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

For a system at a temperature of absolute zero, all thermal fluctuations are frozen out, while quantum fluctuations prevail. These microscopic quantum fluctuations can induce a macroscopic phase transition in the ground state of a many-body system when the relative strength of two competing energy terms is varied across a critical value. Here we observe such a quantum phase transition in a Bose-Einstein condensate with repulsive interactions, held in a three-dimensional optical lattice potential. As the potential depth of the lattice is increased, a transition is observed from a superfluid to a Mott insulator phase. In the superfluid phase, each atom is spread out over the entire lattice, with long-range phase coherence. But in the insulating phase, exact numbers of atoms are localized at individual lattice sites, with no phase coherence across the lattice; this phase is characterized by a gap in the excitation spectrum. We can induce reversible changes between the two ground states of the system.

Quantum Phase Transition From a Superfluid to a Mott Insulator in a Gas of Ultracold Atoms

The term photonic crystals appears because of the analogy between electron waves in crystals and the light waves in artificial periodic dielectric structures. During the recent years the investigation of one-, two-and three-dimensional periodic structures has attracted a widespread attention of the world optics community because of great potentiality of such structures in advanced applied optical fields. The interest in periodic structures has been stimulated by the fast development of semiconductor technology that now allows the fabrication of artificial structures, whose period is comparable with the wavelength of light in the visible and infrared ranges.

http://ieeexplore.ieee.org/iel5/6354/16969/00781867.pdf

Photonic crystals

The assembly of semiconductor nanowires and carbon nanotubes into nanoscale devices and circuits could enable diverse applications in nanoelectronics and photonics1. Individual semiconducting nanowires have already been configured as field-effect transistors2, photodetectors3 and bio/chemical sensors4. More sophisticated light-emitting diodes5 (LEDs) and complementary and diode logic6,7,8 devices have been realized using both n- and p-type semiconducting nanowires or nanotubes. The n- and p-type materials have been incorporated in these latter devices either by crossing p- and n-type nanowires2,5,6,9 or by lithographically defining distinct p- and n-type regions in nanotubes8,10, although both strategies limit device complexity. In the planar semiconductor industry, intricate n- and p-type and more generally compositionally modulated (that is, superlattice) structures are used to enable versatile electronic and photonic functions. Here we demonstrate the synthesis of semiconductor nanowire superlattices from group III–V and group IV materials. (The superlattices are created within the nanowires by repeated modulation of the vapour-phase semiconductor reactants during growth of the wires.) Compositionally modulated superlattices consisting of 2 to 21 layers of GaAs and GaP have been prepared. Furthermore, n-Si/p-Si and n-InP/p-InP modulation doped nanowires have been synthesized. Single-nanowire photoluminescence, electrical transport and electroluminescence measurements show the unique photonic and electronic properties of these nanowire superlattices, and suggest potential applications ranging from nano-barcodes to polarized nanoscale LEDs.

Growth of nanowire superlattice structures for nanoscale photonics and electronics.

A simple and effective processing technique for 3D nanoscale pattern formation in light emitting porous silicon is reported. The technique is based on metal assisted chemical etching and defined by the 2D nanoscale metal pattern.

3D nanoscale pattern formation in porous silicon

While much work has focused on simulation and measurement of plasmon resonances in noble metal nanostructures, usually the simulation tool is used as a confirmation of experimental results. In this work we use a finite difference time domain (FDTD) technique to calculate the plasmon resonance and electric field enhancement of Ag nanoparticles in regular arrays on quartz substrates. Such structures have also been prepared by e-beam lithography, and the plasmon resonance and surface-enhanced Raman scattering strength of arrays with different nanoparticle size and spacing have been investigated. Arrays of cylindrical nanoparticles were fabricated with varying particle size and interparticle spacing. The observed extinction peaks agree very well with the extinction peaks as calculated by FDTD; typically within a few percent. Experimental plasmon peak widths are considerably larger than their ideal values due to inhomogeneous broadening. As expected, the particle array with highest SERS enhancement has its plasmon resonance nearest the laser and Stokes-shifted wavelengths. We believe the FDTD modeling tool is accurate enough to use as a predictive tool for engineering plasmonic nanostructures.

SERS and plasmon resonance of engineered nanoparticle arrays

We present a wideband acousto-optic modulator on a suspended thin-film lithium niobate where both light and acoustic waves are guided simultaneously. The modulator has a center frequency of 1.9 GHz and bandwidth of 70 MHz.

Wideband Acousto-Optical Modulation on Suspended Thin-Film Lithium Niobate

A new micro-cavity design is proposed and structures are realized using a 2D photonic-crystal slab. The cavity consists of seven defect holes that encompass a hexagon and is designed to reduce vertical light leakage. From a direct transmission measurement, a Q-value of 816+/- 30 is achieved at (lambda) =1.55micrometers . This high-Q cavity will enable realistic realization of spontaneous emission modification and on-off optical switches.

Transmission measurement of quality factor in two-dimensional photonic-crystal microcavity

We report cathodoluminescence spectroscopy on Ag triangular nanostructures with specially designed substrates having near-vacuum index and low luminescence. FDTD simulations were carried out to predict the role of substrate and the experimentally observed out-of-plane mode.

Edmond Chow

Papers

3D nanoscale pattern formation in porous silicon

SERS and plasmon resonance of engineered nanoparticle arrays

Wideband Acousto-Optical Modulation on Suspended Thin-Film Lithium Niobate

Transmission measurement of quality factor in two-dimensional photonic-crystal microcavity

Cathodoluminescence Imaging of Plasmonic Modes of Ag Nanostructures