bluuebunny/crossref_metadata_2025 huggingface dataset:
Temporal and spatial occurrence of deep non‐volcanic tremor: From Washington to northern California
Authors: McCausland Wendy , Malone Steve , Johnson Dan
Published: December 2005

Regional network data reveal deep non‐volcanic tremor occurs in five independent sections along the U.S. section of the Cascadia subduction zone with different recurrence intervals. Sizeable tremor episodes occur during periods with no measurable geodetic deformation as well as coincident with episodic slow slip events, and the displacement amplitudes of the tremor with and without geodetic deformation are similar. The tremor depths cover a wide range that does not coincide directly with the subducting slab interface. The tremor can migrate bi‐directionally from the point of initiation, and more than one spatially distinct tremor source can be active at a given time. These results indicate that the tremor is not directly related to the slow slip event. Instead we suggest that the tremor is related to the presence and movement of fluids at depth, which can explain the locations and episodic occurrence as well as the seismic signal characteristics themselves; namely, the limited frequency content, small size, emergent onsets, and prolonged durations with and without geodetic deformation.
Is there a causal relationship between cosmic noise absorption and PMSE?
Authors: Morris Ray J. , Terkildsen Michael B. , Holdsworth David A. , Hyde Mike R.
Published: December 2005

We report on the first Southern Hemisphere comparison between polar mesosphere summer echoes (PMSE) and cosmic noise absorption (CNA). Observations were obtained during the austral summer of 2003–2004 from a 55 MHz MST radar, a 38.2 MHz imaging riometer and a 30 MHz standard riometer all co‐located at Davis, Antarctica (68.6°S). Case study PMSE events suggest that CNA plays a role in the intensification of established dayside PMSE possibly linked with soft electron precipitation from the polar cusp, and indeed with a similar effect and moreover with the creation of night‐side PMSE connected with hard auroral electron precipitation. Although Pearson correlation coefficients are not that high (i.e., 0.423), Spearman rank correlation coefficients of 0.315, with 123 degrees of freedom well above the 99% confidence limits, established that a weak correlation between CNA and PMSE intensity exists. We use this result to discuss two unexplained properties of PMSE: (i) diurnal minimum near ∼15–21 UT; and (ii) non‐linear intensity variation as a function of latitude. Surprisingly, this study presents only the second analysis of this kind using co‐located instruments.
Dynamics of giant volcanic ash clouds from supervolcanic eruptions
Authors: Baines P. G. , Sparks R. S. J.
Published: December 2005

The largest explosive volcanic eruptions that have occurred on Earth generated giant ash clouds from rising plumes that spread in the stratosphere around a height of neutral buoyancy, with estimated supply rates that are in the range 1011 to 1013 m3/s. These giant ash clouds are controlled by a balance between gravity and Coriolis forces, forming spinning bodies of nearly fixed proportions after a few hours and are initially insensitive to stratospheric winds. In contrast, volcanic plumes from eruptions with small to intermediate magnitude spread as inertial intrusions under the influence of stratospheric winds, with the Earth's rotation being unimportant. In the largest eruptions the giant spinning ash clouds typically develop diameters greater than 600 km and up to 6000 km in the most powerful super‐eruptions, thus explaining why areas of continental size can be covered with volcanic ash. The radial expansion and spinning velocities are calculated at tens of metres per second and increase with eruption intensity. Higher spreading velocities carry larger ash grain sizes to a given radius, so that grain size at a given distance from the source increases with eruption intensity, consistent with geological observations.
Alfvén waves and Poynting flux observed simultaneously by Polar and FAST in the plasma sheet boundary layer
Authors: Dombeck J. , Cattell C. , Wygant J. R. , Keiling A. , Scudder J.
Published: December 2005

We present the first simultaneous observations of Alfvén waves at Polar and FAST altitudes, ∼7 RE geocentric and ∼3500 km, respectively, at ∼23 MLT in the main phase of a major geomagnetic storm on 22 October 1999. We compare the Poynting flux for these waves and the electron energy flux at the two spacecraft. We also present a new method of Alfvén wave analysis, examining Poynting flux magnitude and directionality along with the perturbation electric to magnetic field ratio of these waves as a function of wave temporal scale (frequency). The results of this analysis are compared with those expected from kinetic Alfvén wave models. There is a mean net loss of ∼2.1 ergs cm−2 s−1 (mW m−2) in earthward Poynting flux over the altitude region between Polar and FAST, a mean net increase in earthward electron energy flux of up to ∼1.2 ergs cm−2 s−1 over the same region, frequency characteristics consistent with a mixture of Alfvén waves obeying the kinetic Alfvén wave dispersion relation mixed with some coupling to the ionosphere, and high‐frequency kinetic Alfvén wave generation between Polar and FAST. Current models are found to be generally consistent with the study results but are not yet sufficiently well formulated to account for the details, including evidence for temporal and/or spatial modulation of reflectivity.
Charge transfer cross sections for energetic neutral atom data analysis
Authors: Lindsay B. G. , Stebbings R. F.
Published: December 2005

Energetic neutral atom (ENA) detectors have been successfully flown on missions such as the Imager for Magnetopause‐to‐Aurora Global Exploration (IMAGE) and are now an important tool for probing the geospace environment. Interpretation of ENA data, however, requires knowledge of a number of key charge transfer cross sections. Here we present a critical review of the published experimental measurements and recommend a set of parameterized cross sections. The processes considered are charge transfer of H+ and O+ with H, O, N2, and O2 for collision energies from 10 eV to 100 keV. The limitations of the measurement techniques and the probable reliability of the recommended cross sections are addressed.
A rapid multiple‐sample approach to the determination of absolute paleointensity
Authors: Hoffman Kenneth A. , Biggin Andrew J.
Published: December 2005

We present an alternative approach to absolute paleointensity determination, one which involves exactly five heatings, making possible rapid determinations without compromise to matters that insure reliability. While the Thellier‐Thellier method involves a large number of temperature steps to validate a result for a particular specimen, the new approach makes use of the spatial variation in rock magnetic properties. The procedure involves the simultaneous thermal treatment of several subspecimens sampled from different regions throughout the igneous rock unit under investigation. For inclusion of data in a given determination, self‐consistency criteria must be satisfied at the level of individual subsamples as well as at the stage of whole sample core consideration. The use of data taken en masse on a single Arai plot associated with samples from throughout a rock unit eliminates the need for further confirmation of an apparently successful result. The new method takes a balanced approach toward addressing the question of self‐consistency, from intraspecimen to intersample, that we argue is preferable to the common practice of focusing attention primarily on the individual specimen with inadequate consideration paid to consistency throughout a rock unit.
Magnetic stratigraphy of Kimmeridgian‐Aptian sections from Umbria‐Marche (Italy): New details on the M polarity sequence
Authors: Speranza Fabio , Satolli Sara , Mattioli Emanuela , Calamita Fernando
Published: December 2005

The magnetic stratigraphy of the Maiolica and Calcari ad Aptici pelagic limestones is documented from four Umbro‐Marchean land sections (Italy). The overall biostratigraphic age of the sampled strata encompasses the whole Kimmeridgian–Lower Aptian. The data were gathered from two new sections (Arcevia, Contessa) and by resampling more densely than in the past two additional classical sections (Bosso, Gorgo a Cerbara). A detailed record of the polarity chrons M21n‐M14 and M9‐M0 was derived, and no difference was observed with respect to the sequence of M polarity chrons inferred from oceanic magnetic anomalies. Barely measurable remanent magnetization from chron M14 to M10n at Contessa concurred with previous evidence from Bosso, indicating that the Maiolica from Umbria‐Marche is characterized by a “recording gap” during chrons M14n to M11, possibly due to diagenetic magnetite dissolution related to the Late Valanginian carbon isotope event. At Arcevia and Bosso, the boundary between Maiolica and Calcari ad Aptici occurs at the top of chron M19n and in the upper part of chron M20n, respectively, showing that the onset of Maiolica sedimentation may be diachronous by 1.5–2 Myr along the Umbria‐Marche domain. Arcevia is the most expanded Mid‐Upper Tithonian land section documented so far. Here, the subchrons M20n‐1 and M19n‐1 are found to represent 3.2% and 10.1% in time of chrons M20n and M19n, respectively. Evidence is also provided for a reversal excursion occurring within the M20n‐1 subchron. At Bosso, an excursion and a reversal excursion were found within chrons M16n and M16, respectively.
Microwave radar cross sections and Doppler velocities measured in the surf zone
Authors: Farquharson Gordon , Frasier Stephen J. , Raubenheimer Britt , Elgar Steve
Published: December 2005

The relationship between microwave imaging radar measurements of fluid velocities in the surf zone and shoaling, breaking, and broken waves is studied with field observations. Normalized radar cross section (NRCS) and Doppler velocity are estimated from microwave measurements at near‐grazing angles, and in situ fluid velocities are measured with acoustic Doppler velocimeters (ADVs). Joint histograms of radar cross section and Doppler velocity cluster into identifiable distributions. The NRCS values from pixels with large NRCS and high Doppler velocities (>2 m/s) decrease with decreasing bore height to the shoreline, similar to scattering from a cylinder with decreasing radius. The Doppler velocities associated with these regions in the histograms agree well with theoretical wave phase velocities. Radar and ADV measurements of fluid velocities between bore crests have similarly shaped energy density spectra for frequencies above about 0.1 Hz, but energy levels from the radar are an order of magnitude higher than those of the ADV data. Instantaneous interbore Doppler velocities are correlated with ADV measured fluid velocities but are offset by 0.8 m/s. This offset may be due to Bragg wave phase velocities, wind drift, range and azimuth sidelobes, the finite spatial resolution of the radar, and differences between mean flows measured at the surface with radar and flows measured below the surface with ADVs. Shoaling and breaking waves measured through radar grating lobes significantly affect both the Doppler velocities near the edges of the images and the scattering from the rear faces of waves, causing large Doppler velocities to be observed in these regions.
Maximum likelihood estimation of covariance parameters for Bayesian atmospheric trace gas surface flux inversions
Authors: Michalak Anna M. , Hirsch Adam , Bruhwiler Lori , Gurney Kevin R. , Peters Wouter , Tans Pieter P.
Published: December 2005

This paper introduces a Maximum Likelihood (ML) approach for estimating the statistical parameters required for the covariance matrices used in the solution of Bayesian inverse problems aimed at estimating surface fluxes of atmospheric trace gases. The method offers an objective methodology for populating the covariance matrices required in Bayesian inversions, thereby resulting in better estimates of the uncertainty associated with derived fluxes and minimizing the risk of inversions being biased by unrealistic covariance parameters. In addition, a method is presented for estimating the uncertainty associated with these covariance parameters. The ML method is demonstrated using a typical inversion setup with 22 flux regions and 75 observation stations from the National Oceanic and Atmospheric Administration‐Climate Monitoring and Diagnostics Laboratory (NOAA‐CMDL) Cooperative Air Sampling Network with available monthly averaged carbon dioxide data. Flux regions and observation locations are binned according to various characteristics, and the variances of the model‐data mismatch and of the errors associated with the a priori flux distribution are estimated from the available data.
An ensemble data assimilation system to estimate CO2 surface fluxes from atmospheric trace gas observations
Authors: Peters W. , Miller J. B. , Whitaker J. , Denning A. S. , Hirsch A. , Krol M. C. , Zupanski D. , Bruhwiler L. , Tans P. P.
Published: December 2005

We present a data assimilation system to estimate surface fluxes of CO2 and other trace gases from observations of their atmospheric abundances. The system is based on ensemble data assimilation methods under development for Numerical Weather Prediction (NWP) and is the first of its kind to be used for CO2 flux estimation. The system was developed to overcome computational limitations encountered when a large number of observations are used to estimate a large number of unknown surface fluxes. The ensemble data assimilation approach is attractive because it returns an approximation of the covariance, does not need an adjoint model or other linearization of the observation operator, and offers the possibility to optimize fluxes of chemically active trace gases (e.g., CH4, CO) in the same framework. We assess the performance of this new system in a pseudodata experiment that resembles the real problem we will apply this system to. The sensitivity of the method to the choice of several parameters such as the assimilation window size and the number of ensemble members is investigated. We conclude that the system is able to provide satisfactory flux estimates for the relatively large scales resolved by our current observing network and that the loss of information in the approximated covariances is an acceptable price to pay for the efficient computation of a large number of surface fluxes. The full potential of this data assimilation system will be used for near–real time operational estimates of North American CO2 fluxes. This will take advantage of the large amounts of atmospheric data that will be collected by NOAA‐CMDL in conjunction with the implementation of the North American Carbon Program (NACP).
Measurements of trace gas emissions from Australian forest fires and correlations with coincident measurements of aerosol optical depth
Authors: Paton‐Walsh Clare , Jones Nicholas B. , Wilson Stephen R. , Haverd Vanessa , Meier Arndt , Griffith David W. T. , Rinsland Curtis P.
Published: December 2005

We present vertically integrated measurements of C2H2, C2H4, C2H6, HCOOH, CO, H2CO, HCN and NH3 through smoke plumes from Australian forest fires measured by ground‐based solar absorption spectroscopy. The column amounts of these gases are highly correlated with simultaneous, colocated measurements of aerosol optical depth, providing a potential method of mapping biomass‐burning emissions using satellite measurements of aerosol optical depth. We have calculated emission ratios relative to CO for the trace gases using aerosol optical depth as a proxy for CO and converted to emission factors by using an average emission factor for CO from literature measurements of extratropical forest fires. The results show that Australian forest fire emissions are broadly similar to those from other geographical regions except for comparatively low emissions of C2H6.
Response of the climate system to aerosol direct and indirect forcing: Role of cloud feedbacks
Authors: Kristjánsson J. E. , Iversen T. , Kirkevåg A. , Seland Ø. , Debernard J.
Published: December 2005

In this study, the response of the climate system to aerosol direct and indirect radiative forcing is investigated. Several multidecadal equilibrium simulations are carried out, using the NCAR CCM3 framework coupled to a separately developed aerosol treatment. The aerosol treatment includes, e.g., a life cycle scheme for particulate sulfate and black carbon (natural and anthropogenic), calculations of aerosol size distributions and CCN activation, as well as computations of direct and indirect forcing (1st and 2nd indirect effect). In all the simulations the full aerosol treatment is run online, hence responding interactively to changes in climate. By far the largest response is caused by the indirect forcing, with a globally averaged cooling of −1.25 K due to anthropogenic aerosols. The largest temperature reduction is found in the Northern Hemisphere because of a larger aerosol burden there. As a result of this cooling pattern, the Intertropical Convergence Zone is displaced southward by a few hundred kilometers. Interestingly, a similar, though less significant displacement is also found in the experiments with the direct effect alone, even though the globally averaged aerosol induced cooling is much weaker in that case, i.e., −0.08 K. The direct radiative forcing is much stronger at the surface than at the top of the atmosphere, and this leads to a slight weakening of the hydrological cycle. Comparing simulations with direct and indirect forcing combined to those with indirect and direct forcing separately, a residual, caused by nonlinear model feedbacks, is manifested through a reduction in precipitation. This reduction amounts to −0.5% in a global average and exceeds −2.5% in the Arctic, highlighting the role of high‐latitude climate feedbacks. Globally, cloud feedback is negative in the sense that in the colder climate resulting from anthropogenic aerosol forcing, net cloud forcing is reduced by 15% compared to the original climate state. This is caused by a general cloud thinning, especially at high latitudes, while in the most polluted regions, clouds are thicker through the 2nd indirect effect. The 1st indirect effect, on the other hand, remains intact in the presence of climate feedbacks, yielding a similar signature of cloud droplet reduction as in the pure forcing simulations.
A unified model for subaqueous bed form dynamics
Authors: Jerolmack Douglas J. , Mohrig David
Published: December 2005

Bed form evolution remains dynamic even in the special case of steady, uniform flow. Data from the sandy, braided North Loup River, Nebraska, show that roughness features on the channel bottom display a statistical steady state and robust scaling that are maintained through the collective interactions of transient (short‐lived) bed forms. Motivated by such field data, and laboratory observations of bed form growth, we develop a nonlinear stochastic surface evolution model for the topography of bed load dominated sandy rivers in which instantaneous sediment flux explicitly depends on local elevation and slope. This model quantitatively reproduces laboratory observations of initial growth and saturation of bed forms from a flat surface, and also generates long‐term dynamical behavior characteristic of natural systems. We argue that the variability in geometry and kinematics of bed forms in steady flow, and the existence of roughness at all wavelengths up to the largest dunes, are a consequence of the nonlinear relationship between sediment flux and topography, subject to noise.
Cytoskeletal and motor proteins facilitate trafficking of AQP1‐containing vesicles in cholangiocytes
Authors: Tietz Pamela S. , McNiven Mark A. , Splinter Patrick L. , Huang Bing Q. , LaRusso Nicholas F.
Published: December 2005

Background information. We have previously showed that: (i) cholangiocytes contain AQP1 (aquaporin 1) water channels sequestered in intracellular vesicles; and (ii) upon stimulation with choleretic agonists such as secretin or dibutyryl‐cAMP (dbcAMP), the AQP1 vesicles move via microtubules to the apical cholangiocyte membrane to facilitate osmotically driven, passive water movement (i.e. ductal bile secretion). The aim of the present study was to determine which proteins and mechanisms regulate AQP1 trafficking in cholangiocytes.

Results. Using polarized cultured NMCs (normal mouse cholangiocytes) or NRCs (normal rat cholangiocytes) and affinity‐purified antibodies, we performed immunofluorescent confocal microscopy on fixed cells or immunoblotting on cell lysates for actin, tubulin, kinesin and dynein, proteins known to regulate intracellular vesicle trafficking. By immunostaining, the appropriate orientation of the actin (i.e. sub‐apical) and tubulin (i.e. generalized) cytoskeleton was apparent; kinesin and dynein displayed a homogeneous punctate distribution. Immunoblotting showed kinesin and dynein to be present in both cholangiocyte lysates and in isolated AQP1‐containing vesicles. We utilized real‐time fluorescence confocal microscopy of NMCs transfected with a GFP (green fluorescent protein)–AQP1 fusion construct in the presence and absence of dbcAMP.

Conclusions. Our results provide additional insights into the potential molecular mechanisms of ductal bile secretion.
Uncoupled IP3 receptor can function as a Ca2+‐leak channel: cell biological and pathological consequences
Authors: Szlufcik Karolina , Missiaen Ludwig , Parys Jan B. , Callewaert Geert , De Smedt Humbert
Published: December 2005

Ca2+ release via intracellular release channels, IP3Rs (inositol 1,4,5‐trisphosphate receptors) and RyRs (ryanodine receptors), is perhaps the most ubiquitous and versatile cellular signalling mechanism, and is involved in a vast number of cellular processes. In addition to this classical release pathway there is limited, but yet persistent, information about less well‐defined Ca2+‐leak pathways that may play an important role in the control of the Ca2+ load of the endo(sarco)plasmic reticulum. The mechanisms responsible for this ‘basal’ leak are not known, but recent data suggest that both IP3Rs and RyRs may also operate as Ca2+‐leak channels, particularly in pathological conditions. Proteolytic cleavage or biochemical modification (such as hyperphosphorylation or nitrosylation), for example, occurring during conditions of cell stress or apoptosis, can functionally uncouple the cytoplasmic control domains from the channel domain of the receptor. Highly significant information has been obtained from studies of malfunctioning channels in various disorders; for example, RyRs in cardiac malfunction or genetic muscle diseases and IP3Rs in neurodegenerative diseases. In this review we aim to summarize the existing information about functionally uncoupled IP3R and RyR channels, and to discuss the concept that those channels can participate in Ca2+‐leak pathways.
Identifying and explaining epochs of internationalization: a case study
Authors: Eckert Stefan , Mayrhofer Ulrike
Published: December 2005

This research investigates the internationalization process of multinational corporations. The authors identify international epochs that profoundly characterize the internationalization process of companies and explain their emergence. Based on a longitudinal case study of the German company Hoechst and its merger with the French company Rhône‐Poulenc to Aventis, the empirical analysis reveals that international epochs are initiated by significant changes in the power structure of the corporation, such as the appointment of a new CEO or a corporate merger.
New ventures' inward licensing: examining the effects of industry and strategy characteristics
Authors: Zahra Shaker A , Keil Thomas , Maula Markku
Published: December 2005

New ventures compete by creating innovative products. Liabilities of newness and inexperience, limited resources, rapid technological obsolescence and constantly changing market conditions often encourage new ventures to license other companies' technologies to complement and augment their internally developed innovations. Building on the knowledge‐based view of the firm, we propose that the intensity of new ventures' use of inward licensing reflects the demands of their industries and competitive strategies. The results of an empirical study of 361 US new ventures show that industry characteristics and competitive strategy influence their inward licensing as a means of lowering costs and maintaining strategic flexibility while building their capabilities.
Photoluminescence and spectral holeburning in europium-doped MgS nanoparticles
Authors: Hasan Zameer , Dardona Sameh , Konjhodzic Aras
Published: December 2005

Luminescence and power-gated spectral holeburning studies have been performed on Eu-doped MgS nanoparticles. These particles are atomically tailored to produce and control the relative concentration of Eu2+ and Eu3+, which is necessary for power-gated holeburning. The spectral holes are permanent at low temperatures. Optical studies show that the electron-phonon coupling is stronger in nanoparticles than in thin films or microparticles of the same material. This is the reason for inherently broader spectral holes in nanoparticles as compared to microparticle or thin-film samples. Temperature broadening of spectral holes in nanoparticles follows a T2.4 behavior, a faster rate than thin films or microparticles. This behavior can be attributed to the glassy nature of the particles produced.
Surface-induced C–O bond anharmonicity of methoxy adsorbed on Cu(100): Experiments and density-functional theory calculations
Authors: Andersson M. P. , Blomquist J. , Uvdal P.
Published: December 2005

The anharmonic properties of a surface intermediate, methoxy, adsorbed on Cu(100) are investigated by surface infrared overtone spectroscopy and density-functional-theory electronic structure calculations. The anharmonicity is measured in the zero-coverage limit, and it is observed that the anharmonicity is increased upon adsorption as compared with the free methanol. By combining experiments with calculations we demonstrate that modifications of the anharmonicity of the methoxy species is indeed induced by adsorption onto the copper surface and not by the formation of the methoxy species.
Structures and dynamics of protonated ammonia clusters
Authors: Fouqueau Antony , Meuwly Markus
Published: December 2005

The structures and infrared spectra of protonated ammonia clusters NH4+(NH3)n, for n⩽8, are investigated using density functional-theory (DFT) calculations and semiempirical DFT/molecular dynamics simulations. For n<5 the clusters are found to be mostly stable up to 100K, while the larger clusters (n⩾5) isomerize. Temperature effects are taken into account by performing ab initio molecular dynamics simulations with the computationally tractable self-consistent charges density functional tight-binding method. The infrared spectra at 10K for the most stable isomers for n=3–8 compare qualitatively with predissociation experiments, and using a common scaling factor almost quantitative agreement is found. For n⩾6 the notion of multiple isomers present under the experimental conditions is supported. Of the 13 stable structures for n=8 only three are found to survive at 100K. All other clusters isomerize. Cluster structures are inferred from the analysis of the cumulative radial distribution function of the ammonia molecules surrounding the NH4+ core. The infrared spectra are found to be typical for the structure of the clusters, which should help to relate the experimentally measured infrared spectra to the number and identity of the contributing isomers. For clusters that reorganize to a more stable isomer during the dynamics, the infrared spectrum is generally similar to that of the stable isomer itself. The clusters are found to preferably form globular structures, although chain-like arrangements are also among the low-energy configurations.
Characterization of the electronic structure of C50Cl10 by means of soft x-ray spectroscopies
Authors: Brena Barbara , Luo Yi
Published: December 2005

The electronic structure of the last synthesized fullerene molecule, the C50Cl10, has been characterized by theoretical simulation of x-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, and near-edge x-ray-absorption fine structure. All the calculations were performed at the gradient-corrected and hybrid density-functional theory levels. The combination of these techniques provides detailed information about the valence band and the unoccupied molecular orbitals, as well as about the carbon core orbitals.
Charge transfer in FeO: A combined molecular-dynamics and ab initio study
Authors: Kerisit Sebastien , Rosso Kevin M.
Published: December 2005

Molecular-dynamics simulations and ab initio electronic structure calculations were carried out to determine the rate of charge transfer in stoichiometric wüstite (FeO). The charge transfer of interest occurs by II/III valence interchange between nearest-neighbor Fe atoms, with the Fe(III) constituting a “hole” electronic defect. There are two possible nearest-neighbor charge transfers in the FeO lattice, which occur between edge-sharing or corner-sharing FeO6 octahedra. Molecular-dynamics simulations predict charge-transfer rates of 3.7×1011 and 1.9×109s−1 for the edge and corner transfers, respectively, in good agreement with those calculated using an ab initio cluster approach (1.6×1011 and 8.0×108s−1, respectively). The calculated rates are also similar to those along the basal and c-axis directions in hematite (α-Fe2O3) determined previously. Therefore, as is the case for hematite, wüstite is predicted to show anisotropic electrical conductivity. Our findings indicate that a rigid-ion model does not give acceptable results, thus showing the need to account for the change in polarizability of the system upon charge transfer. Our model achieves this by using a simple mechanical shell model. By calculating the electronic coupling matrix elements for many transition state configurations obtained from the molecular-dynamics simulations, we found evidence that the position of the bridging oxygen atoms can greatly affect the amount of electronic coupling between the donor and acceptor states. Finally, we address the effect of oxygen vacancies on the charge transfer. It was found that an oxygen vacancy not only creates a driving force for holes to transport away from the vacancy (or equivalently for electrons to diffuse toward the vacancy) but also lowers the free-energy barriers for charge transfer. In addition, the reorganization energy significantly differed from the nondefective case in a small radius around the defect.
Quantum chemical study of 4f→5d excitations of trivalent lanthanide ions doped in the cubic elpasolite Cs2NaYCl6. Ce3+ to Tb3+
Authors: Ruipérez Fernando , Barandiarán Zoila , Seijo Luis
Published: December 2005

Wave-function-based ab initio calculations on the lowest states of the 4fn,4fn−15d(t2g)1, and 4fn−15d(eg)1 configurations of (LnCl6)3− clusters (Ln=Ce to Tb) embedded in the cubic elpasolite Cs2NaYCl6 have been performed, in an attempt to contribute to a comprehensive understanding of the 4f→5d excitations of lanthanide ions in crystals. Reliable data are provided on the changes of bond lengths and breathing mode vibrational frequencies upon 4f→5d(t2g) and 4f→5d(eg) excitations, as well as on minimum-to-minimum and vertical absorption and emission transitions, and on the Stokes shifts. The available experimental data are discussed and predictions are made. The stabilization of the 4f→5d(baricenter) excitation of the doped ions with respect to the 4f→5d excitations of the free ions, which is a key variable for the understanding of these excitations in solid hosts, is analyzed and found to be due, in two-thirds, to dynamic ligand correlation effects and, in one-third, to orbital relaxation, charge transfer, and covalency effects present in a mean-field approximation.
Excited state molecular structures and reactions directly determined by ultrafast electron diffraction
Authors: Feenstra Jonathan S. , Park Sang Tae , Zewail Ahmed H.
Published: December 2005

In this communication, we report on the use of ultrafast electron diffraction to determine structural dynamics of excited states and reaction products of isolated aromatic carbonyls, acetophenone and benzaldehyde. For a 266nm excitation, a bifurcation of pathways is structurally resolved, one leading to the formation of the triplet state (quinoid structure) and another to chemical products: for benzaldehyde the products are benzene and carbon monoxide (hydrogen migration and bond rupture) while those for acetophenone are the benzoyl and methyl radicals (bond rupture). The refined structures are compared with those predicted by theory. These dark structures and their radiationless transitions define the reduced energy landscape for complex reactions.
Resonant coupling of bound excitons with LO phonons in ZnO: Excitonic polaron states and Fano interference
Authors: Xu S. J. , Xiong Shi-Jie , Shi S. L.
Published: December 2005

We report on a photoluminescence observation of robust excitonic polarons due to resonant coupling of exciton and longitudinal optical (LO) phonon as well as Fano-type interference in high quality ZnO crystal. At low enough temperatures, resonant coupling of excitons and LO phonons leads to not only traditional Stokes lines (SLs) but also up to second-order anti-Stokes lines (ASLs) besides the zero-phonon line (ZPL). The SLs and ASLs are found to be not mirror symmetric with respect to the ZPL, strongly suggesting that they are from different coupling states of exciton and phonons. Besides these spectral features showing the quasiparticle properties of exciton-phonon coupling system, the first-order SL is found to exhibit characteristic Fano lineshape, caused by quantum interference between the LO components of excitonic polarons and the continuous phonon bath. These findings lead to a new insight into fundamental effects of exciton-phonon interactions.
Hole mobility and lifetime in a smectic liquid crystalline photoconductor of a 2-phenylnaphthalene derivative
Authors: Iino Hiroaki , Ohno Akira , Hanna Jun-ichi
Published: December 2005

We have investigated hole transport properties in the smectic mesophases of a 2-phenylnaphthalene derivative 6-(4′-octylphenyl)-2-dodecyloxynaphthalene in detail by using time-of-flight technique. The transient photocurrents were measured in liquid-crystal cells with various thickness from 5to700μm. They were well defined and nondispersive in the smectic A (SmA) phase up to 500μm and in the smectic B (SmB) phase within the entire thickness employed, while they exhibited an exponential decay in the SmA phase at 700μm. The mobilities in the SmA and SmB phases were constant in each mesophase irrespective of the cell thickness, and were 2.5×10−4 and 1.7×10−3cm2∕Vs, respectively. The hole lifetimes were determined to be 10ms and longer than 5ms for the SmA and SmB phases, respectively. We discuss the origin of these lifetimes from the two points of view, i.e., hole trapping by a trace amount of existing impurities and recombination with negative ionic charges. We conclude that impurities are mainly responsible for the present hole lifetime test.
Incoherent interaction of light with electron-acoustic waves
Authors: Marklund Mattias , Shukla Padma K.
Published: December 2005

We present equations governing the interaction between incoherent light and electron-acoustic waves. The modulational instability properties of the system are studied, and the effect of partially coherent light is discussed. It is shown that partial coherence suppresses the modulational instability. However, short-wavelength modes are less affected, and will therefore dominate in, e.g., pulse filamentation. The results may be of importance to space plasmas and laser-plasma systems.
Effect of drift-acoustic waves on magnetic island stability in slab geometry
Authors: Fitzpatrick R. , Waelbroeck F. L.
Published: December 2005

A mathematical formalism is developed for calculating the ion polarization term in the Rutherford island width evolution equation in the presence of drift-acoustic waves. The calculation is fully nonlinear, includes both ion and electron diamagnetic effects, as well as ion compressibility, but is performed in slab geometry. Magnetic islands propagating in a certain range of phase velocities are found to emit drift-acoustic waves. Wave emission gives rise to rapid oscillations in the ion polarization term as the island phase velocity varies, and also generates a net electromagnetic force acting on the island region. Increasing ion compressibility is found to extend the range of phase velocities over which drift-acoustic wave emission occurs in the electron diamagnetic direction.
Metal-ferroelectric-metal heterostructures with Schottky contacts. I. Influence of the ferroelectric properties
Authors: Pintilie L. , Alexe M.
Published: December 2005

A model for metal-ferroelectric-metal heterostructures with Schottky contacts is proposed. The model adapts the general theories of metal-semiconductor rectifying contacts for the particular case of metal-ferroelectric contact by introducing the ferroelectric polarization as a sheet of surface charge located at a finite distance from the electrode interface, a deep trapping level of high concentration, and the static and dynamic values of the dielectric constant. Consequences of the proposed model on relevant quantities of the Schottky contact such as builtin voltage, charge density, and depletion width, as well as on the interpretation of the current-voltage and capacitance-voltage characteristics are discussed in detail.
Pseudoelasticity of martensitic titanium-nickel shape-memory films studied by in situ heating nanoindentation and transmission electron microscopy
Authors: Komvopoulos K. , Ma X.-G.
Published: December 2005

Pseudoelasticity of shape-memory alloys has been commonly associated with reversible austenite-martensite phase transformation characterized by diffusionless, shear-induced atomic rearrangement. In situ heating nanoindentation and transmission electron microscopy results of this study demonstrate that martensitic TiNi films may also exhibit pseudoelasticity over a specific temperature range due to the reversible movement of the twin boundaries. The nanoscale deformation behavior of martensitic TiNi films was examined over certain ranges of normal load and temperature. The underlying mechanisms of the reversible twin boundary movement and the energy dissipated by pseudoelastic and elastic-plastic deformation in the TiNi films are interpreted in the context of in situ heating nanoindentation responses. The obtained experimental evidence is in agreement with a unified description of pseudoelasticity in which the origin of the restoring force responsible for the pseudoelastic behavior of shape-memory alloys is considered to be the formation of metastable pseudotwins.
Noninterfacial-nitride formation ohmic contact mechanism in Si-containing Ti∕Al∕Mo∕Au metallizations on AlGaN∕GaN heterostructures
Authors: Mohammed Fitih M. , Wang Liang , Adesida Ilesanmi
Published: December 2005

Excellent ohmic contact formation to undoped-AlGaN∕GaN heterostructures is achieved by the incorporation of silicon into Ti∕Al∕Mo∕Au metallization. Contact resistance and specific contact resistivity as low as 0.16Ωmm and 6.77×10−7Ωcm2, respectively, have been obtained for the Ti∕Si∕Al∕Si∕Mo∕Au scheme. Transmission electron microscopy has revealed that the ohmic contact formation mechanism depends on the competing interfacial nitride and silicide formation reactions, the latter giving rise to improved contact performance. The formation and penetration of non-nitride reaction products of Si-containing Al–Au intermetallics to depths beyond the AlGaN∕GaN interface were observed. The superior ohmic performance of these schemes suggests that silicide-based low Schottky barrier contact formation may be preferable to an interfacial nitride contact mechanism in achieving improved ohmic behavior.
Nanofilter array chip for fast gel-free biomolecule separation
Authors: Fu Jianping , Mao Pan , Han Jongyoon
Published: December 2005

We report here a microfabricated nanofilter array chip that can size-fractionate sodium dodecyl sulfate (SDS)-protein complexes and small DNA molecules based on the Ogston sieving mechanism. Nanofilter arrays with a gap size of 40–180 nm were fabricated and characterized. Complete separation of SDS-protein complexes and small DNA molecules were achieved in several minutes with a separation length of 5 mm. The fabrication strategy for the nanofilter array chip allows further increasing of the nanofilter density and decreasing of the nanofilter gap size, leading, in principle, to even faster separation.
Influence of an adsorption layer on the structure and stability of surface tension driven flows
Authors: Mizev A.
Published: December 2005

The structure and stability of thermocapillary and solutocapillary flow from a localized source has been experimentally studied in the presence of adsorption layers. It is found that the divergent flow, which is typical for this case, becomes unstable to azimuthally periodic perturbations that lead to the appearance of a surface flow with a multivortex structure. The evolution of the flow structure during an increase of concentration in the adsorption layer is shown. Two possible physical models of the observed instability are put forward.
Drift wave driven zonal flows in plasmas
Authors: Kaladze T. D. , Wu D. J. , Pokhotelov O. A. , Sagdeev R. Z. , Stenflo L. , Shukla P. K.
Published: December 2005

The generation of large-scale zonal flows by small-scale electrostatic drift waves in a plasma is considered. The generation mechanism is based on the parametric excitation of convective cells by finite amplitude drift waves. To describe this process a generalized Hasegawa–Mima equation containing both vector and scalar nonlinearities is used. The drift waves are supposed to have arbitrary wavelengths (as compared with the ion Larmor radius). A set of coupled equations describing the nonlinear interaction of drift waves and zonal flows is deduced. The generation of zonal flows turns out to be due to Reynolds stresses produced by finite amplitude drift waves. It is found that the wave vector of the fastest growing mode is perpendicular to that of the drift pump wave. Explicit expressions for the maximum growth rate as well as for the optimal spatial dimensions of the zonal flows are obtained. A comparison with previous results is carried out. The present theory can be used for interpretations of drift wave observations in laboratory plasmas.
Acoustic channel drop tunneling in a phononic crystal
Authors: Pennec Y. , Djafari-Rouhani B. , Vasseur J. O. , Larabi H. , Khelif A. , Choujaa A. , Benchabane S. , Laude V.
Published: December 2005

We study both theoretically and experimentally the possibility of resonant tunneling of acoustic waves between two parallel guides created in a phononic crystal composed of steel cylinders in water. In the absolute band gap of the phononic crystal, ranging from 250to325kHz, a full transmission band exists for propagation inside a straight waveguide. We show that the transfer of a particular wavelength can occur between two parallel waveguides coupled together through an appropriate coupling structure. The latter is composed of isolated cavities interacting with stubs located at the sides of the waveguides.
Etching silicon wafer without hydrofluoric acid
Authors: Liu Hong , Wang Zhong Lin
Published: December 2005

A one-step hydrofluoric-acid-free hydrothermal-etching technique is demonstrated for the preparation of porous silicon with vertical holes. This method demonstrates a “green” chemical approach for etching a silicon wafer or the preparation of bismuth-silicon nanostructures without toxic acid or applying an external voltage. By controlling the heating temperature (<180°C) and time, nanoscale vertically holed porous silicon has been created. A formation mechanism has been proposed on the basis of experimental observations.
Three-dimensional solitary waves on falling liquid film at low Reynolds numbers
Authors: Alekseenko S. V. , Antipin V. A. , Guzanov V. V. , Kharlamov S. M. , Markovich D. M.
Published: December 2005

In this Letter we present novel results of the experimental study of three-dimensional waves evolving from a localized disturbance on a vertically falling film at low Reynolds numbers 1.25<Re<4.7. This range of Re is close to the values that are typical for residual layers in developed wavy film flow with moderate Reynolds numbers. A spatiotemporal evolution of three-dimensional solitary waves is investigated. Existence of the stationary horseshoe-shaped waves has been demonstrated. The measured wave characteristics are compared with the theoretical solutions.
Optically Pure Aminopolyols and Polyoxamic Acid Derivatives from Aziridine-2-carboxylates
Authors: Dollt Heribert , Zabel Volker
Published: December 2005

Various new chiral building blocks could easily be prepared from optically
pure cis and trans ethyl
3-(1′,3′- dioxolan-4′-yl)aziridine-2-carboxylates. A
stereochemically pure 1,3-dioxolan in the allyl position of an
α-bromoacrylate induced a high
(3R*,4′S*)
selectivity in the Michael addition with an amine. After oxygen at the
inducing centre was exchanged with nitrogen bearing a bulky substituent, the
directing influence of this new group was examined. Solvent effects
influencing the cis/trans ratio of aziridine
formation are discussed.
Quantitative 13C N.M.R. Assay and Assignment of Mixtures from Lipase Digestion of Propane-1,2-diol Dibutyrate
Authors: O'Connor Charmian J. , Barton Richard H.
Published: December 2005

13C nuclear magnetic resonance (n.m.r.) spectra were
obtained at 50 and 100 MHz for mixtures of propanediol, propane-1,2-diol
dibutyrate, propane-1,2-diol 1-butyrate and propane-1,2-diol 2-butyrate in
CDCl3. Distortionless enhancement by polarization
transfer (DEPT) and two-dimensional
13C–1H correlation
spectroscopy were used to confirm shift assignments. Spectra for the 1- and
2-monoesters showed strongly different inductive effects due to the position
of the butyryl chain. These experiments demonstrate the desirability of using
13C n.m.r. rather than 1H n.m.r.
spectroscopy in quantitative speciation of acylated diol complex hydrolysis
mixtures.
1,3-Dipolar Cycloaddition Reactions of the Ylide Derived from 6-Phenacyl-benzo[f][1,7]naphthyridinium Bromide
Authors: Matusiak Grazyna
Published: December 2005

The 1,3-dipolar cycloaddition reactions of 4,6-diazaphenanthrene 6-phenacylide
formed in situ from the quaternary
6-phenacylbenzo[f][1,7]naphthyridinium
bromide in basic medium were examined; methacrylic acid, methyl methacrylate,
butyl vinyl ether, methyl vinyl ketone, maleic anhydride and dimethyl
acetylenedicarboxylate were used as the dipolarophiles.
Syntheses of Angucyclinones Related to Ochromycinone. III. An 11-Hydroxy Isomer and Some Reduced Analogues
Authors: Rozek Tomas , Rozek Tomas , Taylor Dennis K. , Taylor Dennis K. , Tiekink Edward R. T. , Tiekink Edward R. T. , Bowie John H. , Bowie John H.
Published: December 2005

The boron triacetate assisted Diels Alder reaction between racemic
5,5-dimethyl-3-vinylcyclohex- 2-enyl acetate and 5-hydroxynaphthoquinone
yields the racemic 11-hydroxy-3,3-dimethyl-7,12-dioxo-
1,2,3,4,6,6a,7,12,12a,12b-decahydrobenzo[a]anthracen-1-yl
acetate as the sole stereoisomer by regio- and stereo-selective
cis endo addition. Aromatization of the Diels Alder
adduct followed by hydrolysis of the acetate and oxidation of the resultant
1-hydroxy group gives the target angucyclinone,
11-hydroxy-3,3-dimethyl-1,2,3,4,7,12-hexahydrobenzo[a]anthracene-1,7,12-trione,
in an overall yield of 37% from 5-hydroxynaphthoquinone. The regio- and
stereo-selectivity of the Diels Alder addition is confirmed by a combination
of 13C n.m.r. spectroscopy and X-ray crystallography.