A Homotopy-Based Method for Optimization of Hybrid High-Low Thrust Trajectories

Space missions require increasingly more efficient trajectories to provide payload transport and mission goals by means of lowest fuel consumption, a strategic mission design key-point. Recent works demonstrated that the combined (or hybrid) use of chemical and electrical propulsion can give important advantages in terms of fuel consumption, without losing the ability to reach other mission objectives: as an example the Hohmann Spiral Transfer, applied in the case of a transfer to GEO orbit, demonstrated a fuel mass saving between 5-10% of the spacecraft wet mass, whilst satisfying a pre-set boundary constraint for the time of flight. Nevertheless, methods specifically developed for optimizing space trajectories considering the use of hybrid high-low thrust propulsion systems have not been extensively developed, basically because of the intrinsic complexity in the solution of optimal problem equations with existent numerical methods. The study undertaken and presented in this paper develops a numerical strategy for the optimization of hybrid high-low thrust space trajectories. An indirect optimization method has been developed, which makes use of a homotopic approach for numerical convergence improvement. The adoption of a homotopic approach provides a relaxation to the optimal problem, transforming it into a simplest problem to solve in which the optimal problem presents smoother equations and the shooting function acquires an increased convergence radius: the original optimal problem is then reached through a homotopy parameter continuation. Moreover, the use of homotopy can make possible to include a high thrust impulse (treated as velocity discontinuity) to the low thrust optimal control obtained from the indirect method. The impulse magnitude, location and direction are obtained following from a numerical continuation in order to minimize the problem cost function. The initial study carried out in this paper is finally correlated with particular test cases, in order to validate the work developed and to start investigating in which cases the effectiveness of hybrid-thrust propulsion subsists

From Low Thrust to Solar Sailing: A Homotopic Approach

This paper describes a novel method to solve solar-sail minimum-time-of-flight optimal control problems starting from a low-thrust solution. The method is based on a homotopic continuation. This technique allows to link the low-thrust with the solar-sail acceleration, so that the solar-sail solution can be computed starting from the usually easier low-thrust one by means of a numerical iterative approach. Earth-to-Mars transfers have been studied in order to validate the proposed method. A comparison is presented with a conventional solution approach, based on the use of a genetic algorithm. The results show that the novel technique has advantages, in terms of accuracy of the solution and computational time

Academic library administrators perceive value in their librarians\u27 research

Objective – To explore academic library administrators’ perceived value of their librarians’ research, specifically the importance to the profession and the library community.Design – Qualitative, exploratory study using a survey questionnaire.Setting – Academic libraries in the United States of America. Subjects – 23 library administrators. Methods – During the summer of 2010, one of the authors conducted 20-30 minute telephone interviews with 23 academic library administrators. Interviews were recorded and transcribed for coding. Interview questions 1-3 and 8-19 were content-analyzed; the authors described common themes for each of these questions. Items 4-7 had Likert scale response formats, and a mean and standard deviation were computed for each of these items.Main Results – The benefits of librarians’ research included fulfilling tenure-track requirements, enriching relationships with teaching faculty, library faculty recognition, improved services and programs, collaboration with others, research result application to daily issues, development as librarians, and improved knowledge of the research field. The perceived current changes and future issues for university libraries included increased digitization of collections, scholarly communication, and expanded instructional engagement of faculty and students, as well as future economic downturn and budget cuts. Administrators noted several methods that influenced their thinking: professional meetings, reading professional journals, informal discussions with colleagues, and social media such as Facebook and Twitter.Academic library administrators used a variety of methods to support their librarians’ research. These included tenure-track requirements, research incentives, travel funds, grants, sabbaticals, release time, and shared communication about research. Additionally, there was a substantial perceived interrelationship between how librarians’ research benefited the librarian, the library, the university, and the profession. Recognition and new programs and services were thought to benefit all four areas, and monetary rewards were considered benefits for the first three areas.Conclusion – Based on the sample of 23 academic library administrators, the authors conclude that librarians’ research is perceived as valuable to both the academic and library communities

Academic Librarians at Institutions with LIS Programs Assert that Project Management Training is Valuable

Objective - To investigate academic librarians\u27 project management education and training, project management skills and experiences, and perceptions of project management courses within the library and information science (LIS) curriculum. Design - Online questionnaire. Setting - 70 universities worldwide with LIS programs and at least one project management course. Subjects - 4,979 academic librarians were invited to complete the online questionnaire. Methods - From the identified institutions, the authors invited academic librarians to participate in a 17-question survey via e-mail. The survey was available in both English and Spanish and was validated via a pilot trial. A total of 649 individuals participated, for a response rate of 13%. The survey included questions related to geographic region and institution affiliation, university education and librarian training associated with project management, project participation and use of project management software or methods, and project management courses in LIS curriculums, and a final open-ended comment section. Main Results - Of the 649 librarians who participated in the survey, 372 were from North and South America (58%). The next highest number of responses came from Europe (38%), followed by low response rates from Africa, Asia, and Oceania. Respondents reported working in a variety of library departments and identified themselves as being one of a director or manager, assistant librarian, or library page. Of the 436 respondents who reported having a university degree, 215 attended an LIS Master\u27s level program, and 12 studied at the doctoral level. The majority of respondents indicated they have had training in project management, participating in formal coursework, conferences, webinars, or other self-directed learning methods. Of the 459 academic library staff responding to the question, 40% considered project management courses of high importance in the university curriculum and 26 % responded that project management courses were extremely important in their field of expertise and working environment (p. 472). The consensus among participants was that project management courses should be included in both undergraduate and graduate level LIS curricula. Conclusion - The high participation of librarians in project management, compared to the limited formal education received, suggests that courses in project management, including software and methodology, are needed in LIS university curricula. Additionally, less than 40% of academic librarian survey respondents were trained in LIS; other professions are working as librarians and therefore may have insufficient knowledge and skills to manage the projects they direct. The research results confirm the relationship between strategic planning and project management skills. The authors conclude that universities should revise their LIS curricula to include and require additional project management courses. © 2017 Sullo

Opportunities to Uncover, Locate, and Learn: The Library Orientation Scavenger Hunt

Himmelfarb Health Sciences Library implemented a Library Orientation Scavenger Hunt for new medical students. This poster presentation describes the details of the scavenger hunt and the resulting benefits for the library users and staff

L'intelligence pratique du professionnel au service de l'estime de soi de l'élève en milieu scolaire spécialisé: l'exemple spécifique de La Voie Lactée

Dans un système scolaire qui érige en normes les compétences intellectuelles et la performance, les élèves qui souffrent d’importantes difficultés d’apprentissage, et qui ne parviennent donc pas à correspondre à la norme, sont souvent mis à l’écart, placés dans un cursus d’enseignement spécialisé. L’expérience traumatisante de l’école dite conventionnelle et le rejet font que ces élèves souffrent d’une piètre estime d’eux-mêmes. En tant qu’elle occupe un rôle central dans la construction identitaire, la progression et l’épanouissement personnels de chaque individu, l’estime de soi constitue un des leviers essentiels sur lequel devra agir le professionnel de l’enseignement spécialisé pour aider les élèves à appréhender les apprentissages. Tout l’enjeu est donc de renforcer cette estime et, pour ce faire, le professionnel fera appel à son intelligence pratique pour créer une bonne relation avec l’élève afin de renforcer son estime de soi

Optimisation of Low-Thrust and Hybrid Earth-Moon Transfers

This paper presents an optimization procedure to generate fast and low-∆v Earth-Moon transfer trajectories, by exploiting the multi-body dynamics of the Sun-Earth-Moon system. Ideal (first-guess) trajectories are generated at first, using two coupled planar circular restricted three-body problems, one representing the Earth-Moon system, and one representing the Sun-Earth. The trajectories consist of a first ballistic arc in the Sun-Earth system, and a second ballistic arc in the Earth-Moon system. The two are connected at a patching point at one end (with an instantaneous ∆v), and they are bounded at Earth and Moon respectively at the other end. Families of these trajectories are found by means of an evolutionary optimization method. Subsequently, they are used as first-guess for solving an optimal control problem, in which the full three-dimensional 4-body problem is introduced and the patching point is set free. The objective of the optimisation is to reduce the total ∆v, and the time of flight, together with introducing the constraints on the transfer boundary conditions and of the considered propulsion technology. Sets of different optimal trajectories are presented, which represents trade-off options between ∆v and time of flight. These optimal transfers include conventional solar-electric low-thrust and hybrid chemical/solar-electric high/low-thrust, envisaging future spacecraft that can carry both systems. A final comparison is made between the optimal transfers found and only chemical high-thrust optimal solutions retrieved from literature

Preparation and characterisation of whey protein fluid gels:the effects of shear and thermal history

AbstractWith the potential use of fluid gels in structuring fluids, whey protein isolate (WPI) was used as a prerequisite to prepare fluid gels: owing to its high nutritional value and thermal stability on gelling. Fluid gels were prepared via heat-induced gelation of a 10 wt% protein solution under controlled temperature and shear. Physical properties of the resulting gel particles (e.g. size and particle–particle interactions) were found to be dependent on the combination of shear and thermal history. Discrete large aggregates (>120 μm) were obtained at low shear, with aggregate size decreasing (<40 μm) at higher shear. Such microstructural changes in the particles led to the control of the suspension rheology. All suspensions showed a marked shear thinning behaviour associated with particle break-up which was observed to be more apparent for larger aggregates, originally made at low shear. The viscoelastic properties of the particulate systems, once in intimate contact (e.g. high volume fraction) resembled a pseudo solid material. In addition, it was shown that at a given volume fraction, the elasticity of the suspension varied dependant on their original processing conditions, owing to the degree of particle–particle interactions. A qualitative model has therefore been presented for the formation of particles by which the rheology is determined

The Himmelfarb Library Annual Art Show: Celebrating the Creative Abilities of Faculty, Staff, and Students

Himmelfarb Health Sciences Library at the George Washington University has held an annual art show since 1987. Students, staff, faculty, and clinicians from the School of Medicine and Health Sciences, the School of Public Health and Health Services, the School of Nursing, the GW Hospital, and Himmelfarb Health Sciences Library are invited to submit artwork to be displayed throughout the first floor of the library in a month-long display. The talent of the artists is celebrated at an opening reception where light refreshments are served and students, staff, and faculty mingle and view the art. Library art shows serve as an opportunity to share and celebrate talents outside of the health sciences and as an avenue for networking between all members of the library and medical academic arena. The Himmelfarb Health Sciences Library Annual Art Show fosters a sense of community; the spirit of creativity and imagination weaves its way through the opening reception as well as throughout the library during the span of the show. In addition, the art show helps to promote the visibility of the library, not only through art show marketing efforts but also by attracting new and returning patrons to visit and view the art