Endocrine disruptors and obesity

The purpose of this review is to summarise current evidence that some environmental chemicals may be able to interfere in endocrine regulation of energy metabolism and adipose tissue structure. Recent findings demonstrate that such endocrine disrupting chemicals, termed “obesogens”, can promote adipogenesis and cause weight gain. This includes compounds to which the human population is exposed in daily life through their use in pesticides/herbicides, industrial and household products, plastics, detergents, flame retardants and ingredients in personal care products. Animal models and epidemiological studies have shown that an especially sensitive time for exposure is in utero or the neonatal period. In summarising the actions of obesogens, it is noteworthy that as their structures are mainly lipophilic, their ability to increase fat deposition has the added consequence of increasing the capacity for their own retention. This has the potential for a vicious spiral not only of increasing obesity but also increasing retention of other lipophilic pollutant chemicals with an even broader range of adverse actions. This might offer an explanation as to why obesity is an underlying risk factor for so many diseases including cancer

Layer-selective magnetization reversal in GMR layer systems

IrMn-based spin-valve systems with CoFe and CoFe/FeNi combinations serving as hard and soft magnetic layers, respectively, were investigated by polarized soft X-ray scattering at photon energies close to the L absorption edges of the constituent elements. Structural and magnetic information was obtained making use of the XMCD (X-ray magnetic circular dichroism) technique in reflection. Hysteresis loops of the individual layers in the spin-valve system were measured element-selectively by tuning the incidence angle of the radiation, opening the possibility of magnetic depth profiling. (C) 2003 Elsevier B.V. All rights reserved

Understanding the XMLD and its magnetocrystalline anisotropy at the L2,3-edges of 3d transition metals

For amorphous 3d transition metal alloys the XMLD spectrum is shown to be proportional to the energy derivative of the X-ray magnetic circular dichroism (XMCD) spectrum. The situation is much different for crystalline cubic 3d ferromagnets: Here different combinations of the spin-polarized e(g) and t(2g) d-partial densities of states are probed for different magnetization axes. Our ab initio calculations predict a huge magnetocrystalline anisotropy in the XMLD spectra of cubic 3d ferromagnets that is much larger than the anisotropy known for XMCD spectra. (C) 2003 Elsevier B.V. All rights reserved

Direct observation of local ferromagnetism on carbon in

An element-selective investigation of magnetism on carbon in the vicinity of \chem{Fe} atoms in a \chem{C/Fe} multilayer is reported. We utilize resonant magnetic reflectivity of circularly polarized synchrotron radiation which allows us to distinguish unambiguously the local magnetism on carbon from that on \chem{Fe} through individual core-level excitations. Clear magnetic signals of carbon are obtained by exploiting the standing-wave technique. Hysteresis loops of individually excited \chem{C} and \chem{Fe} atoms demonstrate ferromagnetism of \chem{C} at room temperature with a moment of \approx 0.05{\mu_\ab{B}} induced by adjacent \chem{Fe} atoms

Interference Effects in T-MOKE Spectra of Fe Thin Films at the 3p Edges - Theory and Experiment

We present combined rst-principle calculations and experimental results of the transversal magneto-optical Kerr e ect (T-MOKE) of thin Fe lms across the 3p edges using linearly polarized synchrotron radiation. We show that the experimental T-MOKE spectra at the 3p edges of Fe exhibit clear signals that are strongly in uenced by interference e ects. Ab initio calculated T-MOKE asymmetry spectra con rm the importance of interference e ects. The comparison of experimental with calculated spectra reveals some di erences that we attribute to metal/metal interface roughness that is not taken into account in the calculations.Web of Science127246846

Faraday rotation spectra at shallow core levels: 3p edges of Fe, Co, and Ni

We present magneto-optical ( MO) Faraday spectra measured at the 3(p) edges of Fe, Co, and Ni. A polarization analysis of the final state of the transmitted radiation is employed to determine the Faraday rotation at these edges. The MO effect becomes resonantly enhanced at the 3p edges and accordingly large values for the intrinsic rotation constant k of 2.2 x 10(5), 1.5 x 10(5) and 0.8 x 10(5) deg/mm for the three ferromagnetic elements Fe, Co, and Ni, respectively, have been measured. These values are large and comparable to those observed at the 2p edges. This remarkable feature emphasizes the importance of the exchange ( EX) splitting over the spin-orbit ( SO) interaction of the core levels in determining MO effects in the extreme ultra-violet ( EUV) region. From these measurements the complete set of MO constants at the 3p edges has been derived

Magnetocrystalline anisotropy in x-ray magnetic linear dichroism at the 3pp edges of crystalline Fe thin films

X-ray magnetic linear dichroism spectra measured in reflection (XMLD-R) on crystalline bcc Fe thin films across the 3p absorption edges are reported. A series of measurements with varying orientation of the electric field vector of the linear polarized synchrotron radiation with respect to the crystal axes reveals a strong magnetocrystalline anisotropy in the XMLD-R spectra. The spectra agree well with theoretical spectra calculated within the framework of the density-functional theory accounting for the spin-orbital and exchange splitting of the 3p semicore states on an equal footing

X-ray natural birefringence in reflection from graphene

The existence of natural birefringence in x-ray reflection on graphene is demonstrated at energies spanning the carbon 1s absorption edge. This new x-ray effect has been discovered with precision measurements of the polarization-plane rotation and the polarization-ellipticity changes that occur upon reflection of linearly polarized synchrotron radiation on monolayer graphene. Extraordinarily large polarization-plane rotations of up to 30∘, accompanied by a change from linearly to circularly polarized radiation have been measured for graphene on copper. Graphene on single crystalline cobalt, grown on tungsten, exhibits rotation values of up to 17∘. Both graphene systems show resonantly enhanced effects at the π∗ and σ∗ energies. The results are referenced against those obtained for polycrystalline carbon and highly oriented pyrolytic graphite (HOPG), respectively. As expected, polycrystalline carbon shows negligible rotation, whereas a huge maximum rotation of 140∘ has been observed for HOPG that may be considered a graphene multilayer system. HOPG is found to exhibit such large rotation values over a broad energy range, even well beyond the π∗ resonance energy due to the contributions of numerous graphene layers. To explain the origin of the observed natural birefringence of graphene, the Stokes parameters as well as the x-ray natural linear dichroism in reflection have been determined. It is shown that the birefringence directly results from the optical anisotropy related to the orthogonal alignment of π∗ and σ∗ bonds in the graphene layer. Our polarization analysis reveals a strong bonding of graphene on Co with a reduced σ∗ excitation energy and a strong tilt of 50% of the p z orbitals towards diagonal orientation. In contrast, graphene on Cu is weakly bound with an orthogonal orientation of the p z orbitals. Exhibiting such a large natural birefringence that can be controlled through substrate choice, and because of excellent heat conductivity, graphene materials have a potential to be used as tunable x-ray phase shifting λ/4 or λ/2 plates in the design of future high-intensity light sources.Web of Science944art. no. 04542