On-chip natural assembly of silicon photonic bandgap crystals.

Photonic bandgap crystals can reflect light for any direction of propagation in specific wavelength ranges. This property, which can be used to confine, manipulate and guide photons, should allow the creation of all-optical integrated circuits. To achieve this goal, conventional semiconductor nanofabrication techniques have been adapted to make photonic crystals. A potentially simpler and cheaper approach for creating three-dimensional periodic structures is the natural assembly of colloidal microspheres. However, this approach yields irregular, polycrystalline photonic crystals that are difficult to incorporate into a device. More importantly, it leads to many structural defects that can destroy the photonic bandgap. Here we show that by assembling a thin layer of colloidal spheres on a silicon substrate, we can obtain planar, single-crystalline silicon photonic crystals that have defect densities sufficiently low that the bandgap survives. As expected from theory, we observe unity reflectance in two crystalline directions of our photonic crystals around a wavelength of 1.3 micrometres. We also show that additional fabrication steps, intentional doping and patterning, can be performed, so demonstrating the potential for specific device applications.     

PBL教学法在分子生物学实验教学中的应用

文章采用问卷调查和考核方式评价了PBL在分子生物学实验课中应用的效果，结果得出：80％-100％的学生认为PBL教学强化了学生自主学习、交往和团队合作等各种能力，86％的学生认为PBL教学模式应该推广。实验考核的结果显示PBL教学组成绩显著优于对照组（p〈0．05），PBL教学效果好于传统教学。     

Programmable and autonomous computing machine made of biomolecules.

Devices that convert information from one form into another according to a definite procedure are known as automata. One such hypothetical device is the universal Turing machine, which stimulated work leading to the development of modern computers. The Turing machine and its special cases, including finite automata, operate by scanning a data tape, whose striking analogy to information-encoding biopolymers inspired several designs for molecular DNA computers. Laboratory-scale computing using DNA and human-assisted protocols has been demonstrated, but the realization of computing devices operating autonomously on the molecular scale remains rare. Here we describe a programmable finite automaton comprising DNA and DNA-manipulating enzymes that solves computational problems autonomously. The automaton's hardware consists of a restriction nuclease and ligase, the software and input are encoded by double-stranded DNA, and programming amounts to choosing appropriate software molecules. Upon mixing solutions containing these components, the automaton processes the input molecule via a cascade of restriction, hybridization and ligation cycles, producing a detectable output molecule that encodes the automaton's final state, and thus the computational result. In our implementation 1012 automata sharing the same software run independently and in parallel on inputs (which could, in principle, be distinct) in 120 microl solution at room temperature at a combined rate of 109 transitions per second with a transition fidelity greater than 99.8%, consuming less than 10-10 W.     

一种动态校正的AGMM-GPR多模型软测量建模方法

工业过程常常是强非线性的,并有多个工况,传统的软测量方法存在预测能力差,不能有效利用误差信息等缺点.为了有效解决这些问题,提出一种基于自适应高斯混合模型-高斯过程回归(AGMM-GPR)的多模型动态校正软测量建模方法.首先,通过贝叶斯信息准则构建自适应高斯混合模型(AGMM),得到优化的子模型个数;然后,利用GPR方法建立各局部模型,当新的数据到来时,将其隶属于各局部模型的后验概率和预测值融合得到多模型输出;最后,为了进一步提高模型的精度,构建自回归积分滑动平均(ARIMA)模型对多模型输出进行动态反馈校正.通过数值仿真和硫回收装置(SRU)中H2S浓度的估计,验证了所提方法具有良好的预测精度和泛化性能.     

South-polar features on Venus similar to those near the north pole

Venus has no seasons, slow rotation and a very massive atmosphere, which is mainly carbon dioxide with clouds primarily of sulphuric acid droplets. Infrared observations by previous missions to Venus revealed a bright 'dipole' feature surrounded by a cold 'collar' at its north pole. The polar dipole is a 'double-eye' feature at the centre of a vast vortex that rotates around the pole, and is possibly associated with rapid downwelling. The polar cold collar is a wide, shallow river of cold air that circulates around the polar vortex. One outstanding question has been whether the global circulation was symmetric, such that a dipole feature existed at the south pole. Here we report observations of Venus' south-polar region, where we have seen clouds with morphology much like those around the north pole, but rotating somewhat faster than the northern dipole. The vortex may extend down to the lower cloud layers that lie at about 50 km height and perhaps deeper. The spectroscopic properties of the clouds around the south pole are compatible with a sulphuric acid composition.     

Coherent zero-state and pi-state in an exciton-polariton condensate array

The effect of quantum statistics in quantum gases and liquids results in observable collective properties among many-particle systems. One prime example is Bose-Einstein condensation, whose onset in a quantum liquid leads to phenomena such as superfluidity and superconductivity. A Bose-Einstein condensate is generally defined as a macroscopic occupation of a single-particle quantum state, a phenomenon technically referred to as off-diagonal long-range order due to non-vanishing off-diagonal components of the single-particle density matrix. The wavefunction of the condensate is an order parameter whose phase is essential in characterizing the coherence and superfluid phenomena. The long-range spatial coherence leads to the existence of phase-locked multiple condensates in an array of superfluid helium, superconducting Josephson junctions or atomic Bose-Einstein condensates. Under certain circumstances, a quantum phase difference of pi is predicted to develop among weakly coupled Josephson junctions. Such a meta-stable pi-state was discovered in a weak link of superfluid 3He, which is characterized by a 'p-wave' order parameter. The possible existence of such a pi-state in weakly coupled atomic Bose-Einstein condensates has also been proposed, but remains undiscovered. Here we report the observation of spontaneous build-up of in-phase ('zero-state') and antiphase ('pi-state') 'superfluid' states in a solid-state system; an array of exciton-polariton condensates connected by weak periodic potential barriers within a semiconductor microcavity. These in-phase and antiphase states reflect the band structure of the one-dimensional polariton array and the dynamic characteristics of metastable exciton-polariton condensates.     

阻抗测量法及梁的阻抗应答分析

提出了利用压电陶瓷的阻抗测量法的概念,即用压电陶瓷作为驱动源产生动态阻抗信息.测试系统由阻抗分析仪、计算机、压电陶瓷片、铝梁组成.实验将铝梁作为测试对象,在其上粘贴压电陶瓷,通过对阻抗应答、振动模型和压电陶瓷片的粘贴位置的分析,研究梁的阻抗频率特性.实验结果表明,利用阻抗法,容易得到构造物的频率响应特性,应答分析也简单.     

附加应力沿深度变化的砂井地基固结分析

基于等应变固结的假设,考虑附加应力沿地基深度的变化以及涂抹效应和井阻的影响,导出砂井地基固结偏微分方程,求得孔隙水压力和平均固结度的解析解.在随时间变化的预压荷载作用下,对把初始孔隙水压力和附加应力简化为沿深度梯形分布的固结性状进行比较.结果表明,对于深厚砂井地基,附加应力和初始孔隙水压力分布对固结过程具有明显影响,若按均匀分布计算,所得的平均固结度偏小.