Mission design for LISA Pathfinder

Here we describe the mission design for SMART-2/LISA Pathfinder. The best trade-off between the requirements of a low-disturbance environment and communications distance is found to be a free-insertion Lissajous orbit around the first co-linear Lagrange point of the Sun-Earth system L1, 1.5x 10^6 km from Earth. In order to transfer SMART-2/LISA Pathfinder from a low Earth orbit, where it will be placed by a small launcher, the spacecraft carries out a number of apogee-raise manoeuvres, which ultimatively place it to a parabolic escape trajectory towards L1. The challenges of the design of a small mission are met, fulfilling the very demanding technology demonstration requirements without creating excessive requirements on the launch system or the ground segment.Comment: 7 pages, 6 figures, 5th International LISA Symposium, see http://www.landisoft.de/Markus-Landgra

Deep Learning of Retinal Imaging: A Useful Tool for Coronary Artery Calcium Score Prediction in Diabetic Patients

Retina fundus imaging; Deep learning; Medical imagingImatge del fons de la retina; Aprenentatge profund; Imatges mèdiquesImagen del fondo de la retina; Aprendizaje profundo; Imágenes médicasCardiovascular diseases (CVD) are one of the leading causes of death in the developed countries. Previous studies suggest that retina blood vessels provide relevant information on cardiovascular risk. Retina fundus imaging (RFI) is a cheap medical imaging test that is already regularly performed in diabetic population as screening of diabetic retinopathy (DR). Since diabetes is a major cause of CVD, we wanted to explore the use Deep Learning architectures on RFI as a tool for predicting CV risk in this population. Particularly, we use the coronary artery calcium (CAC) score as a marker, and train a convolutional neural network (CNN) to predict whether it surpasses a certain threshold defined by experts. The preliminary experiments on a reduced set of clinically verified patients show promising accuracies. In addition, we observed that elementary clinical data is positively correlated with the risk of suffering from a CV disease. We found that the results from both informational cues are complementary, and we propose two applications that can benefit from the combination of image analysis and clinical data.This research was funded by “RTI2018-095232-B-C22” grant from the Spanish Ministry of Science, Innovation and Universities (FEDER funds)

Resynthesis: Marker-Based Partial Reconstruction of Elite Genotypes in Clonally-Reproducing Plant Species

We propose a method for marker-based selection of cultivars of clonally-reproducing plant species which keeps the basic genetic architecture of a top-performing cultivar (usually a partly heterozygous genotype), with the addition of some agronomically relevant differences (such as production time, product appearance or quality), providing added value to the product or cultivation process. The method is based on selecting a) two complementary nearly-inbred lines from successive selfing generations (ideally only F2 and F3) of large size, that may generate individuals with most of their genome identical to the original cultivar but being homozygous for either of the two component haplotypes in the rest, and b) individuals with such characteristics already occurring in the F2. Option a) allows for introgressing genes from other individuals in one or both of these nearly-inbred lines. Peach, a woody-perennial, clonally-reproduced species, was chosen as a model for a proof of concept of the Resynthesis process due to its biological characteristics: self-compatibility, compact and genetically well-known genome, low recombination rates and relatively short intergeneration time (3–4 years). From 416 F2 seedlings from cultivar Sweet Dream (SD), we obtained seven individuals with 76–94% identity with SD, and selected five pairs of complementary lines with average homozygosity of the two parents ≥0.70 such that crossing would produce some individuals highly similar to SD. The application of this scheme to other species with more complex genomes or biological features, including its generalization to F1 hybrids, is discussed.info:eu-repo/semantics/publishedVersio

The New Tendencies of Environmental Impact Assessment of Livestock Production: A Road Testing of LEAP/FAO Biodiversity Assessment Guidelines in Pastoral Systems in Uruguay

After the publication of the “long shadow of cattle” report, ruminant production systems have received great pressure for their contributions in greenhouse gases (GHG). However, the environmental effects of human activities are much broader than GHG production and in some cases, there are positive contributions. In order to broaden the environmental perspective and with the encouragement of governments, the private sector and NGOs, LEAP-FAO has developed environmental assessment guidelines for the world\u27s livestock production systems. This paper presents a road-testing of the Biodiversity Assessment Guideline at farm scale for six case studies in pastoral livestock systems in Uruguay. The producers involved correspond to farmers with a mixed livestock system (cows and sheep) with a full cycle and areas ranging between 2000 and 5000 hectares. Three of the farms have production based 100% on natural grasslands, while the other three had 30% of their area with sown pastures. The application of the guide at local level implies the use of the system of pressure, state and response indicators (PSR). The recommendation of the guide in its public review version requires a minimum set of 24 indicators, which can also be divided into several measurable variables. The results obtained in this study showed that the complete set is a reliable tool to evaluate the functioning of the systems in terms of their contribution to biodiversity conservation. However, some are more sensitive than others to evaluate changes depending on the scale. For example, the change in land use due to planting of forage crops clearly affects birds and arthropods such as spiders; though, due to scale of habitat use is less clear the global effect in bird population. The state indicators related to richness and diversity of species from different taxonomic groups is very relevant but result the more expensive issue in the assessment. Global indicators as the Ecosystem Integrity Index (EII) show a consistent effect of intensification but the connectivity in the actual percentages of natural grassland substitution is still good

Measuring the mixing efficiency in a simple model of stirring:some analytical results and a quantitative study via Frequency Map Analysis

We prove the existence of invariant curves for a $T$--periodic Hamiltonian system which models a fluid stirring in a cylindrical tank, when $T$ is small and the assigned stirring protocol is piecewise constant. Furthermore, using the Numerical Analysis of the Fundamental Frequency of Laskar, we investigate numerically the break down of invariant curves as $T$ increases and we give a quantitative estimate of the efficiency of the mixing.Comment: 10 figure

Global bifurcations to subcritical magnetorotational dynamo action in Keplerian shear flow

Magnetorotational dynamo action in Keplerian shear flow is a three-dimensional, non-linear magnetohydrodynamic process whose study is relevant to the understanding of accretion processes and magnetic field generation in astrophysics. Transition to this form of dynamo action is subcritical and shares many characteristics of transition to turbulence in non-rotating hydrodynamic shear flows. This suggests that these different fluid systems become active through similar generic bifurcation mechanisms, which in both cases have eluded detailed understanding so far. In this paper, we build on recent work on the two problems to investigate numerically the bifurcation mechanisms at work in the incompressible Keplerian magnetorotational dynamo problem in the shearing box framework. Using numerical techniques imported from dynamical systems research, we show that the onset of chaotic dynamo action at magnetic Prandtl numbers larger than unity is primarily associated with global homoclinic and heteroclinic bifurcations of nonlinear magnetorotational dynamo cycles. These global bifurcations are found to be supplemented by local bifurcations of cycles marking the beginning of period-doubling cascades. The results suggest that nonlinear magnetorotational dynamo cycles provide the pathway to turbulent injection of both kinetic and magnetic energy in incompressible magnetohydrodynamic Keplerian shear flow in the absence of an externally imposed magnetic field. Studying the nonlinear physics and bifurcations of these cycles in different regimes and configurations may subsequently help to better understand the physical conditions of excitation of magnetohydrodynamic turbulence and instability-driven dynamos in a variety of astrophysical systems and laboratory experiments. The detailed characterization of global bifurcations provided for this three-dimensional subcritical fluid dynamics problem may also prove useful for the problem of transition to turbulence in hydrodynamic shear flows

Continuation of the exponentially small transversality for the splitting of separatrices to a whiskered torus with silver ratio

We study the exponentially small splitting of invariant manifolds of whiskered (hyperbolic) tori with two fast frequencies in nearly-integrable Hamiltonian systems whose hyperbolic part is given by a pendulum. We consider a torus whose frequency ratio is the silver number $\Omega=\sqrt{2}-1$. We show that the Poincar\'e-Melnikov method can be applied to establish the existence of 4 transverse homoclinic orbits to the whiskered torus, and provide asymptotic estimates for the tranversality of the splitting whose dependence on the perturbation parameter $\varepsilon$ satisfies a periodicity property. We also prove the continuation of the transversality of the homoclinic orbits for all the sufficiently small values of $\varepsilon$, generalizing the results previously known for the golden number.Comment: 17 pages, 2 figure

Dimethylsulfoniopropionate in corals and its interrelations with bacterial assemblages in coral surface mucus

Corals produce copious amounts of dimethylsulfoniopropionate (DMSP), a sulfur compound thought toplay a role in structuring coral-associated bacterial communities. We tested the hypothesis that a linkage exists betweenDMSP availability in coral tissues and the community dynamics of bacteria in coral surface mucus. We determinedDMSP concentrations in three coral species (Meandrina meandrites, Porites astreoides and Siderastrea siderea) at twosampling depths (5 and 25 m) and times of day (dawn and noon) at Curac¸ao, Southern Caribbean. DMSP concentration(4–409 nmol cm?2 coral surface) varied with host species-specific traits such as Symbiodinium cell abundance, but notwith depth or time of sampling. Exposure of corals to air caused a doubling of their DMSPconcentration. The phylogeneticaffiliation of mucus-associated bacteria was examined by clone libraries targeting three main subclades of the bacterialDMSP demethylase gene (dmdA). dmdA gene abundance was determined by quantitative Polymerase Chain Reaction(qPCR) against a reference housekeeping gene (recA). Overall, a higher availability of DMSP corresponded to a lowerrelative abundance of the dmdA gene, but this pattern was not uniform across all host species or bacterial dmdA subclades,suggesting the existence of distinct DMSP microbial niches or varying dmdA DMSP affinities. This is the first studyquantifying dmdA gene abundance in corals and linking related changes in the community dynamics of DMSP-degradingbacteria to DMSP availability. Our study suggests that DMSP mediates the regulation of microbe

An Exactly Conservative Integrator for the n-Body Problem

The two-dimensional n-body problem of classical mechanics is a non-integrable Hamiltonian system for n > 2. Traditional numerical integration algorithms, which are polynomials in the time step, typically lead to systematic drifts in the computed value of the total energy and angular momentum. Even symplectic integration schemes exactly conserve only an approximate Hamiltonian. We present an algorithm that conserves the true Hamiltonian and the total angular momentum to machine precision. It is derived by applying conventional discretizations in a new space obtained by transformation of the dependent variables. We develop the method first for the restricted circular three-body problem, then for the general two-dimensional three-body problem, and finally for the planar n-body problem. Jacobi coordinates are used to reduce the two-dimensional n-body problem to an (n-1)-body problem that incorporates the constant linear momentum and center of mass constraints. For a four-body choreography, we find that a larger time step can be used with our conservative algorithm than with symplectic and conventional integrators.Comment: 17 pages, 3 figures; to appear in J. Phys. A.: Math. Ge