1,484 research outputs found
Evidence for length-dependent wire expansion, filament dedensification and consequent degradation of critical current density in Ag-alloy sheathed Bi-2212 wires
It is well known that longer Bi-2212 conductors have significantly lower
critical current density (Jc) than shorter ones, and recently it has become
clear that a major cause of this reduction is internal gas pressure generated
during heat treatment, which expands the wire diameter and dedensifies the
Bi-2212 filaments. Here we report on the length-dependent expansion of 5 to 240
cm lengths of state-of-the-art, commercial Ag alloy-sheathed Bi-2212 wire after
full and some partial heat treatments. Detailed image analysis along the wire
length shows that the wire diameter increases with distance from the ends,
longer samples often showing evident damage and leaks provoked by the internal
gas pressure. Comparison of heat treatments carried out just below the melting
point and with the usual melt process makes it clear that melting is crucial to
developing high internal pressure. The decay of Jc away from the ends is
directly correlated to the local wire diameter increase, which decreases the
local Bi-2212 filament mass density and lowers Jc, often by well over 50%. It
is clear that control of the internal gas pressure is crucial to attaining the
full Jc of these very promising round wires and that the very variable
properties of Bi-2212 wires are due to the fact that this internal gas pressure
has so far not been well controlled
Electrodynamics of superconducting pnictide superlattices
It has been recently reported (S. Lee et al., Nature Materials 12, 392, 2013)
that superlattices where layers of the 8% Co-doped BaFe2As2 superconducting
pnictide are intercalated with non superconducting ultrathin layers of either
SrTiO3 or of oxygen-rich BaFe2As2, can be used to control flux pinning, thereby
increasing critical fields and currents, without significantly affecting the
critical temperature of the pristine superconducting material. However, little
is known about the electron properties of these systems. Here we investigate
the electrodynamics of these superconducting pnictide superlattices in the
normal and superconducting state by using infrared reflectivity, from THz to
visible range. We find that multi-gap structure of these superlattices is
preserved, whereas some significant changes are observed in their electronic
structure with respect to those of the original pnictide. Our results suggest
that possible attempts to further increase the flux pinning may lead to a
breakdown of the pnictide superconducting properties.Comment: 4 pages, two figure
The second ESGAR consensus statement on CT colonography
To update quality standards for CT colonography based on consensus among opinion leaders within the European Society of Gastrointestinal and Abdominal Radiology (ESGAR).
A multinational European panel of nine members of the ESGAR CT colonography Working Group (representing six EU countries) used a modified Delphi process to rate their level of agreement on a variety of statements pertaining to the acquisition, interpretation and implementation of CT colonography. Four Delphi rounds were conducted, each at 2 months interval.
The panel elaborated 86 statements.
In the final round the panelists achieved complete consensus in 71 of 86 statements (82 %). Categories including the highest proportion of statements with excellent Cronbach's internal reliability were colon distension, scan parameters, use of intravenous contrast agents, general guidelines on patient preparation, role of CAD and lesion measurement.
Lower internal reliability was achieved for the use of a rectal tube, spasmolytics, decubitus positioning and number of CT data acquisitions, faecal tagging, 2D vs. 3D reading, and reporting.
The recommendations of the consensus should be useful for both the radiologist who is starting a CTC service and for those who have already implemented the technique but whose practice may need updating
High-throughput mutational screening adds clinically important information in myelodysplastic syndromes and secondary or therapy-related acute myeloid leukemia
Nanoscale grains, high irreversibility field, and large critical current density as a function of high energy ball milling time in C-doped magnesium diboride
Magnesium diboride (MgB2) powder was mechanically alloyed by high energy ball
milling with C to a composition of Mg(B0.95C0.05)2 and then sintered at 1000 C
in a hot isostatic press. Milling times varied from 1 minute to 3000 minutes.
Full C incorporation required only 30-60 min of milling. Grain size of sintered
samples decreased with increased milling time to less than 30 nm for 20-50 hrs
of milling. Milling had a weak detrimental effect on connectivity. Strong
irreversibility field (H*) increase (from 13.3 T to 17.2 T at 4.2 K) due to
increased milling time was observed and correlated linearly with inverse grain
size (1/d). As a result, high field Jc benefited greatly from lengthy powder
milling. Jc(8 T, 4.2 K) peaked at > 80,000 A/cm2 with 1200 min of milling
compared with only ~ 26,000 A/cm2 for 60 min of milling. This non-compositional
performance increase is attributed to grain refinement of the unsintered powder
by milling, and to the probable suppression of grain growth by milling-induced
MgO nano-dispersions.Comment: 12 pages, 11 figure
The clinical effectiveness of transurethral incision of the prostate : a systematic review of randomised controlled trials
The original publication is available at www.springerlink.com.Peer reviewedPostprin
Platelet-derived growth factor receptor-β, carrying the activating mutation D849N, accelerates the establishment of B16 melanoma
<p>Abstract</p> <p>Background</p> <p>Platelet-derived growth factor (PDGF)-BB and PDGF receptor (PDGFR)-β are mainly expressed in the developing vasculature, where PDGF-BB is produced by endothelial cells and PDGFR-β is expressed by mural cells, including pericytes. PDGF-BB is produced by most types of solid tumors, and PDGF receptor signaling participates in various processes, including autocrine stimulation of tumor cell growth, recruitment of tumor stroma fibroblasts, and stimulation of tumor angiogenesis. Furthermore, PDGF-BB-producing tumors are characterized by increased pericyte abundance and accelerated tumor growth. Thus, there is a growing interest in the development of tumor treatment strategies by blocking PDGF/PDGFR function. We have recently generated a mouse model carrying an activated PDGFR-β by replacing the highly conserved aspartic acid residue (D) 849 in the activating loop with asparagine (N). This allowed us to investigate, in an orthotopic tumor model, the role of increased stromal PDGFR-β signaling in tumor-stroma interactions.</p> <p>Methods</p> <p>B16 melanoma cells lacking PDGFR-β expression and either mock-transfected or engineered to express PDGF-BB, were injected alone or in combination with matrigel into mice carrying the activated PDGFR-β (D849N) and into wild type mice. The tumor growth rate was followed and the vessel status of tumors, i.e. total vessel area/tumor, average vessel surface and pericyte density of vessels, was analyzed after resection.</p> <p>Results</p> <p>Tumors grown in mice carrying an activated PDGFR-β were established earlier than those in wild-type mice. In this early phase, the total vessel area and the average vessel surface were higher in tumors grown in mice carrying the activated PDGFR-β (D849N) compared to wild-type mice, whereas we did not find a significant difference in the number of tumor vessels and the pericyte abundance around tumor vessels between wild type and mutant mice. At later phases of tumor progression, no significant difference in tumor growth rate was observed between wild type mice and mutant mice, although the pericyte coverage was higher around tumor vessels from mutant mice.</p> <p>Conclusion</p> <p>Our findings suggest that the activated PDGFR-β (D849N) in the host animal increased the total vessel area and the average vessel surface even in PDGF-negative tumors, resulting in a shorter lag phase during tumor establishment.</p
The 4.2 ka event in the central Mediterranean: new data from a Corchia speleothem (Apuan Alps, central Italy)
Abstract. We present new data on the 4.2âka event in the central Mediterranean from
Corchia Cave (Tuscany, central Italy) stalagmite CC27. The stalagmite was
analyzed for stable isotopes (δ13C and δ18O)
and trace elements (Mg, U, P, Y), with all proxies showing a coherent phase
of reduced cave recharge between ca. 4.5 and 4.1âkaâBP. Based on the
current climatological data on cyclogenesis, the reduction in cave recharge
is considered to be associated with the weakening of the cyclone center
located in the Gulf of Genoa in response to reduced advection of air masses
from the Atlantic during winter. These conditions, which closely resemble a
positive North Atlantic Oscillation (NAO) type of configuration, are
associated with cooler and wetter summers with reduced sea warming, which
reduced the western Mediterranean evaporation during autumnâearly winter,
further reducing precipitation
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