4,591 research outputs found
Laboratory Studies of Hypervelocity Impacts on Solar System Analogues
No full textImpact cratering and asteroid collisions are major processes throughout the Solar System. Although previous collision-related impact investigations exist (Flynn et al. 2015, Holsapple et al. 2002 and Burchell et al. 1998 are good examples), in the works covering this broad range of investigation, the targets are non-rotating (for the purposes of catastrophic disruption) and different temperature conditions are not considered (for impact cratering). Accordingly, I present experimental processes and data, regarding hypervelocity impact experiments into analogues of (1) rotating asteroids and (2) temperature dependant terrestrial planetary rock.
During the course of this work, it was necessary to develop new apparatus and new experimental techniques such as three separate target holders to aid in both catastrophic disruption and heated impact projects, a 3-dimensional model analysis of craters and a completely new, statistically robust, technique to determine a complete crater profile called the KDM method where KDM is Kinnear-Deller-Morris.
The main result from this work showed that during an asteroid impact collision where the asteroid is not rotating, the impact energy density for catastrophic disruption is Q*static = 1442 ± 90 J kg-1. However, when the target asteroid was rotating, the condition Q*rotation = 1097 ± 296 J kg-1. The mean value of Q* had thus reduced, but the spread in the data on individual experiments was larger. This leads to two conclusions. The mean value for Q*, based on measurements of many impacts, falls, due to the internal forces acting in the body which are associated with the rotation. This energy term reduction means that the amount of energy to instigate catastrophic disruption is lower and that a rotating asteroid is effectively weaker upon impact than a stationary asteroid. However, the spread in the results indicates that this is not a uniform process, and an individual result for Q* for a rotating or spinning target may be spread over a large range. For the temperature related impacts, as the targets were heated to approximately 1000 K, the target rocks showed an impact dependence more similar to a plastic phase-state than to solidus, due to being held close to temperatures associated with semi-plastic phases. Basalt impact craters displayed this relationship greatest with crater sizes becoming smaller at the higher temperature ranges but larger in the colder brittle solidus temperatures, partly explained in experiments by increased spallation
Vacuum Insulation Panels Applied in Building Constructions
No full textDue to sustainability and due to international treaties, it is desired and required to reduce greenhouse gas emissions drastically. One contributor to these emissions is the burning of fossil fuels for generating power and electricity to be used in and for buildings. Buildings and building-related processes are responsible for about 40% of the primary energy consumption in the European Union. More than half of this energy is applied for heating systems in dwellings and commercial buildings. The European Union therefore has laid down new energy performance requirements for buildings in the European Directive on the Energy Performance of Buildings. Moreover, a reduction of energy losses of buildings during their occupational phase is important for facilitating the implementation of sustainable energy sources in the built environment. Increasing the insulation value of the envelope of buildings may contribute to this reduction of primary energy use. Two strategies can be followed. The first strategy is to increase the thickness of the thermal insulation layer. Until recently, this strategy has primarily been adopted. If, however, German or Swiss Passivhaus standard is applied, the thickness of this insulation layer would increase to beyond 30 cm, resulting in very thick building enclosures. The second, more innovative, strategy for reducing energy losses through the building skin would be the application of more effective thermal insulators. One such more effective thermal insulator is a vacuum insulation panel, abbreviated as VIP. A VIP consists of an open-celled core material which is evacuated and then tightly sealed into a barrier envelope to maintain this vacuum. The vacuum inside the pores of the core material reduces the thermal conductivity of the product significantly, as a result of which the thickness of the insulation layer can be reduced to obtain a certain performance. This reduction of thickness is among the most promising features for large-scale application of VIPs in the building industry. However, integration of VIPs into buildings must be performed very meticulously for several reasons; first, due to its nature a VIP cannot be processed on site and needs careful planning in advance; second, it is very sensitive to mechanical damage thus requiring careful handling; third, thermal bridges along the panel’s edges reduce its performance; fourth, the composite system is highly subjected to aging. This dissertation therefore looks into many of these aspects, presents several calculation tools and shows how VIPs can be applied in façade panels, EPS insulation boards and as under-floor insulation. With the wide-spread proliferation of VIPs in buildings a more sustainable and healthy environment can then be achieved.Building TechnologyArchitectur
Book Review: Reginald M.J. Oduor’s Introduction to Ethics
No full textTITLE OF BOOK: Introduction to Ethics
AUTHOR: Reginald M.J. Oduor
Nairobi: Sophia Publications Ltd., 2009, 116 pages
COVER: Paperback
ISBN: 9966-7457-0-X
This book is a product of more than a decade of Oduor’s experience in teaching ethics (moral philosophy) at the University of Nairobi. In the course of this introduction, the reader gets to see the techniques of philosophic reflection in action, as they are employed to scrutinise various pertinent moral questions
Hypervelocity impact in low earth orbit: finding subtle impactor signatures on the Hubble Space Telescope
No full textpublisher: Elsevier articletitle: Hypervelocity impact in low earth orbit: finding subtle impactor signatures on the Hubble Space Telescope journaltitle: Procedia Engineering articlelink: http://dx.doi.org/10.1016/j.proeng.2017.09.746 content_type: article copyright: © 2017 The Author(s). Published by Elsevier Ltd.© 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the 14th Hypervelocity Impact Symposium 2017. The file attached is the Published/publisher’s pdf version of the article.NHM Repositor
Comments on “Precipitation kinetics of Al–1.12Mg2Si–0.35Si and Al–1.07Mg2Si–0.33Cu alloys”
No full textIt is shown that in analysing DSC data of precipitation reactions in Al–1.12Mg2Si–0.35Si, Al–1.07Mg2Si–0.33Cu and Al–1.0Mg2Si–0.5Ag alloys in work by Gaber et al., accurate values for the activation energies are obtained by applying the method derived by the present author (the Type B-1.92 method). Values obtained from other analysis methods reported by Gaber et al. are less accurate. Averaging activation energies obtained by different methods introduces inaccuracies and obscures these inaccuracies, especially if the set of methods applied includes highly inaccurate ones, such as the Ozawa and Takhor methods
Survival of organic materials in hypervelocity impacts of ice on sand, ice, and water in the laboratory
No full textAcknowledgments We thank STFC for support for the light gas gun at Kent. We wish to acknowledge the technical support provided by Colin Taylor in Aberdeen. We thank the referees for their useful and insightful comments on the manuscript.Peer reviewe
Optical Flow Based State Estimation for an Indoor Micro Aerial Vehicle
No full textThis work addresses the problem of indoor state estimation for autonomous flying vehicles with an optic flow approach. The paper discusses a sensor configuration using six optic flow sensors of the computer mouse type augmented by a three-axis accelerometer to estimate velocity, rotation, attitude and viewing distances. It is shown that the problem is locally observable for a moving vehicle. A Kalman filter is used to extract these states from the sensor data. The resulting approach is tested in a simulation environment evaluating the performance of three Kalman filter algorithms under various noise conditions. Finally, a prototype of the sensor hardware has been built and tested in a laboratory setup. Paper published: Verveld, M.J., Chu, Q.P., De Wagter, C. and Mulder, J.A. “Optic Flow Based State Estimation for an Indoor Micro Air Vehicle” AIAA Guidance, Navigation, and Control Conference, August 2010, Toronto, Canada AIAA 2010-8209, DOI: 10.2514/6.2010-8209Aerospace EngineeringControl & Simulatio
Transient time-averaged spectra of rapidly-modulated semiconductor lasers
No full textUsing the computed solution of multimode rate equations, and including wavelength-chirping effects via the dependence of the refractive index on carrier concentration, it is possible to calculate time-averaged spectra of rapidly-modulated lasers. The averaging time may be used to simulate the effects of measuring equipment with a specific time response. The results show a characteristic line structure within the dominant longitudinal mode spectrum, and are in qualitative agreement with experimental measurements reported by other author
Gift inscription in Minions of the Moon: a little book of song and story
No full textThis edition includes a gift inscription possibly penned by the author, Madison Julius Cawein, "Frank on Valentines Day, 1914. M.J." Madison Julius Cawein (1865-1914).Cawein, Madison Julius, 1865-1914
Cooling and heating rate dependence of precipitation in an Al-Cu alloy
No full textDifferential scanning calorimetry and X-ray diffraction were used to study the cooling and heating rate dependence of precipitation in an Al-1.66 at.% Cu alloy. After homogenizing, cooling at a rate of 22 K min?1 (SC22) is sufficient to retain all copper in solid solution. GP-zone formation during subsequent heat treatment is hindered; this is ascribed to an insufficient number of (excess) vacancies. After a water quench (WQ) a large number of GP zones are formed during subsequent storage at room temperature for 1 h. The heat content of the GP-zone dissolution effect can quantitatively be described in terms of the heat of precipitation of GP I zones and the solid solubilities as derived from the GP I zone solvus. The heat content of the combined ??-/?-phase precipitation effect appeared to be proportional to the number of copper atoms precipitated, yielding an average value for the heat of copper precipitation of 36 kJ mol?1 copper. The activation energy for ??-phase formation is 0.75 eV for SC22 specimens and 1.10 ± 0.10 eV for WQ specimens. The differences in reported activation energies for ??-phase formation are discussed in terms of mobility of dissolve atoms (related to the vacancy concentration), interfacial energy and direction of growth (normal or perpendicular to the ??-phase plate)
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