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See detailData-driven dynamical model indicates that the heat shock response in Chlamydomonas reinhardtii is tailored to handle natural temperature variation
Magni, Stefano UL; Succurro, Antonella; Skupin, Alexander UL et al

in Journal of the Royal Society, Interface (2018), 15(142), 20170965

Global warming exposes plants to severe heat stress, with consequent crop yield reduction. Organisms exposed to high temperature stresses typically protect themselves with a heat shock response (HSR ... [more ▼]

Global warming exposes plants to severe heat stress, with consequent crop yield reduction. Organisms exposed to high temperature stresses typically protect themselves with a heat shock response (HSR), where accumulation of unfolded proteins initiates the synthesis of heat shock proteins through the heat shock transcription factor HSF1. While the molecular mechanisms are qualitatively well characterized, our quantitative understanding of the under- lying dynamics is still very limited. Here, we study the dynamics of HSR in the photosynthetic model organism Chlamydomonas reinhardtii with a data-driven mathematical model of HSR. We based our dynamical model mostly on mass action kinetics, with a few nonlinear terms. The model was parametrized and validated by several independent datasets obtained from the literature. We demonstrate that HSR quantitatively and significantly differs if an increase in temperature of the same magnitude occurs abruptly, as often applied under laboratory conditions, or gradually, which would rather be expected under natural conditions. In contrast to rapid temperature increases, under gradual changes only negligible amounts of misfolded proteins accumulate, indicating that the HSR of C. reinhardtii efficiently avoids the accumulation of misfolded proteins under conditions most likely to prevail in nature. The mathematical model we developed is a flexible tool to simulate the HSR to different conditions and complements the current experimental approaches. [less ▲]

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See detailA systems-wide understanding of photosynthetic acclimation in algae and higher plants
Wanjiku Moejes, Fiona; Matuszyńska, Anna; Adhikari, Kailash et al

in Journal of Experimental Botany (2017), 68(11), 26672681

The ability of phototrophs to colonise different environments relies on robust protection against oxidative stress, a critical requirement for the successful evolutionary transition from water to land ... [more ▼]

The ability of phototrophs to colonise different environments relies on robust protection against oxidative stress, a critical requirement for the successful evolutionary transition from water to land. Photosynthetic organisms have developed numerous strategies to adapt their photosynthetic apparatus to changing light conditions in order to optimise their photosynthetic yield, which is crucial for life on Earth to exist. Photosynthetic acclimation is an excellent example of the complexity of biological systems, where highly diverse processes, ranging from electron excitation over protein protonation to enzymatic processes coupling ion gradients with biosynthetic activity, interact on drastically different timescales from picoseconds to hours. Efficient functioning of the photosynthetic apparatus and its protection is paramount for efficient downstream processes, including metabolism and growth. Modern experimental techniques can be successfully integrated with theoretical and mathematical models to promote our understanding of underlying mechanisms and principles. This review aims to provide a retrospective analysis of multidisciplinary photosynthetic acclimation research carried out by members of the Marie Curie Initial Training Project, AccliPhot, placing the results in a wider context. The review also highlights the applicability of photosynthetic organisms for industry, particularly with regards to the cultivation of microalgae. It intends to demonstrate how theoretical concepts can successfully complement experimental studies broadening our knowledge of common principles in acclimation processes in photosynthetic organisms, as well as in the field of applied microalgal biotechnology. [less ▲]

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See detailAstrophysical aspects of dark matter direct detection
Magni, Stefano UL

Doctoral thesis (2015)

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See detailMaking sense of the local Galactic escape speed estimates in direct dark matter searches
Lavalle, Julien; Magni, Stefano UL

in Physical Review D (2015), 91(2), 023510

Direct detection (DD) of dark matter (DM) candidates in the ≲10 GeV mass range is very sensitive to the tail of their velocity distribution. The important quantity is the maximum weakly interacting ... [more ▼]

Direct detection (DD) of dark matter (DM) candidates in the ≲10 GeV mass range is very sensitive to the tail of their velocity distribution. The important quantity is the maximum weakly interacting massive particle speed in the observer's rest frame, i.e. in average the sum of the local Galactic escape speed v[SUB]esc[/SUB] and of the circular velocity of the Sun v[SUB]c[/SUB]. While the latter has been receiving continuous attention, the former is more difficult to constrain. The RAVE Collaboration has just released a new estimate of v[SUB]esc[/SUB] [T. Piffl et al., Astron. Astrophys. 562, A91 (2014)] that supersedes the previous one [M. C. Smith, et al. Mon. Not. R. Astron. Soc. 379, 755 (2007)], which is of interest in the perspective of reducing the astrophysical uncertainties in DD. Nevertheless, these new estimates cannot be used blindly as they rely on assumptions in the dark halo modeling which induce tight correlations between the escape speed and other local astrophysical parameters. We make a self-consistent study of the implications of the RAVE results on DD assuming isotropic DM velocity distributions, both Maxwellian and ergodic. Taking as references the experimental sensitivities currently achieved by LUX, CRESST-II, and SuperCDMS, we show that (i) the exclusion curves associated with the best-fit points of P14 may be more constraining by up to ˜40 % with respect to standard limits, because the underlying astrophysical correlations induce a larger local DM density, and (ii) the corresponding relative uncertainties inferred in the low weakly interacting massive particle mass region may be moderate, down to 10-15% below 10 GeV. We finally discuss the level of consistency of these results with other independent astrophysical constraints. This analysis is complementary to others based on rotation curves. [less ▲]

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See detailOn the use of the escape speed estimates in setting dark matter direct detection limits
Magni, Stefano UL; Lavalle, J.

in Proceedings, International Conference: "50th Rencontres de Moriond Electroweak Interactions and Unified Theories" La Thuile, Italy, March 14-21 (2015)

The knowledge of the high velocity tail of the WIMP velocity distribution has a strong impact on the way direct detection (DD) may constrain or discover light WIMPs in the GeV mass range. Recently, there ... [more ▼]

The knowledge of the high velocity tail of the WIMP velocity distribution has a strong impact on the way direct detection (DD) may constrain or discover light WIMPs in the GeV mass range. Recently, there have been important observational efforts to estimate the so-called Galactic escape speed at the position of the Earth, for instance the analysis published in early 2014 by the RAVE Collaboration ' , which is of interest in the perspective of reducing the astrophysical uncertainties in DD. Nevertheless, these new estimates cannot be used blindly as they rely on assumptions in the dark halo modeling, which induce tight correlations between the escape speed and other local astrophysical parameters (e.g. the local circular speed and dark matter density). We make a self-consistent study of the implications of the RAVE results on DD assuming isotropic DM velocity distributions, both Maxwellian and ergodic. Taking as reference the experimental sensitivities currently achieved by LUX, CRESST2, and SuperCDMS, we show that the DD constraints on WIMPs (and associated uncertainties) are slightly stronger (moderate). [less ▲]

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See detailRevisiting the escape speed impact on dark matter direct detection
Magni, Stefano UL; Lavalle, J.

in Proceedings, International Conference: "Frontiers of Fundamental Physics '14", Marseille, France, July 15-18 (2014)

The knowledge of the high velocity tail of the WIMP (Weakly Interacting Massive Particles) velocity distribution has a strong impact on the way dark matter direct detection (DMDD) may constrain or ... [more ▼]

The knowledge of the high velocity tail of the WIMP (Weakly Interacting Massive Particles) velocity distribution has a strong impact on the way dark matter direct detection (DMDD) may constrain or discover light WIMPs in the GeV mass range. Recently, there have been important observational efforts to estimate the Galactic escape speed at the position of the Earth, like for instance the analysis published in early 2014 by the RAVE Collaboration (Piffl et al., 2014), which is of interest in the perspective of reducing the astrophysical uncertainties in DMDD. Nevertheless, these new estimates cannot be used blindly as they rely on assumptions on the Milky Way mass distribution, which induce tight correlations between the escape speed and other local astrophysical parameters (circular speed and dark matter density). We make a self-consistent study of the implications of the RAVE results on DMDD assuming isotropic DM velocity distributions, both Maxwellian and ergodic. Taking as reference the experimental sensitivities currently achieved by LUX, CRESST2, and SuperCDMS, we show that the uncertainties inferred for the exclusion curves in the low WIMP mass region are moderate, ranging from 10% to 20% , and that the RAVE results imply large values of r , and so correspond to exclusion curves that are more constraining than the standard ones by 40%. [less ▲]

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See detailBackreaction and the Covariant Formalism of General Relativity
Magni, Stefano UL

Bachelor/master dissertation (2012)

This thesis is a review of backreaction, which is a possible alternative to dark energy and modified gravity. We describe in detail the 3+1 covariant formalism and Frobenius' theorem. We present the ... [more ▼]

This thesis is a review of backreaction, which is a possible alternative to dark energy and modified gravity. We describe in detail the 3+1 covariant formalism and Frobenius' theorem. We present the averaging procedure developed by Buchert, the Buchert equations and the generalization of these equations to the case of general matter. We then generalize to arbitrary number of spatial dimensions. We focus on the case of 2+1 dimensions, where the relation between the topology and the geometry of a surface imposes a global constraint on backreaction. [less ▲]

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