TOTAL MERCURY DETERMINATION IN NAPHTHAS BY EITHER ATOMIC FLUORESCENCE OR ABSORPTION SPECTROSCOPY

Mercury determination in light hydrocarbon fractions and natural gas condensates, has long been an important issue in the oil industry. Mercury has to be monitored, because of the many problems encountered with this metal in reforming and processing. The main objective of this study was to develop a fast reliable methodology to quantify total mercury in naphtha fractions.

Since there is no certified standard analysis procedure for Hg in naphtha, two methodologies with different operating principles were implemented, namely: atomic fluorescence spectroscopy with thermal desorption (AFS-TD) and atomic absorption spectroscopy with electrothermal atomization (AAS-ETA). The statistical treatment applied was paired t-test (95% confidence level), which showed that both techniques are statistically equivalent.     

Classification of equilibria and <Emphasis Type="Italic">Γ</Emphasis>-convergence for the discrete Perona-Malik functional

We give a complete classification of the stability properties of the equilibria for the semi-discrete one-dimensional Perona-Malik equation, with Dirichlet boundary conditions. We also give the Γ-expansion of the corresponding discretized functionals up to the order two, as the discretization parameter goes to zero.     

Property evaluation in The Expert System for Thermodynamics (“TEST”) web application

Ever since its release, TEST has found use as thermodynamic courseware in many universities around the world. TEST offers web-based analysis tools–java applets called daemons–for property evaluation of working substances, energy, entropy, and exergy analysis of generic open and closed systems, IC engines, gas and vapor power cycles, refrigeration, HVAC, combustion, chemical equilibrium, and gas dynamics. Other modules of TEST include animations, problems, examples, and system navigations that are closely integrated with the daemon module to create a comprehensive analysis tool for engineering thermodynamics. In this paper the methodology of thermodynamic state evaluation by TEST is discussed with several examples.     

Hypertext development using a model-based approach

Hypertext development is still, for the most part, at the ‘handcrafting’ level, where each hypertext document must be hand-designed. We present a compiler which takes hyperdocuments designed using a model-based approach and generates stacks executable in Hyper Card. This compiler is implemented in standard SQL over a relational database representation of a hyperdocument designed using the hypermedia design model (HDM). The compiling approach, even though illustrated with HDM, can be used with any ‘structured’ design methodology.     

Effect of natural allergen exposure on non-specific bronchial reactivity in asthmatic farmers

The aim of the study was to assess the seasonal variability of non-specific bronchial reactivity (NSBR) evaluated with methacholine in asthmatic farmers allergic to pollens. Twenty farmers (16 male and four female) with allergy to pollens, e.g. 'Graminae' and 'Parietaria', entered the study. None of the patients had been previously treated with specific immunotherapy. Patients underwent a methacholine challenge at the first visit and then in the subsequent seasons. Four groups of tests were obtained according to the period when the challenge was performed. Group 1: challenges performed in December, January and February; group 2 in March, April and May; group 3 in June, July and August; group 4 in September, October and November. PD20 values were expressed as the natural logarithm of the cumulative dose of methacholine causing at least a 20% fall in FEV1. Bronchial hyperreactivity was highest in summer, followed by spring and autumn; in winter it was much lower. Multiple group analysis (ANOVA) showed statistically significant differences between the groups (P < 0.01). When the groups were compared individually, statistically significant differences existed only between group 1 (winter) and each of the other groups, respectively 2 (spring) (P = 0.02), 3 (summer) (P = 0.004) and 4 (autumn) (P = 0.02). The results underlined the importance of allergic inflammation in determining changes in NSBR. In the region where the study was carried out (central Italy), the grass and Paretaria pollination lasts from March to November. Therefore, farmers had a progressive increase in NSBR from spring to summer and a decrease in fall as a consequence of the varying pollen concentration in different seasons. The level of allergen exposure is, in fact, the main factor that determines the severity of bronchial inflammation, thus affecting NSBR.     

Jejunal interposition for peptic stenosis of the esophagus following esophagomyotomy for achalasia

We compared the prognostic significance of prior angina pectoris in 151 patients > or = 75 years of age admitted for acute myocardial infarction. There was a similar in-hospital course, but the long-term outcome was poorer in patients with prior angina.     

Finite element approximations of singular parabolic problems

An efficient implementation of finite element methods for free boundary parabolic problems in general two dimensional space domains is presented. The Stefan problem, the Hele-Shaw problem and the porous medium equation are included. Backward differences or linearization techniques are used for the time discretization of the problem. The performances of these schemes are discussed with several numerical tests.     

Muscimol suppression of the dorsal cochlear nucleus impairs frequency discrimination in rats

The cochlear nucleus is composed of three sub-nuclei: the dorsal (DCN), anteroventral (AVCN) and posteroventral cochlear nucleus (PVCN). In addition to connections between these sub-nuclei, each nucleus receives frequency specific tonotopically organised input from the cochlea. Evidence suggests that connections from the DCN to the AVCN are inhibitory and organised tonotopically but the functional significance of this pathway has yet to be elucidated. The possible role of this pathway in frequency discrimination using a T-maze behavioural paradigm and DCN suppression was examined. Five rats were trained on a two choice frequency discrimination task. Once frequency difference limens for 10-30% performance above chance were determined, rats had cannulae implanted bilaterally over the DCN. After recovery rats were tested on the behavioural task with nothing, saline and the GABA agonist muscimol injected into the DCN via the cannulae. Muscimol alone significantly reduced the rats ability to perform the task. This performance decrease was attributed to an inability to discriminate high frequency and not low frequency tones suggesting that place and not temporal coding of sound was compromised by DCN suppression. These results are consistent with the hypothesis that inhibitory drive from the DCN to AVCN may be crucial for the fine tuning of frequency information.     

Attenuation Measurements of MF, HF, and VHF Waves over the Ground Surface

A survey on short distance attenuations of MF, HF, and VHF radio waves a few meters above the ground surface has been carried out to find empiric reliable average attenuation laws, with their standard deviation. The results can be used to predict the ranges of communication systems placed near the ground and to fix the limits for the allowable interference fields produced by industrial, scientific, and medical (ISM) equipment.     

Performance and Analysis of a Reverberating Enclosure with Variable Geometry

Mode stirred chambers are discussed. It is shown that, under the basic assumption of isotropy (largely experimentally proven), the coupling equation does not depend on the antenna gain. Chamber losses are examined, both from a general point of view, and in order to determine sensitivity of the measuring technique. An alternative thermodynamic approach is also given.