1,721,073 research outputs found
New in-orbit self-assembly principles and manufacturing techniques
Full text linkMany materials (e.g. different types of inorganic and organic alloys) in the liquid state consist of fine particles or droplets dispersed in an external (fluid) matrix. Once the effects of gravity are no longer felt, the different densities of the involved phases no longer represent a constraint forcing the dispersed particles or droplets to separate from the fluid through sedimentation or flotation; exploring self-assembly principles becomes therefore possible. Self-induced particle ordering is indeed emerging as one of the most relevant or promising approaches to develop in-space heterogeneous systems or materials consisting of parts that can recognize and bind to each other or form specific templates or patterns
New methods for the transport and management of lunar regolith
Full text linkIn the field of space exploration, it is essential to assemble and transport particles for various applications, for example transporting lunar and Martian soil (typically regolith), for mining, to study geological aspects and establish habitats on the Moon or Mars. The ability to synthesize complex materials directly in space or build specific structures on the surface of other planets is one the main challenges to be addressed in such a context. In this regard, the utilization of lunar regolith is being explored with regard to several potential applications, e.g., as feedstock for 3D printing and even as a solidsupport substrate for plant growth, a source for extraction of essential plant-growth nutrients, a substrate for microbial populations in the degradation of wastes, a source of O2 and H2, which may be used to manufacture water [1-3]. However, the lunar and Martian soils are difficult to handle, because they are made of abrasive and reactive materials. Regardless of its intended use, the use of lunar regolith is hindered by its intrinsic nature, which makes its management (transfer from the surface of the Moon inside ‘containers’ or transport inside ‘pipes’) relatively difficult. Lunar regolith is characterized by very strong electrostatic effects and internal friction, which strongly limit its ‘flowability’
Convective states and patterning behavior in Lunar Regolith under the effect of vertical vibrations
Full text linkIn the field of space exploration, it is essential to deal with solid “particles” for various applications, for example transporting lunar and Martian soil (typically regolith), for mining, to study geological aspects and establish habitats on the Moon or Mars. However, methods to handle these materials remain untested because they are made of abrasive and reactive components which by their nature make them hard to handle mechanically. In the present project, novel strategies to manipulate such granular systems based on the application of “vibrations” are explored. Special attention is devoted to the unique states which are produced when such materials are subjected to concurrent vibrations and gravity (vertical shaking). By means of a concerted approach based on experimental work in synergy with relevant computational tools for systems where the assumption of continuum is not applicable, we show that circumstances exist where lunar regolith can behave as a kind of “fluid” and produce interesting patterning behaviors. The problem is parametrically investigated by allowing the frequency and spatial amplitude of the imposed vibrations to span relatively wide intervals for different depths of the considered layer of material (simulant). The results are critically discussed and placed in a proper theoretical context through comparisons with earlier experimental findings where the analysis was limited to monodisperse collection of particles (spheres with fixed density and diameter as opposed to the irregular shape and varying size of lunar regolith)
Access to the space environment and low earth orbit : what are the opportunities
Full text linkFor many years, scientists have been utilising platforms both in orbit and on Earth to conduct fundamental research. The ESA Erasmus archives16, contain a database of more than 4100 funded and/or co-founded R&D experiments related to the space sector, from advanced metallurgical processes in microgravity to how biofilms form. As of September 2023, there are already a number of existing incumbents involved in active flight operations, including Arianne Space, Blue Origin, Boeing, Northrop Grumman, Rocket Lab, SpaceX and Virgin (Galactic) to name a few. There are also a number of active access providers supporting customers to fly R&D payloads in space including organisations like Airbus (Bartolomeo), Axiom Space, Ice Cubes, Space Forge (Forge Star), Kayser Space, Open Cosmos and Sierra Space, again to name a few. These capabilities are augmented through access to analogue platforms on Earth, including Drop Towers (e.g. Zarm Drop Tower), Parabolic flights (e.g. Novespace), Sounding rockets (e.g. Swedish Space Consortium) and centrifuges (e.g. ESA ESTEX Long Arm Centrifuge) allowing researchers to understand the effects of variable gravity on material processes on Earth (examples of research on these platforms is discussed later in this section)
Considerations for material properties and processes in space and their impact
Full text linkGravity dominates everything on Earth, from the way life has developed to the way many types of materials are formed. Onboard spacecrafts orbiting the Earth or other vehicles in free-fall conditions; however, the influence gravity is barely felt. In this “microgravity environment”, scientists can investigate phenomena, which are impossible on Earth or are masked by the presence of gravity. In this condition various effects are significantly altered, in particular convection, buoyancy, hydrostatic pressure and sedimentation.26 27 In this virtual absence of gravity as we know it, therefore, space flight gives scientists a unique opportunity to study various states of matter (solids, liquids and gases), and discern forces and processes that are interwoven or overshadowed in normal gravity. Accordingly, microgravity can be regarded as an important tool for improving our fundamental understanding of several complex phenomena, which are of great interest in several technological fields
Buoyancy-driven flow instabilities in liquid bridges
Full text linkLiquid bridges have attracted much attention over the last four decades as a vehicle for performing experiments on surface-tension-driven flows in well-controlled conditions. The intrinsic advantages of this unique configuration essentially reside in the ability to maximize the ratio between the area of the free surface and that of all the other solid surfaces. As even a cursory perusal of the literature would immediately confirm, however, no experimental works on purely buoyant convective states have been produced to date given the inherent difficulties related to any attempt made to separate buoyancy convection from fluid motion induced by thermocapillary effects. In the present work, an attempt is made to fill this gap by considering water in conditions for which its ability to support Marangoni effects is inhibited. Liquid bridges uniformly heated from below and cooled from above are investigated experimentally by means of a laser-cut technique and the ensuing application of a Particle Image Velocimetry (PIV) technique. The examined imposed temperature differences cover the interval going from the onset of convection from an initial quiescent state up to the development of oscillatory modes of various types. The related analogies and differences with the classical supercritical modes of Marangoni convection are critically discussed
Thermal Flows
Full text linkFlows of thermal origin and heat transfer problems are central in a variety of disciplines and industrial applications. The present book entitled Thermal Flows consists of a collection of studies by distinct investigators and research groups dealing with different types of flows relevant to both natural and technological contexts. Both reviews of the state-of-the-art and new theoretical, numerical and experimental investigations are presented, which illustrate the structure of these flows, their stability behavior, and the possible bifurcations to different patterns of symmetry and/or spatiotemporal regimes. Moreover, different categories of fluids are considered (liquid metals, gases, common fluids such as water and silicone oils, organic and inorganic transparent liquids, and nano-fluids). This information is presented under the hope that it will serve as a new important resource for physicists, engineers and advanced students interested in the physics of non-isothermal fluid systems; fluid mechanics; environmental phenomena; meteorology; geophysics; and thermal, mechanical and materials engineering
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Thermal Flows
No full textFlows of thermal origin and heat transfer problems are central in a variety of disciplines and industrial applications. The present book entitled Thermal Flows consists of a collection of studies by distinct investigators and research groups dealing with different types of flows relevant to both natural and technological contexts. Both reviews of the state-of-the-art and new theoretical, numerical and experimental investigations are presented, which illustrate the structure of these flows, their stability behavior, and the possible bifurcations to different patterns of symmetry and/or spatiotemporal regimes. Moreover, different categories of fluids are considered (liquid metals, gases, common fluids such as water and silicone oils, organic and inorganic transparent liquids, and nanofluids). This information is presented under the hope that it will serve as a new important resource for physicists, engineers and advanced students interested in the physics of non-isothermal fluid systems; fluid mechanics; environmental phenomena; meteorology; geophysics; and thermal, mechanical and materials engineering
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