107 research outputs found
Wave-front phase retrieval in transmission electron microscopy via ptychography
No full textThere are many different strategies that allow the solving of the well-known phase problem corresponding to the loss of phase information during a physical measurement. In microscopy, and, in particular, in transmission electron microscopy, most of these strategies focus on the retrieval of high-resolution information with the importance of lower resolution data often overlooked. Ptychography offers a means to investigate such data. Ptychography is a robust diffractive imaging technique with fast convergence for phase retrieval but, until now, has not been applied at the nanoscale. In this paper, we use the ptychographical iterative engine to retrieve the phase change at the exit plane of metallic nanoparticles using a conventional transmission electron microscope. Ptychographical reconstructions yielded images with a phase resolution of π/10 and a spatial resolution of 1 nm. These results stand as a first step toward aberration-free lensless imaging. The technique lends itself to be an alternative to off-axis electron holography or focal series reconstructio
A Golgi PKD Activity Reporter Reveals a Crucial Role of PKD in Nocodazole‐Induced Golgi Dispersal
No full textThe protein kinase D (PKD) family comprises multifunctional serine/threonine-specific protein kinases with three mammalian isoforms: PKD1, PKD2 and PKD3. A prominent PKD function is the regulation of basolateral-targeted transport carrier fission from the trans-Golgi network (TGN). To visualize site-specific PKD activation at this organelle, we designed a molecular reporter consisting of a PKD-specific substrate sequence fused to enhanced green fluorescent protein (EGFP), specifically targeted to the TGN via the p230 GRIP domain. Quantitative analyses using a phosphospecific antibody and ratiometric fluorescence imaging revealed that Golgi-specific phosphorylation of the reporter was strictly dependent on stimulation of endogenous PKD or transient expression of active PKD constructs. Conversely, PKD-specific pharmacological inhibitors and siRNA-mediated PKD knockdown suppressed reporter phosphorylation. Using this reporter we investigated a potential role for PKD in the regulation of Golgi complex morphology. Interestingly, nocodazole-induced Golgi complex break-up and dispersal was associated with local PKD activation as measured by reporter phosphorylation and this was efficiently blocked by expression of a dominant-negative PKD mutant or PKD depletion. Our data thus identify a novel link between PKD activity and the microtubule cytoskeleton, whereby Golgi complex integrity is regulated
Law & Economics Perspectives on Electricity Regulation
No full textThis paper first reviews some of the main contributions of the new institutional economics to the analysis of the process of competitive transformation of network industries. It shows that neoinstitutional analysis is complementary to the microeconomics of rational pricing, since it accounts for the decisive role of an institutional framework adapted to new transactions. It emphasizes the importance of the political reform process, which draws on the conditions of attractiveness and feasibility to define an initial reorganization of property rights in these industries. The paper then analyzes in this light some of the main challenges ahead for electricity regulation: the question of investment in generation capacities and the link to long term contracts, the regulation of wholesale market power, the support to Renewable Energy Sources for Electricity (RES-E) and the design of new regulatory authorities.Electricity Markets; New Institutional Economics; Law & Economics
Rigidity results for nonlocal phase transitions in the Heisenberg group
No full textInternational audienceIn the Heisenberg group framework, we study rigidity properties for stable solutions of in , . We obtain a Poincar\'e type inequality in connection with a degenerate elliptic equation in ; through an extension (or "lifting") procedure, this inequality will be then used for giving a criterion under which the level sets of the above solutions are minimal surfaces in , i.e. they have vanishing mean curvature
Combining Parametric and Structural Uncertainty in Optimization Modelling for Sustainable Energy Systems
No full textThe swift reduction of human’s carbon footprint is essential to prevent irreversible damage to the climate and to meet climate policy targets. Designing flexible and reliable future energy systems is a big contributor to meeting these goals. While energy system models have improved in the last few decades, they remain vulnerable against parametric and structural uncertainty due to the varying characteristics of parameters and the hardship of modelling all constraints and drivers accurately. This thesis proposes a method that addresses both uncertainty types in energy system modelling by applying SPORES cost optimisation and Monte Carlo scenario modelling simultaneously. The main case study uses 27 input scenarios with varying outcomes for grid electricity price, solar yield and energy consumption to provide insight in a 100 household neighbourhood energy system with heating, cooling, electricity and hydrogen as energy carriers. With 1377 (near-)optimal solutions, a novel approach in analysis and post processing is used to provide 52 useful configuration options that each have their strengths and weaknesses to different political, economical, social and technical drivers. These configurations are tested for cost, security of supply, CO2 emissions and grid dependency. Those results are visualised through ridge plots and statistical tables to provide a clear overview between each configuration’s trade-offs. An example is included to show how those results can be used for improving energy system design in practice.This thesis shows that two methods can successfully be combined into one universal one, while providing valuable design insights for energy systems under uncertainty. Furthermore, this method can be applied to a wide variety of energy systems, as long as its possible components, their technical aspects and their allowed interactions are known beforehand. As many future energy system aspects are uncertain, it should be seen as a vital tool to help speed up the decarbonization.Electrical Engineering | Sustainable Energy Technolog
Selective adhesion of Bacillus cereus spores on heterogeneously wetted silicon nanowires
No full textISI Document Delivery No.: 556ZPTimes Cited: 1Cited Reference Count: 33Galopin, Elisabeth Piret, Gaelle Szunerits, Sabine Lequette, Yannick Faille, Christine Boukherroub, RabahCentre National de la Recherche Scientifique (CNRS); Nord-Pas-de Calais; Agence Nationale de la Recherche[ANR-07-PNRA-009-01 InterSpore]We gratefully acknowledge the Centre National de la Recherche Scientifique (CNRS) and the Nord-Pas-de Calais region for support. We are grateful to G. Ronse, A. Ronse. and M. Clarisse from INRA for technical assistance provided for biological sample preparation. This work has been partially financed by the Agence Nationale de la Recherche under the Programme National de Recherche en Alimentation et Nutrition Humaine, project ANR-07-PNRA-009-01 InterSpore.Amer chemical socWashingtonBoukherroub, R (reprint author), CNRS, IRI, USR 3078, Parc Haute Borne,50 Ave Halley,BP 70478, F-59658 Villeneuve Dascq, [email protected] audienceThe article reports on the selective adhesion of Bacillus cereus spores oil patterned and heterogeneously wetted superhydrophobic silicon nanowires surfaces. Superhydrophilic patterns on superhydrophobic silicon nanowire (SiNW) surfaces were prepared by a standard optical lithography technique. Exposure of the patterned surface to a suspension of B. cercus spores in water led to their specific adsorption in superhydrophobic areas. Comparable results were obtained on a patterned hydrophobic/hydrophilic flat silicon (Si) surface even though at higher concentration of spores wits observed on the hydrophobic areas, its compared to the superhydrophobic regions of the SiNW substrate, The surfaces were characterized using scanning electron microscopy (SEM), fluorescence spectroscopy, and contact angle measurements
Retrieving the Median Volume Diameter with a Polarimetric Cloud Radar
No full textThe knowledge of the raindrop size distribution is key for characterizing precipitation. It is however still a challenge to retrieve it with radars. Several polarimetric and spectral techniques are proposed for cm-wavelength radars (weather radars). What about the mm-wavelength radars (cloud radars), which have a better spatial and time resolution and can still measure light and moderate rain? Knowing that 90% of the rain volume in Europe comes from rainfall rates between 0.1 mm/h and 10 mm/h, this is worthwhile to investigate. The goal of this thesis is to retrieve 1 of the 3 parameters of the modelled gamma raindrop size distribution, the median volume diameter (D0), during stratiform rainfall events using a slantwise profiling dual-frequency polarimetric cloud radar. Focus is given to phase measurements, which are not affected by attenuation. Simulations show that the differential backscatter phase (δco) strongly depends on D0. At mm-wavelength, backscattering and propagation effects need to be disentangled first. To achieve this, an algorithm to detect and characterize Rayleigh plateaus is proposed and implemented. After the application of this algorithm, a methodology to estimate the differential backscatter phase and its error is given. The 95% confidence interval of δco is estimated with the re-sampling method bootstrapping. Using simulation results, an attempt is made to find combinations of D0 and the raindrop size distribution shape parameter μ that match with the confidence interval of δco. The confidence interval of δco restricts D0, but not μ in most cases. This proposed technique is applied for both the 35 and 94 GHz frequency band of the new cloud radar at Cabauw (Ruisdael Observatory site near Utrecht). The resulting 95% confidence intervals of D0 with 35 and 94 GHz and their overlap are compared with in-situ disdrometer measurements of the mass-weighted mean diameter (Dm) which is closely related to D0. The median volume diameter retrieved with the 35 and 94 GHz frequency bands both shows a normalized cross correlation coefficient of 0.845 with the measured Dm of the disdrometer. Therefore, the cloud radar seems to have the capability to provide the detailed variations of the raindrops mean/median diameter like a local disdrometer, but at different heights. Nonetheless, the values differ. The disdrometer provides higher values than the cloud radar. One possible explanation is the inability of the disdrometer to measure raindrops smaller than 0.25 mm and the expected underestimation of the number of raindrops with sizes between 0.25 and 0.375 mm. However, because D0 values retrieved from 35 GHz data are also higher than the ones at 94 GHz, further research, which can use all the methodologies proposed in this master thesis work, is needed to examine the quantitative values of the median volume diameter retrieval. These techniques can be implemented for all the single-frequency cloud radars (94 GHz) of the national Ruisdael Observatory (cloud and precipitation profiling mobile station and Lutjewad site above Groningen).Geoscience and Remote Sensin
NONLOCAL FILTRATION EQUATIONS AND FRACTIONAL CURVATURE FLOWS
No full textIn this thesis, we record the joint work done by the author and Pak Tung Ho concerning the fractional Nirenberg problem with a symmetric assumption, which is addressed through fractional curvature flows on the Riemannian sphere Sn. Furthermore, we present the author’s work on nonlocal filtration equations related to the Heisenberg group Hn. The classical Nirenberg’s problem is to find a conformal metric of an n-dimensional Riemannian manifold such that its scalar curvature is a given function f. A geometric flow has been introduced to study Nirenberg’s problem by Struwe for n = 2 and has been generalized to n ≥ 3 by Chen and Xu on the sphere Sn. Using the scalar curvature flow, Leung and Zhou proved an existence result for prescribing scalar curvature when the given function f possesses certain reflection or rotation symmetry on the Riemannian sphere Sn in their paper. This led naturally to the study of the prescribing fractional order curvature problem with the same symmetric hypothesis on Sn, which has been proved by the author and Pak Tung Ho. Motivated by the extensive investigations of nonlocal filtration equations, utilizing the integral operators instead of the Laplacian operator on the Euclidean space Rn, we work on the same type of equations on the Heisenberg group Hn. We established the existence, uniqueness and large-time behavior of the corresponding solutions. Furthermore, an interesting result stated that a uniform Hölder regularity, as the function value tends to zero, holds for the porous medium type of equations, which can also be adapted to obtain uniform Hölder regularity on Rn
NONLOCAL FILTRATION EQUATIONS AND FRACTIONAL CURVATURE FLOWS
No full textIn this thesis, we record the joint work done by the author and Pak Tung Ho concerning the fractional Nirenberg problem with a symmetric assumption, which is addressed through fractional curvature flows on the Riemannian sphere Sn. Furthermore, we present the author’s work on nonlocal filtration equations related to the Heisenberg group Hn. The classical Nirenberg’s problem is to find a conformal metric of an n-dimensional Riemannian manifold such that its scalar curvature is a given function f. A geometric flow has been introduced to study Nirenberg’s problem by Struwe for n = 2 and has been generalized to n ≥ 3 by Chen and Xu on the sphere Sn. Using the scalar curvature flow, Leung and Zhou proved an existence result for prescribing scalar curvature when the given function f possesses certain reflection or rotation symmetry on the Riemannian sphere Sn in their paper. This led naturally to the study of the prescribing fractional order curvature problem with the same symmetric hypothesis on Sn, which has been proved by the author and Pak Tung Ho. Motivated by the extensive investigations of nonlocal filtration equations, utilizing the integral operators instead of the Laplacian operator on the Euclidean space Rn, we work on the same type of equations on the Heisenberg group Hn. We established the existence, uniqueness and large-time behavior of the corresponding solutions. Furthermore, an interesting result stated that a uniform Hölder regularity, as the function value tends to zero, holds for the porous medium type of equations, which can also be adapted to obtain uniform Hölder regularity on Rn
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