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

to be done in this area. Face recognition is a problem that scarcely clamoured for attention before the computer age but, having surfaced, has involved a wide range of techniques and has attracted the attention of some fine minds (David Mumford was a Fields Medallist in 1974). This singular application of mathematical modelling to a messy applied problem of obvious utility and importance but with no unique solution is a pretty one to share with students: perhaps, returning to the source of our opening quotation, we may invert Duncan's earlier observation, 'There is an art to find the mind's construction in the face!'.

Linear and nonlinear waves, by G. B. Whitham. Pp.636. £50. 1999. ISBN 0 471 35942 4 (Wiley).

To say that this is the best book on the quantum theory of fields is no praise, since to my knowledge it is the only book on this subject But it is a very good and most useful book The original was written in German and appeared in 1942 This is a translation with some minor changes A few remarks have been added, concerning meson theory and nuclear forces, also footnotes referring to modern work in this field, and finally an appendix on the symmetrization of the energy momentum tensor according to Belinfante Quantum Theory of Fields Prof Gregor Wentzel Translated from the German by Charlotte Houtermans and J M Jauch Pp ix + 224, (New York and London: Interscience Publishers, Inc, 1949) 36s

Quantum Theory of Fields

There is a special reason for reviewing this book at this time: it is the 50th edition of a compendium that is known and used frequently in most chemical and physical laboratories in many parts of the world. Surely, a publication that has been published for 56 years, withstanding the vagaries of science in this century, must have had something to offer. There is another reason: while the book is a standard fixture in most chemical and physical laboratories, including those in medical centers, it is not as frequently seen in the laboratories of physician's offices (those either in solo or group practice). I believe that the Handbook can be useful in those laboratories. One of the reasons, among others, is that the various basic items of information it offers may be helpful in new tests, either physical or chemical, which are continuously being published. The basic information may relate

Handbook of Chemistry and Physics

Water striders (Gerris remigis) have remarkable non-wetting legs that enable them to stand effortlessly and move quickly on water, a feature believed to be due to a surface-tension effect caused by secreted wax. We show here, however, that it is the special hierarchical structure of the legs, which are covered by large numbers of oriented tiny hairs (microsetae) with fine nanogrooves, that is more important in inducing this water resistance.

/pdf/biophysics-water-repellent-legs-of-water-striders-3a4p860uri.pdf

Biophysics: Water-repellent legs of water striders

A new guideline for mitigating indoor airborne transmission of COVID-19 prescribes a limit on the time spent in a shared space with an infected individual (Bazant & Bush, 2021) Here, we rephrase this safety guideline in terms of occupancy time and mean exhaled carbon dioxide concentration in an indoor space, thereby enabling the use of CO2 monitors in the risk assessment of airborne transmission of respiratory diseases While CO2 concentration is related to airborne pathogen concentration (Rudnick & Milton, 2003), the guideline developed here accounts for the different physical processes affecting their evolution, such as enhanced pathogen production from vocal activity and pathogen removal via face-mask use, filtration, sedimentation and deactivation Critically, transmission risk depends on the total infectious dose, so necessarily depends on both the pathogen concentration and exposure time The transmission risk is also modulated by the fractions of susceptible, infected and immune persons within a population, which evolve as the pandemic runs its course A mathematical model is developed that enables a prediction of airborne transmission risk from real-time CO2 measurements Illustrative examples of implementing our guideline} are presented using data from CO2 monitoring in university classrooms and office spaces

/pdf/monitoring-carbon-dioxide-to-quantify-the-risk-of-indoor-5cbjud6fms.pdf

Monitoring carbon dioxide to quantify the risk of indoor airborne transmission of COVID-19

The influence of bounding geometry and rotation on the discharge of buoyant fluid from a turbulent axisymmetric plume in an open-ended channel is examined through an experimental study. Both homogenous and stratified ambients are considered. In the non-rotating channel, the plume rises and spreads as a pair of counterflowing gravity currents at either the free surface (in a homogenous ambient) or at the plume's level of neutral buoyancy (in a stratified fluid). Scaling laws and accompanying experiments indicate that in a homogeneous environment, the surface gravity currents emerging from a channel of width W and depth H have a depth h which is independent of plume source conditions:

Experiments on buoyant plumes in a rotating channel

Superradiance and subradiance occur in quantum optics when the emission rate of photons from multiple atoms is enhanced and diminished, respectively, owing to interaction between neighboring atoms. We here demonstrate a classical analog thereof in a theoretical model of droplets walking on a vibrating bath. Two droplets are confined to identical two-level systems, a pair of wells between which the drops may tunnel, joined by an intervening coupling cavity. The resulting classical superradiance is rationalized in terms of the system's non-Markovian, pilot-wave dynamics.

Hydrodynamic superradiance in wave-mediated cooperative tunneling.

We investigate the generation of megaplumes by the release of buoyant hydrothermal fluid from the seafloor. We show that megaplumes may be generated from various modes of venting, including both the instantaneous and continuous release of hydrothermal effluent from either a point or line source. The hydrothermal effluent forms a buoyant plume, which rises through the water column to its neutral buoyancy height and then intrudes laterally to form a neutral cloud. Owing to the influence of the Earth's rotation ƒ, whose magnitude is Ω = ƒ/2, the neutral cloud eventually becomes unstable, giving rise to geostrophic vortices that propagate away from the source. By combining the scaling laws governing turbulent plumes and geostrophic vortices, we establish new relationships between the megaplume geometry and the source conditions. We find that megaplumes whose radius greatly exceeds their height of rise are formed from sources that persist for at least several days, since, in the deep ocean, the radii of eddies produced by short-lived releases of buoyant fluid are comparable to their rise height. Our model predicts the total buoyancy B of the hydrothermal effluent released in forming such megaplume structures. We also calculate the total megaplume heat content in terms of the total buoyancy release and the thermal anomaly of the megaplume, by considering the effects of the ambient stratification in both temperature and salinity on plume properties. Finally, we apply the model to data from three historic megaplume events at the Juan de Fuca ridge.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/1999JC900063

Dimensions and dynamics of megaplumes

The influence of flexibility on the flight of autorotating winged seedpods is examined through an experimental investigation of tumbling rectangular paper strips freely falling in air. Our results suggest the existence of a critical length above which the wing bends. We develop a theoretical model that demonstrates that this buckling is prompted by inertial forces associated with the tumbling motion, and yields a buckling criterion consistent with that observed. We further develop a reduced model for the flight dynamics of flexible tumbling wings, that illustrates the effect of aeroelastic coupling on flight characteristics and explains experimentally observed variations in the wing’s falling speed and range.

John W. M. Bush

Papers

Monitoring carbon dioxide to quantify the risk of indoor airborne transmission of COVID-19

Experiments on buoyant plumes in a rotating channel

Hydrodynamic superradiance in wave-mediated cooperative tunneling.

Dimensions and dynamics of megaplumes

Tumbling dynamics of flexible wings