Multi-peak Fitting Research Articles

Gaussian model analysis and thermal decomposition kinetics of nature fibers

The thermal decomposition of the heartwood and sapwood of eight wood species was investigated using dynamic thermogravimetric analysis in this study. To calculate the activation energy of the heartwood and sapwood, four “model-free” methods were used: the Flynn–Wall–Ozawa method, the modified Coats–Redfern method, the Friedman method, and the Kissinger method. Because the activation energy of the heartwood and sapwood was calculated using model-free methods that did not account for the reaction mechanism of the thermal decomposition of the hardwood and sapwood, the Gaussian multi-peak fitting method. The method did account for the reaction mechanism. The activation energy of the heartwood and sapwood was calculated using various methods in order to compare the results obtained by the various methods and, ultimately, to confirm the reliability of the results. The activation energy of the eight wood species' hardwood and sapwood ranged from 120 kJ/mol to 140 kJ/mol. The activation energy of the heartwood was slightly higher than that of the sapwood within the same wood species. Infrared spectrograms of the selected woods revealed that the heartwood had higher absorption peak intensities in the wavelength range of 3100–3500 cm −1 than the sapwood. This indicates that the heartwood, as opposed to the sapwood, requires more energy to sustain the chemical reaction at this stage. This is one of the primary reasons why heartwood has higher apparent activation energy values than sapwood. Furthermore, softwood had a higher activation energy than hardwood. Furthermore, when compared to other model-free methods, the Friedman method was less reliable for studying the kinetics of pyrolysis in the heartwood and sapwood of the eight wood species.

Tool path regeneration in five-axis flank milling for ruled surface based on error distribution

Five-axis flank milling is widely used in the field of aerospace and automotive industry. However, the accurate model between variety conditions of machining and the errors is difficult to establish directly. It is urgent to obtain a tool path for reducing the errors of the parts. Herein, a tool path regeneration method is proposed for five-axis flank milling of ruled surface according to the actual error distribution. The method contains three steps: First, the errors at the middle of the straight generatrix on the machined surface are calculated according to error distribution, and the corresponding normal vectors are obtained by geometric calculation. Second, multi-peaks Gaussian fitting method is utilized to make connections between parameters in the original tool path and error distribution. Finally, the regenerative tool path is obtained by offsetting original tool path. Machining experiments are performed to test the effectiveness of the proposed tool path regeneration method. The error distribution after tool path regeneration shows that the average error reduces 92.32%, with the surface roughness staying constant. Results show that the proposed tool path regeneration method is effective to improve the accuracy for five-axis flank milling.

Monolithic integration of tandem-FAIMS based on overlapping ion peak separation and weak ion peak discovery for gas detection

High-field asymmetric ion mobility spectroscopy (FAIMS) distinguishes and separates gas-phase ions according to the nonlinear change in ion mobility in a high electric field. However, since the electric field strength cannot be increased infinitely, multiple ion peaks may overlap in a complex sample detection, which can increase the difficulty of identifying ions. This paper designed a chip called tandem-FAIMS and proposed a method to separate ions in a complex sample. The tandem-FAIMS can separate overlapping ion peaks through two-stage dispersion electrodes and draw the corresponding spectrum, which we call the fingerprint. Combining fingerprint and multipeak fitting can lead to higher detection sensitivity. In this paper, benzene, styrene, and their mixture are used as samples to evaluate the effectiveness of the proposed method. The experimental results show that there are overlapping ion peaks in the spectrum under low dispersion voltage (DV=480V,550V), and the proposed method can accurately separate the overlapping ion peaks and obtain ion peak position information. The peak position error is within ±0.5V.

Study of Relaxations in Epoxy/Rubber Composites by Thermally Stimulated Depolarization Current and Dielectric Spectroscopy

Liquid rubber toughened epoxy resins are widely used in electrical equipment and electronic packaging. Previous studies have only investigated the relaxation process of epoxy resins through dielectric spectroscopy. The trap characteristics of the relaxation process by thermally stimulated depolarization current (TSDC) analysis are less studied. In this work, TSDC and broadband dielectric spectroscopy techniques were used to complementarily characterize the dielectric relaxation process of hydroxyl-terminated liquid nitrile-butadiene rubber (HTBN) toughened epoxy resin polymers. The experimental results show that HTBN introduces two new relaxation processes in the epoxy matrix, which are attributed to the α polarization of the rubber molecule and the interfacial polarization based on the correlation between the TSDC and the dielectric spectroscopy data, respectively. The trap parameters of each TSDC current peak were obtained using the multi-peak fitting method. The addition of rubber increases the trap density in epoxy composites significantly, especially for traps with energy levels in the range of 0.5–0.9 eV. The trap energy level of the DC conductivity process increases with increasing rubber concentration. The above results provide analytical ideas for rubber-toughened epoxy resins’ polarization and trap characteristics and theoretical guidance for formulation improvement.

Field-induced rheological characterization of nano/micro-scaled suspensions based on a multi-peak fitting method.

Nano/micro-scaled suspensions used in damping systems, bulletproof materials and flexible machining regions are developing towards external energy field control and multi-type and multi-scale dispersed phase particles. However, the above-mentioned changes make the rheological properties of the fluid more complex, which cannot be characterized efficiently with high quality by traditional constitutive equations. In order to solve the above-mentioned problems, based on the multi-peak fitting characterization method of the Gaussian function, the field-induced rheological constitutive equation of a multi-scale particle suspension turbidity system (MRSTPF as an example) was established. Under the condition of shear distribution and external magnetic field affection, the rheological characteristic curves of the dispersion system were measured using an Antompa MCR301 rheometer. The Origin software was used to fit and characterize the above-mentioned rheological data. The results indicate that the method can effectively establish field-induced constitutive equations of different dispersed systems, and the fitting goodness evaluation parameters are above 95% (R-square) and 90% (adjusted R-square) respectively.

A Method for Correcting the Interference of Overlapping Absorption Lines Using Second Harmonic Spectral Reconstruction

The measurement accuracy of trace gas detection based on infrared absorption spectroscopy is influenced by the overlap of absorption lines. A method for correcting the interference of overlapping absorption lines using second harmonic spectral reconstruction (2f-SR) is proposed to improve the measurement accuracy. 2f-SR includes three parts: measurement of gas temperature and use of the differences in temperature characteristics of absorption lines to correct the temperature error, 2f signal restoration based on laser characteristics to eliminate the influence of waveform change on overlapping absorption lines, and fast multi-peak fitting for the separation of interference from overlapping absorption lines. The CH4 measurement accuracy based on overlapping absorption lines is better than 0.8% using 2f-SR. 2f-SR has a lower minimum detection limit (MDL) and a higher detection accuracy than the separation of overlapping absorption lines based on the direct absorption method. The MDL is reduced by two to three orders of magnitude and reaches the part per million by volume level. 2f-SR has clear advantages for correcting the interference of overlapping absorption lines in terms of both MDL and measurement accuracy.

Surface depth-dependent and microstructural analyses of high performance lithium iron silicate with 15% vanadium modification

The surface, interface and microstructure studies were carried out for the nominal 15% vanadium modified carbon coated lithium iron silicate composite in an effort to understand the enhanced electrochemical performance and decayed cycle performance. The empirical formula was determined to be Li2.09Fe0.78V0.22Si1.29O6.29. It was confirmed that the surface of the as-prepared composite was coated by amorphous carbon with the thickness of approximately 50 nm. Furthermore, the predominant crystal phase changed from monoclinic P21 to orthorhombic Pmn21 after the vanadium modification. The simultaneous presences of multivalent iron (Fe) and vanadium (V) ions were identified by performing multi-peak fitting analyses in the depth-dependent X-ray photoelectron spectroscopic spectra of Fe2p and V2p. The detailed microstructure, interface and surface characterizations provided strong evidence that the partial substitution of divalent iron (Fe2+) with divalent vanadium (V2+) in the structure and the surface modification by vanadium might become possible, leading to 29.1% increase in total carbon content, and 35.8% and 41.3% decreases in the interfacial charge transfer resistance and lithium–ion diffusion coefficient, respectively. The faster interfacial charge transfer kinetics greatly enhanced the initial discharge capacity, while the slower lithium–ion diffusion process apparently degraded the cycle performance.

The effect of coagulation on the removal of algogenic organic matter and the optical parameters for predicting disinfection byproducts

Algae-derived disinfection byproducts (DBPs) are receiving increasing attention. Coagulation is the first water treatment section in removing algogenic organic matter (AOM). However, there is a significant knowledge gap in the effects of coagulation on DBPs produced from AOM. In this study, in view of the multi-component AOM, several analysis methods were combined to investigate the changes in AOM of Microcystic aeruginosa during the coagulation treatment, including ultraviolet–visible absorbance, multi-peaks Gaussian fitting method based on differential absorption spectroscopy, Excitation-emission matrix, and Fourier transform infrared spectroscopic analysis. To identify the characteristic parameters that could indicate the formation of DBPs, the yields of twenty-one DBP species produced from the residual AOM after the coagulation treatment were investigated. The correlations between DBPs and the spectral parameters were also analyzed. The results showed that aluminum salt coagulant could significantly remove protein-like compounds, chlorophyll, and phycocyanin in AOM, but it had a limited ability to precipitate AOM. With the increase of aluminum sulfate coagulant, the yields of DBPs produced from the residual extracellular organic matter decreased, while those produced from the residual intracellular organic matter decreased firstly and then gradually increased. The Pearson’s correlation results showed that the combination of fluorescent regions of protein-like and humic acid-like could be used as an optical surrogate for predicting the formation of DBPs.

Pyrolysis of Tropical Agricultural Crop Waste (Pineapple Residue and Banana Pseudo-Stem): Kinetics, Mechanism and Valorization of Bio-Char

Pineapple residue and banana pseudo-stem are waste from tropical agricultural production. Kinetics, thermodynamics, mechanism during pyrolysis of them and valorization of bio-char were explored. Both biomass decomposed rapidly at 150-500°C and there was a significant mass loss peak for banana pseudo-stem at 650 °C, which indicated that degree of lignification apparently affect pyrolysis characterization of biomass. Activation energy of pineapple residue and banana pseudo-stem was 159-292 and 169-321 kJ/mol based on multi-heating rate method. Whereas based on Gaussian multi-peak fitting method, derivative thermogravimetry (DTG) curves of pineapple residue and banana pseudo-stem were simulated with three or four fitting peaks, corresponding to decomposition of hemicellulose, cellulose and lignin and deep degradation. Interaction between these components intensified complexity of kinetic parameters. The main carbon number of organic volatiles during pyrolysis was C 4 and C 5 for pineapple residue, and that was C2 and C3 for banana pseudo-stem. High content of cellulose and hemicellulose in biomass (pineapple residue) intensified volatilization of volatiles. Porous carbon sourced from pineapple residue and banana pseudo-stems had specific capacitance of 375 F/g and 297 F/g at current density of 0.5 A/g, respectively. Pineapple residue and banana pseudo-stem were potential feedstock for electrochemical materials.

Simulation of solute transport behaviors in saturated karst aquifer system

The karst development makes aquifer have strong anisotropy and heterogeneity. In order to reveal the characteristics of solute transport in the karst fissure–conduit aquifer system, this study presents a physical model of fissure–conduit in laboratory experiments to carry out the solute transport simulation. In this paper, the tracer tests of fissure–conduit combination, fissure, and conduit solute transport process in saturated flow are designed. We found that different aquifer structures and tracer injection points have an influence on the shape of the breakthrough curve. Besides, the two-dimensional dispersion model of tracer injection of the instantaneous point was used to calculate the dispersion parameters of each group of experiments. Then, the dynamic responses of the linear distance (x) between the injection point and the receiving point, initial time (t0), peak time (tm), peak concentration (cm), average tracer transport velocity (V), and porosity (p) of aqueous media to the longitudinal dispersion coefficient are discussed. In addition, according to the measured data, Gaussian multi-peak fitting can be used to reflect the overall shape and change trend of the multi-peak BTC. These results demonstrate the solute transport behaviors in the saturated karst aquifer system, which have important reference significance for solving the engineering environmental problems in the karst area.

Picometer-Precision Atomic Position Tracking through Electron Microscopy.

The modern aberration-corrected scanning transmission electron microscopes (AC-STEM) have successfully achieved direct visualization of atomic columns with sub-angstrom resolution. With this significant progress, advanced image quantification and analysis are still at the early stages. In this work, we present the complete pathway for the metrology of atomic resolution scanning transmission electron microscopy (STEM) images. This includes (1) tips for acquiring high-quality STEM images; (2) denoising and drift-correction for enhancing measurement accuracy; (3) obtaining initial atomic positions; (4) indexing the atoms based on unit cell vectors; (5) quantifying the atom column positions with either 2D-Gaussian single peak fitting or (6) multi-peak fitting routines for slightly overlapping atomic columns; (7) quantification of lattice distortion/strain within the crystal structures or at the defects/interfaces where the lattice periodicity is disrupted; and (8) some common methods to visualize and present the analysis. Furthermore, a simple self-developed free MATLAB app (EASY-STEM) with a graphical user interface (GUI) will be presented. The GUI can assist in the analysis of STEM images without the need for writing dedicated analysis code or software. The advanced data analysis methods presented here can be applied for the local quantification of defect relaxations, local structural distortions, local phase transformations, and non-centrosymmetry in a wide range of materials.

Picometer-Precision Atomic Position Tracking through Electron Microscopy

The modern aberration-corrected scanning transmission electron microscopes (AC-STEM) have successfully achieved direct visualization of atomic columns with sub-angstrom resolution. With this significant progress, advanced image quantification and analysis are still at the early stages. In this work, we present the complete pathway for the metrology of atomic resolution scanning transmission electron microscopy (STEM) images. This includes (1) tips for acquiring high-quality STEM images; (2) denoising and drift-correction for enhancing measurement accuracy; (3) obtaining initial atomic positions; (4) indexing the atoms based on unit cell vectors; (5) quantifying the atom column positions with either 2D-Gaussian single peak fitting or (6) multi-peak fitting routines for slightly overlapping atomic columns; (7) quantification of lattice distortion/strain within the crystal structures or at the defects/interfaces where the lattice periodicity is disrupted; and (8) some common methods to visualize and present the analysis. Furthermore, a simple self-developed free MATLAB app (EASY-STEM) with a graphical user interface (GUI) will be presented. The GUI can assist in the analysis of STEM images without the need for writing dedicated analysis code or software. The advanced data analysis methods presented here can be applied for the local quantification of defect relaxations, local structural distortions, local phase transformations, and non-centrosymmetry in a wide range of materials.

Analysis of pyrolysis behaviors of biomass extractives via non-linear stepwise heating program based on Gaussian multi-peak fitting of differential thermogravimetric curve

The thermal decomposition of extractives can yield additional products, resulting in a different final product distribution of bio-oil, especially for extractives-rich biomass. However, the thermal decompositon behavior of extractives themselves has long been ignored, but deserves deep investigation. Herein, the non-linear stepwise heating program based on Gaussian multi-peak fitting of differential thermogravimetric curve for biomass extractives was designed. Using this stepwise heating program, the pyrolysis process of different chemical substances in biomass extractives was effectively decoupled and systematically studied. As for water-soluble extractives, the evaporation of volatile substances, the thermal decomposition of water-soluble carbohydrates, phenolic substances, and nitrogenous substances proceed in sequence with the increase of temperature during the pyrolysis process. With regard to liposoluble extractives, the pyrolysis included the volatilization of endogenous substances and the thermal decomposition of different lipids into olefins. This work provides a systematic understanding of thermal decomposition process in the extractives of lignocellulosic biomass.

RETRACTED ARTICLE: Coastline geological parameters and beach motion image simulation based on particle swarm optimization

This paper uses the function of neural network-based nonlinear mapping and particle group optimization algorithm to optimize the system, and then uses the particle group optimization algorithm of inertia weight, so as to achieve the goal of optimizing the weight of neural network training. By choosing to encode the geological parameters of the coastline with mpeg-4 and obtain the relevant data, the relevant data of the beach motion image can be obtained, so that the simulation experiment can be carried out. This paper introduces the process of establishing a multi-modal pore size distribution fitting model based on probability density function, and conducts an experimental analysis on the geological parameters and pore structure of two typical shale storage layer samples in China. Finally, the multi-peak opening distribution fitting model and the pore size distribution are obtained through quantitative fitting curves, and the geological parameters of the marine continental shale that affect the pore size distribution are investigated, and the pore size distribution of the shale and the geology of the shale are investigated. In-depth parameter analysis is to explore the thermal maturity of organic matter, and the relationship between its content and mineral composition. In addition, the coastal image simulation is researched focusing on the characteristics of coastal beach recreational sports, the problems existing in the development process, and future development countermeasures. Finally, it is pointed out that the future development trend of coastal beach leisure sports, through the integration of local leisure sports-related characteristics and professional development, so as to achieve the implantation of culture in sports, and the organic combination of the two promotes the economic and ecological environment.

Investigation on in-situ thermal treatment of room-temperature pulsed laser deposition technique: How to improve Cu2ZnSnS4 films for photoelectric application without sulfurization

Is extra sulfurization an indispensable process for synthesizing quaternary chalcogenide? The answer is probably affirmative for most synthesismethods to suppress excessive sulfur vacancies. Pulsed laser deposition (PLD), an acknowledged technique for fabricating films with complex stoichiometry, is a greatalternative approach to prepare Cu2ZnSnS4 (CZTS) films. However, to prevent evaporative losses the deposition temperature (Tis) must be limited below 400 °C, which makes post-annealing process extremely requisite to improve metastable films. Herein we develop an in-situ thermal treatment technique in room-temperature (RT)-PLD-synthesis of CZTS films to evade extra sulfurization process. According to multi-peaks Gaussian fitting analysis, RT-PLD implementing optimized in-situ treatment can broaden solar absorption of CZTS films, potentially contributed by sub-bandgap absorption due to intrinsic natural-intermedium-band effects of I2-II-IV-VI4 chalcogenide compounds. Stabilized chronoamperometry characterization combined with quasi-stoichiometric ratio demonstrates that the RT-PLD technique can equivalently restrain sulfur vacancy generation even without sulfurization. Physical mechanisms associated to order–disorder transitions of polycrystal CZTS during in-situ treatment can interpret morphological “lumpy-smooth-vuggy” transformation along with Tis varied. Therefore, such proposed RT-PLD technique is applicable to prepare polynary compounds with volatile elements and complicated stoichiometry ratio.

Pyrolysis behavior of alternative cork species

Pyrolysis is a useful technique in the characterization of the thermal behavior, kinetics and chemical composition of new materials. Alternative cork feedstocks are obtained from tree species possessing cork-enriched outer barks that are currently unused and could be used in thermal applications such as pyrolysis or gasification. An understanding of their thermal reactions is required, and this study is set to explore the pyrolysis behavior of alternative cork feedstocks from Quercus cerris, Beaucarnea recurvata and Betula pendula. Thermogravimetric analyses were carried out, and kinetics of the pyrolysis reaction were evaluated with isoconversional Vyazovkin method. The application of pyrolysis for estimation of the chemical composition of the corks of these species was also evaluated using Lorentzian multi-peak fitting. Wet chemical and FT-IR analyses were performed to determine the chemical composition of the corks and to compare the Lorentzian multi-peak fitting estimations. The results show that corks from different species have different pyrolytic degradation patterns. Pyrolysis of cork takes place in three major steps and two complementary steps. Lignin as well as suberin contents determine the thermal reactivity of cork. Desuberinised cork shows higher heat resistance at high temperatures than raw cork. Activation energy of cork varies between different species. Lorentzian multi-peak fitting could be used to estimate the chemical composition of cork as an alternative method to wet-chemical methods.

Measurement of Temperature and H2O Concentration in Premixed CH4/Air Flame Using Two Partially Overlapped H2O Absorption Signals in the Near Infrared Region

It is important to monitor the temperature and H2O concentration in a large combustion environment in order to improve combustion (and thermal) efficiency and reduce harmful combustion emissions. However, it is difficult to simultaneously measure both internal temperature and gas concentration in a large combustion system because of the harsh environment with rapid flow. In regard, tunable diode laser absorption spectroscopy, which has the advantages of non-intrusive, high-speed response, and in situ measurement, is highly attractive for measuring the concentration of a specific gas species in the combustion environment. In this study, two partially overlapped H2O absorption signals were used in the tunable diode laser absorption spectroscopy (TDLAS) to measure the temperature and H2O concentration in a premixed CH4/air flame due to the wide selection of wavelengths with high temperature sensitivity and advantages where high frequency modulation can be applied. The wavelength regions of the two partially overlapped H2O absorptions were 1.3492 and 1.34927 μm. The measured signals separated the multi-peak Voigt fitting. As a result, the temperature measured by TDLAS based on multi-peak Voigt fitting in the premixed CH4/air flame was the highest at 1385.80 K for an equivalence ratio of 1.00. It also showed a similarity to those tendencies to the temperature measured by the corrected R-type T/C. In addition, the H2O concentrations measured by TDLAS based on the total integrated absorbance area for various equivalent ratios were consistent with those calculated by the chemical equilibrium simulation. Additionally, the H2O concentration measured at an equivalence ratio of 1.15 was the highest at 18.92%.

Temperature and Pressure Insensitive Spectroscopic Method for Measuring 13CH4 during Oil and Natural Gas Drilling Operations

A novel rugged two-section driving NIR TDLAS scheme was implemented to reduce temperature and pressure sensitivity of methane carbon isotope measurement during oil and natural gas drilling operations. Isotope spectra line groups with same lower energy levels were selected to derive the concentration of 13CH4 and 12CH4. Dynamic pressure linewidth broadening was introduced in the absorbance curve fitting. Various uncontrollable factors such as spectra shift, stretching, and baseline trending were incorporated in the comprehensive multi-peak fitting. The results showed that the sensitivity of isotope ratios to temperature and pressure variation was greatly suppressed. The δ13CH4 uncertainty in the temperature test was 2.8‰ with fitted δ13CH4-T slope of 0.021‰/°C in 25 ± 5°C range. The δ13CH4 uncertainty in the pressure test was 1.4‰ with fitted δ13CH4-P slope of <0.001‰/mbar from 400 to 1000 mbar. The limit standard deviation of long-term test was 0.15‰ (@135 s). The results indicate that our scheme is a promising solution for δ13CH4 measurement during drilling operations due to the enhanced robustness.

Label-free SERS detection of proteins based on machine learning classification of chemo-structural determinants.

Establishing standardized methods for a consistent analysis of spectral data remains a largely underexplored aspect in surface-enhanced Raman spectroscopy (SERS), particularly applied to biological and biomedical research. Here we propose an effective machine learning classification of protein species with closely resembled spectral profiles by a mixed data processing based on principal component analysis (PCA) applied to multipeak fitting on SERS spectra. This strategy simultaneously assures a successful discrimination of proteins and a thorough characterization of the chemostructural differences among them, ultimately opening up new routes for SERS evolution toward sensing applications and diagnostics of interest in life sciences.

Morphological and Biochemical Properties of Human Astrocytes, Microglia, Glioma, and Glioblastoma Cells Using Fourier Transform Infrared Spectroscopy.

BackgroundWith infiltration, high-grade glioma easily causes the boundary between tumor tissue and adjacent tissue to become unclear and results in tumor recurrence at or near the resection margin according to the incomplete surgical resection. Fourier transform infrared spectroscopy (FTIR) technique has been demonstrated to be a useful tool that yields a molecular fingerprint and provides rapid, nondestructive, high-throughput and clinically relevant diagnostic information.Material/MethodsFTIR was used to investigate the morphological and biochemical properties of human astrocytes (HA), microglia (HM1900), glioma cells (U87), and glioblastoma cells (BT325) cultured in vitro to simulate the infiltration area, with the use of multi-peak fitting and principal component analysis (PCA) of amide I of FTIR spectra and the use of hierarchical cluster analysis (HCA).ResultsWe found that the secondary structures of the 4 types of cells were significantly different. The contents of α-helix structure in glial cells was significantly higher than in the glioma cells, but the levels of β-sheet, β-turn, and random coil structures were lower. The 4 types of cells could be clearly separated with 85% for PC1 and 12.2% for PC2.ConclusionsFTIR can be used to distinguish between human astrocytes, microglia, glioma, and glioblastoma cells in vitro. The protein secondary structure can be used as an indicator to distinguish tumor cells from glial cells. Further tissue-based and in vivo studies are needed to determine whether FTIR can identify cerebral glioma.