Potential Weight Benefits of IM7/8552 Hybrid Thin-Ply Composites for Aircraft Structures

Composite materials have increasingly been used for aerospace applications due to improved performance and reduced weight compared to their metallic counterparts. Inclusion of thin-ply material, plies with cured thickness half or less than standard-ply composites, have potential to improve performance and reduce structural weight further. The effect of thin-ply material on the weight of aircraft structure was investigated by examining wing cover weight reduction. To minimize the effects on manufacturing due to using thin plies, hybrid laminates were examined that used thin 45-degree plies to replace their standard-ply counterparts in laminates. Compression after impact (CAI) tests were conducted to examine the possible weight savings that could be gained by increasing the design allowables that were used to size the wing upper cover of a semi-span test article. A large increase in CAI strength was observed for quasi-isotropic hybrid laminates, whereas less improvement was seen for hard hybrid laminates such as found in the wing cover. For laminates design by CAI strength, weight savings of about 13% were found using the hybrid hard laminates compared to the standard-ply laminates. Whether similar weight savings could be expected for structure sized using tension after impact allowables will have to be investigated further. Notched specimens were tested to examine possible weight savings using hybrid laminates in regions that are sized using discrete source damage requirements. As expected, the hybrid laminate had marginal improvements over the standard-ply laminate for compression with a notch present. The hybrid laminate, however, exhibited about 20% lower strength than the standard-ply laminate counterpart for tension with a notch. The failure mode of the hybrid specimens was a brittle, self-similar crack, which differs from the standard-ply specimens that failed by significant amounts of delamination and fiber splitting. In light of the apparent reduction in notched tensile strength, additional investigation is required to assess the use of hybrid laminates for areas containing discrete source damage, and their effect on weight of such regions

Generalized Stable Multivariate Distribution and Anisotropic Dilations

After having closely re-examined the notion of a L\'evy's stable vector, it is shown that the notion of a stable multivariate distribution is more general than previously defined. Indeed, a more intrinsic vector definition is obtained with the help of non isotropic dilations and a related notion of generalized scale. In this framework, the components of a stable vector may not only have distinct Levy's stability indices $\alpha$'s, but the latter may depend on its norm. Indeed, we demonstrate that the Levy's stability index of a vector rather correspond to a linear application than to a scalar, and we show that the former should satisfy a simple spectral property

A Complexity View of Rainfall

We show that rain events are analogous to a variety of nonequilibrium relaxation processes in Nature such as earthquakes and avalanches. Analysis of high-resolution rain data reveals that power laws describe the number of rain events versus size and number of droughts versus duration. In addition, the accumulated water column displays scale-less fluctuations. These statistical properties are the fingerprints of a self-organized critical process and may serve as a benchmark for models of precipitation and atmospheric processes.Comment: 4 pages, 5 figure

The Breeding of Purebred Hogs and the Building Up of a Trade

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A semi-analytical method for calculating rates of new sulfate aerosol formation from the gas phase

International audienceThe formation of new aerosol from the gas phase is commonly represented in atmospheric modeling with parameterizations of the steady state nucleation rate. Present parameterizations are based on classical nucleation theory or on nucleation rates calculated with a numerical aerosol model. These parameterizations reproduce aerosol nucleation rates calculated with a numerical aerosol model only imprecisely. Additional errors can arise when the nucleation rate is used as a surrogate for the production rate of particles of a given size. We discuss these errors and present a method which allows a more precise calculation of steady state sulfate aerosol formation rates. The method is based on the semi-analytical solution of an aerosol system in steady state and on parameterized rate coefficients for H2SO4 uptake and loss by sulfate aerosol particles, calculated from laboratory and theoretical thermodynamic data

Revolutionary Mahdism and resistance to early colonial rule in Northern Nigeria and Niger

African Studies Seminar series. Paper presented May, 1979In early 1906 the French, Germans and British faced a series of challenges to their continued subjugation of the Sokoto Caliphate. An uprising which began in December 1905 in French Niger in the region of Dallol Mawri and Dallol Bosso, 160 km south of Niamey and 250 km west of Sokoto, spread north up the Niger River valley past Niamey through Zaberma and east across the boundary with British Northern Nigeria to the vicinity of Sokoto itself. Several British and French officials were killed. Another rising erupted in German Adamawa, far to the east, and the call for revolt was heard in Bauchi, Gombe, Kontagora and other parts of recently-conquered British territory. As these events demonstrated, resistance to colonial rule did not respect the new boundaries which European imperial decisions had imposed on the Sokoto Caliphate. In the west - around Sokoto and in the Niger valley - resistance against the French and British was reasonably, well coordinated, considering the difficulty of communication. The eastern uprising against the Germans does not appear to have been connected with the western movement and indeed had different roots than its western counterpart. Nonetheless, the risings of 1906 were all Mahdist, advocated the expulsion of the Europeans, and called for the overthrow of those Caliphate officials who did not join the Mahdist cause. The British, French and Germans were successful in crushing these revolts, but the dangers presented by a coordinated revolt were real enough. (2) Not until these revolts were crushed can it be claimed that colonial rule had been firmly established

Multifractal earth topography

International audienceThis paper shows how modern ideas of scaling can be used to model topography with various morphologies and also to accurately characterize topography over wide ranges of scales. Our argument is divided in two parts. We first survey the main topographic models and show that they are based on convolutions of basic structures (singularities) with noises. Focusing on models with large numbers of degrees of freedom (fractional Brownian motion (fBm), fractional Levy motion (fLm), multifractal fractionally integrated flux (FIF) model), we show that they are distinguished by the type of underlying noise. In addition, realistic models require anisotropic singularities; we show how to generalize the basic isotropic (self-similar) models to anisotropic ones. Using numerical simulations, we display the subtle interplay between statistics, singularity structure and resulting topographic morphology. We show how the existence of anisotropic singularities with highly variable statistics can lead to unwarranted conclusions about scale breaking. We then analyze topographic transects from four Digital Elevation Models (DEMs) which collectively span scales from planetary down to 50 cm (4 orders of magnitude larger than in previous studies) and contain more than 2×108 pixels (a hundred times more data than in previous studies). We use power spectra and multiscaling analysis tools to study the global properties of topography. We show that the isotropic scaling for moments of order =2 holds to within ±45% down to scales ˜40 m. We also show that the multifractal FIF is easily compatible with the data, while the monofractal fBm and fLm are not. We estimate the universal parameters (a, C1) characterizing the underlying FIF noise to be (1.79, 0.12), where a is the degree of multifractality (0=a=2, 0 means monofractal) and C1 is the degree of sparseness of the surface (0=C1, 0 means space filling). In the same way, we investigate the variation of multifractal parameters between continents, oceans and continental margins. Our analyses show that no significant variation is found for (a, C1) and that the third parameter H, which is a degree of smoothing (higher H means smoother), is variable: our estimates are H=0.46, 0.66, 0.77 for bathymetry, continents and continental margins. An application we developped here is to use (a, C1) values to correct standard spectra of DEMs for multifractal resolution effects

Characterization of IM7/8552 Thin-Ply and Hybrid Thin-Ply Composites

Composite materials have increasingly been used for aerospace applications due to improved performance and reduced weight compared to their metallic counterparts. Inclusion of thin-ply material, plies with cured thickness half or less than standard composites, have potential to improve performance and reduce structural weight. Limited characterization of thin-ply IM7/8552 material in 30 and 70 grams per square meter fiber areal weights has been carried out using a series of selected American Society for Testing and Materials (ASTM) tests. Tests included unnotched tension, unnotched compression, v-notched rail shear, open-hole tension, and open-hole compression. Unidirectional, cross-ply, quasiisotropic and hybrid hard laminates were included in the study, and were compared to standard-ply laminates. Properties compared include fiber volume, laminate moduli, and failure strength, with failure modes also being examined. The thin-ply specimens exhibited similar or superior performance to standard ply laminates in many of the cases compared. Improvements in strength for laminates containing thin-ply material were seen for unidirectional laminates under unnotched tension, quasi-isotropic laminates under unnotched tension and compression, and hard laminates under open hole tension. Additional investigation is required to determine appropriate ply stacking rules for hybrids of thin and standard plies to avoid undesirable failure modes such as axial splitting. However, the observed performance improvements demonstrated by the conducted ASTM tests of hybrid thin-ply hard laminates could have benefits for improved structural weight in aircraft

Mars' atmosphere: The sister planet, our statistical twin

Satellite-based Martian reanalyses have allowed unprecedented comparisons between our atmosphere and that of our sister planet, underlining various similarities and differences in their respective dynamics. Yet by focusing on large scale structures and deterministic mechanisms they have improved our understanding of the dynamics only over fairly narrow ranges of (near) planetary scales. However, the Reynolds numbers of the flows on both planets are larger than 1011 and dissipation only occurs at centimetric (Mars) or millimetric scales (Earth) so that over most of their scale ranges, the dynamics are fully turbulent. In this paper, we therefore examine the high-level, statistical, turbulent laws for the temperature, horizontal wind, and surface pressure, finding that Earth and Mars have virtually identical statistical exponents so that their statistics are very similar over wide ranges. Therefore, it would seem that with the exception of certain aspects of the largest scales (such as the role of dust in atmospheric heating on Mars, or of water in its various phases on Earth), that the nonlinear dynamics are very similar. We argue that this is a prediction of the classical laws of turbulence when extended to planetary scales and that it supports our use of turbulent laws on both planetary atmospheres

A decadal perspective on north water microbial eukaryotes as Arctic Ocean sentinels

The North Water region, between Greenland and Ellesmere Island, with high populations of marine birds and mammals, is an Arctic icon. Due to climate related changes, seasonal patterns in water column primary production are changing but the implications for the planktonic microbial eukaryote communities that support the ecosystem are unknown. Here we report microbial community phenology in samples collected over 12 years (2005–2018) from July to October and analysed using high throughput 18S rRNA V4 amplicon sequencing. Community composition was tied to seasonality with summer communities more variable than distinct October communities. In summer, sentinel pan- Arctic species, including a diatom in the Chaetoceros socialis-gelidus complex and the picochlorophyte Micromonas polaris dominated phytoplankton and were summer specialists. In autumn, uncultured undescribed open water dinoflagellates were favored, and their ubiquity suggests they are sentinels of arctic autumn conditions. Despite the input of nutrients into surface waters, autumn chlorophyll concentrations remained low, refuting projected scenarios that longer ice-free seasons are synonymous with high autumn production and a diatom dominated bloom. Overall, the summer sentinel microbial taxa are persisting, and a subset oceanic dinoflagellate should be monitored for possible ecosystem shifts as later autumn ice formation becomes prevalent elsewhere