There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

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

[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

Topological photonics is a rapidly emerging field of research in which geometrical and topological ideas are exploited to design and control the behavior of light. Drawing inspiration from the discovery of the quantum Hall effects and topological insulators in condensed matter, recent advances have shown how to engineer analogous effects also for photons, leading to remarkable phenomena such as the robust unidirectional propagation of light, which hold great promise for applications. Thanks to the flexibility and diversity of photonics systems, this field is also opening up new opportunities to realize exotic topological models and to probe and exploit topological effects in new ways. This article reviews experimental and theoretical developments in topological photonics across a wide range of experimental platforms, including photonic crystals, waveguides, metamaterials, cavities, optomechanics, silicon photonics, and circuit QED. A discussion of how changing the dimensionality and symmetries of photonics systems has allowed for the realization of different topological phases is offered, and progress in understanding the interplay of topology with non-Hermitian effects, such as dissipation, is reviewed. As an exciting perspective, topological photonics can be combined with optical nonlinearities, leading toward new collective phenomena and novel strongly correlated states of light, such as an analog of the fractional quantum Hall effect.

Topological Photonics

to be done in this area. Face recognition is a problem that scarcely clamoured for attention before the computer age but, having surfaced, has involved a wide range of techniques and has attracted the attention of some fine minds (David Mumford was a Fields Medallist in 1974). This singular application of mathematical modelling to a messy applied problem of obvious utility and importance but with no unique solution is a pretty one to share with students: perhaps, returning to the source of our opening quotation, we may invert Duncan's earlier observation, 'There is an art to find the mind's construction in the face!'.

Linear and nonlinear waves, by G. B. Whitham. Pp.636. £50. 1999. ISBN 0 471 35942 4 (Wiley).

Transverse electric graphene plasmons are generally weakly confined in the direction perpendicular to the graphene plane. They are featured by a skin depth δ, namely the penetration depth of their evanescent fields into the surrounding environment, much larger than the wavelength λ in free space (e.g., δ > 10λ). The weak spatial confinement of transverse electric graphene plasmons is now the key drawback that limits their practical applications. Here we report the skin depth of TE graphene plasmons can be largely decreased down to the subwavelength scale (e.g., δ   0 (Im(σs)   1.667), where σs and μc are the surface conductivity and chemical potential of monolayer graphene, respectively.

/pdf/confined-transverse-electric-graphene-plasmons-in-negative-4xu4voddgp.pdf

Confined transverse-electric graphene plasmons in negative refractive-index systems

Periodically stacked graphene and its insulating isomorph provide a fascinating structural element in implementing highly functional superlattices at the atomic scale, which offers possibilities in designing nanoelectronic and photonic devices. Using density functional theory (DFT) calculations, we demonstrate that various types of superlattices can be obtained by stacking two-dimensional (2D) materials alternately, namely, graphene, hexagonal boron nitride (h-BN), hydrogenated graphene, and fluorinated graphene. The energy band in layer-stacked superlattices is found to be more sensitive to the barrier width than that in conventional III–V semiconductor superlattices. When adding more than one atomic layer to the barrier in each period, the coupling of electronic wavefunctions in neighboring potential wells can be significantly reduced, which leads to the degeneration of continuous subbands into quantized energy levels. When varying the well width, the energy levels in the potential wells along the L-M direction behave distinctly from those along the K-H direction. Our results indicate that the quantized energy states in atomic-layered superlattices can be effectively tuned by modifying each individual barrier/well layer, enabling atomic-scale material engineering.

Ab initio study of energy-band modulation in graphene-based two-dimensional layered superlattices

Controlling the polarization of light at the extreme nanoscale has long been a major scientific and technological goal of nanophotonics. The authors discuss polarization splitting through ultrathin van der Waals heterostructures in the infrared regime, relying on a mechanism that does not resort to the interference effect. Moreover, the predicted phenomenon is insensitive to the angle of incidence. This work thus identifies a promising platform for tailoring light-matter interaction at the nanoscale, and for the design of advanced nanophotonic elements, such as polarization beam splitters and epsilon-near-zero materials.

/pdf/interferenceless-polarization-splitting-through-nanoscale-36exu25y4d.pdf

Interferenceless polarization splitting through nanoscale van der Waals heterostructures

Besides the well-known negative refraction, a negative refractive-index material can exhibit another two hallmark features, which are the inverse Doppler effect and backward Cherenkov radiation. The former is known as the motion-induced frequency shift that is contrary to the normal Doppler effect, and the latter refers to the Cherenkov radiation whose cone direction is opposite to the source's motion. Here we combine these two features and discuss the Doppler effect inside the backward Cherenkov cone. We reveal that the Doppler effect is not always inversed but can be normal in negative refractive-index systems. A previously un-reported phenomenon of normal Doppler frequency shift is proposed in a regime inside the backward Cherenkov cone, when the source's velocity is two times faster than the phase velocity of light. A realistic metal-insulator-metal structure, which supports metal plasmons with an effective negative refractive index, is adopted to demonstrate the potential realization of this phenomenon.

Normal doppler frequency shift in negative refractive‐index systems

/pdf/directional-polaritonic-excitation-of-circular-huygens-and-dnmmizd9zq.pdf

Xiao Lin

Papers

Confined transverse-electric graphene plasmons in negative refractive-index systems

Ab initio study of energy-band modulation in graphene-based two-dimensional layered superlattices

Interferenceless polarization splitting through nanoscale van der Waals heterostructures

Normal doppler frequency shift in negative refractive‐index systems

Directional Polaritonic Excitation of Circular, Huygens and Janus Dipoles in Graphene-Hexagonal Boron Nitride Heterostructures