Microchemical techniques as applied to radiochemistry

Microchimica Acta - The techniques for investigating the chemistry of radioactive elements usingμg quantities of material are described. These include methods of transfer and carrying out...     

A novel sensitized chemiluminescence: Infrared emissions from thiazine dyes sensitized by singlet oxygen

An unusual infrared chemiluminescence emission (8130Å) of methylene blue, and other thiazine dyes, sensitized by singlet molecular oxygen is reported. This chemiluminescence does not correspond to the ordinary fluorescence of the dye and cannot be explained by previously proposed mechanisms for singlet oxygen sensitized emissions of dyes. From energetic considerations singlet molecular oxygen in its ¹Σ_g⁺ state is postulated as the sensitizing agent for the thiazine dye chemiluminescences. Schemes in which ¹Σ_g⁺ oxygen transfers electronic excitation energy (a) to the lowest triplet state of the dye, (b) to a combined multiplicity state of the lowest triplet state of the dye, and triplet molecular oxygen, or (c) to a charge-transfer state between the dye and oxygen, are compared. The chemiluminescence of methylene blue in aqueous solution may be used as a luminescent probe for ¹Σ_g⁺ oxygen.     

High-tech breakthrough DNA scanner for reading sequence and detecting gene mutation

The 17″×14″ X-ray film, gels, and blots are widely used in DNA research. However, DNA laser scanners are costly and unaffordable for the majority of surveyed biotech scientists who need it. The high-tech breakthrough analytical personal scanner (PS) presented in this report is an inexpensive 1 lb hand-held scanner priced at 2–4% of the bulky and costly 30–95 lb conventional laser scanners. This PS scanner is affordable from an operation budget and biotechnologists, who originate most science breakthroughs, can acquire it to enhance their speed, accuracy, and productivity. Compared to conventional laser scanners that are currently available only through hard-to-get capital-equipment budgets, the new PS scanner offers improved spatial resolution of 20 μm, higher speed (scan up to 17″×14″ molecular X-ray film in 48 s), 1–32,768 gray levels (16-bits), student routines, versatility, and, most important affordability. Its programs image the film, read DNA sequences automatically, and detect gene mutation. In parallel to the wide laboratory use of PC computers instead of mainframes, this PS scanner might become an integral part of a PC-PS powerful and cost-effective system where the PS performs the digital imaging and the PC acts on the data.     

Sharpness of the phase transition in percolation models

The equality of two critical points — the percolation thresholdp _H and the pointp _T where the cluster size distribution ceases to decay exponentially — is proven for all translation invariant independent percolation models on homogeneousd-dimensional lattices (d1). The analysis is based on a pair of new nonlinear partial differential inequalities for an order parameterM(,h), which forh=0 reduces to the percolation densityP — at the bond densityp=1–e ^– in the single parameter case. These are: (1)MhM/h+M ²+MM/, and (2) M/|J|MM/h. Inequality (1) is intriguing in that its derivation provides yet another hint of a ³ structure in percolation models. Moreover, through the elimination of one of its derivatives, (1) yields a pair of ordinary differential inequalities which provide information on the critical exponents and . One of these resembles an Ising model inequality of Fröhlich and Sokal and yields the mean field bound 2, and the other implies the result of Chayes and Chayes that . An inequality identical to (2) is known for Ising models, where it provides the basis for Newman's universal relation and for certain extrapolation principles, which are now made applicable also to independent percolation. These results apply to both finite and long range models, with or without orientation, and extend to periodic and weakly inhomogeneous systems.Research supported in part by the NSF Grant PHY-8605164Also in the Physics Department     

A Study of Composite Heuristic Algorithms

When faced with a difficult combinatorial problem whose optimization may be prohibitively expensive, researchers frequently turn to the study of fast heuristic algorithms in an effort to guarantee near-optimal results. An important aspect in the evaluation of such an algorithm is the determination of its worst-case behaviour, relative to an optimization rule. We here focus attention on schemes for combining two or more heuristics so as demonstrably to improve the worst case that can occur. We survey successful, illustrative examples of such composite algorithms, concentrating on problems of central significance from domains such as scheduling, packing and routeing. We also attempt to illuminate the conditions under which these strategies can be successful and why.     

ON THE OPTIMAL POLICY FOR COMBINED HARVESTING OF INDEPENDENT SPECIES

By a combination of analytical reasoning and numerical experiment it is demonstrated that, for the combined harvesting of two ecologically independent species which grow logistically and are harvested at a rate proportional to both stock level and effort, there is a unique attainable equilibrium which yields positive revenue and to which the approach path satisfies all of Pontryagin's necessary conditions for maximizing the harvest's present value. A simple feedback law governs this approach and is conjectured to be the optimal policy. On that basis, criteria are found for the survival of the less productive species, as a function of the system parameters and initial stocks. An economic interpretation of the equilibrium is also given.     

Periodic behavior of the stochastic Brusselator in the mean-field limit

Summary We prove a propagation of chaos result for the mean-field limit of a model for a trimolecular chemical reaction called Brusselator. Then we show that the pair of nonlinear (i.e. law-dependent) stochastic differential equations describing the evolution of the concentration of the molecules at a given site in the mean field limit has a solution with a periodic law (in t). Finally we identify the limit and establish a central limit theorem for the periodic law in the case where the noise tends to zero.Part of this work was performed while on leave at the Department of Mathematics and Statistics, Carleton University, Ottawa, Canada and supported by NSERC operating grants of M. Csörgö and D. Dawson     

Liposomes as signal amplification reagents for bioassays in microfluidic channels

Liposomes with encapsulated carboxyfluorescein were used in an affinity-based assay to provide signal amplification for small-volume fluorescence measurements. Microfluidic channels were fabricated by imprinting in a plastic substrate material, poly(ethylene terephthalate glycol) (PETG), using a silicon template imprinting tool. Streptavidin was linked to the surface through biotinylated-protein for effective immobilization with minimal nonspecific adsorption of the liposome reagent. Lipids derivatized with biotin were incorporated into the liposome membrane to make the liposomes reactive for affinity assays. Specific binding of the liposomes to microchannel walls, dependence of binding on incubation time, and nonspecific adsorption of the liposome reagent were evaluated. The results of a competitive assay employing liposomes in the microchannels are presented.     

Substitution and condensation reactions with poly(anilineboronic acid): reactivity and characterization of thin films

Poly(anilineboronic acid) thin films are treated under various conditions to achieve substitution or condensation reactions involving the boronic acid moiety. These reactions are studied with polarization modulated infrared reflection absorption spectroscopy, cyclic voltammetry, and UV-vis spectroscopy. The results suggest the single-step formation of substituted polyanilines, such as poly(hydroxyaniline), halogenated polyanilines, and mercury chloride-substituted polyaniline. A condensation reaction of poly(anilineboronic acid) with cis-diol compounds in aqueous solution, as well as with phenylenebisboronic acid and salycilamide in THF, indicates the formation of boronic esters. The latter reactions appear to be a good entry point for the formation of complex or supramolecular polymer structures.