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

Recent years have witnessed many breakthroughs in research on graphene (the first two-dimensional atomic crystal) as well as a significant advance in the mass production of this material. This one-atom-thick fabric of carbon uniquely combines extreme mechanical strength, exceptionally high electronic and thermal conductivities, impermeability to gases, as well as many other supreme properties, all of which make it highly attractive for numerous applications. Here we review recent progress in graphene research and in the development of production methods, and critically analyse the feasibility of various graphene applications.

/pdf/a-roadmap-for-graphene-1nstzmbk5x.pdf

A roadmap for graphene

A fast-Fourier-transform method of topography and interferometry is proposed. By computer processing of a noncontour type of fringe pattern, automatic discrimination is achieved between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour-generation techniques. The method has advantages over moire topography and conventional fringe-contour interferometry in both accuracy and sensitivity. Unlike fringe-scanning techniques, the method is easy to apply because it uses no moving components.

Fourier-transform method of fringe-pattern analysis for computer-based topography and interferometry

A topical review of numerical and experimental studies of supercontinuum generation in photonic crystal fiber is presented over the full range of experimentally reported parameters, from the femtosecond to the continuous-wave regime. Results from numerical simulations are used to discuss the temporal and spectral characteristics of the supercontinuum, and to interpret the physics of the underlying spectral broadening processes. Particular attention is given to the case of supercontinuum generation seeded by femtosecond pulses in the anomalous group velocity dispersion regime of photonic crystal fiber, where the processes of soliton fission, stimulated Raman scattering, and dispersive wave generation are reviewed in detail. The corresponding intensity and phase stability properties of the supercontinuum spectra generated under different conditions are also discussed.

Supercontinuum generation in photonic crystal fiber

Methods and apparatus for ascertaining a relative viscosity characterizing a fluid sample. The fluid sample is illuminated through a scattering membrane adjacent to the fluid with broadband radiation. Scattering from particles within the fluid sample characterized by a distribution of characteristic dimensions spanning at least two orders of magnitude is detected, generating a detector signal as a function of depth relative to a specified surface of the scattering membrane at a plurality of temporal delays. A cross-correlation function of at least one of amplitude, phase and intensity of a scattered optical field is derived for a plurality of depths relative to the specified surface. A mean cross-correlation function is then derived for each depth and fit to obtain a diffusion coefficient, from which a relative viscosity characterizing the fluid is derived.

Method and apparatus for OCT-based viscometry

Nonlinear optical imaging is a versatile tool that has been proven to be exceptionally useful in various research fields. However, due to the use of photomultiplier tubes (PMTs), the wide application of nonlinear optical imaging is limited by the incapability of imaging under ambient light. In this paper, we propose and demonstrate a new optical imaging detection method based on optical parametric amplification (OPA). As a nonlinear optical process, OPA intrinsically rejects ambient light photons by coherence gating. Periodical poled lithium niobate (PPLN) crystals are used in this study as the media for OPA. Compared to bulk nonlinear optical crystals, PPLN crystals support the generation of OPA signal with lower pump power. Therefore, this characteristic of PPLN crystals is particularly beneficial when using high-repetition-rate lasers, which facilitate high-speed optical signal detection, such as in spectroscopy and imaging. A PPLN-based OPA system was built to amplify the emitted imaging signal from second harmonic generation (SHG) and coherent anti-Stokes Raman scattering (CARS) microscopy imaging, and the amplified optical signal was strong enough to be detected by a biased photodiode under ordinary room light conditions. With OPA detection, ambient-light-on SHG and CARS imaging becomes possible, and achieves a similar result as PMT detection under strictly dark environments. These results demonstrate that OPA can be used as a substitute for PMTs in nonlinear optical imaging to adapt it to various applications with complex lighting conditions. 

Nonlinear optical imaging by detection with optical parametric amplification

In this abstract, we describe two computational methods for filtering and unwrapping Doppler optical coherence tomography velocity maps, which enable extended measurement range of fluid velocity. We further demonstrate experimental results of both methods and compare to physical simulations.

Filtering and unwrapping doppler optical coherence tomography velocity maps

Coherent anti-Stokes Raman techniques are increasing the utility of Raman scattering for chemical and biological diagnostics.

Design of Matched Optical Pulses for Coherent Raman Imaging

: Label-free nonlinear optical microscopy has become a powerful tool for biomedical research. However, the possible photodamage risk hinder further clinical applications. To reduce these adverse effects, we constructed a new platform of simultaneous label-free autofluorescence multiharmonic (SLAM) microscopy, featuring 5-channel multimodal imaging, inline photodamage monitoring, and pulse repetition-rate tuning. By the use of a birefringent photonic crystal fiber for spectral broadening (rather than supercontinuum generation) and a prism compressor for pulse pre-chirping, this system allows users to independently adjust pulse width, repetition rate, and energy, which is useful for optimizing imaging condition towards no/minimal photodamage. Also, it demonstrates label-free multichannel imaging at one excitation pulse per image pixel and thus paves the way for improving the imaging speed by a faster optical scanner.

Stephen A. Boppart

Papers

Method and apparatus for OCT-based viscometry

Nonlinear optical imaging by detection with optical parametric amplification

Filtering and unwrapping doppler optical coherence tomography velocity maps

Design of Matched Optical Pulses for Coherent Raman Imaging

Compact simultaneous label-free autofluorescence multi-harmonic (SLAM) microscopy for user-friendly photodamage-monitored imaging