347 research outputs found
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
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 configuration of Mn, and we
determine the parameters of the effective Hamiltonians describing the
and 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 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
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