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• Monte Carlo algorithm is used to evaluate simultaneously the observable and its Jacobian. • Null-collision algorithm (NCA) are very successful when dealing with linear-physics in heterogeneous media. • We showed that NCA are sources of convergence difficulties to sensitivity-evaluations of optical parameter. • We propose an alternative solution. When a Monte Carlo algorithm is used to evaluate a physical observable A , it is possible to slightly modify the algorithm so that it evaluates simultaneously A and the derivatives ∂ ς A of A with respect to each problem-parameter ς. The principle is the following: Monte Carlo considers A as the expectation of a random variable, this expectation is an integral, this integral can be derivated as function of the problem-parameter to give a new integral, and this new integral can in turn be evaluated using Monte Carlo. The two Monte Carlo computations (of A and ∂ ς A) are simultaneous when they make use of the same random samples, i.e. when the two integrals have the exact same structure. It was proven theoretically that this was always possible, but nothing ensures that the two estimators have the same convergence properties: even when a large enough sample-size is used so that A is evaluated very accurately, the evaluation of ∂ ς A using the same sample can remain inaccurate. We discuss here such a pathological example: null-collision algorithms are very successful when dealing with radiative transfer in heterogeneous media, but they are sources of convergence difficulties as soon as sensitivity-evaluations are considered. We analyse theoretically these convergence difficulties and propose an alternative solution. [ABSTRACT FROM AUTHOR]

An accurate understanding of uncertainty is needed to properly interpret methane emission estimates from upstream oil and gas sources in a variety of contexts, from component-level measurements to yearly jurisdiction-wide inventories. To characterize measurement uncertainty, we examine controlled release (CR) data from five different technology providers including quantitative gas imaging (QOGI), tunable diode laser-absorption spectroscopy (TDLAS); and airborne near-infrared hyperspectral (NIR HS) imaging. We introduce a novel empirical method to develop probability distributions of measurements given a true emission rate using the CR data. The approach includes flexible likelihoods which capture complex relationships in the data. An algorithm which provides the distribution of the true emission rate given a measurement is also developed, which synthesizes the measurement with the CR data and external information about the possible true emission rate. The results show that flexible models that accommodate complex nonlinear behavior are needed to adequately model measurement error. We also show that measurement error can vary under different conditions. We demonstrate that measurement uncertainty can be reduced by performing repeated measurements. A limitation of the study is that the collected CR data is collected under controlled conditions that may differ from those in industrial settings. As new CR data become available, the models presented in this paper can be refit to consider more diverse scenarios. The methodology can be extended to explicitly model different conditions to improve performance., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

Mid-wavelength infrared (MWIR) imaging Fourier transform spectrometers (IFTSs) are a promising technology for measuring flare combustion efficiency (CE) and destruction removal efficiency (DRE). These devices generate spectrally resolved intensity images of the flare plume, which may then be used to infer column densities of relevant species along each pixel line-of-sight. In parallel, a 2D projected velocity field may be inferred from the apparent motion of flow features between successive images. Finally, the column densities and velocity field are combined to estimate the mass flow rates for the species needed to calculate the CE or DRE. Since the MWIR IFTS can measure key carbon-containing species in the flare plume, it is possible to measure CE without knowing the fuel flow rate, which is important for fenceline measurements. This work demonstrates this approach on a laboratory heated vent, and then deploys the technique on two working flares: a combustor burning natural gas at a known rate, and a steam-assisted flare at a petrochemical refinery. Analysis of the IFTS data highlights the potential of this approach, but also areas for future development to transform this approach into a reliable technique for quantifying flare emissions. Implications : Our research is motivated by the need to assess hydrocarbon emissions from flaring, which is a critical problem of global significance. For example, recent studies have shown that methane destruction efficiency of flaring from upstream oil may be significantly lower than the commonly assumed figure of 98%; work by Plant et al. , in particular, suggest that this discrepancy amounts to CO 2 emissions from 2 to 8 million automobiles annually, considering the US alone. Similarly, the international energy agency (IEA) estimates a global flare efficiency of 92%, which translates in 8 million tons of CH 4 emitted by flares in 2020. Highlighted by these studies and supported by the World Bank initiatives toward zero routine flaring emissions, there is an urgent need for oil and gas industry to assess their flare methane emission, and overall hydrocarbon emissions. At the very least, it is critical to identify problematic flare operating conditions and means to mitigate flare emissions. Focusing on remote quantification of plume species, the measurement technique and quantification method presented in this paper is a considerable step forward in that direction by computing combustion efficiency and key components for destruction efficiency.

It was recently shown that radiation, conduction and convection can be combined within a single Monte Carlo algorithm and that such an algorithm immediately benefits from state-of-the-art computer-graphics advances when dealing with complex geometries. The theoretical foundations that make this coupling possible are fully exposed for the first time, supporting the intuitive pictures of continuous thermal paths that run through the different physics at work. First, the theoretical frameworks of propagators and Green's functions are used to demonstrate that a coupled model involving different physical phenomena can be probabilized. Second, they are extended and made operational using the Feynman-Kac theory and stochastic processes. Finally, the theoretical framework is supported by a new proposal for an approximation of coupled Brownian trajectories compatible with the algorithmic design required by ray-tracing acceleration techniques in highly refined geometry., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2023 Tregan et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

Guinea pig isolated vestibular type I hair cells (VIHCs) were recently reported by our group to respond to high [KCl] solutions by an irreversible tilt of their neck region and sometimes by a sustained shortening and swelling. A possible osmotic contribution to these shape changes was investigated by substituting gluconate (G) for chloride in the test solution, so as to minimize water influx, and also by changing the osmotic pressure of the extracellular solution. For comparison, similar experiments were also undertaken on cochlear outer hair cells (OHCs). Utricular and ampullar type I hair cells were more difficult to isolate than OHCs and, like them, responded to an isotonic high [KCl] solution by a sustained shortening and widening, which were found to be reversible for most cells when rinsed with the control solution. In a high [KG] solution, all OHCs showed a shortening reversible in the test solution; among the VIHCs tested, two-thirds presented a slight sustained shortening without widening and a third showed a spontaneously reversible shortening, particularly at the neck level. VIHCs exposed to a high [N-methyl-D-glucamine chloride] solution, this impermeant cation replacing K+ for control, presented only a slight sustained shortening. In response to osmotic changes of the bathing medium, both VIHCs and OHCs showed a sustained shortening or elongation (the latter to a lesser degree) for hypo- and hyperosmotic solutions, respectively. The VIHCs and OHCs that presented a reversible shortening in a high [KG] solution widened concomitantly with their shortening, but to a smaller extent compared with what was observed in a high [KCl] solution, and this diameter increase was reversible in the test solution, unlike the widening observed in a hypotonic solution. These results show that a reversible shortening occurred for some VIHCs; they also indicate the involvement of two components in the KCl-induced response: one osmotic and another potassium-dependent.