Coupling and memory in liquid crystal elastomers

The polymer backbone of a side-chain liquid crystal polymer exhibits an anisotropic shape due to the coupling of the liquid crystal orientational order of the mesogenic side-chains to the backbone. The magnitude and sign of this coupling may be controlled by chemical design. The introduction of chemical cross-links in to such a system provides both a memory of the anisotropic organisation and a mechanism by which the microscopic anisotropy can be realised at a macroscopic level. We show how this anisotropic network structure yields new phenomena when electric or mechanical fields are applied.     

Two-Step Synthesis of trans-2-Arylcyclopropane Carboxylates with 98–100 % ee by the Use of a Phosphazene Base

Only the axial diastereomer of sulfonium salts 2 are formed upon alkylation of 1 . Deprotonation of 2 results in ylides, which allow the highly enantioselective cyclopropanation of Michael systems. The chiral auxiliary 1 is recovered and can be reused.     

Influence of copolymer composition of polyestercarbonate on miscibility with poly(butylene terephthalate)

Blends of poly(butylene terephthalate) (PBT) and polyestercarbonate (PEC), copolyesters consisting of polycarbonate (PC) and polyarylate (PAr), have been studied by thermal analysis to determine miscibility. The PBT blends with PAr and PEC containing 30 wt % of carbonate unit or less appeared to be miscible, and the tendency for stable single‐phase was observed to decrease as the content of carbonate unit in PEC copolymer increased. As determined with the crystalline phase behavior, the miscibility of PEC with PBT appeared to have a maximum around 10 ∼ 30 wt % of carbonate content in PEC copolymer, and this result was attributed to the internal repulsion effect between ester and carbonate repeating units in PEC copolymer. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 803–811, 2000     

Two-photon sensor for metal ions derived from azacrown ether

A two-photon sensor for the metal ions derived from azacrown ether as the receptor is reported. The sensor emits strong two-photon fluorescence when excited by 800 nm laser photons. Moreover, the binding constants measured by the one- and two-photon fluorescence are similar. This result may be useful for the design of efficient two-photon fluorescence probes for biological substrates.     

Search for flavor-changing-neutral-current d meson decays

We study the flavor-changing-neutral-current process c-->u micro(+) micro(-) using 1.3 fb(-1) of pp[over ] collisions at square root s = 1.96 TeV recorded by the D0 detector operating at the Fermilab Tevatron Collider. We see clear indications of the charged-current mediated D(s)(+) and D(+)-->phipi(+) --> micro(+)micro(-)pi(+) final states with significance greater than 4 standard deviations above background for the D(+) state. We search for the continuum neutral-current decay of D(+)-->pi(+) micro(+) micro(-) in the dimuon invariant mass spectrum away from the phi resonance. We see no evidence of signal above background and set a limit of B(D(+) --> pi(+) micro(+) micro(-))<3.9 x 10(-6) at the 90% C.L. This limit places the most stringent constraint on new phenomena in the c--> u micro(+) micro(-) transition.     

Application of PIV to over-expanded supersonic flows: Possibilities and limits

Two-dimensional velocity distributions outside a Mach 2.0 supersonic nozzle have been investigated using a digital particle im age velocimetry (PIV). Mean velocities , vor ticity field and volume dilatation field were obtained from PIV images using 0 .33 μm titanium dioxide (TiO₂) particle. The seeding particle of larger size , 1.4 μrn Ti0₂, was also used for the experimental comparison of velocity lag downstream of shock waves. The results have been compared and analyzed with schlieren photographs for the locations of shock waves and over-expanded shock structure to inspect possibilities and limits of a PIV technique to over-expanded supersonic flows. It is found that although the quantitative velocity measurement using PIV on over-expanded supersonic flows with large velocity and pressure gradients is limited, the locations of normal shock and oblique shock waves can be resolved by the axial/radial velocity fields, and over-expanded shock structure can be predicted by vorticity field and volume dilatation field which are acquired from the spatial differential of the velocity field.