scispace - formally typeset
Search or ask a question
Author

Zhifeng Ren

Bio: Zhifeng Ren is an academic researcher from Texas Center for Superconductivity. The author has contributed to research in topics: Thermoelectric effect & Thermoelectric materials. The author has an hindex of 122, co-authored 695 publications receiving 71212 citations. Previous affiliations of Zhifeng Ren include Massachusetts Institute of Technology & University of Cincinnati.


Papers
More filters
Journal ArticleDOI
TL;DR: In this article, the authors studied the interaction of the electromagnetic radiation with a series of thin-film periodic nanostructures evolving from holes to islands, and they showed that the responses of these structures evolve accordingly, with two topologically distinct spectral types for holes and islands.
Abstract: We study interaction of the electromagnetic radiation with a series of thin film periodic nanostructures evolving from holes to islands. We show, through model calculations, simulations, and experiments, that the responses of these structures evolve accordingly, with two topologically distinct spectral types for holes and islands. We find also, that the response at the transitional pattern is singular. We show that the corresponding effective dielectric function follows the critical behavior predicted by the percolation theory and thus the hole-to-island structural evolution in this series is a topological analog of the percolation problem, with the percolation threshold at the transitional pattern.

12 citations

Journal Article
01 Jan 1999-Scopus
TL;DR: XRD values of XRD peaks show that both phases are epitaxial, with in-plane and out-of-plane alignments comparable to those of the underlying Ni and buffer layers (CeO 2 and YSZ).
Abstract: Abstract In-plane aligned superconducting Tl 0.78 Bi 0.22 Sr 1.6 Ba 0.4 Ca 2 Cu 3 O 9 ((Tl,Bi)-1223) films on R olling A ssisted Bi axially T extured S ubstrates (RABiTS) with J c of 4.25×10 5 A/cm 2 at 77 K and zero-field have been synthesized by laser ablation and post-ablation annealing. The as-ablated films were amorphous due to the low substrate temperature during ablation. The amorphous films were then wrapped together with an unfired Tl 0.95 Bi 0.22 Sr 1.6 Ba 0.4 Ca 2 Cu 3 O 9 pellet in silver foil. The whole package was finally annealed in a tube furnace at 780–810°C for 40–60 min in flowing argon to crystallize the films. X-ray diffraction (XRD) shows that the annealed films consist of mainly c -axis aligned (Tl,Bi)-1223 phase with a small amount of (Tl,Bi)-1212 phase. The full width at half maximum (FWHM) values of XRD peaks show that both phases are epitaxial, with in-plane and out-of-plane alignments comparable to those of the underlying Ni and buffer layers (CeO 2 and YSZ). Four-probe transport measurements showed superconducting transition temperatures ( T c s) of 105–109 K depending on the annealing conditions. With external magnetic field applied parallel to the c -axis, irreversibility magnetic fields reached beyond 3 T at 77 K and beyond 5 T at 64 K.

12 citations

Journal ArticleDOI
H L Gao1, H L Gao2, Tong-Yin Zhu1, Hui Wang2, Zhifeng Ren2, X.B. Zhao1 
TL;DR: In this paper, the effect of Pb substitution for Te in La3Te4?xPbx on the thermoelectric properties in the temperature range 300?1100?K was studied on samples synthesized by the melting, ball milling and hot-pressing method.
Abstract: The effect of Pb in La3Te4?xPbx on the thermoelectric properties in the temperature range 300?1100?K was studied on samples synthesized by the melting, ball milling and hot-pressing method. The samples crystallize in the Th3P4structure. A small amount of Pb substitution for Te in La3Te4 reduced the electrical conductivity, but the impurity phase introduced by more Pb significantly enhanced the electrical conductivity. The electrical conductivity of the La3Te3.6Pb0.4 sample reached 2.06???105?S?m?1 at room temperature. The expansion of crystal lattice confirmed from x-ray diffraction patterns and the slight reduction in electrical conductivity all verify the fact that Pb substitutes a Te site when x is small. The Seebeck coefficient increases linearly with temperature for all samples. While the thermal conductivity varies slightly with temperature, the lattice thermal conductivity approaches the minimum value at high temperatures. For La3Te3.7Pb0.3, a power factor of 1.4???10?3?W?m?1?K?2 at 1100?K was achieved with a thermal conductivity of 1.86?W?m?1?K?1, giving a maximum figure-of-merit ZT???0.8 at 1100?K.

12 citations

Journal ArticleDOI
TL;DR: In this article, the Mn-based cathode exhibits a charge time that is only around 1/40 of that by traditional constant-current charge method, while high capacity is acquired simultaneously due to the multivalent conversion.

12 citations


Cited by
More filters
Journal ArticleDOI

[...]

08 Dec 2001-BMJ
TL;DR: There is, I think, something ethereal about i —the square root of minus one, which seems an odd beast at that time—an intruder hovering on the edge of reality.
Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

33,785 citations

28 Jul 2005
TL;DR: PfPMP1)与感染红细胞、树突状组胞以及胎盘的单个或多个受体作用,在黏附及免疫逃避中起关键的作�ly.
Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1(PfPMP1)与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用,在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员,通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

18,940 citations

Journal ArticleDOI
02 Aug 2002-Science
TL;DR: Many potential applications have been proposed for carbon nanotubes, including conductive and high-strength composites; energy storage and energy conversion devices; sensors; field emission displays and radiation sources; hydrogen storage media; and nanometer-sized semiconductor devices, probes, and interconnects.
Abstract: Many potential applications have been proposed for carbon nanotubes, including conductive and high-strength composites; energy storage and energy conversion devices; sensors; field emission displays and radiation sources; hydrogen storage media; and nanometer-sized semiconductor devices, probes, and interconnects. Some of these applications are now realized in products. Others are demonstrated in early to advanced devices, and one, hydrogen storage, is clouded by controversy. Nanotube cost, polydispersity in nanotube type, and limitations in processing and assembly methods are important barriers for some applications of single-walled nanotubes.

9,693 citations