Dynamic control of the Q factor in a photonic crystal nanocavity

High-quality (Q) factor photonic-crystal nanocavities are currently the focus of much interest because they can strongly confine photons in a tiny space. Nanocavities with ultrahigh Q factors of up to 2,000,000 and modal volumes of a cubic wavelength have been realized. If the Q factor could be dynamically controlled within the lifetime of a photon, significant advances would be expected in areas of physics and engineering such as the slowing and/or stopping of light and quantum-information processing. For these applications, the transfer, storage and exchange of photons in nanocavity systems on such a timescale are highly desirable. Here, we present the first demonstration of dynamic control of the Q factor, by constructing a system composed of a nanocavity, a waveguide with nonlinear optical response and a photonic-crystal hetero-interface mirror. The Q factor of the nanocavity was successfully changed from approximately 3,000 to approximately 12,000 within picoseconds.     

Dynamic analysis of an inventory and order based production control system

In an inventory and order based production control system (IOBPCS), there are three fundamental system parameters. One of these, the production delay time, is beyond the control of the IOBPCS designer. Indeed, the production delay may be highly variable with time due to a variety of problems commonly found in manufacturing industry. This uncertainty must be countered by the proper use of a feedback loop which detects and operates on inventory deviations. The IOBPCS designer is thus left with the forward path demand averaging time and feedback path gain to adjust, as best he can.

This paper studies the ability of the IOBPCS to recover from shock demands, and to protect the manufacturing process from random variations in consumption. It is shown that the feedback path is of fundamental importance in good control, and that adequate performance cannot be obtained by feedforward alone. Dynamic recovery is examined graphically by separately identifying the feedforward and feedback components. Random disturbance rejection is studied via the noise bandwidth concept. Finally, performance optimization is undertaken using coefficient plane models related to ‘standard forms’ and hardware systems. One good compromise design achieved has the time-to-adjust inventory, demand averaging time, and production delay time all of comparable magnitude.     

Ultra-smooth GaN membranes by photo-electrochemical etching for photonic applications

Photo-electrochemical, bandgap selective, lateral etching is used to create 200 nm-thick, ultra-smooth GaN membranes, containing 10 pairs of GaN/AlGaN quantum wells. The use of electrolyte concentrations as low as 0.0004 M, along with appropriate excitation power and bias conditions, are shown to enhance the quality of freestanding membranes immensely, with an AFM roughness of 0.65 nm; the best ever reported value for GaN membranes fabricated using a similar technique. Transmission and photoluminescence experiments on these membranes were made possible at cryogenic temperatures by membrane transferring onto a double-side polished sapphire substrate, revealing pronounced excitonic features; the analysis of which strongly suggest that the absorption coefficients of GaN are at least 30 % higher than the values previously reported in the literature.     

Calculated photonic structures for infrared emittance control

Using an available program package based on the transfer-matrix method, we calculated the photonic band structure for two different structures: a quasi-three-dimensional crystal of square air rods in a high-index matrix and an opal structure of high-index spheres in a matrix of low index, epsilon = 1.5. The high index used is representative of gallium arsenide in the thermal infrared range. The geometric parameters of the rod dimension, sphere radius, and lattice constants were chosen to give total reflectance for normal incidence, i.e., minimum thermal emittance, in either one of the two infrared atmospheric windows. For these four photonic crystals, the bulk reflectance spectra and the wavelength-averaged thermal emittance as a function of crystal thickness were calculated. The results reveal that potentially useful thermal signature suppression is obtained for crystals as thin as 20-50 microm, i.e., comparable with that of a paint layer.     

Ionic control of the rupture of fetal membranes

Preterm premature rupture of the chorioamniotic membrane frequently leads to preterm birth and perinatal mortality. To ascertain whether the rupture of these membranes is influenced by variations in environmental pH and sodium concentration, we punctured 180 specimens from 9 membranes that were equilibrated in solutions of different pH, and 196 specimens from 10 membranes that were equilibrated in solutions with different sodium concentrations. Whole-membrane mechanical characteristics—strength, stiffness, toughness and ductility—were measured. These characteristics were defined based on a variant of the weakest-link theory: from a pool of three to five specimens, the specimen that had the lowest values of strength and concomitant values of stiffness, toughness, and ductility represents the mechanical characteristics of the entire membrane section. Strength-related mechanical characteristics—strength, stiffness and toughness—correlated negatively with pH (p<0.001, p<0.001, and p<0.02, respectively), while ductility did not correlate significantly with pH. Membrane hydration and thickness correlated positively with pH (p<0.001). The greatest increase in hydration accompanied by the greatest drop in strength, stiffness and toughness was observed between pH values of 3.68 and 5.58, suggesting that insufficient quantities of vaginal H⁺ could cause—as well as mark—premature rupture of the chorioamniotic membrane. No whole—membrane mechanical characteristics correlated significantly with changes in sodium concentration. Membrane hydration and thickness had slight positive correlations with sodium concentration (p<0.05). Changes solely in the sodium concentration of the amniotic fluid during normal pregnancy are not sufficient to facilitate rupture at term.     

Micromechanics-based wavelength-sensitive photonic beam control architectures and applications

Micromechanics-based wavelength-sensitive photonic delay and amplitude control modules are introduced for multiwavelength photonic applications such as hardware-compressed beam forming in phased-array antennas, timing-error compensation in high-speed long-haul fiber-optic communication networks, and pulse synchronization in photonic analog-to-digital converters and space-time code division multiplexed decoders. The basic delay structure relies on a single-circulator compact reflective parallel path design that features polarization insensitivity, independently controllable optical time-delay and amplitude settings, and fiber compatibility. Switched fiber time delays are proposed that use various micromechanical mechanisms such as mechanically stretched fiber Bragg gratings with comb-drive translational stages or magnetic levitation-based stretchers. Additional, shorter-duration variable time delays are obtained by means of the translational motion of external mirrors and the inherent delays in the zigzag reflective path geometry of the bulk-optic thin-film interference filter-based wavelength multiplexer used in our proposed design. Experiments are performed to test these concepts.     

Color control of natural fluorescent proteins by photonic crystals

The emission of fluorescent proteins inside photonic crystals is studied. It is demonstrated that the apparent emission color of the fluorescent protein can be controlled externally by the photonic crystal. With increasing crystal lattice parameter, the appearance of the proteins turns from orange to red, and suddenly to green. The dramatic color changes agree with the theoretically expected redistribution of light escaping around the stop band of the photonic crystal. Our experiments show the potential of combining biological systems with nanophotonics. This "biophotonic engineering" may be extended to control emission rates and complex F?rster energy-transfer systems obtained by protein engineering.     

Sol–gel derived photonic bandgap coatings for solar control

Sol–gel derived photonic bandgap films have been investigated as possible multilayer coatings for solar control glass applications. Multilayer Bragg mirrors, in particular, have been modelled by the Transfer Matrix method, designed to have either near-UV or near-IR reflectivity, but visible transparency, based on alternating aluminosilicate glass/titania quarter-wave stacks. Such composite multilayer structures have been deposited by sol–gel processing on selected glasses and other types of substrates and their optical characteristics have been measured by optical absorption and reflection spectroscopies, as well as spectroscopic ellipsometry to determine the single layer refractive index and thickness. The UV–visible-IR absorption and reflection characteristics of these multilayer coatings revealed solar control properties, due to the presence of peaks near ∼350–400 nm and ∼900–1000 nm, with reflectivities of the order of 70%, which appear promising for solar control application.     

Coherent control of excited atomic states inside a three-dimensional photonic bandgap

We demonstrate the coherent control of the excited state of an atom embedded in three-dimensional photonic bandgap (3D PBG) structures. The coherent control allows us to obtain a long-lifetime Rabi oscillation or several types of steady-state inversion, depending on the laser phase, in which the relaxation of an excited atom is strongly suppressed. Such a coherent control suggests the possibility of extending the atomic system to a low loss quantum logic gate for optical quantum computation.     

高阶不确定系统的自适应跟踪控制

针对一类未知控制增益的不确定非线性系统,提出了一种自适应跟踪控制方法.文中的不确定性包括时变和时不变参数.基于反步设计法,提出了一种新的自适应控制方法.该方法不采用饱和控制,能保证跟踪误差收敛于零.提出了一个仿真例子,仿真结果说明了该方法的有效性.     

Topographic control of lipid-raft reconstitution in model membranes

Liquid-ordered (L(O)) domains reconstituted in model membranes have provided a useful platform for in vitro studies of the lipid-raft model, in which signalling membrane molecules are thought to be compartmentalized in sphingolipid- and cholesterol-rich domains. These in vitro studies, however, have relied on an uncontrolled phase-separation process that gives a random distribution of L(O) domains. Obviously, a precise control of the size and spatial distribution of the L(O) domains would enable a more systematic large-scale in vitro study of the lipid-raft model. The prerequisite for such capability would be the generation of a well-defined energy landscape for reconstituting the L(O) domain without disrupting the two-dimensional (2D) fluidity of the model membrane. Here we report controlling the reconstitution of the L(O) domains in a spatially selective manner by predefining a landscape of energy barriers using topographic surface modifications. We show that the selective reconstitution spontaneously arises from the 2D brownian motion of nanoscale L(O) domains and signalling molecules captured in these nanodomains, which in turn produce a prescribed, concentrated downstream biochemical process. Our approach opens up the possibility of engineering model biological membranes by taking advantage of the intrinsic 2D fluidity. Moreover, our results indicate that the topographic configuration of cellular membranes could be an important machinery for controlling the lipid raft in vivo.     

Dynamic order batching in bucket brigade order picking systems with consecutive batch windows and non-identical pickers

The blocking mitigation mechanism contained in a batching and sequencing model improves order picking performance in bucket brigade order picking systems by adjusting the batch formation in a given batch window. The batch formation of a given batch window affects the transition to the next batch window and limits the batch formation’s structure in the next window. In addition, imbalance in picker capability increases the variation of batch formation while mitigating blocking delay. Our paper proposes a dynamic indexed batching model to smooth the transition between consecutive batch windows and give a better approximation of non-identical pickers’ capability. We develop a mixed integer programming solution for a dynamic indexed batching model in a bucket brigade order picking system (DIBMB). Simulation experiments show that the DIBMB smooths the transition between batch windows as measured in the delay experienced by the first batch in each batch window. Comparisons to the available batching models show that under DIBMB, the blocking delay gradually increases throughout the sequence of batches.     

非线性系统高阶微分反馈控制

提出了不依赖系统模型的高阶微分反馈控制思想，控制目标是系统输出及其微分和高阶微分逼近设定输入及其微分和高阶微分，极大地提高了对控制品质要求。基于这种思想设计了能高品质地提取量测信号的微分和高阶微分的高阶微分器（HOD, highorder differentiator），该HOD参数少，容易调节，并给出其稳定性、收敛性和滤波特性的证明；另外，对带有未知扰动、模型未知的非线性SISO和MIMO系统分别设计了基于HOD的高阶微分反馈自适应控制器(HODFC, high order differentials feedback adaptive controller)，给出了闭环系统稳定性和鲁棒性分析，并且实现了线性化解耦控制。     

Fabrication and characterization of novel composite membranes composed of photonic crystals and TiO2 nanotube array films

Novel composite membranes composed of photonic crystals (PCs) and TiO₂ nanotube array (TNA) films have been fabricated by combining the room temperature floating self-assembly (RTFSA) method, recently developed by our research group, and the liquid-phase deposition technique. By applying this combined procedure, polystyrene (PS) opal PC/TNA and TiO₂ inverse opal PC/TNA composite membranes were prepared. Scanning electron microscopy and ultraviolet/visible spectroscopy analyses showed that the membrane samples possessed very high crystalline quality. Notably, the ordered packing of the PS microspheres from the top to the bottom of the opal PC film was not affected by the surface roughness of the porous TNA substrate. This is attributed to the self-assembly mechanism of the colloidal particles, which produces a three-dimensional ordered structure in the RTFSA method. Herein, the crystallization of the colloidal particles occurred at the surface of the colloidal suspension, and the crystal growth proceeded downward from the surface of the suspension to the substrate.     

Integrating order release control with due-date assignment rules

This study integrates order release control methods with due-date assignment rules and assesses its impact on the accuracy of inter-operation time estimation and performance of due-date assignment. The assessment is made by using an experimental design with three due-date assignment rules, three scheduling rules and three order release models. The three order release models are: (1) Basic model, in which three due-date assignment rules consider the order arrival time as the order release time; (2) Control model, in which three due-date assignment rules integrate with the order release control method developed here; and (3) Adjustment model, in which the control model integrates with the order release control adjustment developed here. Simulation results in this study indicate that integrating the order release control method with due-date assignment rules will significantly enhance not only the accuracy of interoperation time estimation, but also the performance of due-date assignment rules.     

White-light optical implementation of the fractional fourier transform with adjustable order control

An optical implementation of the fractional Fourier transform (FRT) with broadband illumination is proposed by use of a single imaging element, namely, a blazed diffractive lens. The setup displays an achromatized version of the FRT of order P of any two-dimensional input function. This fractional order can be tuned continuously by shifting of the input along the optical axis. Our compact and flexible configuration is tested with a chirplike input signal, and the good experimental results obtained support the theory.     

Dynamic control of continuous flow processes

A simple and effective method for control of continuous flow processes is presented using two new charts, the Decreased Adjustment and the Mean Square Error Ratio charts. A simulation study illustrates how these charts perform comparably with, or superior to, the best methods currently in use. Further, they have advantages including simplicity and ease of use, good performance without a priori knowledge of a mathematical model of the process, and the ability to operate with a limited number of process adjustments. These charts are ideally suited for many real applications, especially when a human operator must make the adjustments.     

Dynamic order acceptance and scheduling problem with sequence-dependent setup time

This paper studies the order acceptance and scheduling problem under a single machine environment when the orders come stochastically during the planning horizon and a sequence-dependent setup time is required between the processing of different types of orders. The objective is to maximise the expected revenue subject to the due date constraints. The problem is formulated as a stochastic dynamic programming model. A rule based on the opportunity cost of the remaining system capacity for the current system state is proposed to make the order acceptance decisions. The remaining system capacity is estimated by a heuristic which generates a good schedule for the accepted orders. Its opportunity cost is estimated by both mathematical programme and greedy heuristic. Computational experiments show that the profit generated by the integrated dynamic programming decision model is much higher than the widely used first-come-first-accept policy in industries and the benefit increases with the length of planning horizon, the arrival rate and the length of lead time. Acceptance decision based on mathematical programming outperforms greedy heuristic by about 7% and its computational time is short. It also shows that the quality of the solutions generated by the opportunity cost based order acceptance rule is satisfactory.     

Dynamic control of the permanent magnet-assisted reluctance synchronous machine

A digital signal processor-based control system for the permanent magnet-assisted reluctance synchronous machine, with the emphasis on dynamic performance, is proposed. A classical design approach is used to design the current and speed controllers for the machine. The stator current of the machine is controlled in such a way that the current angle in the dq synchronous reference frame is constant. The load-torque is estimated using a state space observer and compensation current based on the estimated load is used to improve the dynamic performance of the drive. The control system design is machine specific as it relies on data from finite-element analysis. Simulated and measured results on a 110-kW power level show that the resulting control system is stable and robust with good dynamic performance     

超滤/微滤膜的结构控制与性能

膜材料是膜技术的核心,膜材料制备过程中的结构控制对膜性能起着决定性的作用.首先简要介绍了近年来国内外UF/MF膜技术与产业的现状,在此基础上综述了研究组近年来在TIPS法制备聚乙烯(PE)中空纤维微孔膜、双向拉伸法制备聚四氟乙烯(PTFE)微孔膜、熔融-纺丝法制备聚偏氟乙烯(PVDF)微孔膜、溶液相转化法制备PVDF超滤膜的膜结构控制和表面改性方面取得的研究进展.