi , Labrador Ana , Beltrán David , Herranz Juan F. , Carpentier Philippe , Bordas Joan
Published: July 2005

A beamline previously used for powder diffraction (BM16) at the European Synchrotron Radiation Facility has been redesigned and rebuilt to carry out both mcromolecular crystallography (MX) and noncrystalline diffraction/scattering (NCD/S) experiments. The MX station has become available for routine user experiments since September 2003 and the NCD/S station is currently being commissioned. The optics are designed so that both the focal spot and flux are good in the 6–17keV energy range (2.1–0.73Å), while the performance is optimal at the selenium K-edge (12.658keV,0.98Å). The MX facility is fully equipped to carry out multiwavelength anomalous dispersion experiments, in particular at the SeK-edge. Moreover, experiments using lower energies such as those of the Mn and FeK-edges are also possible. Here we describe the optical configuration and the setup for MX experiments, as well as a typical example of the experiments carried out so far.
Electronic relaxation dynamics of Ni2+-ion aqueous solution: Molecular-dynamics simulation
Authors: Iuchi Satoru , Morita Akihiro , Kato Shigeki
Published: July 2005

Electronic relaxation dynamics of Ni2+-ion aqueous solution is investigated using molecular-dynamics (MD) simulations with the model-effective Hamiltonian developed previously. The nonadiabatic transition rates from the first three excited states to the ground state are evaluated by the golden rule formula with the adiabatic MD simulations. The MD simulations with the fewest-switch surface-hopping method are also carried out to obtain a more detailed description of the electronic relaxation dynamics among the excited states. We found out that the transitions among the three excited states are very fast, in the order of 10 fs, while the transition between the excited and ground states is slow, about 800 ps. These findings are consistent with the time scales of energy dissipation detected by the transient lens experiment. In both simulations, we explore the effects of the quantum decoherence, where the decoherence functions are derived by the energy-gap dynamics with the displaced harmonic-oscillator model.
Actuating and detecting of microdroplet using slanted finger interdigital transducers
Authors: Wu Tsung-Tsong , Chang I-Hsiang
Published: July 2005

Using surface acoustic wave (SAW) to drive droplets on a piezoelectric chip is a distinctive microfluidic technique developed recently. In the previous research, uniform interdigital transducers (IDTs) were used to radiate SAW amplitude and move the droplets within the same delay line simultaneously. In this paper, we employ slanted finger interdigital transducers (SFITs) to replace uniform IDTs. The merit is that we can move individual droplets at will by varying the frequency. This is because SAW amplitude profile actuated by a SFIT is not uniform along the aperture. The position of the maximum amplitude can be changed by adjusting the input frequency. In addition, we apply the coupling-of-modes model to simulate the amplitude profile and the frequency response of SFITs. Since the transmitted SAW intensity is strongly attenuated by the liquid when SAW hits the droplet, we can use the measured frequency response to detect the position of the droplet and verify the validity of the proposed method; we fabricated a SFIT on an Y128X-LiNbO3 substrate coated with hydrophobic film. The experimental results show good agreement with those predicted by the simulations. We note that the proposed method can further be used to construct a multichannel microfluidic chip.
The HCS∕HSC and HCS+∕HSC+ systems: molecular properties, isomerization, and energetics
Authors: Puzzarini Cristina
Published: July 2005

The isomer pair HCS∕HSC and related cations have been studied by means of a highly accurate level of theory. For all the species investigated the near-equilibrium potential energy surface has been calculated using the coupled cluster method in conjunction with correlation consistent basis sets ranging in size from quadruple to sextuple zeta. After extrapolation to the complete basis set limit, additional corrections due to core-valence correlation and scalar relativistic effects have also been included. Consequently, the molecular and spectroscopic properties as well as the ionization potentials and dissociation energies have been predicted to high accuracy. Isomerization path and energy for both radical and cationic species have also been investigated. Finally, the anharmonic vibrational frequencies have been employed in order to obtain zero-point corrections to ionization potentials, dissociation energies, and isomerization barriers: IP0(HCS)=7.57(4)eV and IP0(HSC)=9.00(5)eV; D0(C–H)=49.29(55)kcal∕mol and D0(S–H)=9.99(37)kcal∕mol; ΔE0(HCS∕HSC)=39.29(49)kcal∕mol, and ΔE0(HCS+∕HSC+)=72.24(75)kcal∕mol.
Experimental and theoretical study on gas-phase ion/molecule reactions of silver trimer cation, Ag3+, with 12-crown-4
Authors: Kumondai Kousuke , Toyoda Michisato , Ishihara Morio , Katakuse Itsuo , Takeuchi Takae , Ikeda Mai , Iwamoto Kenichi
Published: July 2005

The reaction mechanisms of silver trimer cation, Ag3+, with 12-crown-4 (12C4) were studied experimentally and theoretically. Using a cylindrical ion trap time-of-flight mass spectrometer, gas-phase ion/molecule reactions of Ag3+ with 12C4 were observed. Metal-ligand complexes of [Ag(12C4)]+, [Ag3(12C4)]+ and [Ag3(12C4)2]+, and of [Ag(12C4)2]+ and [Ag3(12C4)3]+, were observed as the reaction intermediates and terminal products, respectively. The formations of the [Ag(12C4)]+ and [Ag(12C4)2]+ complexes indicated that the neutral dimer (Ag2) had been eliminated from the trimer cation. From the results of ab initio calculations at the HF/LanL2DZ level of theory and the experiments, it is suggested that three 12C4 molecules can attach to Ag3+ through consecutive reactions and that neutral Ag2 can be easily eliminated from [Ag3(12C4)]+.
Spectroscopic characterization of a molecule with a weak bond: The BrOO radical
Authors: Suma Kohsuke , Sumiyoshi Yoshihiro , Endo Yasuki
Published: July 2005

Pure rotational spectra of the BrOO radical for the Br79 and Br81 isotopomers have been observed using a Fourier transform microwave spectrometer. The radical was produced in a supersonic jet by discharging a mixture gas containing bromine and oxygen diluted in argon. A-type rotational transitions are observed for N″=1−5, Ka=0 with spin doublings and hyperfine splittings due to the nuclear spin of the bromine atom. High-level ab initio calculations by RCCSD(T) and MRCI have also been performed, and results are compared with the experimental data. Molecular structure of BrOO has been discussed based on the present experimental data, supplemented by the tendency among the halogen peroxide series and the results of the ab initio calculations; the Br–O bond is found to be anomalously long and weak. Systematic comparisons with other halogen peroxides have revealed anomalous nature of the X–O (X=halogen atom) bonds for this series of radicals.
One-photon mass-analyzed threshold ionization spectroscopy of CH2BrI: Extensive bending progression, reduced steric effect, and spin-orbit effect in the cation
Authors: Lee Mina , Kim Hyoseok , Lee Yoon Sup , Kim Myung Soo
Published: July 2005

One-photon mass-analyzed threshold ionization (MATI) spectrum of CH2BrI was obtained using coherent vacuum-ultraviolet radiation generated by four-wave difference-frequency mixing in Kr. Unlike CH2ClI investigated previously, a very extensive bending (Br–C–I) progression was observed. Vibrational frequencies of CH2BrI+ were measured from the spectra and the vibrational assignments were made by utilizing frequencies calculated by the density-functional-theory (DFT) method using relativistic effective core potentials with and without the spin-orbit terms. A noticeable spin-orbit effect on the vibrational frequencies was observed from the DFT calculations, even though its influence was not so dramatic as in CH2ClI+. A simple explanation based on the bonding characteristics of the molecular orbitals involved in the ionization is presented to account for the above differences between the MATI spectra of CH2BrI and CH2ClI. The 0-0 band of the CH2BrI spectrum could be identified through the use of combined data from calculations and experiments. The adiabatic ionization energy determined from the position of this band was 9.5944±0.0006eV, which was significantly smaller than the vertical ionization energy reported previously.
A model of the two-stage Hall thruster discharge
Authors: Ahedo E. , Parra F. I.
Published: July 2005

The effect of a third, active electrode placed inside the ceramic chamber of a Hall thruster is analyzed. Both electron-collecting and electron-emitting modes are considered. Significant efficiency enhancement with respect to the single-stage operation can be obtained for a good electron-emitting electrode, placed in an intermediate location of the acceleration region, and for an anode-to-electrode (inner-stage) potential significantly larger than the ionization potential. Optimum values of the electrode location and voltage are determined. The performance improvement is due to a reduction of the energy losses to the chamber walls. This is the consequence of lower Joule heating and thus lower electron temperature in the outer stage. When the ionization process is efficient already in the single-stage operation, (i) two-stage operation does not affect practically the propellant and voltage utilizations and (ii) thrust efficiency decreases when the intermediate electrode works as an electron collector.
Polarized photoreflectance spectroscopy of strained A-plane GaN films on R-plane sapphire
Authors: Ghosh Sandip , Misra Pranob , Grahn H. T. , Imer Bilge , Nakamura Shuji , DenBaars S. P. , Speck J. S.
Published: July 2005

We have investigated a [112¯0]-oriented A-plane GaN film on R-plane sapphire, where the c axis of GaN lies in the film plane, by polarized photoreflectance (PR) spectroscopy. Near the fundamental energy gap of GaN, the PR spectrum with the probe light polarized perpendicular to the c axis exhibits one feature corresponding to a single transition labeled T1. For a polarization parallel to c axis, two different features labeled T2 and T3 are observed at higher energies than the transition T1. In order to explain the origin of these three features, we compare the measured energies with calculations of the transition energies and oscillator strengths of the three band-to-band transitions of GaN near its fundamental gap for an anisotropic in-plane strain in the A plane. The analysis shows that the observed transition energies and polarization properties of the three transitions can be explained by the presence of an overall compressive, anisotropic in-plane strain in the film.
Temperature response and anharmonicity of the optical phonons in GaN nanowires
Authors: Chen Xiang-Bai , Huso Jesse , Morrison John L. , Bergman Leah , Purdy Andrew P.
Published: July 2005

Anharmonic decay mechanisms of longitudinal-optical (LO) phonons in wurtzite-structured GaN nanowires were studied by temperature-dependent Raman scattering at the temperature range of 77–900K. It was found that with increasing temperature, the LO-phonon linewidth increases and the Raman frequency decreases. The LO-linewidth behavior was analyzed in terms of the anharmonic effect of two- and three-phonon decay mechanisms. We found that for a temperature regime up to the Debye temperature ∼830K, the two-phonon decay contributes the major increase to the linewidth and the three-phonon decay mechanism is marginal. The Raman frequency was studied in terms of the anharmonic decay and the thermal expansion of the lattice. Our analysis indicates that the anharmonic interaction due to the two-phonon decay as well as the thermal-expansion contribution both need to be taken into consideration. Additionally, in analyzing the linewidth of the nanowires, a temperature-independent term, which usually is not included when analyzing bulk material, had to be considered. The temperature-independent term reflects the inhomogeneous nature of the crystallite ensemble.
Structural, electrical, and optical properties of transparent gallium oxide thin films grown by plasma-enhanced atomic layer deposition
Authors: Shan F. K. , Liu G. X. , Lee W. J. , Lee G. H. , Kim I. S. , Shin B. C.
Published: July 2005

Gallium oxide (Ga2O3) thin films were deposited on silicon (100) and sapphire (001) substrates using the plasma-enhanced atomic layer deposition (PEALD) technique with an alternating supply of reactant source, [(CH3)2GaNH2]3, and oxygen plasma. The thin films were annealed at different temperatures (500, 700, and 900°C, respectively) in a rapid thermal annealing system for 1min. It was found that Ga2O3 thin films deposited by PEALD showed excellent step coverage characteristics. X-ray diffraction measurements showed that the as-deposited thin film was amorphous. However, the thin films annealed at temperatures higher than 700°C showed a (400) orientation of the monoclinic structure. An atomic force microscope was used to investigate the surface morphologies of the thin films. The thin films showed very smooth surfaces; the roughness of the as-deposited thin film was about 4Å. With increasing annealing temperature, the thin film became rougher compared with that annealed at lower temperatures. A double-beam spectrophotometer was used to measure the transmittances of the thin films on the sapphire substrates. The thin films showed a very high transmittance (nearly 100%). The band-gap energies of the thin films were determined by a linear fit of the transmittance spectra and were calculated to be between 5.0 and 5.24eV. The electrical properties of thin films of Pt/film/Si structure were also investigated. It was found that, with increasing annealing temperature, the insulating characteristics of the Ga2O3 thin films were significantly improved. Spectroscopic ellipsometry was used to derive the refractive indices and the thicknesses of the thin films. The refractive indices of the thin films showed normal dispersion behavior. The refractive indices of the thin films annealed at low temperatures were smaller than those annealed at high temperatures.
Electronic structure of silicon quantum dots: Calculations of energy-gap redshifts due to oxidation
Authors: Nishida Masahiko
Published: July 2005

Electronic state calculations are performed self-consistently using the extended Hückel-type nonorthogonal tight-binding method for two different oxygen configurations (backbonded and double-bonded oxygen configurations) on the H-covered surface of spherical Si35H36, Si47H60, Si71H84, Si136H120, Si148H120, and Si172H120 quantum dots. The size dependence of the effect of oxygen on the electronic structure of the Si dots is studied. Energy gaps calculated for both oxygen configurations can explain oxidation-induced redshifts in photoluminescence (PL) observed in porous Si. However, the energy gaps calculated for the backbonded oxygen model are around 2.2eV and dipole allowed in all Si dots studied, whereas those for the double-bonded oxygen model are gradually decreased with the increase in size (2.3–1.7eV), and optical transitions are dipole forbidden in the Si dots near 1nm across and dipole allowed in the ones near 2nm in diameter. The results calculated for the backbonded oxygen model coincide well with the experimental fact that the PL-peak energies are fixed at ∼2.1eV when porous Si is exposed to air.
Effects of stress and electric field on the electromechanical properties of Pb(Mg1∕3Nb2∕3)O3–0.32PbTiO3 single crystals
Authors: Wan Q. , Chen C. , Shen Y. P.
Published: July 2005

The effects of constant bias stress and electric field on the electromechanical behavior of ⟨001⟩-oriented Pb(Mg1∕3Nb2∕3)O3–0.32PbTiO3 (PMN–0.32PT) relaxor ferroelectric single crystals have been investigated. Both unipolar and bipolar responses are considered. Obtained results show that compressive bias stress with appropriate magnitude can significantly increase the piezoelectric constant. It is also found that bias electric field in the poling direction stabilizes the microstructure of PMN–0.32PT and reduces the hysteresis loss. The observed effects of bias stress and bias electric field on the electromechanical properties of ⟨001⟩-oriented PMN–0.32PT single crystals can be interpreted in terms of phase-transformation-induced polarization rotation through intermediate phases.
Superparamagnetic microbead inductive detector
Authors: Lany M. , Boero G. , Popovic R. S.
Published: July 2005

We developed an inductive system to measure the surface concentration of superparamagnetic microbeads resulting from a bioassay. Our tabletop apparatus, tested with Dynal MyOne™ microbeads, has a detection limit of about 1000beads∕Hz1∕2 (i.e., about 2×1010Bohr magnetons). The system can measure surface concentrations from 0.01% to 100% over the 6mm2 sensitive area with an integration time of 1s.
Enhanced beam currents of P2+, P3+, and P4+ for use in semiconductor ion implanters
Authors: Gushenets V. I. , Bugaev A. S. , Oks E. M. , Hershcovitch A. , Johnson B. M. , Kulevoy T. V. , Poole H. J. , Svarovsky A. Ya.
Published: July 2005

Considerably enhanced yields of P2+ (8.6pmA), P3+ (1.9pmA), and P4+ (0.12pmA) were obtained using a modified Bernas-Calutron ion source. The source design, experimental layout, and results of extensive optimization studies are described. The improved production of multiply charged ions is of particular interest for applications in semiconductor ion implantation facilities.
Rocket-borne instrument for measuring vibrational-rotational temperature and density in the lower thermosphere
Authors: Kurihara Junichi , Oyama Koh-Ichiro
Published: July 2005

We applied the electron beam fluorescence (EBF) technique to measure the vibrational temperature, rotational temperature, and number density of atmospheric molecular nitrogen (N2) in the altitude range of 100–150km. The atmospheric N2 is excited and ionized by electron beam of the energy of 1keV and the subsequent fluorescence of the N2+ first negative band is detected by a sensitive spectrometer, which covers the 360–440nm wavelength range. In contrast to previous rocket-borne photometric measurements using the EBF technique, the spectrometric measurement provides the above three parameters simultaneously and more accurately. Preflight laboratory experiments were carried out in order to test the spectral sensitivity over the whole spectral range, to calibrate the number density from the band intensity, and to know the accuracy of the rotational temperature measurement. Finally, we tried to calibrate the vibrational temperature measurement by using heated N2 gas which is ejected from the small nozzle.
Determination of the complete dielectric polarization of Langmuir monolayers
Authors: Wagner Robert , Yamamoto Tetsuya , Manaka Takaaki , Iwamoto Mitsumasa
Published: July 2005

An experimental instrument has been developed utilizing Brewster angle reflectometry and Maxwell displacement current (MDC) measurement techniques, which are ascribed to the linear and spontaneous polarization, respectively, to investigate orientational order of Langmuir monolayers at an air-water interface. This system has been demonstrated to be sensitive in detecting the orientational order parameters S1 and S2 simultaneously [Sn is defined as the thermodynamic average of Legendre polynomials of nth rank, Sn=⟨Pn(cosθ)⟩]. Using this system in conjunction with a previously established system utilizing second harmonic generation and MDC, which is capable of detecting the orientational order parameters S1 and S3 simultaneously, all three orientational order parameters S1, S2, and S3 can be obtained for Langmuir monolayers. An experiment using the newly developed instrument was conducted on a monolayer comprised of 4-octyl-4′-n-cyanobiphenyl (8CB) molecules to demonstrate the capability of detecting the orientational order parameters S1 and S2 during monolayer compression.
A high efficiency ultrahigh vacuum compatible flat field spectrometer for extreme ultraviolet wavelengths
Authors: Blagojević B. , Le Bigot E.-O. , Fahy K. , Aguilar A. , Makonyi K. , Takács E. , Tan J. N. , Pomeroy J. M. , Burnett J. H. , Gillaspy J. D. , Roberts J. R.
Published: July 2005

A custom, flat field, extreme ultraviolet spectrometer built specifically for use with low power light sources that operate under ultrahigh vacuum conditions is reported. The spectral range of the spectrometer extends from 4 nm to 40 nm. The instrument optimizes the light gathering power and signal-to-noise ratio while achieving good resolution. A detailed description of the spectrometer and design considerations are presented, as well as a procedure that could be used to obtain a synthetic wavelength calibration with the aid of only a single known spectral feature. This synthetic wavelength calibration is compared to a standard wavelength calibration obtained from previously reported spectral lines of Xe, Ar, and Ne ions recorded with this spectrometer.
A systematic shift in the electronic spectra of substituted benzene molecules trapped in helium nanodroplets
Authors: Boatwright Adrian , Besley Nicholas A. , Curtis Sharon , Wright Rossana R. , Stace Anthony J.
Published: July 2005

Electronic spectra (S1←S0) have been recorded from five separate substituted benzene derivatives trapped in helium nanodroplets. Each member of the series is found to exhibit a blueshift with respect to the equivalent transition in the gas phase. Taken together with previous results for benzene, the observed shifts show a remarkably good correlation with changes in electron density that occur within each of the aromatic rings as a result of electronic excitation.
Evidence of the influence of reflections on the Zeff profile measurements in the Tore Supra tokamak and their mitigation
Authors: Schunke B. , Huysmans G. T. A. , Thomas P. R.
Published: July 2005

Reliable experimental determination of the mean effective charge (Zeff) of the plasma is of enormous importance for the impurity control in high temperature plasmas, allowing the performance of various discharge scenarios to be assessed and the benchmarking of model calculations, ideally accompanied by measurements of the Zeff profile. The Zeff is usually calculated using data from line-integrated visible bremsstrahlung measurements, electron density and temperature profiles, and the plasma geometry. On Tore Supra (TS) it had been noticed in the past that hot spots on the inner wall, MARFEs or supra thermal electrons can falsify the signal of the visible bremsstrahlung. More significant, however, was a systematic overestimation of the edge channels, giving unreasonably high edge Zeff values of 30 or even higher. The analysis of dedicated discharges in the present configuration of TS leads us to conclude that this is due to the influence of vessel wall reflections. A newly developed inversion method which takes reflections into account shows that the presence of reflections leads to an overestimation of the outer channels in the reconstruction of the Zeff profile. This is due to the larger relative contribution of the reflections on the edge channels due to the shorter path length through the plasma and the lower bremsstrahlung emission at the edge. We present a model which takes into account this effect and allows a correction procedure to be applied when calculating the Zeff profile. The TS data can be modeled assuming Lambertian (diffusive) reflections with a reflectivity coefficient of 20%–25%, which is in agreement with measurements of the reflectivity of the inner wall of the TS vacuum chamber.
In-line phase-contrast imaging with a laser-based hard x-ray source
Authors: Toth R. , Kieffer J. C. , Fourmaux S. , Ozaki T. , Krol A.
Published: July 2005

We demonstrate the feasibility of phase-contrast imaging with an ultrafast laser-based hard x-ray source. Hard x rays are generated during the interaction of a high-intensity femtosecond laser pulse (10TW,60fs,10Hz) focused onto solid target in a very small spot (3μm diam). Such a novel x-ray source has a number of advantages over other sources previously used for phase-contrast imaging: It is very compact and much cheaper than a synchrotron, it has higher power and better x-ray spectrum control than a microfocal x-ray tube, and it has much higher repetition rate than an x-pinch source. The Kα line at 17keV produced using a solid Mo target, and the in-line imaging geometry have been utilized in this study. Phase-contrast images of test objects and biological samples have been realized. The characteristics of the images are the significant enhancement of interfaces due to an x-ray phase shift that reveal details that were hardly observable, or even undetectable, in absorption images and suppression of optically dense structures well defined in the absorption images. Our study indicates that the absorption and the phase-contrast images obtained with an ultrafast laser-based x-ray source provide complementary information about the imaged objects, thus enriching our arsenal of research tools for laboratory or clinic-based biomedical imaging.
Mixing in a drop moving through a serpentine channel: A computational study
Authors: Muradoglu Metin , Stone Howard A.
Published: July 2005

The chaotic mixing in a drop moving through a winding channel is studied computationally in a two-dimensional setting. The molecular mixing is ignored and only the mixing due to the chaotic advection is considered. Passive tracer particles are used to visualize the mixing patterns and mixing is quantified by two distinct methods. It is found that both the quantification methods are consistent with visual observations as well as with each other. The effects of various non-dimensional parameters on the quality of mixing are studied and it is found that the capillary number, the ratio of the drop phase fluid viscosity to that of the ambient fluid and the relative size of the drop compared to the average channel width are the most critical parameters influencing the mixing. The mixing is found to be weakly dependent on Reynolds number.
Condensation phenomena in nanopores: A Monte Carlo study
Authors: Paul Raja , Rieger Heiko
Published: July 2005

The nonequilibrium dynamics of condensation phenomena in nanopores is studied via Monte Carlo simulations of a lattice-gas model. Hysteretic behavior of the particle density as a function of the density of a reservoir is obtained for various pore geometries in two and three dimensions. The shape of the hysteresis loops depend on the characteristics of the pore geometry. The evaporation of particles from a pore can be fitted to a stretched exponential decay of the particle density. Phase-separation dynamics inside the pore is effectively described by a random walk of the nonwetting phases. Domain evolution is significantly slowed down in the presence of a random wall-particle potential and gives rise to a temperature-dependent growth exponent. A geometric roughness of the pore wall only delays the onset of a pure domain growth.
Near-field scanning photocurrent microscopy of a nanowire photodetector
Authors: Gu Y. , Kwak E.-S. , Lensch J. L. , Allen J. E. , Odom T. W. , Lauhon L. J.
Published: July 2005

A near-field scanning optical microscope was used to image the photocurrent induced by local illumination along the length of a metal-semiconductor-metal (MSM) photodetector made from an individual CdS nanowire. Nanowire MSM photodetectors exhibited photocurrents ∼105 larger than the dark current (<2pA) under uniform monochromatic illumination; under local illumination, the photoresponse was localized to the near-contact regions. Analysis of the spatial variation and bias dependence of the local photocurrent allowed the mechanisms of photocarrier transport and collection to be identified, highlighting the importance of near-field scanning photocurrent microscopy to elucidating the operating principles of nanowire devices.
Fe-catalytic growth of ZnSe nanowires on a ZnSe(001) surface at low temperatures by molecular-beam epitaxy
Authors: Ohno Yutaka , Shirahama Takeo , Takeda Seiji , Ishizumi Atsushi , Kanemitsu Yoshihiko
Published: July 2005

We grew ZnSe needle-like nanowires on a ZnSe∕GaAs epilayer using Fe catalysts by means of molecular-beam epitaxy operated at low temperatures of 250–350 °C, which are comparable to the usual temperatures for fabrication of ZnSe-based optoelectronic devices. The diameters at the tops of the nanowires ranged from 8 to 20 nm, and the typical length was about 200 nm. The number density of the nanowires was the order of 109cm−2. A nanowire was the zinc blende structure and the longitudinal direction was ⟨001⟩,⟨111⟩,⟨110⟩, or ⟨112⟩. Photoluminescence spectroscopy implied that the optical property of the nanowires differs from that of the bulk crystals.