Baseline Correction Procedure Research Articles

Baseline Correction of Ground Motions for Linearly Detrended Accelerograms

ABSTRACT By revisiting the accelerograms from 42 strong-motion stations in Hualien County that recorded the 2018 Mw 6.4 Hualien earthquake, we identified that the released “raw accelerograms” were linearly detrended to remove baselines. Baseline correction for these linearly detrended accelerograms is challenging, because the baseline drift patterns are more complex than typically recognized ones. To deal with this problem, here we propose a jerk correction pattern in addition to our previously proposed tilt correction pattern and cumulative correction pattern. The modified baseline correction procedure corrects all 126 accelerograms for three directions of the 42 strong-motion stations. The recovered ground displacements are consistent with geodetic measurements, demonstrating complex surface deformations in the close vicinity of the Milun fault.

ISREA: An Efficient Peak-Preserving Baseline Correction Algorithm for Raman Spectra.

A critical step in Raman spectroscopy is baseline correction. This procedure eliminates the background signals generated by residual Rayleigh scattering or fluorescence. Baseline correction procedures relying on asymmetric loss functions have been employed recently. They operate with a reduced penalty on positive spectral deviations that essentially push down the baseline estimates from invading Raman peak areas. However, their coupling with polynomial fitting may not be suitable over the whole spectral domain and can yield inconsistent baselines. Their requirement of the specification of a threshold and the non-convexity of the corresponding objective function further complicates the computation. Learning from their pros and cons, we have developed a novel baseline correction procedure called the iterative smoothing-splines with root error adjustment (ISREA) that has three distinct advantages. First, ISREA uses smoothing splines to estimate the baseline that are more flexible than polynomials and capable of capturing complicated trends over the whole spectral domain. Second, ISREA mimics the asymmetric square root loss and removes the need of a threshold. Finally, ISREA avoids the direct optimization of a non-convex loss function by iteratively updating prediction errors and refitting baselines. Through our extensive numerical experiments on a wide variety of spectra including simulated spectra, mineral spectra, and dialysate spectra, we show that ISREA is simple, fast, and can yield consistent and accurate baselines that preserve all the meaningful Raman peaks.

Fitting algorithms and baseline correction influence the results of non-invasive in vivo quantitation of 2-hydroxyglutarate with 1 H-MRS.

1 H-MRS enables non-invasive detection of 2-hydroxyglutarate (2-HG), an oncometabolite accumulating in gliomas carrying mutations in the isocitrate dehydrogenase (IDH) genes. Reliable 2-HG quantitation requires reproducible post-processing, deployment of fitting algorithms and quantitation methods. We prospectively enrolled 38 patients with suspected or recently diagnosed gliomas (IDH mutated n=26). The MRI protocol included a 1 H single voxel PRESS sequence with volumes of usually 8mL or more (20×20×20mm3 ) at TE =97ms and 180° pulse spacing. Our aim was to evaluate the reliability of 2-HG quantitation comparing two frequently used software tools and their respective options of baseline correction (jMRUI with the time domain methods AQSES and QUEST, and LCModel, which analyzes the frequency domain data). For AQSES, degrees of freedom for baseline correction constrains were varied. For LCModel, baseline correction was obtained with and without correction of the unknown background term (predefined macromolecules, lipids). Tissue concentrations were calculated based on the phantom replacement method. Quantitation of 2-HG levels showed similar mean 2-HG tissue concentrations for IDH mutated tumors (2.65mM, range 3.06-2.20) for all methods. Bland-Altman plots (difference plots) did not reveal a systematic bias (fixed bias) for any of the algorithms tested, and we were able to show a significant correlation regarding 2-HG concentration at the same echo time with few statistical outliers (parametric correlation). However, evaluation of outliers suggested that in vivo quantitation of 2-HG is affected not only by the fitting domain (time or frequency), but also by the baseline correction, which is a major contributing factor to the result of 2-HG fitting. Clinical application of 2-HG quantitation as a prognostic or predictive biomarker, particularly in multicenter trials, requires standardized use of fitting methods and baseline correction procedures.

Estimating complicated baselines in analytical signals using the iterative training of Bayesian regularized artificial neural networks

The present work deals with the development of a new baseline correction method based on the comparative learning capabilities of artificial neural networks. The developed method uses the Bayes probability theorem for prevention of the occurrence of the over-fitting and finding a generalized baseline. The developed method has been applied on simulated and real metabolomic gas-chromatography (GC) and Raman data sets. The results revealed that the proposed method can be used to handle different types of baselines with cave, convex, curvelinear, triangular and sinusoidal patterns. For further evaluation of the performances of this method, it has been compared with benchmarking baseline correction methods such as corner-cutting (CC), morphological weighted penalized least squares (MPLS), adaptive iteratively-reweighted penalized least squares (airPLS) and iterative polynomial fitting (iPF). In order to compare the methods, the projected difference resolution (PDR) criterion has been calculated for the data before and after the baseline correction procedure. The calculated values of PDR after the baseline correction using iBRANN, airPLS, MPLS, iPF and CC algorithms for the GC metabolomic data were 4.18, 3.64, 3.88, 1.88 and 3.08, respectively. The obtained results in this work demonstrated that the developed iterative Bayesian regularized neural network (iBRANN) method in this work thoroughly detects the baselines and is superior over the CC, MPLS, airPLS and iPF techniques. A graphical user interface has been developed for the suggested algorithm and can be used for easy implementation of the iBRANN algorithm for the correction of different chromatography, NMR and Raman data sets.

Validation of a correction procedure for removing the optical effects from transmission spectra of thin films on substrates

Transmission spectra of thin films on double side polished substrates feature a quasi sinusoidal baseline superimposed onto the true absorption spectra of the thin film. The quasi sinusoidal baseline is due to strong interference from multiple reflections within the film and can directly affect the relative degree of the measured absorption in the film. In a previous article [S. W. King and M. Milosevic, J. Appl. Phys. 111, 073109 (2012)], we described a method for the removal of these optical effects from infrared transmission spectra. This method renormalizes the spectrum and removes modulations imprinted onto the absorption by interference fringes. Here, we use simulated spectra for a model material to explicitly validate that the proposed correction procedure accurately extracts the pure absorption coefficient of the thin film and is not an ad hoc baseline correction procedure.

Improved Velocity and Displacement Time Histories in Frequency Domain Spectral-Matching Procedures

Existing spectral-matching techniques in the frequency domain distort the displacement time history of the ground motions. In the time domain spectral- matching procedures, scale functions (wavelets) are additive and, with an appropriate scale functional form, extra displacement will not be imposed to the record. However, matching in the frequency domain with a multiplicative scale function applied to the Fourier spectrum requires a special attention in the matching process to have control on the displacement time history. This study shows that thevelocity value at the end of the record is not affected by the Fourier amplitude spectrum scaling, but the displace- ment may linearly increase (or decrease) boundlessly. Two numerical solutions are proposed to solve the displacement drift problem in the frequency domain. Following the proposed frequency domain baseline correction procedure, one does not need to perform baseline correction in the time domain after completing the spectral matching. As a result, acceleration, velocity, and displacement time histories will remain fully compatible, and the boundary conditions of the velocity and displacement time histories will be preserved. The proposed procedure is not limited to spectral-matching methods and can be used with any general filtering process to retain the final dis- placement of the record. The possibility of applying a zero-padding technique to the spectral-matching filter is also discussed. It is shown that applying an appropriate window along with the zero-padding technique can lead to a reasonable displacement time history. The proposed procedures can be easily added to the existing or new frequency domain spectral-matching algorithms without significantly disrupting the spectral-matching process.

An automatic scheme for baseline correction of strong-motion records in coseismic deformation determination

Coseismic deformation can be determined from strong-motion records of large earthquakes. Iwan et al. (Bull Seismol Soc Am 75:1225–1246, 1985) showed that baseline corrections are often required to obtain reliable coseismic deformation because baseline offsets lead to unrealistic permanent displacements. Boore (Bull Seismol Soc Am 91:1199–1211, 2001) demonstrated that different choices of time points for baseline correction can yield realistically looking displacements, but with variable amplitudes. The baseline correction procedure of Wu and Wu (J Seismol 11:159–170, 2007) improved upon Iwan et al. (Bull Seismol Soc Am 75:1225–1246, 1985) and achieved stable results. However, their time points for baseline correction were chosen by a recursive process with an artificial criterion. In this study, we follow the procedure of Wu and Wu (J Seismol 11:159–170, 2007) but use the ratio of energy distribution in accelerograms as the criterion to determine the time points of baseline correction automatically, thus avoiding the manual choice of time points and speeding up the estimation of coseismic deformation. We use the 1999 Chi-Chi earthquake in central Taiwan and the 2003 Chengkung and 2006 Taitung earthquakes in eastern Taiwan to illustrate this new approach. Comparison between the results from this and previous studies shows that our new procedure is suitable for quick and reliable determination of coseismic deformation from strong-motion records.

Unravelling in vitro variables of major importance for the outcome of mass spectrometry-based serum proteomics

The use of mass spectrometry (MS) for analysing low-molecular weight proteins and peptides from biological fluids has a great, yet not fully realized, potential for biomarker discovery. To prune MS-data as much as possible for non-relevant non-biological variation the development of standardized protocols for handling and processing the samples before MS and adjusting data after MS to compensate for method-induced variability are warranted. This calls for knowledge about how different variables contribute to MS-based proteome analyses. In addition, identification of the peptides involved in pre-analytical variation will be helpful in evaluating the clinical significance of predictive models derived from MS data. Using human sera, extraction by weak cation-exchange magnetic beads, and analysis by MALDI-TOF MS we here evaluated pre-analytical variation and identify peptides involved in this. The influences of humidity, temperature, and time for preparation of sera on spectral changes were evaluated. Also, the reproducibility of the methods and the effect of a baseline correction procedure were examined. Low temperatures, short handling times, and a baseline correction procedure minimize the contribution of artifacts to sample variability as observed by MS. The complement split product C3f and fragments thereof appear to be sensitive indicators of sample handling induced modifications. Other peptides that are indicative of such variability are fibrin and kininogen fragments. Using strict experimental guidelines as well as standardized sample collection procedures it is possible to obtain reproducible peak intensities and positions in serum mass profiling using magnetic bead-based fractionation and MALDI-TOF MS.

Microfabricated refractive index gradient based detector for reversed-phase liquid chromatography with mobile phase gradient elution

Typical refractive index (RI) detectors for liquid chromatography (LC) are not well suited to application with mobile phase gradient elution, due to the difficulty in correcting for the detected baseline shift during the gradient. We report a sensitive, highly reproducible, microfabricated refractive index gradient (micro-RIG) detector that performs well with mobile phase gradient elution LC. Since the micro-RIG signal remains on-scale throughout the mobile phase gradient, one can apply a baseline correction procedure. We demonstrate that by collecting two mobile phase gradient blanks and subtracting one of them from the other, a reproducible, flat baseline is achieved. Therefore, subtracting a blank from a separation provides a baseline corrected chromatogram with reasonably high signal-to-noise ratio for eluting analytes. The micro-RIG detector uses a collimated diode laser beam to optically probe a RIG formed perpendicular to the laminar flow direction within a microfabricated borosilicate glass chip. The chip-based design of the detector is suitable for either traditional bench-top or LC-on-a-chip technologies. We report reversed phase high performance liquid chromatography (RP-HPLC) separations of proteins and polymers, over mobile phase gradient conditions of 67% A:33% B to 3% A:97% B by volume, where A is 96% methanol:3.9% water:0.1% trifluoroacetic acid (TFA), and B is 3.9% methanol:96% water:0.1% TFA. The separations were performed on a Jupiter 5 μ C4 300 Å 150 mm × 1.0 mm Phenomenex column at a flow rate of 20 μl/min. Viscosity changes during the mobile phase gradient separation are found to shift the on-chip merge position of the detected concentration gradient (i.e., RIG), in a reproducible fashion. However, this viscosity effect makes detection sensitivity vary throughout the mobile phase gradient, due to moving the optimized position of the probe beam in relation to the analyte concentration gradient being probed. None-the-less, consistent limits of detection (LODs) were achieved. The 3-sigma deflection angle LOD was 16 μrad for micro-RIG detection, corresponding to an injected concentration LOD of 7 ppm (mass/mass) for cytochrome c.

Application of Fourier transform infrared ellipsometry to assess the concentration of biological molecules.

Spectroscopic ellipsometry is a noninvasive optical characterization technique mainly used in the semiconductor field to characterize bare substrates and thin films. In particular, it allows the gathering of information concerning the physical structure of the sample, such as roughness and film thickness, as well as its optical response. In the mid-infrared (IR) range each molecule exhibits a characteristic absorption fingerprint, which makes this technique chemically selective. Phase-modulated IR ellipsometry does not require a baseline correction procedure or suppression of atmospheric CO2 and water-vapor absorption bands, thus greatly reducing the subjectivity in data analysis. We have found that ellipsometric measurements of thin films, such as the solid residuals left on a plane surface after evaporation of a liquid drop containing a given compound in solution, are particularly favorable for dosing purposes because the intensity of IR absorptions shows a linear behavior along a wide range of solution concentrations of the given compound. Our aim is to illustrate with a concrete example and to justify theoretically the linearity experimentally found between radiation absorption and molecule concentration. For the example, we prepared aqueous solutions of glycogen, a molecule of huge biological importance currently tested in biochemical analyses, at concentrations ranging from 1 mg/l to 1 g/l which correspond to those found in physiological conditions. The results of this example are promising for the application of ellipsometry for dosing purposes in biochemistry and biomedicine.

Sensitivity improvement in isotropic mixing (TOCSY) experiments

A simple modification of the two-dimensional TOCSY experiment which leads to a √2 improvement in sensitivity is described. This improvement is achieved by retaining the magnetization transfer pathways from both of the orthogonal, in-phase magnetization components which are present during the isotropic mixing period. In addition, a simple baseline correction procedure which can greatly improve the quality of NMR spectra is described.

Transmission at a central inhibitory synapse. IV. Quantal structure of synaptic noise

1. Continuous segments of synaptic noise were recorded, in 12 experiments, from the voltage-clamped goldfish Mauthner (M-)-cell soma during depolarizations beyond the Cl- equilibrium potential so that spontaneous inhibitory postsynaptic currents (IPSCs) were outward going, i.e., opposite in polarity to excitatory transients. Inhibitory components constituting the noise were detected with a program based on their expected waveforms, and their amplitude distributions were analyzed according to a quantal model to determine whether these responses, presumably because of asynchronous impulses in a population of presynaptic cells, were integral multiples of the same minimal unit. 2. Synaptic noise in the M-cell is predominantly inhibitory, as it is abolished by the glycine antagonist strychnine. IPSC amplitudes varied by 20-fold or more and about one-third were grouped in bursts, with one or several components often occurring during the falling phase of a preceding one. To measure individual amplitudes, a base-line correction procedure was designed to extrapolate the decay of the leading IPSC, on the assumption that it was exponential with a time constant, tau, equal to that obtained by fitting averaged waveforms of distinct IPSCs recorded in quiet periods. Currents were expressed in nanoamperes and, for comparison between experiments, as percentages of the full-sized IPSC evoked by activation of the collateral network. 3. The probability distribution functions (PDFs) of inhibitory events generated with such an analysis had from 5 to 12 clear and equally spaced peaks, larger transients not being included because of their sparsity. These PDFs were fit with a sum of Gaussians, on the assumption that all peaks were integral multiples of the smallest unit and had the same standard deviation, sigma. The fits were statistically satisfactory, according to a chi 2 test, and mean quantal size was 0.63 +/- 0.17% (SD; range, 0.42-1.0%) of the collateral IPSC. 4. In eight experiments, tetrodotoxin (TTX) was subsequently applied topically to block presynaptic impulses and isolate "miniature" responses because of single exocytotic events. It had no apparent nonspecific effects, as indicated by the constancy of M-cell input conductance (8.01 +/- 3.11 microS vs. 7.90 +/- 2.89 microS). Amplitude distributions of residual IPSCs were unimodal and Gaussian, with their mean size (0.60 +/- 0.19%) and average rise time (0.548 +/- 0.128 ms) the same as those of the first peaks of control histograms. The latter parameter was also comparable with that of unitary IPSCs studied previously. These results thus confirmed that spontaneous and evoked events are due to transmitter release from the same afferent population.(ABSTRACT TRUNCATED AT 400 WORDS)

A New Baseline Correction Algorithm Using Objective Criteria

A baseline correction algorithm using a least-squares procedure is developed. Linear or quadratic types of baselines are obtained through successive fitting and rejection of data points on a statistical basis. After the entire spectrum or a subsection is fitted to a least-squares line, the standard error of estimate is utilized as a criterion to determine if the fluctuation of each data point about the line can be thought of as the baseline fluctuation. Comments on various baseline correction procedures are also made.

Effect of Initial Base Motion on Response Spectra

The problems involved in converting earthquake ground acceleration records from analog to digital form for use in structural response calculations are widely recognized. Several different balancing or base line corrections are widely recognized. Several different balancing or base line correction procedures have been proposed over the years. Recent studies have resulted in a standard correction procedure for accelerograms, which was used in producing the EERL.

Spectrophotometric determination of diquat and paraquat in aqueous herbicide formulations.

Methods are described for determining diquat and paraquat, singly and in admixture, in formulations. For determining diquat, ultraviolet absorptiometry at 310 mµ in a sodium acetate buffer solution at pH 4·05 is adopted. Paraquat is determined in a diluted solution by measuring the optical density, at 600 mµ, of the blue free radical produced by reduction with alkaline sodium dithionite. For analysing mixtures containing both diquat and paraquat, these methods are combined and use is made of a base-line correction procedure to compensate for interference of diquat in the determination of paraquat. The error for these methods is established to be within ±2 per cent.