197 research outputs found
Phonon-phonon interactions and phonon damping in carbon nanotubes
We formulate and study the effective low-energy quantum theory of interacting
long-wavelength acoustic phonons in carbon nanotubes within the framework of
continuum elasticity theory. A general and analytical derivation of all three-
and four-phonon processes is provided, and the relevant coupling constants are
determined in terms of few elastic coefficients. Due to the low dimensionality
and the parabolic dispersion, the finite-temperature density of noninteracting
flexural phonons diverges, and a nonperturbative approach to their interactions
is necessary. Within a mean-field description, we find that a dynamical gap
opens. In practice, this gap is thermally smeared, but still has important
consequences. Using our theory, we compute the decay rates of acoustic phonons
due to phonon-phonon and electron-phonon interactions, implying upper bounds
for their quality factor.Comment: 15 pages, 2 figures, published versio
Multi-particle effects in non-equilibrium electron tunnelling and field emission
We investigate energy resolved electric current from various correlated host
materials under out-of-equilibrium conditions. We find that, due to a combined
effect of electron-electron interactions, non-equilibrium and multi-particle
tunnelling, the energy resolved current is finite even above the Fermi edge of
the host material. In most cases, the current density possesses a singularity
at the Fermi level revealing novel manifestations of correlation effects in
electron tunnelling. By means of the Keldysh non-equilibrium technique, the
current density is calculated for one-dimensional interacting electron systems
and for two-dimensional systems, both in the pure limit and in the presence of
disorder. We then specialise to the field emission and provide a comprehensive
theoretical study of this effect in carbon nanotubes.Comment: 22 pages, 8 figures (eps files
Metabolization of [Ru(η6-C6H5CF3)(pta)Cl2]: a cytotoxic RAPTA-type complex with a strongly electron withdrawing arene ligand
The anticancer ruthenium-arene compd. [Ru(η6-C6H5CF3)(pta)Cl2] (pta = 1,3,5-triaza-7-phosphatricyclo[3.3.1.1]decane), termed RAPTA-CF3, with the electron-withdrawing α,α,α-trifluorotoluene ligand, is one of the most cytotoxic RAPTA compds. known. To rationalize the high obsd. cytotoxicity, the hydrolysis of RAPTA-CF3 in water and brine (100 mM sodium chloride) and its reactions with the protein ubiquitin and a double-stranded oligonucleotide (5'-GTATTGGCACGTA-3') were studied using NMR spectroscopy, high-resoln. Fourier transform ion cyclotron resonance mass spectrometry, and gel electrophoresis. The aquation of the ruthenium-chlorido complex was accompanied by a loss of the arene ligand, independent of the chloride concn., which is a special property of the compd. not obsd. for other ruthenium-arene complexes with relatively stable ruthenium-arene bonds. Accordingly, the mass spectra of the biomol. reaction mixts. contained mostly [Ru(pta)]-biomol. adducts, whereas [Ru(pta)(arene)] adducts typical of other RAPTA compds. were not obsd. in the protein or DNA binding studies. Gel electrophoresis expts. revealed a significant degree of decompn. of the oligonucleotide, which was more pronounced in the case of RAPTA-CF3 compared with RAPTA-C. Consequently, facile arene loss appears to be responsible for the increased cytotoxicity of RAPTA-CF3. Graphical abstr.: RAPTA-CF3 is a fast-acting cytotoxic compd. that degrades DNA and has a mode of action fundamentally different from that of other ruthenium(II)-arene compds
Field emission from Luttinger liquids and single-wall carbon nanotubes
We develop a theory for the field emission effect in Luttinger liquids and
single-wall carbon nanotubes at the level of the energy resolved current
distribution. We generalise Fowler-Nordheim relations. Just below the Fermi
edge, we find a power-law vanishing current distribution with the density of
states exponent. The current distribution above the Fermi edge owes its
existence to a peculiar interplay of interactions and correlated tunnelling. It
displays a non-trivial power-law divergence just above the Fermi energy.Comment: 4 pages, 2 figures (eps files
Effective low-energy theory for correlated carbon nanotubes
The low-energy theory for single-wall carbon nanotubes including Coulomb
interactions is derived and analyzed. It describes two fermion chains without
interchain hopping but coupled in a specific way by the interaction. The
strong-coupling properties are studied by bosonization, and consequences for
experiments on single armchair nanotubes are discussed.Comment: 5 pages REVTeX, includes one figur
Spirometry reference equations for central European populations from school age to old age.
Spirometry reference values are important for the interpretation of spirometry results. Reference values should be updated regularly, derived from a population as similar to the population for which they are to be used and span across all ages. Such spirometry reference equations are currently lacking for central European populations. To develop spirometry reference equations for central European populations between 8 and 90 years of age. We used data collected between January 1993 and December 2010 from a central European population. The data was modelled using "Generalized Additive Models for Location, Scale and Shape" (GAMLSS). The spirometry reference equations were derived from 118'891 individuals consisting of 60'624 (51%) females and 58'267 (49%) males. Altogether, there were 18'211 (15.3%) children under the age of 18 years. We developed spirometry reference equations for a central European population between 8 and 90 years of age that can be implemented in a wide range of clinical settings
Analytical solution of the bosonic three-body problem
We revisit the problem of three identical bosons in free space, which
exhibits a universal hierarchy of bound states (Efimov trimers). Modelling a
narrow Feshbach resonance within a two-channel description, we map the integral
equation for the three-body scattering amplitude to a one-dimensional
Schr\"odinger-type single-particle equation, where an analytical solution of
exponential accuracy is obtained. We give exact results for the trimer binding
energies, the three-body parameter, the threshold to the three-atom continuum,
and the recombination rate.Comment: 4 pages, published versio
Nogo-A is secreted in extracellular vesicles, occurs in blood and can influence vascular permeability
Nogo-A is a transmembrane protein with multiple functions in the central nervous system (CNS), including restriction of neurite growth and synaptic plasticity. Thus far, Nogo-A has been predominantly considered a cell contact-dependent ligand signaling via cell surface receptors. Here, we show that Nogo-A can be secreted by cultured cells of neuronal and glial origin in association with extracellular vesicles (EVs). Neuron- and oligodendrocyte-derived Nogo-A containing EVs inhibited fibroblast spreading, and this effect was partially reversed by Nogo-A receptor S1PR2 blockage. EVs purified from HEK cells only inhibited fibroblast spreading upon Nogo-A over-expression. Nogo-A-containing EVs were found in vivo in the blood of healthy mice and rats, as well as in human plasma. Blood Nogo-A concentrations were elevated after acute stroke lesions in mice and rats. Nogo-A active peptides decreased barrier integrity in an in vitro blood-brain barrier model. Stroked mice showed increased dye permeability in peripheral organs when tested 2 weeks after injury. In the Miles assay, an in vivo test to assess leakage of the skin vasculature, a Nogo-A active peptide increased dye permeability. These findings suggest that blood borne, possibly EV-associated Nogo-A could exert long-range regulatory actions on vascular permeability
Plasma amino acids and neopterin in healthy persons with Down’s syndrome
In persons with Down’s syndrome (DS) immunological abnormalities as well as hypothyroidism and Alzheimer type dementia are frequently observed. In addition, the activity of the enzyme cystathionine beta-synthase (CBS) is over-expressed which results in an altered homocysteine metabolism
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Milk and dairy consumption and risk of cardiovascular diseases and all-cause mortality: dose-response meta-analysis of prospective cohort studies
With a growing number of prospective cohort studies, an updated dose-response meta-analysis of milk and dairy products with all-cause mortality, coronary heart disease (CHD) or cardiovascular disease (CVD) have been conducted. PubMed, Embase and Scopus were searched for articles published up to September 2016. Random-effect meta-analyses with summarised dose-response data were performed for total (high-fat/low-fat) dairy, milk, fermented dairy, cheese and yogurt. Non-linear associations were investigated using the spine models and heterogeneity by subgroup analyses. A total of 29 cohort studies were available for meta-analysis, with 938,465 participants and 93,158 mortality, 28,419 CHD and 25,416 CVD cases. No associations were found for total (high-fat/low-fat) dairy, and milk with the health outcomes of mortality, CHD or CVD. Inverse associations were found between total fermented dairy (included sour milk products, cheese or yogurt; per 20 g/day) with mortality (RR 0.98, 95% CI 0.97-0.99; I2 = 94.4%) and CVD risk (RR 0.98, 95% CI 0.97-0.99; I2 = 87.5%). Further analyses of individual fermented dairy of cheese and yogurt showed cheese to have a 2% lower risk of CVD (RR 0.98, 95% CI 0.95-1.00; I2 = 82.6%) per 10 g/day, but not yogurt. All of these marginally inverse associations of totally fermented dairy and cheese were attenuated in sensitivity analyses by removing one large Swedish study. This meta-analysis combining data from 29 prospective cohort studies demonstrated neutral associations between dairy products and cardiovascular and all-cause mortality. For future studies it is important to investigate in more detail how dairy products can be replaced by other foods
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