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.

Enhanced Thermal Stability of W-Ni-Al2O3 Cermet-Based Spectrally Selective Solar Absorbers with Tungsten Infrared Reflectors

Abstract: Solar thermal technologies such as solar hot water and concentrated solar power trough systems rely on spectrally selective solar absorbers. These solar absorbers are designed to efficiently absorb the sunlight while suppressing re-emission of infrared radiation at elevated temperatures. Efforts for the development of such solar absorbers must not only be devoted to their spectral selectivity but also to their thermal stability for high temperature applications. Here, selective solar absorbers based on two cermet layers are fabricated on mechanically polished stainless steel substrates using a magnetron sputtering technique. The targeted operating temperature is 500–600 °C. A detrimental change in the morphology, phase, and optical properties is observed if the cermet layers are deposited on a stainless steel substrate with a thin nickel adhesion layer, which is due to the diffusion of iron atoms from the stainless steel into the cermet layer forming a FeWO4 phase. In order to improve thermal stability and reduce the infrared emittance, tungsten is found to be a good candidate for the infrared reflector layer due to its excellent thermal stability and low infrared emittance. A stable solar absorptance of ≈0.90 is demonstrated, with a total hemispherical emittance of 0.15 at 500 °C.

Pairing Symmetry in Single-Layer Tetragonal Tl2Ba2CuOβ+δ Superconductors

Abstract: A high-resolution scanning superconducting quantum interference device microscopy study of tetragonal single-layer Tl 2 Ba 2 CuO β+δ films, deposited on tricrystal SrTiO 3 substrates, demonstrates the effect of spontaneously generated half flux quanta. This observation shows that in addition to YBa 2 Cu 3 O 7 , the order parameter symmetry in Tl 2 Ba 2 CuO β+δ is consistent with that of a d x 2 - y 2 pair state. This result also rules out any bilayer or twinning effects and any pairing that is incompatible with the fourfold rotational symmetry as in the Tl 2 Ba 2 CuO β+δ superconducting system.

The bridge between the materials and devices of thermoelectric power generators

Abstract: While considerable efforts have been made to develop and improve thermoelectric materials, research on thermoelectric modules is at a relatively early stage because of the gap between material and device technologies. In this review, we discuss the cumulative temperature dependence model to reliably predict the thermoelectric performance of module devices and individual materials for an accurate evaluation of the p–n configuration compared to the conventional model used since the 1950s. In this model, the engineering figure of merit and engineering power factor are direct indicators, and they exhibit linear correlations to efficiency and output power density, respectively. To reconcile the strategy for high material performance and the thermomechanical reliability issue in devices, a new methodology is introduced by defining the engineering thermal conductivity. Beyond thermoelectric materials, the device point of view needs to be actively addressed before thermoelectric generators can be envisioned as power sources.

Thermoelectric Property Study of Nanostructured p‐Type Half‐Heuslers (Hf, Zr, Ti)CoSb0.8Sn0.2

Abstract: Based on the best peak theromoelectric figure-of-merit value (ZT) of ca. 0.8 in Hf0.5Zr0.5CoSb0.8Sn0.2 and ca. 1 in Hf0.8Ti0.2CoSb0.8Sn0.2, the effect of Ti on thermoelectric properties is studied in (Hf, Zr, Ti)CoSb0.8Sn0.2, with the aim of further improving the ZT and reducing the usage of Hf. By either partial replacement of Hf and Zr with Ti in Hf0.5Zr0.5CoSb0.8Sn0.2 or partial replacement of Hf and Ti with Zr in Hf0.8Ti0.2CoSb0.8Sn0.2, a peak ZT of ≥1 is achieved at 800°C in Hf0.44Zr0.44Ti0.12CoSb0.8Sn0.2. This composition has two advantages over the previous two best compositions: higher ZT than Hf0.5Zr0.5CoSb0.8Sn0.2 and less Hf than in Hf0.8Ti0.2CoSb0.8Sn0.2. A higher ZT with less Hf is very much desired since Hf is much more expensive than other constituent elements. The ZT improvement is the result of thermal conductivity reduction due to phonon scattering by both alloy and the nanostructure effect.

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.