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

Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

Phd by thesis

The manipulation of fluids in channels with dimensions of tens of micrometres--microfluidics--has emerged as a distinct new field. Microfluidics has the potential to influence subject areas from chemical synthesis and biological analysis to optics and information technology. But the field is still at an early stage of development. Even as the basic science and technological demonstrations develop, other problems must be addressed: choosing and focusing on initial applications, and developing strategies to complete the cycle of development, including commercialization. The solutions to these problems will require imagination and ingenuity.

The origins and the future of microfluidics

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Self-assembled monolayers of thiolates on metals as a form of nanotechnology.

Self-assembly is the autonomous organization of components into patterns or structures without human intervention. Self-assembling processes are common throughout nature and technology. They involve components from the molecular (crystals) to the planetary (weather systems) scale and many different kinds of interactions. The concept of self-assembly is used increasingly in many disciplines, with a different flavor and emphasis in each.

http://science.sciencemag.org/content/sci/295/5564/2418.full.pdf

Self-assembly at all scales.

Leaf hydraulics II: Vascularized tissues

The motion of thin, torque-free axisymmetric rigid particles with fore-aft symmetry in low Reynolds number linear flows is investigated. The rotational motion of such a particle is fully determined by the effective aspect ratio (κe), defined as the aspect ratio of a spheroid having the same period of rotation as that of the particle. We determine the effective aspect ratio for a family of shapes given by, y(ρ) = κ(1 − ρ2)α where α is a positive parameter, ρ is the radial distance from the particle center in polar coordinates, y is half the thickness of the particle, κ is the aspect ratio of the particle defined as the ratio of the thickness (L) of the particle parallel to the axis of symmetry to its diameter (d) perpendicular to the axis of symmetry. This family includes an oblate spheroid (α=12) and the shape approaches a blunt circular cylinder shape as α → 0. For a thin particle, the effective aspect ratio scales like GA12, where GA is the torque non-dimensionalized by μγd3 acting on a particle held in a fixed alignment in a simple shear flow with its longer dimensions in the flow-vorticity plane. Here, μ is the fluid viscosity and γ is the shear rate. Starting with the integral representation of the Stokes flow, an analysis based on a matched asymptotic expansions approach is performed to determine the scaling of the torque acting on a stationary particle in simple shear flow with κ as the small parameter. Using boundary element method simulations, the exact torques are calculated and the scaling obtained from the analysis is verified. We find that there are two regions of interest that contribute to the torque, a flat outer region covering most of the disk area and a boundary layer region of large slope at the edge. For α>14, the torque is dominated by the stresses acting on the flat surface of the particle and is O(κ2) to the leading order. For these shapes, the effective aspect ratio scales like the aspect ratio of the particle. On the other hand, for α≤14, the leading order torque contribution comes from the boundary layer region. To the leading order, the torque scales as O(κ2logκ) for α=14 and as O(κ32(1−α)) for α<14. In general, a particle with a blunt edge is found to rotate faster than a particle of the same aspect ratio for which the slope of the edge varies slowly. The fastest rotating particle is identified to be a cylindrical disk for which κe = 1.12κ3/4.

http://absimage.aps.org/image/DFD12/MWS_DFD12-2012-002424.pdf

Rotational motion of a thin axisymmetric disk in a low Reynolds number linear flow

The design and analysis of plant-inspired loop heat pipes (LHPs) that would exploit nanoporous membranes to allow for operation with large capillary pressures and superheated liquid are presented. The operating concepts of this superheated loop heat pipe (SHLHP) resemble the transpiration process in vascular plants: reduction of pressure in leaves drives sap flow up from the roots and overcomes gravity, viscous drag, and reduced chemical potential of water in subsaturated soils. We present a model for steady-state operation and a linear response analysis of both the conventional and superheated designs. Our analysis shows that these SHLHPs could: (1) extend the limitations of conventional LHPs imposed by thermodynamic properties of the working fluid, (2) provide efficient heat transfer over long distances and against large accelerations, and (3) allow for operation in a subsaturated state that would eliminate the thermal resistance and entrainment effect of the liquid film of conventional designs. © 2013 American Institute of Chemical Engineers AIChE J 60: 762–777, 2014

Analysis of superheated loop heat pipes exploiting nanoporous wick membranes

Despite its relevance in numerous natural and industrial processes, the solubility of molecular oxygen has never been directly measured in capillary-condensed liquid water. In this article, we measure oxygen solubility in liquid water trapped within nanoporous samples, in metastable equilibrium with a subsaturated vapor. We show that solubility increases two fold at moderate subsaturations (relative humidity ∼0.55). This evolution with relative humidity is in good agreement with a simple thermodynamic prediction using properties of bulk water, previously verified experimentally at positive pressure. Our measurement thus verifies the validity of this macroscopic thermodynamic theory to strong confinement and large negative pressures, where significant nonidealities are expected. This effect has strong implications for important oxygen-dependent chemistries in natural and technological contexts.

Enhanced Oxygen Solubility in Metastable Water under Tension

Vascular plants rely on differences of osmotic pressure to export sugars from regions of synthesis (mature leaves) to sugar sinks (roots, fruits). In this process, known as Munch pressure flow, the loading of sugars from photosynthetic cells to the export conduit (the phloem) is crucial, as it sets the pressure head necessary to power long-distance transport. Whereas most herbaceous plants use active mechanisms to increase phloem concentration above that of the photosynthetic cells, in most tree species, for which transport distances are largest, loading seems to occur via passive symplastic diffusion from the mesophyll to the phloem. Here, we use a synthetic microfluidic model of a passive loader to explore the nonlinear dynamics that arise during export and determine the ability of passive loading to drive long-distance transport. We first demonstrate that in our device, phloem concentration is set by the balance between the resistances to diffusive loading from the source and convective export through the phloem. Convection-limited export corresponds to classical models of Munch transport, where phloem concentration is close to that of the source; in contrast, diffusion-limited export leads to small phloem concentrations and weak scaling of flow rates with the hydraulic resistance. We then show that the effective regime of convection-limited export is predominant in plants with large transport resistances and low xylem pressures. Moreover, hydrostatic pressures developed in our synthetic passive loader can reach botanically relevant values as high as 10 bars. We conclude that passive loading is sufficient to drive long-distance transport in large plants, and that trees are well suited to take full advantage of passive phloem loading strategies.

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Abraham D. Stroock

Papers

Leaf hydraulics II: Vascularized tissues

Rotational motion of a thin axisymmetric disk in a low Reynolds number linear flow

Analysis of superheated loop heat pipes exploiting nanoporous wick membranes

Enhanced Oxygen Solubility in Metastable Water under Tension

Passive phloem loading and long-distance transport in a synthetic tree-on-a-chip