Multiple-length-scale elastic instability mimics parametric resonance of nonlinear oscillators

Spatially confined rigid membranes reorganize their morphology in response to the imposed constraints. A crumpled elastic sheet presents a complex pattern of random folds focusing the deformation energy while compressing a membrane resting on a soft foundation creates a regular pattern of sinusoidal wrinkles with a broad distribution of energy. Here, we study the energy distribution for highly confined membranes and show the emergence of a new morphological instability triggered by a period-doubling bifurcation. A periodic self-organized focalization of the deformation energy is observed provided an up-down symmetry breaking, induced by the intrinsic nonlinearity of the elasticity equations, occurs. The physical model, exhibiting an analogy with parametric resonance in nonlinear oscillator, is a new theoretical toolkit to understand the morphology of various confined systems, such as coated materials or living tissues, e.g., wrinkled skin, internal structure of lungs, internal elastica of an artery, brain convolutions or formation of fingerprints. Moreover, it opens the way to new kind of microfabrication design of multiperiodic or chaotic (aperiodic) surface topography via self-organization.Comment: Submitted for publicatio

Understanding the retinal basis of vision across species

The vertebrate retina first evolved some 500 million years ago in ancestral marine chordates. Since then, the eyes of different species have been tuned to best support their unique visuoecological lifestyles. Visual specializations in eye designs, large-scale inhomogeneities across the retinal surface and local circuit motifs mean that all species' retinas are unique. Computational theories, such as the efficient coding hypothesis, have come a long way towards an explanation of the basic features of retinal organization and function; however, they cannot explain the full extent of retinal diversity within and across species. To build a truly general understanding of vertebrate vision and the retina's computational purpose, it is therefore important to more quantitatively relate different species' retinal functions to their specific natural environments and behavioural requirements. Ultimately, the goal of such efforts should be to build up to a more general theory of vision

Synthesis and characterization of perhydro- and perfluoro-tris\it tris(dehydro)benzene triradicals

Matrixisolationstechnik und quantenchemische Rechnungen wurden zur Synthese und Charakterisierung von drei isomeren Tridehydrobenzolen und ihren perfluorierten Derivaten verwendet. Um diese Zielverbindungen zu erzeugen, wurden Monoiod-isophthalsäureanhydride, Triiodbenzole und Trifluor-triiodbenzole als Precursor eingesetzt und ihre Photo- und Thermochemie umfangreich untersucht. Aufgrund ihrer Infrarotsignale konnten 1,2,3-Tridehydrobenzol und Trifluor-1,3,5-tridehydrobenzol erstmalig in ihren $^{2}A_{1}$ - Grundzuständen charakterisiert werden, während für die Bildung des Trifluor-1,2,3-tridehydrobenzols basierend auf zwei seiner IR Absorptionen vorläufig ein $^{2}B_{2}$ - Grundzustand identifiziert wurde. Die Photo- und Thermochemie der Precursor in Edelgasmatrizes und die elektronischen Strukturen der Zielmoleküle werden in dieser Doktorarbeit diskutiert.Matrix isolation techniques and quantum chemical calculations were used in synthesis and characterization of three isomeric tridehydrobenzenes and their perfluoro- analogues. In order to generate these target systems, isomeric monoiodophthalic anhydrides, triiodobenzenes, and trifluoro-triiodobenzenes were considered as possible precursors, and their photo- and thermochemistry were extensively investigated. Based on the infrared signals, 1,2,3- tridehydrobenzene and trifluoro-1,3,5-tridehydrobenzene were characterized for the first time both in their $^{2}A_{1}$ ground states, whereas the formation of trifluoro-1,2,3-tridehydrobenzene was tentatively identified in its $^{2}B_{2}$ ground state based on two of its IR absorptions. The photo- and thermochemistry of the above precursors in rare gas matrices, and electronic structures of the target tridehydrobenzenes are discussed in this doctoral thesis

Thickness dependent anomalous magnetic behavior in pulsed-laser deposited cobalt ferrite thin film

Cobalt ferrite thin films of different thicknesses were pulsed-laser deposited onto a fused quartz substrate held at ambient temperature (RT) by varying deposition time. The samples were ex-situ annealed at 750 degrees C in air for 2 hours. All the films were characterized by X-ray diffraction, Raman spectroscopy and energy dispersive X-ray analysis. The spontaneous magnetization, 4 pi M-S, was found to be 6130 G for the 50 nm thick sample, and this is higher than that for the bulk cobalt ferrite of 5300 G, by 16%. The 4 pi M-S was found to decrease with the increase in film thickness and an overall decrease of 32% was observed, when the film thickness increased from 50 nm to 600 nm. In contrast the films of the same thicknesses, when deposited at substrate temperature of 750 degrees C showed an increase of 4pMS with the increase in film thickness. The thickness dependence of 4 pi M-S in these nanocrystalline thin films has been explained in terms of the cation distribution and the grain size, which are sensitive to the substrate temperature during deposition

Low Temperature Magnetization Studies of Nanocrystalline Zn-Ferrite Thin Films

A study of temperature dependance of magnetization was carried out on nanocrystaline Zn-ferrite thin films deposited using Pulsed Laser Deposition (PLD) at three different substrate temperatures. The temperature dependence of the films deposited at ambient temperature, 350 and 850 degrees C showed marked difference in the temperature dependence of their magnetization. While the sample deposited at 850 degrees C showed predominantly antiferromagntic grains, the one deposited at 350 degrees C showed a ferrimagnetic behavior. The ambient temperature deposited film showed mainly superparamagnetic grains

Study of pulsed laser deposited magnetite thin film

Magnetite thin film with a predominant (1 1 0) texture has been deposited by pulsed laser ablation of α-Fe2O3 target onto fused quartz substrate. Spontaneous magnetization of 5400 G and room temperature electrical resistivity of 4.2×10−3 Ω cm were measured for an annealed magnetite thin film. Zero-field-cooled magnetization data clearly show the Verwey transition near 120 K through an abrupt change, and is consistent with the resistivity measurement.© Elsevie

RF sputter deposited nanocrystalline (110) magnetite thin film from alpha-Fe2O3 target

Nanocrystalline magnetite thin film was prepared on to fused quartz substrate by sputtering at an rf power of 50 W. X-ray diffraction study showed that the sputtered film was (110) oriented. The stoichiometry in the thin film has been confirmed through a variety of characterization techniques. The room temperature spontaneous magnetization value (4 pi M-s) of the film was 5100 G. This is about 85% of the bulk value. The resistivity of the film showed a sharp change around 120 K, indicative of the Verwey transition

Large room temperature magnetization in nanocrystalline zinc ferrite thin films

Zinc ferrite films were deposited on fused quartz substrate at different temperatures using pulsed laser ablation (PLA) and rf sputtering. X-ray diffraction indicated that all the films were single phase ZnFe2O4 with grain growing in the range of 8-80 nm with substrate temperature. The nanocrystalline films were found to be magnetic and the spontaneous magnetization showed a strong dependence on the grain size, dropping sharply for films with larger grains. A PLA thin film deposited in vacuum at 500 degrees C exhibited a room temperature magnetization value of 5560 G. (c) 200