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.

Neutron scattering study of magnetic phase separation in nanocrystalline La5/8Ca3/8MnO3

Abstract: We demonstrate that magnetic phase separation and competing spin order in the colossal magnetoresistive (CMR) manganites can be directly explored via tuning strain in bulk samples of nanocrystalline La(1-x)Ca(x)MnO(3). Our results show that strain can be reversibly frozen into the lattice in order to stabilize coexisting antiferromagnetic domains within the nominally ferromagnetic metallic state of La(5/8)Ca(3/8)MnO(3). The measurement of tunable phase separation via magnetic neutron powder diffraction presents a direct route of exploring the correlated spin properties of phase separated charge/magnetic order in highly strained CMR materials and opens a potential avenue for realizing intergrain spin tunnel junction networks with enhanced CMR behavior in a chemically homogeneous material.

The challenge of tuning the ratio of lattice/total thermal conductivity toward conversion efficiency vs power density

Abstract: Minimizing the lattice thermal conductivity of thermoelectric materials is essential for preserving the temperature difference during the operation of thermoelectric devices incorporating these materials. During the past two decades, there has been substantial improvement in the thermoelectric figure of merit (zT) due to reduced lattice thermal conductivity. Employing alloying effects in solid-solution compounds is the most common and practical approach for inhibiting lattice thermal conductivity. This Perspective takes the n-type Mg3Sb2−xBix thermoelectric alloys as examples, addressing their lattice thermal conductivity and corresponding zT as functions of their Bi concentration. Additionally, we seek to understand the effect of the lattice contribution to total thermal conductivity for most thermoelectric materials currently being researched. The lattice/total thermal conductivity ratio at the temperature corresponding to the peak zT shows weak material dependence, widely ranging from 0.5 to 0.75, which implies that the lattice thermal conductivity of most thermoelectric materials can be decreased further to improve thermoelectric performance. On the other hand, thermoelectric materials with relatively low ratios exhibit high power factors in their operating temperature ranges, which is ascribed to their excellent electrical performance. These observations provide guidelines to tune transport properties for future applications in thermoelectric power generation.

Phase Inversion of Pickering Emulsions by Electrolyte for Potential Reversible Water-in-Oil Drilling Fluids

Abstract: Pickering emulsions show great potential for the petroleum industry, especially those that can realize emulsion inversion in basic conditions. Developing a simple and green approach to control emul...

Enhancement of critical current density in TlBaCaCuO type superconductors by the addition of SnO2

Abstract: The addition of SnO 2 to a mixture of Tl 2 O 3 and Ba 2 Ca 3 Cu 3 O 7 was found to enhance the critical current density ( J c ) of the subsequently fabricated superconductor. Without SnO 2 , the J c of the silver-sheathed superconductor of optimal thallium content was 7.4 to 7.6×10 3 A/cm 2 at 77 K and zero external magnetic field. With the addition of 0.1 formula-weight of SnO 2 per formula-weight of the superconductor, its J c was raised to 1.1 to 1.2×10 4 A/cm 2 under the same conditions. XRD data show that the ratio of 2223-phase can be greatly increased by the addition of SnO 2 and rapid quenching of the hot pellet in liquid nitrogen. However, SEM and EDAX analyses show that the superconducting phase in the ceramic sample does not contain Sn and suggest that the role of SnO 2 is to stabilize the 2223-phase and improve intergranular or interfacial contact.

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.