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

Recently, Chumak et al. have demonstrated experimentally the time-reversal of microwave spin pulses based on non-adiabatically tuning the wave speed in a spatially-periodic manner [Nat. Comm. 1, 141 (2010)]. Here, we solve the associated wave equations analytically, and give an explicit formula for the reversal efficiency. We discuss the implementation for short optical electromagnetic pulses and show that the new scheme may lead to their accurate time-reversal with efficiency higher than before.

/pdf/broadband-time-reversal-of-optical-pulses-using-a-switchable-4qnmq94cat.pdf

Broadband time-reversal of optical pulses using a switchable photonic-crystal mirror.

The p(2×2) and c(2×2) sulfur overlayers on Ni(100), and the clean Ni(100) surface itself, have been imaged in an ultrahigh-vacuum scanning tunneling microscope and topographic and spectroscopic information was obtained from all three surfaces. These data are compared to theoretical calculations of the surfaces derived using the Green's-function method of Pendry, Pretre, and Krutzen, where the sample Green's function is calculated in a multiple-scattering formalism based on the layer Korringa-Kohn-Rostoker method. Our simple model has proved reasonably successful in predicting the corrugation heights observed on the sulfated nickel surfaces, and confirmed the fact that the difference in height observed between the p(2×2) and the c(2×2) phases is electronic in origin

Scanning-tunneling-microscopy investigation of the p(2×2) and c(2×2) overlayers of S on Ni(100)

Propagation behaviors of electromagnetic waves are governed by the equifrequency surface of the medium. Up to now, ordinary materials, including the medium exist in nature and the man-made metamaterials, always have an equifrequency surface (ellipsoid or hyperboloid) centered at zero k-point. Here we propose a new type of metamaterial possessing multiple index ellipsoids centered at arbitrary nonzero k-points. Their locations in momentum space are determined by the connectivity of a set of interpenetrating metallic scaffolds, whereas the group velocities of the modes are determined by the geometrical details. Such system is a new class of metamaterial whose properties arise from global connectivity and hence can have broadband functionality in applications such as negative refraction, orientation-dependent coupling effect, and cavity without walls, and they are fundamentally different from ordinary resonant metamaterials that are inherently bandwidth limited. We perform microwave experiments to confirm our findings.

/pdf/metamaterials-with-index-ellipsoids-at-arbitrary-k-points-3fxhl6jppt.pdf

Metamaterials with index ellipsoids at arbitrary k -points

Diffuse LEED from simple stepped surfaces

1D systems have proved amenable to both numerical and analytical calculation. Previous work has shown how to construct a theory of averaged quantities in a 1D disordered system for the case of diagonal disorder. In this paper the authors extend the theory to include the case of mixed off-diagonal and diagonal disorder. An explicit expression for the inverse localisation length and density of states is evaluated for several types of disorder including mixed and off-diagonal disorder. In addition they obtain the relations for the localisation length: l approximately=E- nu as E to 0 and l approximately=W-s for pure off-diagonal disorder. Their results are compared with published simulations and are found to be in good agreement.

John B. Pendry

Papers

Broadband time-reversal of optical pulses using a switchable photonic-crystal mirror.

Scanning-tunneling-microscopy investigation of the p(2×2) and c(2×2) overlayers of S on Ni(100)

Metamaterials with index ellipsoids at arbitrary k -points

Diffuse LEED from simple stepped surfaces

Electron localisation in 1D-the general case