1,536 research outputs found
Patterned Irradiation of YBa_2Cu_3O_(7-x) Thin Films
We present a new experiment on YBa_2Cu_3O_{7-x} (YBCO) thin films using
spatially resolved heavy ion irradiation. Structures consisting of a periodic
array of strong and weak pinning channels were created with the help of metal
masks. The channels formed an angle of +/-45 Deg with respect to the symmetry
axis of the photolithographically patterned structures. Investigations of the
anisotropic transport properties of these structures were performed. We found
striking resemblance to guided vortex motion as it was observed in YBCO single
crystals containing an array of unidirected twin boundaries. The use of two
additional test bridges allowed to determine in parallel the resistivities of
the irradiated and unirradiated parts as well as the respective current-voltage
characteristics. These measurements provided the input parameters for a
numerical simulation of the potential distribution of the Hall patterning. In
contrast to the unidirected twin boundaries in our experiment both strong and
weak pinning regions are spatially extended. The interfaces between
unirradiated and irradiated regions therefore form a Bose-glass contact. The
experimentally observed magnetic field dependence of the transverse voltage
vanishes faster than expected from the numerical simulation and we interpret
this as a hydrodynamical interaction between a Bose-glass phase and a vortex
liquid.Comment: 7 pages, 8 Eps figures included. Submitted to PR
Glucose-stimulated insulin production in mice deficient for the PAS kinase PASKIN.
The Per-ARNT-Sim (PAS) domain serine/threonine kinase PASKIN, or PAS kinase, links energy flux and protein synthesis in yeast and regulates glycogen synthase in mammals. A recent report suggested that PASKIN mRNA, protein, and kinase activity are increased in pancreatic islet beta-cells under hyperglycemic conditions and that PASKIN is necessary for insulin gene expression. We previously generated Paskin knockout mice by targeted replacement of the kinase domain with the beta-geo fusion gene encoding beta-galactosidase reporter activity. Here we show that no 5-bromo-4-chloro-3-indolyl-ss-d-galactopyranoside (X-gal) staining was observed in islet beta-cells derived from Paskin knockout mice, irrespective of the ambient glucose concentration, whereas adenoviral expression of the lacZ gene in beta-cells showed strong X-gal staining. No induction of PASKIN mRNA could be detected in insulinoma cell lines or in islet beta-cells. Increasing glucose concentrations resulted in PASKIN-independent induction of insulin mRNA levels and insulin release. PASKIN mRNA levels were high in testes but undetectable in pancreas and in islet beta-cells. Finally, blood glucose levels and glucose tolerance after intraperitoneal glucose injection were indistinguishable between Paskin wild-type and knockout mice. These results suggest that Paskin gene expression is not induced by glucose in pancreatic beta-cells and that glucose-stimulated insulin production is independent of PASKIN
Late Cenozoic Climate History of the Ross Embayment from the AND-1B Drill Hole: Culmination of Three Decades of Antarctic Margin Drilling
Because of the paucity of exposed rock, the direct physical
record of Antarctic Cenozoic glacial history has become
known only recently and then largely from offshore shelf
basins through seismic surveys and drilling. The number
of holes on the continental shelf has been small and largely
confined to three areas (McMurdo Sound, Prydz Bay, and
Antarctic Peninsula), but even in McMurdo Sound, where
Oligocene and early Miocene strata are well cored, the late
Cenozoic is poorly known and dated. The latest Antarctic
geological drilling program, ANDRILL, successfully cored
a 1285-m-long record of climate history spanning the last 13
m.y. from subsea-floor sediment beneath the McMurdo Ice
Shelf (MIS), using drilling systems specially developed for
operating through ice shelves. The cores provide the most
complete Antarctic record to date of ice-sheet and climate
fluctuations for this period of Earth’s history. The >60 cycles
of advance and retreat of the grounded ice margin preserved
in the AND-1B record the evolution of the Antarctic ice sheet
since a profound global cooling step in deep-sea oxygen
isotope records ~14 m.y.a. A feature of particular interest is a
~90-m-thick interval of diatomite deposited during the warm
Pliocene and representing an extended period (~200,000
years) of locally open water, high phytoplankton productivity,
and retreat of the glaciers on land
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