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On spurious and real fluctuations of dynamic functional connectivity during rest
No full textFunctional brain networks reconfigure spontaneously during rest. Such network dynamics can be studied by dynamic functional connectivity (dynFC); i.e., sliding-window correlations between regional brain activity. Key parameters-such as window length and cut-off frequencies for filtering-are not yet systematically studied. In this letter we provide the fundamental theory from signal processing to address these parameter choices when estimating and interpreting dynFC. We guide the reader through several illustrative cases, both simple analytical models and experimental fMRI BOLD data. First, we show how spurious fluctuations in dynFC can arise due to the estimation method when the window length is shorter than the largest wavelength present in both signals, even for deterministic signals with a fixed relationship. Second, we study how real fluctuations of dynFC can be explained using a frequency-based view, which is particularly instructive for signals with multiple frequency components such as fMRI BOLD, demonstrating that fluctuations in sliding-window correlation emerge by interaction between frequency components similar to the phenomenon of beat frequencies. We conclude with practical guidelines for the choice and impact of the window length. (C) 2014 Elsevier Inc. All rights reserved.MIPLABCN
Investigation of the Polyhydroxybutyrate Cycle Regulation and the Redox Homeostasis in Rhodospirillum rubrum during Dark Chemoheterotrophic Growth
No full textAs the world transitions away from fossil-based resources, there is a growing need for innovation in the development of alternative biomolecules and efficient bioprocesses based on renewable feedstocks. Among the promising biobased materials are polyhydroxyalkanoates (PHAs), a family of polyesters naturally produced by microorganisms. PHAs, especially poly(3-hydroxybutyrate) (PHB), offer viable alternatives to conventional plastics in specific applications due to their biocompatibility, biodegradability, and comparable physicochemical properties. However, despite this potential, microbial PHB production remains economically uncompetitive compared to petroleum-based plastics. One promising way to address this challenge is to unravel how PHB synthesis is regulated and integrated into cellular metabolism, in order to improve productivity.
Rhodospirillum rubrum, a purple non-sulfur bacterium (PNSB) with a versatile metabolism, can produce PHB under a wide range of growth conditions. Intracellularly, PHB is both synthesized and degraded simultaneously, forming a dynamic cycle under tight regulation. Yet, the regulation of this cycle and its relationship to the hostâ s metabolism remains poorly understood.
This thesis aims to advance our understanding of the PHB cycle regulation in R. rubrum during chemoheterotrophic growth in particular on acetate. Specifically, we sought to identify environmental factors influencing PHB content and to explore the regulatory mechanisms controlling the PHB cycle under different growing conditions.
We performed transcriptomic profiling across carbon sources and oxygen levels and found that PHB biosynthetic genes are constitutively expressed, while genes responsible for PHB mobilization exhibit condition-specific regulation. This suggests that transcriptional regulation plays a minor role in PHB synthesis, but a more significant role in PHB degradation. Our data also support the idea that the transcriptional regulator PhaR controls carbon partitioning between the ethylmalonyl-CoA (EMC) pathway for biomass formation and the PHB cycle.
To assess whether PHB accumulation functions as an intracellular redox buffer, we used the genetically encoded Peredox biosensor to monitor NADH/NADâ º ratios in vivo. Combined with experiments manipulating dissolved oxygen and adding reductants, our results indicate that PHB can act as an electron sink under certain conditions, likely as part of a broader hierarchy of electron sink mechanisms. This feature could be exploited as a driving force to enhance PHB yields under continuous cultivation. However, culture redox potential and NADH/NADâ º levels did not always correlate with PHB content, suggesting that other redox couples, such as NADPH/NADPâ º, may be more directly involved in the PHB cycle.
Altogether, this work offers new insights into the regulation of PHB metabolism in R. rubrum and provides a foundation for metabolic engineering and bioprocess optimization aimed at reducing the cost of PHB production. In particular, it highlights the role of redox homeostasis in controlling PHB accumulation and points to the potential of growth-associated PHB production on low-cost substrates such as acetate. These findings may also be extended to other types of PHAs and microbial hosts, supporting the development of more efficient and sustainable bioprocesses.LCS
Electric-field-induced orthorhombic to rhombohedral phase transition in [111](C)-oriented 0.92Pb(Zn1/3Nb2/3)O-3-0.08PbTiO(3)
No full textStrain-field measurements and in situ polarized light microscopy have been used to evidence a hysteretic, irreversible electric-field-induced transition to a quasimonodomain rhombohedral phase in [111](C)-oriented, pseudo-orthorhombic PZN-8PT [0.92Pb(Zn1/3Nb2/3)O-3-0.08PbTiO(3)]. This first-order transition most likely occurs following the simplest path O-M-B-R, i.e., via polarization rotation in the (10-1)(C) plane. The measured strain-field loops are compared to those for rhombohedral, [111](C)-oriented PMN-28PT [0.72Pb(Mg1/3Nb2/3)O-3-0.28PbTiO(3)] and PMN-33PT [0.67Pb(Mg1/3Nb2/3)O-3-0.33PbTiO(3)] where no electric-field-induced transition is possible. (C) 2005 American Institute of Physics.L
Coupling Molecular dynamics to a continuum in LibMultiScale: how to address thermal and dislocation issues.
No full textLSM
PLASMA SHAPE AND FUELING DEPENDENCE ON THE SMALL ELMS REGIME IN TCV AND AUG
No full textA series of experiments has been conducted at AUG and TCV to disentangle the role of fueling, plasma triangularity and closeness to a double null (DN) configuration for the onset of the small ELM regime. At AUG, the role of the SOL density has been revisited. Indeed, it turns out that a large density SOL is not a sufficient condition to achieve the type-II (small) ELM regime. This has been demonstrated with a constant gas fueled plasma close to DN which has been progressively shifted down, relaxing therefore the closeness to DN at constant. As the plasma is moved down, Type-I ELMs are progressively restored, finally being the unique ELM regime. It is observed that not only the pedestal top profiles are unchanged, but also the SOL profiles remained unaffected by transition from Type-II to Type-I ELMs. We conclude that the separatrix density is not the unique key parameter and it is hypothesized that the local magnetic shear, modified by the closeness to DN, could play an important role. A small ELM regime with good confinement has been achieved at TCV, a full carbon machine featuring an open divertor. A systematic scan in the fueling rate has been done for both medium and high triangularity shapes. For the latter case, a configuration close to a DN configuration, the stored energy and the pedestal top pressure increase by 5% and 30% respectively compared to the medium triangularity case. For both shapes, as the D2 fueling is increased, the Type-I ELM frequency decreases and small ELMs are observed in between large ones. Finally for the high triangularity, at the maximum fueling rate, the large ELMs are fully suppressed and only the small ELMs remain. As observed in JET and AUG, the pedestal pressure degrades with increasing fueling, up to 40% for the high triangularity scenario, although the stored energy remains almost unchanged. It is also observed that, for both shapes, the density at the separatrix increases with the fueling rate, reaching ne,sep/nG ~0.3 at ne,av/nG~0.75. The small ELM regime at TCV is associated with a coherent mode at about 30 kHz seen by the magnetic probes located at the outboard midplane. The outer target heat loads from IR tomography are reduced by more than a factor of 5 when transiting towards the small ELM regime.SP
Strain-induced dissolution of Y-Ti-O nano-oxides in a consolidated ferritic oxide dispersion strengthened (ODS) steel
No full textThe present study shows the influence of severe plastic deformation on highly stable Y-Ti-O nano-oxides present in ferritic ODS alloys used for nuclear applications. An innovative strain path implying alternated compressions was used to deform the material to an equivalent plastic strain of 13. Energy Filtered Transmission Electron Microscopy and Small Angle Neutron Scattering revealed the strain-induced dissolution of the Y-Ti-O nano-oxides. It appears to be the first time that dissolution of such particles is clearly observed after deformation. Annealing the material enables to re-precipitate the nano-oxides. These results show a strong analogy with the mechanical alloying of ODS powder.LMT
Model #SaveCampusKita Strategi Holistik Mencegah dan Menangani Kekerasan di Perguruan Tinggi Berbasis Aplikasi Lapor Aman
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Early Precipitation Stages of Sigma Phase in Alloy 28 Studied with Scanning Electron Microscopy and Atom Probe Tomography
No full textThis study deals with early stages of sigma phase growth in a high end austenitic stainless steel - Alloy 28 (EN 1.4563/UNS N08028). Its precipitation kinetics was followed by a series of heat treatments at 800 degrees C for holding times up to 30 000 s. The samples were studied with high resolution scanning electron microscopy and atom probe tomography. Detailed image analysis of the micrographs made it possible to quantify the growth rate of the precipitates. It was shown that diffusion limited growth along grain boundaries was about 15 times faster than growth perpendicular to a grain face. By combining the image data with quantitative chemical analysis of the phase boundaries, it was possible to estimate diffusion coefficients in the lattice and in the grain boundaries; grain boundary diffusion coefficients were about 250 times those of the lattice.SCI-STI-S