Modeling, system identification, and control of ASTREX

The modeling, system identification and controller design aspects of the ASTREX precision space structure are presented in this work. Modeling of ASTREX is performed using NASTRAN, TREETOPS and I-DEAS. The models generated range from simple linear time-invariant models to nonlinear models used for large angle simulations. Identification in both the time and frequency domains are presented. The experimental set up and the results from the identification experiments are included. Finally, controller design for ASTREX is presented. Simulation results using this optimal controller demonstrate the controller performance. Finally the future directions and plans for the facility are addressed

Optical observations of NEA 162173 (1999 JU3) during the 2011-2012 apparition

Near-Earth asteroid 162173 (1999 JU3) is a potential target of two asteroid sample return missions, not only because of its accessibility but also because of the first C-type asteroid for exploration missions. The lightcurve-related physical properties of this object were investigated during the 2011-2012 apparition. We aim to confirm the physical parameters useful for JAXA's Hayabusa 2 mission, such as rotational period, absolute magnitude, and phase function. Our data complement previous studies that did not cover low phase angles. With optical imagers and 1-2 m class telescopes, we acquired the photometric data at different phase angles. We independently derived the rotational lightcurve and the phase curve of the asteroid. We have analyzed the lightcurve of 162173 (1999 JU3), and derived a synodic rotational period of 7.625 +/- 0.003 h, the axis ratio a/b = 1.12. The absolute magnitude H_R = 18.69 +/- 0.07 mag and the phase slope of G = -0.09 +/- 0.03 were also obtained based on the observations made during the 2011-2012 apparition.Comment: 4 pages, 3 figure

Scaling laws for the photo-ionisation cross section of two-electron atoms

The cross sections for single-electron photo-ionisation in two-electron atoms show fluctuations which decrease in amplitude when approaching the double-ionisation threshold. Based on semiclassical closed orbit theory, we show that the algebraic decay of the fluctuations can be characterised in terms of a threshold law $\sigma \propto |E|^{\mu}$ as $E \to 0_-$ with exponent $\mu$ obtained as a combination of stability exponents of the triple-collision singularity. It differs from Wannier's exponent dominating double ionisation processes. The details of the fluctuations are linked to a set of infinitely unstable classical orbits starting and ending in the non-regularisable triple collision. The findings are compared with quantum calculations for a model system, namely collinear helium.Comment: 4 pages, 1 figur

Mono-allelic retrotransposon insertion addresses epigenetic transcriptional repression in human genome

Background: Retrotransposons have been extensively studied in plants and animals and have been shown to have an impact on human genome dynamics and evolution. Their ability to move within genomes gives retrotransposons to affect genome instability. Methods: we examined the polymorphic inserted AluYa5, evolutionary young Alu, in the progesterone receptor gene to determine the effects of Alu insertion on molecular environment. We used mono-allelic inserted cell lines which carry both Alu-present and Alu-absent alleles. To determine the epigenetic change and gene expression, we performed restriction enzyme digestion, Pyrosequencing, and Chromatin Immunoprecipitation. Results: We observed that the polymorphic insertion of evolutionally young Alu causes increasing levels of DNA methylation in the surrounding genomic area and generates inactive histone tail modifications. Consequently the Alu insertion deleteriously inactivates the neighboring gene expression. Conclusion: The mono-allelic Alu insertion cell line clearly showed that polymorphic inserted repetitive elements cause the inactivation of neighboring gene expression, bringing aberrant epigenetic changes