Transmission resonances through aperiodic arrays of subwavelength apertures

Resonantly enhanced light transmission through periodic subwavelength aperture arrays perforated in metallic films has generated significant interest because of potential applications in near-field microscopy, photolithography, displays, and thermal emission. The enhanced transmission was originally explained by a mechanism where surface plasmon polaritons (collective electronic excitations in the metal surface) mediate light transmission through the grating. In this picture, structural periodicity is perceived to be crucial in forming the transmission resonances. Here we demonstrate experimentally that, in contrast to the conventional view, sharp transmission resonances can be obtained from aperiodic aperture arrays. Terahertz transmission resonances are observed from several arrays in metallic films that exhibit unusual local n-fold rotational symmetries, where n = 10, 12, 18, 40 and 120. This is accomplished by using quasicrystals with long-range order, as well as a new type of 'quasicrystal approximates' in which the long-range order is somewhat relaxed. We find that strong transmission resonances also form in these aperiodic structures, at frequencies that closely match the discrete Fourier transform vectors in the aperture array structure factor. The shape of these resonances arises from Fano interference of the discrete resonances and the non-resonant transmission band continuum related to the individual holes. Our approach expands potential design parameters for aperture arrays that are aperiodic but contain discrete Fourier transform vectors, and opens new avenues for optoelectronic devices.     

The structure of napelline and songorine

Zusammenfassung Für das Aconitum-Alkaloid Napellin wurden auf Grund einer eingehenden Diskussion des Tatsachenmaterials die Strukturen XI bzw. X vorgeschlagen. Das Alkaloid Songorin ist das dazugehörige Ring-D-Keton.     

Evaluation of the ability of intact platelets to accumulate acridine organge

Summary A new approach to the evaluation of the uptake of fluorescent, probes by intact, cells is described. Acridine organe (AO) was used because it can be selectively accumulated by serotonin-containing granules of platelets. Analysis of the fluorescence signal allows the estimation of the relative volume of the granules and the equilibrium coefficients for AO transport across the cytoplasm and granule membranes. The following results were obtained for human and rabbit platelets: the relative volumes of the granules were 14±1% and 29±2%, the ratios of intragranular-extracellular probe concentration were 2260±382 and 30,000±5500, and the cytoplasm-extracellular medium concentration ratios were 375±60 and 225±60, respectively.     

Lanthanide contraction and magnetism in the heavy rare earth elements

The heavy rare earth elements crystallize into hexagonally close packed (h.c.p.) structures and share a common outer electronic configuration, differing only in the number of 4f electrons they have. These chemically inert 4f electrons set up localized magnetic moments, which are coupled via an indirect exchange interaction involving the conduction electrons. This leads to the formation of a wide variety of magnetic structures, the periodicities of which are often incommensurate with the underlying crystal lattice. Such incommensurate ordering is associated with a 'webbed' topology of the momentum space surface separating the occupied and unoccupied electron states (the Fermi surface). The shape of this surface-and hence the magnetic structure-for the heavy rare earth elements is known to depend on the ratio of the interplanar spacing c and the interatomic, intraplanar spacing a of the h.c.p. lattice. A theoretical understanding of this problem is, however, far from complete. Here, using gadolinium as a prototype for all the heavy rare earth elements, we generate a unified magnetic phase diagram, which unequivocally links the magnetic structures of the heavy rare earths to their lattice parameters. In addition to verifying the importance of the c/a ratio, we find that the atomic unit cell volume plays a separate, distinct role in determining the magnetic properties: we show that the trend from ferromagnetism to incommensurate ordering as atomic number increases is connected to the concomitant decrease in unit cell volume. This volume decrease occurs because of the so-called lanthanide contraction, where the addition of electrons to the poorly shielding 4f orbitals leads to an increase in effective nuclear charge and, correspondingly, a decrease in ionic radii.     

Multifractality in human heartbeat dynamics.

There is evidence that physiological signals under healthy conditions may have a fractal temporal structure. Here we investigate the possibility that time series generated by certain physiological control systems may be members of a special class of complex processes, termed multifractal, which require a large number of exponents to characterize their scaling properties. We report on evidence for multifractality in a biological dynamical system, the healthy human heartbeat, and show that the multifractal character and nonlinear properties of the healthy heart rate are encoded in the Fourier phases. We uncover a loss of multifractality for a life-threatening condition, congestive heart failure.