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.

High throughput growth of zinc oxide nanowires from zinc powder with the assistance of sodium chloride

Abstract: Sodium chloride (NaCl) was found to be very helpful in producing single crystal zinc oxide (ZnO) nanowires in gram quantities. The growth involves heating the mixture of zinc powder and NaCl to 600-700 degrees C in flowing gases of oxygen and argon. A conversion efficiency of 70-80% (Zn to ZnO) was achieved when NaCl was used, and 5-10% without NaCl. The NaCl was completely removed by soaking and rinsing the mixture in water a few times. Photoluminescence spectra using excitation of 325 nm showed a very strong emission only in the visible frequency range, indicating that the surface states dominate the emission.

Ultra-low thermal conductivities of hot-pressed attapulgite and its potential as thermal insulation material

Abstract: In the past, there have been very few reports on thermal properties of attapulgite which is a widely used clay mineral. In this work, we report on extremely low thermal conductivities in attapulgite samples synthesized by hot-pressing. Attapulgite powder was hot-pressed at different temperatures into bulk samples, and a systematic study was conducted on the microstructures and thermal properties. Differential scanning calorimetry analysis shows that hot-pressing induces a rapid dehydration of the attapulgite powders. X-ray diffraction data and scanning/transmission electron microscopy reveal that the hot-pressed attapulgite features high porosity and complex microstructures, including an amorphous phase. As a result, the hot-pressed attapulgite exhibits thermal conductivity less than 2.5 W m−1 K−1 up to 600 °C. For one sample with porosity of 45.7%, the thermal conductivity is as low as 0.34 W m−1 K−1 at 50 °C. This suggests the potential of hot-pressed attapulgite as a candidate for thermal barrier mater...

Power Generation from Nanostructured Half-Heusler Thermoelectrics for Efficient and Robust Energy Harvesting

Abstract: We demonstrate a robust and high-power-density thermoelectric device fabricated using high-performance nanostructured bulk half-Heusler materials. A novel metal-ceramic composite was employed as el...

CALPHAD as a powerful technique for design and fabrication of thermoelectric materials

Abstract: Phase diagrams have always been used as a roadmap for materials research in terms of melting, casting, crystal growth, joining, solid-state reaction, heat treatment, phase transformation, and so on. CALPHAD (CALculation of PHAse Diagram) offers a theoretical instruction through a plausible simulation based on Gibbs energies, which could bypass some difficult experiments, extrapolate to a multicomponent-system or metastable region to get complete thermodynamic and kinetic properties, and improve the consistency and accuracy of the measured phase diagram. The present work takes thermoelectric materials as a paradigm, illustrating how to interpret and utilize phase diagrams as well as other thermodynamic information to design target materials, with the aid of multi-component CALPHAD-base databases and software. Two main aspects including phase design and microstructure modulation are delivered by the fundamentals of CALPHAD modeling and concrete examples of thermoelectric alloys. Opinions about the challenges and potentials of its applications in thermoelectric systems are also pointed out.

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.