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.

Apparatus and methods for solar energy conversion using nanoscale cometal structures

Abstract: An apparatus and methods for solar conversion using nanoscale cometal structures are disclosed herein. The cometal structures may be coaxial and coplanar. A nanoscale optics apparatus for use as a solar cell comprises a plurality of nanoscale cometal structures each including a photovoltaic material located between a first electrical conductor and a second electrical conductor. A method of fabricating solar cells comprises preparing a plurality of nanoscale planar structures; coating a plurality of planar surfaces of the plurality of planar structures with a photovoltaic semiconductor while leaving space between the plurality of planar surfaces; and coating the photovoltaic semiconductor with an outer electrical conductor layer, wherein a portion of the outer electrical conductor layer is located between the planar structures to form coplanar structures.

Pure d x 2 - y 2 order-parameter symmetry in the tetragonal superconductor TI 2 Ba 2 CuO 6+δ

Abstract: Crucial to the successful development of a theoretical model for high-temperature superconductivity is knowledge of the symmetry of the order parameter (or wavefunction) that describes the pairing of electrons in the superconducting state. Several experimental studies1–8provide convincing evidence for an anisotropic order parameter, consistent with a symmetry. But none of these earlier experiments could rule out unambiguously an additional contribution from isotropic s-wave pairing; these experiments either involved superconductors with an orthorhombic crystal structure (for which a mixed s + d state is becoming increasingly recognized as a likely consequence9,10), or their interpretation required detailed modelling of the uncertain effects of disorder and defects. Here we report the results of an experiment designed to circumvent these difficulties: the material studied is the single-layer tetragonal superconductor Tl2Ba2CuO6+δ, and the experimental configuration is such that the interpretation of the results relies solely on symmetry considerations. Our results indicate that this material has pure pairing symmetry, so providing a starting point for understanding the more complex mixed s + d state that appears to characterize other high-temperature superconductors.

Study of the Thermoelectric Properties of Lead Selenide Doped with Boron, Gallium, Indium, or Thallium

Abstract: Group IIIA elements (B, Ga, In, and Tl) have been doped into PbSe for enhancement of thermoelectric properties. The electrical conductivity, Seebeck coefficient, and thermal conductivity were systematically studied. Room-temperature Hall measurements showed an effective increase in the electron concentration upon both Ga and In doping and the hole concentration upon Tl doping to ∼7 × 1019 cm–3. No resonant doping phenomenon was observed when PbSe was doped with B, Ga, or In. The highest room-temperature power factor ∼2.5 × 10–3 W m–1 K–2 was obtained for PbSe doped with 2 atom % B. However, the power factor in B-doped samples decreased with increasing temperature, opposite to the trend for the other dopants. A figure of merit (ZT) of ∼1.2 at ∼873 K was achieved in PbSe doped with 0.5 atom % Ga or In. With Tl doping, modification of the band structure around the Fermi level helped to increase the Seebeck coefficient, and the lattice thermal conductivity decreased, probably as a result of effective phonon s...

Rational design of core-shell-structured CoPx@FeOOH for efficient seawater electrolysis

Abstract: Hydrogen generation by seawater electrolysis is a sustainable approach to renewable-energy conversion which requires efficient catalyst to address challenges such as competing chlorine evolution reaction, chloride corrosion, and catalyst poisoning. Here, core-shell-structured CoPx@FeOOH is designed for selective OER in seawater. This catalyst has high conductivity, large surface area, improved turnover frequency, and optimal absorption energy to OER intermediates, which together lead to excellent catalytic activity. The enhanced chemical stability and corrosion resistance ensure its catalytic performance in seawater. Specifically, it requires overpotentials of 283 and 337 mV to attain current densities of 100 and 500 mA cm−2, respectively, in 1 M KOH seawater, with durability over 80 h of continuous testing without producing any hypochlorite. The CoPx||CoPx@FeOOH pair requires voltages of 1.710 and 1.867 V to attain current densities of 100 and 500 mA cm−2 with a high Faradaic efficiency, showing its great promise for fuel-gas production from seawater.

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.