Spin-axis attitude estimation and magnetometer bias determination for the AMPTE mission

Algorithms were developed for magnetometer biases and spin axis attitude calculation. Numerical examples of the performance of the algorithm are given

Short period attractors and non-ergodic behavior in the deterministic fixed energy sandpile model

We study the asymptotic behaviour of the Bak, Tang, Wiesenfeld sandpile automata as a closed system with fixed energy. We explore the full range of energies characterizing the active phase. The model exhibits strong non-ergodic features by settling into limit-cycles whose period depends on the energy and initial conditions. The asymptotic activity $\rho_a$ (topplings density) shows, as a function of energy density $\zeta$, a devil's staircase behaviour defining a symmetric energy interval-set over which also the period lengths remain constant. The properties of $\zeta$-$\rho_a$ phase diagram can be traced back to the basic symmetries underlying the model's dynamics.Comment: EPL-style, 7 pages, 3 eps figures, revised versio

Reflecting on gold geomicrobiology research: thoughts and considerations for future endeavors

Research in gold (Au) geomicrobiology has developed extensively over the last ten years, as more Au-bearing materials from around the world point towards a consistent story: That microbes interact with Au. In weathering environments, Au is mobile, taking the form of oxidized, soluble complexes or reduced, elemental Au nanoparticles. The transition of Au between aqueous and solid states is attributed to varying geochemical conditions, catalyzed in part by the biosphere. Hence, a global Au-biogeochemical-cycle was proposed. The primary focus of this mini-review is to reflect upon the biogeochemical processes that contribute to what we currently know about Au cycling. In general, the global Au-biogeochemical-cycle begins with the liberation of gold-silver particles from a primary host rock, by physical weathering. Through oxidative-complexation, inorganic and organic soluble-Au complexes are produced. However, in the presence of microbes or other reductants—e.g., clays and Fe-oxides—these Au complexes can be destabilized. The reduction of soluble Au ultimately leads to the bioprecipitation and biomineralization of Au, the product of which can aggregate into larger structures, thereby completing the Au cycle. Evidence of these processes have been “recorded” in the preservation of secondary Au structures that have been observed on Au particles from around the world. These structures—i.e., nanometer-size to micrometer-size Au dissolution and reprecipitation features—are “snap shots” of biogeochemical influences on Au, during its journey in Earth-surface environments. Therefore, microbes can have a profound effect on the occurrence of Au in natural environments, given the nutrients necessary for microbial metabolism are sustained and Au is in the system.Jeremiah Shuster and Frank Reit

Editorial for special issue "geomicrobiology and biogeochemistry of precious metals"

n/aFrank Reith and Jeremiah Shuste

Particle Filtering for Sequential Spacecraft Attitude Estimation

A new spacecraft attitude estimation approach using particle filtering is derived. Based on sequential Monte Carlo simulation, the particle filter approximately represents the prob-ability distribution of the state vector with random samples. The filter formulation is based on the star camera measurements using a gyro-based or attitude dynamics-based model for attitude propagation. Modified Rodrigues parameters are used for attitude parametriza-tion when the sample mean and covariance of the attitude are computed. The ambiguity problem associated with the modified Rodrigues parameters in the mean and covariance computation is addressed as well. By using the uniform attitude probability distribution as the initial attitude distribution and using a gradually decreasing measurement variance in the computation of the importance weights, the particle filter based attitude estimator possesses global convergence properties. Simulation results indicate that the particular particle filter, known as bootstrap filter, with as many as 2000 particles is able to converge from arbitrary initial attitude error and initial gyro bias errors as large as 4500 degrees per hour per axis. I

Biogeochemical gold cycling selects metal-resistant bacteria that promote gold particle transformation

Bacteria catalyze the dissolution and re-precipitation of gold, thereby driving the biogeochemical cycle of gold. Dissolution of gold/silver and re-precipitation of gold transforms gold particles by increasing gold purity. While soluble gold complexes are highly cytotoxic, little is known about how gold cycling affects bacterial communities residing on gold particles. Micro-analysis of gold particles obtained from Western Australia revealed porous textures and aggregates of pure gold nanoparticles, attributable to gold dissolution and re-precipitation, respectively. By interpreting structure and chemistry of particles, the kinetics of gold biogeochemical cycling at the site was estimated to be 1.60 × 10−9 M year−1. Bacterial communities residing on particles were composed of Proteobacteria (42.5%), Bacteroidetes (20.1%), Acidobacteria (19.1%), Firmicutes (8.2%), Actinobacteria (3.7%), and Verrucomicrobia (3.6%). A bacterial enrichment culture obtained from particles contained a similar composition. Exposure of enrichments to increasing concentrations of soluble gold decreased community diversity and selected for metal-resistant bacteria. Lower gold concentrations, which corresponded well with the concentration from the kinetic rate, provided a selective pressure for the selection of metal-resistant organisms while retaining the overall diversity. In conclusion, biogeochemical gold cycling directly influences bacterial communities on gold particles, thereby contributing to a continuum of particle transformation.Santonu Kumar Sanyal, Jeremiah Shuster, Frank Reit