Self-repairing polymers: poly(dioxaborolane)s containing trigonal planar boron

The molecular weight of poly(dioxaborolane)s can be controlled during the polymerization reaction or through post-polymerization processing in such a manner that hydrolytic damage to these materials may be repaired, thereby regenerating the polymer.     

Coherent and incoherent π0 photoproduction from the deuteron

Differential cross-sections for the reactions d (γ,π⁰)d and d (γ,π⁰)pn have been measured at MAMI with the TAPS detector setup in the energy range 140 MeV < E _γ < 306 MeV. By use of the Glasgow tagging spectrometer an 0.8 MeV energy resolution for photons incident on the target was achieved. The π⁰ missing energy resolution was sufficient for a reliable separation of coherent and incoherent channels. The data for the break-up channel exhibit very strong final state interaction effects, whereas the observed angular dependence of the inclusive process d (γ,π⁰)X is in quantitative agreement with predictions for a quasi-free process. The observed absolute d (γ,π⁰)X cross-sections, on the other hand, are significantly smaller than predicted by the quasi-free process for E _γ >∼ 250 MeV. Associating this failure with the π⁰ photoproduction on the neutron would suggest that its cross-section is up to 25% below the presently believed value. Received: 13 February 2001 / Accepted: 13 April 2001     

Multi component self-assembly: supramolecular organic frameworks containing metal-rotaxane subunits (RSOFs)

A facile, one-pot synthesis of rotaxanated supramolecular organic frameworks (RSOFs) is reported. These systems consist of bis-carboxylate anions threaded through the core of tetraimidazolium macrocycles. Trivalent metal cations, yttrium(III) and smaller lanthanides, are used to "lock" the threaded strut in place. This results in the formation of three-dimensional RSOFs.     

Symmetric inertial-confinement-fusion-capsule implosions in a double-z-pinch-driven hohlraum

An inertial-confinement-fusion (ICF) concept using two 60-MA Z pinches to drive a cylindrical hohlraum to 220 eV has been recently proposed. The first capsule implosions relevant to this concept have been performed at the same physical scale with a lower 20-MA current, yielding a 70+/-5 eV capsule drive. The capsule shell shape implies a polar radiation symmetry, the first high-accuracy measurement of this type in a pulsed-power-driven ICF configuration, within a factor of 1.6-4 of that required for scaling to ignition. The convergence ratio of 14-21 is to date the highest in any pulsed-power ICF system.     

Thiazolidine-based organocatalysts for a highly enantioselective direct aldol reaction

A set of enantiopure thiazolidine-based organocatalysts have been synthesized from l-cysteine, in a straightforward manner allowing numerous structural variations. In particular, organocatalyst 3a exhibits the highest catalytic performance working in an aqueous medium. It catalyzed the direct catalytic asymmetric intermolecular aldol reaction between unmodified ketones and an aldehyde with excellent stereocontrol and furnished the corresponding aldol products in up to 99% ee. Compound 3a also showed excellent asymmetric catalytic activity in the asymmetric Michael reaction (up to 99% ee).     

Self‐Assembly of the Cyclic Lipopeptide Daptomycin: Spherical Micelle Formation Does Not Depend on the Presence of Calcium Chloride

The cyclic lipopeptide Daptomycin, used as a treatment for infections where antimicrobial resistance is observed, is shown to self‐assemble into spherical micelles above a critical aggregation concentration. Micelles are observed either in the absence or presence of CaCl₂, in contrast to claims in the literature that CaCl₂ is required for micellization.     

Anion-directed assembly of a three-dimensional metal-organic rotaxane framework

A three-dimensional extended, metal-organic rotaxane framework (MORF) that incorporates encircled "struts" has been synthesized through a one-pot self-assembly process involving a macrocyclic tetraimidazolium "molecular box", naphthalene dicaboxylate dianion, and Zn(II) cations. The present system represents progress towards controlling the features of three-dimensional metal-organic frameworks.     

Controlled transport and focusing of laser-accelerated protons with miniature magnetic devices

This Letter demonstrates the transporting and focusing of laser-accelerated 14 MeV protons by permanent magnet miniature quadrupole lenses providing field gradients of up to 500 T/m. The approach is highly reproducible and predictable, leading to a focal spot of (286 x 173) microm full width at half maximum 50 cm behind the source. It decouples the relativistic laser-proton acceleration from the beam transport, paving the way to optimize both separately. The collimation and the subsequent energy selection obtained are perfectly applicable for upcoming high-energy, high-repetition rate laser systems.     

Demonstration of radiation symmetry control for inertial confinement fusion in double Z-pinch hohlraums

Simulations of a double Z-pinch hohlraum, relevant to the high-yield inertial-confinement-fusion concept, predict that through geometry design the time-integrated P2 Legendre mode drive asymmetry can be systematically controlled from positive to negative coefficient values. Studying capsule elongation, recent experiments on Z confirm such control by varying the secondary hohlraum length. Since the experimental trend and optimum length are correctly modeled, confidence is gained in the simulation tools; the same tools predict capsule drive uniformity sufficient for high-yield fusion ignition.