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

BACKGROUND With a rising global population, increasing energy demands, and impending climate change, major concerns have been raised over the security of our energy future. Developing sustainable, fossil-free pathways to produce fuels and chemicals of global importance could play a major role in reducing carbon dioxide emissions while providing the feedstocks needed to make the products we use on a daily basis. One prospective goal is to develop electrochemical conversion processes that can convert molecules in the atmosphere (e.g., water, carbon dioxide, and nitrogen) into higher-value products (e.g., hydrogen, hydrocarbons, oxygenates, and ammonia) by coupling to renewable energy. Electrocatalysts play a key role in these energy conversion technologies because they increase the rate, efficiency, and selectivity of the chemical transformations involved. Today’s electrocatalysts, however, are inadequate. The grand challenge is to develop advanced electrocatalysts with the enhanced performance needed to enable widespread penetration of clean energy technologies. ADVANCES Over the past decade, substantial progress has been made in understanding several key electrochemical transformations, particularly those that involve water, hydrogen, and oxygen. The combination of theoretical and experimental studies working in concert has proven to be a successful strategy in this respect, yielding a framework to understand catalytic trends that can ultimately provide rational guidance toward the development of improved catalysts. Catalyst design strategies that aim to increase the number of active sites and/or increase the intrinsic activity of each active site have been successfully developed. The field of hydrogen evolution, for example, has seen important breakthroughs over the years in the development of highly active non–precious metal catalysts in acid. Notable advancements have also been made in the design of oxygen reduction and evolution catalysts, although there remains substantial room for improvement. The combination of theory and experiment elucidates the remaining challenges in developing further improved catalysts, often involving scaling relations among reactive intermediates. This understanding serves as an initial platform to design strategies to circumvent technical obstacles, opening up opportunities and approaches to develop higher-performance electrocatalysts for a wide range of reactions. OUTLOOK A systematic framework of combining theory and experiment in electrocatalysis helps to uncover broader governing principles that can be used to understand a wide variety of electrochemical transformations. These principles can be applied to other emerging and promising clean energy reactions, including hydrogen peroxide production, carbon dioxide reduction, and nitrogen reduction, among others. Although current paradigms for catalyst development have been helpful to date, a number of challenges need to be successfully addressed in order to achieve major breakthroughs. One important frontier, for example, is the development of both experimental and computational methods that can rapidly elucidate reaction mechanisms on broad classes of materials and in a wide range of operating conditions (e.g., pH, solvent, electrolyte). Such efforts would build on current frameworks for understanding catalysis to provide the deeper insights needed to fine-tune catalyst properties in an optimal manner. The long-term goal is to continue improving the activity and selectivity of these catalysts in order to realize the prospects of using renewable energy to provide the fuels and chemicals that we need for a sustainable energy future.

/pdf/combining-theory-and-experiment-in-electrocatalysis-insights-3l4yblici7.pdf

Combining theory and experiment in electrocatalysis: Insights into materials design

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.

Low-temperature solution-processed photovoltaics suffer from low efficiencies because of poor exciton or electron-hole diffusion lengths (typically about 10 nanometers). Recent reports of highly efficient CH3NH3PbI3-based solar cells in a broad range of configurations raise a compelling case for understanding the fundamental photophysical mechanisms in these materials. By applying femtosecond transient optical spectroscopy to bilayers that interface this perovskite with either selective-electron or selective-hole extraction materials, we have uncovered concrete evidence of balanced long-range electron-hole diffusion lengths of at least 100 nanometers in solution-processed CH3NH3PbI3. The high photoconversion efficiencies of these systems stem from the comparable optical absorption length and charge-carrier diffusion lengths, transcending the traditional constraints of solution-processed semiconductors.

https://dr.ntu.edu.sg/bitstream/10220/16761/1/long-range balanced electron- and hole-transport lengths in organic-inorganic ch3nh3pbi3.pdf

Long-Range Balanced Electron- and Hole-Transport Lengths in Organic-Inorganic CH3NH3PbI3

Understanding spin-wave dynamics in chiral magnets is a key step for the development of high-speed, spin-wave based spintronic devices that take advantage of chiral and topological spin textures for their operation. Here, we present an experimental and theoretical study of spin-wave dynamics in a cubic B20 FeGe single crystal. Using the combination of waveguide microwave absorption spectroscopy (MAS), micromagnetic simulations, and analytical theory, we identify the resonance dynamics in all magnetic phases (field polarized, conical, helical, and skyrmion phases). Because the resonance frequencies of specific chiral spin textures are unique, a quantitative agreement between our theoretical predictions and experimental findings for all resonance frequencies and spin wave modes enables us to unambiguously identify chiral magnetic phases and to demonstrate that MAS is a powerful tool to efficiently extract a magnetic phase diagram.

Topological spin dynamics in cubic FeGe near room temperature

Eleven organic Lewis bases were investigated as potential ligands (L) on W(6)S(8)L'(6) clusters by exploring ligand exchange reactions to form W(6)S(8)L(6) clusters. Six new homoleptic W(6)S(8)L(6) cluster complexes were prepared and characterized with L = tri-n-butylphosphine (P(n)Bu(3)), triphenylphosphine (PPh(3)), tert-butylisocyanide ((t)BuNC), morpholine, methylamine (MeNH(2)), and tert-butylamine ((t)BuNH(2)). While partial replacement of ligands occurred with diethylamine (Et(2)NH) and dibutylamine (Bu(2)NH), homoleptic clusters could not be prepared by these exchange reactions. When aniline, tribenzylamine, and tri-tert-butylphosphine were the potential ligands, no exchange was observed. From ligand exchange studies of these ligands and others previously studied, a thermodynamic series of binding free energies for ligands on W(6)S(8)L(6) clusters was established as the following: non-Lewis base solvents, aniline, P(t)()Bu(3), etc. << Et(2)NH, Bu(2)NH < (t)BuNH(2) < morpholine, piperidine < or = (n)BuNH(2), MeNH(2) < or = 4-tert-butylpyridine, pyridine < (t)BuNC < tricyclohexylphosphine (PCy(3)) < PPh(3), P(n)Bu(3) < or = triethylphosphine (PEt(3)). Structures of the new cluster complexes were determined by X-ray crystallography. The new compounds were also characterized by NMR spectroscopy and thermogravimetric analyses (TGA). The W-L bond orders and TGA data qualitatively agree with the thermodynamic series above.

Synthesis, Characterization, and Ligand Exchange Studies of W~6~S~8~L~6~ Cluster Compounds

Quantum dot nanoscale semiconductor heterostructures (QDHs) are a class of materials potentially useful for integration into solar energy conversion devices. However, realizing the potential of these heterostructured systems requires the ability to identify and synthesize heterostructures with suitably designed materials, controlled size and morphology of each component, and structural control over their shared interface. In this review, we will present the case for the utility and advantages of chemically synthesized QDHs for solar energy conversion, beginning with an overview of various methods of heterostructured material synthesis and a survey of heretofore reported materials systems. The fundamental charge transfer properties of the resulting materials combinations and their basic design principles will be outlined. Finally, we will discuss representative solar photovoltaic and photoelectrochemical devices employing QDHs (including quantum dot sensitized solar cells, or QDSSCs) and examine how QDH synthesis and design impacts their performance.

Quantum Dot Nanoscale Heterostructures for Solar Energy Conversion

Magnetic skyrmions are stable nanosized spin structures that can be displaced at low electrical current densities. Because of these properties, they have been proposed as building blocks of future electronic devices with unprecedentedly high information density and low energy consumption. The electrical detection of skyrmions via the Topological Hall Effect (THE), has so far been demonstrated only at cryogenic temperatures. Here, we report the observation of a skyrmion Topological Hall Effect near room temperature (276 K) in a mesoscopic lamella of FeGe. This region unambiguously coincides with the skyrmion lattice location revealed by neutron scattering. We provide clear evidence of a reentrant helicoid magnetic phase adjacent to the skyrmion phase, and discuss the large THE amplitude (5 n$\Omega$.cm) in view of the ordinary Hall Effect.

/pdf/skyrmion-topological-hall-effect-near-room-temperature-1mqzz8x3g6.pdf

Skyrmion Topological Hall Effect near Room Temperature

Single-crystal nanorods of half-metallic chromium dioxide (CrO2) were synthesized and structurally characterized. Spin-dependent electrical transport was investigated in individual CrO2 nanorod devices contacted with nonmagnetic metallic electrodes. Negative magnetoresistance (MR) was observed at low temperatures due to the spin-dependent direct tunneling through the contact barrier and the high spin polarization in the half-metallic nanorods. The magnitude of this negative magnetoresistance decreases with increasing bias voltage and temperature due to spin-independent inelastic hopping through the barrier, and a small positive magnetoresistance was found at room temperature. It is believed that the contact barrier and the surface state of the nanorods have great influence on the spin-dependent transport limiting the magnitude of MR effect in this first attempt at spin filter devices of CrO2 nanorods with nonmagnetic contacts.

Song Jin

Papers

Topological spin dynamics in cubic FeGe near room temperature

Synthesis, Characterization, and Ligand Exchange Studies of W~6~S~8~L~6~ Cluster Compounds

Quantum Dot Nanoscale Heterostructures for Solar Energy Conversion

Skyrmion Topological Hall Effect near Room Temperature

Spin-dependent tunneling transport into CrO2 nanorod devices with nonmagnetic contacts.