Convergence of Campylobacter species: implications for bacterial evolution

The nature of species boundaries in bacteria remains controversial. In particular, the mechanisms of bacterial speciation and maintenance in the face of frequent genetic exchange are poorly understood. Here, we report patterns of genetic exchange that show two closely related zoonotic pathogenic species, Campylobacter jejuni and Campylobacter coli, are converging as a consequence of recent changes in gene flow. Population expansion into a novel ecological niche generated by human activity is the most probable explanation for the increase in genetic exchange between these species. Bacterial speciation can therefore occur by mechanisms analogous to those seen in metazoans, where genetic diversification and incipient speciation caused by ecological factors have been reported in several genera.     

Electric field-induced modification of magnetism in thin-film ferromagnets

A large electric field at the surface of a ferromagnetic metal is expected to appreciably change its electron density. In particular, the metal's intrinsic magnetic properties, which are commonly regarded as fixed material constants, will be affected. This requires, however, that the surface has a strong influence on the material's properties, as is the case with ultrathin films. We demonstrated that the magnetocrystalline anisotropy of ordered iron-platinum (FePt) and iron-palladium (FePd) intermetallic compounds can be reversibly modified by an applied electric field when immersed in an electrolyte. A voltage change of -0.6 volts on 2-nanometer-thick films altered the coercivity by -4.5 and +1% in FePt and FePd, respectively. The modification of the magnetic parameters was attributed to a change in the number of unpaired d electrons in response to the applied electric field. Our device structure is general and should be applicable for characterization of other thin-film magnetic systems.     

Reciprocal control of T helper cell and dendritic cell differentiation

It is not known whether subsets of dendritic cells provide different cytokine microenvironments that determine the differentiation of either type-1 T helper (TH1) or TH2 cells. Human monocyte (pDC1)-derived dendritic cells (DC1) were found to induce TH1 differentiation, whereas dendritic cells (DC2) derived from CD4+CD3-CD11c- plasmacytoid cells (pDC2) induced TH2 differentiation by use of a mechanism unaffected by interleukin-4 (IL-4) or IL-12. The TH2 cytokine IL-4 enhanced DC1 maturation and killed pDC2, an effect potentiated by IL-10 but blocked by CD40 ligand and interferon-gamma. Thus, a negative feedback loop from the mature T helper cells may selectively inhibit prolonged TH1 or TH2 responses by regulating survival of the appropriate dendritic cell subset.     

Oxygen isotopes and emerald trade routes since antiquity

Oxygen isotopic compositions of historical emerald artifacts from the Gallo-Roman period to the 18th century indicate that during historical times, artisans worked emeralds originating from deposits supposedly discovered in the 20th century. In antiquity, Pakistani and Egyptian emeralds were traded by way of the Silk Route. Together with Austrian stones, they were the only source of gem-quality emeralds. Immediately after the discovery of the Colombian mines by Spaniards in the 16th century, a new trade route was established, first via Spain to Europe and India and then directly via the Philippines to India. Since then, Colombian emeralds have dominated the emerald trade, and most of the high-quality emeralds cut in the 18th century in India originated from Colombia.     

Design automation for integrated circuits

With the ever-increasing complexity of integrated circuits, manual design methods have become intolerably slow and error-prone. The use of computers to automate some or all of the design process is necessary to minimize both design time and error incidence. In this article are discussed the design and fabrication of integrated circuits, selected techniques of design automation, and the problems associated with such automation.