3,001 research outputs found
Collapsed 2-Dimensional Polymers on a Cylinder
Single partially confined collapsed polymers are studied in two dimensions.
They are described by self-avoiding random walks with nearest-neighbour
attractions below the -point, on the surface of an infinitely long
cylinder. For the simulations we employ the pruned-enriched-Rosenbluth method
(PERM). The same model had previously been studied for free polymers (infinite
lattice, no boundaries) and for polymers on finite lattices with periodic
boundary conditions. We verify the previous estimates of bulk densities, bulk
free energies, and surface tensions. We find that the free energy of a polymer
with fixed length has, for , a minimum at a finite cylinder
radius which diverges as . Furthermore, the surface
tension vanishes roughly as for with
. The density in the interior of a globule scales as
with .Comment: 4 pages, 8 figure
Kaon photoproduction: background contributions, form factors and missing resonances
The photoproduction p(gamma, K+)Lambda process is studied within a
field-theoretic approach. It is shown that the background contributions
constitute an important part of the reaction dynamics. We compare predictions
obtained with three plausible techniques for dealing with these background
contributions. It appears that the extracted resonance parameters drastically
depend on the applied technique. We investigate the implications of the
corrections to the functional form of the hadronic form factor in the contact
term, recently suggested by Davidson and Workman (Phys. Rev. C 63, 025210). The
role of background contributions and hadronic form factors for the
identification of the quantum numbers of ``missing'' resonances is discussed.Comment: 11 pages, 7 eps figures, submitted to Phys. Rev.
Stretched Polymers in a Poor Solvent
Stretched polymers with attractive interaction are studied in two and three
dimensions. They are described by biased self-avoiding random walks with
nearest neighbour attraction. The bias corresponds to opposite forces applied
to the first and last monomers. We show that both in and a phase
transition occurs as this force is increased beyond a critical value, where the
polymer changes from a collapsed globule to a stretched configuration. This
transition is second order in and first order in . For we
predict the transition point quantitatively from properties of the unstretched
polymer. This is not possible in , but even there we can estimate the
transition point precisely, and we can study the scaling at temperatures
slightly below the collapse temperature of the unstretched polymer. We find
very large finite size corrections which would make very difficult the estimate
of the transition point from straightforward simulations.Comment: 10 pages, 16 figure
Capture and inception of bubbles near line vortices
Motivated by the need to predict vortex cavitation inception, a study has been conducted to investigate bubble capture by a concentrated line vortex of core size rcrc and circulation Γ0Γ0 under noncavitating and cavitating conditions. Direct numerical simulations that solve simultaneously for the two phase flow field, as well as a simpler one-way coupled point-particle-tracking model (PTM) were used to investigate the capture process. The capture times were compared to experimental observations. It was found that the point-particle-tracking model can successfully predict the capture of noncavitating small nuclei by a line vortex released far from the vortex axis. The nucleus grows very slowly during capture until the late stages of the process, where bubble/vortex interaction and bubble deformation become important. Consequently, PTM can be used to study the capture of cavitating nuclei by dividing the process into the noncavitating capture of the nucleus, and then the growth of the nucleus in the low-pressure core region. Bubble growth and deformation act to speed up the capture process.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87832/2/022105_1.pd
Characteristic patterns of inter- and intra-hemispheric metabolic connectivity in patients with stable and progressive mild cognitive impairment and Alzheimer's disease
The change in hypometabolism affects the regional links in the brain network. Here, to understand the underlying brain metabolic network deficits during the early stage and disease evolution of AD (Alzheimer disease), we applied correlation analysis to identify the metabolic connectivity patterns using 18F-FDG PET data for NC (normal control), sMCI (stable MCI), pMCI (progressive MCI) and AD, and explore the inter- and intra-hemispheric connectivity between anatomically-defined brain regions. Regions extracted from 90 anatomical structures were used to construct the matrix for measuring the inter- and intra-hemispheric connectivity. The brain connectivity patterns from the metabolic network show a decreasing trend of inter- and intra-hemispheric connections for NC, sMCI, pMCI and AD. Connection of temporal to the frontal or occipital regions is a characteristic pattern for conversion of NC to MCI, and the density of links in the parietal-occipital network is a differential pattern between sMCI and pMCI. The reduction pattern of inter and intra-hemispheric brain connectivity in the metabolic network depends on the disease stages, and is with a decreasing trend with respect to disease severity. Both frontal-occipital and parietal-occipital connectivity patterns in the metabolic network using 18F-FDG PET are the key feature for differentiating disease groups in AD
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