We have synthesized graphene oxide (GO) using Hummer's method which was subsequently reduced (rGO) by hydrazine hydrate. The synthesized GO was coated with poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT-PSS) conducting polymer (CP) to obtain CP-GO which was also further reduced using hydrazine hydrate to form CP-rGO. Scanning electron microscopy, Raman spectroscopy, X-ray diffraction, ultraviolet photoelectron spectroscopy, and X-ray photoelectron spectroscopy, X-ray absorption near-edge structure (XANES) techniques were used to study the electronic and structural properties of GO, rGO, CP-GO, and CP-rGO nanocomposites for biomedical applications. The superconducting quantum interference device method was used to investigate the magnetic properties of the nanocomposites. The electrical conductivity of the CP-GO nanocomposites was found to be ~104 times higher than that of GO due to an increase in sp2 content and subsequent decrease in oxygen functional groups. In rGO, we observed an improved paramagnetic saturation magnetization of approximately 5.6 × 0−3 emu/g at 2 K. The electronic and magnetic behavior of PEDOT-PSS-coated nanocomposites, as a result, were successfully tuned for potential biological and biomedical applications.

Neodymium magnets were independently discovered in 1984 by General Motors and Sumitomo. Today, they are the strongest type of permanent magnets commercially available. They are the most widely used industrial magnets with many applications, including in hard disk drives, cordless tools and magnetic fasteners. We use a vector potential approach, rather than the more usual magnetic potential approach, to derive the three-dimensional (3D) magnetic field for a neodymium magnet, assuming an idealized block geometry and uniform magnetization. For each field or observation point, the 3D solution involves 24 nondimensional quantities, arising from the eight vertex positions of the magnet and the three components of the magnetic field. The only unknown in the model is the value of magnetization, with all other model quantities defined in terms of field position and magnet location. The longitudinal magnetic field component in the direction of magnetization is bounded everywhere, but discontinuous across the magnet faces parallel to the magnetization direction. The transverse magnetic fields are logarithmically unbounded on approaching a vertex of the magnet.

The mineralogy of the silt fraction of a 1.5 m-deep, well developed, intensely weathered, greyish soil profile from a toposequence on a tableland covered by agricultural crops in the upper valley of the Jequitinhonha river basin, Minas Gerais, Brazil, has been studied by X-ray powder diffraction, 57Fe Mössbauer spectroscopy at 298 K and 80 K, and vibrating sample magnetometry. Mössbauer data collected at room temperature indicated about 17 atom% of the iron content of the sample to be structural Fe2+ in phyllosilicates, which X-ray diffraction showed to be mainly halloysite and kaolinite. The magnetization curve also indicates the presence of a ferrimagnetic phase, tentatively identified by Mössbauer spectroscopy as maghemite (γ-Fe2O3).

These findings support a pedogenetic model for this soil profile, by which the remaining Fe2+ bearing minerals were first formed under relatively anoxic palaeo-conditions of an intense hydric regime. Subsequent drier local conditions, due to a much improved drainage, favoured intensive weathering, leading to the presently developed Oxisol. Even under the more oxidative conditions, part of the Fe2+ -containing phyllosilicates still remained in the profile, which is believed to impart the rather unusual greyish colour (Munsell 10YR 3/2) to this deep tropical soil.

Alternative Fenton and Fenton-like systems based on natural Fe oxides are described. The collected materials were modified through controlled reduction with H2 and were characterized by chemical analysis, X-ray diffraction, saturation magnetization measurements, and Mössbauer spectroscopy at 298 and 110 K. The catalytic activities of these original and modified materials were tested by studying the decomposition of H2O2 and the discolouration of methylene blue. Iron oxides present in the samples were mainly hematite and subordinate goethite which, after controlled reduction, were converted to metallic iron and magnetite. The mixture of Fe0 and magnetite in one of these materials was significantly more efficient at H2O2 decomposition and the discolouration of methylene blue than the original Fe3+ oxides. These results suggest that Fe2+ is essential to produce an active Fenton system.

The upper Jequitinhonha Valley is located within the Serra do Espinhaço Meridional mountain range in the State of Minas Gerais, Brazil. The topography is flat or gently undulating with large flat areas known as chapadas (‘high plains’) that are dissected by rivers forming swamps known locally as veredas (‘paths’). The present study is concerned mainly with a representative toposequence in the watershed of the Lagoa do Leandro vereda, a swamp near the city of Minas Novas on a chapada of the highlands of the Alto (Upper) Jequitinhonha region.

The soils of this sequence were studied by a variety of physical and chemical techniques, including Mössbauer, electron spin resonance (ESR) and photoacoustic (PAS) spectroscopies, as well as X-ray diffraction (XRD) and carbon isotope data. Mössbauer spectra of the silt fraction of a grey Xanthic Haplustox (Munsell 10YR 3/2) from the Lagoa do Leandro vereda, referred to here as a ‘Grey Haplustox’ (‘LAC’), proved the existence of Fe2+- and Fe3+-bearing components. Photoacoustic spectroscopy confirmed the presence of Fe2+, as shown by Mössbauer spectroscopy, probably in an octahedrally coordinated site, but the principal optical absorption bands are due to different Fe3+ sites. A ferrimagnetic contribution and three other paramagnetic lines attributed to Fe3+ and Ti3+ were demonstrated by means of ESR. The ESR and PAS results are thus in agreement with the chemical composition and Mössbauer spectroscopy, allowing a detailed characterization of the mineralogy of this silt.

Carbon isotope data indicate the climate to have varied during the past: awetter climate in the Pleistocene, with drier phases in the Late Pleistocene and Holocene, and again a more humid climate 1200 years ago. δ13C data indicate the C3 scrubland vegetation to have occupied the bottom of the vereda in the past (Bispo & Silva, 2014).

Greyish Oxisols that consist chiefly of phyllosilicate minerals of the kaolinite group (which are usually associated with binary oxides and hydroxides) are of common occurrence in tropical soils resulting from leaching and precipitation. Such Oxisols of greyish appearance and similar mineralogy have been described elsewhere from Brazil and, for example, from India. Such soils are therefore proposed here as a new hierarchical level of the Soil Classification System.

The conventional magnetic recording approached the physical frontiers of the recording density. The magnetic recording must face the famous trilemma: In order to increase the recording density, smaller grain volumes are needed, but in order to ensure the thermal stability of recorded information, the anisotropy constant should be increased accordingly; what results is an increased anisotropy field, which requires higher writing fields. Such fields are unavailable with the maximum saturation magnetization obtainable with the magnetic materials of the current heads. In order to overcome these problems, new media structures have been proposed. The most promising is the bit-patterned magnetic media (BPM), intensively studied over the last years with the aim of obtaining obtain an ultra-high recording density of hard-disk drives. A BPM comprises monodisperse high-anisotropy nano-particles in a self-organized patterning. They have a higher thermal stability, a lower noise and a higher signal resolution, which leads to a higher recording density and a better SNR. They eliminate the transition noise and, due to the large fraction of the bit volume occupied by the magnetic dots, improve thermal stability. Nevertheless, some important issues such as long-range patterning, control of the surface roughness, signal readout, etc., remain critical problems to solve. Another challenge is the fact that recording on BPM is sensitive to the material and geometry parameter fluctuations that may lead to additional constraints and require tight synchronization of the write-field misregistration time and bit positions. A possible route to higher recording densities is to use a multilevel recording, where more than two states are stored per dot.

A series of Dy2Co17−xGax polycrystalline samples with x from 0 to 7 were prepared by arc melting. X-ray powder diffraction analysis indicated that these compounds have the hexagonal Th2Ni17 structure for x≤3 and the rhombohedral Th2Zn17 structure for 3.5≤x≤7. The lattice parameters a and c increase linearly with the gallium content until x=5.3. With further increasing the gallium content x up to 7, the lattice parameter c slightly decreases, whereas the lattice parameter a increases more quickly than that for 0≤x≤5.3. The unit-cell volume shows an approximately linear increase of 6.1 Å3/Ga for 0≤x≤3.0 and 10.1 Å3/Ga for 3.5≤x≤7.0, respectively. Rietveld refinement of the Dy2Co11.7Ga5.3 compound reveals that the Ga atoms occupy all the 6c, 9d, 18f, and 18h sites and preferentially occupy the 6c site. The Curie temperature and the saturation magnetization of the rhombohedral Dy2Co17−xGax compounds decrease almost linearly with increasing Ga content.

Two lightning impacts are described from an area near the Inland Ice in West Greenland. The first lightning blasted an outcrop of metacherts. It subsequently split into two branches, which traversed rock outcrops and boulders, leaving behind two white almost straight lines, 30 m and 14 m long, respectively, where all lichens and plants were burned away. On the white lines the upper few millimetres of the traversed boulders were melted to a glass which subsequently peeled off by thermal expansion to leave a rough surface. Magnetic investigation of an amphibolite boulder found on the white line showed that a strong electric current indeed traversed the boulder. A few years later a second lightning impacted on a mountaintop close to the first impact. The second lightning left a trail on the rock surface covered by a thin layer of glass. The glass displays spectacular colours ranging from metallic blue to red, yellow and green.

For an independent percolation model on , where is a homogeneous tree and is a one-dimensional lattice, it is shown, by verifying that the triangle condition is satisfied, that the percolation probability θ (p) is a continuous function of p at the critical point pc, and the critical exponents , γ, δ, and Δ exist and take their mean-field values. Some analogous results for Markov fields on are also obtained.