38 research outputs found
(Z)-tert-Butyl 2-(4-amino-9H-fluoren-9-ylidene)acetate
The title compound, C19H19NO2, obtained as an almost equimolar mixture (as shown by 1H NMR) with the E isomer through a Wittig reaction between 4-amino-9H-fluoren-9-one and the stabilized ylide Ph3P=CHCO2C(CH3)3, was obtained pure in the Z configuration following crystallization from toluene. The molecule shows a planar arrangement of the ring system and the new double bond, whereas the carbonyl O atom forms a 45.1 (3)° dihedral angle with it. The molecules are linked by N—H⋯O hydrogen bonds, forming cyclic structures with R
4
4(24) graph-set motifs. These motifs are connected to each other, giving rise to a sheet structure parallel to the ab plane. The linkage within the sheets is further enhanced by π–π stacking interactions between the fluorene units [centroid–centroid distance = 3.583 (2) Å]
Low-density lipoprotein concentration in the normal left coronary artery tree
<p>Abstract</p> <p>Background</p> <p>The blood flow and transportation of molecules in the cardiovascular system plays a crucial role in the genesis and progression of atherosclerosis. This computational study elucidates the Low Density Lipoprotein (LDL) site concentration in the entire normal human 3D tree of the LCA.</p> <p>Methods</p> <p>A 3D geometry model of the normal human LCA tree is constructed. Angiographic data used for geometry construction correspond to end-diastole. The resulted model includes the LMCA, LAD, LCxA and their main branches. The numerical simulation couples the flow equations with the transport equation applying realistic boundary conditions at the wall.</p> <p>Results</p> <p>High concentration of LDL values appears at bifurcation opposite to the flow dividers in the proximal regions of the Left Coronary Artery (LCA) tree, where atherosclerosis frequently occurs. The area-averaged normalized luminal surface LDL concentrations over the entire LCA tree are, 1.0348, 1.054 and 1.23, for the low, median and high water infiltration velocities, respectively. For the high, median and low molecular diffusivities, the peak values of the normalized LDL luminal surface concentration at the LMCA bifurcation reach 1.065, 1.080 and 1.205, respectively. LCA tree walls are exposed to a cholesterolemic environment although the applied mass and flow conditions refer to normal human geometry and normal mass-flow conditions.</p> <p>Conclusion</p> <p>The relationship between WSS and luminal surface concentration of LDL indicates that LDL is elevated at locations where WSS is low. Concave sides of the LCA tree exhibit higher concentration of LDL than the convex sides. Decreased molecular diffusivity increases the LDL concentration. Increased water infiltration velocity increases the LDL concentration. The regional area of high luminal surface concentration is increased with increasing water infiltration velocity. Regions of high LDL luminal surface concentration do not necessarily co-locate to the sites of lowest WSS. The degree of elevation in luminal surface LDL concentration is mostly affected from the water infiltration velocity at the vessel wall. The paths of the velocities in proximity to the endothelium might be the most important factor for the elevated LDL concentration.</p
Influence of the magnetic field on the plasmonic properties of transparent Ni anti-dot arrays
Extraordinary optical transmission is observed due to the excitation of
surface plasmon polaritons (SPPs) in 2-Dimensional hexagonal anti-dot patterns
of pure Ni thin films, grown on sapphire substrates. A strong enhancement of
the polar Kerr rotation is recorded at the surface plasmon related transmission
maximum. Angular resolved reflectivity measurements under an applied field,
reveal an enhancement and a shift of the normalized reflectivity difference
upon reversal of the magnetic saturation (transverse magneto-optical Kerr
effect-TMOKE). The change of the TMOKE signal clearly shows the magnetic field
modulation of the dispersion relation of SPPs launched in a 2D patterned
ferromagnetic Ni film
(2E,4E,6E)-3-Methyl-7-(pyren-1-yl)octa-2,4,6-trienoic acid
The title compound, C25H20O2, was synthesized by a Wittig reaction between triphenyl[1-(pyren-1-yl)ethyl]phosphonium bromide and ethyl (2E,4E)-3-methyl-6-oxohexa-2,4-dienoate, in the presence of n-butyl lithium, followed by saponification. It was obtained pure in the all-trans configuration following crystallization from ethyl acetate. The asymmetric unit contains two independent molecules (A and B), which are arranged almost parallel to each other within the crystal structure. The triene chain is not coplanar with the pyrene ring system, forming dihedral angles of 52.8 (1) and 42.2 (1)° for molecules A and B, respectively. Intermolecular hydrogen bonds between the carboxyl groups of the molecules link them into centrosymmetric pairs, AA and BB, each with the R
2
2(8) graph-set motif
Magneto-optic enhancement and magnetic properties in Fe antidot films with hexagonal symmetry
The magneto-optic and magnetic properties of hexagonal arrays of holes in optically thin iron films are presented. We analyze their dependence on the hole radius and compare the results to a continuous iron film of the same thickness. We observe a large enhancement of the magneto-optic Kerr rotation with respect to that of the continuous film, at frequencies where surface-plasmon excitations are expected. The spectral position of the Kerr maxima can be tuned by the size and the distance between the holes. Additional simulations are in very good agreement with the experiment and thus confirm the effect of the surface plasmons on the Kerr rotation. The altering of the magnetic properties by the hole array is also visible in the hysteretic behavior of the sample where a significant hardening is observed.E.Th.P. acknowledges the financial support from the Icelandic Science Foundation and the Swedish Foundation for International Cooperation in Research and Higher Education
STINT . M.G. thanks the Helmholtz-Zentrum Berlin for financial support. A.G.-M. and E. F.-V. acknowledge financial support from the EU under Project No. NMP3-SL-2008-214107-Nanomagma and from the Spanish MICINN (Consolider 2010 References No. CSD2008-00023-Funcoat and No. MAT2008-06765-C02-01/NAN . E.F.-V also acknowledges financial support from the CSIC via the JAE-Pre program. The authors acknowledge also the Knut and AliceWallenberg Foundation.Peer reviewe
Surface plasmons and magneto-optic activity in hexagonal Ni anti-dot arrays
The influence of surface plasmons on the magneto-optic activity in a two-dimensional hexagonal array is addressed. The experiments were performed using hexagonal array of circular holes in a ferromagnetic Ni film. Well pronounced troughs are observed in the optical reflectivity, resulting from the presence of surface plasmons. The surface plasmons are found to strongly enhance the magneto-optic response (Kerr rotation), as compared to a continuous film of the same composition. The influence of the hexagonal symmetry of the pattern on the coupling between the plasmonic excitations is demonstrated, using optical diffraction measurements and theoretical calculations of the magneto-optic and of the angular dependence of the optical activity
Melting artificial spin ice
Artificial spin ice arrays of micromagnetic islands are a means of
engineering additional energy scales and frustration into magnetic materials.
Despite much progress in elucidating the properties of such arrays, the `spins'
in the systems studied so far have no thermal dynamics as the kinetic
constraints are too high. Here we address this problem by using a material with
an ordering temperature near room temperature. By measuring the temperature
dependent magnetization in different principal directions, and comparing with
simulations of idealized statistical mechanical models, we confirm a dynamical
`pre-melting' of the artificial spin ice structure at a temperature well below
the intrinsic ordering temperature of the island material. We thus create a
spin ice array that has real thermal dynamics of the artificial spins over an
extended temperature range
О некоторых мерах государственной поддержки субъектов сельскохозяйственной деятельности в рамках интеграционных процессов
Материалы IX Междунар. науч.-практ. конф., Гомель, 26-27 ноября 2015
The importance of the weak: Interaction modifiers in artificial spin ices
The modification of geometry and interactions in two-dimensional magnetic
nanosystems has enabled a range of studies addressing the magnetic order,
collective low-energy dynamics, and emergent magnetic properties, in e.g.
artificial spin ice structures. The common denominator of all these
investigations is the use of Ising-like mesospins as building blocks, in the
form of elongated magnetic islands. Here we introduce a new approach: single
interaction modifiers, using slave-mesospins in the form of discs, within which
the mesospin is free to rotate in the disc plane. We show that by placing these
on the vertices of square artificial spin ice arrays and varying their
diameter, it is possible to tailor the strength and the ratio of the
interaction energies. We demonstrate the existence of degenerate ice-rule
obeying states in square artificial spin ice structures, enabling the
exploration of thermal dynamics in a spin liquid manifold. Furthermore, we even
observe the emergence of flux lattices on larger length-scales, when the energy
landscape of the vertices is reversed. The work highlights the potential of a
design strategy for two-dimensional magnetic nano-architectures, through which
mixed dimensionality of mesospins can be used to promote thermally emergent
mesoscale magnetic states.Comment: 17 pages, including methods, 4 figures. Supplementary information
contains 16 pages and 15 figure