Approche Microfluidique Polyvalente de la Cristallisation

Crystallization is influenced by several parameters such as supersaturation, temperature, environment, and hydrodynamics. Thus, a rapid screening of crystallization conditions is often required during the study of the crystallization of a molecule. But when a small amount of material is available, a suitable experimental tool is essential. The development of microfluidic systems to form microdroplets has gained importance over the past decade (Leng & Salmon, 2009). Microfluidics brings together techniques that allow the manipulation of fluids on submillimeter scale. In our case, the microfluidic system dedicated to crystallization is based on the generation of nano-crystallizers (nanoliter droplets) isolated from each other and in which crystallization can occur independently. Forming hundreds of droplets which are monodisperse in size and experimental conditions, we can make a large number of experiments per condition for statistical studies to meet the stochasticity of the phenomenon of nucleation while consuming little material. Our goal is to create a universal microfluidic assembly which is compatible with all solvents and molecules. Thus, we are interested in simple microfluidic devices which allow generating droplets with PEEK junctions coupled with Teflon tubings which is resistant to many solvents (Ildefonso, Candoni, et al., 2012). From such systems, we have first characterized the hydrodynamic properties of the set-up: we sought to control microfluidic flow and reduce the volumes put-in and we studied the drop generation regimes by a "cross-flowing" method with two immiscible fluids in the T-junction. We present the scaling law of drop size in a systematic way which we relate to tangential shear. As part of the crystallization study of biomolecule, our goal is to screen different crystallization conditions while achieving a large number of experiments per condition for statistical analysis. We have validated our microfluidic set-up for crystallization studies in a viscous media, on the recombinant urate oxidase or the rasburicase in an aqueous solution of PEG. Finally, we integrated a module for on-line characterization of each droplet’s chemical composition.La cristallisation est influencée par plusieurs paramètres tels que la sursaturation, la température, le milieu et l’hydrodynamique. Pour cela le criblage rapide des conditions de cristallisation est souvent exigé lors de l’étude de la cristallisation d’une molécule. Cependant lorsqu’une faible quantité de matière est disponible, un outil expérimental adapté est indispensable. Le développement des systèmes microfluidiques pour former des microgouttelettes a pris de l’importance au cours des dix dernières années (Leng & Salmon, 2009). La microfluidique regroupe l’ensemble des techniques qui permettent la manipulation de fluides à l’échelle submillimétrique. Dans notre cas, le système microfluidique dédié à la cristallisation est basé sur la génération de nanocristallisoirs (gouttes de volume nanométrique) isolés les uns des autres par de l’huile et dans lesquels la cristallisation peut avoir lieu de façon indépendante. En formant des centaines de gouttelettes monodispersées en taille et en conditions expérimentales, nous pouvons réaliser des études statistiques pour répondre à la stochasticité du phénomène de nucléation, ceci tout en consommant peu de matière.Le but de cette thèse est de créer un montage microfluidique universel, qui soit compatible à tout solvant et toute molécule. Pour cela, nous nous sommes inspirés de dispositifs microfluidiques simples qui permettaient de générer des gouttes grâce à des jonctions microfluidiques en PEEK couplés à des capillaires en Téflon, résistants à de nombreux solvants (Ildefonso, Candoni, et al., 2012). A partir de ce genre de systèmes, nous cherchons à contrôler les écoulements microfluidiques et à réduire les volumes mis en jeu. Nous avons alors étudié les régimes de génération des gouttes dans une jonction en T, à partir de deux fluides non-miscibles par la méthode « cross-flowing ». Nous présentons la loi d'échelle de la taille des gouttelettes que nous avons analysée de façon systématique et que nous relions au cisaillement tangentiel.Dans le cadre de l’étude de la cristallisation de biomolécules, notre objectif est de cribler des conditions de cristallisation différentes tout en réalisant un grand nombre d'expériences par condition pour des analyses statistiques. Nous montrons la faisabilité de notre dispositif microfluidique pour l’étude de la cristallisation en variant les conditions de viscosité avec l’exemple de l’urate oxydase recombinante ou rasburicase que nous avons cristallisée dans une solution aqueuse de PEG. Pour finir, nous avons intégré un module de caractérisation en ligne dans notre système microfluidique afin d'analyser la composition chimique de chaque goutte

BaFe2As2 Surface Domains and Domain Walls: Mirroring the Bulk Spin Structure

High-resolution scanning tunneling microscopy (STM) measurements on BaFe2As2-one of the parent compounds of the iron-based superconductors-reveals a (1x1) As-terminated unit cell on the (001) surface. However, there are significant differences of the surface unit cell compared to the bulk: only one of the two As atoms in the unit cell is imaged and domain walls between different (1x1) regions display a C2 symmetry at the surface. It should have been C2v if the STM image reflected the geometric structure of the surface or the orthorhombic bulk. The inequivalent As atoms and the bias dependence of the domain walls indicate that the origin of the STM image is primarily electronic not geometric. We argue that the surface electronic topography mirrors the bulk spin structure of BaFe2As2, via strong orbital-spin coupling

Surface Geometric and Electronic Structure of BaFe2As2(001)

BaFe2As2 exhibits properties characteristic of the parent compounds of the newly discovered iron (Fe)-based high-TC superconductors. By combining the real space imaging of scanning tunneling microscopy/spectroscopy (STM/S) with momentum space quantitative Low Energy Electron Diffraction (LEED) we have identified the surface plane of cleaved BaFe2As2 crystals as the As terminated Fe-As layer - the plane where superconductivity occurs. LEED and STM/S data on the BaFe2As2(001) surface indicate an ordered arsenic (As) - terminated metallic surface without reconstruction or lattice distortion. It is surprising that the STM images the different Fe-As orbitals associated with the orthorhombic structure, not the As atoms in the surface plane.Comment: 12 pages, 4 figure

Pore Characteristics of the Upper Carboniferous Taiyuan Shale in Liaohe Depression

High pressure mercury, nitrogen adsorption, nano-CT, and scanning electron microscope with energy spectrum analysis were conducted on core shale samples for studying the characteristics of Taiyuan formation in the eastern uplift of Liaohe depression. The research results show that the shale gas reservoir pores are mainly open pores such as the wedge-shape pores and parallel-plate pores. By a genetic type, pores mainly include organic pore, pyrite crystal particle pore, illite intragranular pore, illite-smectite mixed layer intragranular pore, and feldspar dissolved pore. The micropore and mesopore play an important role in shale gas reservoir, and their surface area and pore volume are 9.56 m2/g, 0.0414 mL/g, 97.3%, and 68.8% respectively. The pores diameter presents a bimodal distribution with two main peaks at 43 nm and 6.35 μm. Based on the nano-CT, the porosity is 4.36% and the permeability is 204 nD. The brittle minerals played a supportive and protective role for the pores and controlled their spatial distribution

Anthropogenic influences on extremely persistent seasonal precipitation in Southern China during May–June 2022

Precipitation in southern China during April–June 2022 was the highest since 1961. Anthropogenic forcing has reduced the probability of 2022-like Rx30day precipitation by about 45% based on CMIP6 simulations

Inhomogeneous d-wave superconducting state of a doped Mott insulator

Recent scanning tunneling microscope (STM) measurements discovered remarkable electronic inhomogeneity, i.e. nano-scale spatial variations of the local density of states (LDOS) and the superconducting energy gap, in the high-Tc superconductor BSCCO. Based on the experimental findings we conjectured that the inhomogeneity arises from variations in local oxygen doping level and may be generic of doped Mott insulators which behave rather unconventionally in screening the dopant ionic potentials at atomic scales comparable to the short coherence length. Here, we provide theoretical support for this picture. We study a doped Mott insulator within a generalized t-J model, where doping is accompanied by ionic Coulomb potentials centered in the BiO plane. We calculate the LDOS spectrum, the integrated LDOS, and the local superconducting gap, make detailed comparisons to experiments, and find remarkable agreement with the experimental data. We emphasize the unconventional screening in a doped Mott insulator and show that nonlinear screening dominates at nano-meter scales which is the origin of the electronic inhomogeneity. It leads to strong inhomogeneous redistribution of the local hole density and promotes the notion of a local doping concentration. We find that the inhomogeneity structure manifests itself at all energy scales in the STM tunneling differential conductance, and elucidate the similarity and the differences between the data obtained in the constant tunneling current mode and the same data normalized to reflect constant tip-to-sample distance. We also discuss the underdoped case where nonlinear screening of the ionic potential turns the spatial electronic structure into a percolative mixture of patches with smaller pairing gaps embedded in a background with larger gaps to single particle excitations.Comment: 19 pages, final versio

Super‐Resolution Microscopy Reveals Shape and Distribution of Dislocations in Single‐Crystal Nanocomposites

With their potential to offer new properties, single crystals containing nanoparticles provide an attractive class of nanocomposite materials. However, to fully profit from these, it is essential that we can characterise their 3D structures, identifying the locations of individual nanoparticles, and the defects present within the host crystals. Using calcite crystals containing quantum dots as a model system, we here use 3D stochastic optical reconstruction microscopy (STORM) to locate the positions of the nanoparticles within the host crystal. The nanoparticles are shown to preferentially associate with dislocations in a manner previously recognised for atomic impurities, rendering these defects visible by STORM. Our images also demonstrate that the types of dislocations formed at the crystal/substrate interface vary according to the nucleation face, and dislocation loops are observed that have entirely different geometries to classic misfit dislocations. This approach offers a rapid, easily accessed, and non‐destructive method for visualising the dislocations present within crystals, and gives insight into the mechanisms by which additives become occluded within crystals

The intervention of classical and molecular breeding approaches to enhance flooding stress tolerance in soybean – An review

Abiotic stresses and climate changes cause severe loss of yield and quality of crops and reduce the production area worldwide. Flooding stress curtails soybean growth, yield, and quality and ultimately threatens the global food supply chain. Flooding tolerance is a multigenic trait. Tremendous research in molecular breeding explored the potential genomic regions governing flood tolerance in soybean. The most robust way to develop flooding tolerance in soybean is by using molecular methods, including quantitative trait loci (QTL) mapping, identification of transcriptomes, transcription factor analysis, CRISPR/Cas9, and to some extent, genome-wide association studies (GWAS), and multi-omics techniques. These powerful molecular tools have deepened our knowledge about the molecular mechanism of flooding stress tolerance. Besides all this, using conventional breeding methods (hybridization, introduction, and backcrossing) and other agronomic practices is also helpful in combating the rising flooding threats to the soybean crop. The current review aims to summarize recent advancements in breeding flood-tolerant soybean, mainly by using molecular and conventional tools and their prospects. This updated picture will be a treasure trove for future researchers to comprehend the foundation of flooding tolerance in soybean and cover the given research gaps to develop tolerant soybean cultivars able to sustain growth under extreme climatic changes