Automated microdroplet platform for sample manipulation and polymerase chain reaction

We present a fully automated system performing continuous sampling, reagent mixing, and polymerase chain reaction (PCR) in microdroplets transported in immiscible oil. Sample preparation and analysis are totally automated, using an original injection method from a modified 96-well plate layered with three superimposed liquid layers and in-capillary laser-induced fluorescence endpoint detection. The process is continuous, allowing sample droplets to be carried uninterruptedly into the reaction zone while new drops are aspirated from the sample plate. Reproducible amplification, negligible cross-contamination, and detection of low sample concentrations were demonstrated on numerous consecutive sample drops. The system, which opens the route to strong reagents and labor savings in high-throughput applications, was validated on the clinically relevant quantification of progesterone receptor gene expression in human breast cancer cell lines.     

Influence of the addition of thermoplastic preformed particles on the properties of an epoxy/anhydride network

An anhydride/epoxy system is modified by the introduction of thermoplastic microparticles (ORGASOL®). The influence of the presence of polyamide (PA) particles is evaluated on the reactivity of the epoxy/anhydride system below the melting temperature of the thermoplastic. Networks containing various amounts of polyamide are prepared using a cure schedule in order to keep the PA particles below their melting point. Both thermomechanical and mechanical behaviours (glass transition temperature, elastic, plastic and fracture properties) are studied and discussed as a function of the polyamide nature, the particle content and the adhesion between the particles and the matrix.     

Single-chip CMOS pulse generator for UWB systems

This paper presents a single-chip pulse generator developed for Ultra Wide Band (UWB) wireless communication systems based on impulse radio technology. The chip has been integrated in a CMOS 130-nm technology with a single supply voltage of 1.2 V. The basic concept is to combine different delayed edges in order to form a very short duration "logical" pulse, and then filter it, so as to obtain an UWB pulse. It is possible to vary the output pulse shape, and thus the corresponding spectrum, just by acting on the delayed edge combination. Furthermore, the pulse generator supports both position modulation (2-PPM) and polarity modulation (BPSK modulation) in order to convey data through the air. Its power consumption remains less than 10 mW for a raw data rate of up to 160 Mb/s. Spectral and temporal measurements of the single-chip pulse generator are presented with an illustration of the modulation effects on the power spectral density (PSD).     

Tracking aromaticity changes in heavy hydrocarbon processing by monitoring changes in electrical resistivity

In this work, the changes in electrical resistivities of a vacuum residuum are analyzed to determine pyrolysis reaction rates at different temperatures during high temperature processing. Fractions of the residual oil from vacuum distillation were treated at a constant and uniform temperature, and electrical resistance was related to aromaticity. The results show that resistivity behaves like a first order decay-like thermal cracking reaction. This method could replace chemical methods used to determine the temperature necessary for thermal cracking reactions and the kinetic parameters of heavy petroleum fractions.     

Search directions for interior linear-programming methods

Since Karmarkar published his algorithm for linear programming, several different interior directions have been proposed and much effort was spent on the problem transformations needed to apply these new techniques. This paper examines several search directions in a common framework that does not need any problem transformation. These directions prove to be combinations of two problem-dependent vectors, and can all be improved by a bidirectional search procedure.We conclude that there are essentially two polynomial algorithms: Karmarkar's method and the algorithm that follows a central trajectory, and they differ only in a choice of parameters (respectively lower bound and penalty multiplier).Research partly sponsored by CNPq-Brazilian National Council for Scientific and Technological Development, by National Science Foundation Grant ECS-8121149, Office of Naval Research Contract N00014-83-K-0602, AFOSR Grant 83-0361, State of California Microelectronics Innovation and Computer Research Opportunities Program, and General Electric.On leave from COPPE-Federal University of Rio de Janeiro, Cx. Postal 68511, 21941 Rio de Janeiro, RJ, Brasil.     

A simple method for labeling lipids in the bile lipoprotein

A simple method is proposed for the specific radioactive labeling of phosphatidylcholines and cholesterol in the bile lipoprotein complex. It can be used for human and animal bile samples and results in labeling with the desired specific radioactivity and position. Experiments which determined the intermicellar concentration of lipid constituents suggested that incorporation of radioactive lipids could occur through small dialyzable structures termed mixed premicelles in therm odynamic equilibrium with the bile lipoprotein complex.     

Cell culture of tumors alters endogenous poly(ADPR)polymerase expression and activity

Poly(ADP-ribose)polymerase, a chromatin-bound enzyme, actively participates in processes such as cell proliferation, differentiation, and DNA repair and replication. This enzyme is also implicated in cell transformation, and its inhibition has been proposed to potentiate anti-cancer drug activity. Since cells prepared from tumor biopsies and established tumor cell lines are commonly used to evaluate the efficiency of anticancer therapies, we have compared poly(ADP-ribose)polymerase activity in animal tumor cells growing in vivo and in cell culture. Three tumor types were tested: a mastocytoma (P815), a lymphoma (RDM4), and a glioma (C6). Our results show that cell culture alters poly(ADP-ribose)polymerase levels and activity. Endogenous poly(ADP-ribose) activity was several fold higher in exponentially growing cells than in cells freshly recovered from solid or ascitic tumors. Moreover, polymerase activity increased with culture time, reaching a maximum when cells became confluent. Measurements of poly(ADP-ribose)polymerase gene expression and protein amount indicate that lower enzyme activity in tumors grown in vivo are sustained by decreases in poly(ADP-ribose)polymerase mRNA and protein amount. In contrast, the increase in endogenous poly(ADP-ribose)polymerase activity observed in cultured cells was due to enzyme activation and not to de novo protein synthesis. Such differences must be considered when assessing the applicability of cell-culture results to in vivo situations.     

Iterative correction of phase noise and nonlinear distortion in orthogonal frequency division multiplexing (OFDM) systems

In this paper, we present an iterative approach for the cancellation of phase errors induced by local oscillators in anOfdm receiver as well as the distortion resulting from nonlinear amplifiers. We investigate the influence of several parameters on the system performances, such as the modulation scheme, the number of carriers and the clipping ratio. Simulation results prove the effectiveness of the proposed algorithm for the cancellation of phase errors and non-linear distortion. We show that an error floor occurs for high values of the phase noise or the clipping ratio. This effect can be alleviated using an appropriate channel coding scheme, in conjunction with our iterative algorithm, for the correction of residual errors. We also show that the proposed algorithm complexity is nearly a linear function of the number of sub-carriers.     

Chaotic mixing in cross-channel micromixers

In this article we concentrate on a particular micromixer that exploits chaotic trajectories to achieve mixing. The micromixer we consider here is a cross-channel intersection, in which a main stream is perturbed by an oscillatory flow, driven by an external source. Depending on the amplitude and frequency of the oscillatory flow, one obtains wavy and chaotic regimes, reminiscent of a tendril-whorl mapping. The chaotic states, in which material lines are stretched and folded, favour mixing. A spatiotemporal resonance phenomenon, in which the material-line deformation is transient, is shown. An experiment using soft lithography and integrated valves, in which the resonant states are revealed, is described. From a practical viewpoint, the cross-channel micromixer offers a variety of regimes, which can be exploited to mix fluids or separate particles of different sizes. In the context of microsystems, it can be viewed as a 'smart' elementary system.     

Is pleasantness of biscuits and cakes related to their actual or to their perceived sugar and fat contents?

Perceptions of sugar, fat and moisture contents, as well as their influences on pleasantness were investigated in commercial foods. One-hundred-and-two-normal-weight men rated the "pleasantness", "flavour intensity", "moisture", "sweetness" and "fatness" of 39 different biscuits and cakes. Sugar content was accurately perceived up to a maximum content of about 33% weight/weight. The perception of fat content was less accurate and depended on both fat and sugar contents. High sugar contents seemed to decrease perception of fatness. Pleasantness was influenced mainly by sugar content and less by fat content. Pleasantness was better predicted by rated contents than by actual contents; it was even better predicted by the overall flavour intensity. Preferences for high fat stimuli did not appear to be based on conscious perception of their fat content. We conclude that the classical results obtained with simple experimental stimuli remain valid, as a first approximation, for commercial biscuits and cakes, despite their complex sensory characteristics.