Crossover from normal to anomalous diffusion in field-aligned dipolar systems

Using molecular dynamics simulations we investigate the translational dynamics of particles with dipolar interactions in homogenous external fields. For a broad range of concentrations, we find that the anisotropic, yet normal diffusive behavior characterizing weakly coupled systems becomes anomalous both parallel and perpendicular to the field at sufficiently high dipolar coupling and field strength. After the ballistic regime, chain formation first yields cage-like motion in all directions, followed by transient, mixed diffusive-superdiffusive behavior resulting from cooperative motion of the chains. The enhanced dynamics disappears only at higher densities close to crystallization

Non-equilibrium condensation and coarsening of field-driven dipolar colloids

In colloidal suspensions, self-organization processes can be easily fueled by external fields. One particularly interesting class of phenomena occurs in monolayers of dipolar particles that are driven by rotating external fields. Here we report results from a computer simulation study of such systems focusing on the clustering behavior also observed in recent experiments. The key result of this paper is a novel interpretation of this pattern formation phenomenon: We show the clustering to be a by-product of a vapor-liquid first order phase transition. In fact, the observed dynamic coarsening process corresponds to the spindodal demixing that occurs during such a transitionComment: 6 pages, 5 figure

Formation of PAHs and Carbonaceous Solids in Gas-Phase Condensation Experiments

Carbonaceous grains represent a major component of cosmic dust. In order to understand their formation pathways, they have been prepared in the laboratory by gas-phase condensation reactions such as laser pyrolysis and laser ablation. Our studies demonstrate that the temperature in the condensation zone determines the formation pathway of carbonaceous particles. At temperatures lower than 1700 K, the condensation by-products are mainly polycyclic aromatic hydrocarbons (PAHs), that are also the precursors or building blocks for the condensing soot grains. The low-temperature condensates contain PAH mixtures that are mainly composed of volatile 3-5 ring systems. At condensation temperatures higher than 3500 K, fullerene-like carbon grains and fullerene compounds are formed. Fullerene fragments or complete fullerenes equip the nucleating particles. Fullerenes can be identified as soluble components. Consequently, condensation products in cool and hot astrophysical environments such as cool and hot AGB stars or Wolf Rayet stars should be different and should have distinct spectral properties.Comment: 7 pages, 5 figure

The supersymmetric Higgs sector and B-Bbar mixing for large tan beta

We match the Higgs sector of the most general flavour breaking and CP violating minimal supersymmetric standard model (MSSM) onto a generic two-Higgs-doublet model, paying special attention to the definition of tan beta in the effective theory. In particular no tan beta-enhanced loop corrections appear in the relation to tan beta defined in the DRbar scheme in the MSSM. The corrections to the Higgs-mediated flavour-changing amplitudes which result from this matching are especially relevant for the B_d and B_s mass differences dM_s,d for minimal flavour violation, where the superficially leading contribution vanishes. We give a symmetry argument to explain this cancellation and perform a systematic study of all Higgs-mediated effects, including Higgs loops. The corrections to dM_s are at most 7% for mu>0 and M_A < 600 if constraints from other observables are taken into account. For mu<0 they can be larger, but are always less than about 20%. Contrary to recent claims we do not find numerically large contributions here, nor do we find any tan beta-enhanced contributions from loop corrections to the Higgs potential in B^+ -> tau^+ nu or B -> X_s gamma. We further update supersymmetric loop corrections to the Yukawa couplings, where we include all possible CP-violating phases and correct errors in the literature. The possible presence of CP-violating phases generated by Higgs exchange diagrams is briefly discussed as well. Finally we provide improved values for the bag factors P^VLL_1, P^LR_2, and P^SLL_1 at the electroweak scale.Comment: 61 page

Atypical CD3+ CD4(low) cell population in a boy with fatal EBV-infection

A previously healthy 10-year-old Greek boy born to nonconsanguineous healthy parents developed progressive liver disease after acute infectious mononucleosis. EBV-induced autoimmune hepatitis was suspected and treatment was started with high-dose prednisolone, acyclovir and intravenous immunoglobulins. Despite therapy his liver function continuously deteriorated and the child died 9 months later in profound immune deficiency from candida septicemia. Flow cytometric analysis of his lymphocytes revealed a major subpopulation of atypical cells (20.3%) which were CD3+, fitted into the lymphocyte gate bur showed a very low level of CD4 expression, comparable to that of monocytes. After short-time cell culture, the cells became adherent and developed granules and dendrites; We conclude that these cells may represent strongly activated CD4+ T lymphocytes with downregulated CD4 expression or a subtype of dendritic cells