Relative Peak Positions Research Articles

Regional climate and glacial control on high‐resolution oxygen isotope records from Ain el Beida (latest Miocene, northwest Morocco): A cyclostratigraphic analysis in the depth and time domain

High‐resolution benthic and planktonic stable oxygen isotope records are presented for the upper Miocene Ain el Beida (AEB) section in northwestern Morocco and reveal the clear imprint of the (climatic) precession, obliquity, and eccentricity cycles in the interval between 6.5 and 5.5 Ma. The δ18O depth series were transformed into time series using astronomical tuning of the sedimentary color cycles to the 65°N summer insolation curve of the La93 solution with present‐day values for tidal dissipation and dynamical ellipticity. Spectral analysis and band‐pass filtering show that the ratios of the astronomically related spectral peaks are not consistent in the depth and time domain. The inconsistencies are mainly due to variations in sedimentation rate that are positively correlated with precession amplitude (i.e., modulated by eccentricity). In addition, they result from a long‐term trend in sedimentation rate. A simple model of nonlinear response of the sedimentation rate to the eccentricity modulation of precession was used to simulate the observed shifts in the relative position of the spectral peaks in the depth domain. Cross‐spectral analysis was carried out on the δ18O time series and a combined eccentricity, tilt (obliquity), and precession (ETP) curve. The precession‐controlled δ18O signal varies in‐phase with ETP partly as a result of the tuning procedure, while the obliquity related signal reveals a small lag of 2–3 kyr relative to obliquity. This lag is slightly reduced at the time of the Messinian Salinity Crisis (MSC) and increases to 5–6 kyr if the tidal dissipation term in the astronomical solution is reduced to half its present‐day value. The obliquity‐related lag is most likely associated with the slow buildup of ice caps, whereas the precession signal is interpreted as to dominantly reflect regional climate changes comparable to those associated with Mediterranean sapropels. Finally, the benthic δ18O record is compared with open ocean records and discussed in terms of an astronomically tuned oxygen isotope stratigraphic framework.

Relativistic Effects and Polarization in Three High‐Energy Pulsar Models

We present the influence of the special relativistic effects of aberration and light-travel time delay on pulsar high-energy light curves and polarization characteristics predicted by three models: the two-pole caustic model, the outer gap model, and the polar cap model. Position angle curves and degree of polarization are calculated for the models and compared with the optical data on the Crab pulsar. The relative positions of peaks in gamma-ray and radio light curves are discussed in detail for the models. We find that the two-pole caustic model can qualitatively reproduce the optical polarization characteristics of the Crab pulsar: fast swings of the position angle and minima in polarization degree, associated with both peaks. The anticorrelation between the observed flux and the polarization degree (observed in the optical band also for B0656+14) naturally results from the caustic nature of the peaks, which are produced in the model because of the superposition of radiation from many different altitudes, i.e., polarized at different angles. The two-pole caustic model also provides an acceptable interpretation of the main features in the Crab's radio profile. Neither the outer gap model nor the polar cap model is able to reproduce the optical polarization data on the Crab. Although the outer gap model is very successful in reproducing the relative positions of gamma-ray and radio peaks in pulse profiles, it can reproduce the high-energy light curves only when photon emission from regions very close to the light cylinder is included.

Interpreting the signal from a localized fluorescence sensor: a study by angle-resolved XPS and dynamic SIMS

Angle-resolved X-ray photoelectron spectroscopy (XPS) and dynamic secondary ion mass spectroscopy (DSIMS) experiments were conducted to assess the interactions between a diamine curing agent and a glycidoxysilane-modified glass substrate. This effort was motivated by earlier work, in which a fluorescent probe localized in dilute quantities in the silane layer was used to track the penetration of the resin into the silane layer, as well as the resin cure. XPS and DSIMS experiments were performed on the silane layers immersed only in the resin hardener, providing more detailed information about the concentration profile and structural reorganization within the silane layer due specifically to hardener penetration. Dynamic SIMS spectra reveal the presence of hardener in the layer, as indicated by the strong CN − signal throughout the silane layer thickness. The XPS results indicate the presence of an amine gradient within the top 10 nm of the silane coating, with less amine penetration deeper into the silane layer. The XPS data also suggest some level of anisotropy in the molecular structure of the diamine/glycidoxysilane coating, as revealed by the differences in the relative atomic concentrations and peak positions of the C1 s components at two different take-off angles.

Measuring electronic structure of wurtzite InN using electron energy loss spectroscopy

The electronic structure of wurtzite InN has been investigated by electron energy loss spectroscopy (EELS). Spectra of the nitrogen K edge and the indium M4,5 edge have been measured and were compared with calculated partial, N 2p and In 5p conduction band density of states in InN. Excellent agreement on the relative positions of the characteristic peaks were obtained. From low-loss EELS the bulk plasmon energy at 15.5 eV, location of the In 4d deep valence states at about 16.3 eV below the conduction band maximum and strong interband transitions with 6.2 eV excitation energy are also found.

Potentiometric and 19F nuclear magnetic resonance spectroscopic study of fluoride substitution in the GaAl 12 polyoxocation: implications for aluminum (hydr)oxide mineral surfaces

Fluoride replacement of oxygens in the GaO 4Al 12(OH) 24(H 2O)127+(aq) molecule [GaAl 12] was studied via 19F nuclear magnetic resonance (NMR) at 4 < pH < 5 and 278 K in order to elucidate similar reactions at the surfaces of clays. Peaks are identified in the 19F-NMR spectra that correspond to both terminal and bridging fluorides on the GaAl 12 molecule, with relative peak positions similar to those previously identified in fluoridated aluminum (hydr)oxide mineral surfaces (Nordin, J. P., Sullivan, D. J., Phillips, B. L., and Casey, W. H. [1999], “Mechanisms for fluoride-promoted dissolution of bayerite [β-Al(OH) 3(s)] and boehmite [γ-AlOOH(s)]- 19F-NMR spectroscopy and aqueous surface chemistry,” Geochim. Cosmochim. Acta 63, 3513–3524). Fluoride substitutes for oxygen at three different sites in the GaAl 12 molecule, but at dramatically different rates. The kinetics of fluoride substitution follow a rate law that includes parallel and reversible transfer of fluoride from nonbridging sites to the two bridging sites. The essential features of the rate law are as follows: (1) fluoride replaces bound water molecules (η-OH 2) within minutes at 278 K at rates that are quantitatively similar to fluoride uptake by Al(H 2O)63+(aq) to form AlF 2+(aq) at similar conditions; (2) fluoride substitutes onto the two topologically distinct μ 2-OH sites at different rates, as was previously observed for oxygen exchange, but here, the reaction is complete in hours to days at 278 K. Most importantly, rates of fluoride substitution onto μ 2-OH sites are 10 2 times more rapid than the corresponding rates of oxygen exchange with bulk waters, indicating that fluoride considerably labilizes the molecule, as is also observed at the surfaces of minerals. The largest cause of this labilization is the reduced molecular charge on the GaAl 12 upon replacement of bound waters by fluoride, which for mineral surfaces corresponds to a reduction in surface charge density.

The Effect of Chemical Composition and Structure on XPS Binding Energies in Zeolites

The effect of zeolite composition and structure on XPS core level binding energies has been studied for a large class of zeolites (FAU, MFI, MOR, LTA) differing in their counterions (Na, K, Rb, Ca, Mg, Ba) and Si:Al ratio (1 to 160). Whereas absolute binding energies cannot be determined to any reasonable degree of accuracy, relative peak positions can be found with high precision. In this paper, we show that the main effect on binding energy differences between silicon, aluminum, and oxygen is caused by the aluminum content of the zeolite. The effect of the zeolite structure and the co-cation is only minor. It was found that the Si(2p) to Al(2p) XPS peak separation decreases with increasing aluminum content. Quantum chemical calculations have been performed that rationalize these findings in terms of a nonhomogeneous charge distribution in the zeolite framework.

Fine theoretical spectroscopy using symmetry adapted cluster-configuration interaction general-R method: Outer- and inner-valence ionization spectra of CS2 and OCS

Fine theoretical spectroscopy has been presented by the SAC-CI (symmetry adapted cluster-configuration interaction) general-R method for the outer- and inner-valence ionization spectra of CS2 and OCS. The SAC-CI general-R method simulated the experimental spectra quite accurately and the detailed assignments of the satellite peaks were given. For CS2, four outer-valence satellites Πu2 states were calculated, one of which was attributed to the recently observed peak (1′). Numerous Σu+2 and Σg+2 satellite peaks were obtained in the inner-valence region and some of them were dominantly described by triple electron processes; the quadruple R-operators were found to be important for describing these states in the general-R method. For OCS, the relative position of the main peaks was correctly reproduced and the higher R-operators were found to be important for the ordering of A and B states. In the energy region of 24–36 eV, continuous spectra of numerous Σ+2 satellites were obtained, which reproduced the feature of the photoelectron spectrum.

Electronic Raman scattering ofs+g-wave superconductors: Implications for borocarbide superconductors

The electronic Raman scattering of borocarbide superconductors is studied based on the weak-coupling theory with $s+g$-wave gap symmetry. The low-energy behaviors and the relative peak positions can be naturally understood, while the explanation of the detailed shape of the ${B}_{1g}$ peak seems to require a strong inelastic interaction not present in the weak-coupling theory.

Filling factors, structural, and electronic properties ofC60molecules in single-wall carbon nanotubes

We report recent measurements of the electronic and structural properties of bulk samples of ${\mathrm{C}}_{60}$ molecules encapsulated in single-wall carbon nanotubes (so-called peapods) using electron-energy-loss spectroscopy in transmission. We demonstrate that ${\mathrm{C}}_{60}$ peapods with a single-wall carbon nanotube (SWNT) diameter distribution of $1.37\ifmmode\pm\else\textpm\fi{}0.08 \mathrm{nm}$ have an average fullerene filling of 60%. Regarding the electronic and optical properties, the overall shape of the response of the SWNT and the peapods is very similar, but with distinct differences in the fine structure. The interband transitions of the SWNT are slightly downshifted in the peapods, which can be explained by either a small increase of the SWNT diameter or by a change of the intertube interaction. The electronic and optical properties of the encapsulated ${\mathrm{C}}_{60}$ peas closely resemble those of solid fcc ${\mathrm{C}}_{60}$ showing small changes in the relative intensities, peak positions, and peak width, which point to a weak van der Waals interaction between the tubes and the encapsulated fullerenes.

Thin Film Optical Sensors Employing Polyelectrolyte Assembly

This work describes the development of thin film optical sensors for pH, metal ions (ferric and mercury), and 2,4-dinitrotoluene detection. To fabricate the pH sensor, a fluorescent molecule, 1-hydroxypyren-3,6,8-trisulfonate, was assembled with a polycation by an electrostatic layer-by-layer assembly technique. The fluorescent indicator molecule exhibits distinct and well-defined emission peaks for protonated and deprotonated forms. The relative peak positions and intensity of fluorescence of the protonated and deprotonated forms change in response to pH variations. For metal ion (ferric and mercury) and 2,4-dinitrotoluene sensing, the indicator molecules were covalently incorporated into poly(acrylic acid) and subsequently assembled with a polycation employing electrostatic layer-by-layer assembly. The sensor is based on the fluorescence quenching of indicator molecules by electron transfer from indicator to electron-deficient analytes such as ferric ions, mercury, and 2,4-dinitrotoluene. Fluorescence intensities decreased with increasing concentration of analytes. Quenching behavior follows Stern−Volmer bimolecular quenching kinetics. Linear increase in absorbance, film thickness, and emission intensity was observed as a function of number of bilayers deposited in all these films.

Spectral Interferences in Light Element Analysis

Interferences (overlaps) occurring when lines of other elements affect either peak or background measurements can cause errors in quantitative WD analysis, but may be minimised by suitable choices of analysis conditions such as spectrometer crystal, background offsets, and pulse-height analyser settings. Computer spectrum-simulation is much more effective than reference to wavelength tables for investigating interferences. The ‘Virtual WDS’ simulation program developed by the present authors, hitherto applied only to ‘ordinary’ elements (Z ≥ 11), has been extended to light elements for which evaporated multilayers are used in place of true crystals. ‘Virtual WDS’ utilises experimentally recorded light-element K spectra and L and M spectra of heavier elements in the same wavelength range. It is impractical to record all high-order peaks, so computed line profiles are used, with widths and intensities interpolated from a limited set of observations. The relative positions of first and higher order peaks are affected significantly by the refractive index of the multilayer, requiring modification of the Bragg equation. Suppression of high orders by pulse-height analysis is less effective than for ‘normal’ wavelengths, owing to the breadth of the pulse-height distribution for low X-ray energies. Simulation using a Gaussian expression aids optimisation of threshold and window-width settings.

Methods for ELNES-quantification: characterization of the degree of inversion of Mg–Al-spinels

The energy loss near-edge structures in electron energy-loss spectra contain information about bonding characteristics, the electronic structure and coordinations of the excited atoms. We have calculated sets of reference spectra for the normal and for the inverse Mg–Al-spinel using a full multiple scattering approach. By a quantitative comparison of these reference spectra with experimental data ELNES-quantification becomes possible. We characterized the degree of inversion λ by the analysis of the relative peak-intensities and the relative peak-positions within 35 eV beyond the edge onset. The results demonstrate that by using the provided methods ELNES-quantification will become possible when uncertainties in the experiment are reduced and a better fit of the simulations to the experiment is achieved.

Structural, optical and chemical characterization of 300°C, MeV ion implanted and 1700°C annealed 6H-SiC

ABSTRACTThis work deals with the structural, optical and chemical characterization of ion implanted and annealed crystalline SiC. N+ or Al+ ions with various MeV energy and fluence values were implanted at 300°C in 6H-SiC wafers. These processes produced about 1 μm thick doping profiles characterized by a sequence of peaks and valleys across an average plateau value. The annealing process was done in a radio frequency furnace at 1700°C for 30 min in high purity Ar atmosphere. The hot implanted layers show the presence of a weak damage amount, whose profile was estimated by confocal micro-Raman measurements. The annealed samples, in spite of a good crystal recovery, showed the formation of secondary defects as inferred by the Rutherford Back Scattering-Channeling spectrometry. The relative magnitude and position of peaks and valleys in the doping profiles were preserved by the high temperature annealing but the annealed doping profile was displaced towards the surface with respect to the as-implanted profile as shown by the Secondary Ion Mass Spectrometry measurements. No material loss but material densification due to the reordering of the crystalline structure can explain the trend of the chemical profiles.

Angular Parameter for Characterizing Road Surface Microtexture

Development of a device for measuring road surface microtexture and the determination of a microtexture parameter related to wet road/tire friction are discussed. A laser autofocus system was selected from existing devices. The required characteristics were defined from consideration of the contact between wet roads and tires. The autofocus principle is presented briefly, and comparison is made with a tactile system. The microtexture parameter, called the theta parameter, is defined from the useful parts of the texture profiles, that is, those in contact with the tire. It characterizes relative positions of profile peaks. A simple method was proposed to define the peaks. The profile analysis program is presented briefly. Relevance of the theta parameter was validated on surfaces composed of coarse aggregates with planar exposed faces. The specimens were polished using a projection method to emphasize the microtexture contrast between surfaces. Friction was measured using a skid resistance tester (SRT) pendulum. Profiles were measured using both laser and tactile systems. Characteristics of profiles are given. The statistical distribution of theta values obtained on a profile may be described by an exponential function. Close agreement was found between theta values obtained from laser and tactile profiles, values from laser profiles being somewhat lower. The difference is attributed to profile length. Fair correlation was found ( r2 &gt; 0.80) between theta values and SRT friction, and similar tendencies were observed from laser and tactile data.

Network Formation in Nanoparticulate Tin Oxide−Gelatin Thin Films

Electrostatic-charge accumulation and discharge can cause a variety of problems in imaging, electronic, and packaging materials and processes. Nanoparticulate antimony-doped tin oxide containing antistatic layers provide robust electronic conductivity that survives aqueous and thermal processing. Dielectric spectroscopy of tin oxide-gelatin (antistatic) thin films reveals relaxation processes that depend on tin oxide-to-gelatin ratios and upon tin oxide-gelatin film thickness. The frequency maxima of dielectric-loss peaks inversely correlate with surface electrical resistance (SER) measurements. A simple model of a layered heterogeneous dielectric explains the relative position of dielectric-loss peaks in terms of antistatic-layer conductivity. Dielectric measurements of antistatic layers do not require ohmic contact with such layers, and measurements on buried layers are straightforward. An observation of apparent percolation induced by variations in coverage, at constant tin oxide-to-gelatin weight ratio, suggests that the coating conditions and drying processes appear to play a role in network formation and nanoparticulate aggregation. Scaling of (inverse) SER and dielectric-loss peak frequencies above the percolation threshold conforms with scaling expected for electrical-conductivity percolation in three dimensions.

Scaling in energy dependence of relative particle production rates and peak position of ξ distributions in e+e− annihilations

Abstract With the production rates, 〈 n part 〉, of the K 0 , K + , p and Λ and average charged particle multiplicities, 〈 n ch 〉, recently measured at LEP1.5–LEP2, scaling of the relative particle production rates 〈 n part 〉/〈 n ch 〉 is seen in a broad center of mass energy range from s = 29–35 to 183 GeV. The quantity ξ 0 /〈 n ch 〉 1/2 , where ξ 0 is the position of the maximum of the ξ=− ln (2p/ s ) distribution and p is the particle momentum, also scales from 14 to 183 GeV. It is shown that the gaussian shape of the ξ distribution is a simple consequence of longitudinal phase space. The slope parameter in the logarithmic increase of ξ 0 with the center of mass energy must be smaller than 1, as observed experimentally, but this does not necessary imply a manifestation of coherence.

Relativistic XANES calculations of Pu hydrates

A theoretical analysis of x-ray absorption near edge structure (XANES) at L{sub 3} and L{sub 1} edges for Pu hydrates with a formal oxidation state of Pu ranging from +3 to +6, using the {ital ab initio} multiple scattering code FEFF7, is presented. For each hydrate our calculations reproduce well the white line intensity and relative peak positions, which are the features commonly used for formal valence identification. In order to achieve such a degree of coincidence between theory and experiment, it was necessary to use a relativistic Dirac-Fock treatment of atomic densities and mixed Dirac-Fock{endash}local-density-approximation exchange-correlation potentials, not considered in previous actinide studies. We find that most of the white line intensity at L{sub 3} edges originates from scattering of the photoelectron, i.e., x-ray absorption fine structure. We also show that the white line shoulder peak, present in the case of plutonyl compounds (Pu{sup 5+} and Pu{sup 6+}), is due largely to constructive interference of scattering paths containing axial oxygens. Limitations of the FEFF7 code and ways to improve the quantitative agreement between XANES calculations and experimental spectra are also discussed. {copyright} {ital 1998} {ital The American Physical Society}

Structure and composition of oxidized aluminum on NiO(100)

Aluminum was deposited on stoichiometric NiO(100) in 5×10−6 Torr O2 at substrate temperatures of 250 and 800 °C, and the resulting film interfaces were studied by photoemission [x-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS)] and electron diffraction [reflection high-energy electron diffraction (RHEED)]. At 800 °C, RHEED patterns indicate that the growing overlayer interacts with the NiO(100) substrate forming a NiAl2O4 spinel phase. This observation is further supported by XPS and UPS results where peak shapes and relative peak positions correspond to values reported for thick NiAl2O4 films. During film growth at 250 °C, the underlying NiO RHEED pattern becomes diffuse due to formation of an amorphous overlayer. XPS and UPS results indicate that the amorphous film is Al2O3 and that little interaction with the NiO substrate occurs. Postdeposition annealing of the amorphous Al2O3 film to 800 °C in O2 results in a strong reaction at the interface and film crystallization to the NiAl2O4 spinel phase. These results demonstrate that kinetic factors are significant in determining interactions in this system.

Characterization of severe matrix distortions during phase separation from the redistribution of diffracted intensities

Severe matrix deformation has been examined at an early stage of age-hardening in a polycrystalline Brush 25 alloy containing Cu–11.50 at % Be–0.23 at % Co aged at 200°C. Simplified anisotropic elastic models for the atomic displacement field about coherent disc-shaped precipitates provide quantitative estimates of the atomic displacement field in the surrounding matrix. This requires a separation of diffracted intensity into Bragg peaks, static diffuse scattering, and quasilines. The latter originates from the severely distorted zone about the precipitates. Elastic models include single discs, and [1 0 1] stair-step pairs. Ageing at 200°C introduces larger changes in the diffraction profiles than at 315°C. This is observed mainly as large variations in quasiline intensities, as well as in their relative peak positions. Comparisons are made at about one-half the maximum hardness. These variations result from the response of the coherent anisotropic copper matrix to large tetragonal Bain strains in disc-shaped precipitates, and a strong preference for the largest deformations to be perpendicular to the free surface. Quasiline shifts are used along with Vegard's Law to extend the metastable Guinier-Preston (GP)-zone boundary to 200°C. This boundary extension is smooth and continuous with published data, and thereby relates the metastable GP boundary to a highly distorted matrix about disc-shaped precipitates. Disc diameters range from 4.8–6.4 nm with a thickness of 0.29 nm after 16–64 h at 200°C. The [1 0 1] stair-step pair model best fits the experimental results.

The electronic structure of AgF, AgCl and AgBr

Self-consistent local density calculations of the electronic structures of AgF, AgCl and AgBr are carried out by the tight binding linearized muffin-tin orbital-atomic sphere approximation (TB LMTO-ASA) method. The silver 4 d orbital strongly hybridizes with the halogen p orbitals in the valence band and this plays a vital role in the configuration of the total density of states. The relative position of the sharp peaks in the Ag d level and F, Cl, Br p level as well as the band gap values obtained in the total density of states of these silver halides are compared with the previous theoretical and experimental values.