A simple microscopic model for the dynamics of adhesive failure

We consider a microscopic model for the failure of soft adhesives in tension based on ideas of bond rupture under dynamic loading. Focusing on adhesive failure under loading at constant velocity, we demonstrate that bi-modal curves of stress against strain may occur due to effects of finite polymer chain or bond length and characterise the loading conditions under which such bi-modal behaviour is observed. The results of this analysis are in qualitative agreement with experiments performed on unconfined adhesives in which failure does not occur by cavitation.Comment: 11 pages, 5 figure

Probing the Two-Temperature Paradigm: Observational Tests for the Basic Assumptions in ADAFs

We calculate the flux and spectrum of synchrotron radiation produced by high energy electrons and positrons (\epm) in an advection dominated accretion flow (ADAF) around a black hole. The \epm are from the decay of charged pions which are created through proton-proton collisions. We consider both a thermal and power-law energy distribution of protons, and show that the resulting \epm synchrotron emission produces a characteristic spectrum between radio and X-ray frequencies. While previous signatures of the hot protons were only possible at gamma-ray energies, via the production of gamma-rays through neutral pion decay, the present results provide a more observationally tractable way of probing the proton energy distribution and the two temperature structure in these accretion flows. We discuss a number of strong observational predictions from these systems, as well as the recent results of Mahadevan (1998) which appear to confirm the two temperature structure in ADAFs. We show that the results provide support for both a power-law and thermal distribution of protons, with at least a third of the viscous energy going into the power-law.Comment: Submitted to MNRAS. 27 pages including 5 figure

Fiji's Sugar Woes: The Challenge of the Land Tenure System, Ethnicity and the Erosion of EU Sugar Preferences

The non-renewal of land leases since 1997 and the impending withdrawal of the European Union's sugar preferences in 2007 have created major uncertainties in Fiji's sugar industry. In the context of this troubled environment, this paper examines the impact of various socio-economic factors on the viability of the industry by focusing on farm efficiency in sugar cane production. It was found that, in general, farmers were inefficient and produced 25% less than their potential output. Among the farm inputs, land (labour) was relatively the most (least) efficiently used input. Empirical evidence also suggests that the more productive Indian farmers rather than the natives be left to farm cane and that large scale farming should be seriously considered by amalgamating land leases. Lastly, it is possible for Fiji's sugar industry to be sustained with the use of appropriate best farming techniques to improve cane yield, and if there is successful expansion of sugar-related products.Random coefficient production frontier, technical efficiency, sugar cane production, Crop Production/Industries,

Trends in ferromagnetism, hole localization, and acceptor level depth for Mn substitution in

We examine the intrinsic mechanism of ferromagnetism in dilute magnetic semiconductors by analyzing the trends in the electronic structure as the host is changed from GaN to GaP, GaAs and GaSb, keeping the transition metal impurity fixed. In contrast with earlier interpretations which depended on the host semiconductor, we found that a single mechanism is sufficient to explain the ferromagnetic stabilization energy for the entire series.Comment: 4 figures; To appear in Appl. Phys. Let