Reorganization of Functional Networks in Mild Cognitive Impairment

Whether the balance between integration and segregation of information in the brain is damaged in Mild Cognitive Impairment (MCI) subjects is still a matter of debate. Here we characterize the functional network architecture of MCI subjects by means of complex networks analysis. Magnetoencephalograms (MEG) time series obtained during a memory task were evaluated by synchronization likelihood (SL), to quantify the statistical dependence between MEG signals and to obtain the functional networks. Graphs from MCI subjects show an enhancement of the strength of connections, together with an increase in the outreach parameter, suggesting that memory processing in MCI subjects is associated with higher energy expenditure and a tendency toward random structure, which breaks the balance between integration and segregation. All features are reproduced by an evolutionary network model that simulates the degenerative process of a healthy functional network to that associated with MCI. Due to the high rate of conversion from MCI to Alzheimer Disease (AD), these results show that the analysis of functional networks could be an appropriate tool for the early detection of both MCI and AD

25th Annual Computational Neuroscience Meeting: CNS-2016

Abstracts of the 25th Annual Computational Neuroscience Meeting: CNS-2016 Seogwipo City, Jeju-do, South Korea. 2–7 July 201

The low- temperature and high-pressure theromelastic and structural properties of chalcopyrite, CuFeS(2)

The thermoelastic properties of a sample of chalcopyrite from the Palabora mine, South Africa, have been investigated in the temperature range 4.2 - 330 K at ambient pressure, and between 0.22 and 6.81 GPa at ambient temperature. Magnetization measurements indicated a transition to a second antiferromagnetically ordered phase in the region of 53 K; however, all attempts to characterize this magnetic phase by introducing an ordered moment onto the copper site were unsuccessful owing to the small magnitude of the refined magnetic moment. In agreement with other low-temperature crystallographic measurements made on non-antiferromagnetically ordered adamantine-structured semiconducting materials (group IV; I-VII, II-VI, III-V, I-III-VI2, II-IV-V-2 compounds), chalcopyrite exhibits negative linear and volumetric thermal expansion over a significant temperature interval. Calculation of the speeds of sound for a number of high-symmetry wave vectors is consistent with Blackman's model for negative thermal expansion. The unit-cell volume and isochoric heat-capacity have been fitted assuming a two-term Debye internal energy function, with consistent values being found for the two characteristic temperatures. The temperature dependence of the thermodynamic Gruneisen parameter shows a deep minimum of similar to-3 at T/theta(0) similar to 0.55 (theta(0) is the Debye temperature at 0 K) and a high-temperature limit of similar to 0.7; these results are the first demonstration that a chalcopyrite-structured phase behaves in the characteristic manner of the simpler adamantine-structured semiconducting materials. No systematic variation in either the nuclear nor the magnetic structure was found between 4.2 and 330 K, and the vibrational Debye temperatures derived by fitting the temperature dependence of the isotropic atomic displacement parameters show no relationship to features in the phonon density of states function. The bulk modulus of chalcopyrite is 77(2) GPa, in good agreement with that determined by ab initio calculations and a recent X-ray-diffraction study, and its pressure derivative is 2.0(6). At high pressure, chalcopyrite remains antiferromagnetically ordered until 6.7(2) GPa, at which point a transition to an amorphous phase is observed. Slow decompression of this phase leads to only a limited recovery of the crystalline phase

Malleability of uranium: Manipulating the charge-density wave in epitaxial films

We report x-ray synchrotron experiments on epitaxial films of uranium, deposited on niobium and tungsten seed layers. Despite similar lattice parameters for these refractory metals, the uranium epitaxial arrangements are different and the strains propagated along the orthorhombic a axis of the uranium layers are of opposite sign. At low temperatures these changes in epitaxy result in dramatic modifications to the behavior of the charge-density wave in uranium. The differences are explained with the current theory for the electron-phonon coupling in the uranium lattice. Our results emphasize the intriguing possibilities of producing epitaxial films of elements that have complex structures like the light actinides uranium to plutonium.JRC.E.6-Actinide researc

A study of uranium-based multilayers: II. Magnetic properties

SQUID magnetometry and polarised neutron reflectivity measurements have been employed to characterise the magnetic properties of U/Fe, U/Co and U/Gd multilayers. The field dependence of the magnetisation was measured at 10K in magnetic fields from -70kOe to 70kOe. A temperature dependent study of the magnetisation evolution was undertaken for a selection of U/Gd samples. PNR was carried out in a field of 4.4kOe for U/Fe and U/Co samples (at room temperature) and for U/Gd samples (at 10K). Magnetic 'dead' layers of about 15 Angstrom were observed for U/Fe and U/Co samples, consistent with a picture of interdiffused interfaces. A large reduction in the magnetic moment, constant over a wide range of Gd layer thicknesses, was found for the U/Gd system (about 4 Bohr magnetons compared with 7.63 for the bulk metal). This could be understood on the basis of a pinning of Gd moments arising from a column-like growth mechanism of the Gd layers. A study of the effective anisotropy suggests that perpendicular magnetic anisotropy could occur in multilayers consisting of thick U and thin Gd layers. A reduction in the Curie temperature was observed as a function of Gd layer thickness, consistent with a finite-size scaling behaviour.Comment: 18 pages, 8 figures, submitted to J. Phys.: Condens. Matte

Polarised neutron reflectivity from U/Fe, U/Gd multilayers

U/Fe and U/Gd multilayers constitute magnetic systems, which can be used to probe the hybridisation of the 5f electrons of uranium with 3d and 4f electrons, respectively. A range of samples with varying layer thicknesses was prepared by DC sputtering in a UHV chamber. X-ray and neutron reflectivity and X-ray diffraction were used to characterise the structure of the U/Fe [A.M. Beesley, M.F. Thomas, A.D.F. Herring, R.C.C. Ward, M.R. Wells, S. Langridge, S.D. Brown, S.W. Zochowski, L. Bouchenoire, W.G. Stirling, G.H. Lander, J. Phys.: Condens. Matter 16 (2004) 8491] and U/Gd systems. A combination of polarised neutron reflectivity, SQUID magnetometry and X-ray magnetic circular dichroism have revealed an induced moment on the U site in U/Fe structures and a saturation magnetisation which increases with increasing Fe and Gd thickness. © 2006

Polarised neutron reflectivity from U/Fe, U/Gd multilayers

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Magnetism of uranium/iron multilayers: I. Fabrication and characterization

U/Fe multilayers constitute a magnetic system in which the 3d magnetism of the Fe layers will be modified by hybridization with the U 5f electrons. This paper describes a programme of measurements of the magnetic behaviour of these systems beginning with the fabrication and thorough characterization of the samples. Metallic U/Fe multilayers were prepared by DC sputtering in a UHV chamber. A range of samples with measured U thicknesses, t U, in the range 18-66 Å and Fe thicknesses, t Fe, from 7 to 108 Å was fabricated. X-ray and neutron reflectivity measurements showed strong peaks indicating good layer structure and gave a determination of the bilayer thickness. X-ray diffraction analysis showed crystalline α-U and α-Fe for layer thicknesses greater than about 20 Å. The α-Fe is strongly textured with (110) planes in the layer plane. The Fe lattice parameter is larger for the case of thin layers, but approaches the bulk value of 2.866 Å at t Fe ∼ 75 Å. Mössbauer spectra of α-Fe were obtained for t Fe ≥ 18 Å; a non-magnetic component of thickness ∼12 Å per layer is always present. The results from these different experimental techniques are combined to present a detailed description of these multilayer systems