Domain formation in membranes with quenched protein obstacles: Lateral heterogeneity and the connection to universality classes

We show that lateral fluidity in membranes containing quenched protein obstacles belongs to the universality class of the two-dimensional random-field Ising model. The main feature of this class is the absence of a phase transition: there is no critical point, and macroscopic domain formation does not occur. Instead, there is only one phase. This phase is highly heterogeneous, with a structure consisting of micro-domains. The presence of quenched protein obstacles thus provides a mechanism to stabilize lipid rafts in equilibrium. Crucial for two-dimensional random-field Ising universality is that the obstacles are randomly distributed, and have a preferred affinity to one of the lipid species. When these conditions are not met, standard Ising or diluted Ising universality apply. In these cases, a critical point does exist, marking the onset toward macroscopic demixing.Comment: 10 pages, 10 figure

Experiment M115: Special hematologic effects: Dynamic changes in red cell shape in response to the space-flight environment

The significance of the transformations in red cell shape observed during the Skylab study must be considered relative to the limitation of man's participation in extended space flight missions. The results of this one study are not conclusive with respect to this question. Based on these examinations of red cells in normal, healthy men and based on other Skylab experiment data relative to the functional capacity of the red cells in vitro and the performance capacity of man as an integrated system, the changes observed would not appear to be the limiting factor in determining man's stay in space. However, the results of this experiment and the documented red cell mass loss during space flight raise serious questions at this time relative to the selection criteria utilized for passengers and crews of future space flights. Until the specific cause and impact of the red cell shape change on cell survival in vivo can be resolved, individuals with diagnosed hematologic abnormalities should not be considered as prime candidates for missions, especially those of longer duration

A general review of concepts for reducing skin friction, including recommendations for future studies

Four main concepts which have significantly reduced skin friction in experimental studies are discussed; suction, gaseous injection, particle additives, and compliant wall. It is considered possible that each of these concepts could be developed and applied in viable skin friction reduction systems for aircraft application. Problem areas with each concept are discussed, and recommendations for future studies are made

The Infrared Behaviour of the Running Coupling in Landau Gauge QCD

Approximate solutions for the gluon and ghost propagators as well as the running coupling in Landau gauge Yang-Mills theories are presented. These propagators obtained from the corresponding Dyson-Schwinger equations are in remarkable agreement with those of recent lattice calculations. The resulting running coupling possesses an infrared fixed point, $\alpha_S(0) = 8.92/N_c$ for all gauge groups SU($N_c$). Above one GeV the running coupling rapidly approaches its perturbative form.Comment: 8 pages, 3 figures, uses ActaStyle.cls, Invited talk given by R.A. at the conference RENORMALIZATION GROUP 2002, March 10 - 16, 2002, Strba, Slovaki

Fluids with quenched disorder: Scaling of the free energy barrier near critical points

In the context of Monte Carlo simulations, the analysis of the probability distribution $P_L(m)$ of the order parameter $m$, as obtained in simulation boxes of finite linear extension $L$, allows for an easy estimation of the location of the critical point and the critical exponents. For Ising-like systems without quenched disorder, $P_L(m)$ becomes scale invariant at the critical point, where it assumes a characteristic bimodal shape featuring two overlapping peaks. In particular, the ratio between the value of $P_L(m)$ at the peaks ($P_{L, max}$) and the value at the minimum in-between ($P_{L, min}$) becomes $L$-independent at criticality. However, for Ising-like systems with quenched random fields, we argue that instead $\Delta F_L := \ln (P_{L, max} / P_{L, min}) \propto L^\theta$ should be observed, where $\theta>0$ is the "violation of hyperscaling" exponent. Since $\theta$ is substantially non-zero, the scaling of $\Delta F_L$ with system size should be easily detectable in simulations. For two fluid models with quenched disorder, $\Delta F_L$ versus $L$ was measured, and the expected scaling was confirmed. This provides further evidence that fluids with quenched disorder belong to the universality class of the random-field Ising model.Comment: sent to J. Phys. Cond. Mat

Kugo-Ojima confinement criterion, Zwanziger-Gribov horizon condition, and infrared critical exponents in Landau gauge QCD

The Kugo-Ojima confinement criterion and its relation to the infrared behaviour of the gluon and ghost propagators in Landau gauge QCD are reviewed. The realization of this confinement criterion (which in Landau gauge relates to Zwanziger's horizon condition) results from quite general properties of the ghost Dyson-Schwinger equation. The numerical solutions for the gluon and ghost propagators obtained from a truncated set of Dyson-Schwinger equations provide an explicit example for the anticipated infrared behaviour. These results are in good agreement, also quantitatively, with corresponding lattice data obtained recently. The resulting running coupling approaches a fixed point in the infrared, $\alpha(0) = 8.9/N_c$. Solutions for the coupled system of Dyson-Schwinger equations for the quark, gluon and ghost propagators are presented. Dynamical generation of quark masses and thus spontaneous breaking of chiral symmetry is found. In the quenched approximation the quark propagator functions agree well with those of corresponding lattice calculations. For a small number of light flavours the quark, gluon and ghost propagators deviate only slightly from the quenched ones. While the positivity violation of the gluon spectral function is apparent in the gluon propagator, there are no clear indications of positivity violations in the Landau gauge quark propagator.Comment: 10 pages, 4 figures; invited talk presented by R. Alkofer at the International Conference Confinement V Gargnano, Italy, September 10-14, 200

Infrared Exponents and the Running Coupling of Landau gauge QCD and their Relation to Confinement

The infrared behaviour of the gluon and ghost propagators in Landau gauge QCD is reviewed. The Kugo-Ojima confinement criterion and the Gribov-Zwanziger horizon condition result from quite general properties of the ghost Dyson-Schwinger equation. The numerical solutions for the gluon and ghost propagators obtained from a truncated set of Dyson-Schwinger equations provide an explicit example for the anticipated infrared behaviour. The results are in good agreement with corresponding lattice data obtained recently. The resulting running coupling approaches a fix point in the infrared, $\alpha(0) = 8.92/N_c$. Two different fits for the scale dependence of the running coupling are given and discussed.Comment: 3 pages, 3 figures; talk given by R.A. at the conference Quark Nuclear Physics 200