Optimal Spacecraft Guidance

This book is designed for a one-semester course at Utah State University titled MAE 6570 Optimal Spacecraft Guidance. The class meets for 75 minutes, twice per week, for 14 weeks. There are no prerequisites other than graduate standing in engineering. Proficiency in calculus, differential equations, linear algebra, and computer programming is required. Students find that previous experience in space dynamics, linear multivariable control, or optimal control is helpful. The goal of the book and course is for students to develop fundamental skills needed to do professional work in the area of spacecraft guidance. After working through the book, students should have an understanding of the linear quadratic framework, E-guidance, Q-guidance, Apollo descent guidance, and more. To this end, the book contains seven chapters. An approximate timeline for the course is the following. • Chapter 1 | Week 1 • Chapter 2 | Weeks 2 and 3 • Chapter 3 | Weeks 4 and 5 • Chapter 4 | Weeks 6, 7, and 8 • Chapter 5 | Weeks 9 and 10 • Chapter 6 | Weeks 11 and 12 • Chapter 7 | Weeks 13 and 14 Three dynamical models are used throughout to illustrate the concepts. These models are a nonlinear two-body model, a linear flat planet model, and a linear relative orbital motion model. A key feature of the book is its integration of MATLAB implementations into the text as early as possible. For example, Chapter 1 includes a Q-guidance implementation, Chapter 2 includes a polynomial guidance implementation, and so on. Each chapter ends with a set of problems suitable for independent homework. Several of the chapter problems require modification or extension of these implementations. The final two chapters focus on descent guidance and ascent guidance. By this point, students are expected to be coding independently

Temporality, vulnerability, and energy justice in household low carbon innovations

Decarbonisation and innovation will change the affordability of different domestic energy services. This has the potential to alleviate vulnerability to fuel poverty, but it could create new injustices unless the risks are preempted and actively mitigated. In this paper, we ask: In what ways can emerging low-carbon innovations at the household scale complement, and complicate, achieving energy justice objectives? Drawing from four empirical case studies in the United Kingdom, the paper highlights different risks that come from different types of innovation required to tackle different decarbonisation challenges. More specifically, it assesses four particular household innovations—energy service contracts, electric vehicles, solar photovoltaic (PV) panels, and low carbon heating—selected for their fit with a typology of incremental vs. radical technology and modest vs. substantial changes in user practices. It shows how in each case, such innovations come with a collection of opportunities but also threats. In doing so, the paper seeks to unveil the “political economy” of low-carbon innovations, identifying particular tensions alongside who wins and who loses, as well as the scope and temporality of those consequences

Influence of Principals’ Instructional Supervision Practices on Kenya Certificate of Secondary Education (KCSE) Performance in Public Secondary Schools in Makueni County, Kenya

KCSE Performance in Public secondary schools in Makueni County, Kenya has consistently declined between 2014 and 2018. Although no empirical studies have explained the cause of the decline, Principals’ instructional supervision practices may have contributed to the trend necessitating the need for an investigation. This study investigated Influence of Principals’ Instructional Supervision Practices on Kenya Certificate of Secondary Education (KCSE) Performance in Public Secondary Schools in Makueni County, Kenya. The objective of the study was to establish the influence of principals’ instructional supervision practices on KCSE performance in public secondary schools in Makueni County, Kenya. The hypothesis for the study was that there is no statistically significant relationship between principals’ instructional supervision practices and students’ performance in KCSE in public secondary schools in Makueni County, Kenya. The study employed mixed methods research design. The rationale for using the method is that it combines both qualitative and quantitative data within a single study hence complementing each other by integrating their strengths. The target population was all principals and teachers of public secondary schools in Makueni County. The study employed stratified sampling technique for schools, equal allocation sampling technique for both principals and teachers for quantitative phase while maximal variation sampling was used for qualitative phase. Means, percentage and frequencies were used to determine the distribution of variables under study among the respondents and represented in tables and figures. Pearson correlation coefficient was used to test the relationship between principals’ instructional supervision practices and KCSE performance in public secondary schools in Makueni County. The results for quantitative phase indicated that the coefficient of correlation (r) for the objective was 0.6 at significance level of 0.04. Principals interviewed attested that they embraced instructional supervision practices. The study concluded that principals of public secondary schools in Makueni County, Kenya applied effective instructional supervision practices that positively influenced KCSE performance and that  principals’  instructional supervision practices influence  students’ KCSE performance in public secondary schools in Makueni County .The study recommends that principals  be trained on specific instructional supervision strategies to enhance their effectiveness in instructional leadership. Keywords: Supervision, Instructional supervision, principals’ instructional supervision practices, Supervision practices DOI: 10.7176/JEP/11-15-14 Publication date:May 31st 202

Electromigration-Induced Propagation of Nonlinear Surface Waves

Due to the effects of surface electromigration, waves can propagate over the free surface of a current-carrying metallic or semiconducting film of thickness h_0. In this paper, waves of finite amplitude, and slow modulations of these waves, are studied. Periodic wave trains of finite amplitude are found, as well as their dispersion relation. If the film material is isotropic, a wave train with wavelength lambda is unstable if lambda/h_0 < 3.9027..., and is otherwise marginally stable. The equation of motion for slow modulations of a finite amplitude, periodic wave train is shown to be the nonlinear Schrodinger equation. As a result, envelope solitons can travel over the film's surface.Comment: 13 pages, 2 figures. To appear in Phys. Rev.

SCUBA noise alters community structure and cooperation at Pederson’s cleaner shrimp cleaning stations

Recreational SCUBA diving is widespread and increasing on coral reefs worldwide. Standard open-circuit SCUBA equipment is inherently noisy and, by seeking out areas of high biodiversity, divers inadvertently expose reef communities to an intrusive source of anthropogenic noise. Currently, little is known about SCUBA noise as an acoustic stressor, and there is a general lack of empirical evidence on community-level impacts of anthropogenic noise on coral reefs. Here, we conducted a playback experiment on Caribbean reefs to investigate impacts of SCUBA noise on fish communities and interspecific cooperation at ecologically important cleaning stations of the Pederson’s cleaner shrimp Ancylomenes pedersoni. When exposed to SCUBA-noise playback, the total occurrence of fishes at the cleaning stations decreased by 7%, and the community and cleaning clientele compositions were significantly altered, with 27% and 25% of monitored species being affected, respectively. Compared with ambient-sound playback, SCUBA-noise playback resulted in clients having to wait 29% longer for cleaning initiation and receiving 43% less cleaning; however, cheating, signalling, posing and time spent cleaning were not affected by SCUBA-noise playback. Our study is the first to demonstrate experimentally that SCUBA noise can have at least some negative impacts on reef organisms, confirming it as an ecologically relevant pollutant. Moreover, by establishing acoustic disturbance as a likely mechanism for known impacts of diver presence on reef animals, we also identify a potential avenue for mitigation in these valuable ecosystems.</p

Trends in Decline of Antiretroviral Resistance among ARV-Experienced Patients in the HIV Outpatient Study: 1999–2008

Background. Little is known about temporal trends in frequencies of clinically relevant ARV resistance mutations in HIV strains from U.S. patients undergoing genotypic testing (GT) in routine HIV care. Methods. We analyzed cumulative frequency of HIV resistance among patients in the HIV Outpatient Study (HOPS) who, during 1999–2008 and while prescribed antiretrovirals, underwent GT with plasma HIV RNA >1,000 copies/mL. Exposure ≥4 months to each of three major antiretroviral classes (NRTI, NNRTI and PI) was defined as triple-class exposure (TCE). Results. 906 patients contributed 1,570 GT results. The annual frequency of any major resistance mutations decreased during 1999–2008 (88% to 79%, P = 0.05). Resistance to PIs decreased among PI-exposed patients (71% to 46%, P = 0.010) as exposure to ritonavir-boosted PIs increased (6% to 81%, P < 0.001). Non-significant declines were observed in resistance to NRTIs among NRTI-exposed (82% to 67%), and triple-class-resistance among TCE patients (66% to 41%), but not to NNRTIs among NNRTI-exposed. Conclusions. HIV resistance was common but declined in HIV isolates from subgroups of ARV-experienced HOPS patients during 1999–2008. Resistance to PIs among PI-exposed patients decreased, possibly due to increased representation of patients whose only PI exposures were to boosted PIs

Past and possible future evolution of the Yukon Flats southern upland yedoma region, Alaska

The course of permafrost degradation depends on climate, vegetation, disturbance, and excess groundice content and distribution, which vary over time. The first three of these drivers are undergoing considerable change with arctic warming. Using combined lake-sediment records, field observations, aerial observations and LiDAR imagery, we reconstructed the late-Quaternary history of the marginal upland of the Yukon Flats, interior Alaska, a loess-mantled region with massive ground ice and numerous thermokarst lakes that is identified as yedoma. A switch to warmer, moister conditions during deglaciation triggered substantial thermal erosion and transport of silt, which washed into existing basins and formed widespread linear corrugations cutting across the uplands. Lakes began to form via thermokarst as early as 13,000 cal yr BP. Lakes intersect the corrugations, indicating lake formation followed initial landscape instability. Charcoal in basal sediments indicates fire may have influenced lake initiation. Small-scale surface topography revealed by LiDAR images includes deep gullies, features resembling lake drainage channels, and lowered lake shorelines. After ca 10,000 yr BP the region became colonized by dense evergreen conifer forest, which likely served to stabilize and insulate the ground surface, preventing the continuation of the high rates of permafrost degradation recorded in the earliest Holocene. Initial lake lowering and generation of steep local topography favouring drying of uplands, plus a summer water deficit, have also likely combined to shift the system to a more quiescent state through much of the Holocene. However, these changes have not prevented lake drainage events entirely. In 2013, several lakes drained or partially drained, possibly in response to fires and a high spring melt-water volume. The observed pattern of drainage is echoed in the older features preserved on the land surface. Based on the Holocene evolution of the region, increasing regional moisture and/or fire disturbance in the future could lead to an increase in permafrost degradation and lake drainage events