Ultramicroporous membranes for hydrogen separation

Fuel cell systems offer excellent efficiencies when compared to internal combustion engines, which result in reduced fuel consumption and greenhouse gas emissions. One of the areas requiring research for the success of fuel cell technology is the H2 fuel purification to reduce CO, which is a poison to fuel cells. Molecular sieve silica (MSS) membranes have a potential application in this area. In this work showed activated transport, a characteristic of ultramicroporous (dp

A modified discrete random pore model allowing for different initial surface reactivity

We investigate here a modification of the discrete random pore model [Bhatia SK, Vartak BJ, Carbon 1996;34:1383], by including an additional rate constant which takes into account the different reactivity of the initial pore surface having attached functional groups and hydrogens, relative to the subsequently exposed surface. It is observed that the relative initial reactivity has a significant effect on the conversion and structural evolution, underscoring the importance of initial surface chemistry. The model is tested against experimental data on chemically controlled char oxidation and steam gasification at various temperatures. It is seen that the variations of the reaction rate and surface area with conversion are better represented by the present approach than earlier random pore models. The results clearly indicate the improvement of model predictions in the low conversion region, where the effect of the initially attached functional groups and hydrogens is more significant, particularly for char oxidation. It is also seen that, for the data examined, the initial surface chemistry is less important for steam gasification as compared to the oxidation reaction. Further development of the approach must also incorporate the dynamics of surface complexation, which is not considered here.

Transient response of diffusion cell containing a porous solid

Transient response of an adsorbing or non-adsorbing tracer injected as step or square pulse input in a diffusion cell with two flowing streams across the pellet is theoretically investigated in this paper. Exact solutions and the asymptotic solutions in the time domain and in three different limits are obtained by using an integral transform technique and a singular perturbation technique, respectively. Parametric dependence of the concentrations in the top and bottom chambers can be revealed by investigating the asymptotic solutions, which are far simpler than their exact counterpart. In the time domain investigation, it is found that the bottom-chamber concentration is very sensitive to the value of the macropore effective diffusivity. Therefore this concentration could be used to extract diffusivity by fitting in the time domain. The bottom-chamber concentration is also sensitive to flow rate, pellet length chamber volume and the type of input (step and square input).

Mice expressing the E7 oncogene of HPV16 in epithelium show central tolerance, and evidence of peripheral anergising tolerance, to E7-encoded cytotoxic T-lymphocyte epitopes

In order to derive mice which expressed both the E7 open reading frame transgene of human papillomavirus type 16 in skin and MHC class 1 restriction elements for several E7-encoded cytotoxic T-lymphocyte (CTL) epitopes, K14.HPV16E7 mice which express E7 in basal keratinocytes were crossed to the F1 generation with A2.1 K-b transgenic mice which express the MHC binding cleft domains of human HLA A*0201, and murine H-2(b). F1 mice (denoted K14E7xA2.1) expressed E7 in the thymus at least as early as 2-5 days before birth. Immunisation of FVBxA2.1 control mice (transgenic for HLA A*0201 and H-2(b) but not for E7), with two HLA A*0201-restricted epitopes of E7 and one H-2(b)-restricted CTL epitope of E7, gave strong primary CTL responses recognising epitope-pulsed or constitutively E7-expressing syngeneic target cells. In contrast, in immunised K14E7xA2.1 mice, the CTL responses to the H-2(b) epitope and one of the HLA A*0201 CTL epitopes were strongly down-regulated, and to the other HLA A*0201 epitope, completely abolished, as demonstrated by percentage specific killing by bulk splenocyte cultures in cyrotoxicity assays, and by CTL precursor frequency analysis, In thymus-transplanted bone marrow radiation chimeras in which the immune system of K14E7xA2.1 mice was replaced by a FVBxA2.1 immune system, specific immunisation did not result in reemergence of strong E7-directed CTL responses. In agreement with these in vitro findings, specific immunisation failed to significantly alter the course of E7-associated tumour development in K14E7xA2.1 mice. These data are consistent with a model of central deletional CTL tolerance to E7-encoded epitopes recognised in the context of two distinct MHC class 1 restriction elements, and with the possibility of peripheral T-cell anergy maintained by expression of E7 in the skin. (C) 1998 Academic Press.

Cost functions and duality for stochastic technologies

Cost functions dual to stochastic production technologies are derived and their properties are discussed. These cost functions are shown to be consistent with expected-utility maximization without placing serious structural restrictions on the underlying technology.

Human vascular to cardiac tissue selectivity of L- and T-type calcium channel antagonists

1 Voltage-operated calcium channel (VOCC) antagonists are effective antihypertensive and antianginal agents but they also depress myocardial contractility. 2 We compared four L-type calcium channel antagonists, felodipine, nifedipine, amlodipine and verapamil and a relatively T-type selective calcium channel antagonist, mibefradil, on human and rat isolated tissue assays to determine their functional vascular to cardiac tissue selectivity (V/C) ratio. 3 The V/C ratio was calculated as the ratio of the IC50 value of the antagonist that reduced (by 50%) submaximally contracted (K+ 62 mM) human small arteries from the aortic vasa vasorum (vascular, V) mounted in a myograph and the IC50 value of the antagonist that reduced (-)-isoprenaline (6 nM) submaximally stimulated human right atrial trabeculae muscle (cardiac, C) mounted in organ chambers. 4 The average pIC(50) Values (-log IC50 M) for the human vascular preparations were felodipine 8.30, nifedipine 7.78, amlodipine 6.64, verapamil 6.26 and mibefradil 6.22. The average pIC(50) values for the cardiac muscle were felodipine 7.21, nifedipine 6.95, verapamil 6.91, amlodipine 5.94, and mibefradil 4.61. 5 The V/C ratio calculated as antilog [pIC(50)V-pIC(50)C] is thus mibefradil 41, felodipine 12, nifedipine 7, amlodipine 5 and verapamil 0.2. 6 In rat small mesenteric arteries the pIC(50) values for the five drugs were similar to the values for human vasa vasorum arteries contracted by K+ 62 mM. However for methoxamine (10 mu M) contraction in the rat arteries the pIC(50) values were lower for felodipine 7.24 and nifedipine 6.23, but similar for verapamil 6.13, amlodipine 6.28 and mibefradil 5.91. 7 In conclusion in the human tissue assays, the putative T-channel antagonist mibefradil shows the highest vascular to cardiac selectivity ratio; some 3 fold higher than the dihydropyridine, felodipine, and some 200 fold more vascular selective than the phenylalkylamine, verapamil. This favourable vascular to cardiac selectivity for mibefradil, from a new chemical class of VOCC antagonist, may be explained by its putative T-channel selectivity.

Radiographic study of the broadbeach aboriginal dentition

This study forms part of a larger anthropological investigation of the Ngaraangbal Aboriginal Tribe's ancestral burial ground at Broadbeach, Australia. It examines the dentition, records the associated pathology in a noninvasive manner, and relates this to the likely subsistence diet of the tribe. The Broadbeach osteological collection was returned for reburial in 1985; however, radiographic and photographic records of 36 adult males were available. These form the basis of our study. The pathology noted in the study sample was compared with a representative sample (n = 38) of pre-European Aboriginal remains from throughout Queensland for verification purposes only. Rates of dental pathology and injury were calculated from the radiographic and photographic records. There was a significant rate of tooth-wear related intra-bony pathology (4.0%), moderate to severe alveolar bone loss, and heavy dental attrition, of which the mandibular posterior teeth were the most severely affected. Caries prevalence (0.8%) was low for hunter-gatherer populations. A large number of molar pulp chambers had a distinctive cruciate morphology resulting from the formation of secondary dentine and pulp stones. Injuries and abnormalities included upper central incisor avulsion (58.3%) and taurodontism. These results support the proposal that the Ngaraangbal tribe was a hunter-gatherer population subsisting on an abrasive diet that included marine foods. (C) 1998 Wiley-Liss, Inc.

A state-contingent production approach to principal-agent problems with an application to point-source pollution control

Two basic representations of principal-agent relationships, the 'state-space' and 'parameterized distribution' formulations, have emerged. Although the state-space formulation appears more natural, analytical studies using this formulation have had limited success. This paper develops a state-space formulation of the moral-hazard problem using a general representation of production under uncertainty. A closed-form solution for the agency-cost problem is derived. Comparative-static results are deduced. Next we solve the principal's problem of selecting the optimal output given the agency-cost function. The analysis is applied to the problem of point-source pollution control. (C) 1998 Published by Elsevier Science S.A. All rights reserved.