| 1. |
- Beal, Jacob, et al.
(författare)
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Robust estimation of bacterial cell count from optical density
- 2020
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Ingår i: Communications Biology. - : Springer Science and Business Media LLC. - 2399-3642. ; 3:1
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Tidskriftsartikel (refereegranskat)abstract
- Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data.
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| 2. |
- Al-Adili, Ali, et al.
(författare)
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Isomer yields in nuclear fission
- 2021
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Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2100-014X. ; 256
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Tidskriftsartikel (refereegranskat)abstract
- The generation of angular momentum in the fission process is still an open question. To shed light on this topic, we started a series of measurements at the IGISOL-JYFLTRAP facility in Finland. Highprecision measurements of isomeric yield ratios (IYR) are performed with a Penning trap, partly with the aim to extract average root-mean-square (rms) quantities of fragment spin distributions. The newly installed Phase-Imaging Ion-Cyclotron Resonance (PI-ICR) technique allows the separation of masses down to tens of keV, which is suffcient to disentangle many isomers. In this paper, we first summarize the previous measurements on the neutron and proton-induced fission of uranium and thorium, e.g. the odd cadmium and indium isotopes (119 ≤ A ≤ 127). The measurements revealed systematic trends as function of mass number, which stimulated further exploration. A recent measurement was performed at IGISIOL and several new IYR data will soon be published, for the first time. Secondly, we employ the TALYS nuclear-reaction code to model one of the newly measured isomer yields. Detailed GEF and TALYS calculations are discussed for the fragment angular momentum distribution in 134I.
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| 3. |
- Chen, Zhihao, et al.
(författare)
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Effect of Lifestyle on the Adoption of Mobile Services
- 2012
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Ingår i: The eleventh Wuhan international conference on e-business. - : Alfred University. - 9780980051056 ; , s. 390-397
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Konferensbidrag (refereegranskat)abstract
- Although mobile services have gained huge potential market in recent years, the adoption of mobile services has been far slower than expected. Many scholars put forward mobile services adoption models to explore the causes of low adoption of mobile services. But few researchers have explained why different types of services differ in terms of popularity from the view of lifestyle. The authors attempt to explain the adoption of various mobile services in the view of lifestyle through descriptive analysis and ANOVE analysis in China. And the conclusions are as follows: 1) the adoption of different types of mobile services varies with different groups of users, because 2) different groups of users often have their own lifestyles (e.g., new life consciousness, arbitrary consciousness, financial consciousness, etc.), 3) which can significantly affect their intention to adopt various mobile services.
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| 4. |
- Gao, Hongkai, et al.
(författare)
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Stepwise modeling and the importance of internal variables validation to test model realism in a data scarce glacier basin
- 2020
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Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694. ; 591
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Tidskriftsartikel (refereegranskat)abstract
- Model realism is of vital importance in science of hydrology, in terms of realistic representation of hydrological processes and reliability of future prediction. Here, we employed a stepwise modeling approach that leverages flexible model structures and multi-source observations for robust streamflow simulation and internal variables validation with improved model realism. This framework is demonstrated in Yigong Zangbu River (YZR) basin, a data scarce glacier basin in the upper Brahmaputra River. We designed six experiments (Exp1–6) to use modeling as a tool to understand hydrological processes in this remote cold basin with extremely high altitude. In Exp1, we started with a distributed rainfall-runoff model (FLEXD) - representing the case that snow and glacier processes were ignored. Then, we stepwisely added snow and glacier processes into FLEXD, denoted as FLEXD-S (Exp2) and FLEXD-SG (Exp3), respectively, and such improvement of model structure led to significantly improved streamflow estimates. To explore the impact of different precipitation forcing on model performance, FLEXD-SG was driven by Theissen average (Exp3) and three individual stations’ precipitation (Exp4–6). The model realism was tested by observed hydrograph, snow cover area (SCA) and glacier mass balance (GMB). Results showed that a robust and realistic hydrological modeling system was achieved in Exp6. In this modeling study, we learned that: 1) stepwise modeling is effective in investigating catchment behavior, and snow and glacier melting are the dominant hydrological processes in the YZR basin; 2) internal variables validation is beneficial to test model realism in data scarce basin; 3) the FLEXD-SG model calibrated by only one year hydrograph is sufficient to reproduce snow and glacier variations; 4) precipitation of a single station as forcing data could outperform Theissen average; 5) based on the well tested model configuration in Exp6, we analyzed simulated results, and reconstructed the long term hydrography (1961–2013), to support the potential competence for decision making on water resources management in practice. The proposed framework may significantly improve our skills in hydrological modeling over data-poor regions.
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| 5. |
- Gao, Shang, 1982-, et al.
(författare)
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An exploratory study on lifestyles and the adoption of mobile services in China
- 2012
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Ingår i: Proceedings of the 10th International Conference on Advances in Mobile Computing & Multimedia. - New York : Association for Computing Machinery (ACM). - 9781450313070 ; , s. 249-252
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Konferensbidrag (refereegranskat)abstract
- This study examines the relationship between the lifestyles of Chinese consumers and the adoption of mobile services. Based on a sample from 313 respondents from the biggest city in central China, the results show that consumers with different lifestyles have different preferences over a number of identified mobile services. It is found that there are some lifestyle factors, such as the investment consciousness and the financial contentment consciousness, having significant negative impact on the adoption of office/learning tools on mobile devices. Furthermore, Chinese consumers are clustered into four lifestyle segments by two dimensions: the quality-awareness fashionable dimension and the economical dimension. The findings demonstrate that the quality-awareness fashionable dimension has stronger impact than the economical dimension toward the adoption of all the five types of mobile services. © 2012 ACM.
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| 6. |
- Gao, Shang, 1982-, et al.
(författare)
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Lifestyles and mobile services adoption in China
- 2014
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Ingår i: International Journal of E-Business Research. - : IGI Global. - 1548-1131 .- 1548-114X. ; 10:3, s. 36-53
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Tidskriftsartikel (refereegranskat)abstract
- Along with the popularity of mobile devices and advances in wireless technology, mobile services have become more and more prevalent. To the best of knowledge, despite the potential importance of lifestyle, little research has been performed on the effect of various lifestyle factors on mobileservices diffusion, particularly in the Chinese context. This study examines the relationship between the lifestyles of Chinese consumers and the adoption of mobile services. Based on a sample of 313 respondents from the biggest city in central China, one can show that consumers with different lifestyles have different preferences related to a number of the identified mobile services. Furthermore, Chinese consumers are clustered into four lifestyle segments by two dimensions: the quality-awareness fashionable dimension and the economical dimension. The findings demonstrate that the quality-awareness fashionable dimension has stronger impact than the economical dimension toward the adoption of all the five types of mobile services.
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| 7. |
- Gao, Zhihao, et al.
(författare)
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Applying machine learning methods for the analysis of two-dimensional mass spectra
- 2023
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Ingår i: European Physical Journal A. - : Springer Nature. - 1434-6001 .- 1434-601X. ; 59:169
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Tidskriftsartikel (refereegranskat)abstract
- In a measurement of isomeric yield-ratios in fission, the Phase-Imaging Ion-Cyclotron-Resonance technique, which projects the radial motions of ions in the Penning trap (JYFLTRAP) onto a position-sensitive micro-channel plate detector, has been applied. To obtain the yield ratio, that is the relative population of two states of an isomer pair, a novel analysis procedure has been developed to determine the number of detected ions in each state, as well as corrections for the detector efficiency and decay losses. In order to determine the population of the states in cases where their mass difference is too small to reach full separation, a Bayesian Gaussian Mixture model was implemented. The position-dependent efficiency of the micro-channel plate detector was calibrated by mapping it with 133Cs+ ions, and a Gaussian Process was trained with the position data to construct an efficiency function that could be used to correct the recorded distributions. The obtained numbers of counts of excited and ground-state ions were used to derive the isomeric yield ratio, taking into account decay losses as well as feeding from precursors.
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| 8. |
- Gao, Zhihao, et al.
(författare)
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Benchmark of a multi-physics Monte Carlo simulation of an ionguide for neutron-induced fission products
- 2022
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Ingår i: European Physical Journal. - : Springer Nature. - 1286-0042 .- 1286-0050. ; 58:2
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Tidskriftsartikel (refereegranskat)abstract
- To enhance the production of medium-heavy,neutron-rich nuclei, and to facilitate measurements of independentyields of neutron-induced fission, a proton-toneutronconverter and a dedicated ion guide for neutroninducedfission have been developed for the IGISOL facilityat the University of Jyväskylä. The ion guide holds thefissionable targets, and the fission products emerging fromthe targets are collected in helium gas and transported to thedownstream experimental stations.Acomputer model, basedon a combination of MCNPX for modeling the neutron production,the fission code GEF, and GEANT4 for the transportof the fission products, was developed. The model willbe used to improve the setup with respect to the productionand collection of fission products. In this paper we benchmarkthe model by comparing simulations to a measurementin which fission products were implanted in foils located atdifferent positions in the ion guide. In addition, the productsfrom neutron activation in the titanium foil and the uraniumtargets are studied. The result suggests that the neutron fluxat the high-energy part of the neutron spectrum is overestimatedby approximately 40%.However, the transportation offission products in the uranium targets agrees with the experimentwithin 10%. Furthermore, the simulated transportationof fission products in the helium gas achieves almost perfectagreement with the measurement. Hence, we conclude thatthe model, after correction for the neutron flux, is well suitedfor optimization studies of future ion guide designs.
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| 9. |
- Gao, Zhihao
(författare)
-
Benchmark of simulation of an ion guide for neutron-induced fission products
- 2022
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Independent yield distributions of high-energy neutron-induced fission are of importance to achieve a good understanding of fission. Even though the mass and charge yield distributions of thermal neutron-induced fission are well known, there are few experimental data for high-energy neutron-induced fission. In addition to basic research on the fission process, independent yield distributions of high-energy neutron-induced fission play a key role in the development of Generation IV fast nuclear reactors.To facilitate measurements of independent fission yields of high-energy neutron-induced fission, a dedicated ion guide and a proton-neutron converter were developed and put to use in experiments at the isotope separator facility IGISOL in Jyväskylä. In parallel, a simulation model of the system was developed in order to optimize the collecting efficiency of fission products in the ion guide. The model uses the Monte Carlo code MCNPX to simulate the neutron production, the fission model code GEF to simulate the fission process, and GEANT4 for ion transportation. In order to benchmark the simulation model, metal foils were inserted in the ion guide with the purpose of collecting fission products. At the same time, nickel, cobalt and indium foils were located between the pn-converter and the ion guide to record the neutron flux from the pn-converter. After the beam was turned off, and after several days of cooling, g-ray spectroscopy measurements of the foils were conducted using a well shielded HPGe detector. Based on the identified g-ray transitions in the spectroscopy data, the productions of corresponding fission products and neutron activation products were calculated, and then used to benchmark the transportation and collection of fission products, as well as neutron production, in the simulations.The conclusion from the benchmark is that the transportation of fission products in the helium gas, as simulated by GEANT4, agrees very well with the measurement, while the transportation of fission products in the uranium targets agrees with the measurement within 10%. The neutron flux at the high-energy part of the neutron spectrum is overestimated by about 40%.Thanks to the benchmark it has been shown that the predictive power of the model is satisfactory and sufficient for the purpose of modeling the ion guide. Furthermore, the parameters involved in the simulations, such as neutron production, distance between the neutron source and the ion guide, volume of the ion guide and so on, play an important role in the optimization of the setup. However, the lower than expected fission rate suggests that the optimization on these parameters may not be enough to achieve a sufficiently high intensity of fission products, especially for nuclei far from the stability line. To achieve a sufficiently high intensity, an electric field guidance, similar to the RF structure of the CARIBU gas catcher presented in G.Savard et al. Nucl. Inst. Meth. B, 376: 246, 2016, to collect fission products is considered.
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| 10. |
- Gao, Zhihao
(författare)
-
Deducing angular momenta in nuclear fission of 238U
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Background: Angular momenta of fission fragments considerably higher than that of the fissioning nucleus have been observed several times, raising the question of how these high angular momenta are generated. J.Wilson et al. have proposed that the angular momentum is generated after scission, from the collective motion of nucleons in the ruptured neck of the fissioning system. This conclusion is based on observed average angular momenta deduced from γ-ray spectroscopy, which seems to suggest that the angular momentum of a fission fragment is independent from that of the complementary fragment. Willson et al. also propose a model for the angular momentum as a function of mass for fission products in the low and high mass peak. However, there is no systematic study, and hence no model, for the angular momenta of fission fragments in the symmetric mass region.Purpose: To deduce the angular momenta of fission fragments based on the observed isomeric yield ratios in25-MeV proton-induced fission of 238UMethod: A surrogate model of the fission code GEF has been developed to generate properties of primary fission fragments. Based on the excitation energy (Ex) and angular momentum (J) of fission fragments from GEF, an energy versus angular momentum (Ex − J) matrix is reconstructed using a set of parameters. With such matrices as input, the reaction code TALYS is used to calculate the de-excitation of the fission fragments, including the population of the isomers, from which the isomeric yield ratios are obtained. By varying one of the parameters, the root-mean-square angular momentum (Jrms) determining the angular momentum distribution of the matrix, Jrms-dependent isomeric yield ratios are obtained. By matching the calculated ratios with the experimental value, the most likely Jrms for that fragment is obtained. Repeating this procedure for all fragments contributing to anisomeric yield ratio for a given fission product, makes it possible to deduce the average angular momentum of the contributing fragments.Results: Data of 31 isomeric yield ratios were analysed in 25-MeV proton-induced fission of 238U. In seven cases, no conclusive result for the angular momentum could be obtained. However, the average Jrms with uncertainties are presented for 24 different fission products. For the purpose of comparing the result with those of Willson et al., also the average of the average angular momentum (Jav ) with uncertainties is presented.Conclusion: A mass dependency of the average angular momentum is observed in the proton-induced fission of 238U. Moreover, the average angular momenta for mass numbers A≥ 132 could be described by the parameterisation proposed by J. Wilson. However, a significant discrepancy between the Jav of 130Sn and 131Te between the data and the model suggests a different lower limit for the validation of the parameterisation compared to that suggested by Willson et al. In general, higher Jav for A≥ 132 is observed in the present work compared to those from Willson et al.. This is likely due to the higher excitation energy of the fissioning nuclei in this work compared to Wilssons’. Furthermore, systematic measurements of the average angular momenta of fission products in the symmetric mass region are presented for the first time. In this region, a decreasing trend with mass number is observed.
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| 11. |
- Gao, Zhihao, et al.
(författare)
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Fission studies at IGISOL/JYFLTRAP : Simulations of the ion guide for neutron-induced fission and comparison with experimental data
- 2020
-
Ingår i: ND 2019. - : EDP Sciences. - 9782759891061
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Konferensbidrag (refereegranskat)abstract
- For the production of exotic nuclei at the IGISOL facility, an ion guide for neutron-induced fission has been developed and tested in experiments. Fission fragments are produced inside the ion guide and collected using a helium buffer gas. Meanwhile, a GEANT4 model has been developed to simulate the transportation and stopping of the charged fission products. In a recent measurement of neutron-induced fission yields, implantation foils were located at different positions in the ion guide. The gamma spectra from these foils and the fission targets are compared to the results from the GEANT4 simulation.In order to allow fission yield measurements in the low yield regions, towards the tails and in the symmetric part of the mass distribution, the stopping and extraction efficiency of the ion guide has to be significantly improved. This objective can be achieved by increasing the size while introducing electric field guidance using a combination of static electrodes and an RF-carpet. To this end, the GEANT4 model is used to optimise the design of such an ion guide.
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| 12. |
- Gao, Zhihao
(författare)
-
Isomeric yield ratios in nuclear fission
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Isomeric yield ratios (IYR), referring to the relative yield of the high spin states of a nucleus to the total yield of all observed states, is an observable of nuclear fission that has the potential to improve our understanding of the fission dynamics. Apart from that, systematic observations of IYRs can also contribute to other areas, such as the validation of fission models, modelling of the r-process in stellar nucleosynthesis, studies of the antineutrino mixing angle, the safety of present-day nuclear reactors, and the design of advanced reactor systems.With these motivations in mind, an IYR measurement in proton-induced fission was performed at the IGISOL facility in Jyväskylä, Finland. In the measurement, the Penning trap JYFLTRAP was used to separate the excited state from the ground state and to project those onto a position-sensitive MCP detector. The obtained phase images were used to train a Bayesian Gaussian Mixture model to identify the states. After considering corrections for the detector efficiency and radioactive decay, 19 IYRs were obtained.In this thesis, the measurement of IYRs with the IGISOL technique is described, and a systematic study of IYRs in proton-induced fission is presented. Furthermore, the measured ratios are compared with calculations using three different models: the Madland-England (ME) model, the fission model GEF, and the combination of GEF + TALYS. The experimental results show that, in general, the IYR decreases with the spins of measured states. While this, to some degree, confirms the ME model, variations in the IYR between nuclides with the same spin assignments reveal that the model is too simple to predict individual ratios. Furthermore,discrepancies in the IYRs between the measurement and GEF are observed in most cases, indicating a need to optimize the performance of GEF against nuclear data from proton-induced fission. The combination of GEF + TALYS results in an overall under estimation of the observedIYRs, which could be explained by the different assumptions used in GEF and TALYS.To investigate how the angular momenta of the primary fission fragments relate to the IYRs, a surrogate model of GEF has been developed. By reproducing the measured IYR with the calculated ratios from the model, the average angular momentum Jav, is deduced. The Jav for fission products with a mass number greater than 131 show a mass dependency which fits the parameterisation proposed by J. Wilson et al,. For IYRs in the mass region 119 ≤ A < 132, in which no measurements are presented by Wilson, a decrease in the Jav with increasing mass number is observed for the first time.Besides the study of IYRs, a benchmark of a multi-physics simulation model of the ion guide for neutron-induced fission products has been performed using γ-ray spectroscopy data. The results of the benchmark show that the high-energy part of the neutron flux from the simulation with MCNPX is overestimated by about 40 %, while the ion transportation simulated with GEANT4 agrees well with the experimental data. Based on the benchmark, the ion guide can be optimized to achieve high enough intensities of the collected ions to reach reasonable measurement times. In the next step, the addition of electric fields is considered to direct the ions in and to reduce the ion drifting time. However, this task lies outside the scope of this PhD thesis.
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| 13. |
- Gao, Zhihao, et al.
(författare)
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Isomeric yield ratios in proton-induced fission of 238U
- 2023
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Ingår i: Physical Review C. - : American Physical Society. - 2469-9985 .- 2469-9993. ; 108:5
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Tidskriftsartikel (refereegranskat)abstract
- Background: Isomeric yield ratios are an important observable in nuclear fission as they can guide model development by providing insight into the angular momentum generation. Furthermore, isomeric yield ratios are important in applications for nuclear energy, as well as in the study of the r-process in stellar nucleosynthesis, and in the antineutrino mixing angle from reactor spectra. In nuclear data evaluations, the Madland-England model is commonly used to estimate isomeric yield ratios that have not been measured.Purpose: To measure isomeric yield ratios in 25-MeV proton-induced fission of 238U, and to compare the result with the values obtained from the Madland-England model and the fission model code GEF. Furthermore, to evaluate whether the predictions of GEF can be improved by coupling it to the nuclear reaction code TALYS.Methods: Isomeric yield ratios in 25-MeV proton-induced fission of 238U have been measured at the Ion GuideIsotope Separate On-Line facility. The excited state and the ground state were separated by mass using the Phase-Imaging Ion-Cyclotron-Resonance technique in the double Penning trap JYFLTRAP. The number of counts of each state was extracted from the phase-images using a Bayesian Gaussian Mixture model and, after corrections fordetector efficiency and decay, the isomeric yield ratios were derived. The experimental values have been compared with the calculated results from the Madland-England model and the GEF code. Furthermore, GEF has been combined with the nuclear reaction code TALYS, in order to take advantage of the latter codes’ implementation of the Hauser-Feshbach formalism, and the results have been compared with the experimental values.Results: From the measurements, 19 new isomeric yield ratios in 25-MeV proton-induced fission of 238U are reported and are, together with another 12 isomeric yield ratios (IYRs) from a previous campaign, compared with the model calculations. It is shown that, though the models manage to capture some of the features observed, there is room for improvement.Conclusions: As predicted by the Madland-England model, a strong correlation between the measured IYRs and the spins of the long-lived states of the fission products is confirmed. However, the IYRs also vary between nuclides with the same spin-parity of the two states, and systematic trends in the IYRs of close-lying isotopes and isotones with similar nuclear configurations are observed.From the comparison of the experimental data with the prediction of GEF it is concluded that more data from proton-induced fission are needed to optimize the internal parameters of GEF. Furthermore, using a combination of GEF and TALYS in most cases results in an underestimation of the yield ratios. This might be explained by an underestimation of the angular momentum on the initial fission fragments by GEF. Altogether, these results highlight the possibility to use measurements of IYRs to improve model predictions and to study the angular momentum generation in nuclear fission.
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| 14. |
- Gao, Zhihao, et al.
(författare)
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New design and simulation of the ion guide for neutron-induced fission products at the IGISOL facility
- 2023
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Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2100-014X. ; 284
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Tidskriftsartikel (refereegranskat)abstract
- Measurements of independent fission yield distributions in neutron-induced fission at high neutron energies are important for our fundamental understanding of the fission process, and are also relevant for reactor physics applications. So far, measurements of independent fission yields in proton-induced fission have been performed at the IGISOL facility at the University of Jyväskylä, using the Penning trap as a high resolving-power mass-filter. In order to also facilitate measurements of neutron-induced fission, a dedicated ion guide and a proton-to-neutron converter was developed. However, the first measurement indicates that fewer fission products than expected reach the Penning trap. To explore potential reasons and possible improvements, a simulation model was also developed and benchmarked. The benchmark showed that the model is able to reproduce the performance of the ion guide remarkably well and that the main reason for the low yield of fission products is the low collection efficiency of the ion guide.Based on the benchmark, a new ion guide is being designed. In the new design, the positions of the uranium targets and volume of the ion guide have been changed to increase the collection of fission products. This results in a five-fold increase of the yield. However, the collection efficiency of the new ion guide still needs to be improved in order to achieve intensities of the extracted fission products that are large enough to allow for reasonable measurement times.Because the volume of the ion guide is increased significantly, the extraction time of the ions is expected to be longer than that from the previous ion guide. Therefore, an electric field guidance system that consists of a combination of a stationary electric field and an RF-carpet is considered to be deployed. The stationary field, produced from a set of DC-ring electrodes, accelerates the ions towards the RF-carpet at end plate of the ion guide. The RF-carpet consists of a time-dependent field, produced from a radio-frequent structure of concentric rings, with a DC-component that guides the ions towards the exit hole in the center of the end plate. In this paper we present the current status of the simulations and design of the new ion guide.
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| 15. |
- Gjestvang, D., et al.
(författare)
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Examination of how properties of a fissioning system impact isomeric yield ratios of the fragments
- 2023
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Ingår i: Physical Review C. - : American Physical Society. - 2469-9985 .- 2469-9993. ; 108:6
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Tidskriftsartikel (refereegranskat)abstract
- The population of isomeric states in the prompt decay of fission fragments-so-called isomeric yield ratios (IYRs)-is known to be sensitive to the angular momentum J that the fragment emerged with, and may therefore contain valuable information on the mechanism behind the fission process. In this work, we investigate how changes in the fissioning system impact the measured IYRs of fission fragments to learn more about what parameters affect angular momentum generation. To enable this, a new technique for measuring IYRs is first demonstrated. It is based on the time of arrival of discrete gamma rays, and has the advantage that it enables the study of the IYR as a function of properties of the partner nucleus. This technique is used to extract the IYR of 134Te, strongly populated in actinide fission, from the three different fissioning systems: 232Th(n, f), 238U(n, f), at two different neutron energies, as well as 252Cf(sf). The impacts of changing the fissioning system, the compound nuclear excitation energy, the minimum J of the binary partner, and the number of neutrons emitted on the IYR of 134Te are determined. The decay code TALYS is used in combination with the fission simulation code FREYA to calculate the primary fragment angular momentum from the IYR. We find that the IYR of 134Te has a slope of 0.004 +/- 0.002 with increase in compound nucleus (CN) mass. When investigating the impact on the IYR of increased CN excitation energy, we find no change with an energy increase similar to the difference between thermal and fast fission. By varying the mass of the partner fragment emerging with 134Te, it is revealed that the IYR of 134Te is independent of the total amount of prompt neutrons emitted from the fragment pair. This indicates that neutrons carry minimal angular momentum away from the fission fragments. Comparisons with the FREYA+TALYS simulations reveal that the average angular momentum in 134Te following 238U(n, f) is 6.0 h over bar . This is not consistent with the value deduced from recent CGMF calculations. Finally, the IYR sensitivity to the angular momentum of the primary fragment is discussed. These results are not only important to help understanding the underlying mechanism in nuclear fission, but can also be used to constrain and benchmark fission models, and are relevant to the gamma -ray heating problem of reactors.
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| 16. |
- Gomez L, Ana Maria, 1993-, et al.
(författare)
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Determination of the Plasma Delay Time in PIPS detectors for fission fragments at the LOHENGRIN spectrometer
- 2023
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Ingår i: 15<sup>th</sup> International Conference on Nuclear Data for Science and Technology (ND2022). - : EDP Sciences.
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Konferensbidrag (refereegranskat)abstract
- The VElocity foR Direct particle Identification spectrometer (VERDI) is a 2E-2v fission spectrometer that allows the measurement of the total mass distribution of secondary fission fragments with a resolving power of 1-2 u. It consists of two time-of-flight (ToF) arms, with one Micro Channel Plate (MCP) detector and up to 32 Silicon PIPS (Passive Implanted Planar Silicon) detectors per arm. The MCPs provide the start timing signals and the PIPS detectors provide both the energy and the stopping ToF signals. In real conditions, the PIPS signals are affected by the formation of plasma from the interaction between the heavy ions and the detector material. The plasma contributes to a reduction in signal amplitude, resulting in a Pulse Height Defect (PHD), and introduces a signal delay, known as Plasma Delay Time (PDT). An experiment to characterize the PDT and PHD was performed at the LOHENGRIN recoil separator of the Institut Laue Langevin (ILL). Characteristic fission fragments from the 239Pu(n,f) reaction were separated based on their A/Q and E/Q ratios, allowing the measurement of a wide range of energies from 21 to 110 MeV and masses between 80 and 149 u. Six PIPS detectors were characterized to study their individual responses to the PDT and PHD effects. The signals were recorded in a digital acquisition system to completely exploit the offline analysis capabilities. Achieved combined timing and energy resolutions for fission fragments varied between 72(2) ps and 100(4) ps and 1.4% - 2% (FWHM), respectively. Preliminary PHD and PDT data are presented from the masses A=85, 95, 130 and 143. The PHD trends are strongly correlated with both the ion energy and mass. The PDT, on the other hand, shows a strong variation as a function of the ion kinetic energy but a smaller dependence on the ion mass.
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| 17. |
- Kristanl, Matej, et al.
(författare)
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The Seventh Visual Object Tracking VOT2019 Challenge Results
- 2019
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Ingår i: 2019 IEEE/CVF INTERNATIONAL CONFERENCE ON COMPUTER VISION WORKSHOPS (ICCVW). - : IEEE COMPUTER SOC. - 9781728150239 ; , s. 2206-2241
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Konferensbidrag (refereegranskat)abstract
- The Visual Object Tracking challenge VOT2019 is the seventh annual tracker benchmarking activity organized by the VOT initiative. Results of 81 trackers are presented; many are state-of-the-art trackers published at major computer vision conferences or in journals in the recent years. The evaluation included the standard VOT and other popular methodologies for short-term tracking analysis as well as the standard VOT methodology for long-term tracking analysis. The VOT2019 challenge was composed of five challenges focusing on different tracking domains: (i) VOT-ST2019 challenge focused on short-term tracking in RGB, (ii) VOT-RT2019 challenge focused on "real-time" short-term tracking in RGB, (iii) VOT-LT2019 focused on long-term tracking namely coping with target disappearance and reappearance. Two new challenges have been introduced: (iv) VOT-RGBT2019 challenge focused on short-term tracking in RGB and thermal imagery and (v) VOT-RGBD2019 challenge focused on long-term tracking in RGB and depth imagery. The VOT-ST2019, VOT-RT2019 and VOT-LT2019 datasets were refreshed while new datasets were introduced for VOT-RGBT2019 and VOT-RGBD2019. The VOT toolkit has been updated to support both standard short-term, long-term tracking and tracking with multi-channel imagery. Performance of the tested trackers typically by far exceeds standard baselines. The source code for most of the trackers is publicly available from the VOT page. The dataset, the evaluation kit and the results are publicly available at the challenge website(1).
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| 19. |
- Wang, Zhihao, et al.
(författare)
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Current Reference Control Scheme of Voltage Source Converters to Ensure the Existence of Stable Equilibrium Points During Grid Fault
- 2023
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Ingår i: IEEE transactions on power electronics. - : Institute of Electrical and Electronics Engineers (IEEE). - 0885-8993 .- 1941-0107. ; 38:9, s. 10750-10765
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Tidskriftsartikel (refereegranskat)abstract
- Maintaining synchronization with the grid during fault ride-through (FRT) is essential for grid-connected voltage source converters (VSCs). However, improper current references can lead to a loss of synchronization during FRT due to the nonexistence of stable equilibrium points (SEPs). While the mechanism of SEPs has been explained, the development of control schemes ensuring their existence remains challenging due to the difficulty of obtaining real-time grid parameters during FRT. To address this issue, this article proposes a novel current reference control scheme that only requires prefault grid parameters. By analyzing the changes in grid parameters caused by faults and characterizing the correspondence between the during-fault and prefault grid parameters, a voltage-dependent current reference control scheme is proposed. Since no real-time grid parameter estimation is needed during FRT, the proposed control scheme is practical and easy to implement. Simulation studies using DIgSILENT PowerFactory demonstrate that the proposed control scheme enables the VSC to maintain synchronization with the grid under the conditions of short-circuit ratio equaling 1.3 and grid voltage dropping to 0.1 p.u. Moreover, experiments further verify the effectiveness and feasibility of the proposed control scheme.
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