Silicon chemistry in the mesosphere and lower thermosphere

Silicon is one of the most abundant elements in cosmic dust, and meteoric ablation injects a significant amount of Si into the atmosphere above 80 km. In this study, a new model for silicon chemistry in the mesosphere/lower thermosphere is described, based on recent laboratory kinetic studies of Si, SiO, SiO2, and Si+. Electronic structure calculations and statistical rate theory are used to show that the likely fate of SiO2 is a two-step hydration to silicic acid (Si(OH)4), which then polymerizes with metal oxides and hydroxides to form meteoric smoke particles. This chemistry is then incorporated into a whole atmosphere chemistry-climate model. The vertical profiles of Si+ and the Si+/Fe+ ratio are shown to be in good agreement with rocket-borne mass spectrometric measurements between 90 and 110 km. Si+ has consistently been observed to be the major meteoric ion around 110 km; this implies that the relative injection rate of Si from meteoric ablation, compared to metals such as Fe and Mg, is significantly larger than expected based on their relative chondritic abundances. Finally, the global abundances of SiO and Si(OH)4 show clear evidence of the seasonal meteoric input function, which is much less pronounced in the case of other meteoric species

Rotational cooling of heteronuclear molecular ions with ^1-Sigma, ^2-Sigma, ^3-Sigma and ^2-Pi electronic ground states

The translational motion of molecular ions can be effectively cooled sympathetically to translational temperatures below 100 mK in ion traps through Coulomb interactions with laser-cooled atomic ions. The ro-vibrational degrees of freedom, however, are expected to be largely unaffected during translational cooling. We have previously proposed schemes for cooling of the internal degrees of freedom of such translationally cold but internally hot heteronuclear diatomic ions in the simplest case of ^1-Sigma electronic ground state molecules. Here we present a significant simplification of these schemes and make a generalization to the most frequently encountered electronic ground states of heteronuclear molecular ions: ^1-Sigma, ^2-Sigma, ^3-Sigma and ^2-Pi. The schemes are relying on one or two laser driven transitions with the possible inclusion of a tailored incoherent far infrared radiation field.Comment: 16 pages, 13 figure

Ab initio study of alanine polypeptide chains twisting

We have investigated the potential energy surfaces for alanine chains consisting of three and six amino acids. For these molecules we have calculated potential energy surfaces as a function of the Ramachandran angles Phi and Psi, which are widely used for the characterization of the polypeptide chains. These particular degrees of freedom are essential for the characterization of proteins folding process. Calculations have been carried out within ab initio theoretical framework based on the density functional theory and accounting for all the electrons in the system. We have determined stable conformations and calculated the energy barriers for transitions between them. Using a thermodynamic approach, we have estimated the times of characteristic transitions between these conformations. The results of our calculations have been compared with those obtained by other theoretical methods and with the available experimental data extracted from the Protein Data Base. This comparison demonstrates a reasonable correspondence of the most prominent minima on the calculated potential energy surfaces to the experimentally measured angles Phi and Psi for alanine chains appearing in native proteins. We have also investigated the influence of the secondary structure of polypeptide chains on the formation of the potential energy landscape. This analysis has been performed for the sheet and the helix conformations of chains of six amino acids.Comment: 24 pages, 10 figure

Rearrangement of cluster structure during fission processes

Results of molecular dynamics simulations of fission reactions $Na_{10}^{2+} \to Na_7^+ + Na_3^+$ and $Na_{18}^{2+} \to 2 Na_9^+$ are presented. Dependence of the fission barriers on isomer structure of the parent cluster is analyzed. It is demonstrated that the energy necessary for removing homothetic groups of atoms from the parent cluster is largely independent of the isomer form of the parent cluster. Importance of rearrangement of the cluster structure during the fission process is elucidated. This rearrangement may include transition to another isomer state of the parent cluster before actual separation of the daughter fragments begins and/or forming a "neck" between the separating fragments

Impurity effects on the melting of Ni clusters

We demonstrate that the addition of a single carbon impurity leads to significant changes in the thermodynamic properties of Ni clusters consisting of more than a hundred atoms. The magnitude of the change induced is dependent upon the parameters of the Ni-C interaction. Hence, thermodynamic properties of Ni clusters can be effectively tuned by the addition of an impurity of a particular type. We also show that the presence of a carbon impurity considerably changes the mobility and diffusion of atoms in the Ni cluster at temperatures close to its melting point. The calculated diffusion coefficients of the carbon impurity in the Ni cluster can be used for a reliable estimate of the growth rate of carbon nanotubes.Comment: 27 pages, 13 figure

Associations between tooth wear and dental sleep disorders : A narrative overview

Objectives Tooth wear is a common finding in adult patients with dental sleep disorders. The aim of this paper was to review the literature on the possible associations between tooth wear and the following dental sleep disorders: sleep-related oro-facial pain, oral moistening disorders, gastroesophageal reflux disease (GERD), obstructive sleep apnoea syndrome (OSAS) and sleep bruxism. Methods A PubMed search was performed on 1 June 2018 using MeSH terms in the following query: Tooth Wear AND (Facial Pain OR Temporomandibular Joint Disorders OR Xerostomia OR Sialorrhea OR Gastroesophageal Reflux OR Sleep Apnea Syndrome OR Sleep Bruxism). Results The query yielded 706 reports on tooth wear and the mentioned dental sleep disorders. Several associations between tooth wear and the dental sleep disorders were suggested in the literature. It could be concluded that: (a) tooth wear is associated with dental pain and/or hypersensitivity; (b) oral dryness is associated with tooth wear, oro-facial pain and sleep bruxism; (c) GERD is associated with tooth wear, oro-facial pain, oral dryness, OSAS and sleep bruxism; (d) OSAS is associated with oral dryness, GERD and sleep bruxism; and (e) sleep bruxism is associated with tooth wear. Conclusions Tooth wear is associated with the dental sleep disorders oro-facial pain, oral dryness, GERD and sleep bruxism. The dental sleep disorders are interlinked with each other, which leads to indirect associations as well, and makes the consequences of each single condition difficult to disentangle. Knowledge of these associations is clinically relevant, but more research is needed to confirm their validity.Peer reviewe

Geospatial information infrastructures

Manual of Digital Earth / Editors: Huadong Guo, Michael F. Goodchild, Alessandro Annoni .- Springer, 2020 .- ISBN: 978-981-32-9915-3Geospatial information infrastructures (GIIs) provide the technological, semantic,organizationalandlegalstructurethatallowforthediscovery,sharing,and use of geospatial information (GI). In this chapter, we introduce the overall concept and surrounding notions such as geographic information systems (GIS) and spatial datainfrastructures(SDI).WeoutlinethehistoryofGIIsintermsoftheorganizational andtechnologicaldevelopmentsaswellasthecurrentstate-of-art,andreflectonsome of the central challenges and possible future trajectories. We focus on the tension betweenincreasedneedsforstandardizationandtheever-acceleratingtechnological changes. We conclude that GIIs evolved as a strong underpinning contribution to implementation of the Digital Earth vision. In the future, these infrastructures are challengedtobecomeflexibleandrobustenoughtoabsorbandembracetechnological transformationsandtheaccompanyingsocietalandorganizationalimplications.With this contribution, we present the reader a comprehensive overview of the field and a solid basis for reflections about future developments

Extended Hartree-Fock method based on pair density functional theory

A practical electronic structure method in which a two-body functional is the fundamental variable is constructed. The basic formalism of our method is equivalent to Hartree-Fock density matrix functional theory [M. Levy in {\it Density Matrices and Density Functionals}, Ed. R. Erdahl and V. H. Smith Jr., D. Reidel, (1987)]. The implementation of the method consists of solving Hartree-Fock equations and using the resulting orbitals to calculate two-body corrections to account for correlation. The correction terms are constructed so that the energy of the system in the absence of external potentials can be made to correspond to approximate expressions for the energy of the homogeneous electron gas. In this work the approximate expressions we use are based on the high-density limit of the homogeneous electron gas. Self-interaction is excluded from the two-body functional itself. It is shown that our pair density based functional does not suffer from the divergence present in many density functionals when homogeneous scaling is applied. Calculations based on our pair density functional lead to quantitative results for the correlation energies of atomic test cases.Comment: to appear in Physical Review

A Consensus Map in Cultivated Hexaploid Oat Reveals Conserved Grass Synteny with Substantial Subgenome Rearrangement

Citation: Chaffin, A. S., Huang, Y. F., Smith, S., Bekele, W. A., Babiker, E., Gnanesh, B. N., . . . Tinker, N. A. (2016). A Consensus Map in Cultivated Hexaploid Oat Reveals Conserved Grass Synteny with Substantial Subgenome Rearrangement. Plant Genome, 9(2), 21. doi:10.3835/plantgenome2015.10.0102Hexaploid oat (Avena sativa L., 2n = 6x = 42) is a member of the Poaceae family and has a large genome (similar to 12.5 Gb) containing 21 chromosome pairs from three ancestral genomes. Physical rearrangements among parental genomes have hindered the development of linkage maps in this species. The objective of this work was to develop a single high-density consensus linkage map that is representative of the majority of commonly grown oat varieties. Data from a cDNA-derived single-nucleotide polymorphism (SNP) array and genotyping-by-sequencing (GBS) were collected from the progeny of 12 biparental recombinant inbred line populations derived from 19 parents representing oat germplasm cultivated primarily in North America. Linkage groups from all mapping populations were compared to identify 21 clusters of conserved collinearity. Linkage groups within each cluster were then merged into 21 consensus chromosomes, generating a framework consensus map of 7202 markers spanning 2843 cM. An additional 9678 markers were placed on this map with a lower degree of certainty. Assignment to physical chromosomes with high confidence was made for nine chromosomes. Comparison of homeologous regions among oat chromosomes and matches to orthologous regions of rice (Oryza sativa L.) reveal that the hexaploid oat genome has been highly rearranged relative to its ancestral diploid genomes as a result of frequent translocations among chromosomes. Heterogeneous chromosome rearrangements among populations were also evident, probably accounting for the failure of some linkage groups to match the consensus. This work contributes to a further understanding of the organization and evolution of hexaploid grass genomes

Further investigation of confirmed urinary tract infection (UTI) in children under five years: a systematic review.

Background: Further investigation of confirmed UTI in children aims to prevent renal scarring and future complications. Methods: We conducted a systematic review to determine the most effective approach to the further investigation of confirmed urinary tract infection (UTI) in children under five years of age. Results: 73 studies were included. Many studies had methodological limitations or were poorly reported. Effectiveness of further investigations: One study found that routine imaging did not lead to a reduction in recurrent UTIs or renal scarring. Diagnostic accuracy: The studies do not support the use of less invasive tests such as ultrasound as an alternative to renal scintigraphy, either to rule out infection of the upper urinary tract (LR- = 0.57, 95%CI: 0.47, 0.68) and thus to exclude patients from further investigation or to detect renal scarring (LR+ = 3.5, 95% CI: 2.5, 4.8). None of the tests investigated can accurately predict the development of renal scarring. The available evidence supports the consideration of contrast-enhanced ultrasound techniques for detecting vesico-ureteric reflux (VUR), as an alternative to micturating cystourethrography (MCUG) (LR+ = 14.1, 95% CI: 9.5, 20.8; LR- = 0.20, 95%CI: 0.13, 0.29); these techniques have the advantage of not requiring exposure to ionising radiation. Conclusion: There is no evidence to support the clinical effectiveness of routine investigation of children with confirmed UTI. Primary research on the effectiveness, in terms of improved patient outcome, of testing at all stages in the investigation of confirmed urinary tract infection is urgently required