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

Isolated dielectric spheres support resonant electromagnetic (EM) modes which are analogous to electronic orbitals and, like their electronic counterparts, can form bonding or anti-bonding interactions between neighbouring spheres. By irradiating the system with light at the bonding frequency an attractive interaction is induced between the spheres. We suggest that by judicious selection of bonding states we can drive a system towards a desired structure, rather than rely on the structure dictated by gravitational or Van der Waals forces, the latter deriving from the zero point energy population of a state.

Mie resonances and bonding in photonic crystals

Direct methods in low-energy-photoelectron diffraction can provide only approximate locations of atoms close to the emitter. More detailed structural information has to be extracted from the photoelectron diffraction spectra in the traditional way by comparing the results of multiple-scattering calculations for possible structure models to the experimental data. In this paper we propose a linear-superposition scheme for the wave function which reduces the number of full multiple-scattering calculations needed for the structure optimization drastically. This method allows us to explore a parameter space with a much higher dimension than before, which will improve the reliability of structure determinations considerably

Linear-superposition method for the multiple-scattering problem in low-energy-photoelectron diffraction.

Present methods of measuring electronic band structure of solids by photoemission suffer from reduced resolution in kz because the escaping electron has a finite escape depth which broadens its momentum. Thin films grown epitaxially on substrates are predicted to show fine oscillations in their spectra caused by quantisation of hole states. The spacing of peaks is determined by the number of layers and by the group velocity of the band concerned and the peaks are broadened only by the intrinsic lifetime of the hole state. Realistic calculations are presented for silver grown epitaxially on a palladium (001) surface. They show strong differences from pure silver up to thicknesses of at least 7 layers due to the quantisation effects.

https://iopscience.iop.org/article/10.1088/0022-3719/16/2/025/pdf

Removing the limits to accurate band-structure determination by photoemission

The method of 'generalised transfer matrices' previously used to find the average of any power of the transmission coefficient, (tx) is applied to finding ( mod t mod y) in the cases y=0, -2, -4 . . . and Re y>1. These cases include all the integer moments of the conductance, mod t mod 2, and its reciprocal, the resistance. The conductance is the more physically important quantity and is found to have a complicated dependence on chain length. The formulae are valid for any distribution of disorder and all lengths of sample. Limiting cases and numerical results are presented. An anomaly in the energy dependence of the conductance of a binary alloy is discovered.

The statistics of the conductance of one-dimensional disordered chains

A careful analysis is made of the convergence of several perturbative techniques for calculating LEED intensities with the hope of finding a scheme that is both fast and accurate. Carefully calculated scattering factors are used in this analysis. Unfortunately divergence, or poor convergence of the relevant series holds for most theories. However a renormalization for the forward scattering (RFS) results in a highly convergent series (RFS perturbation theory) that is amenable to rapid calculations.

John B. Pendry

Papers

Mie resonances and bonding in photonic crystals

Linear-superposition method for the multiple-scattering problem in low-energy-photoelectron diffraction.

Removing the limits to accurate band-structure determination by photoemission

The statistics of the conductance of one-dimensional disordered chains

Fast perturbation schemes for low energy electron diffraction spectra