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

Much of optics depends on objects being much larger than the wavelength of light: shadows of opaque objects are sharp only if free of diffraction effects, and 'cat's eye' retroreflectors function only if they are large Here, we show how to make theoretically arbitrarily small versions of these devices by exploiting the power of a negatively refracting lens to magnify objects that are smaller than the wavelength, thus creating the effect of a large object while keeping all physical dimensions small We also give a new perspective on the 'perfect lens theorem' on which the paper is based

https://iopscience.iop.org/article/10.1088/1367-2630/11/7/073033/pdf

Shrinking optical devices

Depuis longtemps des methodes directes ont ete mises en oeuvre pour la diffraction de rayons X et la technique de l'atome lourd a inspire cette approche du probleme de surface. Connaissant la structure de la couche sous la surface, on definit une «surface de reference» la plus proche possible de la structure de la surface reelle. On montre l'application de cette methode pour des exemples simples et on propose de futures applications plus sophistiquees

Direct methods in surface crystallography.

Electronic Density of States at Transition-Metal Surfaces

We propose a novel method for generating both propagating and evanescent Bessel beams. To generate propagating Bessel beams we propose using a pair of distributed Bragg reflectors (DBRs) with a resonant point source on one side of the system. Those modes that couple with the localized modes supported by the DBR system will be selectively transmitted. This is used to produce a single narrow band of transmission in κ space that, combined with the circular symmetry of the system, yields a propagating Bessel beam. We present numerical simulations showing that a propagating Bessel beam with central spot size of ∼0.5λ0 can be maintained for a distance in excess of 3000λ0. To generate evanescent Bessel beams we propose using transmission of a resonant point source through a thin film. A transmission resonance is produced as a result of the multiple scattering occurring between the interfaces. This narrow resonance combined with the circular symmetry of the system corresponds to an evanescent Bessel beam. Because propagating modes are also transmitted, although the evanescent transmission resonance is many orders of magnitude greater than the transmission for the propagating modes, within a certain distance the propagating modes swamp the exponentially decaying evanescent ones. Thus there is only a certain regime in which evanescent Bessel beams dominate. However, within this regime the central spot size of the beam can be made significantly smaller than the wavelength of light used. Thus evanescent Bessel beams may have technical application, in high-density recording for example. We present numerical simulations showing that with a simple glass thin film an evanescent Bessel beam with central spot size of ∼0.34λ0 can be maintained for a distance of 0.14λ0. By choice of different material parameters, the central spot size can be made smaller still.

/pdf/generating-bessel-beams-by-use-of-localized-modes-4mz25cz2f6.pdf

Generating Bessel beams by use of localized modes.

The propagation of surface plasmons along rough metal surfaces is investigated with transformation optics. The roughness is modeled on a nanometer scale either by partly embedding a cylinder of metal into the surface (convex rough surface) or by excavating a cylindrical cavity from it (concave rough surface). These two structures can be treated analytically by means of conformal transformation. The interaction of surface plasmons with the singularities of these structures is shown to induce extreme field enhancements. These modes dominate the surface-enhanced Raman-scattering response and enhancement factors of the order of ${10}^{7}$ are predicted. Interestingly, concave rough surfaces are shown to be the best candidates for surface-enhanced Raman scattering due to a stronger field enhancement and a lower sensitivity to the incident light polarization. Our analytical approach also points out the influence of the contact angle between the asperities and the metal surface on the bandwidth and the efficiency of the light-harvesting process.

/pdf/electromagnetic-contribution-to-surface-enhanced-raman-3karechn6q.pdf

John B. Pendry

Papers

Shrinking optical devices

Direct methods in surface crystallography.

Electronic Density of States at Transition-Metal Surfaces

Generating Bessel beams by use of localized modes.

Electromagnetic contribution to surface-enhanced Raman scattering from rough metal surfaces: A transformation optics approach