Optically addressable field effect nano-environments for chemical imaging

An optically addressable field effect device incorporating functionalized nano-environments is demonstrated for the generation of multiple response signatures of a same analyte-sensing material combination. The device can operate unsupervised and different response mechanism can be simultaneously tested and incorporated in a multidimensional response. This proof of concept explores the well-known Pd-H₂ case, while the concept is a breadboard for chemical imaging experiments.     

The reactions of methyl radicals with chloromethanes

The reaction of methyl radicals with CCl₄ and CCl₃Br have been reinvestigated in the gas phase over a wide range of temperatures and pressures using both the photolysis of acetone and the pyrolysis of di-tertiary butyl peroxide (dtBP) as the methyl radical sources. The results are in essential agreement with previous work; however, these new studies provide evidence that at higher pressures the major source of HCl in the reactions is due to methyl radical attack on CH₃CCl₃, formed via the combination of methyl and trichloromethyl radicals. From these investigations Arrhenius parameters for the reactions have been determined: Pyrolysis of dtBP in the presence of relatively high-pressure mixtures of CCl₄ and CCl₃Br resulted in no enhanced methane formation, since, under these conditions, the only termination product is C₂Cl₆, and the HCl precursor CH₃CCl₃ is not formed. A competitive technique has been used in which dtBP was pyrolysed in the gas phase in the presence of high-pressure mixtures of CCl₃Br and a chloromethane. Arrhenius parameters were obtained for the reactions and the results were used to provide information on the importance of polar effects for hydrogen abstraction from halogenated methanes.     

Imaging fingerprinting of excitation emission matrices

The spectral fingerprinting of the excitation emission matrix (EEM) of fluorescent substances is demonstrated using polychromatic light sources and tri-chromatic image detectors. A model of the measured fingerprints explaining their features and classification performance, based on the polychromatic excitation of the indicators is proposed.Substantial amount of spectral information is retained in the fingerprints as corroborated by multivariate analysis and experimental conditions that favor such situation are identified.In average, for five different substances, the model shows a fitting goodness measured by the Pearson's r coefficient and the root mean square deviation of 0.8541 and 0.0247 respectively, while principal component classification patterns satisfactorily compare with the EEM spectroscopy classification and respectively explain 96% and 93% of the information in the fist two principal components.The measurements can be performed using regular computer screens as illumination and web cameras as detectors, which constitute ubiquitous and affordable platforms compatible with distributed evaluations, in contrast to regular instrumentation for EEM measurements.     

Some stochastic models in immunology

Conditional probability arguments and the theory of continuous-time Markov chains are used to develop models for the kinetics of a cell-mediated cytotoxic reaction. While the models are conceptually simple, when fitted to data, they lead to surprising insights into the mechanisms of the immune response. Based on examples and discussion, we demonstrate the potential for creative and relevant application of mathematics within the rapidly developing field of immunology.This work was performed under the auspices of the United States Department of Energy. A.S.P. is the recipient of an N.I.H. Research Career Development Award 5 K04 AI00450-05.     

The thick and thin limiting solutions for combined convection and radiation in the region of a two dimensional stagnation point

The low speed constant property flow of a gray absorbing and emitting gas is studied in the region of a two dimensional stagnation point. Two limiting cases are considered. These correspond to the case where the hydrodynamic boundary layer is either optically thin or optically thick. In the thin case, the errors in the total heat transfer are of the order of one percent for an optical thickness of 001. For the thick case, the three term Taylor series gives an excellent representation for the temperature profile and the best result for the convection heat transfer for an optical thickness of 1.0 and 10.0. The most accurate radiation heat transfer is found by using this profile in the exact numerical expression. The Rosseland expression gives the best representation for the total heat transfer.     

Towards integrated devices for computer screen photo-assisted multi-parameter sensing

The computer screen photo-assisted technique (CSPT) utilizes consumer electronic devices such as computer screens and web cameras for distributed chemical sensing. Key to this method is the development of small and disposable sensing assays able to aid the CSPT optical detection, and the evaluation of multiple indicators. Here we demonstrate CSPT identification of fluorescent indicators from individual 100 μm SU-8 (10) pillars covering an area of 4 mm × 4 mm with a density of 47 elements mm⁻². The extraction of distinctive spectral fingerprints is aided by the exploitation of a three-band Moiré interference that enables the partial Bayer decoding of the CSPT images.     

The Effects of Radiofrequency Electromagnetic Radiation on the Adhesion Behavior of Aqueous Suspensions

The effect of radiofrequency treatment on the adhesion behavior of amidine and carboxylated polystyrene latexes was investigated. The isoelectric points pH(IEP) of copper and zinc were initially measured as 9.4 and 9.5, respectively, using a technique proposed by N. Kallay, Z. Torbic, M. Golic, and E. Matijevic [J. Phys. Chem. 95, 7028 (1991)] based on the attachment of charged colloids to metallic surfaces in an aqueous medium. Statistical analysis showed that the technique was repeatable with a coefficient of variation less than 6% and an accuracy greater than 95%. The effect of a radiofrequency signal (27 MHz) on adhesion behavior was evaluated and it was found that there was reduced attachment at pH values when the colloid and metallic surface were oppositely charged and enhanced attachment between similarly charged particles. It is proposed that this is due to a reduction in the surface potential of the charged particles due to thickening of the adsorbed layer by hydrogen and hydroxyl ions. Copyright 2000 Academic Press.