Water oxidation is the key kinetic bottleneck of photoelectrochemical devices for fuel synthesis. Despite advances in the identification of intermediates, elucidating the catalytic mechanism of this ...multi-redox reaction on metal-oxide photoanodes remains a significant experimental and theoretical challenge. Here, we report an experimental analysis of water oxidation kinetics on four widely studied metal oxides, focusing particularly on haematite. We observe that haematite is able to access a reaction mechanism that is third order in surface-hole density, which is assigned to equilibration between three surface holes and M(OH)-O-M(OH) sites. This reaction exhibits low activation energy (E
≈ 60 meV). Density functional theory is used to determine the energetics of charge accumulation and O-O bond formation on a model haematite (110) surface. The proposed mechanism shows parallels with the function of the oxygen evolving complex of photosystem II, and provides new insights into the mechanism of heterogeneous water oxidation on a metal oxide surface.
Abstract Interacting quasi-one-dimensional zigzag graphene nanoribbons display gapped edge excitations. Although the self-consistent Hartree–Fock fields break chiral symmetry, our work demonstrates ...that zigzag graphene nanoribbons maintain their status as short-range entangled symmetry-protected topological insulators. The relevant symmetry involves combined mirror and time-reversal operations. In undoped ribbons displaying edge ferromagnetism, the band gap edge states with a topological charge form on the zigzag edges. An analysis of the anomalous continuity equation elucidates that this topological charge is induced by the gap term. In low-doped zigzag ribbons, where the ground state exhibits edge spin density waves, this topological charge appears as a nearly zero-energy edge mode. Our system is outside the conventional classification for topological insulators.
Mesocortical corrected dopamine (DA) inputs to the prefrontal cortex (PFC) play a critical role in normal cognitive process and neuropsychiatic pathologies. This DA input regulates aspects of working ...memory function, planning and attention, and its dysfunctions may underlie positive and negative symptoms and cognitive deficits associated with schizophrenia. Despite intense research, there is still a lack of clear understanding of the basic principles of actions of DA in the PFC. In recent years, there has been considerable efforts by many groups to understand the cellular mechanisms of DA modulation of PFC neurons. However, the results of these efforts often lead to contradictions and controversies. One principal feature of DA that is agreed by most researchers is that DA is a neuromodulator and is clearly not an excitatory or inhibitory neurotransmitter. The present article aims to identify certain principles of DA mechanisms by drawing on published, as well as unpublished data from PFC and other CNS sites to shed light on aspects of DA neuromodulation and address some of the existing controversies. Eighteen key features about DA modulation have been identified. These points directly impact on the end result of DA neuromodulation, and in some cases explain why DA does not yield identical effects under all experimental conditions. It will become apparent that DA's actions in PFC are subtle and depend on a variety of factors that can no longer be ignored. Some of these key factors include distinct bell-shaped dose-response profiles of postsynaptic DA effects, different postsynaptic responses that are contingent on the duration of DA receptor stimulation, prolonged duration effects, bidirectional effects following activation of D1 and D2 classes of receptors and membrane potential state and history dependence of subsequent DA actions. It is hoped that these factors will be borne in mind in future research and as a result a more consistent picture of DA neuromodulation in the PFC will emerge. Based on these factors, a theory is proposed for DA's action in PFC. This theory suggests that DA acts to expand or contract the breadth of information held in working memory buffers in PFC networks.
Creep-ageing behaviour of aluminium alloy 2050 with different initial tempers (T34, T84 and as-quenched) has been experimentally investigated under both tension and compression creep-ageing ...conditions, with different stress levels at 155°C for 18h. Corresponding strengthening phenomena have been studied by interrupted creep-ageing tests and subsequent tensile tests. Moreover, the microstructures of some selected specimens after creep-ageing tests have been examined by transmission electron microscopy (TEM) and the precipitation process has been analysed. It has been found that creep strains under tensile stresses are much larger than those under compressive stresses during the tests. A new “double primary creep feature” has been observed in both the as-quenched alloys and the pre-stretched/natural-aged (T34) alloys, in which an intermediate inverse creep stage with an increasing creep strain rate locates between the initial primary+transient steady-state creep stages and the second primary+second steady-state creep stages. While for the alloy with peak-aged initial temper (T84), typical primary and steady-state secondary creep stages are observed during tension creep-ageing tests and little creep strain occurs under compressive stresses of 150 and 175MPa. The mechanisms for these phenomena are discussed in terms of microstructural interactions among the changing dislocations, solute-matrix bonding and precipitates, and their effects on the creep resistance of the alloy during creep-ageing tests are analysed.
Experimental evidence indicates that bainitic ferrite formed by transformation at low temperatures (200–350°C) contains quantities of carbon in solid solution far beyond those expected from ...para-equilibrium. A change in the conventional symmetry of the bainitic ferrite lattice from cubic to tetragonal explains the abnormal solid solubility detected. This carbon supersaturation was measured by atom probe tomography, and the tetragonality of the bainitic ferrite, was characterized by means of X-ray diffraction analysis and high resolution transmission electron microscopy.
Four extreme haze episodes occurred in October 2014 in the North China Plain (NCP). To clarify the formation mechanism of hazes in autumn, strengthened observations were conducted in Beijing from 5 ...October to 2 November. The meteorological parameters, satellite data, chemical compositions and optical properties of aerosols were obtained. The hazes originated from the NCP, developing in the southwest and northeast directions, with the highest concentration of PM2.5 of 469 mu g m-3 in Beijing. The NCP was dominated by a weak high pressure system during the haze episode, which resulted in low surface wind speed and relatively stagnant weather. Moreover, the wind slowed down around Beijing city. The secondary aerosols NO3- was always higher than that of SO42-, which indicated the motor vehicles played a more important part in the hazes in October 2014, even though the oxidation rate from SO2 to SO42- was faster than that of NOx to NO3-. Sudden increases of the concentrations of organic matter, Cl- and BC (black carbon) before each haze episode implied that regional transport of pollutants by biomass burning was important for haze formation during autumn. A satellite map of fire points and the backward trajectories of the air masses also indicated this pollution source. The distinct decrease in the PBL (planetary boundary layer) height during four haze episodes restrained the vertical dispersion of the air pollutants. Water vapor also played a vital role in the formation of hazes by accelerating the chemical transformation of secondary pollutants, leading to hygroscopic growth of aerosols and altering the thermal balance of the atmosphere.
Summary
We explored the association between gut microbiota composition and bone mineral loss in Chinese elderly people by high-throughput 16S ribosomal RNA (rRNA) gene sequencing. Compared with ...controls, a smaller number of operational taxonomic units (OTUs), several taxa with altered abundance, and specific functional pathways were found in individuals with low-bone mineral density (BMD).
Introduction
Gut microbiota plays important roles in human health and associates with a number of diseases. However, few studies explored its association with bone mineral loss in human.
Methods
We collected 102 fecal samples from each eligible individual belonging to low-BMD and control groups for high-throughput 16S rRNA gene sequencing.
Results
The low-BMD individuals had a smaller number of OTUs and bacterial taxa at each level. At the phylum level, Bacteroidetes were more abundant in the low-BMD group; Firmicutes were enriched in the control group; Firmicutes and Actinobacteria positively correlated and Bacteroidetes negatively correlated with the BMD and T-score in all subjects. At the family level, the abundance of Lachnospiraceae in low-BMD individuals reduced and positively correlated with BMD and T-score; meanwhile, BMD increased with increasing Bifidobacteriaceae. At the genus level, low-BMD individuals had decreased proportions of
Roseburia
compared with control ones (
P
< 0.05).
Roseburia
,
Bifidobacterium
, and
Lactobacillus
positively correlated with BMD and T-score. Furthermore, BMD increased with rising abundance of
Bifidobacterium
. Functional prediction revealed that 93 metabolic pathways significantly differed between the two groups (FDR-corrected
P
< 0.05). Most pathways, especially pathways related to LPS biosynthesis, were more abundant in low-BMD individuals than in control ones.
Conclusions
Several taxa with altered abundance and specific functional pathways were discovered in low-BMD individuals. Our findings provide novel epidemiologic evidence to elucidate the underlying microbiota-relevant mechanism in bone mineral loss and osteoporosis.
Urbanization often exerts multiple effects on aquatic and terrestrial organisms, including changes in biodiversity, species composition and ecosystem functions. However, the impacts of urbanization ...on river phytoplankton in subtropical urbanizing watersheds remain largely unknown. Here, we explored the effects of urbanization on phytoplankton community structure (i.e., biomass, community composition and diversity) and function (i.e., resource use efficiency) in a subtropical river at watershed scale in southeast China over 6 years. A total of 318 phytoplankton species belonging into 120 genera and 7 phyla were identified from 108 samples. Bacillariophyta biomass showed an increasing trend with increasing urbanization level. The phytoplankton community shifted from Chlorophyta dominance in rural upstream waters to Bacillariophyta dominance in urbanized downstream waters. Furthermore, phytoplankton diversity and resource use efficiency (RUE = phytoplankton biomass/total phosphorus) were significantly decreased with increasing urbanization level from upstream to downstream. Phytoplankton RUE exhibited a significant positive correlation with species richness, but a negative correlation with phytoplankton evenness. The variation in environmental factors (turbidity, total nitrogen, NH4+-N, total phosphorus, PO43−-P and percentage urbanized area) was significantly correlated with phytoplankton diversity and RUE. Overall, our results revealed the influence of urbanization on phytoplankton community structure and ecosystem function was due to its altering the environmental conditions. Therefore, human-driven urbanization may play crucial roles in shaping the structure and function of phytoplankton communities in subtropical rivers, and the mechanism of this process can provide important information for freshwater sustainable uses, watershed management and conservation.
Display omitted
Summary
Background
Transient elastography is a non‐invasive method for staging liver fibrosis. The meta‐analysis using the hierarchical models to evaluate the diagnostic accuracy of transient ...elastography for the staging of liver fibrosis in patients with chronic hepatitis B was rarely reported.
Aim
A meta‐analysis using the hierarchical models was performed to assess transient elastography for diagnosing and stage liver fibrosis in patients with chronic hepatitis B.
Methods
Electronic databases were searched and studies were identified to assess the diagnostic accuracy of transient elastography in CHB patients for staging fibrosis F ≥ 2, F ≥ 3 and F = 4 with liver biopsy as a reference standard. The hierarchical summary receiver operating characteristic curve and the bivariate models were performed to evaluate the diagnostic accuracy of transient elastography, and meta‐regression analyses were performed to explore the heterogeneity. The quality Assessment of Diagnostic Accuracy Studies‐2 tool was used to assess the quality of studies.
Results
Twenty‐seven studies with a total of 4386 patients were included in the meta‐analysis. The summary sensitivity of transient elastography for staging fibrosis F ≥ 2, F ≥ 3 and F = 4 was 0.806 (95% CI, 0.756–0.847), 0.819 (95% CI, 0.748–0.874) and 0.863 (95% CI, 0.818–0.898), respectively, and the summary specificity was 0.824 (95% CI, 0.761–0.873), 0.866 (95% CI, 0.824–0.899) and 0.875 (95% CI, 0.840–0.903), respectively. The corresponding area under the summary receiver operating characteristic curve was 0.88 (95% CI, 0.85–0.91), 0.91 (95% CI, 0.88–0.93) and 0.93 (95% CI, 0.91–0.95), respectively. Meta‐regression showed that patient age contributed to heterogeneity.
Conclusions
Transient elastography performs well to diagnose liver fibrosis in patients with chronic hepatitis B, which may reduce the use of liver biopsy.
The fidelity of intracellular signaling hinges on the organization of dynamic activity architectures. Spatial compartmentation was first proposed over 30 years ago to explain how diverse G ...protein-coupled receptors achieve specificity despite converging on a ubiquitous messenger, cyclic adenosine monophosphate (cAMP). However, the mechanisms responsible for spatially constraining this diffusible messenger remain elusive. Here, we reveal that the type I regulatory subunit of cAMP-dependent protein kinase (PKA), RIα, undergoes liquid-liquid phase separation (LLPS) as a function of cAMP signaling to form biomolecular condensates enriched in cAMP and PKA activity, critical for effective cAMP compartmentation. We further show that a PKA fusion oncoprotein associated with an atypical liver cancer potently blocks RIα LLPS and induces aberrant cAMP signaling. Loss of RIα LLPS in normal cells increases cell proliferation and induces cell transformation. Our work reveals LLPS as a principal organizer of signaling compartments and highlights the pathological consequences of dysregulating this activity architecture.
Display omitted
•PKA RIα undergoes liquid-liquid phase separation in response to cAMP dynamics•RIα condensates dynamically sequester cAMP and retain high PKA activity•RIα phase separation is necessary for effective cAMP compartmentation•A PKA oncoprotein disrupts RIα bodies, leading to aberrant signaling and growth
cAMP-responsive condensate formation by PKA’s RIα subunit controls local signaling, and disruption of phase separation in this context contributes to tumorigenesis.
PDF
