Charging strategies for electrostatic control of spacecraft formations

Formation control by means of electrostatic forces, generating attractive or repulsive actions by charging the satellites’ surfaces, has been recently proposed for high altitude orbits to precisely maintain the configuration without risk of plume impingement. This paper focuses on electrostatic control and switching strategies for charge distribution in spacecraft formations, taking into account the limits on the power requirements. Two nonlinear global control approaches are presented and applied to two and three satellites’ formations. Then, an optimized charge distribution process among the satellites is discussed and applied to the three spacecraft formation case. Numerical simulations are performed in order to evaluate the advantages and drawbacks of this configuration control technique

Attitude stability and altitude control of a variable-geometry Earth-orbiting solar sail

A variable-geometry solar sail for on-orbit altitude control is investigated. It is shown that, by adjusting the effective area of the sail at favorable times, it is possible to influence the length of the semi-major axis over an extended period of time. This solution can be implemented by adopting a spinning quasi-rhombic pyramidal solar sail which provides the heliostability needed to maintain a passive “sun-pointing” attitude and the freedom to modify the shape of the sail at any time. In particular, this paper investigates the variable-geometry concept through both theoretical and numerical analyses. Stability bounds on the sail design are calculated by means of a first-order analysis, producing conditions on the opening angles of the sail, while gravity gradient torques and solar eclipses are introduced to test the robustness of the concept. The concept targets equatorial orbits above approximately 5,000 km. Numerical results characterize the expected performance, leading to (for example) an increase of 2,200 km per year for a small device at GEO

Attitude and Orbital Dynamics of a Variable-Geometry, Spinning Solar Sail in Earth Orbit

At the ISSS 2013, a novel concept of variable-geometry solar sail was introduced: deployed in the shape of a three-dimensional quasi-rhombic pyramid (QRP), the sail exploited its shape and shift between center of mass and center of pressure to naturally achieve heliostability (stable sun-pointing) throughout the mission. In addition, mechanisms allowed to vary the flare angle of the four booms in opposite pairs, thus allowing to control the area exposed to the sun without the need of slew maneuvers. Using these adjustments in favorable orbital positions, it is possible to build a regular pattern of acceleration to achieve orbit raising or lowering without the need of propulsion system or attitude control. Subsequent more detailed investigations revealed that eclipses, even if lasting only a fraction of the orbit, have a substantial (and negative) impact on the heliostability effect: and even a small residual angular velocity, or disturbance torque, are enough to cause the spacecraft to tumble. In this work, we present a novel and improved concept which allows the sail to preserve its attitude not only with eclipses, but also in presence of disturbance torques such as the gravity gradient. The solution we propose is to add a moderate spin to the solar sail, combined with ring dampers. The gyroscopic stiffness due to the spin guarantees stability during the transient periods of the eclipses, while the heliostability effect, combined with the dampers, cancels any residual unwanted oscillation during the parts of the orbit exposed to the sun, and at the same time guarantees continuous sun-pointing as the apparent direction of the sun rotates throughout the year. Both theoretical and numerical analyses are performed. First, stability bounds on the sail design are calculated, obtaining conditions on the flare angles of the sail, in the different orbital regimes, to test the robustness of the concept. Then, a numerical analysis is performed to validate the study in a simulated scenario where all perturbations are considered, over extended amount of time. The concept targets equatorial orbits above approximately 5,000 km. Results show that an increase of 2,200 km per year for a small device at GEO can be achieved with a CubeSat-sized sail

Assessment of fire damage in concrete structures: new inspection tools and combined interpretation of results

The assessment of fire damage in concrete structures involves two complementary major tasks: on-site investigation and interpretation of the observed evidences. Concerning the first point, some innovative and viable inspection techniques are briefly illustrated in the paper. Their common trait is the ability to provide an immediate feedback, with no need for time-consuming laboratory analyses. As for the interpretation of results, the main issue is to harmonize the information provided by the available diagnostic tools, which is limited to specific ranges of temperature and to definite depths in the exposed concrete cover. The proposed approach relies on the parametric analysis of the compartment temperature developed in a set of realistic fire scenarios. The resulting temperature profiles are then checked against the results of the Non-Destructive inspection techniques, in order to select the most likely thermal input undergone by the structural members

Casting a new light on the democratic spectator

The idea of citizens being mere spectators who "watch" politics is widespread in public and academic debates. Scholarship in relation to democratic theory tends to see spectatorship as a state in which citizens are politically uninterested, isolated, and passive. Although this understanding aptly captures the problems about the idea of spectatorship, it is only a partial awareness and prevents us from seeing that positive forms of spectatorship are also possible. I show that positive spectatorship occurs when citizens show an interest in one or more political problems and, together with others, strive to understand them better. I consider the distinctive elements of this form of spectatorship characterized by careful observance, relationality, and proactivity. I argue that it is normatively desirable, and I reflect on the ways in which positive spectatorship helps thinking about democratizing politics. Relatedly, I also revisit the theatrical metaphor of politics, which is often associated to the concept of spectatorship as something negative for democracy. I argue that, when combined with a proper understanding of spectatorship, the theatrical metaphor can be used originally to envisage ways forward in the democratization of our societies

Dysphagia Management in Schools: A Survey of Speech-Language Pathologists

Introduction: To date, few research studies have evaluated pediatric feeding and swallowing practices in school systems across the United States. This study aims to i) understand the factors that impact a speech-language pathologists (SLPs) level of comfort in providing these services, ii) to identify barriers to service provision, iii) develop a concrete understanding of a SLPs role in providing feeding and swallowing services in a school setting, and iv) to identify the types of service suggested by school-based SLPs in response to a fictional case study. Methods: School-based SLPs and clinical fellows were invited to participate in a 10-15 minute web-based survey. The survey questions focused on basic demographic information, vocational history, barriers to treatment, and clinician comfort level. In addition, survey respondents were asked to develop a treatment plan in response to a fictional case study. In total, 200 anonymous survey responses were collected and analyzed. Results: Descriptive data, summarizing the demographic and vocational factors of the survey respondents, are provided. In addition, independent Pearson Chi-Square analyses were performed to determine the degree of association between the demographic/vocational factors and the SLPs self-reported comfort level. The results of these correlation analyses are reported and discussed. Barriers to dysphagia management and a summary of the services currently provided in the school setting are discussed from the perspective of professional practice issues. Analysis of the case study results indicated a wide range of treatment plans. The most common type of direct intervention suggested was an oral motor exercise regime, followed by diet modifications and the implementation of safe swallow strategies. Discussion: The survey results indicate a number of factors impact clinician comfort level including geographic region, previous medical experience and current service provision. A number of barriers to practice were identified which include academic and/or clinical preparedness and concerns related to the educational relevance of service. Approximately 26.5% of survey respondents indicated that there were providing feeding and swallowing related services in a school setting with 98.1 % of these clinicians providing collaborative consultation. The case study results highlighted the variability in treatment approaches

Ultrastrong light-matter interaction in quantum technologies

120 p.En esta Tesis, hemos analizado teóricamente fenómenos cuánticos novedosos emergentes en el régimenultrafuerte (USC) de interacción entre luz y materia. Nos hemos enfocado en procesos que pueden serobservados usando tecnologías cuánticas actuales o que puedan motivar desarrollos tecnológicospróximos. Los resultados presentados en esta Tesis pueden ser agrupados en dos categorías. Por un lado,hemos estudiado modelos que pueden ser implementados usando circuitos superconductores, unaplataforma cuántica donde el régimen USC puede ser alcanzado de forma natural. En especifico, hemosestudiado la transferencia de excitaciones en cadenas de resonadores cuánticos, generación deentrelazamiento cuántico vía efecto Casimir dinámico y ingeniería de estados cuánticos en el régimenUSC. Por otro lado, hemos desarrollado métodos para reproducir la física de la interacción ultrafuerte ensistemas de iones atrapados y de átomos fríos en retículos ópticos. Esas propuestas aprovechan lasventajas de cada plataforma cuántica para alcanzar regímenes de parámetros e implementar medidas queno son accesibles en implementaciones naturales de los procesos considerados.Los resultados presentado en esta Tesis profundizan nuestra comprensión de fenómenos cuánticosrelativos al régimen ultrafuerte de interacción entre luz y materia. Además, nuestras propuestas aspiran apromover el desarrollo conjunto de herramientas teóricas y técnicas experimentales en esta área deinvestigació

Combined while-drilling techniques for the assessment of deteriorated concrete cover

In this paper the idea of monitoring the resistance encountered while taking a sample from a concrete structure and to combine this data with the analysis of the extracted material has been regarded as a method for detecting the possible deterioration of the concrete cover. In the common case of core drilling, the time spent for a unit penetration proved to be a good indicator of the local material response. Hence, the laboratory analyses can be easily integrated with this preliminary scan of the material quality, which comes at no cost once the acquisition of samples has been planned. On the other hand, hammer-drilling of small holes is a definitely faster and less invasive alternative for inspecting the mechanical response at increasing depth within the cover. Although this method is not intended to provide a material sample, the analysis of the ground-concrete powder and the visual inspection of the remaining hole proved to be a viable alternative to the traditional examination of cores

A comparative analysis of state historic tax credit programs as tools for affordable housing projects

Historic tax credit (HTC) programs and similar financial incentives have historically filled a critical financing gap in the rehabilitation of historic buildings, effectively providing capital to projects that otherwise would not be economically feasible and generating development in small or economically disadvantaged communities. Specifically, state HTC programs parallel to the federal historic tax credit program leverage additional private and local investment and encourage the stewardship and rehabilitation of historic buildings. State HTC programs also generate several benefits throughout local communities, including the creation and preservation of affordable housing units. As cities seek out ways to mitigate a growing number of affordable housing problems and reinvest in their historic built environment, financial incentives at the state level figure to have an important, if not critical, role. Therefore, this thesis cross-analyzes all state historic tax credit programs throughout the United States to determine the most effective attributes for generating rehabilitation projects with affordable housing outcomes. This thesis identifies how state programs can catalyze affordable housing through the historic built environment by way of a comparative analysis of the regulatory structure of state HTC programs and a qualitative synthesis of program data from recent fiscal years. The analysis relies on a national survey of existing enabling legislation across each state, HTC coordinator communication, and case studies to determine the enabling and constraining attributes of state HTC programs as determinants of affordable housing rehabilitations and preservation