Experimental investigation and mechanism analysis on rock damage by high voltage spark discharge in water : effect of electrical conductivity

High voltage spark discharge (HVSD) could generate strong pressure waves that can be combined with a rotary drill bit to improve the penetration rate in unconventional oil and gas drilling. However, there has been little investigation of the effect of electrical conductivity on rock damage and the fragmentation mechanism caused by HVSD. Therefore, we conducted experiments to destroy cement mortar, a rock-like material, in water with five conductivity levels, from 0.5 mS/cm to 20 mS/cm. We measured the discharge parameters, such as breakdown voltage, breakdown delay time, and electrical energy loss, and investigated the damage mechanism from stress waves propagation using X-ray computed tomography. Our study then analyzed the influence of conductivity on the surface damage of the sample by the pore size distribution and the cumulative pore area, as well as studied the dependence of internal damage on conductivity by through-transmission ultrasonic inspection technique. The results indicated that the increase in electrical conductivity decreased the breakdown voltage and breakdown delay time and increased the energy loss, which led to a reduction in the magnitude of the pressure wave and, ultimately, reduced the sample damage. It is worth mentioning that the relationship between the sample damage and electrical conductivity is non-linear, showing a two-stage pattern. The findings suggest that stress waves induced by the pressure waves play a significant role in sample damage where pores and two types of tensile cracks are the main failure features. Compressive stresses close horizontal cracks inside the sample and propagate vertical cracks, forming the tensile cracks-I. Tensile stresses generated at the sample-water interface due to the reflection of stress waves produce the tensile cracks-II. Our study is the first to investigate the relationship between rock damage and electrical conductivity, providing insights to guide the design of drilling tools based on HVSD

Structure and mechanism of the CMR complex for CRISPR-Mediated antiviral immunity

The prokaryotic clusters of regularly interspaced palindromic repeats (CRISPR) system utilizes genomically encoded CRISPR RNA (crRNA), derived from invading viruses and incorporated into ribonucleoprotein complexes with CRISPR-associated (CAS) proteins, to target and degrade viral DNA or RNA on subsequent infection. RNA is targeted by the CMR complex. In Sulfolobus solfataricus, this complex is composed of seven CAS protein subunits (Cmr1-7) and carries a diverse "payload" of targeting crRNA. The crystal structure of Cmr7 and low-resolution structure of the complex are presented. S. solfataricus CMR cleaves RNA targets in an endo-nucleolytic reaction at UA dinucleotides. This activity is dependent on the 8 nt repeat-derived 5' sequence in the crRNA, but not on the presence of a proto-spacer-associated motif (PAM) in the target. Both target and guide RNAs can be cleaved, although a single molecule of guide RNA can support the degradation of multiple targets.Publisher PDFPeer reviewe

Ex vivo Dynamics of Human Glioblastoma Cells in a Microvasculature-on-a-Chip System Correlates with Tumor Heterogeneity and Subtypes

The perivascular niche (PVN) plays an essential role in brain tumor stem-like cell (BTSC) fate control, tumor invasion, and therapeutic resistance. Here, a microvasculature-on-a-chip system as a PVN model is used to evaluate the ex vivo dynamics of BTSCs from ten glioblastoma patients. BTSCs are found to preferentially localize in the perivascular zone, where they exhibit either the lowest motility, as in quiescent cells, or the highest motility, as in the invasive phenotype, with migration over long distance. These results indicate that PVN is a niche for BTSCs, while the microvascular tracks may serve as a path for tumor cell migration. The degree of colocalization between tumor cells and microvessels varies significantly across patients. To validate these results, single-cell transcriptome sequencing (10 patients and 21 750 single cells in total) is performed to identify tumor cell subtypes. The colocalization coefficient is found to positively correlate with proneural (stem-like) or mesenchymal (invasive) but not classical (proliferative) tumor cells. Furthermore, a gene signature profile including PDGFRA correlates strongly with the “homing” of tumor cells to the PVN. These findings demonstrate that the model can recapitulate in vivo tumor cell dynamics and heterogeneity, representing a new route to study patient-specific tumor cell functions

The Global N20 Model Intercomparison Project

Nitrous oxide (N2O) is an important greenhouse gas and also an ozone-depleting substance that has both natural and anthropogenic sources. Large estimation uncertainty remains on the magnitude and spatiotemporal patterns of N2O fluxes and the key drivers of N2O production in the terrestrial biosphere. Some terrestrial biosphere models have been evolved to account for nitrogen processes and to show the capability to simulate N2O emissions from land ecosystems at the global scale, but large discrepancies exist among their estimates primarily because of inconsistent input datasets, simulation protocol, and model structure and parameterization schemes. Based on the consistent model input data and simulation protocol, the global N2O Model Intercomparison Project (NMIP) was initialized with 10 state-of-the-art terrestrial biosphere models that include nitrogen (N) cycling. Specific objectives of NMIP are to 1) unravel the major N cycling processes controlling N2O fluxes in each model and identify the uncertainty sources from model structure, input data, and parameters; 2) quantify the magnitude and spatial and temporal patterns of global and regional N2O fluxes from the preindustrial period (1860) to present and attribute the relative contributions of multiple environmental factors to N2O dynamics; and 3) provide a benchmarking estimate of N2O fluxes through synthesizing the multimodel simulation results and existing estimates from ground-based observations, inventories, and statistical and empirical extrapolations. This study provides detailed descriptions for the NMIP protocol, input data, model structure, and key parameters, along with preliminary simulation results. The global and regional N2O estimation derived from the NMIP is a key component of the global N2O budget synthesis activity jointly led by the Global Carbon Project and the International Nitrogen Initiative

Ammonia-oxidising archaea living at low pH: Insights from comparative genomics

Obligate acidophilic members of the thaumarchaeotal genus Candidatus Nitrosotalea play an important role in nitrification in acidic soils, but their evolutionary and physiological adaptations to acidic environments are still poorly understood, with only a single member of this genus (Ca. N. devanaterra) having its genome sequenced. In this study, we sequenced the genomes of two additional cultured Ca. Nitrosotalea strains, extracted an almost complete Ca. Nitrosotalea metagenome-assembled genome from an acidic fen, and performed comparative genomics of the four Ca. Nitrosotalea genomes with 19 other archaeal ammonia oxidiser genomes. Average nucleotide and amino acid identities revealed that the four Ca. Nitrosotalea strains represent separate species within the genus. The four Ca. Nitrosotalea genomes contained a core set of 103 orthologous gene families absent from all other ammonia-oxidizing archaea and, for most of these gene families, expression could be demonstrated in laboratory culture or the environment via proteomic or metatranscriptomic analyses respectively. Phylogenetic analyses indicated that four of these core gene families were acquired by the Ca. Nitrosotalea common ancestor via horizontal gene transfer from acidophilic representatives of Euryarchaeota. We hypothesize that gene exchange with these acidophiles contributed to the competitive success of the Ca. Nitrosotalea lineage in acidic environments

Ammonia oxidation: Ecology, physiology, biochemistry and why they must all come together

Ammonia oxidation is a fundamental core process in the global biogeochemical nitrogen cycle. Oxidation of ammonia (NH3) to nitrite (NO2 −) is the first and rate-limiting step in nitrification and is carried out by distinct groups of microorganisms. Ammonia oxidation is essential for nutrient turnover in most terrestrial, aquatic and engineered ecosystems and plays a major role, both directly and indirectly, in greenhouse gas production and environmental damage. Although ammonia oxidation has been studied for over a century, this research field has been galvanised in the past decade by the surprising discoveries of novel ammonia oxidising microorganisms. This review reflects on the ammonia oxidation research to date and discusses the major gaps remaining in our knowledge of the biology of ammonia oxidation

Characterisation of proteins involved in CRISPR-mediated antiviral defence in Sulfolobus solfataricus

One of the most surprising realisations to emerge from metagenomics studies in the early ‘00s was that the population of viruses and phages in nature is about 10 times larger than the population of prokaryotic organisms. Thus, bacteria and archaea are under constant pressure to develop resistance methods against a population of viruses with extremely high turnover and evolution rates, in what has been described as an evolutionary “arms race”. A novel, adaptive and heritable immune system encoded by prokaryotic genomes is the CRISPR/Cas system. Arrays of clustered regularly interspersed short palindromic repeats (CRISPR) are able to incorporate viral or plasmid sequences which are then used to inactivate the corresponding invader element via an RNA interference mechanism. A number of CRISPR-associated (Cas) protein families are responsible for the maintenance, expansion and function of the CRISPR loci. This system can be classified in a number of types and subtypes that differ widely in their gene composition and mode of action. This thesis describes the biochemical characteristics of CRISPR-mediated defense in the crenarchaeon Sulfolobus solfataricus. The process of CRISPR loci transcription and their subsequent maturation into small guide crRNA units by the processing endonuclease of the system (Cas6) is investigated. After this step, different pathways and effector proteins are involved in the recognition and silencing of DNA or RNA exogenous nucleic acids. This thesis reports the identification and purification of a native multiprotein complex from S. solfataricus P2, the Cmr complex, a homologue of which has been found to recognise and cleave RNA targets in P. furiosus. The recognition and silencing of DNA targets in E. coli has been shown to involve a multiprotein complex termed CASCADE as well as Cas3, a putative helicase-HD nuclease. S. solfataricus encodes orthologues for the core proteins of this complex, and the formation and function of an archaeal CASCADE is investigated in this thesis

Étude de corrélation entre la gravité clinique et la gravité scannographique chez les patients SARS-CoV-2 positifs aux urgences du CHU de Rouen du 2 mars au 30 juin 2020 : une étude de cohorte rétrospective

Rechercher et quantifier la relation entre les scores de gravité NEWS2/qCSI et l’étendue de l’atteinte au scanner afin d’optimiser la prise en charge des patients? Conception et critère de jugement principal : Etude de corrélation entre la gravité clinique (NEWS2/qCSI) et la gravité scannographique (pourcentage d’atteinte parenchymateuse) sur une cohorte rétrospective monocentrique aux urgences du CHU de Rouen, incluant tous les patients du 2 mars au 30 juin 2020, avec un diagnostic de SARS-COV2 par PCR ou scanner de forte probabilité et une évaluation de l’atteinte parenchymateuse par scanner. Il sera attribué à la corrélation de Pearson entre les scores cliniques pris en variable continue et le scanner thoracique en variable ordinale, une intensité faible entre 0,3 et 0,5; moyenne entre 0,5 et 0,8 et forte au-delà de 0,8. Résultats/Discussion : 165 patients ont été analysés après application des critères d’exclusion et de non-inclusion. Parmi eux 48/165 (29%) sont graves (décès ou réanimation durant le séjour). Les performances des scores étaient moins bonnes que dans la littérature. Les corrélations sont faibles pour NEWS2 (R= 0,48) et qCSI (R= 0,39) après imputation multiples. La distribution éparse des individus en limite sa reproductibilité. Des analyses en sous-groupes ont été réalisées après imputation simple. Les corrélations sur les sous-groupes “début des symptômes” “Conclusion : Il existe une corrélation faible de la gravité entre le score de NEWS2/qCSI et l’atteinte parenchymateuse scannographique avec rho=0,48 et 0,39 respectivement Elle ne permet pas de s’abstenir du scanner aux urgences pour les malades modérées à critique lorsque celui-ci est indiqué

Analysis of the transmission path of factors influencing employee slackness in companies based on ISM-MICMAC

Employee slackness is a prevalent behavior among current corporate employees, and this behavior harms both employee personal development and organizational effectiveness. In this study, factors are extracted from four levels: employee, leader, company, and job, and the relationships of factors influencing employee slackness are sorted out using the explanatory structural model (ISM) and the cross-influence matrix multiplication method (MICMAC), and corresponding conclusions are drawn based on the relevant mechanistic models. The results of the study show that a strong sense of overqualification and less meaningful work as independent group factors have the deepest influence on corporate employees to produce slacking behavior. The findings of this study help enterprises to understand the influencing factors of employees’ slacking behavior at a deeper level; they also provide important management insights for enterprise managers to pay attention to and alleviate employees’ slacking emotions and negative work behaviors