Effect of the deletion of the C region on the structure and hydration of insulin-like growth factor 1: a molecular dynamics investigation

The structure and hydration of insulin-like growth factor 1 and an inactive mutant lacking the C region have been investigated in aqueous solution by molecular dynamics simulation. The overall structures of the two polypeptide resemble those determined by NMR spectroscopy. The deletion of the C region in the wild polypeptide introduces structural stability in the mutant, leading to a better definition of the secondary structure elements. A detailed hydration analysis was performed using the radial distribution functions and energy distributions. The backbone of the mutant is in general more solvent accessible than the wild polypeptide backbone. The structural rearrangements induced in the mutant led to changes in the solvent exposition of Tyr24 and Tyr60, which are residues important for ligand—receptor complex formation. Tyr24 exhibited a similar degree of solvent exposition in both IGF-I and in the mutant; however, its hydroxyl group in the wild polypeptide is better solvated than in the mutant. Tyr60 was found to be solvent exposed in the wild protein, while in the mutant the involvement of its hydroxyl group in intramolecular hydrogen bonds led to it being buried away from the solvent.     

On the Schrödinger equation with a time dependent mass parameter: Nuclear fragmentation theory

We study the dynamics of a system with a coordinate-dependent inertia tensorB _ik (x ₁,...,x _n ), in which one of the coordinates is treated classically,x _j →x _j (t), so that the associated mass parameter becomes time-dependent. As a result, the Hamiltonian must contain a pure imaginary term in order that probability be conserved. The nuclear fragmentation theory is an example of such a system. The inertia parameter associated with the mass fragmentation degree of freedom depends on the relative motion coordinate and, hence, on time. The time dependence of the imaginary term is derived from a fully quantum mechanical treatment, by going to the classical limit in the relative motion variable. A connection is made with the closely related situation which arises if one transforms from an inertial system to one which depends non-linearly on the time.     

Electrical conductivity and stability of concentrated aqueous alumina suspensions

This work describes the effect of solids load and ionic strength on the electrical conductivity (K(S)) of concentrated aqueous suspensions of commercial alpha-alumina (1-35 vol% solids). The results obtained show that the dependency of the electrical conductivity of the suspending liquid (K(L)) on the volume fraction of solids is well described by Maxwell's model. The change in the conductivity of the suspensions relative to that of the suspending liquid (K(S)/K(L)) was found to be inversely proportional to the solids content, as predicted by Maxwell's model. The relative conductivity rate, DeltaK, could be interpreted in terms of the DLVO theory and the particles double layer parameter, kappaa, and used as a stability criterion. As kappaa changes, in response to the changes in ionic strength, so does the conducting to insulating character of the particles and, as such, their contribution to the overall suspension conductivity (expressed by DeltaK). When the particles become insulating, the suspension conductivity decreases when the solids load increases. The turning point in this particle behaviour corresponds to a critical concentration of ions in the solution that destabilises the suspension and is associated with the critical coagulation concentration (ccc). It is the electrical double layer that ultimately determines the conducting or insulating character of the particles, and that character can be made to change, as required for suspension stability, and accessed by the relative conductivity rate.     

Maximal Inequalities for Fractional Lévy and Related Processes

In this article we study processes that are constructed by a convolution of a deterministic kernel with a martingale. A special emphasis is put on the case where the driving martingale is a centred Lévy process, which covers the popular class of fractional Lévy processes. As a main result we show that, under appropriate assumptions on the kernel and the martingale, the maximum process of the corresponding “convoluted martingale” is p-integrable and we derive maximal inequalities in terms of the kernel and of the moments of the driving martingale.     

Neutron transfer dynamics and doorway to fusion in time-dependent Hartree-Fock theory

We analyze the details of mass exchange in the vicinity of the Coulomb barrier for heavy-ion collisions involving neutron-rich nuclei using the time-dependent Hartree-Fock (TDHF) theory. We discuss the time dependence of transfer and show that the potential barriers seen by individual single-particle states can be considerably different than the effective barrier for the two interacting nuclei having a single center of mass. For this reason we observe a substantial transfer probability even at energies below the effective barrier.