Abstract

The turbine of an automotive turbocharger is essentially one acoustic element in the exhaust system which lies between the primary noise source, the gas pulsations through the exhaust valves, and the primary noise radiation element, the exhaust tailpipe orifice. As such, like every other acoustic element of the exhaust system, it has a passive effect on the propagation of the primary exhaust noise. Thus if a comprehensive model of the acoustic propagation through the entire exhaust system of a turbocharged engine is sought, an acoustic model of the turbine is a prerequisite.

This paper presents a preliminary attempt to create such a model. The model is a purely fluid mechanic one, without recourse to any empiricism such as a turbine map. The nonlinear equations of the fluid flow are developed and solved for steady flow, to determine the mean convective flow effects upon the noise. The full time-domain equations are then linearised and solved for a single frequency of sound.

Results are given from both the steady flow and the acoustic analyses. The latter are presented in terms of both transmission loss and four-pole parameters. The model is found to give a rational representation of the passive effect of a turbine rotor.

Abstract

This paper presents a one-dimensional acoustic model for prediction of the frequencies of

self-excited oscillation and acoustic mode shapes in combustion systems. The impedance of

the combustion system is represented in terms of a frequency response function (FRF).

Impedances of the settling and combustion chambers are predicted by using the acoustic

model, taking into account the temperature distribution in the combustion chamber. Reasonably

good agreement between measured and predicted acoustic resonance frequencies and

mode shapes was achieved. Some data on stability regimes are discussed.

# 2003 Elsevier Science Ltd. All rights reserved.

Keywords: Combustion; Instability; Eigen-frequencies; Prediction; Measurement

Increased leukocyte-endothelial cell adhesion is a key early event in the development of retinopathy and atherogenesis in diabetic patients. We recently reported that raised activity of glycosylating enzyme [beta]1,6 acetylglucosaminyltransferase (core 2 GlcNAc-T) is responsible for increased leukocyte-endothelial cell adhesion and capillary occlusion in retinopathy. Here, we demonstrate that elevated glucose increases the activity of core 2 GlcNAc-T and adhesion of human leukocytes to retinal capillary endothelial cells, in a dose-dependent manner, through diabetes-activated serine/threonine protein kinase C beta2 (PKCbeta2)-dependent phosphorylation. This regulatory mechanism, involving phosphorylation of core 2 GlcNAc-T, is also present in polymorphonuclear leukocytes isolated from type 1 and type 2 diabetic patients. Inhibition of PKCbeta2 activation with the specific inhibitor, LY379196, attenuated serine phosphorylation of core 2 GlcNAc-T and prevented increased leukocyte-endothelial cell adhesion. Raised activity of core 2 GlcNAc-T was associated with a threefold increase in O-linked glycosylation of P-selectin glycoprotein ligand-1 on the surface of leukocytes of diabetic patients compared with age-matched control subjects. PKCbeta2-dependent phosphorylation of core 2 GlcNAc-T may thus represent a novel regulatory mechanism for activation of this key enzyme in mediating increased leukocyte-endothelial cell adhesion and capillary occlusion in diabetic retinopathy.

Abstract

Experimental investigations have been carried out to measure axial effective thermal conductivities of

packed beds for a number of particles and catalyst pellets. Measurements were made for three gases (air,

nitrogen and carbon dioxide) in beds packed with ball bearings, copper chromite, chromia alumina, alumina

hollow cylinders and alumina spheres. A glass vacuum vessel was employed for most measurements,

but a thin wall stainless steel vessel was used in a few experiments.

Empirical correlations to predict the axial effective thermal conductivity of packed bed reactors have

been derived from the experimental results.

2002 Elsevier Science Ltd. All rights reserved.

Keywords: Axial thermal conductivities; Packed beds

This paper concerns the adequacy of existing detailed reaction mechanisms for use in computer simulations of combustion systems with injection of gaseous fuels such as hydrogen, and methane. Shock tube induction time data are compiled from the literature and compared to thermodynamic conditions of gas combustion systems to establish validation limits. Existing detailed reaction mechanisms are then used in constant-volume explosion simulations for validation against the shock tube data. A quantitative measure of mechanism accuracy is obtained from the validation study results, and deficiencies in the experimental data and reaction mechanisms are highlighted. 

The preparation and characterization of a cobalt substituted ETS-10 titanosilicate are described. X-ray diffraction shows that cobalt incorporation causes an increase in unit cell dimensions. UV–VIS, EPR, Raman and Co K-edge XANES spectra all show that Co2+ occupies tetrahedral sites, substituting for silicon. The 29Si NMR spectra do not permit identification of which silicon sites in ETS-10 are substituted, but the Co K-edge EXAFS shows clearly that Co2+ substitutes at Si(3Si,1Ti) sites.

A review is given of recent work in the authors' laboratory on the characterization of different forms of nanostructured titania. It is shown that nanocrystalline anatase powders and nanocrystalline anatase thin films differ significantly in their optical properties, due primarily to differences in sintering behaviour on drying. It is argued that the electronic properties of these systems are determined by surface phenomena rather than quantum size effects. The novel titanosilicate zeolite ETS-10 which contains one dimensional “quantum wires” of titania provides an alternative system for studying quantum size effects which has considerable potential for photocatalysis.

The development of Language Engineering and Information Retrieval applications for Arabic require availability of sizeable, reliable corpora of modern Arabic text. These are not routinely available. This paper describes how we constructed an 18.5 million word corpus from Al-Hayat newspaper text, with articles tagged as belonging to one of 7 domains. We outline the profile of the data and how we assessed its representativeness. The literature suggests that the statistical profile of Arabic text is significantly different from that of English in ways that might affect the applicability of standard techniques. The corpus allowed us to verify a collection of experiments which had, so far, only been conducted on small, manually collected datasets. We draw some comparisons with English and conclude that there is evidence that Arabic data is much sparser than English for the same data size.