Windowed Autocorrelation Research Articles

FT-IR and Two-Dimensional Correlation Analysis of the Liquid Crystalline Phase Transitions in the 4-Bromobenzylidene-4′-alkyloxyanilines

The FT-IR spectra of the 4-bromobenzylidene-4'-alkyloxyanilines (nBBAA, for n = 4-12) were studied as a function of temperature. The molten state of the alkyloxy chain in smectic B (SmB), smectic A (SmA), and isotropic phases was analyzed. Generalized two-dimensional (2D) correlation spectroscopy has been applied to study changes in the conformational structure and specific interactions of molecules at phase transition in homologous series of nBBAA. A windowed autocorrelation analysis enabled us to locate transition points basing on the spectroscopic data.

Mean-Square Error in Periodogram Approaches With Adaptive Windowing

Modified periodogram approaches are nonparametric power spectral density (PSD) estimators. Here, we present a method for estimating the mean-square error (MSE) of these PSD estimators. The proposed approach uses the observed data to estimate not only the PSD but also the associated MSE simultaneously. The MSE estimate from the Blackman-Tukey approach can be utilized for comparison and choice of the optimum window among a set of smoothing windows of possibly different lengths. For Bartlett and Welch methods, the MSE estimate can be used for quality evaluation, and also enables the use of an additional smooth windowing for these modified periodogram approaches. The optimum adaptive windowing improves the performance of these approaches in the MSE sense. Furthermore, the optimally windowed autocorrelation estimate can be used for extrapolation with the maximum entropy method (MEM). Our simulation results confirm that the proposed optimum smooth windowing approach effectively improves the performance of modified periodogram PSD estimates in the MSE sense.

Improvement of the Linear Predictive Coding with Windowed Autocorrelation

In this paper, we propose a new procedure for improvement of the linear predictive coding. To reduce the error power incurred by the coding, we interchanged the order of the two procedures of windowing on the signal and linear prediction. This scheme corresponds to LPC extraction with windowed autocorrelation. The proposed method requires more calculational time because it necessitates matrix inversion on more parameters than the conventional technique where an efficient Levinson-Durbin recursive procedure is applicable with smaller parameters. Experimental test over various speech phonemes showed, however, that our procedure yields about 5 % less power distortion compared to the conventional technique. Consequently, the proposed method in this paper is thought to be preferable to the conventional technique as far as the fidelity is concerned. In a separate study of speaker-dependent speech recognition test for 50 isolated words pronounced by 40 people, our approach yielded better performance too.

Effect of Hydrophobic Surfactant Proteins SP-B and SP-C on Phospholipid Monolayers. Protein Structure Studied Using 2D IR and βν Correlation Analysis

We have applied two-dimensional infrared (2D IR) and βν correlation spectroscopy to in-situ IR spectroscopy of pulmonary surfactant proteins SP-B and SP-C in lipid–protein monolayers at the air—water interface. For both SP-B and SP-C, a statistical windowed autocorrelation method identified two separate surface pressure regions that contained maximum amide I intensity changes: 4–25 mN/m and 25–40 mN/m. For SP-C, 2D IR and βν correlation analyses of these regions indicated that SP-C adopts a variety of secondary structure conformations, including α-helix, β-sheet, and an intermolecular aggregation of extended β-sheet structure. The main α-helix band split into two peaks at high surface pressures, indicative of two different helix conformations. At low surface pressures, all conformations of the SP-C molecule reacted identically to increasing surface pressure and reoriented in phase with each other. Above 25 mN/m, however, the increasing surface pressure selectively affected the coexisting protein conformations, leading to an independent reorientation of the protein conformations. The asynchronous 2D IR spectrum of SP-B showed the presence of two α-helix components, consistent with two separate populations of α-helix in SP-B—a hydrophobic fraction associated with the lipid chains and a hydrophilic fraction parallel to the membrane surface. The distribution of correlation intensity between the two α-helix cross peaks indicated that the more hydrophobic helix fraction predominates at low surface pressures whereas the more hydrophilic helix fraction predominates at high surface pressures. The different SP-B secondary structures reacted identically to increasing surface pressure, leading to a reorientation of all SP-B subunits in phase with one another.

Two-dimensional FT-IR correlation analysis of the phase transitions in a liquid crystal, 4′- n-octyl-4-cyanobiphenyl (8CB)

Generalized two-dimensional (2D)-IR correlation analysis has been applied to the temperature resolved IR spectra of 4′- n-octyl-4-cyanobiphenyl (8CB). The analysis revealed IR bands from different functional groups, i.e., CN, biphenyl ring and aliphatic tail that varied when the liquid crystal changed phase from isotropic to nematic or from nematic to smectic-A. When the entire data set is used, information from both phase transitions are encoded in the correlation analysis making unambiguous assignments impossible. A windowed autocorrelation analysis is applied and is able to locate transition points in the data. The data are then partitioned around a singular transition point and a generalized 2D-IR correlation analysis is performed. The correlation analysis from the partitioned data yields unambiguous correlation intensities from the isotropic to nematic phase transition and the nematic to smectic-A phase transition of 8CB.