A Robust Cross-Linking Strategy for Block Copolymer Worms Prepared via Polymerization-Induced Self-Assembly

A poly(glycerol monomethacrylate) (PGMA) chain transfer agent is chain-extended by reversible addition-fragmentation chain transfer (RAFT) statistical copolymerization of 2-hydroxypropyl methacrylate (HPMA) with glycidyl methacrylate (GlyMA) in concentrated aqueous solution via polymerization-induced self-assembly (PISA). A series of five free-standing worm gels is prepared by fixing the overall degree of polymerization of the core-forming block at 144 while varying its GlyMA content from 0 to 20 mol %. 1H NMR kinetics indicated that GlyMA is consumed much faster than HPMA, producing a GlyMA-rich sequence close to the PGMA stabilizer block. Temperature-dependent oscillatory rheological studies indicate that increasing the GlyMA content leads to progressively less thermoresponsive worm gels, with no degelation on cooling being observed for worms containing 20 mol % GlyMA. The epoxy groups in the GlyMA residues can be ring-opened using 3-aminopropyltriethoxysilane (APTES) in order to prepare core cross-linked worms via hydrolysis-condensation with the siloxane groups and/or hydroxyl groups on the HPMA residues. Perhaps surprisingly, 1H NMR analysis indicates that the epoxy-amine reaction and the intermolecular cross-linking occur on similar time scales. Cross-linking leads to stiffer worm gels that do not undergo degelation upon cooling. Dynamic light scattering studies and TEM analyses conducted on linear worms exposed to either methanol (a good solvent for both blocks) or anionic surfactant result in immediate worm dissociation. In contrast, cross-linked worms remain intact under such conditions, provided that the worm cores comprise at least 10 mol % GlyMA

Fermi Surface of the Electron-doped Cuprate Superconductor Nd_{2-x}Ce_xCuO_{4} Probed by High-Field Magnetotransport

We report on the study of the Fermi surface of the electron-doped cuprate superconductor Nd$_{2-x}$Ce$_x$CuO$_{4}$ by measuring the interlayer magnetoresistance as a function of the strength and orientation of the applied magnetic field. We performed experiments in both steady and pulsed magnetic fields on high-quality single crystals with Ce concentrations of $x=0.13$ to 0.17. In the overdoped regime of $x > 0.15$ we found both semiclassical angle-dependent magnetoresistance oscillations (AMRO) and Shubnikov-de Haas (SdH) oscillations. The combined AMRO and SdH data clearly show that the appearance of fast SdH oscillations in strongly overdoped samples is caused by magnetic breakdown. This observation provides clear evidence for a reconstructed multiply-connected Fermi surface up to the very end of the overdoped regime at $x\simeq 0.17$. The strength of the superlattice potential responsible for the reconstructed Fermi surface is found to decrease with increasing doping level and likely vanishes at the same carrier concentration as superconductivity, suggesting a close relation between translational symmetry breaking and superconducting pairing. A detailed analysis of the high-resolution SdH data allowed us to determine the effective cyclotron mass and Dingle temperature, as well as to estimate the magnetic breakdown field in the overdoped regime.Comment: 23 pages, 8 figure

Reflections on undertaking the Probation Qualifying Framework scheme during the transforming rehabilitation changes

This article reflects upon the author’s experience of undertaking the PQF (Probation Qualifying Framework) training scheme during the chaotic period of Transforming Rehabilitation. The author asserts that the uncertainty and precarious nature of the changes were detrimental to an effective learning environment, which ultimately promoted a practice culture of punitiveness and control and did not allow learners the space to be skilful and confident practitioners, comfortable working autonomously. Furthermore, the author contends there is an emerging culture within the NPS (National Probation Service) increasingly fostered on ‘risk management’, which is reflected in the vocational nature of PQF training and is contributing towards a widening cultural gap that is emerging between the community rehabilitation companies and NPS

Exploring attitudes to edgy urban destinations: the case of Deptford, London

The role of tourists and tourism in urban development is not fully understood. Research has focused on tourism districts within city centres, but less is known about tourism in peripheral, less affluent urban districts. These areas can appeal to visitors as edgy alternatives to mainstream destinations. This study establishes who is interested in visiting and why, and it explores the underlying rationale for negative attitudes. The aims are addressed by an in-depth analysis of Deptford in South East London. This area is a relatively deprived part of a world city, albeit one that has long been earmarked as London's next cool district. The study uses a mix of different sources to analyse the case. Responses to a New York Times article on Deptford are analysed and the attitudes of actual visitors and key stakeholders are explored. The discussion includes an examination of different interpretations and attitudes towards the notion of edginess. Edginess is deemed attractive by certain audiences; something linked to a reverence for working-class life in the arts. The study concludes that, whilst edginess is a noted characteristic, what people appreciate about Deptford is its ‘distinctive ordinariness’ – its contrast with more polished and contrived urban districts

Spatial Correlation of Conduction Electrons in Metal with Complicated Geometry Of The Fermi Surface

The "density-density" correlation function of conduction electrons in metal is investigated. It is shown, that the asymptotic behaviour of the CF depends on the shape and the local geometry of the Fermi surface. In particular, the exponent of power law which describes the damping of Friedel oscillations at large r (-4 for an isotropic Fermi gas) is determined by local geometry of the FS. The applications of the obtained results to calculations of the CF in a metal near the electron topological transition and of the RKKY exchange integral are considered as well.Comment: 12 pages, LaTeX, 5 figures upon request (to appear in J.Phys.:CM, 1993

Spectral properties of interacting magnetoelectric particles

The linear magnetoelectric (ME) effect provides a special route for linking magnetic and electric properties. In microwaves, a local ME effect appears due to the dynamical symmetry breakings of magnetic-dipolar modes (MDMs) in a ferrite disk particle. The fact that for MDMs in a ferrite disk one has evident both classical and quantum-like attributes, puts special demands on the methods used for study of interacting ME particles. A proper model for coupled particles should be based on the spectral characteristics of MDM oscillations and an analysis of the overlap integrals for interacting eigen oscillating ME elements. In this paper, we present theoretical studies of spectral properties of literally coupled of MDM ME disks. We show that there exists the "exchange" mechanism of interaction between the particles, which is distinctive from the magnetostatic interaction between magnetic dipoles. The spectral method proposed in this paper may further the development of a theory of ME "molecules" and realization of local ME composites.Comment: 26 pages, 3 figure

Importance of Correlation Effects on Magnetic Anisotropy in Fe and Ni

We calculate magnetic anisotropy energy of Fe and Ni by taking into account the effects of strong electronic correlations, spin-orbit coupling, and non-collinearity of intra-atomic magnetization. The LDA+U method is used and its equivalence to dynamical mean-field theory in the static limit is emphasized. Both experimental magnitude of MAE and direction of magnetization are predicted correctly near U=4 eV for Ni and U=3.5 eV for Fe. Correlations modify one-electron spectra which are now in better agreement with experiments.Comment: 4 pages, 2 figure

A preliminary investigation into the restorative potential of public aquaria exhibits: a UK student-based study

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