Van der Waals interactions of parallel and concentric nanotubes

For sparse materials like graphitic systems and carbon nanotubes the standard density functional theory (DFT) faces significant problems because it cannot accurately describe the van der Waals interactions that are essential to the carbon-nanostructure materials behavior. While standard implementations of DFT can describe the strong chemical binding within an isolated, single-walled carbon nanotube, a new and extended DFT implementation is needed to describe the binding between nanotubes. We here provide the first steps to such an extension for parallel and concentric nanotubes through an electron-density based description of the materials coupling to the electrodynamical field. We thus find a consistent description of the (fully screened) van der Waals interactions that bind the nanotubes across the low-electron-density voids between the nanotubes, in bundles and as multiwalled tubes.Comment: 6 pages, 4 figures (5 figure files

van der Waals interaction of parallel polymers and nanotubes

We study the mutual interactions of simple, parallel polymers and nanotubes, and develop a scheme to include the van der Waals interactions in the framework of density functional theory (DFT) for these molecules at intermediate to long-range separations. We primarily focus on the polymers polyethylene, isotactic polypropylene, and isotactic polyvinylchloride, but our approach applies more generally to all simple polymers and nanotubes. From first-principle DFT calculations we extract the electron density of the polymers and their static electric response. We derive explicit expressions for the van der Waals interaction energy under simple symmetry assumptions.Comment: 8 pages, 2 figures (2 eps figure files

Nature and strength of bonding in a crystal of semiconducting nanotubes: van der Waals density functional calculations and analytical results

The dispersive interaction between nanotubes is investigated through ab initio theory calculations and in an analytical approximation. A van der Waals density functional (vdW-DF) [Phys. Rev. Lett. 92, 246401 (2004)] is used to determine and compare the binding of a pair of nanotubes as well as in a nanotube crystal. To analyze the interaction and determine the importance of morphology, we furthermore compare results of our ab initio calculations with a simple analytical result that we obtain for a pair of well-separated nanotubes. In contrast to traditional density functional theory calculations, the vdW-DF study predicts an intertube vdW bonding with a strength that is consistent with recent observations for the interlayer binding in graphitics. It also produce a nanotube wall-to-wall separation which is in very good agreement with experiments. Moreover, we find that the vdW-DF result for the nanotube-crystal binding energy can be approximated by a sum of nanotube-pair interactions when these are calculated in vdW-DF. This observation suggests a framework for an efficient implementation of quantum-physical modeling of the CNT bundling in more general nanotube bundles, including nanotube yarn and rope structures.Comment: 10 pages, 4 figure

Report of a Botanical Exploration of the Sand-hill Region of Central Nebraska made in the summer of 1893.

Rydberg (1860–1931) was born Sweden and emigrated to the United States in 1882, first to mining camps in upper Michigan and eventually to Wahoo, in Saunders County, Nebraska, where he taught mathematics from 1884 to 1893 at now defunct Luther Academy. In the summers of 1891-1893, 1895, and 1896 he was a field agent for the United States Department of Agriculture and collected plants in Nebraska, South Dakota, Montana, Idaho, Wyoming, and Colorado, and specimens from those and other trips are in the Bessey Herbarium at the University of Nebraska–Lincoln, which house what is now known as the Charles E. Bessey Herbarium (NEB), founded about1872. Rydberg enrolled at the university to study botany with Bessey, earning his first degree in 1891 and his M.A. in 1895. In 1898, he received his Ph.D. under Nathaniel Lord Britton at Columbia University in New York City. He became affiliated with the New York Botanical Garden and spent his remaining career there, eventually becoming its herbarium’s director

LC/MS/MS Analysis of N-Terminal Protein Adducts with Improved Sensitivity: A Comparison of Selected Edman Isothiocyanate Reagents

This study provides a basis for a new and straightforward method for LC/MS/MS-based screening of N-terminal protein adducts. This procedure is denoted the “FIRE procedure” as fluorescein isothiocyanate (FITC) gave superior sensitivity by LC/MS/MS when measuring adducts (R) of electrophilic compounds with a modified Edman procedure. The principles of the FIRE-procedure are that adducts to N-terminal amino acids selectively are detached and measured from of proteins after derivatisation by isothiocyanate Edman reagents. In this study, FITC, 4-N,N-dimethylaminoazobenzene 4′-isothiocyanate (DABITC) and 4-dimethylamino-1-naphthyl isothiocyanate (DNITC) were used to synthesize thiohydantoin analytes from valine and N-methylvaline. The sensitivity by LC/MS/MS was enhanced by up to three orders of magnitude as compared to phenyl isothiocyanate and higher as compared to pentafluorophenyl isothiocyanate. The FITC reagent will enable measurements of low background adduct levels. Synthesized analytes were characterised with, for example, 1H NMR, 13C NMR, LC/MS/MS, and UV

Инновационная модель как инструмент структурных реформ

Обоснованы безальтернативность, первоочередные направления и проблемы внедрения инновационной модели как инструмента экономического роста в современной экономике. Основное внимание уделено финансовым инструментам решения проблемы технического и технологического переоснащения производства

Hepatitis E virus genotype 3 strains and a plethora of other viruses detected in raw and still in tap water

\ua9 2019 The Authors In this study, next generation sequencing was used to explore the virome in 20L up to 10,000L water from different purification steps at two Swedish drinking water treatment plants (DWTPs), and in tap water. One DWTP used ultrafiltration (UF) with 20 nm pores, the other UV light treatment after conventional treatment of the water. Viruses belonging to 26 different families were detected in raw water, in which 6–9 times more sequence reads were found for phages than for known environmental, plant or vertebrate viruses. The total number of viral reads was reduced more than 4-log10 after UF and 3-log10 over UV treatment. However, for some viruses the reduction was 3.5-log10 after UF, as for hepatitis E virus (HEV), which was also detected in tap water, with sequences similar to those in raw water and after treatment. This indicates that HEV had passed through the treatment and entered into the supply network. However, the viability of the viruses is unknown. In tap water 10–130 International Units of HEV RNA/mL were identified, which is a comparable low amount of virus. The risk of getting infected through consumption of tap water is probably negligible, but needs to be investigated. The HEV strains in the waters belonged to subtypes HEV3a and HEV3c/i, which is associated with unknown source of infection in humans infected in Sweden. None of these subtypes are common among pigs or wild boar, the major reservoirs for HEV, indicating that water may play a role in transmitting this virus. The results indicate that monitoring small fecal/oral transmitted viruses in DWTPs may be considered, especially during community outbreaks, to prevent potential transmission by tap water

Divergent β-hairpins determine double-strand versus single-strand substrate recognition of human AlkB-homologues 2 and 3

Human AlkB homologues ABH2 and ABH3 repair 1-methyladenine and 3-methylcytosine in DNA/RNA by oxidative demethylation. The enzymes have similar overall folds and active sites, but are functionally divergent. ABH2 efficiently demethylates both single- and double-stranded (ds) DNA, whereas ABH3 has a strong preference for single-stranded DNA and RNA. We find that divergent F1 β-hairpins in proximity of the active sites of ABH2 and ABH3 are central for substrate specificities. Swapping F1 hairpins between the enzymes resulted in hybrid proteins resembling the donor proteins. Surprisingly, mutation of the intercalating residue F102 had little effect on activity, while the double mutant V101A/F102A was catalytically impaired. These residues form part of an important hydrophobic network only present in ABH2. In this functionally important network, F124 stacks with the flipped out base while L157 apparently functions as a buffer stop to position the lesion in the catalytic pocket for repair. F1 in ABH3 contains charged and polar residues preventing use of dsDNA substrate. Thus, E123 in ABH3 corresponds to F102 in ABH2 and the E123F-variant gained capacity to repair dsDNA with no loss in single strand repair capacity. In conclusion, divergent sequences outside of the active site determine substrate specificities of ABH2 and ABH3

Dietary Acrylamide Intake during Pregnancy and Fetal Growth—Results from the Norwegian Mother and Child Cohort Study (MoBa)

Background: Acrylamide has shown developmental and reproductive toxicity in animals, as well as neurotoxic effects in humans with occupational exposures. Because it is widespread in food and can pass through the human placenta, concerns have been raised about potential developmental effects of dietary exposures in humans