1,243 research outputs found
Genetic markers in s. Paratyphi c reveal primary adaptation to pigs
Salmonella enterica with the identical antigenic formula 6,7:c:1,5 can be differentiated biochemically and by disease syndrome. One grouping, Salmonella Paratyphi C, is currently considered a typhoidal serovar, responsible for enteric fever in humans. The human-restricted typhoidal serovars (S. Typhi and Paratyphi A, B and C) typically display high levels of genome degradation and are cited as an example of convergent evolution for host adaptation in humans. However, S. Paratyphi C presents a different clinical picture to S. Typhi/Paratyphi A, in a patient group with predisposition, raising the possibility that its natural history is different, and that infection is invasive salmonellosis rather than enteric fever. Using whole genome sequencing and metabolic pathway analysis, we compared the genomes of 17 S. Paratyphi C strains to other members of the 6,7:c:1,5 group and to two typhoidal serovars: S. Typhi and Paratyphi A. The genome degradation observed in S. Paratyphi C was much lower than S. Typhi/Paratyphi A, but similar to the other 6,7:c:1,5 strains. Genomic and metabolic comparisons revealed little to no overlap between S. Paratyphi C and the other typhoidal serovars, arguing against convergent evolution and instead providing evidence of a primary adaptation to pigs in accordance with the 6,7:c:1.5 strains
The malleability of uranium: manipulating the charge-density wave in epitaxial films
We report x-ray synchrotron experiments on epitaxial films of uranium,
deposited on niobium and tungsten seed layers. Despite similar lattice
parameters for these refractory metals, the uranium epitaxial arrangements are
different and the strains propagated along the a-axis of the uranium layers are
of opposite sign. At low temperatures these changes in epitaxy result in
dramatic modifications to the behavior of the charge-density wave in uranium.
The differences are explained with the current theory for the electron-phonon
coupling in the uranium lattice. Our results emphasize the intriguing
possibilities of producing epitaxial films of elements that have complex
structures like the light actinides uranium to plutonium.Comment: 6 pages, 6 figure
Late Holocene landscape change history related to the Alpine Fault determined from drowned forests in Lake Poerua, Westland, New Zealand
Lake Poerua is a small, shallow lake that abuts
the scarp of the Alpine Fault on the West Coast of New
Zealand’s South Island. Radiocarbon dates from drowned
podocarp trees on the lake floor, a sediment core from a
rangefront alluvial fan, and living tree ring ages have been
used to deduce the late Holocene history of the lake. Remnant
drowned stumps of kahikatea (Dacrycarpus dacrydioides)
at 1.7–1.9m water depth yield a preferred time-ofdeath
age at 1766–1807 AD, while a dryland podocarp and
kahikatea stumps at 2.4–2.6m yield preferred time-of-death
ages of ca. 1459–1626 AD. These age ranges are matched to,
but offset from, the timings of Alpine Fault rupture events
at ca. 1717 AD, and either ca. 1615 or 1430 AD. Alluvial
fan detritus dated from a core into the toe of a rangefront
alluvial fan, at an equivalent depth to the maximum depth
of the modern lake (6.7 m), yields a calibrated age of AD
1223–1413. This age is similar to the timing of an earlier
Alpine Fault rupture event at ca. 1230AD±50 yr. Kahikatea
trees growing on rangefront fans give ages of up to 270 yr,
which is consistent with alluvial fan aggradation following
the 1717AD earthquake. The elevation levels of the lake and
fan imply a causal and chronological link between lake-level
rise and Alpine Fault rupture. The results of this study suggest
that the growth of large, coalescing alluvial fans (Dry
and Evans Creek fans) originating from landslides within the
rangefront of the Alpine Fault and the rise in the level of
Lake Poerua may occur within a decade or so of large Alpine
Fault earthquakes that rupture adjacent to this area. These
rises have in turn drowned lowland forests that fringed the
lake. Radiocarbon chronologies built using OxCal show that
a series of massive landscape changes beginning with fault
rupture, followed by landsliding, fan sedimentation and lake
expansion. However, drowned Kahikatea trees may be poor
candidates for intimately dating these events, as they may be
able to tolerate water for several decades after metre-scale
lake level rises have occurred
Positional, Reorientational and Bond Orientational Order in DNA Mesophases
We investigate the orientational order of transverse polarization vectors of
long, stiff polymer molecules and their coupling to bond orientational and
positional order in high density mesophases. Homogeneous ordering of transverse
polarization vector promotes distortions in the hexatic phase, whereas
inhomogeneous ordering precipitates crystalization of the 2D sections with
different orientations of the transverse polarization vector on each molecule
in the unit cell. We propose possible scenarios for going from the hexatic
phase, through the distorted hexatic phase to the crystalline phase with an
orthorhombic unit cell observed experimentally for the case of DNA.Comment: 4 pages, 2 figure
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Conformational stability in dinucleoside phosphate crystals. Semiempirical potential energy calculations for uridylyl-3'-5'-adenosine monophosphate (UpA) and guanylyl-3',5'-cytidine monophosphate (GpC)
Classical potential energy calculations were performed for the dinucleoside phosphates UpA and GpC. Two widely accessible low-energy regions of conformation space were found for the w', w pair. That of lowest energy contains conformations similar to helical RNA, with w' and w in the vicinity of 300° and 280°, respectively. All five experimental observations of crystalline GpC, two of ApU, and the helical fragment of ApApA fall in this range. The second lowest region has w' and w at about 20° and 80°, respectively, which is in the general region of one experimentally observed crystalline conformer of UpA, and the nonhelical region of ApApA. It is concluded that GpC and ApU, which were crystallized as either sodium or calcium salts, are shielded from each other in the crystal by the water of hydration and are therefore free to adopt their predicted in vacuo minimum energy helical conformations. By contrast, crystalline UpA had only 1/2 water per molecule, and was forced into higher energy conformations in order to maximize intermolecular hydrogen bonding
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