Calibration Chamber Research Articles

DEM study of the stress fields around the closed-ended displacement pile driven in sand

Three-dimensional discrete element method (DEM) is employed to model the published calibration chamber test of a closed-ended displacement pile driven in sand. To achieve large chamber-to-pile and pile-to-particle size ratios for unbiased predictions, a high-performance graphics processing unit-powered DEM code is utilised in conjunction with the axisymmetric assumption and particle refinement method. The DEM parameters are first calibrated against the drained triaxial compression test data on Fontainebleau sand. Then, the DEM modelling of pile driving demonstrates quantitative agreement with the experimental counterpart in terms of cone resistance, stress contours, and distributions.

Thermal radiation effect measurement in enclosure calibration

The effect of thermal radiation could be the biggest issue in enclosure calibration. Reducing it by taking accurate measurements can improve the calibration uncertainty or calibration measurement capability (CMC). However, there is still less information related to the measurement procedure that can be taken from references such as DKD-R 5-7: Calibration of Climatic Chambers, DKD-R 5-8: Calibration of Hygrometers for Direct Measurement of Relative Humidity, and KAN Pd-02.04: Pedoman Kalibrasi Enklosur Suhu. Moreover, one of those reference documents suggests a value of 0.35 °C as the standard uncertainty contributed by thermal radiation for enclosure temperatures up to about 30 °C above ambient. This large value can be understood as an attempt to produce secure uncertainty since it is not measured directly. Therefore, this study describes the detailed measurement of the effect of thermal radiation. Two enclosures, which are an oven and a climatic chamber, are used as the samples. The oven represents an enclosure with natural thermal convection while the climatic chamber represents an enclosure with flowing air at a certain relative humidity. The thermal radiation effect is measured by two small PRTs class A with a diameter of 3 mm and length of 15 mm. Those PRTs are wrapped in aluminum foil to have low emissivity (ɛ=0.4) and one of them is then painted by Nextel 811-21 to have high emissivity (ɛ=0.97). The resistance outputs from the PRTs are measured by 34401A 6½ Digital Multimeter manufactured by Keysight. Before being used, those PRTs were calibrated in a stirred bath having uncertainty U=0.06 °C with a confidence level of 95 % and coverage factor k=2. The temperature range for the oven is from 60 °C to 140 °C while for the climatic chamber is from 40 %rh to 90 %rh at 20 °C and is from 40 %rh to 90 %rh at 25 °C. A mathematical model is proposed and the results are presented graphically where for the oven the higher temperature is the higher the thermal radiation effect, ranging from ±0.1 °C to ±0.4 °C. Variation of relative humidity inside the climatic chamber does not change the thermal radiation effect since the difference is 0.05 °C which is still within the uncertainty of PRTs

Mathematical aspects of distortion calibration for digital cameras

Nowadays, most human processes are automated by means of computerization. This process has not spared the automotive industry. The latest developments in this field give promise that in the near future, cars will be completely autonomous. However, before that, there is an urgent need to address a number of issues, such as increasing the angle of view for greater coverage of the road with minimal space curvature. It is known that when the angle of view increases, so does the distortion (a mismatch in geometric similarity between an object and its image). This mismatch significantly reduces the accuracy of recognition algorithms. To solve this problem, this paper proposes a calibration method for cameras. The paper deals with mathematical aspects of distortion and the method of calibration of automobile chambers, and calibration errors. The method of static calibration without the use of points at infinity using static templates is proposed. A conventional camera has a small field of view (about 80 degrees). Such angle of view does not provide full scanning of the space; as a result, some of the necessary information remains outside the field of view, which is crucial for automotive industry because road signs, pedestrians, traffic lights might be missed. Therefore, in case of car cameras, the angle of view is increased by introducing distortion aberration. In this case, the field of view increases, yet the geometric similarity between the object and its image is affected. This, in turn, can affect the accuracy of computer vision algorithms. In order to keep the field of view angle large and the similarity between the subject and the object, it is necessary to calibrate the camera. In this paper, a calibration method for wide-angle car cameras is proposed and considered.

Determination of an air kerma-rate correction factor for the S7600 Xoft AxxentⓇ source model

PurposeThe purpose of this work was to provide guidance for the lack of an air-kerma rate standard for the S7600 Xoft Axxent® source by providing a correction factor to apply to the National Institute of Standards and Technology (NIST) traceable S7500 well chamber (WC) calibration coefficient before the development of an S7600 standard at NIST. METHODS AND MATERIALSThe Attix free air chamber (FAC) at the University of Wisconsin Medical Radiation Research Center was used to measure the air-kerma rate at 50 cm for six S7500 and six S7600 sources. These same sources were then measured using five standard imaging HDR1000+ WCs. The measurements made with the FAC were used to calculate source-specific WC calibration coefficients for the S7500 and S7600 source. These results were compared to the NIST traceable calibration coefficients for the S7500 source. The average results for each WC were then averaged together, and a ratio of the S7600 to S7500 WC calibration coefficients was determined. ResultsThe average S7600 air-kerma rate measurement with the FAC was 7% lower than the average air-kerma rate measurements of the S7500 source. On average, the S7500 determined WC calibration coefficients agreed within ±1% of the NIST traceable S7500 values. The S7600 WC calibration coefficients were up to 16% less than the NIST traceable S7500 values. The final correction factor determined to be applied to the NIST traceable S7500 value was 0.8415 with an associated uncertainty of ±8.1% at k = 2. ConclusionsThis work provides a suggested correction factor for the S7600 Xoft Axxent source such that the sources can be accurately implemented in the clinical setting.

Addressing complexities in MPM modeling of calibration chamber cone penetrometer tests in homogenous and highly interlayered soils

Cone penetrometer tests (CPTs) are used to characterize soil for a variety of geotechnical engineering applications, including earthquake-induced liquefaction triggering assessment. Numerical modeling of CPTs is frequently used to better understand soil behavior, soil-penetrometer interaction, and engineering estimates made from CPT data. However, calibrating and validating numerical CPT simulations with experimental calibration chamber (CC) data can be challenging. Specifically, uncertainties in the interpretation of laboratory strength and compression data compound with uncertainties in the CC testing and the assumptions made when developing the numerical model. This article provides a comprehensive review of uncertainties in the calibration and validation of CPT numerical simulations performed in homogenous sand, homogenous clay, and layered sand-clay soil profiles, comparing numerical results with well-documented experimental calibration chamber tests performed at Deltares. In particular, the Material Point Method (MPM) is used to perform the numerical analyses. A framework is presented to assess how uncertainty in the numerical model output is attributed to each input parameter. It is demonstrated that uncertainties can be explored numerically. Finally, recommendations for future experimental and numerical studies of CPTs are provided.

Effect of cyclic loading on the mobilization of unit base resistance of model piles jacked in sand

This paper reports the results of a series of monotonic compressive and cyclic load tests performed on a closed-ended jacked model pile installed in a half-cylindrical calibration chamber with image analysis capabilities. The monotonic compressive load tests were carried out before and after performing a displacement-controlled cyclic load test to determine the impact of cycling on unit base resistance. Digital images of the sand and the model pile were taken during cyclic loading and processed using the digital image correlation (DIC) technique to obtain the cumulative displacement and strain fields in the sand domain. The results show that the ultimate unit base resistance can drop significantly after cycling. The magnitude of the drop in ultimate unit base resistance depends on both the magnitude of the cyclic displacement amplitude and the number of cycles. However, the unit base resistance at plunging increases after large-displacement half-amplitude cycling. The increase in unit base resistance at plunging after cycling is linked to the flow of sand particles to the zone below the conical base, the occurrence of sand particle crushing, and the dilative behavior of the sand outside a bulb of crushed particles formed during cyclic loading. The processed DIC data show that for cyclic displacement half-amplitudes ∆wcyclic less than or equal to 0.25 mm (0.0007B), the cumulative radial and vertical displacements in the soil domain normalized by ∆wcyclic are negligible. Values of ∆wcyclic greater than 0.25 mm produce normalized displacements in the soil domain that increase as the cyclic displacement amplitude increases.

A CFD-based approach to study the deposition and distribution behaviour of 212Pb in a calibration chamber.

Among the several aspects of decay products behavior, deposition is of special significance because of its prominent role in the activity removal from the environment, which eventually results in the occurrence of decay product disequilibrium with the parent gas. This point is particularly important in case of thoron dosimetry where thoron progeny 212Pb accounts for the most of the radiological dose. The deposition depends on the size distribution of decay products and the structure of air turbulence at the air-surface interface. In the present work, the effect of varying air-flow (fan speed) and aerosol count median diameter (CMD) was studied on the deposition and distribution profile of 212Pb using computational fluid dynamics (CFD). The simulations have been carried out in a cubical calibration chamber of volume 8 m3, facilitated at RP&AD, BARC. Simulated results showed that the increase of total depositional loss rate of attached fraction of 212Pb due to increase of the fan speed was significant for CMD up to 400nm, beyond which this effect started becoming less prominent with increasing diameter. Besides, a minimum of the total depositional loss rate curve was seen to be shifted to the higher CMD with increase of the fan speed. CFD results were found to be in good agreement with experimental observations obtained in the controlled conditions with thoron source.

Activity Measurement of 44Sc and Calibration of Activity Measurement Instruments on Production Sites and Clinics.

44Sc is a promising radionuclide for positron emission tomography (PET) in nuclear medicine. As a part of the implementation of a production site for 44Sc, precise knowledge of the activity of the product is necessary. At the Paul Scherrer Institute (PSI) and the University of Bern (UniBE), 44Sc is produced by enriched 44CaO-target irradiation with a cyclotron. The two sites use different techniques for activity measurement, namely a dose calibrator at the PSI and a gamma-ray spectrometry system at UniBE and PSI. In this work, the 44Sc was produced at the PSI, and samples of the product were prepared in dedicated containers for onsite measurements at PSI, UniBE, and the Institute of Radiation Physics (IRA) in Lausanne for precise activity measurement using primary techniques and for the calibration of the reference ionization chambers. An accuracy of 1% was obtained for the activity measurement, allowing for a precise calibration of the dose calibrator and gamma-ray spectrometry of the two production sites. Each production site now has the capability of measuring 44Sc activity with an accuracy of 2%.

Development of walk-in type radon calibration chamber at KRISS

Development of walk-in type radon calibration chamber at KRISS

The influences of partial saturation on cone penetration tests in silty gold tailings

Laboratory-controlled cone penetration test results of a silty gold tailings in a variety of saturated and unsaturated states, obtained using two calibration chambers, are presented then interpreted using a state parameter-based approach. The research was conducted as part of the TAILLIQ project (tailliq.com), funded by the Australian Research Council and six mining companies, and involving four Australian universities.Cone penetration resistances, which increase due to the presence of suction when the tailings are unsaturated, can be normalised using the initial mean effective stress to establish a relationship with the initial state parameter. The relationship is applicable to saturated and unsaturated conditions, as long as the presence of suction hardening as well as the influence of suction on the mean effective stress are accounted for, and as long as the cone penetrations occur under pseudo drained conditions. The relationships enable state parameters and void ratios to be back-calculated from normalised cone penetration resistances.

Laboratory and field evaluation of a low-cost methane sensor and key environmental factors for sensor calibration.

Low-cost sensors enable finer-scale spatiotemporal measurements within the existing methane (CH4) monitoring infrastructure and could help cities mitigate CH4 emissions to meet their climate goals. While initial studies of low-cost CH4 sensors have shown potential for effective CH4 measurement at ambient concentrations, sensor deployment remains limited due to questions about interferences and calibration across environments and seasons. This study evaluates sensor performance across seasons with specific attention paid to the sensor's understudied carbon monoxide (CO) interferences and environmental dependencies through long-term ambient co-location in an urban environment. The sensor was first evaluated in a laboratory using chamber calibration and co-location experiments, and then in the field through two 8 week co-locations with a reference CH4 instrument. In the laboratory, the sensor was sensitive to CH4 concentrations below ambient background concentrations. Different sensor units responded similarly to changing CH4, CO, temperature, and humidity conditions but required individual calibrations to account for differences in sensor response factors. When deployed in-field, co-located with a reference instrument near Baltimore, MD, the sensor captured diurnal trends in hourly CH4 concentration after corrections for temperature, absolute humidity, CO concentration, and hour of day. Variable performance was observed across seasons with the sensor performing well (R 2 = 0.65; percent bias 3.12%; RMSE 0.10 ppm) in the winter validation period and less accurately (R 2 = 0.12; percent bias 3.01%; RMSE 0.08 ppm) in the summer validation period where there was less dynamic range in CH4 concentrations. The results highlight the utility of sensor deployment in more variable ambient CH4 conditions and demonstrate the importance of accounting for temperature and humidity dependencies as well as co-located CO concentrations with low-cost CH4 measurements. We show this can be addressed via Multiple Linear Regression (MLR) models accounting for key covariates to enable urban measurements in areas with CH4 enhancement. Together with individualized calibration prior to deployment, the sensor shows promise for use in low-cost sensor networks and represents a valuable supplement to existing monitoring strategies to identify CH4 hotspots.

Study on Calibration of Artificial Climate Chamber for Biological Application

Artificial climate chamber for biological application is widely used in biological laboratories. Parameters such as temperature, humidity and light intensity of artificial climate chamber can directly decide the accuracy of the experimental results. At present, there is no relevant calibration specification, or method for artificial climate chamber in China. This article presents a novel calibration method for artificial climate chambers for biological application to evaluate temperature, humidity, and light intensity control performance of the equipment, by determine corresponding environmental conditions, calibration standards, location of standards and calculation equations. The calibration results show that the calibration method is scientific and practical for metrological performance evaluation of artificial climate chambers for biological application.

Transition of Standard Dosimetry of Absorbed Dose to Water in External Beam Radiotherapy [Part 1]

The radiotherapy is performed with the aim of delivering the optimal dose to the target volume with minimal side effect of surrounding normal tissue. For this purpose, quality assurance is essential to ensure that the target volume is correctly irradiated in the optimal geometrical arrangement, and the absorbed dose evaluation is essential to ensure that the prescribed dose is correctly delivered. The absorbed doses are generally evaluated using a small cavity ionization chamber that utilizes gas ionization. For the evaluation of absorbed dose to water using ionization chambers, the national dose and charge standards, ionization chambers and electrometer calibration systems are required. And it is also required standard dosimetry protocol that recommend conditions such as fields, depths, and optimal ionization chambers for the measurement, as well as reliable physical data. This manuscript reviews the transition of standard dosimetry of absorbed dose to water in external beam radiotherapy, including the background of dose standards, ionization chamber calibration systems, units, and physical constants.

Use of tactile sensors for horizontal stress measurements on a large calibration chamber

Large flexible calibration chambers (CCs) to evaluate and develop interpretation methods for cone penetration tests (CPTs) in cohesionless soils have been used since the late 1960s. Nevertheless, only average boundary stress values are known in almost all tests already performed. Tactile pressure sensors (TPS) represent a useful tool to assess the stress distribution in an area under loading and have been applied in some geotechnical studies. This study presents the results of CPTs carried out on a large flexible CC in a very loose and a medium-dense fine quartz sand. TPS were placed on the walls of the CC, allowing the measurement of horizontal stresses and their spatial distribution in all test phases: sample formation, lateral and cavity cell filling, piston filling, sample stressing and CPT. In particular, TPS were able to measure the horizontal stresses before the cavity and lateral cell filling – that is, when no information is available about the horizontal stresses in regular tests. The measurements contribute to the discussion on the influence of the CC boundaries on the test results. The results encourage the use of TPS on a more routine basis in large flexible CC testing.

Signal-stabilized Al2O3:C-OSL dosimeter “checking chip” for correcting OSL reader sensitivity variation

Since an OSL reader sensitivity varies 15% over two years, the sensitivity variation should be corrected for every measurement. Conventionally, the OSL reader sensitivity is corrected by either preparing a new reference OSL dosimeter or reusing a reference OSL dosimeter previously used for calibration with corrections for signal depletion and fading effect. To facilitate the correction of the OSL reader sensitivity, a signal-stabilized Al2O3:C-OSL dosimeter “checking chip” was developed in this study. The checking chip has small signal depletion and fading effect, and can correct the OSL reader sensitivity without any corrections. The checking chip was prepared through the following steps. (a) The commercial OSL dosimeter was irradiated with approximately 100 Gy. (b) The irradiated dosimeter was partially bleached by exposing visible light at 30 s to decrease the effect of signal depletion. (c) The partially bleached dosimeter was stored at 50 °C for 30 d to stabilize signal regeneration. To evaluate the usability of the checking chip, dose measurements in a high-energy photon beam were performed for half a year. The absorbed dose to water in a high-energy photon beam was determined by the calibrated ionization chamber and the OSL dosimeter. The sensitivity variation of the OSL reader was corrected by reading the checking chip on every measurement day. The signal stability of the checking chip related to multiple readings and day elapsing were −0.013% per reading and within ±0.5% at 100 d, respectively. The relative standard uncertainty of dose determination with the OSL reader sensitivity correction was 1.7%. The OSL signal of the checking chip was sufficiently stable as a reference signal source and the OSL reader sensitivity variation can be more easily corrected by using the checking chip with the same uncertainty as the conventional method.

Feasibility of implementing a megavoltage ionization chamber calibration service at the secondary standards level

The purpose of this work was to investigate the feasibility of implementing a megavoltage calibration service for ionization chambers at the secondary standards level. Three reference-class ionization chambers were taken to the National Research Council (NRC) Canada for their primary megavoltage calibration service. Quadratic fits were applied to this data and used to determine calibration coefficients specific to the University of Wisconsin Medical Radiation Research Center (UWMRRC) beam qualities. The primary data and UWMRRC data were used to cross calibrate the three chambers. The resulting calibration coefficients were compared to the NRC values and agreement within 1% was observed. The uncertainty budgets developed for this secondary calibration service were found to be at the same level as those provided for a60Co calibration service at the secondary level. These results indicate that this type of service is feasible at the secondary standards level with the same level of uncertainty as the current standard of practice.

Experimental measurement of particle crushing around model piles jacked in a calibration chamber

During installation of driven or jacked piles in sand, particle crushing occurs in a region below the base of these piles. Quantification of the degree and extent of particle crushing during driving or jacking in sand is necessary to improve current design methods. To study the effects of particle crushing on the capacity of piles jacked in uniform silica sand samples, a model pile was jacked and tested in a half-cylindrical calibration chamber with transparent observation windows in its front wall. Annular samples of crushed sand 3 mm in thickness were recovered after testing from several locations along the shaft and the base of the model piles and used to assess particle gradation changes and to calculate breakage parameters. Relationships between the load mobilized at the base of the model piles and three breakage parameters are proposed. Furthermore, the number of jacking strokes (ranging from 1 to 32 in this research) has a negligible effect on the degree of crushing produced during installation and on the measured stresses at the base of the model pile. Analyses of the digital images captured during pile jacking indicate that the silica sand particles in the path of the model pile crush mainly along irregularities and sharp edges. Different zones are identified below the model pile according to the degree of particle crushing. Digital images taken during static loading of the model pile allowed tracking of the displacement paths of individual sand particles during loading.

Characterization of ion chambers set for different metrological applications

In this work, the standard dosimeters for radiotherapy, protection and X-ray dosimetry of the National Institute of Standards (NIS)-Egypt were standardized for metrological application. A set of standard dosimeters composed of 0.3, 0.6 and 30 cm3 ion chambers and NPL, Unidose electrometer was used for charge collection within the used chambers. Different beam qualities such as 60Co, 137Cs and X-ray machines were used as reference beams. The ion chambers and electrometers are traceable to SI units through the calibration at the BIPM every five years. The calibration factor drift of each chamber in air and water was determined and the full uncertainty budget of gamma doses at the reference condition was reported in accordance with the international protocols. Commissioning of the 60Co machine was performed and a comparison between the measured doses and the calculated doses was obtained for one half-life of 60Co. The data showed the high performance of the secondary standard dosimeter of NIS for calibration and metrological application in radiation therapy, protection and the X-ray range. The drift in the ion chamber calibration factor over the course of 2 decades is 0.12, 0.001 and 0.11 respectively, which extracted a ratio of 20%, 0.12% and 10.6% from the combined uncertainty.

A phantom-based study and clinical implementation of brainlab’s treatment planning system for radiosurgical treatments of arteriovenous malformations

Purpose. Development of a simple, phantom-based methodology allowing for pilot applications for the Elements TPS cranio-vascular module and clinical implementation prior to AVM treatments. Methods. A customized phantom was developed to be visible in MRI and CT images. High resolution digital subtraction angiograms (DSAs) and CT images of the phantom were acquired and imported into the Brainlab Elements treatment planning system. A clinical treatment plan with 5 arcs was generated in cranial vascular planning module and delivered to the phantom using a Varian TrueBeam STx Linac equipped with HD-MLCs and Brainlab ExacTrac imaging system for non-coplanar setup verification. The delivered dose was verified using a calibrated ionization chamber placed in the phantom. Upon verification of the TPS workflow, three patients with AVM who have been treated to date at our center using the Brainlab’s cranial vascular module for AVM are presented here for retrospective review. Results. The difference between the planed and measured dose by the ionization chamber was found to be less than 1%. Following a successful dose verification study, a clinical workflow was created. Currently, three AVM patients have been treated successfully. Clinical aspects of imaging and treatment planning consideration are presented in retrospective setting. Conclusions. Dose verification of the Brainlab Elements cranial vascular planning module for intracranial SRS treatments of AVM on Varian TrueBeam was successfully implemented using a custom-made phantom with <1% discrepancy. The Brainlab Elements’ cranial vascular module was successfully implemented in clinical workflow to treat patients with AVM. This manuscript provides a guideline for clinical implementation of frameless Linac-based AVM treatment using the Brainlab Elements TPS.

Cone penetration tests in saturated and unsaturated silty tailings

Laboratory-controlled cone penetration test results for two silty tailings in a variety of saturated and unsaturated states, obtained using two calibration chambers, are presented then interpreted using a state parameter-based approach. For each, the cone penetration resistances, which increase due to the presence of suction when the tailings are unsaturated, can be normalised using the initial mean effective stress to establish a relationship with the initial state parameter. The relationship is applicable to saturated and unsaturated conditions, as long as the presence of suction hardening as well as the influence of suction on the mean effective stress are accounted for, and as long as the cone penetrations occur under drained conditions. The relationships enable state parameters to be back-calculated from normalised cone penetration resistances. The state parameters enable estimations of the tailings’ peak friction angles for drained loadings as well as their propensities to liquefy during undrained loadings. Application is demonstrated using cone penetration test soundings in the tailings storages from which the samples were taken, showing how in situ void ratios and state parameters, as well as future state parameters if the tailings were to become saturated, can be determined. Close agreements with direct measurements of void ratios are shown.