Mass transfer accompanied by parallel reversible chemical reactions

Theoretical effects of parallel reversible chemical reactions on the rate of mass transfer are investigated in this paper. On the basis of the film theory, an analytical equation has been derived for gas absorption accompanied by first-order parallel rversible reactions. Analytical approximate equations have been developed and finite difference techniques applied to study the enhancement of mass transfer by second-order complex reactions. Results of this study indicate that when the diffusion is accompanied by second-order parallel reactions, the mass transfer rate increases with the concentration of the liquid reactant in the bulk, and approaches that of diffusion and first-order parallel reactions if the product of the diffusivity and bulk concentration of the liquid reactant is much larger than that of the gas reactant.     

Simulation of elevated T-waves of an ECG inside a static magnetic field (MRI)

In MRI, the flow of blood in the patient is subjected to a strong static magnetic field (B₀). The movement of charge carriers in a magnetic field causes a magnetofluid dynamic (MFD) effect that induces a voltage across the artery. This induced voltage distorts the ECG signal of the patient and appears as an elevation of the T-wave of the ECG signal. Flow of blood through the aortic arch is perpendicular to the magnetic field and coincides with the occurrence of the T-wave of the ECG. Based on these facts, it is proposed that the elevation in the T-wave occurs because of the voltage induced across the aortic arch. In this paper, the elevation is computed mathematically using the equations of MFD. A method is developed to measure this induced voltage based on discretization of the aortic arch and measuring the blood flow profile in the aorta. The results are compared to the ECG signals measured in humans in the bore of 1.5 T imaging magnet. The computed ECG signals at the 12 leads are very similar to the measured values.     

Concept Lattices for Knowledge Management

The aim of the method presented in this paper is to support the acquisition of new knowledge and to enhance the interactions between knowledge workers. The approach chosen is to facilitate the sharing of those retrieval terms, which members of a community of practice have used to retrieve valuable information. The nature of information-seeking behaviour in on-line information sources is discussed and then the theory of formal concept analysis is introduced. It is subsequently shown how this theory can be applied to analyse the relations between documents and the retrieval terms that people use to access these documents.The result is a concept lattice that contains information on a community's information-seeking behaviour. The concept lattice uncovers relational and contextual information. Retrieval phrases are put into relational context depending on how they are associated by the documents that are of interest to a community of users. The contention made here is that such 'usage-based' structures will provide natural and intuitive access to information sources for communities of users. It is shown how this approach can be used to facilitate the sharing of the retrieval vocabulary to support the acquisition of new knowledge and to enhance the interactions within a community of practice.     

Fine-tuning the fluorescent properties of Li and Na intercalated C60 with hydrogen

In this work we demonstrate how hydrogen can be utilized to fine tune the emission gap of C₆₀ through the formation of direct CH bonds in sodium and lithium intercalated systems (M₆C₆₀H_x). Upon hydrogenation, a shift in the emission spectrum to shorter wavelengths (higher energy) is observed relative to alkali metal free fulleranes (C₆₀H_x) and pure C₆₀. This is attributed to the higher degree of hydrogenation of C₆₀ that can be achieved upon intercalation with alkali metals which increases the sp³ hybridization of the system (decreases conjugation). Quantum yields of the sodium and lithium intercalated fulleranes are 1.3% and 1.8% respectively which are similar to those of alkali metal free fulleranes (1.4%). We also show that polymethyl methacrylate (PMMA) can be infused with the metal intercalated fulleranes to produce a fluorescent polymer with excellent transparency over the visible spectrum. This could potentially lead to further use of these materials in luminescent down shifting applications.     

Modeling and Test Verification for Hardened Integrated Circuits

Hardened dielectrically isolated integrated circuits are being developed to provide an order of magnitude improvement in radiation response over previous bipolar technology. This paper describes (a) the analytical and experimental techniques used to develop the hardened parts, and (b) comparative analytical and test results obtained thus far in the program. The paper describes how (a) various "element" models were defined for CAD usage, (b) how design tolerances were established for the element models, (c) how circuit design margins were established, (d) experimental techniques and equipment used to validate early designs, and (e) comparative analytical and test results.     

Computed axial tomography tandem and ovoids (CATTO) dosimetry: three-dimensional assessment of bladder and rectal doses

The purpose of this work is to compare bladder and rectal dose rates in brachytherapy for carcinoma of the cervix using two different dosimetry systems: traditional orthogonal radiograph-based dosimetry vs. computed axial tomography tandem and ovoids (CATTO) dosimetry. Twenty-two patients with carcinoma of the uterine cervix received the brachytherapy component of their radiotherapy with a computed-tomography compatible Fletcher-Suit-Delclos device. A total of 27 implants were performed. The average maximum bladder dose (Bmax) for the implants was 85.8 cGy/hr using the CATTO system as compared to 42.6 cGy/hr using traditional dosimetry, (P < 0.005). The average maximum rectal dose (R.) using the CATTO system was 59.2 cGy/hr as compared with 46.3 cGy/hr using the traditional system (P < 0.05). The traditional methods for choosing points to determine bladder and rectal dose rates underestimated the true Bmax in all cases and the R. in most. Based on the complication rates published in the literature, it is likely that the maximum tolerance dose of both the rectum and bladder, but especially the bladder, is higher than previously thought.     

Comparative effects of propofol, pentobarbital, and isoflurane on cerebral blood flow and blood volume

While intravenous and volatile anesthetics have widely differing effects on cerebral blood flow (CBF), clinical studies suggest that the relative differences in their effects on intracranial pressure (ICP) may be smaller. Because acute changes in ICP are determined primarily by changes in cerebral blood volume (CBV), we compared the impact of propofol, pentobarbital, and isoflurane on CBF and CBV in rats. Equipotent doses of the three agents were determined by tail-clamp studies. Animals were then anesthetized with propofol (20 mg/kg load, 38 mg.kg-1.h-1 infusion), pentobarbital (30 mg/kg load, 20 mg.kg-1.h-1 infusion), or isoflurane 1.6-1.8%. Two hours later, CBF and CBV were measured using 3H-nicotine as a CBF tracer, and 14C-dextran and 99mTc-labeled red cells as markers for cerebral plasma and red blood cell volumes (CPV and CRBCV), respectively. Total CBV was the sum of CPV and CRBCV. CBF was 2.0-2.6 times greater with isoflurane than with propofol or pentobarbital (137 vs. 67 and 52 ml.100 g-1.min-1, respectively). By contrast, while CBV was greater in the isoflurane group than in either the propofol or pentobarbital groups, the magnitude of the intergroup differences were much smaller (propofol = 2.49 +/- 0.28 ml/100 g; pentobarbital = 2.27 +/- 0.15 ml/100 g; isoflurane = 2.77 +/- 0.24 ml/100 g, mean +/- SD). These results suggest that the simple measurement of CBF may not adequately describe the cerebrovascular effects of an anesthetic, at least with respect to predicting the magnitude of the agents likely effects on ICP.