bluuebunny/crossref_metadata_2025 huggingface dataset:
US‐TEC: A new data assimilation product from the Space Environment Center characterizing the ionospheric total electron content using real‐time GPS data
Authors: Fuller‐Rowell Tim , Araujo‐Pradere Eduardo , Minter Cliff , Codrescu Mihail , Spencer Paul , Robertson Doug , Jacobson Abram R.
Published: December 2006

The potential of data assimilation for operational numerical weather forecasting has been appreciated for many years. For space weather it is a new path that we are just beginning to explore. With the emergence of satellite constellations and the networks of ground‐based observations, sufficient data sources are now available to make the application of data assimilation techniques a viable option. The first space weather product at Space Environment Center (SEC) utilizing data assimilation techniques, US‐TEC, was launched as a test operational product in November 2004. US‐TEC characterizes the ionospheric total electron content (TEC) over the continental United States (CONUS) every 15 min with about a 15‐min latency. US‐TEC is based on a Kalman filter data assimilation scheme driven by a ground‐based network of real‐time GPS stations. The product includes a map of the vertical TEC, an estimate of the uncertainty in the map, and the departure of the TEC from a 10‐day average at that particular universal time. In addition, data files are provided for vertical TEC and the line‐of‐sight electron content to all GPS satellites in view over the CONUS at that time. The information can be used to improve single‐frequency GPS positioning by providing more accurate corrections for the ionospheric signal delay, or it can be used to initialize rapid integer ambiguity resolution schemes for dual‐frequency GPS systems. Validation of US‐TEC indicates an accuracy of the line‐of‐sight electron content of between 2 and 3 TEC units (1 TECU = 1016 el m−2), equivalent to less than 50 cm signal delay at L1 frequencies, which promises value for GPS users. This is the first step along a path that will likely lead to major improvement in space weather forecasting, paralleling the advances achieved in meteorological weather forecasting.
Surface deformation and subsurface slip of the 28 March 1999 Mw = 6.4 west Himalayan Chamoli earthquake from InSAR analysis
Authors: Satyabala S. P. , Bilham Roger
Published: December 2006

We report InSAR observations of coseismic ground deformation caused by the Mw6.4 Chamoli earthquake of March 28, 1999 in the western Himalaya near the surface trace of the Main Central Thrust. Analysis of ERS1/2‐SAR data from ascending and descending tracks reveals surface deformation in a region 30 km by 40 km with a maximum coseismic uplift of ∼60 mm. Assuming that the rupture occurred as a planar uniform slip dislocation in an elastic half space reveals slip of 0.55 ± 0.1 m, strike of N300°E, 15° dip, with fault dimensions of 13 ± 3 km along‐strike and 10 ± 3 km downdip. The corresponding moment magnitude is Mw = 6.2, lower than that derived from seismological methods. With the exception of the recent 2005 Kashmir earthquake, the Chamoli earthquake studied in this paper is the only Himalayan earthquake for which surface deformation data are available from directly above the epicenter.
Simultaneous seismic reflection and physical oceanographic observations of oceanic fine structure in the Kuroshio extension front
Authors: Nakamura Y. , Noguchi T. , Tsuji T. , Itoh S. , Niino H. , Matsuoka T.
Published: December 2006

New simultaneous seismic reflection and physical oceanographic observations east of Japan demonstrate the utility of the seismic reflection method in mapping oceanic fine structure. Synthetic seismograms calculated from temperature and salinity data confirm that seismic reflections correlate with physical oceanographic structures. Seismic reflections at the boundary between the warm Kuroshio and the cold Oyashio water masses correspond to well developed, ∼10 m scale, temperature fine structure. Vertical current profiles suggest that this fine structure is caused by interleaving of these two water masses. We compare our seismic images with acoustic Doppler current profiler (ADCP) intensity maps and discuss similarities and the differences between seismic images and the ADCP maps. Our study demonstrates that even relatively low‐energy seismic sources, in this case a 3.4 l (210 in3) generator‐injector (GI) airgun, can be used to image upper oceanic fine structure.
Relation between lightning return stroke peak current and following continuing current
Authors: Saba M. M. F. , Pinto O. , Ballarotti M. G.
Published: December 2006

The magnitude of the return stroke peak current preceding continuing current (CC) in ground flashes was investigated. This study was performed using a high‐speed camera (1,000 frames/s), an electric field flat‐plate antenna and data provided by the Brazilian Lightning Detection Network (RINDAT). The observation of 454 negative strokes followed by CC with durations from 4 ms to 542 ms revealed that negative strokes combining both peak current greater than 20 kA and CC greater than 40 ms are highly unlikely to occur. However, this was found to be possible for positive strokes. In addition, we found that on average the longer the CC, the lower the return stroke peak current preceding it. Therefore, the average detection efficiency of RINDAT was found to decrease from 62% for negative strokes followed by very‐short CC (less than 10 ms) to 36% for strokes followed by long CC, with an intermediate value of 57% for strokes followed by short (from 10 to 40 ms) CC.
Cassini observations of planetary‐period oscillations of Saturn's magnetopause
Authors: Clarke K. E. , André N. , Andrews D. J. , Coates A. J. , Cowley S. W. H. , Dougherty M. K. , Lewis G. R. , McAndrews H. J. , Nichols J. D. , Robinson T. R. , Wright D. M.
Published: December 2006

Examination of Cassini magnetic field and plasma data in the outer boundary regions of Saturn's magnetosphere shows that magnetopause oscillations at the planetary period commonly occur, in phase with plasma pressure variations inside the magnetosphere. The peak‐to‐trough amplitude of the boundary oscillations mapped to the planet‐Sun line is estimated to be typically ∼2 RS, corresponding to a ∼10% change in the boundary radius. The change in internal pressure required to produce such motions is estimated to be ∼40% of the background values. A qualitative physical picture is proposed in which a compressive wave propagates outward through the sub‐corotating outer magnetospheric plasma, originating from a corotating source in the nearer‐planet region.
Multimodel study of tropical Atlantic variability and change
Authors: Breugem W.‐P. , Hazeleger W. , Haarsma R. J.
Published: December 2006

Interannual variability associated with the zonal and the meridional mode in the tropical Atlantic is studied in nine coupled ocean–atmosphere models for twentieth century climate conditions (TC) and the SRES‐A1B scenario for future greenhouse gas concentrations. For TC, the subtropical part of the meridional mode is reasonably well simulated, in contrast to the deep tropical part of the meridional mode and the zonal mode. A common model bias is that the onset of the meridional mode is preceded by the presence of a zonal mode in boreal fall that extends towards the western boundary of the Atlantic basin and which initiates a Wind‐Evaporation‐SST feedback. As a result of this, there is a spuriously strong interaction between the zonal and the meridional mode. The models that seem to best represent the meridional mode show a weakening for future climate conditions. Biases in the zonal mode are too strong to assess changes.
Polar cap voltage saturation
Authors: MacDougall J. W. , Jayachandran P. T.
Published: December 2006

Cross polar cap voltage saturation has been observed by various measurement techniques. An example of the saturation is shown in this paper and an explanation is proposed in terms of magnetospheric current behavior. The cross cap voltage saturation might be associated with either a voltage source or a current source effect since the cross cap potential and cross cap current are related by Ohm's law. The cross cap current is the difference between the Region 1 current influx to the polar cap boundary and the Region 2 current. Because, during high interplanetary magnetic field (IMF) −Bz conditions, the Region 2 current is significantly enhanced, the cross cap current, and hence cross cap voltage, is not anomalously higher than usual. Our measurements show agreement with Region 2 (partial ring current) enhancement during high IMF −Bz conditions.
Anomalous magnetic properties of brain tissue at low temperature: The 50 K anomaly
Authors: Hirt Ann M. , Brem Franziska , Hanzlik Marianne , Faivre Damien
Published: December 2006

A low‐coercivity phase, identified as magnetite and/or maghemite, is the main iron oxide in brain tissue. Measurement of susceptibility as a function of temperature (χ–T) in brain tissue samples does not show a Verwey transition but instead shows a perturbation around 50 K. A susceptibility anomaly has been reported at this temperature in several studies of multidomain magnetite crystals, which, however, also display a Verwey transition. We have investigated the magnetic characteristics of this 50 K anomaly further in brain and tumor tissue. The magnetic measurements consist of χ–T curves, measured after cooling in zero field (ZFC) or in a field (FC), as well as hysteresis loops. The 50 K anomaly is expressed as a bump in χ–T curves over a 20 K temperature range, with a peak between 44 and 58 K. The magnetic intensity of the samples is weak; however, the anomaly signal is an order of magnitude larger than known effects related to the magnetic ordering of oxygen at 43 K. A phase transition, or magnetic ordering of another phase, does not seem a likely explanation, because both the ZFC and FC curves follow the perturbation, rather than showing a bifurcation at peak susceptibility. This explanation also precludes magnetic blocking of a superparamagnetic component. Hysteresis loops at temperature of the peak perturbation show a splitting of the descending and ascending limbs at the maximum starting field. The magnetic behavior observed in these experiments is consistent with a change in electron activity.
Nonlinear generation and loss of infragravity wave energy
Authors: Henderson Stephen M. , Guza R. T. , Elgar Steve , Herbers T. H. C. , Bowen A. J.
Published: December 2006

Nonlinear energy transfers with sea and swell (frequencies 0.05–0.40 Hz) were responsible for much of the generation and loss of infragravity wave energy (frequencies 0.005–0.050 Hz) observed under moderate‐ and low‐energy conditions on a natural beach. Cases with energetic shear waves were excluded, and mean currents, a likely shear wave energy source, were neglected. Within 150 m of the shore, estimated nonlinear energy transfers to (or from) the infragravity band roughly balanced the divergence (or convergence) of the infragravity energy flux, consistent with a conservative energy equation. Addition of significant dissipation (requiring a bottom drag coefficient exceeding about 10−2) degraded the energy balance.
High‐resolution thermal inertia derived from the Thermal Emission Imaging System (THEMIS): Thermal model and applications
Authors: Fergason Robin L. , Christensen Philip R. , Kieffer Hugh H.
Published: December 2006

Thermal inertia values at 100 m per pixel are determined using nighttime temperature data from the Thermal Emission Imaging System (THEMIS) on the Mars Odyssey spacecraft, producing the highest‐resolution thermal inertia data set to date. THEMIS thermal inertia values have an overall accuracy of ∼20%, a precision of 10–15%, and are consistent with both Thermal Emission Spectrometer orbital and Miniature Thermal Emission Spectrometer surface thermal inertia values. This data set enables the improved quantification of fine‐scale surface details observed in high‐resolution visible images. In the Tharsis region, surface textures and crater rims observed in visible images have no corresponding variation in the THEMIS thermal inertia images, indicating that the dust mantle is pervasive at THEMIS scales and is a minimum of a few centimeters and up to 1–2 m thick. The thermal inertia of bed form material indicates particle diameters expected for aeolian sediments, and these materials are likely currently saltating. Variations in the thermal inertia within interior layered deposits in Hebes Chasma can be distinguished, and the thermal inertia is too low to be consistent with bedrock or a lava flow. Thus a secondary emplacement of volcanic material or a volcanic ash deposit is a more likely method of formation. Higher‐resolution THEMIS thermal inertia enables the identification of exposed bedrock on the Martian surface. In Nili Patera and Ares Vallis, bedrock material corresponds to distinct compositional and morphologic surfaces, indicating that a specific unit is exposed and is likely currently being kept free of unconsolidated material by aeolian processes.
Erosion rates at the Mars Exploration Rover landing sites and long‐term climate change on Mars
Authors: Golombek M. P. , Grant J. A. , Crumpler L. S. , Greeley R. , Arvidson R. E. , Bell J. F. , Weitz C. M. , Sullivan R. , Christensen P. R. , Soderblom L. A. , Squyres S. W.
Published: December 2006

Erosion rates derived from the Gusev cratered plains and the erosion of weak sulfates by saltating sand at Meridiani Planum are so slow that they argue that the present dry and desiccating environment has persisted since the Early Hesperian. In contrast, sedimentary rocks at Meridiani formed in the presence of groundwater and occasional surface water, and many Columbia Hills rocks at Gusev underwent aqueous alteration during the Late Noachian, approximately coeval with a wide variety of geomorphic indicators that indicate a wetter and likely warmer environment. Two‐toned rocks, elevated ventifacts, and perched and undercut rocks indicate localized deflation of the Gusev plains and deposition of an equivalent amount of sediment into craters to form hollows, suggesting average erosion rates of ∼0.03 nm/yr. Erosion of Hesperian craters, modification of Late Amazonian craters, and the concentration of hematite concretions in the soils of Meridiani yield slightly higher average erosion rates of 1–10 nm/yr in the Amazonian. These erosion rates are 2–5 orders of magnitude lower than the slowest continental denudation rates on Earth, indicating that liquid water was not an active erosional agent. Erosion rates for Meridiani just before deposition of the sulfate‐rich sediments and other eroded Noachian areas are comparable with slow denudation rates on Earth that are dominated by liquid water. Available data suggest the climate change at the landing sites from wet and likely warm to dry and desiccating occurred sometime between the Late Noachian and the beginning of the Late Hesperian (3.7–3.5 Ga).
Control of ion species in inductively coupled oxidation plasma by inert gas mixing
Authors: Bai K. H. , Chang H. Y.
Published: December 2006

We have controlled and investigated the ion density ratio ([O+]∕[O2+]) in oxidation plasma by He and Xe mixing. The ion density ratio increases from 0.26 to 0.97 by He mixing, and decreases to 0.015 by Xe mixing. The ratio is a strong function of the electron density and electron temperature. When the other conditions are fixed, the ion density ratio is proportional to the electron density in all the cases: the He∕O2 and Xe∕O2 mixtures as well as pure O2 plasma. This may be due to the increase in the dissociation rate and the process of ionization from O to O+. The rate of increase in the ion density ratio with the electron density is different in the two cases: In the He∕O2 mixture, the rate of increase is slightly higher than that in the pure O2 plasma. However, the rate is very low in the Xe∕O2 mixture. In the Xe∕O2 mixture, the ion density ratio is actually a strong function of the electron temperature rather than the electron density.
Suppression of chemical and electrical instabilities in mesoporous silica films by molecular capping
Authors: Singh A. P. , Gandhi D. D. , Lipp E. , Eizenberg M. , Ramanath G.
Published: December 2006

Mesoporous silica (MPS) thin films are attractive for achieving low relative dielectric permittivity (low k) interlayer isolation in integrated circuit wiring, but are susceptible to instabilities in electrical behavior due to water uptake and copper diffusion. Here, we show that capping MPS films with a trimethyl-group terminated organosilane layer irreversibly suppresses moisture-induced capacitance instabilities, and decreases the relative dielectric permittivity and Cu-induced leakage currents. Analysis of capacitance-voltage and current-voltage characteristics along with infrared spectroscopy shows that the trimethyl organosilanes inhibit hydrogen bonding of water molecules by rendering the dielectric surfaces hydrophobic. These features are promising for tailoring the chemical and interfacial properties and reliability of porous dielectric materials for insulation in device wiring applications.
Current effects and topology of current paths in single crystalline Pr0.7Pb0.3MnO3
Authors: Li Run-Wei , Zhou Xin , Belik Alexei A. , Inoue Jun-ichi , Miki Kazushi , Shen Bao-Gen
Published: December 2006

In electron-phase-separated Pr0.7Pb0.3MnO3 single crystals, nonlinear current effects have been observed above a critical current (Ic), beyond which a metal-insulator transition could be induced by the applied electrical current. We found that the square of Ic was linearly related to the external temperature, which can be well understood based on a local heating-cooling model. Furthermore, the surface area and mass of the current paths in the phase-separated systems were obtained by fitting our experimental data to the model, and a temperature-dependent topology of the current paths was found. In addition, interesting oscillatory behaviors in differential resistance (dV∕dI) were observed at temperatures slightly above the metal-insulator transition temperature, which can be attributed to electron tunneling between isolated ferromagnetic clusters embedded in the insulating paramagnetic matrix.
New class ôN of statistical models: Transfer matrix eigenstates, chain Hamiltonians, factorizable S matrix
Authors: Abdesselam B. , Chakrabarti A.
Published: December 2006

Statistical models corresponding to a new class of braid matrices (ôN;N⩾3) presented in a previous paper are studied. Indices labeling states spanning the Nr dimensional base space of T(r)(θ), the rth order transfer matrix are so chosen that the operators W (the sum of the state labels) and (CP) (the circular permutation of state labels) commute with T(r)(θ). This drastically simplifies the construction of eigenstates, reducing it to solutions of relatively small number of simultaneous linear equations. Roots of unity play a crucial role. Thus for diagonalizing the 81 dimensional space for N=3, r=4, one has to solve a maximal set of five linear equations. A supplementary symmetry relates invariant subspaces pairwise [W=(r,Nr) and so on] so that only one of each pair needs study. The case N=3 is studied fully for r=(1,2,3,4). Basic aspects for all (N,r) are discussed. Full exploitation of such symmetries lead to a formalism quite different from, possibly generalized, algebraic Bethe ansatz. Chain Hamiltonians are studied. The specific types of spin flips they induce and propagate are pointed out. The inverse Cayley transform of the YB matrix giving the potential leading to factorizable S matrix is constructed explicitly for N=3 as also the full set of R̂tt relations. Perspectives are discussed in a final section.
Dielectric properties of Zr-modified Pb(Mg1∕3Ta2∕3)O3 ceramic: Influence of pressure, biasing electric field, and B-site cationic order
Authors: Grubbs R. K. , Venturini E. L. , Samara G. A. , Wang Y. , Setter N.
Published: December 2006

The effects of hydrostatic pressure and biasing dc electric field on the relaxor dielectric response of samples of Pb[(Mg1∕3Ta2∕3)0.95Zr0.05]O3 with 12%, 15%, and 90% B-site cationic order were investigated. Qualitatively similar decreases in the amplitudes of the real part of the dielectric constant (ε′) at both the peak temperatures (Tm) of the ε′(T,ω) response in the high temperature phase, i.e., above Tm, are observed on increasing the three variables: pressure, biasing field, and B-site order - effects that are interpreted in terms of stiffening of the underlying soft ferroelectric mode of the lattice. Strong deviation of the frequency-independent ε′(T) from the Curie-Weiss law above Tm, attributed to correlations among polar nanodomains, gives way to adherence to this law above the Burns temperature Td. This is the temperature where polar nanodomains first make their presence known. The evolution with decreasing temperature below Td of short-range order in the nanodomains is estimated from the ε′(T) response and shows essentially no dependence on the degree of B-site order. The correlation length for the interaction among the polar nanodomains was also estimated from the dielectric data and found to exhibit strong increase (decrease) with temperature (pressure) as T approaches Tm from above - characteristics of perovskite relaxors. A high temperature dielectric relaxation with an activation energy of 1.27eV is observed for the 90% ordered sample, but not for the 12% and 15% ordered samples. This relaxation is attributed to increased oxygen vacancies in the 90% sample that form during the long (64h) annealing time at 1350°C to achieve this high level of ordering.
Structural and thermoelectric properties of epitaxially grown Bi2Te3 thin films and superlattices
Authors: Peranio N. , Eibl O. , Nurnus J.
Published: December 2006

Multi-quantum-well structures of Bi2Te3 are predicted to have a high thermoelectric figure of merit ZT. Bi2Te3 thin films and Bi2Te3∕Bi2(Te0.88Se0.12)3 superlattices (SLs) were grown epitaxially by molecular beam epitaxy on BaF2 substrates with periods of 12 and 6nm, respectively. Reflection high-energy electron diffraction confirmed a layer-by-layer growth, x-ray diffraction yielded the lattice parameters and SL periods and proved epitaxial growth. The in-plane transport coefficients were measured and the thin films and SL had power factors between 28 and 35μW∕cmK2. The lattice thermal conductivity varied between 1.60W∕mK for Bi2Te3 thin films and 1.01W∕mK for a 10nm SL. The best figures of merit ZT were achieved for the SL; however, the values are slightly smaller than those in bulk materials. Thin films and superlattices were investigated in plan view and cross section by transmission electron microscopy. In the Bi2Te3 thin film and SL the dislocation density was found to be 2×1010cm−2. Bending of the SL with amplitudes of 30nm (12nm SL) and 15nm (6nm SL) and a wavelength of 400nm was determined. Threading dislocations were found with a density greater than 2×109cm−2. The superlattice interfaces are strongly bent in the region of the threading dislocations, undisturbed regions have a maximum lateral sie of 500nm. Thin films and SL showed a structural modulation [natural nanostructure (nns)] with a wavelength of 10nm and a wave vector parallel to (1,0,10). This nns was also observed in Bi2Te3 bulk materials and turned out to be of general character for Bi2Te3. The effect of the microstructure on the thermoelectric properties is discussed. The microstructure is governed by the superlattice, the nns, and the dislocations that are present in the films. Our results indicate that the microstructure directly affects the lattice thermal conductivity. Thermopower and electrical conductivity were found to be negatively correlated and no clear dependence of the two quantities on the microstructure could be found.
Theoretical study of nitrogen-doping effects on void formation processes in silicon crystal growth
Authors: Kageshima Hiroyuki , Taguchi Akihito , Wada Kazumi
Published: December 2006

Nitrogen-doping effects in silicon crystal growth have been theoretically studied using thermodynamical simulation based on first-principles calculation results. The results show that the densities of various complexes are determined in the balance between the enthalpy effects and the entropy effects. They also show that about one order larger density of doped nitrogen is required in Czochralski silicon to obtain a void suppression effect similar to that in float-zone silicon. This is because oxygen itself has a weak void suppression effect due to the formation of vacancy-oxygen complexes around the void formation temperature. Competition between nitrogen and oxygen in trapping vacancies around the void formation temperature weakens the nitrogen-doping effect to suppress the void formation in Czochralski silicon. Since doped nitrogen preferentially forms nitrogen-vacancy-oxygen complexes at lower temperatures, the high density nitrogen doping enhances the oxygen precipitate density in Czochralski silicon.
Geometric equivalence of Clifford algebras
Authors: Botman David M. , Joyce William P.
Published: December 2006

We motivate a notion of geometric equivalence that is not the usual notion of algebraic equivalence (or isomorphism of Clifford algebra). Using this definition tilting to the opposite metric is a geometric equivalence in contrast to such algebraic equivalences as Cℓ(3,0)≅Cℓ(1,2) which are not geometric. We define and discuss the classification of partitioned Clifford algebra and the geometric equivalence of Dirac formulations.
Anisotropic electrical conduction from heterogeneous oxidation states in plasma sprayed TiO2 coatings
Authors: Sharma Atin , Gouldstone Andrew , Sampath Sanjay , Gambino Richard J.
Published: December 2006

Microstructural and electrical characterizations of air plasma sprayed TiO2 coatings were carried out to investigate the details of deoxidation during the spray process and the changes following air annealing. The coatings were found to behave as an n-type semiconductor indicating the presence of oxygen vacancies. Direct-current resistivity measurements in plane (ρIP) and through thickness (ρTT) of the coatings as a function of annealing time and temperature showed remarkably large anisotropies (=ρTT∕ρIP) of up to 105. Impedance spectroscopy of the specimens coupled with microstructural analysis revealed that the origin of this anisotropy lies in the heterogeneous deoxidation and reoxidation behavior of the coatings. Due to rapid quenching, the high temperature deoxidation state is preserved in the splat boundaries making them more conductive than the bulk of the splat in the as-sprayed coating. Upon annealing in air, the splat boundaries get selectively oxidized due to faster surface diffusion of oxygen and become more insulating. This behavior, together with the layered morphology of plasma sprayed coatings, results in anisotropy.
Magnetic and chemical properties of Co2MnSi thin films compared to the Co2MnSi∕Al-O interface
Authors: Schmalhorst J. , Sacher M. D. , Höink V. , Reiss G. , Hütten A. , Engel D. , Ehresmann A.
Published: December 2006

The Heusler alloy Co2MnSi with theoretically predicted 100% spin polarization has been successfully implemented in Co2MnSi∕AlOx∕Co7Fe3 magnetic tunnel junctions recently. Here we investigated 100 nm thick Co2MnSi films grown on a vanadium buffer and capped by a thin alumina film. This stack is similar to the lower electrode including the tunneling barrier of magnetic tunnel junctions. By soft x-ray absorption spectroscopy and magnetic circular dichroism in fluorescence and total electron yield detection we determined differences between the chemical and magnetic properties of the Co2MnSi thin films and the Co2MnSi∕AlOx interface. Whereas MnO was formed directly at the interface during plasma oxidation of the Al layer, the interfacial Co was not oxidized and its x-ray absorption line shape at the L2,3 edge was similar to the line shape of bulk Co2MnSi. The atomically ordered bulk Co2MnSi showed characteristic differences in the x-ray absorption spectra in comparison with the disordered samples: in the ordered state of the bulk both, Co and Mn, showed additional shoulders about 4 eV above the L2,3 resonances, a large circular dichroism, and a pronounced x-ray absorption near edge fine structure. The same was found for interfacial Co, whereas for interfacial Mn these features were masked by the characteristic absorption multiplet structure of MnO right at the interface which also resulted in a strong reduction of the interfacial Mn moment in annealed samples.
Dynamical systems analysis for polarization in ferroelectrics
Authors: Bandyopadhyay A. K. , Ray P. C. , Gopalan Venkatraman
Published: December 2006

The nonlinear hysteresis behavior in ferroelectric materials, such as lithium tantalate and lithium niobate, may be explained by dynamical systems analysis. In a previous work, the polarization “domain wall width” was studied in terms of only spatial variation and eventually critical values of polarization were determined to derive the stability zone in the context of Landau-Ginzburg free energy functional. In the present work, the temporal dynamics of the domains themselves are considered by taking the time variation through Euler-Lagrange dynamical equation of motion, which gives rise to a Duffing oscillator differential equation as a governing equation. From this nonlinear Duffing oscillator equation, three cases are studied theoretically: First, with no electric field with and without any damping; secondly, taking the external field as static with damping; and finally, taking an oscillatory electric field with damping. After giving perturbation at the coercive field, the eigenvalues deduced through a Jacobian transformation of the perturbed matrix show interesting cases of stability and instability of polarization for different values of electric field. The possibility of chaos at high oscillatory electric field is also briefly explored merely as a limiting case in terms of the Lyapunov exponents spectrum in our particular ferroelectric system.
Effects of longitudinal field on transmitted near field in doped semi-infinite semiconductors with a surface conducting sheet
Authors: Huang Danhong , Rhodes C. , Alsing P. M. , Cardimona D. A.
Published: December 2006

A unique structure composed of a half-space of air and a semi-infinite doped bulk GaAs covered by an InAs conducting interface sheet is proposed, from which the physics behind the interplay between the effects of transverse sheet current and the longitudinal three-dimensional plasma waves, as well as the effect of evanescent modes, can be explored. The in-plane and perpendicular components of a transverse field are modified by the inclusion of the InAs conducting sheet and a longitudinal field, and the coupling between transverse and longitudinal oscillations of an electromagnetic field parallel and perpendicular to the conducting sheet is made possible by the doped GaAs bulk. Based on this structure, a spatially nonlocal dynamic theory is derived, including the coupling between the transverse and longitudinal oscillations, the image-potential and retardation effects, and the effects of evanescent modes. The existence of the InAs conducting sheet is found to reduce the transmitted field by reflection from the induced sheet current. The longitudinal field is found to further reduce its strength by absorption from an induced longitudinal three-dimensional plasma wave in the doped GaAs bulk. The transmitted near field is modified by the doped electrons in the GaAs bulk with a relative enhancement at small incident angles being overshadowed by the strong reflection from the induced sheet current in the InAs conducting sheet on the surface.
Characteristics of a conducting organic diode with finite (nonzero) Schottky barrier
Authors: Kumar Pankaj , Jain S. C. , Misra Aparna , Kamalasanan M. N. , Kumar Vikram
Published: December 2006

When the transport and Poisson equations are integrated a constant of integration C should be used. If the Schottky barrier (ϕB) between metal electrode and organic semiconductor is zero, the injected carrier density at the contact is equal to that at the Fermi surface of the metal and can be taken as infinity to a good approximation. In this case the constant of integration C becomes zero. But for most cathodes and anodes used in organic devices the Schottky barriers are not zero. In these cases the constant C comes out to be A[J∕P(0)m], where the constant A depends on material parameters, m is a constant more than 1, J is the current density, and P(0)∝exp(−ϕB∕kT) is the injected carrier density. Even for a small value of the Schottky barrier ϕB=0.12eV, P(0) is reduced by two orders of magnitude. For this or smaller value of P(0), C plays an important role in determining the J-V characteristics. We report a theory of J-V characteristics for finite (nonzero) Schottky barriers. Even for small values of the Schottky barrier the results are strikingly different from the conventional theory based on zero barrier. As the barrier increases the deviation from the conventional theory becomes large. For very large values of C, J-V characteristics become Ohmic. We have fabricated ITO/PEDOT:PSS/MEH-PPV/Au diode and measured their J-V characteristics. The theory given in this paper agrees with the experimental data at different temperatures and different sample thicknesses.
Enhanced dielectric properties of highly (100)-oriented Ba(Zr,Ti)O3 thin films grown on La0.7Sr0.3MnO3 bottom layer
Authors: Tang X. G. , Liu Q. X. , Jiang Y. P. , Zheng R. K. , Chan H. L. W.
Published: December 2006

Barium zirconate titanate Ba(Zr0.2Ti0.8)O3 (BZT) thin films on La0.7Sr0.3MnO3 (LSMO)-coated Si and Pt∕Ti∕SiO2∕Si substrates have been prepared by pulsed laser deposition and crystallized in situ at 650°C. Four capacitor types of LSMO∕BZT∕LSMO∕Si, Pt∕BZT∕LSMO∕Si, Pt∕BZT∕Pt∕Si, and Pt∕BZT∕LSMO∕Pt∕Si were prepared to investigate the structural and dielectric properties, tunability, and figure of merits. Among them, the high (100)-oriented BZT films were grown on the (100)-textured LSMO and (111)-textured Pt electrodes. The results show that the LSMO∕BZT∕LSMO∕Si has the highest dielectric constant of 555 and Pt∕BZT∕LSMO∕Pt∕Si has the highest tunability of 73% at 1MHz. The high dielectric constant and tunability have been attributed to the (100) texture of the LSMO bottom layer leading to the decrease of the thickness of the interface of the dead layer.
Endomorphisms on half-sided modular inclusions
Authors: Svegstrup Rolf Dyre
Published: December 2006

In algebraic quantum field theory we consider nets of von Neumann algebras indexed over regions of the space time. Wiesbrock [“Conformal quantum field theory and half-sided modular inclusions of von Neumann algebras,” Commun. Math. Phys. 158, 537–543 (1993)] has shown that strongly additive nets of von Neumann algebras on the circle are in correspondence with standard half-sided modular inclusions. We show that a finite index endomorphism on a half-sided modular inclusion extends to a finite index endomorphism on the corresponding net of von Neumann algebras on the circle. Moreover, we present another approach to encoding endomorphisms on nets of von Neumann algebras on the circle into half-sided modular inclusions. There is a natural way to associate a weight to a Möbius covariant endomorphism. The properties of this weight have been studied by Bertozzini et al. [“Covariant sectors with infinite dimension and positivity of the energy,” Commun. Math. Phys. 193, 471–492 (1998)]. In this paper we show the converse, namely, how to associate a Möbius covariant endomorphism to a given weight under certain assumptions, thus obtaining a correspondence between a class of weights on a half-sided modular inclusion and a subclass of the Möbius covariant endomorphisms on the associated net of von Neumann algebras. This allows us to treat Möbius covariant endomorphisms in terms of weights on half-sided modular inclusions. As our aim is to provide a framework for treating endomorphisms on nets of von Neumann algebras in terms of the apparently simpler objects of weights on half-sided modular inclusions, we lastly give some basic results for manipulations with such weights.
Spectral theory of neutron transport semigroups with partly elastic collision operators
Authors: Sbihi Mohammed
Published: December 2006

This paper deals with spectral properties of a class of neutron transport equations involving partly elastic collision operators introduced by Larsen and Zweifel [J. Math. Phys. 15, 1987–1997 (1974)]. In particular, estimates of the essential type of associated semigroups are given.
Cross-stream-line migration in confined flowing polymer solutions: Theory and simulation
Authors: Hernández-Ortiz Juan P. , Ma Hongbo , de Pablo Juan J. , Graham Michael D.
Published: December 2006

Theory and Brownian dynamics (BD) simulations are used to study cross-stream migration in confined dilute flowing polymer solutions, using bead-spring chain and dumbbell models for the polymer molecules. Different degrees of confinement are explored, from a chain above a single wall to slits whose widths 2h are much bigger than the polymer contour length L and radius of gyration Rg (2h⪢L⪢Rg), much bigger than the radius of gyration but comparable with the contour length (2h∼L>Rg), and comparable with the polymer radius of gyration (2h∼Rg). The results show that except in the latter case, polymer chains migrate in shear flow away from the confining surfaces due to the hydrodynamic interactions between chains and walls. In contrast, when 2h∼Rg, the chain migration in flow is toward the walls. This is a steric effect, caused by extension of the chain in the flow direction and corresponding shrinkage of the chains in the confined direction; here the hydrodynamic effects of each wall cancel one another out. Considering the polymer chain as a Stokeslet-doublet (point-force-dipole) as in a previously developed kinetic theory captures the correct far-field (relative to the walls) behavior. Once a finite-size dipole is used, the theory improves its near-wall predictions. In the regime 2h∼L>Rg, the results are significantly affected by the level of discretization of the polymer chain, i.e., number of springs, because the spatial distribution of the forces exerted by the chain on the fluid acts on the scale of the channel geometry.
Wave-breaking limits for relativistic electrostatic waves in a one-dimensional warm plasma
Authors: Trines R. M. G. M. , Norreys P. A.
Published: December 2006

The propagation of electrostatic plasma waves having relativistic phase speed and amplitude has been studied. The plasma is described as a warm, relativistic, collisionless, nonequilibrium, one-dimensional electron fluid. Wave-breaking limits for the electrostatic field are calculated for nonrelativistic initial plasma temperatures and arbitrary phase velocities, and a correspondence between wave breaking and background particle trapping has been uncovered. Particular care is given to the ultrarelativistic regime (γφ2kBT0∕(mec2)≫1), since conflicting results for this regime have been published in the literature. It is shown here that the ultrarelativistic wave-breaking limit will reach arbitrarily large values for γφ→∞ and fixed initial temperature. Previous results claiming that this limit is bounded even in the limit γφ→∞ are shown to suffer from incorrect application of the relativistic fluid equations and higher, more realistic wave-breaking limits are appropriate.
Experiments and theory of an upstream ionization instability excited by an accelerated electron beam through a current-free double layer
Authors: Aanesland A. , Lieberman M. A. , Charles C. , Boswell R. W.
Published: December 2006

A low-frequency instability varying from 10 to 20kHz has been discovered in the presence of a current-free double layer (DL) in a low-pressure expanding helicon plasma. The instability is observed using various electrostatic probes, such as Langmuir probes floating or biased to ion saturation and emissive probes measuring the plasma potential. A retarding field energy analyzer measuring the ion energy distribution function downstream of the double layer is used together with the LP to simultaneously observe the DL and the instability, confirming their coexistence. The frequency of the instability decreases with increasing neutral pressure, increases with increasing magnetic field in the source and increases with increasing rf power. A theory for an upstream ionization instability has been developed, in which electrons accelerated through the DL increase the ionization upstream and are responsible for the observed instability. The theory is in good agreement with the experimental results and shows that the frequency increases with the potential drop of the double layer and with decreasing chamber radius.
Wave impact loads: The role of the flip-through
Authors: Lugni C. , Brocchini M. , Faltinsen O. M.
Published: December 2006

The impact of waves upon a vertical, rigid wall during sloshing is analyzed with specific focus on the modes that lead to the generation of a flip-through [M. J. Cooker and D. H. Peregrine, “A model for breaking wave impact pressures,” in Proceedings of the 22nd International Conference on Coastal Engineering (ASCE, Delft, 1990), Vol. 2, pp. 1473–1486]. Experimental data, based on a time-resolved particle image velocimetry technique and on a novel free-surface tracking method [M. Miozzi, “Particle image velocimetry using feature tracking and Delaunay tessellation,” in Proceedings of the 12th International Symposium on Applications of Laser Techniques to Fluid Mechanics (2004)], are used to characterize the details of the flip-through dynamics while wave loads are computed by integrating the experimental pressure distributions. Three different flip-through modes are observed and studied in dependence on the amount and modes of air trapping. No air entrapment characterizes a “mode (a) flip-through,” engulfment of a single, well-formed air bubble is typical of a “mode (b)” event, while the generation of a fine-scale air-water mixing occurs for a “mode (c)” event. Upward accelerations of the flip-through jet exceeding 1500g have been measured and the generation/collapse process of a small air cavity is described in conjunction with the available pressure time histories. Predictions of the vertical pressure distributions made with the pressure-impulse model of Cooker and Peregrine [M. J. Cooker and D. H. Peregrine, “Pressure-impulse theory for liquid impact problems,” J. Fluid Mech. 297, 193 (1995)] show good agreement with the experimental data.
Modified control software for imaging ultracold atomic clouds
Authors: Whitaker D. L. , Sharma A. , Brown J. M.
Published: December 2006

A charge-coupled device (CCD) camera capable of taking high-quality images of ultracold atomic samples can often represent a significant portion of the equipment costs in atom trapping experiment. We have modified the commercial control software of a CCD camera designed for astronomical imaging to take absorption images of ultracold rubidium clouds. This camera is sensitive at 780 nm and has been modified to take three successive 16-bit images at full resolution. The control software can be integrated into a Matlab graphical user interface with fitting routines written as Matlab functions. This camera is capable of recording high-quality images at a fraction of the cost of similar cameras typically used in atom trapping experiments.
Linear response functions for a vibrational configuration interaction state
Authors: Christiansen Ove , Kongsted Jacob , Paterson Martin J. , Luis Josep M.
Published: December 2006

Linear response functions are implemented for a vibrational configuration interaction state allowing accurate analytical calculations of pure vibrational contributions to dynamical polarizabilities. Sample calculations are presented for the pure vibrational contributions to the polarizabilities of water and formaldehyde. We discuss the convergence of the results with respect to various details of the vibrational wave function description as well as the potential and property surfaces. We also analyze the frequency dependence of the linear response function and the effect of accounting phenomenologically for the finite lifetime of the excited vibrational states. Finally, we compare the analytical response approach to a sum-over-states approach.
High-reflectivity Cr∕Sc multilayer condenser for compact soft x-ray microscopy
Authors: Stollberg H. , Yulin S. , Takman P. A. C. , Hertz H. M.
Published: December 2006

The condenser is a critical component in compact water-window x-ray microscopes as it influences the exposure time via its efficiency and the resolution via its numerical aperture. Normal-incidence multilayer mirrors can reach large geometrical collection efficiencies and match the numerical aperture of the zone plate but require advanced processing for high total reflectivity. In the present article we demonstrate large-diameter normal-incidence spherical Cr∕Sc multilayer condensers with high and uniform reflectivity. Dc-magnetron sputtering was used to deposit 300 bilayers of Cr∕Sc with a predetermined d-spacing matching the λ=3.374nm operating wavelength on spherical substrates. The mirrors show a uniform reflectivity of ∼3% over the full 58mm diameter condenser area. With these mirrors an improvement in exposure time by a factor of 10 was achieved, thereby improving the performance of the compact x-ray microscope significantly.
New diamond anvil cell system for in situ resistance measurement under extreme conditions
Authors: Li Ming , Gao Chunxiao , Ma Yanzhang , Li Yanchun , Li Xiaodong , Li Hui , Liu Jing , Hao Aimin , He Chunyuan , Huang Xiaowei , Zhang Dongmei , Yu Cuiling
Published: December 2006

We report an alumina-encapsulated microcircuit on a diamond anvil for high-pressure and high-temperature electrical conductivity measurement. An alumina thin film was deposited on a diamond anvil as a thermal insulation layer for laser heating, on which a molybdenum film was deposited and photolithographically fabricated to a van der Pauw circuit. The introduction of the alumina layer significantly improves the laser heating performance. This specially fabricated diamond anvil permits us to measure the resistivity of (Mg0.875Fe0.125)2SiO4 at 3450K and 35GPa in a laser-heated diamond anvil cell. We expect to substantially extend the pressure-temperature scale of in situ resistivity measurement.
Electromagnetic dust-lower-hybrid and dust-magnetosonic waves and their instabilities in a dusty magnetoplasma
Authors: Salimullah M. , Rahman M. M. , Zeba I. , Shah H. A. , Murtaza G. , Shukla P. K.
Published: December 2006

The electromagnetic waves below the ion-cyclotron frequency have been examined in a collisionless and homogeneous dusty plasma in the presence of a dust beam parallel to the direction of the external magnetic field. The low-frequency mixed electromagnetic dust-lower-hybrid and purely transverse magnetosonic waves become unstable for the sheared flow of dust grains and grow in amplitude when the drift velocity of the dust grains exceeds the parallel phase velocity of the waves. The growth rate depends dominantly upon the thermal velocity and density of the electrons.
Direct correlation functions of binary mixtures of hard Gaussian overlap molecules
Authors: Moradi M. , Khordad R.
Published: December 2006

We study the direct correlation function (DCF) of a classical fluid mixture of nonspherical molecules. The components of the mixture are two types of hard ellipsoidal molecules with different elongations, interacting through the hard Gaussian overlap (HGO) model. Two different approaches are used to calculate the DCFs of this fluid, and the results are compared. Here, the Pynn approximation [J. Chem. Phys. 60, 4579 (1974)] is extended to calculate the DCF of the binary mixtures of HGO molecules, then we use a formalism based on the weighted density functional theory introduced by Chamoux and Perera [J. Chem. Phys. 104, 1493 (1996)]. These results are fairly in agreement with each other. The pressure of this system is also calculated using the Fourier zero components of the DCF. The results are in agreement with the Monte Carlo molecular simulation.