114 research outputs found
Observation of Andreev Reflection Enhanced Shot Noise
We have experimentally investigated the quasiparticle shot noise in
NbN/MgO/NbN superconductor - insulator - superconductor tunnel junctions. The
observed shot noise is significantly larger than theoretically expected. We
attribute this to the occurrence of multiple Andreev reflection processes in
pinholes present in the MgO barrier. This mechanism causes the current to flow
in large charge quanta (Andreev clusters), with a voltage dependent average
value of m = 1+ 2 Delta/eV times the electron charge. Because of this charge
enhancement effect, the shot noise is increased by the factor m.Comment: 4 pages, 5 figures include
Universal distribution of transparencies in highly conductive Nb/AlO/Nb junctions
We report the observation of the universal distribution of transparencies,
predicted by Schep and Bauer [Phys. Rev. Lett. {\bf 78}, 3015 (1997)] for dirty
sharp interfaces, in uniform Nb/AlO/Nb junctions with high specific
conductance ( Ohmcm). Experiments used the BCS density of
states in superconducting niobium for transparency distribution probing.
Experimental results for both the dc curves at magnetic-field-suppressed
supercurrent and the Josephson critical current in zero magnetic field coincide
remarkably well with calculations based on the multimode theory of multiple
Andreev reflections and the Schep-Bauer distribution.Comment: 4 pages, 4 figures, references adde
Mesoscopic proximity effect in double barrier Superconductor/Normal Metal junctions
We report transport measurements down to T=60mK of SININ and SNIN structures
in the diffusive limit. We fabricated Al-AlOx/Cu/AlOx/Cu (SININ) and
Al/Cu/AlOx/Cu (SNIN) vertical junctions. For the first time, a zero bias
anomaly was observed in a metallic SININ structure. We attribute this peak of
conductance to coherent multi-reflections of electrons between the two tunnel
barriers. This conductance maximum is quantitatively fitted by the relevant
theory of mesoscopic SININ structures. When the barrier at the SN interface is
removed (SNIN structure), we observe a peak of conductance at finite voltage
accompagnied by an excess of sub-gap conductance.Comment: 4 pages, 4 figures, editorially approved for publication in Phys.
Rev. B Rapid Com
Non-Equilibrium Quasiclassical Theory for Josephson Structures
We present a non-equilibrium quasiclassical formalism suitable for studying
linear response ac properties of Josephson junctions. The non-equilibrium
self-consistency equations are satisfied, to very good accuracy, already in
zeroth iteration. We use the formalism to study ac Josephson effect in a
ballistic superconducting point contact. The real and imaginary parts of the ac
linear conductance are calculated both analytically (at low frequencies) and
numerically (at arbitrary frequency). They show strong temperature, frequency,
and phase dependence. Many anomalous properties appear near phi = pi. We
ascribe them to the presence of zero energy bound states.Comment: 11 pages, 9 figures, Final version to appear in PR
Hamiltonian approach to the ac Josephson effect in superconducting-normal hybrid systems
The ac Josephson effect in hybrid systems of a normal mesoscopic conductor
coupled to two superconducting (S) leads is investigated theoretically. A
general formula of the ac components of time-dependent current is derived which
is valid for arbitrary interactions in the normal region. We apply this formula
to analyze a S-normal-S system where the normal region is a noninteracting
single level quantum dot. We report the physical behavior of time-averaged
nonequilibrium distribution of electrons in the quantum dot, the formation of
Andreev bound states, and ac components of the time-dependent current. The
distribution is found to exhibit a population inversion; and all Andreev bound
states between the superconducting gap carry the same amount of
current and in the same flow direction. The ac components of time-dependent
current show strong oscillatory behavior in marked contrast to the subharmonic
gap structure of the average current.Comment: 23 pages, 10 figures, LaTe
Resonant Andreev reflections in superconductor-carbon-nanotube devices
Resonant Andreev reflection through superconductor-carbon-nanotube devices
was investigated theoretically with a focus on the superconducting proximity
effect. Consistent with a recent experiment, we find that for high transparency
devices on-resonance, the Andreev current is characterized by a large value and
a resistance dip; low-transparency off-resonance devices give the opposite
result. We also give evidence that the observed low-temperature transport
anomaly may be a natural result of Andreev reflection process
Gene expression profiling in sinonasal adenocarcinoma
<p>Abstract</p> <p>Background</p> <p>Sinonasal adenocarcinomas are uncommon tumors which develop in the ethmoid sinus after exposure to wood dust. Although the etiology of these tumors is well defined, very little is known about their molecular basis and no diagnostic tool exists for their early detection in high-risk workers.</p> <p>Methods</p> <p>To identify genes involved in this disease, we performed gene expression profiling using cancer-dedicated microarrays, on nine matched samples of sinonasal adenocarcinomas and non-tumor sinusal tissue. Microarray results were validated by quantitative RT-PCR and immunohistochemistry on two additional sets of tumors.</p> <p>Results</p> <p>Among the genes with significant differential expression we selected <it>LGALS4, ACS5, CLU, SRI and CCT5 </it>for further exploration. The overexpression of <it>LGALS4, ACS5, SRI</it>, <it>CCT5 </it>and the downregulation of <it>CLU </it>were confirmed by quantitative RT-PCR. Immunohistochemistry was performed for LGALS4 (Galectin 4), ACS5 (Acyl-CoA synthetase) and CLU (Clusterin) proteins: LGALS4 was highly up-regulated, particularly in the most differentiated tumors, while CLU was lost in all tumors. The expression of ACS5, was more heterogeneous and no correlation was observed with the tumor type.</p> <p>Conclusion</p> <p>Within our microarray study in sinonasal adenocarcinoma we identified two proteins, LGALS4 and CLU, that were significantly differentially expressed in tumors compared to normal tissue. A further evaluation on a new set of tissues, including precancerous stages and low grade tumors, is necessary to evaluate the possibility of using them as diagnostic markers.</p
2-Hydroxylethyl methacrylate (HEMA), a tooth restoration component, exerts its genotoxic effects in human gingival fibroblasts trough methacrylic acid, an immediate product of its degradation
HEMA (2-hydroxyethyl methacrylate), a methacrylate commonly used in dentistry, was reported to induce genotoxic effects, but their mechanism is not fully understood. HEMA may be degraded by the oral cavity esterases or through mechanical stress following the chewing process. Methacrylic acid (MAA) is the primary product of HEMA degradation. In the present work we compared cytotoxic and genotoxic effects induced by HEMA and MAA in human gingival fibroblasts (HGFs). A 6-h exposure to HEMA or MAA induced a weak decrease in the viability of HGFs. Neither HEMA nor MAA induced strand breaks in the isolated plasmid DNA, but both compounds evoked DNA damage in HGFs, as evaluated by the alkaline comet assay. Oxidative modifications to the DNA bases were monitored by the DNA repair enzymes Endo III and Fpg. DNA damage induced by HEMA and MAA was not persistent and was removed during a 120 min repair incubation. Results from the neutral comet assay indicated that both compounds induced DNA double strand breaks (DSBs) and they were confirmed by the γ-H2AX assay. Both compounds induced apoptosis and perturbed the cell cycle. Therefore, methacrylic acid, a product of HEMA degradation, may be involved in its cytotoxic and genotoxic action
Erratum to: 36th International Symposium on Intensive Care and Emergency Medicine
[This corrects the article DOI: 10.1186/s13054-016-1208-6.]
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