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Berlin Brandenburg

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  • 1
    Language: English
    In: The journal of physical chemistry. B, 07 June 2012, Vol.116(22), pp.6233-49
    Description: We simulate spin relaxation processes, which may be measured by either continuous wave or pulsed magnetic resonance techniques, using trajectory-based simulation methodologies. The spin-lattice relaxation rates are extracted numerically from the relaxation simulations. The rates obtained from the numerical fitting of the relaxation curves are compared to those obtained by direct simulation from the relaxation Bloch-Wangsness-Abragam-Redfield theory (BWART). We have restricted our study to anisotropic rigid-body rotational processes, and to the chemical shift anisotropy (CSA) and a single spin-spin dipolar (END) coupling mechanisms. Examples using electron paramagnetic resonance (EPR) nitroxide and nuclear magnetic resonance (NMR) deuterium quadrupolar systems are provided. The objective is to compare those rates obtained by numerical simulations with the rates obtained by BWART. There is excellent agreement between the simulated and BWART rates for a Hamiltonian describing a single spin (an electron) interacting with the bath through the chemical shift anisotropy (CSA) mechanism undergoing anisotropic rotational diffusion. In contrast, when the Hamiltonian contains both the chemical shift anisotropy (CSA) and the spin-spin dipolar (END) mechanisms, the decay rate of a single exponential fit of the simulated spin-lattice relaxation rate is up to a factor of 0.2 smaller than that predicted by BWART. When the relaxation curves are fit to a double exponential, the slow and fast rates extracted from the decay curves bound the BWART prediction. An extended BWART theory, in the literature, includes the need for multiple relaxation rates and indicates that the multiexponential decay is due to the combined effects of direct and cross-relaxation mechanisms.
    Keywords: Molecular Dynamics Simulation
    ISSN: 15206106
    E-ISSN: 1520-5207
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  • 2
    Language: English
    In: Journal of Hydrology, 17 May 2012, Vol.438-439, pp.1-2
    Keywords: Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
    Source: ScienceDirect Journals (Elsevier)
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  • 3
    In: Water Resources Research, November 2012, Vol.48(11), pp.n/a-n/a
    Keywords: Unsaturated Soils ; Water Films
    ISSN: 0043-1397
    ISSN: Water Resources Research
    E-ISSN: 1944-7973
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  • 4
    In: Learned Publishing, July 2012, Vol.25(3), pp.232-234
    ISSN: 0953-1513
    E-ISSN: 1741-4857
    Source: John Wiley & Sons, Inc.
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  • 5
    Language: English
    In: Learned Publishing, 07/01/2012, Vol.25(3), pp.232-234
    Keywords: Education;
    ISSN: 09531513
    E-ISSN: 17414857
    Source: CrossRef
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  • 6
    Language: English
    In: Coordination Chemistry Reviews, October 2012, Vol.256(19-20), pp.2147-2163
    Description: ► The link between AD, PD and TSE neurodegenerative disease and metal exposure is reviewed. ► Transfer of Mn, Pb, and Hg specific species through barriers is discussed. ► Metal speciation is highlighted in terms of Eh and pH conditions within cell compartments. ► The structure of amyloidogenic Aβ, αS and PrP protein–Cu complexes is well established. ► A pathogenic transconformational PrP change upon Mn to Cu exchange is proposed. Metal ions appear to play an important role in several neurodegenerative (ND) diseases. Evidence suggests that metal ions bind directly to causative amyloidogenic proteins and modulate their aggregation into amyloids, considered to be a key event in the etiology of ND diseases. Apart from this well-documented binding of essential metals to amyloidogenic proteins, other, non-essential metal ions have been considered to be environmental hazards for neuronal disorders, but tight causative relations have yet to be established. The present article provides a review of the potential role of manganese, lead, and mercury as environmental risk factors in ND diseases, and covers in detail environmental availability of these metals, their uptake and distribution in the body and cells, and their role in Alzheimer's, Parkinson's and Prion diseases.
    Keywords: Metals ; Exposure ; Speciation ; Neurodegenerative Diseases ; Prion Protein ; Amyloid Beta, Α-Synuclein ; Chemistry
    ISSN: 0010-8545
    E-ISSN: 1873-3840
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  • 7
    In: Soil Science, 2012, Vol.177(2), pp.111-119
    Description: ABSTRACT: Macroscopic measurements and observations in two-dimensional soil-thin sections indicate that fungal hyphae invade preferentially the larger, air-filled pores in soils. This suggests that the architecture of soils and the microscale distribution of water are likely to influence significantly the dynamics of fungal growth. Unfortunately, techniques are lacking at present to verify this hypothesis experimentally, and as a result, factors that control fungal growth in soils remain poorly understood. Nevertheless, to design appropriate experiments later on, it is useful to indirectly obtain estimates of the effects involved. Such estimates can be obtained via simulation, based on detailed micron-scale X-ray computed tomography information about the soil pore geometry. In this context, this article reports on a series of simulations resulting from the combination of an individual-based fungal growth model, describing in detail the physiological processes involved in fungal growth, and of a Lattice Boltzmann model used to predict the distribution of air-liquid interfaces in soils. Three soil samples with contrasting properties were used as test cases. Several quantitative parameters, including Minkowski functionals, were used to characterize the geometry of pores, air-water interfaces, and fungal hyphae. Simulation results show that the water distribution in the soils is affected more by the pore size distribution than by the porosity of the soils. The presence of water decreased the colonization efficiency of the fungi, as evinced by a decline in the magnitude of all fungal biomass functional measures, in all three samples. The architecture of the soils and water distribution had an effect on the general morphology of the hyphal network, with a “looped” configuration in one soil, due to growing around water droplets. These morphologic differences are satisfactorily discriminated by the Minkowski functionals, applied to the fungal biomass.
    Keywords: Agriculture;
    ISSN: 0038-075X
    E-ISSN: 15389243
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