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

Surface plasmons are waves that propagate along the surface of a conductor. By altering the structure of a metal's surface, the properties of surface plasmons--in particular their interaction with light--can be tailored, which offers the potential for developing new types of photonic device. This could lead to miniaturized photonic circuits with length scales that are much smaller than those currently achieved. Surface plasmons are being explored for their potential in subwavelength optics, data storage, light generation, microscopy and bio-photonics.

/pdf/surface-plasmon-subwavelength-optics-5e55p12p4o.pdf

Surface plasmon subwavelength optics

We present experimental scattering data at microwave frequencies on a structured metamaterial that exhibits a frequency band where the effective index of refraction (n) is negative. The material consists of a two-dimensional array of repeated unit cells of copper strips and split ring resonators on interlocking strips of standard circuit board material. By measuring the scattering angle of the transmitted beam through a prism fabricated from this material, we determine the effective n, appropriate to Snell's law. These experiments directly confirm the predictions of Maxwell's equations that n is given by the negative square root of epsilon.mu for the frequencies where both the permittivity (epsilon) and the permeability (mu) are negative. Configurations of geometrical optical designs are now possible that could not be realized by positive index materials.

/pdf/experimental-verification-of-a-negative-index-of-refraction-37hlxn3tta.pdf

Experimental Verification of a Negative Index of Refraction

We show that microstructures built from nonmagnetic conducting sheets exhibit an effective magnetic permeability /spl mu//sub eff/, which can be tuned to values not accessible in naturally occurring materials, including large imaginary components of /spl mu//sub eff/. The microstructure is on a scale much less than the wavelength of radiation, is not resolved by incident microwaves, and uses a very low density of metal so that structures can be extremely lightweight. Most of the structures are resonant due to internal capacitance and inductance, and resonant enhancement combined with compression of electrical energy into a very small volume greatly enhances the energy density at critical locations in the structure, easily by factors of a million and possibly by much more. Weakly nonlinear materials placed at these critical locations will show greatly enhanced effects raising the possibility of manufacturing active structures whose properties can be switched at will between many states.

/pdf/magnetism-from-conductors-and-enhanced-nonlinear-phenomena-2fpnoamwae.pdf

Magnetism from conductors and enhanced nonlinear phenomena

The emerging field of plasmonics has yielded methods for guiding and localizing light at the nanoscale, well below the scale of the wavelength of light in free space. Now plasmonics researchers are turning their attention to photovoltaics, where design approaches based on plasmonics can be used to improve absorption in photovoltaic devices, permitting a considerable reduction in the physical thickness of solar photovoltaic absorber layers, and yielding new options for solar-cell design. In this review, we survey recent advances at the intersection of plasmonics and photovoltaics and offer an outlook on the future of solar cells based on these principles.

Plasmonics for improved photovoltaic devices

Multiple coincidences in surface structure determinations

We have developed a general methodology for computing electromagnetic (EM) fields and forces in matter, based on solving the macroscopic Maxwell's equations numerically in real space and adopting the time-averaged Maxwell stress tensor formalism. We can treat both dielectric and metallic systems characterized by a local frequency-dependent dielectric function, and of any size and geometry in principle. In this paper, we are particularly interested in calculating forces on nanostructures, induced by a beam of monochromatic light (such as a laser). The motivation behind this particular direction is the facilitation of self assembly in colloidal systems with the aim of aiding the fabrication of photonic crystals. We first look at two homogeneous systems: a half space and a layer. In passing from a low-$\ensuremath{\epsilon}$ to a high-$\ensuremath{\epsilon}$ medium, the light beam always attracts the interface (i.e., the surface force is negative). Thus the surfaces of two liquids separated by a layer of lower $\ensuremath{\epsilon}$ will generally be attracted towards each other, whereas for solids the total force must also be negative. This condition is not satisfied for the EM field of a traveling wave, but may be fulfilled for an evanescent wave. Thus, by shining evanescent light in the region between two solid bodies an attraction between them may be induced. We then study the EM forces induced by a laser beam on a three-dimensional crystal of dielectric spheres of GaP in air. At wavelengths comparable to the lattice constant, multiple scattering effects tune in: band gaps, Bragg scattering. But in all these cases the incident beam induces positive pressure on (and between) the spheres. Much more interesting is the regime where the radiation couples to the EM eigenmodes supported by isolated spheres (Mie resonances). These modes are analogous to electronic orbitals and, like their electronic counterparts, can form bonding and antibonding interactions between neighboring spheres. By irradiating the system with light at the bonding frequency an attractive interaction is induced between the spheres. For moderate intensities of the incident radiation these forces can overcome all other interactions present (gravitational, thermal, and Van der Waals) and may provide the main mechanism for formation of stable crystal structures in colloidal systems.

http://export.arxiv.org/pdf/cond-mat/9802259

Electromagnetic forces in photonic crystals

Electrical permittivity and magnetic permeability are concepts that are deeply embedded in electromagnetism. The electrical permittivity of a material determines its response to an applied electric field, while the permeability summarizes how it reacts to an applied magnetic field. Together the permittivity and permeability determine how the material responds to electromagnetic radiation of all wavelengths. Indeed, the speed of light in vacuum can be defined as c = 1/√0μ0, where 0 is the permittivity of free space and μ0 is the permeability.

Electromagnetic materials enter the negative age

The formula for tunnelling between two objects is fundamental to understanding the scanning tunnelling microscope. Although an exact expression for the one-electron tunnelling current is known, its derivation has previously been complex. Here the authors present a new derivation which is relatively simple and based on physical arguments. They go on to use these methods to show for the first time the connection between the exact formula and the widely used transfer Hamiltonian method of Bardeen. Finally they emphasize the importance of choosing a formula that minimizes the computational effort required to raster the STM tip across a surface.

Theory of the scanning tunnelling microscope

An artificially created material with negative refractive index has opened the door to new phenomena — and controversy. New work finally sets the seal of experimental confirmation on negative refraction.

John B. Pendry

Papers

Multiple coincidences in surface structure determinations

Electromagnetic forces in photonic crystals

Electromagnetic materials enter the negative age

Theory of the scanning tunnelling microscope

Optics: Positively negative