Spectral Peak Height Research Articles

Isotopic analysis of uranium at the picogram level with single-shot laser induced breakdown spectroscopy

Uranium was measured by laser induced breakdown spectroscopy (LIBS) with a limit of detection of 1.3 picograms with spectral-peak height as the analytical parameter, which shows an improvement of several orders of magnitude compared to other reports in the literature. The improvement is a result of optimizing the choice of the U analytical line, the system hardware, and the light collection and detection efficiency. The research established properties of U line emission (intensity, signal-to-background ratio, isotopic splitting, and spectral interferences) to select an optimum wavelength for analysis. The samples were mock particles from dried, monodispersed U solution droplets (∼65 pL in volume) deposited on Si wafers. LIBS emission spectra from several 235U-enriched samples were measured to demonstrate the performance for isotopic analysis. For isotopic measurements, two masses for total U, 100 pg and 325 pg, were studied. The 235U: 238U isotopic ratio was obtained by peak fitting the LIBS spectra without requiring calibration with the use of enriched standards. Depending on the total U mass and the 235U enrichment, typical relative standard deviations of the isotopic analysis ranged from several percent down to about 1%. Further, the developed method and the reported analytical performance were all based on single-shot LIBS. Overall, the study highlights the potential of LIBS as a robust and sensitive technique for isotopic analysis of U-containing particles.

Global sensitivity analysis of a semi-submersible floating wind turbine using a neural network fitting method

The stochastic platform motions of a floating offshore wind turbine (FOWT) significantly affect its load characteristics and power production. It is vital to understand the influence of various input parameters on the global performance of an FOWT to ensure structural safety and power efficiency. This study investigates the influence of key design parameters related to metocean conditions and natural periods of platform motions on wind turbine performance. A global sensitivity analysis (GSA) framework is proposed to map the input-output relation of a 4-MW semi-submersible FOWT. This framework uses fully-coupled numerical analysis and neural network fitting (NNF). Several important parameters are selected, including natural periods of the platform motions, mean wind speed, turbulence intensity, wave spectral peak period and significant wave height. Results demonstrate that natural periods of platform motions and wave conditions have a significant influence on the dynamic responses of the FOWT. Furthermore, statistical analysis reveals that severe sea states and low natural periods of platform motions can increase the operation cycles of the blade pitch system by 20%. The use of NNF method effectively increases the efficiency of the GSA by at least forty times. The proposed framework can be applied to other areas of FOWTs.

Effect of the sudden change of ambient atmosphere on free radicals in coal body by CO2 fire prevention gas injection

ABSTRACT The coal body’s gas environment transforms during the CO2 fire prevention procedure from an oxygenated ambience to a CO2 gas ambience, which in turn prevents the coal body from continuously oxidizing. To investigate the effect of sudden changes in the gas environment to which the coal body is exposed on the microscopic group reactions, the free radical parameters such as ESR in situ spectra, line widths, g-factors, and free radical concentrations of the coal bodies during the gas atmosphere transition at different temperature moments were measured. The findings are as follows: as the injection temperature point for CO2 rises, the spectral peak height increases, and the paramagnetic center of coal shifts at lower temperature in CO2 atmosphere than in dry air atmosphere. After the abrupt change of gas environment, free radical levels first decrease and subsequently rise. Furthermore, the general development rate of free radicals can be slowed down by injecting CO2 at lower temperatures. Meanwhile, at lower temperatures, the higher the temperature point of the minimum g value is, the smaller the maximum g value is. Changes in a gas atmosphere, sudden decrease in line width of ESR spectra of coal bodies, and the line width finally stabilizes around 0.45. CO2 injection at 70°C has the best inhibitory effect on free radicals.

Experimental Study of White Heat Line Formation in Burned Bone Using Fourier Transform Infrared Spectroscopy

In anthropological analysis of burned bone, the presence of a white heat line (WHL) aids in determining a bone’s physical condition prior to burning, distinguishing between those burned fleshed or wet versus dry, making this thermal signature an important source of information regarding the relative timing of burning. While the relationship between WHLs and a bone’s physical condition has been studied, there is a lack of research concerning WHL chemical composition. The present study assessed the composition of WHLs that form on burned bone using Fourier Transform Infrared Spectroscopy (FTIR), including the effects of soft tissue and retention of bone’s organic material on a WHL’s development and appearance. Experimental remains consisted of isolated bones from pig (Sus scrofa), sheep (Ovis aries), white-tailed deer (Odocoileus virginianus), and elk (Cervus elaphus) in five physical conditions: fleshed, defleshed/very wet, partially wet, dry, and dry/soaked. Chemical composition was analyzed using spectral peak heights of the carbonate (CO3) ν3 (1415 cm-1), phosphate (PO4) ν3 (1035 cm-1), and amide I (1660 cm-1) vibrational bands.
 WHLs formed on 8 of 16 bones burned fleshed (50%) compared to 8 of 27 defleshed/very wet (29.6%). The partially wet, dry, and dry/soaked sample groups did not develop a WHL. Results indicate WHLs that formed on fleshed bone contained an increased amount of CO3, PO4, and amide I versus unburned controls. In contrast, WHLs that formed on defleshed/very wet bone contained decreased amounts. Additional research is needed to explore the exact mechanisms causing the formation of WHLs and their physical appearance.

Alpha particles detection using P3HT conducting polymer-coated DAM-ADC

For radiation detection applications, Raman analysis, photoluminescence (PL), and UV–Vis spectroscopy are thoroughly studied using the DAM-ADC (diallyl maleate - allyl diglycol carbonate) detector coated with poly(3-hexylthiophene-2,5-diyl) (P3HT) conducting polymer. A thin Am-241 disk that emits alpha particles with an activity of 340 kBq was used to irradiate the surface of DAM-ADC detector. After irradiation with different fluencies of alpha particles, the spectroscopic analysis confirms that the effects of alpha particles on the DAM–ADC detector coated by P3HT conducting polymer are detectable in Raman spectra and PL spectral emission. Furthermore, the photoluminescence and UV–Vis responses of the DAM–ADC samples are influenced by the track density of the irradiated samples. For Raman, UV–vis, and PL analysis, the spectral peak heights and the area under the peaks show a correlation with the fluencies of alpha particles. For the irradiated samples, all the techniques displayed major spectral alterations, suggesting that they could be used to establish sensitive alpha particle detection methods. For both direct and indirect transitions, the optical band gap was found to decrease with increasing the alpha fluencies.

Numerical Investigations on Wave Remote Sensing from Synthetic X-Band Radar Sea Clutter Images by Using Deep Convolutional Neural Networks

X-band marine radar is an effective tool for sea wave remote sensing. Conventional physical-based methods for acquiring wave parameters from radar sea clutter images use three-dimensional Fourier transform and spectral analysis. They are limited by some assumptions, empirical formulas and the calibration process while obtaining the modulation transfer function (MTF) and signal-to-noise ratio (SNR). Therefore, further improvement of wave inversion accuracy by using the physical-based method presents a challenge. Inspired by the capability of convolutional neural networks (CNN) in image characteristic processing, a deep-learning inversion method based on deep CNN is proposed. No intermediate step or parameter is needed in the CNN-based method, therefore fewer errors are introduced. Wave parameter inversion models were constructed based on CNN to inverse the wave’s spectral peak period and significant wave height. In the present paper, the numerically simulated X-band radar image data were used for a numerical investigation of wave parameters. Results of the conventional spectral analysis and CNN-based methods were compared and the CNN-based method had a higher accuracy on the same data set. The influence of training strategy on CNN-based inversion models was studied to analyze the dependence of a deep-learning inversion model on training data. Additionally, the effects of target parameters on the inversion accuracy of CNN-based models was also studied.

Determining the Liquid Phase Equilibrium Speciation of the CO2–MEA–H2O System Using a Simplified in Situ Fourier Transform Infrared Method

Monoethanolamine (MEA) is commonly used to capture CO2 from combustion gases. A simple, fast, and accurate Fourier transform infrared method, via attenuated total reflectance, was developed to determine the liquid phase equilibrium speciation in related CO2–MEA–H2O systems. Data were collected in a batch reactor at 1 atm pressure, temperatures of 20, 25, and 30 °C, and CO2 loadings of 0–0.6 mol CO2/mol MEA. The main advantage of the method is that only the carbamate (RNHCOO–) spectral peak height and CO2 loading are required to obtain the concentration profiles of the most prominent species present at reaction equilibrium. The profiles obtained were in good agreement (rmsd ∼ 10–3) with the published data from other spectroscopic and titrimetric techniques as well as the predictions of a widely accepted vapor–liquid equilibrium model. The method has the potential to be developed into an in situ method of analysis for real time data acquisition from CO2 sequestration systems using aqueous MEA solvents.

Influence of soil γ-irradiation and spiking on sorption of p,p′-DDE and soil organic matter chemistry

The fate of organic chemicals and their metabolites in soils is often investigated in model matrices having undergone various pre-treatment steps that may qualitatively or quantitatively interfere with the results. Presently, effects associated with soil sterilization by γ-irradiation and soil spiking using an organic solvent were studied in one freshly spiked soil (sterilization prior to contamination) and its field-contaminated (sterilization after contamination) counterpart for the model organic compound 1,1-Dichloro-2,2-bis(4-chlorophenyl)ethene (p,p′-DDE). Changes in the sorption and potential bioavailability of spiked and native p,p′-DDE were measured by supercritical fluid extraction (SFE), XAD-assisted extraction (XAD), and solid-phase microextraction (SPME) and linked to qualitative changes in soil organic matter (SOM) chemistry measured by diffuse reflectance infrared Fourier-transform (DRIFT) spectroscopy. Reduced sorption of p,p´-DDE detected with XAD and SPME was associated more clearly with spiking than with sterilization, but SFE showed a negligible impact. Spiking resulted in an increase of the DRIFT-derived hydrophobicity index, but irradiation did not. Spectral peak height ratio descriptors indicated increasing hydrophobicity and hydrophilicity in pristine soil following sterilization, and a greater reduction of hydrophobic over hydrophilic groups as a consequence of spiking. In parallel, reduced sorption of p,p´-DDE upon spiking was observed. Based on the present samples, γ-irradiation appears to alter soil sorptive properties to a lesser extent when compared to common laboratory processes such as spiking with organic solvents.

Hyperspectral Features of Oil-Polluted Sea Ice and the Response to the Contamination Area Fraction.

Researchers have studied oil spills in open waters using remote sensors, but few have focused on extracting reflectance features of oil pollution on sea ice. An experiment was conducted on natural sea ice in Bohai Bay, China, to obtain the spectral reflectance of oil-contaminated sea ice. The spectral absorption index (SAI), spectral peak height (SPH), and wavelet detail coefficient (DWT d5) were calculated using stepwise multiple linear regression. The reflectances of some false targets were measured and analysed. The simulated false targets were sediment, iron ore fines, coal dust, and the melt pool. The measured reflectances were resampled using five common sensors (GF-2, Landsat8-OLI, Sentinel3-OLCI, MODIS, and AVIRIS). Some significant spectral features could discriminate between oil-polluted and clean sea ice. The indices correlated well with the oil area fractions. All of the adjusted R2 values exceeded 0.9. The SPH model1, based on spectral features at 507–670 and 1627–1746 nm, displayed the best fitting. The resampled data indicated that these multi-spectral and hyper-spectral sensors could be used to detect crude oil on the sea ice if the effect of noise and spatial resolution are neglected. The spectral features and their identified changes may provide reference on sensor design and band selection.

Points, vectors, linear independence and some introductory linear algebra

Most of the previous articles have focused on the application of statistical methods, especially the notion of probability and distributions. However, many chemometricians also like to think about data as points in multidimensional space, and to truly understand multivariate concepts, we need also to appreciate this way of thinking. A point can be represented by a set of numbers, usually arranged in a column, but sometime as a row. Some examples are in Figure 1. These numbers can be anything, and do not, for example, have to represent probabilities. For our purposes, they might represent the concentration of different trace elements in an ancient obsidian arrowhead or the concentration of ingredients in a pharmaceutical preparation. They can be visualized as corresponding to points in multidimensional space, where the numbers are the coordinates in this space. They can either be represented as a column of numbers where the number of rows represents the dimensionality of the space or a row. As an example, can be used to represent a point in a two-dimensional space or in a plane, as illustrated in Figure 2. Our human visual system is limited to perception in a maximum of three dimensions, so if there are more than three numbers, the space is an imagined one. The concept of linear independence of vectors is different to the statistical concept of independence. Many people have come across the concept of a vector from physics and mechanics textbooks, which has both a direction and a length. Most statisticians and mathematicians define a vector differently and use it to represent a point. These in fact correspond to two different but related definitions. A good article can be found online 1. The statistical definition of a vector is also called a position vector, which can be represented by a line from the origin to the point of interest. The vector is illustrated in Figure 2. In most of chemometrics, we use the term vector to refer to a position vector, which definition we will use in the succeeding text. Statisticians often use the concept of points and vectors interchangeably, unlike physicists. Linear algebra is a vast area, first formally described in a modern recognizable form by Hermann Grassmann in 1844 2. An excellent text, which is available online, is by Jim Hefferon 3 for the enthusiasts, and goes into significant detail. A major application is to vector operations. There are many ways of introducing the concept of linear independence—some are geometric, some involve simultaneous equations and some matrix algebra. However, understanding about whether vectors are linearly independent or not is a crucial concept in chemometrics. Each vector might represent, for example, the concentrations of compounds in a series of (chemical) samples or the spectral peak heights in a number of spectra. This concept differs from the statistical concept of independence, and we will see how it relates to other common properties of vectors in the next article.

Photoluminescence detection of alpha particle using DAM-ADC nuclear detector

The photoluminescence (PL) and UV–vis spectral analysis of DAM-ADC (diallyl maleate: DAM, polyallyl diglycol carbonate: ADC) nuclear detector are demonstrated for the first time. The DAM-ADC surfaces were exposed to thin 241Am disk source that emits alpha particles with activity 333kBq. It is found that the track density of the irradiated samples remarkably influences the PL characteristics of the DAM-ADC detector. The spectral peak heights and the integrated intensities under the peaks exhibit linear correlations with correlation coefficient R2=0.9636 and 0.9806, respectively for different alpha particle fluences ranging from 8.16–40.82×107particles/cm2. Additionally, a correlation coefficient R2=0.9734 was achieved for the UV–vis spectral analysis. The linear fitting functions, along with the corresponding fitting parameters were evaluated in each case. Both the PL and the UV–vis data of the irradiated DAM-ADC samples showed considerable spectral differences, and hence they would be used to offer sensitive approaches for alpha particle detection.

Using non-invasive molecular spectroscopic techniques to detect unique aspects of protein Amide functional groups and chemical properties of modeled forage from different sourced-origins

The non-invasive molecular spectroscopic technique-FT/IR is capable to detect the molecular structure spectral features that are associated with biological, nutritional and biodegradation functions. However, to date, few researches have been conducted to use these non-invasive molecular spectroscopic techniques to study forage internal protein structures associated with biodegradation and biological functions. The objectives of this study were to detect unique aspects and association of protein Amide functional groups in terms of protein Amide I and II spectral profiles and chemical properties in the alfalfa forage (Medicago sativa L.) from different sourced-origins. In this study, alfalfa hay with two different origins was used as modeled forage for molecular structure and chemical property study. In each forage origin, five to seven sources were analyzed. The molecular spectral profiles were determined using FT/IR non-invasive molecular spectroscopy. The parameters of protein spectral profiles included functional groups of Amide I, Amide II and Amide I to II ratio. The results show that the modeled forage Amide I and Amide II were centered at 1653cm−1 and 1545cm−1, respectively. The Amide I spectral height and area intensities were from 0.02 to 0.03 and 2.67 to 3.36 AI, respectively. The Amide II spectral height and area intensities were from 0.01 to 0.02 and 0.71 to 0.93 AI, respectively. The Amide I to II spectral peak height and area ratios were from 1.86 to 1.88 and 3.68 to 3.79, respectively. Our results show that the non-invasive molecular spectroscopic techniques are capable to detect forage internal protein structure features which are associated with forage chemical properties.

Structural and optical investigation on alpha particle irradiated CR-39 surface coated by MEH-PPV conducting polymer

Photoluminescence and UV–Vis spectral evaluation of a poly allyl diglycol carbonate (CR-39) detector coated by poly(2-methoxy-5-(2-ethyl-hexyloxy)-1,4-phenylene-vinylene) (MEH-PPV) conducting polymer are demonstrated. The CR-39 surfaces were exposed to thin 241Am disk source that emits alpha particles with activity 333kBq. Surface modification of the detector by MEH-PPV was acquired by a simple dip coating process. Our findings revealed that the spectroscopic analysis using FTIR is insensitive approach to detect the induced modifications in the irradiated samples. Additionally, the track density of the irradiated samples affects significantly the photoluminescence and UV–Vis responses of the CR-39 samples. The spectral peak heights and the integrated intensities under the peaks exhibit linear correlations (correlation coefficient R2=0.9904 to 0.9968) with the fluence of alpha particles. The linear fitting functions together with the corresponding fitting parameters were evaluated. Both techniques exhibited remarkable spectral differences for the irradiated samples, and hence they could be employed to provide sensitive methods for alpha particle detection. Results of sample fabrication and modification, along with structural and optical evaluation are addressed and thoroughly discussed.

Frequency-domain order parameters for the burst and spike synchronization transitions of bursting neurons

We are interested in characterization of synchronization transitions of bursting neurons in the frequency domain. Instantaneous population firing rate (IPFR) [Formula: see text], which is directly obtained from the raster plot of neural spikes, is often used as a realistic collective quantity describing population activities in both the computational and the experimental neuroscience. For the case of spiking neurons, a realistic time-domain order parameter, based on [Formula: see text], was introduced in our recent work to characterize the spike synchronization transition. Unlike the case of spiking neurons, the IPFR [Formula: see text] of bursting neurons exhibits population behaviors with both the slow bursting and the fast spiking timescales. For our aim, we decompose the IPFR [Formula: see text] into the instantaneous population bursting rate [Formula: see text] (describing the bursting behavior) and the instantaneous population spike rate [Formula: see text] (describing the spiking behavior) via frequency filtering, and extend the realistic order parameter to the case of bursting neurons. Thus, we develop the frequency-domain bursting and spiking order parameters which are just the bursting and spiking "coherence factors" [Formula: see text] and [Formula: see text] of the bursting and spiking peaks in the power spectral densities of [Formula: see text] and [Formula: see text] (i.e., "signal to noise" ratio of the spectral peak height and its relative width). Through calculation of [Formula: see text] and [Formula: see text], we obtain the bursting and spiking thresholds beyond which the burst and spike synchronizations break up, respectively. Consequently, it is shown in explicit examples that the frequency-domain bursting and spiking order parameters may be usefully used for characterization of the bursting and the spiking transitions, respectively.

渤海湾春季水体光谱特征分析

基于2011年5月渤海湾典型站点的CTD观测数据和实测光谱数据分析了渤海湾的水体光谱特性。通过对比实测站位水体光谱和温度、盐度、密度、光合有效辐射和叶绿素浓度在水体中的分布状况，分析了海洋环境要素对水体光谱特性的影响。结果表明在510~620 nm光谱范围内，水体光谱辐射峰的高度由叶绿素浓度和光合有效辐射共同作用决定；在380~440 nm和705~800 nm波长范围水体光谱辐射峰的高度不仅受叶绿素浓度和光合有效辐射影响，还受其他环境要素影响。 Based on the CTD data and the measured spectral data of Bohai Bay in May, 2011, the water spec-tral characteristics of typical survey stations are analyzed. In this paper, the effects of marine en-vironmental elements on the spectral properties of the water body are analyzed by comparing water spectra and the distribution of temperature, salinity, density, photosynthetic active radiation and chlorophyll concentration of Bohai Bay. The results showed that the water body spectral radiation peak height is determined by the chlorophyll concentration and photosynthetic active radiation interaction in the 510 - 620 nm spectral range, but it is determined not only by the chlo-rophyll concentration and photosynthetic active radiation interaction, but also by other environ-mental factors in the 380 - 440 nm and 705 - 800 nm spectral range.

Dielectric barrier discharge micro-plasma emission source for the determination of lead in water samples by tungsten coil electro-thermal vaporization

In this study, a fast and simple approach to directly determinate lead in water samples by a low power dielectric barrier discharge (DBD) excitation source was developed using tungsten coil electro-thermal vaporization (WC ETV) for liquid microsample introduction. A 20μL sample was dropped onto the WC, and then the sample went through the drying, pyrolysis, subsequently the analyte was vaporized and swept directly into the dielectric barrier discharge micro-plasma for emission, and the whole process took only 3min. The effects of operating parameters such as plasma gas flow rate, plasma input voltage, pyrolysis current, vaporization current and interferences from concomitant elements were investigated. Under the optimal conditions, the limit of detection (LODs, 3σ) was calculated to be 7.7μgL−1. Repeatability, expressed as the relative standard deviation of the spectral peak height, was 4.6% (n=11) for 0.1mgL−1 lead standard solution. The proposed method was successfully applied to the determinations of Pb in water samples.

Evaluation of a new dielectric barrier discharge excitation source for the determination of arsenic with atomic emission spectrometry

A low power dielectric barrier discharge excitation source was developed to determine arsenic in a cost-effective manner. Arsenic in water was reduced to AsH₃ by hydride generation (HG), which was transported to the miniature dielectric barrier discharge (DBD) excitation source for excitation and optical detection at As 193.7 nm atomic line. The DBD source consists of a quartz tube, a tungsten rod electrode, and a copper coil electrode. The main operation parameters and the potential interferences affecting the determination were investigated. The detection limit for arsenic with the proposed DBD-AES was 4.8 μg L(-1) when the HG products were dried with concentrated H₂SO₄ before introducing to DBD. Repeatability, expressed as the relative standard deviation of the spectral peak height, was 2.8% (n=11) for 0.1 mg L(-1) arsenic solution. The proposed method was successfully applied to the determinations of certified reference material (GBW08605) and nature water samples.

Mutual conversion of bulk and surface acoustic waves in gratings of finite length on half-infinite substrates. II. FE analysis of bulk wave generation

The paper studies numerically the bulk acoustic wave generation by the surface acoustic wave propagating across a grating created on the surface of an elastically anisotropic half-infinite substrate. The computations are fully based on the finite element method. Applying the discrete Fourier transformation to the displacement field found inside the substrate and using an orthogonality relation valid for plane modes we determine separately the spacial spectrum of the quasi longitudinal and the quasi transverse bulk waves, that is, the dependence of the amplitudes of these waves on the tangential component of the wave vector. The dependence is investigated of the central spectral peak height and shape on the frequency of the incident surface wave as well as on the thickness, the width, and the number of strips forming the grating. In particular, it is found that under certain conditions the central peak can be approximated fairly precisely by the central peak of a sinc-function describing the spectrum of the bounded acoustic beam of rectangular shape and of width equal to the length of the grating.

Relation between luminescence and open-circuit voltage in Cu(In,Ga)Se2 solar cells

We report on comparative electroluminescence and photoluminescence measurements on Cu(In,Ga)Se2 solar cells and demonstrate that the spectral peak value or the integrated luminescence spectrum may not always reflect the photovoltaic “quality” in terms of open-circuit voltage. Spectra from Cu(In,Ga)Se2 samples may have a comparable quasi-Fermi level splitting but a different spectral width or peak height, determined by the different sub-gap absorption properties. It is suggested that a more reliable evaluation of luminescence spectra should also consider the analysis in the high-energy spectral range which reflects the quasi-Fermi level splitting and which is shown to better correlate with the open-circuit voltage.

Observation of Picometer Vertical Emittance with a Vertical Undulator

Using a vertical undulator, picometer vertical electron beam emittances have been observed at the Australian Synchrotron storage ring. An APPLE-II type undulator was phased to produce a horizontal magnetic field, which creates a synchrotron radiation field that is very sensitive to the vertical electron beam emittance. The measured ratios of undulator spectral peak heights are evaluated by fitting to simulations of the apparatus. With this apparatus immediately available at most existing electron and positron storage rings, we find this to be an appropriate and novel vertical emittance diagnostic.