Earthquakes, influenza and cycles of Indian kala-azar.

It is suggested that previous data indicate 3 major epidemics of kala-azar in Assam between 1875 and 1950, with inter-epidemic periods of 30-45 and 20 years. This deviates from the popular view of regular cycles with a 10-20 year period. A deterministic mathematical model of kala-azar is used to find the simplest explanation for the timing of the 3 epidemics, paying particular attention to the role of extrinsic (drugs, natural disasters, other infectious diseases) versus intrinsic (host and vector dynamics, birth and death rates, immunity) processes in provoking the second. We conclude that, whilst widespread influenza in 1918-1919 may have magnified the second epidemic, intrinsic population processes provide the simplest explanation for its timing and synchrony throughout Assam. The model also shows that the second inter-epidemic period is expected to be shorter than the first, even in the absence of extrinsic agents, and highlights the importance of a small fraction of patients becoming chronically infectious (with post kala-azar dermal leishmaniasis) after treatment during an epidemic.

Hydrogenated amorphous silicon and silicon nitride deposited at less than 100° C by ECR-PECVD for thin film transistors

A systematic study has been made of the growth of both hydrogenated amorphous silicon (a-Si:H) and silicon nitride (a-SiN) by electron cyclotron resonance plasma enhanced chemical vapour deposition (ECR-PECVD). In the case of a-SiN, helium and nitrogen gas is injected into the system such that it passes through the resonance zone. These highly ionised gases provide sufficient energy to ionise the silane gas, which is injected further downstream. It is demonstrated that a gas phase reaction occurs between the silane and nitrogen species. It is control of the ratio of silane to nitrogen in the plasma which is critical for the production of stoichiometric a-SiN. Material has been produced at 80°C with a Si:N ratio of 1:1.3 a breakdown strength of ∼6 MV cm-1 and resistivity of > 1014 Ω cm. In the case of a-Si:H, helium and hydrogen gas is injected into the ECR zone and silane is injected downstream. It is shown that control of the gas phase reactions is critical in this process also. a-Si:H has been deposited at 80 °C with a dark conductivity of 10-11 Ω-1 cm-1 and a photosensitivity of justbelowl 4×104. Such materials are suitable for use in thin film transistors on plastic substrates.

Friction and material transfer in micro-scale sliding contact between aluminium alloy and steel

A ball-on-flat reciprocating micro-tribometer has been used to measure the friction coefficient between aluminium alloy strip and a steel ball. A relatively small ball and correspondingly low contact load is used to give a contact width of the order of 100μm, closer to asperity contact widths than generally found for this type of test. The effects of load, initial strip surface roughness, lubricants and boundary additives are investigated. It is found that the friction coefficient is significantly reduced by the addition of a lubricant. Observations of the wear tracks and ball surface show that the material transfer from aluminium to the ball is reduced in the presence of the lubricant. The initial friction coefficient is further reduced by the addition of a boundary additive, but the friction coefficient after 8 cycles is unchanged. Copyright © 2004 by Springer Science+Business Media, Inc.