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

Electromagnetic metamaterials are a class of materials that have been artificially structured on a subwavelength scale. They are currently the focus of a great deal of interest because they allow access to previously unrealizable properties such as a negative refractive index. Most metamaterial designs have so far been based on resonant elements, such as split rings, and research has concentrated on microwave frequencies and above. Here, we present the first experimental realization of a non-resonant metamaterial designed to operate at zero frequency. Our samples are based on a recently proposed template for an anisotropic magnetic metamaterial consisting of an array of superconducting plates. Magnetometry experiments show a strong, adjustable diamagnetic response when a field is applied perpendicular to the plates. We have calculated the corresponding effective permeability, which agrees well with theoretical predictions. Applications for this metamaterial may include non-intrusive screening of weak d.c. magnetic fields.

/pdf/a-d-c-magnetic-metamaterial-1nn5s7dn41.pdf

A d.c. magnetic metamaterial

We report on the development and use of a highly anisotropic magnetic metamaterial for near-field imaging. The material consists of an array of Swiss Roll structures, resonant near 21.3 MHz, with a peak value of relative permeability ~35. At this peak, the material transfers an input magnetic field pattern to the output face without loss of intensity and with a spatial resolution equal to the roll diameter. It behaves as a near-field imaging device consisting of a bundle of magnetic wires.

/pdf/metamaterial-endoscope-for-magnetic-field-transfer-near-29rgig650i.pdf

Metamaterial endoscope for magnetic field transfer: near field imaging with magnetic wires.

Transformation optics is an emerging technique for the design of advanced electromagnetic media. Transformation optical devices exploit the form invariance of Maxwell's equations, allowing geometry to play the dominant role in the design process rather than traditional wave or ray optics. The use of coordinate transformations vastly eases the burden of design for a large class of devices, though at the expense of increasing the complexity of the underlying materials used. Although the required constitutive parameters of a transformation optical structure can be challenging-inherently anisotropic and spatially varying, with both magnetic and electric response-nevertheless the parameter requirements can often be met or approximated through the use of artificially structured metamaterials. Here, we review the basic concepts associated with transformation optics and provide several examples to illustrate its application.

Electromagnetic Design With Transformation Optics

Surface plasmons, electromagnetic fields generated by the charge oscillations at the surface of a light-illuminated metallic nanoparticle, are typically described in terms of effective electric dipoles and their dynamics. Scientists discover that adding periodic grooves to the surface of subwavelength metallic disks creates localized surface plasmons of magnetic character in addition to the typical electric ones.

https://link.aps.org/pdf/10.1103/PhysRevX.4.021003

Magnetic localized surface plasmons

A general three-dimensional transformation optics approach is presented that yields analytical expressions for the relevant electromagnetic magnitudes in plasmonic phenomena at singular geometries. This powerful theoretical tool reveals the broadband response and superfocusing properties of touching metal nanospheres and provides an elegant physical description of the prominent field enhancement that takes place at the point of contact between a spherical nanoparticle and a flat metallic surface.

/pdf/collection-and-concentration-of-light-by-touching-spheres-a-3oyr5navoz.pdf

John B. Pendry

Papers

A d.c. magnetic metamaterial

Metamaterial endoscope for magnetic field transfer: near field imaging with magnetic wires.

Electromagnetic Design With Transformation Optics

Magnetic localized surface plasmons

Collection and concentration of light by touching spheres: a transformation optics approach.