Visual perception of colourful petals reminds us of classical fragments

Colour has attracted the interest and attention of many of the most gifted intellects of all time. Ideas of early thinkers were not -and could not have been- grasped on a scientific level without knowledge of a kind that lay far in the future. One character that is being considered is the colourful surfaces of living tissues, which could hardly have been visualized without a corresponding reference to the microscale parallel. Millions of years before man made manipulated synthetic structures, biological systems were using nanoscale architecture to produce striking optical effects. Here we show the microsculpture of the adaxial surface of flower petals from the asphodel, the Stork's-bill and the common poppy by using optical, scanning electron and atomic force microscopy. Microsculpture has been studied in leaves and pollen grains of higher plants. To the best of our knowledge imaging and nanoscale morphometry of petals has not been reported hitherto. Our findings on flower petals' microsculpture may be linked with aspects on colour revealed from ancient literature

Nanosecond and femtosecond ablation of La0.6Ca0.4CoO3: a comparison between plume dynamics and composition of the films

Thin films of La0.6Ca0.4CoO3 were grown by pulsed laser ablation with nanosecond and femtosecond pulses. The films deposited with femtosecond pulses (248nm, 500fs pulse duration) exhibit a higher surface roughness and deficiency in the cobalt content compared to the films deposited with nanosecond pulses (248nm, 20ns pulse duration). The origin of these pronounced differences between the films grown by ns and fs ablation has been studied in detail by time-resolved optical emission spectroscopy and imaging. The plumes generated by nanosecond and femtosecond ablation were analyzed in vacuum and in a background pressure of 60 Pa of oxygen. The ns-induced plume in vacuum exhibits a spherical shape, while for femtosecond ablation the plume is more elongated along the expansion direction, but with similar velocities for ns and fs laser ablation. In the case of ablation in the background gas similar velocities of the plume species are observed for fs and ns laser ablation. The different film compositions are therefore not related to different kinetic energies and different distributions of various species in the plasma plume which has been identified as the origin of the deficiency of species for other material

Quantitative analysis of several random lasers

We prescribe the minimal set of experimental data and parameters that should be reported for random-laser experiments and models. This prescript allows for a quantitative comparison between different experiments, and for a criterion whether a model predicts the outcome of an experiment correctly. In none of more than 150 papers on random lasers that we found these requirements were fulfilled. We have nevertheless been able to analyze a number of published experimental results and recent experiments of our own. Using our method we determined that the most intriguing property of the random laser (spikes) is in fact remarkably similar for different random lasers.Comment: 3 pages, 1 figur

Photoluminescence of hexagonal boron nitride: effect of surface oxidation under UV-laser irradiation

We report on the UV laser induced fluorescence of hexagonal boron nitride (h-BN) following nanosecond laser irradiation of the surface under vacuum and in different environments of nitrogen gas and ambient air. The observed fluorescence bands are tentatively ascribed to impurity and mono (VN), or multiple (m-VN with m = 2 or 3) nitrogen vacancies. A structured fluorescence band between 300 nm and 350 nm is assigned to impurity-band transition and its complex lineshape is attributed to phonon replicas. An additional band at 340 nm, assigned to VN vacancies on surface, is observed under vacuum and quenched by adsorbed molecular oxygen. UV-irradiation of h-BN under vacuum results in a broad asymmetric fluorescence at ~400 nm assigned to m-VN vacancies; further irradiation breaks more B-N bonds enriching the surface with elemental boron. However, no boron deposit appears under irradiation of samples in ambient atmosphere. This effect is explained by oxygen healing of radiation-induced surface defects. Formation of the oxide layer prevents B-N dissociation and preserves the bulk sample stoichiometry

Advances in multispectral and hyperspectral imaging for archaeology and art conservation

Multispectral imaging has been applied to the field of art conservation and art history since the early 1990s. It is attractive as a noninvasive imaging technique because it is fast and hence capable of imaging large areas of an object giving both spatial and spectral information. This paper gives an overview of the different instrumental designs, image processing techniques and various applications of multispectral and hyperspectral imaging to art conservation, art history and archaeology. Recent advances in the development of remote and versatile multispectral and hyperspectral imaging as well as techniques in pigment identification will be presented. Future prospects including combination of spectral imaging with other noninvasive imaging and analytical techniques will be discussed

Open source circuit simulation tools for RF compact semiconductor device modelling

MOS-AK is a European, independent compact modelling forum created by a group of engineers, researchers and compact modelling enthusiasts to promote advanced compact modelling techniques and model standardization using high level behavioral modelling languages such as VHDL-AMS and Verilog-A. This invited paper summarizes recent MOS-AK open source compact model standardization activities and presents advanced topics in MOSEFT modelling, focusing in particular on analogue/RF applications. The paper discusses links between compact models and design methodologies, finally introducing elements of compact model standardization. The open source CAD tools: Qucs, QucsStudio and ngspice all support Verilog-A as a hardware description language for compact model standardization. Latter sections of this paper describe a Verilog-A implementation of the EKV3 MOS transistor model. Additionally, the simulated RF model performance is evaluated and compared with experimental results for 90nm CMOS technology

Elemental mapping of Mg/Ca intensity ratios in marine mollusc shells using laser-induced breakdown spectroscopy

Records of past environmental conditions in shell carbonate are usually derived from compositional analysis (i.e. trace elements, stable oxygen, carbon, and nitrogen isotopes) performed along the direction of the shell’s growth and thus through time. However, compositional variations within isochronous parts of the shell can distort the environmental record and are difficult to assess without extensively mapping the whole shell. Here we apply Laser Induced Breakdown Spectroscopy (LIBS) to efficiently map the elemental change throughout the growth increments of three mollusc shells (Conomurex fasciatus, Ostrea edulis, Anomalocardia flexuosa). We employ an automated LIBS setup to map the Mg/Ca composition of whole shell sections with over 2,000 data points per hour. By assessing the spatial variability of Mg/Ca intensity ratios this method has the potential to mitigate distorted results while increasing the resolution of derived palaeoenvironmental information