Laser microstructuration of three-dimensional enzyme reactors in microfluidic channels

In this paper, we report on the fabrication of three-dimensional (3D) enzymatic microreactors within polydimethylsiloxane microfluidic channels through a photocrosslinking mechanism mediated by the two-photon absorption process at the focal point of pulse lasers, i.e., a sub-nanosecond Nd:YAG microlaser or a femtosecond Ti:Sapphire laser. This approach allows the building of localized 3D trypsin structures with submicron resolution. The fabrication of two different trypsin structures was successfully demonstrated using Eosin Y and Flavin Adenine Dinucleotide as biological photosensitizers: (i) arrays of 3D cylindrical rows and (ii) 3D woodpile structure. The enzymatic activity of the fabricated structures was evaluated by fluorescence spectroscopy using BODIPY FL casein as fluorogenic substrate. The real time investigation of the peptide cleavage into the microfluidic channel demonstrated that the fabricated trypsin microstructures maintain their catalytic activity. This approach opens up the way to complex multistep enzymatic reactions in well-localized regions of microfluidic devices, with great importance in health screening and biomedical diagnostics.     

Robust feedforward design in the presence of LTI/LTV uncertainties

A practical method is proposed for the convex design of robust feedforward controllers which ensures H_∞/L₂ performance in the face of LTI and arbitrarily time‐varying model uncertainties. A technique that computes the global minimum of this difficult infinite dimensional optimization problem is proposed, as well as a suboptimal but computationally less involved algorithm. Convergence is proved. An efficient way to analyse the robustness properties of a closed loop with or without feedforward controller is obtained as a subproblem. A missile example illustrates the efficiency of the scheme: a robust feedforward controller is designed either on the continuum of linearized time‐invariant models (corresponding to trim points) or on a quasi‐LPV model representing the non‐linear one. Copyright © 2007 John Wiley & Sons, Ltd.     

Solidification thermal parameters affecting the columnar-to-equiaxed transition

Experiments were conducted to analyze the columnar-to-equiaxed transition (CET) during the upward unsteady-state directional solidification of Al-Cu and Sn-Pb alloys, under different conditions of superheat and heat-transfer efficiencies at the metal/mold interface. A combined theoretical and experimental approach is developed to quantitatively determine the solidification thermal parameters: transient heat-transfer coefficients, tip growth rates, thermal gradients, and cooling rates. The observed results do not give support to CET criteria based individually either on tip growth rate or temperature gradients ahead of the liquidus isotherm. Rather, the analysis has indicated that a more convenient criterion should encompass both thermal parameters through the tip cooling rate. The columnar growth is expected to prevail throughout the casting for a tip cooling rate higher than a critical value, which depends only on the alloy system and was observed to be about 0.2 K/s for Al-Cu alloys and 0.01 K/s for Sn-Pb alloys in the present investigation.     

Choix langagiers en milieu minoritaire: Attitudes et identité concomitantes.

Studied the relationship between language use and cultural identity. 85 mainly French-speaking students (mean age 16.4 yrs) from the North Shore of Algoma, Ontario, were administered a questionnaire concerning their identification with Ss using English vs French as their most usual mode of communication. Analyses of variance were performed. (English abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Alteration in 5'-nucleotidase activities and composition of liver and brain microsomes of developing rats fed different dietary fats

Four groups of male weanling rats were fed during three months, diets different in the nature of fats and the activity of 5' nucleotidase and fatty acid composition of brain and liver microsomes were studied. Group A were fed a standard commercial diet, group B a fat free-diet and group C and D a fat free-diet, containing respectively 10% of peanut-rapeseed oil and 10% of salmon oil. In brain and liver microsomes, 5'-nucleotidase activity increased throughout the development for all diets (except for the fat-free diet). Slight differences were found in rats fed the peanut-rapeseed oil diet compared to controls estimated at the same time. However, in animals fed the fish-oil diet, 5' nucleotidase had the highest activity in both brain and liver microsomes. Marked changes occurred in the fatty acid patterns of brain and liver microsomes among the various groups. The greatest alterations were found in the liver microsomes. In brain and liver microsomal membranes the fat-free diet induced an increase in monounsaturated fatty acids, an synthesis of eicosatrienoic acid, and a decrease in (n-6) and (n-3) polyunsaturated fatty acids. Animals fed a peanut-rapeseed oil and control diet showed similar fatty acid patterns in liver and brain microsomes. However, when rats were fed a fish-oil diet, the liver microsomal membranes were highly enriched in eicosapentaenoic and docosahexaenoic acids, and simultaneously there was a decrease in arachidonic acid. These results suggest that manipulation of the lipid environment influences 5'-nucleotidase activity by the interaction of the enzyme with specific membrane lipids.     

A heat transfer correlation for natural draft wire-and-tube condensers

A dimensionless correlation to estimate the heat transfer coefficient between the external surfaces of natural draft wire-and-tube condensers and the surrounding air is proposed in this study. The experiments were carried out using a purpose-built testing apparatus that reproduces the actual operating conditions of such heat exchangers. A test section to vary the condenser position in relation to the adjacent surfaces was also developed and mounted within a controlled environmental chamber. The correlation was developed based on a total of 72 experimental data points obtained with 24 different condenser samples with tube outer diameter  ranging from 4.8 to 6.2 mm, number of tube rows from 13 to 25, and number of wire pairs from 10 to 90. The tests were performed with an average temperature difference between the condenser surface and the ambient air ranging from 3.6 to 36.1 °C. The proposed correlation predicts 90% of heat transfer data within an error band of ±10%. Comparisons with other correlations available in the open literature are also reported.     

Surface nanopatterning by organic/inorganic self-assembly and selective local functionalization

Patterning silicon surfaces by well-ordered nanoperforated TiO(2) layers is achieved through a simple block copolymer-assisted liquid deposition technique followed by direct thermal treatment. The crater diameters are tuned between 10 and 50 nm, depending on the molecular weight of the surfactant patterning agent. The formation mechanism of such systems is discussed. The present nanopatterned heterogeneous surfaces (nanoholes with SiO(2) bottom surfaces and TiO(2) walls) are selectively functionalized with two different perfluorinated organic groups. The accessibility to the substrate surface through such nanoholes and the selective distribution of both functions on the surface is evidenced by water-contact-angle measurements, which satisfactorily verify the Cassie relationship. Such systems have wide application prospects in varied fields such as nanotechnology and engineering.