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Influence of simulated vs. satellite-based burned areas on modelled terrestrial carbon fluxes
Get PDFBackground
The Global Carbon Project provides annual updates on anthropogenic and natural components of the Global Carbon Budget. Dynamic Global Vegetation Models (DGVMs) contribute to these estimates and are used to simulate the evolution of terrestrial carbon sinks. However, DGVMs are known to poorly represent disturbances such as fire, leading to uncertainties in estimates of mean, interannual variability (IAV), and trends in land carbon fluxes. To address this issue, we propose a hybrid-process-based assessmentby constraining three DGVMs (OCN, JULES-INFERNO, and ORCHIDEE-MICT) with remotely-sensed burned areas from ESA CCI (FIRECCI51) and climate data from ERA5 reanalysis. We aim to improve the representation of the spatio-temporal variability of regional carbon budgets, namely fire emissions, above-ground biomass carbon (AGC), and vegetation-related variables—leaf area index (LAI) and gross primary productivity (GPP).
Results
Prescribing burned area (BA) in DGVMs reveals contrasting patterns between prognostic (model simulations) and diagnostic (simulations with prescribed BA) runs. As prognostic tends to overestimate BA, particularly across tropical and high-latitude regions, diagnostic simulations correct this issue, by reducing bias and improving the IAV and the agreement with satellite-based datasets of BA and fire emissions in these regions. Moreover, enhanced IAV of AGC is simulated by diagnostic runs, essentially due to better representation of biomass carbon in the mentioned regions. Although moderate improvements are found in LAI and GPP, as the differences between the two runs are more limited, the improvements between prognostic and diagnostic are more evident in their IAV, particularly for LAI, rather than on long-term means, indicating that prescribed fire can improve the representation of some variability patterns.
Conclusions
Prescribing remotely-sensed BA in models can lead to a better representation of global BA, fire emissions and AGC, particularly improving the IAV, reducing bias and enhancing the agreement with satellite datasets. The moderate improvements in vegetation-related variables underscore the need to better constrain fire impacts and vegetation dynamics in models, to enhance the simulation of spatio-temporal variability and dynamics of regional-scale vegetation and carbon-related fluxes
Second-harmonic bichromatic dispersive wave comb generation in a dissipative Kerr temporal soliton Fabry-Perot
Get PDFWe introduce a novel example of space-time analogy, where a dissipative soliton microcomb generates a traveling-wave temporal Fabry-Perot for trapping a bichromatic dispersive comb, generated at the second-harmonic of the pump laser. The fundamental frequency comb is generated in the anomalous dispersion regime, whereas the dispersive comb is generated in the normal dispersion regime. Direct numerical simulations are in excellent agreement with an analytical model
Selectivity for full AAV capsids in affinity capture with camelid ligands
Get PDFThe industry standard for downstream processing of adeno-associated viral vectors (AAV) is purification by affinity capture and anion exchange polishing (AEX). Affinity capture is an attractive method for capturing AAVs as it can remove process-related impurities and selectively enrich AAVs. Full capsids are then separated on AEX-resin from product related impurities based on net surface charge. Enrichment of full capsids remains a big challenge, as biophysical properties of full and empty capsids are very similar. We present a novel approach to enrich full capsids during capture chromatography using affinity resins. We examined the impact of additives (NaCl, MgCl, NaSO), NaCl concentrations (0 – 1000 mM), temperature and different affinity ligands
(POROS™ CaptureSelect™ AAVX, AAV8, AAV9; CaptoAVB and AVIPure AAV8). We tested our approach for the serotypes AAV8 wild type (WT), AAV9 WT and an rAAV2 derivative and demonstrated 2.5-fold full capsid enrichment in a robotic screening. Analyzing an elution peak in fine increments yielded in multiple fractions approaching 100% full capsids. While several affinity resins demonstrated full capsid selectivity, we report that AAVX achieved the highest resolution. The selectivity was then linked to the affinity ligands specific binding
mechanism towards an AAV capsid. This novel capture method offers a trade-off between full capsid yield and purity without the need for additional unit operations while using an already established process. With enriched loading material for the subsequent anion exchange step, the polished elution pool has a higher full-to-total ratio (FTR) compared to a process based on standard affinity capture conditions
Effect of Marangoni forces on interfacial heat and mass transfer driven by surface cooling
Get PDFA fully resolved numerical study was performed to investigate interfacial heat and mass transfer enhanced by the fully developed Rayleigh–Bénard–Marangoni instability in a relatively deep domain. The instability was triggered by evaporative cooling modelled by a constant surface heat flux. The latter allowed for temperature-induced variations in surface tension giving rise to Marangoni forces reinforcing the Rayleigh instability. Simulations were performed at a fixed Rayleigh number (Ra) and a variety of Marangoni numbers (Ma). In each simulation, scalar transport equations for heat and mass concentration at various Schmidt numbers (Sc=16−200) were solved simultaneously. Due to the fixed (warm) temperature prescribed at the bottom of the computational domain, large buoyant plumes emerged quasi-periodically both at the top and bottom. With increasing Marangoni number a decrease in the average convection cell size at the surface was observed, with a simultaneous improvement in near-surface mixing. The presence of high aspect ratio rectangular convection cell footprints was found to be characteristic for Marangoni-dominated flows. Due to the promotion of interfacial mass transfer by Marangoni forces, the power in the scaling of the mass transfer velocity, K∝Sc, was found to decrease from n = 0.50 at Ma = 0 to ≈ 0.438 at Ma = 13.21 × 10. Finally, the existence of a buoyancy-dominated and a Marangoni-dominated regime was investigated in the context of the interfacial heat and mass transfer scaling as a function of Ma + εRa, where ε is a small number determined empirically
Characteristics of diabatically influenced cyclones with high wind damage potential in Europe
Get PDFExtratropical cyclones are the primary driver of midlatitude weather variability, including extreme events with heavy precipitation and severe wind gusts, potentially leading to widespread damage. Both baroclinicity and diabatic heating contribute to cyclone intensification. Examples of severe European winter storms with rapid intensification enhanced through diabatic heating include Lothar (1999), Klaus (2009), and Xynthia (2010). Diabatic heating through cloud condensational processes in extratropical cyclones is associated with the warm conveyor belt (WCB) airstream, among others. Focusing on European winter storms, this study provides a comprehensive assessment of structural differences important for cyclone intensification between cyclones that intensify to a relatively large extent through diabatic processes and cyclones that intensify mostly through baroclinic processes. Considering 247 winter storms affecting western and central Europe from 1979 to 2023, we combine a WCB diagnostic with the pressure tendency equation to quantify the influence of diabatic heating on deepening processes. Our results indicate that diabatic processes have a mean contribution to cyclone intensification of 26.1% (median at 25.3%, 25th and 75th percentiles at 15.2% and 33.4%). Cyclones with a relatively large diabatic influence (>30.7 % diabatic contribution) have similar minimum mean sea-level pressure compared with cyclones with a small diabatic influence (<20.1% diabatic contribution) but exhibit steeper deepening rates, stronger northward displacement, increased precipitation, stronger wind gusts, and more WCB activity. Moreover, they are characterised by increased moisture and warmer temperatures in the WCB inflow, facilitating stronger deepening rates driven by diabatic heating. Our results suggest that WCB activity is a valuable first indicator of the diabatic contribution to cyclone intensification. These findings may be useful for predicting and estimating the risks associated with winter storms that have a relatively large influence of diabatic processes in numerical weather predictions and climate projections
Deep Operator Networks for Hemodynamics Modeling of Mitral Valve Flow
Get PDFDie präzise Charakterisierung hämodynamischer Strömungen ist für die Diagnose und Behandlung kardiovaskulärer Pathologien wie der Mitralklappeninsuffizienz unerlässlich. Während 4D-Flow-MRI volumetrische Daten mit begrenzter Auflösung liefert, bietet die numerische Strömungsmechanik (CFD) eine hohe Genauigkeit, verursacht jedoch erhebliche Rechenkosten. Diese Arbeit adressiert die Lücke zwischen diesen Methoden durch die Entwicklung von Frameworks für maschinelles Lernen, um transiente volumetrische (4D) Strömungsfelder aus spärlichen experimentellen Beobachtungen zu rekonstruieren, die in einer In-vitro-Umgebung gewonnen werden können. Das primäre Ziel besteht in der Lösung des schlecht gestellten Problems, die vollständige 4D-Hämodynamik unter Verwendung begrenzter Eingangsdaten abzuleiten: zeitaufgelöste Druckrandbedingungen und planare Geschwindigkeitsfelder aus der zwei-Komponenten 2D Particle-Image-Velocimetry (2D2C PIV). Die Arbeit evaluiert zwei Architekturstrategien: instanzspezifische physik-informierte neuronale Netze (PINNs) und generalisierte Deep Operator Networks (DeepONets). Synthetische Referenzdaten wurden mittels instationärer Reynolds-gemittelter Navier-Stokes-Simulationen (URANS) eines hämodynamischen Simulators mit verschiedenen Phantomen für Mitralinsuffizienz-Öffnungen generiert. Zwei vereinfachte Datensätze, die stationäre und transiente 2D-Kanalströmungen repräsentieren, dienten der hierarchischen Modellentwicklung. Die Studie vergleicht rein datengetriebene Modelle, physik-erweiterte Modelle mit RANS-Verlustfunktionen und eine hybride "Test-Time-Adaptation"-Strategie, bei der ein vortrainiertes DeepONet anhand spärlicher Zielbeobachtungen feinjustiert wird.
Der PINN-Ansatz scheiterte konsistent an der Lösung des schlecht gestellten Rekonstruktionsproblems und wies Schwierigkeiten bei der Strömungstopologie sowie der zeitlichen Entwicklung über alle Komplexitätsstufen hinweg auf. Im Gegensatz dazu nutzte das DeepONet-Framework erfolgreich Trainingsverteilungen, um als robustes Surrogatmodell zu fungieren. Die hybride Trainingsstrategie erwies sich als entscheidend und reduzierte den Fehler bei stationären Fällen außerhalb der Trainingsverteilung erheblich. In transienten 3D-Anwendungen übertraf das hybride DeepONet die PINNs deutlich, erreichte physikalisch plausible Rekonstruktionen und korrigierte Strahlverläufe bei unbekannten Geometrien. Die Verbesserungen durch die Feinabstimmung blieben jedoch räumlich auf das Überwachungsfenster begrenzt, in dem sie aufgrund der verfügbaren Messdaten am wenigsten benötigt werden, und führten zu unzusammenhängenden volumetrischen Artefakten. Letztlich hat sich das hybride DeepONet-Framework als eine überlegene und recheneffiziente Methode zur Rekonstruktion der 4D-Hämodynamik aus spärlichen Daten etabliert. Obwohl noch erhebliche Herausforderungen hinsichtlich der volumetrischen Kohärenz zu lösen sind, bietet der Ansatz einen vielversprechenden Weg für eine kosteneffiziente, hochgenaue Strömungsanalyse in kardiovaskulären Geometrien
Coupling of SPH and Volume-of-Fluid for multiphase flow
Get PDFA new methodology for coupling Smoothed Particle Hydrodynamics (SPH) with a Finite Volume (FV) solver for multiphase flow is presented. The approach follows a patched-domain strategy in which the two domains are disjointly separated by a discrete coupled boundary. Consequently, the coupled SPH–FV method is able to benefit from both methods’ strengths in their respective domains. The SPH solver employs a custom scheme, whereas a preexisting FV solver employing a Volume-of-Fluid (VoF) multiphase representation is adapted with minor modifications.
Key features of the coupling include the determination of the volume fraction at the coupled boundary, the preservation of the fluid interface, and surface tension modeling in the vicinity of the coupled boundary. The method is validated against a series of benchmark cases, showing very good agreement. To our knowledge, this is the first coupled SPH–FV method that allows interface advection across the coupled boundary for multiphase flow with surface tension
Anisotropies of ultra-high energy particles in cosmic magnetic fields
Get PDFUltrahochenergetische kosmische Strahlen (UHECRs) sind die energiereichsten Teilchen, die im Universum beobachtet werden. Ihre Ankunftsrichtungen liefern wichtige In- formationen über ihren Ursprung und ihre Ausbreitung. Anisotropien am UHECR- Himmel, die als Abweichungen von der Isotropie auftreten, werden von Ablenkungen der UHECR Teilchen im galaktischen (GMF) und extragalaktischen (EGMF) Magnetfeld beeinflusst.
In dieser Arbeit werden Simulationen durchgeführt, um den Einfluss magnetis- cher Ablenkungen auf die Ankunftsrichtungen von UHECRs zu untersuchen. Dabei werden sowohl die kohärente als auch die turbulente Komponente des GMF sowie der Einfluss des EGMF auf beobachtete anisotrope Strukturen berücksichtigt. Eine Likelihood-basierte Analyse wird verwendet, um die Kreuzkorrelation zwischen den durch das GMF abgelenkten Ankunftsrichtungen der UHECRs und einem Quellen- modell, Als Quellmodell wird hierbei ein Katalog von Starburst Galaxien verwendet. Diese Analyse liefert Einblicke in die Abweichung von der isotropen Erwartung, wenn die Ablenkung durch das GMF berücksichtigt werden. Zusätzlich werden Anisotropien mittlerer Winkelgröße am UHECR-Himmel untersucht, um Einschränkungen für die Stärke des EGMF abzuleiten. Systematische Scans über den Signalanteil und den von der EGMF verursachten Winkelverschmierung zeigen, dass Szenarien mit minimalen Beiträgen des Feldes und geringen Signalanteilen die beobachteten Daten erfolgreich reproduzieren. Im Gegensatz dazu führen Parameterkonfigurationen mit hohen Sig- nalanteilen und unzureichenden EGMF-Ablenkungen zu signifikanten Überdichten, die von den Beobachtungen abweichen.
Vergleiche zwischen verschiedenen astrophysikalischen Modellen, einschließlich Variationen des GMF, unterstreichen zusätzlich die entscheidende Rolle der Magnet- felder bei der Gestaltung des UHECR-Himmels. Diese Studie bietet einen statistis- chen Rahmen, um die Kreuzkorrelation zwischen UHECR-Anisotropien und Magnet- feldern zu erforschen. Sie schlägt Einschränkungen für die Stärke solcher Felder vor, indem sie die Bereiche für die Winkelstreuung identifiziert, in denen die Häufung von Ereignissen verringert wird, um die beobachteten anisotropen Merkmale am Himmel zu beschreiben.
Oxaliplatin resistance in pancreatic ductal adenocarcinoma is non‑significantly mediated by diminished drug uptake but is highly linked to a poor apoptotic response to the cytotoxic threat
No full textPancreatic ductal adenocarcinoma (PDAC) resistance to oxaliplatin is associated with diminished drug uptake and a poor molecular apoptotic response; however, the relative contribution of each of these modes of resistance remains unclear. Accordingly, PDAC cell lines (AsPC‑1 and BxPC‑3) and human patient‑derived organoids (hPDOs; h08 and h19) were assessed in the present study, with proliferation assays, atomic absorption spectroscopy‑based quantification of intracellular oxaliplatin, luminogenic caspase 3/7 assays, PCR array‑based transcriptomic analysis and RNA sequencing performed to scrutinize the oxaliplatin resistance phenotype. Notably, AsPC‑1 cells [half maximal inhibitory concentration (IC), 88.8±45 µM were 4.2‑fold more oxaliplatin resistant than BxPC‑3 cells (IC, 21±0.7 µM; P=0.02)]. In addition, when normalized to intracellular platinum levels, AsPC‑1 cells remained 2.5‑fold more resistant than BxPC‑3 (the fold difference was decreased by 40% from 4.2‑fold to 2.5‑fold; P=0.21). In hPDOs, resistant h19 took up oxaliplatin 22% less efficiently than sensitive h08, and the nominal resistance difference was 3.5‑fold, and it remained at 2.8‑fold after controlling for drug accumulation (the fold difference was decreased by 20% from 3.5‑fold to 2.8‑fold; P=0.34). These findings indicated that diminished drug uptake non‑significantly contributed to oxaliplatin resistance, which was in agreement with the rather minor differences in drug transporter expression levels (including ATP7A and ATP7B). Furthermore, when challenged with identical intracellular oxaliplatin levels, AsPC‑1 cells exhibited delayed caspase 3/7 activity initiation, weaker induction of pro‑apoptotic genes BBC3 (1.7‑fold vs. 5‑fold) and PMAIP (2.5‑fold vs. 6‑fold), but stronger enhancement of anti‑apoptotic Jun expression (7‑fold vs. 3‑fold) than BxPC‑3 cells. Taken together, oxaliplatin resistance in PDAC models may be highly linked to a poor apoptotic response, whereas drug uptake seems to be of minor relevance
