A simple photolithography method for microfluidic device fabrication using sunlight as UV source

A straightforward method for microfluidic devices fabrication using sunlight as the ultraviolet (UV) source is established in this work. This method is based on photolithography, but obviates the need for specialized UV exposure facility. Substrates coated with photoresist were placed directly under sun in a perpendicular direction to the sunlight for exposure. Exposure conditions were optimized for patterning features with different kinds of photoresist, photoresist of different thicknesses and dimensions. Exposure time can be adjusted to obtain designed features on a mask with good lateral structure according to the energy measured by UV meter (with a constant intensity of UV in sunlight). Masters produced under optimum exposure conditions were used for the fabrication of several microfluidic devices with different materials, structures, or functions. Resultant devices were shown eminently suitable for microfluidic applications such as electrophoretic separation, multiple gradient generator, and pneumatic valve-based cell culture. This photolithographic method is simple, low cost, easy to operate, and environmental friendly. Especially, the masters can be obtained in parallel simultaneously, which is suitable for chip fabrication for mass production. It is also more attractive for the laboratories, in which the support for photolithographic facility is not available.     

Manipulation and patterning of carbon nanotubes utilizing optically induced dielectrophoretic forces

This study reports an optically driven platform upon which the manipulation and patterning of carbon nanotubes (CNTs) can be accomplished. A photoconductive layer made of amorphous silicon generates a nonuniform electric field within the developed platform at specific optically illuminated sites, which are usually referred to as “virtual electrodes,” that induces dielectrophoretic forces for manipulating the CNTs. The software-controlled light patterns enable a variety of flexible manipulation modes since it is now possible to dynamically reconfigure the optically projected electrode patterns. This approach allows for real-time manipulation and miscellaneous patterning of CNTs. The sorting and separation of bundled and dispersed CNTs is also demonstrated. This developed platform may be promising for rapid fabrication of CNT-based nanosensors together with nanoelectronics, purification as well as classification of synthesized CNTs and other applications requiring nanoscale manipulation.     

Driving characteristics of the electrowetting-on-dielectric device using atomic-layer-deposited aluminum oxide as the dielectric

Electrowetting on dielectric (EWOD) is useful in manipulating droplets for digital (droplet-based) microfluidics, but its high driving voltage over several tens of volts has been a barrier to overcome. This article presents the characteristics of EWOD device with aluminum oxide (Al₂O₃, ε _r  ≈ 10) deposited by atomic layer deposition (ALD), for the first time as the high-k dielectric for lowering the EWOD driving voltage substantially. The EWOD device of the single-plate configuration was fabricated by several steps for the control electrode array of 1 mm × 1 mm squares with 50 μm space, the dielectric layer of 1,270 Å thick ALD Al₂O₃, the reference electrode of 20 μm wide line electrode, and the hydrophobic surface treatment by Teflon-AF coating, respectively. We observed the movement of a 2 μl water droplet in an air environment, applying a voltage between one of the control electrodes and the reference electrode in contact with the droplet. The droplet velocity exponentially depending on the applied voltage below 15 V was obtained. The measured threshold voltage to move the droplet was as low as 3 V which is the lowest voltage reported so far in the EWOD researches. This result opens a possibility of manipulating droplets, without any surfactant or oil treatment, at only a few volts by EWOD using ALD Al₂O₃ as the dielectric.     

Neue Unabhängigkeit für den betrieblichen Datenschutzbeauftragten?

Der betriebliche Datenschutzbeauftragte dient der Selbstkontrolle der verantwortlichen Stelle. Wirksam ist solch eine Selbstkontrolle aber nur dann, wenn der Datenschutzbeauftragte auch Unabh?gigkeit genie?t. Welche Voraussetzungen hierfür erfüllt sein müssen, erl?utert der folgende Beitrag.     

The UK Cleanfeed system — Lessons for the German debate?

As readers of this journal will of course know, the Zugangserschwerungsgesetz has caused considerable and often very profound debate in Germany about the limits of legal and technological interference with the freedom of access to information, culminating in the temporary refusal of the President to sign the law into action. In the UK by contrast, a core aspect of this law, the technical prevention of access to sites hosting illegal content by ISPs, was introduced through the so called “Cleanfeed system” as early as 1996, with little or no public debate, and bypassing by and large all parliamentary procedure and scrutiny. This article has a threefold aim: First, it gives a brief account of the history and implementation of the UK Cleanfeed system1; second, it explains some of its more unusual aspects by putting them into the historical and constitutional context of policing in the UK, and third, it highlights those experiences made with the system that are of direct relevance for the German discussion.     

Modified BVD model of PZT actuator using high-voltage square pulse method for micropumps

The field of micro–electro–mechanical systems and microfabrication has produced micro-total-analysis systems, which are widely used in medicine, diagnostics, and biological and chemical research. For the development of high precision drug delivery systems, micropumps with a lead zirconate titanate (PZT) actuator, which has a fast response time and high resolution, are most likely to be applied in implementations. To improve the performance of PZT micropumps utilized in the microfluidics field, suitable models are required to enable the optimization of the PZT actuator driving circuits. This study proposes a modified Butterworth–Van Dyke (BVD) model which consists of a BVD model in series with an electrical resistance that describes a PZT actuator driven by a square pulse with a relatively high voltage and low frequency for micropump applications. Experiments were conducted to assess parameters of the model at various voltages; they indicate that the electrical resistance is essential for modeling the PZT actuator of the micropump. The electrical model was verified using a SPICE simulation, whose numerical results were compared with the experimental data for the current response of the PZT actuator. The results show a close correlation between the simulation of the electrical model and the measurements of the PZT actuator under real operating conditions.     

Effect of geometry on droplet formation in the squeezing regime in a microfluidic T-junction

In the surface tension-dominated microchannel T-junction, droplets can be formed as a result of the mixing of two dissimilar, immiscible fluids. This article presents results for very low Capillary numbers and different flow rates of the continuous and dispersed phases. Through three-dimensional lattice Boltzmann-based simulations, the mechanism of the formation of “plugs” in the squeezing regime has been examined and the size of the droplets quantified. Results for Re_\textc << 1 Re_{\text{c}} \ll 1 show the dependence of flow rates of the two fluids on the length of the droplets formed, which is compared with existing experimental data. It is shown that the size of plugs formed decreases as the Capillary number increases in the squeezing regime. This article clearly shows that the geometry effect, i.e., the widths of the two channels and the depth of the assembly, plays an important role in the determination of the length of the plugs, a fact that was ignored in earlier experimental correlations.     

Fundamental dynamics of flow through carbon nanotube membranes

The flow of a model non-polar liquid through small carbon nanotubes is studied using non-equilibrium molecular dynamics simulation. We explain how a membrane of small-diameter nanotubes can transport this liquid faster than a membrane consisting of larger-diameter nanotubes. This effect is shown to be back-pressure dependent, and the reasons for this are explored. The flow through the very smallest nanotubes is shown to depend strongly on the depth of the potential inside, suggesting atomic separation can be based on carbon interaction strength as well as physical size. Finally, we demonstrate how increasing the back-pressure can counter-intuitively result in lower exit velocities from a nanotube. Such studies are crucial for optimisation of nanotube membranes.     

Linking denotational semantics with operational semantics for web services

Web Services have become more and more important in these years, and BPEL4WS (BPEL) is a de facto standard for the web service composition and orchestration. It contains several distinct features, including the scope-based compensation and fault handling mechanism. The denotational semantics and operational semantics have been explored for BPEL. The two semantic models should be consistent. This paper considers the linking of these two semantics. Our approach is to derive the denotational semantics from operational semantics for BPEL, which aims for the consistency of the two models. Moreover, the derivation can be applied in exploring the program equivalence easily, especially for parallel programs.     

Sliding mode control of uncertain switched delay systems via hysteresis switching strategy

This paper investigates the robust sliding mode control (SMC) problem for a class of uncertain switched systems with time-varying delay. The sliding surface is constructed such that the sliding motion is completely invariant to all admissible uncertainties. For the case of the known delay-derivative upper bound, by using the multiple Lyapunov functions method, the Hysteresis switching law dependent on the state and the previous value of switching signal are designed to stabilize the sliding motion and avoid the chattering. Variable structure controllers are developed to drive the state of switched systems to reach the sliding surface in finite time and remain on it thereafter. For the case of the unknown delay-derivative upper bound, based on the single Lyapunov function method, the conditions of stabilization are obtained. Finally, a numerical example is given to illustrate the effectiveness of the proposed methods.