Spin coating of hydrophilic polymeric films for enhanced centrifugal flow control by serial siphoning

In this paper, we implement rotational flow control on a polymeric microfluidic “lab-on-a-disc” platform by combining serial siphoning and capillary valving for sequential release of a set of on-board stored liquid reagents into a common (assay) channel. The functionality of this integrated, multi-step, multi-reagent centrifugal assay platform critically depends on the capability to establish very reproducible, capillary-driven priming of the innately only weakly hydrophilic siphon microchannels made from common poly(methyl methacrylate) (PMMA) substrates. Due to the relatively high contact angle of the native PMMA substrate, it was practically impossible to ensure sequential release of on-board stored reagents using the capillary-driven serial siphon valves. In this work, we demonstrate that spin-coated hydrophilic films of poly(vinyl alcohol) (PVA) and (hydroxypropyl)methyl cellulose (HPMC) provide stable contact angles on PMMA substrates for more than 60 days. The deposited films were characterized using contact angle measurements, surface energy calculations and X-ray photoelectron spectroscopy spectra. The PVA and HPMC films reduced the water contact angle of the PMMA substrate from 68° to 22° and 27° while increasing their surface energies from 47 to 62 and 57 mN m^?1, respectively. On the centrifugal microfluidic platform, the films were validated to enable the effective and reproducible priming of the serial siphon microchannels at low rotational frequencies while ensuring that the in-line capillary valves are not opened until their respective burst frequencies are passed. Furthermore, the biocompatibility of the proposed surface modification method was examined, and the platform was used to run a sandwich immunoassay for the detection of human immunoglobulin G, and its performance was proven to be comparable to dynamic coating using surfactants.     

UV‐Induced Cross‐Linking of Poly(ethylene oxide) in Aqueous Solution

Summary: Hydrogels of high‐molecular‐weight poly(ethylene oxide) (PEO) have been obtained in situ by applying a very simple procedure that involves UV cross‐linking of PEO in aqueous solution. The efficiency of the photoactivated cross‐linking of thin layers of PEO in aqueous solution in the presence of (4‐benzoylbenzyl) trimethylammonium chloride as a photoinitiator has been determined at room temperature and in a frozen state (?25 °C). It was found that the efficiency varies with the concentration of PEO solution, the molecular weight of PEO, and especially with the temperature. When the UV cross‐linking was performed in the frozen state, porous hydrogels with very high yield of gel fraction (above 90%) and high cross‐linking density were obtained. After drying the hydrogels, films of 50–150 μm thickness were prepared. The films swell extremely fast in water and act as asymmetric membranes.

SEM of a dried PEO hydrogel obtained by UV cross‐linking of an aqueous solution at room temperature.     

Introduction of disulfide bonds into Bacillus subtilis neutral protease

The effects of engineered disulfide bonds on autodigestion andthermostability of Bacillus subtilis neutral protease (NP-sub)were studied using site-directed mutagenesis. After modellingstudies two locations that might be capable of forming disulfidebonds, both near previously determined autodigestion sites inNP-sub, were selected for the introduction of cysteines. Analysisof mutant enzymes showed that disulfide bonds were indeed formedin vivo, and that the mutant enzymes were fully active. Theintroduced disulfides did not alter the autodigestion patternof the NP-sub. All mutant NP-subs exhibited decreased thermostability,which, by using reducing agents, was shown to be caused by theintroduction of the cysteines and not by the formation of thedisulfides. Mutants containing one cysteine exhibited intermoleculardisulfide formation at elevated temperatures, which, however,was shown not to be the cause of the decreased thermostability.Combining the present data with literature data, it would seemthat the introduction of disulfide bridges is unsuitable forthe stabilization of proteases. Possible explanations for thisphenomenon are discussed.     

A Cmos Interface for Thermocouples with Reference-Junction Compensation

This paper presents a CMOS interface for a thermocouple, includingreference-junction compensation. The interface contains a first-orderoscillator whose period is modulated by the signal from the thermocouple(V_X) and two other signals generated internally. One is abase-emitter voltage (V_BE) and the other is a PTAT voltage(V_PTAT). Linear combinations of the periods corresponding tothese two voltages are made by a µC, to obtain a reference signal anda temperature-dependent signal. The internal signals are required to provideauto-calibration for offset and gain and to measure the interface internaltemperature. Dynamic Element Matching is applied to generate an accurate andreliable PTAT voltage. The inaccuracy in the base-emitter voltage iscalibrated using a vertical PNP substrate transistor with multi-emitterareas. The applied modulator used in the circuit has a second-orderfiltering which suppresses low-frequency (1/f) noise. This filteringproperty enables the use of a low-cost CMOS process for the implementationof the circuit. The interface is able to measure a voltage(V_X) in the range of –27 mV to 100 mV, the measuredaccuracy of the system over a temperature range of –25°C to75°C is 550 ppm of V_X ± 2µV. The inaccuracyin determining the reference-junction temperature is 0.6 K. The measuringtime is 50 ms.     

Modelling and experimental evaluation of reaction kinetics in reactive extraction for chiral separation of amines, amino acids and amino-alcohols

This paper reports on determination of the intrinsic reaction kinetics in reactive extraction of chiral compounds. It is important to know the mass transfer rates and reaction kinetics separately for a reliable scale-up. A kinetic model is developed to interpret the experimental data from the selected model reactor, the modified Lewis cell. The two-phase homogeneous reaction model was selected over the interfacial reaction model, because physical partitioning is considerable in all systems studied. It was shown by simulations and by theoretical considerations that conventional regime analysis fails for reactive extraction in a number of regimes, because the conditions of an irreversible reaction and a negligible resistance to mass transfer in the non-reactive phase are generally not fulfilled in reactive extraction. Furthermore, it follows from the simulations that enhancement of mass transfer by reaction may be partly invisible. Finally, it becomes clear that only the fraction of the species that is in the right ‘extractable’ form should be used in the calculations. As the conventional regime analysis cannot be applied to determine the reaction kinetics in the chiral systems, first the mass transfer rate was measured during physical extraction to determine the location of the main resistance to mass transfer. Then the enhancement of mass transfer was measured during reactive extraction. By model simulation, it was determined how much enhancement of mass transfer should be observable. In this way, it was concluded that the reaction kinetics of the azophenolic crown ether system are between fast and instantaneous, and the reaction kinetics of the Cu(II)-N-dodecyl-L-hydroxyproline system are between slow and fast. The Lewis cell is not the most suitable model contactor to determine reaction kinetics in reactive extraction systems.     

Electrical Systems for Automatic Handling and Electric Heating of Slabs

The availability of large quantities of electrical power and sophisticated means of control has justified the use of induction methods in heating large steel slabs to rolling mill temperatures. Capable of delivering 210 MW, a unique power system, comprising power transformers, autotransformers, static switches, and capacitor banks, provides eighteen induction heaters with controlled electrical energy. The entire system can deliver 600 ton/h of steel to the rolling mill. The basic overall automatic control scheme involves the operations of slab handling control, heater control, static power switching, and computer control. The control functions, including phase balance and demand limit control, are described and discussed. The features and operation of the static power switch, capable of switching close to 10 000 A, are presented. Used as a protective device, the switch can clear up to 210 000-A faults in less than one cycle.     

Improving light fastness of natural dyes on cotton yarn

The objectives of this study were to evaluate the light fastness of selected natural dyes (madder, weld and woad) and the effect of some commonly used antioxidants and UV absorbers on the light fastness of these dyes.

The photofading rate curves of madder and weld fixed on cotton correspond to type II fading rate curves described by Giles. These results are in concordance with those of Cox-Crews. The woad presents a type III fading rate curve, similar to the indigo fading rate curve presented by Cox-Crews.

A poor light fastness of the three natural dyes in comparison with synthetic ones is established beyond question. Nevertheless, the use of some additives can improve this default of natural dyes. In all the cases, the use of UV absorbers or antioxidants improved the light fastness of dyed fabrics. The most effectives were the vitamin C and the gallic acid.     

An End to End Adaptable Architecture for Streaming Media over IP Networks

Wireless networks differ in bandwidth, size and access costs each requiring a set of protocol functions to enable devices to communicate efficiently. Portable multimedia devices such as PDA's and laptops will also vary greatly however all these devices will require optimal multimedia delivery. A traditional method is for sources to limit their transmission rates to accommodate lower bandwidth links, even though high-bandwidth connectivity is available to many participants. This method similar to others does not provide optimum throughput to heterogeneous clients due to its quest for a common denominator bandwidth. In addition, due to the divergence of users and applications, traditional protocol stacks are frequently enriched with additional functionality such as transport protocol functionality, synchronization and presentation coding which can lead to a performance bottleneck due to the insufficient processing power and memory of portable devices.Micro-protocols attempt to eradicate this bottleneck by optimising the protocol stack to the functionality that is actually required by the application. A side effect of this is that it allows a device such as a PDA to offer protocol functions, which would not normally be available due to its memory constraints achievable by downloading necessary micro-protocols for new environments and discarding previous micro-protocols. Multicast media groups overcome the heterogeneous client problem where clients subscribe to different quality of services in accordance with resource availability and move between groups according to bandwidth availability.Chameleon is 100% Java middleware for multimedia streaming to heterogeneous mobile clients, which allows the dynamic configuration of protocols with respect to application requirements and available network resources. We evaluate the dynamic reconfigurability of the middleware in order to demonstrate runtime adaptation. We especially concentrate on the primary quality transformation technique (PQT) of the middleware which enables clients to subscribe to media groups in accordance with available resources and network capacity.     

Slip Effects in Vibrating Wire Experiments on 3He-4He Mixtures

We report enormous slip effects in viscosity measurements on the concentrated and the dilute phase of saturated ³He-⁴He mixtures, using vibrating wires in the temperature range 10-250 mK. The concentrated phase data show that the liquid almost does not stick to the wires. There is striking agreement between the data and the solution of the Navier–Stokes equation with the non-sticking boundary condition of zero transverse momentum between the liquid and the surface of the wire. If the slip is taken into account, we obtain good agreement between the viscosity of concentrated and pure ³He. The dilute phase shows slip of a different nature. The analysis based on Eq. (112) of Højgaard Jensen et al. ¹ resugts in the kinematic viscosity and a parameter β relating the slip length, ζ, to the radius of the wire, a. Instead of the expression for β given in the literature, we propose β=ζ/(2ζ+a), because (1) in the limit of ζ→∞ our expression agrees with the non-sticking boundary condition and (2) only our expression fits under the constraint that ζ∝l _η, where l _η is the viscous mean free path. As long as ζ>2a, our expression fits the data very well with ζ/l _η in the range 50–150, depending on the wire.