86,548 research outputs found
Development of Green Hydrogen Peroxide Monopropellant Rocket Engines and Testing of Advanced Catalytic Beds
No full textWith the financial support of the European Space Agency, Alta S.p.A. in Italy and DELTACAT Ltd. in the United Kingdom are conducting a joint study on the development of two hydrogen peroxide monopropellant thruster prototypes (5 and 25 N vacuum thrust) using advanced catalytic beds. The present article illustrates the results of recent tests on the developed catalysts and the main aspects of the thruster design as well as of the technique used for quantitative determination of the observed decomposition rates. Preliminary results indicate that platinum deposited on a γ−alumina substrate yields the best performance with respect to the other solutions under consideration
Development of green hydrogen peroxide monopropellant rocket engines and testing of advanced catalytic beds
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Variations on the Author
No full text“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
One ring (or two) to hold them all. On the structure and function of protein nanotubes
No full textUnderstanding the structural determinants relevant to the formation of supramolecular assemblies of homo-oligomeric proteins is a traditional and central scope of structural biology. The knowledge thus gained is crucial both to infer their physiological function and exploit their architecture for bionanomaterials design. Protein nanotubes made by one-dimensional (1D) arrays of homo-oligomers can be generated by either a commutative mechanism, yielding an “open” structure (e.g. actin), or a non-commutative mechanism, whereby the final structure is formed by hierarchical self- assembly of intermediate “closed” structures. Examples of the latter process are poorly described and the rules by which they assemble have not been unequivocally defined. We hereby collected and investigated examples of homo-oligomeric circular arrangements that form 1D filaments of stacked rings by the non-commutative mechanism in vivo and in vitro. Based on their quaternary structure, circular arrangements of protein subunits can be subdivided into two groups that we call Rings of Dimers (RoDs), e.g peroxiredoxin and SP1, and Dimers of Rings (DoRs), e.g. thermosome, depending on the sub-structures that can be identified within the assembly (and, in some cases, populated in solution under selected experimental conditions). Structural analysis allowed us to identify the determinants by which ring-like molecular chaperones form filamentous-like assemblies and to formulate a novel hypothesis by which nanotube assembly, molecular chaperone activity and macromolecular crowding may be interconnected
Verification campaign of small test platform hosting electric propulsion systems
No full textThe growing interest of the market in nano-satellites is pushing the technology associated with development of these small platforms Among the enabling technologies, miniaturized electrical propulsion (EP)systems deeply increase the range of missions performed with multi-unit CubeSats (6U+). Actually, the level of readiness of these technologies is still low, due to the lack of effective and safe processes and facilities to verify and validate them before in-orbit demonstration. One of the major issue sis to understand what the mutual impact of an electric propulsion system and the spacecraft technology is, in order to avoid loss of onboard functionalities and anomalies and misbehaviours. The present paper deals with the verification campaign of a versatile test platform based on CubeSat-like technology, able to host a wide range of EP system favouring an effective verification campaign thanks to precise procedures and a proper setup of the facility (the Small Plasma Facility /SPF) of ESA-ESTEC). The platform is equipped with specific sensors and tools, i.e. temperature sensors (NTC), current and voltage sensing circuits, strips of open resistors, magnetometers, silica wafers mounted on the CubeSat faces, and a very precise (24-bit resolution) acquisition system. The objective is to obtain unprecedented information that, integrated with external devices normally used for the verification campaign of propulsion system, e.g. faraday cups and Magnetic Field Mapper, allows to assess the functional behaviour of the integrated system (platform and EP system). The test platform has already been integrated with SPF and the functional test campaign has been successfully performed, demonstrating the test platform is ready for final tests
Performances and Emissions of a Small Size Diesel Powered Generator Fueled with Vegetable Oil and its Water-in Emulsions
No full textDiesel engines are worldwide used in the transport, electricity generation and shaft power and they
burn oil products which can be partially or totally replaced by alternative fuels, such as vegetable oils.
Vegetable oils have physical characteristics close to those of diesel oil and as they are of plant origin,
they have the potential to significantly reduce CO2 emissions into the atmosphere. Nowadays fuelling
compression ignition engine with vegetable oil is a feasible solution, with a relevant number of
working plants, mainly for medium size electric generators; not the same can be told about small size
diesel generators. Few marine propulsion examples are also reported. In this paper, a rapeseed oil and
some its water-in emulsions, in different percentage 5, 10 and 15% v/v, have been fuelled in a small
size Diesel engine used as power generator in a co-generation system. Tests were conducted in a
naturally aspirated Scania DC09 direct injection four-stroke 250kW, 5-cylinders, 9.3 dm3
displacement Diesel engine from low load to 120kW as load conditions. Emulsions were produced on
site by a device that adds steam to vegetable oil, so continuously feeds the engine with emulsified oil
at about 60°C; tests were also carried out with sample emulsions made offline with an ultrasonic
device. Gaseous (CO, HC, NO/NOx, CO2) and particulate emissions have been characterized in steady
state conditions. CO, HC and particulate emissions are strongly reduced by fuelling vegetable oil
emulsions compared to commercial diesel fuel. NOx emission are not significantly affected, rather a
small increase is observed in some conditions; authors believe that an engine optimized for reducing
NOx with diesel oil requires a different injection tuning, not feasible during the experiments
The chemical advantage of sulfur over selenium: controlling the switching-in-function of the moonlighting behaviour of Peroxiredoxin.
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Design of a test platform for miniaturized electric propulsion
No full textNanosatellites represent an emerging opportunity to pursue a broad set of mission goals, including remote sensing, technology demonstration, and communications, at low cost and fast delivery. These new opportunities require a technological improvement to increase capabilities such as orbit change and transfer, formation flying, and constellation build up, close proximity operations and deorbiting. In this sense, miniaturized electrical propulsion systems increase the range of missions performed with multi-unit CubeSats. At subsystem level, many concepts have been recently developed but their level of readiness is limited. Moreover, the integration of propulsion poses new challenges at system level that influence heavily the spacecraft design and its verification. The present research, developed by Politecnico di Torino and supported by ESA, intends to build a flexible test platform and define effective procedures to support the evaluation of suitable propulsion systems for future nanosatellites. The main objectives are to investigate the interaction of propulsion systems with CubeSat-technology from different perspectives (mechanical, electrical, magnetic, and chemical) and to evaluate the performance of the integrated platform. The test platform is a 6U CubeSat able to host electric propulsion systems selected among European solutions, providing mechanical, electrical and data interfaces. A flexible and robust structure holds and protects the propulsion system and avionics, and externally interfaces the test platform with the facility of ESA/ESTEC propulsion laboratory. The on-board Electrical Power System adapts the voltage and power provided by batteries to serve loads up to 2A @ 28V. Different protocols are included in the on-board computer to exchange data and commands with a range of propulsion systems. The test platform is equipped with a wide range of sensors (e.g. temperature sensors, accelerometers, and magnetometers) to measure and acquire parameters both of the propulsion system and of on-board avionics. Data are stored on-board and sent to the ground support system via wired and/or RF links. The test platform operations are controlled through commands sent by the operator and by autonomous onboard routines in charge of managing transitions between operative modes and for detection, identification and recovery of failures. The test platform will be ready in December 2018, and it will represent the first important step for the evaluation of electrical propulsion systems integrated in small satellites. The paper describes into the detail the design and development of the platform and the plan for the test campaign
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