Alternative Calibration Method Research Articles

Solving Groundwater Flow Problems with Time Series Analysis: You May Not Even Need Another Model.

Time series analysis is a data‐driven approach to analyze time series of heads measured in an observation well. Time series models are commonly much simpler and give much better fits than regular groundwater models. Time series analysis with response functions gives insight into why heads vary, while such insight is difficult to gain with black box models out of the artificial intelligence world. An important application is to quantify the contributions to the head variation of different stresses on the aquifer, such as rainfall and evaporation, pumping, and surface water levels. Time series analysis may be applied to answer many groundwater questions without the need for a regular groundwater model, such as what is the drawdown caused by a pumping station? Or, how long will it take before groundwater levels recover after a period of drought? Even when a regular groundwater model is needed to solve a groundwater problem, time series analysis can be of great value. It can be used to clean up the data, identify the major stresses on the aquifer, determine the most important processes that affect flow in the aquifer, and give an indication of the fit that can be expected. In addition, it can be used to determine calibration targets for steady‐state models, and it can provide several alternative calibration methods for transient models. In summary, the overarching message of this paper is that it would be wise to do time series analysis for any application that uses measured groundwater heads.

Rotating-arm method for low speed calibration of hot-wire probes in water applications

An instrument for calibration of hot-wire probes at very low velocities in water applications is introduced. The technique is based on moving a hot-wire probe by means of a rotating-arm device in still water. This simple in situ calibration method is principally beneficial for the investigations of three-dimensional boundary layers which are encountered for instance over rotating disks. In addition to this proposed technique, an existing alternative method in which the calibration is performed against a known reference velocity over a flat surface of a rotating disk is conducted. The comparison of both methods show that the rotating-arm technique is superior to that existing alternative flat-surface calibration method.

Alpha calibration of the Timepix pixel detector exploiting energy information gained from a common electrode signal

An alternative calibration method of pixel detector Timepix has been developed. Unlike a standard per-pixel calibration method where just single pixel tracks of low energy gammas and X-rays are used as an input, the new method is based on the evaluation of charge distribution within multi-pixel tracks of energetic alpha particles. The new method gets practicable if energy of interacting alpha particles is precisely known. The Timepix pixel detector allows a simultaneous run of measurement in the pixel part as well as in the common electrode when a specialized read-out interface FITPix COMBO is used. The common electrode, opposite one to the pixel electrode, provides a natural sum of energy of all affected pixels among which the particle deposited charge has been shared. The distribution of energy between pixels belonging into alpha tracks has been evaluated and dependency between partial energy and time over threshold value counted in individual pixels has been solved. Knowing the energy dependency, it is possible to form a matrix of calibration parameters. The method has been proved for alpha particles of energies in range of 4784 to 7886 keV . The energy resolution of the pixel detector after calibration is comparable to the resolution of common electrode signal.

Development of a Vibroacoustic Stochastic Finite Element Prediction Tool for a CLT Floor

Low frequency impact sound insulation is a challenging task in wooden buildings. Low frequency prediction tools are needed to access the dynamic behavior of a wooden floor in an early design phase to ultimately reduce the low frequency impact noise. However, due to the complexity of wood and different structural details, accurate vibration predictions of wood structures are difficult to attain. Meanwhile, a deterministic model cannot properly represent the real case due to the uncertainties coming from the material properties and geometrical changes. The stochastic approach introduced in this paper aims at quantifying the uncertainties induced by material properties and proposing an alternative calibration method to obtain a relative accurate result instead of the conventional manual calibration. In addition, 100 simulations were calculated in different excitation positions to assess the uncertainties induced by material properties of cross-laminated-timber A comparison between the simulated and measured results was made in order to extract the best combination of Young’s moduli and shear moduli in different directions of the CLT panel.

Performances of different efficiency calibration methods of high-purity-germanium gamma-ray spectrometry in an inter-comparison exercise

This study reports the performances of efficiency calibrations for high-purity-germanium gamma-ray spectrometry using the source-, Laboratory Sourceless Object Calibration Software (LabSOCS)- and ANGLE-based methods in an inter-comparison exercise. Although the results of LabSOCS and ANGLE for 241Am emitting low-energy gamma rays were not very satisfactory, all of the three efficiency calibration methods passed acceptance criteria. The results confirmed the reliability of the calculation codes ANGLE and LabSOCS as alternative efficiency calibration methods in high-purity-germanium gamma spectrometry. This study is likely to promote the further application of the ANGLE and LabSOCS calculation codes in radioactivity measurements.

Direct determination of impurities in high purity chemicals by electrolyte cathode discharge atomic emission spectrometry (ELCAD-AES)

An ELCAD-AES method was reported for direct determination of metallic impurities in different high purity chemicals such as ammonium hydroxide, hydrogen peroxide and sulphuric acid. Direct analysis of these chemicals for their impurities was found to be feasible by ELCAD-AES without going for chemical processing/treatment like dilution or evaporation of matrix. 100% solutions of NH4OH and H2O2 chemicals produced stable ELCAD plasma, whereas 0.5% solution produced stable plasma for H2SO4. As standard addition calibration method to quantify impurities in these chemicals could not be useful, an alternative aqueous calibration method was examined and found to be suitable for their quantification by ELCAD-AES. As the certified reference materials for these chemicals were not available, the ELCAD-AES results were validated with the corresponding graphite furnace atomic absorption spectrometer (GF-AAS) results for NH4OH and H2O2 whereas for sulphuric acid they were validated with inductively coupled plasma optical emission spectrometer (ICP-OES) and supplier's results. ELCAD-AES method was free from matrix related problems and did not demand for the dilution of NH4OH and H2O2. The method was found to be useful for direct determination of trace and ultra trace metallic impurities in NH4OH and H2O2 pure chemicals and also for trace impurities in H2SO4 chemicals. Repeatability and accuracy of this method were found to be <10% and between 10 and 20% respectively. Thus ELCAD-AES could be an alternative analytical, rapid and direct analysis technique to check levels of metallic impurities (i.e. metal salts) and quality of these high purity chemicals for various industries.

Rainfall-runoff modelling using river-stage time series in the absence of reliable discharge information: a case study in the semi-arid Mara River basin

Abstract. Hydrological models play an important role in water resources management. These models generally rely on discharge data for calibration. Discharge time series are normally derived from observed water levels by using a rating curve. However, this method suffers from many uncertainties due to insufficient observations, inadequate rating curve fitting procedures, rating curve extrapolation, and temporal changes in the river geometry. Unfortunately, this problem is prominent in many African river basins. In this study, an alternative calibration method is presented using water-level time series instead of discharge, applied to a semi-distributed rainfall-runoff model for the semi-arid and poorly gauged Mara River basin in Kenya. The modelled discharges were converted into water levels using the Strickler–Manning formula. This method produces an additional model output; this is a “geometric rating curve equation” that relates the modelled discharge to the observed water level using the Strickler–Manning formula and a calibrated slope-roughness parameter. This procedure resulted in good and consistent model results during calibration and validation. The hydrological model was able to reproduce the water levels for the entire basin as well as for the Nyangores sub-catchment in the north. The newly derived geometric rating curves were subsequently compared to the existing rating curves. At the catchment outlet of the Mara, these differed significantly, most likely due to uncertainties in the recorded discharge time series. However, at the “Nyangores” sub-catchment, the geometric and recorded discharge were almost identical. In conclusion, the results obtained for the Mara River basin illustrate that with the proposed calibration method, the water-level time series can be simulated well, and that the discharge-water-level relation can also be derived, even in catchments with uncertain or lacking rating curve information.

A nonvisual eye tracker calibration method for video-based tracking.

Video-based eye trackers have enabled major advancements in our understanding of eye movements through their ease of use and their non-invasiveness. One necessity to obtain accurate eye recordings using video-based trackers is calibration. The aim of the current study was to determine the feasibility and reliability of alternative calibration methods for scenarios in which the standard visual-calibration is not possible. Fourteen participants were tested using the EyeLink 1000 Plus video-based eye tracker, and each completed the following 5-point calibration methods: 1) standard visual-target calibration, 2) described calibration where participants were provided with verbal instructions about where to direct their eyes (without vision of the screen), 3) proprioceptive calibration where participants were asked to look at their hidden finger, 4) replacement calibration, where the visual calibration was performed by 3 different people; the calibrators were temporary substitutes for the participants. Following calibration, participants performed a simple visually-guided saccade task to 16 randomly presented targets on a grid. We found that precision errors were comparable across the alternative calibration methods. In terms of accuracy, compared to the standard calibration, non-visual calibration methods (described and proprioception) led to significantly larger errors, whilst the replacement calibration method had much smaller errors. In conditions where calibration is not possible, for example when testing blind or visually impaired people who are unable to foveate the calibration targets, we suggest that using a single stand-in to perform the calibration is a simple and easy alternative calibration method, which should only cause a minimal decrease in accuracy.

The Multivariate Kyle Model: More is Different

We reconsider the multivariate Kyle model in a risk-neutral setting with a single, perfectly informed rational insider and a rational competitive market maker, setting the price of n correlated securities. We prove the unicity of a symmetric, positive definite solution for the impact matrix and provide insights on its interpretation. We explore its implications from the perspective of empirical market microstructure, and argue that it provides a sensible inference procedure to cure some pathologies encountered in recent attempts to calibrate cross-impact matrices. As an illustration, we determine the empirical cross impact matrix of US Treasuries, and compare the results with recent alternative calibration methods.

Field and laboratory evaluation of a high time resolution x-ray fluorescence instrument for determining the elemental composition of ambient aerosols

Abstract. Measuring the chemical composition of airborne particulate matter (PM) can provide valuable information on the concentration of regulated toxic metals, support modelling approaches for source detection and assist in the identification and validation of abatement techniques. Undertaking these at a high time resolution (1 h or less) enables receptor modelling techniques to be more robustly linked to emission processes. This study describes a comprehensive laboratory and field evaluation of a high time resolution x-ray fluorescence (XRF) instrument (CES XACT 625) for a range of elements (As, Ba, Ca, Cd, Ce, Cl, Cr, Cu, Fe, K, Mn, Mo, Ni, Pb, Pt, S, Sb, Se, Si, Sr, Ti, V and Zn) against alternative techniques: high time resolution mass measurements, high time resolution ion chromatography, aerosol mass spectrometry, and established filter-based, laboratory analysis using inductively coupled plasma mass spectrometry (ICP-MS). Laboratory evaluation was carried out using a novel mass-based calibration technique to independently assess the accuracy of the XRF against laboratory generated aerosols, which resulted in slopes that were not significantly different from unity. This demonstrated that generated particles can serve as an alternative calibration method for this instrument.The XACT was evaluated in three contrasting field deployments; a heavily trafficked roadside site (PM10 and PM2.5), an industrial location downwind of a nickel refinery (PM10) and an urban background location influenced by nearby industries and motorways (PM10). The XRF technique agreed well with the ICP-MS measurements of daily filter samples in all cases with a median R2 of 0.93 and a median slope of 1.07 for the elements As, Ba, Ca, Cr, Cu, Fe, K, Mn, Ni, Pb, Se, Sr, Ti, V and Zn. Differences in the results were attributed to a combination of inlet location and sampling temperature, variable blank levels in filter paper and recovery rates from acid digestion. The XRF technique also agreed well with the other high time resolution measurements but showed a clear positive difference (slopes between 1.41 and 4.6), probably due to differences in the size selection methodology, volatility and water solubility of the PM in aerosol mass spectrometry (SO4) and ion chromatography (Ca, Cl, K and SO4), respectively.A novel filter analysis technique using the XACT showed promising initial results: filters analysed off-line with the XACT compared well to in situ XACT measurements with a median R2 of 0.96 and median slope of 1.07. The resulting range of slopes was comparable to slopes produced in the ICP-MS comparison. This technique provides an opportunity to use the XACT when it is not deployed in the field; thus expanding the potential use of this instrument in future studies.

Image-based SPECT calibration based on the evaluation of the Fraction of Activity in the Field of View

BackgroundSPECT quantification is important for dosimetry in targeted radionuclide therapy (TRT) and the calibration of SPECT images is a crucial stage for image quantification. The current standardized calibration protocol (MIRD 23) uses phantom acquisitions to derive a global calibration factor in specific conditions. It thus requires specific acquisitions for every clinical protocols. We proposed an alternative and complementary image-based calibration method that allows to determine a calibration factor adapted to each patient, radionuclide, and acquisition protocol and that may also be used as an additional independent calibration.ResultsThe proposed method relies on a SPECT/CT acquisition of a given region of interest and an initial whole-body (WB) planar image. First, the conjugate view of WB planar images is computed after scatter and attenuation correction. 3D SPECT images are reconstructed with scatter, attenuation, and collimator-detector response (CDR) corrections and corrected from apparent dead-time. The field of view (FOV) of the SPECT image is then projected on the corrected WB planar image. The fraction of activity located in the area corresponding to the SPECT FOV is then calculated based on the counts on the corrected WB planar image. The Fraction of Activity in Field Of View (FAF) is then proposed to compute the calibration factor as the total number of counts in the SPECT image divided by this activity. Quantification accuracy was compared with the standard calibration method both with phantom experiments and on patient data.Both standard and image-based calibrations give good accuracy on large region of interest on phantom experiments (less than 7% of relative difference compared to ground truth). Apparent dead-time correction allows to reduce the uncertainty associated with standard calibration from 2.5 to 1%. The differences found between both methods were lower than the uncertainty range of the standard calibration (<3%). In patient data, although no ground truth was available, both methods give similar calibration factor (average difference 3.64%).ConclusionsA calibration factor may be computed directly from the acquired SPECT image providing that a WB planar image is also available and if both acquisitions are performed before biological elimination. This method does not require to perform phantom acquisition for every different acquisition conditions and may serve to double check the calibration with an independent factor.

Calibration of low-cost sound level meters using machine learning techniques

The assessment of environmental noise pollution from complex sources that are not represented in traditional noise maps requires a long term monitoring network to manage citizen complaints, a network of low-cost sound level meters is a practical option to analyze real-world cases, however the accuracy of the measurements is a concern when this information is used to evaluate regulation accomplishment. Previous work on low-cost monitoring devices has been carried out in microphone comparison, processing board selection and recently in MEMS microphone use. In the present work the use of reinforcement learning techniques is explored to calibrate the sound pressure levels generated by a low-cost monitoring device using a class one sound level meter as reference in a continuous measurement setup. Machine learning based models are known to take into account strong non-linearities which are effective to get an alternative calibration method for low-cost sensors.

An alternative method for calibration of flow field flow fractionation channels for hydrodynamic radius determination: The nanoemulsion method (featuring multi angle light scattering)

This study suggests a novel method for determination of the channel height in asymmetrical flow field-flow fractionation (AF4), which can be used for calibration of the channel for hydrodynamic radius determinations. The novel method uses an oil-in-water nanoemulsion together with multi angle light scattering (MALS) and elution theory to determine channel height from an AF4 experiment. The method is validated using two orthogonal methods; first, by using standard particle elution experiments and, secondly, by imaging an assembled and carrier liquid filled channel by x-ray computed tomography (XCT). It is concluded that the channel height can be determined with approximately the same accuracy as with the traditional channel height determination technique. However, the nanoemulsion method can be used under more challenging conditions than standard particles, as the nanoemulsion remains stable in a wider pH range than the previously used standard particles. Moreover, the novel method is also more cost effective.

A framework for streamflow prediction in the world’s most severely data-limited regions: Test of applicability and performance in a poorly-gauged region of China

A framework methodology is proposed for streamflow prediction in poorly-gauged rivers located within large-scale regions of sparse hydrometeorologic observation. A multi-criteria model evaluation is developed to select models that balance runoff efficiency with selection of accurate parameter values. Sparse observed data are supplemented by uncertain or low-resolution information, incorporated as ‘soft’ data, to estimate parameter values a priori. Model performance is tested in two catchments within a data-poor region of southwestern China, and results are compared to models selected using alternative calibration methods. While all models perform consistently with respect to runoff efficiency (NSE range of 0.67–0.78), models selected using the proposed multi-objective method may incorporate more representative parameter values than those selected by traditional calibration. Notably, parameter values estimated by the proposed method resonate with direct estimates of catchment subsurface storage capacity (parameter residuals of 20 and 61 mm for maximum soil moisture capacity (Cmax), and 0.91 and 0.48 for soil moisture distribution shape factor (B); where a parameter residual is equal to the centroid of a soft parameter value minus the calibrated parameter value). A model more traditionally calibrated to observed data only (single-objective model) estimates a much lower soil moisture capacity (residuals of Cmax = 475 and 518 mm and B = 1.24 and 0.7). A constrained single-objective model also underestimates maximum soil moisture capacity relative to a priori estimates (residuals of Cmax = 246 and 289 mm). The proposed method may allow managers to more confidently transfer calibrated models to ungauged catchments for streamflow predictions, even in the world’s most data-limited regions.

38. Image-based SPECT calibration based on the Fraction of Activity in Field of view (FAF)

Introduction SPECT quantification is particularly important for dosimetry in Targeted Radionuclide Therapy (TRT) and the calibration of SPECT images is a crucial stage for image quantification. The current standardized calibration protocol (MIRD 23 [1] ) makes use of phantom acquisitions in specific conditions and require an additional phantom calibration for every clinical acquisition protocol. We proposed an alternative and complementary image-based calibration method that allows obtaining a single calibration factor adapted to each patient, radionuclide and acquisition protocol, without specific phantom acquisition. Methods This method consists in SPECT images quantification from WB planar images. First, the conjugate view of WB planar images is computed after scatter and attenuation corrections. 3D SPECT images are acquired in the same patient position, reconstructed with scatter, attenuation and Collimator Detector Response (CDR) corrections, and finally corrected from apparent dead-time. The Field of View (FOV) of the SPECT images is then projected on the corrected WB planar image. The fraction of activity located in the area corresponding to the SPECT FOV is calculated based on the counts on the corrected WB planar image. The Fraction of Activity in Field of View (FAF) is then proposed to compute the calibration factor as the total number of counts in the SPECT image divided by this activity. Quantification accuracy was compared with the standard calibration method both with phantom experiments and on patient data. Results Both standard and our image-based calibrations give good accuracy (ranges of respectively [−0.97; 2.86]% and [0; 3.16]%) on large region of interest on phantom experiments. Apparent dead-time correction allows reducing the uncertainty associated with standard calibration with a coefficient of variation of the calibration factor of 0.17% instead of 2.39%. The differences on accuracy found between both methods on phantom study were lower (1.01% in average) than the uncertainty range with the standard calibration (2.90% in average). On patient study, although the ground truth is unknown, the standard calibration factor is also close (3.96% in average) to the image based patient specific one. Conclusions Calibration was performed directly on the image acquisition of interest. This method allows overriding the errors caused by imperfect attenuation and scattering corrections due to different conditions. This protocol is as accurate as standardized calibration protocol but only requires an additional WB planar acquisition. The main limitation relies on the need of performing the acquisition before patient biological elimination.

Multi-isotope calibration for inductively coupled plasma mass spectrometry.

Multi-isotope calibration (MICal) is a novel approach to calibration for inductively coupled plasma mass spectrometry (ICP-MS). In MICal, only two calibration solutions are required: solution A, composed of 50% vv-1 of sample and 50% vv-1 of a standard solution containing the analytes, and solution B, composed of 50% vv-1 of sample and 50% vv-1 of a blank solution. MICal is based on monitoring the signal intensities of several isotopes of the same analyte in solutions A and B. By plotting the analytical signals from solution A in the x-axis, and from solution B in the y-axis, the analyte concentration in the sample is calculated using the slope of that graph and the concentration of the reference standard added to solution A. As both solutions contain the same amount of sample, matrix-matching is easily achieved. In this proof-of-concept study, MICal was applied to the determination of Ba, Cd, Se, Sn, and Zn in seven certified reference materials with different matrices (e.g., plant materials, flours, and water). In most cases, MICal results presented no statistical difference from the certified values at a 95% confidence level. The new strategy was also compared with traditional calibration methods such as external calibration, internal standardization and standard additions, and recoveries were generally better for MICal. This is a simple, accurate, and fast alternative method for matrix-matching calibration in ICP-MS. Graphical abstract Multi-isotope calibration: fast and innovative matrix-matching calibration for ICP-MS.

The Opiliones tree of life: shedding light on harvestmen relationships through transcriptomics.

Opiliones are iconic arachnids with a Palaeozoic origin and a diversity that reflects ancient biogeographic patterns dating back at least to the times of Pangea. Owing to interest in harvestman diversity, evolution and biogeography, their relationships have been thoroughly studied using morphology and PCR-based Sanger approaches to infer their systematic relationships. More recently, two studies utilized transcriptomics-based phylogenomics to explore their basal relationships and diversification, but sampling was limiting for understanding deep evolutionary patterns, as they lacked good taxon representation at the family level. Here, we analysed a set of the 14 existing transcriptomes with 40 additional ones generated for this study, representing approximately 80% of the extant familial diversity in Opiliones. Our phylogenetic analyses, including a set of data matrices with different gene occupancy and evolutionary rates, and using a multitude of methods correcting for a diversity of factors affecting phylogenomic data matrices, provide a robust and stable Opiliones tree of life, where most families and higher taxa are precisely placed. Our dating analyses using alternative calibration points, methods and analytical parameters provide well-resolved old divergences, consistent with ancient regionalization in Pangea in some groups, and Pangean vicariance in others. The integration of state-of-the-art molecular techniques and analyses, together with the broadest taxonomic sampling to date presented in a phylogenomic study of harvestmen, provide new insights into harvestmen interrelationships, as well as an overview of the general biogeographic patterns of this ancient arthropod group.

Local calibration of creep compliance models of asphalt concrete

Thermal cracking is one of the main asphalt concrete distresses. Asphalt pavements typically experience thermal cracking at an early stage of their service life. The Mechanistic-Empirical Pavement Design (MEPDG) software utilizes a thermal cracking model to predict low temperature performance (NCHRP, 2004). Creep compliance of the asphalt concrete mixture is an essential input to the thermal cracking model. Creep input values are generated by a globally calibrated creep compliance model, based on certain binder and mixture properties. Local calibration is necessary to improve the model performance to account for local materials, environment and other factors.This paper presents the results of two alternative local calibration methods; nonlinear multiple regression and artificial neural network (ANN), and compares their performance to the MEPDG generalized model. In total, 861 data points from 41 specimens representing 14 types of AC mixes were prepared and tested in the laboratory. The creep compliance values were determined in the laboratory and compared to values generated by globally and locally calibrated models. The analysis shows that the MEPDG creep compliance model without local calibration predicts creep values poorly, thus calibration should be a required step in the implementation of MEPDG designs. As expected, both nonlinear regression and ANN model significantly improve the reliability of creep compliance predictions. The ANN model produced the lowest error in creep compliance predictions.

Mechanical analysis of normal force interference on axial force measurement for internal sting balance

For an internal sting balance, the measurement elements of axial force are independent from the measurement elements of other loads. The interference of other loads causes errors in axial force measurement. The existing way to compensate these errors is to perform balance calibration which is basically a mathematical method without mechanical meaning. In this paper, a mechanical analysis is performed to reveal how the normal force causes errors in axial force measurement, based on which a modified Wheatstone bridge equation is presented to serve as an alternative calibration method. Results of case studies show that the presented modified Wheatstone bridge equation can effectively reduce the interference error of normal force on the axial force measurement.

The modification of the thrombin generation test for the clinical assessment of dabigatran etexilate efficiency.

A new oral anticoagulant, dabigatran etexilate (DE, a prodrug of direct thrombin inhibitor (DTI) dabigatran), has been used clinically to prevent thrombosis. The assessment of dabigatran efficiency is necessary in some clinical cases, such as renal insufficiency, risk of bleeding, and drug interactions. However, a specific thrombin generation test (TGT) that is one of the most informative and sensitive to anticoagulant therapy (calibrated automated thrombinography (САТ)) shows a paradoxical increase of test parameters, such as endogenous thrombin potential (ETP) and peak thrombin, in patients receiving DE. The paradoxical behaviour of ETP and peak thrombin in these patients in the presence of DTIs is mostly caused by a decrease in the activity of thrombin in the α2-macroglobulin-thrombin complex that is used as a calibrator in CAT. For a correct estimation of the TGT parameters in patient’s plasma containing DTIs we proposed to use our previously described alternative calibration method that is based on the measurement of the fluorescence signal of a well-known concentration of the reaction product (7-amino-4-methylcoumarin). In this study, the validity of such approach was demonstrated in an ex vivo study in patients with knee replacement and two special patients with multiple myeloma, who received DE for thrombosis prophylaxis.