66 research outputs found
Why NiAl is an itinerant ferromagnet but NiGa is not
NiAl and NiGa are closely related materials on opposite sides of a
ferromagnetic quantum critical point. The Stoner factor of Ni is virtually the
same in both compounds and the density of states is larger in NiGa. So,
according to the Stoner theory, it should be more magnetic, and, in LDA
calculations, it is. However, experimentally, it is a paramagnet, while
NiAl is an itinerant ferromagnet. We show that the critical spin
fluctuations are stronger than in NiGa, due to a weaker q-dependence of the
susceptibility, and this effect is strong enough to reverse the trend. The
approach combines LDA calculations with the Landau theory and the
fluctuation-dissipation theorem using the same momentum cut-off for both
materials. The calculations provide evidence for strong, beyond LDA, spin
fluctuations associated with the critical point in both materials, but stronger
in NiGa than in NiAl.Comment: replaced (incorrect version submitted
The role of pericytes in brain disorders: from the periphery to the brain
It is becoming increasingly apparent that disorders of the brain microvasculature contribute to many neurological disorders. In recent years it has become clear that a major player in these events is the capillary pericyte which, in the brain, is now known to control the blood-brain barrier, regulate blood flow, influence immune cell entry and be crucial for angiogenesis. In this review we consider the under-explored possibility that peripheral diseases which affect the microvasculature, such as hypertension, kidney disease and diabetes, produce central nervous system (CNS) dysfunction by mechanisms affecting capillary pericytes within the CNS. We highlight how cellular messengers produced peripherally can act via signalling pathways within CNS pericytes to reshape blood vessels, restrict blood flow or compromise blood-brain barrier function, thus causing neuronal dysfunction. Increased understanding of how renin-angiotensin, Rho-kinase and PDGFRβ signalling affect CNS pericytes may suggest novel therapeutic approaches to reducing the CNS effects of peripheral disorders
- …