Coupled heat conduction and multiphase change problem accounting for thermal contact resistance

International audienceIn this paper, heat conduction coupled with multiphase changes are considered in a cylindrical multilayer composite accounting for thermal contact resistance depending on contact pressures and roughness parameters. A numerical simulation is proposed using both analytical developments and numerical computations. The presented modeling strategy relies on an algorithm that alternates between heat conduction accounting for volumetric heat sources and a multi-phase change model based on non-isothermal Avrami's equation using the isokinetic assumption. Applications to coiling process (winding of a steel strip on itself) are considered. Indeed, phase changes determine the microstructure of the final material and are responsible for residual stresses that create flatness defects. A Finite Element modeling is used for validating the presented solution and numerical results are presented and discussed

Inverse three-dimensional method for fast evaluation of temperature and heat flux fields during rolling process

International audienceMonitoring and controlling flatness during the rolling process becomes critical for ensuring the product quality. Flatness defects are due to highly three-dimensional phenomena. Indeed, strips with different widths are rolled during the same campaign and cooling systems are heterogeneous along the axial direction to modify the thermal expansion of the roll. Therefore this paper presents a fully three dimensional inverse analytical method to determine the temperature field and heat fluxes (especially at the surface of the roll) by interpreting measurements of temperature done with several thermocouples fully embedded in the roll body and aligned along the axial direction. Since the method is dedicated to on-line interpretation and designed as a tool for adapting the rolling parameters during the rolling process, iterative methods are not studied to avoid long computation times, which justify the development of an analytical solution of the problem. The computation time displayed by Scilab 5.3 with a quadcore 2.8 GHz is around 0.07 s/cycle. The 3D unsteady heat equation is solved analytically in the roll, managing only one assumption so that restrictions of the measurement system (i.e., successive times) are taken into account. The solution is validated by comparing the outputs (surface temperature) and a prescribed temperature field (corresponding to hot rolling conditions). A satisfying 1.1% error is obtained. The accuracy is therefore promising. Furthermore noise sensitivity is evaluated by adding random values to the inputs (temperature computed at a depth of 0.5 mm under the surface) and the accuracy has not bee compromised (1.8%). Therefore good noise robustness is demonstrated

Rapid Environmental Quenching of Satellite Dwarf Galaxies in the Local Group

In the Local Group, nearly all of the dwarf galaxies (M_star < 10^9 M_sun) that are satellites within 300 kpc (the virial radius) of the Milky Way (MW) and Andromeda (M31) have quiescent star formation and little-to-no cold gas. This contrasts strongly with comparatively isolated dwarf galaxies, which are almost all actively star-forming and gas-rich. This near dichotomy implies a rapid transformation of satellite dwarf galaxies after falling into the halos of the MW or M31. We combine the observed quiescent fractions for satellites of the MW and M31 with the infall times of satellites from the Exploring the Local Volume in Simulations (ELVIS) suite of cosmological zoom-in simulations to determine the typical timescales over which environmental processes within the MW/M31 halos remove gas and quench star formation in low-mass satellite galaxies. The quenching timescales for satellites with M_star < 10^8 M_sun are short, < 2 Gyr, and quenching is more rapid at lower M_star. These satellite quenching timescales can be 1 - 2 Gyr longer if one includes the time that satellites were environmentally preprocessed by low-mass groups prior to MW/M31 infall. We compare with quenching timescales for more massive satellites from previous works to synthesize the nature of satellite galaxy quenching across the observable range of M_star = 10^{3-11} M_sun. The satellite quenching timescale increases rapidly with satellite M_star, peaking at ~9.5 Gyr for M_star ~ 10^9 M_sun, and the timescale rapidly decreases at higher M_star to < 5 Gyr at M_star > 5 x 10^9 M_sun. Overall, galaxies with M_star ~ 10^9 M_sun, similar to the Magellanic Clouds, exhibit the longest quenching timescales, regardless of environmental or internal mechanisms.Comment: 6 pages, 3 figures. Accepted in ApJ Letters. Matches published versio

Investigating the Life-cycle of Photosystem II Using Mass Spectrometry

Photosystem II (PSII) is a protein complex found embedded in the thylakoid membranes of all organisms that perform oxygenic photosynthesis. PSII converts sunlight into chemical energy, filling our atmosphere with molecular oxygen in the process and supporting nearly all life on Earth. PSII undergoes frequent light-induced damage as an unavoidable result of the electron transfer reactions it catalyzes. When damaged, PSII is disassembled, repaired, and reassembled in an intricate, tightly regulated process. The structure and mechanism of function of active PSII are relatively well-understood, due to the available crystal structures of the active complex and many years of biochemical and biophysical investigation. However, many aspects of the broader PSII life-cycle are less clear. In this work, several structural aspects of the PSII life-cycle are investigated, with an approach that emphasizes mass spectrometry (MS)-based tools. The field of protein MS is developing rapidly, and, especially in the last several years, MS has become a key tool for addressing a variety of questions in the area of photosynthesis. Chapter 1 provides an in-depth review of the ways in which MS has been, and can be, applied to PSII life-cycle research. This chapter presents the relevant MS-based techniques, as well as the knowledge that has been gained about the PSII life-cycle through their application. The work in Chapter 2 used cross-linking and MS to identify the binding site of the Psb28 protein to PSII. Psb28 binds transiently to a PSII assembly intermediate complex, exerting a protective effect on this complex. However, since Psb28 dissociates before assembly is complete, it is not found in the crystal structure and its structural location within the complex has remained unknown. We used isotope-encoded chemical cross-linking followed by MS to identify the binding partners of Psb28 in the model cyanobacterium Synechocystis sp. PCC 6803, the organism used throughout this work. We identified three cross-links between Psb28 and the α- and β- subunits of cytochrome b559 (PsbE and PsbF), pinpointing the structural location of Psb28 on the cytosolic surface of PSII in close association with these subunits. Our results allow us to propose several mechanisms by which Psb28 could exert its protective effect. In Chapter 3, we used high-resolution tandem MS to identify oxidative modifications in PSII. We found that the total number of modified residues increased by over 50% following light incubation, with the D1 protein showing the most marked increase (3.3-fold) of the proteins we monitored. These results strongly support the idea that ROS are generated as a byproduct of PSII photochemistry and that they damage PSII subunits, especially D1, which has the fastest turnover rate of all the subunits. By mapping the modified residues onto the PSII crystal structure, we found that the lumen-side residues form two nearly continuous, roughly linear arms starting at the Mn4Ca cluster and radiating outward all the way to the surface of PSII. We propose that these two arms are oxygen/ROS exit channels that protect PSII by removing ROS from the complex after they are generated at the Mn4Ca cluster. It has long been believed that PSII must contain such channels, and this study provides the most complete and descriptive molecular-level evidence yet for their existence and location. Chapter 4 describes a study that used cross-linking and MS to identify the binding location of PsbQ on the lumenal surface of PSII. Though PsbQ is a necessary component of PSII complexes with highest oxygen-evolving activity, it is not found in the available cyanobacterial crystal structures. Our results show that PsbQ helps stabilize the PSII dimer, providing a structural basis to explain our biochemical data and previous findings. A novel PSII subcomplex with multiple copies of the PsbQ protein was also discovered, and its characterization is described in this chapter. Based on our results, we propose it is a late PSII assembly intermediate that stabilizes the active PSII dimer just before association of the other lumenal extrinsic proteins PsbU and PsbV

Retrieving Decadal Climate Change from Satellite Radiance Observations-A 100-year CO2 Doubling OSSE Demonstration.

Preparing for climate change depends on the observation and prediction of decadal trends of the environmental variables, which have a direct impact on the sustainability of resources affecting the quality of life on our planet. The NASA Climate Absolute Radiance and Refractivity Observatory (CLARREO) mission is proposed to provide climate quality benchmark spectral radiance observations for the purpose of determining the decadal trends of climate variables, and validating and improving the long-range climate model forecasts needed to prepare for the changing climate of the Earth. The CLARREO will serve as an in-orbit, absolute, radiometric standard for the cross-calibration of hyperspectral radiance spectra observed by the international system of polar operational satellite sounding sensors. Here, we demonstrate that the resulting accurately cross-calibrated polar satellite global infrared spectral radiance trends (e.g., from the Metop IASI instrument considered here) can be interpreted in terms of temperature and water vapor profile trends. This demonstration is performed using atmospheric state data generated for a 100-year period from 2000-2099, produced by a numerical climate model prediction that was forced by the doubling of the global average atmospheric CO2 over the 100-year period. The vertical profiles and spatial distribution of temperature decadal trends were successfully diagnosed by applying a linear regression profile retrieval algorithm to the simulated hyperspectral radiance spectra for the 100-year period. These results indicate that it is possible to detect decadal trends in atmospheric climate variables from high accuracy all-sky satellite infrared radiance spectra using the linear regression retrieval technique

A new sensor for the evaluation of contact stress by inverse analysis during steel strip rolling

International audienceKnowledge of the contact stress between roll and strip becomes a critical factor in modern, high-speed rolling mills. In this paper, an inverse analytical method is developed to determine the contact stress in the roll gap by measuring the stress tensor with fibre optics at only one point inside the roll. Unlike many inverse methods, no matrix inversion is needed because the very small contact length would lead to ill-conditioned matrices. Iterative methods are also not studied because short computation times are desired. This approach uses the theory of elasticity on the assumption that the problem is isothermal and planar and relies on the expansion of holomorphic functions into a power series. On the other hand, the computation time is studied to rapidly optimise the industrial parameters during the rolling process. Hot, cold and temper-rolling simulations are given to demonstrate the accuracy of the method and the feasibility of this new kind of sensor, taking into account the restrictions (e.g., frequency of acquisition) of the local measurement system