40 research outputs found
Simulations of the effects of tin composition gradients on the superconducting properties of Nb3Sn conductors
In powder-in-tube (PIT) Nb3Sn composites, the A15 phase forms between a
central tin-rich core and a coaxial Nb tube, thus causing the tin content and
superconducting properties to vary with radius across the A15 layer. Since this
geometry is also ideal for magnetic characterization of the superconducting
properties with the field parallel to the tube axis, a system of concentric
shells with varying tin content was used to simulate the superconducting
properties, the overall severity of the Sn composition gradient being defined
by an index N. Using well-known scaling relationships and property trends
developed in an earlier experimental study, the critical current density for
each shell was calculated, and from this the magnetic moment of each shell was
found. By summing these moments, experimentally measured properties such as
pinning-force curves and Kramer plots could be simulated. We found that
different tin profiles have only a minor effect on the shape of Kramer plots,
but a pronounced effect on the irreversibility fields defined by the
extrapolation of Kramer plots. In fact, these extrapolated values H_K are very
close to a weighted average of the superconducting properties across the layer
for all N. The difference between H_K and the upper critical field commonly
seen in experiments is a direct consequence of the different ways measurements
probe the simulated Sn gradients. Sn gradients were found to be significantly
deleterious to the critical current density Jc, since reductions to both the
elementary pinning force and the flux pinning scaling field H_K compound the
reduction in Jc. The simulations show that significant gains in Jc of Nb3Sn
strands might be realized by circumventing strong compositional gradients of
tin.Comment: 10 pages, 8 figures, 2 tables, submitted to J. Appl. Phy
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Powder-in-tube (PIT) NbSn conductors for high-field magnets
New Nb/sub 3/Sn conductors, based on the powder-in-tube (PIT) process, have been developed for application in accelerator magnets and high-field solenoids. For application in accelerator magnets, SMI has developed a binary 504 filament PIT conductor by optimizing the manufacturing process and adjustment of the conductor lay-out. It uniquely combines a non-copper current density of 2680 A/mm/sup 2/@10 T with an effective filament diameter of about 20 mu m. This binary conductor may be used in a 10 T, wide bore model separator dipole magnet for the LHC, which is being developed by a collaboration of the University of Twente and CERN. A ternary (Nb/7.5wt%Ta)/sub 3/Sn conductor containing 37 filaments is particularly suited for application in extremely high-field superconducting solenoids. This wire features a copper content of 43%, a non-copper current density of 217 A/mm/sup 2/@20 T and a B/sub c2/ of 25.6 T. The main issues and the experimental results of the development program of PIT Nb/sub 3/Sn conductors are presented and discussed in this paper. (8 refs)
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Restraining FOXO3-dependent transcriptional BMF activation underpins tumour growth and metastasis of E-cadherin-negative breast cancer
Loss of cellular adhesion leads to the progression of breast cancer through acquisition of anchorage independence, also known as resistance to anoikis. Although inactivation of E-cadherin is essential for acquisition of anoikis resistance, it has remained unclear how metastatic breast cancer cells counterbalance the induction of apoptosis without E-cadherin-dependent cellular adhesion. We report here that E-cadherin inactivation in breast cancer cells induces PI3K/AKT-dependent FOXO3 inhibition and identify FOXO3 as a novel and direct transcriptional activator of the pro-apoptotic protein BMF. As a result, E-cadherin-negative breast fail to upregulate BMF upon transfer to anchorage independence, leading to anoikis resistance. Conversely, expression of BMF in E-cadherin-negative metastatic breast cancer cells is sufficient to inhibit tumour growth and dissemination in mice. In conclusion, we have identified repression of BMF as a major cue that underpins anoikis resistance and tumour dissemination in E-cadherin-deficient metastatic breast cancer