Theory of diffusional rotation about the common boundary of a bicrystal

During the creep of polycrystals, individual grains may undergo shape changes, grain boundary sliding and grain rotation. Theoretical studies have focused on the first two of these processes but only recently has the theory of rotation received detailed attention. Diffusional rotation was analysed by Burton [Phil. Mag. A 82 51 (2002); Phil. Mag. 83 2715 (2003)], for a bicrystal with orthorhombic grains of dimensions X, Y and Z with the common boundary in the yz plane and with Z???X,Y. Rate equations were derived and the stress profile over the common boundary predicted, for cases where grain boundary and lattice diffusion predominate. In this paper, the analyses are extended using numerical methods, to the full two- and three-dimensional cases for boundary and lattice diffusion, respectively. For boundary diffusion, the results for Z/Y???1 reproduce those obtained by analytical means and this is regarded as a verification of the numerical method. When Z/Y?=?1, the rotation rates are shown to be about 30% faster, due to the additional diffusion contribution in the z direction. This contribution increases with decreasing values of Z/Y. The stress patterns at the rotating boundary are derived. For lattice diffusion, the stress pattern at the boundary, the shapes of the vacancy potential contours and the variation of the rotation rate with the ratios X/Y and Z/Y are presented.     

Emergence and induction of cellular automata rules via probabilistic reinforcement paradigms

Two simple models of emergence and automated induction are described. In the first, an initially random process comes, over time, to emulate a deterministic process with noise. In the second, an induction algorithm is used to make unbiased best guess estimates of cellular automata rules generating a given time series of binary strings. The general conclusions are as follows: (1) that it may not be possible to distinguish between a stochastic process with selection and reinforcement and a noisy deterministic process; and (2) automated induction algorithms will often be vulnerable to errors of type 1 when faced with random data. In this second case, this leads to a method for study of the modeling class assumed in the induction algorithm. © 2006 Wiley Periodicals, Inc. Complexity 11: 44–57, 2006     

Quantum superarrivals and information transfer through a time-varying boundary

The time-dependent Schrödinger equation is solved numerically for the case of a Gaussian wave packet incident on a time-varying potential barrier. The time evolving reflection and transmission probabilities of the wave packet are computed for several different time-dependent boundary conditions obtained by reducing or increasing the height of the potential barrier. We show that in the case when the barrier height is reduced to zero, a time interval is found during which the reflection probability is larger (superarrivals) compared to the unperturbed case. We further show that the transmission probability exhibits superarrivals when the barrier is raised from zero to a finite value of its height. Superarrivals could be understood by ascribing the features of a real physical field to the Schrödinger wave function which acts as a carrier through which a disturbance, resulting from the boundary condition being perturbed, prpagates from the barrier to the detectors measuring reflected and transmitted probabilities. The speed of propagation of this effect depends upon the rate of reducing or raising the barrier height, thus suggesting an application for secure information transfer using superarrivals.     

Oxidative radical cyclisations for the synthesis of gamma-lactones

The use of manganese(III) acetate in combination with copper(II) triflate allows the synthesis of [3.3.0]-bicyclic gamma-lactones from 4-pentenylmalonates in excellent yields.     

Carbohydrate-protein recognition probed by density functional theory and ab initio calculations including dispersive interactions

Carbohydrate-protein recognition has been studied by electronic structure calculations of complexes of fucose and glucose with toluene, p-hydroxytoluene and 3-methylindole, the latter aromatic molecules being analogues of phenylalanine, tyrosine and tryptophan, respectively. We use mainly a density functional theory model with empirical corrections for the dispersion interactions (DFT-D), this method being validated by comparison with a limited number of high level ab initio calculations. We have calculated both binding energies of the complexes as well as their harmonic vibrational frequencies and proton NMR chemical shifts. We find a range of minimum energy structures in which the aromatic group can bind to either of the two faces of the carbohydrate, the binding being dominated by a combination of OH-pi and CH-pi dispersive interactions. For the fucose-toluene and alpha-methyl glucose-toluene complexes, the most stable structures involve OH-pi interactions, which are reflected in a red shift of the corresponding O-H stretching frequency, in good quantitative agreement with experimental data. For those structures where CH-pi interactions are found we predict a corresponding blue shift in the C-H frequency, which parallels the predicted proton NMR shift. We find that the interactions involving 3-methylindole are somewhat greater than those for toluene and p-hydroxytoluene.     

Mechanism of nitrite reduction at T2Cu centers: electronic structure calculations of catalysis by copper nitrite reductase and by synthetic model compounds

The mechanism of nitrite reduction at the Cu(II) center of both copper nitrite reductase and a number of corresponding synthetic models has been investigated by using both QM/MM and cluster calculations employing density functional theory methods. The mechanism in both cases is found to be very similar. Initially nitrite is bound in a bidentate fashion to the Cu(II) center via the two oxygen atoms. Upon reduction of the copper center, the two possible coordination modes of the protonated nitrite, by either nitrogen or a single oxygen atom, are close in energy, with nitrogen coordination probably preferred. Further protonation of this species leads to N-O bond cleavage, and an electron transfer from the Cu(I) center to the N-O+ ligand, resulting in loss of NO and regeneration of the resting state of the enzyme having a bound water molecule.     

Interactions of speaking condition and auditory feedback on vowel production in postlingually deaf adults with cochlear implants

This study investigates the effects of speaking condition and auditory feedback on vowel production by postlingually deafened adults. Thirteen cochlear implant users produced repetitions of nine American English vowels prior to implantation, and at one month and one year after implantation. There were three speaking conditions (clear, normal, and fast), and two feedback conditions after implantation (implant processor turned on and off). Ten normal-hearing controls were also recorded once. Vowel contrasts in the formant space (expressed in mels) were larger in the clear than in the fast condition, both for controls and for implant users at all three time samples. Implant users also produced differences in duration between clear and fast conditions that were in the range of those obtained from the controls. In agreement with prior work, the implant users had contrast values lower than did the controls. The implant users' contrasts were larger with hearing on than off and improved from one month to one year postimplant. Because the controls and implant users responded similarly to a change in speaking condition, it is inferred that auditory feedback, although demonstrably important for maintaining normative values of vowel contrasts, is not needed to maintain the distinctiveness of those contrasts in different speaking conditions.     

Designer Ligands. Part 5.1 Synthesis of Polydentate Biphenyl Ligands

Polydentate nitrogen donor ligands have been prepared for use in biomimetic dinuclear copper complexes designed to model the enzyme, tyrosinase.