Global Spectral Analysis Research Articles

A global surface drifter data set at hourly resolution

AbstractThe surface drifting buoys, or drifters, of the Global Drifter Program (GDP) are predominantly tracked by the Argos positioning system, providing drifter locations with O(100 m) errors at nonuniform temporal intervals, with an average interval of 1.2 h since January 2005. This data set is thus a rich and global source of information on high‐frequency and small‐scale oceanic processes, yet is still relatively understudied because of the challenges associated with its large size and sampling characteristics. A methodology is described to produce a new high‐resolution global data set since 2005, consisting of drifter locations and velocities estimated at hourly intervals, along with their respective errors. Locations and velocities are obtained by modeling locally in time trajectories as a first‐order polynomial with coefficients obtained by maximizing a likelihood function. This function is derived by modeling the Argos location errors with t location‐scale probability distribution functions. The methodology is motivated by analyzing 82 drifters tracked contemporaneously by Argos and by the Global Positioning System, where the latter is assumed to provide true locations. A global spectral analysis of the velocity variance from the new data set reveals a sharply defined ridge of energy closely following the inertial frequency as a function of latitude, distinct energy peaks near diurnal and semidiurnal frequencies, as well as higher‐frequency peaks located near tidal harmonics as well as near replicates of the inertial frequency. Compared to the spectra that can be obtained using the standard 6‐hourly GDP product, the new data set contains up to 100% more spectral energy at some latitudes.

A new alternating bi-diagonal compact scheme for non-uniform grids

A new compact scheme has been developed for any non-uniform grid. The compact scheme has been developed for spatial discretization and is analyzed here in conjunction with four-stage, fourth order Runge–Kutta (RK4) scheme for time integration while solving the one-dimensional convection equation. The space–time discretization combination is calibrated by subjecting the system to global spectral analysis (GSA) which was developed by the authors' group. Here, the compact scheme has been obtained by using a combination of two bi-diagonal schemes. The novel aspect of this scheme is its application in the physical plane directly without the necessity of mapping or transformations. Some typical cases for problems in acoustics, as well as fluid mechanics, have been studied here and potential use in large eddy simulations (LES) has been demonstrated by solving Navier–Stokes equation for lid driven cavity.

In Process Citation

A novel model for the analysis of the rovibrational structure of a molecule based on anharmonic ladder operators associated with the vibrational degrees of freedom is presented. This is devised as an alternative method for the global spectral analysis of rovibrational data considering vibrational anharmonicities from the outset. The present method is thought up with an effective rovibrational Hamiltonian written in terms of angular momentum components and anharmonic Morse ladder operators, associated with rotational and vibrational degrees of freedom, respectively. The resulting Hamiltonian is diagonalized in a symmetry-adapted basis set expressed as a product of rotational states and individual 1D-Morse wave functions for each local vibrational degree of freedom. This approach has been successfully applied to the study of the vibrational structure (up to polyad 14) and the rovibrational structure (up to polyad 2 and J(max) = 20) of hydrogen sulfide. It was shown that this new global analysis formalism is able to reduce considerably the number of fitted parameters with respect to the spectral analysis carried out for separate polyads.

Improved Fault Diagnosis of Ball Bearings Based on the Global Spectrum of Vibration Signals

This research deals with the discrimination between conditions of faults in rolling element bearings based on a global spectral analysis. This global spectral analysis allows to obtain spectral features with significant discriminatory power. These features are extracted from the envelope spectra of vibration signals without prior knowledge of the bearings specific parameters and the characteristic frequencies. These extracted spectral features will then be the global spectral signature produced by the bearing faults. Since the signature produced by the faults in bearing balls is very weak, and hard to be detected and identified, this paper proposes the linear discriminant analysis as part of the global spectral analysis method in order to improve the diagnosis of ball faults. The application on experimental vibration data acquired from bearings containing different types of faults with different small sizes shows the proficiency of the overall method. The Bhattacharyya distance is used to confirm the efficiency of the obtained results.

Analysis and Design of a New Dispersion Relation Preserving Alternate Direction Bidiagonal Compact Scheme

In the present work bidiagonal schemes have been analyzed first by using global spectral analysis for wave propagation problem. The properties given by the numerical amplification factor, dispersion and phase error are presented for these schemes to study effects on error propagation for 1D convection equation. Analysis of bidiagonal schemes helps in designing a new alternate direction bidiagonal (ADB) spatial scheme with improved numerical dispersion and dissipation properties. Design of the ADB scheme is facilitated by the prefactorization technique given in Hixon and Turkel (J Comput Phys 158:51---70, 2000) and is obtained here by minimizing the error in computing 1D convection equation using the correct stability and error analysis given in Sengupta et al. (J Comput Phys 226:1211---1218, 2007). The ADB scheme for spatial discretization is coupled with four-stage, fourth order accurate Runge---Kutta time marching scheme and optimized for multiple objective functions by classical tools to obtain a new space-time discretization scheme with desired numerical amplification and dispersion properties up to moderate wavenumbers, preserving physical dispersion relation almost exactly. The resultant optimal DRP scheme is fourth order accurate, both in space and time. We have compared this scheme with an accurate compact scheme in reproducing exact solution of 1D convection equation. Two benchmark problems from computational acoustics are shown for further verification of the accuracy of solution obtained by the present method. To demonstrate the practical utility of the method, we have presented the solution of zero pressure gradient flow past semi-infinite flat plate from the receptivity stage to fully developed inhomogeneous turbulent state without any model and compared with published results in Sengupta et al. (Phys Rev E 85:026308, 2012).

Wave properties of fourth-order fully implicit Runge–Kutta time integration schemes

A global spectral analysis of fully implicit, two-stage, fourth-order Runge–Kutta method (IRK2) is presented here. The essential numerical properties of the IRK2 time-integration scheme, viz., nodal amplification factor, phase speed and group velocity have been quantified and plotted at all the nodal points of the computational domain as functions of the CFL (Courant–Friedrichs–Lewy number) and wavenumber for various explicit and implicit spatial discretization schemes. Results show that IRK2 scheme produces neutral stability at all interior nodes for all CFL numbers. This has been shown that while using IRK2 scheme one has to use refined grid at high CFL numbers for dispersion relation preservation property.

Molecular Tweezers with Freely Rotating Linker and Porphyrin Moieties

AbstractMolecular tweezers were synthesised by using a microwave accelerated alkene plus cyclobutane epoxide reaction between norbornyl appended porphyrin moieties and a diepoxide functionalised phenyl diimide spacer. The tweezers contain several rotational degrees of freedom; about the porphyrin with respect to the norbornyl linker, and between the two norbornyl backbone sections. The ability of ZnII metallated tweezer 1 to complex 1,4‐diazabicyclo[2.2.2]octane (DABCO) was studied by UV/Vis and 1H NMR spectroscopy and multivariate global spectral analysis. The system was found to form a strong 1:1 intramolecular complex (1:DABCO) with an association constant of K11 = 8.1 × 107 M–1, transforming to a 1:2 open complex [1:(DABCO)2] with K12 = 2.7 × 109 M–2 at high concentrations of DABCO.

Comparative studies on manganese-based SOD mimetics, including the phosphate effect, by using global spectral analysis

Stopped-flow measurements have been successfully combined with time-resolved UV/vis spectroscopy and global spectral analysis of superoxide decay for the comparative study of catalytic activity of putative manganese SOD (superoxide dismutase) mimetics known in the literature. The SOD activity of the studied complexes decreases in the following order: a) M40403>Mn(III)TM-4-PyP5+>Mn(II)pyane >>EUK-113 at pH 7.4 (M40403=([manganese(II)dichlorido{(4R,9R,14R,19R)-3,10,13,20,26-pentaazatetracyclo[20.3.1.0.4,9014,19]hexacosa-1(26),-22(23),24-triene}], Mn(III)TM-4-PyP5+=Mn(III)meso-tetrakis(N-methylpyridinium-4-yl)porphyrin, Mn(II)Pyane=Mn(II)trans-2,13-dimethyl-3,6,9,12,18-pentaazabicyclo[12.3.1]-octadeca-1(18),14,16-triene, EUK-113=[manganese(III)acetato(6,6′-((1E,1′E)-(ethane-1,2-diylbis(azanylylidene))bis(methanylylidene))bis(2-methoxyphenolate)]) in Hepes buffer (Hepes=4-(2-Hydroxyethyl)piperazine-1-ethanesulfonic acid), b) Mn(III)TM-4-PyP5+>M40403≅Mn(II)pyane >>EUK-113 at pH 8.1 in Hepes buffer and c) Mn(III)TM-4-PyP5+≅Mn(II)pyane>MnCl2>M40403≅EUK-113 at pH 7.4 in phosphate buffer. MnCl2 in Hepes, Mn(III)TSPP3−, Mn(III)TBAP3−, Mn(III)acetate, Mn(II)lactate and Mn(II)EDTA do not exhibit SOD activity (Mn(III)TSPP3−=Mn(III)mesotetrakis(benzoic acid)porphyrin, Mn(III)TBAP3−=Mn(III)mesotetrakis(4-sulfonatophenyl)porphyrin). MnCl2 possess SOD activity that is comparable with those of other mimetics in the presence of phosphate. Our results demonstrate that phosphate anions, independent of ionic strength effect, influence the activity of manganese SOD mimetics, which is crucial for understanding and comparing their biological activity.

Mass spectrometric analysis of protein phosphorylation

Phosphorylation is one of the most common posttranslational modifications of proteins in eukaryotic cells; it plays an important role in a wide spectrum of biological processes. This makes its study an important task for understanding cell functioning mechanisms. The aim of phosphoproteomics is a global mass spectral analysis of the phosphoprotein composition of cells, i.e., phosphoproteome. Nowadays, new effective methods are actively developed, which succeed not only in the detection of phosphorylated proteins but also in the determination of phosphorylated amino acid residues (phosphorylation sites) and in the quantitative comparison of phosphorylation among several specimens. Despite the analysis of protein phosphorylation remains a complicated problem, the available methods nowadays allow the detection of thousands of phosphorylation sites in the very same experiment. The present review covers the main methods utilized in contemporary phosphoproteomics: phosphoprotein and phosphopeptides enrichment as well as the mass spectrometric analysis of protein phosphorylation.

Resolving Nonstationary Spectral Information in Wind Speed Time Series Using the Hilbert–Huang Transform

Abstract This work is motivated by the observation that large-amplitude wind fluctuations on temporal scales of 1–10 h present challenges for the power management of large offshore wind farms. Wind fluctuations on these scales are analyzed at a meteorological measurement mast in the Danish North Sea using a 4-yr time series of 10-min wind speed observations. An adaptive spectral analysis method called the Hilbert–Huang transform is chosen for the analysis, because the nonstationarity of time series of wind speed observations means that they are not well described by a global spectral analysis method such as the Fourier transform. The Hilbert–Huang transform is a local method based on a nonparametric and empirical decomposition of the data followed by calculation of instantaneous amplitudes and frequencies using the Hilbert transform. The Hilbert–Huang transformed 4-yr time series is averaged and summarized to show climatological patterns in the relationship between wind variability and time of day. First, by integrating the Hilbert spectrum along the frequency axis, a scalar time series representing the total variability within a given frequency range is calculated. Second, by calculating average spectra conditional to time of day, the time axis of the Hilbert spectrum is “remapped” to show climatological patterns. Third, the daily patterns in wind variability and wind speed are compared for the four seasons of the year. It is found that the most intense wind variability occurs in autumn even though the strongest observed wind speeds occur in winter.

A PHENOMENOLOGICAL APPROACH TO NORMAL FORM MODELING: A CASE STUDY IN LASER INDUCED NEMATODYNAMICS

An experimental setting for the polarimetric study of optically induced dynamical behavior in nematic liquid crystal films presented by G. Cipparrone, G. Russo, C. Versace, G. Strangi and V. Carbone allowed to identify most notably some behavior which was recognized as gluing bifurcations leading to chaos. This analysis of the data used a comparison with a model for the transition to chaos via gluing bifurcations in optically excited nematic liquid crystals previously proposed by G. Demeter and L. Kramer. The model of these last authors, relying on the original model for chaos by cascade of gluing bifurcations proposed by A. Arneodo, P. Coullet and C. Tresser about twenty years before, does not have the central symmetry which one would expect for minimal dimensional model for chaos in nematics in view of the time series near the gluing bifurcation. What we show here is that the simplest truncated normal forms for gluing with the appropriate symmetry and minimal dimension do exhibit time signals that are embarrassingly similar to the ones that could be found using the above-mentioned experimental settings. It so happens that the gluing bifurcation scenario itself is only visible in limited parameter ranges, and that a substantial aspect of the chaos that can be observed is due to other factors. First, out of the immediate neighborhood of the homoclinic curve, nonlinearity can produce expansion which easily produces chaos when combined with the recurrence induced by the homoclinic behavior. Also, pairs of symmetric homoclinic orbits create extreme sensitivity to noise, so that when the noiseless approach to attracting homoclinic pairs contains a rich behavior, minute noise can transform the complex damping into sustained chaos. As Leonid Shilnikov has taught us, combining global considerations and local spectral analysis near critical points is crucial to understand the phenomenology associated to homoclinic bifurcations in dissipative systems. We see here on an example how this helps construct a phenomenological approach to modeling experiments in nonlinear dissipative contexts.

Potential contribution of maximum subsurface temperature anomalies to the climate variability

AbstractOn the interannual time scale, sea‐surface temperature anomalies (SSTAs) that are concerned with climate variability at global and regional scales have been widely investigated in previous studies. Through the analysis of the monthly 46‐year (1955–2000) expendable bathythermograph data, we show that subsurface temperature anomalies (STAs) can directly affect the SSTAs in the major air–sea interaction regions. Along the equatorial Pacific, four important features for STAs have been characterized. (1) The STAs and SSTAs are well correlated in the eastern equatorial Pacific (EEP) due to the fact that the thermocline anomalies have only to be mixed with the surface over a very short distance. (2) The STAs are always stronger than SSTAs at any location. (3) In the time between El Niño and La Niña, and vice versa, the STAs propagate eastward along the thermocline without mixing with SSTAs in the central Pacific. (4) An El Niño or La Niña can develop only when the maximum positive or the maximum negative STA propagates to the EEP. Inside and outside the tropical basins the STA was more centred on the thermocline than the 20°C isotherm. These features inform us that the maximum STAs (MSTAs) from each vertical STA profile can be used to indicate the anomalous wave‐propagation signal or thermocline variations in the worldwide oceans. This analysis implies that the MSTA is also a potential factor controlling climate variability and is a better indicator than SSTA, because MSTAs memorize the change in air–sea interaction signals and represent a huge deposit of energy in the upper ocean. The correlations between SSTAs and MSTAs with a coefficient of more than 0.60 are predominantly located in the EEP, the northern North Pacific, the southern subtropical Indian Ocean, and the northern North Atlantic Ocean. These correlations are discussed from case and statistical analyses.The leading pattern of SSTAs and MSTAs in the tropical Pacific, Atlantic and Indian Oceans are decomposed using empirical orthogonal functions (EOFs) and their EOF patterns might be able to explain the difference between MSTAs and SSTAs. Their periods of mode series are performed from a global wavelet spectral analysis. Copyright © 2004 Royal Meteorological Society

Spectroscopic evidence for triplet excitation energy transfer among carotenoids in the LH2 complex from photosynthetic bacterium Rhodopseudomonas palustris

The LH2 complex from Rhodopsudomonas (Rps.) palustris is unique in the heterogeneous carotenoid compositions. The dynamics of triplet excited state Carotenoids (3Car* has been investigated by means of sub-microsecond time-resolved absorption spectroscopy both at physiological temperature (295 K) and at cryogenic temperature (77K). Broad and asymmetric T n ←T 1 transient absorption was observed at room temperature following the photo-excitation of Car at 532 nm, which suggests the contribution from various carotenoid compositions having different numbers of conjugated C=C double bonds (Nc=c). The triplet absorption bands of different carotenoids, which superimposed at room temperature, could be clearly distinguished upon decreasing the temperature down to 77 K. At room temperature the shorter-wavelength side of the main Tn04T1 absorption band decayed rapidly to reach a spectral equilibration with a characteristic time constant of ∽1 μs, the same spectral dynamics, however, was not observed at 77 K. The aforementioned spectral dynamics can be explained in terms of the triplet-excitation transfer among heterogeneous carotenoid compositions. Global spectral analysis was applied to the time-resolved spectra at room temperature, which revealed two spectral components peaked at 545 and 565 nm, and assignable to the Tn04 T1 absorption of Cars with Nc=c=11 and Nc=c=13, respectively. Surprisingly, the decay time constant of a shorter-conjugated Car, i.e. 0.72 ώs (aerobic) and 1.36 ώs (anaerobic), is smaller than that of a longer-conjugated Car, i.e. 2.12 us (aerobic) and 3.75 ώs (anaerobic), which is contradictory to the general rule of carotenoids and relative polyenes. The results are explained in terms of triplet-excitation transfer among different types of Cars. It is postulated that two Cars with different conjugation lengths coexist in an α, β-subunit in the LH2 complex.

Investigations of intermediates appearing in the reassociation of the light-harvesting 1 complex of Rhodospirillum rubrum.

We investigated the temperature-mediated reassociation of the B820 subunit of Rs. rubrum to form a light-harvesting 1 complex (LH 1). By combining several spectroscopic techniques with global spectral data analysis fitting, we present evidence for the occurence of two spectral intermediates that appear during the reassociation process. At high temperatures, halfway the reassociation reaction, a prominent intermediate appears that has an absorption maximum around 850 nm, a fluorescence maximum around 860-867 nm, a high anisotropy (0.3 to 0.4) and a circular dichroism spectrum with three or four bands with alternating signs. At lower temperatures, more towards the end of the reassociation process, a second intermediate tends to appear that has an absorption maximum around 860 nm, a fluorescence maximum around 885 nm, a medium to high anisotropy (0.1 to 0.3) and a circular dichroism spectrum with two bands with alternating signs. The latter circular dichroism spectrum has a blueshifted zero-crossing compared to the spectrum of the LH 1 complex. Both intermediates have the spectroscopic features of a small oligomer. In the Q(y) region, the fluorescence anisotropy of both intermediates slightly increases at longer excitation wavelengths, indicative for energy transfer among the pigments within the intermediate oligomers.

Spectroscopic Characterization of Nonnative Conformational States of Cytochrome c

Protein and heme structural changes of ferric and ferrous cytochrome c (Cyt-c) that are induced by electrostatic binding (e.g., liposomes, electrodes), by hydrophobic interactions (e.g., monomeric sodium dodecyl sulfate), by guanidium hydrochloride (GuHCl), and at low pH and high temperature were studied by UV−vis absorption, circular dichroism (CD), electron paramagnetic resonance (EPR), and (surface-enhanced) resonance Raman [(SE)RR] spectroscopy. In a global spectral analysis, all species that differ with respect to the heme structure were identified and characterized in terms of the spin and ligation state of the heme as well as of protein secondary and tertiary structure changes. The results indicate that the upper part of the heme pocket including the Met-80 ligand is the most labile protein region such that this ligand is dissociated from the heme iron in all nonnative Cyt-c states. Among these states, there are two six-coordinated low-spin (LS) configurations with H2O or His-33 serving as the sixt...

Blending HF radar and model velocities in Monterey Bay through normal mode analysis

Nowcasts of the surface velocity field in Monterey Bay are made for the period August 1–9, 1994, using HF radar observations blended with results from a primitive equation model. A spectral method called normal mode analysis was used. Objective spatial and temporal filtering were performed, and stream function, velocity potential, relative vorticity, and horizontal divergence were calculated over the domain. This type of nowcasting permits global spectral analysis of mode amplitudes, calculation of enstrophy, and additional analyses using tools like empirical orthogonal functions. The nowcasts reported here include open boundary flow information from the numerical model. Nowcasts using no open boundary flow information, however, still provide excellent results for locations within the observation footprint. This method, then, is useful for filtering high‐resolution data like HF radar observations, even when open boundary flow information is unavailable. Also, since the nowcast velocity gradient fields were much less noisy than the observations, this may be an effective method for preconditioning high‐resolution observation sets for assimilation into a numerical model.

Subpicosecond reverse saturable absorption in organic and organometallic solutions

Solutions of several carbocyanines, phthalocyanines and naphthalocyanines were studied by time-resolved transient spectroscopy with subpicosecond white-light continuum. The excited-state absorption cross-sections of all compounds were determined from the differential spectra obtained at short delay time after excitation, by a global spectral analysis. All these molecules exhibit an excited-state absorption cross-section higher than that of the ground state at 610 nm. This spectral property gives rise to a reverse saturable absorption (RSA) effect under high laser fluences at this wavelength. Nonlinear transmission of these molecules was measured under increasing laser fluences. A three-level molecular model was used to simulate the measured nonlinear transmission and the best fits were obtained with molecular parameters in good agreement with those deduced from the analysis of the transient spectra. The use of RSA for the energy stabilization of ultrashort laser pulses was demonstrated, and a stabilization coefficient was defined as an efficient tool for characterizing nonlinear behavior of such compounds.

Assessing the Effects of Data Selection with the DAO Physical-Space Statistical Analysis System*

Conventional optimal interpolation (OI) analysis systems solve the standard statistical analysis equations approximately, by invoking a local approximation and a data selection procedure. Although solution of the analysis equations is essentially exact in the recent generation of global spectral variational analysis systems, these new systems also include substantial changes in error covariance modeling, making it difficult to discern whether improvements in analysis and forecast quality are due to exact, global solution of the analysis equations, or to changes in error covariance modeling. The formulation and implementation of a new type of global analysis system at the Data Assimilation Office, termed the Physical-space Statistical Analysis System (PSAS), is described in this article. Since this system operates directly in physical space, it is capable of employing error covariance models identical to those of the predecessor OI system, as well as more advanced models. To focus strictly on the effect of global versus local solution of the analysis equations, a comparison between PSAS and OI analyses is carried out with both systems using identical error covariance models and identical data. Spectral decomposition of the analysis increments reveals that, relative to the PSAS increments, the OI increments have too little power at large horizontal scales and excessive power at small horizontal scales. The OI increments also display an unrealistically large ratio of divergence to vorticity. Dynamical imbalances in the OI-analyzed state can therefore be attributed in part to the approximate local method of solution, and are not entirely due to the simple geostrophic constraint built into the forecast error covariance model. Root-mean-square observation minus 6-h forecast errors in the zonal wind component are substantially smaller for the PSAS system than for the OI system.

Transient absorption of symmetrical carbocyanines

Transient absorption in several symmetrical cyanine and carbncyanine dyes is measured by time-resolved spectroscopy with subpicosecond white-light continuum in a wide spectral range (0.35–1 μm). The results are compared with data available in the literature on ultrashort and long-lived transients. The linear shift law observed here for the S 1 S n absorption bands in the wavelength scale allows one to predict the main induced absorption bands for members of several carbocyanine families (vinylogous series) which have not yet been studied. In the case of the shortest methine chains (cyanines and monocarbocyanines) a tew transient absorption bands are assigned to the formation of photoisomers. The absolute values of the excited-state or photoisomer cross sections of polymethine carbocyanines are evaluated by global spectral analysis, from the measured differential optical density spectra. Several cases of large values (higher than 10) of the absorption cross section ratio (excited/ground state) are found at new wavelengths, which allows applications of photo-induced absorption to photonics and laser technologies over a broad spectral range.

Influence of respiration on heart rate and blood pressure fluctuations.

The dynamics of the respiratory and cardiovascular systems were studied by continuously slowing respiration from 0.46 to 0.05 Hz. The time-frequency distribution and global spectral analysis were used to assess the R-R interval (R-R) and the systolic and diastolic blood pressure fluctuations in 16 healthy subjects. During rest, the nonrespiratory-to-respiratory frequency ratios were not affected by occasional slow breathing, whereas the low- (0.01-0.15 Hz) to high- (0.15-0.3 Hz) frequency indexes for blood pressure were increased (P < 0.05). The respiratory fluctuations in R-R and the systolic and diastolic pressures were paced over the 0.46- to 0.05-Hz range. As respiration slowed to 0.07-0.09 Hz, the frequency content of the respiration and cardiovascular variables increased sharply and nonlinearly to a maximum that exceeded values at higher frequencies (P < 0.001). The nonrespiratory frequency content remained stable in the 0.01- to 0.05-Hz range and did not significantly differ from that at rest. In contrast, the nonstable 0.05- to 0.1-Hz component was suppressed. A slow 0.012- to 0.017-Hz rhythm modulated respiration and hemodynamic fluctuations at both respiratory and nonrespiratory frequencies. The study indicated that respiration input should be considered in the interpretation of global spectra. Furthermore the time-frequency distributions demonstrated that a close nonlinear coupling exists between the respiratory and cardiovascular systems.