Electronic g-tensors of solvated molecules using the polarizable continuum model

We present the implementation of density functional response theory combined with the polarizable continuum model (PCM), enabling first principles calculations of molecular g-tensors of solvated molecules. The calculated g-tensor shifts are compared with experimental g-tensor shifts obtained from electron paramagnetic resonance spectra for a few solvated species. The results indicate qualitative agreement between the calculations and the experimental data for aprotic solvents, whereas PCM fails to reproduce the electronic g-tensor behavior for protic solvents. This failure of PCM for protic solvents can be resolved by including into the model those solvent molecules which are involved in hydrogen bonding with the solute. The results for the protic solvents show that the explicit inclusion of the solvent molecules of the first solvation sphere is not sufficient in order to reproduce the behavior of the electronic g-tensor in protic solvents, and that better agreement with experimental data can be obtained by including the long-range electrostatic effects accounted for by the PCM approach on top of the explicit hydrogen-bonded complexes.     

Crosslinking of PVA and glutaraldehyde in water monitored by viscosity and pulse field gradient NMR: a comparative study

The crosslinking of poly(vinyl alcohol) (PVA) with glutaraldehyde at 80 °C was characterized by viscosity and pulse field gradient (PFG) nuclear magnetic resonance (NMR) techniques. NMR signified an initial dormant period of approximately 6 hr, in which the self‐diffusion coefficient of PVA was found to be constant and independent of time. During the next 7 hr (the “primary” gel period), this induction period was succeeded by a fast decay of the self‐diffusion coefficient of rate (9.13 ± 0.45) × 10⁻⁵ sec⁻¹ followed by a slower decay rate of (3.22 ± 0.30) × 10⁻⁵ sec⁻¹ (the “secondary” gel period). The viscosity of the solution showed the same time behavior, i.e. an initial dormant period (∼ 6 hrs), followed by a fast increase of the viscosity for the next 7 –8 hr. During the “secondary” gel regime, the viscosity became too large to be reliably determined. However, within the time regime where both techniques produced reliable data, they gave identical information regarding the kinetics of the gel process, suggesting that PFG NMR enables in situ monitoring of gelation within porous materials (for instance sandstone). Copyright © 2000 John Wiley & Sons, Ltd.     

The polymerization of butadiene by bis(η3-allylnickeltrifluoroacetate)/tetrachloro-1,4-benzoquinone revisited

The catalytic system bis(n³-allylnickeltrifluoroacetate)/tetrachloro-1,4-benzoquinone, reported in the literature to initiate the living polymerization of butadiene, was re-examined in more detail. All experiments dealing with catalyst-cocatalyst preparation indicate that, although polymerization rates are comparable to those reported previously, the present system is far from perfectly living. The dependence of M̄_n on conversion suggests that chain-transfer, most probably by β-hydride elimination, plays an important role.     

Instability of mercury in specimens of human urine for external quality assessment

An under-recovery of inorganic mercury added to urine and a wide range of results is observed in quality assessment schemes (EQAS) for trace elements. Furthermore, the under-recoveries are inconsistent suggesting features associated with the urine matrix may make the mercury unavailable for measurement. To investigate the instability of mercury in urine the following experiments were set up: (1) a sample of Hg²⁺ in water with various ‘stabilizers’ added was sent to UK external quality assessment scheme participants. (2) Urine was collected from volunteers who also completed a 3-day food diary. Hg, Ca, Mg, Se, uric acid, phosphate, creatinine, reducing substances and protein were measured. Inorganic mercury was spiked into the urine, stabilizers were added and the mercury determined following storage. The results confirmed under-recovery of mercury in association with the urine matrix. Further investigations of how urinary components affect the measurement of mercury are necessary.     

Domain walls in antiferromagnetically coupled multilayer films

We report experimentally observed magnetic domain-wall structures in antiferromagnetically coupled multilayer films with perpendicular anisotropy. Our studies reveal a first-order phase transition from domain walls with no net moment to domain walls with ferromagnetic cores. The transition originates from the competition between dipolar and exchange energies, which we tune by means of layer thickness. Although observed in a synthetic antiferromagnetic system, such domain-wall structures may be expected to occur in A-type antiferromagnets with anisotropic exchange coupling.     

Simulations and Velocity Measurements for a Microparticle in an Evanescent Field

We report theoretical calculations and experimental data for guiding of polystyrene microspheres in the evanescent field of an optical waveguide. The waveguides used in our experiments were made using Cs⁺ ion-exchange in soda lime glass, which gives efficient trapping and high guiding velocities. The computations were done using a generalized version of Mie scattering theory, which gives good agreement with our experimental results. © 2005 The Optical Society of Japan     

A strong uniform boundedness principle in Banach spaces

We discuss the term ``thick" set. With the help of this term we deduce a strong Uniform Boundedness Principle valid for all Banach spaces. As an application we give a new proof of Seever's theorem.