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.

The influence of hydrogen reduction on single crystals of Bi2Sr2CaCu2Oy

Abstract: Single crystals of Bi 2 Sr 2 CaCu 2 O y with transition temperature T c =80 K have been reduced in hydrogen at 400°C. After hydrogen reduction, there is no observable change in crystal cell parameters and the modulation wave vector, q , but apparently both the Meissner fraction and the superconducting transition temperature decrease. The copper K-edge X-ray-absorption near-edge spectra (XANES) in the oxidized crystals with higher T c and the reduced crystals with lower T c show that the difference in local structure around copper could be a main factor governing the observed changes in superconducting properties.

Epitaxial Film Growth of Tl0.78Bi0.22Sr1.6Ba0.4Ca2Cu3O9 on Rolling Assisted Biaxially Textured Nickel Substrates with YSZ And CeO2 Buffer Layers

Abstract: Epitaxial film growth of Tl0.78Bi0.22Sr1.6Ba0.4Ca2Cu3O9 ((Tl,Bi)-1223) on rolling assisted biaxially textured substrates with YSZ and CeO2 buffer layers (RABiTS) has been successfully demonstrated by laser ablation and post-deposition annealing in flowing argon. X-ray diffraction (XRD) θ-2θ spectra showed that the films consisted mainly of c-axis aligned 1223 phase with some intergrown 1212 phase, while XRD Φ-scans of (102) pole figure revealed that the films are also a- and b-axes aligned, with an epitaxy of the «100» of (Tl,Bi)-1223 film on the «110» of the top YSZ buffer layer. Four-terminal electrical transport measurements showed that the zero-resistance transition temperature (Tc) was in the range of 106 - 110 K, and the critical current density (Jc) at 77 K and zero field was about 105 A/cm2 for the entire film width (3 mm) of a longer film (14 mm) which was processed differently from the shorter films (7 mm). For a shorter film (7 mm) that showed better ab-in-plane alignment, the magnetization Jc, at 77 K and extrapolated to zero field, calculated from Bean's model using the full film width (3.5 mm) as the appropriate lateral dimension, was 2 × 105 A/cm2.

Methods for synthesis of semiconductor nanocrystals and thermoelectric compositions

Abstract: The present invention provides methods for synthesis of IV–VI nanostructures, and thermoelectric compositions formed of such structures. In one aspect, the method includes forming a solution of a Group IV reagent, a Group VI reagent and a surfactant. A reducing agent can be added to the solution, and the resultant solution can be maintained at an elevated temperature, e.g., in a range of about 20° C. to about 360° C., for a duration sufficient for generating nanoparticles as binary alloys of the IV–VI elements.

Figure-of-merit enhancement in nanostructured FeSb(2-x)Ag(x) with Ag(1-y)Sb(y) nanoinclusions.

Abstract: We present the figure-of-merit (ZT) improvement in nanostructured FeSb2−xAgx with Ag1−ySby nanoinclusions through a metal/semiconductor interface engineering approach Owing to the interfaces between FeSb2−xAgx and Ag1−ySby phases, as well as the identical work functions, both thermal conductivity and electrical resistivity of the nanocomposites were significantly reduced in the lower temperature regime compared with pure FeSb2 Overall, an improvement of 70% in ZT was achieved for the optimized nanocomposite FeSb1975Ag0025/Ag077Sb023 sample, in which Ag077Sb023 is about 10% by molar ratio The results of this approach clearly demonstrated the metal/semiconductor interface concept and confirmed the potential of strongly correlated material systems as promising thermoelectric materials

I and i

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 …

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

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。

Carbon Nanotubes--the Route Toward Applications

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.