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

The microrelief of plant surfaces, mainly caused by epicuticular wax crystalloids, serves different purposes and often causes effective water repellency. Furthermore, the adhesion of contaminating particles is reduced. Based on experimental data carried out on microscopically smooth (Fagus sylvatica L., Gnetum gnemon L., Heliconia densiflora Verlot, Magnolia grandiflora L.) and rough water-repellent plants (Brassica oleracea L., Colocasia esculenta (L.) Schott., Mutisia decurrens Cav., Nelumbo nucifera Gaertn.), it is shown here for the first time that the interdependence between surface roughness, reduced particle adhesion and water repellency is the keystone in the self-cleaning mechanism of many biological surfaces. The plants were artificially contaminated with various particles and subsequently subjected to artificial rinsing by sprinkler or fog generator. In the case of water-repellent leaves, the particles were removed completely by water droplets that rolled off the surfaces independent of their chemical nature or size. The leaves of N. nucifera afford an impressive demonstration of this effect, which is, therefore, called the “Lotus-Effect” and which may be of great biological and technological importance.

Purity of the sacred lotus, or escape from contamination in biological surfaces

http://experimentationlab.berkeley.edu/sites/default/files/AFMImages/butt_AFM.pdf

Force measurements with the atomic force microscope: Technique, interpretation and applications

Macroscopic thin liquid films are entities that are important in biophysics, physics, and engineering, as well as in natural settings. They can be composed of common liquids such as water or oil, rheologically complex materials such as polymers solutions or melts, or complex mixtures of phases or components. When the films are subjected to the action of various mechanical, thermal, or structural factors, they display interesting dynamic phenomena such as wave propagation, wave steepening, and development of chaotic responses. Such films can display rupture phenomena creating holes, spreading of fronts, and the development of fingers. In this review a unified mathematical theory is presented that takes advantage of the disparity of the length scales and is based on the asymptotic procedure of reduction of the full set of governing equations and boundary conditions to a simplified, highly nonlinear, evolution equation or to a set of equations. As a result of this long-wave theory, a mathematical system is obtained that does not have the mathematical complexity of the original free-boundary problem but does preserve many of the important features of its physics. The basics of the long-wave theory are explained. If, in addition, the Reynolds number of the flow is not too large, the analogy with Reynolds's theory of lubrication can be drawn. A general nonlinear evolution equation or equations are then derived and various particular cases are considered. Each case contains a discussion of the linear stability properties of the base-state solutions and of the nonlinear spatiotemporal evolution of the interface (and other scalar variables, such as temperature or solute concentration). The cases reducing to a single highly nonlinear evolution equation are first examined. These include: (a) films with constant interfacial shear stress and constant surface tension, (b) films with constant surface tension and gravity only, (c) films with van der Waals (long-range molecular) forces and constant surface tension only, (d) films with thermocapillarity, surface tension, and body force only, (e) films with temperature-dependent physical properties, (f) evaporating/condensing films, (g) films on a thick substrate, (h) films on a horizontal cylinder, and (i) films on a rotating disc. The dynamics of the films with a spatial dependence of the base-state solution are then studied. These include the examples of nonuniform temperature or heat flux at liquid-solid boundaries. Problems which reduce to a set of nonlinear evolution equations are considered next. Those include (a) the dynamics of free liquid films, (b) bounded films with interfacial viscosity, and (c) dynamics of soluble and insoluble surfactants in bounded and free films. The spreading of drops on a solid surface and moving contact lines, including effects of heat and mass transport and van der Waals attractions, are then addressed. Several related topics such as falling films and sheets and Hele-Shaw flows are also briefly discussed. The results discussed give motivation for the development of careful experiments which can be used to test the theories and exhibit new phenomena.

Long-scale evolution of thin liquid films

The numerical simulation of flows with interfaces and free-surface flows is a vast topic, with applications to domains as varied as environment, geophysics, engineering, and fundamental physics. In engineering, as well as in other disciplines, the study of liquid-gas interfaces is important in combustion problems with liquid and gas reagents. The formation of droplet clouds or sprays that subsequently burn in combustion chambers originates in interfacial instabilities, such as the Kelvin-Helmholtz instability. What can numerical simulations do to improve our understanding of these phenomena? The limitations of numerical techniques make it impossible to consider more than a few droplets or bubbles. They also force us to stay at low Reynolds or Weber numbers, which prevent us from finding a direct solution to the breakup problem. However, these methods are potentially important. First, the continuous improvement of computational power (or, what amounts to the same, the drop in megaflop price) continuously extends the range of affordable problems. Second, and more importantly, the phenomena we consider often happen on scales of space and time where experimental visualization is difficult or impossible. In such cases, numerical simulation may be a useful prod to the intuition of the physicist, the engineer, or the mathematician. A typical example of interfacial flow is the collision between two liquid droplets. Finding the flow involves the study not only of hydrodynamic fields in the air and water phases but also of the air-water interface. This latter part

Direct numerical simulation of free-surface and interfacial flow

Recent advancements in experimental studies of wetting phenomena have helped to bridge the gap between the progress made in theory and simulation over the past decade, and the experimental evidence or verification of the theoretical predictions. These developments include new measurements of the equilibrium thickness of precursor wetting films on solid and liquid substrates and at the liquid/gas interface, experimental studies of critical adsorption, as well as measurements of the dynamics of wetting and spreading and the nucleation of wetting layers in simple and complex systems. There have also been some recent results on dewetting of solid substrates by liquid films.

Wetting: Statics and dynamics

The melting and freezing of water in a series of mesoporous
silica materials with a hexagonal arrangement of unidimensional cylindrical
pores and narrow pore-size distribution (MCM-41 with pore diameters
from 2.9 to 3.7 nm, and SBA-15 with pore diameters from 4.4 to 11.7
nm) was studied by differential scanning calorimetry (DSC). A lowering of
the melting temperature ΔTm
=
Tmb
−
Tm(R) up to 50 K was found for
water in pores of decreasing radius R. The melting point data can
be represented by a modified Gibbs–Thomson equation, ΔTm(R) =
K/(R-t), with K
=
52 K nm and t
= 0.4 nm, in agreement with an earlier study
of water in MCM-41 materials of pore width 2 to 4 nm. The value of K
agrees with an estimate of the Gibbs–Thomson constant based on thermodynamic
 data for the normal melting point of ice, and the parameter t can
be taken as the thickness of a surface layer of non-frozen water at
the pore wall. DSC scans of the freezing of H2O and D2O
in partially filled pores of SBA-15 reveal a peak pattern depending
on the degree of pore filling ϕ. The different peaks are attributed
 to different states of the liquid in the pore space, iz.
pore water in completely filled regions, and water as an adsorbed film at
the pore wall. These two states coexist in a pore filling range ϕmin<ϕ<1,
but only the film state exists at ϕ<ϕmin.
The freezing peak of pore water appears to be nucleated by external bulk 
ice (at ϕ>1) but exhibits substantial supercooling at ϕ<1.
On the other hand, the peak attributed to the freezing of film water exhibits
no significant supercooling and is found at temperatures near 237 K, almost
independent of ϕ and the pore width of the SBA-15 sample.
The nature of a further (small) peak near 233 K is not yet understood. Contrary
to cooling scans, only one DSC peak is observed in heating scans, independent
of the pore filling. This finding indicates that the adsorbed liquid film
 is metastable relative to the frozen pore liquid.

Melting and freezing of water in ordered mesoporous silica materials

Neutron reflectivity experiments on the interface of pure D2O against thin films of perdeuterated polystyrene (d-PS) spin-coated onto silicon blocks were performed to study the intrinsic structure of the interface of water against hydrophobic substrates. The experiments reveal nonvanishing scattering contrast at the polymer/water interface, although the two materials (d-PS and D2O) have closely similar scattering length densities. Organic (nondeuterated) contaminants or macroscopic air bubbles trapped at the polymer/water interface can be ruled out as the origin of this observation. From a systematic study of this system, it is concluded that the source of the nonvanishing contrast is a depletion of water in the boundary layer against the hydrophobic surface. It is conjectured that this depletion layer represents a precursor layer of submicroscopic gas bubbles recently observed by Tyrrell and Attard. The existence of such gas nanobubbles in the present system is confirmed by atomic force microscopy (AFM) ...

Nanobubbles and Their Precursor Layer at the Interface of Water Against a Hydrophobic Substrate

The adsorption of water in two mesoporous silica materials with cylindrical pores of uniform diameter, MCM-41 and SBA-15, was studied by 1H MAS (MAS=magic angle spinning) and static solid-state NMR spectroscopy. All observed hydrogen atoms are either surface -SiOH groups or hydrogen-bonded water molecules. Unlike MCM-41, some strongly bound water molecules exist at the inner surfaces of SBA-15 that are assigned to surface defects. At higher filling levels, a further difference between MCM-41 and SBA-15 is observed. Water molecules in MCM-41 exhibit a bimodal line distribution of chemical shifts, with one peak at the position of inner-bulk water, and the second peak at the position of water molecules in fast exchange with surface -SiOH groups. In SBA-15, a single line is observed that shifts continuously as the pore filling is increased. This result is attributed to a different pore-filling mechanism for the two silica materials. In MCM-41, due to its small pore diameter (3.3 nm), pore filling by pore condensation (axial-pore-filling mode) occurs at a low relative pressure, corresponding roughly to a single adsorbed monolayer. For SBA-15, owing to its larger pore diameter (8 nm), a gradual increase in the thickness of the adsorbed layer (radial-pore-filling mode) prevails until pore condensation takes place at a higher level of pore filling.

Hydrogen bonding of water confined in mesoporous silica MCM-41 and SBA-15 studied by 1H solid-state NMR.

Freezing and melting of H2O and D2O in the cylindrical pores of well-characterized MCM-41 silica materials (pore diameters from 2.5 to 4.4 nm) was studied by differential scanning calorimetry (DSC) and 1H NMR cryoporometry. Well-resolved DSC melting and freezing peaks were obtained for pore diameters down to 3.0 nm, but not in 2.5 nm pores. The pore size dependence of the melting point depression ΔTm can be represented by the Gibbs–Thomson equation when the existence of a layer of nonfreezing water at the pore walls is taken into account. The DSC measurements also show that the hysteresis connected with the phase transition, and the melting enthalpy of water in the pores, both vanish near a pore diameter D* ≈ 2.8 nm. It is concluded that D* represents a lower limit for first-order melting/freezing in the pores. The NMR spin echo measurements show that a transition from low to high mobility of water molecules takes place in all MCM-41 materials, including the one with 2.5 nm pores, but the transition revealed by NMR occurs at a higher temperature than indicated by the DSC melting peaks. The disagreement between the NMR and DSC transition temperatures becomes more pronounced as the pore size decreases. This is attributed to the fact that with decreasing pore size an increasing fraction of the water molecules is situated in the first and second molecular layers next to the pore wall, and these molecules have slower dynamics than the molecules in the core of the pore.

https://www.uni-muenster.de/imperia/md/content/physikalische_chemie/schoenhoff/pccp_08_mcm.pdf

Gerhard H. Findenegg

Papers

Wetting: Statics and dynamics

Melting and freezing of water in ordered mesoporous silica materials

Nanobubbles and Their Precursor Layer at the Interface of Water Against a Hydrophobic Substrate

Hydrogen bonding of water confined in mesoporous silica MCM-41 and SBA-15 studied by 1H solid-state NMR.

Melting and freezing of water in cylindrical silica nanopores