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Control of positive and negative magnetoresistance in iron oxideâiron nanocomposite thin films for tunable magnetoelectric nanodevices
The perspective of energy-efficient and tunable functional magnetic nanostructures has triggered research efforts in the fields of voltage control of magnetism and spintronics. We investigate the magnetotransport properties of nanocomposite iron oxide/iron thin films with a nominal iron thickness of 5-50 nm and find a positive magnetoresistance at small thicknesses. The highest magnetoresistance was found for 30 nm Fe with +1.1% at 3 T. This anomalous behavior is attributed to the presence of Fe3O4-Fe nanocomposite regions due to grain boundary oxidation. At the Fe3O4/Fe interfaces, spin-polarized electrons in the magnetite can be scattered and reoriented. A crossover to negative magnetoresistance (â0.11%) is achieved at a larger thickness (>40 nm) when interface scattering effects become negligible as more current flows through the iron layer. Electrolytic gating of this system induces voltage-triggered redox reactions in the Fe3O4 regions and thereby enables voltage-tuning of the magnetoresistance with the locally oxidized regions as the active tuning elements. In the low-magnetic-field region (<1 T), a crossover from positive to negative magnetoresistance is achieved by a voltage change of only 1.72 V. At 3 T, a relative change of magnetoresistance about â45% during reduction was achieved for the 30 nm Fe sample. The present low-voltage approach signifies a step forward to practical and tunable room-temperature magnetoresistance-based nanodevices, which can boost the development of nanoscale and energy-efficient magnetic field sensors with high sensitivity, magnetic memories, and magnetoelectric devices in general
Atmospheric Density Uncertainty Quantification for Satellite Conjunction Assessment
Conjunction assessment requires knowledge of the uncertainty in the predicted
orbit. Errors in the atmospheric density are a major source of error in the
prediction of low Earth orbits. Therefore, accurate estimation of the density
and quantification of the uncertainty in the density is required. Most
atmospheric density models, however, do not provide an estimate of the
uncertainty in the density. In this work, we present a new approach to quantify
uncertainties in the density and to include these for calculating the
probability of collision Pc. For this, we employ a recently developed dynamic
reduced-order density model that enables efficient prediction of the
thermospheric density. First, the model is used to obtain accurate estimates of
the density and of the uncertainty in the estimates. Second, the density
uncertainties are propagated forward simultaneously with orbit propagation to
include the density uncertainties for Pc calculation. For this, we account for
the effect of cross-correlation in position uncertainties due to density errors
on the Pc. Finally, the effect of density uncertainties and cross-correlation
on the Pc is assessed. The presented approach provides the distinctive
capability to quantify the uncertainty in atmospheric density and to include
this uncertainty for conjunction assessment while taking into account the
dependence of the density errors on location and time. In addition, the results
show that it is important to consider the effect of cross-correlation on the
Pc, because ignoring this effect can result in severe underestimation of the
collision probability.Comment: 15 pages, 6 figures, 5 table
A global overview on the diet of the dice snake (Natrix tessellata) from a geographical perspective: foraging in atypical habitats and feeding spectrum widening helps colonisation and survival under suboptimal conditions for a piscivorous snake
Synthetic, structural, and spectroscopic studies of sterically crowded tin-chalcogen acenaphthenes
The work in this project was supported by the Engineering and Physical Sciences Research Council (EPSRC) and EaStCHEM.A series of sterically encumbered peri-substituted acenaphthenes have been prepared containing chalcogen and tin moieties at the close 5,6-positions (Acenap[SnPh3][ER], Acenap = acenaphthene-5,6-diyl, ER = SPh (1), SePh (2), TePh (3), SEt (4); Acenap[SnPh2Cl][EPh], E = S (5), Se (6); Acenap[SnBu2Cl][ER], ER = SPh(7), SePh (8), SEt (9)). Two geminally bis(peri-substituted) derivatives ({Acenap[SPh2]}2SnX2, X = Cl (10), Ph (11)) have also been prepared, along with the bromoâsulfur derivative Acenap(Br)(SEt) (15). All 11 chalcogenâtin compounds align a SnâCPh/SnâCl bond along the mean acenaphthene plane and position a chalcogen lone pair in close proximity to the electropositive tin center, promoting the formation of a weakly attractive intramolecular donorâacceptor E¡¡¡SnâCPh/E¡¡¡SnâCl 3c-4e type interaction. The extent of EâSn bonding was investigated by X-ray crystallography and solution-state NMR and was found to be more prevalent in triorganotin chlorides 5â9 in comparison with triphenyltin derivatives 1â4. The increased Lewis acidity of the tin center resulting from coordination of a highly electronegative chlorine atom was found to greatly enhance the lp(E)âĎ*(SnâY) donorâacceptor 3c-4e type interaction, with substantially shorter EâSn peri distances observed in the solid state for triorganotin chlorides 5â9 (âź75% ârvdW) and significant 1J(119Sn,77Se) spinâspin coupling constants (SSCCs) observed for 6 (163 Hz) and 8 (143 Hz) in comparison to that for the triphenyltin derivative 2 (68 Hz). Similar observations were observed for geminally bis(peri-substituted) derivatives 10 and 11.PostprintPeer reviewe
Das Verhalten der Fische in Kreisstr�mungen und in geraden Str�mungen, als Beitrag zur Orientierung der Fische in der freien nat�rlichen Wasserstr�mung
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