Fourier Deconvolution Technique Research Articles

High‐performance Brillouin distributed temperature sensor using Fourier wavelet regularised deconvolution algorithm

In this study, the authors presented a distributed optical fibre temperature sensor whose performance is improved using the optimisation techniques and Fourier wavelet regularised deconvolution (ForWaRD) method. As the input power launched into the sensing fibre is critical, the authors have considered both conventional optimisation technique and evolutionary optimisation techniques namely: genetic algorithm, differential evolution algorithm and particle swarm optimisation algorithm to increase the stimulated Brillouin scattering (SBS) threshold power. Using the optimised value of the parameters and employing evolutionary computing techniques, the proposed 50 km long temperature sensing system offers a 4.7 dB improvement in SBS threshold power over the design of experiment based system. It is being verified that power of the backscattered signals approximately are the convolution of the input pulsed power and corresponding backscatter optical fibre impulse responses. The Fourier wavelet regularised deconvolution (ForWaRD) method is employed to improve the spatial resolution of the proposed sensing system without reducing the pulse width of the input pulse. Employing ForWaRD technique a 10 m better spatial resolution observed as compared with the Fourier deconvolution technique. The proposed 50 km long temperature sensing system exhibits a temperature resolution of 1.85 K because of suppression of SBS threshold and noise reduction.

Fourier transform spectrometer instrument lineshape (ILS) retrieval by Fourier deconvolution

This work presents a Fourier deconvolution (FD) technique for retrieving the instrument lineshape (ILS) function of high-resolution Fourier transform infrared (FTIR) spectrometers. The ILS retrieved by FD is compared with the results obtained using the LINEFIT technique of Hase. The effect of a non-ideal ILS function on quantitative analysis of HBr is explored and improvements in the results of quantitative analyses are demonstrated.

High-resolution imaging of the human retina with a Fourier deconvolution technique.

A high-resolution retinal imaging camera is described that uses a Shack-Hartmann wave-front sensor and a Fourier deconvolution imaging technique. The operation of the camera is discussed in detail and high-resolution retinal images of the human cone mosaic are shown for a retinal patch approximately 10 arc min in diameter from two different retinal locations. The center-to-center cone spacing is shown to be approximately 2.5 microm for the retinal images recorded at 2 degrees temporal from the central fovea and approximately 4 microm for the retinal images recorded at 3 degrees temporal from the central fovea.

Background subtraction for low-loss transmission electron energy-loss spectroscopy

We present a technique for removing the zero-loss background from electron energy-loss spectra at very low energies (down to ∼2 eV), generating results that are superior in a number of ways to the results of standard Fourier deconvolution techniques. Our technique is based on a separately measured background spectrum which is spline-interpolated and matched to the zero-loss peak in the low-loss spectrum using curve-fit techniques. The data points are weighted with the use of a semi-empirical model of the random error in the data produced by a spectrometer. We demonstrate in tests on real-world data that this model accounts for the random error within the energy range of interest. We discuss practical details of implementation and present detailed comparisons of the results of various algorithms on a piece of test data obtained from a carbon nanotube sample. Compared to the standard techniques, our algorithm tends to be more consistent, less dependent on arbitrary parameters, and better able to quantify spectral features with small signal-to-noise ratios, particularly those at very low energies.

X-Ray Microanalysis in the Environmental SEM Using Mapping and Fourier Deconvolution Techniques

X-ray microanalysis of any type of specimen in its natural state without the use of conventional SEM specimen preparation techniques has immense potential in a wide range of scientific and industrial applications. This capability would be particularly useful in microanalysis applications where it is highly desirable to preserve the integrity of the specimen, for example in semiconductor failure analysis and forensic investigations. in principle, this X-ray microanalysis goal can be achieved in an environmental or variable pressure scanning electron microscope (VPSEM) because specimen charging and vacuum stability problems are negated by the presence of a gas in the specimen chamber. However, the accuracy and spatial resolution of X-ray microanalysis in the VPSEM is significantly degraded by the chamber gas as it scatters primary beam electrons, generating spurious X-rays far from the analysis point. to date, two different X-ray measurement strategies have been developed to facilitate X-ray microanalysis at high chamber pressure in the VPSEM.

Two modes of ligand binding in maltose-binding protein of Escherichia coli. Electron paramagnetic resonance study of ligand-induced global conformational changes by site-directed spin labeling.

Binding of ligands to the maltose-binding protein (MBP) of Escherichia coli often causes a global conformational change involving the closure of its two lobes. We have introduced a cysteine residue onto each of these lobes by site-directed mutagenesis and modified these residues with spin labels. Using EPR spectroscopy, we examined the changes, caused by the ligand binding, in distance between the two spin labels, hence between the two lobes. The binding of both maltose and maltotetraose induced a considerable closure of the N- and C-terminal lobes of MBP. Little closure occurred upon the binding of maltotetraitol or beta-cyclodextrin. Previous study by fluorescence and UV differential absorbance spectroscopy (Hall, J. A., Gehring, K., and Nikaido, H. (1997) J. Biol. Chem. 272, 17605-17609) showed that maltose and a large portion of maltotetraose bound to MBP via one mode (R mode or "end-on" mode), which is physiologically active and leads to the subsequent transport of the ligands across the cytoplasmic membrane. In contrast, maltotetraitol and beta-cyclodextrin bound to MBP via a different mode (B mode or "middle" mode), which is physiologically inactive. The present work suggests that the B mode is nonproductive because ligands binding in this manner prevent the closure of the two domains of MBP, and, as a result, the resulting ligand-MBP complex is incapable of interacting properly with the inner membrane-associated transporter complex.

Raman study of complexation in aqueous solutions of magnesium acetate

Raman spectra of aqueous solutions of magnesium acetate at 293 K have been studied in the concentration range 0.65–3.24 M, as have the Raman spectra of the crystallohydrate Mg(CH 3COO) 2·4H 2O. Fourier deconvolution and band fitting techniques have been used to analyse the spectra in three characteristic regions. The gradual evolution of two new components, in addition to the component corresponding to the CC vibration of the free acetate ion, is observed in the CC region of the solutions. These are identified as belonging to mono- and bisacetato complexes. In saturated solutions the bisacetato complexes are the dominating metal-ligand species. Their presence is confirmed also by Fourier deconvolution of the in-plane rocking CO 2 vibration.

Raman study of dioxane–D2O mixtures by analysis of the O–D band structure

AbstractChanges in the isotropic and anisotropic component profiles of the O—D stretching bands of D2O were studied in the range 0–0.5 mole fraction (m.f.) of 1,4—dioxane. The contribution of the CH Raman band of dioxane was subtracted using Raman spectra of dioxane—water mixtures in the same concentration range. A Fourier deconvolution technique was employed to resolve the overlapped components in the spectra. The information on the positions of the components in the isotropic spectra was used to fit them with symmetric components of mixed Gaussian—Lorentzian type. The wavenumbers of the resolved components in the isotropic and anisotropic spectra and the ratio of the intensities of the symmetric Fermi resonance components in the isotropic spectra were used to determine the concentration dependence of intermolecular, intramolecular and Fermi resonance parameters. The intermolecular and intramolecular interaction constants do not change significantly up to about 0.07–0.10 m.f. of dioxane and then gradually decrease. The Fermi resonance constant W does not change noticeably over the concentration range studied. The wavenumbers of the unperturbed O–D oscillator exhibits two different rates of increase with concentration of dioxane. The observed variations in the analysed parameters are interpreted in terms of hydrophobic hydration, hydrophobic interaction and hydrogen bonding in dioxane–water mixtures.

Deconvolution techniques for improving the resolution of long-pulse lidars

Deconvolution techniques are developed for improving lidar resolution when the sampling intervals are shorter than the sensing laser pulse. Such approaches permit the maximum-resolved lidar return in the case of arbitrary-shaped long laser pulses such as those used in CO2 lidars. The general algorithms are based on the Fourier-deconvolution technique as well as on the solution of the first kind of Volterra integral equation. In the case of rectangular pulses a simple and convenient recurrence algorithm is proposed and is analyzed in detail. The effect of stationary additive noise on algorithm performance is investigated. The theoretical analysis is supported by computer simulations demonstrating the increased resolution of the retrieved lidar profiles.

Raman and IR study on the H 2O - CH 3OH mixed solvent at 25°C using fourier deconvolution technique

The intermolecular interactions in water-methanol mixed solvent have been investigated by Raman and infrared studies of the C-H and C-O stretching bands. The Fourier deconvolution method in combination with curve fitting is used to resolve the structure of the overtone of the C-H deformation vibration 2δ s in the Raman spectrum and the C-O band in the infrared spectrum. The changes in the intensities of the Fermi resonance doublet in the C-H stretching region of the Raman spectra and in the structure of the C-O infrared band are explained in terms of the hydrogen bonding interactions between methanol/methanol and methanol/water molecules.

Application of mathematical removal of positron range blurring in positron emission tomography

The range of positrons in tissue is an important limitation to the ultimate spatial resolution achievable in positron emission tomography. In this work, a Fourier deconvolution technique is applied to remove range blurring in images taken by the Donner 600-crystal positron tomograph. Using phantom data, the authors found significant improvement in the image quality and the FWHM for both /sup 68/Ga and /sup 82/Rb. These were successfully corrected so that the images and FWHM almost matched those of /sup 18/F, which has negligible positron range. However, statistical noise was increased by the deconvolution process and it was not practical to recover the full spatial resolution of the tomograph.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Raman study of the “free” OH groups in H2O-H2O2 mixtures using Fourier deconvolution technique

Abstract The frequency behaviour of the component at 3635 cm−1 in the Raman OH stretching spectrum of water, responsible for the so called “free· OH groups is studied for different concentrations of H2O2 in H2O up to 30 mole%. The water Raman band is decomposed by Fourier deconvolution technique (FDT) in the isotropic and anisotropic case. The increase in H2O concentration leads to a decrease in the frequency of the resolved component in both kind of spectra resulting in the apparent gradual vanishing of the high frequency shoulder in the original spectrum. The small frequency shift (35 cm−1) shows that “free” OH oscillators of water form weak hydrogen bonds with H2O2 and supports the idea of bifurcated H bonded weak associates of water molecules.

Behaviour of the high‐frequency component of the OH stretching Raman band of water in H2O2H2O mixtures

AbstractThe Fourier deconvolution technique was applied to the analysis of Raman OH stretching spectra in H2O2H2O mixtures. An intensity decrease and a low‐frequency shift of the resolved high‐frequency component at 3635 cm−1 was established and can be used in the elucidation of physical models explaining the existence of weakly hydrogen‐bonded OH oscillators in liquid water.

Conformational equilibria in n-alkanols. Infrared spectral deconvolution of the unsymmetric hydroxyl band profile

The uncertainty in the separation of the asymmetric profile of the hydroxyl band of normal alcohols has been overcome by the use of a Fourier deconvolution technique which determined component-band parameters to carry out the band separation unambiguously. The nearly similar rotamer population of trans : gauche of 1.6 : 1 in the n-alcohols showed that the n-alkyl chain does not hinder the rotation around the C—O bond. The enthalpy change of gauche–trans conversion in solution (ca. 7 kJ mol–1) was much larger than the torsional barrier in the gaseous state.

Concentration (D2O in H2O) and temperature Raman study of the molecular interactions in the OD stretching spectra of D2O and D2O/H2O mixtures using the fourier deconvolution technique

AbstractThe OD stretching spectra of D2O for temperatures from 5 to 90°C and for concentrations (D2O in H2O) from 100 to 10 mol‐% were studied. These spectra were treated by means of the Fourier deconvolution technique for the first time.Using the positions of the resolved components the coupling constants for intra‐ and inter‐molecular and Fermi resonance interactions and all parameters according to the presented model, for all investigated temperatures, were evaluated. A gradual decrease in all interactions was observed in the concentration study, in accordance with expectations and in agreement with the results for dilute solutions of H2O in D2O.The temperature behaviour of the coupling constants and other parameters were in accordance with the corresponding data for H2O. The only exception is the temperature behaviour of the intramolecular coupling constant. The greater mass of the D atom is one of the probable reasons that lead to the smaller sensitivity of OD frequency to the hydrogen bond fluctuations.All the results verify the assignments and assumptions made according to the model presented and support the continuous model for the water structure.

Raman Temperature Study of 12-Crown-4 Using Fourier Deconvolution of CH Stretching Spectra

Abstract The Raman CH Stretching spectra of 12C4 in water solution, for temperatures from 5 to 80 °C, are studied. For the first time, Fourier deconvolution technique is applied to resolve the overlapped components in the corresponding isotropic and anisotropic spectra. The results are treated by means of a model. explaining the variety of resolved components with a splitting of the unperturbed CH stretching vibration. owing to intramolecular interactions. The temperature behaviour of the coupling constants of these interactions is discussed.

Temperature study of intra‐ and inter‐molecular coupling and Fermi resonance constants in the Raman spectra of liquid water using Fourier deconvolution

AbstractThe structure of the Raman OH stretching band of water has been investigated from 4 to 90 °C using a Fourier deconvolution technique. The overlapped components in the isotropic and anisotropic spectra have been resolved. The information on the positions of the components in the deconvoluted spectra was used for calculation of the constants for intra‐ and inter‐molecular coupling and Fermi resonance and for an estimation of the component frequencies according to the model presented. For the first time, the value of the asymmetric Fermi resonance constant and the temperature dependences of all coupling constants have been obtained. Their temperature behaviour is in good agreement with the data in the literature concerning the different phases of water. It was established that the intramolecular coupling constant increases and the intermolecular coupling constant decreases as the temperature increases. The Fermi resonance constant for symmetric components tends to decrease with increasing temperature. The decrease in the symmetric Fermi resonance interaction with increasing temperature is due to the increase in the distance between the unperturbed fundamental and overtone band positions. The asymmetric Fermi resonance constant tends to increase with increasing temperature and this determines the strengthening of the asymmetric Fermi resonance interaction, which exhibits a limiting value at high temperatures.

Concentration Raman study of intramolecular, intermolecular and Fermi resonance interactions in the OH stretching spectra of dilute solutions of HDO in D2O using Fourier deconvolution technique

The Raman OH stretching spectra of dilute solutions of H20 in D20, from 100 mole per cent to 10 mole per cent concentration, are studied. For the first time the decoupled OH spectra are treated by means of Fourier deconvolution technique. The resolved components in the isotropic and anisotropic spectra are analysed in terms of a model. The frequency and intensity behaviour of the components confirm the suggestion, that strong decoupling of all vibrations with dilution takes place. It is shown that intramolecular and Fermi resonance interactions are negligibly small under 20 mole per cent concentration. On the contrary, a significant intermolecular interaction, with a coupling constant equal to 42 cm−1, is observed down to concentrations of 10 mole per cent. The latter is explained with the significant number of the HDO molecules, which have at least one HDO, or H20 neighbour at this concentration. In respect to intermolecular interaction a dilution of H20 in D20 down to 10 mole per cent concentration is e...

Separation of overlapping core edges in electron energy loss spectra by multiple-least-squares fitting

A multiple-least-squares fitting procedure for quantitating electron energy loss spectra is demonstrated on some strongly overlapping core edges. The method, first applied by Shuman and Somlyo [Ultramicroscopy 21 (1987) 23], takes into account plural inelastic scattering and can be applied under conditions of non-uniform sample thickness where Fourier deconvolution techniques are invalid. By using appropriate reference spectra generated from pure compounds, quantitation of potassium and calcium (L 23 edges) is possible in the presence of carbon (K edge), and sulfur in the presence of phosphorus (L 23 edges). Some of the advantages and limitations of the multiple-least-squares approach are discussed.

Fourier transform infrared spectroscopic studies of the secondary structure and thermal denaturation of CaATPase from rabbit skeletal muscle

Fourier transform i.r. spectroscopy has been used to monitor structural alterations induced by thermal denaturation of the intrinsic membrane protein CaATPase in aqueous media. The protein has been isolated, purified and studied in five forms: 1. (i) In its native lipid environment after isolation from rabbit sarcoplasmic reticulum, both in H 2O and D 2O suspensions. 2. (ii) After both mild and extensive tryptic digestion has cleaved those residues external to the membrane bilayer. 3. (iii) Reconstituted in vesicle form with bovine brain sphingomyelin. Fourier deconvolution techniques have been used to enhance the resolution of the intrinsically overlapped Amide I and Amide II spectral regions. Large spectral alterations apparent in the deconvoluted spectra occur in these regions upon thermal denaturation of the protein which are consistent with the formation of a large proportion of β-antiparallel sheet form. The alteration parallels the loss in ATPase activity. A mild tryptic digestion increases slightly the proportion of α-helix and/or random coil secondary structure. A thermal transition to a form containing a high proportion of β structure is still evident. Extensive tryptic digestion nearly abolishes the alpha helical plus random coil secondary structure, while producing a high proportion of β form which is resistant to further thermally induced structural alterations. Studies of CaATPase reconstituted into vesicles with bovine brain sphingomyelin reveal a higher proportion of β structure than the native enzyme, with further introduction of β structure on thermal denaturation. Both the utility of deconvolution techniques and the necessity for caution in their application are apparent from the current experiments.