Coupled order-parameter system on a scale-free network.

The system of two scalar order parameters on a complex scale-free network is analyzed in the spirit of Landau theory. To add a microscopic background to the phenomenological approach, we also study a particular spin Hamiltonian that leads to coupled scalar order behavior using the mean-field approximation. Our results show that the system is characterized by either of two types of ordering: either one of the two order parameters is zero or both are nonzero but have the same value. While the critical exponents do not differ from those of a model with a single order parameter on a scale-free network, there are notable differences for the amplitude ratios and the susceptibilities. Another peculiarity of the model is that the transverse susceptibility is divergent at all T

Pseudo-knots in helical structures.

It is generally accepted that physical entanglements are essential to explain some mechanical properties of polymers, like viscoelasticity. The current view is that entanglements behave as dynamic links that are destroyed and created in time. It is less clear whether entanglements could alternatively produce local and stable links, with similar effects to chemical bonds. Here we show that local and stable entanglements, that we call physical pseudo-knots, exist and are formed with high probability in helical structures. The energies required to create and destroy physical pseudo-knots can differ by at least one order of magnitude. Together with their localized nature this makes them controllable, opening the possibility for a wide range of applications in material science, nano- and biotechnology. Physical pseudo-knots can also have implications in living systems, that may use them, or try to avoid them and hence be related to disease.

Universal shape characteristics for the mesoscopic star-shaped polymer via dissipative particle dynamics simulations.

In this paper we study the shape characteristics of star-like polymers in various solvent quality using a mesoscopic level of modeling. The dissipative particle dynamics simulations are performed for the homogeneous and four different heterogeneous star polymers with the same molecular weight. We analyse the gyration radius and asphericity at the poor, good and θ-solvent regimes. Detailed explanation based on interplay between enthalpic and entropic contributions to the free energy and analyses on of the asphericity of individual branches are provided to explain the increase of the apsphericity in θ-solvent regime.

Entropy-induced separation of star polymers in porous media.

We present a quantitative picture of the separation of star polymers in a solution where part of the volume is influenced by a porous medium. To this end, we study the impact of long-range-correlated quenched disorder on the entropy and scaling properties of f-arm star polymers in a good solvent. We assume that the disorder is correlated on the polymer length scale with a power-law decay of the pair correlation function g(r) approximately r-a. Applying the field-theoretical renormalization group approach we show in a double expansion in epsilon=4-d and delta=4-a that there is a range of correlation strengths delta for which the disorder changes the scaling behavior of star polymers. In a second approach we calculate for fixed space dimension d=3 and different values of the correlation parameter a the corresponding scaling exponents gammaf that govern entropic effects. We find that gammaf-1, the deviation of gammaf from its mean field value is amplified by the disorder once we increase delta beyond a threshold. The consequences for a solution of diluted chain and star polymers of equal molecular weight inside a porous medium are that star polymers exert a higher osmotic pressure than chain polymers and in general higher branched star polymers are expelled more strongly from the correlated porous medium. Surprisingly, polymer chains will prefer a stronger correlated medium to a less or uncorrelated medium of the same density while the opposite is the case for star polymers.

Universal shape characteristics for the mesoscopic polymer chain via dissipative particle dynamics.

In this paper we study the shape characteristics of a polymer chain in a good solvent using a mesoscopic level of modelling. The dissipative particle dynamics simulations are performed in 3D space at a range of chain lengths N. The scaling laws for the end-to-end distance and gyration radius are examined first and found to hold for [Formula: see text] yielding a reasonably accurate value for the Flory exponent ν. Within the same interval of chain lengths, the asphericity, prolateness and some other shape characteristics of the chain are found to become independent of N. Their mean values are found to agree reasonably well with the respective theoretical results and lattice Monte Carlo (MC) simulations. We found the probability distribution for a wide range of shape characteristics. For the asphericity and prolateness they are quite broad, resembling in form the results of lattice MC simulations. By means of the analytic fitting of these distributions, the most probable values for the shape characteristics are found to supplement their mean values.

Two-dimensional copolymers and multifractality: comparing perturbative expansions, Monte Carlo simulations, and exact results.

We analyze the scaling laws for a set of two different species of long flexible polymer chains joined together at one of their extremities (copolymer stars) in space dimension D=2. We use a formerly constructed field-theoretic description and compare our perturbative results for the scaling exponents with recent conjectures for exact conformal scaling dimensions derived by a conformal invariance technique in the context of D=2 quantum gravity. A simple Monte Carlo simulation brings about reasonable agreement with both approaches. We analyze the remarkable multifractal properties of the spectrum of scaling exponents.

Amphiphilic hard body mixtures.

In order to study ternary amphiphilic mixtures, we introduce a simplistic model of hard spheres corresponding to water and hard needles corresponding to oil and amphiphilic particles, where the hydrophilic head is modeled as a hard sphere and the hydrophobic tail as an infinitely thin needle attached radially to the sphere. For this system, we construct a geometry-based density functional and perform Monte Carlo computer simulations. The equation of state derived from the theory is found to be in remarkable agreement with our simulation results. We investigate the theoretical demixing phase diagram, and find that the predicted trends strongly support the amphiphilic character of the model.

Polymers in long-range-correlated disorder.

We study the scaling properties of polymers in a d-dimensional medium with quenched defects that have power law correlations approximately r(-a) for large separations r. This type of disorder is known to be relevant for magnetic phase transitions. We find strong evidence that this is true also for the polymer case. Applying the field-theoretical renormalization group approach we perform calculations both in a double expansion in epsilon=4-d and delta=4-a up to the one-loop order and second in a fixed dimension (d=3) approach up to the two-loop approximation for different fixed values of the correlation parameter, 2

Where two fractals meet: the scaling of a self-avoiding walk on a percolation cluster.

The scaling properties of self-avoiding walks on a d -dimensional diluted lattice at the percolation threshold are analyzed by a field-theoretical renormalization group approach. To this end we reconsider the model of Phys. Rev. Lett. 63, 2819 (1989)] and argue that via renormalization its multifractal properties are directly accessible. While the former first order perturbation did not agree with the results of other methods our analytic result gives an accurate description of the available MC and exact enumeration data in a wide range of dimensions 2

Phase separation in star-polymer-colloid mixtures.

We examine the demixing transition in star-polymer-colloid mixtures for star arm numbers f=2,6,16,32 and different star-polymer-colloid size ratios 0.18< or =q< or =0.50. Theoretically, we solve the thermodynamically self-consistent Rogers-Young integral equations for binary mixtures using three effective pair potentials obtained from direct molecular computer simulations. The numerical results show a spinodal instability. The demixing binodals are approximately calculated and found to be consistent with experimental observations.

[Sociological aspects of modification of social behavior. Spontaneous action, social stress and individual life style]. / Soziologische Aspekte der Beeinflussung sozialen Verhaltens. Spontanverhalten, sozialer Druck und persönlicher Lebensstil.

To interest people in health behavior there are two different ways. First of all the way using the methods of mass communication or as some call it: "social marketing". But this raises the problems of defining the population that should be referred to and to overcome the resistance of social structure. So generally there are only few chances in succeeding. The other way would be that those people engaged in realizing preventive medicine would try to cooperate with existing groups, organizations or institutions. This seems to be far more successful. To reduce the number of "arbeitsbedingte Krankheiten" (sickness that mainly but not only depends on working conditions) special opportunities are offered by industrial firms.

Star copolymers in porous environments: scaling and its manifestations.

We consider star polymers, consisting of two different polymer species, in a solvent subject to quenched correlated structural obstacles. We assume that the disorder is correlated with a power-law decay of the pair-correlation function g(x)~x(-a). Applying the field-theoretical renormalization group approach in d dimensions, we analyze different scenarios of scaling behavior working to first order of a double ɛ=4-d, δ=4-a expansion. We discuss the influence of the correlated disorder on the resulting scaling laws and possible manifestations such as diffusion-controlled reactions in the vicinity of absorbing traps placed on polymers as well as the effective short-distance interaction between star copolymers.

Entropic equation of state and scaling functions near the critical point in uncorrelated scale-free networks.

We analyze the entropic equation of state for a many-particle interacting system in a scale-free network. The analysis is performed in terms of scaling functions, which are of fundamental interest in the theory of critical phenomena and have previously been theoretically and experimentally explored in the context of various magnetic, fluid, and superconducting systems in two and three dimensions. Here, we obtain general scaling functions for the entropy, the constant-field heat capacity, and the isothermal magnetocaloric coefficient near the critical point in uncorrelated scale-free networks, where the node-degree distribution exponent λ appears to be a global variable and plays a crucial role, similar to the dimensionality d for systems on lattices. This extends the principle of universality to systems on scale-free networks and allows quantification of the impact of fluctuations in the network structure on critical behavior.

Critical phenomena on scale-free networks: logarithmic corrections and scaling functions.

In this paper, we address the logarithmic corrections to the leading power laws that govern thermodynamic quantities as a second-order phase transition point is approached. For phase transitions of spin systems on d-dimensional lattices, such corrections appear at some marginal values of the order parameter or space dimension. We present scaling relations for these exponents. We also consider a spin system on a scale-free network which exhibits logarithmic corrections due to the specific network properties. To this end, we analyze the phase behavior of a model with coupled order parameters on a scale-free network and extract leading and logarithmic correction-to-scaling exponents that determine its field and temperature behavior. Although both nontrivial sets of exponents emerge from the network structure rather than from the spin fluctuations they fulfill the respective thermodynamic scaling relations. For the scale-free networks the logarithmic corrections appear at marginal values of the node degree distribution exponent. In addition we calculate scaling functions, which also exhibit nontrivial dependence on intrinsic network properties.

Spacers' role in the dynamics of hyperbranched polymers.

We investigate hyperbranched polymers (HBPs) and highlight the relation between their architecture and their viscoelastic behavior, while paying special attention to the role of the chainlike spacer segments between branching points. For this we study the dynamics of HBP in solution, based on the generalized Gaussian structure formalism, an extension of the Rouse model, which disregards hydrodynamical and excluded volume effects. For HBP the dynamical effects display, beside the obvious contributions of localized modes on the spacers, also remarkable features, as we highlight based on the exact renormalization procedure recently developed by us in J. Chem. Phys. 123, 034907 (2005). We exemplify these features by analyzing the dynamics of randomly linked star polymers and study the impact both of the length and of the spacers' mobility on the normal modes' spectra. We compute these modes both by numerical diagonalization and also by employing our renormalization procedure; the excellent agreement between these methods allows us to extend the range of investigations to very large HBP.

Polyelectrolyte-surfactant complex: phases of self-assembled structures.

We study the structure of complexes formed between ionic surfactants (SF) and a single oppositely charged polyelectrolyte (PE) chain. For our computer simulation we use the "primitive" electrolyte model: while the polyelectrolyte is modeled by a tethered chain of charged hard sphere beads, the surfactant molecules consist of a single charged head bead tethered to a tail of tethered hard spheres. A hydrophobic attraction between the tail beads is introduced by assuming a Lennard-Jones potential outside the hard-sphere diameter. As a function of the strengths of both the electrostatic and the hydrophobic interactions, we find the following scenario: switching on and increasing the electrostatic forces first leads to a stretching of the PE and then by condensation of SF to the formation of a complex. For vanishing hydrophobic forces this complex has the architecture of a molecular bottle-brush cylindrically centered around the stretched PE molecule. Upon increasing the hydrophobic attraction between the SF tails, a transition occurs inverting this structure to a spherical micelle with a neutral core of SF tails and a charged corona of SF heads with the PE molecule wrapped around. At intermediate hydrophobicity there is a competition between the two structures indicated by a non-monotonic dependence of the shape as function of the Coulomb strength, favoring the cylindrical shape for weak and the spherical micellar complex for strong interaction.

Dynamics of end-linked star-polymer structures.

In this work we focus on the dynamics of macromolecular networks formed by end-linking identical polymer stars. The resulting macromolecular network can then be viewed as consisting of spacers which connect branching points (the cores of the stars). We succeed in analyzing exactly, in the framework of the generalized Gaussian model, the eigenvalue spectrum of such networks. As applications we focus on several topologies, such as regular networks and dendrimers; furthermore, we compare the results to those found for regular hyperbranched structures. In so doing, we also consider situations in which the beads of the cores differ from the beads of the spacers. The analytical procedure which we use involves an exact real-space renormalization, which allows to relate the star network to a (much simpler) network, in which each star is reduced to its core. It turns out that the eigenvalue spectrum of the star-polymer structure consists of two parts: one follows in terms of polynomial equations from the relaxation spectrum of the corresponding renormalized structure, while the second part involves the motion of the spacer chains themselves. Finally, we show exemplarily the situation for copolymeric dendrimers, calculate their spectra, and from them their storage and the loss moduli.

[Reform of the public health service--needs and perspectives]. / Die Reform des öffentlichen Gesundheitsdienstes--Notwendigkeiten und Perspektiven.

The fundamental prerequisite of reorganising public health agencies is to create a new perspective of health policy. At present this realisation is the essence of the renewal of public health in the Anglo-American countries. The reorganisation of public health services in the old and in the new laender of the Federal Republic of Germany would gain by taking stock of the essential points that have been formulated by experts in the Anglo-American countries: the assessment of health problems by epidemiologists and health economists, the development of interorganizational cooperation, and the regional planning of health services. For translating these concepts into reality, public health has an unrivalled lead as far as chances and prerequisites are concerned, but the main obstacle is that continuing education and training are being blocked by the superior administrative bodies, so that there is a lack of experience in epidemiology, health policy and management.

[Rehabilitation from a socio-epidemiological viewpoint--what should and what must be changed?]. / Rehabilitation aus sozialepidemiologischer Sicht--Was sollten, was müssen wir ändern?

Rehabilitation, along with curative treatment and prevention, is a function within a social system of comprehensive measures and services aimed at the maintenance and restoration of good health. Rehabilitation at the same time, however, is a task assigned to specific social service administrations within the structured system of social security. This entails deficits in the effectiveness and efficiency of rehabilitation measures. A working group on "reorientation in health care" has developed proposals for reducing these deficits, bearing reference, in its proposals, to the course of chronic diseases and pointing out the measures that would, in the various disease stages, be capable of securing care continuity as well as of improving the quality of care. Key factors involved are the rehabilitation competence of the primary-care physicians, as well as the competencies of patients themselves.

Multifractality of Brownian motion near absorbing polymers.

We characterize the multifractal behavior of Brownian motion in the vicinity of an absorbing star polymer. We map the problem to an O(M)-symmetric phi(4)-field theory relating higher moments of the Laplacian field of Brownian motion to corresponding composite operators. The resulting spectra of scaling dimensions of these operators display the convexity properties that are necessarily found for multifractal scaling but unusual for power of field operators in field theory. Using a field-theoretic renormalization group approach we obtain the multifractal spectrum for absorption at the core of a polymer star as an asymptotic series. We evaluate these series using resummation techniques.