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

This review summarizes theoretical progress in the field of active matter, placing it in the context of recent experiments. This approach offers a unified framework for the mechanical and statistical properties of living matter: biofilaments and molecular motors in vitro or in vivo, collections of motile microorganisms, animal flocks, and chemical or mechanical imitations. A major goal of this review is to integrate several approaches proposed in the literature, from semimicroscopic to phenomenological. In particular, first considered are ``dry'' systems, defined as those where momentum is not conserved due to friction with a substrate or an embedding porous medium. The differences and similarities between two types of orientationally ordered states, the nematic and the polar, are clarified. Next, the active hydrodynamics of suspensions or ``wet'' systems is discussed and the relation with and difference from the dry case, as well as various large-scale instabilities of these nonequilibrium states of matter, are highlighted. Further highlighted are various large-scale instabilities of these nonequilibrium states of matter. Various semimicroscopic derivations of the continuum theory are discussed and connected, highlighting the unifying and generic nature of the continuum model. Throughout the review, the experimental relevance of these theories for describing bacterial swarms and suspensions, the cytoskeleton of living cells, and vibrated granular material is discussed. Promising extensions toward greater realism in specific contexts from cell biology to animal behavior are suggested, and remarks are given on some exotic active-matter analogs. Last, the outlook for a quantitative understanding of active matter, through the interplay of detailed theory with controlled experiments on simplified systems, with living or artificial constituents, is summarized.

Hydrodynamics of soft active matter

Colloidal particles act in many ways like surfactant molecules, particularly if adsorbed to a fluid–fluid interface. Just as the water or oil-liking tendency of a surfactant is quantified in terms of the hydrophile–lipophile balance (HLB) number, so can that of a spherical particle be described in terms of its wettability via contact angle. Important differences exist, however, between the two types of surface-active material, due in part to the fact that particles are strongly held at interfaces. This review attempts to correlate the behaviour observed in systems containing either particles or surfactant molecules in the areas of adsorption to interfaces, partitioning between phases and solid-stabilised emulsions and foams.

Particles as surfactants—similarities and differences

A theoretical perspective is provided on the glass transition in molecular liquids at thermal equilibrium, on the spatially heterogeneous and aging dynamics of disordered materials, and on the rheology of soft glassy materials. We start with a broad introduction to the field and emphasize its connections with other subjects and its relevance. The important role played by computer simulations in studying and understanding the dynamics of systems close to the glass transition at the molecular level is given. The recent progress on the subject of the spatially heterogeneous dynamics that characterizes structural relaxation in materials with slow dynamics is reviewed. The main theoretical approaches are presented describing the glass transition in supercooled liquids, focusing on theories that have a microscopic, statistical mechanics basis. We describe both successes and failures and critically assess the current status of each of these approaches. The physics of aging dynamics in disordered materials and the rheology of soft glassy materials are then discussed, and recent theoretical progress is described. For each section, an extensive overview is given of the most recent advances, but we also describe in some detail the important open problems that will occupy a central place in this field in the coming years.

Theoretical perspective on the glass transition and amorphous materials

Modern microscopic techniques following the stochastic motion of labelled tracer particles have uncovered significant deviations from the laws of Brownian motion in a variety of animate and inanimate systems. Such anomalous diffusion can have different physical origins, which can be identified from careful data analysis. In particular, single particle tracking provides the entire trajectory of the traced particle, which allows one to evaluate different observables to quantify the dynamics of the system under observation. We here provide an extensive overview over different popular anomalous diffusion models and their properties. We pay special attention to their ergodic properties, highlighting the fact that in several of these models the long time averaged mean squared displacement shows a distinct disparity to the regular, ensemble averaged mean squared displacement. In these cases, data obtained from time averages cannot be interpreted by the standard theoretical results for the ensemble averages. Here we therefore provide a comparison of the main properties of the time averaged mean squared displacement and its statistical behaviour in terms of the scatter of the amplitudes between the time averages obtained from different trajectories. We especially demonstrate how anomalous dynamics may be identified for systems, which, on first sight, appear to be Brownian. Moreover, we discuss the ergodicity breaking parameters for the different anomalous stochastic processes and showcase the physical origins for the various behaviours. This Perspective is intended as a guidebook for both experimentalists and theorists working on systems, which exhibit anomalous diffusion.

/pdf/anomalous-diffusion-models-and-their-properties-non-50bjeilyc7.pdf

Anomalous diffusion models and their properties: non-stationarity, non-ergodicity, and ageing at the centenary of single particle tracking.

A new determination of the shear modulus of the human erythrocyte membrane using optical tweezers.

Context. Understanding the origin and evolution of stellar angular momentum is one of the major challenges of stellar physics.Aims. We present new models for the rotational evolution of solar-like stars between 1 Myr and 10 Gyr with the aim of reproducing the distributions of rotational periods observed for star forming regions and young open clusters within this age range.Methods. The models include a new wind braking law based on recent numerical simulations of magnetized stellar winds and specific dynamo and mass-loss prescriptions are adopted to tie angular momentum loss to angular velocity. The models additionally assume constant angular velocity during the disk accretion phase and allow for decoupling between the radiative core and the convective envelope as soon as the former develops.Results. We have developed rotational evolution models for slow, median, and fast rotators with initial periods of 10, 7, and 1.4 d, respectively. The models reproduce reasonably well the rotational behavior of solar-type stars between 1 Myr and 4.5 Gyr, including pre-main sequence (PMS) to zero-age main sequence (ZAMS) spin up, prompt ZAMS spin down, and the early-main sequence (MS) convergence of surface rotation rates. We find the model parameters accounting for the slow and median rotators are very similar to each other, with a disk lifetime of 5 Myr and a core-envelope coupling timescale of 28−30 Myr. In contrast, fast rotators have both shorter disk lifetimes (2.5 Myr) and core-envelope coupling timescales (12 Myr). We show that a large amount of angular momentum is hidden in the radiative core for as long as 1 Gyr in these models and we discuss the implications for internal differential rotation and lithium depletion. We emphasize that these results are highly dependent on the adopted braking law. We also report a tentative correlation between the initial rotational period and disk lifetime, which suggests that protostellar spin down by massive disks in the embedded phase is at the origin of the initial dispersion of rotation rates in young stars.Conclusions. We conclude that this class of semi-empirical models successfully grasp the main trends of the rotational behavior of solar-type stars as they evolve and make specific predictions that may serve as a guide for further development.

/pdf/improved-angular-momentum-evolution-model-for-solar-like-1nzro44ijv.pdf

Improved angular momentum evolution model for solar-like stars

Context. Understanding the physical processes that dictate the angular momentum evolution of solar-type stars from birth to maturity remains a challenge for stellar physics.Aims. We aim to account for the observed rotational evolution of low-mass stars over the age range from 1 Myr to 10 Gyr. Methods. We developed angular momentum evolution models for 0.5 and 0.8 M ⊙ stars. The parametric models include a new wind braking law based on recent numerical simulations of magnetised stellar winds, specific dynamo and mass-loss rate prescriptions, as well as core-envelope decoupling. We compare model predictions to the distributions of rotational periods measured for low-mass stars belonging to star-forming regions and young open clusters. Furthermore, we explore the mass dependence of model parameters by comparing these new models to the solar-mass models we developed earlier.Results. Rotational evolution models are computed for slow, median, and fast rotators at each stellar mass. The models reproduce reasonably well the rotational behaviour of low-mass stars between 1 Myr and 8−10 Gyr, including pre-main sequence to zero-age main sequence spin up, prompt zero-age main sequence spin down, and early-main sequence convergence of the surface rotation rates. Fast rotators are found to have systematically shorter disk lifetimes than moderate and slow rotators, thus enabling dramatic pre-main sequence spin up. They also have shorter core-envelope coupling timescales, i.e., more uniform internal rotation. As for the mass dependence, lower mass stars require significantly longer core-envelope coupling timescales than solar-type stars, which results in strong differential rotation developing in the stellar interior on the early main sequence. Lower mass stars also require a weaker braking torque to account for their longer spin-down timescale on the early main sequence, while they ultimately converge towards lower rotational velocities than solar-type stars in the longer term because of their reduced moment of inertia. We also find evidence that the mass dependence of the wind braking efficiency may be related to a change in the magnetic topology in lower mass stars.Conclusions. We have included in parametric models the main physical processes that dictate the angular momentum evolution of low-mass stars. The models suggest that these processes are quite sensitive to both mass and instantaneous rotation rate. We have worked out and reported here the main trends of these mass and rotation dependencies, whose origin still have to be addressed through a detailed modelling of magnetised stellar winds, internal angular momentum transport processes, and protoplanetary disk dissipation mechanisms.

https://www.aanda.org/articles/aa/pdf/2015/05/aa25660-15.pdf

Improved angular momentum evolution model for solar-like stars - II. Exploring the mass dependence

We compare and synthesize the results of two microrheological experiments on the cytoskeleton of single cells. In the first one, the creep function J(t) of a cell stretched between two glass plates is measured after applying a constant force step. In the second one, a microbead specifically bound to transmembrane receptors is driven by an oscillating optical trap, and the viscoelastic coefficient Ge(omega) is retrieved. Both J(t) and Ge(omega) exhibit power law behaviors: J(t) = A0(t/t0)alpha and absolute value (Ge(omega)) = G0(omega/omega0)alpha, with the same exponent alpha approximately 0.2. This power law behavior is very robust; alpha is distributed over a narrow range, and shows almost no dependence on the cell type, on the nature of the protein complex which transmits the mechanical stress, nor on the typical length scale of the experiment. On the contrary, the prefactors A0 and G0 appear very sensitive to these parameters. Whereas the exponents alpha are normally distributed over the cell population, the prefactors A0 and G0 follow a log-normal repartition. These results are compared with other data published in the literature. We propose a global interpretation, based on a semiphenomenological model, which involves a broad distribution of relaxation times in the system. The model predicts the power law behavior and the statistical repartition of the mechanical parameters, as experimentally observed for the cells. Moreover, it leads to an estimate of the largest response time in the cytoskeletal network: tau(m) approximately 1000 s.

Power laws in microrheology experiments on living cells: Comparative analysis and modeling.

We present a quantitative experimental study of the implications of the roughening transition both on the equilibrium shape and the growth kinetics of hcp 4 He crystals. On the one hand, we show that, in close analogy with the Kosterlitz-Thouless transition, the crystal curvature does not vanish continuously at the transition. The corresponding value of the surface stiffness is found in good agreement with recent universal predictions. On the other hand, the growth rate of facets increases near their roughening temperature. For the (0001) facet, the dominant process is the two dimensional nucleation. It allows us to measure the variation of the step energy near the transition. Lastly, the facet mobility also increases when the temperature tends to zero. This shows that the mobility of crystalline steps is limited by their interaction with thermal excitations Etude experimentale de l'effet de la transition rugueuse sur la forme d'equilibre et la cinetique de croissance: la courbure du cristal ne s'annule pas continument a la transition, mais presente un saut analogue a celui rencontre dans les transitions de Kosterlitz-Thouless, avec une tension superficielle en accord avec des previsions universelles recentes. Acceleration de la cinetique de croissance des facettes pres de la transition rugueuse

https://hal.archives-ouvertes.fr/jpa-00210148/document

François Gallet

Papers

A new determination of the shear modulus of the human erythrocyte membrane using optical tweezers.

Improved angular momentum evolution model for solar-like stars

Improved angular momentum evolution model for solar-like stars - II. Exploring the mass dependence

Power laws in microrheology experiments on living cells: Comparative analysis and modeling.

Crystal growth and crystal curvature near roughening transitions in hcp 4He