Butterfly Optics Exceed the Theoretical Limits of Conventional Apposition Eyes

Optical experiments on butterfly compound eyes show that they have angular sensitivities narrower than expected from conventional apposition eyes. This superior performance is explained by a theoretical model where the cone stalk is considered as a modecoupling device. In this model the Airy diffraction pattern of the corneal facet excites a combination of the two waveguide modes LP01 and LP02. When the two modes propagate through the cone stalk the power of LP02 is transferred to LP01 alone which is supported by the rhabdom. This mechanism produces a higher on-axis sensitivity and a narrower angular sensitivity than conventional apposition optics. Several predictions of the model were confirmed experimentally.

Photoreceptor Evolution: Ancient Siblings Serve Different Tasks

AbstractPhotoreceptor cells of vertebrate eyes are fundamentally different from those of invertebrate eyes. New work on the brain of a ragworm now suggests that ancestral bilaterians possessed both types of photoreceptor cell

Comment on ``Two Time Scales and Violation of the Fluctuation-Dissipation Theorem in a Finite Dimensional Model for Structural Glasses''

In cond-mat/0002074 Ricci-Tersenghi et al. find two linear regimes in the fluctuation-dissipation relation between density-density correlations and associated responses of the Frustrated Ising Lattice Gas. Here we show that this result does not seem to correspond to the equilibrium quantities of the model, by measuring the overlap distribution P(q) of the density and comparing the FDR expected on the ground of the P(q) with the one measured in the off-equilibrium experiments.Comment: RevTeX, 1 page, 2 eps figures, Comment on F. Ricci-Tersenghi et al., Phys. Rev. Lett. 84, 4473 (2000

Aerosol formation over the Boreal forest in Hyytiälä, Finland: monthly frequency and annual cycles ? the roles of air mass characteristics and synoptic scale meteorology

International audienceNew atmospheric particles with diameters of 3?10 nm and their subsequent growth to cloud condensation nucleus have been observed at various places in the European boundary layer. These events have been observed simultaneously within wide geographical areas (over 1000 km) in connection to specific weather systems, the cold air behind cyclones. Here we show that atmospheric aerosol formation (i.e. nucleation and initial growth) is favoured by the outbreak of cold Arctic air over northern Europe. Aerosol formation was about twice as common in Arctic air as in sub-Polar air, and even more so compared to other air masses. The most important general factor favouring aerosol formation in Arctic air and marine air was weaker competing condensational sink (CS) for the precursor gases (less pre-existing aerosols), while high CS prevented aerosol formation in heated sub-Polar air and mid-latitude air. High SO2 levels favoured nucleation in continental air and high UV-B radiation in sub-tropical air. The critical factor that determined if aerosol formation would start on a day with Arctic air was the UV-B radiation. The same applied to sub-Polar air and continental air, while increased SO2 concentration could trigger formation in heated sub-Polar and mid-latitude air, and reduced CS could cause formation in mid-latitude, marine or mixed/transient air. We speculate that strong emissions of volatile organic compounds from the Boreal forest and strong boundary layer dynamics may have caused aerosol formation in sub-Polar air masses and air in transition from a marine to a continental character. The monthly frequency of Arctic air masses and the probability for photo-chemically driven aerosol formation explains the observed annual cycle in monthly particle formation frequency as well as much of the inter annual variability. The same cyclones that transport cold, clean air from the Arctic to Europe will also transport warm polluted air in the other direction, which help cause the Arctic Haze phenomena. The cyclones have a key role for the atmospheric aerosol life cycle in mid to high latitudes. Due to the observed growth to the size of CCN in one to two days, there is a potential feed back from the effects on the CCN population and cloud albedo even within the same weather system, but also on the climatic time scale

Description of superdeformed bands in light N=Z nuclei using the cranked HFB method

Superdeformed states in light $N=Z$ nuclei are studied by means of the self-consistent cranking calculation (i.e., the P + QQ model based on the cranked Hartree-Fock-Bogoliubov method). Analyses are given for two typical cases of superdeformed bands in the $A \simeq 40$ mass region, that is, bands where backbending is absent ($^{40}$Ca) and present ($^{36}$Ar). Investigations are carried out, particularly for the following points: cross-shell excitations in the sd and pf shells; the role of the g$_{9/2}$ and d$_{5/2}$ orbitals; the effect of the nuclear pairing; and the interplay between triaxiality and band termination.Comment: 17 pages, 18 figures, accepted in Phys. Rev.

Timelike self-similar spherically symmetric perfect-fluid models

Einstein's field equations for timelike self-similar spherically symmetric perfect-fluid models are investigated. The field equations are rewritten as a first-order system of autonomous differential equations. Dimensionless variables are chosen in such a way that the number of equations in the coupled system is reduced as far as possible and so that the reduced phase space becomes compact and regular. The system is subsequently analysed qualitatively using the theory of dynamical systems.Comment: 23 pages, 6 eps-figure

Eddy covariance measurements and parameterisation of traffic related particle emissions in an urban environment

International audienceUrban aerosol sources are important due to the health effects of particles and their potential impact on climate. Our aim has been to quantify and parameterise the urban aerosol source number flux F (particles m-2 s-1), in order to help improve how this source is represented in air quality and climate models. We applied an aerosol eddy covariance flux system 118.0 m above the city of Stockholm. This allowed us to measure the aerosol number flux for particles with diameters >11 nm. Upward source fluxes dominated completely over deposition fluxes in the collected dataset. Therefore, the measured fluxes were regarded as a good approximation of the aerosol surface sources. Upward fluxes were parameterised using a traffic activity (TA) database, which is based on traffic intensity measurement. The footprint (area on the surface from which sources and sinks affect flux measurements, located at one point in space) of the eddy system covered road and building construction areas, forests and residential areas, as well as roads with high traffic density and smaller streets. We found pronounced diurnal cycles in the particle flux data, which were well correlated with the diurnal cycles in traffic activities, strongly supporting the conclusion that the major part of the aerosol fluxes was due to traffic emissions. The emission factor for the fleet mix in the measurement area EFfm=1.4±0.1×1014 veh-1 km-1 was deduced. This agrees fairly well with other studies, although this study has an advantage of representing the actual effective emission from a mixed vehicle fleet. Emission from other sources, not traffic related, account for a F0=14±18×106 m-2 s-1. The urban aerosol source flux can then be written as F=EFfmTA+F0. In a second attempt to find a parameterisation, the friction velocity U* normalised with the average friction velocity has been included, F=EF. This parameterisation results in a somewhat reduced emission factor, 1.3×1014 veh-1 km-1. When multiple linear regression have been used, two emission factors are found, one for light duty vehicles EFLDV=0.3±0.3×1014 veh-1 km-1 and one for heavy-duty vehicles, EFHDV=19.8±4.0×1014 veh-1 km-1, and F0=18±16×106 m-2 s-1. The results show that during weekdays ~70?80% of the emissions came from HDV

Scheduling aircraft landings - the static case

This is the publisher version of the article, obtained from the link below.In this paper, we consider the problem of scheduling aircraft (plane) landings at an airport. This problem is one of deciding a landing time for each plane such that each plane lands within a predetermined time window and that separation criteria between the landing of a plane and the landing of all successive planes are respected. We present a mixed-integer zero–one formulation of the problem for the single runway case and extend it to the multiple runway case. We strengthen the linear programming relaxations of these formulations by introducing additional constraints. Throughout, we discuss how our formulations can be used to model a number of issues (choice of objective function, precedence restrictions, restricting the number of landings in a given time period, runway workload balancing) commonly encountered in practice. The problem is solved optimally using linear programming-based tree search. We also present an effective heuristic algorithm for the problem. Computational results for both the heuristic and the optimal algorithm are presented for a number of test problems involving up to 50 planes and four runways.J.E.Beasley. would like to acknowledge the financial support of the Commonwealth Scientific and Industrial Research Organization, Australia