Engineering topics

Ma, Xiaobo

Publications and source records attributed to Ma, Xiaobo.

3 records

DOE OSTI2019

Influence of Packing Atmosphere on the Microstructures and Transport Properties of Bi-2223/AgAu Tapes

Oxygen partial pressure was the key factor to tune the phase evolution mechanism of Bi-2223 system. In order to investigate the influence of packing atmosphere on the phase formation rate of Bi-2223, microstructures‚ and the current capacity of final tapes‚ 37-filamentary Bi-2223/AgAu tapes were fabricated by powder-in-tube (PIT) process, and the powder packing process operated in the glove box under different atmosphere of pure O{sub 2}‚ air, and N{sub 2}–7.5%O{sub 2}, with the oxygen partial pressure of 100%‚ 25%, and 7.5%, respectively. With different packing atmosphere, the phase formation rate of Bi-2223 increased obviously during the first heat treatment process (HT1). While, based on the same HT1 process, the maximum Bi-2223 phase content was obtained in the tapes with packing atmosphere of N{sub 2}–7.5%O{sub 2}‚ which should be attributed to the suitable Bi-2223 content and distribution. Due to the improvement of superconducting phase content and better texture structure, the critical current density increased with decreasing oxygen partial pressure of packing atmosphere and the maximum value of 19.9 kA/cm{sup 2} was reached. Moreover‚ the in-field current capacities of these Bi-2223/AgAu tapes have also been enhanced with low oxygen partial pressure in packing atmosphere, attributed to the improvements of intergrain connectivity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2018

Effects of Rolling Passes on the Transport Properties of 37-Filamentary AgAu-Sheathed Bi-2223 Tapes

Thirty-seven-filamentary AgAu-sheathed Bi-2223 tapes were fabricated by a powder-in-tube (PIT) process. And, the round wires (ϕ 1.86 mm) were rolled to 0.35-mm tapes with 12, 7, 5, and 4 rolling passes through flat rolling, respectively. The influences of different rolling passes on the core density, deformation, and transport properties of Bi-2223/AgAu tapes were systematically investigated. It was noticed that after rolling, the Vickers microhardness of the superconducting core and deform homogeneity along both the horizontal and vertical directions on the cross section of seven-pass rolled tape were better than those on the tapes with other passes, which proved the larger core density and uniform deformation with the seven-pass rolling process. Meanwhile for the wires with 12 and 7 passes, the AgAu/superconducting core interfaces were much flatter. With the rolling passes decreasing from 12 to 4, the critical current density (J{sub c}) first increased and then decreased. Due to the better homogeneity and flatter interfaces, J{sub c} reached the maximum value of 17.3 kA/cm{sup 2} on the seven-pass sample. Meanwhile, the enhancement of current capacities in magnetic field applied parallel to the Bi-2223/AgAu tape surface could also be recognized as the evidence of improving intergrain connections due to the higher density in seven-pass rolled tapes.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2018

Nephron segment-specific gene expression using AAV vectors

AAV9 vector provides efficient gene transfer in all segments of the renal nephron, with minimum expression in non-renal cells, when administered retrogradely via the ureter. It is important to restrict the transgene expression to the desired cell type within the kidney, so that the physiological endpoints represent the function of the transgene expressed in that specific cell type within kidney. We hypothesized that segment-specific gene expression within the kidney can be accomplished using the highly efficient AAV9 vectors carrying the promoters of genes that are expressed exclusively in the desired segment of the nephron in combination with administration by retrograde infusion into the kidney via the ureter. We constructed AAV vectors carrying eGFP under the control of: kidney-specific cadherin (KSPC) gene promoter for expression in the entire nephron; Na{sup +}/glucose co-transporter (SGLT2) gene promoter for expression in the S1 and S2 segments of the proximal tubule; sodium, potassium, 2 chloride co-transporter (NKCC2) gene promoter for expression in the thick ascending limb of Henle's loop (TALH); E-cadherin (ECAD) gene promoter for expression in the collecting duct (CD); and cytomegalovirus (CMV) early promoter that provides expression in most of the mammalian cells, as control. We tested the specificity of the promoter constructs in vitro for cell type-specific expression in mouse kidney cells in primary culture, followed by retrograde infusion of the AAV vectors via the ureter in the mouse. Our data show that AAV9 vector, in combination with the segment-specific promoters administered by retrograde infusion via the ureter, provides renal nephron segment-specific gene expression.

60 APPLIED LIFE SCIENCES↗