Boundedness and Dissipativity of Truncated Rotations on Uniform Planar Lattices

The finiteness of computer arithmetic can lead to some dramatic differences between the behaviour of a continuous dynamical system and a computer simulation. A thorough rigorous theoretical analysis of what may or what does happen is usually extremely difficult and to date little has been done even in relatively simple contexts. The comparative behaviour of a rotation mapping in the plane and on a uniform lattice in the plane is one such example. Simulations show that the rounding operator applied to a planar rotation mapping more or less preserves the qualitative behaviour of the original mapping, whereas the application of the truncation operator to a planar rotation can lead to quite different dynamical features. In this paper a theoretical justification of the properties of the planar rotation mappings under truncation to a, uniform integer lattice is provided, in particular properties of boundedness and dissipativity are investigated.     

Determination of total mercury in environmental and biological samples by flow injection cold vapour atomic absorption spectrometry

A simple and accurate method has been developed for the determination of total mercury in environmental and biological samples. The method utilises an off-line microwave digestion stage followed by analysis using a flow injection system with detection by cold vapour atomic absorption spectrometry.

The method has been validated using two certified reference materials (DORM-1 dogfish and MESS-2 estuarine sediment) and the results agreed well with the certified values. A detection limit of 0.2 ng g⁻¹ Hg was obtained and no significant interference was observed. The method was finally applied to the determination of mercury in river sediments and canned tuna fish, and gave results in the range 0.1–3.0 mg kg⁻¹.     

Ring size effects. III. Carbonium ion stability as a factor in the course of the pinacol rearrangement

The formation of the initial carbonium ion in the pinacol rearrangement will be the major factor in determining product composition when the reaction is carried out at 0°C with concentrated sulfuric acid.     

Investigation of bicyclic thioketones as triggers for liquid crystal optical switches

The axially chiral bicyclic thioketones 11 and 15 were prepared and investigated for suitability as chiroptical triggers in a liquid crystal optical switch. Irradiation of partially resolved 15 with unpolarized light leads to its conversion to the racemic form (photoracemization). However, irradiation of racemic thioketones 11 and 15 with circularly polarized light does not lead to detectable photoresolution. The lack of photoresolution was traced to inefficiency in intramolecular, through-bond triplet energy transfer. These thioketones are not suitable for use as phototriggers.     

The amperometric detection of thyroid hormones following reverse-phase high-performance liquid chromatography

The principle of an assay of the major thyroid hormones by an electrochemical technique is demonstrated. The separation of 3,3',5-triiodothyronine, 3,3',5'-triiodothyronine, and thyroxine, by reverse-phase high-performance liquid chromatography is followed by their electrochemical oxidation in a thin-layer electrochemical detection cell with a low-temperature isotropic carbon working electrode. The limits of detection found were in the subnanogram range with linear response in the ranges 0–125 ng for T₃ and 0–500 ng for T₄. The approach makes the simultaneous assay of total serum thyroid hormones feasible.     

Determination of Monoterpenes in Oleoresin: A Chemosystematic Study of the Interaction between Fraser Fir (Abies fraseri) and Balsam Woolly Adelgid (Adelges piceae)

The Fraser fir (Abies fraseri), a conifer native to high elevation sites in the southern Appalachians, has suffered severe mortality attributed to an exotic insect, the balsam woolly adelgid (BWA) (Adelges piceae). Fraser fir, like many other plants, produce volatile organic compounds called monoterpenes in a variety of tissues, including the cortical oleoresin found in blisters on the bark. The purpose of this study was to perform a chemosystematic study to evaluate whether differences in monoterpene composition of Fraser fir oleoresin were observed as a function of the season sampled, the presence or absence of BWA infestation, the health of a tree, and the susceptibility of trees to BWA, based on geographic location. Oleoresin was collected in September and December, 1994, at two mountains, Mount Rogers, where the fir were relatively healthy, and Roan Mountain, where heavy to moderate mortality has been observed. The oleoresin samples were dissolved in methylene chloride, and the monoterpenes were determined by gas chromatography. This method was shown to have acceptable precision for chemosystematic studies for five monoterpenes and the total of all monoterpenes. The levels of monoterpenes in oleoresin were statistically the same for most compounds in September and December, although the total monoterpenes were higher in September at Mount Rogers and α-pinene was higher in December at Roan Mountain. Infested and uninfested fir had the same levels of oleoresin monoterpenes at both mountains. No differences in monoterpene levels were observed at Mount Rogers with healthy and unhealthy fir, but at Roan Mountain, the total monoterpene concentrations were different in these categories. A comparison of monoterpene concentrations in oleoresin from Mount Rogers and Roan Mountain showed statistically significant differences for 3-carene, β-phellandrene, and total monoterpenes.     

Liquid chromatographic separation of the thyroid hormones

The liquid Chromatographic separation of 3,3',5-triiodothyronine, 3,3',5'-triiodothyronine, and thyroxine with a nonpolar stationary phase was studied as a function of pH, temperature, organic content of the mobile phase, and ionic strength using aqueous phosphate—acetonitrile, aqueous phosphate—methanol, and aqueous phosphate— n-propanol mobile phase systems. It was demonstrated that the quality of the thyroid hormone separations, as determined by normalized peak capacity values, was unchanged with temperature, remained relatively constant with increasing ionic strength, and was affected to the greatest extent by changes in pH and organic modifier content of the mobile phase. Chromatographic behavior of the compounds studied as a function of these variables was found to be consistent with existing Chromatographic theory and/or empirical observations. Recommended conditions are aqueous phosphate—methanol mobile phase, pH 2–5 (aqueous portion), and high temperature (60–70°C).