Spectroscopic observations of the planets

Spectroscopic observations of planets showing absorption variations in NH3 and CH4 band

Star Polymers Confined in a Nanoslit: A Simulation Test of Scaling and Self-Consistent Field Theories

The free energy cost of confining a star polymer where $f$ flexible polymer chains containing $N$ monomeric units are tethered to a central unit in a slit with two parallel repulsive walls a distance $D$ apart is considered, for good solvent conditions. Also the parallel and perpendicular components of the gyration radius of the star polymer, and the monomer density profile across the slit are obtained. Theoretical descriptions via Flory theory and scaling treatments are outlined, and compared to numerical self-consistent field calculations (applying the Scheutjens-Fleer lattice theory) and to Molecular Dynamics results for a bead-spring model. It is shown that Flory theory and self-consistent field (SCF) theory yield the correct scaling of the parallel linear dimension of the star with $N$, $f$ and $D$, but cannot be used for estimating the free energy cost reliably. We demonstrate that the same problem occurs already for the confinement of chains in cylindrical tubes. We also briefly discuss the problem of a free or grafted star polymer interacting with a single wall, and show that the dependence of confining force on the functionality of the star is different for a star confined in a nanoslit and a star interacting with a single wall, which is due to the absence of a symmetry plane in the latter case.Comment: 15 pages, 9 figures, LaTeX, to appear in Soft Matte

Do crossover functions depend on the shape of the interaction profile?

We examine the crossover from classical to non-classical critical behaviour in two-dimensional systems with a one-component order parameter. Since the degree of universality of the corresponding crossover functions is still subject to debate, we try to induce non-universal effects by adding interactions with a second length scale. Although the crossover functions clearly depend on the range of the interactions, they turn out to be remarkably robust against further variation of the interaction profile. In particular, we find that the earlier observed non-monotonic crossover of the effective susceptibility exponent occurs for several qualitatively different shapes of this profile.Comment: 7 pages + 4 PostScript figures. Accepted for publication in Europhysics Letters. Also available as PDF file at http://www.cond-mat.physik.uni-mainz.de/~luijten/erikpubs.htm

From SN 2010da to NGC 300 ULX-1: Ten Years of Observations of an Unusual High Mass X-Ray Binary in NGC 300

In May 2010, an intermediate luminosity optical transient was discovered in the nearby galaxy NGC 300 by a South African amateur astronomer. In the decade since its discovery, multi-wavelength observations of the misnamed “SN 2010da” have continually reshaped our understanding of this high mass X-ray binary system. In this review, we present an overview of the multi-wavelength observations and attempt to understand the 2010 transient event, and later, the reclassification of this system as NGC 300 ULX-1: a red supergiant + neutron star ultraluminous X-ray source

Coupled Fluctuations near Critical Wetting

Recent work on the complete wetting transition has emphasized the role played by the coupling of fluctuations of the order parameter at the wall and at the depinning fluid interface. Extending this approach to the wetting transition itself we predict a novel crossover effect associated with the decoupling of fluctuations as the temperature is lowered towards the transition temperature T_W. Using this we are able to reanalyse recent Monte-Carlo simulation studies and extract a value \omega(T_W)=0.8 at T_W=0.9T_C in very good agreement with long standing theoretical predictions.Comment: 4 pages, LaTex, 1 postscript figur

Spin transport in magnetic multilayers

We study by extensive Monte Carlo simulations the transport of itinerant spins travelling inside a multilayer composed of three ferromagnetic films antiferromagnetically coupled to each other in a sandwich structure. The two exterior films interact with the middle one through non magnetic spacers. The spin model is the Ising one and the in-plane transport is considered. Various interactions are taken into account. We show that the current of the itinerant spins going through this system depends strongly on the magnetic ordering of the multilayer: at temperatures $T$ below (above) the transition temperature $T_c$, a strong (weak) current is observed. This results in a strong jump of the resistance across $T_c$. Moreover, we observe an anomalous variation, namely a peak, of the spin current in the critical region just above $T_c$. We show that this peak is due to the formation of domains in the temperature region between the low-$T$ ordered phase and the true paramagnetic disordered phase. The existence of such domains is known in the theory of critical phenomena. The behavior of the resistance obtained here is compared to a recent experiment. An excellent agreement with our physical interpretation is observed. We also show and discuss effects of various physical parameters entering our model such as interaction range, strength of electric and magnetic fields and magnetic film and non magnetic spacer thicknesses.Comment: 8 pages, 17 figures, submitted to J. Phys.: Cond Matte

Critical behavior of colloid-polymer mixtures in random porous media

We show that the critical behavior of a colloid-polymer mixture inside a random porous matrix of quenched hard spheres belongs to the universality class of the random-field Ising model. We also demonstrate that random-field effects in colloid-polymer mixtures are surprisingly strong. This makes these systems attractive candidates to study random-field behavior experimentally.Comment: 4 pages, 3 figures, to appear in Phys. Rev. Let