Non-random segregation of sister chromosomes in Escherichia coli

It has long been known that the 5' to 3' polarity of DNA synthesis results in both a leading and lagging strand at all replication forks. Until now, however, there has been no evidence that leading or lagging strands are spatially organized in any way within a cell. Here we show that chromosome segregation in Escherichia coli is not random but is driven in a manner that results in the leading and lagging strands being addressed to particular cellular destinations. These destinations are consistent with the known patterns of chromosome segregation. Our work demonstrates a new level of organization relating to the replication and segregation of the E. coli chromosome.     

Redescription of the Cephalaspidea gastropod Atys jeffreysi (Weinkauff, 1866) (Haminoeidae), with a discussion on the phylogenetic affinities of the Mediterranean species of the genus

Atys jeffreysi is a heterobranch Cephalaspidea gastropod belonging to the family Haminoeidae occurring in the Mediterranean Sea, Madeira and Canary archipelagos. Nearly nothing is known about the internal anatomical features of this species. In this paper we redescribe the species A. jeffreysi based on fine anatomical work and scanning electron microscopy. DNA barcodes are provided for the first time for A. jeffreysi and A. macandrewii, the only two species of the genus native in the Mediterranean Sea. The genetic distance (COI uncorrected p-distance) between them is estimate at 21.6%. A Bayesian molecular phylogeny based on the gene marker cytochrome c oxidase subunit I (COI) including all sequences available of the genera Aliculastrum, Liloa and Atys species did not support a sister relationship between the two Mediterranean species and suggests that they are more closely related to distinct Indo-West Pacific lineages. The complex systematics of the genus Atys is briefly discussed.     

Variable selection in STAR models with neighbourhood effects using genetic algorithms

In this paper we deal with the problem of variable selection in spatiotemporal autoregressive (STAR) models with neighbourhood effects. We propose a procedure to carry out the selection process, taking into account the uncertainty associated with estimation of the parameters and the predictive behaviour of the compared models, in order to give more realism to the analysis. We set up a multi‐objective programming problem that combines the use of different criteria to measure both these aspects. We use genetic algorithms which are very flexible and suitable for our multicriteria decision problem. In particular, the procedure allows us to estimate the number of spatial and temporal nearest neighbours as well as their relative effects. The methodology is illustrated through an application to the real estate market of Zaragoza. Copyright © 2010 John Wiley & Son, Ltd.     

Single-spin addressing in an atomic Mott insulator

Ultracold atoms in optical lattices provide a versatile tool with which to investigate fundamental properties of quantum many-body systems. In particular, the high degree of control of experimental parameters has allowed the study of many interesting phenomena, such as quantum phase transitions and quantum spin dynamics. Here we demonstrate how such control can be implemented at the most fundamental level of a single spin at a specific site of an optical lattice. Using a tightly focused laser beam together with a microwave field, we were able to flip the spin of individual atoms in a Mott insulator with sub-diffraction-limited resolution, well below the lattice spacing. The Mott insulator provided us with a large two-dimensional array of perfectly arranged atoms, in which we created arbitrary spin patterns by sequentially addressing selected lattice sites after freezing out the atom distribution. We directly monitored the tunnelling quantum dynamics of single atoms in the lattice prepared along a single line, and observed that our addressing scheme leaves the atoms in the motional ground state. The results should enable studies of entropy transport and the quantum dynamics of spin impurities, the implementation of novel cooling schemes, and the engineering of quantum many-body phases and various quantum information processing applications.