2,286 research outputs found
Local Nature of Coset Models
The local algebras of the maximal Coset model C_max associated with a chiral
conformal subtheory A\subset B are shown to coincide with the local relative
commutants of A in B, provided A contains a stress energy tensor.
Making the same assumption, the adjoint action of the unique
inner-implementing representation U^A associated with A\subset B on the local
observables in B is found to define net-endomorphisms of B. This property is
exploited for constructing from B a conformally covariant holographic image in
1+1 dimensions which proves useful as a geometric picture for the joint
inclusion A\vee C_max \subset B.
Immediate applications to the analysis of current subalgebras are given and
the relation to normal canonical tensor product subfactors is clarified. A
natural converse of Borchers' theorem on half-sided translations is made
accessible.Comment: 33 pages, no figures; typos, minor improvement
Structure of self-assembled Mn atom chains on Si(001)
Mn has been found to self-assemble into atomic chains running perpendicular
to the surface dimer reconstruction on Si(001). They differ from other atomic
chains by a striking asymmetric appearance in filled state scanning tunneling
microscopy (STM) images. This has prompted complicated structural models
involving up to three Mn atoms per chain unit. Combining STM, atomic force
microscopy and density functional theory we find that a simple necklace-like
chain of single Mn atoms reproduces all their prominent features, including
their asymmetry not captured by current models. The upshot is a remarkably
simpler structure for modelling the electronic and magnetic properties of Mn
atom chains on Si(001).Comment: 5 pages, 4 figure
Harmonically confined, semiflexible polymer in a channel: response to a stretching force and spatial distribution of the endpoints
We consider an inextensible, semiflexible polymer or worm-like chain which is
confined in the transverse direction by a parabolic potential and subject to a
longitudinal force at the ends, so that the polymer is stretched out and
backfolding is negligible. Simple analytic expressions for the partition
function, valid in this regime, are obtained for chains of arbitrary length
with a variety of boundary conditions at the ends. The spatial distribution of
the end points or radial distribution function is also analyzed.Comment: 14 pages including figure
Mechanics of individual keratin bundles in living cells
AbstractAlong with microtubules and microfilaments, intermediate filaments are a major component of the eukaryotic cytoskeleton and play a key role in cell mechanics. In cells, keratin intermediate filaments form networks of bundles that are sparser in structure and have lower connectivity than, for example, actin networks. Because of this, bending and buckling play an important role in these networks. Buckling events, which occur due to compressive intracellular forces and cross-talk between the keratin network and other cytoskeletal components, are measured here in situ. By applying a mechanical model for the bundled filaments, we can access the mechanical properties of both the keratin bundles themselves and the surrounding cytosol. Bundling is characterized by a coupling parameter that describes the strength of the linkage between the individual filaments within a bundle. Our findings suggest that coupling between the filaments is mostly complete, although it becomes weaker for thicker bundles, with some relative movement allowed
Endotaxial Si nanolines in Si(001):H
We present a detailed study of the structural and electronic properties of a
self-assembled silicon nanoline embedded in the H-terminated silicon (001)
surface, known as the Haiku stripe. The nanoline is a perfectly straight and
defect free endotaxial structure of huge aspect ratio; it can grow micrometre
long at a constant width of exactly four Si dimers (1.54nm). Another remarkable
property is its capacity to be exposed to air without suffering any
degradation. The nanoline grows independently of any step edges at tunable
densities, from isolated nanolines to a dense array of nanolines. In addition
to these unique structural characteristics, scanning tunnelling microscopy and
density functional theory reveal a one-dimensional state confined along the
Haiku core. This nanoline is a promising candidate for the long sought after
electronic solid-state one-dimensional model system to explore the fascinating
quantum properties emerging in such reduced dimensionality.Comment: 8 pages, 6 figure
One dimensional Si-in-Si(001) template for single-atom wire growth
Single atom metallic wires of arbitrary length are of immense technological
and scientific interest. We describe a novel silicon-only template enabling the
self-organised growth of isolated micrometer long surface and subsurface
single-atom chains. It consists of a one dimensional, defect-free
reconstruction - the Haiku core, here revealed for the first time in details -
self-assembled on hydrogenated Si(001) terraces, independent of any step edges.
We discuss the potential of this Si-in-Si template as an appealing alternative
to vicinal surfaces for nanoscale patterning.Comment: 3 pages, 2 figure
Modeling and reconstruction in a 3D microwave imaging system
In this paper we discuss the design and modeling of a 3D system for microwave imaging. The antenna system consists of 32 monopoles in a cylindrical configuration. A FDTD model of the system is used in the imaging reconstruction algorithm. Here we show a comparison of the data generated from the numerical FDTD model with measured data, as well as imaging of a simple target using this system. The agreement in the model is good and the imaging of a test object is successful
Shapes of Semiflexible Polymers in Confined Spaces
We investigate the conformations of a semiflexible polymer confined to a
square box. Results of Monte Carlo simulations show the existence of a shape
transition when the persistence length of the polymer becomes comparable to the
dimensions of box. An order parameter is introduced to quantify this behavior.
A simple mean-field model is constructed to study the effect of the shape
transition on the effective persistence length of the polymer.Comment: 8 pages, 20 figure
C-terminales Pro-Endothelin-1 als Verlaufsmarker bei herzchirurgischen Operationen mit kardiopulmonalem Bypass
Bei herzchirurgischen Operationen mit kardiopulmonalem Bypass beeinflusst die Erhöhung des Endothelin-1 (ET-1) Körperfunktionen negativ. Das ist eine Synthesevorstufe des ET-1. Es wurde zu 12 Messzeitpunkten der Verlauf des C-terminalen Pro-ET1 nach herzchirurgischen Engriffen mit kardiopulmonalem Bypass sowie das Langzeitoutcome bei 123 Patienten prospektiv mittels Immunossay bestimmt. Nach 2 Jahren wurde die Überlebensrate erhoben. Es zeigte sich ein spezifischer Verlauf: nach Einleitung der Narkose fielen die Konzentrationen des C-terminale Pro-ET-1 ab, während des Eingriffes blieben sie konstant, postoperativ stiegen sie kontinuierlich an. Die Verläufe der Konzentrationen von Überlebenden und Verstorbenen unterscheidet sich nicht signifikant. Aufgrund des spezifischen Verlaufs könnte der Biomarker für die postoperative, nicht jedoch zur intraoperativen Überwachung von Interesse sein. Pro-ET-1 scheint nicht als Langzeitoutcomeparameter geeignet
Modeling and simulation of phase-transitions in multicomponent aluminum alloy casting
The casting process of aluminum products involves the spatial distribution of alloying elements. It is essential that these elements are uniformly distributed in order to guarantee reliable and consistent products. This requires a good understanding of the main physical mechanisms that affect the solidification, in particular the thermodynamic description and its coupling to the transport processes of heat and mass that take place. The continuum modeling is reviewed and methods for handling the thermodynamics component of multi-element alloys are proposed. Savings in data-storage and computing costs on the order of 100 or more appear possible, when a combination of data-reduction and data-representation methods is used. To test the new approach a simplified model was proposed and shown to qualitatively capture the evolving solidification front
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