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.

Multiferroic phase diagram of Y partially substituted Dy1−xYxMnO3

Abstract: The effect of nonmagnetic Y partial substitution at the Dy site in Dy(1-x)Y(x)MnO(3) up to x=0.2 on magnetism, specific heat, and ferroelectricity is investigated, which resulted in a preliminary multiferroic phase diagram. It is revealed that the Y partial substitution suppresses the Dy-spin ordering point (T(Dy)) and ferroelectric ordering point (T(FE)) but enhances the Mn-spin ordering point (T(N)). The interaction between the spins of Dy and Mn is remarkably affected by Y substitution. The measured electrical polarization depends on the Y substitution in a complex way because the ferroelectricity is sensitive to the interaction between the spins of Dy and Mn. (c) 2011 American Institute of Physics. [doi: 10.1063/1.3536506]

Thermoelectric and mechanical properties on misch metal filled p-type skutterudites Mm0.9Fe4−xCoxSb12

Abstract: Most of the recent work focused on improving the dimensionless figure-of-merit, ZT, of p-type skutterudites uses one or two fillers to tune the electrical and thermal properties. Considering the fact that the different fillers with varying atomic mass and ionic radii can vibrate with different amplitudes to scatter phonons of different mean free paths, we synthesized misch metal filled p-type skutterudites Mm0.9Fe4−xCoxSb12 (where Mm is La0.25Ce0.5Pr0.05Nd0.15Fe0.03, called misch metal). The samples were synthesized by hot pressing nano-powder made by ball milling the annealed ingot of Mm0.9Fe4−xCoxSb12 with varying concentration of cobalt, x. By tuning the Fe/Co ratio, we achieved a thermal conductivity of ∼2 W m−1 K−1 at room temperature and ∼2.3 W m−1 K−1 at about 530 °C and a power factor of ∼30 μW cm−1 K−2 at about 425 °C in Mm0.9Fe3.1Co0.9Sb12, leading to a peak ZT ∼1.1 at about 425 °C. The nano-indentation experiment reveals that hardness and elastic modulus of the material is about 4.2 GPa and 116...

Well-oriented epitaxial gold nanotriangles and bowties on MoS2 for surface-enhanced Raman scattering.

Abstract: We report on epitaxial growth of Au nanotriangles (AuNTs) and bowties consisting of opposing tip-to-tip AuNTs with a few-nanometer gap on n-layer MoS2. These AuNTs exhibit well-defined crystallographic orientations with the average size determined by the MoS2 thickness. Monolayer (1L) MoS2 shows the weakest coalescence, corroborating the layer-dependent interactions among Au and n-layer MoS2. High-resolution transmission electron microscopy characterization confirms the lattice directing of thin MoS2 sheets on the AuNT formation with [111]Au||[001]MoS2 and Au|| MoS2. By introducing misfit dislocation arrays, the system with an 8.8% lattice misfit is stress-free. In particular, subwavelength-sized gold bowtie nanoantennas can be easily found on the MoS2 surface with a spacing gap down to 3 nm and a density up to 1.6 × 1013 m−2. This technique is low cost, time-saving and free of impurities compared to the conventional lithography technologies. Meanwhile, the equilateral AuNTs can enhance Raman signals of thin MoS2 sheets far stronger than that by ordinary gold films, indicating the potential use of AuNTs as SERS substrates for SERS applications.

Dielectric media based on isolated metallic nanostructures

Abstract: We study the dielectric properties of nanocomposites in the 0–15-GHz frequency regime These composites consist of electrically insulated metallic nanoparticles and carbon nanotubes, the elongated nanostructures in this study, uniformly dispersed in a dielectric matrix We find that the properties of these composites depend crucially on the shape and monodispersity of the nanoparticles While at high concentrations the spherical nanoparticles cause only slight modification of the dielectric function of the composite with respect to the matrix, the elongated nanoparticles produce composites with an enhanced real part of the dielectric function and low imaginary part Our theory, which is in excellent agreement with these results, suggests specific ways to further improve the dielectric properties of the composites

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.