MRT of experimental liver abscesses: a comparison of a new blood pool contrast medium with gadolinium-DTPA in animal experiments

PURPOSE: In an experimental pyogenic liver abscess model, the signal intensities were compared intraindividually and interindividually after the application of a new blood pool contrast agent, 24-gadolinium-DTPA (diethylenetriamine-pentaacetic acid) cascade polymer, and after the application of gadopentetate dimeglumine. METHODS: In 20 rabbits with experimentally induced liver abscesses, the relative signal intensities of the liver, abscess centre, abscess wall and portal vein were assessed before and between 30 seconds and 60 minutes after injection of a 25 mumol/kg dose of gadolinium polymer and of 100 mumol/kg of gadolinium-DTPA, respectively. Measurements were performed at 1.5 Tesla, using a head coil and a Flash-2-D sequence. RESULTS: The interindividual comparison (unpaired T-test, p < 0.05) yielded significant differences of the relative signal intensities of the abscess centre (at any time point after contrast-media application), abscess wall (between 15 and 60 minutes after contrast media application), and portal vein (between 30 seconds and 7.5 minutes after contrast media application). The interindividual comparison showed a significantly higher abscess centre-liver contrast (between 30 seconds and 12.5 minutes after contrast media application) and a significantly higher abscess wall-centre contrast (between two and 7.5 minutes after contrast media application) after the application of gadolinium polymer compared with gadopentetate dimeglumine. CONCLUSION: In this animal model, the higher abscess centre-liver contrast after the application of gadolinium polymer was the basis for a better and prolonged visibility of the abscesses, as compared with images acquired after injection of gadopentetate dimeglumine.     

Isobutylene polymerization in the presence of t-BuCl/SnCl4

Summary The effect of tert-butyl chloride in the polymerizations of isobutylene carried out in the presence of SnCl₄ in dichloromethane at temperatures-20°C and-78°C was investigated. Synthesized polyisobutylene samples showed a bimodal molecular weight distribution (MWD) and it was found that the weight content of the lowermolecular weight (LMW) fraction increased with increasing t-BuCl concentration in the polymerization mixture. The effect of ageing of the initiation mixture t-BuCl/SnCl₄ in CH₂Cl₂ prepared in advance on MWD of the PIB samples was also studied. Ageing of the initiation system supports the formation of the LMW fraction and this oily PIB is the only product of the polymerization at-20°C, .     

Solvent induced crystallization of syndiotactic poly(methyl methacrylate) relation to the formation of polymer aggregates in solution

Polymer Bulletin - Solutions of syndiotactic (s) poly (methyl methacrylate) (PMMA) and samples of solid s-PMMA prepared from these solutions were studied by NMR and infrared (IR) spectroscopy and...     

Exploring the costs of technical debt management – a case study

Technical debt is a metaphor for delayed software maintenance tasks. Incurring technical debt may bring short-term benefits to a project, but such benefits are often achieved at the cost of extra work in future, analogous to paying interest on the debt. Currently technical debt is managed implicitly, if at all. However, on large systems, it is too easy to lose track of delayed tasks or to misunderstand their impact. Therefore, we have proposed a new approach to managing technical debt, which we believe to be helpful for software managers to make informed decisions. In this study we explored the costs of the new approach by tracking the technical debt management activities in an on-going software project. The results from the study provided insights into the impact of technical debt management on software projects. In particular, we found that there is a significant start-up cost when beginning to track and monitor technical debt, but the cost of ongoing management soon declines to very reasonable levels.     

Nanoscale Charge Percolation Analysis in Polymer‐Sorted (7,5) Single‐Walled Carbon Nanotube Networks

The current percolation in polymer‐sorted semiconducting (7,5) single‐walled carbon nanotube (SWNT) networks, processed from solution, is investigated using a combination of electrical field‐effect measurements, atomic force microscopy (AFM), and conductive AFM (C‐AFM) techniques. From AFM measurements, the nanotube length in the as‐processed (7,5) SWNTs network is found to range from ≈100 to ≈1500 nm, with a SWNT surface density well above the percolation threshold and a maximum surface coverage ≈58%. Analysis of the field‐effect charge transport measurements in the SWNT network using a 2D homogeneous random‐network stick‐percolation model yields an exponent coefficient for the transistors OFF currents of 16.3. This value is indicative of an almost ideal random network containing only a small concentration of metallic SWNTs. Complementary C‐AFM measurements on the other hand enable visualization of current percolation pathways in the xy plane and reveal the isotropic nature of the as‐spun (7,5) SWNT networks. This work demonstrates the tremendous potential of combining advanced scanning probe techniques with field‐effect charge transport measurements for quantification of key network parameters including current percolation, metallic nanotubes content, surface coverage, and degree of SWNT alignment. Most importantly, the proposed approach is general and applicable to other nanoscale networks, including metallic nanowires as well as hybrid nanocomposites.     

Potential of solar heat pipe vacuum collectors in the desiccant cooling process: Modelling and experimental results

Desiccant cooling is an alternative technique to vapour compression systems. When thermally driven at moderate temperatures, it can be coupled to solar collectors. The use of flat-plate collectors and air collectors has demonstrated low efficiency in the coupling process and so a low potential of solar energy use in desiccant cooling. In this paper the use of heat pipe vacuum tube (HPVT) collectors in a solar desiccant cooling set up is investigated. First, a model for the collectors is proposed and experimentally validated under various operating conditions. A model of the storage tank taking into account thermal stratification is also validated. The experimentally evaluated efficiency of the HPVT collectors for one operating day varies between 0.6 and 0.7. Finally, simulation of the solar desiccant plant cooling a building is performed for different climates over a summer season. The solar fraction and the overall efficiency of the solar plant are calculated for this period and the potential of the vacuum tube collectors is evaluated for application to the desiccant cooling process.     

Untersuchung der Stabilität der doppeltgespeisten Drehstrommaschine mit Hilfe eines linearisierten Modells

Übersicht Die dynamischen Gleichungen der doppeltgespeisten Asynchronmaschine werden um einen stationären Arbeitspunkt linearisiert. Die numerische Berechnung der Eigenwerte des Systems erlaubt eine Stabilitätsuntersuchung für beliebige Maschinenparameter und Arbeitspunkte. Eine digitale Simulation des elektromechanischen Systems bestätigt die durch die Eigenwertberechnung erhaltenen Ergebnisse.

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Stability analysis of the doubly fed asynchronous machine using a linearized modell

Contents The dynamical equations of the doubly fed asynchronous machine are linearized about a steady state operating point. The numerical calculation of the eigenvalues of the system makes a stability analysis possible for every set of machine constants and for every operating point. A digital simulation of the electromechanical system corroborates the results obtained via eigenvalue calculation.

     

Electricity demand loads modeling using AutoRegressive Moving Average (ARMA) models

This study addresses the problem of modeling the electricity demand loads in Greece. The provided actual load data is deseasonilized and an AutoRegressive Moving Average (ARMA) model is fitted on the data off-line, using the Akaike Corrected Information Criterion (AICC). The developed model fits the data in a successful manner. Difficulties occur when the provided data includes noise or errors and also when an on-line/adaptive modeling is required. In both cases and under the assumption that the provided data can be represented by an ARMA model, simultaneous order and parameter estimation of ARMA models under the presence of noise are performed. The produced results indicate that the proposed method, which is based on the multi-model partitioning theory, tackles successfully the studied problem. For validation purposes the produced results are compared with three other established order selection criteria, namely AICC, Akaike's Information Criterion (AIC) and Schwarz's Bayesian Information Criterion (BIC). The developed model could be useful in the studies that concern electricity consumption and electricity prices forecasts.