Strain in crystalline core-shell nanowires

The strain configuration induced by the lattice mismatch in a core-shell nanowire is calculated analytically, taking into account the crystal anisotropy and the difference in stiffness constants of the two materials. The method is applied to nanowires with the wurtzite structure or the zinc-blende structure with the hexagonal / trigonal axis along the nanowire, and the results are compared to available numerical calculations and experimental data. It is also applied to multishell nanowires, and to core-shell nanowires grown along the $$ axis of cubic semiconductors

Discontinuity in development: Kenya’s middle-scale manufacturing industry

This thesis concerns middle-scale enterprise and economic development, focussing on the case of Kenya. The distribution of industry in Kenya is characterised by an apparent underdevelopment of middle-scale enterprise compared with micro- and large-scale, a feature frequently referred to as the 'missing middle'. A further distinctive feature of Kenya's middle is the relatively strong involvement by entrepreneurs of Asian origin. The immediate objective of this thesis is to produce a better understanding of these phenomena, argued to be highly relevant to Kenya’s wider economic development. To understand the position of the middle in Kenya, a new concept frame is put forward based on a broadly institutional approach drawing on both new and old institutional economics. This frame sees the potential for middle-scale enterprise in terms of the economic and social context, with formal and informal institutions playing a role. The notion of discontinuity is introduced to describe interactions between elements of structure which produce an adverse exchange environment for enterprise. It is argued that Kenya has a generally hostile environment for middle- scale enterprise, characterised by discontinuities and uncertainty. Entrepreneurs from Kenya's Asian communities are able to escape these generic problems by use of informal social institutions, accounting for their relative success. Evidence from cases studies of middle-scale enterprises owned by Kenyans of both Asian and African origin, together with secondary data, broadly supports the argument. There are strong indications of discontinuities between large and middle- scale enterprise and within the formal institutional environment. Asian entrepreneurs are observed to rely heavily on informal social institutions to facilitate exchange. Such an option does not appear open to aspirant African entrepreneurs. Supporting the development of Kenya's middle-scale will necessitate addressing the discontinuities undermining its development. Simple deregulation and market liberalisation will not suffice

Atomic-like spin noise in solid-state demonstrated with manganese in cadmium telluride

Spin noise spectroscopy is an optical technique which can probe spin resonances non-perturbatively. First applied to atomic vapours, it revealed detailed information about nuclear magnetism and the hyperfine interaction. In solids, this approach has been limited to carriers in semiconductor heterostructures. Here we show that atomic-like spin fluctuations of Mn ions diluted in CdT e (bulk and quantum wells) can be detected through the Kerr rotation associated to excitonic transitions. Zeeman transitions within and between hyperfine multiplets are clearly observed in zero and small magnetic fields and reveal the local symmetry because of crystal field and strain. The linewidths of these resonances are close to the dipolar limit. The sensitivity is high enough to open the way towards the detection of a few spins in systems where the decoherence due to nuclear spins can be suppressed by isotopic enrichment, and towards spin resonance microscopy with important applications in biology and materials science

Magneto-optical spectroscopy of (Ga,Mn)N epilayers

We report on the magneto-optical spectroscopy and cathodoluminescence of a set of wurtzite (Ga,Mn)N epilayers with a low Mn content, grown by molecular beam epitaxy. The sharpness of the absorption lines associated to the Mn$^{3+}$ internal transitions allows a precise study of its Zeeman effect in both Faraday and Voigt configurations. We obtain a good agreement if we assume a dynamical Jahn-Teller effect in the 3d$^{4}$ configuration of Mn, and we determine the parameters of the effective Hamiltonians describing the $^{5}T\_{2}$ and $^{5}E$ levels, and those of the spin Hamiltonian in the ground spin multiplet, from which the magnetization of the isolated ion can be calculated. On layers grown on transparent substrates, transmission close to the band gap, and the associated magnetic circular dichroism, reveal the presence of the giant Zeeman effect resulting from exchange interactions between the Mn$^{3+}$ ions and the carriers. The spin-hole interaction is found to be ferromagnetic

Magnetization dynamics down to zero field in dilute (Cd,Mn)Te quantum wells

The evolution of the magnetization in (Cd,Mn)Te quantum wells after a short pulse of magnetic field was determined from the giant Zeeman shift of spectroscopic lines. The dynamics in absence of magnetic field was found to be up to three orders of magnitude faster than that at 1 T. Hyperfine interaction and strain are mainly responsible for the fast decay. The influence of a hole gas is clearly visible: at zero field anisotropic holes stabilize the system of Mn ions, while in a magnetic field of 1 T they are known to speed up the decay by opening an additional relaxation channel

Methodological and policy limitations of quantifying the saving of lives: a case study of the Global Fund's approach.

David McCoy and colleagues critique the dominance of "lives saved" models of assessing the impact of health programs, using The Global Fund as a case study. Please see later in the article for the Editors' Summary

Genealogy of the nuclear β-fibrinogen intron 7 in Lissotriton boscai (Caudata, Salamandridae): concordance with mtDNA and implications for phylogeography and speciation

The power of phylogeographic inference resides in its ability to integrate information from multiple sources in an iterative hypothesis- testing framework. In this paper, we build upon previous mtDNA-based hypotheses about the evolutionary history of the Iberian newt Lissotriton boscai using sequences of the highly variable nuclear ß-fibrinogen intron 7. In addition to the nuclear sequences, we produced new mtDNA data across the species range to delineate contact zones and test the congruence between nuclear and mitochondrial datasets at the same level of spatial organization. Through a combination of phylogenetic, phylogeographic continuous diffusion, and genetic landscape modelling analyses, we infer the evolutionary history of the species. We found notable congruence between nuclear and mtDNA datasets, which confirms deep and consistent differentiation between two major lineages that originated in the Miocene. Additionally, we found a new nuclear haplogroup with no mtDNA counterpart, roughly circumscribed to the Iberian Sistema Central mountains, and extensive areas of nuclear admixture across mtDNA lineages. We describe potential historical dispersal routes from an ancestral hypothetical refugium in the western end of the Sistema Central in central Portugal and highlight how deep phylogeographic breaks do not necessarily indicate cryptic speciation events.Peer reviewe

Genealogy of the nuclear β-fibrinogen intron 7 in Lissotriton boscai (Caudata, Salamandridae): concordance with mtDNA and implications for phylogeography and speciation

The power of phylogeographic inference resides in its ability to integrate information from multiple sources in an iterative hypothesis- testing framework. In this paper, we build upon previous mtDNA-based hypotheses about the evolutionary history of the Iberian newt Lissotriton boscai using sequences of the highly variable nuclear ß-fibrinogen intron 7. In addition to the nuclear sequences, we produced new mtDNA data across the species range to delineate contact zones and test the congruence between nuclear and mitochondrial datasets at the same level of spatial organization. Through a combination of phylogenetic, phylogeographic continuous diffusion, and genetic landscape modelling analyses, we infer the evolutionary history of the species. We found notable congruence between nuclear and mtDNA datasets, which confirms deep and consistent differentiation between two major lineages that originated in the Miocene. Additionally, we found a new nuclear haplogroup with no mtDNA counterpart, roughly circumscribed to the Iberian Sistema Central mountains, and extensive areas of nuclear admixture across mtDNA lineages. We describe potential historical dispersal routes from an ancestral hypothetical refugium in the western end of the Sistema Central in central Portugal and highlight how deep phylogeographic breaks do not necessarily indicate cryptic speciation events.Peer reviewe