scholarly journals Coherent light scattering by nanostructured collagen arrays in the caruncles of the malagasy asities (Eurylaimidae: aves)

1999 ◽  
Vol 202 (24) ◽  
pp. 3507-3522 ◽  
Author(s):  
R.O. Prum ◽  
R. Torres ◽  
C. Kovach ◽  
S. Williamson ◽  
S.M. Goodman
Keyword(s):  
Power Spectra ◽  
Coherent Scattering ◽  
Reflectance Spectra ◽  
Two Dimensional ◽  
Collagen Fibres ◽  
Discrete Fourier Analysis ◽  
Near Ultraviolet ◽  
Avian Communication ◽  
Dark Blue ◽  
Prominent Peak

We investigated the anatomy, nanostructure and biophysics of the structurally coloured facial caruncles of three species in a clade of birds endemic to Madagascar (Philepittinae, Eurylaimidae: Aves). Caruncle tissues of all species had reflectance spectra with prominent, peak hues between 403 and 528 nm. Dark blue Neodrepanis tissues had substantial reflectance in the near ultraviolet (320–400 nm), which is visible to birds but not to humans, providing the first evidence of ultraviolet skin colours in birds and the first indications of the possible function of ultraviolet skin colours in avian communication. These structural colours are produced by coherent scattering from arrays of parallel collagen fibres in the dermis. Tissues of Philepitta castanea were organized into hexagonal, crystal-like arrays, whereas Neodrepanis tissues were quasiordered. Predictions of the peak hues of reflectance (λ (max)) using Bragg's law were relatively accurate, but Bragg's law requires physical assumptions that are obviously violated by these structures. A two-dimensional discrete Fourier analysis of the spatial variation in refractive index within the tissues documented that all the tissues are substantially nanostructured at the appropriate spatial scale to scatter visible light coherently. Predicted reflectance spectra based on the two-dimensional Fourier power spectra are relatively accurate at predicting the hue and shape of the reflectance spectra of the tissues. These results confirm that the nanostructure of the collagen arrays determines the colours that are coherently scattered by these tissues. The evolution of the anatomy and nanostructure of asity caruncles is discussed.

scholarly journals Coherent Scattering of Ultraviolet Light by Avian Feather Barbs

The Auk ◽  
2003 ◽  
Vol 120 (1) ◽  
pp. 163-170 ◽  
Author(s):  
Richard O. Prum ◽  
Staffan Andersson ◽  
Rodolfo H. Torres
Keyword(s):  
Rayleigh Scattering ◽  
Power Spectra ◽  
Coherent Scattering ◽  
Mie Scattering ◽  
Two Dimensional ◽  
Structural Colors ◽  
Physical Mechanisms ◽  
Spatial Frequencies ◽  
Transmission Electron ◽  
Alternative Hypotheses

Abstract Ultraviolet (UV) structural colors of avian feathers are produced by the spongy medullary keratin of feather barbs, but various physical mechanisms have been hypothesized to produce those colors, including Rayleigh scattering, Mie scattering, and coherent scattering (i.e. constructive interference). We used two-dimensional Fourier analysis of transmission electron micrographs of the medullary keratin of UV-colored feather barbs of the Blue Whistling Thrush (Myiophonus caeruleus) (Turdidae) to test the alternative hypotheses for production of those UV structural hues. The two-dimensional Fourier power spectra of the tissue reveal a ring-like distribution of peak periodicity at intermediate spatial frequencies (∼0.078 nm −1), which documents that Myiophonus medullary keratin is substantially nanostructured and equivalently ordered in all directions. This nanoscale spatial order falsifies a basic assumption of both the Rayleigh scattering and Mie scattering. A predicted reflectance spectrum based on the Fourier power spectra matches hue of the measured reflectance spectra of the feathers (345 nm). These results demonstrate that the Myiophonus medullary keratin is ordered at the appropriately nanoscale to produce the observed UV hues by coherent scattering.

scholarly journals Colour-producing β-keratin nanofibres in blue penguin ( Eudyptula minor ) feathers

2011 ◽  
Vol 7 (4) ◽  
pp. 543-546 ◽  
Author(s):  
Liliana D'Alba ◽  
Vinodkumar Saranathan ◽  
Julia A. Clarke ◽  
Jakob A. Vinther ◽  
Richard O. Prum ◽  
...  
Keyword(s):  
Self Assembly ◽  
Coherent Scattering ◽  
Two Dimensional ◽  
Collagen Fibres ◽  
Separation Processes ◽  
New Class ◽  
X Ray Scattering ◽  
Absorption Of Light ◽  
Physical Interactions ◽  
Living Organisms

The colours of living organisms are produced by the differential absorption of light by pigments (e.g. carotenoids, melanins) and/or by the physical interactions of light with biological nanostructures, referred to as structural colours. Only two fundamental morphologies of non-iridescent nanostructures are known in feathers, and recent work has proposed that they self-assemble by intracellular phase separation processes. Here, we report a new biophotonic nanostructure in the non-iridescent blue feather barbs of blue penguins ( Eudyptula minor ) composed of parallel β-keratin nanofibres organized into densely packed bundles. Synchrotron small angle X-ray scattering and two-dimensional Fourier analysis of electron micrographs of the barb nanostructure revealed short-range order in the organization of fibres at the appropriate size scale needed to produce the observed colour by coherent scattering. These two-dimensional quasi-ordered penguin nanostructures are convergent with similar arrays of parallel collagen fibres in avian and mammalian skin, but constitute a novel morphology for feathers. The identification of a new class of β-keratin nanostructures adds significantly to the known mechanisms of colour production in birds and suggests additional complexity in their self-assembly.

Emission characteristics of near-ultraviolet two-dimensional organic photonic crystal lasers

2008 ◽  
Vol 50 (2) ◽  
pp. 382-385
Author(s):  
Ying Dong ◽  
Junfeng Song ◽  
Chuanhui Cheng ◽  
Wenhai Jiang ◽  
Shukun Yu ◽  
...  
Keyword(s):  
Photonic Crystal ◽  
Emission Characteristics ◽  
Two Dimensional ◽  
Near Ultraviolet

scholarly journals Simulation of earthquakes with cellular automata

1998 ◽  
Vol 2 (4) ◽  
pp. 267-279 ◽  
Author(s):  
P. G. Akishin ◽  
M. V. Altaisky ◽  
I. Antoniou ◽  
A. D. Budnik ◽  
V. V. Ivanov
Keyword(s):  
Cellular Automata ◽  
Analytical Method ◽  
Power Spectra ◽  
Two Dimensions ◽  
Seismic Events ◽  
Two Dimensional ◽  
Stress Release ◽  
Event Energy

The relation between cellular automata (CA) models of earthquakes and the Burridge–Knopoff (BK) model is studied. It is shown that the CA proposed by P. Bak and C. Tang,although they have rather realistic power spectra, do not correspond to the BK model. We present a modification of the CA which establishes the correspondence with the BK model.An analytical method of studying the evolution of the BK-like CA is proposed. By this method a functional quadratic in stress release, which can be regarded as an analog of the event energy, is constructed. The distribution of seismic events with respect to this “energy” shows rather realistic behavior, even in two dimensions. Special attention is paid to two-dimensional automata; the physical restrictions on compression and shear stiffnesses are imposed.

scholarly journals Two- and three-dimensional numerical simulations of the transition to oscillatory convection in low-Prandtl-number fluids

1998 ◽  
Vol 374 ◽  
pp. 145-171 ◽  
Author(s):  
DANIEL HENRY ◽  
MARC BUFFAT
Keyword(s):  
Prandtl Number ◽  
Relative Concentration ◽  
Three Dimensional ◽  
Power Spectra ◽  
Hadley Circulation ◽  
Time Dependent ◽  
Two Dimensional ◽  
General Behaviour ◽  
Shallow Cavities ◽  
Dependent Flow

The convective flows which arise in shallow cavities filled with low-Prandtl-number fluids when subjected to a horizontal temperature gradient are studied numerically with a finite element method. Attention is focused on a rigid cavity with dimensions 4×2×1, for which experimental data are available. The three-dimensional results indicate that, after a relative concentration of the initial Hadley circulation, a transition to time-dependent flows occurs in the form of a roll oscillation with a purely dynamical origin. This transition corresponds to a Hopf bifurcation with a breaking of symmetry that gives some specific properties to the time evolution of the flow: these properties are shown to be the result of the general behaviour of the dynamical systems. Calculations performed in the case of mercury compare well with the experiments with similar power spectra of the temperature, and this validates the analysis of the nature of the global flow performed in the limiting case Pr=0. All these results are discussed with respect to the linear and nonlinear analyses and to other computational experiments. Numerical results obtained in the corresponding two-dimensional situation give a different transition to the time-dependent flow: it is shown that in the three-dimensional cavity this type of two-dimensional transition is less probable than the observed transition with breaking of symmetry.

scholarly journals Two-Dimensional Near Ultraviolet (2DNUV) Spectroscopic Probe of Structural-Dependent Exciton Dynamics in a Protein

2015 ◽  
Vol 119 (4) ◽  
pp. 1314-1322 ◽  
Author(s):  
Jun Li ◽  
Mingsen Deng ◽  
Dmitri V. Voronine ◽  
Shaul Mukamel ◽  
Jun Jiang
Keyword(s):  
Two Dimensional ◽  
Exciton Dynamics ◽  
Near Ultraviolet ◽  
Spectroscopic Probe

Polarization-dependent difference of the power spectra from two-dimensional random media with different shapes

2009 ◽  
Vol 54 (18) ◽  
pp. 3215-3219 ◽  
Author(s):  
Hai Liu ◽  
JinSong Liu ◽  
JianTao Lü ◽  
KeJia Wang
Keyword(s):  
Random Media ◽  
Power Spectra ◽  
Two Dimensional ◽  
Different Shapes

scholarly journals Subspecific and Temporal Variation in the Structurally Based Coloration of the Ultramarine Grosbeak

The Condor ◽  
2007 ◽  
Vol 109 (1) ◽  
pp. 187-192 ◽  
Author(s):  
Ana S. Barreira ◽  
Dario A. Lijtmaer ◽  
Stephen C. Lougheed ◽  
Pablo L. Tubaro
Keyword(s):  
Temporal Variation ◽  
Gradual Increase ◽  
Color Variation ◽  
Reflectance Spectra ◽  
Plumage Coloration ◽  
Sexual Dichromatism ◽  
Ambient Light ◽  
Uv Reflectance ◽  
Color Differences ◽  
Dark Blue

Abstract Abstract Ultramarine Grosbeaks (Cyanocompsa brissonii) possess a striking sexual dichromatism, with males dark blue and females brown. There are two subspecies in Argentina: the larger-bodied C. b. argentina, which is common in shrubs and semiopen areas, and the smaller C. b. sterea that inhabits forests. We measured reflectance spectra of six plumage patches from study skins to evaluate the possibility of color differences between males of each subspecies and temporal variation in plumage coloration. We found differences between subspecies in color brightness, hue, saturation, and UV chroma in the plumage patches of more conspicuous coloration, which could be related to ambient light differences between the environments that each subspecies inhabits. We also documented temporal color variation in some plumage patches, in particular a gradual decrease of UV reflectance and a gradual increase in hue after molting, possibly attributable to feather wear.

scholarly journals Recent Observations of High-Degree Solar p-Mode Oscillations at the Kitt Peak National Observatory

1983 ◽  
Vol 66 ◽  
pp. 111-111
Author(s):  
Edward J. Rhodes ◽  
John W. Harvey ◽  
Thomas L. Duvall
Keyword(s):  
Solar Atmosphere ◽  
Rotational Velocity ◽  
Solar Spectrum ◽  
Power Spectra ◽  
Solar Chromosphere ◽  
Harmonic Waves ◽  
Two Dimensional ◽  
National Observatory ◽  
Radial Gradient ◽  
High Degree

AbstractA brief summary is given of a program which is currently being carried out with the McMath telescope of the Kitt Peak National Observatory in order to study high-degree (l ≳ 150) solar p-mode oscillations. This program uses a 244 x 248 pixel CID camera and the main spectrograph of the McMath telescope to obtain velocity-time maps of the oscillations which can be converted into two-dimensional (kh – ω) power spectra of the oscillations. Several different regions of the solar spectrum have been used in order to study the oscillations at different elevations in the solar atmosphere. The program concentrates on eastward- and westward-propagating sectoral harmonic waves so that measurements can be made of the absolute rotational velocities of the solar photospheric and shallow sub-photospheric layers. Some preliminary results from this program are now available. First, we have been unable to confirm the existence of a radial gradient in the equatorial rotational velocity as was previously suggested. Second, we have indeed been able to confirm the presence of p-mode waves in the solar chromosphere as was first suggested by Rhodes et al. (1977). Third, we have been able to demonstrate differences in photospheric and chromospheric power spectra.

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