3+1D hydrodynamic simulation of relativistic heavy-ion collisions

We present MUSIC, an implementation of the Kurganov-Tadmor algorithm for relativistic 3+1 dimensional fluid dynamics in heavy-ion collision scenarios. This Riemann-solver-free, second-order, high-resolution scheme is characterized by a very small numerical viscosity and its ability to treat shocks and discontinuities very well. We also incorporate a sophisticated algorithm for the determination of the freeze-out surface using a three dimensional triangulation of the hyper-surface. Implementing a recent lattice based equation of state, we compute p_T-spectra and pseudorapidity distributions for Au+Au collisions at root s = 200 GeV and present results for the anisotropic flow coefficients v_2 and v_4 as a function of both p_T and pseudorapidity. We were able to determine v_4 with high numerical precision, finding that it does not strongly depend on the choice of initial condition or equation of state.Comment: 16 pages, 11 figures, version accepted for publication in PRC, references added, minor typos corrected, more detailed discussion of freeze-out routine adde

A new class of quantum bound states: diprotons in extreme magnetic fields

This paper considers the possibility that two charged particles with an attractive short-ranged potential between them which is not strong enough to form bound states in free space, may bind in uniform magnetic fields. It is shown that in the formal limit where Coulomb repulsion is negligible (q -> 0 and B_0 -> \infty with q B_0 fixed where q is the charge and B_0 the field strength) there always exists a bound state for a system of two identical charged particles in a constant magnetic field, provided that there is a short-range uniformly attractive potential between them. Moreover, it is shown that in this limit {\it any} potential with an attractive s-wave scattering length will posses bound states provided that the range of the potential is much smaller than the characteristic magnetic length, r_0 = (\frac{q B_0}{4})^{-1/2}. For this case, the binding is computed numerically. We estimate the size of the magnetic field needed to approximately reach a regime where the formal limit considered becomes a good approximation to the dynamics. These numerical estimates indicate that two protons in an extremely strong magnetic field such as might be found in a magnetar will bind to form a diproton

Capillary origami: spontaneous wrapping of a droplet with an elastic sheet

The interaction between elasticity and capillarity is used to produce three dimensional structures, through the wrapping of a liquid droplet by a planar sheet. The final encapsulated 3D shape is controlled by tayloring the initial geometry of the flat membrane. A 2D model shows the evolution of open sheets to closed structures and predicts a critical length scale below which encapsulation cannot occur, which is verified experimentally. This {\it elastocapillary length} is found to depend on the thickness as $h^{3/2}$, a scaling favorable to miniaturization which suggests a new way of mass production of 3D micro- or nano-scale objects.Comment: 5 pages, 5 figure

Spin-guides and spin-splitters: Waveguide analogies in one-dimensional spin chains

Here we show a direct mapping between waveguide theory and spin chain transport, opening an alternative approach to quantum information transport in the solid-state. By applying temporally varying control profiles to a spin chain, we design a virtual waveguide or 'spin-guide' to conduct individual spin excitations along defined space-time trajectories of the chain. We explicitly show that the concepts of confinement, adiabatic bend loss and beamsplitting can be mapped from optical waveguide theory to spin-guides (and hence 'spin-splitters'). Importantly, the spatial scale of applied control pulses is required to be large compared to the inter-spin spacing, and thereby allowing the design of scalable control architectures.Comment: 5 figure

Differential Form of the Collision Integral for a Relativistic Plasma

The differential formulation of the Landau-Fokker-Planck collision integral is developed for the case of relativistic electromagnetic interactions.Comment: Plain TeX, 5 page

Decay of a superfluid current of ultra-cold atoms in a toroidal trap

Using a numerical implementation of the truncated Wigner approximation, we simulate the experiment reported by Ramanathan et al. in Phys. Rev. Lett. 106, 130401 (2011), in which a Bose-Einstein condensate is created in a toroidal trap and set into rotation via a phase imprinting technique. A potential barrier is then placed in the trap to study the decay of the superflow. We find that the current decays via thermally activated phase slips, which can also be visualized as vortices crossing the barrier region in the radial direction. Adopting the notion of critical velocity used in the experiment, we determine it to be lower than the local speed of sound at the barrier, in contradiction to the predictions of the zero-temperature Gross-Pitaevskii equation. We map out the superfluid decay rate and critical velocity as a function of temperature and observe a strong dependence. Thermal fluctuations offer a partial explanation of the experimentally observed reduction of the critical velocity from the phonon velocity.Comment: 15 pages. 11 figure

Beating patterns of filaments in viscoelastic fluids

Many swimming microorganisms, such as bacteria and sperm, use flexible flagella to move through viscoelastic media in their natural environments. In this paper we address the effects a viscoelastic fluid has on the motion and beating patterns of elastic filaments. We treat both a passive filament which is actuated at one end, and an active filament with bending forces arising from internal motors distributed along its length. We describe how viscoelasticity modifies the hydrodynamic forces exerted on the filaments, and how these modified forces affect the beating patterns. We show how high viscosity of purely viscous or viscoelastic solutions can lead to the experimentally observed beating patterns of sperm flagella, in which motion is concentrated at the distal end of the flagella

Hyperinsulinism Caused by Paternal-Specific Inheritance of a Recessive Mutation in the Sulfonylurea-Receptor Gene

Neonatal hyperinsulinism (HI) is a genetic disorder of pancreatic b-cells characterized by failure to suppress insulin secretion in the presence of hypoglycemia, resulting in brain damage or death if not adequately treated. Germline mutations in four genes have been associated with HI. Some patients have focal regions of b-cell proliferation (focal HI). Seventy HI probands in whom at least one S U R - 1 mutation was identified were studied. Clinical data from patients with two S U R - 1 mutant alleles were compared with those from patients with single paternally inherited mutations. Thirtyseven probands were homozygous or compound heterozygous for S U R - 1 mutations. In 33 probands, only a single mutation was identified, and in 31, the parental origin of the proband could be determined; in 29, the mutation was on the paternal allele (P \u3c 0.0002). For three of these, pancreatic tissue was available and showed focal b-cell hyperplasia. DNA extracted from the focal lesion and adjacent normal pancreas revealed loss of the maternal chromosome 11p15, resulting in reduction to homozygosity for the S U R - 1 mutation within the focal lesion only. Using the Tdt-mediated dUTP nick end labeling (TUNEL) reaction, apoptotic b-cells were identified exclusively within the focal region. At diagnosis, disease severity was similar in patients with paternally inherited mutations and those with two mutations. For patients who did not undergo surgery, those with only paternal mutations entered clinical remission within 16 ± 6.2 months, compared with 48 ± 23 months for those with two S U R - 1 mutations (P = 0.001). In conclusion, we identified a novel mechanism to explain the pathophysiology of focal HI and provide evidence to suggest that this entity may be self-limiting, since affected b-cells undergo apoptosis

Folding Langmuir Monolayers

The maximum pressure a two-dimensional surfactant monolayer is able to withstand is limited by the collapse instability towards formation of three-dimensional material. We propose a new description for reversible collapse based on a mathematical analogy between the formation of folds in surfactant monolayers and the formation of Griffith Cracks in solid plates under stress. The description, which is tested in a combined microscopy and rheology study of the collapse of a single-phase Langmuir monolayer of 2-hydroxy-tetracosanoic acid (2-OH TCA), provides a connection between the in-plane rheology of LM's and reversible folding

Vortices and Ring Solitons in Bose-Einstein Condensates

The form and stability properties of axisymmetric and spherically symmetric stationary states in two and three dimensions, respectively, are elucidated for Bose-Einstein condensates. These states include the ground state, central vortices, and radial excitations of both. The latter are called ring solitons in two dimensions and spherical shells in three. The nonlinear Schrodinger equation is taken as the fundamental model; both extended and harmonically trapped condensates are considered. It is found that the presence of a vortex stabilizes ring solitons in a harmonic trap, in contrast to the well known instability of such solutions in the optics context. This is the first known example of a dark soliton in the cubic nonlinear Schrodinger equation which is stable in a number of dimensions greater than one.Comment: 15 pages, 9 figures -- final versio