On the stability and growth of single myelin figures

Myelin figures are long thin cylindrical structures that typically grow as a dense tangle when water is added to the concentrated lamellar phase of certain surfactants. We show that, starting from a well-ordered initial state, single myelin figures can be produced in isolation thus allowing a detailed study of their growth and stability. These structures grow with their base at the exposed edges of bilayer stacks from which material is transported into the myelin. Myelins only form and grow in the presence of a driving stress; when the stress is removed, the myelins retract.Comment: 4 pages, 8 figures. Revised version, 1 new figure, additional reference

A new interpretation for the Ds2∗(2573)D^*_{s2}(2573) and the prediction of novel exotic charmed mesons

In this manuscript we study the vector - vector interaction within the hidden gauge formalism in a coupled channel unitary approach. In the sector $C=1,S=1,J=2$ we get a pole in the T-matrix around $2572$ MeV that we identify with the $D^*_{s2}(2573)$, coupling strongly to the $D^*K^*$($D^*_s\phi$($\omega$)) channels. In addition we obtain resonances in other exotic sectors which have not been studied before such as $C=1,S=-1$, $C=2,S=0$ and $C=2,S=1$. This 'flavor-exotic' states are interpreted as $D^*\bar{K^*}$, $D^*D^*$ and $D^*_sD^*$ molecular states but have not been observed yet. In total we obtain nine states with different spin, isospin, charm and strangeness of non $C=0,S=0$ and $C=1,S=0$ character, which have been reported before

Instability of Myelin Tubes under Dehydration: deswelling of layered cylindrical structures

We report experimental observations of an undulational instability of myelin figures. Motivated by this, we examine theoretically the deformation and possible instability of concentric, cylindrical, multi-lamellar membrane structures. Under conditions of osmotic stress (swelling or dehydration), we find a stable, deformed state in which the layer deformation is given by \delta R ~ r^{\sqrt{B_A/(hB)}}, where B_A is the area compression modulus, B is the inter-layer compression modulus, and h is the repeat distance of layers. Also, above a finite threshold of dehydration (or osmotic stress), we find that the system becomes unstable to undulations, first with a characteristic wavelength of order \sqrt{xi d_0}, where xi is the standard smectic penetration depth and d_0 is the thickness of dehydrated region.Comment: 5 pages + 3 figures [revtex 4

Low Mass Dimuons Produced in Relativistic Nuclear Collisions

The NA60 experiment has measured low-mass muon pair production in In-In collisions at 158 A GeV with unprecedented precision. We show that this data is reproduced very well by a dynamical model with parameters scaled from fits to measurements of hadronic transverse mass spectra and Hanbury-Brown and Twiss correlations in Pb-Pb and Pb-Au collisions at the same energy. The data is consistent with in-medium properties of $\rho$ and $\omega$-mesons at finite temperature and density as deduced from empirical forward-scattering amplitudes. Inclusion of the vacuum decay of the $\rho$-meson after freeze-out is necessary for an understanding of the mass and transverse momentum spectrum of dimuons with M \apprle 0.9 {\rm GeV}/c^2.Comment: 4 pages, 3 figures, updated hadronic analysi

Kinetic pathways of multi-phase surfactant systems

The relaxation following a temperature quench of two-phase (lamellar and sponge phase) and three-phase (lamellar, sponge and micellar phase) samples, has been studied in an SDS/octanol/brine system. In the three-phase case we have observed samples that are initially mainly sponge phase with lamellar and micellar phase on the top and bottom respectively. Upon decreasing temperature most of the volume of the sponge phase is replaced by lamellar phase. During the equilibriation we have observed three regimes of behaviour within the sponge phase: (i) disruption in the sponge texture, then (ii) after the sponge phase homogenises there is a lamellar nucleation regime and finally (iii) a bizarre plume connects the lamellar phase with the micellar phase. The relaxation of the two-phase sample proceeds instead in two stages. First lamellar drops nucleate in the sponge phase forming a onion `gel' structure. Over time the lamellar structure compacts while equilibriating into a two phase lamellar/sponge phase sample. We offer possible explanatioins for some of these observations in the context of a general theory for phase kinetics in systems with one fast and one slow variable.Comment: 1 textfile, 20 figures (jpg), to appear in PR

Modification of scattering lengths via magnetic dipole-dipole interactions

We propose a new mechanism for tuning an atomic s-wave scattering length. The effect is caused by virtual transitions between different Zeeman sublevels via magnetic dipole-dipole interactions. These transitions give rise to an effective potential, which, in contrast to standard magnetic interactions, has an isotropic component and thus affects s-wave collisions. Our numerical analysis shows that for chromium-50 the scattering length can be modified up to 15 %.Comment: revtex, 4 pages, 3 figure

Fermion Systems in Discrete Space-Time Exemplifying the Spontaneous Generation of a Causal Structure

As toy models for space-time on the Planck scale, we consider examples of fermion systems in discrete space-time which are composed of one or two particles defined on two up to nine space-time points. We study the self-organization of the particles as described by a variational principle both analytically and numerically. We find an effect of spontaneous symmetry breaking which leads to the emergence of a discrete causal structure.Comment: 37 pages, LaTeX, 12 figures, minor changes (published version

High-harmonic generation from arbitrarily oriented diatomic molecules including nuclear motion and field-free alignment

We present a theoretical model of high-harmonic generation from diatomic molecules. The theory includes effects of alignment as well as nuclear motion and is used to predict results for N$_2$, O$_2$, H$_2$ and D$_2$. The results show that the alignment dependence of high-harmonics is governed by the symmetry of the highest occupied molecular orbital and that the inclusion of the nuclear motion in the theoretical description generally reduces the intensity of the harmonic radiation. We compare our model with experimental results on N$_2$ and O$_2$, and obtain very good agreement.Comment: 12 pages, 8 figures, 2 tables; legends revised on Figs. 1,3,4,6 and