Method of statistical filtering

Minimal formula for bounding the cross correlation between a random forcing function and the state error when this correlation is unknown is used in optimal linear filter theory applications. Use of the bound results in overestimation of the estimation-error covariance

One-sided edge responses in forest birds following restoration treatments

Abstract. We studied the effects of the edge between two forest types on the probability of occurrence of seven species of birds and found that four responded to the edge on only one side. Over 4 years, we measured the responses of forest birds to the edge between ponderosa pine forest undergoing restoration and neighboring untreated stands. Of the seven species analyzed, one occurred most frequently near the edge. Of the remaining six, none responded to the edge in the treated forest, but four responded in the untreated forest. Relatively few studies have examined abundance changes on both sides of an edge between distinct habitats that support similar bird communities, and predictive models of edge effects used for mapping animal responses to habitat change often assume that animal abundance will change on both sides of this sort of edge, declining near the edge in the habitat in which the species is most abundant and increasing near the edge in the habitat in which the species is less abundant. One-sided edge effects, such as those we have documented, may lead to markedly different predictions of the effects of habitat change on bird abundance in heterogeneous landscapes. , Resumen. Estudiamos los efectos de borde entre dos tipos de bosque en la probabilidad de ocurrencia de siete especies de aves y encontramos que cuatro respondieron al borde de un solo lado. Durante cuatro años medimos las respuestas de aves de bosque al borde entre un bosque de pino ponderosa bajo restauración y rodales colindantes sin tratar. De las siete especies analizadas, una presentó mayor frecuencia cerca del borde. De las seis restantes, ninguna respondió al borde en el bosque tratado, pero cuatro mostraron una respuesta al bosque sin tratar. Relativamente pocos estudios han examinado los cambios en la abundancia en ambos lados de un borde entre habitats distintos que albergan comunidades de aves similares. Además, los modelos predictivos de efecto de borde utilizados para mapear las respuestas de animales al cambio de hábitat a menudo asumen que la abundancia animal cambiará en ambos lados de este tipo de borde, disminuyendo cerca del borde en el hábitat en el cual la especie es más abundante e incrementado cerca del borde en el habitat en el cual la especie es menos abundante. Los efectos de borde de un solo lado, tales como los que documentamos, pueden llevar a predicciones marcadamente diferentes de los efectos de cambio de habitat en la abundancia de aves en paisajes heterogéneos

Automated multigravity assist trajectory planning with a modified ant colony algorithm

The paper presents an approach to transcribe a multigravity assist trajectory design problem into an integrated planning and scheduling problem. A modified Ant Colony Optimization (ACO) algorithm is then used to generate optimal plans corresponding to optimal sequences of gravity assists and deep space manoeuvers to reach a given destination. The modified Ant Colony Algorithm is based on a hybridization between standard ACO paradigms and a tabu-based heuristic. The scheduling algorithm is integrated into the trajectory model to provide a fast time-allocation of the events along the trajectory. The approach demonstrated to be very effective on a number of real trajectory design problems

Mirror formation control in the vicinity of an asteroid

Two strategies are presented for the positioning and control of a spacecraft formation designed to focus sunlight onto a point on the surface of asteroid, thereby sublimating the material and ejecting debris creating thrust. In the first approach, the formation is located at artficial equilibrium points around the asteroid and controlled using the force from the solar radiation pressure. The second approach determines the optimal periodic formation orbits, subject to the gravitational perturbations from the asteroid, the solar radiation pressure and the control acceleration derived from a control law

Design of optimal Earth pole-sitter transfers using low thrust propulsion

Recent studies have shown the feasibility of an Earth pole-sitter mission using low-thrust propulsion. This mission concept involves a spacecraft following the Earth's polar axis to have a continuous, hemispherical view of one of the Earth's poles. Such a view will enhance future Earth observation and telecommunications for high latitude and polar regions. To assess the accessibility of the pole-sitter orbit, this paper investigates optimum Earth pole-sitter transfers employing low-thrust propulsion. A launch from low Earth orbit (LEO) by a Soyuz Fregat upper stage is assumed after which a solar-electric-propulsion thruster transfers the spacecraft to the pole-sitter orbit. The objective is to minimise the mass in LEO for a given spacecraft mass to be inserted into the pole-sitter orbit. The results are compared with a ballistic transfer that exploits the manifolds winding off the pole-sitter orbit. It is shown that, with respect to the ballistic case, low-thrust propulsion can achieve significant mass savings in excess of 200 kg for a pole-sitter spacecraft of 1000 kg upon insertion. To finally obtain a full low-thrust transfer from LEO up to the pole-sitter orbit, the Fregat launch is replaced by a low-thrust, minimum time spiral through an orbital averaging technique, which provides further mass savings, but at the cost of an increased time of flight

Forward Symplectic Integrators and the Long Time Phase Error in Periodic Motions

We show that when time-reversible symplectic algorithms are used to solve periodic motions, the energy error after one period is generally two orders higher than that of the algorithm. By use of correctable algorithms, we show that the phase error can also be eliminated two orders higher than that of the integrator. The use of fourth order forward time step integrators can result in sixth order accuracy for the phase error and eighth accuracy in the periodic energy. We study the 1-D harmonic oscillator and the 2-D Kepler problem in great details, and compare the effectiveness of some recent fourth order algorithms.Comment: Submitted to Phys. Rev. E, 29 Page

Summer CO2 evasion from streams and rivers in the Kolyma River basin, north-east Siberia

Inland water systems are generally supersaturated in carbon dioxide (CO2) and are increasingly recognized as playing an important role in the global carbon cycle. The Arctic may be particularly important in this respect, given the abundance of inland waters and carbon contained in Arctic soils; however, a lack of trace gas measurements from small streams in the Arctic currently limits this understanding.We investigated the spatial variability of CO2 evasion during the summer low-flow period from streams and rivers in the northern portion of the Kolyma River basin in north-eastern Siberia. To this end, partial pressure of carbon dioxide (pCO2) and gas exchange velocities (k) were measured at a diverse set of streams and rivers to calculate CO2 evasion fluxes. We combined these CO2 evasion estimates with satellite remote sensing and geographic information system techniques to calculate total areal CO2 emissions. Our results show that small streams are substantial sources of atmospheric CO2 owing to high pCO2 and k, despite being a small portion of total inland water surface area. In contrast, large rivers were generally near equilibrium with atmospheric CO2. Extrapolating our findings across the Panteleikha-Ambolikha sub-watersheds demonstrated that small streams play a major role in CO2 evasion, accounting for 86% of the total summer CO2 emissions from inland waters within these two sub-watersheds. Further expansion of these regional CO2 emission estimates across time and space will be critical to accurately quantify and understand the role of Arctic streams and rivers in the global carbon budget

Benthic Biofilm Controls on Fine Particle Dynamics in Streams

Este artículo contiene 15 páginas, 7 figuras, 3 tablas.Benthic (streambed) biofilms metabolize a substantial fraction of particulate organic matter and nutrient inputs to streams. These microbial communities comprise a significant proportion of overall biomass in headwater streams, and they present a primary control on the transformation and export of labile organic carbon. Biofilm growth has been linked to enhanced fine particle deposition and retention, a feedback that confers a distinct advantage for the acquisition and utilization of energy sources. We quantified the influence of biofilm structure on fine particle deposition and resuspension in experimental stream mesocosms. Biofilms were grown in identical 3 m recirculating flumes over periods of 18–47 days to obtain a range of biofilm characteristics. Fluorescent, 8 mm particles were introduced to each flume, and their concentrations in the water column were monitored over a 30 min period. We measured particle concentrations using a flow cytometer and mesoscale (10 mm to 1 cm) biofilm structure using optical coherence tomography. Particle deposition-resuspension dynamics were determined by fitting results to a stochastic mobile-immobile model, which showed that retention timescales for particles within the biofilm-covered streambeds followed a power-law residence time distribution. Particle retention times increased with biofilm areal coverage, biofilm roughness, and mean biofilm height. Our findings suggest that biofilm structural parameters are key predictors of particle retention in streams and rivers.This study was funded by a Marie Curie Intra- European Fellowship to WRH (FP7- PEOPLE-2011-IEF-302297) and an Austrian Science Fund grant to T.J.B. (START Y420-B17). K.R.R. was supported by a CUAHSI Pathfinder fellowship and U.S. NSF Graduate Research Fellowship. J.D.D. was supported by a Fulbright-Spain fellowship. The modeling effort was supported by U.S. NSF grants EAR- 1215898 and EAR-1344280 to AIP. Supporting data are provided at doi:10.6084/m9.figshare.4252193.Peer reviewe

Asymptotic solution for the two-body problem with constant tangencial acceleration

An analytical solution of the two body problem perturbed by a constant tangential acceleration is derived with the aid of perturbation theory. The solution, which is valid for circular and elliptic orbits with generic eccentricity, describes the instantaneous time variation of all orbital elements. A comparison with high-accuracy numerical results shows that the analytical method can be effectively applied to multiple-revolution low-thrust orbit transfer around planets and in interplanetary space with negligible error

A Tentative Modeling Study of the Effect of Wall Reactions on Oxidation Phenomena

This paper gives details of a tentative modeling study that investigates the inhibiting effect of internal reactor walls treated with acid..