Sparse matrix methods research using the CSM testbed software system

Research is described on sparse matrix techniques for the Computational Structural Mechanics (CSM) Testbed. The primary objective was to compare the performance of state-of-the-art techniques for solving sparse systems with those that are currently available in the CSM Testbed. Thus, one of the first tasks was to become familiar with the structure of the testbed, and to install some or all of the SPARSPAK package in the testbed. A suite of subroutines to extract from the data base the relevant structural and numerical information about the matrix equations was written, and all the demonstration problems distributed with the testbed were successfully solved. These codes were documented, and performance studies comparing the SPARSPAK technology to the methods currently in the testbed were completed. In addition, some preliminary studies were done comparing some recently developed out-of-core techniques with the performance of the testbed processor INV

Models of genetic drift as limiting forms of the Lotka-Volterra competition model

The relationship between the Moran model and stochastic Lotka-Volterra competition (SLVC) model is explored via timescale separation arguments. For neutral systems the two are found to be equivalent at long times. For systems with selective pressure, their behavior differs. It is argued that the SLVC is preferable to the Moran model since in the SLVC population size is regulated by competition, rather than arbitrarily fixed as in the Moran model. As a consequence, ambiguities found in the Moran model associated with the introduction of more complex processes, such as selection, are avoided.Comment: 5 pages, 4 figure

A New Galaxy in the Local Group: the Antlia Dwarf Galaxy

We report the discovery of new member of the Local Group in the constellation of Antlia. Optically the system appears to be a typical dwarf spheroidal galaxy of type dE3.5 with no apparent young blue stars or unusual features. A color-magnitude diagram in I, V-I shows the tip of the red giant branch, giving a distance modulus of 25.3 +/- 0.2 (1.15 Mpc +/- 0.1) and a metallicity of -1.6 +/- 0.3. Although Antlia is in a relatively isolated part of the Local Group it is only 1.2 degrees away on the sky from the Local Group dwarf NGC3109, and may be an associated system.Comment: AJ in press, 15 pages, 7 figures, figure 2 in b/w for space saving, full postscript version available at http://www.ast.cam.ac.uk/~gkth/antlia-pp.htm

A CGE Analysis of the Harbinson Proposal: Outcomes for the EU25

In this study, we employ the Harbinson proposal and July Framework to compare a ‘likely’ Doha scenario with an ‘inclusive’ baseline. The key aim is to assess the impacts across EU member states. More specifically, we (i) employ the latest version 6 of the GTAP database, (ii) explicitly model CAP mechanisms (e.g., quotas, decoupled payments, set-aside, CAP budget etc.) to more accurately assess the asymmetric trade led welfare effects on selected EU member states, and (iii) introduce binding overhangs into domestic support, export subsidies and more importantly market access commitments. Whilst the EU regions benefit from the multilateral reform proposals, the gains are weakened considerably by the tariff binding overhangs, where the EU25 only gain ten per cent of their potential trade led welfare gain from the proposals. On this basis, a more positive stance must be applied if the Doha Reforms are to yield a meaningful outcome for all.Research Methods/ Statistical Methods,

Continuous representation of wind stress and wind stress curl over the world ocean

A continuous wind stress distribution over the world oceans is derived by fitting a spline function representation to the values of the wind stress given by Hellerman (1968) for each season and for the annual mean. The derived wind stress is then used to obtain a representation for the curl of the wind stress over the same region, and steadystate, Sverdrup transport calculations are calculated from the curl for each set of data. The derived transports for the western boundary currents do not agree with observed estimates...

Design and Validation of an Autonomous Mission Manager towards Coordinated Multi-Spacecraft Missions

For ambitious upcoming aerospace missions, autonomy will play a crucial role in achieving complex mission goals and reducing the burden for ground operations. Standalone spacecraft can leverage autonomy concepts to optimize data collection and ensure robust operation. For spacecraft clusters, autonomy can additionally provide a feasible method of ensuring coordination through onboard peer-to-peer scheduling. However, in exchange for providing flexible mission capabilities and operational convenience, autonomy introduces additional uncertainty and software complexity, which complicates the mission assurance process. This research presents a framework for designing and testing schedules consisting of heavily constrained tasks. The core of this framework, the Schedule Manager (SM), manages tasks by associating constraints with each task including time windows, task priority, conflict categories, and resource requirements, which assures that tasks will only run when capable. This increased control over individual tasks also improves the modularity of the overall mission plan, and provides a built-in fail-safe in the event of unexpected task failure through the loading of predefined contingency schedules. The SM can use estimated task durations and resource requirements to simulate schedules ahead of time, which can be used on the ground for schedule validation and onboard as a method of prognostics and to calculate resource availability windows. The ability to predict availability windows onboard and dynamically adjust depending upon currently scheduled tasks enables peer-to-peer tasking and scheduling. For example, a spacecraft can schedule a coordinated action by broadcasting the task requirements in an availability window request to all applicable spacecraft. Then, based upon the availability windows received from each spacecraft, the coordinating spacecraft can then issue a final task scheduling command with a much lower probability of conflict. The SM has been integrated with the core Flight System (cFS) from NASA, which has flight heritage on previous successful large-scale missions such as the Lunar and Dust Environment Explorer (LADEE). This integration is in the form of a cFS application called the cFS Schedule Manager (CSM), which will manage the operations for the Space Test Program Houston 7 Configurable and Autonomous Sensor Processing Research (STP-H7-CASPR) experiment that is planned for launch on SpaceX-24 to the International SpaceStation (ISS) in December 2021. Software validation was achieved with cFS unit tests, functional tests, and code analysis tools. Demonstrations were built using the COSMOS ground station and the 42 spacecraft simulator, and these were tested with a cluster of development boards in the loop as representative flight hardware