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- Lai, En Yin, et al.
(författare)
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Pressure induces intracellular calcium changes in juxtaglomerular cells in perfused afferent arterioles
- 2011
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Ingår i: Hypertension Research. - : Springer Science and Business Media LLC. - 0916-9636 .- 1348-4214. ; 34:8, s. 942-948
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Tidskriftsartikel (refereegranskat)abstract
- Calcium (Ca(2+)) has an important role in nearly all types of cellular secretion, with a particularly novel role in the juxtaglomerular (JG) cells in the kidney. In JG cells, Ca(2+) inhibits renin secretion, which is a major regulator of blood pressure and renal hemodynamics. However, whether alterations in afferent arteriolar (Af-Art) pressure change intracellular Ca(2+) concentration ([Ca(2+)](i)) in JG cells and whether [Ca(2+)](i) comes from extracellular or intracellular sources remains unknown. We hypothesize that increases in perfusion pressure in the Af-Art result in elevations in [Ca(2+)](i) in JG cells. We isolated and perfused Af-Art of C57BL6 mice and measured changes in [Ca(2+)](i) in JG cells in response to perfusion pressure changes. The JG cells' [Ca(2+)](i) was 93.3 +/- 2.2 nM at 60 mm Hg perfusion pressure and increased to 111.3 +/- 13.4, 119.6 +/- 7.3, 130.3 +/- 2.9 and 140.8 +/- 12.1 nM at 80, 100, 120 and 140 mm Hg, respectively. At 120 mm Hg, increases in [Ca(2+)](i) were reduced in mice receiving the following treatments: (1) the mechanosensitive cation channel blocker, gadolinium (94.6 +/- 7.5 nM); (2) L-type calcium channel blocker, nifedipine (105.8 +/- 7.5 nM); and (3) calcium-free solution plus ethylene glycol tetraacetic acid (96.0 +/- 5.8 nM). Meanwhile, the phospholipase C inhibitor, inositol triphosphate receptor inhibitor, T-type calcium channel blocker, N-type calcium channel blocker and Ca(2+)-ATPase inhibitor did not influence changes in [Ca(2+)](i) in JG cells. In summary, JG cell [Ca(2+)](i) rise as perfusion pressure increases; furthermore, the calcium comes from extracellular sources, specifically mechanosensitive cation channels and L-type calcium channels.
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| 2. |
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| 3. |
- Liu, Ruisheng, et al.
(författare)
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Assembling ferromagnetic single-electron transistors by atomic force microscopy
- 2007
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Ingår i: Nanotechnology. - Bristol : Institute of Physics (IOP). - 0957-4484 .- 1361-6528. ; 18:5, s. 055302-
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate the assembly of nanoscale ferromagnetic single-electron transistors using atomic force microscopy for imaging as well as for nanoscale manipulation. A single 30 nm Au disc, forming the central island of the transistor, is manipulated with angstrom precision into the gap between a plasma-oxidized Ni source and drain electrodes. The tunnel resistances can be tuned in real time during the device fabrication by repositioning the Au disc. Transport measurements reveal long-term stable single-electron transistor characteristics at 4.2 K. The well-controlled devices with very small central islands facilitate future in-depth studies of the interplay between Coulomb blockade, spin-dependent tunnelling and spin accumulation in ferromagnetic single-electron transistors at elevated temperatures.
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| 4. |
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| 5. |
- Liu, Ruisheng, 1972-, et al.
(författare)
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Ferromagnetic single-electron transistors fabricated by atomic force microscopy
- 2006
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Konferensbidrag (refereegranskat)abstract
- We report on the fabrication and magneto-transport measurements of Ni/Au/Ni ferromagnetic single-electron transistors (F-SETs), fabricated by atomic force microscopy. By positioning a single Au disc (30 nm in diameter) into the gap between the Ni drain and source electrodes (of width 220 nm and 80 nm, respectively) step-by-step with Angstrom precision, and using plasma-processed NiOx as tunneling barriers, we can successfully fabricate F-SETs of high quality and substantial stability. The characteristic time interval of the device between two successive tunneling events is 10ps. The absence of any clear features in the transport related to the applied external magnetic field indicates that no spin-accumulation is maintained in the central Au disc. This interesting result indicates that the spin-relaxation time inside the central island should be shorter than 10ps. Based on these findings, we will discuss possible mechanisms of spin-relaxation in metal nano-structures triggered by spin-orbit interaction.
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| 6. |
- Liu, Ruisheng, et al.
(författare)
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Large magnetoresistance in Co/Ni/Co ferromagnetic single electron transistors
- 2007
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Ingår i: Applied Physics Letters. - New York : American Institute of Physics. - 0003-6951 .- 1077-3118. ; 90:12, s. 123111-
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Tidskriftsartikel (refereegranskat)abstract
- The authors report on magnetotransport investigations of nanoscaled ferromagnetic Co/Ni/Co single electron transistors. As a result of reduced size, the devices exhibit single electron transistor characteristics at 4.2 K. Magnetotransport measurements carried out at 1.8 K reveal tunneling magnetoresistance (TMR) traces with negative coercive fields, which the authors interpret in terms of a switching mechanism driven by the shape anisotropy of the central wirelike Ni island. A large TMR of about 18% is observed within a finite source-drain bias regime. The TMR decreases rapidly with increasing bias, which the authors tentatively attribute to excitation of magnons in the central island.
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| 7. |
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| 8. |
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| 9. |
- Liu, Ruisheng, et al.
(författare)
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Nanoscaled ferromagnetic single electron transistors
- 2007
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Ingår i: [Host publication title missing]. - Piscataway, N.J. : IEEE Press. ; 1-3, s. 420-423, s. 420-421
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We report on a summary of fabricating and characterizing nanoscaled ferromagnetic single-electron transistors (F-SETs). One type of device is assembled with an atomic force microscope. A single 30 nm Au disc, forming the central island of the transistor, is manipulated with Angstrom precision into the gap between plasma oxidized Ni source and drain electrodes which are designed with different geometries to facilitate magnetic moment reversal at different magnetic fields. The tunnel resistances can be tuned in real-time during the device fabrication by re-positioning the An disc. A second type of device with Co electrodes and a central Au island is fabricated using a high-precision alignment procedure invoked during e-beam writing. Both devices exhibit single-electron transistor characteristics at 4.2K. From magnetotransport measurements carried out at 1.7K, we found that it is more efficient to realize spin injection and detection in Co/Au/Co devices fabricated with the second technique. A maximum TMR of about 4% was observed in these devices.
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| 10. |
- Liu, Ruisheng, et al.
(författare)
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Probing spin accumulation in Ni/Au/Ni single-electron transistors with efficient spin injection and detection electrodes
- 2007
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Ingår i: Nano letters (Print). - Washington, DC : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 7:1, s. 81-85
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated spin accumulation in Ni/Au/Ni single-electron transistors assembled by atomic force microscopy. The fabrication technique is unique in that unconventional hybrid devices can be realized with unprecedented control, including real-time tunable tunnel resistances. A grid of Au disks, 30 nm in diameter and 30 nm thick, is prepared on a SiO2 surface by conventional e-beam writing. Subsequently, 30 nm thick ferromagnetic Ni source, drain, and side-gate electrodes are formed in similar process steps. The width and length of the source and drain electrodes were different to exhibit different coercive switching fields. Tunnel barriers of NiO are realized by sequential Ar and O2 plasma treatment. By use of an atomic force microscope with specially designed software, a single nonmagnetic Au nanodisk is positioned into the 25 nm gap between the source and drain electrodes. The resistance of the device is monitored in real time while the Au disk is manipulated step-by-step with angstrom-level precision. Transport measurements in magnetic field at 1.7 K reveal no clear spin accumulation in the device, which can be attributed to fast spin relaxation in the Au disk. From numerical simulations using the rate-equation approach of orthodox Coulomb blockade theory, we can put an upper bound of a few nanoseconds on the spin-relaxation time for electrons in the Au disk. To confirm the magnetic switching characteristics and spin injection efficiency of the Ni electrodes, we fabricated a test structure consisting of a Ni/NiO/Ni magnetic tunnel junction with asymmetric dimensions of the electrodes similar to those of the single-electron transistors. Magnetoresistance measurements on the test device exhibited clear signs of magnetic reversal and a maximum tunneling magnetoresistance of 10%, from which we deduced a spin polarization of about 22% in the Ni electrodes. © 2007 American Chemical Society.
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