Hybrid Fuzzy Logic and Extremum Seeking Attitude Control of Solar Sail Spacecraft

This thesis explores four controllers applied to the attitude control of a solar sail craft with control masses with the goal of showing benefits over more standard control schemes. The controllers examined in this paper are: 1) a PID controller that incorporates a discrete extremum seeking algorithm, 2) a type-1 fuzzy logic controller that incorporates a discrete extremum seeking algorithm, 3) a type-1 fuzzy logic controller, and 4) a type-2 fuzzy logic controller. The first two controllers are examined for their ability to quickly converge to a set of optimal gains over time. The latter two controllers are evaluated for their ability to maintain stability with respect to model uncertainty and sensor noise. The four controllers discussed in this paper are compared against other control techniques that have already been shown in previously published literature to provide good control performance when applied to this system

Vertical Flight Society (VFS) 8th Annual Student Design Competition

Every year the Vertical Flight Society (VFS), a professional society for vertical takeoff or vertical lift vehicles, sponsors a student design competition in order to foster innovation and interest in vertical flight technology. The University of Portland sponsored a five-person mechanical engineering team to compete in the 8th annual Micro Air Vehicle (MAV) Student Challenge. The team created an MAV that was capable of transporting a bag of sand from one set area to another. This required the development of a vehicle body, component selection, and testing. While the competition was ultimately cancelled, the team was successful in the creation of a vehicle

Chemical fractionation of deuterium in the protosolar nebula

Understanding gas-grain chemistry of deuterium in star-forming objects may help to explain their history and present state. We aim to clarify how processes in ices affect the deuterium fractionation. In this regard, we investigate a Solar-mass protostellar envelope using an astrochemical rate-equation model that considers bulk-ice chem- istry. The results show a general agreement with the molecular D/H abundance ratios observed in low-mass protostars. The simultaneous processes of ice accumulation and rapid synthesis of HD on grain surfaces in the prestellar core hampers the deuteration of icy species. The observed very high D/H ratios exceeding 10 per cent, i.e., super- deuteration, are reproduced for formaldehyde and dimethyl ether, but not for other species in the protostellar envelope phase. Chemical transformations in bulk ice lower D/H ratios of icy species and do not help explaining the super-deuteration. In the protostellar phase, the D2O/HDO abundance ratio was calculated to be higher than the HDO/H2O ratio owing to gas-phase chemistry. Species that undergo evaporation from ices have high molecular D/H ratio and a high gas-phase abundance.Comment: 11 pages, 4 tables, 6 figures; +3 figures in appendix. Accepted for publication in MNRA

Proficiency-Based Grading: Can We Practice What They Preach?

The practice of assessing and grading students on their ability to demonstrate proficiency related to a standard has grown significantly in K–12 settings over the past decade. This article invites teacher educators to consider how to respond to this trend by examining an approach for preparing teacher candidates to participate effectively in proficiency-based systems. The process of integrating a proficiency-based grading strand into one undergraduate assessment course for elementary teacher candidates is described to illustrate how an approach advocated in the K–12 environment may be adapted to a higher education setting. Reflections on both the challenges and the benefits of the adaptation suggest that approaching course design from a proficiency-based perspective, while perhaps most valuable in a course that builds candidates’ assessment literacy, can also enhance teacher educators’ efforts to design purposeful course experiences in other arenas

Temperature Spectra of Interstellar Dust Grains Heated by Cosmic Rays. III. Mixed Composition Grains

Icy grains in the interstellar medium and star-formation regions consist of a variety of materials. Such composite grains interact differently with cosmic-ray (CR) particles compared to simple single-material grains. We aim to calculate the spectra of energies and temperatures of mixed-composition grains undergoing whole-grain heating by CRs. The grains were assumed to consist of a mixture of carbon and olivine, covered by ices consisting of carbon oxides and water. The energy and temperature spectra for grains with radii 0.05; 0.1, and 0.2 microns impacted by CRs were calculated for eight values of column density, relevant to molecular clouds and star-forming cores. The approach takes into account changes in ice thickness and composition with increasing column density. These detailed data for CR interaction with interstellar grains are intended for applications in astrochemical models. The main finding is that the a more accurate approach on grain heat capacity and other factors prevent a frequent heating of 0.1 micron or larger icy grains to high temperatures.Comment: Accepted in ApJS. Machine-readable data available from authors or the journa

Evaporative cooling of icy interstellar grains II. Key parameters

Context. Evaporative (sublimation) cooling of icy interstellar grains occurs when the grains have been suddenly heated by a cosmic-ray (CR) particle or other process. It results in thermal desorption of icy species, affecting the chemical composition of interstellar clouds. Aims. We investigate details on sublimation cooling, obtaining necessary knowledge before this process is considered in astrochemical models. Methods. We employed a numerical code that describes the sublimation of molecules from an icy grain, layer by layer, also considering a limited diffusion of bulk-ice molecules toward the surface before they sublimate. We studied a grain, suddenly heated to peak temperature T, which cools via sublimation and radiation. Results. A number of questions were answered. The choice of grain heat capacity C has a limited effect on the number of sublimated molecules N, if the grain temperature T > 40K. For grains with different sizes, CR-induced desorption is most efficient for rather small grains with a core radius of a ~ 0.02 micron. CR-induced sublimation of CO2 ice can occur only from small grains if their peak temperature is T > 80K and there is a lack of other volatiles. The presence of H2 molecules on grain surface hastens their cooling and thus significantly reduces N for other sublimated molecules for T < 30K. Finally, if there is no diffusion and subsequent sublimation of bulk-ice molecules (i.e., sublimation occurs only from the surface layer), sublimation yields do not exceed 1-2 monolayers and, if T > 50K, N does not increase with increasing T. Conclusions. Important details regarding the sublimation cooling of icy interstellar grains were clarified, which will enable a proper consideration of this process in astrochemical modeling.Comment: Accepted for publication in A&