A simple model for a two-stage chemical reaction with diffusion

We analyse the evolution of a two-stage chemical reaction betweentwo neighbouring plumes of reactants. Under the assumption thatthe plumes are approximately Gaussian we derive a system ofordinary differential equations for the total amount, the centroidand the variance of each reactant. We compare the solution ofthese equations with full numerical simulation of the reaction.Excellent agreement is obtained, with solution of the near-Gaussianmodel requiring considerably less computational effort thanthe full simulations. Of key importance is the yield of thereaction, and we discuss this feature in particular.     

Preparation and characterization of cross-linked hyaluronan nanoparticles

The present investigation describes the synthesis and characterization of novel biodegradable nanoparticles based on hyaluronic acid (HA). The diamine, 2,2′(ethylenedioxy)bis(ethylamine) was used for cross-linking of the HA linear chains. The condensation reaction of amino groups and pendant carboxyl groups of HA was performed in aqueous media at room temperature using water-soluble carbodiimide. The prepared nanosystems, aqueous solutions, or dispersions of nanoparticles were stable, transparent, or mildly opalescent systems depending on the ratio of cross-linking, findings consistent with values of transmittance above 77%. The structure of products was determined by nuclear magnetic resonance spectroscopy, and the particle size was identified by laser light scattering (DLS) and transmission electron microscopy (TEM) measurements. Particle size measured by TEM varied less than 130 nm; in the swollen state, the average size of the particles measured by DLS was in the range of 30–140 nm depending on the ratio of cross-linking and the molecular weight of HA. Formation of cross-linked nanoparticles results in a viscosity drop compared to the viscosity of the corresponding solution of the HA, and this trend becomes decreasingly appreciable as the molecular weight of HA decreases.     

Zero modes for the boundary giant magnons

We study the fermion zero-mode dynamics for open strings ending on the giant graviton branes. For the open string ending on the Z=0$Z=0$ brane, the quantization of the fermion zero-modes of boundary giant magnons reproduces the 256 states of the boundary degrees with the precise realization of the SU(2|2)×SU(2|2)$\mathit{SU}(2|2)\times \mathit{SU}(2|2)$ symmetry algebra. Also for the open string ending on the Y=0$Y=0$ brane, we reproduce the unique vacuum state from the fermion zero-modes.     

Surface reconstruction: A physical realization of two-dimensional Ising and XY-models

The reconstruction transitions on certain clean metal surfaces are shown to be isomorphous with two-dimensional models of phase transitions. Specifically, the Pt, Ir, and Au(110) transitions correspond to the 2d-Ising model, the W(100) transition to the 2d?XY model with cubic anisotropy. The Mo (100) reconstruction is described in terms of the Kosterlitz-Thouless picture of the 2d-XY model. Experiments (LEED or He diffraction) are suggested to check theories of 2d systems.     

On the structure of phenylisocyanide

Microwave spectra of phenylisocyanide,

(I), 2-D-phenylisocyanide, 2,4-D₂-phenylisocyanide, and 2,4,6-D₃-phenylisocyanide were recorded and analyzed. Assuming the structural identity of the C₆H(3)H(4)H(5) fragments of I and of phenylcyanide (II). A C(1)-N distance of 1.410 Å and an

distance of 1.142 Å followed. The effects of changing some of the assumptions are discussed.     

Rotational spectra of isotopic di-thioformic acids with a structure of trans HCSSH: Ab initio estimates of cis/trans structures,energies, dipole moments,and torsional barrier

Microwave transitions (18.6–40 GHz) of ground-level trans HC³⁴S³²SH, HC³²S³⁴SH, HC³²S³²S²H and of cis HC³²S³²S²H have been observed and assigned. Rotational and distortion constants have been calculated. These data with earlier data for trans/cis HC³²S³²SH are not sufficient to fix an r_s or r₀ structure for trans HCSSH. Instead, an “iterative” structure of trans HCSSH has been derived making full use of all data obtained for isotopic trans species. An ab initio estimate of the geometry of trans HCSSH agrees with the iterative structure within expectation. This also holds for the calculated energy difference ?(cis) - ?(trans) and for calculated dipole moment components μ_a along the a axis of least moment of inertia.     

Scale dependent dimension of luminous matter in the universe

We suggest a geometrical model for the distribution of luminous matter in the Universe, where the apparent dimension, D(l), increases linearly with the logarithm of the scale l. Beyond the correlation length, xi, the Universe is homogeneous, and D = 3. Comparison with data from the SARS redshift catalog, and the LEDA database provides a good fit with a correlation length xi approximately 300 Mpc. This type of scaling structure was recently discovered in a simple reaction-diffusion "forest-fire" model, indicating a broad class of scaling phenomena.