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Department of Life Sciences
1,635
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356
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Department of Physics
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Department of Chemical Engineering
6,241
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Publication History View all

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    ABSTRACT: Corbard & Thompson analyzed quantitatively the strong radial differential rotation that exists in a thin layer near the solar surface. We investigate the role of this radial shear in driving a flux transport dynamo operating with such a rotation profile. We show that despite being strong, near-surface radial shear effectively contributes only ∼1 kG (∼30% of the total) to the toroidal fields produced there unless an abnormally high, surface a-effect is included. While 3 kG spot formation from ∼1–2 kG toroidal fields by convective collapse cannot be ruled out, the evolutionary pattern of these model fields indicates that the polarities of spots formed from the near-surface toroidal field would violate the observed polarity relationship with polar fields. This supports previous results that large-scale solar dynamos generate intense toroidal fields in the tachocline, from which buoyant magnetic loops rise to the photosphere to produce spots. Polar fields generated in flux transport models are commonly much higher than observed. We show here that by adding enhanced diffusion in the supergranulation layer (originally proposed by Leighton), near-surface toroidal fields undergo large diffusive decay preventing spot formation from them, as well as reducing polar fields closer to the observed values. However, the weaker polar fields lead to the regeneration of a toroidal field of less than ∼10 kG at the convection zone base, too weak to produce spots that emerge in low latitudes, unless an additional poloidal field is produced at the tachocline. This is achieved by a tachocline a-effect, previously shown to be necessary for coupling the north and south hemispheres to ensure toroidal and poloidal fields that are antisymmetric about the equator.
    The Astrophysical Journal 02/2016; 575(1):41-45. DOI:10.1086/342555
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    ABSTRACT: This paper studies the evolution of wage inequality in Turkey using household labour force survey data from 2002 to 2010. Between 2002 and 2004, the relative supply of more-educated workers to less-educated workers remained constant while their relative wages decreased in favour of less-educated workers. However, between 2004 and 2010, the relative supply of more-educated workers to less-educated workers rose, while their relative wages remained constant or kept increasing in favour of more-educated workers. This suggests factors other than those implied by a simple supply-demand model are involved, such as skill-biased technical change or minimum wage variations. The decomposition of wage inequality reveals that the price (wage) effect dominates the composition effect particularly in the first period. Our results show that the real minimum wage hike in 2004 corresponds to a major institutional change, which proved to be welfare-increasing in terms of wage inequality. The upper-tail (90/50) wage inequality decreased between 2002 and 2004 and stayed constant thereafter, whereas the lower-tail (50/10) wage inequality decreased throughout the period. Our findings thus provide evidence supporting the institutional argument for explaining wage inequality.
    Economics of Transition 01/2015; 23(1). DOI:10.1111/ecot.12058
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    ABSTRACT: A rostral brainstem structure, the pedunculopontine nucleus (PPN), is severely affected by Parkinson's disease (PD) pathology and is regarded a promising target for therapeutic deep-brain stimulation (DBS). However, understanding the PPN's role in PD and assessing the potential of DBS are hampered by the lack of a suitable model of PPN degeneration. Rats were rendered Parkinsonian through a unilateral substantia nigra pars compacta (SNpc) stereotaxic injection of the proteasome inhibitor Lactacystin, to investigate whether the lesion's pathological effects spread to impact the integrity of PPN cholinergic neurons which are affected in PD. At 5 weeks post-surgery, stereological analysis revealed that the lesion caused a 48 % loss of dopaminergic SNpc neurons and a 61 % loss of PPN cholinergic neurons, accompanied by substantial somatic hypotrophy in the remaining cholinergic neurons. Magnetic resonance imaging revealed T2 signal hyper-/hypointensity in the PPN of the injected hemisphere, respectively at weeks 3 and 5 post-lesion. Moreover, isolated PPN cholinergic neurons revealed no significant alterations in key autophagy mRNA levels, suggesting that autophagy-related mechanisms fail to protect the PPN against Lactacystin-induced cellular changes. Hence, the current results suggest that the Lactacystin PD model offers a suitable model for investigating the role of the PPN in PD.
    Brain Structure and Function 01/2015; 220(1):479-500. DOI:10.1007/s00429-013-0669-5

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  • Address
    South Kensington Campus, London, SW7 2AZ, London, United Kingdom
  • Head of Institution
    Sir Keith O’Nions
  • Website
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