Limit cycles in predator-prey communities

Essentially all models that have been proposed for predator-prey systems are shown to possess either a stable point equilibrium or a stable limit cycle. This stable limit cycle, an explicitly nonlinear feature, is commonly overlooked in conventional analyses of these models. Such a stable limit cycle provides a satisfying explanation for those animal communities in which populations are observed to oscillate in a rather reproducible periodic manner.     

Redesigning nature's poisons to create anti-tumor reagents

Immunotoxins are conjugates of cell-reactive antibodies and toxins or their subunits. In this report, the chemistry, biology, pharmacokinetics, and anti-tumor effects of first generation immunotoxins; the preparation of improved second generation immunotoxins that display greater anti-tumor efficacy; and the role of genetic engineering in creating third-generation immunotoxins are discussed.     

Human-mouse cell hybrids: a suggestion of structural mutation for dipeptidase-2 deficiency in mouse cells

The dipeptidase-2 enzyme is inactive in certain cultured cell lines from the mouse. In somatic cell hybrids between such deficient cells and diploid human fibroblasts, the mouse deficiency was complemented when the homologous human peptidase-A was retained. The results suggested that the murine peptidase deficiency was the result of a structural mutation, rather than a regulatory one.     

A perovskite oxide optimized for oxygen evolution catalysis from molecular orbital principles

The efficiency of many energy storage technologies, such as rechargeable metal-air batteries and hydrogen production from water splitting, is limited by the slow kinetics of the oxygen evolution reaction (OER). We found that Ba(0.5)Sr(0.5)Co(0.8)Fe(0.2)O(3-δ) (BSCF) catalyzes the OER with intrinsic activity that is at least an order of magnitude higher than that of the state-of-the-art iridium oxide catalyst in alkaline media. The high activity of BSCF was predicted from a design principle established by systematic examination of more than 10 transition metal oxides, which showed that the intrinsic OER activity exhibits a volcano-shaped dependence on the occupancy of the 3d electron with an e(g) symmetry of surface transition metal cations in an oxide. The peak OER activity was predicted to be at an e(g) occupancy close to unity, with high covalency of transition metal-oxygen bonds.