3,067 research outputs found
Raft Instability of Biopolymer Gels
Following recent X-ray diffraction experiments by Wong, Li, and Safinya on
biopolymer gels, we apply Onsager excluded volume theory to a nematic mixture
of rigid rods and strong ``'' cross-linkers obtaining a long-ranged,
highly anisotropic depletion attraction between the linkers. This attraction
leads to breakdown of the percolation theory for this class of gels, to
breakdown of Onsager's second-order virial method, and to formation of
heterogeneities in the form of raft-like ribbons.Comment: 5 pages, 4 figure
Nomadic firms in a globalizing economy: A comparative study
The location patterns of modern firms appear to exhibit floating patternswith a tendency towards footlooseness. The spatial-economic dynamics - sometimes across teh border - of firms is encapsulated in the term 'nomadic firms'. This paper adresses the issue of nomadic behaviour of firms against the background of globalisation trends. After a critical discussion of globalisation phenomena and a review of the literature on nomadic entrepreneurial behaviour, the paper sets out t formaulate a series of relevant hypotheses of spatial relocation behaviour of international firms in a globalizing network economy. The analytical framework is tested by means of interviews among actual or potential nomadic firms, in both the Netherlands and abroad. Infrastructure quality and geographical accessibility appear to play an important role, but also opportunity seeking behaviour has a prominent place in nomadic behaviour. The comparitive study among the various firms located in various countries, which aims to identify the critical relocation factors, is based on principles of modern meta-analysis.
Effective adhesion strength of specifically bound vesicles
A theoretical approach has been undertaken in order to model the
thermodynamic equilibrium of a vesicle adhering to a flat substrate. The
vesicle is treated in a canonical description with a fixed number of sites. A
finite number of these sites are occupied by mobile ligands that are capable of
interacting with a discrete number of receptors immobilized on the substrate.
Explicit consideration of the bending energy of the vesicle shape has shown
that the problem of the vesicle shape can be decoupled from the determination
of the optimum allocation of ligands over the vesicle. The allocation of bound
and free ligands in the vesicle could be determined as a function of the size
of the contact zone, the ligand-receptor binding strength and the concentration
of the system constituents. Several approximate solutions for different regions
of system parameters are determined and in particular, the distinction between
receptor-dominated equilibria and ligand-dominated equilibria is found to be
important. The crossover between these two types of solutions is found to occur
at a critical size of the contact zone. The presented approach enables the
calculation of the effective adhesion strength of the vesicle and thus permits
meaningful comparisons with relevant experiments as well as connecting the
presented model with the proven success of the continuum approach for modeling
the shapes of adhering vesicles. The behavior of the effective adhesion
strength is analyzed in detail and several approximate expressions for it are
given.Comment: 19 pages, 6 figures. To appear in Phys. Rev.
Adhesion-induced phase separation of multiple species of membrane junctions
A theory is presented for the membrane junction separation induced by the
adhesion between two biomimetic membranes that contain two different types of
anchored junctions (receptor/ligand complexes). The analysis shows that several
mechanisms contribute to the membrane junction separation. These mechanisms
include (i) the height difference between type-1 and type-2 junctions is the
main factor which drives the junction separation, (ii) when type-1 and type-2
junctions have different rigidities against stretch and compression, the
``softer'' junctions are the ``favored'' species, and the aggregation of the
softer junction can occur, (iii) the elasticity of the membranes mediates a
non-local interaction between the junctions, (iv) the thermally activated shape
fluctuations of the membranes also contribute to the junction separation by
inducing another non-local interaction between the junctions and renormalizing
the binding energy of the junctions. The combined effect of these mechanisms is
that when junction separation occurs, the system separates into two domains
with different relative and total junction densities.Comment: 23 pages, 6 figure
Phase diagram of the random field Ising model on the Bethe lattice
The phase diagram of the random field Ising model on the Bethe lattice with a
symmetric dichotomous random field is closely investigated with respect to the
transition between the ferromagnetic and paramagnetic regime. Refining
arguments of Bleher, Ruiz and Zagrebnov [J. Stat. Phys. 93, 33 (1998)] an exact
upper bound for the existence of a unique paramagnetic phase is found which
considerably improves the earlier results. Several numerical estimates of
transition lines between a ferromagnetic and a paramagnetic regime are
presented. The obtained results do not coincide with a lower bound for the
onset of ferromagnetism proposed by Bruinsma [Phys. Rev. B 30, 289 (1984)]. If
the latter one proves correct this would hint to a region of coexistence of
stable ferromagnetic phases and a stable paramagnetic phase.Comment: Article has been condensed and reorganized; Figs 3,5,6 merged; Fig 4
omitted; Some discussion added at end of Sec. III; 9 pages, 5 figs, RevTeX4,
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