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Dynamic regulation of glycosylation of the neural cell adhesion molecule (NCAM) by an unusual large negatively charged polysialic acid (PSA) is the major prerequisite for correct formation of brain circuitries during development and for normal synaptic plasticity, learning and memory in the adult. Traditionally, PSA is viewed as a de-adhesive highly hydrated molecule, which interferes with cell adhesion and promotes cellular/synaptic dynamics by steric hindrance. Analysis of synaptic functions of PSA–NCAM highlighted additional features of this molecule. First, PSA promotes interaction of NCAM with heparan sulfate proteoglycans and thus stimulates synaptogenesis. Second, PSA–NCAM modulates glutamate receptors: it restrains activity of extrasynaptic GluN2B-containing NMDA receptors and facilitates activity of a subset of AMPA receptors. Perturbation in polysialylation and/or NCAM expression in mouse models recapitulates many symptoms of human brain disorders such as schizophrenia, depression, anxiety and Alzheimer's disease.

The temperature dependence of viscosity of glass-forming liquids near the glass transition temperature Tg (at which viscosity η = 1012 Pa s) is given by the fragility index m = d log 10 η d ( T g / T ) T = T g , which is unique for each material. Therefore, m should not depend on the type of the model functions used to describe the viscous behavior. Using this condition, we modified the three-fitting-parameter viscosity equations, i.e., Vogel–Fulcher–Tammann (VFT) and Avramov equations, into one-fitting parameter equations. Both modified equations contain the glass transition temperature Tg and fragility index m as material constants, allowing a direct comparison of the modified equations. Experimental viscosity data are required over a wide temperature range to determine the three-fitting parameters of the VFT and Avramov equations, restricting their applicability. However, the modified equations developed here provide a convenient method of modeling the temperature dependence of viscosity by using the experimentally accessible parameters Tg and m. The modified one-fitting parameter equations were used to analyze viscous behavior of a number of oxide and organic glass-forming liquids. Based on this analysis, it was concluded that the modified Avramov equation describes the experimental data better than the modified VFT equation. Taking into account that the modified VFT equation predicts infinite viscosity at a finite temperature T0, while the modified Avramov equation predicts a continuous increase in viscosity with a decrease in temperature down to the absolute zero, the obtained results may indicate that the oxide and organic super-cooled liquids do not experience dynamic divergence when they are cooled below the glass transition temperature. Strong physical interpretations are developed for all of the parameters used in present equations to model the temperature dependence of viscosity, giving an important improvement over earlier phenomenological models.

A representative model for the atomic structure of amorphous Al alloys is proposed based on the fundamental structure-forming principle of high packing efficiency, topological concepts, and available partial and total radial distribution functions from diffraction studies. Selection of rare earth (RE)-centered atomic clusters as representative structural elements in this model is supported by the large coordination number (∼17±2), efficient atomic packing (100±5%), and small mean intersolute spacing (∼2 atom diameters center-to-center) associated with RE solutes in amorphous Al alloys. Using Al–Y and Al–Y–Ni alloys as a base, five idealized Y-centered clusters and two Ni-centered clusters are described with specific atomic configurations that are consistent with the observed coordination numbers and high density relative to crystalline alloys of the same composition. Significant configurational complexity, required for an amorphous structure, is offered by this structural model. A distribution in Y–Y intersolute spacing is provided by the model that is consistent with the expectation of a random distribution of Y atoms. Topological similarities with other amorphous metal alloy systems suggest that the structure described here for amorphous Al may also be relevant for many other amorphous metals with marginal glass-forming ability (critical cooling rate⩾1000 K/s), including alloys based on Mg, Fe, Ni and Co.

A topological model is proposed for metallic glass formation through destabilization of the host crystalline lattice by substitutional and/or interstitial solute elements. A solute element may partition between substitutional and interstitial sites and the model calculates relative site frequency as a function of the strain energy associated with each site. The strain energy, in turn, depends upon solute and solvent elastic properties and relative sizes, and upon temperature. The crystalline lattice is destabilized leading to amorphization when solute elements produce a critical internal strain required to change local coordination numbers. Fractions of solute atoms in interstitial and substitutional sites and the internal strain introduced by these atoms are calculated as functions of atomic radii and elastic moduli of solvent and solute elements and the absolute temperature. The critical concentration of a solute element required to destabilize the crystalline lattice of a binary alloy is also calculated as a function of the radius ratio R=RB/RA of the solute and solvent elements. In the range of 0.5

A topological model for metallic glass formation is proposed. A critical feature of this model is that a solute occupying either substitutional or interstitial sites in the host crystalline lattice can destabilize the lattice by producing a critical internal strain and changing the local coordination number. Further, the element may partition between these two types of site and the relative site frequency is a function of the strain energy associated with each site. According to the model, the critical concentration of a solute required to amorphize the alloy decreases, reaches a minimum and then increases as the atomic size of the solute decreases relative to the size of the matrix atom.

A topological approach based on analysis of atomic size distributions has been developed and applied to multicomponent amorphous alloys with different glass-forming ability. The atomic size distributions were obtained by plotting atomic concentrations versus atomic radii of constitutive elements. Ordinary amorphous alloys with high critical cooling rates were found to have single-peak distributions with a concave downward shape. These amorphous systems have at least one alloying element with a smaller radius, and at least one alloying element with a larger radius relative to the base element. The concentration of an alloying element decreases rapidly as the difference in the atomic sizes of the base element and the alloying element increases. Atomic size distributions of Zr, Pd, or Ln-based bulk amorphous alloys, which have a critical cooling rate in the range of 1–100 K/s, have a completely different, concave upward shape with a minimum at an intermediate atomic size. The base alloying element in these alloys has the largest atomic size and the smallest atom often has the next-highest concentration. A model that explains the concave upward shape of atomic size distributions for the bulk amorphous alloys is suggested. This model takes into account that all alloying elements in bulk glass formers are smaller than the matrix element, and some of them are located in interstitial sites while others substitute for matrix atoms in a reference crystalline solid solution. The interstitial and substitutional atoms attract each other and produce short-range ordered atomic configurations that stabilize the amorphous state. According to this model, the critical concentration of an interstitial element required to amorphize the alloy increases with increasing size difference from the matrix atom.