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- Hugger, S, et al.
(författare)
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Magnetic-barrier-induced conductance fluctuations in quantum wires
- 2008
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 78:16, s. 165307-
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Tidskriftsartikel (refereegranskat)abstract
- Quasiballistic semiconductor quantum wires are exposed to localized perpendicular magnetic fields, also known as magnetic barriers. Pronounced, reproducible conductance fluctuations as a function of the magnetic barrier amplitude are observed. The fluctuations are strongly temperature dependent and remain visible up to temperatures of approximate to 10 K. Simulations based on recursive Greens functions suggest that the conductance fluctuations originate from parametric interferences of the electronic wave functions, which experience scattering between the magnetic barrier and the electrostatic potential landscape.
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- da Silva Xavier, Gabriela, et al.
(författare)
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TCF7L2 regulates late events in insulin secretion from pancreatic islet beta-cells
- 2009
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Ingår i: Diabetes. - : American Diabetes Association. - 0012-1797 .- 1939-327X. ; 58:4, s. 894-905
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE: Polymorphisms in the human TCF7L2 gene are associated with reduced insulin secretion and an increased risk of type 2 diabetes. However, the mechanisms by which TCF7L2 affect insulin secretion are still unclear. We define the effects of TCF7L2 expression level on mature beta-cell function and suggest a potential mechanism for its actions. RESEARCH DESIGN AND METHODS: TCF7L2 expression in rodent islets and beta-cell lines was altered using RNAi or adenoviral transduction. Beta-cell gene profiles were measured by quantitative real-time PCR and the effects on intracellular signaling and exocytosis by live cell imaging, electron microscopy, and patch clamp electrophysiology. RESULTS: Reducing TCF7L2 expression levels by RNAi decreased glucose- but not KCl-induced insulin secretion. The glucose-induced increments in both ATP/ADP ratio and cytosolic free Ca2+ concentration ([Ca2+]i) were increased compared with controls. Overexpression of TCF7L2 exerted minor inhibitory effects on glucose-regulated changes in [Ca2+]i and insulin release. Gene expression profiling in TCF7L2-silenced cells revealed increased levels of mRNA encoding syntaxin 1A but decreased Munc18–1 and ZnT8 mRNA. Whereas the number of morphologically docked vesicles was unchanged by TCF7L2 suppression, secretory granule movement increased and capacitance changes decreased, indicative of defective vesicle fusion. CONCLUSION: TCF7L2 is involved in maintaining expression of beta-cell genes regulating secretory granule fusion. Defective insulin exocytosis may thus underlie increased diabetes incidence in carriers of the at-risk TCF7L2 alleles.
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- Stepantsov, EA, et al.
(författare)
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Grain boundary weak link in a-b plane in MgB2 film
- 2006
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 89:21
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Tidskriftsartikel (refereegranskat)abstract
- The authors have fabricated the Mg B2 bridges 850-6000 nm in width on bicrystal (111) MgO substrates with in-plane grain boundaries of the two types: 13°13° 〈110〉 and 13°13° 〈112〉. Annealing in oxygen of the films on 〈110〉 bicrystal substrates leads to a systematic decrease of critical current, a widening of the transition temperature width, and an improvement of the shape of IV curve that finally looks more like a Josephson junction. They have measured a response of such samples to the microwave radiation at 110 GHz with the voltage amplitude up to 0.5 mV.
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- Tarasov, Mikhail, 1954, et al.
(författare)
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Superconducting weak bonds at grain boundaries in MgB2
- 2007
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Ingår i: JETP Letters. - 1090-6487 .- 0021-3640. ; 105:3, s. 636-641
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Tidskriftsartikel (refereegranskat)abstract
- The possibility of preparing bicrystalline Josephson junctions and bolometers based on superconducting MgB2 on specially prepared bicrystalline MgO substrates is investigated. Microbridges 0.85–6.00 μm in width, intersecting the bicrystalline interface, are formed in epitaxial bicrystalline MgB2 films grown on these substrates. It is found that annealing of bicrystalline samples in oxygen leads to a systematic decrease in the critical current, an increase in the temperature width of the superconducting transition region, and to an improvement of the current-voltage (IV) characteristic, which becomes close in shape to the IV characteristic of a Josephson junction. The response of such a junction to radiation at a frequency of 110 GHz with an amplitude attaining 0.5 mV is measured.
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