Stretched chemical bonds in Si6H6: A transition from ring currents to localized pi-electrons?

Motivated by solid-state studies on the cleavage force in Si, and the consequent stretching of chemical bonds, we here study bond stretching in the, as yet unsynthesized, free space molecule Si6H6. We address the question as to whether substantial bond stretching (but constrained to uniform scaling on all bonds) can result in a transition from ring current behaviour, characteristic say of benzene at its equilibrium geometry, to localized pi-electrons on Si atoms. Some calculations are also recorded on dissociation into 6 SiH radicals. While the main studies have been carried out by unrestricted Hartree-Fock (HF) theory, the influence of electron correlation has been examined using two forms of density functional theory. Planar Si6H6 treated by HF is bound to be unstable, not all vibrational frequencies being real. Some buckling is then allowed, which results in real frequencies and stability. Evidence is then provided that the non-planar structure, as the Si-Si distance is increased, exhibits pi-electron localization in the range 1.2-1.5 times the equilibrium distance

Not a melting pot: Plant species aggregate in their non-native range

Aim Plant species continue to be moved outside of their native range by human activities. Here, we aim to determine whether, once introduced, plants assimilate into native communities or whether they aggregate, thus forming mosaics of native- and alien-rich communities. Alien species might aggregate in their non-native range owing to shared habitat preferences, such as their tendency to establish in high-biomass, species-poor areas. Location Twenty-two herbaceous grasslands in 14 countries, mainly in the temperate zone. Time period 2012-2016. Major taxa studied Plants. Methods We used a globally coordinated survey. Within this survey, we found 46 plant species, predominantly from Eurasia, for which we had co-occurrence data in their native and non-native ranges. We tested for differences in co-occurrence patterns of 46 species between their native (home) and non-native (away) range. We also tested whether species had similar habitat preferences, by testing for differences in total biomass and species richness of the patches that species occupy in their native and non-native ranges. Results We found the same species to show different patterns of association depending on whether they were in their native or non-native range. Alien species were negatively associated with native species; instead, they aggregated with other alien species in species-poor, high-biomass communities in their non-native range compared with their native range. Main conclusions The strong differences between the native (home) and non-native (away) range in species co-occurrence patterns are evidence that the way in which species associate with resident communities in their non-native range is not species dependent, but is instead a property of being away from their native range. These results thus highlight that species might undergo important ecological changes when introduced away from their native range. Overall, we show origin-dependent associations that result in novel communities, in which alien-rich patches exist within a mosaic of native-dominated communities

Forebrain Deletion of the Vesicular Acetylcholine Transporter Results in Deficits in Executive Function, Metabolic, and RNA Splicing Abnormalities in the Prefrontal Cortex

One of the key brain regions in cognitive processing and executive function is the prefrontal cortex (PFC), which receives cholinergic input from basal forebrain cholinergic neurons. We evaluated the contribution of synaptically released acetylcholine (ACh) to executive function by genetically targeting the vesicular acetylcholine transporter (VAChT) in the mouse forebrain. Executive function was assessed using a pairwise visual discrimination paradigm and the 5-choice serial reaction time task (5-CSRT). In the pairwise test, VAChT-deficient mice were able to learn, but were impaired in reversal learning, suggesting that these mice present cognitive inflexibility. Interestingly, VAChT-targeted mice took longer to reach criteria in the 5-CSRT. Although their performance was indistinguishable from that of control mice during low attentional demand, increased attentional demand revealed striking deficits in VAChT-deleted mice. Galantamine, a cholinesterase inhibitor used in Alzheimer\u27s disease, significantly improved the performance of control mice, but not of VAChT-deficient mice on the 5-CSRT. In vivo magnetic resonance spectroscopy showed altered levels of two neurochemical markers of neuronal function, taurine and lactate, suggesting altered PFC metabolism in VAChT-deficient mice. The PFC of these mice displayed a drastic reduction in the splicing factor heterogeneous nuclear ribonucleoprotein A2/B1 (hnRNPA2/B1), whose cholinergic-mediated reduction was previously demonstrated in Alzheimer\u27s disease. Consequently, several key hnRNPA2/B1 target transcripts involved in neuronal function present changes in alternative splicing in VAChT-deficient mice, including pyruvate kinase M, a key enzyme involved in lactate metabolism. We propose that VAChT-targeted mice can be used to model and to dissect the neurochemical basis of executive abnormalities

Linked MRI signatures of the brain\u27s acute and persistent response to concussion in female varsity rugby players

Acute brain changes are expected after concussion, yet there is growing evidence of persistent abnormalities well beyond clinical recovery and clearance to return to play. Multiparametric MRI is a powerful approach to non-invasively study structure-function relationships in the brain, however it remains challenging to interpret the complex and heterogeneous cascade of brain changes that manifest after concussion. Emerging conjunctive, data-driven analysis approaches like linked independent component analysis can integrate structural and functional imaging data to produce linked components that describe the shared inter-subject variance across images. These linked components not only offer the potential of a more comprehensive understanding of the underlying neurobiology of concussion, but can also provide reliable information at the level of an individual athlete. In this study, we analyzed resting-state functional MRI (rs-fMRI) and diffusion tensor imaging (DTI) within a cohort of female varsity rugby players (n = 52) through the in-and off-season, including concussed athletes (n = 21) who were studied longitudinally at three days, three months and six months after a diagnosed concussion. Linked components representing co-varying white matter microstructure and functional network connectivity characterized (a) the brain\u27s acute response to concussion and (b) persistent alterations beyond clinical recovery. Furthermore, we demonstrate that these long-term brain changes related to specific aspects of a concussion history and allowed us to monitor individual athletes before and longitudinally after a diagnosed concussion

Can management intensity be more important than environmental factors? A case study along an extreme elevation gradient from central Italian cereal fields

This paper aims to assess the importance of environmental and management factors determining the weed species composition along a strong elevation gradient. A total of 76 cereal fields (39 low input and 37 intensively managed) were sampled along an elevation gradient in central Italy. Explanatory variables were recorded for each field to elucidate the role of large-scale spatial trends, of site-specific abiotic environmental conditions and of field management characters. Redundancy analysis was used to assess the relative importance of each environmental variable in explaining the variation in species composition. Our results indicate that variation in weed species composition is strongly determined by altitude, mean annual precipitation, mean annual temperature and also by soil characteristics. However, the level of intensification proved to be the most influential variable. There was a significant difference in species richness and composition between low-input and intensively managed fields. Intensification leads to considerable species loss at both lower and higher elevations. Low-input fields had 296 species in total, while intensively managed fields had only 196

Detection of active caspase-3 in mouse models of stroke and Alzheimer\u27s disease with a novel dual positron emission tomography/fluorescent tracer [ \u3csup\u3e68\u3c/sup\u3e Ga]Ga-TC3-OGDOTA

© 2019 Valeriy G. Ostapchenko et al. Apoptosis is a feature of stroke and Alzheimer\u27s disease (AD), yet there is no accepted method to detect or follow apoptosis in the brain in vivo. We developed a bifunctional tracer [ 68 Ga]Ga-TC3-OGDOTA containing a cell-penetrating peptide separated from fluorescent Oregon Green and 68 Ga-bound labels by the caspase-3 recognition peptide DEVD. We hypothesized that this design would allow [ 68 Ga]Ga-TC3-OGDOTA to accumulate in apoptotic cells. In vitro, Ga-TC3-OGDOTA labeled apoptotic neurons following exposure to camptothecin, oxygen-glucose deprivation, and β-amyloid oligomers. In vivo, PET showed accumulation of [ 68 Ga]Ga-TC3-OGDOTA in the brain of mouse models of stroke or AD. Optical clearing revealed colocalization of [ 68 Ga]Ga-TC3-OGDOTA and cleaved caspase-3 in brain cells. In stroke, [ 68 Ga]Ga-TC3-OGDOTA accumulated in neurons in the penumbra area, whereas in AD mice [ 68 Ga]Ga-TC3-OGDOTA was found in single cells in the forebrain and diffusely around amyloid plaques. In summary, this bifunctional tracer is selectively associated with apoptotic cells in vitro and in vivo in brain disease models and represents a novel tool for apoptosis detection that can be used in neurodegenerative diseases

Mathematical practice, crowdsourcing, and social machines

The highest level of mathematics has traditionally been seen as a solitary endeavour, to produce a proof for review and acceptance by research peers. Mathematics is now at a remarkable inflexion point, with new technology radically extending the power and limits of individuals. Crowdsourcing pulls together diverse experts to solve problems; symbolic computation tackles huge routine calculations; and computers check proofs too long and complicated for humans to comprehend. Mathematical practice is an emerging interdisciplinary field which draws on philosophy and social science to understand how mathematics is produced. Online mathematical activity provides a novel and rich source of data for empirical investigation of mathematical practice - for example the community question answering system {\it mathoverflow} contains around 40,000 mathematical conversations, and {\it polymath} collaborations provide transcripts of the process of discovering proofs. Our preliminary investigations have demonstrated the importance of "soft" aspects such as analogy and creativity, alongside deduction and proof, in the production of mathematics, and have given us new ways to think about the roles of people and machines in creating new mathematical knowledge. We discuss further investigation of these resources and what it might reveal. Crowdsourced mathematical activity is an example of a "social machine", a new paradigm, identified by Berners-Lee, for viewing a combination of people and computers as a single problem-solving entity, and the subject of major international research endeavours. We outline a future research agenda for mathematics social machines, a combination of people, computers, and mathematical archives to create and apply mathematics, with the potential to change the way people do mathematics, and to transform the reach, pace, and impact of mathematics research.Comment: To appear, Springer LNCS, Proceedings of Conferences on Intelligent Computer Mathematics, CICM 2013, July 2013 Bath, U

Standardization of measles, mumps and rubella assays to enable comparisons of seroprevalence data across 21 European countries and Australia

The aim of the European Sero-Epidemiology Network is to establish comparability of the serological surveillance of vaccine-preventable diseases in Europe. The designated reference laboratory (RL) for measles, mumps, rubella (MMR) prepared and tested a panel of 151 sera by the reference enzyme immunoassay (rEIA). Laboratories in 21 countries tested the panel for antibodies against MMR using their usual assay (a total of 16 different EIAs) and the results were plotted against the reference results in order to obtain equations for the standardization of national serum surveys. The RL also tested the panel by the plaque neutralization test (PNT). Large differences in qualitative results were found compared to the RL. Well-fitting standardization equations with R20·8 were obtained for almost all laboratories through regression of the quantitative results against those of the RL. When compared to PNT, the rEIA had a sensitivity of 95·3%, 92·8% and 100% and a specificity of 100%, 87·1% and 92·8% for measles, mumps and rubella, respectively. The need for standardization was highlighted by substantial inter-country differences. Standardization was successful and the selected standardization equations allowed the conversion of local serological results into common units and enabled direct comparison of seroprevalence data of the participating countrie

NTPDases in the neuroendocrine hypothalamus: Possible energy regulators of the positive gonadotrophin feedback

<p>Abstract</p> <p>Background</p> <p>Brain-derived ectonucleoside triphosphate diphosphohydrolases (NTPDases) have been known as plasma membrane-incorporated enzymes with their ATP-hydrolyzing domain outside of the cell. As such, these enzymes are thought to regulate purinergic intercellular signaling by hydrolyzing ATP to ADP-AMP, thus regulating the availability of specific ligands for various P2X and P2Y purinergic receptors. The role of NTPDases in the central nervous system is little understood. The two major reasons are the insufficient knowledge of the precise localization of these enzymes in neural structures, and the lack of specific inhibitors for the various NTPDases. To fill these gaps, we recently studied the presence of neuron-specific NTPDase3 in the mitochondria of hypothalamic excitatory neurons by morphological and functional methods. Results from those studies suggested that intramitochondrial regulation of ATP levels may play a permissive role in the neural regulation of physiological functions by tuning the level of ATP-carried energy that is needed for neuronal functions, such as neurotransmission and/or intracellular signaling.</p> <p>Presentation of the hypothesis</p> <p>In the lack of highly specific inhibitors, the determination of the precise function and role of NTPDases is hardly feasable. Yet, here we attempt to find an approach to investigate a possible role for hypothalamic NTPDase3 in the initiation of the midcycle luteinizing hormone (LH) surge, as such a biological role was implied by our recent findings. Here we hypothesize that NTPDase-activity in neurons of the AN may play a permissive role in the regulation of the estrogen-induced pituitary LH-surge.</p> <p>Testing the hypothesis</p> <p>We propose to test our hypothesis on ovariectomized rats, by stereotaxically injecting 17beta-estradiol and/or an NTPDase-inhibitor into the arcuate nucleus and determine the consequential levels of blood LH, mitochondrial respiration rates from arcuate nucleus synaptosomal preparations, NTPDase3-expression from arcuate nucleus tissue samples, all compared to sham and intact controls.</p> <p>Implications of the hypothesis</p> <p>Results from these studies may lead to the conclusion that estrogen may modulate the activity of mitochondrial, synapse-linked NTPDase3, and may show a correlation between mitochondrial NTPDase3-activity and the regulation of LH-release by estrogen.</p