196 research outputs found
Energetics and Possible Formation and Decay Mechanisms of Vortices in Helium Nanodroplets
The energy and angular momentum of both straight and curved vortex states of
a helium nanodroplet are examined as a function of droplet size. For droplets
in the size range of many experiments, it is found that during the pickup of
heavy solutes, a significant fraction of events deposit sufficient energy and
angular momentum to form a straight vortex line. Curved vortex lines exist down
to nearly zero angular momentum and energy, and thus could in principle form in
almost any collision. Further, the coalescence of smaller droplets during the
cooling by expansion could also deposit sufficient angular momentum to form
vortex lines. Despite their high energy, most vortices are predicted to be
stable at the final temperature (0.38 K) of helium nanodroplets due to lack of
decay channels that conserve both energy and angular momentum.Comment: 10 pages, 8 figures, RevTex 4, submitted to Phys. Rev.
A superfluid hydrodynamic model for the enhanced moments of inertia of molecules in liquid 4He
We present a superfluid hydrodynamic model for the increase in moment of
inertia, , of molecules rotating in liquid He. The static
inhomogeneous He density around each molecule (calculated using the Orsay-Paris
liquid He density functional) is assumed to adiabatically follow the
rotation of the molecule. We find that the values created by the
viscousless and irrotational flow are in good agreement with the observed
increases for several molecules [ OCS, (HCN), HCCCN, and HCCCH ]. For
HCN and HCCH, our model substantially overestimates . This is likely
to result from a (partial) breakdown of the adiabatic following approximation.Comment: 4 pages, 1 eps figure, corrected version of published paper. Erratum
has been submitted for change
Replication by the Epistasis Project of the interaction between the genes for IL-6 and IL-10 in the risk of Alzheimer's disease
Background: Chronic inflammation is a characteristic of Alzheimer's disease (AD). An interaction associated with the risk of AD has been reported between polymorphisms in the regulatory regions of the genes for the pro-inflammatory cytokine, interleukin-6 (IL-6, gene: IL6), and the anti-inflammatory cytokine, interleukin-10 (IL-10, gene: IL10).Methods: We examined this interaction in the Epistasis Project, a collaboration of 7 AD research groups, contributing DNA samples from 1,757 cases of AD and 6,295 controls.Results: We replicated the interaction. For IL6 rs2069837 AA x IL10 rs1800871 CC, the synergy factor (SF) was 1.63 (95% confidence interval: 1.10-2.41, p = 0.01), controlling for centre, age, gender and apolipoprotein E epsilon 4 (APOE epsilon 4) genotype. Our results are consistent between North Europe (SF = 1.7, p = 0.03) and North Spain (SF = 2.0, p = 0.09). Further replication may require a meta-analysis. However, association due to linkage disequilibrium with other polymorphisms in the regulatory regions of these genes cannot be excluded.Conclusion: We suggest that dysregulation of both IL-6 and IL-10 in some elderly people, due in part to genetic variations in the two genes, contributes to the development of AD. Thus, inflammation facilitates the onset of sporadic AD
Molecular Dynamics for Fermions
The time-dependent variational principle for many-body trial states is used
to discuss the relation between the approaches of different molecular dynamics
models to describe indistinguishable fermions. Early attempts to include
effects of the Pauli principle by means of nonlocal potentials as well as more
recent models which work with antisymmetrized many-body states are reviewed
under these premises.
Keywords: Many-body theory; Fermion system; Molecular dynamics; Wave-packet
dynamics; Time-dependent variational principle; Statistical properties;
Canonical ensemble; Ergodicity; Time averagingComment: 97 pages, 13 postscript figures. To be published in July 2000 issue
of Reviews of Modern Physics. More information at http://www-aix.gsi.de/~fmd
The dopamine ÎČ-hydroxylase -1021C/T polymorphism is associated with the risk of Alzheimer's disease in the Epistasis Project
Contains fulltext :
88930.pdf (publisher's version ) (Open Access)BACKGROUND: The loss of noradrenergic neurones of the locus coeruleus is a major feature of Alzheimer's disease (AD). Dopamine beta-hydroxylase (DBH) catalyses the conversion of dopamine to noradrenaline. Interactions have been reported between the low-activity -1021T allele (rs1611115) of DBH and polymorphisms of the pro-inflammatory cytokine genes, IL1A and IL6, contributing to the risk of AD. We therefore examined the associations with AD of the DBH -1021T allele and of the above interactions in the Epistasis Project, with 1757 cases of AD and 6294 elderly controls. METHODS: We genotyped eight single nucleotide polymorphisms (SNPs) in the three genes, DBH, IL1A and IL6. We used logistic regression models and synergy factor analysis to examine potential interactions and associations with AD. RESULTS: We found that the presence of the -1021T allele was associated with AD: odds ratio = 1.2 (95% confidence interval: 1.06-1.4, p = 0.005). This association was nearly restricted to men < 75 years old: odds ratio = 2.2 (1.4-3.3, 0.0004). We also found an interaction between the presence of DBH -1021T and the -889TT genotype (rs1800587) of IL1A: synergy factor = 1.9 (1.2-3.1, 0.005). All these results were consistent between North Europe and North Spain. CONCLUSIONS: Extensive, previous evidence (reviewed here) indicates an important role for noradrenaline in the control of inflammation in the brain. Thus, the -1021T allele with presumed low activity may be associated with misregulation of inflammation, which could contribute to the onset of AD. We suggest that such misregulation is the predominant mechanism of the association we report here
Rise to modern levels of ocean oxygenation coincided with the Cambrian radiation of animals.
The early diversification of animals (âŒ630âMa), and their development into both motile and macroscopic forms (âŒ575-565âMa), has been linked to stepwise increases in the oxygenation of Earth's surface environment. However, establishing such a linkage between oxygen and evolution for the later Cambrian 'explosion' (540-520âMa) of new, energy-sapping body plans and behaviours has proved more elusive. Here we present new molybdenum isotope data, which demonstrate that the areal extent of oxygenated bottom waters increased in step with the early Cambrian bioradiation of animals and eukaryotic phytoplankton. Modern-like oxygen levels characterized the ocean at âŒ521âMa for the first time in Earth history. This marks the first establishment of a key environmental factor in modern-like ecosystems, where animals benefit from, and also contribute to, the 'homeostasis' of marine redox conditions
Search for subsolar-mass black hole binaries in the second part of Advanced LIGOâs and Advanced Virgoâs third observing run
We describe a search for gravitational waves from compact binaries with at least one component with mass 0.2âMââ1.0âMâ and mass ratio q â„ 0.1 in Advanced LIGO and Advanced Virgo data collected between 1 November 2019, 15:00 UTC and 27 March 2020, 17:00 UTC. No signals were detected. The most significant candidate has a false alarm rate of 0.2yrâ1
â . We estimate the sensitivity of our search over the entirety of Advanced LIGOâs and Advanced Virgoâs third observing run, and present the most stringent limits to date on the merger rate of binary black holes with at least one subsolar-mass component. We use the upper limits to constrain two fiducial scenarios that could produce subsolar-mass black holes: primordial black holes (PBH) and a model of dissipative dark matter. The PBH model uses recent prescriptions for the merger rate of PBH binaries that include a rate suppression factor to effectively account for PBH early binary disruptions. If the PBHs are monochromatically distributed, we can exclude a dark matter fraction in PBHs fPBH âłâ0.6 (at 90% confidence) in the probed subsolar-mass range. However, if we allow for broad PBH mass distributions we are unable to rule out fPBH = 1. For the dissipative model, where the dark matter has chemistry that allows a small fraction to cool and collapse into black holes, we find an upper bound fDBH < 10â5 on the fraction of atomic dark matter collapsed into black holes
Precision physics of simple atoms: QED tests, nuclear structure and fundamental constants
Quantum electrodynamics is the first successful and still the most successful
quantum field theory. Simple atoms, being essentially QED systems, allow highly
accurate theoretical predictions. Because of their simple spectra, such atoms
have been also efficiently studied experimentally frequently offering the most
precisely measured quantities. Our review is devoted to comparison of theory
and experiment in the field of precision physics of light simple atoms. In
particular, we consider the Lamb shift in the hydrogen atom, the hyperfine
structure in hydrogen, deuterium, helium-3 ion, muonium and positronium, as
well as a number of other transitions in positronium. Additionally to a
spectrum of unperturbed atoms, we consider annihilation decay of positronium
and the g factor of bound particles in various two-body atoms. Special
attention is paid to the uncertainty of the QED calculations due to the
uncalculated higher-order corrections and effects of the nuclear structure. We
also discuss applications of simple atoms to determination of several
fundamental constants
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