Magnetoresistance due to Domain Walls in Micron Scale Fe Wires with Stripe Domains

The magnetoresistance (MR) associated with domain boundaries has been investigated in microfabricated bcc Fe (0.65 to 20 $\mu$m linewidth) wires with controlled stripe domains. Domain configurations have been characterized using magnetic force microscopy. MR measurements as a function of field angle, temperature and domain configuration are used to estimate MR contributions due to resistivity anisotropy and domain walls. Evidence is presented that domain boundaries enhance the conductivity in such microstructures over a broad range of temperatures (1.5 K to 80 K).Comment: 8 pages, 3 postscript figures, and 2 jpg images (Fig 1 and 2) to appear in IEEE Transactions on Magnetics (Fall 1998

Domain Wall Resistance based on Landauer's Formula

The scattering of the electron by a domain wall in a nano-wire is calculated perturbatively to the lowest order. The resistance is calculated by use of Landauer's formula. The result is shown to agree with the result of the linear response theory if the equilibrium is assumed in the four-terminal case

Ballistic and diffuse transport through a ferromagnetic domain wall

We study transport through ballistic and diffuse ferromagnetic domain walls in a two-band Stoner model with a rotating magnetization direction. For a ballistic domain wall, the change in the conductance due to the domain wall scattering is obtained from an adiabatic approximation valid when the length of the domain wall is much longer than the Fermi wavelength. In diffuse systems, the change in the resistivity is calculated using a diagrammatic technique to the lowest order in the domain wall scattering and taking into account spin-dependent scattering lifetimes and screening of the domain wall potential.Comment: 9 pages, 3 figures, to appear in Phys. Rev.

Faraday rotation maps of disk galaxies

Faraday rotation is one of the most widely used observables to infer the strength and configuration of the magnetic field in the ionised gas of the Milky Way and nearby spiral galaxies. Here we compute synthetic Faraday rotation maps at $z=0$ for a set of disk galaxies from the Auriga high-resolution cosmological simulations, for different observer positions within and outside the galaxy. We find that the strength of the Faraday rotation of our simulated galaxies for a hypothetic observer at the solar circle is broadly consistent with the Faraday rotation seen for the Milky Way. The same holds for an observer outside the galaxy and the observed signal of the nearby spiral galaxy M51. However, we also find that the structure and angular power spectra of the synthetic all-sky Faraday rotation maps vary strongly with azimuthal position along the solar circle. We argue that this variation is a result of the structure of the magnetic field of the galaxy that is dominated by an azimuthal magnetic field ordered scales of several kpc, but has radial and vertical magnetic field components that are only ordered on scales of 1-2 kpc. Because the magnetic field strength decreases exponentially with height above the disk, the Faraday rotation for an observer at the solar circle is dominated by the local environment. This represents a severe obstacle for attempts to reconstruct the global magnetic field of the Milky Way from Faraday rotation maps alone without including additional observables.Comment: 10 pages, 10 figures, accepted by MNRA

The Sun's Preferred Longitudes and the Coupling of Magnetic Dynamo Modes

Observations show that solar activity is distributed non-axisymmetrically, concentrating at "preferred longitudes". This indicates the important role of non-axisymmetric magnetic fields in the origin of solar activity. We investigate the generation of the non-axisymmetric fields and their coupling with axisymmetric solar magnetic field. Our kinematic generation (dynamo) model operating in a sphere includes solar differential rotation, which approximates the differential rotation obtained by inversion of helioseismic data, modelled distributions of the turbulent resistivity, non-axisymmetric mean helicity, and meridional circulation in the convection zone. We find that (1) the non-axisymmetric modes are localised near the base of the convection zone, where the formation of active regions starts, and at latitudes around $30^{\circ}$; (2) the coupling of non-axisymmetric and axisymmetric modes causes the non-axisymmetric mode to follow the solar cycle; the phase relations between the modes are found. (3) The rate of rotation of the first non-axisymmetric mode is close to that determined in the interplanetary space.Comment: 22 pages, 18 figures. Accepted for publication in the Astrophysical Journa

Enhancing Developing Country Access to Eco-Innovation: The Case of Technology Transfer and Climate Change in a Post-2012 Policy Framework

The deployment of eco-innovations in developing countries is a key driver of their contribution to efficiently addressing global environmental challenges. It is also a key driver of markets for eco-innovation and sustainable economic development. This report explores the barriers developing countries face in accessing markets for eco-innovation. It outlines the key considerations policy needs to address to overcome these barriers and discusses the extent to which selected existing policy mechanisms and organisation have achieved this. The key finding of the report is that the majority of existing policy mechanisms fails to recognise the critical importance of developing indigenous eco-innovation capabilities amongst developing country firms. Indigenous eco-innovation capabilities are essential to facilitating both the diffusion of existing ecoinnovations within developing countries and sustainable economic development based on the adoption, adaption and development of environmentally sound technologies that fit with the bespoke conditions faced by developing countries. Building up eco-innovation capabilities in developing countries requires a shift away from the current focus on large project based approaches which emphasise the transfer of the hardware aspects of clean technologies, towards approaches that emphasise flows of codified knowledge (know-how and know-why) and tacit knowledge. Policy also needs to be improved to better respond to the context-specific technological and cultural requirements which vary inter- and intra-nationally

Negative Domain Wall Contribution to the Resistivity of Microfabricated Fe Wires

The effect of domain walls on electron transport has been investigated in microfabricated Fe wires (0.65 to 20 $\mu m$ linewidths) with controlled stripe domains. Magnetoresistance (MR) measurements as a function of domain wall density, temperature and the angle of the applied field are used to determine the low field MR contributions due to conventional sources in ferromagnetic materials and that due to the erasure of domain walls. A negative domain wall contribution to the resistivity is found. This result is discussed in light of a recent theoretical study of the effect of domain walls on quantum transport.Comment: 7 pages, 4 postscript figures and 1 jpg image (Fig. 1

Solar dynamo

No abstract available

Melatonin: A Cutaneous Perspective on its Production, Metabolism, and Functions

Melatonin, an evolutionarily ancient derivative of serotonin with hormonal properties, is the main neuroendocrine secretory product of the pineal gland. Although melatonin is best known to regulate circadian rhythmicity and lower vertebrate skin pigmentation, the full spectrum of functional activities of this free radical-scavenging molecule, which also induces/promotes complex antioxidative and DNA repair systems, includes immunomodulatory, thermoregulatory, and antitumor properties. Because this plethora of functional melatonin properties still awaits to be fully appreciated by dermatologists, the current review synthesizes the main features that render melatonin a promising candidate for the management of several dermatoses associated with substantial oxidative damage. We also review why melatonin promises to be useful in skin cancer prevention, skin photo- and radioprotection, and as an inducer of repair mechanisms that facilitate the recovery of human skin from environmental damage. The fact that human skin and hair follicles not only express functional melatonin receptors but also engage in substantial, extrapineal melatonin synthesis further encourages one to systematically explore how the skin's melatonin system can be therapeutically targeted in future clinical dermatology and enrolled for preventive medicine strategies