479 research outputs found
Superconducting properties of MgB2 thin films prepared on flexible plastic substrates
Superconducting MgB2 thin films were prepared on 50-micrometer-thick,
flexible polyamide Kapton-E foils by vacuum co-deposition of Mg and B
precursors with nominal thickness of about 100 nm and a special ex-situ rapid
annealing process in an Ar or vacuum atmosphere. In the optimal annealing
process, the Mg-B films were heated to approximately 600 C, but at the same
time, the backside of the structures was attached to a water-cooled radiator to
avoid overheating of the plastic substrate. The resulting MgB2 films were
amorphous with the onset of the superconducting transition at T_(c,on) about 33
K and the transition width of approximately 3 K. The critical current density
was > 7x10^5 A/cm^2 at 4.2 K, and its temperature dependence indicated a
granular film composition with a network of intergranular weak links. The films
could be deposited on large-area foils (up to 400 cm^2) and, after processing,
cut into any shapes (e.g., stripes) with scissors or bent multiple times,
without any observed degradation of their superconducting properties.Comment: 3 figure
Switching the Conductance of a Molecular Junction using a Proton Transfer Reaction
A novel mechanism for switching a molecular junction based on a proton
transfer reaction triggered by an external electrostatic field is proposed. As
a specific example to demonstrate the feasibility of the mechanism, the
tautomers [2,5-(4-hydroxypyridine)] and {2,5-[4(1H)-pyridone]} are considered.
Employing a combination of first-principles electronic structure calculations
and Landauer transport theory, we show that both tautomers exhibit very
different conductance properties and realize the "on" and "off" states of a
molecular switch. Moreover, we provide a proof of principle that both forms can
be reversibly converted into each other using an external electrostatic field.Comment: 14 pages, 5 figure
Time-resolved dynamics of the superconducting two-gap state in MgB2 thin films
Femtosecond pump-probe studies show that carrier dynamics in MgB2 films is
governed by the sub-ps electron-phonon (e-ph) relaxation present at all
temperatures, the few-ps e-ph process well pronounced below 70 K, and the
sub-ns superconducting relaxation below Tc. The amplitude of the
superconducting component versus temperature follows the superposition of the
isotropic dirty gap and the 3-dimensional gap dependences, closing at two
different Tc values. The time constant of the few-ps relaxation exhibits a
double-divergence at temperatures corresponding to the Tc's of the two gaps.Comment: Accepted for publication in Phys.Rev.Let
Excited States of Proton-bound DNA/RNA Base Homo-dimers: Pyrimidines
We are presenting the electronic photo fragment spectra of the protonated
pyrimidine DNA bases homo-dimers. Only the thymine dimer exhibits a well
structured vibrational progression, while protonated monomer shows broad
vibrational bands. This shows that proton bonding can block some non radiative
processes present in the monomer.Comment: We acknowledge the use of the computing facility cluster GMPCS of the
LUMAT federation (FR LUMAT 2764
Immunohistochemical and transcriptional expression of Matrix Metalloproteinases in full-term human umbilical cord and Human Umbilical Vein Endothelial Cells
Matrix metalloproteinases (MMPs) are extracellular zinc-dependent endopeptidases involved in the degradation and remodelling of extracellular matrix in physiological and pathological processes. MMPs also have a role on cell proliferation, migration, differentiation, angiogenesis and apoptosis. Umbilical cord is a special organ subjected to many changes during pre-natal life and whose cells can maintain a certain degree of plasticity also in post-natal period; for example recently they have been used as a source of stem cells.
In this work we investigated the expression of MMPs in human umbilical cord and Human Umbilical Vein Endothelial Cells (HUVEC) though immunohistochemistry, RT-PCR and gelatin zymography. MMP-2 protein is expressed in the amniotic epithelium of human umbilical cord and in few sub-epithelial fibroblasts, while MMP-3 and MMP-10 only in the umbilical epithelium. MMP-8, MMP-9 and MMP-13 immunoreactivity is localised in the epithelium and in Wharton\u2019s jelly mesenchymal cells. Immunocytochemistry also revealed protein expression for MMP-2, 3, 8, 9 and 10 in cultured HUVEC.
In agreement with immunohistochemical data, RT-PCR analysis performed on samples of whole umbilical cord confirmed the transcriptional expression for the genes encoding all the six matrix metalloproteinases investigated, while in HUVEC only the expression of MMP-2, 3, 9, 10 and 13 mRNAs was detected.
Gelatin zymograpgy showed a clear MMP-2 and MMP-9 enzymatic activity in the conditioned medium of HUVEC at different culture passages, suggesting that HUVEC secrete gelatinases, that afterwards undergo extracellular activation, and this ability is not affected by passage number
The Gaseous Electronics Conference radioâfrequency reference cell: A defined parallelâplate radioâfrequency system for experimental and theoretical studies of plasmaâprocessing discharges
A ââreference cellââ for generating radioâfrequency (rf) glow discharges in gases at a frequency of 13.56 MHz is described. The reference cell provides an experimental platform for comparing plasma measurements carried out in a common reactor geometry by different experimental groups, thereby enhancing the transfer of knowledge and insight gained in rf discharge studies. The results of performing ostensibly identical measurements on six of these cells in five different laboratories are analyzed and discussed. Measurements were made of plasma voltage and current characteristics for discharges in pure argon at specified values of applied voltages, gas pressures, and gas flow rates. Data are presented on relevant electrical quantities derived from Fourier analysis of the voltage and current wave forms. Amplitudes, phase shifts, selfâbias voltages, and power dissipation were measured. Each of the cells was characterized in terms of its measured internal reactive components. Comparing results from different cells provides an indication of the degree of precision needed to define the electrical configuration and operating parameters in order to achieve identical performance at various laboratories. The results show, for example, that the external circuit, including the reactive components of the rf power source, can significantly influence the discharge. Results obtained in reference cells with identical rf power sources demonstrate that considerable progress has been made in developing a phenomenological understanding of the conditions needed to obtain reproducible discharge conditions in independent reference cells.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70394/2/RSINAK-65-1-140-1.pd
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