Surface polishing of quartz-based microfluidic channels using CO<Subscript>2</Subscript> laser

Recently, microgrinding using a polycrystalline diamond tool has been introduced to fabricate microchannels and structures from quartz (fused silica). Compared to wet or dry etching processes, the grinding process is very simple and time-efficient for prototyping. However, the roughness of the machined surface remains an issue, because the surface is covered with many small cracks. Poor surface roughness can affect fluid flow in the microfluidic channels. To reduce the surface roughness of microchannels generated by a grinding process, this study presents the laser polishing of quartz and investigates the effects of the translational speed and pitch of a laser spot on the surface roughness and shape accuracy of microchannels.     

Rapid prototyping of PMMA microfluidic chips utilizing a CO<Subscript>2</Subscript> laser

A commercially available CO₂ laser scriber is used to perform the direct-writing ablation of polymethyl-methacrylate (PMMA) substrates for microfluidic applications. The microfluidic designs are created using commercial layout software and are converted into the command signals required to drive the laser scriber in such a way as to reproduce the desired microchannel configuration on the surface of a PMMA substrate. The aspect ratio and surface quality of the ablated microchannels are examined using scanning electron microscopy and atomic force microscopy surface measurement techniques. The results show that a smooth channel wall can be obtained without the need for a post-machining annealing operation by performing the scribing process with the CO₂ laser beam in an unfocused condition. The practicality of the proposed approach is demonstrated by fabricating two microfluidic chips, namely a cytometer, and an integrating microfluidic chip for methanol detection, respectively. The results confirm that the proposed unfocused ablation technique represents a viable solution for the rapid and economic fabrication of a wide variety of PMMA-based microfluidic chips.     

Fabrication of polystyrene microfluidic devices using a pulsed CO<Subscript>2</Subscript> laser system

In this article, we described a simple and rapid method for fabrication of droplet microfluidic devices on polystyrene substrate using a CO₂ laser system. The effects of the laser power and the cutting speed on the depth, width and aspect ratio of the microchannels fabricated on polystyrene were investigated. The polystyrene microfluidic channels were encapsulated using a hot press bonding technique. The experimental results showed that both discrete droplets and laminar flows could be obtained in the device.     

Microfluidic analysis of CO<Subscript>2</Subscript> bubble dynamics using thermal lattice-Boltzmann method

By means of microfluidic analysis with a thermal lattice-Boltzmann method, we investigated the hydrophilic, thermal and geometric effects on the dynamics of CO₂ bubbles at anode microchannels (e.g., porous layers and flow channels) of a micro-direct methanol fuel cell. The simulation results show that a more hydrophilic wall provides an additional attractive force to the aqueous methanol in the flow direction and that moves the CO₂ bubble more easily. The bubble propagates quicker in the microchannel with a positive temperature gradient imposed from the inlet to the exit, mainly due to the Marangoni effect. Regarding the geometric effect of the microchannel, the bubble moves more rapidly in a divergent microchannel than in a straight or convergent channel. On the basis of the quantitative evaluation of hydrophilic, thermal and geometric effects, we are able to design the bubble-removal technique in micro fuel cells.     

Remote measurement of chemical warfare agents by differential absorption CO<Subscript>2</Subscript> lidar

The possibilities of remote sensing of chemical warfare agents by the differential absorption method are analyzed. The CO₂ laser emission lines suitable for sensing chemical warfare agents with accounting for disturbing absorption by water vapor were chosen. The detection range of chemical warfare agents is obtained for a lidar based on CO₂ laser. Factors influencing upon the sensing range have been analyzed.     

Influence of doping upon the phase change characteristics of Ge<Subscript>2</Subscript>Sb<Subscript>2</Subscript>Te<Subscript>5</Subscript>

The influence of doping upon the phase change characteristics of Ge₂Sb₂Te₅ (GST) has been determined with a variety of techniques including four-point-probe electrical resistance measurements, grazing incidence X-ray diffraction (XRD), X-ray reflectometry (XRR) and a variable incident angle spectroscopic ellipsometer (VASE) and a static tester. Doping with Bi, Sn or In maintains the NaCl-type crystalline structure of GST but expands the lattice due to the larger atomic radii. Sufficient optical contrast is exhibited and can be presumably correlated with the pronounced density change upon crystallization. In the Bi and Sn doped case transition temperatures are reduced with regard to the undoped case. Ultra-fast crystallization within 10 ns is demonstrated, which is correlated with a single NaCl-structure phase and a lower transition temperature arising from the weaker bonds. In the In doped case, however, crystallization is retarded, which can be correlated with the observed phase separation and the increased transition temperature.     

Experimental study of drying effects during supercritical CO<Subscript>2</Subscript> displacement in a pore network

Underground storage in geological aquifers is one of the most important options for large-scale mitigation of CO₂. During the supercritical CO₂ (scCO₂) injection process, water dissolved in scCO₂ may have significant impact on the displacement process. In this study, a series of wet scCO₂ (WscCO₂, 100% water saturation) and dry scCO₂ (DscCO₂, 0% water saturation) displacement experiments were conducted in micromodels for a large range of flow rates. The displacement was visualized using fluorescence microscopy. Results showed that DscCO₂ saturations were up to 3.3 times larger than WscCO₂ saturations when the capillary fingering dominated the displacement. The specific interfacial areas and mobile fractions for the DscCO₂ displacements were also much larger than those for WscCO₂. The capillary forces combined with drying effects are identified as the leading causes for the considerably higher DscCO₂ sweep efficiency. Results from this study showed the important impact of mutual solubility of scCO₂ and water on the displacement process and saturation of scCO₂ (S_scCO2), suggesting that the conventional model describing the relationship between capillary pressure and S_scCO2 needs to be modified for the effect of the mutual dissolution of multiple phases to more adequately describe the scCO₂ displacement process in saline aquifer formation.     

On Supersymmetric M-brane configurations with an R<Stack><Subscript>*</Subscript><Superscript>1,1</Superscript></Stack> /Z<Subscript>2</Subscript> submanifold

We obtain new examples of partly supersymmetric M-brane solutions defined on products of Ricci-flat manifolds, which contain a two-dimensional Lorentzian submanifold R _* ^1,1 /Z ₂ with one parallel spinor. The examples belong to the following configurations: M2, M5, M2 ∩M5 and M5 ∩M5. Among them, an M2 solution with N = 1/32 fractional number of preserved supersymmetries is presented.     

Numerical investigation of formation and dissolution of CO<Subscript>2</Subscript> bubbles within silicone oil in a cross-junction microchannel

In this paper, a numerical investigation is conducted to study the formation and dissolution process of CO₂ bubbles within silicone oil in a cross-junction microchannel. A coupled multiphase–multicomponent computational fluid dynamics model based on the volume-of-fluid method is used, which is able to capture the physics of the multiphase bubble formation, dissolution mass transfer, and the tracking of the dissolved CO₂ species. The computational model is firstly validated with experimental results where good agreement is attained. Next, the model is used to investigate the bubble formation process at the cross-junction in the presence of dissolution and also the bubble evolution as it is transported along the downstream channel. It is revealed that during bubble formation, there is a high concentration of CO₂ solute around the cross-junction walls, as silicone oil flow to this region is minimal. As the CO₂ bubble travels downstream, the transport of the CO₂ solute is largely driven by the local flow currents of the silicone oil within the vicinity of the bubble. An extensive parametric study is also conducted, looking at the effects of varying the surface tension, diffusion coefficient and flow rates. The results demonstrate that the initial CO₂ bubble length and period of bubble formation are most affected by the flow rate, while the mass transfer is most strongly governed by the diffusion coefficient.     

H<Subscript>2</Subscript>-optimal tuning algorithms for fixed structure controllers

An H₂-method of optimal tuning is proposed for a fixed order controller. The SISO plant model is considered in state space. The H₂-method of tuning parameter design is based on the minimization of a transient process closeness criterion for appropriate open-loop and closed-loop control systems and their reference models. The controller tuning algorithms use the plant parameter estimations obtained during the plant parameter identification. The analytical expressions are obtained for the square of H₂-norm of a stable dynamic system. The following theorem is proven: the minimum necessary conditions for the functionals of transfer function H₂-norm of open-loop and closed-loop systems are the same as the minimum necessary conditions for the Frobenius norm of the controller parameter tuning polynomial.     

Micromachined SiO<Subscript>2</Subscript> microcantilever for high sensitive moisture sensor

Ultra-sensitive and selective moisture sensors are needed in various industries for processing control or environmental monitoring. As an outstanding sensor platform, surface-stress sensing microcantilevers have potential application in moisture detection. To enlarge the deflection of the microcantilever under surface stress induced by specific reactions, a new SiO₂ microcantilever is developed which features a much lower Young’s modulus than conventional Si or SiN_x microcantilevers. For comparing SiO₂ cantilever with Si cantilevers, a model of the cantilever sensor is given by using both analysis and simulation, resulting in good agreement with the experimental data. The results demonstrate the SiO₂ cantilever can achieve a much higher sensitivity than the Si cantilever. In order to fabricate this device, a new fabrication process using isotropic combined with anisotropic dry etching to release the SiO₂ microcantilever beam by ICP (Inductively Coupled Plasma) was developed and investigated. This new process not only obtains a high etch rate at 9.1 μm/min, but also provides good profile controllability, and a flexibility of device design. Attributed to the high sensitivity, a significant deflection amplitude of the surface modified SiO₂ microcantilever was observed upon exposure to 1% relative humidity. The SiO₂ cantilevers are promising for inexpensive and highly sensitive moisture detection.     

Algorithms for P<Subscript>4</Subscript>-Comparability Graph Recognition and Acyclic P<Subscript>4</Subscript>-Transitive Orientation

We consider two problems pertaining to P₄-comparability graphs, namely, the problem of recognizing whether a simple undirected graph is a P₄-comparability graph and the problem of producing an acyclic P₄-transitive orientation of a P₄-comparability graph. These problems have been considered by Hoàng and Reed who described O(n⁴)- and O(n⁵)-time algorithms for their solution, respectively, where n is the number of vertices of the input graph. Faster algorithms have recently been presented by Raschle and Simon, and by Nikolopoulos and Palios; the time complexity of these algorithms for either problem is O(n + m²), where m is the number of edges of the graph. In this paper we describe O(n m)-time and O(n + m)-space algorithms for the recognition and the acyclic P₄-transitive orientation problems on P₄-comparability graphs. The algorithms rely on properties of the P₄-components of a graph, which we establish, and on the efficient construction of the P₄-components by means of the BFS-trees of the complement of the graph rooted at each of its vertices, without however explicitly computing the complement. Both algorithms are simple and use simple data structures.     

CdF<Subscript>2</Subscript>:Ga crystal application for dynamic joint transform correlator

Dynamical holographic joint transform correlator that uses cadmium fluoride crystal with gallium bistable impurity centers to generate real-time matched filters is proposed. Optical scheme features and the correlator performance are presented. Output correlation signals of object discrimination both experimentally obtained and theoretically calculated are demonstrated. Industrial object recognition illustrates possible practical application of the correlator proposed. The article is published in the original.     

Pareto optimal generalized <Emphasis Type="Italic">H</Emphasis><Subscript>2</Subscript>-control and vibroprotection problems

We consider a novel multi-objective control problem where the criteria are generalized H ₂-norms of transfer matrices of individual channels from the disturbance input to various objective outputs. We obtain necessary conditions for Pareto optimality. We show that synthesis of Pareto optimal controls can be done in terms of linear matrix inequalities based on optimizing Germeier’s convolution, which also turns out to be the generalized H ₂-norm of the closed-loop system with output composed of the objective outputs multiplied by scalars. As applications we consider multi-objective problems of vibration isolation and oscillation suppression with new types of criteria.     

<Emphasis Type="BoldItalic">H</Emphasis><Subscript>2</Subscript>-Control and the Separation Principle for Discrete-Time Markovian Jump Linear Systems

In this paper we consider the H₂-control problem of discrete-time Markovian jump linear systems. We assume that only an output and the jump parameters are available to the controller. It is desired to design a dynamic Markovian jump controller such that the closed-loop system is mean square stable and minimizes the H₂-norm of the system. As in the case with no jumps, we show that an optimal controller can be obtained from two sets of coupled algebraic Riccati equations, one associated with the optimal control problem when the state variable is available, and the other associated with the optimal filtering problem. This is the principle of separation for discrete-time Markovian jump linear systems. When there is only one mode of operation our results coincide with the traditional separation principle for the H₂-control of discrete-time linear systems. Date received: June 1, 2001. Date revised: October 13, 2003.     

States on <Emphasis Type="Italic">R</Emphasis><Subscript>0</Subscript> algebras

The aim of this paper is to introduce the notion of states on R ₀ algebras and investigate some of their properties. We prove that every R ₀ algebra possesses at least one state. Moreover, we investigate states on weak R ₀ algebras and give some examples to show that, in contrast to R ₀ algebras, there exist weak R ₀ algebras which have no states. We also derive the condition under which finite linearly ordered weak R ₀ algebras have a state. This work is supported by NSFC (No.60605017).     

<Emphasis Type="Italic">L</Emphasis><Subscript>2</Subscript> disturbance attenuation control for input saturated spacecraft attitude stabilization without angular velocity measurements

This work explores a novel efficient and low-cost control scheme for rigid spacecraft attitude stabilization problem, in which the unavailability of angular velocity measurements is considered. The resulting controller is independent on spacecraft inertia parameters, and explicit accounts for control input saturation with angular velocity measurements eliminated. Moreover, the proposed control law allows L ₂ gain of the closed-loop attitude system to be chosen arbitrarily small so as to achieve any level of L ₂ disturbance attenuation. Numerical simulation results are also presented to highlight those highly desirable features.     

Generalized fuzzy filters of <Emphasis Type="Italic">R</Emphasis><Subscript>0</Subscript>-algebras

In this paper, we introduce the notions of interval valued -fuzzy filters and interval valued -fuzzy Boolean (implicative) filters in R ₀-algebras and investigate some of their related properties. Some characterization theorems of these generalized fuzzy filters are derived. In particular, we prove that an interval valued fuzzy set F in R ₀-algebras is an interval valued -fuzzy Boolean filter if and only if it is an interval valued -fuzzy implicative filter.     

An Augmented Lagrangian Method for <Emphasis Type=Italic>TV</Emphasis><Subscript><Emphasis Type=Italic>g</Emphasis></Subscript>+<Emphasis Type=Italic>L</Emphasis><Superscript>1</Superscript>-norm Minimization

In this paper, the minimization of a weighted total variation regularization term (denoted TV _g ) with L ¹ norm as the data fidelity term is addressed using the Uzawa block relaxation method. The unconstrained minimization problem is transformed into a saddle-point problem by introducing a suitable auxiliary unknown. Applying a Uzawa block relaxation method to the corresponding augmented Lagrangian functional, we obtain a new numerical algorithm in which the main unknown is computed using Chambolle projection algorithm. The auxiliary unknown is computed explicitly. Numerical experiments show the availability of our algorithm for salt and pepper noise removal or shape retrieval and also its robustness against the choice of the penalty parameter. This last property is useful to attain the convergence in a reduced number of iterations leading to efficient numerical schemes. The specific role of the function g in TV _g is also investigated and we highlight the fact that an appropriate choice leads to a significant improvement of the denoising results. Using this property, we propose a whole algorithm for salt and pepper noise removal (denoted UBR-EDGE) that is able to handle high noise levels at a low computational cost. Shape retrieval and geometric filtering are also investigated by taking into account the geometric properties of the model.