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

Conventional optical components rely on gradual phase shifts accumulated during light propagation to shape light beams. New degrees of freedom are attained by introducing abrupt phase changes over the scale of the wavelength. A two-dimensional array of optical resonators with spatially varying phase response and subwavelength separation can imprint such phase discontinuities on propagating light as it traverses the interface between two media. Anomalous reflection and refraction phenomena are observed in this regime in optically thin arrays of metallic antennas on silicon with a linear phase variation along the interface, which are in excellent agreement with generalized laws derived from Fermat’s principle. Phase discontinuities provide great flexibility in the design of light beams, as illustrated by the generation of optical vortices through use of planar designer metallic interfaces.

http://www.zenogaburro.it/papers/LightPropagation.pdf

Light Propagation with Phase Discontinuities: Generalized Laws of Reflection and Refraction

Metamaterials are artificially fabricated materials that allow for the control of light and acoustic waves in a manner that is not possible in nature. This Review covers the recent developments in the study of so-called metasurfaces, which offer the possibility of controlling light with ultrathin, planar optical components. Conventional optical components such as lenses, waveplates and holograms rely on light propagation over distances much larger than the wavelength to shape wavefronts. In this way substantial changes of the amplitude, phase or polarization of light waves are gradually accumulated along the optical path. This Review focuses on recent developments on flat, ultrathin optical components dubbed 'metasurfaces' that produce abrupt changes over the scale of the free-space wavelength in the phase, amplitude and/or polarization of a light beam. Metasurfaces are generally created by assembling arrays of miniature, anisotropic light scatterers (that is, resonators such as optical antennas). The spacing between antennas and their dimensions are much smaller than the wavelength. As a result the metasurfaces, on account of Huygens principle, are able to mould optical wavefronts into arbitrary shapes with subwavelength resolution by introducing spatial variations in the optical response of the light scatterers. Such gradient metasurfaces go beyond the well-established technology of frequency selective surfaces made of periodic structures and are extending to new spectral regions the functionalities of conventional microwave and millimetre-wave transmit-arrays and reflect-arrays. Metasurfaces can also be created by using ultrathin films of materials with large optical losses. By using the controllable abrupt phase shifts associated with reflection or transmission of light waves at the interface between lossy materials, such metasurfaces operate like optically thin cavities that strongly modify the light spectrum. Technology opportunities in various spectral regions and their potential advantages in replacing existing optical components are discussed.

Flat Optics With Designer Metasurfaces

Electrospinning is a highly versatile method to process solutions or melts, mainly of polymers, into continuous fibers with diameters ranging from a few micrometers to a few nanometers. This technique is applicable to virtually every soluble or fusible polymer. The polymers can be chemically modified and can also be tailored with additives ranging from simple carbon-black particles to complex species such as enzymes, viruses, and bacteria. Electrospinning appears to be straightforward, but is a rather intricate process that depends on a multitude of molecular, process, and technical parameters. The method provides access to entirely new materials, which may have complex chemical structures. Electrospinning is not only a focus of intense academic investigation; the technique is already being applied in many technological areas.

Electrospinning: A Fascinating Method for the Preparation of Ultrathin Fibers

Printed organic smart devices characterized by nonlinear optical In this study, we demonstrate that nonlinear optical microscopy is a promising technique to characterize organic printed electronics. Using ultrashort laser pulses we stimulate two-photon absorption in a roll coated polymer semiconductor and map the resulting two-photon induced photoluminescence (TPPL) and second harmonic response. First, we show that the different nonlinear optical signals can be used to discriminate between the polymer semiconductor material and embedded metal nanoparticles which constitute the electrode in a real device. Next we demonstrate that the TPPL quenches when applying a current between source and drain; this decrease can be used to determine the electrical characteristic of the device [1]. Finally, we show that the TPPL increases with higher temperature in the 20 120 °C range, closely following the supported current characteristics of the semiconductor. With this technique, we can recognize different nanomaterials and we propose that the TPPL is a good indicator to map and monitor the charge carrier density and the molecular packing of the printed polymer material. Importantly, simple calculations based on the signal levels, suggest that this technique can be extended to the real time mapping of the polymer semiconductor film, even during the printing process, in which the high printing speed poses the need for equally high acquisition rates.

https://orbit.dtu.dk/files/134707807/book_of_abstracts_38.pdf

Printed organic smart devices characterized by nonlinear optical

Faraday Discussions have a splendid reputation in stimulating scientic debates
along the traditions set by Michael Faraday himself. The Faraday Discussion 178 on
nanoplasmonics has been particularly appropriate. Nanoplasmonics is the science
of harnessing the interaction of light and matter on the nanometer scale. Plasmonics
is a highly interdisciplinary eld bridging between physics, chemistry,
modern nanotechnology and nanophotonics. Michael Faraday, rstly a chemist with
original contributions in electrochemistry, paved fundamental roads in physics,
establishing the basic concepts of the electromagnetic eld in physics and the effect
of magnetism on rays of light. He pointed out the peculiar effect metal particles have
on light and the importance of the particle size. He mentioned gold as especially
tted for experiments, a tradition carried on until today.1 As such, the spirit and
scientic foundations of Michael Faraday have been ever-present at the Burlington
house gathering in February 2015 (Fig. 1). Here, highlights of the presented papers
and discussions are summarized with an eye on future perspectives.

Nanoplasmonics: Concluding remarks

I will present both deterministic scanning antenna and stochastic localisation mapping of the nanoscale antenna-molecule interaction, towards stronger coupling, bright single photon sources, rate enhancement and spectral control.

The Nanophotonic Dialogue between Antennas and Molecules

riccardo.sapienza@icfo.es To comprehend light matter interaction should we first decipher its components or instead understand the interplay between its building blocks and its underlying complexity? In a journey from the nanoscale dimension of a single fluorescent molecule to the macroscopic scale of self-assembled mm-sized photonic materials I will discuss light transport and lasing. I will show how we can get inspiration from recent advances in the synthesis of 3D nanophotonic materials [

Controlling light emission: from single molecules to random lasing

Ultrafast transient microscopy is a key tool to study the photophysical properties of materials in space and time, but current implementations are limited to ≈1-μm fields of view, offering no statistical information for heterogeneous samples. Recently, we demonstrated wide-field transient imaging based on multiplexed off-axis holography. Here, we perform ultrafast microscopy in parallel around a hundred diffraction-limited excitation spots over a ≈60-μm field of view, which not only automatically samples the photophysical heterogeneity of the sample over a large area but can also be used to obtain a 10-fold increase in signal-to-noise ratio by computing an average spot. We apply our microscope to study the carrier diffusion processes in methylammonium lead bromide perovskites. We observe strong diffusion due to the presence of hot carriers during the first picosecond and slower diffusion afterward. We also describe how many-body kinetics can be misleadingly interpreted as strong diffusion at high excitation densities, while at weak excitation, real diffusion is observed. Therefore, the vast increase in sensitivity offered by this technique benefits the study of carrier transport not only by reducing data acquisition times but also by enabling the measurement of the much smaller signals generated at low carrier densities. 

https://spj.science.org/doi/pdf/10.34133/ultrafastscience.0032?download=true

Niek F. van Hulst

Papers

Printed organic smart devices characterized by nonlinear optical

Nanoplasmonics: Concluding remarks

The Nanophotonic Dialogue between Antennas and Molecules

Controlling light emission: from single molecules to random lasing

High-sensitivity visualization of ultrafast carrier diffusion by widefield holographic microscopy