597 research outputs found
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A Hybrid Algorithm for Topology Optimization of Additive Manufactured Structures
Most topology (TO) algorithms involve the penalization of intricate structural features to eliminate manufacturing difficulties. Since additive manufacturing is less dependent on manufacturing
constraints, it becomes necessary to adapt these algorithms for AM. We propose a hybrid algorithm
consisting of an adaptive meshing strategy (AMS) and a modified form of the bidirectional evolutionary structural optimization (BESO) method. By solving a standard cantilever problem, we show
that the hybrid method offers improved performance over the standard BESO method. It is proposed
that the new method is more suitable for optimizing structures for AM in a computational efficient
manner.Mechanical Engineerin
Sensors for ceramic components in advanced propulsion systems
This report includes: (1) a survey of the current methods for the measurement of surface temperature of ceramic materials suitable for use as hot section flowpath components in aircraft gas turbine engines; (2) analysis and selection of three sensing techniques with potential to extend surface temperature measurement capability beyond current limits; and (3) design, manufacture, and evaluation of the three selected techniques which include the following: platinum rhodium thin film thermocouple on alumina and mullite substrates; doped silicon carbide thin film thermocouple on silicon carbide, silicon nitride, and aluminum nitride substrates; and long and short wavelength radiation pyrometry on the substrates listed above plus yttria stabilized zirconia. Measurement of surface emittance of these materials at elevated temperature was included as part of this effort
Volcanic-aerosol-induced changes in stratospheric ozone following the eruption of Mount Pinatubo
Measurements of lower stratospheric ozone in the Tropics using electrochemical concentrations cell (ECC) sondes and the airborne UV Differential Absorption Lidar (DIAL) system after the eruption of Mt. Pinatubo are compared with the Stratospheric Aerosol and Gas Experiment 2 (SAGE 2) and ECC sonde measurements from below the eruption to determine what changes have occurred as a result. Aerosol data from the Advanced Very High Resolution Radiometer (AVHRR) and the visible and IR wavelengths of the lidar system are used to examine the relationship between aerosols and ozone changes. Ozone decreases of 30 percent at altitudes between 19 and 26 km, partial column (16-28 km) decreases of about 27 D.U., and slight increases (5.4 D.U.) between 28 and 31 km are found in comparison with SAGE 2 climatological values
Calculation of The Band Gap Energy and Study of Cross Luminescence in Alkaline-Earth Dihalide Crystals
The band gap energy as well as the possibility of cross luminescence
processes in alkaline-earth dihalide crystals have been calculated using the ab
initio Perturbed-Ion (PI) model. The gap is calculated in several ways: as a
difference between one-electron energy eigenvalues and as a difference between
total energies of appropriate electronic states of the crystal, both at the HF
level and with inclusion of Coulomb correlation effects. In order to study the
possibility of ocurrence of cross luminescence in these materials, the energy
difference between the valence band and the upmost core band for some
representative crystals has been calculated. Both calculated band gap energies
and cross luminescence predictions compare very well with the available
experimental results.Comment: LaTeX file containing 8 pages plus 1 postscript figure. Final version
accepted for publication in The Journal of the Physical Society of Japan. It
contains a more complete list of references, as well as a more detailed
comparison with previous theoretical investigations on the subjec
A characteristics framework for Semantic Information Systems Standards
Semantic Information Systems (IS) Standards play a critical role in the development of the networked economy. While their importance is undoubted by all stakeholdersâsuch as businesses, policy makers, researchers, developersâthe current state of research leaves a number of questions unaddressed. Terminological confusion exists around the notions of âbusiness semanticsâ, âbusiness-to-business interoperabilityâ, and âinteroperability standardsâ amongst others. And, moreover, a comprehensive understanding about the characteristics of Semantic IS Standards is missing. The paper addresses this gap in literature by developing a characteristics framework for Semantic IS Standards. Two case studies are used to check the applicability of the framework in a âreal-lifeâ context. The framework lays the foundation for future research in an important field of the IS discipline and supports practitioners in their efforts to analyze, compare, and evaluate Semantic IS Standard
Mechanical properties of Ti-6Al-4V selectively laser melted parts with body-centred-cubic lattices of varying cell size
Significant weight savings in parts can be made through the use of additive manufacture (AM), a process which enables the construction of more complex geometries, such as functionally graded lattices, than can be achieved conventionally. The existing framework describing the mechanical properties of lattices places strong emphasis on one property, the relative density of the repeating cells, but there are other properties to consider if lattices are to be used effectively. In this work, we explore the effects of cell size and number of cells, attempting to construct more complete models for the mechanical performance of lattices. This was achieved by examining the modulus and ultimate tensile strength of latticed tensile specimens with a range of unit cell sizes and fixed relative density. Understanding how these mechanical properties depend upon the lattice design variables is crucial for the development of design tools, such as finite element methods, that deliver the best performance from AM latticed parts. We observed significant reductions in modulus and strength with increasing cell size, and these reductions cannot be explained by increasing strut porosity as has previously been suggested. We obtained power law relationships for the mechanical properties of the latticed specimens as a function of cell size, which are similar in form to the existing laws for the relative density dependence. These can be used to predict the properties of latticed column structures comprised of body-centred-cubic (BCC) cells, and may also be adapted for other part geometries. In addition, we propose a novel way to analyse the tensile modulus data, which considers a relative lattice cell size rather than an absolute size. This may lead to more general models for the mechanical properties of lattice structures, applicable to parts of varying size
LSST: from Science Drivers to Reference Design and Anticipated Data Products
(Abridged) We describe here the most ambitious survey currently planned in
the optical, the Large Synoptic Survey Telescope (LSST). A vast array of
science will be enabled by a single wide-deep-fast sky survey, and LSST will
have unique survey capability in the faint time domain. The LSST design is
driven by four main science themes: probing dark energy and dark matter, taking
an inventory of the Solar System, exploring the transient optical sky, and
mapping the Milky Way. LSST will be a wide-field ground-based system sited at
Cerro Pach\'{o}n in northern Chile. The telescope will have an 8.4 m (6.5 m
effective) primary mirror, a 9.6 deg field of view, and a 3.2 Gigapixel
camera. The standard observing sequence will consist of pairs of 15-second
exposures in a given field, with two such visits in each pointing in a given
night. With these repeats, the LSST system is capable of imaging about 10,000
square degrees of sky in a single filter in three nights. The typical 5
point-source depth in a single visit in will be (AB). The
project is in the construction phase and will begin regular survey operations
by 2022. The survey area will be contained within 30,000 deg with
, and will be imaged multiple times in six bands, ,
covering the wavelength range 320--1050 nm. About 90\% of the observing time
will be devoted to a deep-wide-fast survey mode which will uniformly observe a
18,000 deg region about 800 times (summed over all six bands) during the
anticipated 10 years of operations, and yield a coadded map to . The
remaining 10\% of the observing time will be allocated to projects such as a
Very Deep and Fast time domain survey. The goal is to make LSST data products,
including a relational database of about 32 trillion observations of 40 billion
objects, available to the public and scientists around the world.Comment: 57 pages, 32 color figures, version with high-resolution figures
available from https://www.lsst.org/overvie
Stress ocupacional e alteração do Estatuto da Carreira Docente portuguĂȘs
Este estudo foi realizado com 1162 professores, tendo como objetivo analisar a experiĂȘncia de stress e a sĂndrome de âburnoutâ, antes a apĂłs a alteração do Estatuto da Carreira Docente em Portugal. Assim, foram efetuadas duas avaliaçÔes em momentos temporais distintos, assumindo-se um plano transversal de recolha de dados (2004/2005, n=689 e 2008/2009, n=473). O protocolo de avaliação incluiu medidas de fontes de stress (QuestionĂĄrio de Stress nos Professores, Gomes, Silva, Mourisco, Mota, & Montenegro, 2006) e de âburnoutâ (InventĂĄrio de âBurnoutâ de Maslach â VersĂŁo para Professores, Maslach, Jackson, & Leiter, 1996; Maslach, Jackson, & Schwab, 1996, Adaptação de Gomes et al., 2006). Os resultados indicaram que a experiĂȘncia de stress e de âburnoutâ aumentou entre as duas avaliaçÔes, verificando-se em 2008/2009 aumentos em ĂĄreas relacionadas com as pressĂ”es de tempo/excesso de trabalho e com o trabalho burocrĂĄtico/administrativo e, inversamente, diminuiçÔes em ĂĄreas relacionadas com as diferentes capacidades e motivaçÔes dos alunos. Quanto Ă predição da sĂndrome de âburnoutâ, nĂŁo se verificaram alteraçÔes substanciais nas variĂĄveis preditoras nos dois momentos. Em sĂntese, os resultados indicaram aumentos nas exigĂȘncias profissionais dos professores, mas nĂŁo se pode afirmar que tal se deva Ă s alteraçÔes do Estatuto da Carreira Docente uma vez que nĂŁo observĂĄmos alteraçÔes no stress associado Ă carreira docente.(undefined
Reimagining Nashville : The Changing Place of Country
For as long as there has been country music, Nashville has been its spiritual if not actual home. This city of recording studios, rehearsal spaces, music shops and venues is one of a small number of cities associated with a specific music genre and the creative cultures and attention this inevitably attracts. But just as heritage is never fixed and always becoming, Nashville - and the perception of Nashville - is changing, to the point where it may no longer have the primacy it once held. In a globalised music industry where not all country music is from Nashville, nor even the United States, new âNashvillesâ emerge and grow, commensurate with actual or relative decline in the prominence of the original. This might be considered a heritage dilemma (heritage âat riskâ, and a challenge to traditional views on authenticity), but equally the argument can be made for a new heritage replacing or augmenting the old. By considering the cityâs âat riskâ status, and assessing the fictional representation of a reimagined Nashville in the Scottish city of Glasgow in the 2018 film Wild Rose, we explore this dilemma, and its challenge to heritage convention
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