Detector Arrangement Research Articles

A comparative study of optimization models for the gas detector placement in process facilities

Gas detector network is an important layer of protection in process facilities for prevention gas leakage accidents. But traditional standards just provide basic principles for the installation of detectors. In this study, three stochastic programming (SP) models are developed and contrasted, namely minimal detection time P-Median model (MDTP), minimal leakage concentration P-Median model (MLCP), and minimal individual risk P-median model (MIRP). Meanwhile all possible leak scenarios are identified based on the combination of wind field set and leakage sources. And clustering analysis is used to filter similar scenarios and select representative leak scenarios. The leak consequences are predicted by computational fluid dynamics (CFD) method and the results are served as the input data of these SP models. A case study is carried out in a diesel hydrogenation unit.

Experimental and numerical investigation of gas diffusion under an urban underground construction

• Built 10 m full-scaled utility tunnel mockup for experimental research. • Evaluated different air supply diffuser models and turbulence models. • Qualitative and quantitative comparisons for model performances. Rapid increase of urban underground constructions has a great consideration of underground environment safety and how to expel toxic gasses out of tunnels effectively. The utility tunnel is a typical urban tunnel construction with multiple underground pipelines including gas pipelines, and it is necessary to investigate characteristic of gas diffusion and monitor gas leakage to ensure tunnel safety. In this study, the experimental measurements of airflow and gas distributions were conducted in a 10 m full-scaled utility tunnel mockup, and gas diffusion characteristic was also investigated. Numerical simulation of utility tunnel leakage was also conducted by computational fluid dynamics (CFD). Different turbulence models and different air supply diffuser models were compared via the experimental results based on visualization and the relative root-mean-square error (RRMSE) index, which quantitated the difference between the numerical and experimental results. The results showed that the standard k − ε turbulence model and random air opening model could provide better results than other models. According to the experimental data analysis, it was necessary to consider the optimization of monitoring detector arrangements in actual utility tunnels. This study provided basic experimental data and the validated numerical model for the leakage source identification and underground tunnels simulation research.

Determining minimum number and placement of fault detectors in transmission network for fault location observability

This paper presents a new minimal placement strategy of fault detectors for fault-location on the transmission network. The proposed methodology includes two offline and online algorithms. First, the topology of a transmission network is analyzed, and the proposed offline algorithm is employed to determine the minimum number and location of detectors. Based on the arrival time of initial traveling wave-front acquired by the installed detectors, the online algorithm is introduced to identify the fault occurrence time as well as fault location. In order to extract the traveling wave from post-fault signals and construct the online algorithm, morphological edge detection (MED) filter is adopted. Extensive simulation studies based on the electromagnetic transients program and MATLAB Software have been carried out to evaluate the accuracy and reliability of the proposed method.

245 ps-TOF brain-dedicated PET prototype with a hemispherical detector arrangement

Brain PET, which has led research in molecular imaging and diagnosis of brain cancer, epilepsy and neurodegenerative disorders, is being spotlighted again to promote earlier diagnosis of dementia with the advent of amyloid and tau tracers. To meet this demand, in this paper, we developed a brain-dedicated PET imaging device with a hemispherical detector arrangement, which provides comparable sensitivity with fewer detectors than conventional cylindrical geometries. The introduction of the time-of-flight (TOF) measurement capability was a key point for the development to get a gain in the image signal-to-noise ratio. Currently, whole-body PET scanners with around 200–400 ps coincidence resolving time (CRT) are commercially available. In order to obtain the same TOF gain which can be obtained with 400 ps CRT for a 30 cm diameter object, 267 ps CRT will be required for a 20 cm diameter object such as the human head. In this work, therefore, we aimed at developing a TOF brain-dedicated PET prototype with the hemisphere detector arrangement and the CRT faster than 267 ps. The detector was composed of a 12 × 12 lutetium fine silicate (LFS) array coupled with a 12 × 12 multi-pixel photon counter (MPPC) array. Each LFS crystal with a size of 4.14 × 4.14 × 10 mm3 was individually coupled to a separate MPPC. Singles list-mode data from each detector were stored, and coincidences were identified using a coincidence-detection software algorithm. The CRT of 245 ps was finally achieved as the system average after a fine timing correction. For image reconstruction, we implemented the list-mode TOF-OSEM. For a small rod phantom, rods of 3 mm diameter were clearly separated. Also, images of the 3D Hoffman brain phantom, which demonstrated clear contrast between gray and white matter, supported the effect of TOF information.

Understanding Micromechanical Material Behavior Using Synchrotron X-rays and In Situ Loading

With the flux of high-energy, deeply penetrating X-rays that a 3rd-generation synchrotron source can provide and the current generation of large fast area detectors, the development and use of synchrotron X-ray methods have experienced impressive growth over the past two decades. This paper describes the current state of an important subset of synchrotron methods—high-energy X-ray diffraction employing in situ loading. These methods, which are known by many acronyms such as 3D X-ray diffraction (3DXRD), diffraction contrast tomography (DCT), and high-energy X-ray diffraction microscopy (HEDM), have shifted the focus of alloy characterization to include crystal scale behaviors in addition to microstructure and have made it possible to track the evolution of a polycrystalline aggregate during loading conditions that mimic alloy processing or in-service conditions. The paper is delineated into methods for characterizing elastic behavior including measuring the stress tensor experienced by each crystal and the inelastic response including crystal plasticity, phase transformations, and the onset of damage. We discuss beam size and detector placement, resolution, and speed in the context of the spatial and temporal resolution and scope of the resulting data. Work that emphasizes material models and the interface of data with various numerical simulations and machine learning is presented.

Optimal Placement of Detectors to Minimize Casualties in an Intentional Attack

This article proposes a mathematical model to optimally locate a set of detectors in such a way that the expected number of casualties in a given threat area can be minimized. The reliability of a detector is often a function of the duration that the threat remains within the effective radius. To accurately detect any threat event and to avoid any false alarm, in this article, two sets of detectors, primary and secondary, are utilized; the primary detectors rely on the secondary set as reinforcement to confirm or deny that a threat is present. The problem is formulated as a nonlinear binary integer programming model and then solved as a linearized branch and bound algorithm. A number of sensitivity analyses are performed to illustrate the robustness of the model and to draw key managerial insights. Experimental results reveal that a two-layer detection system will significantly minimize the expected number of casualties in a given threat area as opposed to a one-layer detection system.

Improving 3-D Imaging Breast Cancer Diagnosis Systems Using a New Method for Placement of Near-infrared Sources and Detectors

The objective of this research is to improve the 3-D imaging system using near-infrared light emission in breast tissue to achieve a more accurate diagnosis of the tumor. Experimental results in this research on this imaging system indicate that a more accurate diagnosis of abnormal areas depends on the location of the sources and detectors. Therefore, an improved location model has been proposed to determine a more suitable placement of sources and detectors. In this article, no human breast cancer samples were examined due to inaccessibility to a 3-D imaging system using near-infrared lights. Since such experiments should be conducted several times to obtain more accurate reconstructed images, the proposed method was evaluated using the optical images reconstruction toolbox of NIRFAST 7.2 in the MATLAB programming environment. The results were then compared with the results of similar articles. The obtained results showed that the proposed placement of sources and detectors can detect abnormal areas with a much lower error rate. Furthermore, the proposed placement of sources and detectors achieved a good result in simultaneously diagnosing two abnormal areas.

Optimization of gas detector placement considering scenario probability and detector reliability in oil refinery installation

Gas detection system is a critical layer of protection in process safety. Leak scenario probability and detector reliability are two key factors in the optimization of gas detector placement. However, they are easily neglected in previous studies, which may lead to an inaccurate evaluation of the optimization solutions. In this study, a stochastic programming (SP) optimization method is proposed considering these two factors. In order to quantitatively represent the probability of leak scenarios, a complete accident scenario set (CASS) is built combining leak sources and wind fields. Then, the computational fluid dynamics (CFD) method is adopted for consequence modeling of gas dispersion. The Markov model is developed to predict the detector reliability. With the objective of minimal cumulative detection time (MCDT), the SP formulation considering scenario probability and detector reliability (MCDT-SPR) is proposed. By introducing the particle swarm optimization (PSO) algorithm, the optimization formulations can be solved. A case study is investigated on a diesel hydrogenation refining unit. Results validate this approach is promising to improve the detection efficiency. This method is more practical and matching with the actual industrial environment, where the leak scenarios and the detector reliability can change dynamically in real process setting.

The circular electron-positron collider beam energy measurement with Compton scattering and beam tracking method.

The beam energy of the circular electron-positron collider should be measured precisely to the order of 1 MeV, in order to decrease the uncertainty of the Higgs/W/Z bosons' mass measurement. For this purpose, a lepton bunch is extracted from the collider and collides with an Yttrium-Aluminum-Garnet laser pulse. After the inverse Compton scattering, the main beam and the scattered beam pass through an analytical magnetic field and are deflected to different angles. At the end of the drift beam pipes, the deflecting distances are detected with the spatial resolution of several microns. The systematic uncertainties caused by the detector arrangement, the magnetic field, the angle between the detector plane and the incident beam, and the synchrotron radiation are discussed in detail. The simulations of the statistical errors are given with a toy Monte Carlo sample. With some proper corrections, the beam energy uncertainty of the Higgs mode is around 2 MeV. Our method is applicable to different operating modes of the collider.

Design study of a brain-dedicated time-of-flight PET system with a hemispherical detector arrangement

Time-of-flight (TOF) is now a standard technology for positron emission tomography (PET), but its effective use for small diameter PET systems has not been studied well. In this paper, we simulated a brain-dedicated TOF-PET system with a hemispherical detector arrangement. We modeled a Hamamatsu TOF-PET module (C13500-4075LC-12) with 280 ps coincidence resolving time (CRT), in which a 12 × 12 array of multi pixel photon counters (MPPCs) is connected to a lutetium fine silicate (LFS) crystal array of 4.1 × 4.1 mm2 cross section each, based on one-to-one coupling. On the other hand, spatial resolution degradation due to the parallax error should be carefully addressed for the small diameter PET systems. The ideal PET detector would have both depth-of-interaction (DOI) and TOF capabilities, but typical DOI detectors that are based on light sharing tend to degrade TOF performance. Therefore, in this work, we investigated non-DOI detectors with an appropriate crystal length, which was a compromise between suppressed parallax error and decreased sensitivity. Using GEANT4, we compared two TOF detectors, a 20 mm long non-DOI and a 10 mm long non-DOI, with a non-TOF, 4-layer DOI detector with a total length of 20 mm (i.e. 5 × 4 mm). We simulated a contrast phantom and evaluated the relationship between the contrast recovery coefficient (CRC) and the noise level (the coefficient of variation, COV) for reconstructed images. The 10 mm long non-DOI, which reduces the parallax error at the cost of sensitivity loss, showed better imaging quality than the 20 mm long non-DOI. For example, the CRC value of a 10 mm hot sphere at COV = 20% was 72% for the 10 mm long non-DOI, which was 1.2 times higher than that of the 20 mm long non-DOI. The converged CRC values for the 10 mm long non-DOI were almost equivalent to those of the non-TOF 4-layer DOI, and the 10 mm long non-DOI converged faster than the non-TOF 4-layer DOI did. Based on the simulation results, we evaluated a one-pair prototype system of the TOF-PET detectors with 10 mm crystal length, which yielded the CRT of 250 ± 8 ps. In summary, we demonstrated support for feasibility of the brain-dedicated TOF-PET system with the hemispherical detector arrangement.

Monitor Points Selection in CFD FLACS for Gas Detector Placement

Gas detector first invented was in 1815 to detect the presence of the methane gas and becomes part of a safety system when it is capable to detect the gas leakage and decrease the risk of major accident occurrence. However, the efficiency of the gas detector has been questioned among industry people due to unable to measure the effectiveness of the gas detector quantitatively. Industry people has a problem on how many and where should they locate the gas detector. This study explained the very beginning steps on how to determine the number and location of the gas detector should be installed. This research simulated the gas explosion cloud by using CFD FLACS at highly hazardous area by setting the four parameters with different values of wind speed, wind direction, leak rate and leak direction. In order to optimize the placement of the gas detector, three objectives need to be achieved: 1) to obtain the fastest response time of the gas detector to any gas leakage, 2) to ensure the availability of the gas detection system in worst conditions and 3) to place the gas detector in the potentially hazardous area. The locations of the gas detector meet the objectives based on the approach applied in this study.

QUANTOM® − Optimization of the online neutron flux measurement system

For the final disposal of radioactive waste, the waste packages have to meet the acceptance requirements defined by national licensing and supervisory authorities. Nondestructive methods are very much preferred over destructive methods for the qualification or re-qualification. Existing nondestructive methods as integral or segmented gamma scanning or neutron counting only determine the isotope specific activity but do not allow quantifying other non-radioactive hazardous substances. These should have been documented during creation, conditioning, and packaging of the waste. But especially for legacy waste, this documentation is often poor or even missing. This gap is to be filled by the QUANTOM® measurement device that will determine the mass fraction of elements within a 200-l-drum using the Prompt- and Delayed- Gamma-Neutron-Activation-Analysis. In order to obtain a spatially resolved characterization, it will employ a segmented scanning approach. For the determination of the absolute mass fractions, the neutron flux inside the drum has to be known accurately. As the waste itself will alter the neutron distribution and flux, it is not possible to calculate the latter a priori from the gamma measurement. Hence the neutron flux has to be measured simultaneously with the gamma radiation. In this presentation, we will introduce the system for measuring the thermal neutron flux surrounding the waste drum from which the flux within the waste package has to be reconstructed. We performed a simulation study to score several possible detector placements for an improved reconstruction performance. We will show the outcome of these calculations and present the final design of the detector arrangement.

Comparative studies of photo-acoustic gas analyzers based on tunable CO2 lasers with external and intracavity detector arrangement

The results of comparative studies of laser photo-acoustic (PA) gas analyzers with external and intracavity arrangement of resonant differential photo-acoustic detector (PAD) are presented. An automated tunable waveguide RF-excited CO2 laser was used in the PA gas analyzers. During the experiments, the optimal design of the resonant differential PAD was determined, in which the various models of microphones were tested. Studies of the effect of gas flow rate through the PAD, measurements of gas absorption spectrum (CO2) at different PAD resonant frequencies have been carried out. Two versions of transportable PA gas analyzers with different detector arrangements are developed and tested: outside and inside the cavity of tunable CO2 laser. For an integration time of 1 s, the minimum detectable absorption for the external PA gas analyzer is αmin = 7.5 × 10−10 cm−1, for the intracavity PA gas analyzer αmin ~ (3.5 ± 0.4) × 10−10 cm−1. It is shown that the value of the minimum detectable absorption αmin is practically independent of the external or intracavity location of the differential PAD, i.e. from the power of CO2 laser radiation in the range of ~1.5–100 W.

Modified NEMA NU-2 performance evaluation methods for a brain-dedicated PET system with a hemispherical detector arrangement**This study is partially supported by ATOX Co., Ltd., Japan.

Brain PET imaging has important roles in neurology, neuro-oncology and molecular imaging research. We have developed a helmet-type PET prototype and have shown that the proposed hemispherical geometry had high potential for realizing high-sensitivity and low-cost brain imaging. However, there is no standard performance evaluation method for helmet-type PET, which would be a bottleneck to its commercialization. Therefore, we investigated appropriate performance evaluation methods for a helmet-type PET based on the NEMA NU 2-2018 standards. For those measurement methods that are not applicable to the helmet-type PET, we changed them while keeping the basic concept of the original NEMA standards. We measured spatial resolution, sensitivity, scatter fraction, count rate characteristics, accuracy of corrections for count losses and randoms, and image quality. We partially changed the measurement methods by making brain-size phantoms and by optimizing the length or the position of radioactive sources. The spatial resolution was 2.8 mm at 1-cm offset position by the filtered back-projection method. Sensitivities measured by the NEMA original setup and the proposed setup were 13.4 and 57.1 kcps/MBq. The respective values measured with our developed brain-size scatter phantom and with the conventional whole-body-size scatter phantom were: scatter fractions of 35% and 35%; peak NECRs of 25.1 kcps at 3.2 kBq/ml and 19.8 kcps at 2.6 kBq/ml ; and maximum absolute biases of 5.5% and 16.0%. The image quality was evaluated with the developed brain-size phantom, and good image quality was obtained. The helmet-type PET prototype showed high-sensitivity even with the small number of 54 detectors. The spatial resolution was better than 4.0 mm over the field-of-view. In conclusion, we proposed the performance evaluation methods for a brain-dedicated PET system with a hemispherical geometry. The proposed method could facilitate evaluation of performance characteristics of brain-dedicated PET scanners and optimization of its scanning and reconstruction parameters.

Miniature and fully portable gradient capillary liquid chromatograph

A robust, portable and miniature battery powered gradient capillary liquid chromatograph (total weight ∼2.7 kg, without battery ∼2.0 kg), with integrated microfluidic injection, column heating and high sensitivity low-UV absorbance detection is presented. The portable capillary chromatograph, was applied with a packed reversed-phase capillary column (100 mm × 300 μm I.D., 5 μm ODS), housed within an integrated capillary column heater controlled by a proportional-integral-derivative (PID) chip module. The system delivered retention time and peak area relative standard deviation in isocratic mode of <0.7% (n = 10) and <3.3% (n = 10), respectively, and <0.1% (n = 10) and <2.3% (n = 10) respectively, for gradient elution mode. Detection was based upon a 255 nm light-emitting diode (LED) using one of two commercial capillary flow-cell options, namely a high sensitivity 12 nL Agilent capillary z-cell (HSDC) and a 45 nL Thermo Fisher Scientific UZ-View™ flow cell (UZFC). The HSDC, housed within a 3D printed detector arrangement, gave an effective pathlength of 1.01 mm (84% of nominal pathlength) and stray light of only 0.2%. Limits of detection for four test small molecule pharmaceuticals ranged from 65 to 101 μg L−1 based upon a 316 nL injection volume, with separation efficiencies of between 18,000 and 29,700 N m−1, with sub-4 min run times. The portable capillary LC system was successfully coupled to a small footprint portable mass spectrometer (Microsaic 4500 MiD) to demonstrate compatibility and ‘point-of-need’ miniaturised LC-MS capability.

Formula omitted]-[formula omitted] fast timing at X-ray energies and investigation on various timing deviations

We report on systematic γ-γ fast-timing measurements by using four cylindrical 1.5′′×1.5′′ LaBr3(Ce) scintillator detectors which were installed in compact geometry around the focal plane of the Lohengrin fission-fragment separator at the Institut Laue–Langevin in Grenoble, France. Unconventional γ-ray sources as 185Os and 187W were produced by thermal-neutron activation to provide nearly prompt low-energy γ and K-X rays with average γ- and X-ray multiplicity equal to two. Due to practically no contribution of Compton background, highly precise results of time-walk measurements down to 40 keV are presented. Timing deviations related to different phenomena have been investigated, such as the geometry of an extended γ-ray source and the detector arrangement, long-term timing shifts and the timing contributions of the Compton background and the inter-detector Compton-scattering. The geometrical timing deviations are shown to be minimized using a multi-element detector array with a centrally symmetric arrangement relative to the center of the focal plane. Time-correction formula are proposed as analytical corrections for long-term time shifts, the time contributions of the Compton background and the position-dependent change of the time walk for cases where the calibration source cannot be placed at the center of the focal plane.

Development of scattering based glucose sensor using hydrothermally synthesized cuprous oxide nanoparticles

The aim of the present paper is to develop an optical glucose sensor employing the scattering effect of light. The cuprous oxide nanoparticles were prepared by a hydrothermal route. The surface morphology, elemental distribution and the average crystallite size of the synthesized nanoparticles have been analyzed by using SEM, EDX and XRD techniques respectively. The SEM images show the spherical structure of cuprous oxide nanoparticle and the highest peak of the cuprous and oxygen in the EDX illustrates the formation of cuprous oxide nanoparticles. The XRD confirms that the Cu2O was successfully synthesized by hydrothermal route with its crystallite size 12.33 nm. The optical characterization of the film was carried out by UV–VIS spectroscopy and optical band gap was found as 3.98 eV. The optical glucose sensing behavior of the sensor was investigated by the perpendicular arrangement of laser and detector employing the solution of glucose and cuprous oxide as a scattering medium. The maximum sensitivity of the sensor was recorded as 7.19 nW/mole and the % of sensor response as 898.

Multi-objective optimization considering cost-benefit ratio for the placement of gas detectors in oil refinery installations

It is of great importance for an oil refinery installation to have an effectively designed gas detection system. The majority of current research on the optimization of gas detector placement focuses on a single-objective stochastic programming (SP) approach. However, it is actually a multi-objective optimization problem, trying to obtain optimal solutions with conflicting criteria. This paper proposes a multi-objective optimization method for detector placement, achieving a balance between the detection efficiency improvement and the required investment. Based on the leakage scenario and the consequence modelling, the cumulative death probability (CDP) in the whole unit is quantitatively represented. The reduced fatality can also be evaluated according to the detection time. Then, a cost-benefit ratio (CBR) model of the gas detector investment and benefit from fatality reduction can be established. With the objective of minimizing both the CDP and CBR, a multi-objective layout optimization model considering the cost-benefit (MLOM-CB) is proposed. A non-dominated sorting genetic algorithm-II (NSGA-II) is used to obtain acceptable results. The optimization of hydrogen sulfide gas detector placement is taken as a case study. Results demonstrate that this approach can improve the detection efficiency of gas detector networks and the flexibility of decision-making for gas detector investment.

A mathematical programming approach for the optimal placement of flame detectors in petrochemical facilities

Flame detectors provide an important layer of protection for personnel in petrochemical plants, but effective placement can be challenging. A mixed-integer nonlinear programming formulation is proposed for optimal placement of flame detectors while considering non-uniform probabilities of detection failure. We show that this approach allows for the placement of fire detectors using a fixed sensor budget and outperforms models that do not account for imperfect detection. We develop a linear relaxation to the formulation and an efficient solution algorithm that achieves global optimality with reasonable computational effort. We integrate this problem formulation into the Python package, Chama, and demonstrate the effectiveness of this formulation on a small test case and on two real-world case studies using the fire and gas mapping software, Kenexis Effigy.

A stochastic programming approach for the optimization of gas detector placement in offshore platforms

In offshore platforms, effective gas detection system is an essential layer of protection for preventing potential gas release accident from turning to fire and explosion disasters. However, according to statistics the actual efficiency of gas detection systems is still unsatisfactory. In this work, a stochastic programming (SP) approach is proposed to arrange gas detectors in optimal places. Combined with meteorological data and the hydrocarbon releases (HCR) database, the equipment leakage scenarios are envisaged. The computational fluid dynamics (CFD) commercial code Ansys-Fluent is used to simulate selected scenarios and predict the consequences. With the objective of minimizing the cumulative risk of gas leakage scenarios, a stochastic mixed-integer linear programming formulation based on p-median value theorem is proposed. Then particle swarm optimization (PSO) algorithm is used to solve the optimization model. The gas detector placement optimization on an oil drilling production platform (DPP) is also carried out as a case example. This methodology can be used in the design phase of offshore platform and can hopefully enhance the performance of the gas detection system.