The effect of roundoff noise in a state-space digital controller is investigated for a discrete-time control system. An analytical expression of the roundoff noise gain is obtained, with which the optimal realization problem is solved on the set of fully parametrized realizations. A sparse structure is derived and analyzed in terms of roundoff noise performance. The problem of finding optimized sparse structures is solved. A design example is given, which shows that the optimized sparse realization beats the fully parametrized optimal realization in terms of roundoff noise gain and computation efficiency.
Abstract Site-testing is crucial for achieving the goal of scientific research and analysis of meteorological and optical observing conditions, one of the associated basic tasks. As one of three potential sites to host the 12-meter Large Optical/infrared Telescope (LOT), the Muztagh-ata site, which is located on the Pamir Plateau in Xinjiang, in west China, began its site-testing task in the spring of 2017. In this paper, we firstly start with an introduction to the site and then present a statistical analysis of the ground-level meteorological properties such as air temperature, barometric pressure, relative humidity, and wind speed and direction, recorded by an automatic weather station with standard meteorological sensors for a two-year duration. We also show the monitoring results of sky brightness during this period.
Astronomy research has entered an increasingly data-intensive, or “big data” era. Exponential growth in the size of astronomical archives brings with it completely new requirements and challenges for data storage, computing power, networks, software, algorithms, and even research methods. Astronomers and experts in information and computation technology (ICT) are working together to simplify knowledge discovery within these massive data sets. Worldwide astronomical archives are connected through the virtual observatory (VO) framework, which provides interoperability standards and services that have allowed the creation of a global astronomical data grid. Astroinformatics, a bridge between astronomy and ICT and applied computer science, aims to engage a broader community of researchers both as contributors to and as consumers of the new methodology for data-intensive astronomy, thus building upon the data-grid foudations established by the VO framework. Data mining (DM), knowledge discovery in databases (KDD), machine learning, and visualization techniques have become a necessity. In this paper, the challenges facing modern astronomical research are briefly described, the concepts underlying the VO and astroinformatics and the latest progress in these fields are introduced, and the need for DM and KDD techniques in astronomy is discussed.
Abstract A large ground-based optical/infrared telescope is being planned for a world-class astronomical site in China. The cloud-free night percentage is the primary meteorological consideration for evaluating candidate sites. The data from GMS and NOAA satellites and the MODIS instrument were utilized in this research, covering the period from 1996 to 2015. Our data analysis benefits from overlapping results from different independent teams as well as a uniform analysis of selected sites using GMS+NOAA data. Although significant ground-based monitoring is needed to validate these findings, we identify three different geographical regions with a high percentage of cloud-free conditions (∼83% on average), which is slightly lower than at Mauna Kea and Cerro Armazones (∼85% on average) and were chosen for the large international projects TMT and ELT respectively. Our study finds evidence that cloud distributions and the seasonal changes affected by the prevailing westerly winds and summer monsoons reduce the cloud cover in areas influenced by the westerlies. This is consistent with the expectations from climate change models and is suggestive that most of the identified sites will have reduced cloud cover in the future.
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