Enhancing the economics of satellite constellations via staged deployment and orbital reconfiguration

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2003.Includes bibliographical references (p. 171-175).The "traditional" way of designing constellations of communications satellites is to optimize the design for a specific global capacity. This approach is based on a forecast of the expected number of users and their activity level, both of which are highly uncertain. It can lead to economic failure if the actual demand is smaller than the one predicted. This thesis presents an alternative approach to the design process to reduce the economic risks. It proposes to deploy constellations in a staged manner, starting with a smaller, more affordable capacity that can be increased if necessary. When the capacity is increased, additional satellites have to be launched and the existing constellation needs to be reconfigured on orbit. Technically, it implies that particular design elements are initially embedded in the design to allow the reconfiguration. Such elements are called "real options" and give decision makers the right but not the obligation to increase the capacity of the system after its initial deployment. This approach reframes the design objectives. Instead of determining an optimal design for a specific capacity, paths of architectures are sought in the trade space. A general framework is presented to identify the paths that offer the most flexibility given different demand scenarios. It is then applied to LEO constellations of communications satellites. Improvements in the life cycle costs on the order of 30% can be obtained for different discount rates and volatilities. This value of flexibility has to be compared to the actual price of the real options. A general method is proposed to study this problem and two technical solutions are proposed.by Mathieu Chaize.S.M

Les normes et les règles de rédaction d’un savoir gestuel : l’exemple des livres d’escrime à la fin du Moyen Age

Dans le processus de rédaction d’un savoir technique gestuel, trois éléments sont incontournables : les mots, l’ordre du propos et son éventuelle illustration graphique. Ensembles, ces éléments sont le support de la compréhension, mais des témoins de normes intellectuelles qui président à la confection de la source historique. Les livres traitant des Arts Martiaux, les livres d’armes, ne font pas exception à cette règle. En essaimant tout au long des XVIe et XVe siècles des textes, des illustrations, des vocabulaires et des énoncés spécifiques, ils offrent un regard précieux sur les traditions techniques et intellectuelles de la fin du Moyen Age et du début de l’époque Moderne.Cet article a pour ambition de présenter les contraintes de la rédaction d’un livre d’armes et les outils, normés, qui contribuent à surmonter ces mêmes contraintes. En présentant, à travers les deux grandes traditions techniques martiales de la fin du Moyen Age, les normes de conception et de rédaction d’un savoir gestuel, ce travail montrera que les structures et les normes de rédaction ne sont pas de simples supports de compréhension. Ce sont aussi, mais surtout des éléments constitutifs des techniques que l’on cherche à appréhender. La nature des documents supplante ainsi leur nature de simple témoin technique pour les transformer en véritables témoins des modes de pensées des techniques gestuelles de la fin du Moyen Age. En appliquant la norme à la technique, en modifiant parfois cette dernière pour qu’elle respecte les règles, les auteurs de livres d’armes ont ainsi fait plus que conserver des techniques. Ils ont témoignés des racines intellectuelles des traditions gestuelles.In the writing process of technical knowledge, three elements are essential: words, order of words and the possible graphic illustration. Together, these elements support the understanding, but also act as witnesses of intellectual standards that govern the creation of this historical source. Books about Martial Arts, or fighting-books, are no exception to this rule. Analyzing texts, illustrations, vocabularies and specific statements from the fourteenths and fifteenth centuries, we find a valuable perspective on the technical and intellectual traditions of the late Middle Ages and early Modern period.This article aims to present the constraints of writing a standardized fighting-book as well as tools that help to overcome these constraints. Through the two major traditions of martial techniques in the late Middle-Ages - design standards and writing gestural knowledge - this work brings to light that structure and drafting standards are not mere understanding tools. They are also, but mainly technical elements that we seek to understand. Thus, the nature of the documents supersedes their role of simple technical indicators and transforms them into true witnesses of the thought processes of gestural techniques in the late Middle-Ages. By applying the standard technique, changing it at times so as to comply with the rules, the authors of fighting-books have done more than preserve techniques. They have testified the intellectual roots of these gestual traditions

Protein encapsulation in liposomes: efficiency depends on interactions between protein and phospholipid bilayer.

BACKGROUND: We investigated the encapsulation mechanism of enzymes into liposomes. The existing protocols to achieve high encapsulation efficiencies are basically optimized for chemically stable molecules. Enzymes, however, are fragile and encapsulation requires in addition the preservation of their functionality. Using acetylcholinesterase as a model, we found that most protocols lead to a rapid denaturation of the enzyme with loss in the functionality and therefore inappropriate for such an application. The most appropriate method is based on lipid film hydration but had a very low efficiency. RESULTS: To improve it and to propose a standard procedure for enzyme encapsulation, we separate each step and we studied the effect of each parameter on encapsulation: lipid and buffer composition and effect of the different physical treatment as freeze-thaw cycle or liposomes extrusion. We found that by increasing the lipid concentration, increasing the number of freeze-thaw cycles and enhancing the interactions of the enzyme with the liposome lipid surface more than 40% of the initial total activity can be encapsulated. CONCLUSION: We propose here an optimized procedure to encapsulate fragile enzymes into liposomes. Optimal encapsulation is achieved by induction of a specific interaction between the enzyme and the lipid surface

Intensive care unit admission in chronic obstructive pulmonary disease: patient information and the physician’s decision-making process

International audienceIntroduction: ICU admission is required in more than 25% of patients with chronic obstructive pulmonary disease (COPD) at some time during the course of the disease. However, only limited information is available on how physicians communicate with COPD patients about ICU admission. Methods: COPD patients and relatives from 19 French ICUs were interviewed at ICU discharge about their knowledge of COPD. French pulmonologists self-reported their practices for informing and discussing intensive care treatment preferences with COPD patients. Finally, pulmonologists and ICU physicians reported barriers and facilitators for transfer of COPD patients to the ICU and to propose invasive mechanical ventilation. Results: Self-report questionnaires were filled in by 126 COPD patients and 102 relatives, and 173 pulmonologists and 135 ICU physicians were interviewed. For 41% (n = 39) of patients and 54% (n = 51) of relatives, ICU admission had never been expected prior to admission. One half of patients were not routinely informed by their pulmonologist about possible ICU admission at some time during the course of COPD. Moreover, treatment options (that is, non-invasive ventilation, intubation and mechanical ventilation or tracheotomy) were not explained to COPD patients during regular pulmonologist visits. Pulmonologists and ICU physician have different perceptions of the decision-making process pertaining to ICU admission and intubation. Conclusions: The information provided by pulmonologists to patients and families concerning the prognosis of COPD, the risks of ICU admission and specific care could be improved in order to deliver ICU care in accordance with the patient's personal values and preferences. Given the discrepancies in the decision-making process between pulmonologists and intensivists, a more collaborative approach should probably be discussed

The effect of surfactant chain length on the morphology of poly(methyl methacrylate) microcapsules for fragrance oil encapsulation

The solvent evaporation method for producing microcapsules relies upon the correct wetting conditions between the three phases involved in the synthesis to allow core-shell morphologies to form. By measuring the interfacial tensions between the oil, polymer and aqueous phases, spreading coefficients can be calculated, allowing the capsule morphology to be predicted. In this work we explore the effect of surfactant chain length on capsule morphology using poly(methyl methacrylate) as the polymer and hexadecane as the core. We compared the predicted morphologies obtained using the polymer as a solid, and the polymer dissolved in dichloromethane to represent the point at which capsule formation begins. We found that using the polymer in its final, solid form gave predictions which were more consistent with our observations. The method was applied to successfully predict the capsule morphologies obtained when commercial fragrance oils were encapsulated

First demonstration of 30 eVee ionization energy resolution with Ricochet germanium cryogenic bolometers

The future Ricochet experiment aims to search for new physics in the electroweak sector by measuring the Coherent Elastic Neutrino-Nucleus Scattering process from reactor antineutrinos with high precision down to the sub-100 eV nuclear recoil energy range. While the Ricochet collaboration is currently building the experimental setup at the reactor site, it is also finalizing the cryogenic detector arrays that will be integrated into the cryostat at the Institut Laue Langevin in early 2024. In this paper, we report on recent progress from the Ge cryogenic detector technology, called the CryoCube. More specifically, we present the first demonstration of a 30~eVee (electron equivalent) baseline ionization resolution (RMS) achieved with an early design of the detector assembly and its dedicated High Electron Mobility Transistor (HEMT) based front-end electronics. This represents an order of magnitude improvement over the best ionization resolutions obtained on similar heat-and-ionization germanium cryogenic detectors from the EDELWEISS and SuperCDMS dark matter experiments, and a factor of three improvement compared to the first fully-cryogenic HEMT-based preamplifier coupled to a CDMS-II germanium detector. Additionally, we discuss the implications of these results in the context of the future Ricochet experiment and its expected background mitigation performance.Comment: 10 pages, 5 figures, 1 tabl

Fast neutron background characterization of the future Ricochet experiment at the ILL research nuclear reactor

The future Ricochet experiment aims at searching for new physics in the electroweak sector by providing a high precision measurement of the Coherent Elastic Neutrino-Nucleus Scattering (CENNS) process down to the sub-100 eV nuclear recoil energy range. The experiment will deploy a kg-scale low-energy-threshold detector array combining Ge and Zn target crystals 8.8 meters away from the 58 MW research nuclear reactor core of the Institut Laue Langevin (ILL) in Grenoble, France. Currently, the Ricochet collaboration is characterizing the backgrounds at its future experimental site in order to optimize the experiment's shielding design. The most threatening background component, which cannot be actively rejected by particle identification, consists of keV-scale neutron-induced nuclear recoils. These initial fast neutrons are generated by the reactor core and surrounding experiments (reactogenics), and by the cosmic rays producing primary neutrons and muon-induced neutrons in the surrounding materials. In this paper, we present the Ricochet neutron background characterization using $^3$He proportional counters which exhibit a high sensitivity to thermal, epithermal and fast neutrons. We compare these measurements to the Ricochet Geant4 simulations to validate our reactogenic and cosmogenic neutron background estimations. Eventually, we present our estimated neutron background for the future Ricochet experiment and the resulting CENNS detection significance.Comment: 14 pages, 14 figures, 1 tabl