A Study of the Slow Release of Urea from Microcapsules with TDI as the Wall-Sealing Treatment

The release of urea from ethylcellulose coated microcapsules was efficiently reduced by post-treatment with toluene-2,4-diisocyanate (TDI) in n-hexane. Our results show that TDI can be used as a sealant which modifies the shell characteristics of the ethylcellulose film. The modification is rather complicated in that it probably includes cross-linking between ethylcellulose and TDI, a reaction between urea and TDI, and biuret or polyurea formation from TDI absorbed on the microcapsules surface with moisture. The influence of post-treated conditions on the release of urea from ethylcellulose shell was studied.     

Liquid-Crystalline Behaviour in the n-Alkyl Gluconamides and Other Related Carbohydrates

Many alkyl derivatives of carbohydrates are used as detergents for cell wall membranes. This study describes the liquid-crystalline properties of a number of these systems. The combination of a hydrophilic carbohydrate moiety and a hydrophobic aliphatic substituent leads to the formation of both thermotropic and lyotropic liquid-crystal mesophases. Materials with this structural combination are suspected to form interdigitated bilayer smectic A phases. The central core region of the layer is held together by dynamic hydrogen-bonding between the neighbouring carbohydrate moieties, whereas the terminal aliphatic chains create fluidity between layers.     

Dynamical multiple-time stepping methods for overcoming resonance instabilities

Current molecular dynamics simulations of biomolecules using multiple time steps to update the slowly changing force are hampered by instabilities beginning at time steps near the half period of the fastest vibrating mode. These "resonance" instabilities have became a critical barrier preventing the long time simulation of biomolecular dynamics. Attempts to tame these instabilities by altering the slowly changing force and efforts to damp them out by Langevin dynamics do not address the fundamental cause of these instabilities. In this work, we trace the instability to the nonanalytic character of the underlying spectrum and show that a correct splitting of the Hamiltonian, which renders the spectrum analytic, restores stability. The resulting Hamiltonian dictates that in addition to updating the momentum due to the slowly changing force, one must also update the position with a modified mass. Thus multiple-time stepping must be done dynamically.     

Four novel lignans from Rodgersia podophylla

Four novel lignans were isolated from the rhizomes of Rodgersia podophylla. It is interesting to note that an unusual 2,4-dihydroxyphenyl moiety was found in these compounds in addition to an acetylenic functionality in compounds 3 and 4.     

Crossover from a molecular Bose-Einstein condensate to a degenerate Fermi gas

We demonstrate a reversible conversion of a 6Li2 molecular Bose-Einstein condensate to a degenerate Fermi gas of atoms by adiabatically crossing a Feshbach resonance. By optical in situ imaging, we observe a smooth change of the cloud size in the crossover regime. On the Feshbach resonance, the ensemble is strongly interacting and the measured cloud size is 75(7)% of the one of a noninteracting zero-temperature Fermi gas. The high condensate fraction of more than 90% and the adiabatic crossover suggest our Fermi gas to be cold enough to form a superfluid.     

Experimental evaluation of a non-linear coded excitation method for contrast imaging

Previously, we have shown that for a single bubble, using chirps as the excitation signal improves both the linear and the non-linear response. Computer simulations of randomly distributed contrast agent bubbles show an increase of 10-13 dB in response when comparing pulse excitations with chirp excitations that have equal bandwidths and peak amplitudes. Second harmonic compression of simulated bubble echoes with chirp excitation shows low side-lobe levels and limited loss of axial resolution when compared to pulse excitation. Experimental results from water tank measurements with SonoVue contrast agent are in agreement with computer simulations showing increased signal-to-noise ratio and an increase of approximately 12 dB at the second harmonic when comparing pulse and chirp excitation.     

Multi-parameter characterization of the longitudinal plasma profile of a filament: a comparative study

The longitudinal plasma profile of a laboratory scale filament induced by the propagation of an intense femtosecond laser pulse in air was measured simultaneously by three different methods. Each of them is based on a specific property of the filament, including electromagnetic pulse emission, backward emitted nitrogen fluorescence, and acoustic wave generation. Although each of above methods has been separately reported, it is the first time that a simultaneous multi-parameter measurement on a laser filament is presented. Such multiparameter measurement allows a direct comparison between the different methods, and a better understating of the dynamics of a filament from its generation through multi-photon/tunnel ionization (MPI/TI) to its damping through acoustic wave emission. The advantages as well as drawbacks of each method are analyzed in a comparative way. PACS 42.65.Jx; 42.68.Ay; 42.68.Wt     

Further evidence of dimer emission from superradiant travelling wave laser of concentrated aqueous solution of rhodamine 6G and B

The new emission bands of the superradiant travelling-wave lasers from concentrated aqueous rhodamine B and rhodamine 6G were quenched by the addition of a small amount of triton X-100. This further supports the hypothesis that the new emission band could be due to the dimers of the dyes.