Effect of Stretching on the Structure of Cylinder- and Sphere-Forming Styrene-Isoprene-Styrene Block Copolymers

Two styrene-isoprene-styrene block copolymers Vector 4111 and 4113, exhibiting cylindrical (18 wt % PS) and spherical (16 wt % PS) morphology, respectively, have been examined under uniaxial elongation up to 200% strain. On the basis of stress-strain data, mechanical properties are compared for isotropic and oriented polystyrene domains. The structure at various stages of deformation has been determined from SAXS patterns in three planes and two principal deformation directions with respect to orientation. Samples showed a very high degree of hexagonal packing, resulting in an X-ray pattern taken parallel to the cylinder alignment approaching single crystal ordering. Cylinders were aligned with the closest packed planes parallel to film surface. Particular attention has been paid to a lattice deformation process occurring during the first stretching and relaxation cycle. For a copolymer with oriented cylindrical morphology the deformation was affine up to 120% strain. The microdomain spacing was calculated parallel and perpendicular to the stretching direction. The cylindrical microstructure orientation, quantified by Hermans' orientation factor reduced during elongation of oriented polymer, while the elongation of isotropic sample caused an increase of orientation. Deformation of all studied morphologies was reversible.

Block copolymers of ethylene oxide and phenyl glycidyl ether: micellization, gelation, and drug solubilization

Three triblock copolymers of ethylene oxide and phenyl glycidyl ether, type E(m)G(n)E(m), where G = OCH2-CH(CH2OC6H5) and E = OCH2CH2, were synthesized and characterized by gel-permeation chromatography, matrix-assisted laser desorption ionization time-of-flight mass spectrometry, and NMR spectroscopy. Their association properties in aqueous solution were investigated by surface tensiometry and light scattering, yielding values of the critical micelle concentration (cmc), the hydrodynamic radius, and the association number. Gel boundaries in concentrated micellar solution were investigated by tube inversion, and for one copolymer, the temperature and frequency dependence of the dynamic moduli served to confirm and extend the phase diagram and to highlight gel properties. Small-angle X-ray scattering was used to investigate gel structure. The overall aim of the work was to define a block copolymer micellar system with better solubilization capacity for poorly soluble aromatic drugs than had been achieved so far by use of block copoly(oxyalkylene)s. Judged by the solubilization of griseofulvin in aqueous solutions of the E(m)G(n)E(m) copolymers, this aim was achieved.

Thermo-responsive poly(methyl methacrylate)-block-poly(N-isopropylacrylamide) block copolymers synthesized by RAFT polymerization: micellization and gelation

RAFT polymerization was used to prepare PMMA-b-PNIPAM copolymers. Two different chain transfer agents, tBDB and MCPDB, were used to mediate the sequential polymerizations. Micellar solutions and gels were prepared from the resulting copolymers in aqueous solution. When heated above T-c of PNIPAM (about 31 degrees C), DLS revealed that PNIPAM coronas collapsed, resulting in aggregation of the original micelles. The micellar gels underwent syneresis above T-c as water was expelled from the ordered gel structure, the lattice periodicity of which was determined by SANS. A large decrease in lattice spacing was observed above T-c. The gel became more viscoelastic at high temperature, as revealed by shear rheometry which showed a large increase in G".

In situ formation of gold nanoparticles with a thermoresponsive block copolymer corona

Gold nanoparticles with a polymer coating exhibiting large and reversible thermoresponsiveness are prepared via a one-pot synthesis method using narrow polydispersity thermoresponsive block copolymers. (C) 2007 Elsevier B.V. All rights reserved.

Exploring block construction and mental imagery: evidence of atypical orientation discrimination in Williams syndrome

The visuospatial perceptual abilities of individuals with Williams syndrome (WS) were investigated in two experiments. Experiment I measured the ability of participants to discriminate between oblique and between nonoblique orientations. Individuals with WS showed a smaller effect of obliqueness in response time, when compared to controls matched for nonverbal mental age. Experiment 2 investigated the possibility that this deviant pattern of orientation discrimination accounts for the poor ability to perform mental rotation in WS (Farran, Jarrold, & Gathercole, 2001). A size transformation task was employed, which shares the image transformation requirements of mental rotation, but not the orientation discrimination demands. Individuals with WS performed at the same level as controls. The results suggest a deviance at the perceptual level in WS, in processing orientation, which fractionates from the ability to mentally transform images.

Verification and FPGA circuits of a block-2 fast path-based predictor

This paper formally derives a new path-based neural branch prediction algorithm (FPP) into blocks of size two for a lower hardware solution while maintaining similar input-output characteristic to the algorithm. The blocked solution, here referred to as B2P algorithm, is obtained using graph theory and retiming methods. Verification approaches were exercised to show that prediction performances obtained from the FPP and B2P algorithms differ within one mis-prediction per thousand instructions using a known framework for branch prediction evaluation. For a chosen FPGA device, circuits generated from the B2P algorithm showed average area savings of over 25% against circuits for the FPP algorithm with similar time performances thus making the proposed blocked predictor superior from a practical viewpoint.

PIC based detection for distributed space-time block coding under imperfect synchronisation

A parallel interference cancellation (PIC) detection scheme is proposed to suppress the impact of imperfect synchronisation. By treating as interference the extra components in the received signal caused by timing misalignment, the PIC detector not only offers much improved performance but also retains a low structural and computational complexity.

Distributed space-time block coding with incremental relay: performance improvement under imperfect synchronisation

This paper addresses the impact of imperfect synchronisation on D-STBC when combined with incremental relay. To suppress such an impact, a novel detection scheme is proposed, which retains the two key features of the STBC principle: simplicity (i.e. linear computational complexity), and optimality (i.e. maximum likelihood). These two features make the new detector very suitable for low power wireless networks (e.g. sensor networks).

A simple optimum detector for distributed space-time block coding under imperfect synchronisation

Most research on D-STBC has assumed that cooperative relay nodes are perfectly synchronised. Since such an assumption is difficult to achieve in many practical systems, this paper proposes a simple yet optimum detector for the case of two relay nodes, which proves to be much more robust against timing misalignment than the conventional STBC detector.

Distributed space-time block coding for 3 and 4 relay nodes: Imperfect synchronisation and a solution

Most research on distributed space time block coding (STBC) has so far focused on the case of 2 relay nodes and assumed that the relay nodes are perfectly synchronised at the symbol level. By applying STBC to 3-or 4-relay node systems, this paper shows that imperfect synchronisation causes significant performance degradation to the conventional detector. To this end, we propose a new STBC detection solution based on the principle of parallel interference cancellation (PIC). The PIC detector is moderate in computational complexity but is very effective in suppressing the impact of imperfect synchronisation.

Orthogonal space-time block codes for free-space IM/DD optical links

Use of orthogonal space-time block codes (STBCs) with multiple transmitters and receivers can improve signal quality. However, in optical intensity modulated signals, output of the transmitter is non-negative and hence standard orthogonal STBC schemes need to be modified. A generalised framework for applying orthogonal STBCs for free-space IM/DD optical links is presented.

A block coprocessor for user data rate improvements to GPRS coding scheme 4

The general packet radio service (GPRS) has been developed to allow packet data to be transported efficiently over an existing circuit-switched radio network, such as GSM. The main application of GPRS are in transporting Internet protocol (IP) datagrams from web servers (for telemetry or for mobile Internet browsers). Four GPRS baseband coding schemes are defined to offer a trade-off in requested data rates versus propagation channel conditions. However, data rates in the order of > 100 kbits/s are only achievable if the simplest coding scheme is used (CS-4) which offers little error detection and correction (EDC) (requiring excellent SNR) and the receiver hardware is capable of full duplex which is not currently available in the consumer market. A simple EDC scheme to improve the GPRS block error rate (BLER) performance is presented, particularly for CS-4, however gains in other coding schemes are seen. For every GPRS radio block that is corrected by the EDC scheme, the block does not need to be retransmitted releasing bandwidth in the channel and improving the user's application data rate. As GPRS requires intensive processing in the baseband, a viable field programmable gate array (FPGA) solution is presented in this paper.

PIC detector for distributed space-time block coding under imperfect synchronisation

A parallel interference cancellation (PIC) detection scheme is proposed to suppress the impact of imperfect synchronisation. By treating as interference the extra components in the received signal caused by timing misalignment, the PIC detector not only offers much improved performance but also retains a low structural and computational complexity.