| 1. |
- Ainsbury, Elizabeth, et al.
(författare)
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Integration of new biological and physical retrospective dosimetry methods into EU emergency response plans - joint RENEB and EURADOS inter-laboratory comparisons
- 2017
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Ingår i: International Journal of Radiation Biology. - : Informa UK Limited. - 0955-3002 .- 1362-3095. ; 93:1, s. 99-109
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: RENEB, 'Realising the European Network of Biodosimetry and Physical Retrospective Dosimetry,' is a network for research and emergency response mutual assistance in biodosimetry within the EU. Within this extremely active network, a number of new dosimetry methods have recently been proposed or developed. There is a requirement to test and/or validate these candidate techniques and inter-comparison exercises are a well-established method for such validation. Materials and methods: The authors present details of inter-comparisons of four such new methods: dicentric chromosome analysis including telomere and centromere staining; the gene expression assay carried out in whole blood; Raman spectroscopy on blood lymphocytes, and detection of radiation induced thermoluminescent signals in glass screens taken from mobile phones. Results: In general the results show good agreement between the laboratories and methods within the expected levels of uncertainty, and thus demonstrate that there is a lot of potential for each of the candidate techniques. Conclusions: Further work is required before the new methods can be included within the suite of reliable dosimetry methods for use by RENEB partners and others in routine and emergency response scenarios.
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| 2. |
- Lokachari, Nitin, et al.
(författare)
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A comprehensive experimental and kinetic modeling study of di-isobutylene isomers : Part 1
- 2023
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Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 251
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Tidskriftsartikel (refereegranskat)abstract
- Di-isobutylene has received significant attention as a promising fuel blendstock, as it can be synthesized via biological routes and is a short-listed molecule from the Co-Optima initiative. Di-isobutylene is also popularly used as an alkene representative in multi-component surrogate models for engine studies of gasoline fuels. However, there is limited experimental data available in the literature for neat di-isobutylene under engine-like conditions. Hence, most existing di-isobutylene models have not been extensively validated, particularly at lower temperatures (< 1000 K). Most gasoline surrogate models include the di-isobutylene sub-mechanism published by Metcalfe et al. [1] with little or no modification. The current study is undertaken to develop a detailed kinetic model for di-isobutylene and validate the model using a wide range of relevant experimental data. Part 1 of this study exclusively focuses on the low- to intermediate temperature kinetics of di-isobutylene. An upcoming part 2 discusses the high-temperature model development and validation of the relevant experimental targets. Ignition delay time measurements for the di-isobutylene isomers were performed at pressures ranging from 15 – 30 bar at equivalence ratios of 0.5, 1.0, and 2.0 diluted in air and in the temperature range 650 – 900 K using two independent rapid compression machine facilities. In addition, measurements of species identified during the oxidation of these isomers were performed in a jet-stirred reactor and in a rapid compression machine. A detailed kinetic model for the di-isobutylene isomers is developed to capture the wide range of new experimental targets. For the first time, a comprehensive low-temperature chemistry submodel is included. The differences in the important reaction pathways for the accurate prediction of the oxidation of the two DIB isomers are compared using reaction path analysis. The most sensitive reactions controlling the ignition delay times of the DIB isomers under the pressure and temperature conditions necessary for autoignition in engines are identified.
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| 3. |
- Lokachari, Nitin, et al.
(författare)
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A comprehensive experimental and kinetic modeling study of di-isobutylene isomers : Part 2
- 2023
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Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 251
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Tidskriftsartikel (refereegranskat)abstract
- A wide variety of high temperature experimental data obtained in this study complement the data on the oxidation of the two di-isobutylene isomers presented in Part I and offers a basis for an extensive validation of the kinetic model developed in this study. Due to the increasing importance of unimolecular decomposition reactions in high-temperature combustion, we have investigated the di-isobutylene isomers in high dilution utilizing a pyrolysis microflow reactor and detected radical intermediates and stable products using vacuum ultraviolet (VUV) synchrotron radiation and photoelectron photoion coincidence (PEPICO) spectroscopy. Additional speciation data at oxidative conditions were also recorded utilizing a plug flow reactor at atmospheric pressure in the temperature range 725–1150 K at equivalence ratios of 1.0 and 3.0 and at residence times of 0.35 s and 0.22 s, respectively. Combustion products were analyzed using gas chromatography (GC) and mass spectrometry (MS). Ignition delay time measurements for di-isobutylene were performed at pressures of 15 and 30 bar at equivalence ratios of 0.5, 1.0, and 2.0 diluted in ‘air’ in the temperature range 900–1400 K using a high-pressure shock-tube facility. New measurements of the laminar burning velocities of di-isobutylene/air flames are also presented. The experiments were performed using the heat flux method at atmospheric pressure and initial temperatures of 298–358 K. Moreover, data consistency was assessed with the help of analysis of the temperature and pressure dependencies of laminar burning velocity measurements, which was interpreted using an empirical power-law expression. Electronic structure calculations were performed to compute the energy barriers to the formation of many of the product species formed. The predictions of the present mechanism were found to be in adequate agreement with the wide variety of experimental measurements performed.
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| 4. |
- Pfeffer, Julia, et al.
(författare)
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Evaluating surface and subsurface water storage variations at small time and space scales from relative gravity measurements in semiarid Niger
- 2013
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Ingår i: Water Resources Research. - : American Geophysical Union (AGU). - 0043-1397 .- 1944-7973. ; 49:6, s. 3276-3291
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Tidskriftsartikel (refereegranskat)abstract
- The acquisition of reliable data sets representative of hydrological regimes and their variations is a critical concern for water resource assessment. For the subsurface, traditional approaches based on probe measurements, core analysis, and well data can be laborious, expensive, and highly intrusive, while only yielding sparse data sets. For this study, an innovative field survey, merging relative microgravimetry, magnetic resonance soundings, and hydrological measurements, was conducted to evaluate both surface and subsurface water storage variations in a semiarid Sahelian area. The instrumental setup was implemented in the lower part of a typical hillslope feeding to a temporary pond. Weekly measurements were carried out using relative spring gravimeters during 3 months of the rainy season in 2009 over a 350 × 500 m2 network of 12 microgravity stations. Gravity variations of small to medium amplitude (≤220 nm s-2) were measured with accuracies better than 50 nm s-2, revealing significant variations of the water storage at small time (from 1 week up to 3 months) and space (from a couple of meters up to a few hundred meters) scales. Consistent spatial organization of the water storage variations were detected, suggesting high infiltration at the outlet of a small gully. The comparison with hydrological measurements and magnetic resonance soundings involved that most of the microgravity variations came from the heterogeneity in the vadose zone. The results highlight the potential of time lapse microgravity surveys for detecting intraseasonal water storage variations and providing rich space-time data sets for process investigation or hydrological model calibration/ evaluation.
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| 5. |
- Chauvat, Guillaume, et al.
(författare)
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Global linear analysis of a jet in cross-flow at low velocity ratios
- 2020
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Ingår i: Journal of Fluid Mechanics. - : CAMBRIDGE UNIV PRESS. - 0022-1120 .- 1469-7645. ; 889
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Tidskriftsartikel (refereegranskat)abstract
- The stability of the jet in cross-flow is investigated using a complete set-up including the flow inside the pipe. First, direct simulations were performed to find the critical velocity ratio as a function of the Reynolds number, keeping the boundary-layer displacement thickness fixed. At all Reynolds numbers investigated, there exists a steady regime at low velocity ratios. As the velocity ratio is increased, a bifurcation to a limit cycle composed of hairpin vortices is observed. The critical bulk velocity ratio is found at approximately for the Reynolds number , above which a global mode of the system becomes unstable. An impulse response analysis was performed and characteristics of the generated wave packets were analysed, which confirmed results of our global mode analysis. In order to study the sensitivity of this flow, we performed transient growth computations and also computed the optimal periodic forcing and its response. Even well below this stability limit, at , large transient growth ( in energy amplification) is possible and the resolvent norm of the linearized Navier-Stokes operator peaks above . This is accompanied with an extreme sensitivity of the spectrum to numerical details, making the computation of a few tens of eigenvalues close to the limit of what can be achieved with double precision arithmetic. We demonstrate that including the meshing of the jet pipe in the simulations does not change qualitatively the dynamics of the flow when compared to the simple Dirichlet boundary condition representing the jet velocity profile. This is in agreement with the recent experimental results of Klotz et al. (J. Fluid Mech., vol. 863, 2019, pp. 386-406) and in contrast to previous studies of Cambonie & Aider (Phys. Fluids, vol. 26, 2014, 084101). Our simulations also show that a small amount of noise at subcritical velocity ratios may trigger the shedding of hairpin vortices.
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| 6. |
- Duchemin, Wandrille, et al.
(författare)
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RecPhyloXML : a format for reconciled gene trees
- 2018
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Ingår i: Bioinformatics. - : Oxford University Press (OUP). - 1367-4803 .- 1367-4811. ; 34:21, s. 3646-3652
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Tidskriftsartikel (refereegranskat)abstract
- Motivation: A reconciliation is an annotation of the nodes of a gene tree with evolutionary events-for example, speciation, gene duplication, transfer, loss, etc. -along with a mapping onto a species tree. Many algorithms and software produce or use reconciliations but often using different reconciliation formats, regarding the type of events considered or whether the species tree is dated or not. This complicates the comparison and communication between different programs. Results: Here, we gather a consortium of software developers in gene tree species tree reconciliation to propose and endorse a format that aims to promote an integrative-albeit flexible-specification of phylogenetic reconciliations. This format, named recPhyloXML, is accompanied by several tools such as a reconciled tree visualizer and conversion utilities.
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| 7. |
- Gorgolewski, Krzysztof J., et al.
(författare)
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BIDS apps: Improving ease of use, accessibility, and reproducibility of neuroimaging data analysis methods
- 2017
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Ingår i: PloS Computational Biology. - : Public Library of Science (PLoS). - 1553-734X .- 1553-7358. ; 13:3
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Tidskriftsartikel (refereegranskat)abstract
- The rate of progress in human neurosciences is limited by the inability to easily apply a wide range of analysis methods to the plethora of different datasets acquired in labs around the world. In this work, we introduce a framework for creating, testing, versioning and archiving portable applications for analyzing neuroimaging data organized and described in compliance with the Brain Imaging Data Structure (BIDS). The portability of these applications (BIDS Apps) is achieved by using container technologies that encapsulate all binary and other dependencies in one convenient package. BIDS Apps run on all three major operating systems with no need for complex setup and configuration and thanks to the comprehensiveness of the BIDS standard they require little manual user input. Previous containerized data processing solutions were limited to single user environments and not compatible with most multi-tenant High Performance Computing systems. BIDS Apps overcome this limitation by taking advantage of the Singularity container technology. As a proof of concept, this work is accompanied by 22 ready to use BIDS Apps, packaging a diverse set of commonly used neuroimaging algorithms.
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| 8. |
- Jourdain, Guillaume, 1984, et al.
(författare)
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Application of dynamic mode decomposition to acoustic-modes identification and damping in a 3-dimensional chamber with baffled injectors
- 2013
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Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 1095-8568 .- 0022-460X. ; 332:18, s. 4308-4323
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Tidskriftsartikel (refereegranskat)abstract
- The dynamic mode decomposition (DMD) is applied to a 3-dimensional chamber in order to identify acoustic resonant modes and quantify their damping. The DMD is one of post-processing methods, which can be applicable with acoustic field information in a full or a partial domain from numerical and experimental data. For application of the DMD method, the 3-dimensional chamber with baffled injectors is selected, in which gaps in baffled injectors enhanced acoustic damping and it has been shown that there exists an optimum gap for maximum damping in the previous works. Damping coefficients are evaluated in order to investigate whether the DMD method is able to predict the influence of gaps in baffled injectors on the damping of the first tangential (1T) mode or not. In addition to the IT mode, the first longitudinal (1L) mode, the 1T1L mode, and higher modes are extracted and damping coefficients for them are estimated using the DMD method on 2-dimensional planes and they reveal that the baffle gap affects significantly only specific modes and show a good agreement with the damping factors from the previous work in predicting the optimum gap for maximum acoustic damping.
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| 9. |
- Chauvat, Guillaume, 1991-
(författare)
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Receptivity, Stability and Sensitivity analysis of two- and three-dimensional flows
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This work deals with various aspects of boundary-layer stability. Modal and non-modal approaches are first used in the study of the global stability of a jet in crossflow. This flow case presents a global instability in some regimes which results from a Hopf bifurcation from a steady wake to a limit cycle consisting of a shedding of hairpin vortices. The effects of non-normality are studied in relation with transient growth and numerical accuracy. It is shown that the equations must be solved to a very high accuracy in order to properly capture the spectrum and that the computational domain must be very long due to the elongated core of the instability. Non-modal techniques do not suffer from such issues. The so-called acoustic receptivity of a flat plate with a leading-edge is analysed using a global modes approach. This leads to a spatio-temporal analysis in which the modes must be corrected for the imaginary part of the eigenvalues. This correction involves the Parabolised Stability Equations (PSE). This work confirms results previously obtained through different methods. The stability of two- and three-dimensional boundary-layer flows in the presence of surface irregularities such as steps, gaps or humps is also studied using Direct Numerical Simulation (DNS). It is found that all the surface irregularities have a destabilising effect on stability of two-dimensional boundary layers, with the rectangular hump case being the most dangerous one. In the case of three-dimensional boundary layers the effects are more complex. Our results accurately reproduce the steady flows, caused by small forward-facing steps, from an experimental setup, and the interaction of saturated crossflow vortices with unsteady noise is discussed. This work also describes a new method related to modal decomposition of compressible flows with shocks. Traditional linear techniques such as the Proper Orthogonal Decomposition (POD) struggle to capture strong nonlinear phenomena such as shock motion. The proposed shock-fitting approach tackles this issue by interpolating data onto a grid following the discontinuities. This requires detecting and parametrising the shocks, then mapping the original flow fields onto a reference mesh. A method to generate this mapping in two-dimensional domains is presented. Then the method is applied to two two-dimensional cases in ascending complexity. In addition to faster decay of the singular values, the modes obtained are cleaner and devoid of oscillations around the shocks.
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| 10. |
- Tocci, F., et al.
(författare)
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The Effect of 2-D Surface Irregularities on Laminar-Turbulent Transition : A Comparison of Numerical Methodologies
- 2021
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Ingår i: Notes on Numerical Fluid Mechanics and Multidisciplinary Design. - Cham : Springer Nature. ; , s. 246-256
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Konferensbidrag (refereegranskat)abstract
- The applicability of Local Stability Theory (LST), Parabolized Stability Equations (PSE) and the Adaptive Harmonic Linearized Navier-Stokes (AHLNS) approach is investigated in the presence of 2-D surface irregularities through comparison with Direct Numerical Simulations (DNS). Remarkably good agreement between DNS and AHLNS is obtained for the amplification curves of Tollmien-Schlichting (TS) waves in all the cases studied. The LST and PSE results exhibit differences which are discussed in relation to the local distortion of the boundary layer induced by the irregularities.
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