pseudo-Voigt Function Research Articles

Optimized neural network for temperature extraction from Brillouin scattering spectra

Abstract The nonlinear mapping characteristic of artificial neural network (ANN) is suitable for temperature extraction from Brillouin scattering spectra in optical fiber sensing system. To further improve the generalization ability of neural network, an optimized method for ANN training is proposed in this paper. Firstly, a set of noisy training data with different linewidth under various temperatures and frequency scanning intervals is constructed by using Pseudo-Voigt function and is entered into networks for training. Then, the ANNs with optimized parameters are tested by the measured Brillouin scattering spectra, which are from an established Brillouin optical time domain reflectometry (BOTDR) sensing system. Finally, the temperature distribution information of the sensing fiber is extracted directly. The experimental results show that the ANNs trained by the proposed method obtain better temperature extraction accuracy than that obtained by other ANNs, which indicates that the generalization ability and adaptability of ANN are enhanced for temperature extraction in Brillouin optical fiber sensing system.

Morphological and Structural Changes in Titanium Dioxide during the Fragmentation Process

The structural and morphological changes of titanium dioxide particles in the process of ultrafine fragmentation have been studied by means of the X-ray diffraction analysis and BET method based on N2 adsorption-desorption. The sizes of crystallites and microdeformations that indicated a breakage of their structural order with the formation of new phase fragments similar to brookite have been calculated from broadening of diffraction reflections using the method of approximation applying the pseudo-Voigt function. In the study of the morphology of titanium phase particles, it was determined that nitrogen adsorption was described by the isotherm of the IVa type in the p/p0 range of 0.1–0.95 and by the isotherm of the II type at p/p0 higher than 0.95 after mechanical activation in the presence of surface-active substance (SAS). The hysteresis loop of the samples' isotherms is related to the H3 type, which is characteristic of particles with a lamellar morphology. The porous particle system was represented by mesopores of a diameter varying within the range of 20–50 nm. The total volume of micropores was not higher than 10% of their total volume. A monophase product with a rutile structure and the crystallites' size increase was formed from the activated sample at annealing. The specific surface area of titanium dioxide after annealing varied in the range of 6.5–7.5 m2/g, which is about three times higher than the same value for conventional rutile grades.

Investigation of structural, microstructural and magnetic properties of YbxY1-xF3 solid solutions

In this investigation, we have synthesized YbxY1-xF3 solid solutions by fluorination of yttrium and ytterbium sesquioxides with ammonium hydrogen difluoride. According to the XRD analysis, all synthesized YbxY1-xF3 samples have an orthorhombic crystal structure belonging to the β-YF3 structural type. The refinement of crystal structure was done by the Rietveld method within the Pnma space group using the TCH pseudo-Voigt function. The anisotropic peak broadening was analyzed, and the average apparent crystallite size is about 50 nm with a small anisotropy of shape, while the significant microstrain that is highly anisotropic is present in all samples. The temperature-dependent magnetic susceptibility was analyzed by applying the model of a free ion perturbed by the crystal field. We have obtained the effective magnetic quantum numbers Mieff of four Kramer's doublets of Yb3+ ion along with the entire crystal field splitting of the 2F7/2 manifold of Yb3+ in YF3. The acquired maximum energy splitting of the ground level is about 150 K in our most diluted samples. The field-dependent isothermal magnetization measurements were carried out at various temperatures and analyzed by classical Langevin function. Results obtained from magnetic measurements show that all YbxY1-xF3 (x ≠ 0) solid solutions exhibit pure paramagnetic behavior in the whole temperature range from 2 to 300 K, with a predominant antiferromagnetic exchange interactions.

Structural Transformations of TiO2 during Mechanical Activation and Subsequent Annealing

The metastable structure state of the anatase phase of titanium dioxide has been shown to be a favorable basis for a targeted influence on it with the aim of producing new oxide phases consisting of nanoparticles and, accordingly, having a new combination of properties. Mechanical activation and subsequent annealing of the activated powders result in a sequence of phase transformations (anatase–brookite–rutile), thereby ensuring structural ordering of titanium dioxide. Transformations of the titanium oxide phases have been studied in detail by X-ray diffraction. We have evaluated the crystallite (coherent scattering domain) size and internal strain (e) from diffraction line broadening by profile fitting with the pseudo-Voigt function. The average particle size was 20 nm after mechanical activation, whereas heat treatment increased it by almost a factor of 2. Similar results have been obtained for internal strain. The pore system of the particles is formed by mesopores. The hysteresis loop observed in nitrogen sorption–desorption isotherms suggests that the titanium dioxide particles have platelike morphology. The results obtained in this study have been used to develop innovative technology of a special grade of titanium dioxide for the preparation of thermally stable glues with dielectric properties and high tensile and shear strength.

Thickness and tensile stress determination of black silicon layers by spectral reflectance and Raman scattering

Abstract In this work black silicon (b-Si) samples were prepared by anodic (electrochemical) etching of p-type silicon substrate in solution of hydrofluoric acid (HF). We studied influence of anodic etching conditions (etching time, electrical potential and current) on the spectral reflectance and Raman scattering spectra. Optical properties of b-Si structures were experimentally studied by UV-VIS (AvaSpec-2048) and Raman (Thermo DXR Raman) spectrometers. B-Si layer thickness of formed substrate were determined by using SCOUT software. Effective medium approximation theory (Looyenga) was used in construction of the reflectance model. Influence of the deformation of crystal lattice introduced during the substrate etching was studied by Raman scattering method. Teoretical model of the 1st order Raman scattering profile was constructed by using pseudo-Voigt function and the profile parameters were extracted. The values of biaxial tensile stress were estimated by using optimized Raman profile parameters.

Specifics of the data processing of precession electron diffraction tomography data and their implementation in the program PETS2.0.

Electron diffraction tomography (EDT) data are in many ways similar to X-ray diffraction data. However, they also present certain specifics. One of the most noteworthy is the specific rocking curve observed for EDT data collected using the precession electron diffraction method. This double-peaked curve (dubbed `the camel') may be described with an approximation based on a circular integral of a pseudo-Voigt function and used for intensity extraction by profile fitting. Another specific aspect of electron diffraction data is the high likelihood of errors in the estimation of the crystal orientation, which may arise from the inaccuracies of the goniometer reading, crystal deformations or crystal movement during the data collection. A method for the refinement of crystal orientation for each frame individually is proposed based on the least-squares optimization of simulated diffraction patterns. This method provides typical angular accuracy of the frame orientations of less than 0.05°. These features were implemented in the computer program PETS 2.0. The implementation of the complete data processing workflow in the program PETS and the incorporation of the features specific for electron diffraction data is also described.

Sensitive acetone detection with a mid-IR interband cascade laser and wavelength modulation spectroscopy

An efficient method for the detection of acetone, an important biomarker in exhaled breath, by utilizing wavelength modulation spectroscopy (WMS) with a mid-infrared distributed feedback interband cascade laser (DFB-ICL) is presented. The performance of the DFB-ICL laser is characterized, and its linewidth is measured to be $\mbox{(3}.\mbox{39} \pm 0.\mbox{15)}$(3.39±0.15) MHz by beating the output with an auxiliary mid-IR frequency comb over 50 ms. The measured asymmetric acetone absorption profile with the center wavelength around 3367 nm is fitted by the pseudo-Voigt function. The phase shift between the intensity and frequency modulations is determined and used for processing the results. The sensor is tested by performing measurements with calibration mixtures of acetone in nitrogen, and the detection limits of 0.58 ppm and 0.12 ppm were determined with 1 s and 60 s signal averaging times, respectively. Our work shows that wavelength modulation spectroscopy with a DFB-ICL laser complimented by a multipass cell for higher sensitivity can be efficiently used for acetone detection and is promising for sensitive breath analysis.

Comparation of X-ray diffraction pattern refinement using Rietica and MAUD of ZnO nanoparticles and nanorods

ZnO nanoparticles and nanorods were synthesized using a simple co-precipitation method. X-ray diffractometry was used to investigate the purity and nanocrystallinity of the final powders. Rietveld refinements for x-ray diffraction data of the nanopowders have been done using Rietica and MAUD softwares. The study was to compare the adjusted parameters in the models where Voigt and pseudo-Voigt functions, respectively, are used as profiles adopted in the softwares. Refinements using Rietica gives Lorentzian and Gaussian peak broadening components and preferred orientation parameter. The peak broadening components can be used to estimate crystallite size and non-uniform microstrain. MAUD can directly give crystallite size and its distribution parameter, microstrain and preferred orientation value. Further study and investigation using scanning electron microscopy (SEM) are required to confirm the accuracy of the diffraction size results.

Temperature constraints by Raman spectroscopy of organic matter in volatile-rich clasts and carbonaceous chondrites

An important question regarding the formation of the solar system is how planetary bodies developed from dust and ice into the planets and planetary bodies. A particularly interesting topic is the thermal evolution of carbonaceous chondrites and volatile-rich clasts that could have originated from CM- and CI-like parent bodies. Two types of these volatile-rich clasts, which are a particular type of dark clasts, can be found. These clasts are mineralogically very similar to CM and CI chondrites and can occasionally be found in achondritic meteorites. Mineral assemblages suggest that both CM and CI chondrites as well as volatile-rich clasts experienced low peak temperatures. However, these mineral assemblages only offer large estimated temperature ranges to describe the thermal history of CM and CI chondrites, and the thermal history of volatile-rich clasts has not been previously described. In this study, to gain a better understanding of the thermal history of both CM and CI chondrites and volatile-rich clasts, we estimated peak temperatures of 30 volatile-rich clasts (16 CI-, and 14 CM-like) in 10 different host meteorites (4 polymict ureilites, 5 polymict eucrites and 1 howardite) by Raman carbon thermometry. An automated method was developed in order to describe over 4000 collected Raman spectra using four pseudovoigt functions. The full width half maximum (FWHM) of the D1-band was then used to calculate peak temperatures. Results were then compared to Raman data of 8 different well-studied carbonaceous chondrites (including CI and CM chondrites) to evaluate the suggestion that volatile-rich clasts are composed of similar material to the equivalent CI and CM chondrites. Our results show that the peak temperatures experienced by CI-like clasts range between 30–110 °C with an average of about 65 ± 25 °C; the peak temperatures experienced by CM-like clasts range from 50 to 110 °C with an average of about 70 ± 25 °C. Six of the 8 studied carbonaceous chondrites (CM, CI, CR or C2ungr) also plot in the same low-temperature range between 50 °C and 75 °C and can thus be considered to have formed under similar temperature conditions as the volatile-rich clasts. This is in agreement with previous suggestions, based on their mineral compositions that volatile-rich clasts and CI and CM carbonaceous chondrites are composed of similar materials. The peak temperatures for carbonaceous chondrites determined in this study considerably reduce the range of temperature estimates proposed previously for these chondrites by different methods. By highlighting the ability of our methodology to evaluate data in an automated way, this study shows that Raman carbon thermometry is a good analytical technique for obtaining information about peak temperatures in small and delicate samples.

Results of magnetometry data processing for non-destructive testing of compressive mechanical stress levels in steels

We plotted the fields of measurement coil signal as functions inversely proportional to reversible magnetisation in low-carbon St20 steel plates subjected to plastic tensile strain. Performing an additional approximation of our experimental data using three pseudo-Voigt functions allowed us to detect the information concerning irreversible motion of the 90-degree domain walls that are most sensitive to mechanical stresses. As a result of performing mathematical processing of experimental data we managed to improve validity of estimating the fields of stress-induced magnetic anisotropy and mechanical stresses.

An asymmetric fitting function for condensed-phase Raman spectroscopy.

Asymmetric lineshapes are experimentally observed in the Raman spectra of different classes of condensed matter. Determination of the peak parameters, typically done with symmetric pseudo-Voigt functions, in such situations yields unreliable results. While a wide choice of asymmetric fitting functions is possible, for the function to be practically useful, it should satisfy several criteria: simple analytic form, minimum parameters, description of the symmetric shape as "zero case", estimation of the desired peak parameters in a straightforward way and, above all, adequate description of the experimental data. In this work we formulate the asymmetric pseudo-Voigt function by damped perturbation of the original symmetric shapes with one asymmetry-related parameter. The damped character of the perturbation ensures by construction consistent behavior of the line tails. We test the asymmetric function by fitting the experimental Raman spectra. The results show that the function is able to describe a wide range of experimentally observed asymmetries for different natures of asymmetric broadening, including 3D and 2D crystals, nanoparticles, polymers, and molecular solids and liquids.

The role of different network modifying cations on the speciation of the Co2 + complex in silicates and implication in the investigation of historical glasses

In the last decades the speciation of the cobalt complex in a glass matrix has been extensively studied. Bivalent cobalt ions in glasses of different composition commonly adopt a tetrahedral coordination, though hexa- or penta-coordinated species are also possible. Changes in the absorbance spectrum of Co-doped glasses were attested in previous studies according to the introduction of different modifying cations. A shifting of the first sub-band characterizing the typical triplets of tetrahedral Co2+ ions in both the visible and near infrared regions was observed, but discrepancies in literature suggested a relevant role of glass composition on the definition of the optical signature of cobalt. Co-doped glasses with different composition (soda-lime, potash-lime, mixed alkali and ZnO-Na2O-CaO-SiO2) were studied via Fiber Optic Reflectance Spectroscopy (FORS). Pseudo-Voigt functions were used for the deconvolution of the absorbance spectra and the features of the bands characteristic of each cobalt complex were investigated. The structural role played by each modifying cation and the fundamental implications of glass basicity on the speciation of different Co-complexes were stressed. Changes in glass structure resulted in different equilibria between the three absorbing species whose specific optical signatures in the 480–530nm region interact to determine the resulting absorbance spectrum.

Single-particle excitation of core states in epitaxial silicene

Recent studies of core-level x-ray photoelectron spectroscopy (XPS) spectra of silicene on ${\mathrm{ZrB}}_{2}(0001)$ were found to be inconsistent with the density of states (DOS) of a planar-like structure that has been proposed as the ground state by density functional theory (DFT). To resolve the discrepancy, a reexamination of the XPS spectra and direct theoretical access of accurate single-particle excitation energies are desired. By analyzing the XPS data using symmetric Voigt functions, different binding energies and their sequence of Si $2p$ orbitals can be assigned from previously reported ones where asymmetric pseudo-Voigt functions are adopted. Theoretically, we have adopted an approach developed very recently, which follows the sophisticated $\mathrm{\ensuremath{\Delta}}$ self-consistent field $(\mathrm{\ensuremath{\Delta}}\mathrm{SCF})$ methods, to study the single-particle excitation of core states. In the calculations, each single-particle energy and the renormalized core-hole charge density are calculated straightforwardly via two SCF calculations. By comparing the results, the theoretical core-level absolute binding energies including the splitting due to spin-orbit coupling are in good agreement with the observed high-resolution XPS spectra. The good agreement not only resolves the puzzling discrepancy between experiment and theory (DOS) but also advocates the success of DFT in describing many-body interactions of electrons at the surface.

Modulating the electronic structure of lanthanum manganite by ruthenium doping for enhanced photocatalytic water oxidation.

To the best of our knowledge this is the first report in which ruthenium doped polycrystalline lanthanum manganite, LaMn1-xRuxO3 (x = 0.0-0.4), having high efficacy for oxygen production from water without the use of any sacrificial reagent or co-catalyst and as an efficient photocatalyst for dye degradation is reported. Ruthenium doping alters the crystal structure of the parent LaMnO3 (LMO) due to the induced chemical pressure of the larger Ru4+ ion, which facilitates a bond angle of 180° in the Mn3+-O-Mn4+ plane resulting in the easy extraction of a photo-generated charge carrier population leading to enhanced photocatalytic activity. Rietveld refinements reveal that the parent compound LMO crystallizes in the rhombohedral phase, while upon an increase in the doping concentration of ruthenium, the phase of the compounds changes from the rhombohedral to the cubic phase. The percentage contribution of each phase has been estimated using the sixth-order polynomial and pseudo-Voigt function. Typically, all the compositions, LaMn1-xRuxO3 (x = 0.0-0.4), were prepared by a conventional solid state route and studied for their photocatalytic activity. The synthesized compounds were investigated by powder X-ray diffraction (PXRD), UV-visible diffuse reflectance spectroscopy (DRS), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS) analysis. The structure-property correlation of the compound is presented based on Rietveld refinement combined with the experimental data. The as-prepared compounds show efficient photocatalytic oxygen gas production from water without the use of any co-catalyst or sacrificial reagents. Among the five compositions, LaMn0.7Ru0.3O3 shows the highest O2 production efficiency (4.73 mmol g-1 h-1) with an apparent quantum yield (AQY) of 7.43%. These ruthenium doped compositions also exhibit superior dye degradation properties, studied by taking the industrial dye methyl orange (MO) as the model compound.

Structural and magnetic properties of turmeric functionalized CoFe2O4 nanocomposite powder**Project supported by the University of Guilan and the Iran Nanotechnology Initiative Council.

The structural and magnetic properties of the synthesized pure and functionalized CoFe2O4 magnetic nanoparticles (NPs) are studied by analyzing the results from the x-ray diffraction (XRD), transmission electron microscopy (TEM), FT–IR spectroscopy, thermogravimetry (TG), and vibrating sample magnetometer (VSM). To extract the structure and lattice parameters from the XRD analysis results, we first apply the pseudo-Voigt model function to the experimental data obtained from XRD analysis and then the Rietveld algorithm is used in order to optimize the model function to estimate the true intensity values. Our simulated intensities are in good agreement with the experimental peaks, therefore, all structural parameters such as crystallite size and lattice constant are achieved through this simulation. Magnetic analysis reveals that the synthesized functionalized NPs have a saturation magnetization almost equal to that of pure nanoparticles (PNPs). It is also found that the presence of the turmeric causes a small reduction in coercivity of the functionalized NPs in comparison with PNP. Our TGA and FTIR results show that the turmeric is bonded very well to the surface of the NPs. So it can be inferred that a nancomposite (NC) powder of turmeric and nanoparticles is produced. As an application, the anti-arsenic characteristic of turmeric makes the synthesized functionalized NPs or NC powder a good candidate for arsenic removal from polluted industrial waste water.

In-situ X-ray diffraction during tensile deformation of ultrafine-grained copper using synchrotron radiation

At the synchrotron facility, Super Photon Ring – 8 GeV, in-situ X-ray diffraction during tensile deformation was conducted on ultrafine-grained Cu with a grain size of about 300 nm fabricated by equal-channel angular pressing. The diffraction profile was observed with the time resolution of about 1 s using multiple MYTHEN detectors, and the diffraction angle and the full-width at half-maximum of some Bragg peaks were determined using the pseudo-Voigt function. From the analysis of Bragg peaks, it was found out that there are microscopically three regions; elastic, plastic and transition regions. The 0.2% proof stress obtained from the stress–strain curve locates within the microscopic transition region. Microstrain was evaluated using the Williamson–Hall method and the dislocation density was also obtained from the microstrain. The dislocation density starts increasing before 0.2% proof stress, which is associated with dislocation bow-out and emission from grain boundaries. The Taylor relationship seems to be still satisfied after 0.2% proof stress.

Quantitative XRD Analysis of Binary Blends of Siliceous Fly Ash and Hydrated Cement

AbstractQuantitative analysis of the amorphous phase in binary blends of siliceous fly ash and hydrated cement is presented using the Partial Or No Known Crystal Structure (PONKCS) method. In binary blends, the total amorphous phase contains contributions from the glassy phase in fly ash and amorphous components of hydrated cement. A single pseudo-Voigt function is found to adequately fit the broad hump in the X-ray diffraction pattern resulting from diffuse scattering produced by the glassy phase in siliceous fly ash. The weight fractions of the amorphous component of hydrated cement and the glassy phase of siliceous fly ash in a binary blend are determined using the fitted profiles for the X-ray diffraction (XRD) patterns. For low lime content of less than 5%, the peak characteristics of the fitted function for the broad hump in the XRD pattern of fly ash are nominally identical for different oxide compositions of the glassy phase. The PONKCS method is shown to provide good accuracy in determining silic...

State-of-health estimation of LiFePO4/graphite batteries based on a model using differential capacity

A model for expressing the differential capacity characteristics of the LiFePO4 (LFP)/graphite battery for the state-of-health (SOH) estimation was proposed. Our model was based on the deformed pseudo-Voigt peak function with several parameters which are directly associated with the phase transition behavior of the active LFP and graphite materials. Charge/discharge cycle tests for accelerated battery fading were performed under a constant high-temperature condition (40 and 45 °C). The SOH estimation was carried out at different fading point of the battery using a part of the responses for the differential capacity versus voltage (dQ/dV vs. V) against the charging process at the rate of C/5 under constant temperature of 25 °C. The changes in the variables of the model with cycling were correlated to the generally mentioned phenomena that the main factors determining the capacity fading of the LFP/graphite battery are the loss of Li+ by a side reaction and that of the active electrode materials. In addition, the robustness related to the charge/discharge history was confirmed, since the memory effect of the LFP/graphite battery, being induced by the previous condition for use, has an influence on the dQ/dV vs. V. The evaluated SOH errors were within ±3%.

A new asymmetric Pseudo‐Voigt function for more efficient fitting of XPS lines

Asymmetric peak profiles for the application in spectroscopy can be obtained in a simple way by substituting the usually constant full width at half maximum parameter in Pseudo-Voigt functions with an energy-dependent expression, for instance of sigmoidal shape. While this approach has been successfully applied to vibrational spectra, we find that the resulting curves are less suitable for least-squares fits of X-ray photoelectron spectroscopy (XPS) data. However, if one additionally allows a variable displacement of the sigmoidal step relative to the peak, excellent fitting results can be obtained. We demonstrate the applicability of our extended approach on several inherently asymmetric XPS lines, i.e. the C 1s signal of graphite and C2H2/Pd(100), the 3d5/2–3d3/2 doublet of palladium, and the 4f7/2–4f5/2 doublet of platinum. Comparison of the corresponding fit results with the results obtained by the application of more elaborate, theory-based line profiles (Doniach-Sunjic and Mahan functions) shows that the modified Pseudo-Voigt function gives practically identical results in terms of peak shape and area, while requiring much less computational effort since no convolution procedures are required for its calculation. Thus, this function is most suitable for application in one of the following situations: (i) the peak shape of a given signal is known but cannot be calculated with ease, and (ii) the theoretical peak shape is not (yet) known, however, one wants to perform a first quantitative screening of the data at issue. Copyright © 2014 John Wiley & Sons, Ltd.

XRD and TEM study of bainitic ferrite plate thickness in nanostructured, carbide free bainitic steels

It is well documented that much of the strength and hardness of nanostructured, carbide free bainitic steels come from the very small thickness of bainitic ferrite plates. In the current work, the Williamson–Hall method has been used to determine the bainitic ferrite plate thickness. The fitting of X-ray peaks to various functions showed good coefficient of determination values for Gaussian function compared to the Cauchy and Pseudo-Voigt functions. The thickness of bainitic ferrite plates was measured by distinguishing the contribution of very small plates on peak broadening from the lattice microstrain and instrumental effects. The results showed that by decreasing the transformation temperature the bainitic ferrite plate thickness decreases. The determined thicknesses were compared with that of measured from transmission electron microscope micrographs. There is a good qualitative and quantitative agreement between the thicknesses measured using both methods.