Determination Of Peak Positions Research Articles

Quasi-real-time range monitoring by in-beam PET: a case for 15O

A fast and reliable range monitoring method is required to take full advantage of the high linear energy transfer provided by therapeutic ion beams like carbon and oxygen while minimizing damage to healthy tissue due to range uncertainties. Quasi-real-time range monitoring using in-beam positron emission tomography (PET) with therapeutic beams of positron-emitters of carbon and oxygen is a promising approach. The number of implanted ions and the time required for an unambiguous range verification are decisive factors for choosing a candidate isotope. An experimental study was performed at the FRS fragment-separator of GSI Helmholtzzentrum für Schwerionenforschung GmbH, Germany, to investigate the evolution of positron annihilation activity profiles during the implantation of ^{14}O and ^{15}O ion beams in a PMMA phantom. The positron activity profile was imaged by a dual-panel version of a Siemens Biograph mCT PET scanner. Results from a similar experiment using ion beams of carbon positron-emitters ^{11}C and ^{10}C performed at the same experimental setup were used for comparison. Owing to their shorter half-lives, the number of implanted ions required for a precise positron annihilation activity peak determination is lower for ^{10}C compared to ^{11}C and likewise for ^{14}O compared to ^{15}O, but their lower production cross-sections make it difficult to produce them at therapeutically relevant intensities. With a similar production cross-section and a 10 times shorter half-life than ^{11}C, ^{15}O provides a faster conclusive positron annihilation activity peak position determination for a lower number of implanted ions compared to ^{11}C. A figure of merit formulation was developed for the quantitative comparison of therapy-relevant positron-emitting beams in the context of quasi-real-time beam monitoring. In conclusion, this study demonstrates that among the positron emitters of carbon and oxygen, ^{15}O is the most feasible candidate for quasi-real-time range monitoring by in-beam PET that can be produced at therapeutically relevant intensities. Additionally, this study demonstrated that the in-flight production and separation method can produce beams of therapeutic quality, in terms of purity, energy, and energy spread.

R PEAK DETERMINATION USING A WDFR ALGORITHM AND ADAPTIVE THRESHOLD

The determination of the R peak position in the ECG signal helps physicians not only to know the heart rate per minute, but also to monitor the patient’s health related to heart disease. This paper proposes a system to accurately determine the R peak position in the ECG signal. The system consists of a pre-processing block for filtering out noise using a WDFR algorithm and highlighting the amplitude of the R peak and a threshold value is calculated for determining the R peak. In this research, the MIT-BIH ECG dataset with 48 records are used for evaluation of the system. The results of the SEN, +P, DER and ACC parameters related to the system quality are 99.70%, 99.59%, 0.70% and 99.31%, respectively. The obtained performance of the proposed R peak position determination system is very high and can be applied to determine the R peak of the ECG signal measuring devices in practice.

Liquid film thickness measurements on a plate based on brightness curve analysis with acute PLIF method

Normal planar laser induced fluorescence (N-PLIF) method has been widely applied in liquid film imaging and thickness measurements in circular tubes with large curvatures, but meets great challenges in liquid film thickness measurements in circular tubes with small curvatures or at plates. An alternative method is to place both the incident laser sheet and the camera below the bottom interface of a plate, forming the acute PLIF (A-PLIF) method with an acute laser optical path and camera alignment. However, the liquid film thickness measurements based on direct imaging with the A-PLIF method are still challenged by the decrease of image contrast and indistinct interfaces. This work further explores the A-PLIF method with a novel image processing approach through both static liquid film and moving liquid film measurements. In static liquid film measurements, brightness curves along the liquid film thickness direction are extracted to compare with numerical simulation results based on ray-tracing approach, in which the laser intensity attenuation, laser sheet thickness, fluorescence spectrum and top interface reflection are considered. The comparison indicates that out-of-focus imaging is the dominant factor for the expanding of measured brightness curves. Three distinct regions, i.e. the increasing region, slowly decreasing region and rapidly decreasing region, are identified on the brightness curves and the main fluorescence source of each region is analyzed theoretically. It is concluded that the total width of the two decreasing regions shows strong correlation to the liquid film thickness, which facilitates the evaluation of liquid film thickness through peak position determination of the brightness curve and linear fitting of the rapidly decreasing region. This method is further tested in the moving liquid film thickness measurement in a cross-flow tunnel at various cross-sections, which shows that it can be applied to the liquid film imaging and thickness measurements on small curvature or flat surfaces.

GIWAXS-SIIRkit: scattering intensity, indexing and refraction calculation toolkit for grazing-incidence wide-angle X-ray scattering of organic materials

Grazing-incidence wide-angle X-ray scattering (GIWAXS) has become an increasingly popular technique for quantitative structural characterization and comparison of thin films. For this purpose, accurate intensity normalization and peak position determination are crucial. At present, few tools exist to estimate the uncertainties of these measurements. Here, a simulation package is introduced called GIWAXS-SIIRkit, where SIIR stands for scattering intensity, indexing and refraction. The package contains several tools that are freely available for download and can be executed in MATLAB. The package includes three functionalities: estimation of the relative scattering intensity and the corresponding uncertainty based on experimental setup and sample dimensions; extraction and indexing of peak positions to approximate the crystal structure of organic materials starting from calibrated GIWAXS patterns; and analysis of the effects of refraction on peak positions. Each tool is based on a graphical user interface and designed to have a short learning curve. A user guide is provided with detailed usage instruction, tips for adding functionality and customization, and exemplary files.

Overtone spectroscopy of v(C=O) stretching vibration of hexafluoroacetone: Experimental and ab initio determination of peak positions, absolute intensities, and band shapes

Infrared overtone spectra of the ν(C = O) stretching vibration (ν1) of gaseous hexafluoroacetone ((CF3)2C = O, HFA) were recorded in the spectral range of 7450-3300 cm-1 with a resolution of 0.1 cm-1. Experimental absolute IR intensities and vibrational band centers of the overtones 2ν1, 3ν1, 4ν1 of HFA were measured and compared with their ab initio counterparts, calculated by the second-order canonical vibrational perturbation theory (CVPT2). A hybrid potential energy surface (PES) was evaluated using the quantum-mechanical models MP2/cc-pVQZ for harmonic and MP2/cc-pVTZ for anharmonic parts. Cubic surfaces of dipole moment components were determined using the MP2/cc-pVTZ model. The predicted IR intensities for the first and second overtones reproduced the experimental values with a discrepancy of 6% and 9%, respectively. A weak Fermi resonance between the first overtone 2ν1 and combination tone ν1 + ν2 + ν8 was predicted. The appropriate model was employed for simulating the bands studied using: (i) the asymmetric-top vibration-rotational structure of the ν1 mode, (ii) the inhomogeneous band structure due to contributions of the vibrational states populated at the room temperature, and (iii) the homogeneous broadening of each vibration-rotation transition due to the intramolecular vibrational redistribution (IVR). The rotational and vibrational anharmonic constants were taken from the ab initio calculations, whereas the IVR data were obtained from the experimental data of Chekalin et al. (JPCA 2014, 118:955) with a time resolution of ≈100 fs. A good level of agreement of the predicted shapes of bands studied with experiment is achieved.

Calibration of Raman wavenumber in large Raman images using a mercury‐argon lamp

AbstractRaman imaging is an emerging tool for the analysis of meteorites, as it is capable of describing mineralogy, carbon composition/speciation, and crystal orientation all within a petrographic context. Adequately examining the heterogeneous composition of a meteorite often requires long image collection times on the timescale of days. However, the wavenumber calibration of the Raman spectrometer drifts over long timescales resulting in low wavenumber precision for the Raman spectra comprising a large Raman image. This decrease in wavenumber precision can compromise the analysis of geological markers that can provide important information on a meteorite sample. We examine, in detail, the change in bandwidth and wavenumber of the Raman bands and Hg–Ar emission lines in our Raman images as a function of time and laboratory temperature. To overcome the drift in calibration, we utilize a commercial WITec Raman instrument with a built‐in Hg–Ar calibration lamp to individually calibrate each spectrum in the Raman image. We show that using the Hg–Ar calibration, we can improve the wavenumber precision for the spectra in our Raman images from ~±0.15 to ~±0.05 cm−1 for Raman spectra collected over multiple days. This is important as it improves measurements of mineral chemistry, latent strain, and other features that are dependent upon accurate peak position determination. We also examine the spectral signal‐to‐noise ratio needed to minimize the wavenumber error when fitting bands to Gaussian/Lorentzian profiles. We then use our results to suggest a general method for calibrating the wavenumber of Raman spectra in large Raman images.

Detecting Fermi-level shifts by Auger electron spectroscopy in Si and GaAs

In this paper, changes in surface Fermi-level of Si and GaAs, caused by doping and cleaning, are investigated by Auger electron spectroscopy. Based on the Auger voltage contrast, we compared the Auger transition peak energy but with higher accuracy by using a more accurate analyzer and an improved peak position determination method.For silicon, a peak shift as large as 0.46 eV was detected when comparing a cleaned p-type and n-type wafer, which corresponds rather well with the theoretical difference in Fermi-levels. If no cleaning was applied, the peak position did not differ significantly for both wafer types, indicating Fermi-level pinning in the band gap.For GaAs, peak shifts were detected after cleaning with HF and (NH4)2S-solutions in an inert atmosphere (N2-gas). Although the (NH4)2S-cleaning in N2 is very efficient in removing the oxygen from the surface, the observed Ga- and As-peak shifts are smaller than those obtained after the HF-cleaning. It is shown that the magnitude of the shift is related to the surface composition. After Si-deposition on the (NH4)2S-cleaned surface, the Fermi-level shifts back to a similar position as observed for an as-received wafer, indicating that this combination is not successful in unpinning the Fermi-level of GaAs.

Multiple scattering in grazing-incidence X-raydiffraction: impact on lattice-constant determinationin thin films.

Dynamical scattering effects are observed in grazing-incidence X-ray diffraction experiments using an organic thin film of 2,2':6',2''-ternaphthalene grown on oxidized silicon as substrate. Here, a splitting of all Bragg peaks in the out-of-plane direction (z-direction) has been observed, the magnitude of which depends both on the incidence angle of the primary beam and the out-of-plane angle of the scattered beam. The incident angle was varied between 0.09° and 0.25° for synchrotron radiation of 10.5 keV. This study reveals comparable intensities of the split peaks with a maximum for incidence angles close to the critical angle of total external reflection of the substrate. This observation is rationalized by two different scattering pathways resulting in diffraction peaks at different positions at the detector. In order to minimize the splitting, the data suggest either using incident angles well below the critical angle of total reflection or angles well above, which sufficiently attenuates the contributions from the second scattering path. This study highlights that the refraction of X-rays in (organic) thin films has to be corrected accordingly to allow for the determination of peak positions with sufficient accuracy. Based thereon, a reliable determination of the lattice constants becomes feasible, which is required for crystallographic structure solutions from thin films.

EPID‐based verification of the MLC performance for dynamic IMRT and VMAT

In advanced radiotherapy treatments such as intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT), verification of the performance of the multileaf collimator (MLC) is an essential part of the linac QA program. The purpose of this study is to use the existing measurement methods for geometric QA of the MLCs and extend them to more comprehensive evaluation techniques, and to develop dedicated robust algorithms to quantitatively investigate the MLC performance in a fast, accurate, and efficient manner. The behavior of leaves was investigated in the step-and-shoot mode by the analysis of integrated electronic portal imaging device (EPID) images acquired during picket fence tests at fixed gantry angles and arc delivery. The MLC was also studied in dynamic mode by the analysis of cine EPID images of a sliding gap pattern delivered in a variety of conditions including different leaf speeds, deliveries at fixed gantry angles or in arc mode, and changing the direction of leaf motion. The accuracy of the method was tested by detection of the intentionally inserted errors in the delivery patterns. The algorithm developed for the picket fence analysis was able to find each individual leaf position, gap width, and leaf bank skewness in addition to the deviations from expected leaf positions with respect to the beam central axis with sub-pixel accuracy. For the three tested linacs over a period of 5 months, the maximum change in the gap width was 0.5 mm, the maximum deviation from the expected leaf positions was 0.1 mm and the MLC skewness was up to 0.2°. The algorithm developed for the sliding gap analysis could determine the velocity and acceleration∕deceleration of each individual leaf as well as the gap width. There was a slight decrease in the accuracy of leaf performance with increasing leaf speeds. The analysis results were presented through several graphs. The accuracy of the method was assessed as 0.01 mm for both the gap size and peak position determination. This study provides fast, easy, and accurate test methods for routine QA of the MLC performance and helps in faster troubleshooting of MLC problems in both IMRT and VMAT treatments.

Experimental determination of the Raman CH 4 symmetric stretching ( ν1) band position from 1–650 bar and 0.3–22 °C: Application to fluid inclusion studies

The position of the Raman methane (CH 4) symmetric stretching band ( ν 1) over the range 1–650 bar and 0.3–22 °C has been determined using a high-pressure optical cell mounted on a Raman microprobe. Two neon emission lines that closely bracket the CH 4 band were collected simultaneously with each CH 4 spectrum. The peak position was determined after least squares fitting using a summed Gaussian–Lorentzian method, resulting in a precision of ≈±0.02 cm −1 in peak position determination. The CH 4 ν 1 band position shifts to lower wave number with increasing pressure. At a given pressure, the band shifts to lower wave number with decreasing temperature, and the magnitude of the temperature shift increases with increasing pressure. The relationship between the Raman CH 4 ν 1 band position and temperature and pressure determined here may be used to estimate the internal pressure in natural or synthetic CH 4-bearing fluid inclusions. This information, in turn, may be used to determine the density of pure CH 4 fluid inclusions and the salinity of CH 4-bearing aqueous inclusions.

Shifted-basis technique improves accuracy of peak position determination in Fourier transform mass spectrometry

The present paper suggests a new algorithm for estimation of peak positions in FTMS spectra. It is shown theoretically and experimentally that the new technique yields superior results compared to the currently applied techniques, when the noise level is high and/or the peaks are located close to each other. Cases are presented where the deviation from the true mass could be mistaken for space charge effect, while the shift is in fact solely due to the shortcomings of the current techniques and can be corrected by applying the shifted-basis technique. In two out of three cases, this technique gave more accurate (>5 times) result compared to the conventional analysis. In the third case, where the signal was high compared to the noise, the results were comparable. The new technique can be used to achieve better mass accuracy for noisy and not well resolved spectra, and to further investigate the features of the space charge effect.

Shifted-basis technique improves accuracy of peak position determination in Fourier transform mass spectrometry

Shifted-basis technique improves accuracy of peak position determination in Fourier transform mass spectrometry

An Interactive Dry Lab Introduction to Vibrational Raman Spectroscopy Using Carbon Tetrachloride

An introduction to vibrational Raman spectroscopy is presented in a dry lab format that utilizes free software to add interactivity. Relevant IR and Raman spectra of carbon tetrachloride are systematically compared and analyzed on the basis of a broad review of general vibrational spectroscopy. Included in the discussion are the classic physical and group theory descriptions of IR and Raman spectroscopy, depolarization measurements, the application of Boltzmann analysis for sample temperature calculations, isotope effects visible under high-resolution conditions, and a full description of the Raman instrument and conditions used to acquire all spectra. The software utilized to provide interactivity allows determination of peak positions and intensities, which means data acquisition is the only experience students lack. All spectra are available on the Internet, as is the free software that allows viewing and manipulation.

Near-edge x-ray absorption fine structure and Raman characterization of amorphous and nanostructured carbon films

Amorphous and nanostructured carbon films were grown by using two different techniques: ion sputtering and cluster beam deposition. The films were studied by near-edge x-ray absorption fine structure (NEXAFS) and Raman spectroscopy. Depending on the precursors, atoms, or clusters, the films are characterized by a different sp2/sp3 ratio which influences the mechanical and the electronic properties. Due to the sensitivities of NEXAFS (local order) and Raman (medium-range order), we have characterized and compared the structure of the films over different length scales. The complementarity of NEXAFS and Raman techniques for the characterization of disordered forms of carbon is here presented and discussed. We also present an original method of NEXAFS spectra calibration allowing a better determination of peak positions.

A comparative study of elastic recoil detection analysis (ERDA), electron energy loss spectroscopy (EELS) and X-ray photoelectron spectroscopy (XPS) for structural analysis of amorphous carbon nitride films

A set of carbon and carbon nitride films has been prepared by ion-beam-assisted filtered cathodic vacuum arc deposition. The films were examined by elastic recoil detection analysis (ERDA), electron energy loss spectroscopy (EELS) and X-ray photoelectron spectroscopy (XPS). ERDA provides the stoichiometry and mass density of the samples. This study covers the range of 0 up to 29 at.% N and 2.9 g cm −3 down to 2.0 g cm −3 respectively. The carbon K-edge and the plasmon loss were examined by EELS. The C 1s and N 1s core level spectra were recorded by XPS. The main result is that for significant nitrogen contents the mass density, and hence the plasmon energy and very likely the sp 3 -fraction, is reduced considerably. The C 1s signals of the carbon nitride layers show a multi-peak structure but the peaks are rather broad and an accurate determination of peak positions is not possible. The splitting of the N 1s signal in four contributions at about 398, 400, 400.6 and 402 eV is observed only for the low density carbon nitrides. A CN x sample with a density of 2.6 g cm −3 and equal amounts of sp 2 - and sp 3 -bonded carbon shows only a single peak. We show that the components in the N 1s multi-peak structure can be related to atomic arrangements in a fully sp 2 -bonded network. In particular, the component at 398 eV does not necessarily indicate the presence of a material similar to β-C 3 N 4 .

Filtering data from a drift-chamber detector using neural networks

Abstract This paper describes the implementation of an analog neural network chip (Intel 80170NX ETANN) to filter a multi-signal read-out from flash-ADCs used in a liquid argon time projection chamber (ICARUS). The training and subsequent testing of the network is discussed in some detail. A network consisting of multiple sub-networks is proposed to perform signal filtering, determination of peak position and track finding.

Description and peak-position determination of a single X-ray diffraction profile for high-accuracy lattice-parameter measurements by the Bond method. II. Testing and choice of description

The reliability of the results of the peak-position determination by means of various approximating functions – the polynomials and shape functions considered in paper I [Gatdecka (1993). Acta Cryst. A49, 106–115] – was examined based on test calculations in which both measurement data and computer-simulated data were used. It was found that accurate peak-position determination must be based on a reasonable physical and statistical model of the diffraction profile. The statistical model is required to provide an objective criterion of the goodness of fit. The goodness of fit is a necessary but not sufficient requirement for obtaining accurate results. To provide unbiased and stable enough (independent of scanning range) results, the function to be used must, in addition, be continuous and give a good approximation to known physical models of the diffraction profile. It was proved that the use of a reasonable shape function – here, a pseudo-Voigt function with a linear (or exponential) asymmetric factor, the best of the functions considered – leads to accurate enough and highly stable results. Results obtained using polynomials, even when the goodness of fit is being carefully checked, are no more precise and are less stable and so less accurate than those obtained using the carefully selected shape function. Only in the case of a parabola – the simplest and the most preferred among polynomials – there is a possibility of reducing the bias of outcomes by an extrapolation of results obtained for various scanning ranges. However, the improvement also requires a reasonable model (here, the shape function mentioned above).

Description and peak-position determination of a single X-ray diffraction profile for high-accuracy lattice-parameter measurements by the Bond method. I. An analysis of descriptions available

The accuracy of lattice-parameter measurements is defined by the actual error of Bragg-angle determination. The total error in the angular position determined (peak position) – corresponding to the Bragg angle – depends on the experiment itself (physical and geometrical aberrations) and on the method of calculation used. The aim of this paper is to find the best method of approximation of the measurement data to ensure a given accuracy – here, 1 part in 106 – with the assumption that the technique and the method used for correcting the aberrations allow this accuracy. Considering some disadvantages of interpolation and approximation with polynomials, commonly used in practice, it is suggested the calculations are based on a model of the measured diffraction profile. In the present paper (paper I), desired properties of such a model are discussed. Various possible descriptions of the diffraction profile – including popular `shape functions' widely used in practice – are collected in a unified and standardized form and classified and analysed, with account taken of (i) physical aspects, (ii) mathematical aspects, (iii) statistical aspects and (iv) practical aspects (applications), with premises resulting from the measurement method, the Bond method [Bond (1960). Acta Cryst. 13, 814–818]. A special emphasis has been put on the best description of the moderate asymmetry characterizing the reflections from nearly perfect single crystals and on statistical properties of the model.

Determination of peak positions and areas from wide‐scan XPS spectra

AbstractIt has been found that by taking transforms of both Gaussian and Lorentzian line shapes into polynomial representations, it is possible in many instances to determine peak position, peak intensity and the full‐width at half‐maximum (FWHM) from wide‐scan XPS spectra that have a low number of data points per electron‐volt. This approach was tested with several samples, ranging from an insulator, Al2O3, to an excellent conductor, sputter‐cleaned gold. Several data sets were constructed from narrow‐scan spectra with points selected about 1 eV apart to simulate wide‐scan spectra. Then, comparisons were made between values calculated with a non‐linear least‐squares fit that used all of the data points from a given spectrum, and the polynomial procedure with the simulated wide‐scan data. It was found that the peak positions usually agreed to within 0.1 eV between the methods. The FWHM and intensities agreed to ∼20%. The area ratios usually were within ∼10%. Comparisons between actual and simulated wide‐scan data showed similar area ratio agreement. However, there appeared to be a systematic difference in the peak position of ∼0.5 eV, which was due to the spectrometer used in this study. Thus, in many cases, estimates of the relative atomic amounts can be made with those results from the polynomial procedure that would be comparable to those obtained from non‐linear least‐squares analysis of narrow‐scan data. The effects of such factors as baseline, overlapping peaks, computational techniques and line shape on the use of the polynomial method are discussed also.

Three dimensional strain measurements with x-ray energy dispersive spectroscopy

A feasibility study was performed to show the ability of energy dispersive x-ray diffraction (EDXRD) to measure three dimensional strain distributions in thick industrial materials. Photon energies up to 130 keV were used to guarantee penetration through the sample and curve fitting techniques applied to peak position determination. This system was used to measure the strain gradient through the thickness of a 9.5 mm thick cantilevered steel bar.