Fluorenyl-containing sulfonated poly(aryl ether ether ketone ketone)s (SPFEEKK) for fuel cell applications

A series of fluorenyl-containing sulfonated poly(aryl ether ether ketone ketone)s (SPFEEKK) were synthesized via aromatic nucleophilic substitution polymerization. The sulfonation content (SC) was controlled by the feed ratios of sulfonated and nonsulfonated monomers. Flexible and strong membranes in the sulfonic acid form were obtained from cast membranes in the sodium salt forms by treatment with acid. The thermal properties, water uptake, swelling ratio, water state, oxidative stability, proton conductivity and methanol permeability were investigated. All the polymers had proton conductivities greater than 1 × 10⁻² S/cm at room temperature, and the conductivity values of m-SPFEEKK-80 and p-SPFEEKK-80 were up to 1.86 × 10⁻¹ and 1.78 × 10⁻¹ S/cm at 100 °C. This series of polymers also possessed good dimensional stability in water and low methanol crossover.     

Driven dynamics and rotary echo of a qubit tunably coupled to a harmonic oscillator

We have investigated the driven dynamics of a superconducting flux qubit that is tunably coupled to a microwave resonator. We find that the qubit experiences an oscillating field mediated by off-resonant driving of the resonator, leading to strong modifications of the qubit Rabi frequency. This opens an additional noise channel, and we find that low-frequency noise in the coupling parameter causes a reduction of the coherence time during driven evolution. The noise can be mitigated with the rotary-echo pulse sequence, which, for driven systems, is analogous to the Hahn-echo sequence.     

O-Doped Nanographenes: A Pyrano/Pyrylium Route Towards Semiconducting Cationic Mixed-Valence Complexes

Herein we report an efficient synthesis to prepare O-doped nanographenes derived from the π-extension of pyrene. The derivatives are highly fluorescent and feature low oxidation potentials. Using electrooxidation, crystals of cationic mixed-valence (MV) complexes were grown in which the organic salts organize into face-to-face π-stacks, a favorable solid-state arrangement for organic electronics. Variable-temperature electron paramagnetic resonance (EPR) measurements and relaxation studies suggest a strong electron delocalization along the longitudinal axis of the columnar π-stacking architectures. Electric measurements of single crystals of the MV salts show a semiconducting behavior with a remarkably high conductivity at room temperature. These findings support the notion that π-extension of heteroatom-doped polycyclic aromatic hydrocarbons is an attractive approach to fabricate nanographenes with a broad spectrum of semiconducting properties and high charge mobilities.     

Parameter estimation in moving boundary problems

We describe an approximation scheme which can be used to estimate unknown parameters in moving boundary problems. The model equations we consider are fairly general nonlinear diffusion/reaction equations of one spatial variable. Here we give conditions on the parameter sets and model equations under which we can prove that the estimates obtained using the approximations will converge to best-fit parameters for the original model equations. We conclude with a numerical example.     

Erratum to: Tensionless contact of a finite circular plate

In the electronic version of the original article, the issue number shown in the header of the article opening page was wrong. It should be Issue 5 as in Acta Mechanica Sinica (2012) 28(5): 1374-1381.     

O- radical ions on MgO: a tool for a structural description of the surface

The present contribution aims to show that detailed information on structure and location of surface defective sites (surface vacancies, low co-ordination sites) can be obtained by combining data on the chemical reactivity of polycrystalline surfaces and EPR data. The use of nitrous oxide for bleaching trapped electron centres at the surface of MgO produces a remarkable variety of O^- species, which differ in their values of the energy splitting (δE) term between the p_z and the other two p orbitals of the radical ion. This indicates the existence of a corresponding variety of surface traps having different structural features.     

Multilayer hydrous oxide growth on copper in base and its correlation with previously reported electrocatalytic data for this electrode system

A repetitive potential cycling procedure was used to produce a specific multilayer hydrous oxide film on copper in base at 60 °C. Such a deposit undergoes reduction in a quasi-reversible manner at ca. −0.1 V (RHE), i.e. at a potential that is unrelated to Pourbaix data for copper but, as demonstrated previously, is of major significance with regard to the electrocatalytic behaviour of this electrode system. In accordance with the incipient hydrous oxide/adatom mediator model of electrocatalysis, an active surface state of the metal (Cu*) is assumed to be involved both in electrocatalysis and as a primary product in the hydrous oxide reduction reaction. While the latter process occurs very rapidly at −0.1 V, it is not usually reversible as it is accompanied by subsequent rapid loss of the active state of the metal. The same general approach was used previously to explain the hydrous oxide and electrocatalytic behaviour of a range of noble metals. Received: 28 August 1999 / Accepted: 11 November 1999     

Synthesis,self‐assembly and adsorption of PEO–PLA block copolymers onto colloidal polystyrene

A series of amphiphilic block copolymers composed of poly(ethylene oxide) and poly(lactide) were synthesized and their solution properties studied using static and dynamic light scattering. These materials self‐assemble in aqueous media with the hydrodynamic radius increasing with increasing hydrophobic fraction in the copolymer. To ascertain the potential for use of these materials as degradable coatings in delivery applications, block copolymers of varying compositions were adsorbed onto a series of colloidal polystyrene particles with varying radii, and the thickness of the adsorbed layer was determined from changes in the hydrodynamic size. The adlayer thicknesses ranged from 3 to 14 nm with varying block copolymer compositions, and colloid radii. The trends fit well with theoretical models for adlayer thickness, with the exception of the smallest colloids. In these systems, we propose that the colloids may become encapsulated into the block copolymer assembly. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 244–252, 2008     

Exchange enhanced sensitivity gain for solvent-exchangeable protons in 2D 1H-15N heteronuclear correlation spectra acquired with band-selective pulses

Conformational or chemical exchange can cause significant sensitivity loss in NMR spectroscopy through resonance broadening for nuclear spins involved in these processes. While this effect may sometimes be alleviated by manipulating experimental conditions such as temperature, pH, and buffers, conditions optimal for all resonances are not always achievable. As a consequence, any means of recovering or minimizing this exchange-induced sensitivity loss is potentially of significant value in regaining information otherwise lost. We report the experimental observation of significant sensitivity gain for nuclear spins undergoing chemical exchange with solvent (water) at exchange rates ca 1-10 s(-1) in (1)H-(15)N correlation spectra of proteins acquired with band-selective pulses (the SOFAST-HMQC sequence).     

Pulsed arterial spin labeling perfusion imaging at 3 T: estimating the number of subjects required in common designs of clinical trials

Pulsed arterial spin labeling (PASL) is an increasingly common technique for noninvasively measuring cerebral blood flow (CBF) and has previously been shown to have good repeatability. It is likely to find a place in clinical trials and in particular the investigation of pharmaceutical agents active in the central nervous system. We aimed to estimate the sample sizes necessary to detect regional changes in CBF in common types of clinical trial design including (a) between groups, (b) a two-period crossover and (3) within-session single dosing. Whole brain CBF data were acquired at 3 T in two independent groups of healthy volunteers at rest; one of the groups underwent a repeat scan. Using these data, we were able to estimate between-groups, between-session and within-session variability along with regional mean estimates of CBF. We assessed the number of PASL tag-control image pairs that was needed to provide stable regional estimates of CBF and variability of regional CBF across groups. Forty tag-control image pairs, which take approximately 3 min to acquire using a single inversion label delay time, were adequate for providing stable CBF estimates at the group level. Power calculations based on the variance estimates of regional CBF measurements suggest that comparatively small cohorts are adequate. For example, detecting a 15% change in CBF, depending on the region of interest, requires from 7-15 subjects per group in a crossover design, 6-10 subjects in a within-session design and 20-41 subjects in a between-groups design. Such sample sizes make feasible the use of such CBF measurements in clinical trials of drugs.