Calibration Transfer Function Research Articles

An assessment of multivariate predictions of various properties of crude oil on two ATR/IR spectrometers

About sixty commercially relevant crude oil samples are acquired on two spectrometers that are linked by a calibration transfer function and analyzed through PLS regression. About twenty multivariate models for distillation fractions are built and tested, as well as the models for API, acids, and sulfur. The parallel acquisition of samples on both spectrometers allows for deriving calibration and predictions errors for the models that use calibration transfer function as well as for the models independently built and tested on each of the used spectrometers. Testing of all available samples reveals that the calibration transfer approach produces notably higher prediction errors in comparison to the testing on the spectrometer on which the models are developed. Splitting the samples so that exact same sets for calibration and testing are used on both spectrometers (no calibration transfer) reveals that one spectrometer performs clearly better than the other although both operate under the same operating procedure and pass the same operational qualification. Comparison of the spectra of crude oils acquired on both spectrometers that are consistently identified as outliers on one of the spectrometers does not indicate any easily identifiable spectral differences. The results of this study indicate that the prediction errors may significantly differ depending on the performance of the spectrometers employed despite them nominally passing the qualification criteria, thus being nearly equivalent.

In situ 3D spatiotemporal measurement of soluble biomarkers in spheroid culture

BackgroundAdvanced cell culture techniques such as 3D bioprinting and hydrogel-based cell embedding techniques harbor many new and exciting opportunities to study cells in environments that closely recapitulate in vivo conditions. Researchers often study these environments using fluorescence microscopy to visualize the protein association with objects such as cells within the 3D environment, yet quantification of concentration profiles in the microenvironment has remained elusive.ObjectiveDemonstrate an assay that enables near real-time in situ biomarker detection and spatiotemporal quantification of biomarker concentration in 3D cell culture.MethodsA distributed bead-based immuno-assay was used in 3D cell culture to continuously measure the time-dependent concentration gradient of various biomarkers by sequestering soluble target molecules and concentrating the fluorescence intensity of these tagged proteins. Timelapse confocal microscopy was used to measure the in situ fluorescence intensity profile and a calibration curve was separately generated. Application of a calibration transfer function to in situ data is used to quantify spatiotemporal concentration.ResultsExample assays utilize an osteosarcoma spheroid as a case study for a quantitative single-plexed gel encapsulated assay, and a qualitative multi-plexed 3D-bioprinted assay. In both cases, a time-varying cytokine concentration gradient is measured. An estimation for the production rate of the IL-8 cytokine per second per osteosarcoma cell results from fitting an analytical function for continuous point source diffusion to the measured concentration gradient and reveals that spheroid production approaches nearly 0.18 fg/s of IL-8 after 18 h in culture.ConclusionsTheoretical and experimental demonstration of bead-based immunoassays in diffusion-limited environments such as 3D cell culture is shown, and includes example measurements of various cytokines produced by an osteosarcoma spheroid. Proper calibration and use of this assay is exhaustively explored for the case of diffusion-limited Langmuir kinetics of a spherical adsorber.

High-Precision Automatic Calibration Modeling of Point Light Source Tracking Systems.

To realize high-precision and high-frequency unattended site calibration and detection of satellites, automatic direction adjustment must be implemented in mirror arrays. This paper proposes a high-precision automatic calibration model based on a novel point light source tracking system for mirror arrays. A camera automatically observes the solar vector, and an observation equation coupling the image space and local coordinate systems is established. High-precision calibration of the system is realized through geometric error calculation of multipoint observation data. Moreover, model error analysis and solar tracking verification experiments are conducted. The standard deviations of the pitch angle and azimuth angle errors are 0.0176° and 0.0305°, respectively. The root mean square errors of the image centroid contrast are 2.0995 and 0.8689 pixels along the x- and y-axes, respectively. The corresponding pixel angular resolution errors are 0.0377° and 0.0144°, and the comprehensive angle resolution error is 0.0403°. The calculated model values are consistent with the measured data, validating the model. The proposed point light source tracking system can satisfy the requirements of high-resolution, high-precision, high-frequency on-orbit satellite radiometric calibration and modulation transfer function detection.

Incorporating Calibrated Numerical Models in Estimating Moduli of Compacted Geomaterials from Integrated Intelligent Compaction Measurements and Laboratory Testing

Proof rolling after completion of compaction of earthwork using intelligent compaction (IC) technology can be used to assess the uniformity of the compacted geomaterials and to identify less stiff compacted areas. To better understand the process of quality management using IC technology, a three-dimensional finite element model was developed to document the theoretical limitations and the sensitivity of IC technology. The model can also be used for setting the target values, and can be part of a methodology to extract the moduli of geomaterials in more rigorous and defensible specifications. Different levels of complexity in relation to linear versus nonlinear behavior of geomaterial and different levels of roller operating conditions (static versus dynamic, moving versus stationary) can be assigned to the model. Such model can only be used with confidence if it is calibrated and validated with experimental field data. Five test sites including single-layer (subgrade only) and two-layer (subgrade and base) geosystems were instrumented using in-ground sensors for calibrating the model. Different vibratory IC rollers from different manufacturers were used to implement IC tests at vibratory stationary as well as moving conditions at the test sites. In all scenarios, a locally calibrated transfer function was necessary to accommodate the differences in the numerical models and vibration data obtained from the IC measurements on test sections with distinct geomaterial conditions. The study also concluded that the predictive power of the numerical models improves if the field measurements and laboratory data are integrated, and more importantly the variability of the materials is incoprorated.

Perceptually-Transparent Online Estimation of Two-Channel Room Transfer Function for Sound Calibration

Sound calibration is employed in many commercial audio systems for improving sound quality. This process includes the estimation of the room transfer function (RTF) between each loudspeaker and a microphone located at the listeners’ position. Current methods for RTF estimation employ calibration signals, such as noise or tones, in a dedicated process applied to each loudspeaker separately. Such an estimation disrupts normal playback, is time consuming, and requires user intervention. A perceptually-transparent online RTF estimation method for a two-channel system, which employs calibration signals generated using the original audio signals and complementary filters, is proposed in this article. These calibration signals are uncorrelated across the two channels, which facilitates the online estimation of both channels using a single microphone. Estimation performance is investigated for an experimental system and displays low estimation errors. Finally, a subjective evaluation via a listening test shows that playback of calibration signals is perceptually-transparent under some of the conditions investigated.

Nacelle power curve measurement with spinner anemometer and uncertainty evaluation

Abstract. The objective of this investigation was to verify the feasibility of using the spinner anemometer calibration and nacelle transfer function determined on one reference wind turbine, in order to assess the power performance of a second identical turbine. An experiment was set up with a met mast in a position suitable to measure the power curve of the two wind turbines, both equipped with a spinner anemometer. An IEC 61400-12-1-compliant power curve was then measured for both wind turbines using the met mast. The NTF (nacelle transfer function) was measured on the reference wind turbine and then applied to both turbines to calculate the free wind speed. For each of the two wind turbines, the power curve (PC) was measured with the met mast and the nacelle power curve (NPC) with the spinner anemometer. Four power curves (two PCs and two NPCs) were compared in terms of AEP (annual energy production) for a Rayleigh wind speed probability distribution. For each wind turbine, the NPC agreed with the corresponding PC within 0.10 % of AEP for the reference wind turbine and within 0.38 % for the second wind turbine, for a mean wind speed of 8 m s−1.

Derivation of temporally continuous LAI reference maps through combining the LAINet observation system with CACAO

Leaf area index (LAI) products are now routinely generated from remote sensing and widely used in most land surface process models. Assessing the uncertainties associated with these LAI products is essential for their proper application. In validation activities, LAI reference maps serve as the bridge to upscale the field measurements to coarse resolution. Currently, the temporally continuous validation is attracting increasing attention. Therefore, there is an urgent requirement for the temporally continuous LAI reference maps. However, two main problems hinder the generation of temporally continuous LAI reference maps: 1) How to obtain temporally continuous field measurements, effectively and inexpensively? 2) How to obtain temporally continuous and fine spatial resolution satellite images which are synchronous with the field measurements? This paper proposed a method to address the above two problems based on the combination of the wireless sensor network technology and a data blending approach. Firstly, the temporally continuous effective LAI was obtained through the analysis of multi-angle gap fraction measured by LAINet observation system (developed with wireless sensor network technology), and the temporally continuous NDVI was reconstructed through CACAO (Consistent Adjustment of the Climatology to Actual Observations, a data blending approach). Then, a transfer function relating reconstructed NDVI to field measured LAI was calibrated through exponential function fitting. Finally, the temporally continuous LAI reference maps were generated by applying the calibrated transfer function to the reconstructed NDVI. Performances of the proposed method were evaluated over a crop site. Results show that the reconstructed LAI reference maps agree well with the original LAI reference maps derived from the Landsat-8 OLI NDVI (R2=0.90, RMSE=0.27 at 30m resolution, R2=0.97, RMSE=0.09 at 1km resolution). The derived temporally continuous LAI reference maps were then used as benchmark to validate the MOD15A2 LAI product. Generally, the MOD15A2 LAI has a relatively high accuracy (R2=0.53, RMSE=0.31), and captures the overall vegetation phenology well. But its value shows an obvious underestimation with a bias of −0.30. The results of this study contribute to the assessment of temporal dynamics of uncertainty in LAI products, which will benefit the long-term vegetation monitoring and data assimilation.

Intercalibration of Microwave Radiometer Brightness Temperatures for the Global Precipitation Measurement Mission

A technique for comparing spaceborne microwave radiometer brightness temperatures (Tb) is described in the context of the upcoming National Aeronautics and Space Administration Global Precipitation Measurement (GPM) mission. The GPM mission strategy is to measure precipitation globally with high temporal resolution by using a constellation of satellite radiometers logically united by the GPM core satellite, which will be in a non-sun-synchronous medium inclination orbit. The usefulness of the combined product depends on the consistency of precipitation retrievals from the various microwave radiometers. The Tb calibration requirement to achieve such consistency demands first that Tb's from the individual radiometers be free of instrument and measurement artifacts and, second, that these self-consistent Tb's will be translated to a common standard (GPM core) for the unification of the precipitation retrieval. The intersatellite radiometric calibration technique described herein serves both the purposes by comparing individual radiometer observations to radiative transfer model (RTM) simulations (for “self-consistency” check) and by using a double-difference technique (to establish a linear calibration transfer function from one radiometer to another). This double-difference technique subtracts the RTM-simulated difference from the observed difference between a pair of radiometer Tb's. To establish a linear inter-radiometer calibration transfer function, comparisons at both the cold (ocean) and the warm (land) end of the Tb's are necessary so that, using these two points, slope and offset coefficients are determined. To this end, a simplified calibration transfer technique at the warm end (over the Amazon and Congo rain forest) is introduced. Finally, an error model is described that provides an estimate of the uncertainty of the radiometric bias estimate between comparison radiometer channels.

Calibration details for the impulse peak insertion loss measurement

The American National Standard ANSI S12.42-2010 specifies the measurement of hearing protector performance in the presence of impulse noise. A series of calibration impulses are recorded from an acoustic test fixture (ATF) and a field microphone for peak sound pressure levels of 130, 150, and 170 dB. The averaged acoustic transfer function between the ATF and field microphone is calculated as follows: H¯ATF¯−FF¯(f)=〈FFT¯(PATF,i(t))/FFT(PFF,i(t))〉.¯ The transfer function is computed for each of the ranges of impulse levels and is applied to the field microphone measurements to estimate the unoccluded fixture levels of the ATF when hearing protection is being tested. This method allows a comparison between occluded and unoccluded waveforms. The calibration transfer function is affected by the time-alignment of the field impulse peaks, time-windowing of the impulses, and compensation for any dc bias. Time-alignment significantly affected the accuracy of predicting individual calibration levels with H¯ATF¯−FF¯. The prediction error variance was less at 170 dB than at 130 dB impulses. The time-window was varied from 2.5 to 100 ms preceding the peak of the field impulse. [Portions of this work were supported by the U.S. EPA Interagency Agreement DW75921973-01-0.]

Bimolecular recombination in ambipolar organic field effect transistors

In ambipolar organic field effect transistors (OFET) the shape of the channel potential is intimately related to the recombination zone width W, and hence to the electron–hole recombination strength. Experimentally, the recombination profile can be assessed by scanning Kelvin probe microscopy (SKPM). However, surface potentials as measured by SKPM are distorted due to spurious capacitive couplings. Here, we present a (de)convolution method with an experimentally calibrated transfer function to reconstruct the actual surface potential from a measured SKPM response and vice versa. Using this scheme, we find W = 0.5 μm for a nickel dithiolene OFET, which translates into a recombination rate that is two orders of magnitude below the value expected for Langevin recombination.

A new technique for the measurement of the normal incidence absorption coefficient using an impedance tube and a single microphone with fixed position

The normal incidence absorption coefficient of acoustic materials can be measured inside an impedance tube with different settings for the microphone(s). The two most widespread techniques are the standing wave method using a probe microphone and side‐mounted two‐microphone techniques. Errors that can occur here are related to phase mismatch between the two microphones and the knowledge of the exact locations of the (acoustic centre of the) microphones and test sample. These problems have (partially) been solved by, for example, calibrating the microphones by swapping them and calculating a calibration transfer function or by using one microphone techniques. In this article we will present a novel technique which will also avoid the need for the knowledge of the exact microphone location by continuously moving the sample under test. Different results will be presented and compared to the traditional techniques.

A Comparative Study on Impact Force Prediction on a Railway Track-like Structure

The ability to estimate an impact force being imparted onto a structure is highly valuable to its overall health monitoring scheme. This study compares impact force prediction on a railway track-like structure by a number of methods. One proposed technique utilized to estimate dynamic impacts on railway tracks involve correlating a root mean square (RMS) calculation of the track response over a selected frequency bandwidth with different impact force levels. Another technique involves the use of strain gauges configured into a full bridge circuit to reconstruct the time history of the impact force on the track structure. A third method utilizes a classical inverse analysis approach to reconstruct the force time history with a calibrated transfer function in the frequency domain. This article uses both finite element and experimental techniques to evaluate the aforementioned methods with regard to input impacts with constant magnitude and varying durations. It is seen that the RMS method is not effective in predicting impact forces with like magnitudes but varying durations. This is because the RMS relies on measuring energy in the response spectra, which varies according to input impact energy. It was also shown that measuring strain is an effective method of reconstructing an impact force waveform; however its efficacy is reduced when the impact event becomes highly dynamic. This is because strain relies on structural deformation, which is dependent on the loading time history. It is seen that an inverse analysis technique, which relies on the calibration of a frequency response function to facilitate the reconstruction of impact forces is relatively immune to varying impact durations. This is due to the structure’s relative linearity over the lower frequency region, which is a critical consideration when choosing the inverse analysis method.

Dynamic calibration of a sensor gas calorimeter for measurement of heat generation rates during kinetic of adsorption experiments

A procedure for dynamic calibration of a sensor gas calorimeter, resulting with a calibration transfer function, instead with a calibration line, is presented. The main factors influencing the calibration transfer function have been assessed. The calibration transfer function enables measurement of the heat generation rates during adsorption, necessary for obtaining a complete picture about adsorption kinetics.

Transfer function of FBS-3A feedback broadband seismometer

FBS-3A feedback broadband seismometer has been widely utilized in observation networks up to now. Therefore, it is very important and practically meaningful for the application of this kind of sensor to fulfill some relative research work about its transfer function and for the analysis to the data recorded and the further development of the seismometer. In this paper, from the viewpoint of achieving its working principle, method of systematic analysis is applied to deduce the transfer functions, including both the transfer function for calibration and that for measurement. Moreover, on the basis of that, the distribution of its zeroes and poles in a complex frequency domain is analyzed, which provides a convincing evidence to simplify this seismometer sytem from a high-order one to a two-order one. And the emulation of the frequency characteristics of FBS-3A is presented in this paper. On the whole, the aim of this article is to do some theoretical work about the earthquake observation sensor, and also to introduce the method of making systematic analysis in a complex frequency domain to the research and the development of the seismometers.