Double scattering of light from biophotonic nanostructures with short-range order

We investigate the physical mechanism for color production by isotropic nanostructures with short-range order in bird feather barbs. While the primary peak in optical scattering spectra results from constructive interference of singly-scattered light, many species exhibit secondary peaks with distinct characteristic. Our experimental and numerical studies show that these secondary peaks result from double scattering of light by the correlated structures. Without an analog in periodic or random structures, such a phenomenon is unique for short-range ordered structures, and has been widely used by nature for non-iridescent structural coloration.Comment: 10 pages, 4 figure

Net exchange reformulation of radiative transfer in the CO2 15um band on Mars

International audienceThe Net Exchange Formulation (NEF) is an alternative to the usual radiative transfer formulation. It was proposed by two authors in 1967, but until now, this formulation has been used only in a very few cases for atmospheric studies. The aim of this paper is to present the NEF and its main advantages, and to illustrate them in the case of planet Mars. In the NEF, the radiative fluxes are no more considered. The basic variables are the net exchange rates between each pair of atmospheric layers i,j. NEF offers a meaningful matrix representation of radiative exchanges, allows to quantify the dominant contributions to the local heating rates and provides a general framework to develop approximations satisfying reciprocity of radiative transfer as well as first and second principle of thermodynamic. This may be very useful to develop fast radiative codes for GCMs. We present a radiative code developed along those lines for a GCM of Mars. We show that computing the most important optical exchange factors at each time step and the others exchange factors only a few times a day strongly reduces the CPU time without any significant precision lost. With this solution, the CPU time increases proportionally to the number N of the vertical layers and no more proportionally to its square N^2. We also investigate some specific points such as numerical instabilities that may appear in the high atmosphere and errors that may be introduced if inappropriate treatments are performed when reflection at the surface occurs

Institutional Response to Crisis

The Institutional Response to Crisis panel focuses on analyzing and understanding institutions and the crises they might face, more specifically the limits and opportunities for preparing for a crisis, responding to crises, and the long-term consequences of crises. The panelists provide both theoretical analyses and specific, personal experiences to discuss these points. As panel moderator Noah Pickus, the director of the Kenan Institute for Ethics at Duke University stated in his opening: Crises are no rare thing in human history and it seems as if of late we turn around everyday and there\u27s another one that stares us in the face. Questions/themes/discussion topics Should institutions respond to crises? How do institutions respond to crises? Response to crisis as a springboard for long term change within an institution Leadership opportunities within a crisi

Net-Exchange parameterization of infrared radiative transfers in Venus' atmosphere

International audienceThermal radiation within Venus atmosphere is analyzed in close details. Prominent features are identified, which are then used to design a parameterization (a highly simplified and yet accurate enough model) to be used in General Circulation Models. The analysis is based on a net exchange formulation, using a set of gaseous and cloud optical data chosen among available referenced data. The accuracy of the proposed parameterization methodology is controlled against Monte Carlo simulations, assuming that the optical data are exact. Then, the accuracy level corresponding to our present optical data choice is discussed by comparison with available observations, concentrating on the most unknown aspects of Venus thermal radiation, namely the deep atmosphere opacity and the cloud composition and structure

Independent polarisation control of multiple optical traps

We present a system which uses a single spatial light modulator to control the spin angular momentum of multiple optical traps. These traps may be independently controlled both in terms of spatial location and in terms of their spin angular momentum content. The system relies on a spatial light modulator used in a "split-screen" configuration to generate beams of orthogonal polarisation states which are subsequently combined at a polarising beam splitter. Defining the phase difference between the beams with the spatial light modulator enables control of the polarisation state of the light. We demonstrate the functionality of the system by controlling the rotation and orientation of birefringent vaterite crystals within holographic optical tweezers

New generation of climate models track recent unprecedented changes in Earth's radiation budget observed by CERES

We compare top‐of‐atmosphere (TOA) radiative fluxes observed by the Clouds and the Earth's Radiant Energy System (CERES) and simulated by seven general circulation models forced with observed sea‐surface temperature (SST) and sea‐ice boundary conditions. In response to increased SSTs along the equator and over the eastern Pacific (EP) following the so‐called global warming “hiatus” of the early 21st century, simulated TOA flux changes are remarkably similar to CERES. Both show outgoing shortwave and longwave TOA flux changes that largely cancel over the west and central tropical Pacific, and large reductions in shortwave flux for EP low‐cloud regions. A model's ability to represent changes in the relationship between global mean net TOA flux and surface temperature depends upon how well it represents shortwave flux changes in low‐cloud regions, with most showing too little sensitivity to EP SST changes, suggesting a “pattern effect” that may be too weak compared to observations

Reconciling atmospheric and oceanic views of the transient climate response to emissions

The Transient Climate Response to Emissions (TCRE), the ratio of surface warming and cumulative carbon emissions, is controlled by a product of thermal and carbon contributions. The carbon contribution involves the airborne fraction and the ratio of ocean saturated and atmospheric carbon inventories, with this ratio controlled by ocean carbonate chemistry. The evolution of the carbon contribution to the TCRE is illustrated in a hierarchy of models: a box model of the atmosphere‐ocean and an Earth system model, both integrated for 1,000 years, and a suite of Earth system models integrated for 140 years. For all models, there is the same generic carbonate chemistry response: An acidifying ocean during emissions leads to a decrease in the ratio of the ocean saturated and atmospheric carbon inventories and the carbon contribution to the TCRE. Hence, ocean carbonate chemistry is important in controlling the magnitude of the TCRE and its evolution in time