69 research outputs found
Singling out the effect of quenched disorder in the phase diagram of cuprates
We investigate the specific influence of structural disorder on the
suppression of antiferromagnetic order and on the emergence of cuprate
superconductivity. We single out pure disorder, by focusing on a series of
YEuBaCuO samples at fixed oxygen content
, in the range . The gradual Y/Eu isovalent substitution
smoothly drives the system through the Mott-insulator to superconductor
transition from a full antiferromagnet with N\'eel transition K at
to a bulk superconductor with superconducting critical temperature
K at , YBaCuO. The electronic properties are
finely tuned by gradual lattice deformations induced by the different cationic
radii of the two lanthanides, inducing a continuous change of the basal Cu(1)-O
chain length, as well as a controlled amount of disorder in the active
Cu(2)O bilayers. We check that internal charge transfer from the basal to
the active plane is entirely responsible for the doping of the latter and we
show that superconductivity emerges with orthorhombicity. By comparing
transition temperatures with those of the isoelectronic clean system we
deterime the influence of pure structural disorder connected with the Y/Eu
alloy.Comment: 10 pages 11 figures, submitted to Journal of Physics: Condensed
Matter, Special Issue in memory of Prof. Sandro Massid
Evolutionary plasticity of developmental gene regulatory network architecture
Sea stars and sea urchins evolved from a last common ancestor that lived at the end of the Cambrian, approximately half a billion years ago. In a previous comparative study of the gene regulatory networks (GRNs) that embody the genomic program for embryogenesis in these animals, we discovered an almost perfectly conserved five-gene network subcircuit required for endoderm specification. We show here that the GRN structure upstream and downstream of the conserved network kernel has, by contrast, diverged extensively. Mesoderm specification is accomplished quite differently; the Delta–Notch signaling system is used in radically distinct ways; and various regulatory genes have been coopted to different functions. The conservation of the conserved kernel is thus the more remarkable. The results indicate types of network linkage subject to evolutionary change. An emergent theme is that subcircuit design may be preserved even while the identity of genes performing given roles changes because of alteration in their cis-regulatory control systems
The genome of the sea urchin Strongylocentrotus purpuratus
We report the sequence and analysis of the 814-megabase genome of the sea urchin Strongylocentrotus
purpuratus, a model for developmental and systems biology. The sequencing strategy combined
whole-genome shotgun and bacterial artificial chromosome (BAC) sequences. This use of BAC clones,
aided by a pooling strategy, overcame difficulties associated with high heterozygosity of the genome.
The genome encodes about 23,300 genes, including many previously thought to be vertebrate
innovations or known only outside the deuterostomes. This echinoderm genome provides an
evolutionary outgroup for the chordates and yields insights into the evolution of deuterostomes
CRYSRULER: an Integrated System of Computer Programs for Crystal Structure Analysis on Personal Computers
A system of programs and routines is presented that is expressly designed to be user friendly, as much as possible, and to give the real possibility of performing all the stages of crystallographic computation on a personal computer. The package has been developed in a modular way to support adapted versions of some popular crystallographic programs, such as MULTAN, SHELX, PLUTO, ORTEP and PARST. Original facilities are provided for file and system management and molecular graphics on screen display, plotter and matrix printer. The result is a powerful menu-assisted package, which represents the first example of an independent crystallographic work station running under the MS–DOS operating system. The package has been implemented on an IBM AT and can be used without modifications on any XT/AT-compatible personal computer
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