Gaussian Peak Fitting Research Articles

From medical strategy to foodborne prophylactic strategy: Stabilizing dental collagen with aloin.

Infectious oral diseases are longstanding global public health concerns. However, traditional medical approaches to address these diseases are costly, traumatic, and prone to relapse. Here, we propose a foodborne prophylactic strategy using aloin to safeguard dental collagen. The effect of aloin on the stability of dental collagen was evaluated by treating dentin with a solution containing aloin (0.1 mg/mL) for 2 min. This concentration is comparable to the natural aloin content of edible aloe. Furthermore, we investigated the mechanisms underlying the interactions between aloin and dentin collagen. Our findings, obtained through fluorescence spectroscopy, attenuated total reflection Fourier transform infrared spectroscopy, Gaussian peak fitting, circular dichroism spectroscopy, and X-ray diffraction, revealed that aloin interacts with dental collagen through noncovalent bonding, specifically hydrogen bonding insitu. This interaction leads to a reduction in the distance between molecules and an increase in the proportion of stable α-helical chains in the dental collagen. The ultimate tensile strength and thermogravimetric analysis demonstrated that dental collagen treated with aloin exhibited improved mechanical strength and thermostability. Additionally, the release of hydroxyproline, cross-linked carboxy-terminal telopeptide of type I collagen, and C-terminal cross-linked telopeptide of type I collagen, along with weight loss, indicated an enhancement in the enzymatic stability of dental collagen. These findings suggest that aloin administration could be a daily, nondestructive, and cost-effective strategy for managing infectious oral diseases.

Low current driven bidirectional violet light emitting diode based on p-GaN/n-InN heterojunction

The fabrication of a low current bidirectional driven violet p-GaN/n-InN heterojunction light-emitting diode (LED) by the radio-frequency (RF) magnetron sputtering is reported in this paper. The indium nitride (InN) films grown at different substrate temperatures were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), UV-2600 spectrophotometer and Hall test system, and the optimum substrate temperature was found to be 250 °C. The bidirectional electroluminescence (EL) behavior and the luminescence mechanism of the diode have been investigated. Based on the above, the bidirectional EL and the effect of ambient temperature (room temperature (RT) to 80 °C) on the luminescence properties of the diode have been investigated. The diode can be driven bidirectionally at very low currents (0.03 mA under forward and 0.01 mA under reverse) and produce high-brightness violet light at forward currents of 1–5 mA and reverse currents of 1–3 mA. Finally, the EL spectra were subjected to the Gaussian peak fitting process combined with energy band diagrams to analysis the luminescence mechanism of the diode. The EL spectra all show predominantly violet emission and interface defects emissions under different polarity current drive. The proposed bidirectional violet LED based on p-GaN/n-InN heterojunction will be a potential commodity for the bidirectional driven LED market in the future.

Temperature and anion ligand field dependence of LnCl3 (Ln = Nd, Dy, Sm) electronic absorption spectra in LiCl–KCl eutectic molten salt

A comprehensive knowledge of the coordination, bonding, and speciation of elements in molten salt mixtures is necessary to understand and predict the chemical and physical properties of the salt. Absorption spectroscopy can yield information about the chemistry of species of interest in alkali halide molten salt mixtures by revealing information about the electronic structure and transitions of those species. In this study, ultraviolet (UV), visible (vis), and near-infrared (NIR) absorption spectroscopy was used to examine changes to the electronic structure of trivalent Nd, Sm, and Dy in LiCl–KCl eutectic molten salt with changes in temperature and the anion composition of the melt. With increasing temperature, changes to spectral features suggest a distortion of the coordination complexes. Changes to lineshape with the substitution of alternative halide anions were examined and analyzed, revealing differences in the coordination for I− versus F− with the lanthanides. Gaussian peak fitting was used to show that the changes in lineshape with the progressive addition of F− anions can be explained by the superposition of a set of absorption bands from complexes with all Cl− anion ligands and a set of blueshifted absorption bands from complexes containing both F− and Cl− anion ligands. This work yields a new method to analyze and interpret change to electronic absorption spectra for f-block elements dissolved in alkali halide molten salts as well as new observations of the interactions of larger and smaller halide anions with lanthanides in Cl−-based molten salts.

Evolution of conformation and thermal properties of bovine hides collagen in the sodium sulphide solution

Conformations of secondary and super secondary structure from bovine hides collagen are very important for constructing collagen molecular space structure, and directly related to its properties. In this work, the evolutional mechanism of the collagen conformation in the environment of sodium sulphide (Na2S) solution is periodically studied by FT-IR spectroscopy, the Gaussian peak fitting of secondary derivative, and auxiliary methods such as SDS-PAGE, SEM and TG. As a result, the three polypeptide chains structure of bovine hide collagen was hardly affected by the ions of OH−, HS− and S2−. The conformation of collagen molecules such as β-turn, triple helix and β-strand were gradually evolved into unordered structure and α-helix with the sequential addition of OH−, HS− and S2−, which is because the hydrogen bond inside collagen molecular is extended or opened with the increase of the synergistic effect of pH and reducibility of HS− and S2− in the solution. The bound water content and thermal properties of the treated collagen molecules are decreased. Finally, the order of the hydrolysis ability to collagen is NaOH < NaHS < Na2S at the same condition, which was confirmed by measuring the content of hydroxyproline from their solutions after treating the collagen. This work provides very important information for understanding the evolutional mechanism of bovine hide collagen conformation in the Na2S solution, developing the alternatives of sulfide, extraction of collagen, tanning, and application of collagen in biological and material science.

Effects of the ionizing irradiation of γ-rays, X-rays, and UV-rays on the optical properties of Ag-contained/Ag-free photo-thermo-refractive glass

To simulate the effects of ionizing irradiation on photo-thermo-refractive (PTR) glass in a cosmic environment, the optical properties changes under ionizing irradiation (γ-, X- and UV-ray) were investigated on PTR-glass with and without Ag doped (named as PTR-S and PTR-F, respectively) samples. Thermoluminescence (TL), transmission electron microscopy (TEM) measurements, UV-VIS absorption spectroscopy analysis, Gaussian peak fitting, and continuous wave electron paramagnetic resonance (CW-EPR) were used to determine the species of the irradiation-induced color centers. The radiation resistance properties of the Ag-species on the PTR-S glass were evaluated by comparing the defect center concentrations in the irradiated PTR-S and PTR-F glasses. The results showed that absorption in PTR-F and PTR-S glass increased significantly with increasing γ-irradiation dose, which was related to HC1, HC2, E′, L, ETC defect centers and Ag-species, and the formation of HC1, HC2, E’, and L-centers was reduced by the doping of Ag into the PTR-S glass matrix. Compared with the γ-irradiation, X-irradiation showed a similar effect. In comparison, UV-irradiation induced fewer defect centers and smaller Ag (NPs). This discrepancy could be caused by variations in photon energies.

Mechanical degradation estimation of thermosets by peak shift assessment: General approach using infrared spectroscopy

Until now, detecting weak spots in composite structures remains a key challenge in the aviation industry. The correct assessment of the load-bearing capability after structural overloading or the occurrence of barely-visible damages is particularly important to maintain structural integrity. Nonetheless, a reliable and overarching non-destructive inspection method to estimate the residual mechanical properties while covering all major damage scenarios has not been found yet. Several non-destructive techniques have been proposed to approach these challenges and are already in place for specific damage cases. However, each technique has its sources of information and therefore, limitations in practice due to a lack of generalisation. In this work, we present a concept and approach to gain access to the residual mechanical properties of a thermosetting polymer solely based on its inherent material state independent from its life-cycle history. Therefore, the material state is obtained by combining Fourier-transformed infrared spectroscopy with feature extraction algorithms based on Gaussian peak fitting. As proof of concept, tensile, creep, and cyclic tests are conducted to demonstrate this approach's advantage. A complementary theoretical investigation using quantum chemical calculations is employed to support the experimental work by identifying the investigated polymer's characteristic vibrational modes and predicting their evolution during the experiments. The results show that the quantification of molecular changes can estimate the material state and that the method is suitable to improve the understanding of the degradation processes and severity. This publication shall particularly serve as the basis for further research to study the interaction between molecular forces and material properties.

Determination of the Mono and Dibromo Derivatives Ratio Resulting from Semiconductor Bromination Using Ultraviolet-visible Absorption Spectroscopy and Gaussian Peak Fitting.

The chemical-industrial production of organic semiconductors urgently needs a cheap and fast approach to determine the components' proportion of the reaction system. In the present work, the Gaussian peak fitting method was applied to process monobromo and dibromo-substituted perylene diimide mixed solutions' ultraviolet-visible absorption curves. The functional relationship formula between the peak-intensity ratio and the component ratio is then concluded. Finally, field experiments of the perylene imide brominating reaction can be used to confirm that such a formula is able to accurately calculate the proportion of ingredients in the synthesis reaction solution system.

Monitoring the characteristics and removal of natural organic matter fractions in selected South African water treatment plants

Abstract This study used spectroscopic methods to investigate the fate and dynamics of natural organic matter (NOM) as it traverses the treatment train at three water treatment plants (WTPs) in South Africa. The character, quantity, and removability of NOM at specific treatment stages was investigated by measuring changes in dissolved organic carbon (DOC) concentration, specific ultra-violet absorbance, UV absorbance, various spectroscopic indices, and maximum fluorescence intensity levels. A novel method of identifying and quantifying fluorescent fractions by combining synchronous fluorescence spectroscopy (SFS) and Gaussian peak fitting is presented. The dynamics of NOM removal were modeled using 2D-SFS correlation spectroscopy. Humic and fulvic substances dominated coastal plants and were the most amenable for removal by coagulation as shown by Hermanus WTP (plant H), which had a 42% DOC removal at the coagulation stage. Tyrosine-like, tryptophan-like and microbial humic-like substances were degraded or transformed concurrently at plant Flag Bushiole (FB) whereas, at plant H, fulvic-like matter was transformed first followed by tyrosine-like then humic-like matter. Through 2D-SFS, this study revealed that NOM transformation was varied as a consequence of NOM character, the type and dosage of treatment chemicals used, and WTPs operational parameters.

Fast Demodulation of Fiber Bragg Grating Wavelength From Low-Resolution Spectral Measurements Using Buneman Frequency Estimation

This paper presents a fast demodulation algorithm to determine fiber Bragg grating (FBG) from spectra acquired by low wavelength resolution spectrometers. A modified and improved Buneman frequency estimation algorithm is employed in tracking FBG wavelength and eliminating FBG wavelength discontinuities in real-time wavelength demodulation calculations. The FBG demodulation algorithm was tested using a 512-element detector array spectrometer with a 156 pm/element resolution. At a 2-kHz spectrum acquisition rate, the demodulation algorithm achieved a 0.048 pm Bragg wavelength resolution. The computational efficiency and robustness of the new algorithm was compared with a Gaussian FBG peak fitting method. Our method provides a real-time demodulation scheme to track FBG wavelength using low-resolution spectrometers or tunable lasers. It has the potential to significantly reduce the cost of FBG interrogation systems that are employed in high-sensitivity and high-speed sensing applications.

A reference-beam multi-slit autocollimator built using off-the-shelf components with variable number of slits and increased sensitivity at frequencies from 1 to 100 Hz

Optical levers for precision angle measurement have the advantage of exerting only a negligible force on the object being measured. Also, in autocollimating configuration, optical levers are insensitive to longitudinal movements of the target mirror. In this article, a reference-beam multi-slit autocollimator with variable number of slits, built from cost-effective off-the-shelf components, is presented. Further, an optimized algorithm for data processing is introduced, reducing computational effort for repeated Gaussian peak fitting. In the described setup, by adjusting the number of slits, the measurement range can be increased at the cost of sensitivity, and vice versa. In the tested configuration with 28 slits, the device has a measurement range of 12 mrad, and a sensitivity in the order of nrad/Hz starting at frequencies of 0.1 Hz, with increased sensitivity compared to other recently described autocollimators at frequencies over 1 Hz.

Mpfit: a robust method for fitting atomic resolution images with multiple Gaussian peaks

The standard technique for sub-pixel estimation of atom positions from atomic resolution scanning transmission electron microscopy images relies on fitting intensity maxima or minima with a two-dimensional Gaussian function. While this is a widespread method of measurement, it can be error prone in images with non-zero aberrations, strong intensity differences between adjacent atoms or in situations where the neighboring atom positions approach the resolution limit of the microscope. Here we demonstrate mpfit, an atom finding algorithm that iteratively calculates a series of overlapping two-dimensional Gaussian functions to fit the experimental dataset and then subsequently uses a subset of the calculated Gaussian functions to perform sub-pixel refinement of atom positions. Based on both simulated and experimental datasets presented in this work, this approach gives lower errors when compared to the commonly used single Gaussian peak fitting approach and demonstrates increased robustness over a wider range of experimental conditions.

Analysis of Polyphosphate during the Enhanced Biological Phosphorus Removal process using Fourier Transform Infrared (FTIR) spectroscopy

Two enhanced biological phosphorus removal (EBPR) reactors were operated in synthetic wastewater with different Chemical Oxygen Demand/Phosphorus (COD/P) ratios. The sludge samples at different sample times were lyophilized and characterized by Fourier Transform Infrared (FTIR) spectroscopy. Results showed that the infrared spectral curves from two reactors were similar but the intensities were different at specific wavenumbers. The spectral intensities at 1260cm-1 and 890cm-1 of the sludge samples from the reactor at low COD/P ratios were relatively stronger, but those of the reactor at high COD/P ratios were relatively weaker. The principal component projection plot of FTIR spectra analyzed with principal components analysis (PCA) showed that the sludge samples at the same COD/P ratios assembled together implicating the principal component projection plot could discriminate the sludge samples from different reactor. The infrared peak near 890cm-1 was separated and integrated with Gaussian peak fitting method. The integrated areas were correlated to the polyphosphate content in the sludge. Results showed that the prediction values were in good accordance with those determined by chemical method. This work provides a new method for the recognition of polyphosphate in sludge and provides a basis for the rapid determination of polyphosphate.

The rheological, mechanical and templating effects of graphene oxide nanosheets in filled gel spun polyacrylonitrile

Polyacrylonitrile (PAN) in dimethylformamide solution containing 0.25 or 1 wt% graphene oxide (GO) was gel spun to tapes. Scanning electron microscopy of tapes showed compact staircase cross-sections hallmarking the gel spun products. Low shear rate rheometry of the tape precursors revealed a viscosity increase, while the structural viscosity indexes of dispersions dropped to 40 and 70% at high shear rates by 0.25 and 1 wt% GO inclusion, respectively. Furthermore, the sol–gel transition temperature of PAN solution was enhanced by about 2.5 and 10 °C with 0.25 and 1 wt% GO inclusion, respectively. Strain sweep test implied a gel-to-sol transition from 9 to 28% by 1 wt% GO inclusion. The experimental reinforcement coefficient corresponded the aligned Halpin–Tsai model confirming the suitable dispersion preparation route namely master batch dilution implementing strong interphase formation among the PAN chains and GO platelets. Molecular evolution analysis during air stabilization through a combined second derivative of FTIR spectra, Gaussian peak fitting represented by Isd index, indicated the initial cyclization at 290 °C followed by its enhanced rate. Final Isd was noticed to be 48% higher for the tapes containing GO nanosheets. GO inclusion not only enhanced the tape heat of stabilizations but also differentiated its proportional Isd and toughness dependency based on the heat of stabilization.

Autler-Townes splitting of ultracold cesium Rydberg atoms

Autler-Townes (A-T) splitting, known as an AC Stark effect, shows a change of an absorption/emission spectral line of a probe beam when an oscillating field is tuned in resonance with the atomic or molecular transition. The A-T splitting is observed in different three-level atoms and widely investigated in a vapor cell and in a magneto-optical trap (MOT). The A-T splitting plays an important role in the atom-based microwave electric-field measurements where a cascade three-level system involving Rydberg state is adopted. In this work, an A-T splitting is observed in an ultracold cesium Rydberg gas, which is cooled down to about 100 pK and center density is about 1010 cm-3 in a conventional MOT by using the laser cooling technology. We present the A-T spectrum in a ladder three-level atomic system involving a 34D5/2 Rydberg state. The cesium ground state (6S1/2), excited state (6P3/2) and Rydberg state (34D5/2) constitute a Rydberg three-level system. A coupling laser, locked to the Rydberg transition by using a Rydberg electromagnetically induced transparency signal that is obtained from a cesium room-temperature vapor cell, couples 6P3/2 (F'=5) 34D5/2 Rydberg transition. A weak probe laser, stabilized to a ground-state transition by using a polarization spectroscopy, is swept, covering the transition 6S1/2 (F=4) 6P3/2 (F'=5) with a double-passed acousto-optic modulator. The probe and coupling lasers are counter-propagated through the MOT center. The power of probe light is 200 pW, corresponding Rabi frequency p=21.05 MHz. During the experiment, 50 s after turning off the trapping laser, both the coupling and probe beams are switched on and last 100 s. The A-T spectrum as a function of the probe detuning is detected with a single-photon counter module detector. We use Gaussian multiple peak fitting to obtain the positions of the A-T peaks and the A-T splitting. The measured A-T splitting is proportional to the Rabi frequency of the coupling light. We numerically solve the density matrix equations to obtain the A-T spectrum, and the calculations reproduce A-T spectra well. The measured A-T splitting shows good agreement with the theoretical calculation for Rabi frequency of the coupling light c29 MHz. The A-T splitting is less than the calculation for the case of c29 MHz, the deviation is mainly attributed to the increased dephasing rate induced by the strong interaction between Rydberg atoms, whose number increases with the coupling laser Rabi frequency. In this work, the adopted method for the cascade three-level system involving Rydberg state is also suitable for -and V-type cases.

Gaussian and linear deconvolution of LC-MS/MS chromatograms of the eight aminobutyric acid isomers

Isomeric molecules present a challenge for analytical resolution and quantification, even with MS-based detection. The eight aminobutyric acid (ABA) isomers are of interest for their various biological activities, particularly γ-aminobutyric acid (GABA) and the d- and l-isomers of β-aminoisobutyric acid (β-AIBA; BAIBA). This study aimed to investigate LC-MS/MS-based resolution of these ABA isomers as their Marfey's (Mar) reagent derivatives. HPLC was able to separate three Mar-ABA isomers l-β-ABA (l-BABA), and l- and d-α-ABA (AABA) completely, with three isomers (GABA, and d/l-BAIBA) in one chromatographic cluster, and two isomers (α-AIBA (AAIBA) and d-BABA) in a second cluster. Partially separated cluster components were deconvoluted using Gaussian peak fitting except for GABA and d-BAIBA. MS/MS detection of Marfey's derivatized ABA isomers provided six MS/MS fragments, with substantially different intensity profiles between structural isomers. This allowed linear deconvolution of ABA isomer peaks. Combining HPLC separation with linear and Gaussian deconvolution allowed resolution of all eight ABA isomers. Application to human serum found a substantial level of l-AABA (13 μM), an intermediate level of l-BAIBA (0.8 μM), and low but detectable levels (<0.2 μM) of GABA, l-BABA, AAIBA, d-BAIBA, and d-AABA. This approach should be useful for LC-MS/MS deconvolution of other challenging groups of isomeric molecules.

One-pot synthesis of bicyclic polystyrene by combination of ATRP and click chemistry

A series of bicyclic polystyrenes of different molecular weights was synthesized in one-pot by atom transfer radical polymerization followed by click chemistry. The bicyclic polystyrenes were formed simultaneously with branched polystyrene impurities due to side reactions during click coupling. The pure bicyclic polystyrenes were obtained by selective precipitation. The purity of bicyclic polystyrenes before purification was determined by Gaussian multiple peak fitting from SEC trace. The bicyclic polymers were characterized by SEC, 1H NMR, and FTIR spectroscopy. Open image in new window

Measurement and Modeling of Extra-Column Effects Due to Injection and Connections in Capillary Liquid Chromatography

As column volumes continue to decrease, extra-column band broadening has become an increasingly important consideration when determining column performance. Combined contributions due to the injector and connecting tubing in a capillary LC system were measured and found to be larger than expected by Taylor-Aris theory. Variance from sigma-type and tau-type broadening was isolated from eluted peaks using the Foley-Dorsey Exponentially Modified Gaussian peak fitting model and confirmed with computational fluid dynamics. It was found that the tau-type contributions were the main cause for the excessive broadening because of poorly-swept volumes at the connection between the injector and tubing. To reduce tau-type contributions (and peak tailing), a timed pinch mode could be used for analyte injection.

Investigations on the photoluminescence spectra and its defect-related nature for the ultraviolet transmitting fluoride-containing phosphate-based glasses

Two types of fluoride-containing phosphate-based glasses were prepared under the reducing and ambient air atmosphere, respectively. And the interrelation between the micro-defects and luminescence for these glasses was investigated by studying their absorption, photoluminescence emission (PL) and excitation (PLE) spectra as well as electron spin resonance (ESR) spectra. The emission spectra under the excitation at 351nm and the excitation spectra by monitoring the emission wavelength at 433nm, 454nm, 505nm, 645nm and 780nm, together with the absorption spectra of these two types of glasses were investigated through Gaussian peak fitting method. Their photoluminescence spectra exhibit a general character with a broadband emission at around 430nm and a minor band at around 645nm. The photoluminescence excitation spectra and absorption spectra indicate that the Gaussian peak fitting of the emission spectra with the maximum at about 433, 455, 505 and 645nm, respectively, are closely associated with phosphate-related oxygen hole center defects and fluorine-related color centers. In addition, the emission and excitation spectra of the glass samples after the thermal treatment process in hydrogen atmosphere manifest that the reducing conditions promote the formation of phosphate-related oxygen hole center defects, oxygen related hole center defects and fluorine-related non-paramagnetic color centers as well as PO43− defects, while decrease the concentration level of Fe3+ and PO32− defects. The investigations on the glasses' photoluminescence properties and their changes with the glass melting and thermal treatment atmosphere will promote the further development in preparation technology of the fluoride-containing phosphate-based glasses.

Improved synthesis of bicyclic polystyrenes by ATRP and “click” reaction

A series of bicyclic polystyrenes were prepared by combining atom transfer radical polymerization and click coupling reaction. To investigate effect of experimental parameters, bicyclic polymers were prepared by changing types of ligands for click chemistry, concentration of polymers and coupling agents, feed rate of polymers and coupling agents, concentration of catalyst, and types of coupling agents. Purities of bicyclic polymers were estimated from SEC traces by Gaussian multiple peak fitting and subsequent peak integration. The purity of bicyclic polystyrene was achieved up to 78% when the reaction was conducted using CuBr/PMDETA catalyst and coupling agent having electron withdrawing group in diluted condition by slow addition of precursor polymer and coupling agent.

PIV camera response to high frequency signal: comparison of CCD and CMOS cameras using particle image simulation

We present a quantitative comparison between FlowMaster3 CCD and Phantom V9.1 CMOS cameras’ response in the scope of application to particle image velocimetry (PIV). First, the subpixel response is characterized using a specifically designed set-up. The crosstalk between adjacent pixels for the two cameras is then estimated and compared. Then, the camera response is experimentally characterized using particle image simulation. Based on a three-point Gaussian peak fitting, the bias and RMS errors between locations of simulated and real images for the two cameras are accurately calculated using a homemade program. The results show that, although the pixel response is not perfect, the optical crosstalk between adjacent pixels stays relatively low and the accuracy of the position determination of an ideal PIV particle image is much better than expected.