A major challenge in the development of new battery materials is understanding their fundamental mechanisms of operation and degradation. Their microscopically inhomogeneous nature calls for ...characterization tools that provide operando and localized information from individual grains and particles. Here, we describe an approach that enables imaging the nanoscale distribution of ions during electrochemical charging of a battery in a transmission electron microscope liquid flow cell. We use valence energy-loss spectroscopy to track both solvated and intercalated ions, with electronic structure fingerprints of the solvated ions identified using an ab initio nonlinear response theory. Equipped with the new electrochemical cell holder, nanoscale spectroscopy and theory, we have been able to determine the lithiation state of a LiFePO4 electrode and surrounding aqueous electrolyte in real time with nanoscale resolution during electrochemical charge and discharge. We follow lithium transfer between electrode and electrolyte and image charging dynamics in the cathode. We observe competing delithiation mechanisms such as core–shell and anisotropic growth occurring in parallel for different particles under the same conditions. This technique represents a general approach for the operando nanoscale imaging of electrochemically active ions in the electrode and electrolyte in a wide range of electrical energy storage systems.
The genus Enterococcus includes some of the most important nosocomial multidrug-resistant organisms, and these pathogens usually affect patients who are debilitated by other, concurrent illnesses and ...undergoing prolonged hospitalization. This Review discusses the factors involved in the changing epidemiology of enterococcal infections, with an emphasis on Enterococcus faecium as an emergent and challenging nosocomial problem. The effects of antibiotics on the gut microbiota and on colonization with vancomycin-resistant enterococci are highlighted, including how enterococci benefit from the antibiotic-mediated eradication of gram-negative members of the gut microbiota. Analyses of enterococcal genomes indicate that there are certain genetic lineages, including an E. faecium clade of ancient origin, with the ability to succeed in the hospital environment, and the possible virulence determinants that are found in these genetic lineages are discussed. Finally, we review the most important mechanisms of resistance to the antibiotics that are used to treat vancomycin-resistant enterococci.
Emergence of resistance among the most important bacterial pathogens is recognized as a major public health threat affecting humans worldwide. Multidrug-resistant organisms have not only emerged in ...the hospital environment but are now often identified in community settings, suggesting that reservoirs of antibiotic-resistant bacteria are present outside the hospital. The bacterial response to the antibiotic "attack" is the prime example of bacterial adaptation and the pinnacle of evolution. "Survival of the fittest" is a consequence of an immense genetic plasticity of bacterial pathogens that trigger specific responses that result in mutational adaptations, acquisition of genetic material, or alteration of gene expression producing resistance to virtually all antibiotics currently available in clinical practice. Therefore, understanding the biochemical and genetic basis of resistance is of paramount importance to design strategies to curtail the emergence and spread of resistance and to devise innovative therapeutic approaches against multidrug-resistant organisms. In this chapter, we will describe in detail the major mechanisms of antibiotic resistance encountered in clinical practice, providing specific examples in relevant bacterial pathogens.
This work explores the use of joint density functional theory, an extension of density functional theory for the ab initio description of electronic systems in thermodynamic equilibrium with a liquid ...environment, to describe electrochemical systems. After reviewing the physics of the underlying fundamental electrochemical concepts, we identify the mapping between commonly measured electrochemical observables and microscopically computable quantities within an, in principle, exact theoretical framework. We then introduce a simple, computationally efficient approximate functional which we find to be quite successful in capturing a priori basic electrochemical phenomena, including the capacitive Stern and diffusive Gouy-Chapman regions in the electrochemical double layer, quantitative values for interfacial capacitance, and electrochemical potentials of zero charge for a series of metals. We explore surface charging with applied potential and are able to place our ab initio results directly on the scale associated with the standard hydrogen electrode (SHE). Finally, we provide explicit details for implementation within standard density functional theory software packages at negligible computational cost over standard calculations carried out within vacuum environments.
Nucleotide binding site, leucine-rich repeat receptors (NLRs) are canonical resistance (R) genes in plants, fungi and animals, functioning as central (helper) and peripheral (sensor) genes in a ...signalling network. We investigate NLR evolution during the colonization of novel habitats in a model tomato species, Solanum chilense.
We used R-gene enrichment sequencing to obtain polymorphism data at NLRs of 140 plants sampled across 14 populations covering the whole species range. We inferred the past demographic history of habitat colonization by resequencing whole genomes from three S. chilense plants from three key populations and performing approximate Bayesian computation using data from the 14 populations.
Using these parameters, we simulated the genetic differentiation statistics distribution expected under neutral NLR evolution and identified small subsets of outlier NLRs exhibiting signatures of selection across populations.
NLRs under selection between habitats are more often helper genes, whereas those showing signatures of adaptation in single populations are more often sensor-NLRs. Thus, centrality in the NLR network does not constrain NLR evolvability, and new mutations in central genes in the network are key for R-gene adaptation during colonization of different habitats.
•A global intercomparison of fifteen clear-sky irradiance models is proposed.•A common gridded hourly input database spanning one year is used.•Larger inter-model discrepancies found in direct ...irradiance than in global irradiance.•The highest differences found in Asia, Middle East and central and northern Africa.•Modeling improvements required for situations with high aerosol load.
Clear-sky irradiance (CSI) modeling constitutes an essential component of the evaluation of the solar resource at any location, and is involved in a large number of applications. In solar applications, most common CSI models provide broadband irradiance predictions based on a number of simplifications and/or empirical components compared to the rigorous radiative transfer models used in atmospheric sciences. Thus, these common CSI models have to undergo continuous quality assurance evaluations to delineate the range of validity of such simplifications. Traditionally, these evaluations have consisted in direct comparisons against high-quality ground observations. A review of 36 such validation studies of the literature is provided here, highlighting which CSI models were recommended over different climatic areas. This review underlines the difficulty of generalizing these results due to a number of methodological difficulties. In particular, the availability of ground observations is limited and does not cover the full extent of the atmospheric conditions over which the CSI models are regularly operated. In this review study, fifteen of the most highly cited CSI models of the literature are compared to each other using a global synthetic input database built from atmospheric reanalyses. It guarantees that most of the operating conditions of CSI models are potentially covered. The study focuses on the global horizontal (GHI) and direct normal (DNI) irradiance predictions of the CSI models. Overall, a better agreement for GHI than for DNI is found. The largest inter-model discrepancies span throughout Asia, the Middle East and central and northern Africa, precisely coinciding with some of the regions with the highest interest for solar energy applications. The most important sources of discrepancies are traced down to high loads of aerosols, high site elevations, and low solar altitudes. Usage of the Linke turbidity factor as input to a popular type of simplified CSI model is found to be a significant source of uncertainty, preventing accurate simultaneous predictions of GHI and DNI. Other models, which tend to mispredict GHI or DNI over, e.g., hazy areas, are identified.
Neuroprotective actions of flavonoids Gutierrez-Merino, C; Lopez-Sanchez, C; Lagoa, R ...
Current medicinal chemistry,
03/2011, Letnik:
18, Številka:
8
Journal Article
Recenzirano
The experimental evidences accumulated during last years point out a relevant role of oxidative stress in neurodegeneration. As anti-cellular oxidative stress agents flavonoids can act either as ...direct chemical antioxidants, the classic view of flavonoids as antioxidants, or as modulators of enzymes and metabolic and signaling pathways leading to an overshot of reactive oxygen species (ROS) formation, a more recently emerging concept. Flavonoids, a large family of natural antioxidants, undergo a significant hepatic metabolism leading to flavonoid-derived metabolites that are also bioactive as antioxidant agents. The development of more efficient flavonoid's based anti-oxidative stress therapies should also take into account their bioavailability in the brain using alternate administration protocols, and also that the major ROS triggering the cellular oxidative stress are not the same for all neurodegenerative insults and diseases. On these grounds, we have reviewed the reports on neuroprotection by different classes of flavonoids on cellular cultures and model animals. In addition, as they are now becoming valuable pharmacological drugs, due to their low toxicity, the reported adverse effects of flavonoids in model experimental animals and humans are briefly discussed.
PDF
