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 …

I and i

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。

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

The interest in nanoscale materials stems from the fact that new properties are acquired at this length scale and, equally important, that these properties * To whom correspondence should be addressed. Phone, 404-8940292; fax, 404-894-0294; e-mail, mostafa.el-sayed@ chemistry.gatech.edu. † Case Western Reserve UniversitysMillis 2258. ‡ Phone, 216-368-5918; fax, 216-368-3006; e-mail, burda@case.edu. § Georgia Institute of Technology. 1025 Chem. Rev. 2005, 105, 1025−1102

Chemistry and properties of nanocrystals of different shapes.

Since the discovery of mechanically exfoliated graphene in 2004, research on ultrathin two-dimensional (2D) nanomaterials has grown exponentially in the fields of condensed matter physics, material science, chemistry, and nanotechnology. Highlighting their compelling physical, chemical, electronic, and optical properties, as well as their various potential applications, in this Review, we summarize the state-of-art progress on the ultrathin 2D nanomaterials with a particular emphasis on their recent advances. First, we introduce the unique advances on ultrathin 2D nanomaterials, followed by the description of their composition and crystal structures. The assortments of their synthetic methods are then summarized, including insights on their advantages and limitations, alongside some recommendations on suitable characterization techniques. We also discuss in detail the utilization of these ultrathin 2D nanomaterials for wide ranges of potential applications among the electronics/optoelectronics, electrocat...

Recent Advances in Ultrathin Two-Dimensional Nanomaterials

Nitrogen (N)-doped carbon materials exhibit high electrocatalytic activity for the oxygen reduction reaction (ORR), which is essential for several renewable energy systems. However, the ORR active site (or sites) is unclear, which retards further developments of high-performance catalysts. Here, we characterized the ORR active site by using newly designed graphite (highly oriented pyrolitic graphite) model catalysts with well-defined π conjugation and well-controlled doping of N species. The ORR active site is created by pyridinic N. Carbon dioxide adsorption experiments indicated that pyridinic N also creates Lewis basic sites. The specific activities per pyridinic N in the HOPG model catalysts are comparable with those of N-doped graphene powder catalysts. Thus, the ORR active sites in N-doped carbon materials are carbon atoms with Lewis basicity next to pyridinic N.

Active sites of nitrogen-doped carbon materials for oxygen reduction reaction clarified using model catalysts

Nitrogen-doped carbon nanomaterials are known to exhibit good electrocatalytic activity for the oxygen reduction reaction (ORR). However, the structure of the ORR active site and optimum content of nitrogen in the carbon lattice for ORR activity remains unknown. In this study, a series of vertically aligned carbon nanotubes (VA-CNTs) with a surface nitrogen concentration of 0, 4.3, 5.6, 8.4, and 10.7 atom % is prepared by the alumina template technique and characterized with XRD, Raman spectroscopy, SEM, and XPS. Electrocatalytic ORR activity is investigated by rotating disk electrode (RDE) voltammetry. Among them, VA-CNTs with a nitrogen concentration of 8.4 atom % exhibited the best ORR performance. This is ascribed to a greater number of pyridinic-type nitrogen sites. The good performance of less expensive nitrogen-doped CNTs makes the ORR electrodes a viable alternative to platinum for energy conversion device applications.

In Search of the Active Site in Nitrogen-Doped Carbon Nanotube Electrodes for the Oxygen Reduction Reaction

By means of density functional theory computations, we systematically investigated the adsorption and diffusion of lithium on the recently synthesized VS2 monolayer, in comparison with MoS2 monolayer and graphite. Intrinsically metallic, VS2 monolayer has a higher theoretical capacity (466 mAh/g), a lower or similar Li diffusion barrier as compared to MoS2 and graphite, and has a low average open-circuit voltage of 0.93 V (vs Li/Li+). Our results suggest that VS2 monolayer can be utilized as a promising anode material for Li ion batteries with high power density and fast charge/discharge rates.

Metallic VS2 Monolayer: A Promising 2D Anode Material for Lithium Ion Batteries

By means of density functional theory computations, we systematically investigated the adsorption and diffusion of Li on the 2-D MoS2 nanosheets and 1-D zigzag MoS2 nanoribbons (ZMoS2NRs), in comparison with MoS2 bulk. Although the Li mobility can be significantly facilitated in MoS2 nanosheets, their decreased Li binding energies make them less attractive for cathode applications. Because of the presence of unique edge states, ZMoS2NRs have a remarkably enhanced binding interaction with Li without sacrificing the Li mobility, and thus are promising as cathode materials of Li-ion batteries with a high power density and fast charge/discharge rates.

Enhanced Li Adsorption and Diffusion on MoS2 Zigzag Nanoribbons by Edge Effects: A Computational Study.

Computational Screening of Efficient Single‐Atom Catalysts Based on Graphitic Carbon Nitride (g‐C3N4) for Nitrogen Electroreduction

In recent years, two-dimensional (2D) materials, including graphene and inorganic graphene analogs (IGAs), have been the subject of intensive studies due to their novel chemical and physical properties. With apparent high surface-to-volume ratio, 2D materials are promising electrode candidates for lithium ion batteries (LIBs). Compared with three-dimensional bulk crystals, 2D materials have superior structural characteristics, and thus can exhibit higher specific capacity and better high-rate stability. In particular, composites consisting of graphene and IGAs could have enhanced electrochemical performances due to the specific synergic effects, which open up new frontiers in fundamental science and technology. Although the explorations of using IGAs for lithium storage have begun very recently, a timely overview in this field is necessary for developing improved electrode candidates. In this feature article, we summarize the ongoing efforts and studies from both experimental and theoretical communities on developing graphene and IGAs as LIB electrodes. Compared with graphene, we put more emphasis on IGAs, such as transition metal oxides, dichalcogenides, and MXenes, and illustrate the significant advantages of IGAs as electrodes. We also show that due to the effective synergic interactions between graphene and IGAs, their composites step further to achieve reversible high-capacity LIBs. Finally, we discuss the problems and limitations for the practical application of 2D materials to LIBs.

Carlos R. Cabrera

Papers

In Search of the Active Site in Nitrogen-Doped Carbon Nanotube Electrodes for the Oxygen Reduction Reaction

Metallic VS2 Monolayer: A Promising 2D Anode Material for Lithium Ion Batteries

Enhanced Li Adsorption and Diffusion on MoS2 Zigzag Nanoribbons by Edge Effects: A Computational Study.

Computational Screening of Efficient Single‐Atom Catalysts Based on Graphitic Carbon Nitride (g‐C3N4) for Nitrogen Electroreduction

Graphene, inorganic graphene analogs and their composites for lithium ion batteries