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

Merchants of Doubt. How a Handful of Scientists Obscured the Truth on Issues from Tobacco Smoke to Global Warming

A detailed chemical kinetic model has been used to study dimethyl ether (DME) oxidation over a wide range of conditions. Experimental results obtained in a jet-stirred reactor (JSR) at I and 10 atm, 0.2 < 0 < 2.5, and 800 < T < 1300 K were modeled, in addition to those generated in a shock tube at 13 and 40 bar, 0 = 1.0 and 650 :5 T :5 1300 K. The JSR results are particularly valuable as they include concentration profiles of reactants, intermediates and products pertinent to the oxidation of DME. These data test the Idnetic model severely, as it must be able to predict the correct distribution and concentrations of intermediate and final products formed in the oxidation process. Additionally, the shock tube results are very useful, as they were taken at low temperatures and at high pressures, and thus undergo negative temperature dependence (NTC) behavior. This behavior is characteristic of the oxidation of saturated hydrocarbon fuels, (e.g. the primary reference fuels, n-heptane and iso- octane) under similar conditions. The numerical model consists of 78 chemical species and 336 chemical reactions. The thermodynamic properties of unknown species pertaining to DME oxidation were calculated using THERM.

/pdf/wide-range-modeling-study-of-dimethyl-ether-oxidation-pnag57ojwu.pdf

Wide range modeling study of dimethyl ether oxidation

Soot formation in laminar counterflow flames

The mechanism of carbon particulate (soot) inception has been a subject of numerous studies and debates. The article begins with a critical review of prior proposals, proceeds to the analysis of factors enabling the development of a meaningful nucleation flux, and then introduces new ideas that lead to the fulfillment of these requirements. In the new proposal, a rotationally-activated dimer is formed in the collision of an aromatic molecule and an aromatic radical; the two react during the lifetime of the dimer to form a stable, doubly-bonded bridge between them, with the reaction rooted in a five-member ring present on the molecule edge. Several such reactions were examined theoretically and the most promising one generated a measurable nucleation flux. The consistency of the proposed model with known aspects of soot particle nanostructure is discussed. The foundation of the new model is fundamentally the H-Abstraction-Carbon-Addition (HACA) mechanism with the reaction affinity enhanced by rotational excitation.

On the mechanism of soot nucleation.

Chain reactions of resonance-stabilized radicals turn molecules into clusters and nanoparticles Humans have used the high-temperature synthesis of carbon particles as a source of pigments since prehistoric times (1), and today, “carbon blacks” are used in tires, inks, coatings, plastics, and electrical applications. For most substances, solid particles become gases when heated, but solid soot forms from gaseous molecules at high temperature through a mechanism that is still not understood. The high-temperature synthesis of carbon particles (see the figure) occurs under oxygen-starved conditions where simple hydrocarbons can grow into larger molecules, especially polycyclic aromatic hydrocarbons (PAHs), in the gas phase. These large molecules cluster into carbon nanoparticles, a process often referred to as soot inception. The carbon nanoparticles then grow and aggregate to form larger, fractal-like structures. On page 997 of this issue, Johansson et al. (2) propose a new mechanism based on chain reactions of resonance-stabilized radical (RSR) species to explain this transition from gas-phase molecules to nanoparticles.

https://science.sciencemag.org/content/sci/361/6406/978.full.pdf

A radical approach to soot formation

Understanding the formation and growth of polycyclic aromatic hydrocarbons (PAHs) and young soot from n-dodecane in a sooting laminar coflow diffusion flame

Investigation of PAH and soot formation in a dimethyl ether (DME) laminar coflow diffusion flame

The relationship between soot surface growth, soot nanostructure and reactant temperature (Tr) in a coflow diffusion ethylene flame was investigated with multiple experimental techniques. The Tr was raised by heating the coflow air. Three cases, with 300K, 473K, and 673K Tr, respectively, were studied. Laser-induced Incandescence revealed that increasing Tr promotes soot formation. Although soot primary particle diameter (dp) also increases with Tr, the increase in dp slows down after 473K Tr, suggesting that there is a deceleration in soot surface growth. Transmission Electron Microscopy (TEM) imaging showed that increased Tr promotes soot aggregation and yields larger and more mature primary particles. The assessment of the Selected Area Electron Diffraction (SAED) patterns indicated that, at 673K Tr, there is a growth of lattice planes. Raman spectroscopy revealed further structural details. By assessing the band intensity ratios, soot for the Tr of 673K has more curved nanostructures. The deceleration of soot surface growth may be explained by surface aging, which is characterized by an increase in curved nanostructures.

Tirthankar Mitra

Papers

A radical approach to soot formation

Understanding the formation and growth of polycyclic aromatic hydrocarbons (PAHs) and young soot from n-dodecane in a sooting laminar coflow diffusion flame

Investigation of PAH and soot formation in a dimethyl ether (DME) laminar coflow diffusion flame

The effect of elevated reactant temperatures on soot nanostructures in a coflow diffusion ethylene flame

Polycyclic aromatic hydrocarbon formation in a flame of the alkylated aromatic trimethylbenzene compared to those of the alkane dodecane